Kinetic growth of binary compounds by reactive magnetron sputtering

CENTRE NATIONAL DE LA RECHERCHE
SCIENTIFIQUE
INSTITUT DES MATÉRIAUX JEAN ROUXEL
Postdoctoral report
Kinetic growth of binary compounds by reactive
magnetron sputtering
Author: Dr. Javier García Molleja
Director: Dr. Pierre-Yves Jouan
Laboratoire des Plasmas et des Couches Minces
Institut des Matériaux Jean Rouxel - Université de Nantes
2014

Kinetic growth of binary compounds by reactive
sputtering magnetron
Javier García Molleja
Postdoctoral report

Contents
I Introduction 11
0.1 Agradecimientos . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
0.2 Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
0.3 Resumen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
0.4 Résumé . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
II Theoretical background 15
1 HiPIMS concepts 17
1.1 Discharge process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
1.2 Ion distribution with mass spectrometry . . . . . . . . . . . . . . . . . . . 19
2 The role of metastable Ar in HiPIMS 23
2.1 Population and depopulation mechanisms . . . . . . . . . . . . . . . . . . . 25
2.2 The role of the Penning ionization . . . . . . . . . . . . . . . . . . . . . . . 26
2.3 Presence of reactive gases . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
III Experimental analyses 29
3 Devices and techniques used 31
3.1 Plasma reactor and procedure . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Prolometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
3.3 X-Ray Diraction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33
3.4 Energy Dispersive Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . 33
3.5 X-Ray Photoelectron Spectroscopy . . . . . . . . . . . . . . . . . . . . . . 33
3.6 Resistivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
4 CrN kinetic growth under dierent parameters 37
4.1 Chromium nitride: general concepts . . . . . . . . . . . . . . . . . . . . . . 37
4.2 Experimental procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37
3

4 CONTENTS
4.3 Results under target-substrate distance of 3 cm . . . . . . . . . . . . . . . 38
4.3.1 Thickness analysis by prolometry . . . . . . . . . . . . . . . . . . 39
4.3.2 θ/2θ analysis of crystalline structure . . . . . . . . . . . . . . . . . 41
4.4 Results under target-substrate distance of 5 cm . . . . . . . . . . . . . . . 44
4.4.1 Sample thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44
4.4.2 Crystallographic analysis by θ/2θ of CrN thin lms . . . . . . . . . 46
4.5 Fine-θ/2θ analysis of CrN lms deposited with a high amount of N2 . . . . 48
4.6 Elemental analysis with EDS technique . . . . . . . . . . . . . . . . . . . . 53
4.7 XPS surface analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54
4.8 Residual stress evolution with dierent experimental parameters selected . 57
5 NiO lm characterization and properties 61
5.1 Nickel oxide: general concepts . . . . . . . . . . . . . . . . . . . . . . . . . 61
5.2 Experimental procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
5.2.1 The role of the free mean path . . . . . . . . . . . . . . . . . . . . . 63
5.3 NiO deposited with dierent thicknesses . . . . . . . . . . . . . . . . . . . 64
5.3.1 θ/2θ XRD analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . 64
5.3.2 Residual stress development with oxygen content and thickness vari-
ation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67
5.3.3 Electrical resistivity measurements . . . . . . . . . . . . . . . . . . 69
5.3.4 Variation of resistivity at low temperatures . . . . . . . . . . . . . . 71
5.4 NiO deposited under dierent bias values . . . . . . . . . . . . . . . . . . . 73
5.4.1 Prolometry results . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.4.2 X-Ray analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75
5.4.3 Residual stresses obtained by the NelsonRiley method . . . . . . . 78
5.4.4 EDS analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.4.5 Resistivity measurements . . . . . . . . . . . . . . . . . . . . . . . . 80
5.4.6 Resistivity in temperature measured in NiO15-300V sample . . . . 80
IV Final remarks 83
6 Conclusions 85
6.1 In English . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85
6.2 En español . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

List of Figures
1.1 a) Target current during HiPIMS discharge with dierent energies, DC-
like plateau is magnied. b) Voltage current during a HiPIMS pulse with
dierent energies [Greczynski, 2010]. . . . . . . . . . . . . . . . . . . . . . 18
1.2 a) Shape of the magnetic eld and current density in HiPIMS plasma dis-
charge. b) Cross-eld ion transport responsible of the sideways ion deec-
tion [Sarakinos, 2010]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
1.3 Double ion distribution for each detected species in a HiPIMS discharge.
Note the long tails obtained by mass spectrometry in time-integrated spec-
tra [Jouan, 2010]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
1.4 Mass spectrometry in energy-integrated mode. The maximum is obtained
during the rst stages and in the post-discharge ions arrive into the sub-
strate, too [Jouan, 2010]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
1.5 Mass spectrometry spectra in the energy-integrated mode during a HiPIMS
discharge in Ar-N2 gas using a Cr target [Greczynski, 2010]. . . . . . . . . 22
2.1 Calculated velocity distribution at the middle of the cell (z = 0) and the
wall surface (z = d) [Ohta, 2002]. . . . . . . . . . . . . . . . . . . . . . . . 23
2.2 Calculated two-dimensional density proles of the four 4s levels in the rf
discharge [Bogaerts, 2000]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 24
2.3 Spatial distribution of the emission (811 nm) at dierent currents during
the plateau (1.4 ms). The cathode is on the right side at 14 mm [Lotito, 2011]. 24
2.4 Temporal distribution concerning the emission populating the Ar
m
at dif-
ferent distances from the cathode [Lotito, 2011]. . . . . . . . . . . . . . . . 24
2.5 Two-dimensional images of argon atom emission at 811.5 nm [Jackson, 2001]. 25
2.6 Two-dimensional images of the
3
P0 metastable argon atom state at 4.0 ms
by a) absorption at 794.8 nm and b) laser induced uorescence [Jackson, 2001]. 26
2.7 Graph showing the temporal prole of some elements pertaining to a Cu
cathode with Ar background gas measured through a pulsed GD time-of-
ight mass spectrometer [Lotito, 2011]. . . . . . . . . . . . . . . . . . . . . 26
2.8 Emission of the pulsed GD at 1 hPa and 8.5 mA a) during plateau (1400
ms) b) in the afterglow (1555 ms) [Lotito, 2011]. . . . . . . . . . . . . . . . 27
5

6 LIST OF FIGURES
2.9 Emission intensity at 811.5 nm at a) 4 mm and b) 8 mm vs. time to
show the eect of nitrogen on the afterpeak emissions in an argon PGD
[Jackson, 2003]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
2.10 Emission from the 811.5-nm line as a function of time to show the eect of
decreasing nitrogen in the discharge. The times labeled in the gure refer
to the time after the nitrogen valve was closed [Jackson, 2003]. . . . . . . . 28
2.11 Argon ion signal at m/z = 40 vs. time to show the eect of nitrogen on
the steady-state and afterpeak number densities [Jackson, 2003]. . . . . . . 28
3.1 Experimental plasma reactor used in this report located at Pulvérisation
laboratory [Nguyen, 2013]. . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
3.2 Sketch of four-point probe method and the Van der Pauw conguration. . . 35
4.1 Cathode voltage in function of the nitrogen amount in the gas discharge.
Current of 180 mA and total pressure of 10.10 mTorr. Hysteresis starts at
11 % N2 and nishes at 36 % N2. . . . . . . . . . . . . . . . . . . . . . . . 40
4.2 Thicknesses obtained by prolometry of Cr and CrN samples obtained at
3 cm of target-substrate distance and high power condition. . . . . . . . . 40
4.3 Sample thicknesses. Target-substrate distance of 3 cm, low power used. . . 41
4.4 θ/2θ diractograms showing the CrN and Cr peaks at high power condition.
Upper image is for 5 mTorr of working pressure and lower image is for 10
mTorr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.5 θ/2θ diractograms in the 2θ = 35 − 45◦
range obtained at low power
condition. Upper image: 5 mTorr of working pressure, lower image: 10
mTorr of working pressure. . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
4.6 Thickness measurements obtained by prolometry with samples with dif-
ferent working pressure and nitrogen content. Target-substrate of 5 cm and
low power are xed. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45
4.7 Prolometry of samples obtained varying the total pressure and the N2
amount but target-substrate distance (5 cm) and high power as constants. 46
4.8 θ/2θ spectra obtained in lms deposited with high power. Left image is
for Cr and CrN lms deposited at 5 mTorr of working pressure and right
image is for 10 mTorr. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46
4.9 Left: θ/2θ spectra of Cr and CrN thin lms at 5 mTorr of working pressure.
Right: diractograms of Cr and CrN obtained at 10 mTorr or working
pressure. Low power condition and d = 5 cm. . . . . . . . . . . . . . . . . 47
4.10 CrN phase diagram [Bertrand, 1997]. . . . . . . . . . . . . . . . . . . . . 48
4.11 Change of deposition rate according the nitrogen percentage used in the
working atmosphere [Berg, 1996]. . . . . . . . . . . . . . . . . . . . . . . . 49
4.12 Phase change with voltage bias applied [Olaya, 2005]. . . . . . . . . . . . . 50

LIST OF FIGURES 7
4.13 Fine-θ/2θ analyses at 5 mTorr of working pressure deposited at 3 cm and
low power (upper left), at 3 cm and high power (upper right), and at 5 cm
and high power (lower part). . . . . . . . . . . . . . . . . . . . . . . . . . . 51
4.14 Fine-θ/2θ analyses obtained at 10 mTorr, 3 cm and low power (left) and
at 10 mTorr, 3 cm and high power (right). . . . . . . . . . . . . . . . . . . 51
4.15 Change of the lattice parameter value with the energy of the impinging ion.
Defective structure provoked lattice shrinkage [Olaya, 2006]. . . . . . . . . 52
4.16 Phase change with molecular nitrogen addition in the working atmosphere
[Lin, 2009]. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52
4.17 CrN75-10-3-10HP XPS surface composition of oxygen (far left), carbon
(left), chromium (right) and nitrogen (far right). . . . . . . . . . . . . . . . 54
4.18 Bulk elemental values of O (far left), C (left), Cr (right), and N (far right)
in CrN75-10-3-10HP thin lm. . . . . . . . . . . . . . . . . . . . . . . . . . 55
4.19 Surface elemental percentages of CrN75-10-5-10 sample obtained by XPS
analyses. O (far left), C (left), Cr (right), and N (far right) elements are
presented. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56
4.20 Internal elemental composition of CrN75-10-5-10 thin lm obtained by
XPS. Oxygen is in the far left region, carbon in the left, chromium in
the right and nitrogen in the far right. . . . . . . . . . . . . . . . . . . . . 56
4.21 Residual stress evolution after N2 addition in the working atmosphere. 10-
3-10 and 10-5-10HP experimental conditions selected. . . . . . . . . . . . . 58
4.22 Stress evolution under varying nitrogen percentages and target-substrate
distances and working pressure (10 mTorr) and power (high condition) xed. 58
4.23 Stress evolution changing the nitrogen content and the total working pres-
sure. Low power and d = 5 cm parameter are constants. . . . . . . . . . . 59
4.24 Residual stress development in function of power applied and the varia-
tion of nitrogen content. Fixed working pressure to 10 mTorr and target-
substrate distance to 5 cm. . . . . . . . . . . . . . . . . . . . . . . . . . . . 59
5.1 The ve target voltage regions when oxygen percentage is changed: 1)
nickel sputtering, 2) metallic regime, 3) transition regime, 4) partially poi-
soned regime, and 5) fully poisoned regime [Karpinski, 2011]. . . . . . . . . 61
5.2 X-Ray diractograms obtained in the Bragg-Brentano mode with dierent
thicknesses. a) NiO12, b) NiO15, c) NiO21, and d) NiO28. . . . . . . . . . 65
5.3 Corrected plane contribution with thickness increase. Upper left: NiO12,
upper right: NiO15, lower left: NiO21, lower right: NiO28. . . . . . . . . . 66
5.4 Plane contribution at a particular thickness and oxygen variation. Upper
left: 300 nm thick, upper right: 500 nm thick, lower part: 1000 nm thick.
Pale gray: nickel deposition, dark gray: metallic region, orange: transition
regime, yellow: partially poisoned mode, blue: fully poisoned mode. . . . . 67

8 LIST OF FIGURES
5.5 Residual stress with thickness in NiO thin lms deposited with dierent
molecular oxygen content in the working atmosphere: a) NiO12, b) NiO15,
c) NiO21, d) NiO28. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.6 Electrical resistivity measured by the four-point probe method. a) NiO12,
b) NiO15, c) NiO21, d) NiO28. . . . . . . . . . . . . . . . . . . . . . . . . 70
5.7 Electrical resistivity comparison with dierent molecular oxygen content.
Note that O percentages are depicted in relative amounts with regard the
Ar gas ow (10.0 sccm). . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71
5.8 Electrical resistivity in temperature measured in He atmosphere from 290 K
to 60 K. a) NiO21-50nm, b) NiO21-500nm, c) NiO28-50nm, d) NiO28-500nm. 72
5.9 Comparison of activation energy at high temperatures of each experimental
condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.10 X-Ray diractograms for each molecular oxygen percentage used and dif-
ferent DC biases imposed to the sample holder (from oating to −500 V.
a) NiO12, b) NiO15, c) NiO21, d) NiO28. . . . . . . . . . . . . . . . . . . . 75
5.11 Corrected plane contribution under dierent oxygen percentages and bias
voltages. a) NiO12, b) NiO15, c) NiO21, d) NiO28. . . . . . . . . . . . . . 76
5.12 Corrected plane contribution at xed bias voltage and the variation of
molecular oxygen percentage (relative to the argon total ow). a) Floating,
b) 200 V, c) 500 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77
5.13 Residual stresses of NiO thin lms under dierent bias voltages. Red:
NiO12, green: NiO15, blue: NiO21 and cyan: NiO28 are the colours used
to graph these stress values. . . . . . . . . . . . . . . . . . . . . . . . . . . 79
5.14 Electrical resistivity at room temperature of NiO15 thin lms deposited on
glass. Dierent substrate biases were used. . . . . . . . . . . . . . . . . . . 80
5.15 Arrhenius plot of change of resistivity with temperature in NiO15-300V
sample. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

List of Tables
3.1 Binding energies from selected elements. . . . . . . . . . . . . . . . . . . . 34
4.1 Experimental results for CrN and Cr thin lms under low power conditions.
Target-substrate distance equal to 3 cm. . . . . . . . . . . . . . . . . . . . 38
4.2 Experimental results obtained at d = 3 cm and high power condition. . . . 39
4.3 Diraction peaks from polycrystalline Cr and CrN in the 2θ = 35 − 45◦
region. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41
4.4 Lattice parameters. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
4.5 Experimental results obtained at d = 5 cm and low power condition. . . . . 44
4.6 Experimental results for CrN and Cr thin lms under high power condi-
tions. Target-substrate distance equal to 5 cm. . . . . . . . . . . . . . . . . 44
4.7 Lattice parameters obtained from θ/2θ measurements of Cr and CrN thin
lms obtained at target-substrate distance of 5 cm. . . . . . . . . . . . . . 47
4.8 Cr and N element percentages calculated with EDS technique. . . . . . . . 53
4.9 Oxygen element percentages calculated with EDS technique. . . . . . . . . 54
4.10 Elemental percentages after XPS analyses in the CrN surface and bulk of
CrN75-10-3-10HP and CrN75-10-5-10 samples. . . . . . . . . . . . . . . . . 55
5.1 NiO deposition rates with dierent O2 content. . . . . . . . . . . . . . . . . 64
5.2 2θ angular position of the main diraction planes of NiO and Ni compounds. 64
5.3 Lattice parameters calculated following the NelsonRiley method with
dierent O2 and thickness. . . . . . . . . . . . . . . . . . . . . . . . . . . . 68
5.4 Activation energy values. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73
5.5 NiO-thin lm thicknesses obtained by prolometry. These thin lms were
deposited under bias conditions. means irregular surface, so the thick-
ness calculation was not possible, mnp means measuremet not performed
for this condition. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74
5.6 Lattice parameters obtained after NelsonRiley method. Each bias voltage
and O2 percentage was calculated. Note that NiO28-50V was the only
amorphous sample. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78
9

10 LIST OF TABLES
5.7 EDS elemental composition of NiO15 samples deposited under dierent
bias voltages. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

13
0.1 Agradecimientos
Apoyemos la vida del ser humano
ignoremos las fronteras
vayamos por senderos de la vida
neguemos cualquier anulación.
Manuel García (fragmento de su poema Manos en libertad)
He de empezar agradeciendo de todo corazón a mi esposa Geo por plantear (y sobre-
llevar) conmigo esta aventura llena de posibilidades desde un punto de vista tanto laboral
como de aprendizaje, a pesar de la distancia y los problemas ocasionales. Mi familia
natural y política también merecen mi más sincero agradecimiento.
Gracias sinceras para Pierre-Yves, quien apostó por mí para reforzar la colaboración
entre Nantes y Rosario, a la par que aportaba mis puntos de vista y experiencia, junto a
un aprendizaje sobre nuevas técnicas, compuestos y aplicaciones en campos todavía por
explorar y por tanto completamente atrayentes.
He de saludar al doctor Pierre-Yves Tessier, responsable del grupo PCM por interesarse
siempre por mis investigaciones y preguntar sobre mi pasado en el campo de la investi-
gación. Agradezco a todos los investigadores y becarios de la sección Couches Minces
Homogènes del PCM por sus aportes e ideas. En especial tengo un especial recuerdo de
la conjunción del grupo de almuerzo y salidas nocturnas: Nicolas, los dos Julien, Axel,
Salma, Antoine, Laëtitia, Sylvain, Romain, Madec y Sabine. Un recuerdo además para
mis compañeros de ocina: Yehya, Stéphane, Damien y el aprendiz Pipaud.
Agradezco al CNRS (delegación de Bretaña y Países del Loira) por la beca postdoctoral
concedida, así como a la Université de Nantes (Faculté de Sciences et Techniques) y al
CEISAM (Chimie et Interdisciplinarité: Synthèse, Analyse, Modélisation).
También guardo un especial recuerdo a Pablo por su ayuda y sugerencias durante todo
el postdoctorado, así como los viajes de turismo por todo el oeste de Francia. La agru-
pación internacional con la que he tenido asiduo contacto me han hecho ver muchas más
perspectivas sobre el mundo exterior, así como la desmiticación de tópicos y la amistad
por todo el globo. Amigos y amigas de Estados Unidos, Chile, Cuba, México, Uruguay,
Argentina, España, Portugal, Alemania, Italia, Turquía, Kazajistán, Uzbekistán, Indone-
sia, Australia y Japón, un fuerte abrazo.
Finalmente y como homenaje, deploro la pérdida de nuestro querido Aldo (integrante
del IFIR rosarino) y deseo el retorno en perfectas condiciones de Antonio (estudiante de
la UCO cordobesa).
0.2 Abstract
This report has a theoretical section and an experimental one. In the former, HiPIMS
fundamentals and characteristics are described. Moreover, metastable argon population
Javier García Molleja Postdoctoral report

14
mechanism are sketched.
In the experimental section, CrN and NiO kinetic growths have been analysed. The
inuence of rective gases and experimental conditions have been considered in order to
determine the crystalline structure and residual stress development. Elemental composi-
tion and the role of contaminants were included in these characterizations. Finally, NiO
resistivity in function of thickness and bias were studied, and the role of oxygen content
and temperature, too.
0.3 Resumen
Este informe contiene una sección teórica y otra práctica. En la primera se indican los
fundamentos y características importantes de la técnica HiPIMS, además de centrarse en
los mecanismos que crean y sostienen los estados metaestables del argón.
En la parte experimental se han estudiado las cinéticas de crecimiento del CrN y del
NiO. La inuencia del gas reactivo y de los parámetros de deposición se analizaron para
determinar la estructura cristalina y las tensiones residuales desarrolladas. La composición
elemental y la presencia de contaminantes también fueron tema de estudio. Finalmente,
la determinación de la resistividad del NiO en función de su espesor y la polarización
fueron temas de investigación, junto con la variación de oxígeno y temperatura.
0.4 Résumé
Ce rapport contient une partie théorique et une partie pratique. Dans le premier les
principes fondamentaux et les caractéristiques importantes de la technique HiPIMS sont
indiqués. En plus, ce nécessaire de se concentrer sur les mécanismes qui créent et souti-
ennent les états métastables du argon.
Dans la partie expérimentale, nous avons étudié la cinétique de croissance de CrN et
de NiO. L'inuence du gaz réactif et les paramètres de dépôt ont été analysés an de
déterminer la structure cristalline et la contrainte résiduelle développée. La composition
élémentaire et les contaminants ont également fait l'objet d'une étude. Enn, la détermi-
nation de la résistivité de NiO en termes de leur épaisseur et de la polarisation sont des
sujets de recherche, en même temps que l'oxygène et les variations de température.
Postdoctoral report Javier García Molleja

Part II
Theoretical background
15

Chapter 1
HiPIMS concepts
1.1 Discharge process
Typical magnetron sputtering technique is based mainly in the ejection of neutral atoms
from the target. However, ions are preferred instead of neutral because of the capability
of ow redirection using electric elds [Sarakinos, 2010]. Moreover, there is a possibility
of reaction enhancement: not only neutral and excited atoms must be considered, but
ionic species, too.
This is the basis of IPVD, Ionized Plasma Vapour Deposition, so imposing inductive
elds the number of plasma ions increase in great manner [Helmersson, 2006]. There is
another technique based on the power density used in the magnetron. If target has a
power density that lies in the kW/cm
2
range the ionization factor will increase. How-
ever, there are some problems related to this idea, mainly the danger of target melting
[Guðmundsson, 2012] because of the poor cooling rate of magnetrons. A possible solution
is by using a pulsed discharge, so the high power density is only delivered during a few
microseconds. The rest of the time the power is o. In average, the total power density
is similar to the classical DC magnetron discharge, but the power peaks are many orders
above this value [Ehiasarian, 2003]. This is the basis of the HiPIMS (High Power Impulse
Magnetron Sputtering) technique.
The behaviour of this type of discharge is dierent from the typical DC magnetron
sputtering. In order to maximize the ion production it is possible to use unbalanced mag-
netrons that conne ions in the magnetic lines towards to the sample holder [Helmersson, 2006].
Not only the main parameter is the magnetic eld, but the power source is a key factor.
For example, depending on the gas atmosphere, the power supply device and the pres-
ence or not of pre-discharge, it could be an important time delay between the switch on
in power source and the plasma breakdown itself [Greczynski, 2010]. This is important
when short pulses are selected.
Inversely, very long pulses provoke a discharge with a DC-like plateau after the rst
17

18 CHAPTER 1. HIPIMS CONCEPTS
current peak [Greczynski, 2010]. The HiPIMS process is saturated and the discharge has
a behaviour typical from DC discharges. Moreover, very long pulses provoke damages
in targets by melting. Indeed, target voltage is dependent on the discharge energy and
after noisy eects could be dierences in the voltage delivered during the pulse duration
[Alami, 2009].
Figure 1.1: a) Target current during HiPIMS discharge with dierent energies, DC-like
plateau is magnied. b) Voltage current during a HiPIMS pulse with dierent energies
[Greczynski, 2010].
Thin lms deposited with HiPIMS develop an homogeneous stack, with no voids nor
columnar growth. However, it is customary obtain lower deposition rates than in DC
magnetron sputtering [Konstantinidis, 2006]. This is an important drawback in industry
but this eect has not been fully understood [Konstantinidis, 2006b]. Self-sputtering is
an important factor to consider. It is based on the quick ionization of sputtered particles
and their backattraction to the target [Bohlmark, 2005] [Anders, 2007], developing more
collision cascades and particle sputtering [Sarakinos, 2010]. This is interesting because in
some experimental conditions, gas atmosphere can be eliminated and the plasma discharge
is self-sustained. However, in the point of view of deposition the number of ions that reach
the substrate are severely reduced. But this is not the unique eect to consider in HiPIMS
discharges when low deposition rate is studied. Some recent experiments showed that at
high powers there was an important sideways ion deection, so a lot of ions are ejected
in a direction towards the reactor walls [Lundin, 2012].

CHAPTER 1. HIPIMS CONCEPTS 19
Figure 1.2: a) Shape of the magnetic eld and current density in HiPIMS plasma
discharge. b) Cross-eld ion transport responsible of the sideways ion deection
[Sarakinos, 2010].
Moreover, there is another eect called sputter wind based on the gas rarefaction
[Guðmundsson, 2012]. The energetic target ions collide with the neutral gas and this
collision provokes that Ar atoms are energized. With high kinetic energy (apart from
excitation and ionization processes) the gas atmosphere will expand and the pressure will
decrease, so the number of ions attracted to the target is severely lowered. Only when the
gas atmosphere is thermalized and its temperature decreases the plasma gas will behave
like a DC discharge. On the other hand, it is possible to consider other eects that have
an inuence in the ion transport like the distribution of electron energy [Lundin, 2008]
[Pajdarová, 2009] and the consequent ambipolar diusion [De Poucques, 2006] [Hecimovic, 2008].
1.2 Ion distribution with mass spectrometry
Mass spectrometry is a useful tool in order to know the main populations arriving to
the substrate during plasma dicharge (and during the post-discharge, also) [Jouan, 2010].

There are two dierent measurement modes: time-integrated and energy-integrated. The
rst one considers all ions arriving to the substrate independent of the time arrival, so
these ions obey an energy distribution [Jouan, 2010]. The second one makes an energy
average, so the important data are the time arrival of ions [Greczynski, 2010].
In the mass spectrometer, the extractor orice is often at ground potential, but if
it is referenced to a negative potential, more low-energy ions are attracted inside the
spectrometer [Jouan, 2010]. With this conguration only the rst part of the curve is
enhanced.
In time-integrated spectra it is possible to see a high population of ions and double
ionized ions coming from the magnetron target. And this ion population is higher than the
noble and reactive gas ions [Bohlmark, 2005]. However, neutral particles are the majority
arriving to the substrate. In this conguration two populations can be seen:
• At low energies there is a peak emerged by particles that suered collisional pro-
cesses. These particles are thermalized in the gas atmosphere and obey the Maxwell
Boltzmann distribution [Alami, 2009]. The intensity maximum is imposed by the
oating potential.
• At high energies a long population tail can be observed in HiPIMS discharges. These
particles come from the backscattered neutral atoms in the target [Takagi, 2006] and
from the sputtered target particles. This particles obtained by sputtering obey the
SigmundThompson distribution [Hecimovic, 2008]:
F =
CE
(E + Eb)3
,
with C a constant, E the energy and Eb the binding energy. The average energy of
this distribution is ¯E ≈ Eb 2 ln EM
Eb
− 3 , with EM the maximum energy imposed
by the power supply.
Figure 1.3: Double ion distribution for each detected species in a HiPIMS discharge. Note
the long tails obtained by mass spectrometry in time-integrated spectra [Jouan, 2010].

CHAPTER 1. HIPIMS CONCEPTS 21
It is worth to mention that in some cases a third peak appears due to shockwave
processes with the reactor walls [Hecimovic, 2008].
When energy-integrated spectra are considered it is possible to know the moment of
ion arrival and their populations [Hala, 2010]. When a reactive gas is used it is pos-
sible to work under poisoned conditions but the maximum energy is severely reduced
[Greczynski, 2010].
Figure 1.4: Mass spectrometry in energy-integrated mode. The maximum is obtained
during the rst stages and in the post-discharge ions arrive into the substrate, too
[Jouan, 2010].
It is observed that the rst particles reaching the substrate are the faster target ions,
backscattered ions and Ar
+
ions [Anders, 2007]. With N2 as reactive gas, N
+
2 particles
are detected in the beginning of the discharge, after that, N
+
, created in the target
(backscattering) is detected in combination with target ions [Greczynski, 2010]. Both
species grow in intensity during the rst microseconds, but at long times this trend is
reversed and Ar
+
and N
+
2 prevail, like in DC sputtering discharges [Poolcharuansin, 2010].
The ionic species can be detected in the post-discharge regime, too [Jouan, 2010].
It is important to mention that the maxima of the doubly-ionized target ions signal
coincide with the rising portions of the single-ionized target ions peaks, meaning that
doubly charged ions are most eectively produced during the time interval when single
charged ions possess a very broad energy spectrum [Greczynski, 2010].

Figure 1.5: Mass spectrometry spectra in the energy-integrated mode during a HiPIMS
discharge in Ar-N2 gas using a Cr target [Greczynski, 2010].

Chapter 2
The role of metastable Ar in HiPIMS
It is known that metastable Ar can play as energy reservoir during HiPIMS discharges, so
it is important to see which mechanisms promotes Ar
m
formation and Ar
m
destruction.
This energy reservoir is related to the process of maintaining the creation (including in
the afterglow regime) of relevant ion species during the plasma dicharge and thin lm
deposition.
The most relevant metastables states in argon atoms are
3
P2 and
3
P0 [Jackson, 2001]
[Lotito, 2011]. It is remarkable that the velocity proles of these Ar
m
states are bimodal
[Patterson, 1999], so shockwave eects and disturbances are the main responsibles of Ar
m
loss. But these loss processes are not the only ones in a discharge [Bogaerts, 1997], so
thermalizing collisions and wall-plasma interactions should be accounted for [Ohta, 2002]
in order to quantify the mechanisms of anisotropic Ar
m
population destruction.
Figure 2.1: Calculated velocity distribution at the middle of the cell (z = 0) and the wall
surface (z = d) [Ohta, 2002].
However, careful measurements prove that there are two peaks in the number density
prole of Ar
m
: one is located near the cathode and the other is located at the sheath-
plasma boundary [Bogaerts, 1997]. Concerning these peaks, some authors point that both
are created by local producion and loss processes (by electron impact excitation), but not
by atom diusion [Bogaerts, 1997]. Indeed, other authors point that it is the same peak,
but shifted in the afterglow temporal regime [Lotito, 2011].
23

24 CHAPTER 2. THE ROLE OF METASTABLE AR IN HIPIMS
Figure 2.2: Calculated two-dimensional density proles of the four 4s levels in the rf
discharge [Bogaerts, 2000].
There are several studies that conrm that at low energies, a peak splitting can be
seen: one remaining at the same place and other moving away the cathode [Lotito, 2011].
Figure 2.3: Spatial distribution of the emission (811 nm) at dierent currents during the
plateau (1.4 ms). The cathode is on the right side at 14 mm [Lotito, 2011].
Figure 2.4: Temporal distribution concerning the emission populating the Ar
m
at dierent
distances from the cathode [Lotito, 2011].

CHAPTER 2. THE ROLE OF METASTABLE AR IN HIPIMS 25
2.1 Population and depopulation mechanisms
There are several excitation processes that provoke the creation of Ar
m
and its destruction.
One of the most important is the direct electron impact excitation from the ground
state. Moreover, the stepwise excitation from lower excited levels is another important
production process [Bogaerts, 2000].
These processes are triggered in lower levels, so there are other processes that cre-
ate metastable atoms triggered in higher energy levels: radiative decay and electron
impact de-excitation. Finally, another relevant mechanism is the fast atom-ion impact
[Jackson, 2001].
Not only the population processes should be accounted for. Loss processes are very
important, too. For example, electron impact excitation to higher levels and de-excitation
to lower levels, together with radiative decay to lower levels are important during the
plasma discharge [Bogaerts, 2000]. Another important depopulation mechanism is the
Hornbeck-Molnar associative ionization, when these high energy levels are started from
the 4d and 4s levels.
During the afterglow regime there is a dierent behaviour than in the discharge ON
regime. For example, the bulk of both the
3
P2 and
3
P0 metastable states are formed 4−7
mm further from the cathode surface than during the plateau [Jackson, 2001]. Under this
condition, argon ion-electron recombination followed by radiative relaxation is the most
probable mechanism of populating these levels.
Figure 2.5: Two-dimensional images of argon atom emission at 811.5 nm [Jackson, 2001].

Figure 2.6: Two-dimensional images of the
3
P0 metastable argon atom state at 4.0 ms by
a) absorption at 794.8 nm and b) laser induced uorescence [Jackson, 2001].
2.2 The role of the Penning ionization
The Penning ionization mechanism (G∗
+ M → G + M+
+ e−
) is relevant in plasma
discharges with metastable argon present in it. There are results showing that the area of
optimal overlap between the plasma plume and the discharge is about 6 mm away from the
cathode, if ion production through Penning ionization should be favored [Lotito, 2011].
In order to maintain this phenomenon it is necessary that at the same time the power
density in the pulsed discharge should be maintained relatively high.
Figure 2.7: Graph showing the temporal prole of some elements pertaining to a Cu
cathode with Ar background gas measured through a pulsed GD time-of-ight mass spec-
trometer [Lotito, 2011].

CHAPTER 2. THE ROLE OF METASTABLE AR IN HIPIMS 27
Although Penning ionization certainly plays an important role in the generation of
analyte ions throughout the discharge pulse, and particularly during the afterglow, when
direct electron impact ionization becomes less likely due to a decrease of the electron
density, it cannot explain the manifold increase of the analyte ion signal observed by
mass spectrometry during the afterglow [Lotito, 2011]. Perhaps, there is a possible role
of Ar2 dimers and dimer ions in the formation of the afterglow.
Figure 2.8: Emission of the pulsed GD at 1 hPa and 8.5 mA a) during plateau (1400 ms)
b) in the afterglow (1555 ms) [Lotito, 2011].
2.3 Presence of reactive gases
It is important to see the eects of other gases than argon in the working atmosphere. For
example, many plasma discharges are triggered in gas mixtures using both, noble gases
and reactive gases.
Only with 1 % of N2 the excitation processes are changed [Jackson, 2003]. Working
atmospheres with nitrogen gas show a transfer of energy from excited argon atoms to ni-
trogen molecules during the voltage-on period, with a subsequent reduction in the number
of metastable states of argon [Jackson, 2003]. This reduction in metastable atoms reduces
the ionization of sputtered atoms during the voltage-on period, but does not signicantly
impact emissions from excited analyte atoms because the latter are created mostly via
collisions with electrons. On the other hand, in the afterglow, argon ion recombination
leads to an increase in metastable states by Penning ionization.

Figure 2.9: Emission intensity at 811.5 nm at a) 4 mm and b) 8 mm vs. time to show the
eect of nitrogen on the afterpeak emissions in an argon PGD [Jackson, 2003].
So, when nitrogen is added it prevents electrons from collisionally cooling in the af-
terpeak due to superelastic collisions with vibrationally excited states of N2, formed during
the voltage-on period [Jackson, 2003]. These superelastic collisions delay the onset of re-
combination because fast electrons recombine less readily than slow electrons, so ions and
electrons are lost by diusion to the walls.
Figure 2.10: Emission from the 811.5-nm line as a function of time to show the eect of
decreasing nitrogen in the discharge. The times labeled in the gure refer to the time
after the nitrogen valve was closed [Jackson, 2003].
Figure 2.11: Argon ion signal at m/z = 40 vs. time to show the eect of nitrogen on the
steady-state and afterpeak number densities [Jackson, 2003].

Part III
Experimental analyses
29

Chapter 3
Devices and techniques used
3.1 Plasma reactor and procedure
A 9.4-L reactor made from stainless steel was used in Pulvérisation laboratory in Plasmas
et Couches Minces group. There was nine ports in the lateral side and two ports in the
lower part and in the upper one, respectively. Linked to this reactor there was a secondary
chamber to insert the samples and obtain secondary vacuum. This little chamber was
vented with molecular nitrogen and the load lock was opened when a rough vacuum of
9.90 mTorr was reached.
In the upper port the magnetron was placed. The magnetic eld was unbalanced
and the target had 2 inches (5.08 cm) of diameter and 6.35 mm of thickness (KURT J.
LESTER). The surface was 20.27 cm
2
and the metal purity was 99.95 %. In the lower
port there was a turbomolecular pump LEYBOLD Turbovac 361 backed with a rotatory
pump TRIVAC. This pump is connected with the secondary chamber, too. The base
pressure was 10−7
Torr. All connection valves were LEYCON.
Figure 3.1: Experimental plasma reactor used in this report located at Pulvérisation
laboratory [Nguyen, 2013].
The gas owmeters were BROOKS Smart mass ow. A dedicated software was used
31

32 CHAPTER 3. DEVICES AND TECHNIQUES USED
in order to adjust the total ow: 20, 50 or 100 sccm. Vaccum gauges were a Pirani
CERAVAC and other Peening ALCATEL.
The gases used were argon, nitrogen and oxygen from ALPHAGAZ with 99.995 %
of purity. After several argon purges the new base pressure was 10−5
Torr. Under this
condition samples were inserted in the main reactor using a shaft.
The typical power supply was a HÜTTINGER source with control of voltage, current
and power in DC conditions. In bias conditions, TECHNIX High Voltage Power Supply
with regulation in voltage and current in DC mode was used.
Target cleaning has been obtained after pure argon sputtering during 5 minutes at 10
mTorr. Samples were protected by a shutter and the load lock is used in order to avoid
leaks from the secondary chamber. After that, 10 min of pre-sputtering has been done in
order to obtain a stationary condition in the discharge with the intended working atmo-
sphere and selected pressure. Time measurement was started after the shutter removal.
Power supply was self-regulated and one of the three parameters (current in CrN thin
lm deposition and power in NiO thin lm deposition) was xed. Working pressure was
adjusted using the turbomolecular valve.
When the experiment was concluded, power supply was o and the atmosphere totally
removed. The shaft was inserted again in the main reactor and the sample was placed in
the secondary chamber a couple of minutes to improve the cooling process.
Samples were Si (100) and glass. Silicon samples were cleaned with ethanol and acetone
and dried with dry nitrogen. Glass samples were cleaned only with dry N2.
3.2 Prolometry
Samples, marked prior to lm deposition with indelible ink, are cleaned with ultrasounds
during 15 min in an ethanol bath in a BIOBLOCK Scientic device. Previous to the
placement in the DEKTAK 8 prolometer, samples were cleaned again with distilled
water and compressed air. This device is placed at Prolomètre laboratory in Plasmas et
Couches Minces group with Nicole Langlois as responsible during the measurements.
A prolometer is a device used to measure the roughness of a surface and this de-
vice gives the dierence between the high and low points of a surface in nanometers
[Balasenthil]. The prolometer used is in contact mode with a stylus of 2.5 µm point
radius and 90
◦
between opposite faces. With this conguration thicknesses from 10 nm
to 1 mm can be easily measured and the horizontal resolution is controlled by the scan
speed and the data signal sampling rate. There is no reason to previous surface modelling
and with a load of 29,43 µN (3 mg) soft and hard samples can be measured. Double
measurement and in both borders of the groove could provide an averaged value.
This prolometer is enclosed in order to reduce the noise provoked by wind or any
kind of movement.

CHAPTER 3. DEVICES AND TECHNIQUES USED 33
3.3 X-Ray Diraction
Diraction is the constructive interference of X-rays in a crystalline sample. This condition
is veried by the Bragg's law [Cullity, 1956]. This law relates the diraction angle θ, the
crystallographic planes dhkl and the wavelength λ:
2dhkl sin θ = λ.
A SIEMENS Diraktometer D5000 with a source of CuKα rays is used. The wave-
length was 1.5418 Å. This device is enclosed and placed in Difractomètre INEL Rayons
X laboratory in Matériaux Inorganiques pour l'Optique et le Stockage group with Pierre-
Emmanuel Petit as responsible during measurements.
The tube was at 40 kV of voltage and 40 mA of current. The Soller slits in the IN
and the OUT regions had 1 mm of vertical aperture. A Ni lter discarded the CuKβ
contribution and a nal slit of 0.2 mm was placed in front of the scintillator detector.
The angular increase was 0.03
◦
and the accumulating time was 1 s. Peak position were
calibrated with PCPDFWIN standards and data were analysed with Origin software.
3.4 Energy Dispersive Spectroscopy
EDS measurements were performed in a Jeol JSM 5800LV device located at Microbalayage
2 laboratory in Centre de Micro-Caractérisation and with Luan Nguyen as responsible
during measurements.
Energetic electron bombardment provokes ionizations in deeper orbitals, so the funda-
mental state is broken. In order to correct this, an upper electron descends and occupies
this hole. The energy excess is released as X-ray photon [Goldstein, 2003]. This energy
is dependent on the element and the orbital, so it is possible to identify the element and
its chemical state.
For CrN thin lms voltage used was 15 kV during 60 s. The base pressure was 5.6·10−6
Torr and the current was stabilized in 501 nA. The channels used were 4096 and the
magnication was 3000X. On the other hand, for NiO thin lms voltage was 5 kV and
current was 1.307 nA with 2948 channels. Acquisition time and base pressure were the
same.
3.5 X-Ray Photoelectron Spectroscopy
The device used was KRATOS Analytical located at XPS Kratos Nova laboratory in
Plasmas et Couches Minces group. Indeed, Nicolas Bouts was the responsible in-charge
during measurements. Base pressure was 1 · 10−8
mbar and an aluminum anode was used
(energy of 1486.6 eV, corresponding to the AlKα line) as X-ray source.

After surface measurements, data were obtained from the bulk located at 4 nm depth.
Erosion time was 120 s using an Ar
+
gun with an energy of 500 eV. Tabulated elemental
positions were
Element Orbital Energy (eV)
C 1s 238.8
N 1s 401.6
O 1s 532.0
Cr 2p 583.7
Table 3.1: Binding energies from selected elements.
XPS is based on the photoelectron eect: a photon of a denied energy provokes the
ejection of an electron, so the atom is ionized. This electron has a kinetic energy, so if
the photon energy is known and the kinetic energy can be measured, the binding energy
is quickly obtained:
Ek = hν − EB.
Binding energies from each element and each orbital are tabulated, so it is possible to know
the element that ejected the electron [Feldman, 1986]. This technique needs high vacuum
conditions and only the surface atoms could be measured, so sputtering techniques are
used in order to perform XPS in deep layers.
3.6 Resistivity
Resistivity measurements were developed at Couches Minces et Résistivité laboratory in
Physique des Matériaux et Nanostructures group. The responsible during measurements
was Étienne Janod. A KEITHLEY 236 device in the four-point probe conguation has
been used.
The Van der Pauw method was used, so the thin lm needs to be quasi-2D, homo-
geneous and without voids. With silver paint the electrodes were obtained: two long
electrodes at each end and two short electrodes in the middle, with separation of L. The
sample is located at an insulating substrate holder, glass for example. The substrate has
a surface of S obtained by the lm thickness and the long silver electrode lenght. With
thin gold wires (40 µm of diameter) the short electrodes are connected to the substrate
holder, so the connections with the measurement device is possible. In order to perform
the measurement, the I+
and the I−
terminals are connected with the two long electrodes
and the V +
and the V −
terminals are connected with the two short electrodes, but not
mixed, i.e. obeying the I+
− V +
− V −
− I−
sequence [Van der Pauw, 1958].

CHAPTER 3. DEVICES AND TECHNIQUES USED 35
Figure 3.2: Sketch of four-point probe method and the Van der Pauw conguration.
Imposing some current (positive and negative) value the voltage measured must be
similar (but with dierent sign). A true measurement is obtained when simetrical be-
haviour is obtained, after several minutes because of the transient eects. Indeed, each
measurement must obey the Ohm's law (multiplying by two the current performs the
double of voltage). If both conditions are fullled the resistance is [Van der Pauw, 1958]
R =
|V +
| + |V −
|
2I
.
When low voltage values are measured the resistance value is accurated. So, knowing
these values are neccesary to obtain the resistivity value:
ρ =
S
L
R.
The resistivity of the elements used were the following ones:
• Glass: 20 PΩ cm
• Silver: 1.59 µΩ cm
• Gold: 2.44 µΩ cm
• Nickel: 0.96 nΩ cm
• Nickel oxide: 180 TΩ cm
Moreover, when resistivity measurements are obtained at low temperatures with the
four-point probe method, start temperature was 290 K and ultimate temperature was 55
K. The sample is located in a cane inserted in a compressor that reduces the temperature.
This cane must be purged with a turbomolecular pump backed with a Roots pump and
lled the cavity with 1 atm of He gas. Moreover, the compressor zone must be evacuated

until a pressure of 10−5
mbar. The process is repeated, from high to low temperatures
and from low to high temperatures.
The variation of R with the temperature obeys an Arrhenius plot:
R = Ke
−
EA
kBT
,
with K a constant, EA the activation energy (with a gap energy of 3.8 eV for NiO) and
kB the Boltzmann's constant.

Chapter 4
CrN kinetic growth under dierent
parameters
4.1 Chromium nitride: general concepts
Chromium nitride (CrN) is an extremely hard coating with high temperature resis-
tance and improved corrosion resistance. Dense, non-porous CrN has a fcc structure
with low residual compressive stresses. Chromium nitride is inert and stable material,
which good adhesion (by molecular bonding) to the substrate and a mirror-like nish
[Chromium Nitride]. In tribology, CrN develops low friction and good protection to the
substrate. It is important to mention that these coatings mimick the substrate features
and they cover these substrates in an uniform fashion in a huge range of thicknesses.
CrN is non-toxic and non-oxidizing but it has good electrical conduction properties.
Moreover, CrN is a possible replacement of TiN in functional components [Chromium Nitride]
and there are applications in protection of precision components in abrasive environments.
Its stability under high temperatures (close to 700
◦
C) and chemical inertness are good
options for movable parts with close tolerance. CrN can be bonded to many substrates
and there is no bubbling.
4.2 Experimental procedure
A plan must be devised in order to characterize the CrN thin lms. The parameter
variation is a key to know the subjacent mechanism of lm growth [Rebholz, 1999], so in
this report some important parameters have been varied:
• The molecular nitrogen percentage in the working gas: 0 %, 20 %, 30 %, and 75 %
of N2. Argon balance.
• The total working pressure: 5 mTorr and 10 mTorr.
37

38 CHAPTER 4. CRN KINETIC GROWTH UNDER DIFFERENT PARAMETERS
• The target-substrate distance: 3 cm and 5 cm.
• The DC density power used: high power, 6−9 W/cm
2
and low power, 2−3 W/cm
2
.
In this report clean Si(100) have been used as substrates. The total ux was xed
at 10.0 sccm in all the experiments using always a gas mixture of argon and molecular
nitrogen (both of 99.995 % of purity). The target is composed by a circular disk of Cr
(99.95 % purity) with dimensions of 5.08 cm diameter and 6.35 mm thick. Deposition
time, after target cleaning and pre-sputtering procedure, was xed at 10 min.
Samples are labelled as Cr(N%)-p-d-t(HP). Cr identies pure chromium deposition and
CrN identies chromium nitride deposition with % the percentage of molecular nitrogen
used, p the pressure used, d the target-substrate imposed, and t the deposition time. HP
is used in lms deposited under high power conditions, so under low power conditions
there is no label.
4.3 Results under target-substrate distance of 3 cm
In order to clarify such a high quantity of CrN samples the results have been divided
by the target-substrate distance parameter. Beginning with d = 3 cm the experimental
results for low power deposition condition are shown in the next table.
N2 (%) p (mTorr) V (V) I (A) P (W) S (W/cm
2
)
0 5.02 264 0.145 38.25 1.89
0 10.12 245 0.171 41.85 2.07
20 4.97 319 0.171 54.55 2.69
20 9.95 293 0.171 50.10 2.47
30 5.08 325 0.171 55.58 2.74
30 10.17 295 0.171 50.32 2.48
75 5.10 350 0.145 50.72 2.50
75 10.07 299 0.171 51.13 2.52
Table 4.1: Experimental results for CrN and Cr thin lms under low power conditions.
Target-substrate distance equal to 3 cm.
The lms are dependent on the substrate cleanliness [Demaree, 1996], so several de-
positions presented bubbling and poor adherence. Repeated runs have been done in these
cases, improving the cleaning process and lowering the current in order to eliminate pos-
sible mechanism of peeling.
The experimental parameters at 3 cm of target-substrate distance and high power
conditions are consigned in the following table:

CHAPTER 4. CRN KINETIC GROWTH UNDER DIFFERENT PARAMETERS 39
2
)
0 5.08 327 0.52 170.04 8.39
0 10.10 298 0.52 154.96 7.64
20 5.01 377 0.52 196.04 9.68
20 9.98 351 0.52 182.50 9.01
30 4.98 388 0.52 201.76 9.95
30 10.03 336 0.40 134.40 6.63
75 5.97 392 0.40 156.80 7.74
75 10.07 334 0.40 133.40 6.58
Table 4.2: Experimental results obtained at d = 3 cm and high power condition.
In some cases, in order to preserve the target integrity the DC power applied was
lowered. In order to do that, the current was reduced [Sundar, 2009].
A visual inspection is useful to check the main features obtained after the deposition
process. It was observed severe peeling in Cr-5-3-10HP and bubbling in Cr-10-3-10HP.
This was caused by combination of target-substrate distance and the high power used.
Moreover, CrN75-5-3-10HP presented bubbling, too.
In CrN75-5-3-10 there was bubbling, because of a bad cleaning process or power slightly
elevated (∼ 61 W). So, several re-runs of this sample were done lowering the power
and with cleaning process improvement but this technique was unsuccessful. Only after
reaching a density power of 2.50 W/cm
2
the density of bubbles reached a low value.
Maybe, the particular combination between the target-substrate distance and the low
pressure under a high amount of molecular nitrogen could play an important role.
Optical inspections provided more results. At low power, adherence was good, but
not in the case of Cr-5-3-10 and Cr-10-3-10 samples. Although Cr-10-3-10 sample in
principle had a good adherence, after the cleaning process previous prolometry a peeling
was detected in huge regions. Moreover, Cr-5-3-10 sample had better adherence than the
one obtained at high power condition, but the adherence performance was similar to the
Cr-10-3-10 one. A possible explanation is the intense Cr bombardment in the Cr growing
lm, when the target-substrate distance avoids the sputtered Cr collision with the gas
atoms/molecules [Aouadi, 2002].
4.3.1 Thickness analysis by prolometry
Using prolometry a clear trend is devised when a target-substrate distance was imposed.
More nitrogen content in the gas mixture was translated to a lower thicknesses because
of the target poisoning eects [Rebholz, 1999]. There was a reduction in the secondary
electron emission coecient when the target is nitrided than when the target was only
Cr pure [Baborowski, 1996]. The hysteresis loop and the dierences in voltage fall in the
cathode were evidences of this eect.

Figure 4.1: Cathode voltage in function of the nitrogen amount in the gas discharge.
Current of 180 mA and total pressure of 10.10 mTorr. Hysteresis starts at 11 % N2 and
nishes at 36 % N2.
Other interesting aspect is the higher thicknesses when high power condition is applied.
High power values were reached by a high deposition rate [Demaree, 1996]. On the other
hand, CrN thin lms obtained at high power conditions had lower thicknesses when they
were deposited at high working pressure, i.e. 10 mTorr. Perhaps, the explanation is that
more pressure means more collisions and particle scattering than at low working pressure
conditions.
However, when low power condition was considered there were two dierent behaviours
when the working pressure was changed.
• Cr and CrN presented that at high pressures the thickness was higher than at low
pressures.
• CrN20 y CrN75 presented that at high pressures the thickness was lower.
Figure 4.2: Thicknesses obtained by prolometry of Cr and CrN samples obtained at 3
cm of target-substrate distance and high power condition.
This is a bit confusing in order to understand these dierent behaviours. In order to
understand this, experimental parameter examination is very important. Cathode voltage

was higher at 5 mTorr of working pressure and only the Cr and CrN75 samples were
deposited at 154 mA (the rest at 171 mA). So, a partial conclusion gives that at higher
power densities, higher thicknesses [Amezawa, 2007]. Then, ignoring Cr samples and
assuming that with error bars CrN30-5-3-10 and CrN30-10-3-10 had the same thickness
(347.09 ± 3.75 nm the former, 351.92 ± 1.68 nm the latter), lower working pressures
developed higher thicknesses was demostrated.
Figure 4.3: Sample thicknesses. Target-substrate distance of 3 cm, low power used.
4.3.2 θ/2θ analysis of crystalline structure
XRD spectra are convoluted with a high amount of artifacts. They arose probably from
the detector itself, because the sample holder was plastic, i.e. an amorphous material. In
order to do a complete study those peaks must be calibrated and erased.
In this section the diraction range considered was between 35
◦
and 45
◦
, because the
two rst peak from CrN are located in this region [Jagielski, 2000]. CuKα radiation,
whose wavelength is 1.5418 Å, was used in these characterizations. Then, tabulated CrN
and Cr have the following peaks and these planes in the above mentioned region:
Plane 2θ (
◦
)
Cr(110) 44.636
CrN(111) 37.570
CrN(200) 43.729
Table 4.3: Diraction peaks from polycrystalline Cr and CrN in the 2θ = 35−45◦
region.
According to the tabulated values obtained from PCPDFWIN the lattice parameters
of these compounds are 2.895 Å for Cr (bcc structure) and 4.140 Å for CrN (fcc structure).

Figure 4.4: θ/2θ diractograms showing the CrN and Cr peaks at high power condition.
Upper image is for 5 mTorr of working pressure and lower image is for 10 mTorr.
For target-substrate distance of 3 cm the lattice parameters of each condition could
be calculated. In this case the main peak was considered in order to do the calculation:
N2 (%) 5-3-10HP (Å) 5-3-10 (Å) 10-3-10HP (Å) 10-3-10 (Å)
0 2.8786 2.8836 2.8800
20 4.1425 4.1423
30 4.1617 4.1416 4.1479
75 4.2227 4.1963 4.1669 4.1599
Table 4.4: Lattice parameters.
It is possible to see that at high power condition the obtention of crystalline phases
is very dicult [Berg, 1996]. Perhaps, the short target-substrate distance and the low
power provoke an energetic impingement and the surface resputtering is an important
mechanism. Indeed, in CrN30-5-3-10HP sample Cr phase is present. Another interesting

thing is that at higher pressures peaks are present but their intensity is not elevated,
perhaps caused by the reduced number of particles arriving to the substrate of Si(100).
So, at elevated power densities the formation of CrN is severely inhibited.
Figure 4.5: θ/2θ diractograms in the 2θ = 35−45◦
range obtained at low power condition.
Upper image: 5 mTorr of working pressure, lower image: 10 mTorr of working pressure.
When low power condition is analysed peaks are more denite than in gure (4.4).
This is another evidence in order to assure the role of surface resputtering. Indeed, at
10 mTorr of working pressure peaks are more intense than at 5 mTorr, so more particles
arrive to the substrate. There is a contradiction with the earlier statement done for high
power condition, but like in prolometry results, power density and free mean paths play
a crucial role in the growth process.
Thus, CrN structure was obtained at low power conditions and in all cases crystal
structure was obtained. Furthermore, when dierent power supply is compared is clearly
seen that the crystal structure is predominantly present in samples coated at low power
condition.

4.4 Results under target-substrate distance of 5 cm
After the initial characterization of CrN thin lms deposited under a target-substrate
distance of 3 cm at low and high power conditions, it is necessary to do the same for CrN
thin lms obtained at target-substrate distance of 5 cm. Under this condition, the lm's
experimental parameters obtained at low power are presented in the following table:
2
)
0 5.10 263 0.18 47.34 2.34
0 10.03 244 0.18 43.92 2.17
20 5.04 320 0.18 57.60 2.84
20 9.97 294 0.18 52.92 2.61
30 5.01 332 0.18 59.67 2.95
30 10.03 297 0.18 53.46 2.64
75 5.94 337 0.18 60.66 2.99
75 10.02 299 0.18 53.82 2.66
Table 4.5: Experimental results obtained at d = 5 cm and low power condition.
Following these results, it is mandatory to complete the results showing the experi-
mental parameters under high power deposition at d = 5 cm. In the next case it worths
to mention that CrN75-5-5-10HP was deposited at 6.31 mTorr, because of the discharge
instability at low pressures when the nitrogen percentage is so elevated. On the other
hand, other parameters have been xed with the rest of the samples.
2
)
0 5.05 298 0.40 119.20 5.88
0 9.98 275 0.40 110.00 5.43
20 5.05 356 0.40 142.40 7.03
20 9.95 326 0.40 130.40 6.43
30 5.14 364 0.37 134.68 6.64
30 9.97 347 0.40 138.80 6.85
75 6.31 373 0.38 140.53 6.93
75 10.04 325 0.40 130.00 6.41
Table 4.6: Experimental results for CrN and Cr thin lms under high power conditions.
Target-substrate distance equal to 5 cm.
4.4.1 Sample thickness
Thickness has been measured by several prolometry tests. With a target-substrate dis-
tance of 5 cm some results are similar to 3 cm of target-substrate distance. For example,

when the molecular nitrogen amount in the atmosphere is elevated, the cathode target
is poisoned [Rebholz, 1999], so the deposition rate is lower, provoking lms with lower
thicknesses after 10 min of deposition [Volz, 1998]. Moreover, at high power condition
thickneeses are higher than at low power condition, related with the amount of sputtered
material.
Comparing results at 3 cm and 5 cm, in all cases thicknesses are higher when the target-
substrate distance was 3 cm [Aouadi, 2002], because of the low probability of collision (and
scattering) under this experimental condition, i.e. the free mean path is higher than 3
cm, but lower than 5 cm.
At low power condition, higher thicknesses are reached at 10 mTorr because of the
higher number of particles reaching the substrate. Only in CrN75 samples there is an
apparent contradiction. But the values are close to each other, so it is provoked by the
total target poisoning.
Figure 4.6: Thickness measurements obtained by prolometry with samples with dierent
working pressure and nitrogen content. Target-substrate of 5 cm and low power are xed.
On the other hand, at high power condition the thickness values with the total working
pressure has a complex behaviour: while Cr and and CrN30 show that higher pressure
means higher thickness, CrN20 and CrN75 samples show that higher pressure means lower
thickness. Like in the thickness characterization for 3 cm target-substrate samples, Cr
lms are discarded in order to focus only in CrN thin lms. It is important to say that
CrN30-10-5-10HP thickness (626.46 nm) surpasses both CrN20 samples (591.24 nm for 5
mTorr and 578.09 nm for 10 mTorr). But, in general, high energy particles avoids quick
growth, so at lower pressures good thicknesses are obtained.

Figure 4.7: Prolometry of samples obtained varying the total pressure and the N2 amount
but target-substrate distance (5 cm) and high power as constants.
Finally, when samples are compared regarding their target-substrate value, it is pos-
sible to say that at hihg power conditions the behaviour is the same: low power, higher
thickness, but a low power there is no the same trend. At 3 cm of target-substrate dis-
tance low pressure promotes the deposition rate and at 5 cm high pressure promotes the
deposition rate. Perhaps the role of free mean path is more relevant when low power
conditions are used during the deposition process.
4.4.2 Crystallographic analysis by θ/2θ of CrN thin lms
θ/2θ analyses have been carried on in Cr and CrN thin lms when the target-substrate
distance was 5 cm. At this time the range measured is 2θ = 35 − 45◦
in order to avoid
artifacts generated by the goniometer and its detector.
Figure 4.8: θ/2θ spectra obtained in lms deposited with high power. Left image is for Cr
and CrN lms deposited at 5 mTorr of working pressure and right image is for 10 mTorr.
When the lms were obtained using low pressure and high power in CrN20 lm only
chromium is detected and for CrN30 and CrN75 thin lms chromium nitride structure

was present but the peaks had low intensity. Moreover, when these lms were deposited
at high pressures the CrN structure was clearly present. Severe particle bombardment
hinders the development of CrN crystalline phase, eect reduced when the proportion of
molecular nitrogen in the atmosphere is elevated.
N2 (%) 5-5-10HP (Å) 5-5-10 (Å) 10-5-10HP (Å) 10-5-10 (Å)
0 2.8746 2.8746 2.8802 2.8806
20 4.1312 4.1204 4.1312
30 4.1255 4.1364 4.1255 4.1312
75 4.1720 4.1623 4.1486 4.1416
Table 4.7: Lattice parameters obtained from θ/2θ measurements of Cr and CrN thin lms
obtained at target-substrate distance of 5 cm.
In this table and in the former (cf. gure 4.4) a clear trend with the molecular
nitrogen introduction is detected [Volz, 1998]. For each condition of pressure, supplied
power or target-substrate distance the CrN lattice parameter grows with the amount of
N2 in the working atmosphere. In θ/2θ gures a peak shifting for CrN(111) was present
[Dasgupta, 2006]. This shifting was towards lower angular values so in a fcc structure
this means that the lattice parameter increased [Tsujimura, 2002]. Nitrogen excess was
located in the fcc interstitial sites and more nitrogen atoms were lodged in proportion with
the molecular nitrogen amount. The presence of these nitrogen atoms provoked lattice
distortion and lattice parameter growth [Engel, 1998].
Figure 4.9: Left: θ/2θ spectra of Cr and CrN thin lms at 5 mTorr of working pressure.
Right: diractograms of Cr and CrN obtained at 10 mTorr or working pressure. Low
power condition and d = 5 cm.
When only thin lms obtained at low power condition were considered CrN crystal
structure was always measured but at 5 mTorr the peak intensity was weak, perhaps the

combination of low power and high target-substrate distance, i.e. the free mean path is
lower than 5 cm so collisional processes were triggered. CrN75-5-5-10 sample is almost
amorphous, because of the high amount of nitrogen lodged in the cell and the severe
distortion which this cell suered [Engel, 1998]. When the working pressure was changed
to 10 mTorr the intensity was weak but not in the same extent than the lms obtained
at 5 mTorr.
Finally, it is interesting to say that there were several dierences between lms ob-
tained at low power condition and the ones obtained at high power condition. Low power
density promoted the appearance of CrN crystalline phase but these peaks had low in-
tensity.
4.5 Fine-θ/2θ analysis of CrN lms deposited with a
high amount of N2
The results obtained stated an expanded CrN phase when the molecular nitrogen used
in the working atmosphere was very high. Interestingly, the peak position of CrN(111)
and CrN(200) overlapped the typical Cr2N (110) and (200) plane positions, respectively.
Cr2N has high hardness and high corrosion resistance, but CrN has optimal wear resistance
[Zhang, 2008]. So, these properties are clues in order to characterize their values and make
a comparison to distinguish which compound was obtained.
Figure 4.10: CrN phase diagram [Bertrand, 1997].
In order to verify if there was a phase transition from CrN to Cr2N phase, a careful
analysis has been done. θ/2θ diractograms has been obtained using an angular step of
∆2θ = 0.02◦
with accumulating time of ∆t = 1.5 s. Two regions have been analysed
2θ = 35◦
− 45◦
and 68.5◦
− 69.5◦
.
Using these data it was possible to do a better measurement and using the measured
position of Si(400) peak and the tabulated value for this diraction using CuKα light, i.e.
2θ = 69.205◦
, a calibration process was possible. Correcting the peak shifting between

tabulated Si(400) and measured Si(400) (almost 0.090
◦
) the true peak position could be
obtained.
Firstly, the CrN phase diagram shows that over 50.0 % of nitrogen content only CrN
phase is present [Bertrand, 1997]. Only with low content of nitrogen Cr is obtained and
Cr2N when percentage is 30.3 % [Berg, 1996]. Another clue is that depositions under 200
◦
C inhibit phase mixture due to dierent values of enthalpy of formation [Pakala, 1996]
and over 300
◦
C there is a phase mixture, but under high percentages of N2 only CrN
phase is present [Era, 2005].
Figure 4.11: Change of deposition rate according the nitrogen percentage used in the
working atmosphere [Berg, 1996].
In standard conditions (1 atm of pressure, 25
◦
C of temperature) the enthalpy of
formation for CrN is −117.15 kJ/mol and for Cr2N is −125.52 kJ/mol. Following a
polynomial equation it was possible the calculation of these values at 473 K, because
of the experimental conditions assured a temperature below from 200
◦
C. Thus, at 473
K, CrN enthalpy of formation was −108.6309 kJ/mol and −112.9815 kJ/mol, so under
these conditions is more probable the formation of Cr2N compounds. This is against
[Pakala, 1996] prediction but it is important to remember that magnetron sputtering is a
technique developed far from the thermodinamical equilibrium, so these predictions must
be considered carefully.
Film deposition under bias improves Cr2N compactness. On the other hand, CrN
deposited under bias conditions provoked a defective single phase [Aouadi, 2002]. These
statements hinder the process of phase identication, thus ne-θ/2θ could be a tecnique
in order to discard instrumental errors and allow clear phase identication.
Moreover, it is interesting to see N2 ux over voltage behaviour and it is important to
know that (002) plane minimizes surface energy [Zhang, 2008]. Furthermore, high biases
provoke lower lm adherence and lower lm hardness [Lee, 2008]. There is a risk of phase
coexistence at high nitrogen contents if deposition has been done without bias and with
unbalanced magnetron [Olaya, 2005], but if the quantity of N in the cell is higher than
the number of Cr atoms there is only a pure phase (the CrN one).

Figure 4.12: Phase change with voltage bias applied [Olaya, 2005].
On the other hand, higher ion population arriving to the substrate promotes the CrN
phase and voltage bias only aects to the texture [Shah, 2010]. (111) plane has the lower
strain energy and grain size grows with higher Ar content in the atmosphere. Finally,
cluster formation during the path is promoted if there are a high number of collisions.
With these considerations the X-ray analysis can be done. CrN samples obtained at 5
mTorr, 3 cm of target-substrate distance and high power are mainly CrN compound, so
Cr2N presence was discarded. Not only CrN75 thin lms have been measured but CrN30
and CrN20 thin lms, too. It is worth to mention that the lattice parameter increases if
the structure is stressed, so stresses provoke a CrN(111) peak shifting [Dasgupta, 2006].
In the same conditions but with high power a clear identication was not possible, possibly
because of this. Indeed, non-stoichiometric lms deposited by sputtering has behaviours
out of the phase diagram predictions, i.e. morphological changes are detected [Zhao, 2004].
In sputtering, for example, target-substrate distance (changed from 3 cm to 5 cm, for
example) has an inuence on plasma voltage and electron temperature [Olaya, 2006] and
lattice parameter changes with plasma energy (measured as eV/at) and surface defects.

Figure 4.13: Fine-θ/2θ analyses at 5 mTorr of working pressure deposited at 3 cm and
low power (upper left), at 3 cm and high power (upper right), and at 5 cm and high power
(lower part).
When thin lms deposited at pressures of 10 mTorr are considered and low power
conditions, it is important to know that a low deposition rate promotes CrN phase
[Ensinger, 2012]. In order to clarify the phase composition, all peak positions from Cr,
CrN and Cr2N are displayed. Finally, it is possible to state that when molecular nitrogen
atmosphere is over 70 % CrN phase is present, but diraction peaks are severely shifted
[Lin, 2009].
Figure 4.14: Fine-θ/2θ analyses obtained at 10 mTorr, 3 cm and low power (left) and at
10 mTorr, 3 cm and high power (right).

After this, many peaks are discarded as having the Cr2N phase. Only three peaks
remain as suspects: CrN75-5-5-10HP, CrN75-5-3-10HP and CrN75-5-3-10. Film thickness
can play an important role on stress development, because mass density and residual
streeses are related to the thickness [Chekour, 2005]. Changing the growth mode or the
grain size are ohter important parameters [Mercs, 2007].
Figure 4.15: Change of the lattice parameter value with the energy of the impinging ion.
Defective structure provoked lattice shrinkage [Olaya, 2006].
Figure 4.16: Phase change with molecular nitrogen addition in the working atmosphere
[Lin, 2009].
Under high power conditions there was a fast change of peak position with thickness
and this mentioned change was slower at low power conditions. Perhaps, the suspect

lms are under high residual stresses, so there were lattice distortions (or, in a minor
probability, a phase change). During lm growth itself high compressive stresses were
measured [Chekour, 2005] in controlled experiments.
4.6 Elemental analysis with EDS technique
EDS technique is the ultimate tool in order to verify the CrN presence in all the samples,
including the ones with diraction peaks severely shifted. Fine-θ/2θ analyses showed that
samples deposited under a low quantity of N2 were CrN and samples deposited at 75 %
of molecular nitrogen probably were CrN but with expanded lattice parameter. With
EDS it was possible to conrm this statement according with the Cr:N ratio measured
[Tacikowski, 2011].
Sample Cr (at%) N (at%)
CrN75-5-5-10-HP 39.6 60.4
CrN75-5-5-10 33.1 66.9
CrN75-10-5-10HP 38.4 61.6
CrN75-10-5-10 33.9 66.1
CrN75-5-3-10HP 42.7 57.3
CrN75-5-3-10 35.8 64.2
CrN75-10-3-10HP 41.9 58.1
CrN75-10-3-10 36.3 63.7
Table 4.8: Cr and N element percentages calculated with EDS technique.
So, under high amounts of molecular nitrogen in the working atmosphere is logical to
detect a peak shifting, because of lattice expansion by microstresses [Tan, 2011]. It was
clearly seen that CrN lms were not stoichiometric, with N-excess, then their diraction
patterns were shifted after the nitrogen entrance in the interstitial sites [Baborowski, 1996]
and the development of compressive stresses.
Finally, this N-excess discarded the Cr2N presence. Furthermore, lm thicknesses may
induce compressive stresses also (when a particular thickness is reached).
In table 4.8 interesting data can be obtained. For example, high power conditions
increased the Cr proportion (but the N-rich non-stoichiometry is conserved anyway) be-
cause of the improvement of the Cr sputtering. Moreover, when the working pressure was
changed there was slight dierences in the amount of chromium in the deposited lms: at
low power condition more pressure increased the Cr quantity, but at high power conditions
more pressure reduced the Cr quantity due to, probably, the scattering eects with the
atmosphere or the enhancement of N arrival. It is worth to mention that these dierences
are minimum. Finally, a target-substrate reduction improved the Cr percentage in the
CrN thin lms.

Sample O (at%)
CrN75-5-5-10HP 11.13
CrN75-5-5-10 16.02
CrN75-10-5-10HP 16.89
CrN75-10-5-10 24.75
CrN75-5-3-10HP 9.03
CrN75-5-3-10 12.72
CrN75-10-3-10HP 10.20
CrN75-10-3-10 15.41
Table 4.9: Oxygen element percentages calculated with EDS technique.
Calculation about the oxygen present in the thin lm as a contaminant was done.
Under high power conditions the O percentage was severely reduced, in the same manner
if the working pressure is lowered and the target-substrate, too. Avoiding Cr collisions
with the atmosphere gases and the residual ones improve the lm quality.
4.7 XPS surface analysis
Figure 4.17: CrN75-10-3-10HP XPS surface composition of oxygen (far left), carbon (left),
chromium (right) and nitrogen (far right).
This technique is useful in order to determine if the high oxygen percentage detected by
EDS characterization is only located on the lm surface or if this contaminant is present in
the working atmosphere and O is located in the lm bulk [Jagielski, 2000]. EDS technique
analyses the surface and the bulk and depending on the voltage imposed the contribution
of the surface elements could be overestimated. So, XPS analyses can determine the

elemental composition in the surface and in other region of the bulk using Ar
+
sputtering
in order to remove the upper layers [Era, 2005].
Figure 4.18: Bulk elemental values of O (far left), C (left), Cr (right), and N (far right)
in CrN75-10-3-10HP thin lm.
Only two CrN thin lms were selected: one of them (CrN75-10-5-10) with a high
amount of oxygen and the other (CrN75-10-3-10HP) with a low amount of O.
Element CrN75-10-3-10HP (%) CrN75-10-5-10 (%)
Surface Bulk Surface Bulk
O 1s 15.20 4.65 14.99 9.47
C 1s 44.79 3.67 57.24 13.85
Cr 2p 19.23 53.66 13.34 48.52
N 1s 20.79 38.01 14.43 28.15
Table 4.10: Elemental percentages after XPS analyses in the CrN surface and bulk of
CrN75-10-3-10HP and CrN75-10-5-10 samples.
O and C contaminants, were reduced in the bulk, so these contaminants are in the
surface after the atmosphere exposure. In other words, there were not high amount of
impurities in the working atmosphere during the deposition process. Thus, carbon and
oxygen were present in the surface in a high amount, but in the bulk the presence of
nitrogen and chromium were overwhelming.

Figure 4.19: Surface elemental percentages of CrN75-10-5-10 sample obtained by XPS
analyses. O (far left), C (left), Cr (right), and N (far right) elements are presented.
Comparing dierent samples showed that lms deposited with high power have a low
quantity of contaminants in bulk and a surface with low quantity of C contaminant with
regard to the lm deposited with low power. On the other hand, XPS detected a great
amount of chromium and small amount of nitrogen, but this eect was provoked by the
Ar
+
preferential sputtering [Jagielski, 2000] [Feldman, 1986]. Moreover, the amount of Cr
and N in the bulk were improved in CrN thin lms deposited under high power conditions,
showing that enhanced Cr energetic arrival promoted better lms.
Figure 4.20: Internal elemental composition of CrN75-10-5-10 thin lm obtained by XPS.
Oxygen is in the far left region, carbon in the left, chromium in the right and nitrogen in
the far right.
Comparing binding energies, the energy related to the C signal in bulk region is similar
to the tabulated value; however, in the surface this binding energy is higher than the

tabulated value. There is no such a high dierences between the two samples observed.
Regarding O signal, all peaks are located at lower energies than the tabulated value. Bulk
values in both samples are similar but in surface of CrN75-10-5-10 sample, this binding
energy is closer to the tabulated value. With N signal these energy values are lower than
the tabulated one and in bulk these values are close to the tabulated binding energy.
Moreover, Cr signals are at higher binding energies and the surface values are similar for
the two samples analysed. Bulk CrN75-10-3-10HP has the lower binding energy.
Finally, according with the dierent peak position in the energy axis and the appear-
ance of two peaks in Cr 2p signal, a possible formation in the very surface of hard Cr3C2
phase was suggested, but several analyses must be done in order to verify this statement
[Tsujimura, 2002].
4.8 Residual stress evolution with dierent experimen-
tal parameters selected
The tabulated lattice parameter for CrN is a = 4.140 Å, so according to the lattice
parameters measured, it is possible to obtain the residual stress in the CrN thin lms.
The residual stress can be calculated following this equation [Mallikarjuna Reddy, 2011]:
σ = −
E
2ν
a − a0
a0
,
where E = 200 GPa is the Young modulus for CrN, ν = 0.2 is de Poisson's ratio for
CrN, a is the tabulated lattice parameter and a0 is the measured lattice parameter. With
this equation, negative values represent tensile stresses and positive values represent com-
pressive stresses. It is customary that compressive stresses are negative velues, so our
calculation are given with GPa units.
After the stress calculation it was easy to compare the stress performance with the
change of experimental parameters. When only the nitrogen content in the atmosphere
was changed and the other parameters were xed, there was a gradual stress increase
[Engel, 1998]. The lower growth rate could be responsible of this augmentation, but the
main role possibly was the high amount of interstitial nitrogen lodged in the fcc crystal
structure, thus, compressive stresses were developed [Demaree, 1996].

Figure 4.21: Residual stress evolution after N2 addition in the working atmosphere. 10-
3-10 and 10-5-10HP experimental conditions selected.
Stress evolution with the molecular nitrogen content and the target-substrate variation
could be possible to do. For comparison, samples deposited at high power condition and 10
mTorr of working pressure were selected. At d = 3 cm the residual stress was higher than
at d = 5 cm, because of more distance implied lower energy and deected trajectories, so
the compressive stress development was hard to obtain [Nouveau, 2005]. At low power
and 10 mTorr this trend is hard to obtain. The stress increase with N2 content is related
again with the interstitial nitrogen population [Engel, 1998].
Figure 4.22: Stress evolution under varying nitrogen percentages and target-substrate
distances and working pressure (10 mTorr) and power (high condition) xed.
The next case analysed was the pressure variation with N2 change, too. Under low
power conditions and target-substrate distance of 5 cm it was observed that low pressure
provoked major changes in stress than high pressure [Nouveau, 2005]. Interestingly, in the
beginning, with 20 % N2 content, both stress values were the same but nitrogen addition
provoked higher dissimilar values. Only for 75 % N2 the stresses were compressive and

sample with 10 mTorr are almost stress-free. Tensile stresses are provoked by nitrogen
vacancies and metallic regions, so the addition of nitrogen reduced this eect.
High pressure conditions means more particles colliding with the sample, so a kind
of stress evolution can be explained by this, but at low pressure conditions the energetic
particles provoked structural changes and the stress developing measured.
Figure 4.23: Stress evolution changing the nitrogen content and the total working pressure.
Low power and d = 5 cm parameter are constants.
Figure 4.24: Residual stress development in function of power applied and the variation
of nitrogen content. Fixed working pressure to 10 mTorr and target-substrate distance to
5 cm.
Finally, xing the working pressure to 10 mTorr and the target-substrate distance to
5 cm it was possible to measure the eect of the power applied. When the molecular
nitrogen content was 20 % or 30 % the residual stress was tensile and under low power
conditions the samples are quasi stress-free [Nouveau, 2005]. The tensile behaviour at high
power condition could be provoked by the intense bombardment and the development of
nitrogen vacancies at these low nitrogen percentages. After that, there was a crossover

when N2 was 75 %. Stresses changed to compressive, but under low power conditions
and the other experimental parameters the stress development is almost zero. Under high
power the huge nitrogen amount developed compressive stress and with a higher value
with regard to the low power condition, perhaps again the high particle energy played an
important role, with the creation at this time of chromium vacancies.

Chapter 5
NiO lm characterization and
properties
5.1 Nickel oxide: general concepts
Nickel oxide (NiO) is a ceramic compound with many good properties in industry and
technology. At high temperatures, NiO has a fcc crystal structure, but under 525 K there
is a change to rhombohedral one with α = β = γ = 60.07◦
and with antiferromagnetic
properties [Neumann, 1984]. However, several analyses showed that the planar spacing
is similar to a fcc structure, so it is common to allocate NiO compounds as pseudo-fcc
crystal [Karpinski, 2011].
Figure 5.1: The ve target voltage regions when oxygen percentage is changed: 1) nickel
sputtering, 2) metallic regime, 3) transition regime, 4) partially poisoned regime, and 5)
fully poisoned regime [Karpinski, 2011].
Stoichiometric NiO is hard to obtain [Hotov`y, 1998] and it depends on the target
61

62 CHAPTER 5. NIO FILM CHARACTERIZATION AND PROPERTIES
voltage regime in Ni sputtering with Ar-O2 as working atmosphere [Karpinski, 2011].
Indeed, NiO is a typical p−type conductor because the O-excess in its structure. This
non-stoichiometry provokes electrical conduction by holes and nickel vacancies [Seo, 2004].
Changing the molecular oxygen percentage develops changes in the stoichiometry by two
main processes of vacancy creation:
O2
NiO
→ 2OO + 2VNi + 4h·
O2
NiO
→ Oi + VNi + OO + 4h·
The rst process is the substitutional mechanism and the second one is the interstitial
mechanism. Electrochromism can be detected in NiO lms with oxygen addition or
elimination [Lin, 2008]: NiO lms are transparent, but NiO1−x lms are opaque due to
the defects and the delocalized electrial holes, congured as colour centres, i.e. Ni
3+
ions
[Ma, 2013]. Bleaching and colouring states are reversible with temperature or electrical
changes. Moreover, gas sensor application is possible measuring the changes of resistivity
when the NiO detector is in contact with particular gases [Hotov`y, 1998].
NiO is applied in photovoltaic cells as buer layer in order to improve the ligh har-
vesting eciency and the conversion of photons in electrical carriers [Nguyen, 2013]. In
the eld of batteries and transistors [Seo, 2004] the use of NiO has huge interest because
of it is a Mott-Hubbard insulator [Adler, 1970], a class of insulator that under the classi-
cal band theories is conductor but experimentally is insulator because of the interaction
between band of like character, as 3d character in NiO case [Adler, 1970]. Electrons in
these orbitals interact and provoke Coulomb repulsion avoiding overlapping.
Indeed, NiO has resistive switching properties [Seo, 2005] in unipolar and bipolar
modes. After a forming current NiO thin lm act as conductor (Set condition) but after a
current threshold reached it changes to an insulating nature (Reset condition). These two
states (ON and OFF) are very stable in a high range of voltages, time and temperatures
with resistivities dierent in several orders of magnitude [Ahn, 2011] [Kügeler, 2010].
5.2 Experimental procedure
In order to deposit NiO lms, several parameters were xed. First, the working pressure
was 5 mTorr in all depositions, and the target-substrate distance was maintained at 3 cm.
Moreover, the total power applied was 100 W.
A pure Ni target was used in all the experiments, cleaned by Ar plasma and pre-
sputtered several minutes before the shutter removal. Molecular oxygen and argon were
used as atmosphere of high purity. The total gas ow was varied according to the amount
of molecular oxygen selected, but argon was xed to 10.0 sccm in all experiments.
Glass substrates (ESCO100, 18x18 mm
2
ERIE Scientic), cleaned only with dried
nitrogen blast, were used. The working atmospheres contained 12, 15, 21 and 28 % of

CHAPTER 5. NIO FILM CHARACTERIZATION AND PROPERTIES 63
molecular oxygen with argon balance (7, 9, 13 and 19 % relative to the maximum gas
ow, 10.0 sccm). This assured that NiO lms were deposited in each dierent discharge
regime observed in the target voltage evolution with O2 addition. Thus, respectively, NiO
lms have been deposited in the metallic region, the transition one, the partially poisoned
mode and the fully poisoned mode.
After few experiments, a clear determination of the growth rate could be done. So
after time deposition adjust was possible to deposit NiO thin lms with controlled thick-
nesses [Mocuta, 2000]. Indeed, a DC bias could be used in order to compare the NiO
behaviour after the change of kinetical parameters in the Ni and O ions attracted by the
susbrate holder electrical eld [Awais, 2010]. A clear drawback was the insulating nature
of substrates, but the biased environment could play an important role.
The deposited lms were labeled as NiO%-Xa, with % the molecular oxygen percentage
in the working atmosphere, X the selected parameter (thickness or bias), and a the units
of bias (V) or thickness (nm). It is important to mention that when bias was varied the
deposition time was always 10 min and when thickness was varied the substate holder
was always oating.
5.2.1 The role of the free mean path
It was seen that the sputtered target particles follow the Sigmund-Thompson distribution.
Considering as projectiles only Ar
+
ions with energy between 400 and 450 eV, SRIM
simulations give that the Ni sputtering yield is between 1.62 and 1.74 at/ion, respectively
[Ziegler, 2013]. These nickel particles have a mean energy of 19.81 − 20.63 eV/at if SRIM
parameters are used. If the theoretical expression is considered, the mean energy is
23.73−26.61 eV/at. Furthermore, the fraction of backscattered Ar is only the 5.64−5.78
% of total particles.
The next idea is conrm that the Ni sputtered particles arrive to the substrate with
this mean energy or not. That is, if the free mean path is greater or lower than the
target-substate distance (3 cm in this case). A complex expression considering several
species must be selected [Chen, 2005]:
λ =
1
n
x=1 πnxσ2
1x 1 + m01
m0x
,
with λ, the free mean path; nx the particle density of the species x; σ2
1x, the sum of the
projectile and the species x cross-sections (and divided by 2), and m the mass of the
projectile and the rest of the species.
In order to simplify, only neutral particles are considered, but the working gas con-
tents argon, atomic oxygen and molecular oxygen. Interestingly, using Optical Emission
Spectroscopy the O2:O ratio is calculated as 1:4, showing that the energetic electrons play
a crucial role in this reactor conguration. Under these assumptions, the free mean path

varies between 3.509 cm (NiO12 condition) and 3.333 cm (NiO28 condition), so there are
no collisions during the trip. Moreover, if only argon gas is considered (with an Ar
+
:Ar
ratio of 3:97), λ = 3.57 cm, assuring that all the energy extracted during the sputtering
is deposited on the substrate surface.
5.3 NiO deposited with dierent thicknesses
NiO thin lms have been deposited with dierent thicknesses: 10, 50, 100, 300, 500,
and 1000 nm [Mocuta, 2000]. The previous deposition rate characterization gave us the
following values:
O2 (%) 12 15 21 28
ξ (nm/min) 164.97 117.17 75.967 87.542
Table 5.1: NiO deposition rates with dierent O2 content.
With these parameters known the deposition times could be easily calculated. All
parameters were carefully controlled during the dierent experiments. It was observed a
growth rate reduction with O2, so the role of target poisoning [Hotov`y, 2003] is relevant
and it dicults the Ni sputtering.
5.3.1 θ/2θ XRD analyses
Diractograms were useful in order to obtain a clear comparison between dierent molec-
ular oxygen percentages. Also, the change of thickness could verify the kinetic growth of
these samples [Mallikarjuna Reddy, 2011b] [Payne, 2007]. With proper software CuKα2
line could be substracted, so quick identication with database values was accomplished.
Plane NiO (
◦
) Ni (
◦
)
(111) 37.092 44.599
(200) 43.095 51.909
(220) 62.584 76.807
(311) 75.042 93.217
(222) 79.008 98.082
Table 5.2: 2θ angular position of the main diraction planes of NiO and Ni compounds.
Regarding dierent thicknesses it was possible to see that using glass substrates and
with the experimental parameters used, crystallinity was reached in lms with 100 nm
thick and above. So, in the most cases, lms 10 nm and 50 nm thick were amor-
phous. After this value, there was crystalline development with a kind of (111) texture

CHAPTER 5. NIO FILM CHARACTERIZATION AND PROPERTIES 65
[Mallick, 2010], because at these initial stages (111) is the prevalent one in growth terms.
It is worth to mention that (111) planes has a lot of adsorption sites and lm growth in
this plane consumes low energies [Lindahl, 2009].
When big grains were developed during the coarsening and growth processes, other
mechanism began to inuence in the kinetic process. Thick lms had a kind of (200)
texture because of this plane reduces the surface energy [Chen, 2008] [Jang, 2008]. Thus,
lms grew in this plane faster than the (111) one.
Figure 5.2: X-Ray diractograms obtained in the Bragg-Brentano mode with dierent
thicknesses. a) NiO12, b) NiO15, c) NiO21, and d) NiO28.
NiO lms were deposited with dierent O2 percentages, so the target voltage region
was dierent in each of these. For example, NiO12 was deposited in the metallic regime.
This was clearly observed because of the arising of crystalline Ni. In some positions, there
were peak overlapping, so it was necessary a careful peak measurement. The other lms,
were deposited in the transition and in the poisoned regimes, so only NiO was detected by
XRD. It was observed that in NiO12 many other peaks arose (not only (111) and (200)
peaks) and in NiO15 samples the (222) peak prevailed at some extent.
Regarding the powder texture in the database it was possible to do a peak calibration
in order to know the true texture of these lms. Measuring the contribution of each NiO

peak in the powder sample and applying the following equation [Makhlouf, 2008]
TGhkl =
I(hkl)
Is
(hkl)
1
n
n
i=1
Ii(hkl)
Is
i(hkl)
,
with I(hkl) the intensity of (hkl) peak measured and Is
(hkl) the intensity of (hkl) standard
peak, it was possible to understand the dierent peak contribution.
With thickness increase there was a reduction of (311) plane contribution in NiO12
lms and a (220) contribution increase. These peaks prevailed perhaps due to the inter-
action with the growth of Ni agglomerates with an important crystallinity and related
texture [Payne, 2007]. Perhaps Ni(111) and Ni(200) consumed the nickel arriving on the
surface, so NiO grew with Ni remnants and promoted other planes than the (111) and
(200) ones. In NiO15 lms, always (222) prevailed and (200) plane increased when the
thickness has been augmented. As (111) and (222) planes are equivalent, this behaviour
could be explained by the surface energy reduction. Moreover, NiO21 and NiO28 pre-
sented (111) and (200) textures, typical from the poisoned mode. With thickness increase,
(200) texture prevailed [Karpinski, 2012].
Figure 5.3: Corrected plane contribution with thickness increase. Upper left: NiO12,
upper right: NiO15, lower left: NiO21, lower right: NiO28.
Furthermore, when corrected contributions were reordered with regard to the thick-
ness, an important clue was discovered when the O2 contribution was changed [Hotov`y, 2003].

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