This document discusses antireflection coatings. [1] Antireflection coatings are applied to optical surfaces to reduce reflection and improve efficiency. [2] They work through destructive interference between light reflecting off the coating surface and light reflecting off the underlying surface. [3] Common techniques for depositing antireflection coatings include chemical vapor deposition, physical vapor deposition, and plasma-enhanced chemical vapor deposition.

1. EPL - 211
Presentatio
n
on
Antireflection coatings
Presented by –
Ajay Singh
2010ph10821

2. ANTIREFLECTION COATINGS
REFLECTIO
N

3. What is antireflective coating ?
Antireflective or anti-reflection (AR) coating is a type of optical
coating applied to the surface of lenses and other optical devices to
reduce reflection.This improves the efficiency of the system since less
light is lost.
Antireflection is achieved by destructive interference between……
coating coating
Where does blue light disappear ?

4. ’
For destructive interference Δ = (2m+1) λ/2
2nd = (2m+1) λ/2 => d = λ/4nc = λ’/4
d = minimum required thickness of coating
λ’ = wavelength in coating medium

5. Formation of antireflection coating
CHEMICAL VAPOUR DEPOSITION
:
 Layer deposition involves chemical reactions
 Large density films
 Good stoichiometry & uniformity over large surface area.
 SiO2 SiN, SiON, SiOC , and TiO2 with proper thickness are
the common AR material deposited chemically.
LIMITITATION :
 Required high temp to produce high quality material and for
many application the substrate cannot tolerate being heated
so not useful in that case .

6. PHYSICAL VAPOUR DEPOSITION
 A variety of vacuum deposition
 Purely physical process , no
chemical reaction involved.
 Process involved three steps:
• Evaporation
• Transportation
• Deposition
 multiple coating layers possible
 MgF2 coating on glass

7. Advantages of PVD
 Almost any type of inorganic material can be
used as well as some kinds of organic materials.
 The process is more environmentally friendly
than processes such CVD.
Disadvantages
 High capital cost
 Equipment size large because vacuum required
 Processes requiring large amounts of heat require
appropriate cooling systems
 The rate of coating deposition is usually quite slow

8. PLASMA ENHANSED CHEMICAL VAPOUR DEPOSITION
 Combined process of both CVD and PVD
 a process used to deposit thin films from a gas state
(vapour)
to a solid state on a substrate.
 Chemical reactions are involved in the process, which
occur after creation of a plasma of the reacting gases
 The plasma is generally created by RF (AC) frequency
or DC discharge between two electrodes, the space
between which is filled with the reacting gases.
 Processing plasmas are typically operated at pressures

9. of a few millitorr to a few torr , although arc discharges and
inductive plasmas can be ignited at atmospheric pressure

10. Advantages of PECVD
 Plasma enhanced CVD is most useful because it can deposit layers on fragile
substrates that cannot withstand the high temperatures of other CVD methods
 Plasma enhanced CVD systems allow for greater control of the film
composition, density, and film stress.
 Higher deposition rate at low temperature relatively
Disadvantages
 Plasma can cause damage to the substrate surface when either secondary
electrons collide with the wafer surface or the energy of the ion bombard-
ment becomes too high.
 High cost.

11. How much reflection while using AR coating ?
Can be reduced up to ~ 0.2%

12. APPLICATION OF ANTIREFLECTION COATING
 Anti-reflection coated optical windows
 Reflex free sight glasses
 Laser scanner windows
 Contrast enhancement
 Anti glare coated instrument windows
 Sensor technology Glass with MgF2 coating
 Low reflection camera windows
 Holography components
 Antireflection coated glass for displays
 In microelectronic photolithography to
reduce image (substrate) distortions .
solar cell with SiO coating

13. Reference links :
 http://en.wikipedia.org/wiki/anti-reflectivecoating
 http://www.pgoonline.com/intl/katalog/antireflection.html
 http://hyperphysics.phy-
astr.gsu.edu/hbase/phyopt/antiref.html
 http://www.rp-photonics.com/anti_reflection_coatings.html
 http://www.guardian.com/oracleprd/groups/guardiandotco
m
 http://www.pveducation.org/pvcdrom/design/anti-reflection-
coatings
 http://www.eere.energy.gov/basics/renewable_energy/pv_
contacts_coatings.html