1. Using CFD (Computational Fluid Dynamics) to find
the uniformity problem in semiconductor furnace
process
Tzu-Jeng Hsu 徐子正

2. Problem of uniformity
• Problem description
– oxidation process with atmosphere (AP) furnace
– There are totally 150 wafers in the furnace.
– From 10th to 25th wafers’ uniformity is worse than
other wafers
• The phenomena of problem
– Must be the first run after periodic maintenance
for the furnace.

3. Vertical furnace
inlet
outlet
Showerhead
Structure of vertical furnace
Boat
Inner
tube
Outer
tube
outlet
inlet
Shower
head
wafers
wafers
• All hydrogen gas
has burn to water
vapor under
temperature 800
C. The mixing
flow is only for
H2O and O2
• Inlet is attached
on outer tube,
outlet is attached
on inner tube .
• Gas in flowing
from outer
tube(inlet), and
flow out on
bottom of inner
tube (outlet)

4. After ignition, 1.31094 seconds
• Time is 1.3109e seconds
• Color is the H2O concentration,
rad is 0.2394, blue is zero H2O.
• Outer tube is filled with H2O vapor
(red color)
• Inner tube bottom is blue color,
which is represent with none of
H2O and 100% nitrogen gasOuter
tube
Inner
tube

5. After ignition, 3.31094 seconds
• Time is 3.3109e seconds
Outer
tube
Inner
tube

6. After ignition, 52.3109 seconds
• Time is 52.3109 seconds
• All tubes are near uniform with
H2O (max. concentration is 0.2394)
Outer
tube
Inner
tube

7. 反應啟動後時間: 第3秒
紊流區
紊流造成
濃度不均勻
俯視圖
動線-側視圖
動線-俯視圖

8. Compare the turbulence
between 3rd seconds and 52nd seconds
• The turbulence is existing both 3rd seconds condition and
52nd seconds condition.
• The turbulence is the root cause of uniformity problem.
Left figure is concentration, right figure is the turbulence
52nd seconds3rd seconds
turbulence turbulence
Left figure is concentration, right figure is the turbulence

9. Simulation result and summary
• In this simulation, the transition state of flow
is initially from 0 second (inlet) flow into tubes,
and continuously flow 180 seconds stopped.
• The 1st wafer covered with H2O at 46th second
• At 140th second, all wafers will be fully and
uniformly covered with H2Ocentration in tube.
• Between the 46th second and the 140th second,
is not uniform situation. It’s the root cause of
wafer film thickness variation.

10. Simulation Model
Base on the FLUENT
(CFD, computation fluid dynamics)

11. Model information of simulation
• CFD (computational fluid dynamics) software: FLUENT (ANSYS Inc.)
• Gas phase with species transportation model,
• Operation pressure :near normal atmosphere(755 torr~760yorr)
• Energy conservation: With temperature consideration, 800C
• Turbulence model : K- model with realize option.
• Inlet flow rate : total 10 liter/min gas, 65% oxygen, 35% hydrogen
• Mesh : ~5.8 million tetrahedron elements with ANSYS MESH
• Computation time : 36 hours with 4 cores 2.1Mhz (8 threads)
parallel calculation.
• Pre-process software : Design-Modeler
• Post-process software : ANSYS CFD-post