-Honors Thesis DefenseIn Situ Ellipsometry of Surfaces in an
Ultrahigh Vacuum Thin Film
Deposition Chamber
Joseph Choi
Department of Physics and Astronomy,
Brigham Young University
June 19, 2001
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
1
Definition of Terms
UHV (ultrahigh vacuum)- Base pressure < 10-9 torr.
(Atmospheric pressure is 7.6 x 102 torr)
Ellipsometry- Optical measurement technique of
reflection, transmission, optical constants, and thickness
using polarization of light.
In situ- Measurement inside the chamber without opening
to the atmosphere.
Evaporation- Deposition of material by thermally heating
it using metallic boats with high resistance.
Sputtering- Deposition by bombarding positive ions onto
the material, and physically vaporizing it.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
2
Research Goals
Building:
Build a UHV (ultrahigh vacuum) chamber
with in situ ellipsometry, sputtering, and
evaporation capabilities.
Measurement / Modeling:
Measure and develop model for thin film
oxidation.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
3
Motivation – Study of Oxidation
Reflectance of
a silicon film
can vary from
70% to below
5% dependent
on oxidation.
Immediate
oxidization
when exposed
to atmosphere.
(Model of a silicon film produced using IMD©)
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Thesis Description
Design and building of vacuum chamber from
stainless steel body made by Varian, Inc. – Since
April 2000.
UHV, ellipsometry, deposition, procedures.
Ruthenium thin film ( 290 Å) sputtered in HV
(high vacuum;10-8-10-6 torr).
Real-time in situ ellipsometric measurements to
analyze Ru thin film and its oxidation.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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UHV Vacuum (10-9 torr)
Benefit- Purity of film:
- Comparison with HV (10-6 torr): Gas flux  1 cm2/sec.
Achieving UHV:
- Cleanliness: No oil; cleaning agents (hexane, methanol).
- Bake out: > 250 ºC to eliminate water, hydrogen, speed
degassing.
- Parts: Minimize o-rings, use metal-to-metal seals.
- Material: Low outgas rates (Aluminum, stainless steel).
- Machining: Inert gas welding or vacuum brazing.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Conflat flangeCopper seal
Thermocouple
Bake out power controlVariac + Transformer
Cleaning agentMethanol
6/28/2016
Heating tapeBake out
Joseph Choi, Dept. of Physics,
Brigham Young University
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Vacuum Pumps
Principle
- Cold trap.
- Large surface area.
Sorption pumps
- Atmosphere to roughing
pressure (10-3 torr).
Cryopump
- To UHV pressure.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Overview of Components
The Ellipsometer[1]
-
-
-
Usage of p- and s- polarization
of the E(Electric)-field.
Measurement of Ψ and Δ:
Ψ: Magnitude of p- to sreflectance ratio.
Δ: Difference in phase of pand s- reflection.
Ψ and Δ related by reflectance:
Rp
 tan(  )ei
Rs
Optical constants, thickness
obtainable with computer using
Ψ, Δ.
6/28/2016
Geometry of an ellipsometric experiment, showing
the p- and s- directions
[1]J.A.Woollam
Co., Inc., Guide to Using WVASE32TM.
Joseph Choi, Dept. of Physics,
Brigham Young University
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6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
10
Overview of Components (cont.)
Sputter Gun
-
We use Mighty MAK 4” from US
Inc.
Principle of Operation:[2]
1. Under vacuum, fill chamber with
noble gas. Our chamber uses Ar.
2. By applying a mostly negative
potential (0.5 - 5kV) to the target
material, while grounding the outer
parts, Ar is positively ionized and
bombards the target material,
physically knocking the atoms off
onto the film.
[2] http://www.sputteringmaterials.com/sputtering_technology.htm
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Sputter Gun Mechanism in Vacuum Chamber
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Overview of Components (cont.)
Evaporator
-
-
-
A 3 boat evaporator using 4
medium current feedthroughs
from MDC.
Alumina ceramic shields to
protect cross-contamination.
Principle of Operation:
Heating of metallic boats using
current; thermally evaporate
material.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Overview of Components (cont.)
Sample Stage
- Hold film.
Shutter
- Controlled deposition.
Crystal Monitor
(MaxTek, Inc.)
- Measure deposition rate
and amount.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
14
Overview of Components (cont.)
Oxygen line
O2
- UHV leak valve.
- Controlled oxidation of
sample.
Argon line
- Gas medium for plasma.
- To vent chamber.
Ar
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
15
Ruthenium Thin Film
May 3, 2001: Ru
sputtered in 1x10-6 torr.
Real-time in situ analysis:
in HV, Ar venting,
atmosphere.
Improved Ru optical
constants.
RuO2 thickness fit.
Little apparent oxidation .
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Current Status
Base vacuum
pressure- 1.5 x 10-7
torr.
Training:
Evaporator installed
with chromium boat.
Bake out and pump
down chamber.
In situ analysis of
chromium.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Comments on Length of Thesis
Majority of research was in building the
UHV system- over a year.
Training purpose:
Recording of effort that goes into building a
vacuum deposition system.
Understanding of procedures and components.
Details to clarify possible questions of system.
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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Credits and Thanks
Dr. David Allred
J.J. Warriner, Greg Harris
Zach Barton, Brian
Schramm
Department of Physics and
Astronomy, Honors
Department
ORCA, Multi-cultural
Scholarship, SPIE
6/28/2016
Joseph Choi, Dept. of Physics,
Brigham Young University
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