1. -Honors Thesis Defense- In 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
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

2. Joseph Choi, Dept. of Physics, Brigham Young University
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.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

3. Joseph Choi, Dept. of Physics, Brigham Young University
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.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

4. 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©)
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

5. Joseph Choi, Dept. of Physics, Brigham Young University
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; torr).
Real-time in situ ellipsometric measurements to analyze Ru thin film and its oxidation.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

6. Joseph Choi, Dept. of Physics, Brigham Young University
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.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

7. Conflat flange- Copper seal
Thermocouple
Bake out power control- Variac + Transformer
Cleaning agent- Methanol
Heating tape- Bake out
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

8. Joseph Choi, Dept. of Physics, Brigham Young University
Vacuum Pumps
Principle
- Cold trap.
- Large surface area.
Sorption pumps
- Atmosphere to roughing pressure (10-3 torr).
Cryopump
- To UHV pressure.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

9. 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 s- reflectance ratio.
Δ: Difference in phase of p- and s- reflection.
Ψ and Δ related by reflectance:
Optical constants, thickness obtainable with computer using Ψ, Δ.
Geometry of an ellipsometric experiment, showing the p- and s- directions
[1]J.A.Woollam Co., Inc., Guide to Using WVASE32TM.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

10. Joseph Choi, Dept. of Physics, Brigham Young University
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

11. 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 ( kV) 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]
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

12. Sputter Gun Mechanism in Vacuum Chamber
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

13. 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.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

14. Overview of Components (cont.)
Sample Stage
- Hold film.
Shutter
- Controlled deposition.
Crystal Monitor (MaxTek, Inc.)
- Measure deposition rate and amount.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

15. Overview of Components (cont.)
Oxygen line
- UHV leak valve.
- Controlled oxidation of sample.
Argon line
- Gas medium for plasma.
- To vent chamber. O2 Ar
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

16. Joseph Choi, Dept. of Physics, Brigham Young University
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 .
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

17. Joseph Choi, Dept. of Physics, Brigham Young University
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.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

18. 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.
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University

19. Joseph Choi, Dept. of Physics, Brigham Young University
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
11/17/2018
Joseph Choi, Dept. of Physics, Brigham Young University