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Analysis of
Anomalous Film
Growth when Yttrium
Oxide Thin Films are
Exposed to 7.2eV
Light
Alison Wells
Dr. David D. Allred
Devon Mortenson
Kristal Chamberlain

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Background

Group members took some samples to Berkeley for measurements using the Advanced Light
Source.

When they got back needed to put it in the plasma cleaner.

Why? Because there is a sort of “gunk” composed mainly of hydrocarbons deposited on samples.

Problem: the plasma cleaner was broken.

Solution: Use the excimer (VUV) lamp instead.

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Background Continued
The Mystery

After approximately 5 minutes under the VUV lamp, the sample became visibly thicker.

Use ellipsometry measurements to determine if this is true.

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Ellipsometry Measurements: Y2O3
Before cleaning: 24.94 nm
100
80
60
40
20
Generated and Experimental
Model Fit
Exp Y -E 75°
Model Fit
Exp D -E 75°
0
1.0
2.0
3.0
4.0
Photon Energy (eV)
5.0
4 srough
3 polycarb
2 ema y2o3/30% void
1 sio2_jaw
0 si_jaw
6.0
200
100
0
-100
-200
7.0
0.500 nm
0.000 nm
24.733 nm
2.000 nm
1 mm
After 5 min VUV: 31.061 nm
100
80
60
40
20
Generated and Experimental
Model Fit
Exp
Exp
Y -E 70°
Y -E 72°
Exp
Exp
Y -E 74°
Y -E 76°
Exp Y -E 78°
Exp Y -E 80°
Model Fit
Exp
Exp
D -E 70°
D -E 72°
Exp D -E 74°
Exp
Exp
D -E 76°
D -E 78°
Exp D -E 80°
300
200
100
0
0
1.0
2.0
3.0
4.0
Photon Energy (eV)
5.0
-100
6.0
3 srough 0.500 nm
2 y2o3 constants based on 091130b on si 31.061 nm
1 sio2_jaw
0 si_jaw
1.800 nm
1 mm

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In Search for an Answer
Big question is: What’s going on here?
90
80
70
60
50
40
30
20
10
0
0
Thickness vs. Time under VUV
091130b sample
10 20
Time (min)
30 40
Piece 1

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First Theories

First thought: the yttrium is not fully oxidized.

Too thick

Is it possible that the VUV lamp is actually depositing material onto the sample?


Not possible that more Y
2
O
3 is being added to film.
Subject a blank silicon substrate to same VUV treatment and look for film deposition.

No growth

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First Set of Conclusions
It doesn’t seem likely that the VUV lamp is depositing material onto our film.

Oxidation of Silicon Substrate

Thickness decreases in furnace

Only other option is that what is already on the film is somehow being altered.

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Second theories and Tests (cont.)
Necessity of VUV Interaction with Sample
100
Effects of Glass Shield on Film Growth
90
80
70
60
50
40
30
20
10
0 unshielded sample glass shielded sample before after

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Second theories and Tests (cont.)
Necessity of an ozone
Comparing Film Growth
100
80
60
40
20
0
Argon purge Nitrogen
Purge
Atmosphere
Before
After

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Look at Neighboring
Oxide
What would happen to a scandium oxide when exposed to same VUV treatment.

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Comparing Oxides
Water in the voids
Y2O3

May be slightly hydroscopic

Reactively Sputtered sample
Sc2O3

Insoluble in water

Natural oxidation vs. reactive sputtering

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Ellipsometry Measurements:
Natural Oxidized Sc2O3
Before VUV: 22.842 nm After 40 min: 23.310 nm

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Ellipsometry Measurements:
Reactively Sputtered Sc2O3
Before Cleaning: 12.528 nm After 5 min VUV: 13.218 nm

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Ellipsometry Measurements:
Reactively Sputtered Sc2O3
After 10 min VUV: 14.406 nm After 20 min VUV: 15.524 nm

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Ellipsometry Measurements:
Reactively Sputtered Sc2O3
After 40 min VUV: 17.902 nm After 70 min VUV: 17.203 nm

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The Mystery Continues
Future Work

Thicker Films

Use XPS to look at oxygen to metal ration

Observe other oxides

Deposit Silicon cap over samples

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Thank You
Brigham Young University Physics Department
Dr. David D. Allred
BYU Thin Film Optics Research Group