ANALYSIS OF ANOMALOUS FILM GROWTH WHEN
YTTRIUM OXIDE IS EXPOSED TO VACUUMULTRAVIOLET LIGHT
Presenter: Devon R. Mortensen
Contributors: Thomas McConkie
David D. Allred
The Setup




Group members took some samples to Berkeley for
measurements using the Advanced Light Source.
When they got back we needed to measure the thickness of
one of the Y2O3 film samples. Before we could do this we
needed to put it in the plasma cleaner.
 Why? Because there is a sort of “gunk” composed mainly
of hydrocarbons that permeates all space and likes to
deposit itself on samples.
Problem: the plasma cleaner was broken.
Solution: Let’s use the excimer (VUV) lamp instead. This lamp
generates photons at 7.2eV, which are so energetic that
they only go about 1 cm in air before they are absorbed.
Enter the Mystery


After approximately 5 minutes under the VUV lamp,
the sample became visibly thicker.
Use ellipsometry measurements to determine if this
is true.
 Before
cleaning: 24.94 nm
Generated and Experimental
100
200
Model Fit
Exp Y -E 75°
Model Fit
Exp D-E 75°
100
60
0
40
-100
20
0
1.0
2.0
3.0
4.0
5.0
Photon Energy (eV)
6.0
-200
7.0
D in degrees
Y in degrees
80
4
3
2
1
0
srough
polycarb
ema y2o3/30% void
sio2_jaw
si_jaw
0.500 nm
0.000 nm
24.733 nm
2.000 nm
1 mm
Thick.2 =24.733±0.139 nm
Ellipsometry Measurements
 After
5 min VUV: 31.061 nm
Generated and Experimental
100
300
Model Fit
Exp Y -E 70°
Exp Y -E 72°
Exp Y -E 74°
Exp Y -E 76°
Exp Y -E 78°
Exp Y -E 80°
Model Fit
Exp D-E 70°
Exp D-E 72°
Exp D-E 74°
Exp D-E 76°
Exp D-E 78°
Exp D-E 80°
60
40
20
0
1.0
2.0

200
100
D in degrees
Y in degrees
80
3
2
1
0
srough
y2o3 constants based on 091130b on si
sio2_jaw
si_jaw
Thick.2 =31.061±0.0717 nm
0
3.0
4.0
Photon Energy (eV)
5.0
-100
6.0
As you can see this is quite a significant change.
24.94 nm
0.500 nm
31.061 nm
1.800 nm
1 mm
31.06 nm
Search for the Answer
Big question is: What’s going on here?
First thought: the yttrium is not fully oxidized.


Thickness vs. Time under VUV
091130b sample
90
80
Thickness (nm)
70
60
Piece 1
50
Theory
40
If the yttrium were
complete unoxidized
expected film growth
would be 3.34 nm
Actually film growth
was 6.12 nm
30
20
10
0
0
10
20
Time (min)
30
40
Second Theory

Is it possible that the VUV lamp is actually
depositing material onto the sample?
 Not
possible that more Y2O3 is being added to film.
 Perhaps it is knocking molecules off of the support base
and these molecules are finding their way to the
sample.

Subject a blank silicon substrate to same VUV
treatment and look for film deposition.
Blank Silicon Wafer

Before VUV:
Generated and Experimental
50
180
Model Fit
Exp Y -E 75°
Model Fit
Exp D-E 75°
150
120
30
90
20
60
10
0
1.0

30
2.0
3.0
4.0
5.0
Photon Energy (eV)
6.0
srough
0.000 nm
y2o3 constants based on 091130b on si after0.000
5 minnm
vuv
sio2_jaw
2.074 nm
si_jaw
1 mm
MSE=5.786
Thick.1 =2.074±0.0081 nm
0
7.0
180
Model Fit
Exp Y -E 75°
Model Fit
Exp D-E 75°
40
150
120
30
90
20
60
10
30
2.0
3.0
4.0
5.0
Photon Energy (eV)
6.0
0
7.0
D in degrees
Y in degrees
3
2
1
0
After
5 min VUV:
Generated and Experimental
50
0
1.0
D in degrees
Y in degrees
40
3
2
1
0
srough
0.000 nm
y2o3 constants based on 091130b on si after0.000
5 minnm
vuv
sio2_jaw
2.221 nm
si_jaw
1 mm
MSE=6.713
Thick.1 =2.221±0.00942 nm
Blank Silicon Wafer

After 10 min VUV:
Generated and Experimental
50
180
Model Fit
Exp Y -E 75°
Model Fit
Exp D-E 75°
150
120
30
90
20
60
10
0
1.0

D in degrees
Y in degrees
40
30
2.0
3.0
4.0
5.0
Photon Energy (eV)
6.0
3
2
1
0
srough
y2o3 constants based on 091130b on si
sio2_jaw
si_jaw
MSE=9.096
0.000 nm
0.000 nm
1.797 nm
1 mm
Thick.1 =1.797±0.012nm
0
7.0
After 25 min VUV:
Generated and Experimental
50
180
Model Fit
Exp Y -E 75°
Model Fit
Exp D-E 75°
150
120
30
90
20
60
10
0
1.0
30
2.0
3.0
4.0
5.0
Photon Energy (eV)
6.0
0
7.0
D in degrees
Y in degrees
40
3
2
1
0
srough
0.100 nm
ema y2o3 constants based on 091130b on si0.000
after 10
nmmin
sio2_jaw
1.863 nm
si_jaw
1 mm
MSE=8.125
Thick.1=1.863±0.0112nm
First Set of Conclusions





No apparent change in thickness of the silicon
witness.
It doesn’t seem likely that the VUV lamp is
depositing material onto our film.
Only other option is that what is already on the film
is somehow being altered.
It is possible that the Y2O3 is catalyzing the
oxidation of the silicon wafer underneath.
Let’s take a closer look at what is happening to the
optical constants:
Optical Constants




At 2.4 eV (516 nm light) Y2O3 has an index of
refraction of 1.938
Silicon dioxide has an index of 1.466
The formation of SiO2 should lower the total index of
the material.
The data was fit using a Cauchy model, allowing the
parameters to vary to fit for optical constants.
Optical Constants
Index of Refraction at 2.4 eV
2
1.9
n
1.8
Sample
1.7
SiO2
Y2O3
Y2O3 w/ 20% voids
1.6
1.5
1.4
0
5
10
15
Exposure time to VUV (min)
20
Effects of the Furnace


It seems that the possibility of silicon oxidation is a
viable one.
If the silicon has indeed become oxidized the
thickness should not go down when placed in a
furnace.
 SiO2 is
quite stable and silicon wants to be oxidized
anyway.

Before furnace:
Generated and Experimental
100
300
Model Fit
Exp Y -E 70°
Exp Y -E 72°
Exp Y -E 74°
Exp Y -E 76°
Exp Y -E 78°
Exp Y -E 80°
Model Fit
Exp D-E 70°
Exp D-E 72°
Exp D-E 74°
Exp D-E 76°
Exp D-E 78°
Exp D-E 80°
60
40
20
0
1.0

2.0
3.0
4.0
5.0
Photon Energy (eV)
200
D in degrees
Y in degrees
80
100
0
6.0
0.500 nm
98.259 nm
1.800 nm
1 mm
MSE=58.82 Thick.2 =98.259±0.168 nm
-200
7.0
After 2 hours in furnace:
Generated and Experimental
150
Model Fit
Exp Y -E 70°
Exp Y -E 72°
Exp Y -E 74°
Exp Y -E 76°
Exp Y -E 78°
Exp Y -E 80°
Model Fit
Exp D-E 70°
Exp D-E 72°
Exp D-E 74°
Exp D-E 76°
Exp D-E 78°
Exp D-E 80°
60
40
20
2.0
3.0
4.0
5.0
Photon Energy (eV)
100
50
0
D in degrees
Y in degrees
srough
y2o3 constants based on 091130b on si
sio2_jaw
si_jaw
-100
80
0
1.0
3
2
1
0
3
2
1
0
srough
y2o3 constants based on 091130b on si
sio2_jaw
si_jaw
0.500 nm
16.938 nm
1.800 nm
1 mm
MSE=17.41 Thick.2 =16.938±0.016 nm
-50
6.0
-100
7.0
Over an 80% decrease in thickness
The Mystery Continues

Maybe the sample is simply being puffed up.
 Boiling
water
 Ozonide
The Mystery Continues

How would we be able to tell?
 TEM
imaging might be able to reveal what is
happening to the structure of our sample.

Need to reconcile one important piece of data.
A
piece of the same sample, when first put in the
plasma cleaner, exhibits none of these effects.