Transcript Document

Updates of Iowa State University
S. Dumpala, S. Broderick and K. Rajan
Sep – 18, 2013
Summary
• Refinements in Environmental chamber set up for in-situ gas reactions
• Oxidation studies of Al using new set up of E-cell
• Preliminary analysis of silicon oxidation results in comparison with ReaxFF
simulations (Adri’s papers)
• Further analysis of silicon oxidation growth mechanisms and sub oxide
species at different temperatures
• Study of Si tips from Maryland using APT
Aluminum Oxidation
E-Cell
APT Results
Bulk Alumina Phase
 3D atomic scale interfacial analysis
(structural and chemical)
 Stoichiometry of different phases observed
 Inter-diffusional characteristics of elements
Bulk Al Phase
Reduced Contamination with In-situ E-Cell Oxidation
Ex-situ Oxidation
Unkown peaks.
In-situ E-cell Oxidation
•
Numerous additional peaks representing contamination that were detected in ex-situ
oxidation were absent in in-situ oxidation results.
Increased Mass Resolution with In-situ E-Cell Oxidation
Ex-situ Oxidation
In-situ E-cell Oxidation
Unkown peaks.
•
Lower mass resolution with longer tails of the peaks were seen in ex-situ
APT of Si Tips from Maryland : Anode Voltage: 250 V of Argon exposure
Bare Si Tip
50 monolayers
150 monolayers
• Laser APT – 1nj (laser power)
• Higher Ar content in beam exposed tips compared to bare Si tip
Bare Si Tip
Mass Spectra
50 monolayers
1. Small peak of Ar
150 monolayers
2. Check other condition tips
(Different beam currents)
3. Different deposition thickness
of monolayers
4. FIM studies
Oxidation of Silicon
ReasFF Simulations
APT- Experimental
• Hyper thermal oxidation (atomic
and molecular oxygen beam
source)
• Plasma oxidation (ambient oxygen)
• Dynamic study
• Static study (post deposition study)
• Smaller time scales (3pc)
• Longer time scales (minutes)
• Monolayer detection
• Sub nano scale detection
Interfacial Diffusion – Interfacial Width
383 K
100
548 K
2 nm
90
90
80
Concentration (at%)
Concentration (at%)
2.5 nm
100
70
60
50
40
30
20
10
80
70
60
50
40
30
20
10
0
0
-5
-4
-3
-2
-1
0
1
Distance (nm)
-4
-2
0
2
3
2
4
5
-5
4
-4
-4
-3
-2
-2
-1
0
1
Distance (nm)
0
2
2
3
4
4
5
-2
-2
0
0
2
2
Diffusion Profiles – Sub Oxides
100
90
Region II
Region I
Concentration (at%)
Region III
70
60
50
40
30
20
80
2.5 nm
548 K
50
40
30
20
0
0
-3
25
-2
-1
0
1
2
3
4
Region I
Region II
60
10
-4
Region III
70
10
-5
-5
5
-4
-3
-2
-1
0
1
2
3
4
5
Distance (nm)
Distance (nm)
20
Si2O %
20
SiO
15
SiO2
10
5
Concentration (at%)
Concentration (at%)
100
90
80
Concentration (at%)
2 nm
383 K
18
16
Si2O %
14
SiO
12
SiO2
Si2O %
10
SiO2
SiO
8
6
4
2
0
0
-5
-4
-3
-2
-1
0
1
Distance (nm)
2
3
4
5
-5
-4
-3
-2
-1
0
1
Distance (nm)
2
3
4
5
Analysis of Interfacial Sub Oxides – Comparison of Simulations with APT
Average Concentration (at%)
ReaxFF Simulation
6
Atom Probe (Interfacial Region)
Si2O
5
SiO
4
SiO2
3
Si2
SiO
2
1
0
• Interface region – Between bulk Si, and bulk
silica (region II from proxigrams)
• The total number of sub oxide species
Region II
Region III
increase with increase temperature, observed
similar trend in APT results
• Relative amounts/ratio of Si+1 (Si2O), Si+2
(SiO) at two different temperatures agrees
with simulations
• Silica layer – 1. Surface, 2. Bulk (Si+4
components in interface)
Average Concentration (at%)
383 K
8
Si2O
7
SiO
6
5
548 K
SiO2
4
3
2
1
0
383 K
548 K
Analysis of Si+4 (SiO2) Oxides – Comparison of Simulations with APT
16
Average Concentration (at%)
ReaxFF Simulation
Atom Probe (Silica Region)
14
Si2O
12
SiO
10
SiO2
8
6
4
2
0
383 K
•
548 K
For 8 ML, the number of Si4+ components is much higher at low temperatures
than at high temperatures, indicating that the initial growth of the silica (SiO2)
Region
II
Region
layer
occurs
much faster at low
thanIIIat high temperature
• After 32 ML, number of Si4+ components is almost same at all temperatures
indicating that the silica layer now grows faster at higher temperatures, but its
nucleation started later
• APT results also indicate the presence of almost same number of Si4+(SiO2)
components at both the temperatures
Growth Mechanism - Low Temperature
ReaxFF
- 300 K
500
450
400
350
APT
300
- 383 K
25
100
Region II
Region I
70
200
60
50
40150
30
20
100
20
15
Average Concentration (at%)
Region III
80
Concentration (at%)
90250
Concentration (at%)
14
2 nm
Si2O %
12
SiO
10
SiO2
10
5
10
0
-5
50
•
•
-4
-3
-2
-1
0
Distance (nm)
1
2
3
4
5
Si2O
SiO
SiO2
8
Si2O %
SiO2
6
SiO
4
2
0
0
-5
-4
-3
-2
-1
0
1
2
3
4
5
Region I
Region II
Region III
Distance (nm)
0
Stage
I - Growth of sub oxides and an incipient silica layer growth
I
Region II
III
Stage II -1)Region
Continued
growth of
sub oxides and alsoRegion
growth
of silica observed, 2) Inward
growth rate of sub oxides drops (high activation energy) (mainly Si2O) due to fast
-3
-2
-1
0
1
2
3
4
5
conversion of Si+1 Si+2 Si+4
• Stage III, IV - Growth of sub oxides and silica slowed down
Growth Mechanism - High Temperature
ReaxFF - 1300 K
500
450
400
350
APT300- 548 K
80
Region III
200
70
Region I
Region II
60
50
150
40
30
100
20
14
18
Si2O % 12
16
10
SiO
14
12
SiO2
10
8
6
4
2
10
-5
-4
-3
-2
-1
0
1
2
3
4
-5
5
SiO
SiO2
S
8
Si2O %
S
SiO
S
6
SiO2
4
2
-4
-3
-2
-1
0
1
2
3
4
5
Region I
Region II
Region III
Distance (nm)
Distance (nm)
20
Si2O
0
0
50
0
•
•
Average Concentration (at%)
90
Concentration (at%)
2.5 nm
250
Concentration (at%)
100
16
20
0
18
Concentration (at%)
Regionof
I sub oxides and
Region
Region
III growth
Stage I - Growth
anII incipient silica
layer
Si2O %
14
SiO
Stage II -1) Continued growth
of sub oxides and also growth of silica observed, 2) Inward
12
SiO2
-310 growth
-2 rate-1of sub
0 oxides
1
2
3 does
4 not drop
5
still continues
as in lower temperature case
• 8 Stage III, IV – 1) Continued growth of sub oxides (interstitial neutral oxygen atoms
6
4 surmount the activation energy barrier at threshold T of 500 K), 2) Interface (consisting of
2
sub oxides) is thicker than low T and 3) Inward growth of silica slows down
0
16
Si2O %
SiO
SiO2
Effect of Temperature on Growth Mechanism
500
ReaxFF
450
400
350
300 - 383 K
APT
25
Region III
80
Region II
500
70
Concentration (at%)
250
90
Concentration (at%)
14
2 nm
Region I
200
60
50
450
150
40
30
20
100
10
0
-5
-4
50
400
350
-3
Si2O %
20
12
10
SiO
15
Average Concentration (at%)
100
SiO2
Si2O %
-1
0
1
2
3
4
SiO
5
-4
-3
-2
-1
0
1
2
3
4
20
Region I
2.5 nm
-1
Region II
0
Region I
1
150
40
30
100
20
Region II
Region III
18
60
50
Region I
2
3
16
4
14
Si2O % 12
5
SiO
14
12
SiO2
10
8
6
4
10
2
10
-5
-4
-3
-2
Region II
Region III
-1
0
Distance (nm)
1
2
3
4
5
Si2O
SiO
SiO2
8
Si2O %
SiO
6
SiO2
4
2
0
0
50
0
2
5
Average Concentration (at%)
70
-2
Region III
200
4
16
Concentration (at%)
Concentration (at%)
90
-3
80
6
Distance (nm)
Distance (nm)
250
SiO2
8
0
-5
5
300
APT
0 - 548 K
100
SiO
SiO2
10
0
-2
Si2O
-5
-4
-3
-2
-1
0
1
Distance (nm)
2
3
4
5
Region I
Region II
Region III
Future
•
Study of thermal oxidation (silicon) case
• Analysis of bonding information in different regions (bulk, interface) from APT
data that could offer complimentary information to the bond length and bong
angle analysis by ReaxFF.