Purpose of the work
The work described below was conducted in 2019 by Sarah Elisabeth Hussein El Dib (s135170) and Evgeniy Shkondin, DTU Nanolab as a part of the master project in collaboration with the DTU Photonics Department.
The prepared samples were investigated by X-ray Reflectivity (XRR) and Spectroscopic Ellipsometry. The idea is to investigate the initial growth of Al2O3 and TiO2 on conventional Si samples (with native oxide) and compare characterization results provided by two different techniques: X-ray reflectivity and Spectroscopic Ellipsometry.
The deposition of ultrathin layers (with thickness below 10 nm) is difficult to characterize with ellipsometry alone, because of the model complexity. The prepared samples consist of a thin ALD film, but in order to properly distinguish it, the native oxide and surface moisture (with adventitious carbon contamination) should be taken into account since whey both have thicknesses comparable to ALD ultra-thin layer. For this purpose, the XRR method was employed.
Deposition characteristics
A sequence of samples has been made by deposition Al2O3 and TiO2 on flat natively oxidized Si (100) samples. The thickness setpoints were chosen to be 2, 4, 6, and 8 nm, and a number of cycles calculated from the published growth rates which were verified for thicker films (20-100nm).
Deposition of Al2O3
The standard recipe for deposition of Al2O3 on flat and high aspect ratio structures has been used.
Equipment: ALD-1
Recipe: AL2O3
Assumed deposition rate: 0.097 nm/cycle
Temperature: 200 oC
|
|
TMA
|
H2O
|
| Nitrogen flow
|
150 sccm
|
200 sccm
|
| Pulse time
|
0.1 s
|
0.1 s
|
| Purge time
|
3.0 s
|
4.0 s
|
Number of cycles: 20, 40, 60, 80 for 2nm, 4nm, 6 nm and 8 nm respectively.
Deposition of TiO2
The standard recipe for deposition of amorphous TiO2 on flat and high aspect ratio structures has been used.
Recipe: amorphous TiO2,
Equipment: ALD-2
Assumed deposition rate: 0.0385 nm/cycle
Temperature: 150 oC
|
|
TiCl4
|
H2O
|
| Nitrogen flow
|
150 sccm
|
150 sccm
|
| Pulse time
|
0.1 s
|
0.1 s
|
| Purge time
|
4.0 s
|
6.0 s
|
Number of cycles: 52, 104, 156, 208 for 2nm, 4nm, 6 nm and 8 nm respectively.
X-ray reflectivity results
X-ray reflectivity (XRR) profiles for Al2O3 and TiO2 films at different number of cycles has been obtained using Rigaku XRD SmartLab equipment. Fitting procesure was performed using commercial GlobalFit software assuming the model based on Si substrate with native oxide followed by the deposited ALD layer with thin moisture surface. The results are summarized in a tables below.
Si reference samples
| Physical properties of Si reference sample with and without native oxide
|
|
|
Si native oxide
|
Si substrate
|
Fitting parameters
|
| Sample
|
SiO2 Thickness (nm)
|
SiO2 Density (g/cm3)
|
SiO2 Roughness (nm)
|
Si Thickness (nm)
|
Si Density (g/cm3)
|
Si Roughness (nm)
|
Intensity
|
Background
|
Fitting area (Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle 2\Theta}
)
|
R
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \Chi}
|
| Si without native oxide
|
-
|
-
|
-
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.4258
|
0.248
|
1.11841
|
2.93034E-5
|
0.4089-2.0
|
0.00593
|
0.00027
|
| Si with native oxide
|
1.597
|
2.05880
|
0.406
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42354
|
0.985
|
1.04529
|
1.0E-1
|
0.3018-4.0
|
0.01035
|
0.00067
|
|
|
Thin films samples
- All XRR scans.
-
All Al2O3 samples scan.
-
All TiO2 samples scan.
bla bla bla
| XRR results for Al2O3 layers
|
|
|
Top layer (moisture)
|
Main layer
|
Si native oxide
|
Si substrate
|
| Number of cycles
|
Moisture thickness (nm)
|
Moisture density (g/cm3)
|
Moisture roughness (nm)
|
Al2O3 thickness (nm)
|
Al2O3 density (g/cm3)
|
Al2O3 roughness (nm)
|
SiO2 thickness (nm)
|
SiO2 density (g/cm3)
|
SiO2 roughness (nm)
|
Si thickness (nm)
|
Si density (g/cm3)
|
Si roughness (nm)
|
| 20
|
0.999
|
1.51773
|
0.261
|
1.931
|
2.75145
|
0.404
|
1.980
|
2.08289
|
0.549
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42104
|
0.502
|
| 40
|
0.985
|
1.50054
|
0.281
|
4.123
|
2.77059
|
0.428
|
1.986
|
2.07963
|
0.526
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42121
|
0.502
|
| 60
|
0.996
|
1.3700
|
0.231
|
6.347
|
2.77008
|
0.439
|
1.973
|
2.09212
|
0.563
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42311
|
0.529
|
| 80
|
1.223
|
2.41786
|
0.552
|
8.047
|
2.81335
|
0.560
|
1.891
|
2.09533
|
0.588
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42343
|
0.472
|
|
|
bla bla bla
| XRR results for TiO2 layers
|
|
|
Top layer (moisture)
|
Main layer
|
Si native oxide
|
Si substrate
|
| Number of cycles
|
Moisture thickness (nm)
|
Moisture density (g/cm3)
|
Moisture roughness (nm)
|
TiO2 thickness (nm)
|
TiO2 density (g/cm3)
|
TiO2 roughness (nm)
|
SiO2 thickness (nm)
|
SiO2 density (g/cm3)
|
SiO2 roughness (nm)
|
Si thickness (nm)
|
Si density (g/cm3)
|
Si roughness (nm)
|
| 52
|
1.080
|
2.97461
|
0.735
|
1.515
|
3.48298
|
0.716
|
1.893
|
2.04014
|
0.242
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42202
|
0.229
|
| 104
|
0.626
|
2.30889
|
0.509
|
4.892
|
3.50986
|
0.147
|
1.515
|
2.00387
|
0.543
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42747
|
0.640
|
| 156
|
0.704
|
2.05235
|
0.440
|
7.294
|
3.30327
|
0.106
|
1.709
|
2.06712
|
0.454
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42545
|
0.574
|
| 208
|
0.683
|
1.96283
|
0.373
|
9.541
|
3.40667
|
0.011
|
1.535
|
2.07875
|
0.493
|
Failed to parse (SVG (MathML can be enabled via browser plugin): Invalid response ("Math extension cannot connect to Restbase.") from server "https://wikimedia.org/api/rest_v1/":): {\displaystyle \infty}
|
2.42552
|
0.818
|
|
|
blabla bla
- All XRR scans.
-
All Al2O3 samples scan.
-
All TiO2 samples scan.
Sample considers to have ALD layer with top moisture deposited on natively oxidized silicon.
Measuring Si reference sample with and without native oxide.
All Al2O3 samples scan.
All TiO2 samples scan.
All Al2O3 samples scan.
All TiO2 samples scan.
