Specific Process Knowledge/Characterization/XRD/XRD SmartLab/ALD deposited alumina and titania XRR

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 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.

• Sample model used in XRR analysis.
• 
  Sample considers to have ALD layer with top moisture deposited on natively oxidized silicon.

Si reference samples

• All XRR scans.
• 
  Measuring Si reference sample with and without native oxide.

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 ($2\Theta$) R $\mathrm {X}$ Si without native oxide - - - $\infty$ 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 $\infty$ 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.

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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 $\infty$ 2.42104 0.502 40 0.985 1.50054 0.281 4.123 2.77059 0.428 1.986 2.07963 0.526 $\infty$ 2.42121 0.502 60 0.996 1.3700 0.231 6.347 2.77008 0.439 1.973 2.09212 0.563 $\infty$ 2.42311 0.529 80 1.223 2.41786 0.552 8.047 2.81335 0.560 1.891 2.09533 0.588 $\infty$ 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 $\infty$ 2.42202 0.229 104 0.626 2.30889 0.509 4.892 3.50986 0.147 1.515 2.00387 0.543 $\infty$ 2.42747 0.640 156 0.704 2.05235 0.440 7.294 3.30327 0.106 1.709 2.06712 0.454 $\infty$ 2.42545 0.574 208 0.683 1.96283 0.373 9.541 3.40667 0.011 1.535 2.07875 0.493 $\infty$ 2.42552 0.818

blabla bla

• All XRR scans.
• 
  All Al₂O₃ samples scan.
• 
  All TiO₂ samples scan.