Specific Process Knowledge/Thin film deposition/ALD2 (PEALD)/AlN deposition using ALD2

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General Information

The AlN process should never run above 350 °C due to the decomposition of the trimethylaluminium. As already mentioned in the general ALD2 (PEALD) page oxides and nitrides cannot be deposited at the same time. Since the aluminium nitride requires the plasma source, we run all plasma processes without the thermal lid. The substrate temperature is around 50 °C lower than the setpoint, because the chamber volume becomes bigger without the thermal lid.

Results from the acceptance test

During the acceptance test, AlN was deposited using TMA and N2 plasma. We have modified and improved recipes since.

Deposition of AlN using TMA and NH3 plasma

Recipe name: AlN NH3 plasma

Temperature window: 250 °C - 350 °C

The deposition rate is measure to be 0.137 nm/cycle for 350 °C with growth delay of 144 cycles.

TMA NH3
Nitrogen flow 100 sccm 150 sccm
Pulse time 0.1 s 5 s
Purge time 8 s 30 s


Plasma source settings
RF power (W) Ar carrier flow (sccm) Plasma gas flow (sccm) t1 stabilization (s) t2 RF Power on (s)
3000 150 100 1 3.4


Note! Remember to obey the relation: [Pulse time - (t1+t2)] > 0.5 s

Evgeniy Shkondin, DTU Nanolab, 2020.

Spectroscopic ellipsometry

The spectroscopic ellipsometry measurements were conducted by using VASE Ellipsometer. The purpose of the investigation is to evaluate refractive index and dielectric function as well as to analyse the growth rate and uniformity.


Refractive index and permittivity

Thickness distribution and uniformity


Ellipsometry results for AlN deposited with TMA and NH3 plasma
Number of cycles Temperature (°C) Average thicknes (nm) Minimum thickness (nm) Maximum thickness (nm) Standard deviation Procent deviation (%)
500 350 42.9565 41.7422 43.4888 0.42652 2.0331
568 350 66.1824 64.2685 67.4074 0.7256 2.3714
852 350 103.8306 100.8147 106.1143 1.2407 2.552
1136 350 128.1302 124.8565 131.037 1.444 2.4118
1704 350 203.6618 198.1933 210.8584 2.7121 3.1094
2272 350 298.1225 293.8553 305.0185 2.3923 1.8723


Evgeniy Shkondin, DTU Nanolab, 2020.

X-ray photoelectron spectroscopy

XPS measurements of all samples has been performed using XPS K-Alpha equipment. The purpose of the investigation is to get idea about film stoichiometry and possible contamination.

Stoichiometry

Stoichiometry results for AlN deposited with TMA and NH3 plasma
Number of cycles 568 852 1136 1704 2272
Average thickness (nm) 66.18 103.83 128.13 203.66 298.12
Al (at.%) 47.54 48.15 47.82 47.77 47.61
N (at.%) 40.80 40.60 41.13 41.01 41.11
O (at.%) 11.66 11.25 11.05 11.22 11.28

Presence of Oxygen and Carbon

Traces of carbon is found in the deposited films, their origine is not clear, but most likely due to TMA decomposition. Another source is incomplete ALD reaction.

Evgeniy Shkondin, DTU Nanolab, 2020.