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.

• results from the acceptance test (old material) .

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

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  Deposition function for AlN with NH₃ plasma (350 °C)
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  Deposition of AlN with NH₃ plasma (500 cycles, 350 °C) on si trench template. It is worth mention, that the process will not be good to passivate structures with an aspect ratio above 10.

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

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  Refractive index and absorption koefficient as a function of wavelength.
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  Real and imaginary permittivity as a function of wavelength.

Thickness distribution and uniformity

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  Thickness distribution across the 100 mm wafer (350C 500cycles)
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  Thickness distribution across the 100 mm wafer (350C 568cycles)
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  Thickness distribution across the 100 mm wafer (350C 852cycles)
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  Thickness distribution across the 100 mm wafer (350C 1136cycles)
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  Thickness distribution across the 100 mm wafer (350C 1704cycles)
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  Thickness distribution across the 100 mm wafer (350C 2272cycles)

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. Oxygen is present in the film (up to 11 at.%)

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  C1s signal
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  O1s signal

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  C1s signal
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  O1s signal

Evgeniy Shkondin, DTU Nanolab, 2020.