Presented by Dr. Markus Bosund Silicon nitride is a widely used material in semiconductor applications‚ such as gate dielectrics‚ III/V surface passivation and etch stop layer. PEALD SiNx films have been previously grown using aminosilanes like BTBAS with N2 plasma [1]. These processes generally have a relatively low growth rate of 0.15 - 0.21 Å/cycle and high film quality can only be reached at above 300 °C deposition temperatures. Trisilylamine (TSA) has been previously combined with N2/H2 plasma at 300–400 °C [2]‚ NH3 plasma at 50–400 °C [3] and N2 plasma at 250 – 350 °C [4] to grow PEALD SiNx films. However‚ in these works the low temperature range has remained either inaccessible or uncharted. In this work we explored the PEALD TSA-N2 plasma process with a wide deposition temperature range from 50 to 350 °C. Focus was given to the electrical and optical properties of the films. A Beneq TFS 200 capacitively coupled hot wall plasma ALD reactor was used at direct plasma mode. It was found that reactor temperature‚ and plasma power and time had the highest impact on the film properties. Film deposition was observed at temperatures as low as 50 °C. Metal insulator semiconductor (MIS) structures were used to determine the breakdown field and leakage current at different temperatures. Films were dipped in 1 % HF solution for etch rate determination.

1. Film Properties of ALD SiNx
Deposited by Trisilylamine
and N2 Plasma.
Markus Bosund, Kalle Niiranen, Patrick Rabinzohn,
Mikael Saarniheimo, Emma Salmi, Sami Sneck

2. 9/16/2019
Outline
• Experimental setup
• Deposition data
• Film Properties
• Elemental analysis (XPS)
• XRD and XRR
• Optical properties and band gap
• Etching properties (HF)
• Conclusions

3. 9/16/2019
Experiments
• Beneq TFS 200
• Direct CCP plasma mode
• Plasma frequency 13.6 MHz
• Hot-wall, Cross-flow plasma ALD reactor
• Sample cooled down in load lock 10 min
to prevent oxidation.
• Trisilylamine (TSA) as the Si precursor
• N2 as the plasma gas

4. 9/16/2019
Deposition Data
• Growth rate depends on the reactor temperature.
• Low temp SiNx process (but what is the film quality?)
• Plasma power also effects on the growth rate
• Growth rate also affected by plasma radical/ion density (N radicals have very short
lifetime)
• Growth rate higher compared to the e.g. BTBAS + N2 plasma (0.14 Å/cycle)
Sigma/ave = 2.6 %

5. 9/16/2019
XRR and XRD Results
• No XRD peaks were found from appr. 100 nm
thick samples. –> amorphous from 50 to 300
°C
• XRR density increases with the deposition
temperature clearly
• Probably correlates with hydrogen
concentration
• Temperature has only minor effect on
roughness.
Deposition
temperature
(°C)
Thickness
(nm)
Density
(g/cm3)
Roughness
(nm)
50 91,7 2,84 1,19
200 109,4 2,92 1,21
300 86,8 3,00 1,07

6. 9/16/2019
Elemental Analysis
50 °C
200 °C
300 °C
• XPS depth profiles of films grown at 50-300 °C
• Films deposited on HF etched Si
• Film is homogenous
• Surface oxidation ~ 5 nm or less
• SiNx/Si boundary is almost oxygen free

7. 9/16/2019
Temperature Effect on Atomic Concentrations
• Temperature increasement leads to the lower
Si concentration  closer to the Si3N4
• Bulk oxygen concentration stays below 1.7 %
• 50 °C film still has relatively similar atomic
concentrations compared to the samples
grown at 200 and 300 °C
Reactor
temperature
(°C)
Si N C O
50 48,66 49,64 0,88 0,83
200 48,46 48,97 0,91 1,66
300 47,44 49,69 1,28 1,58

8. 9/16/2019
Optical Data
• PerkinElmer Lambda 900
spectrophotometer
• Temperature only has minor effect on n
or k.
• 300 °C produced slightly higher refractive
index.
• Absorption limit at 250 nm.
• No absorption observed at visible
wavelength.
𝑛 = 𝐴 +
𝐵
λ
4
Cauchy's equationDeposition
temperature
(°C)
A B (nm
-4
)
50 2,00 7,97 x 108
200 2,00 7,43 x 10
8
300 2,00 10,9 x 10
8

9. 9/16/2019
Optical Band Gap of SiNx
• Optical band gap of SiNx was
determined using tauc plot.
• No clear difference between
different deposition
temperatures was observed.
• 5 eV band gap is in good
agreement with the earlier
published CVD deposited
SiNx films [1]
[1] J.Bauer, phys.stat. sol.(a) 39, 411 (1977)
Deposition
temperature
(°C)
Eg (eV)
50 5,01
200 4,98
300 5,00

10. 9/16/2019
HF Etch Rate
• Linear etching rate
• 50 °C film has clearly higher etching
rate
• Low etch rate correlates with
1) high deposition temperature,
2) low leakage current and
3) high film density by XRR.

11. 9/16/2019
HF Etch Rate (2/2)
Precursors Method
Deposition
temperature
(°C)
Etching
method
Etch rate
(nm/min)
Ref.
SiH2Cl2 +NH3 LPCVD 700 500:1 HF 0,30 2
SiH2Cl2 +NH3 ALD 450 500:1 HF 8,00 2
SiH2Cl2 +NH3 ALD 500 100:1 HF 0,16 1
BTBAS+N2 plasma PEALD 350 100:1 HF 0,19 Beneq 2015
TSA + N2 plasma PEALD 50 100:1 HF 0,16 This work
TSA + N2 plasma PEALD 200 100:1 HF 0,05 This work
TSA + N2 plasma PEALD 300 100:1 HF 0,03 This work
[1] Journal of the Korean Physical Society, Vol. 45, No. 5, November 2004, pp. 1352-1355
[2] Won-Jun Lee et al. Journal of the Korean Physical Society, Vol. 47, November 2005, pp. S598-
S602

12. 9/16/2019
Conclusions
• Film properties of PEALD SiNx was investicated.
• Wide temperature window from 50 to 300 °C
• High growth rate silicon nitride process.
• Deposition temperature had:
• clear effect on electrical propeties.
• minor effect on optical properties
• Low oxygen and carbon impurities (1.7 % and
1.3 % respectively)

13. 9/16/2019
Acknowledgements