60 MHz VHF-PECVD for
SN-2-SiNx andMicrocrystalline Si Film
Samco Inc. Technical Report vol.114 / July 2021
MatchingUnitH2
Process gases

Shower head

SN-2Plasma
SubstrateN2HeaterCopyright © 2022 Samco Inc. All Rights Reserved.

Heater

VHF (60 MHz)
Generator

Introduction
Samco has been developing plasma enhanced chemical vapor deposition (PECVD) technology using
liquid precursors along with conventional PECVD technology for silicon oxide and silicon nitride films
using SiH4 as the source gas. Furthermore, we provide superior stress control PECVD technology using
dual-frequency - the combination of 13.56 MHz and 400 kHz. In order to meet our customers’ demands,
we now introduce VHF-PECVD technology using 60 MHz. The study outlined below shows the results ofSiNx deposition and a Si crystallinity evaluation using Samco’s unique liquid precursor, SN-2.

Benefits of VHF

H2

VHF (60 MHz)
Generator

Process gases
Shower head

SN-2

PlasmaSubstrate

N2
HeaterHeater

70

2.2

60

2.15

50

2.1

40
2.05
30
220

1.95

100

1.90Figure 1. Schematic of VHF-PECVD reaction chamber.

Refractive index at 633 nmMatchingUnit

Deposition rate [nm/min]Compared with 13.56 MHz, VHF has superior characteristics such as a higher plasma density and low
ion bombardment. It enables high-speed deposition, reduction of the surface damage on the film interface
and substrate, and formation of micro-crystalline Si for deposition of a-Si. VHF-PECVD is expected to bea good candidate for insulation and passivation films on electronics and high-frequency devices, which
require a significantly lower plasma damage.

0.25

0.5

H2 flow ratio (H2/(N2+H2))(a) Deposition rate and refractive index
300120Tensile250100200
Stress [MPa]Figure 1 shows the system configuration used in thisstudy. The combination of SN-2 and N2 can form theSiNx film, but the hydrogen from the SN-2 precursor
remaining in the film causes deterioration of itsquality. We introduced H2 as an additional processgas, and evaluated film quality by changing theH2/N2 ratio while keeping a constant total flow rate ofH2 + N2. The film's quality was evaluated by thedeposition rate, refractive index, film stress, and16BHF wet etch rate. Process conditions were aVHF power of 100 W and a stage temperature of350 °C. Figure 2 shows that increasing the H2 flow
ratio leads to the compressive stress of the SiNx film,
shifting from tensile to a more compressively
stressed film, and a lower wet etch rate.

80

150
100

60

50

40

Compressive

020-50-100

16BHF etch rate [nm/min]SN-2-SiNx Deposition

000.250.5

H2 flow ratio (H2/(N2+H2))(b) Stress and 16BHF etch rate
Figure 2. (a) Deposition rate, refractive index,(b) stress, and 16BHF etch rate vs H2 flow ratio
to the total of N2 and H2 flow.

Copyright © 2022 Samco Inc. All Rights Reserved.

Figure 3 shows the FTIR spectroscopic evaluation ofSiNx films deposited with the H2 flow ratio of 40%
and 0%, respectively. The difference between the H2flow ratio of 40% and 0% is found in the intensity ofthe Si-N and Si-H bonds. The film at 40% shows adecrease in the Si-H bond. This indicates that H2
flow reduces the hydrogen in the film, and the film
composition is getting closer to Si3N4. A similar trendwas observed for 13.56 MHz PECVD technology,
suggesting that our extensive process expertise on
SiNx deposition at 13.56 MHz is also applicable to60 MHz VHF-PECVD. In addition, while the refractive
index of the SiNx film was as high as 2.15, we could
control index down to 2.00 by adjusting the processparameters.

AbsorbanceH2 flow ratio:

N2 + H 240%
0%

Si-H
N-H

4400

3400

2400

1400

400

Wavenumber [cm -1 ]Figure 3. FTIR spectroscopic evaluation ofH2 flow ratio of 40% vs 0%.

Si (111)2θ = 28.6°

Si (220)2θ = 47.5°

Intensity (cps)

Evaluation of SN-2-Si Film Crystallinity
Figure 4 shows the X-ray diffraction results ofcomparing the SN-2-Si with SiH4-Si film deposition
on c-plane sapphire using VHF-PECVD. The VHF
power was 100 W, and the stage temperature was
250 °C. The pattern (1) shows intense peaks at
preferential orientation Si (111): 2θ = 28.6°, Si (220):2θ = 47.5°, and Si (311): 2θ = 56.3 °. Pattern (1) andpattern (2) show intense peaks at the same position,suggesting
thatwecoulddepositthemicrocrystalline Si film using SN-2 as well as SiH4.

Si-N

H2Si (311)2θ = 56.3°(1) SN-2 + H 2(2) SiH 4 + H 22θ [°]Figure 4. Comparison of Si film crystallinity of SN-2
and SiH4 by X-ray diffraction.

Figure Conclusion
4. Comparison of Si film crystallinity of SN-2
andSiHby
X-ray thatdiffraction.
4 report
Figure This
4.
Comparisonof tune
Si thefilm crystallinity of SN-2
demonstrates
we couldand SiHbydiffraction.
SN-2-SiN
filmX-rayquality depositedusing VHF-PECVD
4xby adjusting the H2 flow rate. The SN-2-SiNx film
deposited by VHF-PECVD shows the sametendencies as that of desposited using 13.56 MHzPECVD. We also evaluated the SN-2-Si crystallinity
by X-ray diffraction, and the result suggests that Si
deposited in VHF-PECVD can be microcrystallized,
in a manner similar to deposition using SiH4 PECVD.
We are developing a process to apply SN-2-SiNx
VHF-PECVD deposition to radio-frequency (RF)devices such as GaN/GaAs/InP HEMTs and plasma
discharge damage-sensitive devices such asphotodiodes, thin-film transistors, and solar cellapplications. Samco keeps providing new andinnovative solutions to meet our customers’
demands.

VHF-PECVD System for R&D
Compact footprint

PD-220NL

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