24G06
Effects of Nanoparticle Inclusion on Properties of Si Films
Deposited by Plasma CVD
プラズマCVDで成膜したSi薄膜へのナノ粒子含有の効果	 
Masaharu Shiratani1, Yeonwon Kim1, Takeaki Matsunaga1, Hyunwoong Seo2,
Kunihiro Kamataki3, Giichiro Uchida1, Naho Itagaki1, Kazunori Koga1,
白谷正治1，金 淵元1，松永剛明1，徐 鉉雄2，鎌滝晋礼3，内田儀一郎1，板垣奈穂1，古閑一憲1，
1

Graduate School of Information Science and Electrical Engineering, 2Center of Plasma Nano-interface Engineering,
3
Center for Research and Advancement in Higher Education
Kyushu University, Fukuoka 819-0395, Japan1
九州大学大学院システム情報科学府, 2九州大学プラズマ界面工学センター,
3
九州大学高等教育開発推進センター 〒819-0373 福岡市西区元岡744ウエスト2号館4F423号室
We have investigated effects of nanoparticle inclusion on properties of a-Si:H films and mc-Si:H films
using the multi-hollow discharge plasma CVD method. Minor deposition species (nanoparticles in thisstudy) modify considerably properties of a-Si:H films and mc-Si:H films.

2. Experimental
Multi-hollow discharge plasma CVD reactor
consists of one powered electrode and a pair ofgrounded electrodes to generate plasma as shown inFig. 1[3]. 60MHz voltage was applied to theelectrode to sustain the discharges in the holes inthe electrodes.
Pure SiH4 or H2+SiH4 was supplied to the reactor.
The total pressure and gas flow rate were 0.5-2 Torr
and 15-150 sccm, respectively. The substrate holder
was set vertically or perpendicularly to the gas flow.
The substrate temperature (TS) was 250oC.
Information on chemical bonds in films wasobtained by FTIR. Crystallinity (XC) wasdetermined with a Raman spectroscope (Jasco,NRS-3100). Deposition rate (Rd) was obtained asfilm thickness divided by deposition time.
3. Experimental results and discussion
3-1. a-Si:H films
First, we study effects of amorphous Si
nanoparticle inclusion on properties of a-Si:H films.
Figure 2 shows FTIR spectrum of nanoparticles
formed in pure discharge plasmas. While SiH andMulti-hollow
plasma CVD reactor
SiH
2 bonds exist in nanoparticles, SiH2 bonds havelarger absorption.

HOS

104
velocity (cm/s)

1. Introduction
A-Si:H and mc-Si:H films are dominantmaterials for thin film solar cells. These films arewidely deposited by plasma CVD. Nanoparticles
are often formed in such CVD plasmas and may
modify properties of films [1-7]. Here we reporteffects of nanoparticle inclusion on properties ofa-Si:H films and mc-Si:H films.

103
102
101

si

Top vi

Ref: K.Koga, et al., JJAP 48, L1430 (2005).
Fig. 1. Schematic diagram of a multi-hollow discharge
CVD reactor.

Figure 3 shows FTIR spectra for a-Si:H films
deposited in the downstream region and in theupstream region. The films in the downstream
region have predominant SiH absorption and smallSiH2 one, while the films in the upstream region
only have SiH absorption. The films in thedownstream region contain nanoparticles of 1% involume fraction, whereas the films in the upstream
region do not contain them (<0.01% in volumefraction). These results suggests that SiH2 bonds are
originated from nanoparticle inclusion. Suchnanoparticle inclusion brings about light induceddegradation of a-Si:H films, because SiH2 bonds are
weaker than SiH ones. This consideration isconsistent with the fact that the films in theupstream show little light induced degradation,
whereas the films in the downstream region show
significant light induced degradation.
clusters

0.1

Si-H2 bonds

absorbance

0.08
0.06
0.04

Si-H bonds

Fig. 4. A cross sectional SEM of mc-Si:H films
deposited in the upstream region.

0.02
01900 1950 2000 2050 2100 2150 2200

downstream.
wavenumber (cm-1)
The results in Figs. 2 and 4 indicate that films without
containing clusters have few SiH2 bonds and are highly
Fig. 2. FTIR spectrum of nanoparticles formed in purestable against light exposure, whereas those containingdischarge plasmas.
clusters deposited in the downstream region have Si-H2

0.8
0.6
downstream

0.4

Fig.Fig.
3. 3.
FTIR
filmsanddepositedin theFTIRspectra
spectraforof a-Si:H
films. Solid
broken line
downstream
andforinupstream
the upstream
region.
show FTIR region
spectrumand downstream
region, respectively.

properties
a-Si:Hfilms andmc-Si:H
Since
SiH3 is theofmain
film growth
precursor
in SiHfilms.
4discharges, the contribution ratio of HOS radicals to theAcknowledgements
films growthis given by[Si m Hwork[Si m H 2m +partlyand 3).
2 m +1 ]
2 ] (m=2supportedThisby the% was[SiH 3 ][SiH 4 ]Si

3-1. mc-Si:Hfilms(a) downstream
Next, we study effects of crystalline
nanoparticle inclusion on properties of mc-Si:Hfilms. Nanoparticle inclusion has little effects on
deposition rate and crystallinity. The volume
fraction of (220) crystalline orientation crystals of
the films without nano-particles is higher than thatwith nano-particles. A cross sectional SEM ofmc-Si:H films deposited in the upstream region isshown in Fig. 4, while that in the downstream
region is shown in Fig. 5. The film without
nanoparticles
has columnar gran growth, whereas(b) upstream
the film with nanoparticles has inverted conicalgrowth. Therefore, nanoparticle inclusion of 1%
volume fraction considerably modifies the crystal
grain growth in mc-Si:H films.

NewEnergy and Industrial Technology Development
Organization (NEDO) and Photovoltaic Power-1
10Generation
Technology Research Association(a) downstream region(PVTEC).
-2[Si2H6]/[SiH4]
10References

42200]/[SiH ]2100[1] -3M. Shiratani, et al., Thin Solid Films 427 (2003) 1.
10[2] K. Koga, et al., Appl. Phys.
Lett. 77 (2000) 196.
v =13cm/sg[SiH8]/[SiH] Sci.
-4[3]K.
Koga,etJ.
Vac.
& Technol. A 22 (2004)
3 al.,
4101536.
v =52cm/s-5g[4]Phys, 48 (2005) L1430.
10 K. Koga, et al., Jpn . J.Appl.
(b)
upstreamregion[5] W. M. Nakamura, et al., J. Phys.: Conference Series-2
10 100 (2008) 082018.
[Si2H6]/[SiH4][6] W. M. Nakamura, et al., IEEE Trans. Plasma Sci. 36-310 (2008) 888.
[7] -4W. M. Nakamura,Surf.
[SietHal.,]/[SiH] & Coat. Technol. 205
3 8410 (2010) 5241.

2m+22000

wavenumber (cm-1)

m1900

where kdm is the rate coefficient of SimH2m+1 generation due
inclusion on properties of a-Si:H films andto electron impact dissociation of SimH2m+2 and #m themc-Si:H films using the multi-hollow discharge
characteristic lifetime of Sim H2m+1. The steady state density
CVD method. Minor deposition speciesof Sim Hplasma
2m+1 can be written in the form(nanoparticlesthis study) modify considerably[Si m H 2 m +1 ] = #inm k dm ne [Si m H 2 m + 2 ][Si Hupstream
01800

films

We have investigated effects of nanoparticle

0.2[SimH2m+2]/[SiH4]

absorbance (arb. units)

1bonds of 1 atomic % and show metastability. However,these results do not exclude possibility of the contributionof HOS radicals SixHy (x ! 2, y " 2x+1) to the Si-H2 bondformation, since these radicals probably exist in thedischarges. To obtain information on contribution of HOS
radicals such as Si2H5 and Si3H7 to the film growth,compared to that of SiH3, being the predominant deposition
radical. We have measured signal intensities of m/e = 30,60, and 90 for detecting SiH4, Si2H6 and Si3H8 with QMS.
We estimatedof HOS SEM
radicalsofto theFig. 5. theA contribution
cross sectional
mc-Si:H
film growthusing inthethe
assumption
as follows.
deposited
downstream
region. The rateequation of the steady state density of Sim H2m+1 (m=1, 2and 3) radicals may be given byd[Si m H 2m +1 ][Si H]
4. Conclusions= kdm ne [Si m H 2m + 2 ] $ m 2m +1dt
#m-5100

5 10 15 20 25 30 35
discharge power P (W)

Fig. 5. Dependence of [Sim H2m+2]/[SiH4] (m=2 and 3)
on discharge power P in (a) downstream and (b)upstream region for
SiH4 2.5sccm, H2 10sccm, and