24P011-O
Radical Flux Evaluation to Microcrystalline Silicon Films Depositedby Multi-Hollow Discharge Plasma CVD
マルチホロー放電プラズマで作製した微結晶シリコン膜へのラジカルフラックス評価
Yeonwon Kim1, Takeaki Matsunaga1, Hyunwoong Seo2, Kunihiro Kamataki3,
Giichiro Uchida1, Naho Itagaki1, Kazunori Koga1, Masaharu Shiratani1
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，白谷正治11

Graduate School of Information Science and Electrical Engineering,
2
Center 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
To evaluate radical fluxes for microcrystalline silicon film deposition, Si films were deposited in a
combinatorial way using a multi-hollow discharge plasma CVD method. Film crystallinity varied with thedistance from the powered electrode. Based on the film deposition rate and Raman crystallinity, weproposed a method to estimate hydrogen flux. This evaluation of hydrogen flux is one of useful way tounderstand a process window of µc-Si:H films.

2. Experimental
A multi-hollow discharge plasma CVD reactor
consists of one powered electrode and a pair ofgrounded electrodes to generate plasma as shown inFig. 1[3].
The silane dilution ratio R=([H2]+[SiH4])/[SiH4]
was kept at 300. The total pressure and gas flowrate were sustained at 2Torr and 150sccm,respectively. The substrate holder was set verticallyon the powered electrode to obtain information on

spatial distribution of deposition radicals. The
substrate temperatures (TS) were varied from RT to250oC.Crystallinity (XC) was determined with aRamanspectroscope(Jasco,NRS-3100).
Deposition rate (Rd) was obtained as film thickness
divided by deposition time.
distance from electrode lz (mm)1. Introduction
Microcrystalline silicon(μc-Si:H) films haveattracted much attention as materials of thebottom-cells in Si thin film tandem photovoltaics[1]. However, thedeposition rate of μc-Si:H isvery low due to the low SiH4 density underrelatively low partial pressure conditions using
Plasma Enhanced Chemical Vapor Deposition(PECVD). Even though high pressure depletion
regime has been proposed as an alternative
deposition method to overcome above difficulties[2], a narrow process window which determined by
H and Si radical flux makes it difficult to fabricate
device quality microcrystalline silicon films.
In this study, Si films were deposited in a
combinatorial way using a multi-hollow discharge
plasma CVD method. We present a new approach
to flux evaluation, by which we discuss a process
window of μc-Si film deposition.

pump
SiH3
film
quartz substrate
grounded substrate holderHdischarge region
powered electrodegrounded electrode50403020100～

gas inlet

Fig.1. Schematic diagram of a multi-hollow discharge
CVD reactor.

3. Experimental results and discussion
Figure 2 shows (a)Rd and (b)XC as a function of
the distance from the electrode l, respectively. The
Rd of each film in Fig. 2 (a) decreases exponentiallywith l for l>5 mm because SiH3 density, which is
the main deposition precursor for high-quality films,decreases exponentially with l due to their loss atthe surfaces of reactor wall. The XC in Fig. 2 (b) ishigher near the discharge region and drops sharply

1RT
100oC
250oC

(a)

0.1

Si(cm-2s-1)

10(b)
0.8
0.6
0.4
0.2c

Raman crystallinity

0.01

X =(I520+I500)/(I520+I500+I480)

with decreasing TS.
At high substrate temperature ΓH is high near theelectrode region resulting in widening the highcrystallinity region. These results show that theincrease of Ts is one possible way to obtain a wide
process window of µc-Si:H films.

005

1015202530

35

flux ratioH/Sidepostion rate Rd (nm/s)

in the crystalline/amorphous transition region
around l=20-40mm.

161015200(b)10090To obtain further information on the contributionof each flux to film deposition near the discharge
region, SiH3 flux (Si = nvth/4) was deduced using
the following equation [4]:
 M Si  nvth    s   (1)
Rd SiH 3    N A  Si  4  1   2   

where Rd is deposition rate, MSi = 28.09 g/mol of
the atom molar mass, NA = 6.02×1023 /mol of theAvogadro number, and ρSi = 2.2 g/cm3 the film
specific gravity. The sticking probability s and thesurface reaction probability β of SiH3, being thepredominant deposition precursor, were 0.1 and0.28, respectively.
To determine Si, we considered Rd of onlya-Si:H region, and extrapolated towards the µc-Si:Hregion as Si of c-Si region as shown in Fig.3 (a)because the Rd of c-Si region is determined by thebalance between deposition due to Si and etching
due to H whereas a-Si:H region is predominantly
by deposition due to Si. Figure 3 (b) shows a fluxratio of H atoms to SiH3 radicals estimated using
the relationship between ΓH/ΓSi and Xc reported byS. Nunomura, et al.[5]. Figure 3 (c) shows ldependence of H atom flux estimated using Si inFig. 3(a) and H/Si in Fig. 3(c). H decreases withincreasing l and the gradient of H becomes sharper

H(cm-2s-1)

distance from electrode l (mm)Fig.2. Dependence of (a) deposition rate and (b)crystallinity XC on the distance from the electrode l.

RT
100oC
250oC

(a)

(c)
10171016051015202530

35

distance from electrode l (mm)Fig.3. Dependence of (a)ΓSi,(b) ΓH/ΓSi and (c)ΓH
on the distance from the electrode l.

4. Conclusion
Si thin films were deposited in a combinatorial
way using the multi-hollow discharge plasma CVD
method. Based on the film deposition rate andRaman crystallinity, we proposed the method toestimate hydrogen flux. This evaluation ofhydrogen flux is one of useful way to understand aprocess window of µc-Si:H films.
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