24P006-O
Precursors of a-CNx:H films from the decomposition of CH3CN
with the microwave discharged products of Ar
Arのマイクロ波放電フローによるCH3CNの分解: a-CNx:H膜の前駆体
Ayumi Yamamoto, Hitoshi Araki, Akira Wada, and Haruhiko Ito
山元愛弓, 新木一志，和田晃，伊藤治彦
Nagaoka University of Technology
1603-1, kamitomioka, Nagaoka, Niigata 940-2188, Japan
長岡技術科学大学 〒940-2188 新潟県長岡市上富岡町1603-1
The decomposition reaction of CH3CN induced by the microwave discharge flow of Ar was applied to theformation of hydrogenated amorphous carbon nitride (a-CNx:H) films. A discussion was developed
whether CN(X2Σ+) radicals are the dominant source of N atoms of films based on the ratios of the fluxes
Φa-CN/ΦCN(X) evaluated for the cases of CH3CN and BrCN as the starting materials. The flux of CN(X2Σ+)radicals arrived onto the film surface, ΦCN(X), was evaluated from the number density of CN(X2Σ+) radicals
determined from the intensity of the laser-induced fluorescence spectrum of the CN(A2Πi-X2Σ+), 4-0 band
together with the flow speed measured by the time-resolved emission. The flux of N atoms incorporated
into films, Φa-CN, was evaluated from the atomic composition analysis by XPS and the film mass.
According to the discussions on the difference of the above ratios and on the electron densities in thereaction region, CN(X2Σ+) radicals are suggested to be the dominant N source of a-CNx:H films.

1. Introduction
Amorphous carbon nitride (a-CNx) films areformed by using the decompositions of BrCN andCH3CN with the microwave (MW) discharge flowof Ar. In the case of BrCN, CN radicals are formed
almost selectively. Therefore, the main nitrogensource of a-CNx is CN(X2Σ+) radicals, and thesticking probability, s, of CN(X2Σ+) radicals can be
determined with a simple scheme as [1-5](1)s=Φa-CN/ΦCN(X)
In the case of the flowing-afterglow apparatus usedin this study, ΦCN(X) can be evaluated from thenumber density of CN(X2Σ+) radicals, nCN(X),determined by using the laser-induced fluorescence(LIF) spectrum of the CN(A2Πi-X2Σ+) transition andthe flow speed, V, in units of m s-1, as nCN(X)V. Φa-CN
can be evaluated from the mass of the CNcomponent of the film, w, the deposition time, td,
and the area of the substrate, A, as wL/MtdA, where
L and M are the Avogadro constant and themolecular mass of CN, respectively. In the case ofCH3CN, however, other radicals are suspected tocontribute as the N source of films. In this paper,
the s values obtained by using BrCN and CH3CN as
the starting materials are represented as sBrCN andsCH3CN, respectively. The following three cases may
be possible.
(A) If the precursor of a-CNx:H in the case ofCH3CN is specifically CN(X2Σ+) radicals, sCH3CN
may be identical with sBrCN.
(B) If other radicals contribute to the deposition ofa-CNx:H in addition to CN(X2Σ+), sCH3CN may belarger than sBrCN.

(C) If the rate of the surface recombination [6] ofCN(X2Σ+) is higher in a-CNx:H films formed fromCH3CN than that in a-CNx films formed from BrCN,
sCH3CN may be smaller than sBrCN.
Based on these considerations, sCH3CN is evaluatedin this study, and is compared to sBrCN to discuss thepossibility that CN(X2Σ+) radicals are the dominant
N source of a-CNx:H in the case of CH3CN.
2. ExperimentFig. 1 shows the experimental arrangement forthe deposition of a-CNx and a-CNx:H films. Ar(0.2-0.4 Torr) was excited by MW discharge (2.45GHz, 60W). BrCN or CH3CN were introduced
through a nozzle to deposit films on the Si
substrates set just downstream (=10 mm) of thenozzle tip. The mass, W, of films were measured
with the deposition time of td=1 h. The LIF
spectrum of the CN(A2Πi-X2Σ+), 4-0 band, wasobserved using a dye laser pumped by the 2-nd
harmonic of a Nd:YAG laser. In this experiment,
the Si substrate was not used and the dye-laser
beam was introduced into the position of the Sisubstrate. V was evaluated from a time-resolved
emission measurements by modulating the MW
discharge using a pluse generator. The
compositional analysis was made by using XPS.
The electro-static probe measurements were madein this study to evaluate the density, ne, and thetemperature, Te of electrons.

ArP2O5MW0.3
BrCN desiccated

0.25

BrCN H2O added

0.2
P2O5SisBrCNorCH3CN

CH3CN

0.15
0.1
0.05

PUMPFig. 1 Schematic of the MWCVD apparatus

00

3. Results and discussion
Fig. 2(a) shows the observed LIF spectrum of theCN(A2Πi-X2Σ+), 4-0 band. A simulation analysis
was made as shown in Fig. 2(b) to evaluate theintensity of the individual transition. This intensity
was calibrated against Rayleigh scattering intensityof Ar, from which was evaluated the numberdensity of the individual vibration-rotation levels ofCN, nCN(X)(v, J). Then, nCN(X) was evaluated asnCN(X) = ∑ nCN(X) (v, J )(2)v,JThe compositional analysis was made by using XPS
as listed in Table 1. In addition to C and N, O and Br
were detected. Then, w was determined from observed
W by excluding the masses of O and Br and byassuming that all the N atoms form CN bonds. Fig. 3
shows the dependencies of sCH3CN and sBrCN on ne.
The sCH3CN and sBrCN values have negative
dependencies on PAr irrespective of theexperimental conditions. The sCH3CN values are ingood agreement with sBrCN obtained under theH2O-added condition [5]. In addition, the ne values
obtained in the case of CH3CN are almost identicalwith those obtained in the case of BrCN under theH2O-added condition. These comparisons indicate thatthe s values depend strongly on ne and that sCH3CN andsBrCN are almost identical under the similar conditionof ne.
(a) Obs.

(b) Cal.

618

619

620

621

622

623

624

625

626

Wavelength [nm]2 2Πi-X2Σ+), 4-0 band.
Fig. 2 LIF spectra of theFig.
CN(A(a) Observed. (b) Simulated.

Table 1Table1 Compositional analysis
CNOBr[N]/([N]+[C])BrCN

41313450.43

CH3CN622513-0.28

123

ne [1012 m-3]
Fig. 3 Dependencies of sCH3CN and sBrCN on ne

4. Conclusion
In this study, a novel method of analysis wasdeveloped to discuss whether CN(X2Σ+) radicals are
the dominant N source of a-CNx:H films formed
from the decomposition reaction of CH3CN withthe MW discharge products of Ar. The basic idea isthe comparison of the ratios of the fluxes+Φa-CN/ΦCN(X) evaluated for the cases of CH3CN andBrCN as the starting materials. The 4-0 band of theCN(A2Πi-X2Σ+) transition was observed by the LIF
spectroscopic method, and the intensity of thetransitions was calibrated against Rayleighscattering intensity of Ar, yielding the number
density of CN(X2Σ+) radicals. From these densities
together with the flow speed measured by the+ a-CN
time-resolved emission, ΦCN(X) was evaluated. Φwas evaluated from the atomic-composition
analysis by XPS and the film mass. According tothe discussions on the difference of the above ratios
and on the electron densities of the reaction region,
CN(X2Σ+) radicals are suggested to be the dominant
N source of a-CNx:H films formed from thedecomposition of CH3CN induced by the MW
plasma flow of Ar. From the above considerations,the case (A) described above may be applicable tothe present sCH3CN.
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