24P013-O
Fabrication of a-CNx films by plasma decomposition of BrCNBrCN の放電分解による a-CNx 薄膜の形成
Kohtaro Okada, Teppei Tsuda, Hiroki Akasaka, Hidetoshi Saitoh, Haruhiko Ito
岡田亘太郎, 津田哲平，赤坂大樹，斎藤秀俊, 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
Amorphous carbon nitride (a-CNx) films with high nitrogen content ([N]/([N]+[C])=0.35−0.5) are formedby the RF discharge of the gas mixture of BrCN, Ar and N2. Compositional analysis was made by XPS. TheCN(B2Σ+−X2Σ+) emission spectra were observed. A correlation between the emission intensity and the [N] /([N] + [C]) ratio indicates the mechanism of the incorporation of N atoms when N2 is introduced.

1. Introduction
Amorphous carbon nitride (a-CNx) films havebeen attracted much attention due to theexpectation of their mechanical hardness [1].
This expectation is based on the shortness of
the length (1.48 Ǻ) of the C-N bonds
compared with that (1.54 Ǻ) of C-C in the sp3
hybridized state [2]. Therefore, it has been thecentral problem in the field of the synthesis ofa-CNx to incorporate N atoms as much aspossible. However, it is difficult to obtainhigh-N content by using the frequently-usedmethod of the RF discharge of the gas mixtureof N2 and hydrocarbons. Ito and co-workers
have developed an alternative method todeposit a-CNx films by using thedecomposition of BrCN with the microwave
discharge flow of Ar [3]. This reaction
produces efficiently CN radicals whichbecome the precursor of the film formation,
leading to the high-N content ([N]/([N]+[C])≦0.5) of the resultant films [4]. In this study,
a-CNx films are deposited by using theRF-plasma decomposition of BrCN diluted
with Ar. In this reaction system, it is suspectedthat CN radicals may be further decomposed
into C and N atoms. This “excessdecomposition” may lead to the lowering ofthe [N]/([N]+[C]) ratio below 0.5, because thesticking probability of N atoms is quite small,
0.0041 [5]. In this experiment, N2 was added
to the reaction system to “compensate” the Ncontent of films. The observation on theCN(B2Σ+−X2Σ+) emission spectra was made todiscuss the mechanism of this “compensationof N atoms” .

2. ExperimentalFig. 1 shows the experimental arrangement for thedeposition of a-CNx films. Si substrates were placedon the centers of the RF and grounded electrodes.
After the chamber was evacuated <3 mTorr, Ar (0.1Torr) was introduced through a desiccant (P2O5).
Prior to the film deposition, RF plasma of Ar wasgenerated for 4 h. Then, BrCN and N2 wereintroduced into the chamber through P2O5. Films
were deposited for 2 h. The partial pressures of Arand N2 (PAr and PN2, respectively) were in the rangeof 0.0−0.3 Torr where the total pressure was kept
constant to 0.3 Torr. After the deposition, films wereanalyzed by XPS, Raman, and IR. The opticalemission spectra of the CN (B2Σ+−X2Σ+) transition
were observed.
Matching
RFBox

Fig.1

P2O5Ar , N2

P2O5BrCN

RF-plasma CVD apparatus

3. Results and discussion
The results of the compositional analysis using XPS
are listed in Tables 1 and 2. According to theseresults, nitrogen content of the films were increased
by introducing N2.
Table 1 Compositional analysis ( Grounded electrode )Ar [Torr]

N2 [Torr]

CNOBr

0.3
0.2
0.1
000.1
0.2
0.3

54
44
41
46

3035
41
39

101313106855

Table 2 Compositional analysis ( RF-electrodeelectrode )N2 [Torr]
00.1
0.2
0.3

C55
48
4351

N2535
42360.5

O
14
10
106Br
6757

[N]/([N]+[C]) ratio
Fig. 2 shows the variation of the [N]/as a function of PN2. The ratio was ≈0.35 under thecondition that N2 was not introduced. When PN2
was increased, the [N]/([N]+[C]) ratio increased.
This ratio became the maximum (≈0.5≈0.5) under thecondition of PN2=0.2
0.2 Torr. The ratio dropped to 0.45
when Ar was not introduced.

Fig. 2 Change of the nitrogen content
as a function of PN2

Fig. 3 shows the emission
mission spectrum of the2 +2 +CN(B Σ −X Σ ) transition under the condition ofPAr=0.1 Torr and PN2=0.2 Torr. Fig. 4 shows thevariation of the intensity of the CN
CN(B2Σ+−X2Σ+)emission spectrum as a function of PN2. In thisfigure the intensity observed for PN2=0.3 Torr wasnormalized to 1. As shown in Fig.
ig. 4, the highest
emission intensity was observed under thecondition of PN2=0.2 Torr.

385

386

387
388
389
Wavelength [nm]Fig. 3 Emission spectrum of theCN(B2Σ+−X2Σ+) transition

CN（（B-X）[arb. units]
Ｉ CN

0.4
1

1.5

22.5

Ｉ CN（（B-X）） [arb. units]
Fig. 5 Nitrogen content vs. emission intensity

Fig. 5 shows the variation of the nitrogen content as
a function of the emission intensity. From Fig. 5, astrong correlation was observed between theemission intensity and the nitrogen content. The
result shown in Fig. 5 indicates that CN radicals are
the main source of nitrogen of films even under thecondition of introducing N2. Accordingly themechanism of the “compensation of N atoms” inthe films may be that C atoms produced via the“excess decomposition” of BrCN react with thedischarged product of N2 to form CN radicals which
deposit to form a-CNx with [N]/([N]+[C])[N]/([N]+≈0.5.
4. Concluding remarks
subFilms of a-CNx were deposited onto Si substrates
using the RF plasma excitation of the gas mixtureof BrCN and Ar. By introducing N2 into the reaction
region, the N contents of films were controlled as
0.35−0.5; films formed under the condition of
PAr=0.1 Torr and PN2=0.1 Torr has the highest[N]/([N]+[C]) (=0.5).. According to the correlation
between the [N]/([N]+[C])[C]) ratio of films and theCN(B2Σ+−X2Σ+) emission intensity, the effect of theN2 addition was elucidated; the discharged productsof N2 react with C atoms produced via the “excessdecomposition” of BrCN to form CN radicals
which becomes the precursor of the film formation.
References

21.5
10.5
00.10.2
N2 partial pressure [Torr]

0.45

390

2.50N/[N+C]

Ar [Torr]
0.3
0.2
0.1
00.3

Fig. 4 Variation of the CN(B2Σ+−X2Σ+) emission
intensity as a function of PN2[1] W. Kulisch, Deposition of Diamond-LikeDiamondSuperhardMaterials, Springer-Verlag,Verlag, Berlin, 1999[2] J. R. Fuhr and W. L. Wiese, in: D. R. Lide (Ed.), CRC
Handbook of Chemistry and Physics, CRC Press,BocaRaton, 1998, Chap. 9.
[3] H. Ito, N, Ito, T. Takahashi, H. Takamatsu, D. Tanakaand H. Saitoh: Jpn. J. Appl. Phys. 39, 1371(2000)[4] A. Wada, H. Araki and H. Ito, J. Phys. D Appl. Phys.
43 (2010) 045021.
[5] T. Nakano, H. Toyoda, and H. Sugai, Jpn. J. Appl.
Phys. 30 (1991) 2912.