23P011-O
Pulsed Supermagnetron Plasma Deposition of a-CNx:H Films
for Field Emission Use
パルス変調スーパーマグネトロンプラズマによる電界電子放出用a-CNx:H膜の堆積Haruhisa Kinoshita and Tanaka Sumio
木下治久，田中純雄
Research Institute of Electronics, Shizuoka University
3-5-1 Johoku, Naka-ku, Hamamatsu 432-8011, Japan
静岡大学電子工学研究所，〒432-8011 静岡県浜松市中区城北3-5-1
Supermagnetron plasma was applied to the deposition of amorphous CNx:H (a-CNx:H) films. The range ofelectrode rf power (UPRF/LORF) was selected as 200 (Continuous)/50–800 (Pulsed) W, and films weredeposited using i-C4H10/N2 plasma. The range for the duty ratio of pulsed rf power was selected as 12.5%.
The optical band gap was decreased with increases in LORF. Hardness was increased with LORF. The
lowest threshold electric field was observed to be 11 V/μm at UPRF/LORF of 50-200/400 W.

2. Experimenta-CNx:H films were deposited using a pulsed
supermagnetron plasma CVD apparatus. Two
different rf power sources with the same rf
frequency (13.56 MHz) were controlled tomodulate rf amplitude using a pulse generator, andwere supplied to two electrodes. A magnetic field of
about 80 G was applied in parallel with the twoelectrode surfaces. The deposition substrates wereplaced on the lower electrode. The lower electrodewas heated to 100°C during the film deposition.

i-C4H10 (50 sccm) and N2 (120 sccm) wereintroduced into the CVD chamber, and the gaspressure was maintained at 30 mTorr. The bonding
configurations of a-CNx:H were measured by using
a Fourier transform infrared (FTIR) spectrometer.
The hardness of the films was determined by adynamic ultra-micro-hardness tester. The opticalband gap was estimated from the Tauc formulausing optical absorption data specified by theUV/VIS/NIR spectrometer.
3. Results and Discussion
The FT-IR absorption spectra of a-CNx films
were measured, and are shown in Fig. 1. Broadabsorption band of C=C, C=N, C=C, CH2 and CH3
bonds (1100- 1700 cm-1) was observed in all theUPRF : 200W
Duty Ratio : 12.5%
Gas Pressure : 30mTorr(LORF)

ABSORBANCE (a.u.)

1. Introduction
Amorphous carbon (a-C) films have received
considerable attention due to its high chemicalstability, optical transparency, high mechanicalhardness with low dielectric constant. It was foundthat both the optical and electrical properties, aswell as their mechanical properties, can be modified
by nitrogen incorporation [1]. In the case of
supermagnetron plasma chemical vapor deposition(CVD), it is important to control the substratetemperature from its heating by bombardment ofhigh energy ions. Pulsed cooling using pulsed
plasma is effective to avoid overheating of thesubstrate. Pulsed plasma CVD is effective todeposit low residual stress a-CNx:H films [2]. Low
residual stress films are effective to form electronic
devices such as field emitter and photovoltaic cellwith high reliability [3]. Low substrate temperature
is favorable to avoid degradation of the quality ofunderlying layers and the reliability of electronic
devices. High internal stress makes it difficult todeposit thick films by delaminating from thesubstrate.

800W
400W

200W

50W

O-H N-H

4000

3500

C-H

C≡C,C≡N

C-C,C-H & C-N

3000 2500 2000 1500
-1
WAVENUMBER (cm )1000

Fig. 1 Dependence of FT-IR absorption spectra onLORF.

45

UPRF : 200WLORF : Pulse
Duty Ratio : 12.5%
Gas Pressure : 30mTorr

40353025Hardness of Glass

201510500200400600800
1000
LOWER ELECTRODE RF POWER (W)Fig. 3 Dependence of hardness on LORF.

1.2

0.8

0.4

00200
400600800
1000
LOWER ELECTRODE RF POWER (W)Fig. 2 Dependence of optical band gap on LORF.

The hardness was measured as a function ofLORF, as shown in Fig. 3. The hardness wasincreased from 8 to 35 GPa with the increase ofLORF from 50 to 800 W. a-CNx film with many Hatoms (LORF: 50 and 200 W) was soft and thatwith less H atoms (LORF: 800 W) was hard. For
reference, we measured the hardness of quartz glass(SiO2), which was 22 GPa.
These a-CNx films of about 200 nm thickness
were deposited on p-Si substrates, and their fieldemission characteristics were measured.
Theelectron emission characteristics of these flat a-CNx
films were measured, as shown in Fig. 4.
Emission threshold electric field (ETH) wasdecreased from 17 to 11 V/μm with the decrease ofLORF from 800 to 50 W. The films with many Hatoms showed lower ETH characteristics. The FN
plots of these a-CNx films shown in the inset of Fig.
4 were nearly linear.

10
UPRF : 200W
Duty Ratio : 12.5%
Press. : 30mTorr

1LORF
800W
400W
200W
50W

0.1

0.01-10Log I/V2 (A/V2)

1.6

2

UPRF : 200W
LORF : Pulse
Duty Ratio : 12.5%
Gas Pressure : 30mTorr

EMISSION CURRENT DENSITY (mA/cm )OPTICAL BAND GAP (eV)250

HARDNESS (GPa)films (LORF: 50-800 W). Absorption band atabout 2930 cm-1 (CH3, CH2, and CH bonds) wasdecreased with the increase of LORF, however thatof 3300 cm-1 (NH bond) was increased with theincrease of LORF. That of 3500 cm-1 (OH bonds)
was observed in two films deposited at LORF of 50
and 200 W. From these experimental data, twofilms deposited at 50 and 200 W were found toinclude many H atoms. The film deposited at 800
W included less H atoms.
Fig.2 shows the optical band gap of formed
a-CNx:H films. At LORF of 50 W, optical band gap
was about 1.9 eV. It was decreased with the increaseof LORF. The lowest value of about 0.6 eV wasobtained at LORF of 800 W.

0.001-11-12-13-14
0.5 0.9 1.3 1.7-1
1000/V (V )0.00010102030
ELECTRIC FIELD (V/μm)

40Fig. 4 Dependence of electron emission characteristics on LORF.

4. Conclusion
a-CNx films were deposited using pulsed
supermagnetron CVD. Broad absorption spectra ofCH3, CH2, CH, NH and OH bonds were observed in
the films deposited at LORF of 50 and 200 W, but
not observed in that (LORF: 800 W). ETH ofelectron field emission was decreased from 17 to 11
V/μm with the decrease of LORF from 800 to 50
W.
References[1] P.Wood, T.Wydeven and O.Tsuji, Thin Solid Films
258, 151 (1995).
[2] S. Kumar, P. N. Dixit. D. Sarangi and R.
Bhattacharyya, J. Appl. Phys. 85, 3866 (1999).
[3] H. Kinoshita and H. Suzuki, J. Mod. Phys., 2, 398(2011).