22P062-P
Irradiation of Ar/CH4/H2 Pulse Modulated Induction Thermal Plasmas
to Si Substrate
変調制御した高熱流Ar/CH4/H2誘導熱プラズマのSi基板照射実験
Kenta Fujimoto, Yosuke Haruta, Yasunori Tanaka and Yoshihiko Uesugi
藤本健太, 春多洋佑, 田中康規, 上杉喜彦
Division of Electrical and Computer Engineering, Kanazawa University,Kakuma, Kanazawa 920-1192, Japan
金沢大学自然科学研究科電子情報工学専攻，〒920-1192 金沢市角間町
The silicon substrate was irradiated by Ar/CH4/H2 Pulse Modulated Induction Thermal Plasma (PMITP) at15 kW. The irradiated surface of the substrate was analyzed by a scanning electron microscope (SEM) andRaman spectroscopy. Results showed that the substrate irradiated by the PMITP had a sharp peak at 1328
cm-1 which indicates diamond of Raman shift, while the substrate by the non modulated thermal plasmas
has a large G-band. The SEM results showed that polycrystalline diamond films were grown almost
uniformly in 25x25 mm2 in case of PMITP.

2. Experimental setup and conditions
Fig. 1 illustrates a configuration of the plasma
torch for PMITP. The plasma torch is composed oftwo coaxial quartz tubes with a 330 mm length.
Argon gas was supplied as a sheath gas along theinside quartz tube. Experimental conditions aresummarized in Table 1. Methane and hydrogen gas
mixture was supplied through a water-cooled
stainless steel tube inserted from the top of theplasma torch. Total gas flow rate including CH4/H2
mixture was fixed at 70 slpm. Methane gas flowrate and hydrogen gas flow rate was fixed at 30
sccm and 3 slpm, respectively. Pressure in thechamber was fixed at 180 torr. The quantity‘On-time’, which is the time duration with higher

current level (HCL), was set to 10 ms, and‘Off-time’, the time duration with lower current
level (LCL), was set to 5 ms for PMITP. We also
defined ‘SCL’, shimmer current level as a ratio ofLCL/HCL [3]. The SCL was set to 100% and 40%.
The condition 100%SCL is equivalent tonon-modulated condition. A water-cooled specimen
holder was installed downstream of the chamber,where a silicon substrate was put. The silicon
substrate has a size of approximately 25×25 mm2.
Input power to the non-modulated plasma and thePMITP was adjusted to make the substratetemperature 980 oC in each. Thus, the input power
was 9.3 kW for the non-modulated plasma, whilst it
was 14.5 kW for the PMITP. The substratetemperature was measured by a radiation
thermometer from the observation window. The
irradiated surface of the substrate was analyzed by
Raman spectroscopy and the scanning electron
microscope (SEM). To study the gas composition
around the substrate, a quadrupole mass
spectrometer (QMS) was used to detect gases
around the substrate surface from Ar/CH4/H2PMITP. Irradiation time was six hours.
Cooling waterOn Time

Coil current

1. Introduction
The inductively coupled thermal plasma (ICTP)
is widely used for many material processings [1,2]because of its high enthalpy and high reaction
activity. To obtain a further effective radical sourcewith high controllability of the gas temperature, wehave developed a pulse-modulated induction
thermal plasma (PMITP) system [3]. This PMITP
system can modulate the coil current amplitude of
the order of several hundreds amperes. On the otherhand, much attention has been paid to carbon
materials including graphene, carbon nanotube,
fullerene, DLC and diamond. The diamond is apromising material, for example, for surface coatingwith high hardness. This report describes results ona trial irradiation test of a high pressure high-power
Ar/CH4/H2 PMITP to the Si substrate. It was foundthat use of the PMITP provided the uniform
polycrystalline diamond films deposited on the Sisubstrates, although the non-modulated thermal
plasma does non-uniform one.

Ar gas

Probe gas
(CH4+H2)

Off TimeTime

155 mmCoil 8 turns

Sample holder (SUS304)
200 mmSi(100)substrate・25×25 mm2・Thickness：

Cooling water

600 mm

Fig.1. Schematic diagram of plasma torch andchamber.

3.3 Mass spectra
Fig.5 shows the mass spectra measured aroundthe substrate using a QMS to study gas composition
irradiated. This figure implies that use of theAr/CH4/H2 PMITP decreased the CH4, CH3, CH2
and CH density as compared to the non-modulated
thermal plasmas. We expect from this figure thatthe dissociation of CH4 was promoted by thePMITP.
4. Conclusion
Polycrystalline diamond was deposited on Si(100)substrate using Ar/CH4/H2 PMITP. The substrate

BB

3 mm

Position A(The center of the substrate)-11334 cm

G bandFig.3. SEM images of the surface polycrystalline
diamond films deposited on Si(100) by PMITP.
Intensity [a.u.] Intensity [a.u.]

3 mm

Non Modulated Plasma
Si-11328 cm

Pulse Modulated Plasma

Position B(The edge of the substrate)-11329 cmSi

Non Modulated Plasma

400

Pulse Modulated Plasma

600

800

1000

1200

1400

1600

-1

Raman Shift [cm ]Fig.4. Raman spectra of carbon films on silicon
substrates.
-8

C2H2OH

C2H
C2C

10CH3-11

W/O plasma
Non Modulated plasma
Pulse Modulatedplasma
CH210CH-10

CH4-910Ar

H2O+H210H

3.2 Raman spectra
Fig. 4 shows the Raman spectra of the carbon
films irradiated by the non-modulated plasma andthe PMITP. This figure includes Raman shift results
for two positions on Si substrate designated byA(center) and B(edge) in Fig.2. For thenon-modulated plasma, the peak at 520 cm-1 wasfound on both position A and B. This peak comesfrom the silicon of the substrate. The band at 1580
cm-1 is attributed to the graphite which has been
assigned to the predicted E2g C-C stretching mode.
The Raman line at 1334 cm-1 is the characteristic
signature of the diamond structure [4]. These peaks
cannot be found in position B. On the other hand,
only the sharp Raman spectra peak around 1328
cm-1 could be measured for the substrate irradiatedby the PMITP. This peak can be clearly seen for
two positions A and B. The peak at 520 cm-1
disappeared, which indicates that the components ofthe graphite (shown at 1550 cm-1) decreased byusing PMITP.

A{

3. Results and discussions
3.1 The surface of substrates irradiated by PMITP
Fig.2. (a) and (b) shows photos of the Si
substrate surface irradiated by the induction thermal
plasma. In case of non-modulated plasma
irradiaiton, carbon films were non-uniformly
deposited on the substrate surface. On the otherhand, the PMITP offers almost uniform carbon
films grown in region 25 x 25 mm2. Fig.3 shows a
SEM image of the surface irradiated by the PMITP,
which indicates polycrystalline film there.

A(a)Non modulation(b)Pulse Modulation
Fig.2. The surface of Si substrates irradiated by induction
thermal plasma.

Ion current [A]Table 1. Growth conditions
Gas flow rate
Ar/ H2/ CH4
67/3/0.03 slpm
Substrate
Si (100)
Substrate temperature
980oC
Total gas pressure
180 torr
Input power
Non Modulation(100%SCL)
9.3 kW
Pulse Modulation(40%SCL)
14.5 kW-1210-13

10

1 2 311 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26m/z

Fig.5. Mass spectrum of Ar/CH4/H2.
by the PMITP shows a sharper peak of diamond at 1328
cm-1 in Raman spectra as compared to non-modulated
thermal plasmas. The PMITP provided more uniform
polycrystalline diamond films grown in 25 x 25 mm2.

Acknowledgments
The authors are grateful to Dr. Haruyuki Yasui
for performing Raman spectroscopic analysis.
References[1] T. Ishigaki, et al, Sci. Technol. Advanced Master. 6,111(2005).
[2] W. R. Chen, et al, Surface Coating Technol., 197,
109(2005).
[3] Y. Tanaka, et al, Appl. Phys. Lett., 89,031501.
[4] Diane S., et al, J.Mater. Res., Vol. 4, No.2, (1989)