Fabrication of Diamond and Diamond-Like Carbon by Low Pressure Inductively Coupled Plasma CVD
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KATSUYUKI OKADA, SHOJIRO KOMATSU, TAKAMASA ISHIGAKI, AND SEIICHIRO MATSUMOTO National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305, Japan
ABSTRACT
A 13.56 MHz inductively coupled plasma(ICP) system has been applied to fabricate diamond and diamond-like carbon from a CH 4/H2 /Ar plasma. The characterizations of the obtained deposits by transmission electron diffraction, reflection high energy electron diffraction, and Raman scattering revealed that the deposits are diamond crystallites, with crystal sizes -1 ,a m, and that they partially include disordered microcrystalline graphite. Although contamination due to etching of the quartz tube exists, this was drastically suppressed by the electrostatic shield(Faraday shield).
I.INTRODUCTION
Recent plasma dry processes require wide area and high density plasmas at low pressures. An electron cyclotron resonance(ECR) plasma was first developed to meet these conditions. Subsequently, a helicon-wave excited plasma was developed. It has been recently found I that the density of an inductively coupled plasma(ICP) becomes high at low pressures(< l Torr) . It is reported 2 that the plasma density after the transition from a low density E-discharge to a high density H-discharge reaches - 1012 cm- 3 . It is necessary in plasma-enhanced chemical vapor deposition(PE-CVD) to get a sufficient radical flux for deposition. Thus the ICP is thought to be an expected method for PE-CVD at low pressures. In this study, a 13.56 MHz ICP system has been utilized as a radical source, and applied to fabricate diamond and diamond-like carbon from a CH 4 /H2 /Ar plasma.
2.EXPERIMENT
The plasma torch designed in this study was modeled on the collimated plasma beam reactor 3 . The schematic view of the plasma reactor system is illustrated in Figure 1. It consisted of a water-cooled quartz tube surrounded with a teflon tube placed at the bottom of a stainless-steel chamber. A plasma beam was generated by an aperture made of BN at the bottom of the chamber. In the gas inlet system, sheath gas was introduced to flow fast along the reactor-tube wall, while source gas was admitted along the central axis of the reactor. To change the velocity of the source gas, two types of nozzle for source gas were used; one was 6.5 mm in inner diameter(ID), and the other was 1.2 mm in ID. The chamber was pre-evacuated to -1-X 10-3 Torr by a mechanical booster pump( 1500 I/min). An electrostatic shield 1,4 (Faraday shield) was placed between the RF coil and the quartz tube to rule out the electrostatic coupling from RF coil to plasmas. The quartz tube was wrapped with a grounded copper plate slitted at regular intervals along the azimuthal 157 Mat. Res. Soc. Symp. Proc. Vol. 363 01995 Materials Research Society
direction. The substrate holder was manipulated from the top of the chamber. Molybdenum plates and silicon (100) wafers( 0 10 mm) were used as a substrate. The substrate was heated by a tungsten filament. The substrate temperature(Ts) was monitored with a sheathed thermoc
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