Preparation of microcrystalline diamond in a low pressure inductively coupled plasma
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Preparation of microcrystalline diamond in a low pressure inductively coupled plasma Katsuyuki Okada, Shojiro Komatsu, and Seiichiro Matsumoto National Institute for Research in Inorganic Materials, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan (Received 4 February 1998; accepted 17 May 1998)
A 13.56 MHz low pressure inductively coupled plasma (ICP) has been applied to prepare diamond films. The Faraday shield drastically suppressed the electrostatic coupling, which frequently causes contamination due to the etching of the quartz tube. The characterizations of the obtained deposits by scanning electron microscopy (SEM), transmission electron diffraction (TED), and reflection high energy electron diffraction (RHEED) revealed that the deposits are composed of microcrystalline diamond and disordered microcrystalline graphite. The CO additive to a CH4yH2 plasma brought about the morphological change from a scale-like deposit to a particle one. Besides, the number of encountered particles was increased with an increase of CO additive. The TED and RHEED observations showed that non-diamond carbon was effectively removed with an increase of CO additive. These results indicate that oxygen-contained radicals produced by the addition of CO play an effective role in the removal of non-diamond carbon in the diamond growth conditions and that the CO additive makes the supersaturation degree of carbon large.
I. INTRODUCTION
Recent plasma dry processes (e.g., deposition, coating, etching) require wide area and high density plasma at low pressures (, 1 Torr).1 An electron cyclotron resonance (ECR) plasma was first developed to meet these conditions. Subsequently, a helicon-wave excited plasma was employed. It was found2 that the density of an inductively coupled plasma (ICP) becomes high at low pressures. Amorim et al.3 reported that the plasma density of ICP after the transition from a low density E-discharge to a high density H-discharge reaches 1012 cm23 . 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 a promising method for PECVD at low pressures. On the other hand, a microwave plasma is most commonly used for the PE-CVD of diamond films,4 in which the conventional pressure of deposition is of the order of a few 10 Torr. An ECR is the only plasma that is used for diamond deposition below 1 Torr.5 While Bozeman et al.6 reported the diamond deposition at 4 Torr by using a planar ICP, there are a few reports7,8 that describe the synthesis of diamond by low pressure ICP. However, the growth conditions in a low pressure ICP have not yet optimized. It is consequently required to establish the synthesis of diamond in a low pressure ICP and to find out the optimum growth condition. In the PE-CVD of diamond films, the addition of oxygen to the CH4yH2 system was intended to get a high growth rate and/or an improvement of the quality 578
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J. Mater. Res., Vol. 1
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