Etching of polycrystalline diamond films by electron beam assisted plasma
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Etching of polycrystalline diamond films by electron beam assisted plasma Koji Kobashi, Shigeaki Miyauchi, Koichi Miyata, and Kozo Nishimura Kobe Steel, Ltd., Electronics Research Laboratory, 5-5, Takatsuka-dai 1-chome, Nishi-ku, Kobe 651-22, Japan
Jorge J. Rocca Department of Electrical Engineering, Colorado State University, Fort Collins, Colorado 80523 (Received 20 November 1995; accepted 4 June 1996)
Polycrystalline diamond films were processed in a direct current plasma produced by a self-focused electron beam using combinations of H2 , O2 , and He as the processing gas. The film surfaces were observed by scanning electron microscopy, and characterized by x-ray photoelectron spectroscopy. It was found that for the case in which O2 was included in the processing gas, a high density of etch pits appeared on (100) faces of diamond grains, and oxygen was either physisorbed or chemisorbed at the film surface. It was demonstrated that the etching apparatus used was capable of forming at least a 5-mm wide pattern of polycrystalline diamond film.
I. INTRODUCTION
Etching of diamond films has been investigated by many researchers using various techniques which are summarized1–11 in Table I. However, direct-current (dc) plasma has not been used for etching of diamond, and only few attempts have been done to fabricate patterns of diamond films by etching.12 The present paper describes a novel technique for etching polycrystalline diamond films using dc plasma. The apparatus used was based on an invention of a self-focused electron beam generator for gas lasers by Rocca et al.,21–23 and will be called an Electron Beam-Assisted Plasma Etching (EBAPE) system. It is featured by a cathode with a concave surface and a high operational pressure up to about 10 Torr (1 Torr 133 Pa). In the present study, a combination of O2 , H2 , and He was used as the processing gas. The film surfaces before and after plasma treatment were observed by scanning electron microscopy (SEM), and characterized by x-ray photoelectron spectroscopy (XPS). Finally, a pattern formation of diamond film by etching was demonstrated using the same apparatus. II. EXPERIMENTAL
The structure of the EBAPE system is schematically shown in Fig. 1. The inner diameter of the chamber is 200 mm. The cathode head was aluminum with a concave surface, whose diameter and curvature were 75 mm and 200 mm, respectively. The cathode head was mounted on a water-cooled copper stage which was linked to a dc generator. The chamber wall as well as the specimen holder were grounded. The aluminum surface of the cathode was oxidized during the operation either by the processing gas or the residual air and water vapor 2744
http://journals.cambridge.org
J. Mater. Res., Vol. 11, No. 11, Nov 1996
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in the chamber. Owing to the concave cathode surface, the plasma sheath was curved along the cathode surface, which resulted in a self-focused electron beam without an opposing anode. The diamond specimen was placed on
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