The Role of Atomic Hydrogen and Oxygen in Low Temperature Growth of Diamond by Microwave Plasma Assisted CVD
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THE ROLE OF ATOMIC HYDROGEN AND OXYGEN IN LOW TEMPERATURE GROWTH OF DIAMOND BY MICROWAVE PLASMA ASSISTED CVD Y. MURANAKA, H. YAMASHITA, H. MIYADERA Hitachi Research Laboratory, Hitachi Ltd., 4026 Kuji-cho, Hitachi-shi, Ibaraki-ken, Japan 319-12 ABSTRACT Diamond films grown in the microwave plasmas of CO(7-8%)-O 2 (0-2.2%)-H 2 systems in the range of 130-750*C were characterized by scanning electron microscopy, Raman spectroscopy, and cathodoluminescence (CL) studies. The films grown in the CO-0 2-H 2 system had much better crystallinity than those grown in the CO-H 2 system. This was because oxygen extremely purified diamond films by suppressing polyacetylene inclusion, and prohibited the vacancy formation in the crystallites. These oxygen functions have indicated the possibility that high quality diamond films (FWI-tM of the diamond Raman peak =4.0-4. lcm-1 ) close to natural diamond (FWHM=3.0cm-') were obtained in the CO(8%)-0 2(2.2%)-H2 system between 400 and 750'C. Though crystallinity deterioration occurred at 130*C , the obtained film (FWHM=10.2cm-1) in the CO(8%)-0 2(2.2%)-H 2 system was of good crystallinity comparable to those (FWHM=7-21cm-1) grown by conventional CVD processes and gas systems between 590 and 1327°C. The CO-0 2 -H2 microwave plasma was concluded to be one of the best environment for the low temperature growth of highly purified diamond films of good crystallinity. INTRODUCTION Low temperature growth of pure diamond films (LTGPD) is an important goal for the extension of diamond applications towards semiconductor, optical emitting materials as well as optical and mechanical coating materials or heat sinks. Attempts of LTGPD have only recently been begun. Polycrystalline diamond was synthesized in a CH 4 -0 2-H 2 system at an average substrate temperature (Ts) of 400'C using a pulsed microwave plasma discharge system [1]. Diamond growth below 400"C was also confirmed in the same gas system using a lower output microwave (260W, for the purpose of lowering Ts) [2]. Others employed a magnetomicrowave plasma and demonstrated the growth of high quality diamond films at 580'C, while confirming diamond growth at 500'C [3]. dc plasma CVD has been recently applied for diamond synthesis on an Al substrate between 140 and 480'C, and it was reported that nanocrystalline diamond containing a large amount of amorphous phase was formed at 140°C [4]. Though low temperature growth of diamond polycrystalline films was demonstrated by these previous studies, highly crystallized and purified films has never been deposited. Diamond films prepared in the microwave plasma of the CO-H 2 system contains polyacetylene (P.A.) component other than diamond crystallites [5]. In particular, P.A. inclusion enhances on lowering Ts, resulting in the decay of diamond crystallinity [6]. Atomic hydrogen has a function of suppressing P. A. inclusion by prohibiting the polymerization of gas phase unsaturated hydrocarbon on a growth surface [5]. Accordingly, highly purified diamond films are expected to be grown in excess atomic h
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