The Early Stages of Microwave-Assisted Chemical Vapor Deposition of Diamond on Fused Silica Substrates
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THE EARLY STAGES OF MICROWAVE-ASSISTED CHEMICAL VAPOR DEPOSITION OF DIAMOND ON FUSED SILICA SUBSTRATES J. RANKIN', Y. SHIGESATO", R.E. BOEKENHAUER, R. CSENCSITS, D.C. PAINE, AND B.W. SHELDON Brown University, Division of Engineering, Providence, RI 02912 ABSTRACT The early stages of the microwave assisted chemical vapor deposition of diamond on fused silica and silicon substrates were examined with Raman spectroscopy and scanning electron microscopy. Grain size as a function of time was determined for both substrates. Grains formed on fused silica were larger, with smoother growth surfaces than those formed on silicon substrates under the same conditions. For deposition on silica, the particle morphology changes from cuboid to cubo-octahedral for deposition times between 5 and 15 minutes. Also, the glass surfaces were etched during the pretreatment and deposition stages. These results are discussed in terms of mass transport limited growth, and chemical interactions between the gas-phase and the substrate surface. INTRODUCTION The chemical vapor deposition of diamond films on silicon has recently received considerable attention [1-3]. There has also been a growing interest in the study of deposition of these films on glass substrates [4,5]. In particular, diamond films on glass are potentially useful as ultra-hard, transparent coatings. The current study focuses on the earliest stages of diamond nucleation and growth, at times where isolated grains and the substrate are both observable. The silica surfaces undergo significant roughening during the early stages of deposition. Also, there were several significant differences between diamond growth on fused silica and silicon. DESCRIPTION OF EXPERIMENTS High purity fused silica' substrates were used for most of this work. These substrates were abraded using 5 micron diamond paste and cleaned in an ultrasonic bath of acetone, followed by rinses in acetone and methanol. Diamond deposition was conducted in a microwave plasma system."+ All substrates were subjected to an in-situ pre-deposition treatment under the following conditions: 920oC, 5 kPa (37.5 Torr), 1200 W microwave power, and H 2 gas at 496 sccm for 15 minutes. The diamond deposition was performed under the same conditions as the pre-treatment with the addition of 4 sccm CH 4
"also affiliated "also affiliated
with the Bunting Institute, Radcliffe College, Cambridge, MA. with Asahi Glass, Yokohama, Japan.
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Asahi Glass, Yokohama, Japan, total impurities < 100 ppm.
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Model HPM/M, Applied Science and Technology, Inc., Woburn, MA. Mat. Res. Soc. Symp. Proc. Vol. 270. @1992 Materials Research Society
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(0.8%). For this study the deposition times were varied from 5 to 120 minutes, with all other experimental variables held constant. For comparison, several deposition runs were also conducted on single crystal, (100) oriented Si substrates. These samples were subjected to the same surface preparation, pretreatment, and deposition conditions as their fused silica analogs. Raman spectroscopy was used to exa
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