Transmission Electron Microscopy Study of Diamond Films Grown by Plasma Deposition
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TRANSMISSION ELECTRON MICROSCOPY STUDY OF DIAMOND FILMS GROWN BY PLASMA DEPOSITION
M.S. Wong, W.A. Chiou, F.R. Chen, D.X. U and R.P.H. Chang Materials Research Center, Northwestern University, Evanston, IL 60208
ABSTRACT The morphology and crystal structure of diamond crystallites grown by radio frequency (RF) and microwave (MW) plasma enhanced chemical vapor deposition (PECVD) under comparable conditions are examined by electron microscopy and found to be a strong function of the plasma. A novel TEM sample preparation method is developed to examine the internal structure of diamond as well as interfacial structure between diamond and substrate by direct deposition of diamond crystallites on prethinned metal grids. The diamond crystallites grown by RF PECVD are highly defective and composed of nanocrystalline grains of random orientation while those grown by MW PECVD are wellfaceted and process near perfect long range order in crystal structure.
INTRODUCTION Thin diamond films grown by the plasma deposition method at pressure lower than 1 atm and temperature below 1000 0 C have shown potential application in the chemical, electronic and metals industry.[1-4] The diamond films grown by radio frequency (RF) and microwave (MW) plasma enhanced chemical vapor deposition (PECVD) have been examined by X-ray diffraction, Auger and Raman spectroscopy as well as by various techniques of electron microscopy including TEM, STEM, HREM and SEM. The TEM studies of diamond grown by PECVD methods have been limited.[5-8] This is due to the fact that the PECVD technique for diamond growth is relatively new and most efforts are on the development of new deposition methods and the improvement of deposition conditions to achieve higher growth rate and better film quality. In addition, TEM sample preparation is rather difficult and time-consuming.
The microscopy studies provide detailed information on the diamond crystal structure, morphology, defects, and the diamond-substrate interface property. By using the electron microscopy techniques we have studied diamond crystallites grown on polycrystalline Mo
and Si single crystal
substrates as a function of process parameters
and deposition apparatus.
Mat. Res. Soc. Symp. Proc. Vot. 139. @1989 Materials Research Society
364
EXPERIMENTAL Diamond particles and films on Si (100) and polycrystalline Mo substrates were produced by RF and MW PECVD techniques. A detailed description of the deposition apparatus is given elsewhere.[9] The deposition conditions for the samples used in this TEM study are pressures of 40 mbar, gas composition of 0.5% methane and 0.2% oxygen in hydrogen gas at total flow rate of 200 sccm (MW) and 2000 sccm (RF) and substrate temperature around 925 0 C. In order to examine the internal and interfacial structure of the diamond film on substrate, three different techniques have been utilized for sample preparation. They are (1) the conventional epoxy-embedding technique for cross-sectional TEM, (2) a method wherein the substrate is removed by chemical etching and
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