Growth of Diamond from Sputtered Atomic Carbon and Atomic Hydrogen
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GROWTH OF DIAMOND FROM SPUTTERED ATOMIC CARBON AND ATOMIC HYDROGEN. DARIN S. OLSON, MICHAEL A. KELLY, SANJIV KAPOOR, AND STIG 1B. HAGSTROM Department of Materials Science and Engineering, Stanford University, Stanford CA 94305 ABSTRACT Diamond thin films were grown on a scratched silicon crystal surface by a novel CVD technique. The substrate was exposed to a bombardment of sputtered carbon atoms from a graphite target in a helium DC glow discharge, and subsequently exposed to atomic hydrogen generated by a hot tungsten filament. The resulting diamond films were characterized by Raman spectroscopy and SEM. Deposited film quality, and growth rate are presented as a function of carbon flux, and atomic hydrogen flux. The observed increase in growth rate with atomic hydrogen indicates that a surface reaction mechanism may be responsible for growth. The saturation of the utilization of carbon confirms that the diamond growth is probably a surface reaction. Based on this work we propose that the growth of diamond films in the sequential CVD reactor is most likely governed by surface reactions, and that the necessity of gas phase precursors can be precluded. INTRODUCTION The wide interest in the growth of diamond films has been prompted by the material properties of diamond in combination with a broad range of potential applications. Hydrogen and hydrocarbon gas mixtures have been used extensively for synthesis [1-31, focusing attention, to date, on the gas phase precursors involved in the growth of diamond [4,5,6]. The understanding of the nucleation and growth processes has been impeded by the complex gas phase chemistry. Additionally the relatively high operating pressure complicates in situ diagnostics thus impeding direct verification of proposed growth models [7,8]. In order to understand the diamond deposition process we have constructed a novel sequential reactor which has four isolated gas environments. The chemistry and excitation of each environment can be independently varied. This permits, for example, an increase in the amount of atomic hydrogen incident on the substrate independent from the amount of carbon. The substrate is rotated over the sources, being exposed to each source sequentially. The exposure time to each source is as short as 10 milliseconds, shorter than that used in other approaches to alternating chemistry [9]. Thus, deposition parameters such as growth rate and film quality can be correlated to single chemical species and some indication of the importance of certain growth processes involved is also possible. We present here the deposition of diamond by the simplest chemistry. A scratched silicon substrate is exposed to a sputtered flux of atomic carbon, and subsequently to a flux of3 atomic hydrogen. Our results indicate that film thickness (growth rate) and film quality (sp content) are a function of the flux of atomic carbon and atomic hydrogen bombarding the growing surface, suggesting a growth mechanism that is described in terms of surface reactions. REACTOR DESCRIPTION AND PERFORMAN
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