Insights into the ion-assisted nucleation of diamond on silicon
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Insights into the ion-assisted nucleation of diamond on silicon Sean P. McGinnis,a) Michael A. Kelly, and Stig B. Hagstr¨om Department of Materials Science and Engineering, Stanford University, Stanford, California 94305-2205 (Received 10 July 1996; accepted 14 May 1997)
The ion-assisted nucleation of diamond was studied in a microwave plasma chemical vapor deposition system to gain insights into the processes controlling this phenomenon. The dependence of the nucleation density on bias voltage and temperature, as well as experiments with an electrically isolated substrate, are consistent with an ion bombardment mechanism for diamond nucleation. However, the growth of these nuclei is dominated by neutral species rather than ions. Measurements of the bias current under various conditions also provide details on the roles of the incident ion flux and substrate electron emission during this process. Furthermore, Monte Carlo simulations of the ion energy distribution at the substrate are compared to experimental measurements. Preferential sputtering, thermal spike, and carbon subplantation nucleation mechanisms are assessed based on the experimental and modeling results.
I. INTRODUCTION
Due to unique thermal, mechanical, chemical, and electrical properties, the potential of diamond as a material for advanced technologies has been well documented. However, limitations in the deposition of diamond thin films have prevented their widespread use in most applications. The poor heterogeneous nucleation of diamond is one severe problem for diamond thin film applications. Diamond nucleation is extremely poor on nearly all substrates, with nucleation densities typically less than ,105 cm–2 when substrate pretreatments are not used. In fact, the nucleation of diamond is generally so poor that thin continuous diamond films cannot be deposited without substrate pretreatments. A common pretreatment to enhance diamond nucleation is the abrasion, by various methods, of the substrate with diamond powder. Nucleation densities are increased to ,108 cm–2 and continuous polycrystalline diamond thin films can be routinely grown using diamondabraded substrates. For many industrial applications, however, there are practical problems with this technique including mechanical damage to the substrate and limited process control. Moreover, from a basic research perspective, since diamond grows homoepitaxially on the residual nanocrystalline diamond seeds following such pretreatments,1,2 few insights into the heterogeneous nucleation of diamond are gained when diamond scratched substrates are used. In contrast, ion-assisted nucleation is a wellestablished technique which provides nucleation densities in excess of 1010 cm–2 for diamond thin films.3–6 Also referred to as bias-enhanced nucleation (BEN) a)
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J. Mater. Res., Vol. 12, No. 12, Dec 1997
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