Improved uniformity and selected area deposition of diamond by the oxy-acetylene flame method
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The role of SiO2 in nucleation of diamond has been investigated in an oxy-acetylene flame. It was found that growth methods that minimize SiO2 formation enhance diamond nucleation. A short pretreatment of a scratched Si surface in a low oxygen-to-acetylene ratio flame, at a distance 1.5 cm from the flame core, significantly improved uniformity of subsequent diamond growth. When scratched surfaces were intentionally oxidized, nucleation of diamond was completely inhibited. By using a mask to controllably deposit SiO2 on a scratched Si surface, highly selective deposition of diamond was achieved with resolution below 5 yttm. These results are discussed with reference to competing oxidation and carbon formation processes that take place during the nucleation of diamond. During the nucleation stage, carbon may be deposited on the scratched Si via a route in which the Si surface catalyzes carbon formation reactions that are otherwise kinetically unfavorable. The formation of an oxide layer, on the other hand, would act to passivate the surface, and thus inhibit carbon formation via a catalytic route. The decomposition of CO to C and CO2 is given as an example of a reaction that is favored at temperatures below 1000 K, but requires surface catalysis to proceed because it remains frozen out in the gas phase due to a very slow reaction rate.
I. INTRODUCTION Since the growth of diamond by oxy-acetylene torch was first reported by Hirose,1 a significant amount of work has focused on understanding the flame chemistry2"5 as well as growth dynamics6 in order to improve the uniformity of diamond films. While a high density, annular ring of diamond forms at the perimeter of the flame, a significant problem has been the lack of growth in the central region of the flame front.3"5 It has been suggested that a large radial variation in flame chemistry may be responsible for these observations.3'5 Various strategies have been employed to minimize this nonuniformity. Oaks et al.5 found that growth was more uniform when the substrate was moved 6 mm from the flame core; they concluded that concentrations of flame species were more homogeneous in this region of the flame. Others have improved uniformity by growing diamond with the substrate at an angle relative to the flame direction. For instance, Tzeng et al.1 grew at a 70° angle relative to the flame to obtain complete films on Si. However, it seems that in those cases where uniform diamond films were achieved, growth had to be preceded by a low oxygen-to-acetylene ratio (Rf) pretreatment. Thus, Ravi et al.8 used a short, low Rf pretreatment to significantly improve film coherence, whereas Tzeng et al.1 also reported a low Rf (0.85) pretreatment to be necessary in their work at large angles relative to the flame. 2144 http://journals.cambridge.org
J. Mater. Res., Vol. 7, No. 8, Aug 1992 Downloaded: 15 Mar 2015
In this report the deposition of pinhole-free diamond films on Si, over the entire flame, front is described. A key factor in obtaining these films was a pretreatment that was
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