Selective growth of diamond crystals on the apex of silicon pyramids
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Diamond crystals have been selectively grown on the apex of anisotropically chemically etched silicon pyramids. A novel process sequence is developed which exposes a patterned sharp apex of silicon pyramids surrounded by thermally grown sihco,^dioxide to a high pressure microwave plasma-assisted chemical vapor deposition (HPMACVD) process where the reactant feed gases are methane and hydrogen. The nucleation rate of diamond is very high on the sharp edge of a silicon mesa structure or an apex of a silicon pyramid, as anticipated. Selective growth of diamond particles on the apex of silicon pyramids fabricated using various approaches was analyzed by scanning electron microscopy.
I. INTRODUCTION Mirror-smooth finished silicon surfaces have a very low nucleation density for diamond growth. Scratching or damaging the silicon surfaces using a diamond paste has substantially enhanced the nucleation density of diamond growth by several orders of magnitude.1" Hirabayashi et at have treated the damaged silicon surface with Ar+ ion beams prior to the diamond growth studies to achieve the selective diamond growth.4 Ar+ ion beam scanning over the damaged silicon surface has minimized the scratch density by rounding off the sharp edges of damage performed by ultrasonic agitation in ethylalcohol solvent containing diamond particles. Our work resulted in selective diamond growth over a silicon surface by using thermal oxidation of the damaged silicon surface using a silicon nitride mask to minimize the sharp edges by rounding off in the undesired (oxide grown) diamond growth areas.5"7 Do the above observations indicate that the sharp edges are active sites or very low free energy sites for nucleation of diamond growth? We have considered the above results as a guideline and assumed the apex of anisotropically etched silicon pyramids as a nucleation site for diamond growth. If an apex of a pyramid is a nucleation site for diamond growth, it should in principle have a high growth rate. Figure 1 is a scanning electron micrograph of diamond particles grown on chemically etched silicon mesa structure (diamond deposition time: ~5.75 h). It is obvious from the micrograph that the diamond tends to nucleate on the sharp edge of a silicon mesa. The apparent area of the sharp edge is considerably smaller than the apparent flat surface area of the silicon in the micrograph. But, approximately 50% of the diamond nucleation has occurred on the sharp edge irrespective of the lower area ratio. This paper delineates the process flow steps to grow diamond particles selectively on the J. Mater. Res., Vol. 7, No. 5, May 1992 http://journals.cambridge.org
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FIG. 1. Scanning electron micrograph of the diamond particles grown on a mesa structure of silicon.
apices of anisotropically etched silicon pyramids fabricated with and without diamond paste treatment prior to the fabrication of pyramids to substantiate the idea of a tendency of diamond nucleation on the sharp edges. II. EXPERIMENTAL DETAILS A commercially available hig
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