Surface carbon saturation as a means of CVD diamond nucleation enhancement

During the initial stages of deposition, the growth of CVD diamond is accom panied by annihilation processes such as dissolution of diamond seeds into the substrate, and their etching by HF-activated hydrogen. As a result of s uch competing processes, only sufficiently large diamond particles survive and contribute to the build-up of the diamond film. This situation prevails until a stable substrate surface is formed. To increase the nucleation den sity, the growth rate of diamond crystallites must be enhanced relative to their annihilation rate during the initial stages of deposition. In this wo rk, using silicon substrates, we attempted to do so, by creating a large ca rbon supply on the substrate surface prior to diamond deposition. Carbon wa s accumulated by means of different pre-deposition steps: (1) exposure to a high CH4 concentration (10 vol%) under CVD conditions, (2) d.c.-glow disch arge of a H-2/CH4 gas mixture (9 vol% CH4), and (3) are discharge of a carb on rod. The effect of titanium metal particles on the subsequent deposition was studied. To distinguish, in the deposited film, between carbon from th e pre-deposited layer, and carbon from the gas phase, isotopic (CH4)-C-13 w as used during the CVD process. High-resolution electron microscopy (HRSEM) , contact-mode atomic force microscopy (AFM), and micro-Raman spectroscopy were used to characterize the samples. The etching by the hot filament (HF) activated hydrogen was found to be the dominant cause for annihilation of growth centers on silicon substrates. C-13 labeling experiments have shown that excess surface carbon hinders diamond debris etching, rather than part icipates in subsequent growth. In contrast, metal additives such as Ti prom ote growth, conditioned by their direct exposure to the gas phase. (C) 1999 Elsevier Science S.A. All rights reserved.