Surface carbon saturation as a means of CVD diamond nucleation enhancement

Abstract

Abstract During the initial stages of deposition, the growth of CVD diamond is accompanied by annihilation processes such as dissolution of diamond seeds into the substrate, and their etching by HF-activated hydrogen. As a result of such 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 density, the growth rate of diamond crystallites must be enhanced relative to their annihilation rate during the initial stages of deposition. In this work, using silicon substrates, we attempted to do so, by creating a large carbon supply on the substrate surface prior to diamond deposition. Carbon was accumulated by means of different pre-deposition steps: (1) exposure to a high CH4 concentration (10 vol%) under CVD conditions, (2) d.c.-glow discharge of a H2/CH4 gas mixture (9 vol% CH4), and (3) arc discharge of a carbon rod. The effect of titanium metal particles on the subsequent deposition was studied. To distinguish, in the deposited film, between carbon from the pre-deposited layer, and carbon from the gas phase, isotopic 13 CH 4 was 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. 13 C labeling experiments have shown that excess surface carbon hinders diamond debris etching, rather than participates in subsequent growth. In contrast, metal additives such as Ti promote growth, conditioned by their direct exposure to the gas phase.