Ion induced nucleation of diamond

Abstract

The process of bias enhanced nucleation of microwave chemical vapour deposited diamond on silicon is characterised using plasma diagnostics, scanning and transmission electron microscopy (TEM), Raman spectroscopy, and X-ray diffraction. The nucleation density is measured as a function of bias voltage, methane gas flow rate, and temperature. The nucleation density is found to be increased above 650°C and reach a maximum at around -250 V which corresponds to an ion energy of 70 to 90 eV. This is close to the optimum energy for ion subplantation, responsible for sp3 bonding in diamond-like carbon. This is taken as strong evidence that nucleation enhancement involves ion subplantation. To prove the influence of ion subplantation on the nucleation process and to reduce the description of the diamond nucleation process to physical parameters such as ion energy, substrate temperature, and film forming particle flux, films are prepared with a low pressure plasma beam source (BPS). The PBS films are prepared at an energy per C atom of 83 eV and in a temperature range of 30 to 800°C. Two characteristic temperature thresholds have been found: above 260°C the highly tetrahedrally bonded amorphous material, which is very compact and smooth with densities above 2.7 g/cm3 and internal stresses above 8 GPa changes immediately into a sp2 bonded, stress reduced (<2 GPa) structure, with densities below 2.2 g/cm3 and a very rough surface. Above 450°C, the hydrogen content is mainly evolved and the films turn into a more ordered structure with crystal impacts and a less rough surface. These films are very similar to bias-MW-CVD deposited two phase structures and lead to comparable nucleation densities when they are used as substrates in a standard microwave diamond deposition process.