Large area deposition of boron doped nano-crystalline diamond films at low temperatures using microwave plasma enhanced chemical vapour deposition with linear antenna delivery

Abstract

We report on the preparation and characterisation of boron (B) doped nano-crystalline diamond (B-NCD) layers grown over large areas (up to 50 cm × 30 cm) and at low substrate temperatures (< 650 °C) using microwave plasma enhanced linear antenna chemical vapour deposition apparatus (MW-LA-PECVD). B-NCD layers were grown in H2/CH4/CO2 and H2/CH4 gas mixtures with added trimethylboron (TMB). Layers with thicknesses of 150 nm to 1 μm have been prepared with B/C ratios up to 15000 ppm over a range of CO2/CH4 ratios to study the effect of oxygen (O) on the incorporation rate of B into the solid phase and the effect on the quality of the B-NCD with respect to sp3/sp2 ratio. Experimental results show the reduction of boron acceptor concentration with increasing CO2 concentration. Higher sp3/sp2 ratios were measured by Raman spectroscopy with increasing TMB concentration in the gas phase without CO2. Incorporation of high concentrations of B (up to 1.75 × 1021 cm3) in the solid is demonstrated as measured by neutron depth profiling, Hall effect and spectroscopic ellipsometry.