Sulfur addition to microwave activated CH4/CO2 gas mixtures used for diamond CVD: growth studies and gas phase investigations

Abstract

Microwave plasma chemical vapour deposition (MPCVD) has been used to deposit diamond films with H2S additions of 0–5000 ppm to a 51% CH4/49% CO2 plasma, with growth carried out for two different substrate temperatures (620 and 900 °C). Film morphology, growth rate and quality are all observed to deteriorate with increased H2S addition, as investigated by scanning electron microscopy (SEM) and laser Raman spectroscopy (LRS). H2S addition also appears to alter the resistivity of films, as measured by the four-point probe method, however X-ray photoelectron spectroscopy (XPS) revealed little incorporation of sulfur. The plasma chemistry leading to film deposition has been investigated using optical emission spectroscopy (OES), in which H2S addition leads to a reduction in C2* and CH* intensities. Molecular beam mass spectrometry (MBMS) measurements have detected a build-up in CS, CS2, SO and SO2 concentrations with addition of H2S. Experimental results have been compared to CHEMKIN simulations of plasma chemistry and S-incorporation has been investigated in terms of the product of CHEMKIN predicted mole fractions of CH3 and CS, [CH3] × [CS].