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].