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 H 2 S additions of 0-5000 ppm to a 51% CH 4 /49% CO 2 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 H 2 S addition, as investigated by scanning electron microscopy (SEM) and laser Raman spectroscopy (LRS). H 2 S 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 H 2 S addition leads to a reduction in C 2 * and CH* intensities. Molecular beam mass spectrometry (MBMS) measurements have detected a build-up in CS, CS 2 , SO and SO 2 concentrations with addition of H 2 S. 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 CH 3 and CS, [CH 3

Theoretical models for doping diamond for semiconductor applications

“…Analysis of the gas-phase chemistry where sulfur is present suggests its role may be one of modification of the key growth species [115][116][117][118]. Nevertheless, analysis such as SIMS [119] and particle induced X-ray emission spectroscopy (PIXE) [110,120] clearly shows that sulfur is incorporated during growth, the mechanisms for which have some theoretical support [121,122].…”