Microwave plasma chemical vapour deposition of high purity diamond films

Abstract

Diamond films have been deposited in a spherical (diameter 400 mm) ultrahigh vacuum chamber (base pressure less than 10 −8 mbar) by microwave plasma decomposition of hydrogen-methane gas mixtures. A separately pumped loadlock prevents nitrogen contamination of the growth chamber when substrates up to 100 mm in diameter enter or leave. During deposition the plasma ball sits above the substrate and is remote from the chamber walls, which prevents contamination of the films by material etched from the chamber or substrate. Mass spectrometry and optical emission spectrometry continuously monitor the process during growth. Laser interferometry has been used to measure the in situ deposition rate. The diamond films have been characterized by a variety of techniques including scanning electron microscopy, X-ray photoelectron spectroscopy, electron energy loss spectroscopy, X-ray diffraction, laser ionization mass analysis, Raman scattering, IR spectroscopy and cathodoluminescence. These techniques show that the films contain only carbon and a low concentration of hydrogen, with no other impurities such as nitrogen or silicon.