Determination of diamond film quality during growth using in situ Raman spectroscopy

Abstract

An in situ Raman spectroscopy system has been used to study the growth, by hot filament chemical vapor deposition (HFCVD), of diamond films on molybdenum substrates. We compare diamond films grown using CH 4 concentrations of 0.2%, 0.3%, and 0.5% in H 2. We show that the linewidth of the diamond phonon can be used as an in situ measure of film “quality”. The real-time measurements also provide a quantitative determination of optical absorption length, another measure of film quality. As the CH 4 concentration is lowered, the phonon linewidth decreases, the absorption length increases, and the film morphology improves. For a given film, the initial diamond has a large linewidth, and is thus highly defected. As the film thickens, the linewidth decreases, indicating that the defect density decreases. Stress effects in the growing films are evaluated from the time evolution of the Raman shift of the diamond phonon. Corrections made using a phonon-confinement model suggest that the majority of the change in the Raman shift as a film thickens can be attributed to domain-size effects. The results indicate that the films are under compressive stress from the onset of growth and that the magnitude of the stress is greater in the lower quality films. Upon cooling the diamond films from the growth temperature to room temperature, the linewidth of the diamond phonon is found to have a minimum at about 200°C.