DETERMINATION OF DIAMOND FILM QUALITY DURING GROWTH USING IN-SITU RAMAN-SPECTROSCOPY

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 CH4 con centrations 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 ''qua lity''. The real-time measurements also provide a quantitative determi nation of optical absorption length, another measure of film quality. As the CH4 concentration is lowered, the phonon linewidth decreases, t he absorption length increases, and the film morphology improves. For a given film, the initial diamond has a large linewidth, and is thus h ighly defected. As the film thickens, the linewidth decreases, indicat ing that the defect density decreases. Stress effects in the growing f ilms are evaluated from the time evolution of the Raman shift of the d iamond phonon. Corrections made using a phonon-confinement model sugge st that the majority of the change in the Raman shift as a film thicke ns can be attributed to domain-size effects. The results indicate that the films are under compressive stress from the onset of growth and t hat the magnitude of the stress is greater in the lower quality films. Upon cooling the diamond films from the growth temperature to room te mperature, the linewidth of the diamond phonon is found to have a mini mum at about 200 degrees C.