Preparation And Research Of High-quality Optical Grade Diamond Films

CVD diamond films possess excellent prospects in the field of IR windows and high-power laser windows due to its excellent optical performance. Currently developedcountries have mastered the more comprehensive preparation techniques of optical gradeCVD diamond films, but in China, the study of optical grade diamond film depositionprocess and the influence of the inherent still lag behind. In this paper, using microwaveplasma chemical vapor deposition (MPCVD) method to deposit optical grade diamondfilms on the surface of monocrystalline silicon, the nucleation temperature, growthtemperature, carbon concentration and oxygen addition which impact on the growth ofdiamond films were studied.The experimental results about substrate temperature show that lower nucleationtemperature (720℃)will improve the nucleation density, but will increase the content ofnon-diamond phase in film; higher nucleation temperature (800℃) is benefit to growdiamond films with higher diamond phase as well as to eliminate the internal stress of thefilm.Increasing growth temperatures can inhibit the formation of non-diamond phase andsecondary nucleation, thereby promoting the growth of crystal diamond and the increase ofsp3phase. But the crystal faces of diamond film will be etched, of which the opticalproperties of will be reduced, when the temperature is too high (>900℃).The experimental about the carbon concentration show that the growth rate ofdiamond film is faster with higher methane concentrations, but the deposited diamondfilms have more non-diamond phase which affect the optical performance. Relatively lowcarbon concentration (CH4: H2=3:200) is conducive to the growth of high-quality opticalgrade diamond films.Keeping the carbon concentration constant, the addition of a small amount of oxygencan improve the crystallinity of the film, reduce the content of non-diamond phase, andalso can increase the growth rate of diamond film. With the increase of oxygenconcentration, the grain size, growth rate and quality will all decrease. Based on these researches, the diamond films with well quality have been prepared inthe deposition condition of high carbon concentration and growth temperature as well asaddition a small amount of oxygen. The films have relative high uniformity and largergrain size. And the full width at half maximum of the diamond Raman peak is5.2cm-1, theaverage infrared transmittance of65%which is close to the theoretical limit of71%. Theinvestigation gives a theoretical direction to preparation high quality transparent films.