Growth of cubic boron nitride and boron-carbon-nitrogen coatings using N-trimethylborazine in an electron cyclotron resonance plasma process

Abstract

N-Trimethylborazine vapour was fed into the downstream region of an electron cyclotron resonance (ECR) plasma source to deposit cubic boron nitride and hard boron-carbon-nitrogen (BCN:H) coatings. For the growth of nanocrystalline cubic boron nitride, an argon-nitrogen mixture was used as plasma gas and the substrate was heated to a temperature of above 800°C. Furthermore, a negative substrate bias was applied by connecting the substrate holder with a low frequency (100–450 kHz) generator. The application of a negative substrate bias is essential for the formation of a high cubic BN fraction in the coatings. N-Trimethylborazine led to hard BCN:H films if argon was used as plasma gas, a negative bias was applied at the substrate, and no external substrate heating was employed. These BCN:H coatings exhibit mechanical properties comparable with those of diamond-like a-C:H material but show, in contrast to a-C:H, a higher transparency. The influence of gas composition, pressure, substrate temperature, microwave power, and substrate bias on the growth of cubic boron nitride and BCN:H coatings are discussed. N-Trimethylborazine is a non-corrosive and non-explosive liquid with a low toxicity. Owing to these merits, its handling is uncomplicated compared with diborane or borontrihalides and promising for future applications of cubic boron nitride and BCN:H coatings.