Preparation of Si-N-B films by CVD techniques: Effect of SiH4 addition to B2H6 and NH3 gas mixtures

Boron nitride films (B/N>1) were obtained from diborane and ammonia gas mixtures by chemical vapour deposition (CVD) techniques. A gradual transition from the amorphous to the hexagonal (turbostratic) structure is observed when the [B2H6]/[NH3] gas flow ratio is increased from 0.05 to 0.5. The addition of SiH4, to the gas mixture (B2H6/NH3/H-2) produces important changes in the reaction process. Silane molecules react with ammonia forming Si-N bonds, thus limiting the amount of NH3 molecules available to react with the diborane molecules present in the reactor. From the two parallel reactions, B2H6 + NH3 and SiH4 + NH3, hard Si-N-B composites are obtained. For a given ammonia Bow rate, the atomic composition of the Si-N-B system is mainly determined by the [SiH4]/[B2H6] ratio. Following these results, a series of samples with variable composition was deposited changing the [SiH4]/[B2H6] ratio. The composition and structure of the films were analysed by infrared (IR), Auger electron (AES) and X-ray photoelectron (XPS) spectroscopies. Microhardness measurements were also made, and related to the silicon content of the films.