Preparation of Si[sbnd]N[sbnd]B films by CVD techniques: effect of SiH4 addition to B2H6 and NH3 gas mixtures

Abstract

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/H2) produces important changes in the reaction process. Silane molecules react with ammonia forming SiN 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 flow 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.