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 ga s mixtures by chemical vapour deposition (CVD) techniques. A gradual t ransition 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) pro duces important changes in the reaction process. Silane molecules reac t with ammonia forming Si-N bonds, thus limiting the amount of NH3 mol ecules available to react with the diborane molecules present in the r eactor. From the two parallel reactions, B2H6 + NH3 and SiH4 + NH3, ha rd Si-N-B composites are obtained. For a given ammonia Bow rate, the a tomic composition of the Si-N-B system is mainly determined by the [Si H4]/[B2H6] ratio. Following these results, a series of samples with va riable 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. M icrohardness measurements were also made, and related to the silicon c ontent of the films.