Chemical vapor deposition of films in the boron and nitrogen system

The hot filament assisted chemical vapor deposition of B-N solids using different boron source gases (BCl{dollar}sb3{dollar} and B{dollar}sb2rm Hsb6{dollar}) with NH{dollar}sb3{dollar} and H{dollar}sb2{dollar} was demonstrated and the reaction conditions necessary to deposit well crystallized B{dollar}rmsb{lcub}x{rcub}{dollar}N products established. These results are consistent with other results in that high temperatures and highly nitrogen rich atmosperes are necessary for the formation of a well crystallized reaction product. The stoichiometric ratio of boron to nitrogen of even well crystallized material product was found to vary widely, from very boron rich to approximately B{dollar}sb4{dollar}N. The morphology of the deposits and the apparent stoichiometric ratio of boron to nitrogen were studied for different substrate temperatures and different ratios of N to B in the feed gas mixtures. The relevant thermochemistry and structural energetics that favor the formation of more or less disordered boron rich solids are discussed. A serious revision of the B-N phase diagram is suggested, one allowing a wide range of nitrogen compositions with boron to nitrogen ratios greater than unity.; The formation of a previously unreported phase of the approximate stoichiometry of B{dollar}sb4{dollar}N is demonstrated. This boron rich phase likely belongs to the same rhombohedral structural family as B{dollar}sb4{dollar}C and related compounds of technological and engineering interest. This structural family tolerates a very wide range of boron rich stoichiometries, forming a wide range of both pnictides and chalcogenides with the ready formation of highly disordered and non-crystalline solids analogous to amorphous boron. This is suggested as one reason why most vapor phase deposition efforts result in boron-rich thin films. In addition to requiring a major revision of the B-N phase diagram, these results seriously challenge the many published claims of CVD and PVD cubic boron nitride synthesis based on the presence of infrared absorption in the range of 1000 to 1100 cm{dollar}sp{lcub}-1{rcub}{dollar}. It is shown that widely published characterization data is rationalized by the formation of poorly crystallized mixtures of disordered or turbostratic layer structure (hexagonal) BN with the rhombohedral B{dollar}rmsb{lcub}x{rcub}{dollar}N phase described herein.