Synthesis and structure of chemically vapour-deposited boron nitride

Abstract

Chemically vapour-deposited boron nitride (CVD-BN) plates have been synthesized on a graphite substrate by the reaction of the BCl₃-NH₃-H₂ gas system in a deposition temperature (T _dep) range from 1200 to 2000° C, with a total gas pressure (P _tot) which was varied from 5 to 60 torr. The effects ofP _tot andT _dep on the crystal structure and the microstructure of the CVD-BN plate were investigated. Turbostratic BN(t-BN) was deposited above 10 torr, at anyT _dep in the range investigated. The interlayer spacing (c ₀/2), the crystallite size (Lc) and the preferred orientation (PO) were strongly affected byT _dep. The t-BN obtained at lowT _dep had largec ₀/2 and smallLc andPO. AsT _dep increased,c ₀/2 tended to decrease whereasLc increased and thec-plane of the crystallites became oriented parallel to the deposition surface. At aP _tot of 5 torr, a mixture of t-BN and h-BN (hexagonal BN) was deposited at anyT _dep above 1700° C, and two kinds of t-BN different inc ₀/2 co-deposited at aT _dep below 1600° C. Moreover, it was indicated that r-BN (rhombohedral BN) was included in the deposits obtained at aP _tot of 5 torr and aT _dep of 1500 to 1600° C.