Effects of the substrate bias on the formation of cubic boron nitride by inductively coupled plasma enhanced chemical vapor deposition

Abstract

Cubic boron nitride (cBN) films were prepared on 2×2 cm² Si(100) substrates from the B₂H₆+N₂+He+Ar system at 900 °C by low pressure inductively coupled plasma (ICP) enhanced chemical vapor deposition. ICP was generated by 13.56‐MHz 7‐kW input at 1×10⁻³ Torr. The effects of the sheath potential on the formation of boron nitride polymorphism have been mainly investigated. Films were deposited at various self‐bias potentials by varying an auxiliary 13.56‐MHz radio‐frequency power to the substrate. The plasma potential measured by an emissive probe method at 11 mm above the substrate was constant irrespective of the rf input power to the substrate. The deposition rates derived from the thickness observation are in good agreement with those estimated from the infrared absorption spectroscopy by evaluating the absorption coefficients of cubic BN (at 1060 cm⁻¹) and hexagonal BN (at 1370 cm⁻¹) to be 23 000 cm⁻¹ and 30 000 cm⁻¹, respectively. Using these values, growth rates of cubic and hexagonal BN have been estimated as the functions of the sheath potential. The optimum sheath voltage for cBN growth in this study was 80–86 V, at which the cBN content of the film reached about 75%.