Low Energy Ion Impact-enhanced Growth of Cubic Boron Nitride in a Supersonic Nitrogen/argon Plasma Flow
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Low energy ion impact-enhanced growth of cubic boron nitride in a supersonic nitrogen/argon plasma flow D. H. Berns and M. A. Cappelli Mechanical Engineering Department, Stanford University, Stanford, California 94305-3032 (Received 10 October 1996; accepted 24 February 1997)
This paper describes the growth and analysis of cubic boron nitride films in a low-density, supersonic nitrogen/argon plasma flow into which boron trichloride gas was injected. Both hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN) were synthesized using this apparatus. Phase selectivity is obtained by applying a relatively low negative bias voltage to the substrate. All of the films described in this paper were grown on h100j silicon wafers at substrate temperatures varying from 400–700 ±C. Boron nitride films with greater than 90% cubic phase were successfully synthesized with this method. The films were analyzed using infrared spectroscopy, x-ray photoelectron spectroscopy, and scanning electron microscopy. The volumetric percentages of the hexagonal and cubic phases were determined from model fits to the infrared transmission spectra of the films. X-ray photoelectron spectroscopy provided qualitative evidence for the presence and/or lack of sp 2 bonding through the identification of a p-plasmon feature in the spectra. Infrared reflectance spectra are used to provide insight into the growth mechanisms leading to c-BN formation and have revealed features which are not present in the transmission spectra, specifically the 1305 cm21 LO mode of c-BN and the 1610 cm21 LO mode of h-BN. The mean ion energies involved with this bias-enhanced chemical vapor deposition (CVD) process are much lower than the ion energies in traditional physical vapor deposition (PVD) processes; however, the ion fluxes (currents) used in this CVD process are at least an order of magnitude higher, resulting in a total momentum transfer to the deposited atoms through ion bombardment that is at least equal to or greater than that reported for many ion-enhanced PVD processes.
I. INTRODUCTION
Success in the chemical vapor deposition (CVD) of diamond films1–3 has prompted numerous studies expanding CVD methods to the deposition of other metastable ceramics. Previously we have developed a process of diamond film deposition using low-density, supersonic arcjet flows.4–8 The successful application of these arcjets to diamond synthesis led us to explore the possibility of synthesizing cubic boron nitride (c-BN) and carbon nitride (CNx ).9 In this paper we present an experimental study of c-BN growth on h100j silicon in a low density, supersonic plasma generated by an arcjet operating on mixtures of nitrogen (N2 ) and argon (Ar) with boron trichloride (BCl3 ) injected downstream into the expanding plasma plume. The properties and potential importance of c-BN for many applications have been described in several papers,10–22 and only a brief review will be provided here. As with carbon, boron nitride can exist as both hexag
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