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Microstructural studies of boron nitride films deposited by microwave plasma-assisted chemical vapor deposition by using trimethyl borazine precursor A. Ratna Phania) Department of Physics, University of L’Aquila, L’Aquila, 67100, Italy (Received 5 August 1996; accepted 10 August 1998)

Thin films of cubic boron nitride (c-BN) were synthesized using an organometallic precursor trimethylborazine (TMB) which contains both boron and nitrogen in 1 : 1 stoichiometric ratio. The films were deposited at different temperatures ranging from 300 to 500 ±C at a pressure of 2 Torr and at 360 W microwave power, using N2 as carrier gas. The deposited films were characterized by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and scanning electron microscopy (SEM), which reveal the presence of amorphous BN and crystalline c-BN in varying proportions. The x-ray diffraction pattern of the deposited films showed a strongest peak at 2u ­ 57.1± where ˚ agreed well with the (111) crystallographic the interplanar distance value, d ­ 2.06 A, orientation of c-BN phase.

I. INTRODUCTION

Cubic boron nitride (c-BN) is an interesting III–V compound because it has almost has the same hardness and thermal conductivity as diamond. c-BN is a promising ceramic material for use as a high coating for tribological applications as well as a very useful material for semiconductor applications under a variety of environmental conditions. In recent years considerable interest has been aroused in developing suitable techniques for the synthesis of c-BN films. These techniques include N2 ion implantation,1 ion plating,2–5 plasma chemical transport,6 radio frequency sputtering,7–12 ion beam,13–15 rf plasma CVD,16 and electron cyclotron resonance plasma CVD17 which have been reported. In the previous work,18–24 c-BN films were synthesized at 500 ±C on various substrates such as silicon, NaCl, Cu, Ni, etc. by means of organometallic chemical vapor deposition process (MOCVD). Previously BN films were deposited by the chemical vapor deposition (CVD) method from different organometallic single source precursors such as diethylaminoborane (DEAB),18 trimethylborazine (TMB),20 and aminodiborane (ADB)21 containing coordinate covalent bond, covalent bond, and ionic bond, respectively, at a substrate temperature of 500 ±C. It was our observation that the precursor containing covalent bond (TMB) forms c-BN preferentially over h-BN when compared to the coordinate and ionic bond precursors. It was for this reason the trimethylborazine precursor was used in

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II. SYNTHESIS OF TRIMETHYLBORAZINE PRECURSOR

Synthesis of trimethylborazine25 contains two steps. Step one includes the preparation of dimethylamino hydrogen chloride from dimethyl amine and con.HCl in the presence of diethyl ether solvent. Step two includes treating of diethylamino-hydrogenchloride with sodium borohydride. The contents were refluxed for about 24 h in the presence of dry tetrahydrofuran (THF) solvent at 65 ±C in N2 atmosphere.