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PREPARATION OF BORON NITRIDE FILMS BY RF REACTIVE SPUTTERING

P.K. BANERJEE, B. CHATERJEE, J.S. KIM AND S.S. MITRA Thin Film Research Laboratory, Department of Electrical Engineering, University of Rhode Island, Kingston, RI 02881, USA

ABSTRACT Boron nitride films were deposited by rf reactive sputtering. The composition of the film was determined by X-ray photo-electron spectroscopy(XPS). Optical properties of boron nitride were studied by IR spectroscopy. Resultant films showed optical characteristics similar to those of hexagonal boron nitride. The ratio of boron to nitrogen was varied from 3.11 to 1.45 by varying the amount of nitrogen. Resulting films have refractive index in the range of 2.05 - 3.21.

1. INTRODUCTION Boron nitride is a wide bandgap semiconductor and it has many useful properties [14] such as, chemical inertness, high resistivity and excellent thermal conductivity, and mechanical hardness. There are numerous potential applications of boron nitride such as high-quality insulator[4,6], passivation layers[5], heat-conducting coatings[3,6-7], wearresistant coating[3-6], insulating layer for metal-oxide-semiconductors[7], masks for x-ray lithography[3,5] and high temperature electronic devices[3-8]. BN thin films can be deposited by several methods [3,5-8] including rf sputtering. Although several authors[4,6,9] have reported on optical properties and structures of sputtered BN films, these results vary widely. Therefore, the effect of deposition parameters on composition and structure of rf sputtered boron nitride films need to be further studied systematically. In our research BN films were prepared by rf reactive sputtering from a boron nitride target and the optical properties and composition of these films were studied as a function of nitrogen pressure.

Mat. Res. Soc. Symp. Proc. Vol. 228. @1992 Materials Research Society

274

2. EXPERIMENTAL DETAILS Boron nitride films were fabricated by rf sputtering from a BN target(99.99%). All depositions were carried out at room temperature in Ar/N

2

mixture. The partial pressure

of nitrogen was varied from 0.2 mTorr to 5.0 mT. The total pressure of Ar/N

2

mixture

was kept fixed at 8 mTorr for all depositions. The distance between the target and the substrate was 65mm.

Deposition rate of boron nitride films was 25 - 40A/min. The

binding energy of B is and N Is in the resultant films were determined by XPS using 1253.6 eV Mg Ka radiation as the excitation source and an analyzer energy of 71.55 eV. All peaks were referenced to is peaks of adventitious carbon at 284.6 eV, measured at an accuracy of 0.1 eV. The ratio of boron-to nitrogen was determined from the ratio of the area of B is and N Is peaks. Infrared transmission and reflectance over the wavenumber of 2000cm-

1

- 600cm-1 was measured by a double beam IR spectrophotometer. Refractive

index was determined by ellipsometer at a wavelength of 6328A.

3. RESULTS AND DISCUSSION Infrared transmission spectra of boron nitride films is shown in Fig. 1. BN has been known to have two IR absorp