Novel Methods for Deposition of Boron Carbide Films
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NOVEL METHODS FOR DEPOSITION OF BORON CARBIDE FILMS
J. MAZUROWSKIa'b, S. BARAL-TOSHa, G. RAMSEYERb, J.T. SPENCERc, YOON-GI KIMa, AND P.A. DOWBENa a) Department of Physics, Syracuse University, Syracuse, New York 13244-1130 b) General Electric Co., Electronics Laboratory, Electronics Park, Syracuse, New York, 13221 c) Department of Chemistry, Syracuse University, Syracuse, New York 13244-4100
ABSTRACT By combining pentaborane (BsH5) and decarborane (B10H1 4) with methane in a plasma reactor, a variety of boron-carbides can be made over a wide range of compositions. The resulting thin films have uniform composition and appear to be polycrystalline.
INTRODUCTION Boron carbides are of considerable interest because of their potential semiconductor properties [1,2] and because these materials are very hard, chemically inert and retain a high modulus of elasticity [3]. Boron carbides have applications as neutron absorbent materials [4-8], wear resistant hard coatings, and armor coatings [3,9,101. There are a number of unusual boron containing films with hardness values comparable to diamond [9,10,11]. Until now boron carbides fabricated via chemical vapor deposition typically employ BC13 reacted with a hydrocarbon (typically methane) [12-16] though variations of this approach using BC13 + CC14 [17,18] or BBr 3 [19-211 have been employed. We have demonstrated that decarborane is a suitable boron source material for the fabrication of boron and boron nitride coating [22,23] and we now demonstrate that a wide range of boron carbide stochiometries can be fabricated by combining boranes and methane in an rf plasma reactor.
EXPERIMENTAL Decarborane (14), B10H 14, is an airstable white crystalline solid with a vapor pressure of several Torr at room temperature. The vapor pressure was increased for these experiments by heating (the vapor pressure at 100"C is 19 Torr), since the decarborane (14) decomposes only above 170"C [24]. The pentaborane (9), B5H9 , with a vapor pressure of 209 Torr at 25°C, was a vapor under the operating conditions of our experiment.
Mat. Res. Soc. Symp. Proc. Vol. 190. Q1991 Materials Research Society
102
The radio-frequency plasma deposition studies were carried out in a small 3-inch 13.56 mHz rf plasma reactor with a 1-inch plate separation. The typical rf power output of the reactor was 20W, but could be increased to 100W. The sample substrates (quartz glass or silicon) were mounted on the ground plate of the two plate system, with the other plate connected to the rf network. The system used a commercial if generator and impedance matcher. Methane was used as the carbon source and no carrier gas was used. Film composition was determined by Auger electron spectroscopy calibrated with B4C after removing surface impurities resulting from exposure to air.
RESULTS After setting up a stable gas mixture of the gaseous borane and methane the plasma was initiated and a film was deposited. The results for decarborane and pentaborane are summarized in tables one and two. Considering that the source gas
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