Pyrolysis and film growth studies of phosphinoborane compounds

Abstract

Chemical vapor deposition experiments were conducted using phosphinoborane compounds of the type [R 2BPR′ 2] n , where R  CH 2CH 3 ( 1) or CH 3 ( 2), R′ C(CH 3) 3, and R  CH 2CH 3 ( 3) or CH 3 ( 4), R′  Si(CH 3) 3. Thin films were deposited on Si substrates at 300–850°C under vacuum using 1–3, while no film formed using 4. All films contained considerable carbon (C/B = 0.67–7) and were deficient in phosphorus (P/B = 0-0.5) according to Auger electron spectroscopy. For 3, silicon was incorporated in the films (Si/B = 0.9–2). The preferential loss of phosphorus was nearly complete at higher pyrolysis temperatures that favor formation of carbon-rich films. Volatile products of the decompositions were observed by in situ mass spectroscopy and by 1H nuclear magnetic resonance analysis of the condensate in a liquid nitrogen cooled trap. The products indicate that β-hydrogen elimination of alkene from boron is a preferred reaction pathway, while concerted elimination reactions appear to be inefficient. Although these phosphinoborane compounds do not appear to be suitable precursors for pure boron phosphide, the B-P-C films obtained are chemically inert and may be of interest as protective coatings.