Molecular Precursors to Boron Nitride then Films: the Reactions of Diborane with Ammonia and with Hydrazine on Ru(0001)
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MOLECULAR PRECURSORS TO BORON NITRIDE THEN FILMS: THE REACTIONS OF DIBORANE WITH AMMONIA AND WITH HYDRAZINE ON Ru(0001)
Charles M. Truong, Jos6 A. Rodriguez, Ming-Cheng Wu and D. W. Goodman Texas A&M University, Department of Chemistry, College Station, Texas 77843-3255 ABSTRACT
The coadsorption and reaction of diborane with ammonia and with hydrazine on Ru(0001) have been studied using X-ray photoelectron spectroscopy (XPS) and thermal desorption mass spectroscopy (TDS). Diborane is found to decompose to atomic boron and hydrogen upon adsorption at T>200K. Multilayers of diborane and ammonia, deposited at 90K on Ru(0001), react when annealed to 600K. The XPS results indicate that boron-nitrogen adlayers can be formed by this reaction. These boron-nitrogen films are boron-rich and.decompose at temperatures higher than 1100K. Our TDS studies reveal that hydrazine decomposes extensively to NH 3, N2, N and H on Ru(0001). Due to its higher reactivity, boron-nitrogen films of B/N stoichiometric ratio near unity are obtained when hydrazine is used rather than ammonia. In our studies, these films were formed by either simultaneously dosing B2H6 and N2H 4 at 450K or by coadsorption of the reactants at 90K and subsequent annealing to 450K. These studies have shown that diborane and hydrazine can be successfully used as molecular precursors in the low temperature deposition of boron nitride thin-films. INTRODUCTION
Boron nitride thin films have found widespread industrial applications because of its unique combination of chemical and physical properties. This material has low density, good thermal conductivity, excellent chemical inertness and electrical resistivity. Thin films of boron nitride have been employed as dielectrics in the electronic device technology and as hardness coatings for machine tools [1,2]. Boron nitride thin films are commonly produced by pyrolysis or by plasma decomposition of mixtures of boron halides or hydrides with nitrogen or ammonia [3,4]. In this present work, we study the interactions of diborane with ammonia and also with hydrazine on Ru(0001) surface using thermal desorption mass spectroscopy (TDS) and X-ray photoelectron spectroscopy (XPS). Diborane and ammonia are used as volatile chemical precursors to BN thin films prepared in most thermal and plasma-enhanced chemical vapor depositions (CVD and PECVD) [5,6]. However, to our knowledge, no CVD or PE-CVD system has been reported that utilize diborane and hydrazine as reactants.
Mat. Res. Soc. Symp. Proc. Vol. 250. ©1992 Materials Research Society
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EXPERIMENTAL The experiments were carried out in an apparatus described in reference [7]. This apparatus consists of a ultra high vacuum chamber (ultimate pressure < 5x101° torr) equipped with a hemispherical electron analyzer for XPS and Auger spectroscopy, LEED screen and a quadrupole mass-spectrometer for thermal desorption mass spectroscopy. The Ru(0001) sample was spot-welded to a manipulator which was capable of resistive heating to 1500K and electron-beam heating up to 2400K. The
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