Organometallic CVD of CoGa and Related Bimetallic thin Films from Novel Single Source Precursors
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ORGANOMETALLIC CVD OF CoGa AND RELATED BIMETALLIC THIN FILMS FROM NOVEL SINGLE SOURCE PRECURSORS
ROLAND A. FISCHER Anorganisch-chemisches Institut der Technischen Universitlt Munchen, LichtenbergstraBe 4, D-W8046 Garching, Germany.
ABSTRACT A series of volatile heterodinuclear organometallic compounds of the general formula L(CO)nM-ER 1 R 2 (D) (L = CO, 115-C 5H5, P(CH 3 ) 3 ; n = 1-4; M = Mn, Fe, Co, Ni; E = Al, Ga, In; R = H, alkyl; D = 0- or N-donor ligand) was synthesized and characterized. These compounds exist either as low melting solids or liquids with vapor pressures typically around 10-50 mTorr at room temperature. The possibility to grow bimetallic thin films ME (e.g. CoAl, CoGa, Coin, Niln etc.) from those single source molecular precursors by thermally induced low pressure OMCVD was investigated. It was shown that the thin film composition, namely the metal stoichiometry, can be controlled by the ligand set at the metal atoms.
INTRODUCTION The control of the stoichiometry in multicomponent thin fims prepared by chemical vapor deposition. techniques is usually achieved by precisely adjusting the molar ratio of several individual source compounds in the vapor phase. These source materials typically deposit at significantly different rates on a substrate at a given temperature. Therefore, a huge set of process parameters is often to be optimized in order to obtain good quality fims. From this a challenge for chemists has originated during the last few years, namely to design and synthesize alternative precursors, which contain all elemental constituents of the film in one single molecule. The idea behind this is to incorporate all essential information for the deposition process into the molecular structure of the source compound. This will leave pressure and temperature as the only process parameters to control. Considerable efforts have been directed towards such single source precursors for compound semiconductors, refractory materials (e.g. borides, carbides, nitrides) and ceramics [1]. However only scattered reports are in the literature concerning the deposition of mixed metal or alloy thin films from single sources [2-4]. We got attracted to this point, since certain intermetallic compounds such as CoAl, NiAl, CoGa, RhGa etc. have been shown to be promising novel contact metals on III/V-semiconductors. These materials form acitve Schottky barriers and/or Ohmic contacts of superior thermal stability [5-9]. Usually, such mixed metal thin films are grown by MBE-techniques, but most recently it was beautifully demonstrated, that epitaxial CoGa-films can be obtained on GaAs(100) as well by OMCVD from two differnt sources [10]. It was also recognized, that such bimetallic materials can be deposited from single sources [11]. Progress in this latter direction is, however, severely limited by the availability of heterodinuclear compounds that meet important requirements, including (i) appropriate metal combination, (ii) sufficient volatility, (iii) low heteroatom content in the ligand sphere, (iv) mild p
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