Organometallic Chemical Vapor Deposition: The Roles of Precursor Design and Growth Ambient in Film Properties
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Abstract Examples of chemical control in CVD of metallic and ceramic films are highlighted. Specific attention is paid to the complexity of precursor design. The effect of reactor environment on growth chemistry is investigated. Examples where reducing or oxidizing atmospheres provide a high level of control over deposit composition are outlined. The system examined centers on yttrium and yttria. These materials are, in general, desired less for their optical or electronic properties and more for their structural properties. Thus, the rigid purity demands of the microelectronics industry are somewhat relaxed. Nevertheless, critical attention must be paid to the issues of vapor pressure and decomposition profile. Where sufficient data is available to justify it, some explaination of the issues relevent to vapor pressure is presented. Introduction For refractory metals and ceramics, one attractive mode of deposition is CVD. This is a consequence of the need for uniform coverage of non-flat parts, a demand met only by non-lineof-sight coating techniques. Thus, in general, physical deposition techniques are inapplicable to the requirements. Often, the compositions to be deposited derive from readily available, large scale precursors. In the instances where this is an incorrect assumption, it becomes necessary to prepare new source compounds tailored for the deposition of a specific composition.' For the case of elemental yttrium, no previous sources have met this role. In this report, details of the method to increase vapor pressures of less-volatile compounds are described, 2 as well as the technique for growth of carbon- and oxygen-free metallic yttrium films. Results Ligands Htmhd A modification of a previous method 3 was employed and optimized to permit the isolation of high purity (>98% by GC/MS) material in high yield (>90%, based on pinacolone charged as a reactant) following a simple and rapid workup of the crude reaction mixture. Htmod Substantial economic benefit, based on prices listed in the Aldrich catalog, was realized by a change in the reactants, relative to a previous method.4 195
Mat. Res. Soc. Symp. Proc. Vol. 363 01995 Materials Research Society
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Each method relies upon a traditional Claisen condensation between an ester and a methyl ketone. They differ only in the penultimate location of the terminal groups present in the 13diketone product. The benefit is realized in the relative cost of the two routes, each leading to an identical product (Eq. 1 = $38.26 / mol; Eq. 2 = $29.09 / mol). Metal Ligand Complexes Hydrous [Y(tmhd) 3 • H20]2 This compound was prepared following minor modification of a previously published general route to compounds of the formula M(tmhd) 3, where M represents a trivalent lanthanide, or pseudolanthanide, ion. 5 Following a workup described in the literature, this method consistently yielded a hydrated product whose structure is s
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