1. Field of the Invention
This invention relates to novel reagents for use in thin film deposition processes such as chemical vapor deposition (CVD) and atomic layer deposition (ALD). These reagents can be used for deposition of materials containing silicon and/or phosphorus along with metals and/or oxygen, commonly called metal oxides, silicates or metal phosphates, or silicon dioxide.
2. Description of the Related Art
Chemical vapor deposition (CVD) is a widely-used process for forming solid materials, such as coatings or powders, from reactants in the vapor phase. Comprehensive reviews of CVD processes have been given recently in CVD of Nonmetals, W. S. Rees, Jr., Editor, VCH Publishers, Weinheim, Germany, 1996; CVD of Compound Semiconductors, A. C. Jones and P. O'Brien, VCH, 1996; and The Chemistry of Metal CVD, T. Kodas and M. Hampden-Smith, Editors, VCH, 1994.
In CVD processes, a reactant vapor or vapor mixture is brought into contact with a heated surface on which a thin film is deposited. In a related form of CVD, two reactant vapors are alternately exposed to the heated surface. This form of CVD is often called atomic layer deposition (ALD). For suitable reactants, ALD can provide improved step coverage and thickness uniformity compared to CVD with mixed vapors. For a review of ALD, see the paper by Mikko Ritala in Applied Surface Science, volume 112, pages 223-230 (1997).
Coatings of metal silicates have many applications or potential applications. For example, silicates of zirconium, hafnium, yttrium or lanthanum are being considered as potential replacements for silicon dioxide in gate insulators in silicon semiconductor technology. See, for example, A. Kingon et al., Nature, volume 406, pages 1032-1038 (2000). In Science, (volume 288, pages 319 to 321 (2000)), Ritala et al. report the use of the sequential ALD reaction of metal chlorides and silicon alkoxides to produce metal silicates, including zirconium silicate. However, this reaction deposits films containing residual chlorine, which can be deleterious to the properties of the film or to its adhesion to substrates or subsequent coatings. The chlorine in the precursors can also corrode metal substrates or the apparatus used for the deposition. Thus it would be advantageous to have chlorine-free precursors for CVD or ALD of metal silicates or oxides.
ALD of silicon dioxide has been achieved by Klaus et al., U.S. Pat. No. 6,090,442 (2000), but the deposition rate is very slow and the substrate temperature is limited to values near room temperature.
Lithium phosphate is a material of current interest as a lithium ion conductor in lithium batteries. Currently there is no known process for CVD or ALD of lithium phosphate.