Alternative Organometallic Precursors for CVD of Tungsten
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ALTERNATIVE ORGANOMETALLIC PRECURSORS FOR CVD OF TUNGSTEN
Rein U. Kirss*, Douglas Gordon** and Peter S. Kirlin** Northeastern University, Department of Chemistry, Boston, MA 02115 ATM, Inc., 7 Commerce Drive, Danbury, CT, 06810
*
Abstract Two solid, air stable, volatile tungsten complexes, tris(methylvinylketone) tungsten, I. and tris(butadiene)tungsten, II, have been investigated as precursors for chemical vapor deposition (CVD) of tungsten containing films. Thermal gravimetic analysis, (TGA), of I and II under argon showed the onset of decomposition at 140'C and 150'C, respectively. A rapid weight decrease corresponding to loss of all three ligands, methylvinyl ketone or butadiene, was observed. Tungsten film growth under hydrogen using I was investigated on Si, SiO 2 , Cu, TiN, Si, and Pt substrates. Selective tungsten film growth on platinum using a hydrogen carrier was observed at temperatures above 200'C. No appreciable tungsten deposition was observed on clean Si, Si02, Cu or TiN surfaces below 400°C. No oxygen or carbon was detected in these films to the level of EDX analysis (-1%) for depositions at 200"C. Increased growth temperatures resulted in increasing amounts of oxygen incorporation. The films grown at 200"C were smooth whereas cracking was observed in films grown at 300"C. The volatile products from the deposition were identified by a combination of gas chromatography and mass spectrometry. Small amounts of methylvinylketone, and methylethylketone were observed. Higher molecular weight species are as yet unidentified, but constituted the majority of the products. Introduction There is continuing interest in chemical vapor deposition of tungsten for metallization in microelectronic devices. [1] The search for new tungsten precursors is driven by the deficiencies of tungsten hexafluoride in certain applications including the corrosivity of hydrogen fluoride and the need to selectively deposit on silicon over a wide range of conditions. Organometallic compounds with carefully selected ligand sets are attractive precursors for reducing growth temperatures without sacrificing purity by yielding hydrocarbon products, exclusively, upon pyrolysis. [2] Alternative precursors to WF6 include tungsten hexacarbonyl, [3], tetra(allyl)tungsten [4] ditungstenhexakis (cyclohexyloxide) [5], and bis(cyclopentadienyl) tungsten dihydride. [6] Films prepared from tungsten carbonyl, W(CO)6, were found to be contaminated with carbon and oxygen, requiring a high temperature anneal (700"C) to reduce the residual contaminants to acceptable levels (e. g. < 0.1% Oxygen). [3] Deposition from tetra(allyl)tungsten, W(11 3 -C 3 H5 )4 , led to primarily tungsten carbide films [4] while W 2 (OC 6 H11 )6 decomposed upon attempted transport. [5] Films deposited from Cp 2 WH 2 under H2 contained significant amounts of carbon, but the carbon impurities could be reduced to about 5 atom % by co-deposition of 2-4 atom % platinum. [6] Mat. Res. Soc. Symp. Proc. Vol. 282. 01993 Materials Research Society
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A common feature between Cp
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