Open Access Dissertation
Date of Award
Charles H. Winter
Thin films of a variety of materials have shown great potential in the fields of microelectronics, catalysis, and energy applications. Vapor deposition methods, including PVD and CVD, have been traditionally used as the primary method to deposit these thin films. However, these methods do not provide the necessary thickness uniformity and conformality needed for future uses of these thin films as they shrink to smaller dimensions. ALD provides a high degree of uniformity and conformality due to the intrinsic nature of the self-limited reaction mechanism of an ALD process.
The research herein focuses on two metals that have untapped potential in the field of ALD, molybdenum and magnesium. The use of molybdenum thin films has been suggested to replace copper as an interconnect material. The currently reported deposition techniques do not afford thin films needed for high-quality interconnect materials. New reducing agents for MoCl5 are explored. Molybdenum metal thin films are deposited using oxalic acid as a reducing agent by ALD in a temperature range of 325-500 °C. The resulting films are similar in composition to molybdenum thin films deposited by CVD with a small amount of oxygen and carbon impurities. The use of formic acid instead achieves deposition of high purity MoC at 400-450 °C. Alternate reducing agents for MoCl5 include bis(trimethylsilyl) six-membered rings to deposited Mo2C thin films between 360 and 400 °C. All depositions show saturation of the surface reactive sites during deposition showing that these are ALD processes.
Magnesium complexes were synthesized and studied as potential ALD in-situ intermediates. Magnesium has an electrochemical potential that is more negative than any other metal that has previously been deposited by thermal ALD (-2.38 V). A variety of (tris(trimethylsilyl)silyl)(alkyl)magnesium and (tris(trimethylsilyl)silyl)(aryl)magnesium complexes was synthesized. These compounds were characterized and their thermal decomposition products were explored to see if the formation of these products in an ALD process could result in magnesium metal deposition. This resulted in a rearrangement into the homoleptic di-silyl and di-alkyl complexes instead of the proposed reductive elimination of an alkyl-silyl compound leaving magnesium metal.
New compounds were characterized using H1 and C13 NMR, thermogravimetric analysis, single crystal x-ray diffraction measurements, melting point measurements, and thermal decomposition studies. New ALD processes discovered were optimized for reproducible deposition. The composition of the resulting thin films was determined by scanning electron microscopy, four-point resistivity measurements, atomic force microscopy, X-ray photoelectron spectroscopy, and X-ray diffractometry.
Overbeek, Michael David, "Synthesis Of Molybdenum Containing Thin Films Using Organic Reducing Agents And Synthesis Of Magnesium Silyl Intermediate Complexes For Use In Atomic Layer Deposition" (2022). Wayne State University Dissertations. 3578.