Low Temperature Chemical Vapor Deposition Using Atomic Layer Deposition Chemistry
Chemical vapor deposition (CVD) techniques rely on high temperatures to activate the chemical decomposition of precursors on the substrate surface. Lower temperatures are applied in atomic layer deposition (ALD), where deliberate pyrolysis of the precursor is avoided to favor self-saturating surface reactions between two or more reactive partners. In ALD the substrate is exposed sequentially to two properly separated reactive precursors that interact on the surface, which is detrimental to the growth rate but offers exceptional conformality of the obtained films. We demonstrate the adaption of an ALD type reaction to a high vacuum CVD process; i.e., we deposited homogeneous titanium dioxide thin films on flat substrates by exposing simultaneously substrates with titanium isopropoxide and water at ALD typical temperatures (175-225 degrees C) in a high vacuum environment obtaining growth rates of up to 2 nm.min(-1). We identified different growth regimes as a function of precursor impinging rates and substrate temperature-namely, a titanium tetraisopropoxide (TTIP) flux limited and a chemical reaction limited regime. Additionally, we examined the precursor deposition efficiency, chemical composition, and surface morphology of the deposit in the different growth regimes. Our technique allows the migration of ALD reaction chemistry into HV-CVD and reveals additionally-independently of reactor geometries-new insights for the understanding of ALD, in particular in terms of surface kinetics.