Low Temperature Chemical Vapor Deposition Using Atomic Layer Deposition Chemistry

Abstract

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 selfsaturating 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°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.

Controlled deposition of titanium oxide overcoats by non-hydrolytic sol gel for improved catalyst selectivity and stability

“…Due to the lower reactivity of self-condensation compared to hydrolytic cleavage, we expected the precursor to react preferentially with the substrate surface. As Ti-Cl bonds are more reactive than Ti-O i Pr toward hydrolysis [46,47], we postulated a surface condensation model where surface hydroxyls reacted primarily with the chloride ligands, leading to the formation of HCl. Each titanium center could react with one or two hydroxyl groups, yielding a mono or bis-grafted species (Fig.…”

Self-limiting atomic layer deposition of barium oxide and barium titanate thin films using a novel pyrrole based precursor

“…This agrees with the experiments in which several H 2 O pulses allow the reaction to proceed as also reported for other known metal-oxide ALD chemistries. 41,42 B. Characterization of BaO films X-ray photoelectron spectroscopy (XPS) depth profile reflects the overall quantitative Ba and O compositional uniformity (Fig.…”

Low Temperature Epitaxial Barium Titanate Thin Film Growth in High Vacuum CVD

“…[19] Recently, we have pointed out that low temperature growth of thin films of titanium dioxide in HV-CVD can be realized using ALD chemistry. [15,20] Due to the suppression of gas phase reactions during precursor transport, more reactive precursor combinations can be employed simultaneously without the risk of spontaneous gas phase nucleation. Therefore, our strategy lies in the utilization of the previously discussed ALD chemistry in an HV-CVD process.…”

“…HV-CVD is a versatile technique for low temperature depositions as it allows the utilization of highly reactive precursor chemistries commonly used only in ALD processes. [14,15] Compared to conventional CVD processes, the high vacuum environment guarantees that gas phase reactions between the precursor molecules are negligible. We will summarize the principles and particularities of this deposition technique and describe in detail the epitaxial growth of the thin films.…”