Growth behavior and structural analysis of atomic layer deposited SnxTi1-xOy films.

Atomic layer deposition (ALD) of mixed oxides has attracted increasing research attention in recent years due to its excellent capability of film composition tuning. This in turn highlights the importance of understanding the underlying surface chemistry which dictates how a film of desired composition is achieved. In this work, the authors examined the ability of atomic layer deposition to precisely control the film thickness and composition by studying the growth behavior of Sn_xTi_1-xO_y thin films deposited from an alkylamide Ti(IV) precursor, a β-diketonate Sn(II) precursor and ozone. A set of samples with various compositions were deposited by controlling the ALD cycle ratio (ALDCR) of tin oxide/titanium oxide using our custom-built, warm-wall reactor. Both alloy- and laminate-type of growths were attempted by changing numbers of ALD subcycles while maintaining the cycle ratio. Growth rates, calculated based on the thicknesses measured by spectroscopic ellipsometery and x-ray reflectivity, showed a deviating pattern from that of linear interpolation using binary ALD processes, marked by an almost constant ~0.06 nm/cycle. Film composition, determined by x-ray photoelectron spectroscopy, exhibited a concave upward dependence on ALDCR. The chemisorption density of each precursor was determined by x-ray reflectivity, and a linearly ALDCR-dependent decrease was observed. Structural analysis using x-ray diffraction showed a transition from anatase to SnO₂ rutile when Sn content in the film was varied from 0 to 1, for O₂ annealed samples. At ~17 at. % Sn, a mixture of anatase and rutile phases was found. Other factors, such as surface roughness and surface chemical species, were examined in the attempt to account for the decreased chemisorption. [ABSTRACT FROM AUTHOR]