Study of thin film deposition processes employing variable kinetic energy, highly collimated neutral molecular beams

Abstract

Supersonic molecular beams have been investigated as alternative sources for thin film deposition employing a custom designed ultrahigh vacuum reactor. Molecular beam flux produced in this reactor has been measured as a function of gas flow rate, gas composition, and nozzle temperature. An efficient method to measure kinetics of thin film deposition has been developed that allows a large amount of kinetic data (i.e., deposition rate and incubation time) to be gathered per deposition experiment on a single substrate. Film thickness uniformity has been measured under two limiting conditions, which permitted the estimation of both flux and temperature spatial variations across the substrate. The kinetics of epitaxial silicon thin film deposition using Si2H6 has been examined as a function of incident beam kinetic energy (0.5–2.2 eV) and substrate temperature (550–750 °C). Calculated Si incorporation probabilities agree favorably with reaction probabilities previously measured in our laboratory employing a different apparatus and an alternative technique. The kinetics of Si1−xGex thin film growth using mixtures of Si2H6 and GeH4 were also investigated as a function of substrate temperature. In this case the Ge thin film composition was measured as a function of Ge composition of the beam. The incubation period associated with polycrystalline Si deposition on SiO2 has been investigated as a function of substrate temperature and incident beam kinetic energy. The incubation period decreases with both increasing substrate temperature and incident beam kinetic energy. SiC thin film deposition on Si(100) using SiH3CH3 (Ei=2.0 eV) has been investigated and the growth rate depends rather weakly on substrate temperature. Thin film morphology has been characterized using atomic force microscopy, while film crystallinity for polycrystalline and epitaxial films has been examined using x-ray diffraction and low energy electron diffraction, respectively. Epitaxial Si films exhibit a strong (2×1)+(1×2) pattern and a root-mean-square (rms) roughness of <1 nm, while polycrystalline films show 〈111〉, 〈220〉, and 〈311〉 reflections and a rms roughness of 8–25 nm, which increases with film thickness and deposition temperature.