Direct simulation Monte Carlo modeling of silicon thin film deposition using supersonic beams

Deposition of epitaxial silicon thin films through the seeding of silicon hydride molecules in a supersonic beam of light carrier gas is modeled using the direct simulation Monte Carlo (DSMC) technique. In this process, a hyperthermal collimated beam is formed by rapid expansion through a nozzle orifice and then refined through a skimmer/beam defining device structure. The fundamental characteristics of the process are evaluated quantitatively through a gas dynamics approach. General features of the internal supersonic flows are described. The interaction between supersonic jets and the skimmer is discussed. The numerical simulations provide detailed surface properties such as molecular beam incident flux, angle and kinetic energy as the precursor molecules impact on the substrate surface. Good agreement is achieved for comparisons of the computational results with the experimental measurements for the film growth rate and precursor incident flux.; After being extensively tested and validated, the numerical technique is employed to examine a wide range of physical and geometry space and to explore the possibility of process scale-up to an industrial manufacturing level. Three supersonic source configurations are proposed and investigated. They are two dimensional slit sources, axisymmetric annular ring sources and three dimensional multiple discrete nozzle sources. Two dimensional slit sources are found not appropriate for high energy deposition due to smaller expansion ratios. The relatively high back pressure induces excessive molecular scattering and causes significant energy loss for disilane molecules. It is demonstrated that the use of axisymmetric ring nozzle sources can significantly increase the deposition area and improve the film uniformity, while maintaining reasonable high impact energies. One source configuration involving four equally spaced supersonic jets located in a circular fashion is found most successful in depositing uniform silicon films over a large area. A film has been developed in an area of 18 cm in diameter, at a growth rate over 200 A/min in a virtual commercial reactor. The molecular beam energy obtained under these conditions is approximately 1.3 eV.