A REFLECTION HIGH-ENERGY ELECTRON-DIFFRACTION STUDY OF SI SURFACES DURING GAS SOURCE MBE GROWTH FROM DISILANE

The growth of silicon from a gas source molecular beam epitaxy system (Si-GSMBE) using disilane (Si2H6) was investigated. Both the Si(001) and Si(111) surfaces were studied using reflection high-energy electron diffraction (RHEED). For the Si(111) surface intensity oscillations were measured as a function of both substrate temperature and disilane flow rate. Within the substrate temperature range of 490 to 570-degrees-C where growth proceeded two-dimensionally, well-defined intensity oscillations corresponding to bilayer growth could be observed along the [211BAR] and [110BAR] azimuths. The oscillation frequencies were found to increase with increasing substrate temperature as well as disilane flow rate. At lower temperatures where no dissociative adsorption of disilane occurred, intensity oscillations were not observed. At higher temperatures, growth entered the step flow regime and the intensity oscillations were weak or absent. In the case of Si(001) surfaces, oscillations of the specular beam in both the [010] and [110] azimuths have been measured as a function of substrate temperature and disilane flow rate. Strong and damped oscillations are observed between 610 and 680-degrees-C in the two-dimensional growth regime. At higher temperatures growth by step propagation dominated, while at lower temperatures growth became three-dimensional (3D) and consequently oscillations were weak or absent. Oscillations of the fractional order and specular beams in the [110] azimuths indicate that growth occurs in a monolayer rather than a bilayer fashion, on Si(001) surfaces. Growth rates, as determined by the intensity oscillations, were found to be approximately 40% greater on the (100) surfaces at low temperatures (510-degrees-C-590-degrees-C). An Ahrrenius plot, however, indicates a similar activation energy, E(A), for both the (111) and (001) surfaces.