8 - Atomic Processes on the Silicon Surface

Abstract

In this chapter the ability to study atomic processes on the Si surface during sublimation, growth, oxygen etching, and gold adsorption by in situ ultrahigh vacuum reflection electron microscopy (a unique method developed in ISP SB RAS) are reviewed. Using this technique, a surface instability called the step-bunching phenomenon was discovered previously, it is however, still poorly understood due to many unknown parameters of adatom/advacancy step interactions. Observation of gold adsorption induced step-bunching depending on an annealing time at a temperature of T=900°C suggests that a surface-bulk defect exchange is also involved in the formation of instability. The dynamics of two-dimensional vacancy island formation on 120-µm step-free terraces shows that sublimation is defined by adatom detachment from steps up to a critical temperature of Tcrit~1180°C, while adatom diffusion length falls from ~55 (970°C) to ~7µm due to recombination with the vacancies. At Tcrit>1180°C, sublimation is dominated by the straightforward evaporation of surface atoms reserving vacancies that interact with steps. From the studies of Si growth on the step-bunched Si(111)-(7×7) surface, a crucial role of step permeability in 2D island nucleation and growth (2DNG) kinetics has been revealed. Step permeability is a key factor in pyramid-like growth on terraces exceeding the critical width for 2DNG. We show that quantitative parameters of adatom/vacancy diffusion and their interactions with steps (Schwöbel barriers) can be determined.