Low energy ion-surface interaction and epitaxial growth in the SiGe system

Citation

Tsai, Cho-Jen (1992) Low energy ion-surface interaction and epitaxial growth in the SiGe system. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/886t-t311. https://resolver.caltech.edu/CaltechETD:etd-08152007-092600

Abstract

The structure of a growing epitaxial film is controlled by the relative rate of different surface processes. Low energy ion beams (50-500 eV) can be used to provide energy to adatoms on the surface and atoms in the near-surface region of a growing film. Thus, a low energy ion beam can be employed as a tool to modify surface kinetics. The study of the effects of the beam-induced defects on the epitaxial growth can also provide valuable insights into intrinsic growth processes by altering the relative rate of various surface kinetics. The work contained in this thesis is focused on the role of defects produced by low energy ion bombardment in modification of epitaxial growth of Si, Ge, and SiGe alloy films. In the first two chapters, theoretical and technical aspects of X-ray rocking curve diffractometry which is one of the principal analytic methods used in this thesis is discussed. The high-resolution X-ray diffractometer built at Caltech and the dynamical theory of X-ray diffraction are briefly discussed. The last four chapters are focused on the manner in which low energy ion beam bombardment affect the structural properties and growth kinetics of epitaxial films. One of the most important factors determining the changes that occur in ion-assisted epitaxy is the ion energy used to stimulate the growth processes, which determines the relative number of surface displacements and bulk displacements. The effect of bulk displacement defects on an epitaxial film structure is discussed in Chapter 3. In Chapter 4, a simple moving boundary diffusion model in conjunction with thermal spike activated kinetics is presented to describe the bulk defect incorporation process. The moving boundary diffusion model has also been used to describe the adatom concentration on the vicinal Si surface and the low energy dopant incorporation processes. Surface displacements produced by low energy ion bombardment has a dramatic effect on the growth mode of epitaxial Ge films on Si(100); this is the main theme of Chapter 5. In the initial stages of Ge growth on Si, a layer-by-layer growth followed by island growth was observed in conventional (thermal) molecular beam epitaxial growth. Island formation is inhibited by low energy ion bombardment during epitaxial growth which can prolong the layer-by-layer growth mode to greater thicknesses than for thermal growth. In Chapter 6, the effect of the low energy ion bombardment on the misfit accommodation of the lattice mismatched system is discussed. The point defects injected by the low energy ion bombardment impede dislocation motion in the growing epitaxial film and cause misfit strain to be accommodated by the threading dislocations which greatly enhances the misorientation between a film and its substrate.

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