| The mechanism responsible for the solid phase epitaxy of silicon has been the subject of much research and speculation, undoubtedly because of its technological applications in the electronic activation of ion implanted semiconductors, in the recrystallization of amorphous silicon for silicon on insulator (especially silicon on sapphire) devices, and in potential three-dimensional circuit integration schemes. In this study, transmission electron microscopy data was acquired to determine the microstructural origin of the improved electronic mobility of chemically vapor deposited silicon on sapphire twice treated with solid phase epitaxy (in double solid phase epitaxy) and was correlated with channeling Rutherford backscattering spectrometry data to demonstrate the removal of crystallographic defects (primarily micro-twins) from the initial material that produced this improvement. To elucidate the mechanisms underlying the fundamental solid phase epitaxy process, in situ conventional transmission electron microscopy was employed and the technique improved by incorporation of internal temperature standards to provide quantifiable data which yielded accurate values for kinetic parameters of solid phase epitaxy in both intrinsic and doped silicon. These methods were extended to in situ high resolution transmission electron microscopy to obtain the first "direct" observations of the atomic mechanisms that are involved in such a solid state reaction at controlled elevated temperatures. In situ high resolution transmission electron microscopy provided crucial observations for differentiating between competing theories for solid phase epitaxy, which was demonstrated by the observation of "micro-bursts" of crystallization characteristic of a chain reaction mechanism, and experimentally supported the hypothesis that intermediate catalytic species mediate the kinetics during solid phase epitaxy. Based on these in situ transmission electron microscopy observations and a careful review of the literature, a parametric model was developed for the progress of the solid phase epitaxy reaction, which for the first time unifies the results of numerous researchers under a variety of experimental conditions, and has implications for models of interface-controlled reactions, more generally. |
