Microstructural evolution of oxygen implanted silicon during annealing processes

Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (X PS), and electron energy loss spectroscopy (EELS) have been employed to cha racterize the microstructures, oxygen distributions, and chemical bonding s tates of SIMOX (Separation by IMplanted OXygen) wafers. Silicon substrates were implanted at 550 degrees C with 2x10(17) and 4x10(17) cm(-2) 180 keV o xygen ions, followed by annealing at various temperatures. EELS spectra ind icated that the chemical bonding state between Si and oxygen changed at 100 0 degrees C anneal, though there was no appreciable change in the microstru ctures observed by TEM below 1000 degrees C anneal. Above 1100 degrees C, o xygen precipitates were preferentially formed around the peak positions of the detect and oxygen concentrations in the as-implanted samples. These pre cipitates aggregated to reduce the surface energy, and their size increased with temperature. After 1350 degrees C anneal. a continuous buried oxide l ayer was formed in the higher-dose specimen, while the upper- and lower-pre cipitates remained separately in the lower-dose one. The XPS profiles did n ot change at the later stage of annealing processes in the 2x10(17) cm(-2) sample, though the precipitates became larger in size. This suggests that t he oxygen diffusion mostly occurs along the lateral direction but does not along the vertical one in this sample (C) 1999 Elsevier Science B.V. All ri ghts reserved.