Analysis of the crystallization kinetics and microstructure of polycrystalline SiGe films by optical techniques

In this work, two optical techniques, Raman spectroscopy and ultraviolet reflectance, have been used to characterize the solid phase crystallization kinetics and the microstructure of SiGe films deposited by LPCVD on oxidized Si wafers. The results have been compared to those obtained by X-ray diffractometry. The Ge fraction of the films (x) was in the 0-0.38 interval. The samples were crystallized at temperatures ranging from 525 to 600 degrees C. The crystallization kinetics follows Avrami's model. Two different behaviours have been observed depending on the Ge fraction of the films and the crystallization temperature: a) Either the three experimental techniques yield similar results, or b) the crystallization process, as monitored by UV reflectance and Raman spectroscopy, exhibits a greater incubation time than the one obtained if X-ray diffractometry is used. The results are discussed in terms of the identification of the nucleation sites, taking into account the probe depth of the different techniques and the preferred orientations of the grains. These techniques have also been used to characterize the presence of defects, the overall crystallinity and the surface roughness of the fully crystallized films. The results are correlated to the grain morphology and grain size, obtained by means of transmission electron microscopy.