Solid-phase crystallization of amorphous Si0.7Ge0.3/Si and Si/Si0.7Ge0.3 bilayer films on SiO2

We have investigated the solid phase crystallization of a-(Si/Si0.7Ge0.3) and a-(Si0.7Ge0.3/Si) bilayer films deposited on SiO2 for an annealing temperature of 550 degrees C. It was found that, in case of a-(Si(0.7)G(0.3)/Si), nucleation of crystalline phases occurred at the free surface, while in a-(Si/Si0.7Ge0.3) crystalline phase nucleated at Si0.7Ge0.3/SiO2 interface. The crystallization rate of an a-(Si0.7Ge0.3/Si) is much slower than that of an a-(Si/Si(0.7)G(0.3)) films. After full crystallization, poly-(Si0.7Ge0.3/Si) has many equiaxed grains and the defect density of the upper Si0.7Ge0.3 was much lower than that of lower Si0.7Ge0.3 in a poly-(Si/Si0.7Ge0.3) film whose grain morphology was elliptical. The average grain size of poly-(Si0.7Ge0.3/Si) was similar to 7 mu m and this film had strong (111) preferential orientation, while poly-(Si/Si0.7Ge0.3) had weak (311) or random oriented grains with the average size of similar to 0.3 mu m.