Lateral crystallization of amorphous silicon by germanium seeding

This paper investigates the time and temperature dependence of amorphous silicon lateral crystallization when polycrystalline germanium is used as a seed. Dramatically different crystallization behaviour is observed for heavy and light crystallization anneals. For a heavy anneal of 40 h at 550 °C increased crystallization of the amorphous silicon is seen in all areas beneath the germanium seed compared with areas without any germanium, as has been reported previously. In contrast for light anneals at 500 °C crystallization of the amorphous silicon only occurs around the perimeter of the germanium seed. The perimeter lateral crystallization is reasonably uniform, reaching a distance of 500 nm after a 60 h anneal at 500 °C. Transmission electron microscopy (TEM) shows that the crystallized material is polycrystalline and made up of grains with various orientations. This different behaviour for short and long anneal times suggests that two different mechanisms are taking place; we speculate that the perimeter crystallization is due to stress.