Al-induced crystallization of an amorphous Si thin film in a polycrystalline Al/native SiO2/amorphous Si structure

Al-induced crystallization of an amorphous Si (a-Si) thin film in a polycrystalline Al/native SiO2/a-Si structure has been investigated on an atomic level using cross-sectional high-resolution transmission electron microscopy. A 7-nm polycrystalline Al layer was thermally deposited onto a 50-nm a-Si thin film, deposited by low-pressure chemical vapor deposition and covered with a 2.2-nm layer of native SiO2. The a-Si thin film in this structure was partially crystallized at 250 degrees C and completely crystallized at 500 degrees C after 30 min. Lattice fringes of Si(111) were observed in the original Al layer and interfacial native SiO2 layer after the annealing process. From the above results, it was concluded that Al-induced crystallization of the a-Si thin film occurred by interdiffusion of Al and Si atoms through the native oxide layer even though the 2.2-nm native SiO2 layer was not removed completely at the Al/a-Si interface. A possible model, that can be used to explain the Al-induced crystallization phenomena by taking into account the changes that take place within or near the native SiO2 layer during the annealing process, was proposed.