Al-Induced Crystallization of an Amorphous Si Thin Film in a Polycrystalline Al/Native SiO₂/Amorphous Si Structure

Abstract

Al-induced crystallization of an amorphous Si (a-Si) thin film in a polycrystalline Al/native SiO 2 /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 SiO 2 . The a-Si thin film in this structure was partially crystallized at 250°Cand completely crystallized at 500°C after 30 min. Lattice fringes of Si(111) were observed in the original Al layer and interfacial native SiO 2 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 SiO 2 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 SiO 2 layer during the annealing process, was proposed.