Dr.-Ing. Simon Kraschewski
The process of metal-induced crystallization describes the low temperature crystallization of amorphous semiconductors, for example Si (a-Si), in the presence of certain metals, like Al, which form a eutectic system with Si . The phenomenon is exploited in the so-called Al-induced layer exchange (AlILE) process enabling fabrication of thin polycrystalline Si films with large grain size on cheap substrates. In AlILE a layered stack of Al and a-Si with a thin AlOx interlayer is annealed at 180-550 °C resulting in a complete layer exchange of the Si and Al layer accompanied by crystallization of Si (c-Si) in the initial place of the Al layer. According to the literature [1-4] AlILE is based on the interplay of 5 elementary processes which are illustrated in Figure 1.
The AlILE process can be enhanced using a Ti/TiOx layer as barrier layer, this leads to up to 250 µm . Figure 2 shows an in situ series of STEM images. The occurence of a secondary phase (Ti(Al Si)3) can be observed before the layer exchange starts. This secondary phase plays a majore role in the suppression of nucleation of new Si nuclei, so the Si nuclei have much more space to grow compared with normal AlILE.
Fig.1: Mechanism of the AlILE process: 1. Dissolution of Si atoms in the amorphous Si (a-Si) layer, 2. Diffusion of Si atoms through AlOx barrier layer, 3. Diffusion of Si atoms through Al, 4. Crystallization of Si (c-Si) followed by lateral growth and 5. Transport of Al (“Push up”) of Al into top layer.
Fig. 2: In situ experiments on Ti.AlILE: At first the formation of the Ti enriched secondary phase and after that the Si crystallization due to the layer exchange.
 O. Nast et al., Appl. Phys. Lett. 73, (1998).
 P. I. Widenborg and A. G. Aberle, J. Cryst. Growth 242 (2002).
 A. Sarikov et al., J. Non-Cryst. Solids 352 (2006).
 B. I. Birajdar et al., Scr. Mater. 66 (2012).
 T. Antesberger, et al., J. Appl. Phys. 112 (2012)