Elucidation of the layer exchange mechanism in the formation of polycrystalline silicon by aluminum-induced crystallization

Aluminum-induced crystallization of amorphous silicon is studied as a promi sing low-temperature alternative to solid-phase and laser crystallization. Its advantages for the formation of polycrystalline silicon on foreign subs trates are the possible usage of simple techniques, such as thermal evapora tion and dc magnetron sputtering deposition, and relatively short processin g times in the range of 1 h. The overall process of the Al and Si layer exc hange during annealing at temperatures below the eutectic temperature of 57 7 degrees C is investigated by various microscopy techniques. It is shown t hat the ratio of the Al and a-Si layer thicknesses is vitally important for the formation of continuous polycrystalline silicon films on glass substra tes. The grain size of these films is dependent on the annealing temperatur e and evidence is given that grain sizes of 20 mu m and more can be achieve d. The poly-Si films are described as solid solutions containing 3x10(19) c m(-3) Al atoms as solute. Only a fraction of the solute is located at subst itutional sites, and therefore, electrically active leading to the p-type c haracter of the polycrystalline silicon films. Additional Al is trapped in the form of small clusters between the continuous Si layer and the substrat e. The interaction of the Al and Si layers is discussed as a diffusion-cont rolled process where the depletion of Si solute in the Al matrix around gro wing Si grains is of major importance for the overall crystallization proce ss and the size of the resulting Si grains. (C) 2000 American Institute of Physics. [S0021-8979(00)00809-4].