TEM INSITU INVESTIGATIONS OF THE CRYSTALLIZATION BEHAVIOR OF AMORPHOUS-SILICON THIN-FILMS

The crystallization of amorphous silicon thin films deposited on SiO2 layers was in situ studied in a high-voltage electron microscope. The layers, grown by the LPCVD technique, were heated up to temperatures between 600 and 750°C for up to 70 minutes. The investigations have shown that the crystallization behaviour differs for undoped and phosphorus-doped layers. Amorphous deposited silicon layers contain small crystallites already after the doping process (implantation at room temperature) which grow parallel to 〈111〉 directions of the underlying silicon substrate. The most dominant morphology of the growing crystallites displays a needle-like shape; the ratio of the length (longitudinal axis) to the width is close to 2, independent of the doping. The pre-existing crystallites in the phosphorus-doped material influence the twin frequency in the crystallites. Respective reasons are discussed on the basis of the TEM results. © 1990.