Stacked SOI layers obtained by zone melting recrystallization

The authors report on lamp heated ZMR (zone melting recrystallization) of two silicon layers, stacked on top of each other and separated by an oxide layer in between. A 1.5-μm thermal oxide was grown on (100) silicon wafer. Then an 0.5-μm amorphous silicon layer followed by a 2-μm TEOS oxide was deposited. The process continued with deposition of a second 0.8-μm amorphous silicon layer followed by a 2-μm TEOS oxide layer. Finally, the wafers were coated with 30-nm LPCVD (low-pressure chemical vapor deposition) Si₃N₄. After ZMR the top silicon layer showed straight nonbranching defect trails with a typical spacing of about 50 μm. The defect patterns in the 0.5-μm layer underneath did not seem to be correlated with those of the layer above. On the contrary, classical branched subgrain boundaries were encountered in the bottom layer. An explanation of different solidification front morphologies in both layers is offered