Photoluminescence mapping study of gettering effect of polycrystalline Si on ultrathin silicon-on-insulator

High-resolution photoluminescence (PL) mapping measurement was performed to study the gettering effect of polycrystalline Si on ultrathin silicon-on-insulator (SOI) wafers. A 150-mm-diam Unibond SOI wafer was patterned and partially gettered by polycrystalline Si process at 600°C for 1 h. Then the wafer was annealed in H 2 atmosphere at 400°C for 1 h. PL mapping clearly demonstrated the difference between the gettered and ungettered parts, before and after H 2 annealing. Before H 2 annealing, almost no variation was obvious between the gettered and ungettered parts. After H 2 annealing, however, we found the PL intensity was substantially increased, and the gettered area gave 24.7% higher PL intensity than the ungettered part. This coincided with the results of charge pumping measurements, which indicated a negligible difference of the interface trap density for the two areas before H 2 annealing, while remarkable decrease of this density for the gettered region after H 2 annealing. H 2 annealing thus decreased the interface trap density, and made the gettering effect more obvious. This result indicated that PL mapping is effective and sensitive in characterizing the gettering effect of ultrathin SOI structures.