Multi-layered nanocavities in silicon with sequential helium implantation/anneal

Nanocavities in Si formed by He ion implantation and anneal are of interest for impurity gettering in Si technology, localized lifetime control in power devices, and in layer splitting techniques used in wafer bonding. We have obtained multiple cavity layers with cascade He implants (40–160 keV, 2 × 10 15–4 × 10 16 cm −2) by the use of sequential thermal anneals. This behavior is intimately related to the vacancy generation process necessary for cavity formation. Transmission electron microscopy data reveal that, under isothermal anneal, the cavity shape changes from a distinct, aligned hexagonal geometry to a rounded spheroidal shape with increasing anneal time. Deep level transient spectroscopy measurements of the cavity region show broad minority carrier (electron in p-type Si) peaks indicative of the effect of defect clusters. They also exhibit metastable behavior under temperature cycling, suggestive of change in structural configuration of the cavity defects.