Defects in silicon induced by high energy helium implantation and their evolution during anneals

Transmission electron microscopy has been used to study the bubbles and the extended defect formation in crystalline Si implanted with helium at a dose of 10(17) cm(-2) at 1.6 MeV and annealed at 800 degreesC, as a function of the annealing time of 16.7-1020 min. Below the bubble layer located near the mean projected range, Frank dislocation loops are observed in addition to long rod-like {113} defects. During the initial annealing stage only Frank loops bound to bubbles are present. Whereas the bubble morphology does not change greatly during longer annealing times, we observe a strong evolution of extended defects located behind the band of bubbles. Indeed, after a 30 min annealing, Frank loops and (113) defects resulting from the precipitation of Si interstitials are observed. Then the dissolution of {113} defects takes place and only Frank loops remain. The Frank loops are homogeneously distributed up to 500 nm below the bubble layer and are of equal size. After a 1020 min anneal, no more extended defects are observed behind the buried layer. These results are discussed and compared with those obtained after keV implantation.