Effects of A Top SiO_2 Surface Layer on Cavity Formation and Helium Desorption in Silicon

摘要

Cz n-type Si(100) samples with and without a top SiO_2 layer were implanted with 40 keV helium ions at the same dose of 5 × 10~(16)cm~(-2). Cross-sectional transmission electron microscopy (XTEM) and thermal desorption spectrosco-py (THDS) were used to study the thermal evolution of cavities upon and helium thermal release, respectively. XTEM results show that the presence of the top SiO_2 layer could suppress the thermal growth of cavities mainly formed in the region close to the SiO_2/Si interface, which leads to the reduction in both the cavity band and cavity density. THDS results reveal that the top oxide layer could act as an effective barrier for the migration of helium atoms to the surface, and it thus gives rise to the formation of more overpresurrized bubbles and to the occurrence of a third release peak located at about 1100 K. The results were qualitively discussed by considering the role of the oxide surface layer in defect migration and evolution upon annealing.