Study of Cu diffusion in ultra thin bonded SOI wafers evaluated by using radioactive isotope tracers

The behavior in silicon for heavy metal elements, which have great influence on device process yield, has been studied for polished wafers and epitaxial wafers. Since thickness uniformity and crystal quality of SOI (silicon on insulator) layers have been improved for thin film SOI wafers, they will be applied to CMOS LSI devices in the near future. However, the behavior of impurities such as heavy metal elements in thin film SOI has not been investigated because of the difficulty of chemical analysis due to the thin film silicon layer and due to addition of contamination during evaluation. In this work, the behavior of Cu in thin film SOI and the BOX (buried oxide layer) was investigated for the first time by using radioactive isotope tracers, which can avoid the evaluation error by contamination from circumstances and step etching.