Comparison of SiGe Virtual Substrates for the Fabrication of Strained Silicon-on-Insulator (sSOI) Using Wafer Bonding and Layer Transfer

Abstract

Different methods of preparing sSOI wafers have been analyzed. The initial virtual substrate wafers are characterized by a 17 - 20 nm thick strained silicon layer grown either on a thick relaxed SiGe layer on a graded buffer or on a thin SiGe buffer relaxed by He implantation. Bonding and layer transfer experiments using different oxide layers proved that strained silicon layers are completely transferred if designed PE-CVD oxide layers were used. For both types of virtual substrates the oxide layers are deposited on top of the strained silicon and bonded to non-oxidized (blank) silicon wafers. A perfect layers transfer is obtained for virtual substrates having thick SiGe buffer layers (type A) even at 350ºC, while annealing at 450ºC is required for substrates with thin SiGe buffer layers (type B). The lower annealing temperature for substrates of type A is caused by the lower activation energy for blistering. The hydrogen implantation is here into the SiGe. For type B substrates the hydrogen implantation is into the underlying Si requiring a higher temperature for layer splitting (higher activation energy for Si).