Evaluation of wafer bonding and etch back for SOI technology

Film quality and crystalline perfection of SOI layers obtained by bonding and etch back silicon-on-insulator (BESOI) technology have been studied. In particular, the various mechanisms of defect generation that contribute to a degradation of the original bulk Si quality in the superficial Si layer of such SOI structures have been investigated. Utilizing transmission x-ray topography combined with transmission electron microscopy (TEM), the critical processing parameters causing defect generation have been identified and the principal mechanisms of dislocation nucleation have been elucidated. Strain compensated bonded SOI wafers have also been evaluated by non-destructive elastic light scattering and optical beam induced current (OBIC) to obtain topographic defect maps of entire SOI wafers. This analytical technique has the capability to comprehensively characterize surface and subsurface morphological features which result from the bonding and thinning processing steps. A comparison of wafer bonding and etch back technology with different etch stop fabrication techniques is presented. In this review, it is demonstrated that the presence of a boron-doped etch stop layer, with its accompanying lattice contraction and strain compensation, represents a key difference in the observed morphological patterns of bonded SOI wafers.