Thick Bonded Silicon-On-Insulator Wafer with Polysilicon Interlayer for Gettering of Metal Impurities

Abstract

A new technique for extrinsic gettering of transition-metal impurities in thick bonded SOI (BSOI) wafers is presented. Technique is based on adding a thin polycrystalline silicon layer between the active layer and buried oxide by means of direct wafer bonding. Gettering efficiencies of over 98 % of iron in active layer were demonstrated even after a high temperature heat treatment. Testing of wafers in CMOS processes showed a clear improvement of the gate oxide integrity, even approaching that of conventional bulk silicon wafers. Poly-Si interlayer showed no measurable effects on critical BSOI characteristics such as interfacial voids, bond strength, active layer thickness uniformity or sacrificial oxide etching. The residual stress was also very low. The results suggest that the thin poly-Si layer has minimal effect on fabrication of the MEMS elements.