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A new technique for gettering of transition-metal impurities in thick bonded SOI (BSOI) wafers is demonstrated. A thin poly-Si interlayer was placed between the active silicon layer and the buried oxide by direct wafer bonding. 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 layer showed no measurable effects on BSOI characteristics such as bond strength, interfacial voids, or sacrificial oxide etching, and the residual stress was very low. The results suggest that a thin poly-Si layer has minimal effect on fabrication of the MEMS elements.

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.

We have studied iron gettering from monocrystalline silicon device layer into polycrystalline silicon (polysilicon) interlayer in thick bonded silicon‐on‐insulator (SOI) wafers. The results show that the polysilicon interlayer acts as an efficient gettering layer for iron. The gettering takes place via both the segregation and precipitation although the dominant gettering mechanism is segregation at low contamination levels. The activation energy of the segregation coefficient between the monocrystalline silicon and the polysilicon interlayer was found to be Ea = 1.9 ± 0.2 eV.

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