Formation of a bonded SOI interface using a spin-on dielectric

The formation of a bonded interface between thermally oxidized silicon wafers forms the basis for the bond-and-etchback SOI (BESOI) technology. Conventional bonding approaches require a high degree of planarity over the wafer surfaces. Significant nonplanarity caused by particles or other defects on the wafer surfaces can result in substantial yield loss during the bonding process. Furthermore, the bond-and-etchback technique might be extendable to a Gate-All-Around SOI process if the buried polysilicon gate could be patterned before the bonding step. However, the non-planarity of the wafer resulting from the definition of the buried polysilicon gate would prevent bonding this wafer to an unpatterned wafer via the conventional bond-and-etchback approach. We describe an approach to wafer bonding that includes the formation of a spin-on dielectric on one or both of the wafer surfaces. This spin-on glass has the advantage that it can subsume defects on the wafer surfaces resulting in a high degree of planarity even over particles as large as the film thickness when boron and/or phosphorus are incorporated into the glass and a thermal reflow step is included.