US Patent 7384857 Method to fabricate completely isolated silicon regions

The construction of Shallow Trench Isolation, STI, regions is integrated in to a SIMOX fabrication process for a Silicon On Insulator, SOI, wafer. Prior to the beginning of the SOI process, a preferred nitrogen (N2) implant is applied to the silicon wafer in areas designated as active regions. The nitrogen modifies the oxidation rate of later implanted oxygen. Regions where the N2 is implanted result in thinner oxide layers. The SIMOX process can begin following the implantation of nitrogen. This results in buried regions of thick and thin oxide layers at fixed depths in the Si substrate. Excess Si on top of the buried thick and thin oxide regions can be polished down to the thick oxide regions to form the active device regions over the thin oxide regions. Thus, the SOI wafer exhibits an STI structure upon completion of the SOI process without a need for additional STI manufacturing steps.