Gate oxide integrity testing on SOI wafers without test structure fabrication

Gate oxide integrity (GOI) is of increasing concern for IC manufacturers, as dielectric thicknesses continue to shrink. GOI testing on SOI wafers is essentially different from testing on bulk, in that the wafer backside is dielectrically isolated by the buried oxide and cannot be used as an electrode. Conventional GOI testing on SOI is done on MOS structures, with a front contact on the SOI film. The fabrication is time consuming, as it requires at least four mask steps (e.g. LOCOS, gate, contact, metal) and it introduce extrinsic defects in the SOI material. There is therefore a need for a faster method, with results more directly related to the silicon film quality. In this work, we demonstrate for the first time a fast GOI test for SOI wafers, needing no other structure than the oxide itself and enabling rapid feedback on a SOI process. The described implementation uses Hg dots, but other types of contacts may be used, such as metal pads or polysilicon pads, to simulate real MOS gates.