A high-performance directly insertable self-alignedultra-radiation-hard and enhanced isolation field-oxide technology forgigahertz Si-CMOS VLSI

A field-oxide structure for radiation-hard CMOS VLSI is described. It is a three-layer structure consisting of a thin thermal oxide, a doped polysilicon sheet deposited on the thin oxide, and a thick CVD oxide layer deposited on the polysilicon. The polysilicon sheet is maintained at the substrate potential by, e.g. using n-type poly-Si over the n-tub and p-type poly-Si over the p-tub or p-substrate and allowing contacts to be made through the thin oxide. The small effective electrical thickness of the thin oxide combined with the ground potential of the polysilicon enhances the radiation hardness and maintains good isolation even at radiation levels as high as 10⁸ rads and above. This structure is self-aligned to the active regions and directly insertable into a submicrometer CMOS VLSI without any changes in the circuit design. The circuits made with this technology can operate at 2.5-3 GHz even after a total dose of 50-100 Mrad