A high-performance directly insertable self-aligned ultra-rad-hard and enhanced isolation field-oxide technology for gigahertz silicon NMOS/CMOS VLSI

The authors describe a novel field-oxide structure for rad-hard NMOS/CMOS VLSI. This is a three-layer structure consisting of a thin thermal oxide, a doped polysilicon sheet deposited on the thin oxide, and a thick CVD (chemical-vapor-deposited) oxide layer on the polysilicon. The small effective electrical thickness of the 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. For 100-A gate oxide, the subthreshold leakage of a MOSFET (MOS field effect transistor) with a field shield structure is less than 10^-13 A/μm, and the off current is less than 10^-12 A/μm, after a total dose of 100 Mrad. This structure is self-aligned and directly insertable into submicron NMOS/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