Reverse L-shape sealed poly-buffer LOCOS technology

A description is presented of a new LOCOS (local oxidation of silicon) isolation process, reverse-L-shaped sealed poly-buffer LOCOS (RLS-PBL), which can effectively eliminate the bird's beak without introducing defects. In this process, the pad oxide film is selectively etched, using the silicon nitride/polysilicon stack as a mask to form undercut portions. Thermal oxidation is then performed to grow a new thin oxide film to cover the entire silicon surface, including the undercut portions, in order to provide a new stress-buffer oxide film prior to a thin silicon nitride deposition. The reverse-L-shape sealed silicon nitride spacer is formed by RIE etching. Reverse leakage currents of NMOS submicrometer MOSFET devices, edge diodes, and capacitors fabricated by the new isolation process are comparable to those of conventional LOCOS and poly-buffer LOCOS, and are much superior to those of sealed-interface LOCOS. The defect-free mechanism and nearly zero bird's beak characteristics are attributed to the stress-absorption polycrystalline film in conjunction with the special reverse-L-shape silicon nitride spacer design.<>