Prevention of active area shrinkage using polysilicon stepped shallow trench isolation technology

Polysilicon stepped shallow trench isolation (PS-STI) using an Si3N4/Poly-Si/SiO2 stacked mask is proposed for 0.14 mum and beyond. The PS-STI profile has a poly-Si step length and a protrusion in the trench sidewall after PS-STI etching. The poly-Si is oxidised to form a thin liner oxide, and then a small bird's beak is grown. With this step, the penetration of the small bird's beak into the active area is prevented, increasing the active area and giving better process margins. Because of the increased active area due to the step length oxidation. the reduced contact resistance results in an increased drain current.