The elimination of poly stringer in double poly AMS technology development

Defects found during the fabrication of poly-insulator-poly (PIP) analog mixed signal (AMS) device using 0.35mum CMOS technology process had revealed the existence of poly stringers. The formation of stringer is due to topography of the double poly PIP capacitor structure. The challenge in eliminating the stringer is to develop an optimal polysilicon gate etch process that can remove the stringer completely as well as maintaining a good polysilicon gate profile at logic CMOS area. Three types of approaches have been experimented to solve the stringer issue. It is proven that combining a thinner bottom plate (poly1) film together with an optimized polysilicon gate etching condition had been successful in eliminating the stringer completely