Simplified planarization process for polysilicon filled trenches

摘要

The method of planarizing polysilicon-filled trenches involves first filling the trenches with an undoped polysilicon until the upper surface is substantially planar. The polycrystalline silicon is then heavily doped by means of diffusion of a dopant from the upper surface. The time and temperature of the diffusion are carefully controlled providing for the dopant to penetrate the polysilicon to a depth level with the tops of the trenches. A selective etchant is then utilized which removes the heavily doped polysilicon and leaves the undoped polysilicon untouched in the trenches.