Patent ID: 7749874

Claim:
A method for fabricating a CMOS image sensor including a pinned photodiode and an associated transfer gate such that the pinned photodiode includes a deep implant region diffused into a substrate and aligned with a first side edge of a polycrystalline silicon (polysilicon) gate structure of the transfer gate, wherein the method comprises: forming a dielectric layer on an upper surface of the substrate; forming a polysilicon layer on the dielectric layer; etching a portion of the polysilicon layer to expose a drain side region of the substrate, and to form a partially formed gate structure having a second side edge; implanting a second dopant into the exposed drain side region of the substrate adjacent to the second side edge of the partially formed gate structure such that a shallow implant region is formed that is self-aligned to the second side edge of the partially formed gate structure; forming a mask material layer over the shallow implant region and the partially formed gate structure; patterning mask material layer to form a gate mask such that a portion of the partially formed gate structure is exposed adjacent to a side edge of said gate mask; etching said exposed portion of the partially formed gate structure to form said gate structure having said first side edge self-aligned to the side edge of said gate mask; and forming said deep implant region by implanting a dopant into the substrate adjacent to the first side edge using a relatively high energy implant process such that the deep implant region is self-aligned to the first side edge of the gate structure, wherein the gate mask is retained on the gate structure during forming of said deep implant region.