Gate n-well/p-substrate photodiode

Abstract

A photodiode sensor structure includes a first dopant type substrate with a first surface and a second dopant type well region with a second surface. The second dopant type well region is formed in the first dopant type substrate such that the first surface and the second surface are substantially co-planar to form a diode surface. An interface between the second dopant type well region and the first dopant type substrate at the diode surface forms a diode junction. A poly silicon region is formed along the periphery of the entire diode junction. The poly silicon region provides the p-n junction of the photodiode with a physical shield to prevent any process damage from being introduced after the poly silicon processing (including damages from processes such as dielectric deposition/pattern, metal deposition/pattern, and/or via/contact hole etching), thereby reducing leakage current. The poly silicon region can also provide the p-n junction of the photodiode with an electrical shield to prevent any possible trapped charges at higher levels of dielectric above the junctions to affect the surface potential and/or prevent the formation of conducting channels between the p-n regions, thereby reducing leakage current.