Patent ID: 7851275

Claim:
A method for fabricating a pixel of an image sensor, wherein the pixel comprises a floating diffusion region configured to receive photocharges from a photodetector of the pixel, a MOS drive transistor having a gate and configured as a source follower, and a MOS reset transistor having a drain, the method comprising: depositing an isolating field oxide about a peripheral portion of an area of a substrate to define an active region in the substrate; forming a lightly doped diffusion region in the active region of the substrate; forming a gate oxide layer over the active region, wherein the gate oxide layer further extends over a gate region of the MOS drive transistor; forming a first polysilicon layer over the gate oxide layer in the active region, wherein the first polysilicon layer further extends over the gate oxide layer of the gate region of the MOS drive transistor; forming a contact mask over the first polysilicon layer in the active region, wherein the contact mask leaves at least a portion of the first polysilicon layer exposed as an unmasked region; performing an ion-implantation process to direct ions through the first polysilicon layer and into the gate oxide layer to break down the gate oxide layer in the unmasked region to render the gate oxide layer in the unmasked region conductive thereby providing an electrically conductive path between the first polysilicon layer and the lightly doped diffusion region; removing the contact mask; forming a second polysilicon layer over the first polysilicon layer; performing gate masking and etching processes to pattern the first and second polysilicon layers, wherein the first and second polysilicon layers are patterned to form the gate of the MOS drive transistor, and wherein the first and second polysilicon layers are patterned to provide a conductive path between the broken-down gate oxide layer in the active region and either the gate of the MOS drive transistor or drain of the reset transistor; and forming a highly doped diffusion region in the active region of the substrate to form the floating diffusion region, wherein the floating gate diffusion region is in contact with the lightly doped diffusion region.