Patent ID: 8883524

Claim:
A method of forming a sensor, comprising: providing a substrate comprising a pixel region and a logic region, the pixel region having a first area and the logic region having a first gate of a first transistor; forming an oxide layer covering the first area within the pixel region and covering the first gate within the logic region; forming a spacer layer and a buffer layer over the oxide layer; forming a photoresist layer on the buffer layer over the pixel region, wherein the photoresist layer has an opening exposing a first part of the buffer layer over the first area; performing a first etching to remove the first part of the buffer layer to expose a first part of the spacer layer over the first area, and to remove the buffer layer to expose the spacer layer over the first gate, while leaving a remaining part of the buffer layer covered by the photoresist layer intact; removing the photoresist layer; performing a second etching to remove the remaining part of the buffer layer, remove the first part of the spacer layer to expose a first part of the oxide layer on the first area, while leaving a second part of the spacer layer over the pixel region, and remove the spacer layer over the first gate to expose the oxide layer on the first gate, while keeping the spacer layer around the first gate; and performing a third etching to remove the first part of the oxide layer to expose the first area, and remove the oxide layer on the first gate to expose the first gate.