Method for fabricating complementary metal-oxide-semiconductor image sensor

A method of manufacturing an active pixel cell, comprising:

• removing a portion of a workpiece to define a protrusion extending from an upper surface of a bulk;
• implanting a first dopant in the bulk;
• forming an insulating feature over the protrusion and the upper surface of the bulk;
• forming a conductive feature over the insulating feature, wherein the forming of the conductive feature comprises:
• depositing a conductive layer, and
• patterning the conductive layer to expose a first portion of a top surface of the protrusion and to maintain the conductive layer over a second portion of the top surface of the protrusion;
• and
• implanting a second dopant in the protrusion, wherein the second dopant has a same conductivity type as the first dopant.

A method of fabricating an image sensor, comprising:

• implanting a first dopant in a substrate;
• removing a portion of the substrate to define a protrusion, wherein the removing the portion of the substrate defines a first surface surrounding the protrusion, the protrusion has a first width, and a region of the first dopant remains in the protrusion;
• forming a conductive feature over the protrusion;
• implanting a second dopant in the protrusion, wherein the second dopant has a same conductivity type as the first dopant, and the implanting of the second dopant defines a second doped region having a second width less than the first width;
• and
• implanting a third dopant in the substrate, wherein the third dopant has a different conductive type from the first dopant.