Mechanisms for forming backside illuminated image sensor device structure

A method for manufacturing a backside illuminated image sensor device structure comprising:

• providing a substrate having a front side and a back side;
• forming a polysilicon layer over the front side of the substrate;
• forming a buffer layer over the polysilicon layer;
• forming an etch stop layer over the buffer layer;
• forming a hard mask layer over the etch stop layer;
• patterning the hard mask layer;
• performing an implant process from the front side of the substrate to form a radiation sensing region in the substrate;
• removing the hard mask layer by a first removing process;
• removing the etch stop layer by a second removing process;
• and
• removing the buffer layer by a third removing process.

A method for manufacturing a backside illuminated image sensor device structure comprising:

• providing a substrate having a front side and a back side;
• forming a polysilicon layer over the front side of the substrate;
• forming a buffer layer over the polysilicon layer;
• forming an etch stop layer over the buffer layer;
• forming a hard mask layer over the etch stop layer;
• patterning the hard mask layer;
• performing an implant process from the front side of the substrate to form a radiation sensing region in the substrate;
• removing the hard mask layer, the etch stop layer, and the buffer layer;
• and
• patterning the polysilicon layer to form a gate structure.