Method of forming metal oxide semiconductor photodiode isolation structures

A method, comprising:

• forming a photodiode in a silicon substrate;
• and
• forming a deep trench isolation (DTI) structure, comprising a liner layer and a dielectric formed over the liner layer, in the silicon substrate,
• wherein forming the DTI structure comprises:
• conformally depositing the liner layer on sidewalls of a trench and on a bottom surface of the trench,
• wherein the liner layer comprises a metal oxide;
• conformally depositing a doping layer on surfaces of the liner layer on the sidewalls of the trench and the bottom surface of the trench;
• performing an ion implantation operation to drive metal atoms from the doping layer into the liner layer;
• removing the doping layer from the surfaces of the liner layer on the sidewalls of the trench and the bottom surface of the trench,
• wherein the doping layer is removed in a wet etching operation, and
• wherein the wet etching operation is performed with a mixture of ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2), and water (H2O), or a mixture of hydrochloric acid (HCl), hydrogen peroxide (H2O2), and water (H2O);
• and
• filling the trench with the dielectric,
• wherein the DTI structure is adjacent to the photodiode and electrically insulates the photodiode.

A method, comprising:

• forming, in a substrate, a deep p-well region (DPW);
• forming, in the substrate, a photodiode for a pixel sensor of a pixel array;
• forming, in the substrate, a trench extending to the DPW;
• lining sidewalls of the trench and a bottom surface of the trench with a liner layer,
• wherein the liner layer comprises a metal oxide;
• conformally depositing a doping layer on surfaces of the liner layer on the sidewalls of the trench and the bottom surface of the trench;
• driving zinc, gallium, or a combination thereof from the doping layer into the liner layer;
• removing the doping layer from the surfaces of the liner layer on the sidewalls of the trench and the bottom surface of the trench,
• wherein the doping layer is removed in a wet etching operation, and
• wherein the wet etching operation is performed with a mixture of ammonium hydroxide (NH4OH), hydrogen peroxide (H2O2), and water (H2O), or a mixture of hydrochloric acid (HCl), hydrogen peroxide (H2O2), and water (H2O);
• and
• filling the trench with a dielectric material over the liner layer to form a deep trench isolation (DTI) structure.