Method for manufacturing an optical sensor

A method of manufacturing an optical sensor, comprising:

• providing a semiconductive layer having an electrical circuit area and an optical sensing area;
• forming an electrical contact directly over the electrical circuit area;
• forming a plurality of metal layers and metal vias over the electrical contact while covering the optical sensing area with intermetal dielectrics;
• forming an aperture in the intermetal dielectric over the optical sensing area;
• and
• depositing a metal layer conforming to a sidewall of the aperture and over a top surface of the intermetal dielectric;
• etching back the metal layer to obtain a metal spacer only at the sidewall of the aperture;
• depositing dielectric into the aperture and covering the metal layer;
• removing the dielectric from the top surface of the intermetal dielectric;
• forming a thick metal layer on the top surface of the intermetal dielectric;
• and
• forming an opening aligning with the optical sensing area in the thick metal layer to form a continuous surface from a cross sectional perspective, wherein the continuous surface is composed of a surface of the metal spacer facing the dielectric in aperture and a side of the thick metal layer, and the thick metal layer covers the electrical circuit area.