Patent ID: 8575035

Claim:
A method of forming trenches in a semiconductor layer of an image sensor, the method comprising: forming a first layer of a first material over the semiconductor layer of a wafer; forming a second layer of a second material over a first portion of the first layer, wherein the second material is an oxide; forming a first opening through the first layer by exposing the wafer to a first etchant that etches the first material, but does not substantially etch the second material; extending the first opening into the semiconductor layer to form a first trench by exposing the wafer to a second etchant, wherein neither the first opening nor the first trench extend through the second layer; forming a second opening through the second layer by exposing the wafer to a third etchant that does not substantially etch the semiconductor layer, wherein the wafer is exposed to the second etchant that extends the first opening prior to being exposed to the third etchant that forms the second opening, the third etchant being a wet etchant; extending the second opening by exposing the wafer to a fourth etchant that etches the first layer but does not substantially etch the semiconductor layer; and extending the first trench and forming a second trench in the semiconductor layer below the second opening by exposing the wafer to a fifth etchant.