Patent ID: 8318583

Claim:
A method of forming an isolation structure, comprising: providing a semiconductor substrate comprising a first region, a second region, and a third region; performing a first patterning process of etching the semiconductor substrate to form at least one first trench in the first region and at least one second trench in the second region, wherein the first and second trenches have a same first depth measured with respect to bottommost surfaces of the first and second trenches, respectively; performing a second patterning process of etching the semiconductor substrate to form at least one third trench in the third region and at least one fourth trench in the second region, wherein the fourth trench extends from the bottommost surface of the second trench, the third trench has a second depth measured with respect to a bottommost surface of the third trench, and the fourth trench has a third depth measured with respect to a bottommost surface of the fourth trench; and forming an isolation layer filling the first to fourth trenches, wherein the first and second depths are different from each other.