Patent ID: 7858490

Claim:
A method of manufacturing a semiconductor device having a first area and a second area, comprising the steps of: forming a first silicon insulating film over a silicon substrate; forming a first trench in said first silicon insulating film and said silicon substrate in said first area and a second trench in said first silicon insulating film and said silicon substrate in said second area; forming a mask layer in said first trench formed in said first area and over said first silicon insulating film in said first area; etching said silicon substrate using said mask layer and said first silicon insulating film as a mask, so as to form said second trench deeper than said first trench and remove an upper portion of said first silicon insulating film in said second area; removing said mask layer; forming a second silicon insulating film over said first silicon insulating film so as to bury said first and said second trenches; and removing both said first and said second silicon insulating films over said silicon substrate so as to form an isolation structure in said first and said second trenches, wherein said step of forming said first trench and said second trench includes a step of forming a third trench at a boundary between said first area and said second area and said third trench has a first portion in said first area and a second portion in said second area, said step of etching said silicon substrate includes a step of etching said silicon substrate using said mask layer and said first silicon insulating film as a mask, so as to form said second portion of said third trench in said second area which has a substantially same depth as said second trench, and after said step of etching said silicon substrate, said third trench has said first portion having a substantially same depth as said first trench and said second portion having a substantially same depth as said second trench.