Patent ID: 7550363

Claim:
A method of fabricating a semiconductor device comprising: forming a first hard mask pattern on a semiconductor substrate; forming a plurality of first trenches having a first depth in a first region of the substrate by etching the substrate through the first hard mask pattern; filling the first trenches with a first insulation material to form first device isolation layers; removing the first hard mask pattern; forming a second hard mask pattern on the substrate after removing the first hard mask pattern, the second hard mask pattern covering the first device isolation layers; forming a plurality of second trenches having a second depth in a second region of the substrate by etching the substrate through the second hard mask pattern, wherein at least a portion of each of the second trenches is formed in a respective portion of the substrate that is covered by the first hard mask pattern while etching the substrate to form the first trenches; and, filling the second trenches with a second insulation material to form second device isolation layers.