Patent ID: 8017495

Claim:
A method of forming an isolation layer structure, comprising: removing upper portions of a substrate using gate structures thereon as an etching mask to form first and second trenches in first and second regions, respectively, the first and second trenches defined by recessed top surfaces of the substrate and sidewalls of the gate structures, the first having a first width, and the second trench having a second width larger than the first width; forming first and second oxide layer patterns on inner walls of the first and second trenches, respectively, the first oxide layer pattern partially filling the first trench and having no void therein; and forming third and fourth oxide layer patterns on the first and second oxide layer patterns, respectively, the third oxide layer pattern filling a remaining portion of the first trench and having no void therein, and the fourth oxide layer pattern filling a remaining portion of the second trench and having a first void therein.