Method of forming isolation layer of semiconductor device

A method of forming an isolation layer of a semiconductor device, the method comprising:

• forming first trenches in an isolation region of a semiconductor substrate;
• oxidizing sidewalls and a bottom surface of each of the first trenches by a radical oxidization process to form a first oxide layer;
• forming an oxidization-prevention spacer on the sidewalls of each of the first trenches;
• forming second trenches in the isolation region below the corresponding first trenches, wherein each second trench is narrower and deeper than the corresponding first trench;
• filling the second trenches with a second oxide layer;
• and
• filling the first trenches with an insulating layer.

A method of forming an isolation layer of a semiconductor device, the method comprising:

• forming a tunnel insulating layer, an electronic storage layer and an isolation mask over a semiconductor substrate;
• etching the isolation mask, the electronic storage layer, the tunnel insulating layer and the semiconductor substrate of an isolation region to form first trenches;
• oxidizing sidewalls and a bottom surface of each of the first trenches by a radical oxidization process to form a first oxide layer;
• forming oxidization-prevention spacers on the sidewalls of the first trenches, the electronic storage layer and the isolation mask;
• forming second trenches in the isolation region below the first trenches, wherein each second trench is narrower and deeper than the corresponding first trench, wherein the second trenches are formed using the oxidation prevention spacers as a mask;
• filling the second trenches with a second oxide layer;
• and
• filling the first trenches with an insulating layer.