Method of manufacturing semiconductor device

A method comprising:

• forming a first dielectric pattern over a semiconductor substrate, and performing a first etching process to form at least one trench in the semiconductor substrate;
• exposing an edge portion of the trench;
• performing an oxidation process over the semiconductor substrate to round the edge portion of the trench;
• forming a second dielectric over the semiconductor substrate thereby filling the trench;
• performing a planarization process on the second dielectric formed over the semiconductor substrate;
• forming a photoresist pattern over the second dielectric corresponding to the trench;
• performing a second etching process to form a second dielectric pattern filling the trench;
• removing the photoresist pattern formed over the second dielectric pattern;
• and
• performing a second cleaning process on the semiconductor substrate comprising the trench filled with the second dielectric pattern to form a device isolation layer, which is formed by removing a portion of the second dielectric pattern filling the trench,
• wherein a portion of the second dielectric remains on the first dielectric pattern after the performing of the planarization process on the second dielectric.