Isolation structure, semiconductor device having the same, and method for fabricating the isolation structure

An isolation structure of a semiconductor device, comprising:

• a trench formed in a substrate;
• a first oxide layer formed in a bottom surface and an inner sidewall of the trench;
• a nitride layer formed on the first oxide layer;
• a second oxide layer formed on the nitride layer;
• a filler formed on the second oxide layer to fill a part of inside of the trench;
• and
• a fourth oxide layer filling an upper portion of the filler of the trench to a height above an upper surface of the trench.

A method for fabricating an isolation structure of a semiconductor device, the method comprising:

• forming a deep trench by etching a substrate a plurality of times;
• forming a first oxide layer along an inner side of the deep trench and then annealing the first oxide layer;
• forming a second oxide layer on the first oxide layer and then annealing the second oxide layer;
• filling a portion of an inside of the deep trench on the second oxide layer with a filler;
• etching such that upper portions of the first and second oxide layers are recessed downward the deep trench;
• etching the filler so that the filler exists on only portion of the inside of the deep trench;
• and
• forming a fourth oxide layer on the first oxide layer, the second oxide layer and the filler.