Method for forming device isolation layer of a semiconductor device

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

• providing a silicon substrate having a substructure of a predetermined configuration;
• depositing a nitride layer on a top of the silicon substrate;
• forming a trench on a device isolation region of the silicon substrate;
• depositing a gap filling oxide layer on the trench and a portion of the silicon substrate which does not form the trench;
• forming a photoresist pattern on the gap filling oxide layer of the device isolation region;
• oxidizing the photoresist pattern by performing a first oxidation process;
• removing a portion of the gap filling oxide layer by using the oxidized photoresist pattern as a mask to form a first intermediate structure;
• planarizing the first intermediate structure to a top of the nitride layer by using a chemical mechanical polishing process;
• removing the nitride layer to form a second intermediate structure;
• forming an amorphous silicon layer on a top of the second intermediate structure;
• etching a front of the amorphous silicon layer to form an amorphous silicon spacer on a side wall of an extruded field oxide layer;
• and
• oxidizing the spacer by performing a second oxidation process.