Method for forming dual oxide layers at bottom of trench

In a method of forming dual oxide layers at the bottom of a trench wherein a substrate has a trench which includes a bottom and a sidewall;

• wherein the trench is formed on the substrate by forming a mask oxide layer on the substrate, defining the mask oxide layer to form a patterned mask oxide layer and exposing a partial surface of the substrate to form a window, and using the patterned mask oxide layer as an etching mask to form the trench in the window;
• wherein a first oxide layer is formed on the sidewall and the bottom of the trench of the substrate, wherein a photoresist layer fills the trench of the substrate;
• wherein the patterned mask oxide layer and a part of the first oxide layer are removed to leave a remaining first oxide layer at the bottom of the trench;
• wherein the photoresist layer is removed;
• wherein a second oxide layer is formed on the substrate covering at least the remaining first oxide layer;
• wherein the improvement comprises, prior to removing the patterned mask oxide layer, a part of the first oxide layer, and the photoresist layer:
• partially etching back the photoresist layer to leave a remaining photoresist layer in the trench, the height of the remaining photoresist layer being lower than the depth of the trench;
• and
• performing a curing treatment of the remaining photoresist layer.

A method of forming dual oxide layers at the bottom of a trench, the method comprising:

• providing a substrate;
• forming a mask oxide layer on the substrate;
• defining the mask oxide layer to form a patterned mask oxide layer and exposing a partial surface of the substrate to form a window;
• using the patterned mask oxide layer as an etching mask to form the trench in the window;
• forming a first oxide layer on a sidewall and a bottom of the trench of the substrate;
• forming a photoresist layer on the substrate, the photoresist layer filling the trench of the substrate;
• partially etching back the photoresist layer to leave a remaining photoresist layer in the trench, the height of the remaining photoresist layer being lower than the depth of the trench;
• performing a curing treatment of the remaining photoresist layer;
• removing the patterned mask oxide layer and a portion of the first oxide layer to leave a remaining first oxide layer at the bottom of the trench;
• removing the remaining photoresist layer;
• and
• forming a second oxide layer on the substrate covering at least the remaining first oxide layer.