Method of Forming Trench in Semiconductor Substrate

A method of forming a trench in a substrate, comprising:

• providing a substrate;
• forming a first patterned mask layer on the substrate, wherein the first patterned mask layer has a first trench;
• forming a material layer comprehensively on the substrate, wherein the material layer is formed on a bottom surface and at least a sidewall of the first trench;
• forming a second patterned mask layer on the material layer to completely fill the first trench;
• removing a portion of the material layer and maintaining the portion of the material layer between the second patterned mask layer and the substrate to form at least a second trench between the first patterned mask layer and the second patterned mask layer;
• and
• after forming the second trench, performing an etching process by using the first patterned mask layer and the second patterned mask layer as a mask.