Method for fabricating a patterned structure of a semiconductor device

A method for fabricating a patterned structure in a semiconductor device, comprising:

• forming a target layer, a first mask and a first patterned mask on a substrate sequentially;
• performing a first etching process to etch away a portion of the first mask and a portion of the target layer by using the first patterned mask as an etching mask so that a plurality of characteristic structures is formed on the substrate, wherein each of the characteristic structures comprises a patterned first mask and a patterned target layer;
• forming a second patterned mask on the substrate, wherein the second patterned mask covers a portion of the characteristic structures and exposes a predetermined region;
• performing a second etching process to fully eliminate the characteristic structures and the second patterned mask within the predetermined region so that a first trench is formed in the predetermined region;
• and
• after forming the first trench, performing a third etching process to fully eliminate the target layer exposed from the patterned first mask by using the patterned first masks as etching masks.