Method for forming semiconductor structures

A method, comprising:

• sequentially forming a first stacking layer and a first patterning layer on a substrate;
• forming a first patterning photoresist layer having a first opening on the first patterning layer;
• trimming the first patterning photoresist layer;
• transferring a first pattern of the trimmed first patterning photoresist layer to the first patterning layer;
• performing a first pattern reversal process to reverse the first pattern of the first patterning layer into a second opening, wherein the second opening extends to the first stacking layer;
• forming a second patterning layer in and on the second opening;
• forming a second patterning photoresist layer having a third opening on the second patterning layer;
• transferring a second pattern of the second patterning photoresist layer to the first stacking layer so that the first stacking layer has the second opening and the third opening;
• performing a second pattern reversal process to reverse a third pattern between the second opening and the third opening into a fourth opening;
• and
• extending the fourth opening to the substrate.