Via patterning using multiple photo multiple etch

A method comprising:

• forming a dielectric layer;
• forming a first trench and a second trench in the dielectric layer;
• forming a photo resist comprising a first portion over the dielectric layer, and a second portion and a third portion filling the first trench and the second trench, respectively;
• forming a mask layer over the photo resist;
• in a first etching step, forming a first opening in the mask layer, wherein the first opening is vertically aligned to a portion of the first trench;
• in a second etching step, forming a second opening in the mask layer, wherein the second opening is vertically aligned to a portion of the second trench, wherein the first etching step and the second etching step are separate etching steps;
• patterning the photo resist using the mask layer as an etching mask;
• removing the photo resist;
• filling a conductive material into the first trench and the second trench;
• and
• performing a planarization on the conductive material and the dielectric layer, wherein the dielectric layer remains after the planarization.

A method comprising:

• forming a first photo resist having a portion over a dielectric layer;
• forming a first mask layer over the first photo resist;
• forming a second mask layer over the first mask layer;
• forming a third mask layer over the second mask layer;
• forming a second photo resist over the third mask layer and patterning the second photo resist;
• patterning the third mask layer using the second photo resist as a first etching mask to form a first opening in the third mask layer;
• removing the second photo resist;
• forming and patterning a third photo resist over the third mask layer;
• patterning the third mask layer using the third photo resist as a second etching mask to form a second opening in the third mask layer;
• removing the third photo resist;
• extending the first opening and the second opening into the first mask layer;
• and
• patterning the first photo resist using the first mask layer as an etching mask.