Semiconductor device and method of forming the same

A method of forming a semiconductor device, comprising:

• forming a first dielectric layer;
• forming an etching stop layer on the first dielectric layer;
• forming a second dielectric layer on the etching stop layer;
• forming a first patterned mask layer on the second dielectric layer;
• patterning the second dielectric layer and the etching stop layer by using the first patterned mask layer as an etching mask to form an opening in the second dielectric layer and the etching stop layer;
• removing the first patterned mask layer;
• forming an additional dielectric layer in the opening;
• forming a second patterned mask layer on the second dielectric layer and the additional dielectric layer, wherein the second patterned mask layer has a mask opening to expose a portion of a top surface of the second dielectric layer, and a portion of a top surface of the additional dielectric layer, and the mask opening is disposed directly above a portion of the additional dielectric layer that is embedded in the etching stop layer;
• performing an etching process according to the second patterned mask layer to remove portions of the second dielectric layer, the additional dielectric layer, the etching stop layer, and the first dielectric layer, thereby forming a bit line trench in the first dielectric layer, the second dielectric layer, the etching stop layer and the additional dielectric layer and a via hole in the first dielectric layer;
• removing the second patterned mask layer;
• and
• filling a conductive material in the bit line trench and the via hole, to form a bit line in the bit line trench and a conductive contact in the via hole.