Semiconductor device with contact having tapered profile and method for fabricating the same

A method for fabricating a semiconductor device, comprising:

• providing a substrate comprising a first region and a second region;
• forming a first gate structure on first region of the substrate and a second gate structure on the second region of the substrate;
• forming a first dielectric layer on the substrate to cover the first gate structure, wherein the first dielectric layer comprises atoms comprising phosphorus, arsenic, antimony, or boron;
• forming a second dielectric layer on the first dielectric layer and above the first region of the substrate;
• forming a first contact comprising:
• a first lower portion along the first dielectric layer and contacting a top surface of the first gate structure;
• and
• a first upper portion along the second dielectric layer and on the first lower portion;
• and
• forming a second contact comprising:
• a second lower portion contacting a top surface of the second gate structure and a sidewall of the second gate structure;
• and
• a second upper portion on the second lower portion;
• forming a third dielectric layer on the second dielectric layer, wherein the third dielectric layer comprises atoms comprising phosphorus, arsenic, antimony, or boron;
• and
• forming a fourth dielectric layer positioned on the third dielectric layer, wherein the fourth dielectric layer comprises atoms comprising phosphorus, arsenic, antimony, or boron;
• wherein sidewalls of the first lower portion are tapered and sidewalls of the second lower portion are substantially vertical;
• wherein a concentration of atoms of the second dielectric layer is greater than a concentration of atoms of the first dielectric layer;
• wherein a concentration of atoms of the fourth dielectric layer is greater than a concentration of atoms of the third dielectric layer.