Semiconductor device structure with spacer

A semiconductor device structure, comprising:

• a substrate;
• a gate stack over the substrate;
• a spacer over a side of the gate stack;
• and
• a dielectric layer over the substrate, wherein the dielectric layer has an upper portion and a first lower portion, a part of the upper portion close to the first lower portion is wider than the first lower portion, and the upper portion has a curved sloped sidewall.

A semiconductor device structure, comprising:

• a substrate;
• a gate stack over the substrate;
• a spacer over a side of the gate stack;
• and
• an etch stop layer covering a sidewall of the spacer, wherein the etch stop layer has a first recess, the etch stop layer has an upper portion and a lower portion, the lower portion is under the first recess, the upper portion has a concave curved sidewall facing away from the gate stack, and an upper surface of the lower portion faces away from the substrate.