Structure and formation method of semiconductor device structure

A semiconductor device structure, comprising:

• a fin structure over a semiconductor substrate;
• a gate stack covering a portion of the fin structure;
• a spacer element over a sidewall of the gate stack, wherein the spacer element comprises a first layer and a second layer, the second layer is a single dielectric layer, a top surface of the first layer is lower than a top surface of the second layer, a dielectric constant of the first layer is greater than a dielectric constant of the second layer, and the gate stack is in contact with the first layer and the second layer;
• a source or drain structure over the semiconductor substrate, wherein the second layer extends from a sidewall of the source or drain structure to a top surface of the source or drain structure;
• and
• a dielectric layer over the source or drain structure, wherein the second layer is in direct contact with a top surface of the dielectric layer and a top surface of the gate stack.

A semiconductor device structure, comprising:

• a gate stack covering a fin structure and including a gate dielectric layer;
• a spacer element over a sidewall of the gate stack, wherein the spacer element comprises a first layer and a second layer, and wherein the second layer is separated from the fin structure by the first layer, a topmost surface of the first layer is in contact with a bottommost surface of the second layer, a dielectric constant of the first layer is greater than a dielectric constant of the second layer, and the gate dielectric layer of the gate stack is in contact with the first layer and the second layer;
• a source or drain structure over the fin structure, wherein the gate stack and the source or drain structure sandwich the second layer;
• and
• a dielectric layer over the source or drain structure, wherein the second layer is in direct contact with a top surface of the dielectric layer and a top surface of the gate stack.