Spacer structure for semiconductor device and method for forming the same

A method, comprising:

• forming a fin structure over a substrate;
• forming a recess structure in the fin structure;
• forming a dielectric layer over the recess structure;
• and
• performing an oxygen-free cyclic etching process to etch the dielectric layer, comprising:
• performing a first etching process with a first etchant to remove a first portion of the dielectric layer, wherein the first etchant comprises a first halogen element;
• and
• performing a second etching process with a second etchant to remove a second portion of the dielectric layer, wherein the second etchant comprises a second halogen element different from the first halogen element.

A method, comprising:

• forming a gate structure over a first portion of a substrate;
• forming a recess structure over a second portion of the substrate;
• forming a dielectric layer in the recess structure and over the second portion of the substrate;
• performing a cyclic etching process to etch the dielectric layer to expose the second portion of the substrate, comprising:
• performing a first etching process to remove a first portion of the dielectric layer, wherein performing the first etching process comprises etching the first portion of the substrate at a first etching rate;
• and
• performing a second etching process to remove a second portion of the dielectric layer, wherein performing the second etching process comprises etching the first portion of the substrate with a second etching rate less than the first etching rate;
• and
• forming a source/drain (S/D) contact structure in the recess structure and over the dielectric layer.