Spacer structure for semiconductor device and method for forming the same

A method, comprising:

• forming a sacrificial layer on a substrate;
• forming a channel layer on the sacrificial layer;
• removing a portion of the sacrificial layer to form a recess under the channel layer;
• forming a dielectric layer on a side surface of the channel layer to fill the recess;
• performing a first etching process to etch the dielectric layer, wherein performing the first etching process comprises providing a first halogen element;
• and
• performing a second etching process to etch the dielectric layer, wherein performing the second etching process comprises providing a second halogen element different from the first halogen element.

A method, comprising:

• growing, on a substrate, a plurality of channel layers and a plurality of sacrificial layers alternately stacking with each other;
• removing, from side surfaces of the plurality of sacrificial layers, a portion of each of the plurality of sacrificial layers to form a plurality of recess structures;
• forming a dielectric layer in the plurality of recess structures and on side surfaces of the plurality of channel layers;
• and
• selectively etching the dielectric layer to form a plurality of inner spacer structures, comprising:
• performing a first oxygen-free etching process, wherein the dielectric layer is etched at a first etching rate;
• and
• performing a second oxygen-free etching process, wherein the dielectric layer is etched at a second etching rate less than the first etching rate.