Semiconductor manufacturing process

A semiconductor manufacturing process, comprising:

• forming a trench in a semiconductor structure;
• depositing an oxide layer on sidewalls of the trench;
• forming a solid-state by-product layer on surfaces of a bottom and the sidewalls of the trench by introducing a first etchant gas to react with a naturally occurred oxide layer at the bottom of the trench and the deposited oxide layer on the sidewalls of the trench, wherein the solid-state by-product layer has a thickness on the bottom less than a thickness on the sidewalls;
• introducing a second etchant gas into the trench to react with the solid-state by-product layer on the bottom and the sidewalls, thereby removing the naturally occurred oxide layer and a portion of the solid-state by-product layer from the bottom of the trench and providing a thinned solid-state by-product layer on the sidewalls to protect the deposited oxide layer;
• and
• removing, by a heating process, the thinned solid-state by-product layer from the sidewalls of the trench, exposing the deposited oxide layer and a surface portion of the semiconductor structure in the trench.