Semiconductor device and fabrication method thereof

A fabrication method of a semiconductor device, comprising:

• providing a base substrate, having a first gate dielectric film thereon;
• forming a first gate electrode layer on a portion of the first gate dielectric film;
• forming an offset sidewall film on the first gate dielectric film, wherein the offset sidewall film covers sidewalls of the first gate electrode layer;
• after forming the offset sidewall film, forming lightly doped regions in the base substrate on sides of the first gate electrode layer;
• after forming the lightly doped regions, removing the offset sidewall film and removing a portion of the first gate dielectric film such that a remaining portion of the first gate dielectric film is under the first gate electrode layer and as a first gate dielectric layer;
• forming sidewall spacers, wherein the sidewall spacers cover sidewall surfaces of both the first gate electrode layer and the first gate dielectric layer;
• forming source/drain doped regions in the base substrate on sides of each of the first gate electrode layer, the first gate dielectric layer, and the sidewall spacers;
• forming a dielectric layer over the source/drain doped regions and the base substrate, wherein the dielectric layer covers sidewall surfaces of the sidewall spacers;
• and
• forming a gate opening in the dielectric layer by etching off the first gate electrode layer and the first gate dielectric layer, wherein the sidewall spacers remain on sidewalls of the gate opening.