Semiconductor device having source and drain in active region and manufacturing method for same

A semiconductor device, comprising:

• a substrate;
• a first active region on the substrate;
• a first gate structure on the first active region, where the first gate structure comprises a first gate dielectric layer positioned on the first active region, a first gate positioned on the first gate dielectric layer, and a first buffer layer positioned on the first gate;
• a first source and a first drain positioned in the first active region, where the first source and the first drain are respectively on two sides of the first gate structure, the first gate structure is not positioned directly above any portion of the first source nor the first drain, and a top surface of the first source is level with and directly next to a bottom surface of the first gate dielectric layer without an intervening structure between the top surface of the first source and the bottom surface of the first gate dielectric layer, where a top surface of the first drain is level with and directly next to the bottom surface of the first gate dielectric layer without an intervening structure between the top surface of the first drain and the bottom surface of the first gate dielectric layer;
• and
• two spacers respectively positioned on side surfaces on two sides of the first gate without contacting surfaces of the first buffer layer, positioned directly above the first gate dielectric layer, and abutting against a top surface of the first gate dielectric layer without covering end top surfaces of the first gate dielectric layer at both ends of the first gate dielectric layer, side surfaces of the two spacers only contacting the first gate;
• wherein a size of the first drain is larger than a size of the first source, the size of the first drain comprises a horizontal size of a portion of the first drain exposed on a top surface of the first active region along a channel direction and the size of the first source comprises a horizontal size of a portion of the first source exposed on the top surface of the first active region along the channel direction.