Semiconductor device including metal gate structure with specified profile and method for manufacturing the same

A method for manufacturing a semiconductor device, comprising:

• forming a dummy material layer on a semiconductor substrate including a main portion and a fin portion disposed on the main portion, such that the dummy material layer is disposed across the fin portion of the semiconductor substrate;
• patterning the dummy material layer to form a dummy gate structure that is disposed across the fin portion of the semiconductor substrate and that includes an upper portion and a lower portion connected between the upper portion of the dummy gate structure and the main portion of the semiconductor substrate, the lower portion of the dummy gate structure having a width in a horizontal direction parallel to an extension direction of the fin portion of the semiconductor substrate, the upper portion of the dummy gate structure having a width in the horizontal direction, and the width of lower portion of the dummy gate structure being greater than the width of the upper portion of the dummy gate structure;
• and
• trimming the lower portion of the dummy gate structure by an etching process such that the lower portion of the dummy gate structure, after being trimmed, has a width in the horizontal direction which is less than a width of the upper portion of the dummy gate structure in the horizontal direction.

A semiconductor device, comprising:

• a semiconductor substrate including a main portion and a fin portion disposed on the main portion;
• a metal gate structure disposed across the fin portion of the semiconductor substrate, and including an upper metal gate portion and a lower metal gate portion connected between the upper metal gate portion and the main portion of the semiconductor substrate, the lower metal gate portion having a width in a horizontal direction parallel to an extension direction of the fin portion of the semiconductor substrate, the upper metal gate portion having a width in the horizontal direction, and the width of the lower metal gate portion being less than the width of the upper metal gate portion;
• and
• a pair of source/drain structures disposed at two opposite sides of the metal gate structure.