Semiconductor structure with hard mask and method for manufacturing the same

A method for manufacturing a semiconductor structure, comprising:

• forming fins over a substrate, wherein the fins comprise first semiconductor layers and second semiconductor layers alternating stacked over base fins;
• forming an isolation structure around the fins;
• forming a dummy interfacial layer over the fins and the isolation structure;
• forming a dummy gate electrode over the dummy interfacial layer;
• removing the dummy gate electrode to form a gate trench exposing the dummy interfacial layer;
• forming a hard mask layer covering the dummy interfacial layer over the isolation structure;
• removing the second semiconductor layers in the gate trench;
• and
• forming a gate structure in the gate trench, wherein the gate structure wraps around the first semiconductor layers and interfaces the hard mask layers and the dummy interfacial layer.

A method for manufacturing a semiconductor structure, comprising:

• forming fins over a substrate, wherein each of the fins comprises a base fin protruding from the substrate, and first semiconductor layers and second semiconductor layers alternating stacked over the base fin;
• forming an isolation structure around the base fins;
• forming a dummy gate structure over the fins and the isolation structure, wherein the dummy gate structure has a dummy interfacial layer and a dummy gate electrode over the dummy interfacial layer;
• forming source/drain features on opposite sides of the dummy gate structure;
• removing the dummy gate electrode to form a gate trench;
• forming a hard mask layer over the isolation structure and the dummy interfacial layer;
• removing the second semiconductor layers in the gate trench;
• and
• forming a gate structure in the gate trench, wherein the gate structure wraps around the first semiconductor layers and over the hard mask layer, wherein a bottom surface of the hard mask layer is lower than top surfaces of the base fins of the fins.