Semiconductor structure and method for manufacturing the same

A method for manufacturing a semiconductor structure, comprising:

• forming a fin over a substrate and extending in a first direction, wherein the fin comprises a single crystal layer over the substrate and first semiconductor layers and second semiconductor layers alternating stacked over the single crystal layer;
• forming a dummy gate structure over the fin and extending in a second direction, wherein the second direction is perpendicular to the first direction;
• forming silicon germanium layers on opposite sides of the dummy gate structure in the first direction;
• forming source/drain features over the silicon germanium layers and on opposite sides of the dummy gate structure in the first direction;
• replacing the dummy gate structure and the first semiconductor layers with a gate structure wrapping around the second semiconductor layers;
• replacing the substrate with a first dielectric layer under the single crystal layer and the silicon germanium layers;
• forming an opening in the first dielectric layer to expose one of the silicon germanium layers;
• removing the one of the silicon germanium layers;
• and
• forming a via in the opening and electrically connected to one of the source/drain features.

A semiconductor structure, comprising:

• an etch stop layer;
• semiconductor layers over the etch stop layer and vertically spaced apart from each other;
• a gate structure wrapping around the semiconductor layers;
• source/drain features attached to the semiconductor layers;
• a first dielectric layer under the etch stop layer and the source/drain features;
• a via passing through the first dielectric layer and electrically connected to one of the source/drain features;
• and
• a second dielectric layer under the first dielectric layer, wherein the second dielectric layer is in contact with the via.