Contact structure for stacked multi-gate device

A semiconductor structure, comprising:

• a first bottom source/drain feature and a second bottom source/drain feature;
• a stack of first channel members extending between the first bottom source/drain feature and the second bottom source/drain feature;
• a bottom gate structure wrapping around each of the stack of first channel members;
• a first separation layer over the first bottom source/drain feature;
• a second separation layer over the second bottom source/drain feature;
• a first top source/drain feature disposed over the first separation layer;
• a second top source/drain feature disposed over the second separation layer;
• a stack of second channel members extending between the first top source/drain feature and the second top source/drain feature;
• a top gate structure wrapping around each of the stack of second channel members;
• a first frontside contact disposed over and in contact with the first top source/drain feature;
• a second frontside contact extending through the second top source/drain feature and the second separation layer to be in contact with the second bottom source/drain feature;
• and
• a first backside contact below and in contact with the first bottom source/drain feature;
• and
• a second backside contact below and in contact with the second bottom source/drain feature,
• wherein the bottom gate structure is electrically insulated from the top gate structure.

A method, comprising:

• receiving a workpiece including a substrate and a stack over the substrate, the stack including a plurality of channel layers interleaved by a plurality of sacrificial layers, the plurality of channel layers including a plurality of bottom channel layer and a plurality of top channel layers disposed over the plurality of bottom channel layer;
• patterning the stack and a portion of the substrate into a fin-shaped structure, the fin-shaped structure comprising a source/drain region;
• recessing the source/drain region to form a source/drain trench, exposing sidewalls of the plurality of channel layers;
• depositing a bottom source/drain feature in the source/drain trench to be in contact with the plurality of bottom channel layers;
• depositing a separation layer over the bottom source/drain feature;
• depositing a top source/drain feature over the separation layer to be in contact with the plurality of top channel layers, the top source/drain feature comprising a gap that exposes the separation layer;
• forming a filler layer in the gap;
• forming a contact opening through the filler layer and the separation layer to expose the bottom source/drain feature;
• and
• forming a contact feature in the contact opening.