Backside contact

A semiconductor structure, comprising:

• a source feature and a drain feature;
• a plurality of channel members disposed over a backside dielectric layer, the plurality of channel members extending between the source feature and the drain feature along a first direction, the plurality of channel members being stacked along a second direction perpendicular to the first direction;
• a gate structure wrapping around each of the plurality of channel members;
• and
• a backside source contact disposed in the backside dielectric layer, the backside source contact comprising a first portion adjacent the source feature and a second portion away from the source feature,
• wherein the first portion comprises a first width along the first direction and the second portion comprises a second width along the first direction,
• wherein the first portion comprises a first height along the second direction and the second portion comprises a second height along the second direction,
• wherein the first width is different from the second width,
• wherein the first height is smaller than the second height.

A semiconductor structure, comprising:

• a first epitaxial feature and a second epitaxial feature;
• a plurality of nanostructure disposed over a backside dielectric layer, the plurality of nanostructure extending between the first epitaxial feature and the second epitaxial feature along a direction;
• a backside contact disposed in the backside dielectric layer and directly below the first epitaxial feature;
• and
• a silicon germanium feature disposed in the backside dielectric layer and directly below the second epitaxial feature,
• wherein the backside contact includes a top portion adjacent the first epitaxial feature and a bottom portion away from the first epitaxial feature,
• wherein a width of the top portion along the direction is different from a width of the bottom portion along the direction.