Semiconductor devices with backside power rail and method thereof

A method comprising:

• providing a structure having a substrate, a source feature and a drain feature over the substrate, one or more channel layers connecting the source and the drain features, a gate structure between the source and the drain features and engaging the one or more channel layers, and one or more dielectric layers disposed over the source and the drain features;
• forming a source contact hole and a drain contact hole that penetrate through the one or more dielectric layers and expose the source feature and the drain feature respectively;
• forming a source contact and a drain contact in the source contact hole and the drain contact hole respectively;
• forming an etch mask that covers the drain contact and exposes the source contact;
• removing the source contact through the etch mask, thereby reclaiming at least a portion of the source contact hole;
• and
• depositing a first dielectric cap in at least the portion of the source contact hole.

A method comprising:

• providing a structure having a substrate, first and second source/drain features over the substrate, one or more channel layers connecting the first and the second source/drain features, a high-k metal gate between the first and the second source/drain features and engaging the one or more channel layers, and one or more dielectric layers disposed over the first and the second source/drain features;
• forming first and second contacts that go through the one or more dielectric layers and electrically connected to the first and the second source/drain features respectively;
• forming an etch mask that exposes the first contact and covers the second contact;
• removing the first contact through the etch mask, resulting in a first trench over the first source/drain feature;
• depositing a first dielectric cap in the first trench;
• forming a first via over the second contact and electrically connected to the second contact;
• forming a first interconnect structure over the first via and electrically connected to the first via, wherein the first dielectric cap isolates the first source/drain feature from the first interconnect structure;
• forming a second via under the first source/drain feature and electrically connected to the first source/drain feature;
• and
• forming a second interconnect structure under the second via and electrically connected to the second via.