Semiconductor device with backside vias and method of fabrication thereof

A method, comprising:

• providing a structure having a frontside and a backside, the structure including a substrate at the backside of the structure and a fin at the frontside of the structure;
• forming an isolation structure on sidewalls of the fin;
• epitaxially growing a source/drain feature on the fin;
• depositing a contact etch stop layer on the source/drain feature;
• depositing an interlayer dielectric layer on the contact etch stop layer;
• thinning down the structure from the backside of the structure until the isolation structure is exposed;
• recessing the isolation structure such that a bottom portion of the fin protrudes from the isolation structure;
• depositing a backside dielectric layer on sidewalls of the bottom portion of the fin, wherein the backside dielectric layer covers the isolation structure;
• etching the fin from the backside of the structure to form a backside trench exposing a bottom surface of the source/drain feature, wherein during the etching of the fin the backside dielectric layer remains intact;
• depositing a conductive feature in the backside trench;
• and
• forming a metal wiring layer on the backside of the structure, wherein the metal wiring layer electrically couples to the source/drain feature through the conductive feature.

A semiconductor structure, comprising:

• first and second source/drain epitaxial features;
• one or more nanostructures connecting the first and second source/drain epitaxial features;
• a gate structure engaging the one or more nanostructures, wherein the first and second source/drain epitaxial features, the one or more nanostructures, and the gate structure are at a frontside of the semiconductor structure;
• a metal wiring layer at a backside of the semiconductor structure;
• a conductive feature directly under the first source/drain epitaxial feature and connecting the metal wiring layer and the first source/drain epitaxial feature;
• a fin-shape base directly under the second source/drain epitaxial feature;
• an isolation structure disposed on sidewalls of the fin-shape base and the conductive feature;
• and
• a backside dielectric layer covering a bottom surface of the isolation structure, wherein the conductive feature extends through the backside dielectric layer and in physical contact with a bottom surface of the backside dielectric layer.