Self-aligned contacts for walled nanosheet and forksheet field effect transistor devices

A method of forming a semiconductor device comprising a first field-effect transistor (FET) device and a second FET device, the method comprising:

• forming, on a semiconductor substrate, a first transistor structure and a second transistor structure separated by a first trench, the first trench comprising a first dielectric wall protruding above a top surface of the transistor structures,
• wherein each of the first and the second transistor structures comprises a plurality of stacked nanosheets forming a channel structure, and a source portion and a drain portion horizontally separated by the channel structure;
• depositing a contact material over the transistor structures and the first dielectric wall, thereby filling the first trench and contacting a first source/drain portion of the first transistor structure and a first source/drain portion of the second transistor structure;
• and
• etching back the contact material below a top surface of the first dielectric wall, thereby forming a first contact contacting the first source/drain portion of the first transistor structure, and a second contact contacting the first source/drain portion of the second transistor structure,
• wherein forming the first transistor structure and the second transistor structure on the semiconductor substrate comprises:
• prior to the formation of the first dielectric wall:
• etching the semiconductor substrate through the first trench,
• thereby forming a substrate trench, and
• forming a buried power rail (BPR) in the substrate trench;
• and
• prior to depositing the contact material, applying a mask layer including an opening exposing at least a portion of the first source/drain portion of the first transistor structure, a portion of the first trench between the first transistor structure and the first dielectric wall, and a portion of the first dielectric wall, the mask layer covering another portion of the first dielectric wall;
• exposing the BPR by etching through the exposed portion of the first trench;
• and
• removing the mask layer.