US Patent 10998234 Nanosheet bottom isolation and source or drain epitaxial growth

Embodiments of the present invention are directed to a method that prevents punch-through of a bottom isolation layer and improves the quality of the source/drain epitaxial growth in a nanosheet semiconductor structure. In a non-limiting embodiment of the invention, a bottom isolation structure is formed over a substrate. The bottom isolation structure includes a tri-layer stack in a first region of the substrate and a bi-layer stack in a second region of the substrate. A nanosheet stack is formed over the bottom isolation structure in the first region of the substrate. A gate is formed over a channel region of the nanosheet stack.