Semiconductor device with isolation structures

A method, comprising:

• forming a fin structure on a substrate, wherein the forming the fin structure comprises:
• forming a superlattice structure with first and second nanostructured layers on a sacrificial substrate;
• depositing an isolation layer on the superlattice structure;
• depositing a silicon layer on the isolation layer;
• forming a bi-layer isolation structure on the silicon layer;
• and
• removing the sacrificial substrate;
• forming a polysilicon structure on the superlattice structure;
• forming a source/drain region on the fin structure;
• removing the polysilicon structure and the second nanostructured layers to form gate openings;
• and
• forming a gate-all-around structure within the gate openings.

A semiconductor device, comprising:

• a substrate;
• a fin structure with a base structure disposed on the substrate and a superlattice structure disposed on the base structure,
• wherein the base structure comprises a bi-layer isolation structure disposed on the substrate, a semiconductor layer disposed on the bi-layer isolation structure, and a channel isolation layer disposed on a first portion of the semiconductor layer;
• a source/drain region disposed on a second portion of the semiconductor layer;
• and
• a gate-all-around structure disposed on the superlattice structure.