Semiconductor device and method for forming the same

A method, comprising:

• forming a fin structure over a substrate;
• forming a first dielectric layer over the substrate and covering the fin structure;
• forming first semiconductor layers over a first side of the first dielectric layer;
• forming a first gate structure wrapping around each of the first semiconductor layers;
• forming first source/drain epitaxy structures over the second semiconductor layers and on opposite sides of the first gate structure;
• removing the substrate to expose a second side of the first dielectric layer opposite to the first side of the first dielectric layer;
• etching back the first dielectric layer from the second side of the first dielectric layer to expose sidewalls of the fin structure;
• forming a second gate structure over the semiconductor fin;
• and
• forming source/drain contacts over the semiconductor fin and on opposite sides of the second gate structure.

A semiconductor device, comprising:

• a dielectric layer;
• a p-type transistor over a first side of the dielectric layer, wherein the p-type transistor comprises:
• a semiconductor channel layer;
• a first gate structure over the semiconductor channel layer;
• and
• source/drain epitaxy structures on opposite sides of the first gate structure;
• and
• an n-type transistor over a second side of the dielectric layer opposite to the first side of the dielectric layer, wherein the n-type transistor comprises:
• a semiconductive oxide channel layer;
• a second gate structure over the semiconductive oxide channel layer;
• and
• source/drain contacts on opposite sides of the second gate structure.