Semiconductor structure and method of forming thereof

A method of forming a semiconductor structure, comprising:

• forming a semiconductor epitaxial layer on a first semiconductor substrate;
• forming a first recess on a first side of the semiconductor epitaxial layer;
• forming a gate structure in the first recess of the semiconductor epitaxial layer;
• forming a first source/drain doped region on the first side of the semiconductor epitaxial layer outside the first recess;
• forming an adhesive layer covering the first side of the semiconductor epitaxial layer;
• fixing the first side of the semiconductor epitaxial layer on a transfer substrate by the adhesive layer;
• flipping the semiconductor epitaxial layer and the first semiconductor substrate;
• removing the first semiconductor substrate to expose a second side of the semiconductor epitaxial layer opposite of the first side;
• forming a second recess recessed from the second side of the semiconductor epitaxial layer and aligned with the gate structure;
• forming a second source/drain doped region in the second recess aligned with the gate structure, wherein the first source/drain doped region, the gate structure and the second source/drain doped region form a transistor;
• filling a conductive layer in the second recess;
• connecting a second semiconductor substrate to the conductive layer;
• forming a metal layer on the second semiconductor substrate;
• and
• removing the adhesive layer and the transfer substrate.