Semiconductor structure and manufacturing method thereof

A method, comprising:

• receiving a composite substrate including a first region and a second region, the composite substrate comprising a semiconductor substrate and an insulator layer over the semiconductor substrate;
• bonding a silicon layer to the composite substrate;
• forming a trench in the first region through the silicon layer;
• growing an initial epitaxial layer to fill the trench, the initial epitaxial layer including an upper surface higher than an upper surface of the silicon layer;
• thinning the initial epitaxial layer to cause the upper surface of the initial epitaxial layer to be lower than the upper surface of the silicon layer;
• and
• causing the upper surface of the initial epitaxial layer to be level with the upper surface of the silicon layer.

A semiconductor structure, comprising:

• a semiconductor substrate and including a first region and a second region;
• a trap-rich layer over the semiconductor substrate in the second region;
• an insulator layer in the second region over the trap-rich layer;
• an epitaxial layer extending over the insulator layer across the first region and the second region;
• an isolation region between the first region and the second region;
• a transistor layer over the epitaxial layer, the transistor layer including a first transistor and a second transistor in the first region and the second region, respectively;
• a first well region in the epitaxial layer in the second region;
• and
• a first source/drain region and a second source/drain region arranged within the first well region, wherein the epitaxial layer separates the first well region from the insulator layer.