Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a substrate;
• a first dielectric fin and a second dielectric fin disposed over the substrate, wherein a bottom surface of the first dielectric fin is lower than a bottom surface of the second dielectric fin;
• a semiconductor fin disposed over the substrate, wherein the semiconductor fin is between the first dielectric fin and the second dielectric fin, and a distance between the first dielectric fin and the semiconductor fin is less than a distance between the second dielectric fin and the semiconductor fin;
• and
• a metal gate structure crossing the first dielectric fin, the second dielectric fin, and the semiconductor fin.

A semiconductor device, comprising:

• a substrate comprising a semiconductor fin;
• a first dielectric fin over the substrate;
• a first epitaxy structure over the first semiconductor fin, wherein a first sidewall of the first epitaxy structure is in contact with the first dielectric fin;
• a contact etch stop layer over the first epitaxy structure, wherein a second sidewall of the first epitaxy structure farthest from the first sidewall of the first epitaxy structure is in contact with the contact etch stop layer;
• and
• a metal gate structure crossing the semiconductor fin and the first dielectric fin.