Fin structure of FinFET

A fin field-effect transistor (FinFET), comprising:

• a mesa having a first semiconductor material;
• a U-shaped feature formed in and extending above the mesa;
• a rectangular-shaped feature disposed in and extending above the U-shaped feature;
• a channel having a second semiconductor material different from the first semiconductor material, the channel formed on the rectangular-shaped feature and extending to the top of the U-shaped feature on two sides of the rectangular-shaped feature;
• source/drain regions on the mesa on opposing sides of the rectangular-shaped feature and extending to opposing sides of the channel, the source/drain regions having the second semiconductor material;
• a gate dielectric disposed over the channel;
• and
• a gate electrode disposed over the gate dielectric.

A method of forming a fin structure, comprising:

• forming a mesa having a first semiconductor material;
• forming a first isolation feature in and extending above the mesa;
• forming a second isolation feature extending over the first isolation feature and having a smaller width than the first isolation feature;
• and
• forming a channel over and onto opposing sides of the second isolation feature, wherein the channel has a second semiconductor material different from the first semiconductor material.