Finfet and fabrication method thereof

A fabrication method of a fin-shaped field-effect transistor (FinFET), comprising the steps of:

• providing a substrate;
• depositing a shallow trench isolation (STI) layer on the substrate;
• depositing a plurality of alternative layers of oxygen-containing dielectric layers and insulating layers on the STI layer;
• forming a trench through the STI layer and the pluralities of alternative layers of the oxygen-containing dielectric layers and the insulating layers by a first etching process;
• selectively etching the insulating layers of the pluralities of alternative layer in an inner side wall of the trench by a second etching process to make the inner side wall of the trench have a vertical stacked bowls cross-sectional shape;
• selective epitaxially growing a buffer layer on the substrate in the trench;
• selective epitaxially growing a III-V group material on the buffer layer in the trench;
• selectively removing the pluralities of alternative layers of the oxygen-containing dielectric layers and the insulating layers;
• thermal oxidizing the buffer layer to form an oxide-isolation layer between the substrate and the III-V group material;
• depositing a high dielectric constant dielectric layer on an upper layer of the STI layer and a surrounding of the III-V group material;
• and
• depositing a conducting material surrounding the high dielectric constant dielectric layer for forming a gate electrode.