Fin field-effect transistor and fabrication method thereof

A method for fabricating fin-field effect transistors, comprising:

• providing a substrate;
• forming a plurality of fins protruding from a surface of the substrate;
• forming a plurality of isolation layers on the surface of the substrate between adjacent fins;
• forming a transitional layer, at least having atoms identical to atoms of the plurality of fins, on side and top surfaces of the plurality of fins and on the plurality of isolation layers, by a deposition process;
• and
• performing an oxidation process to convert the transitional layer and a surface portion of the plurality of fins into a dielectric material on a remaining portion of the plurality of fins and on a remaining portion of the plurality of isolation layers, wherein a thickness of the transitional layer is smaller than a thickness of the dielectric material, the thickness of the transitional layer is in a range of approximately 5 Ř40 Å and the thickness of the dielectric material is in a range of approximately 10 Ř60 Å.