Fin semiconductor device and method for making the same

A method for manufacturing a fin semiconductor device, comprising steps of:

• providing a substrate comprising a stack of layers on the substrate;
• etching the substrate to form a fin channel structure for a first time, wherein the fin channel structure protrudes from the substrate;
• forming a protective layer comprising a first portion on a top surface of the fin channel structure and a second portion on two sidewalls of the fin channel structure, wherein the protective layer comprises silicon oxide;
• etching the substrate for a second time having a combined vertical dry etch and a lateral dry etch, wherein the vertical dry etch extends the fin channel structure deeper into the substrate and removes lower parts of the second portion of the protective layer to expose the sidewalls of the fin channel structure, wherein the lateral dry etch reacts with the sidewalls of the fin channel structure to reduce a width of a base part of the fin channel structure without changing a width of an upper part of the fin channel structure;
• oxidizing the base part of the fin channel structure, without affecting the upper part of the fin channel structure;
• removing the protective layer from the fin channel structure;
• and
• removing the oxidized base part of the fin channel structure to suspend the upper part of the fin channel structure over the substrate.