Process for fabricating silicon-on-nothing MOSFETs

A method of forming a semiconductor device, the method comprising:

• providing a silicon substrate;
• epitaxially growing a sacrificial layer on the silicon substrate;
• epitaxially growing a silicon layer on the sacrificial layer;
• forming a gate dielectric over the silicon layer;
• forming a gate electrode over the gate dielectric;
• forming a spacer on sidewalls of the gate dielectric and the gate electrode;
• etching the silicon layer, the sacrificial layer, and the silicon substrate along the spacer to form a recess;
• removing the sacrificial layer to form an air-gap between the silicon layer and the silicon substrate;
• forming dielectric layers on exposed surfaces of the silicon layer and the silicon substrate, wherein the dielectric layers comprise first portions inside the air-gap, and second portions outside the air-gap;
• removing the second portions of the dielectric layers and during the step of removing the second portions of the dielectric layers, keeping top surfaces of the first portions of the dielectric layers exposed to the air-gap;
• and
• epitaxially growing a semiconductor material to fill the recess, wherein the air-gap is substantially free from the semiconductor material.

A method comprising:

• providing a substrate;
• forming an air-gap over the substrate;
• forming a semiconductor layer over the air-gap;
• forming a first silicon oxide layer between the semiconductor layer and the air-gap;
• removing sidewall portions of the first silicon oxide layer and during the step of removing sidewall portions of the first silicon oxide layer, keeping a top surface of a non-sidewall portion of the first silicon oxide layer exposed to the air-gap;
• forming a gate dielectric layer over the semiconductor layer;
• and
• forming a gate electrode over the gate dielectric layer.