Patent ID: 7879677

Claim:
A method of forming a FinFET comprising: forming a mask pattern that defines a fin region on a semiconductor substrate; etching the semiconductor substrate using the mask pattern as an etch mask to form a fin that protrudes from the semiconductor substrate and a trench on both sides of the fin; forming a device isolation layer in the trench on both sides of the fin; forming an insulating layer under the fin, wherein the insulating layer is directly connected to the device isolation layer and has a different thickness than the device isolation layer; forming a gate insulating layer on the fin; and forming a gate electrode that crosses over the fin, wherein the gate insulating layer is between the gate electrode and the fin, wherein forming the device isolation layer and forming the insulating layer comprise: forming a spacer covering sidewalls of the fin; performing an oxidation process to form the device isolation layer in the trench and, simultaneously, to form the insulating layer under the fin; and removing the spacer, wherein a central portion of the insulating layer between the fin and the substrate is thinner than outer portions of the insulating layer adjacent to edges of the fin.