Methods of fabricating gate insulating layers in gate trenches and methods of fabricating semiconductor devices including the same

A method of fabricating a semiconductor device, comprising:

• loading a substrate into a plasma processing chamber, wherein the substrate includes a field region defining an active region, and a gate trench partially exposing the active region and the field region;
• forming a first gate oxide layer on the active region exposed in the gate trench;
• unloading the substrate having the first gate oxide layer formed thereon from the plasma processing chamber, and loading the substrate into a thermal processing furnace;
• forming a gate insulating layer by forming a second gate oxide layer between the active region and the first gate oxide layer;
• and
• unloading the substrate having the gate insulating layer formed thereon from the thermal processing furnace.

A method of fabricating a gate insulating layer, comprising:

• forming a field region defining an active region in a substrate;
• forming a gate trench in which the active region and the field region in the substrate are at least partially exposed;
• forming a first gate oxide layer on horizontal and vertical side surfaces of the active region at least partially exposed in the gate trench by primarily oxidizing the horizontal and vertical side surfaces of the active region;
• and
• forming a second gate oxide layer between the horizontal and vertical side surfaces of the active region and the first gate oxide layer by secondarily oxidizing the horizontal and vertical side surfaces of the active region.