Semiconductor device having air gap and method of fabricating the same

A semiconductor device, comprising:

• tunneling insulating layers on upper surfaces of active regions of a substrate;
• floating gate electrodes on the tunneling insulating layers;
• an isolation trench formed in the substrate to define the active regions, space the tunneling insulating layers, and isolate the floating gate electrodes, the isolation trench having an air gap disposed therein;
• a first insulating layer on lateral surfaces of the floating gate electrodes, the first insulating layer hermetically sealing a top portion of the isolation trench to define the air gap;
• and
• a second insulating layer, a third insulating layer, and a control gate electrode stacked on the floating gate electrodes and the first insulating layer.

A semiconductor device, comprising:

• tunneling insulating layers on active regions of a substrate;
• floating gate electrodes on the tunneling insulating layers;
• an isolation trench within the substrate, the isolation trench defining the active regions;
• a lower insulating layer on the floating gate electrodes, at least a portion of the lower insulating layer being within the isolation trench and the portion of the lower insulating layer having varying thicknesses within the isolation trench, and the lower insulating layer being configured to hermetically seal the isolation trench to define an air gap under the lower insulating layer within the isolation trench;
• and
• a middle insulating layer, an upper insulating layer, a control gate electrode, and a gate capping layer stacked on the lower insulating layer.