Semiconductor devices having buried metal silicide layers and methods of fabricating the same

1. A semiconductor device comprising:

a substrate; and

a plurality of active pillars disposed on the substrate and spaced apart from each other by first trenches and second trenches which are alternately arrayed, each of the active pillars including an active region stacked on a buried metal silicide pattern;

a filling insulation layer that fills the first trenches; and a partial insulation layer disposed in the second trenches and having an upper surface that is level with bottom surfaces of the buried metal silicide patterns;

capping insulation patterns disposed on the plurality of active pillars;

spacers disposed on sidewalls of the capping insulation patterns, the spacers extending onto sidewalls of the transistor active regions of the second trenches under the capping insulation patterns, wherein lower surfaces of the spacers are level with upper surfaces of the buried metal silicide patterns; and

a lower insulation pattern extending between spacers on sidewalls and defining an air gap between the partial insulation layer and the lower insulation pattern.

2. The semiconductor device of claim 1 , wherein the partial insulation layer includes a silicon oxide layer.

3. The semiconductor device of claim 1 , wherein the capping insulation patterns include a silicon nitride layer.

4. The semiconductor device of claim 1 , wherein the buried metal silicide patterns include a cobalt silicide layer.

5. The semiconductor device of claim 1 , wherein the impurity junction regions in the active region include an upper impurity region disposed in an upper portion of the active region and a lower impurity region disposed in a lower portion of the active region.