US Patent 10026746 Memory devices using etching stop layers

A memory device may include a gate structure including a plurality of gate electrode layers and a plurality of insulating layers alternately stacked on a substrate, a plurality of etching stop layers, extending from the insulating layers respectively, being on respective lower portions of the gate electrode layers; and a plurality of contacts connected to the gate electrode layers above upper portions of the etching stop layers, respectively, wherein respective ones of the etching stop layers include an air gap therein.