SEMICONDUCTOR DEVICES AND METHODS OF FABRICATING THE SAME

A semiconductor device includes horizontal patterns on a substrate and the horizontal patterns have at least one opening therein, a pad pattern in an upper region of the opening, an insulating gap fill structure in the opening, the insulating gap fill structure is between the pad pattern and the substrate, and the insulating gap fill structure includes a first gap fill pattern and a second gap fill pattern. The first gap fill pattern includes a first oxide and the second gap fill pattern includes a second oxide, and the second oxide has a different etching selectivity from that of the first oxide. The device further includes a semiconductor pattern that is between a sidewall of the gap fill structure and sidewalls of the horizontal patterns and between a sidewall of the pad pattern and the sidewalls of the horizontal patterns.