Three dimensional memory device and method for fabricating the same

A three dimensional (3D) memory device comprising:

• a substrate, having a concave portion extending along a first direction into the substrate from a surface thereof;
• a multi-layers stack, including a plurality of conductive layers and a plurality of insulating layers alternatively stacked along the first direction on a bottom of the concave portion, and having at least one recess passing through the conductive layers and the insulating layers along the first direction, wherein the at least one recess has a cross-sectional bottom profile and a cross-sectional opening profile perpendicular to the first direction and the cross-sectional bottom profile has a size substantially greater than that of the cross-sectional opening profile;
• a capping layer, covering sidewalls of the at least one recess and contacting to the plurality of conductive layers;
• and
• a dielectric material, formed on the capping layer and at least partially filled in the at least one recess.