Three-dimensional semiconductor memory devices

A three-dimensional semiconductor memory device, comprising:

• a first stack structure on a substrate;
• and
• a second stack structure on the first stack structure, the second stack structure having a bottom surface;
• the first stack structure having a first vertical channel hole from the substrate to the bottom surface of the second stack structure, the first vertical channel hole having top diameter, a first inner side surface, and a buffer pattern on the first inner side surface and adjacent to the bottom surface of the second stack structure,
• wherein the first inner side surface has an upper portion, the upper portion including a first position and a second position, which are spaced apart from each other and are located at a same level;
• the second stack structure having a second vertical channel hole on the first vertical channel hole, the second vertical channel hole having a bottom diameter that is smaller than the top diameter of the first vertical channel hole, and a second inner side surface;
• and
• the buffer pattern having a width on the first position is-different from a width of the buffer pattern on the second position.

A three-dimensional semiconductor memory device, comprising:

• a block structure on a substrate;
• the block structure having a vertical channel hole to the substrate, the vertical channel hole having an inner side surface, the inner side surface having a corner region;
• and
• a buffer pattern in the corner region.