Semiconductor memory device and manufacturing method of the semiconductor memory device

A method of manufacturing a semiconductor memory device, the method comprising:

• forming a first stack structure including a plurality of lower layers stacked in a vertical direction;
• forming a second stack structure including a plurality of intermediate layers stacked in the vertical direction on the first stack structure;
• forming a third stack structure including a plurality of upper layers stacked in the vertical direction on the second stack structure;
• etching the third stack structure such that reference regions respectively exposing upper surfaces of the upper layers having different depths are defined;
• forming a mask pattern including openings opening the reference regions on the third stack structure;
• and
• forming a plurality of grooves respectively opening upper surfaces of the lower layers by etching the upper layers, the second stack structure, and the first stack structure, using the mask pattern as an etch barrier, the plurality of grooves respectively overlapping the reference regions, wherein the plurality of grooves are formed such that a plurality of steps are formed along sidewalls of each of the grooves.