| CPC H01L 23/535 (2013.01) [H10B 43/27 (2023.02); H10B 43/40 (2023.02); H10D 88/00 (2025.01)] | 20 Claims |

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1. A three-dimensional semiconductor memory device, comprising:
a substrate including a first region and a second region;
a stack structure including a plurality of interlayer dielectric layers and a plurality of gate electrodes that are alternately and repeatedly stacked on the substrate, the stack structure having a stepwise structure on the second region;
a mold structure adjacent to the stack structure on the first region, the mold structure including a plurality of interlayer dielectric layers and a plurality of sacrificial layers that are alternately and repeatedly stacked on the substrate;
a first separation structure crossing the stack structure and extending along a first direction from the first region toward the second region; and
a second separation structure crossing the mold structure and extending in the first direction on the first region,
wherein a level of a top surface of the first separation structure is higher than a level of a top surface of the second separation structure.
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