Three-dimensional memory device and method for forming the same

A three-dimensional (3D) memory device, comprising:

• a plurality of memory blocks, each memory block comprising:
• a memory stack comprising interleaved conductive layers and first dielectric layers;
• a plurality of channel structures each extending through the memory stack;
• and
• a slit structure extending through the memory stack;
• and
• a separation block extending laterally to separate two adjacent memory blocks, the separation block comprising:
• a dielectric stack comprising interleaved second dielectric layers and the first dielectric layers.

A method for forming a three-dimensional (3D) memory device, comprising:

• forming a stack structure comprising a plurality of first dielectric layers and a plurality of second dielectric layers alternatingly arranged on a substrate;
• forming a plurality of channel structures extending through the stack structure in a plurality of memory planes;
• forming a plurality of openings extending through the stack structure in the plurality of memory planes;
• removing a first portion of the plurality of second dielectric layers in the plurality of memory planes to form a plurality of cavities and maintaining a second portion of the plurality of second dielectric layers in a separation block between adjacent memory planes;
• forming a plurality of word lines in the plurality of cavities;
• and
• forming a plurality of slit structures in the plurality of openings.