Semiconductor devices having adjoined via structures formed by bonding and methods for forming the same

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

• a first semiconductor structure comprising:
• a first memory stack;
• a plurality of first NAND memory strings extending through the first memory stack,
• a first bonding layer comprising a plurality of first bonding contacts positioned within the first bonding layer and extending from one side of the first bonding layer to another side of the first bonding layer, and
• a first via structure extending vertically through the first bonding layer, a first interconnect layer, and a memory layer wherein the first memory stack and the first NAND memory strings are arranged and into the first semiconductor structure;
• and
• a second semiconductor structure comprising:
• a second memory stack;
• a plurality of second NAND memory strings extending through the first memory stack,
• a second bonding layer comprising a plurality of second bonding contacts, and
• a second via structure extending vertically through the second bonding layer and into the second semiconductor structure;
• and
• a bonding interface between the first bonding layer and the second bonding layer,
• wherein:
• the first bonding contacts are in contact with the second bonding contacts at the bonding interface, and at an opposite side of the bonding interface, the first bonding contacts are in direct contact with an interconnect of the first interconnect layer, the interconnect being connected with the memory layer;
• a lateral dimension of each of the first and second bonding contacts is smaller than that of each of the first via structure and the second via structure, at the bonding interface;
• and
• the first via structure is in contact with the second via structure and sidewalls of the first via structure and the second via structures have a staggered profile at the bonding interface.