Bonded semiconductor die assembly containing through-stack via structures and methods for making the same

A method of forming a bonded assembly, comprising:

• providing a first three-dimensional memory die comprising a first alternating stack of first insulating layers and first electrically conductive layers, first memory structures located in the first alternating stack, and a first stepped dielectric material portion contacting stepped surfaces of the first alternating stack;
• and
• bonding a second three-dimensional memory die to the first three-dimensional memory die, wherein the second three-dimensional memory die comprises a second alternating stack of second insulating layers and second electrically conductive layers, second memory structures located in the second alternating stack, and a second stepped dielectric material portion contacting stepped surfaces of the second alternating stack;
• wherein:
• the first three-dimensional memory die is located between driver circuit devices and the second three-dimensional memory die;
• the first electrically conductive layers have different lateral extents along the first horizontal direction that decrease with a respective vertical distance from the driver circuit devices;
• and
• the second electrically conductive layers have different lateral extents along the first horizontal direction that increase with the respective vertical distance from the driver circuit devices.