Three-dimensional memory device including crack-resistant backside passivation structure and methods of forming the same

A method of forming a device structure, comprising:

• forming a combination of a three-dimensional memory array and a dielectric material portion over a first side of a source layer that overlies a carrier substrate, wherein the three-dimensional memory array comprises a three-dimensional array of memory elements embedded in an alternating stack of insulating layers and electrically conductive layers, and the dielectric material portion is located adjacent to the alternating stack;
• forming connection via structures through the dielectric material portion;
• removing the carrier substrate;
• forming a backside connection pad cavity through at least the source layer after removing the carrier substrate;
• depositing and patterning a backside isolation layer, wherein the backside isolation layer comprises a first horizontally-extending portion located within the backside connection pad cavity and comprising a first inner sidewall having a first proximal edge that is in contact with a horizontal surface of the dielectric material portion and having a first distal edge that is spaced from the dielectric material portion by a vertical thickness of the first horizontally-extending portion, a second horizontally-extending portion that is located over a second side of the source layer, and a connecting portion that connects the first horizontally-extending portion and the second horizontally-extending portion and that comprises a second inner sidewall having a second distal edge that is adjoined to a distal horizontal surface of the second horizontally-extending portion;
• and
• forming a backside connection pad structure, wherein the backside connection pad structure comprises a proximal portion contacting end surfaces of the connection via structures, a distal portion located over the second horizontally-extending portion of the backside isolation layer, and a connecting portion that connects the proximal portion and the distal portion, wherein a lateral distance between an inner sidewall and an outer sidewall of the connecting portion of the backside connection pad structure within a first horizontal plane containing the second distal edge is greater than a lateral distance between the first distal edge and the second distal edge of the backside isolation layer.