Three-dimensional memory device containing contact via structure extending through source contact layer and dielectric spacer assembly and methods of making the same

A method of forming a three-dimensional memory device, comprising:

• forming in-process source-level material layers comprising a lower source-level material layer, a lower dielectric liner layer, and a source-level sacrificial layer over a substrate;
• forming an annular dielectric isolation structure through at least the source-level sacrificial layer;
• forming an upper dielectric liner layer and an upper source-level material layer over the annular dielectric isolation structure;
• forming an alternating stack of insulating layers and spacer material layers over the in-process source-level material layers, wherein the spacer material layers are formed as, or are subsequently replaced with, electrically conductive layers;
• forming a memory stack structure through the alternating stack, the upper source-level material layer, the upper dielectric liner layer, and the source-level sacrificial layer, wherein the memory stack structure comprises a memory film and a vertical semiconductor channel;
• forming a source cavity by removing portions of the source-level sacrificial layer outside the annular dielectric isolation structure and by removing portions of the upper and lower dielectric liner layers;
• etching a portion of the memory film exposed in the source cavity to physically expose a sidewall of the vertical semiconductor channel;
• forming a source contact layer in the source cavity and in contact with the sidewall of the vertical semiconductor channel;
• and
• forming a through-memory-level contact via structure through the alternating stack, the upper source-level material layer, an opening inside the annular dielectric isolation structure, and the lower source-level material layer.