Three-dimensional memory devices with lateral block isolation structures and methods of forming the same

A method, comprising:

• forming a vertically alternating sequence of insulating layers and sacrificial material layers over a substrate, wherein the sacrificial material layers comprise a dielectric material;
• forming backside trenches and an isolation trench through the vertically alternating sequence, wherein the backside trenches laterally extend along the first horizontal direction and are laterally spaced apart along a second horizontal direction, and the isolation trench laterally extends along the second horizontal direction and is laterally spaced from the backside trenches along the first horizontal direction;
• forming an isolation cavity by laterally expanding the isolation trench, wherein alternating stacks of insulating strips and sacrificial material strips are formed, wherein the insulating strips are portions of the insulating layers that are located between a respective neighboring pair of backside trenches, wherein the sacrificial material strips are discrete remaining portions of the sacrificial material layers, and wherein each of the sacrificial material strips is laterally spaced apart from all other sacrificial material strips located at a same vertical level by a combination of the backside trenches and the isolation cavity;
• forming a dielectric isolation structure in the isolation cavity;
• and
• replacing the sacrificial material strips with electrically conductive strips to form alternating stacks of a respective subset of the insulating strips and a respective subset of the electrically conductive strips.