Memory circuitry and methods used in forming memory circuitry

Abstract

Memory circuitry comprising strings of memory cells comprises vertically-alternating insulative tiers and conductive tiers that extend from a memory-array region into a stair-step region across an intermediate region that is between the memory-array region and the stair-step region. The insulative tiers and the conductive tiers comprise memory blocks upper portions of which individually comprise sub-blocks. Sub-block trenches are in the upper portions individually between immediately-laterally-adjacent of the sub-blocks. Strings of memory cells in the memory-array region comprise channel-material strings that extend through the insulative tiers and the conductive tiers in the memory blocks and in the sub-blocks. The sub-block trenches in the memory-array region, in the intermediate region, and in the stair-step region individually have a top. The top of individual of the sub-block trenches in the stair-step region has a narrowest-width that is larger than a narrowest-width of the top of the individual sub-block trenches in the intermediate region. The narrowest-width of the top of the individual sub-block trenches in the intermediate region is larger than a narrowest-width of the top of the individual sub-block trenches in the memory-array region. Other embodiments, including method, are disclosed.