Integrated circuitry comprising a memory array comprising strings of memory cells and methods used in forming a memory array comprising strings of memory cells

Abstract

A method used in forming a memory array comprising strings of memory cells comprises forming a lower portion of a stack that will comprise vertically-alternating conductive tiers and insulative tiers. The stack comprises laterally-spaced memory-block regions. The lower portion comprises multiple lower of the conductive tiers and multiple lower of the insulative tiers. The lower insulative tiers comprise insulative material. The lower conductive tiers comprise sacrificial material that is of different composition from that of the insulative material. The sacrificial material is replaced with conducting material. After the replacing of the sacrificial material, the vertically-alternating conductive tiers and insulative tiers of an upper portion of the stack are formed above the lower portion. The upper portion comprises multiple upper of the conductive tiers and multiple upper of the insulative tiers. The upper insulative tiers comprise insulating material. The upper conductive tiers comprise sacrifice material that is of different composition from that of the conducting material, the insulating material, and the insulative material. The sacrifice material is replaced with conductive material. Other embodiments, including structure independent of method, are disclosed.