Memory arrays and methods used in forming a memory array

A method used in forming a memory array comprises forming a stack comprising vertically-alternating insulative tiers and wordline tiers. The stack comprises an insulator tier above the wordline tiers. The insulator tier comprises first insulator material comprising silicon, nitrogen, and one or more of carbon, oxygen, boron, and phosphorus. The first insulator material is patterned to form first horizontally-elongated trenches in the insulator tier. Second insulator material is formed in the first trenches along sidewalls of the first insulator material. The second insulator material is of different composition from that of the first insulator material and narrows the first trenches. After forming the second insulator material, second horizontally-elongated trenches are formed through the insulative tiers and the wordline tiers. The second trenches are horizontally along the narrowed first trenches laterally between and below the second insulator material. Elevationally-extending strings of memory cells are formed in the stack. Structure independent of method is disclosed.