Memory circuitry and method used in forming memory circuitry

Abstract

Memory circuitry comprising strings of memory cells comprises a stack comprising vertically-alternating insulative tiers and conductive tiers. Channel-material strings of memory cells extend through the insulative tiers and the conductive tiers in a memory-array region. The insulative tiers and the conductive tiers extend from the memory-array region into a stair-step region. The stair-step region comprises a cavity comprising a flight of stairs in a first vertical cross-section along a first direction. Insulating material is in the cavity above the flight of stairs. The insulating material comprises first material atop treads of the stairs of the flight of stairs. Individual of the treads comprise conducting material of one of the conductive tiers. Insulative second material of different composition from that of the first material is directly above the first material. The first material has an uppermost surface in the cavity that is below an uppermost surface of the insulative second material in the cavity. Conductive vias extend through the first material and the insulative second material. Individual of the conductive vias are directly above and directly against the conducting material of the respective tread. Other embodiments, including method, are disclosed.