Memory arrays comprising strings of memory cells and methods used in forming a memory array comprising strings of memory cells

A method used in forming a memory array comprising strings of memory cells, comprising:

• forming a conductor tier comprising conductor material on a substrate, the conductor tier having a top surface comprising the conductor material;
• forming sacrificial plugs in locations where individual channel-material strings will be formed, the sacrificial plugs individually having a top surface that is at or below the top surface of the conductor tier and being of different composition from an upper portion of the conductor material;
• forming a lower portion of a stack that will comprise vertically-alternating first tiers and second tiers directly above the conductor tier and the sacrificial plugs, the stack comprising laterally-spaced memory-block regions, material of the first tiers being of different composition from material of the second tiers, a lowest of the first tiers comprising sacrificial material;
• forming the vertically-alternating first tiers and second tiers of an upper portion of the stack directly above the lower portion and the sacrificial plugs;
• etching channel openings through the first tiers and the second tiers to the sacrificial plugs;
• removing the sacrificial plugs through the channel openings;
• after removing the sacrificial plugs, forming a channel-material-string construction in individual ones of the channel openings;
• forming horizontally-elongated trenches into the stack that are individually laterally-between immediately-laterally-adjacent of the memory-block regions, the trenches extending through the upper portion of the stack to the lowest first tier and exposing the sacrificial material therein;
• isotropically etching the exposed sacrificial material from the lowest first tier through the trenches;
• and
• after the isotropically etching, forming conductive material in the lowest first tier that directly electrically couples together the channel material of the channel-material-string construction and the conductor material of the conductor tier.