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

A memory array comprising strings of memory cells, comprising:

• a vertical stack comprising alternating insulative tiers and conductive tiers, the conductive tiers individually comprising conductive lines;
• the strings of memory cells in the stack comprising channel material extending through the insulative tiers and the conductive tiers;
• individual of the memory cells comprising the channel material, a gate region that is part of one of the conductive lines in individual of the conductive tiers, and a memory structure laterally-between the gate region and the channel material in the individual conductive tiers;
• walls individually extending through the insulative tiers and the conductive tiers laterally between immediately-adjacent of the conductive lines, the walls individually comprising laterally-outer insulative material and a core material spanning laterally-between the laterally-outer insulative material, the laterally-outer insulative material comprising at least one of an insulative nitride and elemental-form boron;
• and
• wherein, in a vertical cross-section, the laterally-outer insulative-material on each side of the core material has a lateral width of 1% to 20% of an uppermost minimum lateral width of the individual wall in the vertical cross-section.

A memory array comprising strings of memory cells, comprising:

• a vertical stack comprising alternating insulative tiers and conductive tiers, the conductive tiers individually comprising conductive lines comprising conducting material;
• the strings of memory cells in the stack comprising channel material extending through the insulative tiers and the conductive tiers;
• individual of the memory cells comprising the channel material, a gate region that is part of one of the conductive lines in individual of the conductive tiers, and a memory structure laterally-between the gate region and the channel material in the individual conductive tiers;
• and
• walls individually extending through the insulative tiers and the conductive tiers laterally-between two of the conductive lines, the walls individually comprising laterally-outer insulative material and a core material spanning laterally-between the laterally-outer insulative material, the laterally-outer insulative material comprising an insulative nitride and elemental-form boron that is directly against the conducting material of the conductive lines, the core material comprising:
• a laterally-outer silicon dioxide that is directly against said insulative nitride and elemental-form boron;
• and
• polysilicon directly against and spanning laterally-between said laterally-outer silicon dioxide.