Integrated circuitry, memory circuitry comprising strings of memory cells, and methods used in forming integrated circuitry

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

• forming a stack comprising vertically-alternating first tiers and second tiers, the stack extending from individual die areas to and across scribe-line area that is between immediately-adjacent of the individual die areas, the stack comprising a memory-array region within the individual die areas and a horizontal area in the scribe-line area, channel-material strings extending through the first and second tiers in the memory-array region;
• forming a registration mark in the horizontal area of the scribe-line area, the registration mark comprising:
• parallel first bars atop the stack having first spaces therebetween;
• and
• a masking material directly above the stack, the first bars, and the first spaces;
• the masking material comprising parallel second bars having second spaces therebetween, the second spaces individually having width that is less than width of individual of the second bars, some of the masking material being spaced laterally-outward of the second bars, vertical thickness of the some masking material that is laterally-outward of the second bars having a vertical thickness laterally-outward of the first spaces that is greater than vertical thickness of the second bars, ratio of the vertical thickness of the some masking material that is laterally-outward of the second bars divided by the width of the second bars being 6.0 to 9.6;
• forming a flight of stairs in the stack in the scribe-line area that circumferentially-surrounds the horizontal area, the stairs individually comprising a tread comprising one of the first tiers and one of the second tiers;
• and
• after forming the registration mark, cutting through the first bars, the first and second tiers, and the flight of stairs in the scribe-line area to form individual die that individually comprise one of the individual die areas.