Memory circuitry and method used in forming memory circuitry
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 flight of stairs extending along a first direction. Multiple different-depth treads in individual of the stairs extend along a second direction that is orthogonal to the first direction. Individual of the multiple different-depth treads comprise conducting material of one of the conductive tiers. The multiple different-depth treads in the individual stairs comprise in lateral-succession along the second direction a first higher-depth tread, a lower-depth tread, and a second higher-depth tread. Methods are also disclosed.
1 . A method used in forming memory circuitry, comprising:
forming a stack comprising vertically-alternating first tiers and second tiers, the stack extending from a memory-array region into a stair-step region, the first tiers being conductive and the second tiers being insulative at least in a finished-circuitry construction;
forming a stair-step structure in the stair-step region, the stair-step structure comprising a first flight of stairs extending along a first direction and a second flight of stairs extending along the first direction and opposing the first flight of stairs, each stair of the first and second flights of stairs comprising at least two of the first tiers and at least two of the second tiers, the first and second flights of stairs being separated by a cavity;
forming a spacer-forming layer within the cavity;
anisotropically etching the spacer-forming material to form first and second spacers that extend along the first direction directly above the first flight of stairs, the first and second spacers being spaced from one another in a second direction that is orthogonal to the first direction; and
using the first and second spacers as a mask while etching there-between through one of the first tiers and one of the second tiers within one individual of the stairs to form two higher-depth treads having a lower-depth tread there-between in the individual stairs along the second direction, the two higher-depth treads and the lower-depth tread individually comprising conducting material of individual of the first tiers in the finished-circuitry construction.
2 . The method of claim 1 wherein the two higher-depth treads are at the same elevation relative one another.
3 . The method of claim 1 wherein one of the two higher-depth treads is operative in the finished-circuitry construction and the other of the two higher-depth treads is dummy in the finished-circuitry construction.
4 . The method of claim 3 comprising forming a through-array-via through the other higher-depth tread.
5 . The method of claim 4 wherein the one higher-depth tread is devoid of any through-array-via extending there-through.
6 . The method of claim 1 being devoid of use of any photoresist in patterning horizontal outlines of any of the two higher-depth and lower-depth treads with respect to each of the individual stairs.
7 . The method of claim 1 wherein the first and second spacers are of different composition from those of the first and second tiers.
8 . The method of claim 1 wherein the first and second spacers are of the same composition relative one another.
9 . The method of claim 8 wherein the same composition at least predominantly comprises carbon.
10 . The method of claim 1 wherein the first and second spacers are of the same lateral-width in the second direction.
11 . The method of claim 10 wherein lateral-width in the second direction of space that is between the first and second spacers is the same as the same lateral-width in the second direction of the first and second spacers.
12 . The method of claim 1 wherein the individual stairs have three and only three treads in the finished-circuitry construction, the three treads being the two higher-depth and lower-depth treads.