Arrays of elevationally-extending strings of memory cells and methods used in forming an array of elevationally-extending strings of memory cells

1. A method used in forming an array of elevationally-extending strings of memory cells, comprising:

forming a stack comprising vertically-alternating insulative tiers and wordline tiers, the stack comprising an etch-stop tier between a first tier and a second tier of the stack, the etch-stop tier being of different composition from those of the insulative tiers and the wordline tiers;

etching into the insulative tiers and the wordline tiers that are above the etch-stop tier to the etch-stop tier to form channel openings that have individual bases comprising the etch-stop tier, the etching into the insulative tiers and the wordline tiers that are above the etch-stop tier being stopped atop or within etch-stop material of the etch-stop tier such that the individual bases of the channel openings have lowest surfaces comprising the etch-stop material;

penetrating through the etch-stop tier to extend individual of the channel openings there-through;

after extending the individual channel openings through the etch-stop tier, etching into and through the insulative tiers and the wordline tiers that are below the etch-stop tier to extend the individual channel openings deeper into the stack below the etch-stop tier; and

forming transistor channel material in the individual channel openings elevationally along the etch-stop tier and along the insulative tiers and the wordline tiers that are above and below the etch-stop tier.

2. The method of claim 1 wherein the first tier is a top tier of the stack and the second tier is a bottom tier of the stack.

3. The method of claim 1 wherein the etch-stop tier is insulative.

4. The method of claim 1 wherein the etching to the etch-stop tier over-etches partially into the etch-stop tier.

5. The method of claim 4 wherein the etching to the etch-stop tier over-etches into less than half of vertical thickness of the etch-stop tier.

6. The method of claim 1 wherein the penetrating comprises dry anisotropic etching of the etch-stop tier.

7. The method of claim 1 wherein the penetrating comprises wet etching of the etch-stop tier.

8. The method of claim 1 wherein the penetrating comprises etching that etches the etch-stop tier radially-outward relative to the individual channel openings to form an annular recess projecting radially-outward relative to the individual channel openings.

9. The method of claim 8 further comprising forming transistor charge-storage material in the individual channel openings, some of the charge-storage material being formed within the annular recesses.

10. The method of claim 8 further comprising forming transistor charge-blocking material in the individual channel openings, some of the charge-blocking material being formed within the annular recesses.

11. The method of claim 8 further comprising forming transistor charge-blocking material and transistor charge-storage material in the individual channel openings, some of the charge-blocking material and some of the transistor charge-storage material being formed within the annular recesses.

12. The method of claim 1 comprising:

providing the wordline tiers to comprise control-gate material having terminal ends corresponding to control-gate regions of individual memory cells, charge-storage material between the transistor channel material and the control-gate regions, insulative charge-passage material between the transistor channel material and the charge-storage material, and a charge-blocking region between the charge-storage material and individual of the control-gate regions; and

providing the control-gate material after forming the transistor channel material.

13. The method of claim 12 wherein the etch-stop tier is one of the wordline tiers, and further comprising replacing the etch-stop tier with the control-gate material after forming the transistor channel material.

14. The method of claim 1 comprising:

providing the wordline tiers to comprise control-gate material having terminal ends corresponding to control-gate regions of individual memory cells, charge-storage material between the transistor channel material and the control-gate regions, insulative charge-passage material between the transistor channel material and the charge-storage material, and a charge-blocking region between the charge-storage material and individual of the control-gate regions; and

providing the control-gate material before forming the transistor channel material.

15. The method of claim 1 wherein the etch-stop tier is one of the insulative tiers.

16. A method used in forming an array of elevationally-extending strings of memory cells, comprising:

forming a stack comprising vertically-alternating insulative tiers and wordline tiers, the stack comprising an etch-stop tier between a first tier and a second tier of the stack, the etch-stop tier being of different composition from those of the insulative tiers and the wordline tiers;

etching into the insulative tiers and the wordline tiers that are above the etch-stop tier to the etch-stop tier to form channel openings that have individual bases comprising the etch-stop tier;

penetrating through the etch-stop tier to extend individual of the channel openings there-through;

after extending the individual channel openings through the etch-stop tier, etching into and through the insulative tiers and the wordline tiers that are below the etch-stop tier to extend the individual channel openings deeper into the stack below the etch-stop tier;

forming transistor channel material in the individual channel openings elevationally along the etch-stop tier and along the insulative tiers and the wordline tiers that are above and below the etch-stop tier; and

the etch-stop tier comprising an oxide comprising at least one of Mg and Hf.

17. The method of claim 16 wherein the oxide comprises Mg.

18. The method of claim 16 wherein the oxide comprises Hf.

19. The method of claim 16 wherein the oxide comprises Mg and Hf.

20. The method of claim 16 wherein the oxide comprises Al.

21. The method of claim 16 wherein the oxide comprises Si.

22. A method used in forming an array of elevationally-extending strings of memory cells, comprising:

forming a stack comprising vertically-alternating insulative tiers and wordline tiers, the stack comprising an etch-stop tier between a first tier and a second tier of the stack, the etch-stop tier being of different composition from those of the insulative tiers and the wordline tiers;

etching into the insulative tiers and the wordline tiers that are above the etch-stop tier to the etch-stop tier to form channel openings that have individual bases comprising the etch-stop tier;

penetrating through the etch-stop tier to extend individual of the channel openings there-through;

after extending the individual channel openings through the etch-stop tier, etching into and through the insulative tiers and the wordline tiers that are below the etch-stop tier to extend the individual channel openings deeper into the stack below the etch-stop tier;

forming transistor channel material in the individual channel openings elevationally along the etch-stop tier and along the insulative tiers and the wordline tiers that are above and below the etch-stop tier; and

forming a liner along sidewalls of the individual channel openings prior to and at least some of which remains during the penetrating.

23. The method of claim 22 comprising removing the liner after the penetrating.

24. The method of claim 23 comprising removing the liner before the etching into and through the insulative tiers and the wordline tiers that are below the etch-stop tier to extend the individual channel openings deeper into the stack below the etch-stop tier.

25. The method of claim 22 comprising:

forming the liner across the individual etch-stop tier bases prior to the penetrating; and

removing the liner from being across a central-portion of the individual etch-stop tier bases prior to the penetrating.

26. A method used in forming an array of elevationally-extending strings of memory cells, comprising:

forming a stack comprising vertically-alternating insulative tiers and wordline tiers, the stack comprising an etch-stop tier between a first tier and a second tier of the stack, the etch-stop tier being of different composition from those of the insulative tiers and the wordline tiers, the etch-stop tier comprising a homogenous layer extending continuously across the stack;

etching into the insulative tiers and the wordline tiers that are above the etch-stop tier to the etch-stop tier to form channel openings that have individual bases comprising the etch-stop tier;

penetrating through the etch-stop tier to extend individual of the channel openings there-through;

after extending the individual channel openings through the etch-stop tier, etching into and through the insulative tiers and the wordline tiers that are below the etch-stop tier to extend the individual channel openings deeper into the stack below the etch-stop tier; and

forming transistor channel material in the individual channel openings elevationally along the etch-stop tier and along the insulative tiers and the wordline tiers that are above and below the etch-stop tier.