Etching polysilicon
Methods and compositions for etching polysilicon including aqueous compositions containing nitric acid and ammonium fluoride, and apparatus formed thereby.
1. A method, comprising:
exposing polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride;
wherein the aqueous composition comprises a water content of less than 39 wt %.
2. The method of claim 1 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition comprises a water content of less than or equal to 35 wt %.
3. The method of claim 1 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition comprises 65-70 wt % nitric acid and 0.06-0.6 wt % ammonium fluoride.
4. The method of claim 3 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition further comprises hydrofluoric acid.
5. The method of claim 3 or 4 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition further comprises poly-carboxylic acid at 0.4 wt % or less.
6. The method of claim 5 , further comprising exposing the polysilicon to the aqueous composition comprising poly-carboxylic acid at 0.4 wt % or less, wherein the poly-carboxylic acid is oxalic acid.
7. The method of claim 1 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition comprises 65-70 wt % nitric acid, 0.06-0.6 wt % ammonium fluoride, 0.00-0.08 wt % hydrofluoric acid, and oxalic acid at 0.4 wt % or less.
8. The method of claim 1 , wherein exposing polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride comprises exposing the polysilicon to the aqueous composition in the presence of an oxide.
9. The method of claim 7 , wherein exposing the polysilicon to the aqueous composition in the presence of an oxide comprises exposing the polysilicon to the aqueous composition in the presence of a silicon oxide or a silicon oxynitride.
10. The method of claim 1 , wherein exposing polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride comprises exposing a boron-doped polysilicon to the aqueous composition.
11. The method of claim 10 , further comprising exposing the boron-doped polysilicon to the aqueous composition in the presence of a silicon oxide or a silicon oxynitride.
12. A method of forming NAND string of memory cells, comprising:
forming alternating instances of polysilicon and oxide;
forming an opening through the alternating instances of polysilicon and oxide;
removing portions of the instances of polysilicon selective to the instances of oxide; and
for at least one of the instances of polysilicon, following removal of the portions of the instances of polysilicon, forming a data-storage structure between the at least one instance of polysilicon and a semiconductor;
wherein removing portions of the instances of polysilicon selective to the instances of oxide comprises:
exposing the instances of polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride;
wherein the aqueous composition comprises a water content of less than 39 wt %.
13. The method of claim 12 , wherein exposing the instances of polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride comprises exposing the instances of polysilicon to the aqueous composition, wherein the aqueous composition comprises 65-70 wt % nitric acid, 0.06-0.6 wt % ammonium fluoride, and oxalic acid at 0.4 wt % or less.
14. The method of claim 12 , wherein exposing the instances of polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride comprises exposing the polysilicon to the aqueous composition, wherein the aqueous composition consists essentially of nitric acid, poly-carboxylic acid, ammonium fluoride, and water.
15. The method of claim 12 , further comprising:
forming a first dielectric between the data-storage structure and the semiconductor; and
forming a second dielectric between the data-storage structure and the at least one instance of polysilicon.
16. The method of claim 15 , wherein forming the second dielectric comprises forming a thermal oxide on the at least one instance of polysilicon and forming another dielectric on the thermal oxide.
17. The method of claim 12 , wherein forming a data-storage structure between the at least one instance of polysilicon and a semiconductor comprises forming a second polysilicon and exposing the second polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride.
18. The method of claim 4 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition further comprises hydrofluoric acid at 0.08 wt % or less.
19. The method of claim 4 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition further comprises poly-carboxylic acid at 0.4 wt % or less.
20. The method of claim 13 , wherein exposing the instances of polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride comprises exposing the instances of polysilicon to the aqueous composition, wherein the aqueous composition further comprises hydrofluoric acid at 0.08 wt % or less.
21. A method, comprising:
exposing polysilicon to an aqueous composition comprising nitric acid, poly-carboxylic acid and ammonium fluoride;
wherein the aqueous composition comprises 65-70 wt % nitric acid;
wherein the aqueous composition comprises 0.06-0.6 wt % ammonium fluoride; and
wherein the aqueous composition comprises poly-carboxylic acid at 0.4 wt % or less.
22. The method of claim 21 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition further comprises hydrofluoric acid.
23. The method of claim 22 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition further comprises hydrofluoric acid at 0.08 wt % or less.
24. The method of claim 23 , further comprising exposing the polysilicon to the aqueous composition, wherein the aqueous composition consists essentially of nitric acid, ammonium fluoride, poly-carboxylic acid, hydrofluoric acid and water.