Method of making a three-dimensional memory device using composite hard masks for formation of deep via openings
A method includes forming an alternating stack of first and second layers, forming a composite hard mask layer over the alternating stack, forming openings in the hard mask, and forming via openings through the alternating stack by performing an anisotropic etch process that transfers a pattern of the openings in the composite hard mask layer through the alternating stack. The compositing hard mask includes a first cladding material layer which has higher etch resistance than upper and lower patterning films of the composite hard mask.
1. A method of forming a semiconductor structure, comprising:
forming an alternating stack of first material layers and second material layers over a substrate;
forming a composite hard mask layer over the alternating stack, wherein the composite hard mask layer comprises a layer stack including a lower patterning film, a first cladding material layer overlying the lower patterning film, and an upper patterning film overlying the first cladding material layer;
forming a patterned photoresist layer including openings therethrough over the composite hard mask layer;
forming openings in the hard mask layer by performing a hard-mask-open anisotropic etch process that transfers a pattern of the openings in the photoresist layer through the hard mask layer; and
forming via openings through the alternating stack by performing an anisotropic etch process that transfers a pattern of the openings in the composite hard mask layer through the alternating stack,
wherein the upper patterning film functions as an etch mask at least during an initial phase of the anisotropic etch process and the first cladding material layer functions as an etch mask at least during a subsequent phase of the anisotropic etch process, and wherein the first cladding material layer has higher etch resistance than the upper patterning film and the lower patterning film during the anisotropic etch process.
2. The method of claim 1 , wherein the anisotropic etch process etches the alternating stack at a higher etch rate than the first cladding material layer, and collaterally etches the first cladding material layer at a lower etch rate than a material of the upper and the lower patterning films.
3. The method of claim 1 , wherein:
the lower patterning film comprises a first carbon-based material including carbon at a first atomic percentage in a range from 75% to 100%; and
the upper patterning film comprises a second carbon-based material including carbon at a second atomic percentage in a range from 75% to 100%.
4. The method of claim 3 , wherein the first cladding material layer comprises a transition metal layer.
5. The method of claim 4 , wherein the transition metal layer comprises tungsten, titanium, tantalum, niobium, molybdenum, or ruthenium.
6. The method of claim 4 , wherein the first cladding material layer further comprises:
a bottom adhesion liner contacting a bottom surface of the transition metal layer; and
a top adhesion liner contacting a top surface of the transition metal layer.
7. The method of claim 6 , wherein each of the bottom adhesion layer and the top adhesion layer comprise a respective material selected from a boron-carbon alloy material, a boron-nitrogen alloy material, or a metal nitride material.
8. The method of claim 3 , wherein the first cladding material layer comprises a conductive metal nitride material or a conductive metal carbide material.
9. The method of claim 3 , wherein the first cladding material layer comprises a semiconductor material or a dielectric metal oxide material having a dielectric constant greater than 7.9.
10. The method of claim 1 , further comprising performing a selective cladding material deposition process that grows an additional cladding material after performing the hard-mask-open anisotropic etch process and prior to performing the anisotropic etch process, wherein the additional cladding material grows from sidewalls of openings through the first cladding material layer, and does not grow from surfaces of the lower patterning film or from surfaces of the upper patterning film.
11. The method of claim 1 , wherein the composite hard mask layer further comprises:
an intermediate patterning film that is formed over the first cladding material layer; and
a second cladding material layer that is formed over the intermediate patterning film.
12. The method of claim 11 , wherein:
the upper patterning film is formed over the second cladding material layer; and
the hard-mask-open anisotropic etch process etches through the second cladding material layer and the intermediate patterning film prior to etching through the first cladding material layer and the lower patterning film.
13. The method of claim 12 , wherein each of the first cladding material layer and the second cladding material layer comprises a respective cladding material that is selected from:
a transition metal layer;
a conductive metal nitride material;
a conductive metal carbide material;
a semiconductor material; or
a dielectric metal oxide material having a dielectric constant greater than 7.9.
14. The method of claim 12 , wherein the first cladding material layer and the second cladding material layer have different material compositions.
15. The method of claim 12 , further comprising:
selectively growing an additional cladding material from a top surface and sidewalls of the second cladding material layer after the top surface of the second cladding material layer is exposed after an initial portion of the anisotropic etch step; and
continuing the anisotropic etch process after the selectively growing the additional cladding material.
16. The method of claim 12 , further comprising:
non-conformally depositing an additional cladding material over a top surface and sidewalls of the second cladding material layer after the top surface of the second cladding material layer is exposed after an initial portion of the anisotropic etch step, without depositing the additional cladding material on sidewalls of the alternating stack exposed in the via openings; and
continuing the anisotropic etch process after the non-conformally depositing the additional cladding material.
17. The method of claim 1 , further comprising:
selectively growing an additional cladding material from a top surface and sidewalls of the first cladding material layer after the top surface of the first cladding material layer is exposed after an initial portion of the anisotropic etch step; and
continuing the anisotropic etch process after the selectively growing the additional cladding material.
18. The method of claim 1 , further comprising:
non-conformally depositing an additional cladding material over a top surface and sidewalls of the first cladding material layer after the top surface of the first cladding material layer is exposed after an initial portion of the anisotropic etch step, without depositing the additional cladding material on sidewalls of the alternating stack exposed in the via openings; and
continuing the anisotropic etch process after the non-conformally depositing the additional cladding material.
19. The method of claim 1 , further comprising removing remaining portions of the composite hard mask after the anisotropic etch process.
20. The method of claim 1 , further comprising:
forming memory opening fill structures in the via openings, wherein each of the memory opening fill structures comprises a respective vertical semiconductor channel and a respective vertical stack of memory elements; and
replacing the second material layers with electrically conductive layers after formation of the memory opening fill structures.