Method of making a three-dimensional memory device using composite hard masks for formation of deep via openings
A method of forming a structure includes forming an alternating stack of first material layers and second material layers over a substrate, forming a first etch mask material layer, forming a first cladding liner, and forming a via opening through the alternating stack by performing an anisotropic etch process that employs a combination of at least the first cladding liner and the first etch mask material layer as a composite etch mask structure.
1. A method of forming a structure, comprising:
forming an alternating stack of first material layers and second material layers over a substrate;
forming a first etch mask material layer comprising a first etch mask material over the alternating stack;
forming a first cladding liner comprising a first cladding material on a top surface of the first etch mask material layer and on a sidewall of the first etch mask material layer; and
forming a via opening through the alternating stack by performing an anisotropic etch process that employs a combination of at least the first cladding liner and the first etch mask material layer;
wherein:
the anisotropic etch process comprises a first anisotropic etch step that etches materials of the alternating stack selective to the first etch mask material and the first cladding material;
the first anisotropic etch step collaterally removes a horizontally-extending portion of the first cladding liner and collaterally vertically recesses the first etch mask material layer such that a vertically-extending portion of the first cladding liner protrudes above a top surface of a remaining portion of the first etch mask material layer during the first anisotropic etch step; and
the top surface of the remaining portion of the first etch mask material layer has a concave vertical cross-sectional profile which functions as an ion trap during the first anisotropic etch step.
2. The method of claim 1 , wherein the step of forming the first etch mask material layer comprises anisotropically depositing the first etch mask material and isotropically recessing the first etch mask material.
3. The method of claim 2 , wherein the step of forming the first cladding liner comprises anisotropically depositing the first cladding material over the first etch mask material layer and isotropically recessing the first cladding material.
4. The method of claim 2 , wherein the step of forming the first cladding liner comprises performing a selective material deposition process that grows the first cladding material from physically exposed surfaces of the first etch mask material layer.
5. The method of claim 1 , further comprising:
forming a mask layer over the alternating stack prior to forming the first etch mask material layer; and
forming an opening in the mask layer.
6. The method of claim 5 , wherein:
the first etch mask material layer is located entirely above a first horizontal plane including a top surface of the mask layer; and
the composite etch mask structure further comprises the mask layer.
7. The method of claim 1 , wherein the first anisotropic etch step employs a first etch chemistry having a higher etch selectivity for the first etch mask material than for the first cladding material.
8. The method of claim 7 , wherein the top surface of the remaining portion of the first etch mask material layer is adjoined to an inner sidewall of the vertically-extending portion of the first cladding liner.
9. The method of claim 1 , wherein a vertically-extending portion of the first cladding liner has a variable lateral width that increases with a vertical distance from a topmost surface of the alternating stack.
10. The method of claim 1 , further comprising forming a combination of a second etch mask material layer and a second cladding liner over the first cladding liner, wherein the combination of the second etch mask layer and the second cladding liner has a pattern that replicates a pattern of the first cladding liner.
11. The method of claim 10 , wherein:
the second cladding liner comprises a same material as the first cladding liner; and
the second etch mask material layer comprises a same material as the first etch mask material layer.
12. The method of claim 10 , wherein:
the second etch mask material layer is formed by anisotropically depositing a second etch mask material and isotropically recessing the second etch mask material; and
the second cladding liner is formed by anisotropically depositing a second cladding material and isotropically recessing the second cladding material.
13. The method of claim 12 , wherein the second etch mask material layer is formed entirely above a second horizontal plane including a top surface of the first cladding liner.
14. The method of claim 12 , further comprising forming a combination of a third etch mask material layer and a third cladding liner over the second cladding liner, wherein the combination of the third etch mask layer and the third cladding liner has a pattern that replicates the pattern of the second cladding liner.
15. The method of claim 14 , wherein:
the third etch mask material layer is formed by anisotropically depositing a third etch mask material and isotropically recessing the third etch mask material; and
the third cladding liner is formed by anisotropically depositing a third cladding material and isotropically recessing the second cladding material.
16. The method of claim 1 , wherein each of the first etch mask material and the first cladding material is selected from:
carbon-based material comprising carbon atoms at a respective atomic percentage that is greater than 50%;
silicon carbide;
elemental metal;
intermetallic alloy;
metallic nitride material; or
dielectric metal oxide material.
17. The method of claim 1 , wherein:
the first etch mask material comprises a carbon-based material including carbon atoms at an atomic percentage greater than 95%; and
the first cladding material comprises a metal doped carbon or a metal or a metal silicide.
18. The method of claim 5 , further comprising forming an in-process via opening through a subset of layers within the alternating stack by performing an additional anisotropic etch process employing the mask layer after formation of the opening in the mask layer.
19. The method of claim 18 , wherein:
the first etch mask material layer is formed after formation of the in-process via opening; and
the via opening is formed by vertically extending the in-process via opening using the anisotropic etch process that employs the combination of at least the mask layer, the first cladding liner and the first etch mask material layer.
20. The method of claim 19 , wherein:
the first material layers comprise silicon oxide layers;
the second material layers comprise silicon nitride layers; and
the anisotropic etch process comprises a reactive ion etch step that employs at least one of O 2 , N 2 O, H 2 , CO 2 , or NH 3 .