Method of making a three-dimensional memory device using composite hard masks for formation of deep via openings
An alternating stack of first material layers and second material layers can be formed over a semiconductor material layer. A patterning film is formed over the alternating stack, and openings are formed through the patterning film. Via openings are formed through the alternating stack at least to a top surface of the semiconductor material layer by performing a first anisotropic etch process that transfers a pattern of the openings in the patterning film. A cladding liner can be formed on a top surface of the patterning film and sidewalls of the openings in the pattering film. The via openings can be vertically extended through the semiconductor material layer at least to a bottom surface of the semiconductor material layer by performing a second anisotropic etch process employing the cladding liner as an etch mask.
1. A method of forming a semiconductor structure, comprising:
forming an alternating stack of first material layers and second material layers over a semiconductor material layer;
forming a patterning film over the alternating stack;
forming openings through the patterning film;
forming via openings through the alternating stack at least to a top surface of the semiconductor material layer by performing a first anisotropic etch process that transfers a pattern of the openings in the patterning film;
forming a cladding liner on a top surface of the patterning film and sidewalls of the openings in the pattering film; and
vertically extending the via openings through the semiconductor material layer by performing a second anisotropic etch process employing the cladding liner as an etch mask.
2. The method of claim 1 , wherein the cladding liner comprises a horizontally-extending portion that overlies the top surface of the patterning film and a plurality of vertically-extending tubular portions having a respective upper edge that is adjoined to the horizontally-extending portion.
3. The method of claim 1 , wherein the cladding liner does not contact any sidewall of the alternating stack.
4. The method of claim 1 , wherein an entirety of the cladding liner is located above a horizontal plane located at a bottom surface of the patterning film.
5. The method of claim 1 , wherein the cladding liner consists essentially of a metallic material.
6. The method of claim 5 , wherein the cladding liner consists essentially of at least one material selected from Ru, Co, Mo, W, TaN, TiN, or WN.
7. The method of claim 5 , wherein the cladding liner is formed by anisotropic deposition of a metallic material over the patterning film after the first anisotropic etch process.
8. The method of claim 7 , wherein the cladding liner is deposited by a physical vapor deposition process or an atomic layer deposition process.
9. The method of claim 7 , wherein:
the cladding liner comprises a plurality of vertically-extending tubular portions located on sidewalls of the openings in the patterning film; and
each of the plurality of vertically-extending tubular portions of the cladding liner has a variable lateral width that increases with a vertical distance from the semiconductor material layer.
10. The method of claim 5 , wherein the cladding liner is formed by a selective metallic material deposition process that grows a metallic material from physically exposed surfaces of patterning film while suppressing growth of the metallic material from surfaces of the alternating stack and from surfaces of the semiconductor material layer.
11. The method of claim 10 , wherein the selective metallic material deposition process comprises an atomic layer deposition (ALD) process or a chemical vapor deposition (CVD) process.
12. The method of claim 10 , wherein:
the cladding liner comprises a plurality of vertically-extending tubular portions located on sidewalls of the openings in the patterning film; and
each of the plurality of vertically-extending tubular portions of the cladding liner has a uniform lateral thickness.
13. The method of claim 12 , wherein the cladding liner comprises a horizontally-extending portion that overlies the patterning film and having a same vertical thickness and the uniform lateral thickness.
14. The method of claim 1 , wherein the patterning film comprises amorphous carbon or diamond-like carbon at an atomic percentage in a range from 80% to 100%.
15. The method of claim 14 , wherein the patterning film has a homogenous material composition throughout.
16. The method of claim 14 , wherein the patterning film comprises:
a lower patterning film layer that comprises carbon atoms at an atomic percentage in a range from 99% to 100%; and
an upper patterning film layer that comprises at least one of boron or tungsten at an atomic concentration in a range from 0.2% to 20.
17. The method of claim 16 , wherein the cladding liner is formed by a selective deposition process that grows a cladding material from physically exposed surfaces of the upper patterning film layer while suppressing growth of the cladding material from surfaces of the lower patterning film layer, the alternating stack, and the semiconductor material layer.
18. The method of claim 1 , further comprising:
performing an ashing or a lift-off process that removes patterning film layer after the second anisotropic etch process; and
removing the cladding liner from above the alternating stack by lifting off the cladding liner during the ashing or lift-off process.
19. The method of claim 1 , further comprising:
forming semiconductor devices on substrate located below the semiconductor material layer;
forming lower-level metal interconnect structures embedded in lower-level dielectric material layers over the substrate, wherein the lower-level metal interconnect structures are electrically connected to the semiconductor devices; and
forming a layer stack including, from bottom to top, a lower source-level semiconductor layer, a source-level sacrificial layer, and the semiconductor material layer, wherein the second anisotropic etch process etches through the semiconductor material layer and the source-level sacrificial layer and into an upper portion of the lower source-level semiconductor layer.
20. The method of claim 19 , further comprising:
forming memory opening fill structures each comprising a memory film and a vertical semiconductor channel in the respective via openings;
forming a backside trench through the alternating stack, the semiconductor material layer and the source-level sacrificial layer and into an upper portion of the lower source-level semiconductor layer;
selectively etching the source-level sacrificial layer through the backside trench to form a source cavity;
etching a portion of the memory films exposed in the source cavity to expose sidewalls of the vertical semiconductor channels in the source cavity; and
forming a doped semiconductor source contact layer in the source cavity, wherein the doped semiconductor source contact layer contacts the exposed sidewalls of the vertical semiconductor channels.