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 an etch mask material layer containing an opening over the alternating stack; performing a first anisotropic etch process that etches unmasked upper portions of the alternating stack to form a via opening below the opening in the etch mask material layer; forming a combination of a non-conformal cladding liner and a conformal sacrificial spacer layer over the etch mask material layer and in peripheral portions of the via opening; performing a punch-through process that etches a horizontally-extending portion of the conformal sacrificial spacer layer from a bottom portion of the via opening; and vertically extending the via opening by performing a second anisotropic etch process that etches unmasked lower portions of the alternating stack selective to the non-conformal cladding liner and the conformal sacrificial spacer layer.
1 . A method of forming a structure, comprising:
forming an alternating stack of first material layers and second material layers over a substrate;
forming an etch mask material layer containing an opening over the alternating stack;
performing a first anisotropic etch process that etches unmasked upper portions of the alternating stack to form a via opening below the opening in the etch mask material layer;
forming a combination of a non-conformal cladding liner and a conformal sacrificial spacer layer over the etch mask material layer and in peripheral portions of the via opening;
performing a punch-through process that etches a horizontally-extending portion of the conformal sacrificial spacer layer from a bottom portion of the via opening; and
vertically extending the via opening by performing a second anisotropic etch process that etches unmasked lower portions of the alternating stack selective to the non-conformal cladding liner and the conformal sacrificial spacer layer.
2 . The method of claim 1 , wherein:
the non-conformal cladding liner is deposited by performing an anisotropic deposition process; and
the conformal sacrificial spacer layer is deposited by performing a conformal deposition process.
3 . The method of claim 2 , wherein:
the non-conformal cladding liner is deposited by a physical vapor deposition process or by a plasma-enhanced chemical vapor deposition process; and
the conformal sacrificial spacer layer is deposited by a low pressure chemical vapor deposition process or an atomic layer deposition process.
4 . The method of claim 1 , wherein the non-conformal cladding liner has a different composition than the conformal sacrificial spacer layer.
5 . The method of claim 4 , wherein the sacrificial spacer layer comprises amorphous silicon or polysilicon.
6 . The method of claim 4 , wherein the sacrificial spacer layer comprises undoped amorphous carbon, boron doped amorphous carbon, tungsten doped amorphous carbon, diamond-like carbon, graphene-like carbon or boron nitride.
7 . The method of claim 4 , wherein the non-conformal cladding liner comprises an electrically conductive material.
8 . The method of claim 7 , wherein the non-conformal cladding liner consists essentially of ruthenium, tungsten, molybdenum, titanium, tantalum, tungsten nitride, molybdenum nitride, titanium nitride, tantalum nitride, tungsten carbide, titanium carbide, or tantalum carbide.
9 . The method of claim 4 , wherein the non-conformal cladding liner comprises diamond-like carbon or silicon carbide.
10 . The method of claim 4 , wherein the non-conformal cladding liner comprises a dielectric metal oxide material having a dielectric constant greater than 7.9.
11 . The method of claim 1 , wherein:
the conformal sacrificial spacer layer is deposited directly on a top surface and a sidewall of the etch mask material layer and on a sidewall of the via opening; and
the non-conformal cladding liner is deposited on a top surface of the conformal sacrificial spacer layer.
12 . The method of claim 1 , wherein:
the non-conformal cladding liner is deposited directly on a top surface and a sidewall of the etch mask material layer; and
the conformal sacrificial spacer layer is deposited on a top surface of the non-conformal cladding liner and on a sidewall of the via opening.
13 . The method of claim 1 , wherein the etch mask material comprises a carbon-based material including carbon atoms at an atomic percentage greater than 95%.
14 . The method of claim 1 , wherein each of the first anisotropic etch process and the second anisotropic etch process comprise a respective reactive ion etch process.
15 . The method of claim 1 , wherein:
the first material layers comprise silicon oxide layers; and
the second material layers comprise silicon nitride layers.
16 . The method of claim 1 , wherein the non-conformal cladding liner and the conformal sacrificial spacer layer are completely removed collaterally during the second anisotropic etch process.
17 . The method of claim 1 , wherein:
the etch mask material layer contains additional openings therein, wherein the opening and the additional openings are arranged as a two-dimensional periodic array;
additional via openings are formed underneath the additional openings in the etch mask material layer during the first anisotropic etch process; and
the additional via openings are vertically extended through the alternating stack during the second anisotropic etch process.
18 . The method of claim 1 , wherein:
the opening through the etch mask material layer has an aspect ratio of at least 3 prior to performing the first anisotropic etch process;
the via opening has an aspect ratio of at least 10 after performing the first anisotropic etch process; and
the via opening has an aspect ratio of at least 20 after performing the second anisotropic etch process.
19 . The method of claim 1 , further comprising:
forming a blanket etch mask material layer having a uniform thickness and free of an opening therethrough over the alternating stack;
applying a photoresist layer over the blanket etch mask material layer;
lithographically patterning the photoresist layer to form at least one opening therethrough; and
anisotropically etching the blanket etch mask material layer employing the photoresist layer as an etch mask to form the etch mask material layer containing the opening therethrough.
20 . The method of claim 1 , further comprising forming a memory opening fill structure in the via opening, wherein the memory opening fill structure comprises a vertical semiconductor channel and a memory film.