U.S. patent application number 15/098253 was filed with the patent office on 2017-10-19 for nano-imprinted self-aligned multi-level processing method.
The applicant listed for this patent is Western Digital Technologies, Inc.. Invention is credited to Mac D. APODACA, Daniel Robert SHEPARD.
Application Number | 20170301729 15/098253 |
Document ID | / |
Family ID | 60038459 |
Filed Date | 2017-10-19 |
United States Patent
Application |
20170301729 |
Kind Code |
A1 |
APODACA; Mac D. ; et
al. |
October 19, 2017 |
NANO-IMPRINTED SELF-ALIGNED MULTI-LEVEL PROCESSING METHOD
Abstract
The present disclosure generally relates to fine geometry
electrical circuits and methods of manufacture thereof. More
specifically, methods for forming 3D cross-point memory arrays
using a single nano-imprint lithography step and no
photolithography are disclosed. The method includes imprinting a
multilevel topography pattern, transferring the multilevel
topography pattern to a substrate, filling the etched multilevel
topography pattern with hard mask material, planarizing the hard
mask material to expose a first portion of the substrate, etching a
first trench in the first portion of the substrate, depositing a
first plurality of layers in the first trench, planarizing the hard
mask material to expose a second portion of the substrate, etching
a second trench in the second portion of the substrate and
depositing a second plurality of layers in the second trench. The
method is repeated until a 4F.sup.2 3D cross-point memory array has
been formed.
Inventors: |
APODACA; Mac D.; (San Jose,
CA) ; SHEPARD; Daniel Robert; (North Hampton,
NH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Western Digital Technologies, Inc. |
San Jose |
CA |
US |
|
|
Family ID: |
60038459 |
Appl. No.: |
15/098253 |
Filed: |
April 13, 2016 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 45/1233 20130101;
H01L 45/04 20130101; H01L 45/085 20130101; H01L 27/11551 20130101;
H01L 27/10823 20130101; H01L 27/10864 20130101; H01L 27/2427
20130101; H01L 27/10876 20130101; H01L 29/1037 20130101; H01L
27/2481 20130101; H01L 27/11521 20130101; H01L 27/112 20130101;
H01L 45/1266 20130101; H01L 45/1683 20130101; H01L 27/249 20130101;
H01L 45/06 20130101 |
International
Class: |
H01L 27/24 20060101
H01L027/24; H01L 45/00 20060101 H01L045/00; H01L 27/24 20060101
H01L027/24; H01L 45/00 20060101 H01L045/00; H01L 45/00 20060101
H01L045/00; H01L 45/00 20060101 H01L045/00 |
Claims
1-8. (canceled)
9. A method comprising: planarizing a hard mask material to expose
a first portion of a substrate; etching a first trench into the
first portion of the substrate; depositing a first plurality of
layers in the first trench; planarizing the hard mask material to
expose a second portion of the substrate; etching a second trench
into the second portion of the substrate; depositing a second
plurality of layers in the second trench; planarizing the hard mask
material to expose a third portion of the substrate; etching a
third trench into the third portion of the substrate; and
depositing a third plurality of layers in the third trench, wherein
the first portion has a first height, the second portion has a
second height and the third portion has a third height, and wherein
the second height is less than the first height and the third
height is less than the second height.
10. A method comprising: planarizing a hard mask material to expose
a first portion of a substrate; etching a first trench into the
first portion of the substrate; depositing a first plurality of
layers in the first trench; planarizing the hard mask material to
expose a second portion of the substrate; etching a second trench
into the second portion of the substrate; depositing a second
plurality of layers in the second trench; planarizing the hard mask
material to expose a third portion of the substrate; etching a
third trench into the third portion of the substrate; and
depositing a third plurality of layers in the third trench, wherein
the first planarized hard mask material covers the second portion
and the third portion.
11. A method comprising: planarizing a hard mask material to expose
a first portion of a substrate; etching a first trench into the
first portion of the substrate; depositing a first plurality of
layers in the first trench; planarizing the hard mask material to
expose a second portion of the substrate; etching a second trench
into the second portion of the substrate; depositing a second
plurality of layers in the second trench; planarizing the hard mask
material to expose a third portion of the substrate; etching a
third trench into the third portion of the substrate; and
depositing a third plurality of layers in the third trench, wherein
the second planarized hard mask material covers the first portion
and the third portion.
12. A method comprising: planarizing a hard mask material to expose
a first portion of a substrate; etching a first trench into the
first portion of the substrate; depositing a first plurality of
layers in the first trench; planarizing the hard mask material to
expose a second portion of the substrate; etching a second trench
into the second portion of the substrate; depositing a second
plurality of layers in the second trench; planarizing the hard mask
material to expose a third portion of the substrate; etching a
third trench into the third portion of the substrate; and
depositing a third plurality of layers in the third trench, wherein
the third planarized hard mask material covers the first portion
and the second portion.
13. A method, comprising: planarzing a hard mask material to expose
a first portion of a substrate; etching a first trench into the
first portion of the substrate; filling the first trench with a
first metal material; etching the first metal material to form a
first layer of first metal material; filling the first trench with
a dielectric material; etching the dielectric material; filling the
first trench with the first metal material; etching the first metal
material to form a second layer of first metal material; filling
the first trench with the dielectric material; etching the
dielectric material; and filling the first trench with a first
additional amount of hard mask material.
14. The method of claim 13, further comprising: planarizing the
hard mask material to expose a second portion of the substrate;
etching a second trench into the second portion of the substrate;
filling the second trench with the first metal material; etching
the first metal material to form a third layer of first metal
material.
15. The method of claim 14, further comprising: filling the second
trench with a memory cell information storage material; etching the
memory cell information storage material to form a first layer of
memory cell information storage material; filling the second trench
with an ovonic threshold switching material; and etching the ovonic
threshold switching material to form a first layer of ovonic
threshold switching material.
16. The method of claim 15, further comprising: filling the second
trench with a second metal material; etching the second metal
material to form a first layer of second metal material; filling
the trench with the dielectric material; etching the dielectric
material; filling the second trench with the first metal material;
and etching the first metal material to form a fourth layer of
first metal material.
17. The method of claim 16, further comprising: filling the second
trench with the memory cell information storage material; etching
the memory cell information storage material to form a second layer
of memory cell information storage material; filling the second
trench with the ovonic threshold switching material; and etching
the ovonic threshold switching material to form a second layer of
ovonic threshold switching material.
18. The method of claim 17, further comprising: filling the second
trench with the second metal material; etching the second metal
material to form a second layer of second metal material; and
filling the second trench with a second additional amount of hard
mask material.
19. The method of claim 18, further comprising: planarzing the hard
mask material to expose a third portion of the substrate; etching a
third trench into the third portion of the substrate; filling the
third trench with the second metal material; and etching the second
metal material to form a third layer of second metal material.
20. The method of claim 19, wherein the wherein the first portion
has a first height, the second portion has a second height and the
third portion has a third height, and wherein the second height is
less than the first height and the third height is less than the
second height.
21. The method of claim 19, wherein the first planarized hard mask
material covers the second portion and the third portion.
22. The method of claim 19, wherein the second planarized hard mask
material covers the first portion and the third portion.
23. The method of claim 19, wherein the third planarized hard mask
material covers the first portion and the second portion.
24. The method of claim 19, further comprising: filling the third
trench with a dielectric material; etching the dielectric material;
filling the third trench with the second metal material; and
etching the second metal material to form a fourth layer of second
metal material.
Description
BACKGROUND OF THE DISCLOSURE
Field of the Disclosure
[0001] Embodiments of the present disclosure generally relate to
data storage and computer memory systems, and more particularly to
methods of fabricating fine geometry electrical circuits, such as
3D cross-point memory arrays.
Description of the Related Art
[0002] Semiconductor manufacturing of memory devices allows for
high density to be achieved by constructing the arrays of data bits
at very small geometries. The memory arrays include memory element
layers and selector layers sandwiched between first metal layers
and second metal layers, which run orthogonal the first metal
layers. A single memory array may include a plurality of each of
the aforementioned layers.
[0003] Because of the orthogonal orientation, memory arrays are
traditionally constructed one layer at a time using a lithography
step at each layer to rotate the pattern. Lithographic patterning,
however, has its disadvantages. Lithography is the most costly step
in a semiconductor manufacturing process, especially when those
steps are for patterning the bit lines and words lines of a
cross-point memory array at the finest geometry. Furthermore, each
lithographic patterning step for each layer of final memory takes
time and alignment of each of the layers takes additional time and
may reduce overall yield.
[0004] Thus, there is a need in the art for an improved method for
forming fine geometry electrical circuits, such as 3D cross-point
memory arrays.
SUMMARY OF THE DISCLOSURE
[0005] The present disclosure generally relates to fine geometry
electrical circuits and methods of manufacture thereof. More
specifically, methods for forming 3D cross-point memory arrays
using a single nano-imprint lithography step and no
photolithography are disclosed. The method includes imprinting a
multilevel topography pattern, transferring the multilevel
topography pattern to a substrate, filling the etched multilevel
topography pattern with hard mask material, planarizing the hard
mask material to expose a first portion of the substrate, etching a
first trench in the first portion of the substrate, depositing a
first plurality of layers in the first trench, planarizing the hard
mask material to expose a second portion of the substrate, etching
a second trench in the second portion of the substrate and
depositing a second plurality of layers in the second trench. The
method is repeated until a 4F.sup.2 3D cross-point memory array has
been formed.
[0006] In one embodiment, a memory device is disclosed. The memory
device includes a first plurality of layers disposed in a first
trench, a second plurality of layers in a second trench and a third
plurality of layers in a third trench. The first plurality of
layers includes a first layer of first metal material and a second
layer of first metal material. The second plurality of layers
includes a third layer of first metal material, a first layer of
second metal material, a fourth layer of first metal material and a
second layer of second metal material. The third layer of first
metal material is coplanar with the first layer of first metal
material in the first trench. The fourth layer of first metal
material is coplanar with the second layer of first metal material
in the first trench. The third plurality of layers disposed in a
third trench includes a third layer of second metal material and a
fourth layer of second metal material. The third layer of second
metal material is coplanar with the first layer of second metal
material. The fourth layer of second metal material is coplanar
with the second layer of second metal material. A depth of the
first trench and a depth of the second trench are equal. A depth of
the third trench is less than the depth of the first trench and the
depth of the second trench.
[0007] In another embodiment, a method is disclosed. The method
includes planarzing a hard mask material to expose a first portion
of a substrate, etching a first trench into the first portion of
the substrate, depositing a first plurality of layers in the first
trench, planarizing the hard mask material to expose a second
portion of a substrate, etching a second trench into the second
portion of the substrate and depositing a second plurality of
layers in the second trench.
[0008] In another embodiment, a method is disclosed. The method
includes planarzing a hard mask material to expose a first portion
of a substrate, etching a first trench into the first portion of
the substrate, filling the first trench with a first metal
material, etching the first metal material to form a first layer of
first metal material, filling the first trench with a dielectric
material, etching the dielectric material, filling the first trench
with the first metal material, etching the first metal material to
form a second layer of first metal material, filling the first
trench with the dielectric material, etching the dielectric
material and filling the first trench with a first additional
amount of hard mask material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] So that the manner in which the above recited features of
the present disclosure can be understood in detail, a more
particular description of the disclosure, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this disclosure and are therefore not to be considered limiting of
its scope, for the disclosure may admit to other equally effective
embodiments.
[0010] FIG. 1 is a schematic diagram of a memory array according to
one embodiment described herein.
[0011] FIG. 2 is a schematic perspective view of the memory array
according to one embodiment described herein.
[0012] FIG. 3 illustrates operations of a method for forming a 3D
cross-point memory array according to embodiments described
herein.
[0013] FIGS. 4A-4Y depict a 3D cross-point memory array at various
stages of the methods described herein.
[0014] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
disclosed in one embodiment may be beneficially utilized on other
embodiments without specific recitation.
DETAILED DESCRIPTION
[0015] In the following, reference is made to embodiments of the
disclosure. However, it should be understood that the disclosure is
not limited to specific described embodiments. Instead, any
combination of the following features and elements, whether related
to different embodiments or not, is contemplated to implement and
practice the disclosure. Furthermore, although embodiments of the
disclosure may achieve advantages over other possible solutions
and/or over the prior art, whether or not a particular advantage is
achieved by a given embodiment is not limiting of the disclosure.
Thus, the following aspects, features, embodiments and advantages
are merely illustrative and are not considered elements or
limitations of the appended claims except where explicitly recited
in a claim(s). Likewise, reference to "the disclosure" shall not be
construed as a generalization of any inventive subject matter
disclosed herein and shall not be considered to be an element or
limitation of the appended claims except where explicitly recited
in a claim(s).
[0016] The present disclosure generally relates to fine geometry
electrical circuits and methods of manufacture thereof. More
specifically, methods for forming 3D cross-point memory arrays
using a single nano-imprint lithography step and no
photolithography are disclosed. The method includes imprinting a
multilevel topography pattern, transferring the multilevel
topography pattern to a substrate, filling the etched multilevel
topography pattern with hard mask material, planarizing the hard
mask material to expose a first portion of the substrate, etching a
first trench in the first portion of the substrate, depositing a
first plurality of layers in the first trench, planarizing the hard
mask material to expose a second portion of the substrate, etching
a second trench in the second portion of the substrate and
depositing a second plurality of layers in the second trench. The
method is repeated until a 4F.sup.2 3D cross-point memory array has
been formed.
[0017] FIG. 1 is a schematic diagram of a memory array 100
according to one embodiment described herein. The memory array 100
includes a plurality of memory cells 102, a first plurality of
parallel lines 104 and a second plurality of parallel lines 106.
The first plurality of parallel lines 104 runs orthogonal to the
second plurality of parallel lines 106. The first plurality of
parallel lines 104 may represent bit lines and the second plurality
of parallel lines 106 may represent word lines. Each memory cell
102 is coupled to a bit line 104 and a word line 106. Co-linear
memory cells 102 are coupled to one common line and one line not in
common with the other co-linear memory cells 102.
[0018] FIG. 2 is a schematic perspective view of the above
described memory array 100 according to one embodiment described
herein. The first plurality of parallel lines 104 is disposed in a
common plane. The second plurality of parallel lines 106 is
disposed in a common plane spaced above the first plurality of
parallel lines 104. The memory array 100 is arranged such that a
first memory cell 102A is coupled to a first line 104A of the first
plurality of parallel lines 104. The first memory cell 102A is also
coupled to a first line 106A of the second plurality of parallel
lines 106. A second memory cell 102B is coupled to the first line
104A and a second line 106B of the second plurality of parallel
lines 106. A third memory cell 102C is coupled to a second line
104B of the first plurality of parallel lines 104. The third memory
cell 102C is also coupled to the first line 106A. A fourth memory
cell 102D is coupled to both the second line 104B and second line
106B. It is to be understood that while four lines 104A-104D of the
first plurality of parallel lines 104 are shown, more or less lines
may be present. Additionally, it is also to be understood that
while four lines 106A-106D are shown of the second plurality of
parallel lines 106, more or less lines may be present.
[0019] While 4F.sup.2 is a typical limit for cross-point memories,
it is contemplated that the memory cell footprint may also be
larger or smaller than 4F.sup.2 in certain embodiments of the
present disclosure. In some embodiments, the space between the
memory cells may be smaller than 1F, thus less than 4F.sup.2. In
other embodiments, for example, in most MRAM devices, the space
between the memory cells may be larger than 12F.sup.2, and thus
greater than 4F.sup.2. If the memory cell stores two or more bits
per cell, the area is generally divided by the number of bits in
order to calculate the effective footprint of a memory cell. As
such, each memory cell of the present disclosure may have a
sub-lithographic footprint (i.e., a footprint smaller than less
than 4F.sup.2), a 4F.sup.2 footprint, or a footprint greater than
4F.sup.2. The amount of logic located at each memory cell may be
located to enable the formation of the defined pulse while fitting
within a footprint of greater than, less than, or equal to
4F.sup.2.
[0020] FIG. 3 illustrates operations of a method 300 for forming a
3D cross-point memory array according to embodiments described
herein. FIGS. 4A-4Y depict a 3D cross-point memory array 400 at
various stages of the methods described herein. Prior to operation
310, the method begins with the imprinting of a multilevel
topography pattern. The multilevel topography pattern is then
transferred to the substrate 402. The pattern may be transferred
using any suitable etching process. The multilevel topography
pattern etched into the substrate 402 is then filled with a hard
mask material 404. Filling the multilevel topography pattern may be
accomplished by physical vapor deposition (PVD), chemical vapor
deposition (CVD) or any other suitable deposition process. The
substrate 402 may be an oxide material or any other suitable
substrate material. The hard mask material 404 may be any suitable
hard mask material.
[0021] At operation 310, the hard mask material 404 is planarized
to expose a first portion 402A of the substrate 402, as shown in
FIG. 4A. As a result of the patterning of the multilevel topography
pattern into the substrate 402, the first portion 402A has a first
height. The planarization may be performed by chemical mechanical
planarization (CMP), which is a polishing process utilizing
chemical and mechanical forces for surface smoothing. By
planarizing the hard mask material 404 to expose the first portion
402A, the hard mask material 404 protects all of the substrate 402
except for the exposed first portion 402A. At operation 320, a
first trench 406 is etched into the first portion 402A of the
substrate 402, as shown in FIG. 4B. The first trench 406 is not
etched all the way through the first portion 402A of the substrate
402. In other words a portion of the substrate 402 remains at the
bottom of the first trench 406. In one example, etching the first
trench 406 may be accomplished using a reactive ion etch (RIE).
Alternatively, etching the first trench 406 may be accomplished by
placing an etch stop barrier at the desired depth of the first
trench 406 or by using a timed etch to etch the first trench 406
down to the desired depth.
[0022] At operation 330, a first plurality of layers is deposited
in the first trench 406. More specifically, the first trench 406 is
filled with a first metal material 408, as shown in FIG. 4C. The
first metal material 408 may be physical vapor deposition (PVD)
Tungsten or any other suitable metal material. The first metal
material 408 is then etched back down to form a first layer 408A of
first metal material 408 at the bottom of the first trench 406, as
shown in FIG. 4D. The etching of the first metal material 408 may
be a timed etch or any other suitable etch process. Next, the first
trench 406 is filled with a dielectric material 410, as shown in
FIG. 4E. The dielectric material 410 may be an oxide dielectric
material or any suitable dielectric material. The dielectric
material 410 is then etched back down to a desired depth in the
first trench 406, as shown in FIG. 4F. The etching of the
dielectric material 410 may be a timed etch or any other suitable
etch process.
[0023] Next, the first trench 406 is again filled with the first
metal material 408, as shown in FIG. 4G. The first metal material
408 is then etched back down to form a second layer 408B of the
first metal material 408 in the first trench 406, as shown in FIG.
4H. The etching of the first metal material 408 may be a timed etch
or any other suitable etch process. The first trench 406 is
re-filled with the dielectric material 410, as shown in FIG. 4I.
The dielectric material 410 is then etched back down to a desired
depth in the first trench 406, as shown in FIG. 4J. The etching of
the dielectric material 410 may be a timed etch or any other
suitable etch process. The first trench 406 is then filled a first
additional amount of hard mask material 404A, as shown in FIG.
4K.
[0024] While the paragraphs above describe deposition of a first
layer 408A of first metal material 408 and a second layer 408B of
first metal material 408, the above described operations may be
repeated to deposit additional layers of the first metal material
408 in the first trench 406. For example, the operations may be
repeated to deposit two additional layers of the first metal
material 408 in the first trench 406 such that a 4F.sup.2 3D
cross-point memory array may be formed.
[0025] At operation 340, the hard mask material 404 is planarized
to expose a second portion 402B of the substrate 402, as shown in
FIG. 4L. The exposed section portion 402B of the substrate 402 is
self-aligned to the first portion 402A of the substrate 402. The
section portion 402B has a second height that is less than the
first height of the first portion 402A. The planarization may be
performed by CMP planarization. By planarizing the hard mask
material 404 to expose the second portion 402B, the hard mask
material 404 protects all of the substrate 402 except for the
exposed second portion 402B. At operation 350, a second trench 412
is etched into the second portion 402B of the substrate 402, as
shown in FIG. 4M. The second trench 412 is etched down such that
the bottom of the second trench 412 is coplanar with the bottom of
the first trench 406 and a portion of the substrate 402 remains at
the bottom of the second trench 412. In one example, etching the
second trench 412 may be accomplished using an RIE etch.
Alternatively, etching the second trench 412 may be accomplished by
placing an etch stop barrier at the desired depth of the second
trench 412 or by using a timed etch to etch the second trench 412
down to the desired depth.
[0026] At operation 360, a second plurality of layers is deposited
in the second trench 412. The second trench 412 is first filled
with the first metal material 408. The first metal material 408 is
then etched back down such that a third layer 408C of first metal
material 408 is formed coplanar with the first layer 408A of first
metal material 408, as shown in FIG. 4N. The third layer 408C and
the first layer 408A are disposed coplanar to one another such that
they connect and begin to form either a word line or a bit line of
a 4F.sup.2 3D cross-point memory array.
[0027] The second trench 412 is then filled with a memory cell
information storage material 414. The memory cell information
storage material 414 may be a resistive random access memory (RAM)
material, a phase change material or any other suitable memory cell
information storage material. The memory cell information storage
material 414 is then etched back down to a desired depth and a
first layer 414A of memory cell information storage material 414 is
disposed over the third layer 408C of first metal material 408, as
shown in FIG. 4O. In one example, the first layer 414A of memory
cell information storage material 414 is disposed on and in contact
with the third layer 408C of the first metal material 408. The
etching of the memory cell information storage material 414 may be
a timed etch or any other suitable etching process.
[0028] Next, the second trench 412 is filled with an ovonic
threshold switching (OTS) material 416. The OTS material 416 is
then etched back down to a desired depth and a first layer 416A of
OTS material 416 is disposed over the first layer 414A of memory
cell information storage material 414, as shown in FIG. 4P. In one
example, the first layer 416A of OTS material 416 is disposed on
and in contact with the first layer 414A of the memory cell
information storage material 414. The etching of the OTS material
416 may be a timed etch or any other suitable etching process.
[0029] The second trench 412 is then filled with a second metal
material 418. The second metal material 418 may be Titanium Nitride
or any other suitable metal material. The second metal material 418
is then etched back down to form a first layer 418A of second metal
material 418 over the first layer 416A of OTS material 416, as
shown in FIG. 4Q. The etching of the second metal material 418 may
be a timed etch or any other suitable etch process.
[0030] The second trench 412 is then filled with the dielectric
material 410. The dielectric material 410 is then etched back down
to a desired depth in the second trench 412, as shown in FIG. 4R.
The etching of the dielectric material 410 may be a timed etch or
any other suitable etch process.
[0031] The aforementioned operations are repeated to form
additional layers in the second trench, including a fourth layer
408D of first metal material 408, a second layer 414B of memory
cell information storage material 414, a second layer 416B of OTS
material 416, and a second layer 418B of second metal material 418,
as shown in FIG. 4S. In one example, the fourth layer 408D of the
first metal material 408 is disposed over the dielectric material
410, the second layer 414B of memory cell information storage
material 414 is disposed over the fourth layer 408D of the first
metal material 408, the second layer 416B of OTS material 416 is
disposed over the second layer 414B of memory cell information
storage material 414, and the second layer 418B of second metal
material 418 is disposed over the second layer 416B of OTS material
416. In a further example, the fourth layer 408D of the first metal
material 408 is disposed on and in contact with the dielectric
material 410, the second layer 414B of memory cell information
storage material 414 is disposed on and in contact with the fourth
layer 408D of the first metal material 408, the second layer 416B
of OTS material 416 is disposed on and in contact with the second
layer 414B of memory cell information storage material 414, and the
second layer 418B of second metal material 418 is disposed on and
in contact with the second layer 416B of OTS material 416. The
aforementioned operations may be repeated such that a 4F.sup.2 3D
cross-point memory array may be formed.
[0032] After the second plurality of layers has been formed in the
second trench 412, a second additional amount of hard mask material
404B is deposited in the second trench 412. The hard mask material
404 is then planarized to expose a third portion 402C of the
substrate 402, as shown in FIG. 4T. The exposed third portion 402C
of the substrate 402 is self-aligned to the second portion 402B of
the substrate 402. The third portion 402C has a third height that
is less than the second height of the second portion 402B and the
first height of the first portion 402A. The planarization may be
performed by CMP planarization. By planarizing the hard mask
material 404 to expose the third portion 402C, the hard mask
material 404 protects all of the substrate 402 except for the
exposed third portion 402C. A third trench 420 is etched into the
third portion 402C of the substrate 402, as shown in FIG. 4U. The
third trench 420 is etched down such that the bottom of the third
trench 420 is coplanar with the bottom of the first layer 418A of
second metal material 418. In one example, etching the third trench
420 may be accomplished using an RIE etch. Alternatively, etching
the third trench 420 may be accomplished by placing an etch stop
barrier at the desired depth of the third trench 420 or by using a
timed etch to etch the third trench 420 down to the desired
depth.
[0033] Next, the third trench 420 is filled with a third plurality
of layers. The third trench 420 is first filled with second metal
material 418. The second metal material 418 is then etched back
down such that a third layer 418C of second metal material 418 is
formed at the bottom of the third trench 420 and coplanar with the
first layer 418A of second metal material 418, as shown in FIG. 4V.
The third layer 418C and the first layer 418A are disposed coplanar
to one another such that they connect and begin to form either a
word line or a bit line of a 4F.sup.2 3D cross-point memory array.
The etching of the second metal material 418 may be a timed etch or
any other suitable etch process.
[0034] Next, the third trench 420 is filled with dielectric
material 410. The dielectric material 410 is then etched back down
such that the top surface of the dielectric material 410 in the
third trench 420 is coplanar with the bottom surface of the second
layer 418B of second metal material 418 in the second trench 412,
as shown in FIG. 4W. The etching of the dielectric material 410 may
be a timed etch or any other suitable etch process.
[0035] Then, the third trench 420 is again filled with the second
metal material 418. The second metal material 418 is then etched
back down such that a fourth layer 418D of second metal material
418 is formed coplanar with the second layer 418B of second metal
material 418, as shown in FIG. 4X. The fourth layer 418D and the
second layer 418B are disposed coplanar to one another such that
they connect and begin to form another word line or bit line of a
4F.sup.2 3D cross-point memory array. The etching of the second
metal material 418 may be a timed etch or any other suitable etch
process.
[0036] The above described operations result in a memory device, as
shown in FIG. 4Y. The memory device includes a first plurality of
layers disposed in the first trench 406, a second plurality of
layers disposed in the second trench 412 and a third plurality of
layers disposed in the third trench 420. The depths of the first
trench 406 and the second trench 412 are equal. The depth of the
third trench 420 is less than the depth of the first trench 406 and
the second trench 412. More specifically, the bottom of the first
trench is coplanar with the top surface of the first layer 416A of
OTS material 416. The first plurality of layers disposed in the
first trench 406 includes the first layer 408A of first metal
material 408, a layer of dielectric material 410 over the first
layer 408A of first metal material 408, and the second layer 408B
of first metal material 408 sandwiched between layers of dielectric
material 410.
[0037] The second plurality of layers disposed in the second trench
412 includes the third layer 408C of first metal material, the
first layer 414A of memory cell information storage material 414,
the first layer 416A of OTS material 416, the first layer 418A of
second metal material 418, a layer of dielectric material 410, the
fourth layer 408D of first metal material 408, the second layer
414B of memory cell information storage material 414, the second
layer 416B of OTS material 416, and the second layer 418B of second
metal material 418. The third layer 408C of first metal material
408 is coplanar with the first layer 408A of first metal material
408 in the first trench 406. The fourth layer 408D of first metal
material 408 is coplanar with the second layer 408B of first metal
material 408 in the first trench 406.
[0038] The third plurality of layers disposed in the third trench
420 includes the third layer 418C of second metal material 418, a
layer of dielectric material 410, and the fourth layer 418D of
second metal material 418. The third layer 418C of second metal
material 418 is coplanar with the first layer 418A of second metal
material 418 in the second trench 412. The fourth layer 418D of
second metal material 418 is coplanar with the second layer 418B of
second metal material 418 in the second trench 412.
[0039] The above described operations may be repeated to deposit
additional layers in additional trenches which may be formed in the
remaining exposed areas of the substrate 402, which correspond to
cross-points at which memory cells, word lines, or bit lines need
to be formed as part of a 4F.sup.2 3D cross-point memory array. In
other words, the above described building sequence may be repeated
for each depth of the originally imprinted multilevel topography
pattern. Each of the resulting plurality of layer stacks connects
to their adjacent stacks to form the fine geometry electrical
circuit.
[0040] Benefits of the present disclosure include manufacturing a
3D cross-point memory array using only a single nano-imprint
lithography patterning step and no photolithography steps. These
methods result in cost-efficient and time-efficient production of
memory devices having very fine geometries.
[0041] In summation, the present disclosure generally relates to
fine geometry electrical circuits and methods of manufacture
thereof. More specifically, methods for forming 3D cross-point
memory arrays using a single nano-imprint lithography step and no
photolithography are disclosed. The method includes imprinting a
multilevel topography pattern, transferring the multilevel
topography pattern to a substrate, filling the etched multilevel
topography pattern with hard mask material, planarizing the hard
mask material to expose a first portion of the substrate, etching a
first trench in the first portion of the substrate, depositing a
first plurality of layers in the first trench, planarizing the hard
mask material to expose a second portion of the substrate, etching
a second trench in the second portion of the substrate and
depositing a second plurality of layers in the second trench. The
method is repeated until a 4F.sup.2 3D cross-point memory array has
been formed.
[0042] While the foregoing is directed to embodiments of the
present disclosure, other and further embodiments of the disclosure
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
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