U.S. patent application number 16/813682 was filed with the patent office on 2021-09-09 for structurally stable self-aligned subtractive vias.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Dominik METZLER, Sagarika Mukesh, CHANRO PARK, Timothy Mathew Philip.
Application Number | 20210280465 16/813682 |
Document ID | / |
Family ID | 1000005795488 |
Filed Date | 2021-09-09 |
United States Patent
Application |
20210280465 |
Kind Code |
A1 |
Mukesh; Sagarika ; et
al. |
September 9, 2021 |
Structurally Stable Self-Aligned Subtractive Vias
Abstract
Techniques for forming self-aligned subtractive top vias using a
via hardmask supported by scaffolding are provided. In one aspect,
a method of forming top vias includes: forming metal lines on a
substrate using line hardmasks; patterning vias in the line
hardmasks; filling the vias and trenches in between the metal lines
with a via hardmask material to form via hardmasks and a
scaffolding adjacent to and supporting the via hardmasks; removing
the line hardmasks; and recessing the metal lines using the via
hardmasks to form the top vias that are self-aligned with the metal
lines. The scaffolding can also be placed prior to patterning of
the vias in the line hardmasks. A structure formed in accordance
with the present techniques containing top vias is also
provided.
Inventors: |
Mukesh; Sagarika; (Albany,
NY) ; METZLER; Dominik; (Clifton Park, NY) ;
PARK; CHANRO; (Clifton Park, NY) ; Philip; Timothy
Mathew; (Albany, NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
1000005795488 |
Appl. No.: |
16/813682 |
Filed: |
March 9, 2020 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 23/5226 20130101;
H01L 21/76885 20130101; H01L 21/76897 20130101; H01L 21/32139
20130101 |
International
Class: |
H01L 21/768 20060101
H01L021/768; H01L 21/3213 20060101 H01L021/3213; H01L 23/522
20060101 H01L023/522 |
Claims
1. A method of forming top vias, the method comprising the steps
of: forming metal lines on a substrate using line hardmasks;
patterning vias in the line hardmasks; filling the vias and
trenches in between the metal lines with a via hardmask material,
wherein the via hardmask material filling the vias comprises via
hardmasks, and wherein the via hardmask material filling the
trenches in between the metal lines comprises a scaffolding
adjacent to and supporting the via hardmasks; removing the line
hardmasks; and recessing the metal lines using the via hardmasks to
form the top vias that are self-aligned with the metal lines.
2. The method of claim 1, further comprising the step of: removing
the via hardmasks and the scaffolding.
3. The method of claim 1, wherein the metal lines comprise a metal
selected from the group consisting of: cobalt (Co), ruthenium (Ru),
tungsten (W), and combinations thereof.
4. The method of claim 1, wherein the line hardmasks comprise a
material selected from the group consisting of: silicon nitride
(SiN), silicon oxynitride (SiON), silicon carbide nitride (SiCN),
silicon oxide (SiOx), and combinations thereof.
5. The method of claim 1, further comprising the steps of:
depositing an organic planarizing layer (OPL) onto the line
hardmasks and the metal lines, and filling the trenches in between
the metal lines; patterning the vias in the OPL and in the line
hardmasks; and removing the OPL.
6. The method of claim 1, wherein the via hardmask material is
selected from the group consisting of: SiOx, spin-on-glass, and
combinations thereof.
7. The method of claim 1, further comprising the steps of: burying
the metal lines in an interlayer dielectric (ILD); and polishing
the ILD to expose a top of the top vias.
8. The method of claim 1, further comprising the steps of: cutting
at least one of the metal lines into segments with a line cut
trench in between the segments; and filling the vias, the trenches
in between the metal lines, and the line cut trench with the via
hardmask material.
9. The method of claim 8, wherein at least one of the top vias is
self-aligned with an end of at least one of the segments.
10. A method of forming top vias, the method comprising the steps
of: forming metal lines on a substrate using line hardmasks;
filling trenches in between the metal lines with a via hardmask
material; patterning vias in the line hardmasks; filling the vias
with the via hardmask material, wherein the via hardmask material
filling the vias comprises via hardmasks, and wherein the via
hardmask material filling the trenches in between the metal lines
comprises a scaffolding adjacent to and supporting the via
hardmasks; removing the line hardmasks; and recessing the metal
lines using the via hardmasks to form the top vias that are
self-aligned with the metal lines.
11. The method of claim 10, further comprising the step of:
removing the via hardmasks and the scaffolding.
12. The method of claim 10, wherein the metal lines comprise a
metal selected from the group consisting of: Co, Ru, W, and
combinations thereof.
13. The method of claim 10, wherein the line hardmasks comprise a
material selected from the group consisting of: SiN, SiON, SiCN,
SiOx, and combinations thereof.
14. The method of claim 10, further comprising the steps of:
depositing an OPL onto the line hardmasks and the metal lines over
the scaffolding; patterning the vias in the OPL and in the line
hardmasks; and removing the OPL.
15. The method of claim 10, wherein the via hardmask material is
selected from the group consisting of: SiOx, spin-on-glass, and
combinations thereof.
16. The method of claim 10, further comprising the steps of:
burying the metal lines in an ILD; and polishing the ILD to expose
a top of the top vias.
17. The method of claim 10, further comprising the steps of:
cutting at least one of the metal lines into segments with a line
cut trench in between the segments; and filling the vias, the
trenches in between the metal lines, and the line cut trench with
the via hardmask material.
18. A structure, comprising: metal lines formed on a substrate; top
vias self-aligned with the metal lines; via hardmasks disposed on
the top vias; and a scaffolding, disposed in trenches between the
metal lines, adjacent to and supporting the via hardmasks.
19. The structure of claim 18, wherein via hardmasks and the
scaffolding are formed from a via hardmask material selected from
the group consisting of: SiOx, spin-on-glass, and combinations
thereof.
20. The structure of claim 18, further comprising: an ILD
surrounding the metal lines and the top vias.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to top vias in a back-end-of
line (BEOL) interconnect structure, and more particularly, to
techniques for forming self-aligned subtractive top vias in a BEOL
interconnect structure using a via hardmask supported by
scaffolding for structural stability.
BACKGROUND OF THE INVENTION
[0002] A subtractive etch process can be employed to form vias over
metal lines (also referred to herein as "top vias") in a
back-end-of line (BEOL) interconnect structure. To do so, tall
metal lines are formed and via hardmasks are placed over the metal
lines. The via hardmasks are then used to recess the tall metal
lines to form the top vias. Advantageously, this subtractive
etching process permits the formation of structures without any
interface between the metal lines and the top vias.
[0003] There are, however, some notable challenges associated with
this process. For instance, the via hardmasks are both tall and
narrow and thus tend to fall over due to a lack of structural
stability. Such a collapse of the via hardmask can lead to unwanted
defects in the final pattern such as missing vias, unwanted vias,
or pattern collapse as well as high defectivity.
[0004] Accordingly, techniques for forming self-aligned subtractive
vias that are structurally stable would be desirable.
SUMMARY OF THE INVENTION
[0005] The present invention provides techniques for forming
self-aligned subtractive top vias using a via hardmask supported by
scaffolding for structural stability. In one aspect of the
invention, a method of forming top vias is provided. The method
includes: forming metal lines on a substrate using line hardmasks;
patterning vias in the line hardmasks; filling the vias and
trenches in between the metal lines with a via hardmask material,
wherein the via hardmask material filling the vias forms via
hardmasks, and wherein the via hardmask material filling the
trenches in between the metal lines forms a scaffolding adjacent to
and supporting the via hardmasks; removing the line hardmasks; and
recessing the metal lines using the via hardmasks to form the top
vias that are self-aligned with the metal lines.
[0006] In another aspect of the invention, another method of
forming top vias is provided. The method includes: forming metal
lines on a substrate using line hardmasks; filling trenches in
between the metal lines with a via hardmask material; patterning
vias in the line hardmasks; filling the vias with the via hardmask
material, wherein the via hardmask material filling the vias forms
via hardmasks, and wherein the via hardmask material filling the
trenches in between the metal lines forms a scaffolding adjacent to
and supporting the via hardmasks; removing the line hardmasks; and
recessing the metal lines using the via hardmasks to form the top
vias that are self-aligned with the metal lines.
[0007] In yet another aspect of the invention, a structure is
provided. The structure includes: metal lines formed on a
substrate; top vias self-aligned with the metal lines; via
hardmasks disposed on the top vias; and a scaffolding, disposed in
trenches between the metal lines, adjacent to and supporting the
via hardmasks.
[0008] A more complete understanding of the present invention, as
well as further features and advantages of the present invention,
will be obtained by reference to the following detailed description
and drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a top-down diagram illustrating metal lines having
been formed on a substrate using line hardmasks and at least one of
the metal lines having been cut into multiple segments with a line
cut trench in between the segments according to an embodiment of
the present invention;
[0010] FIG. 2A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the metal lines having been formed on the
substrate using the line hardmasks, and FIG. 2B is a
cross-sectional diagram, through one of the metal lines,
illustrating at least one of the metal lines having been cut into
multiple segments with a line cut trench in between the segments
according to an embodiment of the present invention;
[0011] FIG. 3A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating an organic planarizing layer (OPL) having
been deposited onto the line hardmasks and metal lines, filling
trenches in between the metal lines, and vias having been patterned
in the OPL and in the line hardmasks over the metal lines/metal
line segment, and FIG. 3B is a cross-sectional diagram, through one
of the metal lines, illustrating the OPL having been deposited onto
the line hardmasks and metal lines, filling the line cut trench in
between the segments, and the vias having been patterned in the OPL
and in the line hardmasks over the metal lines/metal line segment
according to an embodiment of the present invention;
[0012] FIG. 4A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the vias and the trenches in between the
metal lines having been filled with a via hardmask material to form
via hardmasks and a scaffolding, and FIG. 4B is a cross-sectional
diagram, through one of the metal lines, illustrating the vias and
the line cut trench in between the segments having been filled with
the via hardmask material to form the via hardmasks and the
scaffolding according to an embodiment of the present
invention;
[0013] FIG. 5 is a top-down diagram illustrating the line hardmasks
having been selectively removed according to an embodiment of the
present invention;
[0014] FIG. 6A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the line hardmasks having been
selectively removed, and FIG. 6B is a cross-sectional diagram,
through one of the metal lines, illustrating the line hardmasks
having been selectively removed according to an embodiment of the
present invention;
[0015] FIG. 7A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating an etch having been employed to recess
the metal lines/metal line segments using the via hardmasks to form
subtractive top vias self-aligned with the metal lines/metal line
segments, and FIG. 7B is a cross-sectional diagram, through one of
the metal lines, illustrating the etch having been employed to
recess the metal lines/metal line segments using the via hardmasks
to form subtractive top vias self-aligned with the metal
lines/metal line segments according to an embodiment of the present
invention;
[0016] FIG. 8 is a top-down diagram illustrating the via hardmasks
and scaffolding having been removed according to an embodiment of
the present invention;
[0017] FIG. 9A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the via hardmasks and scaffolding having
been removed, and FIG. 9B is a cross-sectional diagram, through one
of the metal lines, illustrating the via hardmasks and scaffolding
having been removed according to an embodiment of the present
invention;
[0018] FIG. 10A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the top vias and metal lines/metal line
segments having been buried in an interlayer dielectric (ILD) which
is then polished down to (and exposing) the tops of the top vias,
and FIG. 10B is a cross-sectional diagram, through one of the metal
lines, illustrating the top vias and metal lines/metal line
segments having been buried in the ILD which is then polished down
to (and exposing) the tops of the top vias according to an
embodiment of the present invention;
[0019] FIG. 11 is a top-down diagram illustrating metal lines
having been formed on a substrate using line hardmasks, at least
one of the metal lines having been cut into multiple segments with
a line cut trench in between the segments, and trenches in between
the metal lines having been filled with a via hardmask material to
form a scaffolding according to an embodiment of the present
invention;
[0020] FIG. 12A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the metal lines having been formed on the
substrate using the line hardmasks, and the trenches in between the
metal lines having been filled with the via hardmask material to
form the scaffolding, and FIG. 12B is a cross-sectional diagram,
through one of the metal lines, illustrating the metal lines having
been formed on the substrate using the line hardmasks, and the line
cut trench in between the segments having been filled with the via
hardmask material to form the scaffolding according to an
embodiment of the present invention;
[0021] FIG. 13A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating an OPL having been deposited onto the
line hardmasks and metal lines over the scaffolding, and vias
having been patterned in the OPL and in the line hardmasks over the
metal lines/metal line segment, and FIG. 13B is a cross-sectional
diagram, through one of the metal lines, illustrating the OPL
having been deposited onto the line hardmasks and metal lines over
the scaffolding, and the vias having been patterned in the OPL and
in the line hardmasks over the metal lines/metal line segment
according to an embodiment of the present invention;
[0022] FIG. 14A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the vias having been filled with the via
hardmask material to form via hardmasks, and FIG. 14B is a
cross-sectional diagram, through one of the metal lines,
illustrating the vias having been filled with the via hardmask
material to form the via hardmasks according to an embodiment of
the present invention;
[0023] FIG. 15 is a top-down diagram illustrating the line
hardmasks having been selectively removed according to an
embodiment of the present invention;
[0024] FIG. 16A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the line hardmasks having been
selectively removed, and FIG. 16B is a cross-sectional diagram,
through one of the metal lines, illustrating the line hardmasks
having been selectively removed according to an embodiment of the
present invention;
[0025] FIG. 17A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating an etch having been employed to recess
the metal lines/metal line segments using the via hardmasks to form
subtractive top vias self-aligned with the metal lines/metal line
segments, and FIG. 17B is a cross-sectional diagram, through one of
the metal lines, illustrating the etch having been employed to
recess the metal lines/metal line segments using the via hardmasks
to form subtractive top vias self-aligned with the metal
lines/metal line segments according to an embodiment of the present
invention;
[0026] FIG. 18 is a top-down diagram illustrating the via hardmasks
and scaffolding having been removed according to an embodiment of
the present invention; and
[0027] FIG. 19A is a cross-sectional diagram, perpendicular to the
metal lines, illustrating the via hardmasks and scaffolding having
been removed, and the top vias and metal lines/metal line segments
having been buried in an ILD which is then polished down to (and
exposing) the tops of the top vias, and FIG. 19B is a
cross-sectional diagram, through one of the metal lines,
illustrating the via hardmasks and scaffolding having been removed,
and the top vias and metal lines/metal line segments having been
buried in the ILD which is then polished down to (and exposing) the
tops of the top vias according to an embodiment of the present
invention.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0028] Provided herein are techniques for forming self-aligned
subtractive top vias in a back-end-of line (BEOL) interconnect
structure. Advantageously, instead of having unstable via plug
hardmasks as in conventional flows, the present techniques involve
placing an excess of the via plug hardmask material such that the
via plug hardmask material acts as both a hardmask for recessing
the metal lines to form the top vias and as scaffolding for the
overall structure. As such, the problems associated with collapse
of the via hardmasks such as missing vias, unwanted vias and/or
pattern collapse can be avoided. As will be described in detail
below, this scaffolding can be placed either after patterning of
the top vias in the line hardmask (see FIGS. 1-10) or before
patterning of the top vias in the line hardmask (see FIGS.
11-19).
[0029] A first exemplary embodiment for forming top vias in a BEOL
interconnect structure is now described by way of reference to
FIGS. 1-10. The following description will reference both top-down
views of the structure at various stages of the process as well as
cross-sectional cuts through the structure. Namely, referring to
FIG. 1 (a top-down view) the process begins with the formation of a
plurality of metal lines 106 on a substrate 102.
[0030] According to an exemplary embodiment, substrate 102 is a
bulk semiconductor wafer, such as a bulk silicon (Si), bulk
germanium (Ge), bulk silicon germanium (SiGe) and/or bulk III-V
semiconductor wafer. Alternatively, substrate 102 can be a
semiconductor-on-insulator (SOI) wafer. A SOI wafer includes a SOI
layer separated from an underlying substrate by a buried insulator.
When the buried insulator is an oxide it is referred to herein as a
buried oxide or BOX. The SOI layer can include any suitable
semiconductor, such as Si, Ge, SiGe, and/or a III-V semiconductor.
Substrate 102 may already have pre-built structures (not shown)
such as transistors, diodes, capacitors, resistors, isolation
regions (e.g., shallow trench isolation (STI) regions),
interconnects, wiring, etc.
[0031] Standard lithography and etching techniques can be employed
to form the metal lines 106 on substrate 102. For instance, a metal
layer is first deposited onto the substrate 102. By way of example
only, suitable metals for the metal layer include, but are not
limited to, cobalt (Co), ruthenium (Ru) and/or tungsten (W). A
process such as evaporation, sputtering, or electrochemical plating
can be employed to deposit the metal layer onto the substrate
102.
[0032] Line hardmasks 104 are then formed on the metal layer
marking the footprint and location of the metal lines 106. It is
notable that in the top-down depiction provided in FIG. 1, dashed
lines are used to represent the outline of the line hardmasks 104
in order to show the underlying metal lines 106. Depictions of the
line hardmasks 104 over the metal lines 106 are also provided in
the cross-sectional views described below. Suitable materials for
the line hardmasks 104 include, but are not limited to, nitride
hardmask materials such as silicon nitride (SiN), silicon
oxynitride (SiON), silicon carbide nitride (SiCN), and/or oxide
hardmask materials such as silicon oxide (SiOx). Line hardmasks 104
can be formed using a patterning technique such as lithography
followed by an etching process. Suitable etching processes include,
but are not limited to, a directional (anisotropic) etching process
such as reactive ion etching (ME). Alternatively, the line
hardmasks 104 can be formed by other suitable techniques, including
but not limited to, sidewall image transfer (SIT), self-aligned
double patterning (SADP), self-aligned quadruple patterning (SAQP),
and other self-aligned multiple patterning (SAMP).
[0033] The pattern from the line hardmasks 104 is then transferred
to the underlying metal layer to form the metal lines 106. A
directional (anisotropic) etching process such as ME can be
employed for the metal line etch. As shown in FIG. 1, at least one
of the metal lines 106 is cut into multiple segments, e.g.,
segments 106a and 106b. Advantageously, as will be described in
detail below, the present process can be employed to form top vias
self-aligned to the end of one or more of these metal line
segments. To form this cut in the metal line, the corresponding
line hardmask 104 is cut into multiple segments, e.g., segments
104a and 104b, prior to patterning of the metal layer. See FIG. 1.
Thus, when the pattern is transferred from the line hardmasks 104
to the metal layer, the cut between segments 104a and 104b will be
transferred to the underlying metal line, forming segments 106a and
106b.
[0034] As shown in FIG. 1, different cross-sectional views of the
interconnect structure will be provided in the figures that follow.
One cross-sectional cut (X-X') will be perpendicular to the metal
lines 106, and another cross-sectional cut (Y-Y') will be parallel
to the metal lines 106, through a given one of the metal lines 106
(in this case the metal line 106 that has been cut into segments
106a and 106b). For instance, FIG. 2A (a cross-sectional cut X-X')
illustrates line hardmasks 104 having been used to pattern metal
lines 106 on the substrate 102. The patterning of metal lines 106
forms trenches 202 in between the metal lines 106. As shown in FIG.
2B (a cross-sectional cut Y-Y'), at least one of the line hardmasks
104 is cut into multiple segments 104a and 104b. Thus, when the
pattern from the line hardmasks 104 is transferred to the metal
lines 106, at least one of the metal lines 106 will be cut into
multiple segments 106a and 106b. This process forms line cut trench
204 in between segments 106a and 106b of the at least one cut metal
line 106.
[0035] As shown in FIG. 3A (a cross-sectional cut X-X') and FIG. 3B
(a cross-sectional cut Y-Y'), an organic planarizing layer (OPL)
302 is then deposited onto the line hardmasks 104 and metal lines
106, filling the trenches 202 in between the metal lines 106 and
the line cut trench 204 in between segments 106a and 106b of the at
least one cut metal line 106. A casting process such as spin
coating or spray coating can be employed to deposit the OPL 302.
Following deposition, the OPL 302 can be planarized using a process
such as chemical-mechanical polishing (CMP).
[0036] Standard lithography and etching techniques are the used to
pattern vias 304, 306 and 308 in the OPL 302 and in the line
hardmasks 104 over the metal lines 106/metal line segment 106a. A
directional (anisotropic) etching process such as RIE can be used
for the via etch. Namely, as shown in FIG. 3A via 304 extends
through OPL 302 and the line hardmask 104 over a given one of the
metal lines 106, and via 306 extends through the OPL 302 and line
hardmask segment 104b over metal line segment 106b. As shown in
FIG. 3B, via 308 is adjacent to a side of via 306 opposite the line
cut trench 204, and extends through the OPL 302 and the line
hardmask segment 104b over the metal line segment 106b.
[0037] Following patterning of vias 304, 306 and 308, the OPL 302
is removed. The OPL 302 can be removed using a process such as
ashing. Removal of the OPL 302 reopens the trenches 202 in between
the metal lines 106, and the line cut trench 204 in between
segments 106a and 106b of the at least one cut metal line 106.
[0038] As shown in FIG. 4A (a cross-sectional cut X-X') and FIG. 4B
(a cross-sectional cut Y-Y'), the vias 304, 306 and 308, the
trenches 202 in between the metal lines 106, and the line cut
trench 204 in between segments 106a and 106b of the at least one
cut metal line 106 are then filled with a via hardmask material
402. Suitable via hardmask materials 402 include, but are not
limited to, oxide hardmask materials such as SiOx and/or
spin-on-glass (SOG). A process such as chemical vapor deposition
(CVD), atomic layer deposition (ALD), physical vapor deposition
(PVD), spin-coating and/or spray coating can be employed to deposit
the via hardmask material 402. Following deposition, the via
hardmask materials 402 can be planarized using a process such as
CMP.
[0039] Specifically, as shown in FIG. 4A the via hardmask material
402 is deposited into the trenches 202 in between the metal lines
106, and into the vias 304 and 306. The via hardmask material 402
deposited into the vias 304 and 306 is present over the metal lines
106/metal line segment 106b and will serve as the via hardmasks
(via HM) for recessing the metal lines 106/metal line segment 106b
to form the top vias (see below). The via hardmask material 402
deposited into the trenches 202 in between the metal lines 106
forms the scaffolding (scaff.) adjacent to the via hardmasks.
Advantageously, this scaffolding physically supports the via
hardmasks and prevents the via hardmasks from collapse.
[0040] As shown in FIG. 4B, the via hardmask material 402 is
deposited into the line cut trench 204 in between segments 106a and
106b of the at least one cut metal line 106, and into the vias 306
and 308. As above, the via hardmask material 402 deposited into the
vias 304 and 306 is present over the metal line segment 106b and
will serve as the via hardmasks for forming the top vias (see
below), whereas the via hardmask material 402 deposited into the
line cut trench 204 forms the scaffolding adjacent to, and
supporting the via hardmasks.
[0041] The line hardmasks 104/line hardmask segments 104a and 104b
are then removed selective to the via hardmask material 402. See
FIG. 5 (a top-down view). According to an exemplary embodiment, the
line hardmasks 104/line hardmask segments 104a and 104b are
selectively removed using a non-directional (isotropic) etching
process such as a wet chemical etch. As shown in FIG. 5, the via
hardmasks are supported on at least two sides by the adjacent
scaffolding. As described above, the via hardmasks and scaffolding
are both formed from via hardmask material 402.
[0042] FIG. 6A (a cross-sectional cut X-X') and FIG. 6B (a
cross-sectional cut Y-Y') illustrate the line hardmasks 104/line
hardmask segments 104a and 104b having been selectively removed. As
shown in FIG. 6A and FIG. 6B, the via hardmasks over the metal
lines 106/metal line segment 106b are supported on at least two
sides by the adjacent scaffolding. Both the via hardmasks and
scaffolding are formed from via hardmask material 402.
[0043] With the via hardmasks (and supporting scaffolding) in place
marking the footprint and location of the top vias, an etch is then
employed to recess the metal lines 106/metal line segments 106a and
106b. See FIG. 7A (a cross-sectional cut X-X') and FIG. 7B (a
cross-sectional cut Y-Y'). As shown in FIG. 7A and FIG. 7B, this
recess etch forms subtractive top vias 702, 704 and 706 in metal
lines 106/metal line segment 106b.
[0044] Following formation of top vias 702, 704 and 706 in metal
lines 106/metal line segment 106b, the via hardmasks and
scaffolding (i.e., via hardmask material 402) is then removed. See
FIG. 8 (a top-down view). According to an exemplary embodiment, the
via hardmask material 402 is removed using a non-directional
(isotropic) etching process such as a wet chemical etch. As shown
in FIG. 8, top vias 702, 704 and 706 are now present over select
metal lines 106. Notably, by way of the present process, the top
vias 702, 704 and 706 are self-aligned with the underlying metal
lines 106, including top via 704 that is self-aligned with the end
of metal line segment 106b.
[0045] FIG. 9A (a cross-sectional cut X-X') and FIG. 9B (a
cross-sectional cut Y-Y') illustrate the via hardmasks and
scaffolding (i.e., via hardmask material 402) having been
selectively removed. As shown in FIG. 9A and FIG. 9B, the top vias
702, 704 and 706 formed by the present process are self-aligned
with the underlying metal lines 106, including top via 704 that is
self-aligned with the end of metal line segment 106b.
[0046] Following removal of the via hardmasks and scaffolding, the
top vias 702, 704 and 706, and metal lines 106/metal line segments
106a and 106b then buried in an interlayer dielectric (ILD) 1002.
See FIG. 10A (a cross-sectional cut X-X') and FIG. 10B (a
cross-sectional cut Y-Y'). Suitable ILD 1002 materials include, but
are not limited to, oxide low-.kappa. materials such as silicon
oxide (SiOx) and/or oxide ultralow-.kappa. interlayer dielectric
(ULK-ILD) materials, e.g., having a dielectric constant .kappa. of
less than 2.7. By comparison, silicon dioxide (SiO.sub.2) has a
dielectric constant .kappa. value of 3.9. Suitable ultralow-.kappa.
dielectric materials include, but are not limited to, porous
organosilicate glass (pSiCOH). A process such as CVD, ALD, or PVD
can be employed to deposit the ILD 1002 surrounding the top vias
702, 704 and 706, and metal lines 106/metal line segments 106a and
106b. Following deposition, the ILD 1002 can be polished using a
process such as CMP. As shown in FIG. 10A and FIG. 10B, according
to an exemplary embodiment, the ILD 1002 is polished down to (and
exposing) the tops of the top vias 702, 704 and 706.
[0047] As provided above, the scaffolding can also be placed
earlier on in the process, such as prior to patterning of the top
vias in the line hardmasks. This alternative embodiment is now
described by way of reference to FIGS. 11-19. As above, the
following description will reference both top-down views of the
structure at various stages of the process as well as
cross-sectional cuts through the structure. Like structures will be
numbered alike in the following description and associated
figures.
[0048] Referring to FIG. 11 (a top-down view) the process begins in
the same manner as above with the formation of a plurality of metal
lines 106 (e.g., Co, Ru and/or W) on a substrate 102 using line
hardmasks 104 (e.g., SiN, SiON, SiCN and/or SiOx--the outlines of
which are depicted using dashed lines in order to show the
underlying metal lines 106). Suitable substrate 102 configurations
were provided above. As shown in FIG. 11, at least one of the line
hardmasks 104 and underlying metal lines 106 is cut into multiple
segments 104a/104b and 106a/106b, respectively, having a line cut
trench 204 therebetween.
[0049] In contrast to the example above, the trenches 202 in
between the metal lines 106 and the line cut trench 204 in between
the segments 106a and 106b of the at least one cut metal line 106
are next filled with the via hardmask material 1202 to form the
scaffolding (Scaff.). As provided above, suitable via hardmask
materials 1202 include, but are not limited to, SiOx and/or SOG
which can be deposited using a process such as CVD, ALD, PVD,
spin-coating and/or spray coating. By contrast, in the previous
example, the trenches 202 in between the metal lines 106 and the
line cut trench 204 in between the segments 106a and 106b were
filled concurrently to form the scaffolding and via hardmasks in
the same step.
[0050] This scaffolding-first embodiment is further illustrated in
FIG. 12A (a cross-sectional cut X-X') and FIG. 12B (a
cross-sectional cut Y-Y'). Namely, FIG. 12A illustrates the line
hardmasks 104 having been used to pattern metal lines 106/metal
line segments 106b on the substrate 102. Trenches 202 present in
between the metal lines 106/metal line segments 106b are then
filled with the via hardmask material 1202, forming the present
scaffolding support structure. Following deposition, the via
hardmask material 1202 can be planarized using a process such as
CMP. Similarly, FIG. 12B illustrates the line hardmasks 104 having
been used to pattern metal line segments 106a and 106b on the
substrate 102. The line cut trench 204 present in between metal
line segments 106a and 106b is then filled with the via hardmask
material 1202, forming the present scaffolding support structure.
Following deposition, the via hardmask material 1202 can be
planarized using a process such as CMP.
[0051] As shown in FIG. 13A (a cross-sectional cut X-X') and FIG.
13B (a cross-sectional cut Y-Y'), an OPL 1302 is then deposited
onto the line hardmasks 104/line hardmask segments 104a and 104b,
and metal lines 106/metal line segments 106a/106b, over the
scaffolding. A casting process such as spin coating or spray
coating can be employed to deposit the OPL 1302. Following
deposition, the OPL 1302 can be planarized using a process such as
CMP.
[0052] In the same manner as described above, standard lithography
and etching techniques are then used to pattern vias 1304, 1306 and
1308 in the OPL 1302 and line hardmasks 104/line hardmask segment
104b. A directional (anisotropic) etching process such as RIE can
be used for the via etch. Namely, as shown in FIG. 13A via 1304
extends through OPL 1302 and the line hardmask 104 over a given one
of the metal lines 106, and via 1306 extends through the OPL 1302
and line hardmask segment 104b over metal line segment 106b. As
shown in FIG. 13B, via 1308 is adjacent to a side of via 1306
opposite the line cut trench 204, and extends through the OPL 1302
and the line hardmask segment 104b over the metal line segment
106b. Following patterning of vias 1304, 1306 and 1308, the OPL
1302 is removed. The OPL 1302 can be removed using a process such
as ashing.
[0053] As shown in FIG. 14A (a cross-sectional cut X-X') and FIG.
14B (a cross-sectional cut Y-Y'), the vias 1304, 1306 and 1308 are
then filled with a via hardmask material 1402 to form the via
hardmasks. Notably, the trenches 202 in between the metal lines 106
and the line cut trench 204 in between the segments 106a and 106b
have already been filled with via hardmask material 1202 to form
the scaffolding (see above). According to an exemplary embodiment,
the same material is used as via hardmask material 1202 and via
hardmask material 1402, e.g., SiOx and/or SOG. In this embodiment,
the via hardmask material 1402 to form the via hardmasks is being
filled separately from the scaffolding. Thus, it is likely that the
via hardmasks here will not be at the same height as the
scaffolding. See, e.g., FIG. 14A and FIG. 14B. However, there could
be topography around the metal lines in any of the embodiments
provided herein.
[0054] Specifically, as shown in FIG. 14A the via hardmask material
1402 deposited into the vias 1304 and 1306 is present over the
metal lines 106/metal line segment 106b and will serve as the via
hardmasks (via HM). Similarly, as shown in FIG. 14B the via
hardmask material 1402 deposited into the vias 1306 and 1308 is
present over the metal line segment 106b and will also serve as the
via hardmasks. Advantageously, the scaffolding adjacent to the via
hardmasks physically supports the via hardmasks, preventing
collapse of the via hardmasks during top via patterning.
[0055] The line hardmasks 104/line hardmask segments 104a and 104b
are then removed selective to the via hardmask material 1202/1402,
e.g., using a non-directional (isotropic) etching process such as a
wet chemical etch. See FIG. 15 (a top-down view). As shown in FIG.
15, the via hardmasks are supported on at least two sides by the
adjacent scaffolding.
[0056] FIG. 16A (a cross-sectional cut X-X') and FIG. 16B (a
cross-sectional cut Y-Y') illustrate the line hardmasks 104/line
hardmask segments 104a and 104b having been selectively removed. As
shown in FIG. 16A and FIG. 16B, the via hardmasks over the metal
lines 106/metal line segment 106b are supported on at least two
sides by the adjacent scaffolding.
[0057] With the via hardmasks (and supporting scaffolding) in place
marking the footprint and location of the top vias, an etch is then
employed to recess the metal lines 106/metal line segments 106a and
106b. See FIG. 17A (a cross-sectional cut X-X') and FIG. 17B (a
cross-sectional cut Y-Y'). As shown in FIG. 17A and FIG. 17B, this
recess etch forms subtractive top vias 1702, 1704 and 1706 in metal
lines 106/metal line segment 106b.
[0058] Following formation of top vias 1702, 1704 and 1706 in metal
lines 106/metal line segment 106b, the via hardmasks and
scaffolding (i.e., via hardmask material 1202/1402) is then
removed. See FIG. 18 (a top-down view). As provided above, the via
hardmask material 1202/1402 can be removed using a non-directional
(isotropic) etching process such as a wet chemical etch. As shown
in FIG. 18, top vias 1702, 1704 and 1706 are now present over
select metal lines 106. Notably, by way of the present process, the
top vias 1702, 1704 and 1706 are self-aligned with the underlying
metal lines 106, including top via 1704 that is self-aligned with
the end of metal line segment 106b.
[0059] FIG. 19A (a cross-sectional cut X-X') and FIG. 19B (a
cross-sectional cut Y-Y') illustrate the via hardmasks and
scaffolding (i.e., via hardmask material 402) having been
selectively removed, and the top vias 1702, 1704 and 1706, and
metal lines 106/metal line segments 106a and 106b having been
buried in an ILD 1902. As shown in FIG. 19A and FIG. 19B, the top
vias 1702, 1704 and 1706 formed by the present process are
self-aligned with the underlying metal lines 106, including top via
1704 that is self-aligned with the end of metal line segment
106b.
[0060] As provided above, suitable ILD 1902 materials include, but
are not limited to, SiOx and/or oxide ULK-ILD materials such as
pSiCOH. As shown in FIG. 19A and FIG. 19B, following deposition the
ILD 1902 can be planarized using a process such as CMP. According
to an exemplary embodiment, the ILD 1902 is polished down to (and
exposing) the tops of the top vias 1702, 1704 and 1706.
[0061] Although illustrative embodiments of the present invention
have been described herein, it is to be understood that the
invention is not limited to those precise embodiments, and that
various other changes and modifications may be made by one skilled
in the art without departing from the scope of the invention.
* * * * *