U.S. patent application number 10/457217 was filed with the patent office on 2004-12-09 for composite low-k dielectric structure.
Invention is credited to Cowley, Andy, Kim, Sun-Oo, Naujok, Markus.
Application Number | 20040248400 10/457217 |
Document ID | / |
Family ID | 33490323 |
Filed Date | 2004-12-09 |
United States Patent
Application |
20040248400 |
Kind Code |
A1 |
Kim, Sun-Oo ; et
al. |
December 9, 2004 |
Composite low-k dielectric structure
Abstract
A method of forming a composite intermetal dielectric structure
is provided. An initial intermetal dielectric structure is
provided, which includes a first dielectric layer and two
conducting lines. The two conducting lines are located in the first
dielectric layer. A portion of the first dielectric layer is
removed between the conducting lines to form a trench. The trench
is filled with a second dielectric material. The second dielectric
material is a low-k dielectric having a dielectric constant less
than that of the first dielectric layer.
Inventors: |
Kim, Sun-Oo; (Fishkill,
NY) ; Naujok, Markus; (Hsin- Chu City, TW) ;
Cowley, Andy; (Wappingers Falls, NY) |
Correspondence
Address: |
SLATER & MATSIL, L.L.P.
17950 PRESTON RD, SUITE 1000
DALLAS
TX
75252-5793
US
|
Family ID: |
33490323 |
Appl. No.: |
10/457217 |
Filed: |
June 9, 2003 |
Current U.S.
Class: |
438/633 ;
257/E21.576; 257/E21.589; 438/637 |
Current CPC
Class: |
H01L 21/76835 20130101;
H01L 21/76829 20130101; H01L 21/76885 20130101; Y10S 438/958
20130101 |
Class at
Publication: |
438/633 ;
438/637 |
International
Class: |
H01L 021/4763 |
Claims
1. A method of forming a composite intermetal dielectric structure,
comprising: providing an initial intermetal dielectric structure
comprising a first dielectric layer and two conducting lines,
wherein the two conducting lines are located in the first
dielectric layer; forming a nonconductive patterned trench mask
over the initial intermetal dielectric structure; removing a
portion of the first dielectric layer between the conducting lines
to form a trench in alignment with the trench mask; and filling the
trench with a second dielectric material, wherein the second
dielectric material is a low-k dielectric having a dielectric
constant less than that of the first dielectric layer.
2. The method of claim 1, wherein the initial intermetal dielectric
structure further comprises a liner layer formed between each of
the conducting lines and the first dielectric layer, and wherein
the trench is formed between the liner layers of the conducting
lines.
3. The method of claim 2, wherein the providing of the initial
intermetal dielectric structure comprises: depositing the liner
layer, wherein the second dielectric material is not compatible
with the liner layer deposition.
4. The method of claim 1, wherein the removing of the first
dielectric layer portion includes removing a portion of the trench
mask to form the trench.
5. The method of claim 4, wherein the forming of the patterned
trench mask comprises: depositing the trench mask, wherein the
second dielectric material is not compatible with the trench mask
deposition.
6. The method of claim 1, further comprising: forming a cap layer
over the second dielectric material.
7. The method of claim 1, further comprising: etching the second
dielectric material so that it is recessed relative to the
conducting lines; forming a cap layer over the second dielectric
material; and planarizing the cap layer to be substantially
coplanar with the conducting lines.
8. The method of claim 1, wherein the first dielectric layer is
made from a low-k dielectric material.
9. The method of claim 1, further comprising: forming a cap layer
over the composite intermetal dielectric structure.
10. The method of claim 1, wherein the providing of the initial
intermetal dielectric structure comprises: depositing conductive
material to form the conducting lines, wherein the second
dielectric material is not compatible with the conductive material
deposition.
11. The method of claim 1, wherein the providing of the initial
intermetal dielectric structure comprises: performing a planarizing
process on the conducting lines, wherein the second dielectric
material is not compatible with the planarizing process for the
conducting lines.
12. The method of claim 1, wherein the second dielectric material
is porous.
13. The method of claim 1, wherein the first dielectric layer is
made from a material having a mechanical strength greater than that
of the second dielectric material.
14. A method of fabricating a semiconductor device, comprising:
forming a first dielectric layer; forming openings in the first
dielectric layer using a damascene process; filling the openings
with conductive material to form conducting lines and/or vias;
performing a chemical mechanical polish to remove excess conductive
material and to provide a substantially planar upper surface;
forming a nonconductive patterned trench mask; patterning and
etching away select portions of the first dielectric layer between
at least two conducting lines to form trenches in alignment with
the trench mask; and depositing a second dielectric material in the
trenches, wherein the second dielectric material is a low-k
dielectric material having a dielectric constant value less than
that of the first dielectric layer.
15. The method of claim 14, wherein the conductive material
comprises copper.
16. The method of claim 14, wherein the first dielectric layer is a
low-k dielectric material.
17.-19. Cancelled
20. A method of fabricating a semiconductor device, comprising:
providing an initial intermetal dielectric structure comprising a
layer of a first dielectric material and a conducting line, wherein
the conducting line is located at least partially in the first
dielectric material; forming a nonconductive patterned trench mask
over the initial intermetal dielectric structure; removing a
portion of the first dielectric material adjacent the conducting
line to form a trench in the layer, the trench being in alignment
with the trench mask; and filling the trench with a second
dielectric material, wherein the second dielectric material is a
low-k dielectric having a dielectric constant less than that of the
first dielectric material, and such that the second dielectric
material is located between the conducting line and the first
dielectric material.
21. The method of claim 20, wherein the removing of the first
dielectric material portion includes removing a portion of the
trench mask.
22. The method of claim 20, further comprising: forming a cap layer
over the second dielectric material.
23. The method of claim 20, wherein the first dielectric material
is a low-k dielectric material.
24. The method of claim 20, wherein the first dielectric material
has a mechanical strength greater than that of the second
dielectric material.
25. A semiconductor device comprising: a first level portion of an
intermetal dielectric structure comprising a conducting line
comprising a conductive material; a first dielectric material; and
a second dielectric material located between the conducting line
and the first dielectric material, wherein the second dielectric
material is a low-k dielectric material having a dielectric
constant value less than that of the first dielectric material.
26. The semiconductor device of claim 25, wherein the first
dielectric material is a low-k dielectric material.
27. The semiconductor device of claim 25, wherein the first
dielectric material has a mechanical strength greater than that of
the second dielectric material.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to fabrication processes and
structures for semiconductor devices. In one aspect, it relates to
a composite low-k dielectric structure.
BACKGROUND
[0002] Low-k dielectric materials are dielectric materials having a
dielectric constant (k) lower than that of thermal silicon dioxide
(i.e., k<3.9). The minimum value of k is 1.0 for air. Hence,
Low-k dielectric materials are dielectric material having a
dielectric constant between 1.0 and 3.9.
[0003] The use of low-k dielectric materials are important in the
advancement of integrated circuit applications for semiconductor
devices. One advantageous use of low-k materials in semiconductor
devices is between conductor lines or structures (e.g., intermetal
dielectric structures). The RC delay in switching is one factor
that limits the operating speed of semiconductor devices. Generally
as RC delay increases, the maximum operating speed of a
semiconductor device decreases. RC delay can be reduced by
decreasing resistance (R) in the conducting lines/structures and/or
by decreasing the parasitic capacitance (C) developed between
conducting lines/structures. This parasitic capacitance can be
reduced by using dielectric materials with smaller permittivity
values, which low-k dielectric materials provide.
[0004] One of the primary dielectric materials of choice for use
between conducting lines in an intermetal dielectric structure has
been silicon dioxide (SiO.sub.2) due to its dielectric
characteristics, its mechanical strength, and its ease of
processing. However, silicon dioxide typically has a dielectric
constant ranging from k=3.9 to 4.5, depending on the method of
forming it. This k value is too high for most integrated circuit
applications below about 0.18 .mu.m. Thus, as the geometries of
semiconductor devices have continued to shrink, there has been a
push to develop and use new dielectric materials with
dielectric-constant values much lower than that of silicon dioxide,
i.e., low-k dielectric materials.
[0005] There are many trade-offs that must be considered when
attempting to implement a low-k dielectric material. For example,
the mechanical strength and mechanical performance of low-k
materials typically decreases as the value of k decreases. Also,
many low-k dielectric materials having desirable electrical
properties may be incompatible with other adjacent materials and/or
processes used to form or process such adjacent materials. Thus, a
need exists for ways to implement low-k dielectric materials to
obtain the lowered parasitic capacitance advantages even though
such low-k dielectric materials may have less mechanical strength
and/or incompatibility issues.
[0006] FIG. 1 shows a conventional intermetal dielectric structure
20 formed using single damascene and dual damascene processes, for
example. In forming the structure 20 of FIG. 1 using conventional
processes, a dielectric layer 21 is typically formed first. Then, a
hard mask layer 24 is formed and patterned. Next, openings for
conductor lines 26 and vias 28 are patterned, etched, and filled
with a liner layer 30 and a conductive material (e.g., aluminum,
copper, and/or tungsten). Thus, the dielectric layer 21 is present
during several subsequent processing steps, any of which could have
the potential to damage, change, or negatively affect the
dielectric layer 21 (i.e., being incompatible with the dielectric
layer 21).
[0007] Usually in a conventional damascene process of forming an
intermetal dielectric structure 20 (e.g., as shown in FIG. 1),
several integration issues must be addressed with respect to the
choice of low-k dielectric material utilized for the dielectric
layer 21. The low-k dielectric material usually needs to be
mechanically strong and structurally stable. The low-k dielectric
material typically needs to be CMP compatible (chemically and
mechanically) to withstand any CMP processes involved while the
dielectric material is present. Because a hard mask 24 is
frequently used during the damascene processing, the low-k
dielectric material may need to be compatible with the hard mask
material and processes for forming, patterning, and/or removing the
hard mask layer 24. Furthermore, the low-k dielectric material
chosen will usually need to be compatible with the liner deposition
and/or conductor deposition processes.
[0008] Because there are so many compatibility issues to consider
when trying to implement, introduce, or test a new low-k dielectric
material into a conventional intermetal dielectric structure 20
(see e.g., FIG. 1), the complexity, time, and cost of developing
and testing new low-k dielectrics can be quite large. Hence, there
is a need for a way to reduce the complexity, time, and cost of
testing and implementing new low-k materials.
BRIEF SUMMARY OF THE INVENTION
[0009] The problems and needs outlined above are addressed by the
present invention. In accordance with one aspect of the present
invention, a method of forming a composite intermetal dielectric
structure is provided. This method includes the following steps,
the order of which may vary. An initial intermetal dielectric
structure is provided, which includes a first dielectric layer and
two conducting lines. The two conducting lines are located in the
first dielectric layer. A portion of the first dielectric layer is
removed between the conducting lines to form a trench. The trench
is filled with a second dielectric material. The second dielectric
material is a low-k dielectric having a dielectric constant less
than that of the first dielectric layer.
[0010] The initial intermetal dielectric structure may further
include a liner layer formed between each of the conducting lines
and the first dielectric layer, and the trench may be formed
between the liner layers. The initial intermetal dielectric
structure may further include a hard mask layer atop the first
dielectric layer, and the removing of the first dielectric layer
portion may include removing a portion of the hard mask layer to
form the trench. A cap layer may be formed over the second
dielectric material. The second dielectric material may be etched
so that it is recessed relative to the conducting lines, a cap
layer may be formed over the second dielectric material, and the
cap layer may be planarized to be substantially coplanar with the
conducting lines. The first dielectric layer is preferably made
from a low-k dielectric material. A cap layer may be formed over
the composite intermetal dielectric structure. The second
dielectric material may or may not be compatible with the
process(es) for depositing the conductive lines, the process(es)
for planarizing the conducting lines. The second dielectric
material may be porous. The first dielectric layer is preferably
made from a material having a mechanical strength greater than that
of the second dielectric material.
[0011] In accordance with another aspect of the present invention,
a method of fabricating a semiconductor device is provided. This
method includes the following steps, the order of which may vary. A
first dielectric layer is formed. Openings are formed in the first
dielectric layer using a damascene process. The openings are filled
with conductive material to form conducting lines and/or vias. A
chemical mechanical polish (CMP) is performed to remove excess
conductive material (if any) and to provide a substantially planar
upper surface. Select portions of the first dielectric layer are
patterned and etched away between at least two conducting lines to
form trenches. A second dielectric material is formed in the
trenches. The second dielectric material is a low-k dielectric
material having a dielectric constant value less than that of the
first dielectric layer. The conductive material may include copper,
for example. The first dielectric layer is preferably a low-k
dielectric material.
[0012] In accordance with yet another aspect of the present
invention, a method of fabricating a semiconductor device is
provided. A blanket layer of conductive material is formed.
Conductive lines are formed in the conductive material layer. A
first dielectric layer is formed between and beside the conductive
lines. Select portions of the first dielectric layer are patterned
and etched away between at least two conducting lines to form
trenches. A second dielectric material is deposited in the
trenches. The second dielectric material is a low-k dielectric
material having a dielectric constant value less than that of the
first dielectric layer. The conductive material may include
aluminum, for example. The first dielectric layer is preferably a
low-k dielectric material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] Other objects and advantages of the invention will become
apparent upon reading the following detailed description and upon
referencing the accompanying drawings, in which:
[0014] FIG. 1 is a cross-section schematic showing a conventional
intermetal dielectric structure;
[0015] FIGS. 2 and 3 illustrate a process for a first embodiment of
the present invention;
[0016] FIG. 4 shows the structure of FIG. 3 having a cap layer
formed thereon;
[0017] FIGS. 5 and 6 illustrate part of a process for a second
embodiment of the present invention;
[0018] FIG. 7 shows a structure formed in accordance with a third
embodiment of the present invention;
[0019] FIG. 8 shows a structure formed in accordance with a fourth
embodiment of the present invention;
[0020] FIG. 9 shows a structure formed in accordance with a fifth
embodiment of the present invention;
[0021] FIG. 10 shows a structure formed in accordance with a sixth
embodiment of the present invention; and
[0022] FIG. 11-17 illustrate other embodiments of the present
invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0023] Referring now to the drawings, wherein like reference
numbers are used herein to designate like elements throughout the
various views, illustrative embodiments of the present invention
are shown and described. The figures are not necessarily drawn to
scale, and in some instances the drawings have been exaggerated
and/or simplified in places for illustrative purposes only. One of
ordinary skill in the art will appreciate the many possible
applications and variations of the present invention based on the
following illustrative embodiments of the present invention.
[0024] Generally, an embodiment of the present invention provides a
composite low-k structure and methods of fabricating the same.
FIGS. 1-3 illustrate a method of fabricating a composite low-k
magnetic structure in accordance with a first embodiment of the
present invention. FIG. 1 is a cross-section view of a portion from
a semiconductor device focusing on an intermetal dielectric
structure 20. The conventional intermetal dielectric structure 20
shown in FIG. 1 may have been formed by single-damascene and/or
dual-damascene processes, for example. The conventional structure
20 shown in FIG. 1 provides an initial intermetal dielectric
structure from which to build a composite intermetal dielectric
structure of the first embodiment. The initial intermetal
dielectric structure 20 may be fabricated using conventional
processes, for example. However, the invention is not limited by
the processes used to obtain the initial intermetal dielectric
structure 20.
[0025] The initial intermetal dielectric structure 20 of FIG. 1 has
a first dielectric layer 21, which may or may not be formed from a
low-k dielectric material. Conducting lines 26 are formed in the
first dielectric layer 21. As is often needed, a liner layer 30 is
located between the conducting lines 26 and the first dielectric
layer 21. However, the liner layer 30 may not be present in some
applications. A via 28 is shown extending from one of the
conducting lines 26 in FIG. 1. A hard mask 24 is located atop the
first dielectric layer 21. This hard mask 24 may have several
functions. For example, the hard mask 24 may have been used for
patterning openings in the first dielectric layer 21 where the
conducting lines 26 and via 28 are formed. Also, the hard mask 24
may act as a cap layer or barrier layer for the material of the
first dielectric layer 21 to protect it from damage, erosion, or
material changes during other processing steps occurring after the
formation of the first dielectric layer 21.
[0026] The conducting lines 26 and the via 28 of the initial
intermetal dielectric structure 20 (see FIG. 1) may be made from a
variety of materials, including but not limited to: copper, copper
alloys, aluminum, aluminum alloys, gold, silver, platinum,
tungsten, tungsten alloys, heavily doped polysilicon, or any
combination thereof, for example. Preferably, the conducting lines
26 are made from a material having a low resistance to help reduce
the RC delay. Preferably, the conducting lines 26 are made from
cooper or some copper alloy, for example. The liner layer 30 (if
present) may be made from a variety of materials, including but not
limited to: tantalum, tantalum nitride, tantalum-silicon-nitride,
tungsten, tungsten nitride, refractory metal, or any combination
thereof, for example.
[0027] Having the initial intermetal dielectric structure 20 of
FIG. 1 in place, trenches 40 are formed in the structure as shown
in FIG. 2. The trenches 40 may be formed using conventional
patterning and etching techniques. For example, a photoresist layer
(not shown) may be formed over the structure 20 of FIG. 1. Then,
the photoresist layer may be patterned using photolithography, and
the trenches 40 may be etched in alignment with the patterned
photoresist layer (not shown). After forming the trenches 40, the
photoresist layer may then be removed to provide the structure 42
shown in FIG. 2. The etching of the trenches 40 may be performed
using any of a variety of etching techniques, such as wet etching,
reactive ion etching (RIE), and/or ion milling, for example.
Preferably, the etching of the trenches 40 is performed using RIE
to provide anisotropic etching. One of ordinary skill in the art
will realize that many different patterning and etching processes
and/or etch chemistries may be used to form the trenches 40.
[0028] As shown in FIG. 2, the sides 44 of the trenches 40 are
preferably formed along the liner layer 30. However, the trenches
40 may also be formed into or through the liner layer 30, at the
edge of a conducting line 26, or partially within a conducting line
26, for example. In other embodiments not shown, the trenches 40
may be formed only within the first dielectric layer 21 such that a
portion of the first dielectric layer remains between a side 44 of
the trench 40 and the liner layer 30 (or between a side 44 of the
trench 40 and the conducting line 26 where no liner layer 30 is
present). In some applications, depending on the materials used, it
may be possible to use an etch that is selective against etching
the liner layer 30, for example, to contribute to etch control.
[0029] There are several techniques that may be used to control the
stopping point of the etching to control the depth of the trenches
40, although the precision of the trench depth may not be critical
for some intermetal dielectric layer applications. The etching
depth may be controlled using a timed process, an endpoint signal
control, an etch stop layer, or any combination thereof, for
example. The depth of the trenches 40 may vary for different
embodiments or different applications, as needed.
[0030] After the trenches 40 are formed, a second dielectric
material 52 is deposited within the trenches 40, as shown in FIG.
3. The second dielectric material 52 is a low-k dielectric material
with a dielectric constant (k) less than that of the first
dielectric layer 21. There are a number of techniques that may be
used to deposit the second dielectric material 52 into the trenches
40, including (but not necessarily limited to): chemical vapor
deposition (CVD), physical vapor deposition (PVD), spin-on
deposition, or sputtering, for example. When depositing the second
dielectric material 52 into the trenches 40, the second dielectric
material 52 may underfill, flush fill, or overfill the trenches 40.
If the second dielectric material 52 overfills the trenches 40, a
planarizing process (e.g., chemical mechanical polishing (CMP) or
etch back) may be used, for example, to provide a substantially
planar upper surface 54, as shown in FIG. 3.
[0031] The first dielectric layer 21 may be made from a variety of
materials, include but not limited to: silicon oxide, silicon
nitride, or low-k dielectric material, for example. The second
dielectric material 52 may be made from a variety of low-k
materials. Preferably the first dielectric layer 21 and second
dielectric material 52 are formed from different low-k materials.
It is preferred that the material used for the first dielectric
layer 21 is mechanically stronger than that of the second
dielectric material 52. It is also preferably that the first
dielectric layer 21 is more compatible with other processes
occurring after the formation of the first dielectric layer 21 than
the second dielectric material 52 would be if formed when the first
dielectric layer 21 is formed.
[0032] However, there may be a case where the first dielectric
layer 21 is made from the same low-k dielectric material as that of
the second dielectric material 52. For example, suppose the
material of the first dielectric layer 21 is not compatible with
all processes subsequent to its formation, and a portion of the
first dielectric layer 21 is damaged or changed. The second
dielectric material 52 may be substituted for some or all of the
damaged or changed portions of the first dielectric layer 21 (e.g.,
in critical regions where the use of low-k material is most
effective for reducing RC delay).
[0033] The hard mask 24 of FIG. 1 may be made from a variety of
materials, including but not limited to: silicon nitride or silicon
oxide, for example. The hard mask 24 may be important for use if
the first dielectric layer 21 is not compatible with or is
intolerant to subsequent metal deposition steps, such as UVD,
IPUVD, or CVD. However, there may be embodiments where the hard
mask 24 may be removed prior to the formation of the trenches 40
for the second dielectric material 52, depending upon the material
choice for the first dielectric layer 21 and the subsequent metal
deposition processes, for example.
[0034] It may also be desirable to form a cap layer or barrier
layer 58 over the second dielectric layer 52 to protect it from
damage or changes during subsequent processes. FIG. 4 shows the
composite intermetal dielectric structure 60 of FIG. 3 with a cap
layer 58 formed over the structure 60. Often if another intermetal
dielectric layer structure (not shown) is to be formed over the
existing intermetal dielectric structure 60 (e.g., FIG. 3), a
barrier layer 58 will be formed over the existing intermetal
dielectric structure anyway for other reasons, such as being an
etch stop layer. Thus, the cap layer 58 of FIG. 4 may serve
numerous functions within the overall structure of the
semiconductor device.
[0035] FIGS. 5 and 6 illustrate a second embodiment of the present
invention. In the second embodiment, the second dielectric material
52 is recessed relative to the upper surface 54 of the structure 60
and/or relative to the conducting lines 26. Such recess 62 may be
present due to intentional (or unintentional) underfilling of the
trenches 40 with the second dielectric material 52, for example.
Also, such recess 62 may be formed after the second dielectric
material 52 is deposited with a flush fill or overfill of the
trenches 40 by etching the second dielectric material 52 after it
is deposited. Such etching may be performed using a selective etch
and/or using a patterned masking technique, for example.
[0036] In the second embodiment, the recess region 62 above the
second dielectric material 52 is filled with a cap layer or barrier
layer 58 atop the second dielectric material 52, as shown in FIG.
6. It may be necessary or desirable to planarize the intermetal
dielectric structure 60 after the deposition of the cap layer 58 to
provide a planar upper surface 54, as shown in FIG. 6.
[0037] In a third embodiment of the present invention, the second
dielectric material 52 and the hard mask 24 may be recessed
relative to the conducting lines 26 and then covered with a cap
layer 58, as shown in FIG. 7. FIG. 8 shows a fourth embodiment of
the present invention where the hard mask 24 is not present in the
composite intermetal dielectric structure 60 (e.g., the hard mask
24 may have been removed prior to forming the second dielectric
layer 52).
[0038] FIG. 9 shows a fifth embodiment of the present invention,
where there is no hard mask layer 24 over the first dielectric
layer 21, but the second dielectric material 52 is recessed
relative to the first dielectric layer 21 and the conducting lines
26, and the second dielectric material 52 is covered with a cap
layer 58. FIG. 10 shows a sixth embodiment of the present
invention, where there is no hard mask 24 over the first dielectric
layer 21, but the second dielectric material 52 and the first
dielectric layer 21 are recessed relative to the conducting lines
26, and a cap layer 58 is formed atop the second dielectric
material 52 and atop the first dielectric layer 21. With the
benefit of this disclosure, one of ordinary skill in the art may
realize many other embodiments of composite intermetal dielectric
structures 60 fabricated in accordance with fabrication methods of
the present invention.
[0039] Various methods and embodiments of the present invention may
provide any combination of the following advantages. A composite
intermetal dielectric structure 60 allows for tailored electrical
properties at select regions. The insertion of very low-k
dielectric materials 52 at select locations after the formation of
other structures reduces and/or eliminates compatibility issues in
processing. One reason for reduced compatibility issues is that the
initial intermetal dielectric structure 20 is formed (with the
conducting lines 26 and vias 28 in place) before the formation of
the second dielectric material 52 (e.g., very low-k dielectric
material). Hence, the second dielectric material 52 need not be
compatible with the processes used to form the liner layer 30, the
conducting lines 26, and/or the vias 28. Another advantage is that
already tested and developed methods of forming the initial
intermetal dielectric structure 20 (see e.g., FIG. 1) may be used
in conjunction with an embodiment of the present invention.
[0040] Yet another advantage is that the second dielectric material
52 may be a low-k dielectric material that is mechanically weak
(e.g., low modulus, low hardness, soft, and/or prone to cracking)
relative to the first dielectric layer 21. In such case, the first
dielectric layer 21 may be relied upon to provide structural
stability to the composite intermetal dielectric structure 60,
while the second dielectric material 52 provides desirable
electrical characteristics in select regions (e.g., where RC delay
factors need to be reduced between conducting lines 26).
[0041] With a conventional intermetal dielectric structure 20, the
introduction of a new low-k material typically requires numerous
integration and compatibility issues to be addressed, such as
compatibility with subsequent CMP processes, compatibility with
subsequent metal deposition processes, and/or compatibility with
subsequent etching processes, for example. The processes and
structures of embodiments for the present invention may provide the
advantage of avoiding or significantly reducing these integration
and/or compatibility issues. The ability to quickly and easily
integrate, introduce, and/or test new low-k materials into a
composite intermetal dielectric structure 60 using a process and
structure of the present invention may greatly reduce the time and
cost of developing and using new low-k materials.
[0042] The use of a composite intermetal dielectric structure 60 in
accordance with an embodiment of the present invention provides the
advantage of having a more robust and structurally stable low-k
structure with good electrical performance and better package
reliability, as compared to using the same low-k material (as used
for the second dielectric material) in a conventional structure 20
of FIG. 1 (i.e., using the very low-k material of the second
dielectric material 52 as the material for the first dielectric
layer 21 in a conventional structure 20). Thus, an embodiment of
the present invention provides a structurally sound intermetal
dielectric structure while having tailored regions with desirable
electrical characteristics (i.e., low-k). This may provide enhanced
mechanical stability for the total stack of intermetal dielectric
layers as well.
[0043] Furthermore, the second dielectric material 52 need not be
compatible with a copper CMP process used in forming the conducting
lines 26, for example. Delamination due to weak interfaces between
layers may be overcome by using a more aggressive copper CMP
process on the first dielectric layer 21. Then a more benign CMP
process may be used to planarize the second dielectric material 52.
Because the second dielectric material 52 is not present during the
more aggressive copper CMP process, the compatibility of the second
dielectric material 52 with the copper CMP process is not an issue.
This may also reduce or eliminate distortion of thin conducting
lines 26 due to lack of support from surrounding low-k material
during processing of the conducting lines 26 (e.g., CMP) because
the first dielectric material 21 may be made from a stronger
material than that of the second dielectric material 52.
[0044] The second dielectric material 52 also need not be
compatible with processes of depositing a liner layer 30 because it
is formed after the liner layer deposition. Hence, in the case of
porous low-k material used as the second dielectric material 52,
the pores would not interfere with the liner deposition
process.
[0045] When using an embodiment of the present invention, the
second dielectric material 52 need not be compatible with a hard
mask 24 used on the first dielectric layer 21 during the formation
of the conducting lines 26. The hard mask 24 may be removed before
the formation of the second dielectric material 52, for example.
Also, because the hard mask 24 may be removed before the formation
of the second dielectric material 52 or because part of the hard
mask 24 may be etched away during the formation of the trenches 40
for the second dielectric material 52 (see e.g., FIG. 2), the hard
mask 24 need not remain to increase the overall dielectric constant
value for the material between the conducting lines 26 on the
composite structure 60.
[0046] Although extra processing steps may be needed to form a
composite intermetal dielectric structure 60 using a process of the
present invention (e.g., one mask, one etch, one deposition, and
one planarizing step), the results may justify such extra
processing steps. Also, the advantages of the present invention may
outweigh the cost and time required for extra processing steps
needed to implement an embodiment of the present invention.
[0047] Each of the illustrated embodiments in FIGS. 1-10 shows
conducting lines 26 and a via 28 formed using a damascene process,
based on the initial intermetal dielectric structure 20 of FIG. 1.
It is understood, however, that the present invention may also be
used with conductors that are formed by blanket deposition and
patterning (e.g., as is commonly used to form aluminum lines). In
this case, the first dielectric layer 21 (see FIG. 1) may be formed
after patterning the conducting lines 26, for example, and this
first dielectric layer 21 may or may not be planarized with a top
surface of the conducting lines 26.
[0048] FIGS. 11-17 illustrate a method of additional embodiments of
the present invention. FIGS. 11-13 illustrate conventional
processing steps that are often used for conducting lines made from
aluminum, for example. A blanket layer of conducting material 26 is
deposited on an underlying layer 67, as shown in FIG. 11. The
underlying layer 67 is shown merely for illustrative purposes here.
The underlying layer 67 may be any other layer, such as a
substrate, another intermetal dielectric layer, or a device formed
on or in a substrate, for example. The blanket layer of conductive
material is then patterned and etched to form conducting lines 26,
as shown in FIG. 12, which may be provided using conventional
processes, for example. Next, a first dielectric layer 21 is
deposited over the conducting lines 26 to provide a conventional
intermetal dielectric structure 120, which is shown in FIG. 13.
Hence, the conventional intermetal dielectric structure 120 of FIG.
13 provides an initial intermetal dielectric structure for an
embodiment of the present invention.
[0049] Referring now to FIG. 14, select portions of the first
dielectric layer 21 are removed (e.g., patterned and etched) to
form trenches 40. As shown in FIG. 15, the trenches 40 are filled
with a second dielectric material 52 to form a composite intermetal
dielectric structure 160. The second dielectric material 52 is a
low-k dielectric material having a dielectric constant (k) value
less than that of the first dielectric layer 26. After forming the
composite intermetal dielectric structure 160 of FIG. 15, the
structure 160 may or may not be planarized (e.g., CMP, etch back)
to prepare the structure 160 for subsequent layers or processes.
FIG. 16 illustrates an embodiment where the composite intermetal
dielectric structure 160 has been planarized, for example. Also, if
needed or desired, a cap layer or barrier layer 58 may be formed
atop the composite intermetal dielectric structure 160, as shown in
FIG. 17. Also, conductive vias (not shown) may be formed in the
first dielectric layer before the formation of the trenches 40 and
before filling the trenches 40 with a second dielectric material
52.
[0050] It will be appreciated by those skilled in the art having
the benefit of this disclosure that embodiments the present
invention provide a composite low-k dielectric structure. It should
be understood that the drawings and detailed description herein are
to be regarded in an illustrative rather than a restrictive manner,
and are not intended to limit the invention to the particular forms
and examples disclosed. On the contrary, the invention includes any
further modifications, changes, rearrangements, substitutions,
alternatives, design choices, and embodiments apparent to those of
ordinary skill in the art, without departing from the spirit and
scope of this invention, as defined by the following claims. Thus,
it is intended that the following claims be interpreted to embrace
all such further modifications, changes, rearrangements,
substitutions, alternatives, design choices, and embodiments.
* * * * *