U.S. patent application number 10/268735 was filed with the patent office on 2003-04-03 for barrier and seed layer system.
This patent application is currently assigned to LSI Logic Corporation. Invention is credited to Catabay, Wilbur G., Kumar, Kiran, Wang, Zhihai.
Application Number | 20030064593 10/268735 |
Document ID | / |
Family ID | 24690436 |
Filed Date | 2003-04-03 |
United States Patent
Application |
20030064593 |
Kind Code |
A1 |
Kumar, Kiran ; et
al. |
April 3, 2003 |
Barrier and seed layer system
Abstract
A method for creating a highly reflective surface on an
electroplated conduction layer. A barrier layer is deposited on a
substrate using a self ionized plasma deposition process. The
barrier layer has a thickness of no more than about one hundred
angstroms. An adhesion layer is deposited on the barrier layer,
using a self ionized plasma deposition process. A seed layer is
deposited on the adhesion layer, also using a self ionized plasma
deposition process, at a bias of no les than about one hundred and
fifty watts. The combination of the barrier layer, adhesion layer,
and seed layer is at times referred to herein as the barrier seed
layer. The conduction layer is electroplated on the seed layer,
thereby forming the highly reflective surface on the conduction
layer, where the highly reflective surface has a reflectance of
greater than about seventy percent.
Inventors: |
Kumar, Kiran; (Sunnyvale,
CA) ; Wang, Zhihai; (Sunnyvale, CA) ; Catabay,
Wilbur G.; (Saratoga, CA) |
Correspondence
Address: |
LSI Logic Corporation
1551 McCarthy Blvd.
M/S: D-106 Patent Department
Milpitas
CA
95035
US
|
Assignee: |
LSI Logic Corporation
|
Family ID: |
24690436 |
Appl. No.: |
10/268735 |
Filed: |
October 10, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10268735 |
Oct 10, 2002 |
|
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09670448 |
Sep 26, 2000 |
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6486064 |
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Current U.S.
Class: |
438/689 ;
257/E21.268; 257/E21.285; 257/E21.302; 257/E21.337 |
Current CPC
Class: |
H01L 21/2652 20130101;
Y10S 438/957 20130101; H01L 29/6659 20130101; H01L 21/31662
20130101; H01L 21/28247 20130101; Y10S 438/914 20130101; H01L
21/3144 20130101; H01L 21/3211 20130101 |
Class at
Publication: |
438/689 |
International
Class: |
H01L 021/302; H01L
021/461 |
Claims
What is claimed is:
1. A method for creating a highly reflective surface on an
electroplated conduction layer, the method comprising the steps of:
depositing a barrier layer on a substrate using a self ionized
plasma deposition process, the barrier layer having a thickness of
no more than about one hundred angstroms, depositing an adhesion
layer on the barrier layer using a self ionized plasma deposition
process, depositing a seed layer on the adhesion layer using a self
ionized plasma deposition process at a bias of no less than about
one hundred and fifty watts, and electroplating the conduction
layer on the seed layer, thereby forming the highly reflective
surface on the conduction layer, where the highly reflective
surface has a reflectance of greater than about seventy
percent.
2. The method of claim 1 wherein the barrier layer comprises
tantalum nitride.
3. The method of claim 1 wherein the adhesion layer comprises
tantalum.
4. The method of claim 1 wherein the seed layer comprises
copper.
5. The method of claim 1 wherein the conduction layer comprises
copper.
6. The method of claim 1 wherein the barrier layer, adhesion layer,
and seed layer system exhibits a substantially constant mean sheet
resistance over time.
7. The method of claim 1 wherein the barrier layer is deposited
with an alternating current bias of no less than about three
hundred watts.
8. The method of claim 1 wherein the adhesion layer is deposited
with an alternating current bias of no less than about three
hundred watts.
9. The method of claim 1 wherein the seed layer is deposited with
an alternating current bias of no less than about three hundred
watts.
10. The method of claim 1 wherein the barrier layer and the
adhesion layer are deposited to a total thickness that is
sufficient to ensure an adequate barrier between the conduction
layer and the substrate.
11. An integrated circuit having a conductive metal system made by
the method of claim 1.
12. A method for creating a highly reflective surface on a metal
layer system having a substantially constant mean sheet resistance,
the method comprising the steps of: depositing a barrier layer on a
substrate using a self ionized plasma deposition process, the
barrier layer having a thickness of no more than about one hundred
angstroms, depositing an adhesion layer on the barrier layer using
a self ionized plasma deposition process, depositing a seed layer
on the adhesion layer using a self ionized plasma deposition
process at a bias of no less than about one hundred and fifty
watts, and electroplating a conduction layer on the seed layer,
thereby forming the highly reflective surface on the conduction
layer, where the highly reflective surface has a reflectance of
greater than about seventy percent.
13. The method of claim 12 wherein the barrier layer comprises
tantalum nitride.
14. The method of claim 12 wherein the adhesion layer comprises
tantalum.
15. The method of claim 12 wherein the seed layer comprises
copper.
16. The method of claim 12 wherein the conduction layer comprises
copper.
17. The method of claim 12 wherein the barrier layer is deposited
with an alternating current bias of no less than about three
hundred watts.
18. The method of claim 12 wherein the adhesion layer is deposited
with an alternating current bias of no less than about three
hundred watts.
19. The method of claim 12 wherein the seed layer is deposited with
an alternating current bias of no less than about three hundred
watts.
20. An integrated circuit having a conductive metal system made by
the method of claim 12.
Description
FIELD
[0001] The invention relates generally to the field of integrated
circuit fabrication and, in particular, to improved metallization
methods useful in the production of semiconductor devices.
BACKGROUND
[0002] During the manufacture of integrated circuits, such as
semiconducting devices, various conductive and insulative layers of
material are deposited on a substrate to provide circuits and
interconnects between the circuits. As integrated circuits continue
to shrink in size and become more powerful, newer and better
manufacturing techniques are devised to improve their
performance.
[0003] It is desirable for the metallization process to provide
surfaces that have high reflectivity. Reflectivity is an indication
of the surface roughness, or smoothness, as determined by the
amount of light reflected from the surface. Surfaces with a low
reflectivity are typically rougher than surfaces of the same
material that have a high reflectivity. The reflectivity is
expressed in terms of a percentage, based on the intensity of the
reflected light compared to the intensity of the incident light. A
highly reflective surface tends to be easier to planarize using a
process such as chemical mechanical polishing.
[0004] Metal layers that are electroplated on sputtered barrier and
seed layer systems typically exhibit a high degree of surface
roughness. This is especially true for copper layers that are
electroplated on top of a tantalum nitride, tantalum barrier layer
and copper seed layer that are deposited using a self ionized
plasma sputter process. High surface roughness of the electroplated
copper layers manifests itself as a relatively low reflectance,
which condition is also called haze, which in other words is a
reflectance that is below about seventy percent.
[0005] Self ionized plasma deposited barrier seed layer also
typically exhibit a high degree of instability. As the layer self
anneals, the mean sheet resistance and sheet resistance uniformity
tend to change for several hours or so after deposition. The
reflectivity problems and resistivity problems, described above,
adversely affect later processes such as the chemical mechanical
polishing step, and tends to impact line resistance and
electromigration properties of the layer.
[0006] There exists a need, therefore, for improved methods of
manufacture to enhance the uniformity of the underlying layers and
increase the reflectance of the plated layers, while at the same
time maintaining adequate barrier layers between the electroplated
layer and the substrate.
SUMMARY
[0007] The above and other needs are met by a method for creating a
highly reflective surface on an electroplated conduction layer. A
barrier layer is deposited on a substrate using a self ionized
plasma deposition process. The barrier layer has a thickness of no
more than about one hundred angstroms. An adhesion layer is
deposited on the barrier layer, using a self ionized plasma
deposition process. A seed layer is deposited on the adhesion
layer, also using a self ionized plasma deposition process, at a
bias of no less than about one hundred and fifty watts. The
combination of the barrier layer, adhesion layer, and seed layer is
at times referred to herein as the barrier seed layer. The
conduction layer is electroplated on the seed layer, thereby
forming the highly reflective surface on the conduction layer,
where the highly reflective surface has a reflectance of greater
than about seventy percent.
[0008] In another aspect the invention provides a method for
creating a highly reflective surface on a metal layer system having
a substantially constant mean sheet resistance. A barrier layer is
deposited on a substrate using a self ionized plasma deposition
process. The barrier layer has a thickness of no more than about
one hundred angstroms. An adhesion layer is deposited on the
barrier layer, using a self ionized plasma deposition process. A
seed layer is deposited on the adhesion layer, also using a self
ionized plasma deposition process, at a bias of no less than about
one hundred and fifty watts. A conduction layer is electroplated on
the seed layer, thereby forming the highly reflective surface on
the conduction layer, where the highly reflective surface has a
reflectance of greater than about seventy percent.
[0009] An advantage of the invention is that the electroplated
conduction layer deposited on the barrier seed layer formed as
described above exhibits a significantly higher reflectance, or in
other words much lower surface roughness, than an electroplated
conduction layer deposited on a barrier seed layer formed by prior
art processes. Furthermore, the self ionized plasma deposited
barrier seed layer as described above tends to be more uniform and
stable over time with respect to the mean sheet resistance of the
layer, which may indicate a lower degree of self annealing. Because
the mean sheet resistance of the barrier seed layer is relatively
constant over time, the amount of elapsed time between the barrier
seed layer deposition and the electroplating step is less critical,
and may be substantially shorter. The process is also tends to
reduce electromigration within the electroplated conduction
layer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Further advantages of the invention are apparent by
reference to the detailed description when considered in
conjunction with the figures, which are not to scale so as to more
clearly show the details, wherein like reference numbers indicate
like elements throughout the several views, and wherein:
[0011] FIGS. 1-5 are cross sectional views of a substrate
illustrating the steps for depositing the layers according to the
present invention,
[0012] FIG. 6 is a graphical comparison of the change in mean sheet
resistance over time for substrates containing layers made
according to the present invention and prior art methods, and
[0013] FIG. 7 is a graphical comparison of the change in mean sheet
resistance standard deviation percentage over time for substrates
containing layers made according to the present invention and prior
art methods.
DETAILED DESCRIPTION
[0014] FIGS. 1-5 depict a method for applying various layers to a
substrate 12, such as a semiconducting substrate for the formation
of an integrated circuit 10. The invention is particularly
applicable to metal interconnects provided in vias, such as in a
copper dual damascene structure. However, the invention is equally
applicable to electroplating of other metal structures on other
substrates. As used herein, a reference to a metal also includes
various alloys of the metal.
[0015] In a preferred embodiment, a method according to the
invention is directed to applying a barrier seed layer to a
substrate 12 of an integrated circuit 10, so that the electroplated
metal deposited on the barrier seed layer exhibits high reflectance
and reduced electromigration. While the layers according to the
invention may be applied directly to a silicon substrate, it is
preferable to apply such layers to insulating or dielectric layers
already on the silicon substrate. Suitable dielectric or insulating
layers may include silicon oxide, such as silicon dioxide, silicon
nitride, glass, and other such materials. For clarity and
simplicity in the explanation, only the layers applied according to
the present invention are shown and discussed in detail herein.
[0016] To apply a barrier seed layer to a substrate 12, the
substrate 12 is preferably inserted in a deposition chamber. In the
case of electroplated copper, the barrier seed layer is preferably
a barrier layer of tantalum nitride, an adhesion layer of tantalum,
and a seed layer of copper, most preferably deposited in that
order. The deposition process employed is most preferably a self
ionized plasma physical vapor deposition process. The three
deposition processes may be conducted in separate deposition
chambers, such as in a cluster tool, or may alternately be
conducted in a single deposition chamber.
[0017] A barrier layer 14 is applied to the substrate 12, as
depicted in FIG. 2. The barrier layer 14 is preferably tantalum
nitride. The barrier layer 14 is preferably applied with a
thickness of no more than about one hundred angstroms. The
relatively thin barrier layer 14 tends to result in an increase in
smoothness and reflectance of the electroplated conduction layer,
as described in more detail below. The barrier layer 14 is
preferably applied in a self ionized plasma with an alternating
current bias of no less than about three hundred watts. Other
parameters for the deposition are set as for standard
processing.
[0018] An adhesion layer 16 is preferably applied to the barrier
layer 14, as depicted in FIG. 2. The adhesion layer 16 is
preferably tantalum. As with the barrier layer 14, the adhesion
layer 16 of tantalum is preferably applied in an self ionized
plasma deposition using an alternating current bias of no less than
about three hundred watts. As before, other parameters for the
deposition are set as for standard processing.
[0019] By selecting a barrier layer 14 thickness of no more than
about one hundred angstroms, the adhesion layer 16 thickness is
selected within relatively wide limits, provided the overall
properties of the barrier layer 14 and the adhesion layer 16 are
sufficient to inhibit migration of metal ions, such as from the
subsequent layers, into the substrate 12.
[0020] With reference to FIG. 4, a seed layer 18, preferably
containing metal ions similar to or compatible with the metal to be
applied using the subsequent electroplating process, is then
deposited on the adhesion layer 16. The seed layer 18 is preferably
copper. Preferably, the seed layer 18 is deposited with a thickness
of from about one thousand angstroms to about two thousand
angstroms, and most preferably about twelve hundred and fifty
angstroms. As with the barrier layer 14 and adhesion layer 16, the
seed layer 18 is preferably applied in a self ionized plasma
deposition with an alternating current bias of no less than about
one hundred and fifty watts, and most preferably no less than about
three hundred watts. As before, other parameters for the deposition
are set as for standard processing.
[0021] As depicted in FIG. 5, a conduction layer 20 is preferably
deposited on top of the seed layer 18. The conduction layer 20 is
preferably deposited in an electroplating process. Most preferably,
the conduction layer 20 is formed of the same material as the seed
layer 18, which is most preferably copper. The conduction layer 20
is preferably formed according to standard processing. However,
because of the novel deposition process parameters used for the
deposition of the barrier seed layer as described above, the
conduction layer 20 tends to have a reflectance that is
dramatically enhanced over that produced by prior art processes.
Further, the conduction layer 20 also tends to be more resistant to
electromigration.
[0022] An advantage of the invention when using self ionized plasma
deposition processes as described above to apply the barrier seed
layer to the substrate 12 is that the barrier seed layer tends to
exhibit a significantly more stable mean sheet resistance and
resistance uniformity over time. Accordingly, it is believed that
self annealing of the self ionized plasma deposited barrier seed
layer is less than with prior art processing. A comparison of the
resistance properties of the barrier seed layer and the
electroplated copper conductance layer 20 reflectance properties
for various barrier adhesion layer thicknesses and seed layer 18
bias powers are given in Table 1.
1 TABLE 1 Barrier Adhesion Seed Seed Conduction Conduction Layer
Layer Layer Seed Layer Layer Mean Layer Mean Thickness Thickness
Bias Layer RSM Reflectance Reflectance (angstroms) (angstroms)
(watts) RSM SD % (%) Std Dev. % 1 100 100 50 0.15 10.58 26.7 49.8 2
100 100 300 0.20 3.63 73.6 15.1 3 100 150 50 0.15 9.86 26.7 47.4 4
100 150 300 0.2 3.44 69.9 15.1 5 150 100 50 0.14 5.11 15.6 38.8 6
150 100 300 0.19 7.51 42.3 49.4 7 150 150 50 0.14 5.78 15.4 42.9 8
150 150 300 0.2 5.8 47.7 41.5 9 83 125 175 0.19 3.13 79.1 1.6 10
167 125 175 0.16 11.34 26.1 66.4 11 125 83 175 0.17 8.66 39.3 38.6
12 125 167 175 0.17 10.43 28.7 55.6 13 125 125 0 0.13 5.11 16.9
26.4 14 125 125 385 0.21 3.8 71.8 15.3 15 125 125 175 0.17 10.21
31.9 46.6 16 125 125 175 0.17 8.99 31.5 50.6 17 125 125 175 0.17
8.7 34.3 43.7 18 125 125 175 0.17 8.54 34.4 46.9 19 125 125 175
0.17 9.17 34.8 40.3 20 125 125 175 0.17 8.69 32.5 46.9
[0023] As shown in Table 1, the lowest standard deviation
percentage (SD %) for the mean sheet resistance (RSM) and
conduction layer 20 reflectance occurred with a tantalum nitride
barrier layer 14 thickness of eighty-three angstroms, a tantalum
adhesion layer 16 thickness of one hundred and twenty-five
angstroms, and a copper seed layer 18 bias of one hundred and
seventy-five watts. The standard deviation of the reflectance tends
to be best when the reflectance percentage is the highest. There
tends to be excellent correlation between the standard deviation of
the reflectance of the electroplated copper conduction layer 20 and
the standard deviation of the mean sheet resistance of the barrier
seed layer. This correlation tends to provide support for the
theory that the uniformity of the grain size of the copper seed
layer 18 is determinative of the mean sheet resistance uniformity
and electroplated copper conduction layer 20 reflectance
properties.
[0024] Increasing the tantalum nitride barrier layer 14 thickness
to one hundred angstroms or above tended to require a higher copper
seed layer 18 bias (samples 2, 4 and 14) in order to achieve
relatively uniform mean sheet resistance and mean reflectance of
the electroplated conduction layer 20. A mean reflectance of
greater than about seventy percent was not observed at a copper
seed layer 18 bias of less than one hundred and fifty watts, as
shown by samples 1, 3, 5 and 7, regardless of the thickness of the
barrier layer 14 and the adhesion layer 16.
[0025] All of the samples in Table 1 tend to indicate that the
adhesion layer 16 thickness has little or no impact on the
reflectance of the conduction layer 20, especially at a higher
copper seed layer 18 bias. As seen by samples 2, 4 and 14, only
with a copper seed layer 18 bias of greater than about two hundred
watts was a uniformity of the electroplated copper conduction layer
20 reflectance of about fifteen percent or less observed. The above
samples also show that the mean sheet resistance of the seed layer
18 tends to increase with the copper seed layer 18 bias, which may
be a result of the resputtering effect that leads to layer
thinning.
[0026] A comparison of the mean sheet resistance of the barrier
seed layer made according to the present invention and by prior art
processes is shown graphically in FIGS. 6 and 7. The data for the
mean sheet resistance aging and standard deviation were obtained
from a barrier seed layer made as follows:
[0027] Curve A of FIG. 6 and curve D of FIG. 7 were generated from
aging data for ninety angstroms of a tantalum nitride barrier layer
14, one hundred and sixty angstroms of a tantalum adhesion layer
16, and fifteen hundred angstroms of a copper seed layer 18, each
deposited by self ionized plasma deposition at three hundred watts
alternating current bias. Curve B of FIG. 6 and curve C of FIG. 7
were generated from aging data for one hundred and fifty angstroms
of a tantalum nitride barrier layer 14, and one hundred angstroms
of a tantalum adhesion layer 16, each deposited by self ionized
plasma deposition at three hundred watts alternating current bias,
and fifteen hundred angstroms of a copper seed layer 18 deposited
by self ionized plasma deposition at fifty watts alternating
current bias.
[0028] As shown by FIGS. 6 and 7, the mean sheet resistance and
standard deviation percentage of the barrier seed layer of the
present invention (curves A and D) are relatively constant over
time, whereas the mean sheet resistance and standard deviation
percentage of the barrier seed layer made by a conventional process
vary significantly over time. It is indicated, based on the data
given in Table 1, that the reflectance of a metal conductive layer
20 applied by an electroplating process to the barrier seed layer
made according to the present invention exhibits substantially
higher reflectance, typically above about seventy percent, and that
subsequent chemical mechanical polishing of the conductive layer 20
proceeds in a substantially uniform manner from substrate to
substrate. As a result of the observed stability of the barrier
seed layer provided according to the present invention, the time
before which the conduction layer 20 is deposited on the barrier
seed layer is less critical, providing increased manufacturing
freedom.
[0029] Most preferably, the barrier seed layer is formed by a self
ionized plasma deposition with an alternating current bias of no
less than about three hundred watts, where the tantalum nitride
barrier layer 14 is deposited to about ninety angstroms, the
tantalum adhesion layer 16 is deposited to about one hundred and
sixty angstroms, and the copper seed layer 18 is deposited to about
twelve hundred and fifty angstroms.
[0030] It is appreciated that there are many steps that are
required to accomplish the processing as described above, and that
some intermediate steps, such as patterning, etching and stripping
steps, have been omitted. However, those steps which are not
completely described above are preferably accomplished according to
the processes that are known to be compatible with the materials
and processes as described above. Those steps which are not
described herein have been omitted so as to not unnecessarily
encumber this description of the more relevant portions of the
invention.
[0031] The foregoing description of preferred embodiments for this
invention have been presented for purposes of illustration and
description. They are not intended to be exhaustive or to limit the
invention to the precise form disclosed. Obvious modifications or
variations are possible in light of the above teachings. The
embodiments are chosen and described in an effort to provide the
best illustrations of the principles of the invention and its
practical application, and to thereby enable one of ordinary skill
in the art to utilize the invention in various embodiments and with
various modifications as is suited to the particular use
contemplated. All such modifications and variations are within the
scope of the invention as determined by the appended claims when
interpreted in accordance with the breadth to which they are
fairly, legally, and equitably entitled.
* * * * *