U.S. patent application number 11/410229 was filed with the patent office on 2006-08-24 for method to improve palanarity of electroplated copper.
This patent application is currently assigned to Taiwan Semiconductor Manufacturing Company, Ltd.. Invention is credited to Shih-Wei Chou, Ming-Wei Lin, Ming-Hsing Tsai.
Application Number | 20060189127 11/410229 |
Document ID | / |
Family ID | 34795012 |
Filed Date | 2006-08-24 |
United States Patent
Application |
20060189127 |
Kind Code |
A1 |
Chou; Shih-Wei ; et
al. |
August 24, 2006 |
Method to improve palanarity of electroplated copper
Abstract
Narrow trenches in a substrate tend to fill more rapidly than
wide trenches This results in a non-planar surface once all
trenches have been filled. The present invention solves this
problem by performing the electro-deposition in two steps. The
plating bath used during the first step, is optimized for filling
narrow trenches while the plating bath used during the second step,
is optimized for filling wide trenches. The net result is a final
layer having a planar surface, with all trenches being properly
filled.
Inventors: |
Chou; Shih-Wei; (Taipei,
TW) ; Tsai; Ming-Hsing; (Chu-Pei City, TW) ;
Lin; Ming-Wei; (Chu-Pei City, TW) |
Correspondence
Address: |
HAYNES AND BOONE, LLP
901 MAIN STREET, SUITE 3100
DALLAS
TX
75202
US
|
Assignee: |
Taiwan Semiconductor Manufacturing
Company, Ltd.
Hsin-Chu
TW
|
Family ID: |
34795012 |
Appl. No.: |
11/410229 |
Filed: |
April 24, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10763306 |
Jan 23, 2004 |
7064068 |
|
|
11410229 |
Apr 24, 2006 |
|
|
|
Current U.S.
Class: |
438/638 ;
257/E21.175; 257/E21.583; 257/E21.585; 438/674; 438/687 |
Current CPC
Class: |
C25D 7/123 20130101;
H01L 21/7684 20130101; C25D 5/10 20130101; H01L 21/76877 20130101;
C25D 3/38 20130101; H01L 21/2885 20130101; H05K 3/423 20130101 |
Class at
Publication: |
438/638 ;
438/687; 438/674 |
International
Class: |
H01L 21/44 20060101
H01L021/44 |
Claims
1. A process for filling trenches with copper, comprising:
providing a silicon wafer having an upper surface in which are a
plurality of trenches that have at least two different widths, all
trenches being lined with a conductive barrier layer; providing an
aqueous solution that comprises at least one copper salt; forming a
first plating solution that contains a first concentration, in said
aqueous solution, of a first accelerator additive; forming a second
plating solution that contains a second concentration, in said
aqueous solution, of a second accelerator additive, said second
concentration being greater than said first concentration; filling
a container with said first plating solution and immersing said
wafer therein, then electroplating onto said upper surface a first
thickness of copper that is sufficient to overfill all trenches
whose width is less than an amount while under-filling all trenches
whose width is greater than said amount; while leaving said wafer
in container, replacing said first plating solution with said
second plating solution; and then electroplating on said wafer a
second thickness of copper that is sufficient to overfill all
trenches.
2. The process described in claim 1 wherein the step, of replacing
said first plating solution with said second plating solution,
further comprises a continuous change in accelerator concentration
without interruption of electroplating.
3. The process described in claim 1 wherein said aqueous solution
further comprises 10-50 g/L copper salts, 5-300 g/L
H.sub.2SO.sub.4, and 20-100 ppm HCI.
4. The process described in claim 1 wherein said first accelerator
additive is 3-mercapto-1propanesulfonate at a concentration that is
between about 10 and 100 ppm.
5. The process described in claim 1 wherein said second accelerator
additive is 3sulfopropyl disulfide.
6. The process described in claim 5 wherein said second accelerator
additive concentration is between about 10-100 ppm.
7. The process described in claim 1 wherein said accelerator
additive is sulfonated sulfonated acetylthiourea,
3-mercapto-1propanesulfonate, dibenzyl-dithio-carbammat,
2-mercaptoethanesulfonate, or n,n-dimethyl-dithiocabamic
acid-(3-sulfopropyl)ester.
8. A process for filling trenches with copper, comprising:
providing a silicon wafer having an upper surface in which are a
plurality of trenches that have at least two different widths, all
trenches being lined with a seed layer; providing an aqueous
solution that comprises at least one copper salt; forming a first
plating solution that contains a first concentration, in said
aqueous solution, of a first accelerator additive; forming a second
plating solution that contains a second concentration, in said
aqueous solution, of a second accelerator additive, said second
concentration being greater than said first concentration; filling
a plating bath with said first plating solution and immersing said
wafer therein, then electroplating onto said seed layer a first
thickness of copper that is sufficient to overfill all trenches
whose width is less than an amount while under-filling all trenches
whose width is greater than said amount; while leaving said wafer
in said plating bath, replacing said first plating solution with
said second plating solution; and then electroplating on said wafer
a second thickness of copper that is sufficient to overfill all
trenches.
9. The process described in claim 8 wherein the step, of replacing
said first plating solution with said second plating solution,
further comprises a continuous change in accelerator concentration
without interruption of electroplating.
10. The process described in claim 9 wherein said aqueous solution
further comprises 10-50 g/L copper salts, 5-300 g/L
H.sub.2SO.sub.4, and 20-100 ppm HCl.
11. The process described in claim 9 wherein said first accelerator
additive is (3-sulfopropyl) disulfide, 3-mercapto-propylsulfonic at
a concentration that is between about 10-100 ppm.
12. The process described in claim 9 wherein said second
accelerator additive is 3sulfopropyl disulfide.
13. The process described in claim 12 wherein said second
accelerator additive concentration is between about 10-100 ppm.
14. The process described in claim 9 wherein said second
accelerator additive is sulfonated acetylthiourea,
3-mercapto-1propanesulfonate, dibenzyl-dithio-carbammat,
2-mercaptoethanesulfonate, or n,n-dimethyl-dithiocabamic
acid-(3-sulfopropyl)ester.
15. The process described in claim 8 wherein said seed layer is
copper, or copper doped with titanium, magnesium, zirconium, tin,
or zinc.
Description
RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/763,306 filed Jan. 23, 2004 entitled, "Method to Improve of
Electroplated Copper".
FIELD OF THE INVENTION
[0002] The invention relates to the general field of integrated
circuits with particular reference to filling trenches with
metal.
BACKGROUND OF THE INVENTION
[0003] With the introduction of the damascene process, the
formation of wires by filling trenches has become routine.
Additionally, particularly for the case of copper-filled trenches,
the method of choice for depositing the metal has been
electroplating. However, as trenches have become narrower and
narrower, it has become necessary to employ a range of additives
that need to be included in the plating solution to give the best
filling results. The technology involved is further complicated by
the fact that the effects of these multiple additives are often
interactive.
[0004] We can identify three broad additive types:
[0005] Accelerators serve to increase the deposition rate during
electroplating. They are usually small organic molecules containing
a polar sulfur, oxygen, or nitrogen functional group. In addition
to increasing the deposition-rate, they promote denser nucleation
which leads to the growth of films having a finer grain structure.
Accelerators are usually present in the plating bath at a low
concentration level (1-25 ppm).
[0006] Suppressors are additives that reduce the plating rate and
are usually present in the plating bath at higher concentrations
(200-2,000 ppm), so that their concentration at the interface is
not strongly dependent on their rate of mass transfer or diffusion
to the wafer surface. They are generally polymeric surfactants with
high molecular weight such as polyethylene glycol (PEG). The
suppressor molecules slow down the deposition rate by adsorbing on
the wafer surface where they form a diffusion barrier.
[0007] Levelers are additives whose purpose is to reduce surface
roughness. They are similar to suppressors in that they reduce
deposition rate. However, they are present in very small
concentrations (<25 ppm) so their blocking effects at the
surface are highly localized. The net effect is that they
selectively reduce deposition on the high spots thereby giving the
low spots a chance to `catch up`.
[0008] It has been known for some time that narrow trenches
(typically having widths less than about 1 microns) tend to fill
more rapidly than wide trenches (typically having widths greater
than about 2 microns). This results in problems of the type
schematically illustrated in FIG. 1. Seen there, in cross-section,
is a portion of a substrate (typically a silicon wafer) 11 in whose
upper surface several narrow trenches 12 and one wide trench 13
have been formed. After electro-deposition of metal layer 14 the
latter is found to have the profile shown, i.e. it locally thicker
over the narrow trenches and locally thinner over the wide
trench.
[0009] The general approach that the prior art has taken to dealing
with this problem has been to try to balance the concentrations of
the various additives so as to find a single formulation that works
well for both narrow and wide trenches simultaneously. As will be
shown, the present invention has abandoned this approach in favor
of a two-step plating method.
[0010] A routine search of the prior art was performed with the
following references of interest being found:
[0011] In U.S. Pat. No. 6,346,479 B1, Woo et al. show an
electroplating process of first filling holes using an
electroplating process that has been optimized for conformal
coating followed by a second electroplating step that has been
optimized for non-conformal coating. Trench width is not explicitly
taught as a criterion for determining which solution to use
where.
[0012] Chen et al., in U.S. Pat. No. 6,207,222 B1, show multi-step
plating to fill a Cu dual damascene opening while U.S. Pat. No.
6,140,241 (Shue et al.), U.S. Pat. No. 6,136,707 (Cohen), and U.S.
Pat. No. 5,814,557 (Venkatranman) all show related plating
processes.
SUMMARY OF THE INVENTION
[0013] It has been an object of at least one embodiment of the
present invention to provide a process for filling trenches in a
substrate by depositing a metal layer through electroplating.
[0014] Another object of at least one embodiment of the present
invention has been that said trenches have at least two different
widths.
[0015] Still another object of at least one embodiment of the
present invention has been that, at the conclusion of said process,
said metal layer has a planar surface.
[0016] These objects have been achieved by performing the
electro-deposition in two steps. The plating bath used during the
first step, is optimized for filling narrow trenches while the
plating bath used during the second step, is optimized for filling
wide trenches. The net result is a final layer having a planar
surface, with all trenches being properly filled.
DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 illustrates a problem associated with filling,
through electroplating, a surface that contains trenches whose
widths vary over a wide range.
[0018] FIG. 2 is a plot of deposition rate vs. concentration for
two different accelerator additives.
[0019] FIG. 3 is a schematic cross-section through a substrate part
way through the process of the present invention.
[0020] FIG. 4 is a schematic cross-section through a substrate at
the conclusion of the process of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0021] Some examples of accelerators are 3-sulfopropyldisulfide, 41
sulfonated acetylthiourea, 3-mercapto-1-propanesulfonate (MPSA),
and dibenzyl-dithio-carbammate.
[0022] The precise concentration of accelerator additive that is
needed to produce a given deposition rate can vary from one
additive to another. We illustrate this in FIG. 2 which compares
the effects of two different chemicals when added to a plating bath
as an accelerator. Curves 21 and 22 are plots of `potential
difference needed to initiate plating` (which equates with film
growth rate) vs. additive concentration in parts per thousand.
Thus, although both curves are similar in form, the chemical
associated with curve 21 is less effective than the one associated
with curve 22. Examples of the former include
3-sulfopropyldisulfide, while examples of the latter include
3-mercapto-1-propanesulfonate (MPSA).
[0023] The process of the present invention begins with the
provision of silicon wafer 11 (as seen for example in FIG. 1) in
whose upper surface there are multiple trenches having a range of
widths. These trenches will have been lined with a barrier layer to
contain the copper. This barrier layer may be of a material such as
TiN that is sufficiently conductive to serve as a cathode for the
copper deposition and/or an additional seed layer of copper, or
copper doped with titanium, magnesium, zirconium, tin, or zinc, may
first be laid down as a seed layer.
[0024] Also provided at the start of the process is an aqueous
solution of at least one copper salt. A typical formulation for
this aqueous solution would be 10-50 g/l cap.sub.1 SGHS, 5-300 g/l
H.sub.2SO.sub.4, and 20-100 ppm HCl. Two plating solutions are then
formed from this. Each is the original aqueous copper solution to
which an accelerator chemical has been added. A different chemical
may be used for each plating solution and, in general, the additive
concentration in the second plating solution will be greater than
in the first one.
[0025] Examples of accelerator additives suitable for use in the
first plating solution include (but are not limited to)
3-sulfopropyldisulfide and 3-mercapto-1-propanesulfonate (MPSA) at
a concentration that is between about 10 and 100 ppm. Additionally,
the first plating solution will include a short chain polymer (less
than about 200 units per chain) having low molecular weight (less
than about 10,000).
[0026] For the second plating solution, our preferred accelerator
additive has been 3-sulfopropyl disulfide at a concentration is
between about 10 and 50 ppm, but other accelerator additives such
as sulfonated acetylthiourea, 3-mercapto-1-propanesulfonate,
dibenzyl-dithio-carbammate-, 2-mercaptoethanesulfonate, or
n,n-dimethyl-dithiocabamic acid-(3-sulfopropyl)ester could also
have been used. Additionally, the second plating solution will
include a long chain polymer (more than about 1,000 units per
chain) having high molecular weight (more than about 50,000).
[0027] Then, in a bath that contains the first plating solution,
electroplating onto the wafer surface is initiated and allowed to
proceed until sufficient copper has been deposited to overfill all
trenches whose width is less than about 0.2 microns while
under-filling all trenches whose width exceeds this. At this point,
the thickness of deposited copper would typically be between about
0.1 and 0.2 microns. The result is illustrated in FIG. 3 where it
can be seen that the narrow trenches 12 have uniformly over-filled
while wide trench 13 is till only partially filled. It is clear
that if electroplating were allowed to continue under these
conditions, the result would be as was seen in FIG. 1.
[0028] Instead, in a departure from the prior art, the wafer is now
transferred to a second bath that contains the second of the two
plating solutions mentioned above, i.e. to a plating solution in
which there is dissolved a more powerful accelerator additive
and/or a higher concentration of accelerator. Electroplating is now
resumed. The plating solution in the second bath is now such as to
be optimized for filling wide trenches. The result is that
electroplated material in the trench builds up faster than outside
it so that electroplated layer 44 (FIG. 4) that is obtained once
the wide trenches have been overfilled, ends up with a surface that
is essentially planar, for an additional copper thickness that is
between about 0.3 and 0.5 microns.
[0029] Two other embodiments of the present invention apply the
above process with some modifications. Both additional embodiments
still make use of two different solutions but only a single plating
chamber, or container, is required. Such an approach is useful, for
example, in a small-scale operation such as a pilot line.
[0030] In the first of these additional embodiments, when the first
plating step has been completed (narrow trenches overfilled), the
wafer is left in place (so that electrical connections to it need
not be disconnected), the first plating solution is emptied out of
the container, is replaced by the second plating solution, and
plating is resumed.
[0031] In the second additional embodiment, when the first plating
step has been completed (narrow trenches overfilled), the wafer is
left in place (so that electrical connections to it need not be
disconnected), while the first plating solution is gradually and
continuously replaced by the second plating solution. If the only
difference between the two plating solutions is in the
concentration of the accelerator additive, the step can be further
simplified by merely adding additional accelerant to the bath. In
this embodiment, there is no need to terminate electro-deposition
while the solutions are being changed it being, in fact,
advantageous to allow deposition to continue since, as the plating
solution composition changes, it becomes steadily more suited to
wider and wider trenches.
[0032] Table I below provides a summary of the composition of the
two baths: TABLE-US-00001 Concentration Chemical Components Bath 1
Bath 2 VMS Cu/H2S04/Cl 3060 g/L Cu, 5-30 g/L 15-60 g/L Cu, 5-300
g/L H2S04 and 20-100 mg/L H2S04 and 20-100 mg/L (ppm) C1 (ppm) CI
Accelerator Bis (3-sulfopropyl) disulfide, 10-30 ppm 5-10 ppm
3-mercapto-propylsulfonic acid, 3-sulfopropul)ester Suppressor
Polyalkylene glycols, 50-200 ppm 200-1000 ppm Polyoxyalkyene
glycols, copolymer of polyoxyalkyenes Leveler Alkylated
polyalkyleneimine, 0 ppm 1-20 ppm 2-mercatothiazoline
* * * * *