U.S. patent application number 10/772687 was filed with the patent office on 2004-11-11 for process and system for providing electrochemical processing solution with reduced oxygen and gas content.
Invention is credited to Basol, Bulent M..
Application Number | 20040222100 10/772687 |
Document ID | / |
Family ID | 33415924 |
Filed Date | 2004-11-11 |
United States Patent
Application |
20040222100 |
Kind Code |
A1 |
Basol, Bulent M. |
November 11, 2004 |
Process and system for providing electrochemical processing
solution with reduced oxygen and gas content
Abstract
The present invention provides a method and system for
electrochemically processing a workpiece surface using a process
solution that is degassed and deoxygenated. A deoxygenation step of
the process solution substantially removes dissolved oxygen from
the process solution by utilizing a treatment gas. In a following
degassing step, remaining oxygen, the treatment gas and other gases
are removed from the process solution by degassing the deoxygenated
solution in a degasser. After degassing, the process solution is
used to electrochemically process the workpiece surface.
Inventors: |
Basol, Bulent M.; (Manhattan
Beach, CA) |
Correspondence
Address: |
NUTOOL, INC
LEGAL DEPARTMENT
1655 MCCANDLESS DRIVE
MILPITAS
CA
95035
US
|
Family ID: |
33415924 |
Appl. No.: |
10/772687 |
Filed: |
February 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10772687 |
Feb 5, 2004 |
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10425782 |
Apr 29, 2003 |
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Current U.S.
Class: |
205/99 ; 205/291;
257/E21.175 |
Current CPC
Class: |
C23C 18/38 20130101;
B24B 37/042 20130101; C25D 21/18 20130101; B24B 57/02 20130101;
C25D 21/04 20130101; H01L 21/2885 20130101; C23C 18/1617 20130101;
C25D 7/123 20130101 |
Class at
Publication: |
205/099 ;
205/291 |
International
Class: |
C25D 003/38 |
Claims
I claim:
1. A method of electrochemically processing a conductive surface of
a workpiece using a process solution, comprising the steps of:
deoxygenating the process solution to substantially remove oxygen
from the process solution; degassing the process solution, after
deoxygenating, to remove gases; and electrochemically processing
the surface of the workpiece with the process solution that is
deoxygenated and degassed.
2. The method of claim 1, wherein the step of deoxygenating
comprises introducing a treatment gas into the process
solution.
3. The method of claim 2, wherein the step of degassing removes the
treatment gas along with gases from the process solution.
4. The method of claim 3, wherein the degassing step further
reduces the amount of remaining oxygen.
5. The method of claim 1, wherein the step of processing comprises
electrochemical deposition.
6. The method of claim 5, wherein the electrochemical deposition
comprises copper electrodeposition.
7. A system for removing gasses from a process solution that is
used to process a workpiece surface, comprising: a holding tank for
holding the process solution; a deoxygenator for receiving the
process solution from the holding tank to substantially reduce
oxygen content in the process solution; and a degasser for
receiving the process solution, which is deoxygenated, from the
deoxygenator to remove substantially all gases from the process
solution.
8. The system of claim 7, further comprising at least one
processing unit for receiving the process solution from the
degasser to process the workpiece surface.
9. The system of claim 7, wherein the deoxygenator treats the
process solution with a treatment gas to reduce the oxygen
content.
10. The system of claim 9, wherein the treatment gas is
nitrogen.
11. The system of claim 9, wherein the degasser removes the
treatment gas as it removes substantially all gases.
12. The system of claim 7, further comprising the step of returning
the process solution back to the holding tank after using the
process solution to process the workpiece surface.
13. The system of claim 7, further comprising a first line for
flowing the process solution from the holding tank to the
deoxygenator.
14. The system of claim 13, further comprising a second line to
flow the process solution from the degasser back to the holding
tank.
15. The system of claim 14, further comprising at least one
processing unit for receiving the process solution from the holding
tank to process the workpiece surface.
16. The system of claim 15, further comprising a third line for
flowing the process solution from the holding tank to the at least
one processing unit.
17. The system of claim 16, further comprising a fourth line for
flowing the process solution from the at least one processing unit
to the holding tank.
18. The system of claim 8, wherein the at least one processing unit
is an electrodeposition unit.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 10/425,782 filed Apr. 29, 2003 (NT-294), which
is incorporated herein by reference.
FIELD
[0002] The present invention relates to manufacture of
semiconductor integrated circuits and, more particularly to a
method for electrochemical deposition or polishing of conductive
layers.
BACKGROUND
[0003] Conventional semiconductor devices generally include a
semiconductor substrate, such as a silicon substrate, and a
plurality of sequentially formed dielectric interlayers such as
silicon dioxide and conductive paths or interconnects made of
conductive materials. Copper and copper-alloys have recently
received considerable attention as interconnect materials because
of their superior electro-migration and low resistivity
characteristics. Interconnects are usually formed by filling copper
in features or cavities etched into the dielectric layers by a
metallization process. The preferred method of copper metallization
is electroplating. In an integrated circuit, multiple levels of
interconnect networks laterally extend with respect to the
substrate surface. Interconnects formed in sequential layers can be
electrically connected using vias.
[0004] In a typical process, first an insulating layer is formed on
the semiconductor substrate. Patterning and etching processes are
performed to form features or cavities such as trenches and vias in
the insulating layer. Then, a barrier/glue layer and a seed layer
are deposited over the patterned surface and a conductor such as
copper is electroplated to fill all the features. However, the
plating process, in addition to filling the features with copper,
also deposits excess copper over the top surface of the substrate.
This excess copper is called an "overburden" and needs to be
removed during a subsequent process step. In standard plating
processes, this overburden copper has a large topography since the
Electrochemical Deposition (ECD) process coats large features on
the wafer in a conformal manner. Conventionally, after the copper
plating, CMP process is employed to first globally planarize this
topographic surface and then to reduce the thickness of the
overburden copper layer down to the level of the surface of the
barrier layer, which is also later removed leaving conductors only
in the cavities.
[0005] During the copper electrodeposition process, specially
formulated plating solutions or electrolytes are used. An exemplary
electrolyte contains water, acid (such as sulfuric acid), ionic
species of copper, chloride ions and certain additives, which
affect the properties and the plating behavior of the deposited
material. Typical electroplating baths contain at least two of the
three types of commercially available additives such as
accelerators, suppressors and levelers.
[0006] Electroplating solutions such as the commonly used copper
sulfate solutions employed for copper film deposition naturally
contain dissolved air since they are in contact with air. While in
use in plating tools these electrolytes may further get saturated
with air since they are often cycled between the plating cell and
an electrolyte tank. After being used in the plating cell for
plating copper onto the workpiece surface, electrolyte is directed
to the main tank, and after filtration and chemical composition
adjustment, it is pumped into the plating cell. Such re-cycling
minimizes electrolyte waste, however, at the same time it increases
air dissolution into the electrolyte. In some prior art approaches,
a nitrogen blanket has been used over the electrolyte tank and
other parts of the system to minimize exposure of electrolyte
surface to air and specifically to the oxygen in the air. There
have also been methods that involved injecting or bubbling nitrogen
gas into the electrolyte to specifically reduce the dissolved
oxygen content of the electrolyte. Such efforts can reduce the
concentration of dissolved oxygen in the solution, however it does
not reduce the total dissolved gas content of the solution. In
fact, such approaches can enhance the dissolution of the used gas,
such as nitrogen, into the electrolyte. In other words, gas content
in the electrolyte would still be high, although its chemical
composition would be different.
[0007] Dissolved gas in plating electrolytes creates several
problems. First, dissolved gas in any liquid causes initiation and
growth of bubbles on surfaces touching the liquid. For example,
when a workpiece, such as a semiconductor wafer is immersed into a
copper-plating electrolyte with dissolved gas in it, micro-bubbles
of gas often spontaneously initiate on the surface of the wafer.
Initiation and growth rate of such micro-bubbles are expected to be
a function of the degree of saturation of the liquid by the gas.
Highly agitated electrolytes in the presence of a gas, such as air,
are highly saturated with air and therefore bubbles form on
surfaces touching such electrolytes very easily.
[0008] Degassing of the plating electrolyte used in electrochemical
plating or electrochemical etching/polishing processes reduces the
dissolved air content of the electrolyte. Since air contains
oxygen, dissolved oxygen content is also reduced in the
process.
[0009] Reducing, even further, the oxygen content of electrolytes
used in electrochemical processes such as electroplating is
desirable. Reduced oxygen content in the electrolyte reduces
oxidation of the organic additives (such as brighteners or
accelerators, suppressors, levelers etc), which are commonly
included in the formulation of such solutions. Reduction of
oxidation of additives, in turn, extends the lifetime of organic
additives and reduces overall process cost. Organic additives, once
oxidized, loose their ability to provide good properties to the
deposited layer and thus need to be replenished. During
electrochemical deposition processes, as thin seed layers enter an
electrolyte, the seed layers are chemically attacked by the
electrolyte if the electrolyte contains high level of dissolved
oxygen. Electrolytes containing dissolved oxygen have stronger
oxidizing property. Therefore, their chemical etching strength is
high. Further, if the process solution is a deposition solution,
such as a copper electrochemical deposition solution or a copper
electroless deposition solution, films grown using electrolytes
with less dissolved oxygen are expected to contain less oxygen.
Reduction of oxygen impurity in the deposited layer, such as a
copper layer, on the other hand, increases its grain size,
especially after the layer is annealed. Less oxide in the copper
layer and larger grain size, reduce its electrical resistivity,
which is very important in electronics applications, such as
interconnect applications.
[0010] Review of aforementioned factors, therefore, indicates that
there is a need to reduce the oxygen content of electrochemical
processing solutions and at the same time reduce their gas
content.
SUMMARY
[0011] Present invention provides a method and a system for
removing oxygen and other gasses, or at least minimizing their
content, from the process solutions used in wet chemical or
electrochemical processes. The present invention substantially
removes dissolved oxygen from the process solution by deoxygenating
the process solution in a deoxygenator and then degassing it in a
degasser to further remove, if any, remaining oxygen along with
other dissolved gasses in the process solution. The deoxygenator
removes oxygen by bubbling a treatment gas into the process
solution. In the following degassing step, the treatment gas is
also removed from the process solution along with other gasses and
the remaining oxygen. After deoxygenating and degassing, the
process solution is used for wet processing, such as
electrodepositing copper onto, a conductive surface of a
semiconductor wafer.
[0012] In an aspect of the present invention provides a method of
electrochemically processing a conductive surface of a workpiece
using a process solution. The method first includes deoxygenating
the process solution to substantially remove oxygen from the
process solution. After deoxygenating, the process solution is
degassed to remove gasses. Next, the surface of the workpiece is
electrochemically processed with the process solution that is
deoxygenated and degassed.
[0013] In another aspect of the present invention, a system for
removing gasses from a process solution, that is used to process a
workpiece surface, is provided. The system includes a holding tank
for holding the process solution, a deoxygenator for receiving the
process solution from the holding tank to substantially reduce
oxygen content in the process solution, and a degasser for
receiving the process solution, which is deoxygenated, from the
deoxygenator to remove substantially all gases from the process
solution.
[0014] These and other features and advantages of the present
invention will be described below with reference to the associated
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a schematic illustration of an electrochemical
mechanical processing system;
[0016] FIG. 2 is a schematic illustration of an embodiment of a
system of the present invention including a deoxygenator and a
degasser; and
[0017] FIG. 3 is a schematic illustration of another embodiment of
a system of the present invention including a deoxygenator and a
degasser.
DETAILED DESCRIPTION
[0018] Present invention provides a method and a system for
substantially removing dissolved gas and oxygen content from
process solutions used in wet processes. Wet processes may include
electrochemical processes (such as electrochemical deposition),
electrochemical mechanical processes (such as electrochemical
mechanical deposition or polishing), electroless processes (such as
electroless deposition), chemical processes (such as chemical
etching) and chemical mechanical processes (such as chemical
mechanical polishing). The present invention substantially reduces
the oxygen content of the process solution by deoxygenating the
process solution in a deoxygenator and then degassing it in a
degasser to further reduce the oxygen content along with other
dissolved gasses in the process solution.
[0019] A process of the present invention may be exemplified by
deoxygenating and degassing a process solution used in an
electrochemical mechanical processing (ECMPR) system or station 50
shown in FIG. 1.
[0020] The (ECMPR) system 50 includes a carrier head 53, a pad 54
having openings 56, and a carrier head 53. The carrier head holds a
wafer 52 with a front surface 51 to process in system 50. The
carrier head 53 can rotate and move the wafer vertically
(z-direction) and laterally (x or y directions). The pad 54 is
supported by a perforated support structure 58 having openings 59.
A filter 60 is placed under the support structure or between the
support structure and the pad. As shown in FIG. 1, the width and
length of the pad 54 may be such designed that the width of the pad
may be shorter than the diameter of the wafer. The length of the
pad 54 may be longer than the diameter of the wafer 52. Electrical
contacts 62 may touch the edge of the wafer 52 and connect the
surface 51 to a terminal of a power supply 63. A process solution
64, which is contained in a chamber 66, is delivered to the space
between the filter 60 and an electrode 68. The electrode 68 is
connected to a terminal of the power supply. During a deposition
process, the electrode 68 is an anode that is connected to the
positive terminal of the power supply while the surface 51 of the
wafer 52 is negatively polarized by the other terminal of the power
supply. During material removal processes such as electrochemical
mechanical polishing, however, the electrode 68 is polarized
negatively while the wafer surface is polarized positively. The
solution passes through the filter, the openings in the support
structure as well as the pad, and wets the surface of the wafer.
The process solution is delivered to the chamber 66 through a
solution inlet 64 from a process solution tank (see FIGS. 2 and 3).
The used process solution 70 leaves the chamber from an upper edge
of the chamber 66 and circulated back to the process solution tank.
The process solution may be an electroplating solution for
electrochemical deposition or electrochemical mechanical deposition
processes, and an electropolishing or electroetching solution for
the electrochemical polishing or electrochemical mechanical
polishing processes. Exemplary deoxygenating and degassing
procedures for the process solution will be described with help of
FIGS. 2 and 3. It should be noted that although an ECMPR system and
process is selected to describe the invention, the invention could
be used in any electroplating, electroless plating, chemical
etching or electropolishing process as mentioned above.
[0021] As shown in FIG. 2, a processing system 100 may comprise a
holding tank or a solution tank 102 that is connected to a wet
processing unit comprising a number of wet processing stations 104.
The wet processing stations in FIGS. 2 and 3 may be electrochemical
process stations, electrochemical mechanical process stations,
chemical process stations, chemical mechanical process stations, or
any combination thereof. Solution tank 102 is also connected to a
pump 105, a deoxygenator 106 and a degasser 108. In this
embodiment, a process solution 110 in the solution tank undergoes
two cycling operations. The process solution is filled into the
tank through an inlet 103. In a first cycling operation, the pump
105 delivers the solution I 10 in the tank to the deoxygenator 106
and the degasser through a first line 112 with a first solution
flow 111A. In this respect, the process solution 110 is first
deoxygenated in the deoxygenator to reduce the dissolved oxygen
content in it. Deoxygenated process solution is then degassed in
the degasser 108 and delivered to a second line 114 with a second
solution flow 111B. Deoxgenator may increase the overall gas
content in the solution as it reduces the content of oxygen. For
example, some deoxygenators introduce inert gases such as nitrogen
(N.sub.2), argon (Ar), helium (He), or even hydrogen (H.sub.2) into
the solution. Treatment gases may be introduced by sparging,
bubbling or injecting a gas into the process solution. Such a
treatment knocks out or sweeps the oxygen in the solution, but
during the process, the treatment gas itself may dissolve into the
solution. Therefore, after the deoxygenation process, the overall
dissolved oxygen content in the solution is reduced but the total
dissolved gas content is the same or even higher due to the
introduced gas. To get rid of the excessive gas in the solution,
the solution is directed next into the degasser 108. Degasser takes
out the excess gas along with an additional portion of the
remaining oxygen. Excess gas may comprise any undesirable dissolved
or undissolved gas in the solution. In this case, Excess gases
comprise treatment gas and other dissolved gases that have been
already in the process solution. This way a solution with both low
gas and low oxygen content is obtained, that could not be obtained
by the degasser only or the deoxygenator only. As an example, if we
reference 100% gas and 100% oxygen content for an electrolyte that
is not treated, after the deoxygenation, dissolved oxygen content
may go down to 20% and dissolved gas content may still be 100%.
After the degassing step, the dissolved gas content may go down to
15% and the oxygen content may be reduced to less than 5%. The
second line 114 delivers the process solution in second solution
flow 111B, which is deoxygenated and degassed, back to the solution
tank 102. This cycle is either continuous or intermittent. In other
words, deoxygenating and degassing may be carried out either
continuously or only part of the time.
[0022] In a second cycling operation, through a third line 116, the
process solution 110 with very low oxygen and gas content is
delivered to the wet processing stations 104 with a third solution
flow 111C. Delivery of the process solution may be provided with a
pump (not shown) in the third line. The delivery may be performed
through an intake manifold 118 connecting the line 116 to each
process station 104. The intake manifold 118 may include valves
(not shown) to switch on and off the third solution flow 111C to
each station. Used process solution from each station is received
by a solution exit manifold 120 and is delivered to a fourth line
122 as a fourth solution flow 111D. The fourth line 122 delivers
the fourth solution flow 111D, which is the used process solution,
back to the process solution tank where additives may be added to
replenish the process solution. Alternatively, the replenishment
may be done in a replenishment tank (not shown). In this case, the
fourth solution flow may be first delivered into a replenishment
tank. Due to the process that is performed using the process
solution in the stations, the oxygen content and the gas content of
the process solution in the fourth flow may be high. After
filtering the solution and adding additives in the replenishment
tank, the process solution is delivered to the solution tank to mix
with the existing solution in the solution tank. The delivery of
the fourth flow or the used solution into the solution tank may be
done intermittently or continuously to keep the oxygen and gas
levels in the process solution under predetermined limits.
[0023] The process of the present invention keeps the oxygen and
other gas content in the process solution low. During the process,
both cycling operations run simultaneous or in discontinuous modes.
In simultaneous mode, cycling speed of the first cycling operation
is kept substantially higher than the second cycling operation to
preserve the levels of oxygen and gas in predetermined limits in
the solution tank. In discontinuous mode, the fourth line 122 may
be turned off periodically by a valve (not shown) to allow first
cycling operation to deoxygenate and degas the process solution in
the tank 102 and to deliver this solution to the third line 116 for
processing. As the fourth line 122 is turned off the used solution,
as the fourth flow 111D, in this line may be flowed into a
temporary storage tank (not shown) so that when the fourth line is
open again the solution in the temporary solution tank can be
delivered back to the fourth line or into the solution tank. As the
fourth line is opened, the third line 116 is turned off so that the
used solution can be delivered to the solution tank to be
deoxygenated and degassed by the first cycling operation. In this
case, since the used solution is mixed with the solution having
very low oxygen and gas levels, the oxygenating and degassing take
less time. Once the deoxygenating and degassing are complete, the
third line is opened and the fourth line is turned off as described
above for another process run. Of course, it is possible to use the
invention in a mode where the degassed and deoxygenated process
solution is used at the process stations 104 and then discarded
instead of returning the used solution to the solution tank
102.
[0024] As shown in FIG. 3, another processing system 200 according
to an embodiment of the present invention uses degassed process
solution. The system 200 may comprise a solution tank 202 that is
connected to a wet processing unit comprising a number of wet
processing stations 204. In this embodiment, a deoxygenator 206 and
a degasser 208 are connected between the solution tank 202 and the
processing stations 204. In operation, a process solution 210 in
the tank is first delivered to the deoxygenator and then the
degasser through a first line 212 as a first solution flow 211A.
The process solution is filled into the tank through an inlet 203.
The process solution is deoxygenated and delivered to a second line
214 as a second solution flow 211B. The second line 214 delivers
the second solution flow 211B of process solution, which is
deoxygenated and degassed, to the processing stations 204. The
delivery may be performed through an intake manifold 216 connecting
the line 214 to each processing station 204. The intake manifold
216 may include valves (not shown) to switch on and off the second
solution flow 211B to each station. Used process solution from each
station is received by a solution exit manifold 218 as a third
solution flow 211C and is delivered to a third line 220 for
recycling. The third line 220 delivers the third flow 211C, which
is the used solution, back to the solution tank to be replenished
and degassed. Alternatively, the replenishment may be done in a
replenishment tank (not shown). In this case, the third solution
flow may be first delivered into a replenishment tank and then to
the solution tank. After filtering the solution and adding
additives in the replenishment tank, the process solution is
delivered to the solution tank. It should be noted that, in system
200, instead of one degasser 208, multiple degassers may be used by
connecting each to the lines of the manifold that are connected to
the processing stations 204.
[0025] It should be noted that FIGS. 2 and 3 show the system only
in a high level form without necessarily showing all the valves,
pumps, and filtration arrangements that may be employed. Further,
in such systems, instead of one deoxygenator and one degasser,
multiple deoxygenators and degassers may be used. In one
embodiment, both or one of the deoxygenator and degasser may be
placed in the solution tank itself. Further, the deoxygenator and
degasser may be separately connected to the holding tank. In this
approach, for example, in a first circulation, the deoxygenator may
receive the process solution from a first intake line, and after
deoxygenating the solution, the deoxygenated solution may be
returned to the holding tank through a second return line.
Similarly, in a second circulation, the process solution is
received from a second intake line and degassed. After degassing,
the solution is returned to the holding tank through a second
return line. Placement of deoxygenator and degassers in FIGS. 2 and
3 may also be varied.
[0026] Although various preferred embodiments and the best mode
have been described in detail above, those skilled in the art will
readily appreciate that many modifications of the exemplary
embodiment are possible without materially departing from the novel
teachings and advantages of this invention.
* * * * *