U.S. patent application number 09/924080 was filed with the patent office on 2003-02-13 for apparatus and method of evaluating electroplating solutions and conditions.
This patent application is currently assigned to Applied Materials, Inc.. Invention is credited to Dixit, Girish A., Kovarsky, Nicolay, Sun, Zhi-Wen.
Application Number | 20030029726 09/924080 |
Document ID | / |
Family ID | 25449681 |
Filed Date | 2003-02-13 |
United States Patent
Application |
20030029726 |
Kind Code |
A1 |
Kovarsky, Nicolay ; et
al. |
February 13, 2003 |
Apparatus and method of evaluating electroplating solutions and
conditions
Abstract
The present invention generally relates to an apparatus and
method of evaluating electroplating solutions and conditions. In
one embodiment, the method of evaluating electroplating solutions
comprises utilizing an electrochemical measuring cell having a
working electrode having a lid with at least one hole, a counter
electrode, and a reference electrode. The working electrode, the
counter electrode, and the reference electrode are immersed in at
least one sample of at least one electroplating solution. The lid
is disposed over the working electrode forming a chamber between
the working electrode and the lid. The lid further has a hole to
allow an electroplating solution to flow into the chamber and reach
the working electrode. The potential of the working electrode in
the sample of the electroplating solution is measured over time
with a constant current supplied to the working electrode. The
electrochemical measurements may be used to determine which
solutions are capable of bottom-up filling and may be used to
estimate the optimal electroplating parameters. In still another
embodiment, the present invention relates to an apparatus for
electroplating a substrate comprises a chamber body, an anode
disposed in the chamber body, a contact ring disposed in the
chamber body, one or more power supplies coupled to the anode and
the contact ring, and an electrochemical measuring cell disposed in
the chamber body or coupled to an electrolyte output coupled to the
chamber body.
Inventors: |
Kovarsky, Nicolay;
(Sunnyvale, CA) ; Sun, Zhi-Wen; (San Jose, CA)
; Dixit, Girish A.; (San Jose, CA) |
Correspondence
Address: |
APPLIED MATERIALS, INC.
2881 SCOTT BLVD. M/S 2061
SANTA CLARA
CA
95050
US
|
Assignee: |
Applied Materials, Inc.
|
Family ID: |
25449681 |
Appl. No.: |
09/924080 |
Filed: |
August 7, 2001 |
Current U.S.
Class: |
205/81 ;
204/230.1 |
Current CPC
Class: |
C25D 21/12 20130101 |
Class at
Publication: |
205/81 ;
204/230.1 |
International
Class: |
C25D 021/12; C25D
005/00; C25D 017/00 |
Claims
1. Method of evaluating an electroplating solution, comprising:
immersing a working electrode, a counter electrode, and a reference
electrode in a sample of an electroplating solution; measuring a
potential of the working electrode in the sample of the
electroplating solution over time with a constant current supplied
to the working electrode; and identifying whether the
electroplating solution is capable of obtaining bottom-up growth at
the constant current in a feature of a substrate.
2. The method of claim 1, wherein identifying whether the
electroplating solution is capable of obtaining bottom-up growth at
the constant current in a feature of a substrate comprises
determining whether the potential of the working electrode over
time exhibits a relative minimum at the constant current.
3. The method of claim 2, further comprising estimating a time to
initiate bottom-up growth in the feature from the relative
minimum.
4. The method of claim 1, wherein the electroplating solution
comprises inhibitors and accelerators.
5. The method of claim 1, wherein measuring the potential of the
working electrode comprises utilizing a lid disposed over the
working electrode, the lid forming a chamber between the working
electrode and the lid, and the lid having at least one hole formed
therethrough.
6. The method of claim 5, wherein the chamber has a volume of less
than about 100 mm.sup.2 and the at least one hole has a total
combined cross-sectional area equal to or less than about 30% of an
exposed area of the working electrode.
7. Method of evaluating an electroplating solution, comprising:
immersing a working electrode, a counter electrode, and a reference
electrode in a sample of an electroplating solution; measuring a
potential of the working electrode in the sample of the
electroplating solution over time with a constant current supplied
to the working electrode; and determining whether the potential of
the working electrode over time exhibits a relative minimum at the
constant current.
8. The method of claim 7, wherein the electroplating solution
comprises inhibitors and accelerators.
9. The method of claim 7, wherein measuring the potential of the
working electrode comprises utilizing a lid disposed over the
working electrode, the lid forming a chamber between the working
electrode and the lid, and the lid having at least one hole formed
therethrough.
10. The method of claim 9, wherein the chamber has a volume of less
than about 100 mm.sup.2 and the at least one hole has a total
combined cross-sectional area equal to or less than about 30% of an
exposed area of the working electrode.
11. Method of evaluating an electroplating solution, comprising:
immersing a working electrode, a counter electrode, and a reference
electrode in a sample of an electroplating solution, the
electroplating solution comprising inhibitors and accelerators;
measuring a potential of the working electrode in the sample of the
electroplating solution over time with a constant current supplied
to the working electrode by utilizing a lid disposed over the
working electrode, the lid forming a chamber between the working
electrode and the lid, the lid having at least one hole formed
therethrough, the chamber having a volume of less than about 100
mm.sup.2 and the at least one hole having a total combined
cross-sectional area equal to or less than about 30% of an exposed
area of the working electrode; and determining whether the
potential of the working electrode over time exhibits a relative
minimum at the constant current.
12. Method of evaluating an electroplating solution, comprising:
performing a plurality of trials, each trial comprising: immersing
a working electrode, a counter electrode, and a reference electrode
in a sample of an electroplating solution; measuring a potential of
the working electrode in the sample of the electroplating solution
over time with a constant current supplied to the working
electrode; and identifying whether the electroplating solution is
capable of obtaining bottom-up growth at the constant current in a
feature of a substrate.
13. The method of claim 12, wherein performing a plurality of
trials comprises evaluating a plurality of electroplating solutions
at the same constant current.
14. The method of claim 12, wherein performing a plurality of
trials comprises evaluating one electroplating solution at a
plurality of constant currents.
15. The method of claim 12, wherein performing a plurality of
trials comprises evaluating a plurality of electroplating solutions
at a plurality of constant currents.
16. The method of claim 12, wherein performing a plurality of
trials comprises evaluating at least one electroplating solution at
one or more constant currents at a plurality of temperatures.
17. The method of claim 12, wherein identifying whether the
electroplating solution is capable of obtaining bottom-up growth at
the constant current in a feature of a substrate comprises
determining whether the potential of the working electrode over
time exhibits a relative minimum at the constant current.
18. The method of claim 17, further comprising estimating a time to
initiate bottom-up growth in the feature from the relative
minimum.
19. The method of claim 17, further comprising comparing the slopes
of the potentials of the trials which exhibit a relative minimum to
determine a relative rate of bottom-up growth.
20. The method of claim 12, wherein the electroplating solution
comprises inhibitors and accelerators.
21. Apparatus for evaluating electroplating solutions, comprising:
a working electrode; a lid disposed over the working electrode and
forming a chamber between the working electrode and the lid, the
lid having at least one hole formed therethrough; a counter
electrode; a reference electrode; a galvanostat coupled to the
working electrode and the counter electrode; and a voltmeter
coupled to the working electrode and the reference electrode.
22. The apparatus of claim 21, wherein the lid has a bottom wall
and a sidewall, the at least one hole being disposed in the bottom
wall.
23. The apparatus of claim 21, wherein the lid has a bottom wall
and a sidewall, the at least one hole being disposed in the
sidewall.
24. The apparatus of claim 21, wherein the lid is removable.
25. The apparatus of claim 21, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 30%
of an exposed area of the working electrode.
26. The apparatus of claim 21, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 10%
of an exposed area of the working electrode.
27. The apparatus of claim 21, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 0.8
mm.sup.2.
28. The apparatus of claim 21, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 0.1
mm.sup.2.
29. The apparatus of claim 21, wherein the chamber has a volume of
less than about 100 mm.sup.3.
30. The apparatus of claim 21, wherein the at least one hole
comprises a single hole.
31. The apparatus of claim 21, wherein the at least one hole
comprises a plurality of holes.
32. The apparatus of claim 21, wherein the at least one hole
comprises a porous membrane.
33. Apparatus for evaluating electroplating solutions, comprising:
a working electrode; a lid disposed over the working electrode, the
lid comprising at least one hole; and a chamber formed between the
working electrode and the lid.
34. The apparatus of claim 33, wherein the lid has a bottom wall
and a sidewall, the at least one hole being disposed in the bottom
wall.
35. The apparatus of claim 33, wherein the lid has a bottom wall
and a sidewall, the at least one hole being disposed in the
sidewall.
36. The apparatus of claim 33, wherein the lid is removable.
37. The apparatus of claim 33, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 30%
of an exposed area of the working electrode.
38. The apparatus of claim 33, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 10%
of an exposed area of the working electrode.
39. The apparatus of claim 33, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 0.8
mm.sup.2.
40. The apparatus of claim 33, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 0.1
mm.sup.2.
41. The apparatus of claim 33, wherein the chamber has a volume of
less than about 100 mm.sup.3.
42. The apparatus of claim 33, wherein the at least one hole
comprises a single hole.
43. The apparatus of claim 33, wherein the at least one hole
comprises a plurality of holes.
44. The apparatus of claim 33, wherein the at least one hole
comprises a porous membrane.
45. An apparatus for electroplating a substrate; comprising: a
chamber body; an anode disposed in the chamber body; a contact ring
disposed in the chamber body; one or more power supplies coupled to
the anode and the contact ring; and an electrochemical measuring
cell having a working electrode, a counter electrode, and a
reference electrode.
46. The apparatus of claim 45, wherein the electrochemical
measuring cell is disposed in the chamber body.
47. The apparatus of claim 46, wherein the electrochemical
measuring cell is disposed in the chamber body outside a flow of
electroplating solution from the anode to the contact ring.
48. The apparatus of claim 45, further comprising an electrolyte
output coupled to the chamber body, the electrochemical measuring
cell being coupled to the electrolyte output.
49. The apparatus of claim 45, further comprising: an electrolyte
input supply coupled to the chamber body; and a controller coupled
to the electrochemical measuring cell and the electrolyte input
supply.
50. The apparatus of claim 49, wherein the controller is adapted to
control the electrolyte input supply to add a chemical solution to
the chamber body.
51. The apparatus of claim 50, wherein the electrolyte input supply
is a regeneration element adapted to recirculate electroplating
solution to the chamber body.
52. The apparatus of claim 45, further including a galvanostat
coupled to the working electrode and the counter electrode of the
electrochemical measuring cell and a voltmeter coupled to the
working electrode and the reference electrode of the
electrochemical measuring cell.
53. The apparatus of claim 45, wherein the electrochemical
measuring cell has a lid disposed over the working electrode and
forming a chamber between the working electrode and the lid, the
lid having at least one hole formed therethrough.
54. The apparatus of claim 53, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 30%
of an exposed area of the working electrode.
55. The apparatus of claim 53, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 10%
of an exposed area of the working electrode.
56. The apparatus of claim 53, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 0.8
mm.sup.2.
57. The apparatus of claim 53, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 0.1
mm.sup.2.
58. The apparatus of claim 53, wherein the chamber has a volume of
less than about 100 mm.sup.3.
59. The apparatus of claim 53, wherein the at least one hole
comprises a single hole.
60. The apparatus of claim 53, wherein the at least one hole
comprises a plurality of holes.
61. The apparatus of claim 53, wherein the at least one hole
comprises a porous membrane.
62. An apparatus for electroplating a substrate; comprising: a
chamber body; an anode disposed in the chamber body; a contact ring
disposed in the chamber body; one or more power supplies coupled to
the anode and the contact ring; and an electrochemical measuring
cell having a working electrode, a counter electrode, a reference
electrode, and a lid disposed over the working electrode, wherein
the lid forms a chamber between the working electrode and the lid,
and the lid has at least one hole having a total combined
cross-sectional area equal to or less than about 30% of an exposed
area of the working electrode formed therethrough.
63. The apparatus of claim 62, wherein the at least one hole has a
total combined cross-sectional area equal to or less than about 10%
of an exposed area of the working electrode.
64. The apparatus of claim 62, wherein the chamber has a volume of
less than about 100 mm.sup.3.
65. The apparatus of claim 62, wherein the at least one hole
comprises a single hole.
66. The apparatus of claim 62, wherein the at least one hole
comprises a plurality of holes.
67. The apparatus of claim 62, wherein the at least one hole
comprises a porous membrane.
68. An apparatus for electroplating a substrate; comprising: a
chamber body; an anode disposed in the chamber body; a contact ring
disposed in the chamber body; one or more power supplies coupled to
the anode and the contact ring; an electrolyte input supply coupled
to the chamber body, an electrochemical measuring cell having a
working electrode, a counter electrode, and a reference electrode,
and a controller coupled to the electrochemical measuring cell and
the electrolyte input supply.
69. The apparatus of claim 68, wherein the controller is adapted to
control the electrolyte input supply to add a chemical solution to
the chamber body.
70. The apparatus of claim 69, wherein the electrolyte input supply
is a regeneration element adapted to recirculate electroplating
solution to the chamber body
71. A method of evaluating an electroplating solution, comprising:
contacting an electrochemical measuring cell with an electroplating
solution of an electroplating chamber, the electrochemical
measuring cell comprising a working electrode, a counter electrode,
and a reference electrode; and measuring a potential of the working
electrode over time with a constant current supplied to the working
electrode to provide a potential trace.
72. The method of claim 71, wherein contacting the electrochemical
measuring cell with the electroplating solution comprises disposing
the electrochemical measuring cell within a chamber body of the
electroplating chamber.
73. The method of claim 71, wherein contacting the electrochemical
measuring cell with the electroplating solution comprises coupling
the electrochemical measuring cell to an electrolyte output of the
electroplating chamber.
74. The method of claim 71, further comprising evaluating the
potential trace.
75. The method of claim 74, wherein evaluating the potential trace
comprises determining whether the potential trace exhibits a
relative minimum.
76. The method of claim 75, wherein evaluating the potential trace
further comprises determining a time interval when the relative
minimum occurs.
77. The method of claim 74, wherein evaluating the potential trace
comprises evaluating the slope of the potential trace.
78. The method of claim 74, wherein evaluating the potential trace
comprises comparing the potential to at least one other potential
trace.
79. The method of claim 71, further comprising adding a chemical
solution to the electroplating chamber based upon the potential
trace.
80. The method of claim 79, wherein adding the chemical solution to
the electroplating chamber is automatically performed by a
controller coupled to the electrochemical measuring cell.
81. The method of claim 71, wherein the electroplating solution
comprises inhibitors and accelerators.
82. A method of evaluating an electroplating solution, comprising:
contacting an electrochemical measuring cell with an electroplating
solution of an electroplating chamber, the electrochemical
measuring cell comprising a working electrode, a counter electrode,
and a reference electrode; measuring a potential of the working
electrode over time with a constant current supplied to the working
electrode to provide a potential trace; and and adding a chemical
solution to the electroplating chamber based upon the potential
trace.
83. The method of claim 82, wherein adding the chemical solution to
the electroplating chamber is automatically performed by a
controller coupled to the electrochemical measuring cell.
84. The method of claim 82, wherein the electroplating solution
comprises inhibitors and accelerators.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention generally relates to an apparatus and
method of evaluating electroplating solutions and conditions.
[0003] 2. Description of the Related Art
[0004] Reliably producing sub-micron and smaller features is one of
the key technologies for the next generation of very large scale
integration (VLSI) and ultra large scale integration (ULSI) of
semiconductor devices. However, as the fringes of circuit
technology are pressed, the shrinking dimensions of interconnects
in VLSI and ULSI technology have placed additional demands on the
processing capabilities. The multilevel interconnects that lie at
the heart of this technology require precise processing of high
aspect ratio features, such as vias and other interconnects.
Reliable formation of these interconnects is very important to VLSI
and ULSI success and to the continued effort to increase circuit
density and quality of individual substrates.
[0005] As circuit densities increase, the widths of vias, contacts
and other features, as well as the dielectric materials between
them, decrease to sub-micron dimensions, whereas the thickness of
the dielectric layers remains substantially constant, with the
result that the aspect ratios for the features, i.e., their height
divided by width, increases. Many traditional deposition processes
have difficulty filling sub-micron structures where the aspect
ratio exceeds 2:1, and particularly where the aspect ratio exceeds
4:1. Therefore, there is a great amount of ongoing effort being
directed at the formation of substantially void-free, sub-micron
features having high aspect ratios.
[0006] Currently, copper and its alloys have become the metals of
choice for submicron interconnect technology because copper has a
lower resistivity than aluminum, (1.7 .mu..OMEGA.-cm compared to
3.1 .mu..OMEGA.-cm for aluminum), and a higher current carrying
capacity and significantly higher electromigration resistance.
These characteristics are important for supporting the higher
current densities experienced at high levels of integration and
increased device speed. Further, copper has a good thermal
conductivity and is available in a highly pure state.
[0007] Electroplating of conductive materials, such as copper, is
one process being used to fill high aspect ratio features on
substrates. Electroplating processes typically require a thin,
electrically conductive seed layer to be deposited on the
substrate. Electroplating is accomplished by applying an electrical
current to the seed layer and exposing the substrate to an
electrolytic solution containing metal ions which plate over the
seed layer. The seed layer typically comprises a conductive metal,
such as copper, and is conventionally deposited on the substrate
using physical vapor deposition (PVD) or chemical vapor deposition
(CVD) techniques. One problem in electroplating of conductive
materials to fill a feature is that electroplated metal grows in
all directions. Therefore, if near the mouth of a feature the rate
of electroplating of the metal is high, a bridge may form over the
mouth of the feature prior to complete filling of the feature and
thus may leave a void in the feature. The void may change the
operating characteristics of the interconnect feature and may cause
improper operation and premature breakdown of the device.
[0008] Superconformal or superfilling electrodeposition is one
method of electroplating directed to filling features without the
formation of voids. In superconformal electrodeposition at least
one suppressor and at least one accelerator are added to the
electroplating solution. It is believed that the suppressors
inhibit electroplating of the substrate by striking a surface of
the substrate and reducing the active surface area of the substrate
available for the metal reduction process of electroplating. The
suppressors are typically high molecular weight compounds, such as
polyethers or other polymers. Since suppressors are typically used
in dilute concentrations, it is believed that the transport of the
suppressors to the surface of the substrate is a diffusion process.
Under a diffusion process, the flux of the suppressors should be
greater on the field areas and around the mouth of a feature rather
than on the bottom of the feature. In comparison with the
suppressors, molecules of the accelerators are much smaller and
penetrate more easily to the bottom of the feature. For
electroplating solutions having a superfill effect, the
concentration ratio of accelerators-to-suppressors under
electrolysis near the bottom of the feature increases leading to an
increase in the metal deposition rate at the bottom of the feature
or so-called "bottom-up" or superfill effect. As a consequence,
electroplating occurs more rapidly on the bottom of a feature than
on the field areas or on the edges of the mouth of a feature
resulting in a "bottom-up" growth of the electroplated metal in the
feature. Bottom-up growth reduces the likelihood of a formation of
a bridge closing the mouth of a feature.
[0009] Typical electroplating solutions may comprise metal ions, pH
adjusters, buffering salts, suppressors, accelerators, reducing
agents, levelers, chelating agents, stabilizers, other
electrolytes, and/or other additives. Typical suppressors include
polyethers, such as polyethylene glycol, or other polymers, such as
polypropylene, which act to inhibit the rate of electroplating.
Typical accelerators include sulfides or disulfides, such as
bis(3-sulfopropyl) disulfide, which are added to affect the
microstructure of the electrodeposited metal. Because of the
numerous possible compositions of an electroplating solutions, it
may be difficult to predict the overall mechanism of an
electroplating solution during electroplating. For example, for an
electroplating solution containing suppressors and accelerators it
is difficult to determine whether the electroplating solution will
exhibit bottom-up growth at a particular electroplating parameter.
Therefore, there is a need for a method and an apparatus for
evaluating electroplating solutions.
[0010] A journal article entitled "Superconformal Electrodeposition
of Copper in 500-900 nm Features," T. P. Moffat et al., Journal of
the Electrochemical Society, 147 (12), p. 4524-4535 (2000) reports
a study of electroplating solutions with and without suppressors
and accelerators. The article reports that in the presence of
suppressors and accelerators, the current-potential deposition
reveals a wide hysteresis under direct and back potential scan,
which does not take place in additive-free electroplating
solutions. This hysteresis can indicate that the electroplating
solution has the ability for superfill effect. However, this
hysteresis response is inherent for electroplating solutions
without superfill ability as well. Therefore, this method cannot be
used to estimate superfilling ability of an electroplating solution
or to estimate the optimal electroplating conditions.
[0011] Therefore, there is a need for an improved apparatus and
method of evaluating electroplating solutions and conditions
SUMMARY OF THE INVENTION
[0012] The present invention generally relates to an apparatus and
method of evaluating electroplating solutions and conditions. In
particular, the present invention relates to an apparatus and
method of evaluating electroplating solutions containing additives,
such as suppressors and accelerators.
[0013] In one embodiment, the method of evaluating electroplating
solutions comprises utilizing an electrochemical measuring cell
having a working electrode having a lid with at least one hole, a
counter electrode, and a reference electrode. The working
electrode, the counter electrode, and the reference electrode are
immersed in at least one sample of at least one electroplating
solution. The potential of the working electrode in the sample of
the electroplating solution is measured over time with a constant
current supplied to the working electrode. The electrochemical
measurements may be used to determine which solutions are capable
of bottom-up filling and may be used to estimate the optimal
electroplating parameters.
[0014] In still another embodiment, the method of evaluating
electroplating solutions comprises contacting an electrochemical
measuring cell with an electroplating solution of an electroplating
chamber. The electrochemical measuring cell comprises a working
electrode, a counter electrode, and a reference electrode. Then, a
potential of the working electrode is measured over time with a
constant current supplied to the working electrode to provide a
potential trace.
[0015] In one embodiment, the apparatus for evaluating
electroplating solutions comprises a working electrode and a lid
disposed over the working electrode. A chamber is formed between
the working electrode and the lid. The lid further has at least one
hole to allow an electroplating solution to flow into the chamber
and reach the working electrode. In one aspect, the working
electrode imitates the conditions occurring during electroplating
in a feature.
[0016] In another embodiment, the apparatus for evaluating
electroplating solutions, comprises a working electrode, a counter
electrode, a reference electrode, a galvanostat coupled to the
working electrode and the counter electrode to provide a constant
current to the working electrode, and a voltmeter coupled between
the working electrode and the reference electrode to measure the
potential of the working electrode. The apparatus further comprises
a lid disposed over the working electrode forming a chamber between
the working electrode and the lid. The lid further has at least one
hole to allow an electroplating solution to flow into the chamber
and reach the working electrode.
[0017] In still another embodiment, the present invention relates
to an apparatus for electroplating a substrate. The apparatus
comprises a chamber body, an anode disposed in the chamber body, a
contact ring disposed in the chamber body, one or more power
supplies coupled to the anode and the contact ring, and an
electrochemical measuring cell having a working electrode, a
counter electrode, and a reference electrode. In one aspect, the
electrochemical measuring cell may be disposed in the chamber body.
In another aspect, the electrochemical measuring cell may be
coupled to an electrolyte output coupled to the chamber body.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] So that the manner in which the above recited features,
advantages and objects of the present invention are attained and
can be understood in detail, a more particular description of the
invention, briefly summarized above, may be had by reference to the
embodiments thereof which are illustrated in the appended
drawings.
[0019] It is to be noted, however, that the appended drawings
illustrate only typical embodiments of this invention and are
therefore not to be considered limiting of its scope, for the
invention may admit to other equally effective embodiments.
[0020] FIG. 1 is a schematic cross-sectional view of one embodiment
of an electrochemical measuring cell.
[0021] FIG. 2 is a schematic cross-sectional view of another
embodiment of an electrochemical measuring cell.
[0022] FIG. 3 is a graph of traces of the potential of a working
electrode over time of samples of an electroplating solution
evaluated at different constant currents.
[0023] FIG. 4 is a graph of traces of the potential of a working
electrode over time of samples of another electroplating solution
evaluated at different constant currents.
[0024] FIG. 5 is a schematic cross-sectional view of one embodiment
of an electrochemical measuring cell used in conjunction with one
embodiment of an electroplating chamber.
[0025] FIGS. 6a-6c are bottom views of embodiments of a lid of a
working electrode having at least one hole.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] FIG. 1 is a schematic cross-sectional view of one embodiment
of an electrochemical measuring cell 10 useful in evaluating
electroplating solutions. The cell 10 comprises a working electrode
12, a counter electrode 14, and a reference electrode 16 immersed
in a solution 18. A galvanostat device 20 is coupled to the cell to
control the current through the cell 10 at a preset value. A
voltmeter 21 is coupled between the working electrode 12 and the
reference electrode 16 to measure the potential of the working
electrode 12.
[0027] A current is applied to the cell 10 so that the working
electrode 12 acts as a cathode of the cell 10 and so that the
counter electrode 14 acts as an anode of the cell 10. The reference
electrode 16 is used as a reference point against which the
potential of the working electrode 12 can be measured.
[0028] An example of a working electrode 12 is a copper wire
electrode, a platinum rotating disk electrode, etc. An example of a
counter electrode 14 is a copper electrode, a titanium electrode, a
stainless steel electrode, etc. An example of a reference electrode
16 is a saturated calomel electrode, a hydrogen electrode, a
silver/silver-chloride electrode, a copper/copper sulfate
electrode, or any other electrode assemblies that have an electrode
potential independent of the electrolyte used in the cell 10.
[0029] The working electrode 12 is separated from the bulk solution
18a of the cell 10 by a lid 22. The lid 22 may be removable or may
be integral to the working electrode 12. The lid 22 is shaped and
sized so that there is a chamber 23 formed between the working
electrode 12 and the lid 22. The lid 22 may be adjusted to adjust
the size of the chamber 23. The lid 22 has at least one hole 24
which allows the solution 18 to flow though the hole 24 into the
chamber 23 prior to reaching the working electrode 12. FIGS. 6a-6c,
are bottom views of the lid 22 illustrating embodiments of the lid
having at least one hole 24a. The lid may have a single hole as
shown in FIG. 6a, the lid may have a plurality of holes 24b as
shown in FIG. 6b, or the lid may have a plurality of holes
comprising a porous membrane 24c as shown in FIG. 6c. The size of
each hole is preferably small to imitate the mouth of a feature.
The diameter of each hole is equal to or greater than the diameter
of a mouth of a feature. In one embodiment, the total combined
cross-sectional area of hole(s) 24 (whether a single hole, a
plurality of holes, or a porous membrane) is equal to or less than
about 30% of the exposed area 13 of the working electrode 12,
preferably equal to or less than about 10% of the exposed area of
the working electrode. In another embodiment, the total combined
cross-sectional area of hole(s) 24 (whether a single hole, a
plurality of holes, or a porous membrane) is equal to or less than
about 0.8 mm.sup.2, preferably equal to or less than about 0.1
mm.sup.2.
[0030] The lid 22 may be adapted so that the chamber 23 is any
volume, but the volume is preferably small to imitate the
electroplating conditions occurring in a feature formed in the
dielectric layer deposited over a semiconductor substrate. For
example, the volume of the chamber 23 may be less than about 100
mm.sup.3.
[0031] In one embodiment, the at least one hole 24 may be formed at
the side of the lid 22 (as shown in FIG. 2) in order to be
positioned closer to the reference electrode 16 in order to more
accurately measure the potential of the working electrode 12 by
reducing the distance and, thus, the ohmic drop between the
reference electrode 16 and the working electrode 12. In another
embodiment, the working electrode 12 may be positioned adjacent the
at least one hole 24 of the working electrode 12 in order to more
accurately measure the potential at the working electrode 12 by
reducing the distance and, thus, the ohmic drop between the
reference electrode 16 and the working electrode 12. In still
another embodiment, the distance between the working electrode 12
and the reference electrode 16 is kept constant between samples of
electroplating solutions in order to increase the precision of the
apparatus in evaluating different samples of electroplating
solutions.
[0032] One embodiment of a method of evaluating electroplating
solutions comprises measuring the potential of the working
electrode 12 over time under a constant current supplied to the
working electrode 12 by utilizing an electrochemical measuring
cell, such as cell 10, containing the electroplating solution to be
evaluated. In one embodiment, the bulk solution 18a is not agitated
so that non-electrolytes in the electroplating solution, such as
suppressors or accelerators, are limited to movement through the
electroplating solution by a diffusion process rather than a
convection process. The method may comprise evaluating samples of
the same electroplating solutions at different constant currents.
The method may comprise evaluating samples of different
electroplating solutions at the same constant current. The method
may further comprise evaluating samples of the electroplating
solutions at different temperatures.
[0033] For example, an electroplating solution containing 0.3 M of
copper sulfate (CuSO.sub.4), about 10% by weight of sulfuric acid
(H.sub.2SO.sub.4), about 60 ppm of chloride ion, 15 ml/L of the
suppressor polyoxypropylene-polyoxyetheylene copolymer, and 5 ml/L
of the accelerator mercapto-propane-sulfonate, was evaluated in an
electrochemical measuring cell, such as cell 10 with a working
electrode 12, a counter electrode 14, and a reference electrode 16.
The at least one hole 24 of the lid 22 on the working electrode 12
comprised a single hole having a diameter between about 0.1 mm and
about 0.2 mm and the volume of the chamber 23 of the lid 22 was
between about 60 mm.sup.3 and about 80 mm.sup.3. Samples of the
electroplating solution were evaluated at about room temperature.
The working electrode 12, the counter electrode 14, and the
reference electrode 16 were placed in the cell 10 and were immersed
in the electroplating solution. The potential of the working
electrode 12 over time under constant current supplied to the
working electrode by a galvanostat device 20 was measured.
[0034] FIG. 3 is a graph of traces of the potential of the working
electrode 12 over time of samples of the electroplating solution
evaluated at different constant currents. Potential of the working
electrode in volts is graphed on the y-axis and time in seconds is
graphed on the x-axis. Trace 30 is of a sample of the
electroplating solution at a constant current of about 5
mA/cm.sup.2 through the working electrode 12. Trace 31 is of
another sample of the electroplating solution at a constant current
of about 10 mA/cm.sup.2 through the working electrode 12. Trace 32
is of another sample of the electroplating solution at a constant
current of about 15 mA/cm.sup.2 through the working electrode 12.
Trace 33 is of another sample of the electroplating solution at a
constant current of about 25 mA/cm.sup.2 through the working
electrode. Both trace 31 and trace 32 show a relative minimum 34 in
which the slope of the traces becomes positive. Trace 30 and trace
33 do not show a relative minimum. It has been observed by scanning
electron microscope photographs of semiconductor substrates
electroplated with this electroplating solution at room temperature
that at current densities at the cathode of about 10 mA/cm.sup.2
and about 15 mA/cm.sup.2 bottom-up growth occurs while at current
densities of about 5 mA/cm.sup.2 and 20 mA/cm.sup.2 bottom-up
growth does not occur.
[0035] Not wishing to be bound by any one theory, it is believed
that the amount of additives and other components of electroplating
solutions in the chamber 23 are decreasing faster than the amount
of additives and other components of the electroplating solution
entering the chamber 23. The amount of additives in the chamber 23
may be decreasing as a result of leaving the chamber, being broken
down under the current, and/or being consumed in the electroplated
film. The depletion rates of suppressors and accelerators are
different. To provide superfill effect, the suppressors must
deplete faster than the accelerators. When the surface
concentration ratio of accelerators-to-suppressors become such that
the accelerators start to dominate in chamber 23, a potential trace
of the working electrode at constant current exhibits a relative
minimum on the negative potential trace. The relative minimum
indicates that electroplating now proceeds at the working electrode
12 more easily. The greater the positive slope (dE/dt) of the
negative potential trace indicates that the electroplating
conditions may occur more readily at the working electrode 12.
[0036] It is believed that the mechanism of an electroplating
solution occurring at the lid of the working electrode is similar
to the mechanism occurring at a feature of a substrate. Therefore,
a potential trace which exhibits a relative minimum indicates an
electroplating solution which at that current density is capable of
bottom-up filling in a feature of a substrate because the relative
minimum indicates neutralization of the suppressor's action under
these electroplating conditions On the other hand, a potential
trace which does not exhibit a relative minimum indicates an
electroplating solution which at that current density bottom-up
filling in feature of a substrate does not occur because the
concentration changes of all the components of the electroplating
solution, including accelerators and suppressors, do not increase
the ability and ease of electroplating. Furthermore, the slope of
the traces can be used to determine the relative rates of bottom-up
filling occurring in a feature of a substrate.
[0037] In addition, the time interval of when the relative minimum
occurs in the potential trace can be used to estimate a time when
bottom-up filling occurs in a feature of a substrate. The time
interval .DELTA.T.sub.w of the working electrode from the beginning
of electrolysis to the relative minimum is proportional to the
transition time .DELTA.T.sub.f of a feature of a substrate required
for bottom-up electroplating to begin. The transition time
.DELTA.T.sub.f of a feature must be shorter than that of the
working electrode because the diffusion flow of the components of
the electroplating solution into the feature comes through a
opening which has an area that is smaller than the inner surface
area of the feature where electrodeposition proceeds. On the other
hand, the working electrode is flat and, hence, the area of the
diffusion flow and the area of the electrode surface are the same.
The transition time .DELTA.T.sub.f of a feature is approximated to
be proportional to the time interval .DELTA.T.sub.w of the working
electrode by a factor of the flow of electroplating solution per
the inner surface area of the feature as shown in Equation #1
below.
.DELTA..sup.T.sub.f=(S.sub.o/S).sub.f.DELTA.T.sub.wtm Equation
1:
[0038] wherein (S.sub.o).sub.f stands for the surface area of the
opening or mouth of a feature which approximates the flow of bulk
electroplating solution through the mouth of the feature, and
(S).sub.f stands for the plateable inner surface area of the
feature.
[0039] Equation 1 can be used to estimate the transition time
.DELTA.T.sub.f of a feature of a substrate required for bottom-up
electroplating to begin. For example, for a feature having a
circular mouth having a diameter of about 0.2 .mu.m and a height of
about 1.0 .mu.m, the surface area of the mouth (S.sub.o).sub.f of
the feature would be .pi.(0.2/2).sup.2=0.0314 .mu.m.sup.2 and the
surface area of the feature (S.sub.o).sub.f would be equal to the
area of the walls plus the area of the bottom of the feature which
is equal to .pi.(0.2 .mu.m)(1.0 .mu.m)+0.0314 .mu.m.sup.2=0.660
.mu.m.sup.2. Therefore, (S.sub.o/S).sub.f is equal to about
{fraction (1/21)} (0.0314/0.660). For trace 31, as shown in FIG. 3,
which has a relative minimum at about 115 seconds, bottom-up
filling is estimated to begin in the feature in about 5.5 seconds
({fraction (1/21)}.times.115 seconds).
[0040] FIG. 4 is a graph of the traces of the potential of the
working electrode 12 over time of samples of another electroplating
solution evaluated at different constant currents. The
electroplating solution contained about 0.3 M of copper sulfate
(CuSO.sub.4), about 10% by weight of sulfuric acid
(H.sub.2SO.sub.4), and about 60 ppm of chloride ion The
electroplating solution was evaluated in an electrochemical
measuring cell, such as cell 10 with a working electrode 12, a
counter electrode 14, and a reference electrode 16. The diameter of
the hole 24 of the lid 22 on the working electrode 12 was between
about 0.1 mm and about 0.2 mm and the volume of the chamber 23 of
the lid 22 was between about 60 mm.sup.3 and 80 mm.sup.3. The
solution was evaluated at about room temperature. Trace 40 is a
sample of the electroplating solution at a constant current of 5
mA/cm.sup.2 through the working electrode 12. Trace 41 is a sample
of the electroplating solution at a constant current of 10
mA/cm.sup.2 through the working electrode 12. Trace 42 is a sample
of the electroplating solution at a constant current of 15
mA/cm.sup.2 through the working electrode 12. Trace 43 is a sample
of the electroplating solution at a constant current of 25
mA/cm.sup.2 through the working electrode. Traces 40-44 do not show
a relative minimum. Thus, this electroplating solution under these
current densities at about room temperature do not exhibit
bottom-up filling.
[0041] Thus, the present apparatus and method may be used to screen
electroplating solutions to determine which electroplating
solutions exhibit bottom-up filling at a certain current density at
a certain temperature. Furthermore, the transition time for when
bottom-up filling of a feature of a substrate begins to occur can
be estimated. In addition, the relative rates of bottom-up filling
may be compared between samples of electroplating solutions. Thus,
electroplating parameters, such as concentrations of the
electroplating solution, current density, temperature, and time,
may be optimized.
[0042] In one embodiment, the electrochemical measuring cell may be
used separately apart from an electroplating chamber to optimize
electroplating conditions. In another embodiment, the
electrochemical measuring cell may be used in conjunction with an
electroplating chamber to optimize electroplating conditions.
[0043] FIG. 5 is a schematic cross-sectional view of one embodiment
of the electrochemical measuring cell 110 used in conjunction with
one embodiment of an electroplating chamber 50, known as a fountain
plater. The electrochemical measuring cell 110 comprises a working
electrode 112, a counter electrode 114, and a reference electrode
116 adapted to contact the electroplating solution. A galvanostat
device 120 is coupled to the cell to control the current through
the cell 110 at a preset value. A voltmeter 121 is coupled between
the working electrode 112 and the reference electrode 116 to
measure the potential of the working electrode 112.
[0044] The working electrode 112 is separated from the bulk
electroplating solution by a lid 122. The lid 122 may be removable
or may be integral to the working electrode 112. The lid 122 is
shaped and sized so that there is a chamber 123 formed between the
working electrode 112 and the lid 122. The lid 122 may be adjusted
to adjust the size of the chamber 123. The lid 122 has at least one
hole 124 which allows the solution 118 to flow though the hole 124
into the chamber 123 prior to reaching the working electrode 112.
The lid 122 may have a single hole, the lid may have a plurality of
holes, or the lid may have a plurality of holes comprising a porous
membrane. The size of each hole is preferably small to imitate the
mouth of a feature. The diameter of each hole is equal to or
greater than the diameter of a mouth of a feature. In one
embodiment, the total combined cross-sectional area of hole(s) 124
(whether a single hole, a plurality of holes, or a porous membrane)
is equal to or less than about 30% of the exposed area 113 of the
working electrode 112, preferably equal to or less than about 10%
of the area of the working electrode. In another embodiment, the
total combined cross-sectional area of hole(s) 24 (whether a single
hole, a plurality of holes, or a porous membrane) is equal to or
less than about 0.8 mm.sup.2, preferably equal to or less than
about 0.1 mm.sup.2. The lid 122 may be adapted so that the chamber
123 is any volume, but the volume is preferably small to imitate
the electroplating conditions occurring in a feature formed in the
dielectric layer deposited over a semiconductor substrate. For
example, the volume of the chamber 123 may be less than about 100
mm.sup.3.
[0045] The electroplating chamber 50 may include a top opening 52
and a movable substrate support 54 adapted to be positioned through
the top opening 52 to support a substrate 56 in an electroplating
solution. A contact ring 60 is configured to secure and support a
substrate 56 in position during electroplating, and permits the
electroplating solution contained in the electroplating chamber 50
to contact the surface 55 of the substrate 56 while it is immersed
in an electroplating solution. A negative pole of a power supply 64
is connected to a plurality of contacts 62 of the contact ring 60
which are typically mounted about the periphery of the substrate 56
to provide multiple circuit pathways to the substrate 56. An anode
assembly 58 may be disposed near a bottom portion of the
electroplating chamber 50. The anode assembly 58 is coupled to a
positive pole of the power supply 64.
[0046] An electroplating solution is supplied to a cavity 68 or
chamber body defined within the electroplating chamber 50 via
electrolyte input port 70 from electrolyte input supply 72. The
electrolyte supply 72 may provide an electroplating solution
comprising inhibitors, accelerators, metal ions, pH adjustors,
buffering salts, reducing agents, levelers, chelating agents,
stabilizers, other electrolytes, other additives, or combinations
thereof. During electroplating, the electroplating solution is
supplied to the cavity 68 so that the electroplating solution
overflows from a lip 69 into an annular drain 76. The annular drain
76 drains into electrolyte output port 78 which discharges to
electrolyte output 80. In one embodiment, the electrolyte output 80
may be connected to the electrolyte input supply 72 to provide a
closed loop for the electroplating solution contained within the
electroplating chamber 50, such that the electroplating solution
may be recirculated in the electroplating chamber 50. The motion
associated with the recirculation of the electroplating solution
also assists in transporting the electroplating solution from the
anode assembly 58 to the surface 55 of the substrate 56. In one
embodiment, the electrolyte input supply 72 may act as a
regeneration element in which the electroplating solution is
replenished, refreshed, or replaced with a chemical solution which
may comprise inhibitors, accelerators, metal ions, pH adjustors,
buffering salts, reducing agents, levelers, chelating agents,
stabilizers, other electrolytes, other additives, or combinations
thereof.
[0047] The substrate 56 is positioned within an upper portion 54 of
the cell 50, such that the electroplating solution flows along the
surface 55 of the substrate 56 during operation. A negative charge
applied from the negative pole of the power supply 64 via the
contacts 62 to a seed layer deposited on plating surface 55 of
substrate 56 in effect makes the substrate a cathode. The metal
ions may be added to the electroplating solution and/or may be
supplied by a consumable anode assembly. The seed layer formed on
the surface 55 of the substrate 56 attracts metal ions carried by
the electroplating solution to electroplate a metal on a surface 55
of a substrate 56. The anode assembly 58 may optionally further
include a permeable membrane 88 covering the anode assembly 58 to
prevent the contamination of the substrate 56 from anode sludge
produced by a consumable anode.
[0048] The electrochemical measuring cell 110 may be positioned
anywhere inside the cavity 68 of the electroplating chamber 50 as
long as the electrochemical measuring cell is in contact with the
electroplating solution. For example, as shown in FIG. 5, the
electrochemical measuring cell 110 may be positioned in area 90.
For example, the electrochemical measuring cell 110 may also be
positioned in area 94. In one aspect, the electrochemical measuring
cell 110 is positioned in the chamber body outside a flow of the
electroplating solution from the anode assembly 58 to the contact
ring 60 in order to prevent disrupting the flow of electroplating
solution to the substrate 56 and causing non-uniformity in the
electroplating of the substrate 56. For example, the
electrochemical measuring cell 110 may be positioned in area
90.
[0049] The electrochemical measuring cell 110 may also be coupled
to the electrolyte output 80. For example, the electrochemical
measuring cell 110 may be positioned anywhere between the annular
drain 76 and the electrolyte input port 70. For example, the
electrochemical measuring cell 110 may be positioned at area 98.
The electrochemical measuring cell 110 may be positioned prior or
after the electrolyte input supply 72.
[0050] The electrochemical measuring cell 110 may be coupled to a
controller 99 which directs the electrochemical measuring cell 110
in monitoring and evaluating the electroplating solution. For
example, the electrochemical cell 110 may be coupled to the
controller 99 through the galvanostat 120 and the voltmeter 121.
The controller 99 may also be coupled to the electrolyte input
supply 72 to direct the electrolyte input supply 72 to add a
chemical solution to the cavity 68 of the electroplating chamber 50
in order to replenish, refresh, or replace the electroplating
solution of the electroplating chamber 50 based upon the
measurements of the electrochemical measuring cell 110.
[0051] In one embodiment, the electrochemical measuring cell 110
may monitor or evaluate the electroplating solution in situ while a
substrate is being electroplated in the electroplating chamber 50.
Alternatively, the electrochemical measuring cell 110 may monitor
or evaluate the electroplating solution before or after a substrate
is electroplated. In addition, the electrochemical measuring cell
110 may compare electroplating conditions of an electroplating
solution used to electroplate one substrate from another.
[0052] In one embodiment, the electrochemical measuring cell 110
may monitor and evaluate an electroplating solution by measuring
the potential of the working electrode 12 over time at a certain
constant current to provide a potential trace. The potential trace
may be analyzed to determine the electroplating conditions that
will result from an electroplating solution. The potential trace
may be compared with other potential traces to determine the
electroplating conditions that will result from an electroplating
solution. For example, if the slopes of the potential traces from
an electroplating solution used to electroplate one substrate from
an electroplating solution used to electroplate another substrate
(of course, this may be the same electroplating solution used to
electroplate both substrates in which the composition of the
electroplating solution has changed over time) change, then this
may show that the rate of bottom-up filling is changing. In another
example, if a potential trace of a certain electroplating used to
process one or more substrates no longer shows a minimum, this may
signal that the electroplating solution is no longer capable of
bottom-up growth. In another example, if a potential trace of a
certain electroplating solution used to process one or more
substrates shows a longer and longer time period in where the
minimum occurs, this may indicate that the electroplating solution
is less effective in providing bottom-up growth. As a consequence,
the electrolyte input supply 72 may add a chemical solution to the
electroplating chamber to refresh, replenish, or replace the
electroplating solution used based upon the evaluation from the
electrochemical measuring cell 110.
[0053] While the foregoing is directed to embodiments of the
present invention, other and further embodiments of the invention
may be devised without departing from the basic scope thereof, and
the scope thereof is determined by the claims that follow.
* * * * *