U.S. patent application number 10/457277 was filed with the patent office on 2003-11-06 for electroplating bath control.
This patent application is currently assigned to Shipley Company, L.L.C.. Invention is credited to Binstead, Robert A., Calvert, Jeffrey M..
Application Number | 20030205476 10/457277 |
Document ID | / |
Family ID | 26724005 |
Filed Date | 2003-11-06 |
United States Patent
Application |
20030205476 |
Kind Code |
A1 |
Calvert, Jeffrey M. ; et
al. |
November 6, 2003 |
Electroplating bath control
Abstract
Disclosed is a method of analyzing organic components in an
electroplating bath. Also disclosed is a method of controlling
electroplating baths by monitoring the components of the plating
bath in real-time.
Inventors: |
Calvert, Jeffrey M.; (Acton,
MA) ; Binstead, Robert A.; (Marlborough, MA) |
Correspondence
Address: |
EDWARDS & ANGELL, LLP
P.O. Box 9169
Boston
MA
02209
US
|
Assignee: |
Shipley Company, L.L.C.
Marlborough
MA
|
Family ID: |
26724005 |
Appl. No.: |
10/457277 |
Filed: |
June 9, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10457277 |
Jun 9, 2003 |
|
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|
10046507 |
Oct 19, 2001 |
|
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60242348 |
Oct 20, 2000 |
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Current U.S.
Class: |
205/82 |
Current CPC
Class: |
Y10T 436/24 20150115;
C25D 21/14 20130101; C25D 21/12 20130101 |
Class at
Publication: |
205/82 |
International
Class: |
C25D 021/12 |
Claims
What is claimed is:
1. A method for determining the level of components in an
electroplating bath comprising the steps of: a) obtaining a
plurality of solutions wherein each solution has known and
different concentrations of an analyte, but where the quantity of
the analyte in each solution differs from the quantity in the other
solutions; b) providing an apparatus having a first chamber and a
second chamber, the first chamber being separated from the second
chamber by a liquid-impermeable, gas-permeable membrane; c)
introducing each solution individually into the first chamber and
carrying out a predetermined sequence of steps including: i)
reducing the pressure in the second chamber relative to the first
chamber to produce a gas stream; ii) directing at least a portion
of the gas stream to a mass spectrometer; iii) measuring a
characteristic mass/charge peak for the analyte; d) for each
solution, correlating the quantity of analyte with the measurement
of the characteristic mass/charge peak; e) introducing a bath
having an unknown quantity of the analyte into the first chamber;
f) performing the predetermined sequence of steps; and g) choosing
from the correlation in step d) a quantity of the analyte which
corresponds to the recorded characteristic mass/charge peak
measurement for the analyte.
2. The method of claim 1 wherein the analyte is selected from
brightener, accelerator, suppressor, leveler or mixtures
thereof.
3. The method of claim 1 wherein the electroplating bath is
selected from copper, nickel, chromiurn, zinc, tin, gold, silver,
and their alloys.
4. The method of claim 3 wherein the copper electroplating bath
comprises a source of copper ions and an electrolyte.
5. The method of claim 4 wherein the electrolyte is acidic.
6. The method of claim 1 wherein the first chamber further
comprises a working electrode, an auxiliary electrode and a
reference electrode.
7. The method of claim 6 wherein a reducing potential is applied to
the working electrode in step c) prior to step i).
8. The method of claim 1 wherein the membrane comprises an inert,
non-conductive material.
9. The method of claim 1 wherein the pressure in the second chamber
is reduced by application of a vacuum.
10. An electroplating system comprising an electroplating tank
suitable for containing an electroplating bath, the tank having an
outlet for directing a portion of an electroplating bath to an
apparatus for determining the level of components in the
electroplating bath, the apparatus comprising: a first chamber
separated from a second chamber by a liquid-impermeable,
gas-permeable membrane; a means for reducing the pressure in the
second chamber relative to the first chamber to produce a gas
stream; and a means for directing at least a portion of the gas
stream to a mass spectrometer.
11. The electroplating system of claim 10 wherein the first chamber
further comprises a working electrode, an auxiliary electrode and a
reference electrode.
12. The electroplating system of claim 11 further comprising a
power source for controlling an electrochemical potential of the
working electrode.
13. The electroplating system of claim 10 wherein the membrane
comprises an inert, non-conductive material.
14. The electroplating system of claim 10 further comprising a
vacuum source.
15. The electroplating system of claim 11 further comprising a
controlling means for adding organic components to the
electroplating bath.
16. The electroplating system of claim 15 wherein the controlling
means is connected to the mass spectrometer.
17. The electroplating system of claim 15 wherein the organic
components are selected from brighteners, accelerators,
suppressors, levelers or mixtures thereof.
18. The electroplating system of claim 10 wherein the working
electrode comprises a noble metal or the base metal of the
electroplating bath.
19. A method for electrolytically depositing metal on a substrate
comprising the steps of: a) contacting the substrate with an
electroplating bath comprising a source of metal ions, and
electrolyte and one or more organic additives; b) subjecting the
electroplating bath to sufficient current density for a period of
time sufficient to deposit a desired thickness of metal on the
substrate; and c) monitoring the one or more organic additives by
i) obtaining a plurality of solutions wherein each solution has
known and different concentrations of an organic additive, but
where the quantity of the organic additive in each solution differs
from the quantity in the other solutions; ii) providing an
apparatus having a first chamber and a second chamber, the first
chamber being separated from the second chamber by a
liquid-impermeable, gas-permeable membrane; iii) introducing each
solution individually into the first chamber and carrying out a
predetermined sequence of steps including: aa) reducing the
pressure in the second chamber relative to the first chamber to
produce a gas stream; bb) directing at least a portion of the gas
stream to a mass spectrometer; cc) measuring a characteristic
mass/charge peak for the organic additive; iv) for each solution,
correlating the quantity of organic additive with the measurement
of the characteristic mass/charge peak; v) introducing a portion of
the electroplating bath having an unknown quantity of the organic
additive into the first chamber; vi) performing the predetermined
sequence of steps; and vii) choosing from the correlation in step
iv) a quantity of the organic additive which corresponds to the
recorded characteristic mass/charge peak measurement for the
organic additive.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates generally to the field of
control of electroplating baths. In particular, the present
invention relates to the control of electroplating baths using
real-time monitoring of the bath components.
[0002] Electroplating baths for copper and other metals are
typically aqueous, or mostly aqueous, solutions composed of metal
compounds or salts, ionic electrolytes, and various additives such
as brighteners, suppressors, levelers, accelerators, surfactants,
defoamers, and the like. These electroplating baths, which are used
to deposit metals or semimetals such as copper, nickel, gold,
palladium, platinum, ruthenium, rhodium, tin, zinc, antimony, or
alloys such as copper-tin (brass), copper-zinc (bronze), tin-lead,
nickel-tungsten, cobalt-tungsten-phosphid- e, and the like are used
in applications such as the fabrication of electronic devices and
components, such as conductive circuits for printed circuit boards,
multichip modules, semiconductor devices and the like.
[0003] Reliable operation of these electroplating baths in a
manufacturing process requires that methods of analysis are
employed to determine the appropriate concentrations of the reagent
species for bath startup. These analysis methods are also used to
determine the concentrations of species in the bath during
operation, often with on-line feedback control, to allow the
components of the bath to be monitored and adjusted as required to
maintain concentrations within pre-determined limits. Bath analysis
methods are also used to determine the chemical identity and
concentrations of species that are produced in the bath as a
consequence of chemical and electrochemical reactions that take
place during bath operation and/or idling. Such bath analysis
methods include cyclic voltammetric stripping ("CVS"), cyclic pulse
voltammetric stripping ("CPVS"), open circuit potential ("OCP")
measurement, AC impedance, high pressure liquid chromatography
("HPLC"), ion chromatography ("IC"), titrimetry, gravimetric
analysis, optical spectroscopy, and the like. See, for example,
U.S. Pat. No. 5,223,118 (Sonnenberg et al.) and U.S. Pat. No.
4,917,774 (Fisher). Chromatographic techniques such as HPLC and IC
are useful laboratory methods for analyzing various components of
plating baths, but they have not been widely implemented in
commercial bath analysis systems. Titrimetric and gravimetric
techniques are more widely used than chromatographic methods, but
these methods require the use of various additional chemistries
(titrants, complexants, precipitants) and are difficult to
implement in an on-line, real-time configuration.
[0004] Electrochemical techniques such as CVS and CPVS have been
most widely used in commercial applications for analysis of plating
baths because these methods are reliable and are particularly
well-suited to on-line, real-time analysis. However, the
electrochemical techniques are also limited in several aspects.
Each technique measures a current flow in response to a changing
applied potential across an electrochemical cell containing the
plating solution. The current is a response that reflects the
aggregate of all of the electrochemical reactions that occur in the
cell at a given potential. These techniques are generally unable to
distinguish between different or competing reactions that occur at
the same potential. These electrochemical techniques also are not
specific to particular chemical species in the solution, so the
changing concentration of individual species cannot be directly
measured.
[0005] In the operation of commercial electroplating baths, it is
very important to be able to measure and control the individual
components of the plating bath, particularly the organic additives.
These materials are typically present in the plating bath in small
amounts relative to the metal salts or electrolytes. However, the
additives play a major role in controlling both the characteristics
of the deposition process such as the plating rate, as well as the
physical properties of the deposit such as uniformity, grain size,
ductility, stress, surface roughness, and the like. In a typical
electroplating bath two, three, or even more additives may be
deliberately formulated into the bath to provide the desired
plating characteristics and deposit properties. Techniques such as
CVS, CPVS, or OCP can only measure the overall electrochemical
behavior of a plating bath but can not independently determine the
concentrations of the various additive species in the bath without
resorting to complex analysis schemes that involve the use of
special calibration solutions or other similar approaches.
Additionally, additives are often small organic molecules or
polymers that either undergo electrochemical, chemical, or other
reactions (such as surface adsorption) under the applied potential
conditions at which the electroplating process takes place. These
reactions can change some portion of the original additive species
to different species. The relative proportions and chemical or
electrochemical activities of these new species can change over
time, depending on the conditions of use of the plating bath. The
changing concentrations of species and their activities affects the
electrochemical behavior of the plating bath and ultimately can
affect the properties of the deposits produced from the bath. It is
very difficult to determine the nature of these reaction products
in the electroplating bath by conventional electrochemical methods
or measure their changing concentrations over time, yet these
species may actually be the most important ones to measure and
control in order to optimize the properties of the electrodeposited
films.
[0006] Differential electrochemical mass spectrometry ("DEMS") has
been used to detect various chemical species, such as the evolution
of carbon dioxide gas from an electrochemical reaction. This
technique has never been applied to the analysis of organic
components in an electroplating bath.
[0007] Thus, there is a continuing need for a method that can more
accurately determine the specific nature of the additive species
and their reaction products that are present in an electroplating
bath and to measure their concentrations on-line, in real-time, and
over time as the electroplating reaction proceeds.
SUMMARY OF THE INVENTION
[0008] It has been surprisingly found that the present method
provides on-line, real-time analysis of electroplating bath
components. According to the present method, all organic additives
in an electroplating bath may be monitored simultaneously.
[0009] In one aspect, the present invention provides a method for
determining the level of components in an electroplating bath
including the steps of: a) obtaining a plurality of solutions
wherein each solution has known and different concentrations of an
analyte, but where the quantity of the analyte in each solution
differs from the quantity in the other solutions; b) providing an
apparatus having a first chamber and a second chamber, the first
chamber being separated from the second chamber by a
liquid-impermeable, gas-permeable membrane; c) introducing each
solution individually into the first chamber and carrying out a
predetermined sequence of steps including: i) reducing the pressure
in the second chamber relative to the first chamber to produce a
gas stream; ii) directing at least a portion of the gas stream to a
mass spectrometer; iii) measuring a characteristic mass/charge peak
for the analyte; d) for each solution, correlating the quantity of
analyte with the measurement of the characteristic mass/charge
peak; e) introducing a bath having an unknown quantity of the
analyte into the first chamber; f) performing the predetermined
sequence of steps; and g) choosing from the correlation in step d)
a quantity of the analyte which corresponds to the recorded
characteristic mass/charge peak measurement for the analyte.
[0010] In a second aspect, the present invention includes an
electroplating system including an electroplating tank containing
an electroplating bath, the tank having an outlet for directing a
portion of the electroplating bath to an apparatus for determining
the level of components in the electroplating bath, the apparatus
including a first chamber separated from a second chamber by a
liquid-impermeable, gas-permeable membrane, a means for reducing
the pressure in the second chamber relative to the first chamber to
produce a gas stream, and a means for directing at least a portion
of the gas stream to a mass spectrometer.
[0011] In a third aspect, the present invention provides a method
for electrolytically depositing metal on a substrate including the
steps of: a) contacting the substrate with an electroplating bath
including a source of metal ions, and electrolyte and one or more
organic additives; b) subjecting the electroplating bath to
sufficient current density for a period of time sufficient to
deposit a desired thickness of metal on the substrate; and c)
monitoring the one or more organic additives by i) obtaining a
plurality of solutions wherein each solution has known and
different concentrations of an organic additive, but where the
quantity of the organic additive in each solution differs from the
quantity in the other solutions; ii) providing an apparatus having
a first chamber and a second chamber, the first chamber being
separated from the second chamber by a liquid-impermeable,
gas-permeable membrane; iii) introducing each solution individually
into the first chamber and carrying out a predetermined sequence of
steps including: aa) reducing the pressure in the second chamber
relative to the first chamber to produce a gas stream; bb)
directing at least a portion of the gas stream to a mass
spectrometer; cc) measuring a characteristic mass/charge peak for
the organic additive; iv) for each solution, correlating the
quantity of organic additive with the measurement of the
characteristic mass/charge peak; v) introducing a portion of the
electroplating bath having an unknown quantity of the organic
additive into the first chamber; vi) performing the predetermined
sequence of steps; and vii) choosing from the correlation in step
iv) a quantity of the organic additive which corresponds to the
recorded characteristic mass/charge peak measurement for the
organic additive.
BRIEF DESCRIPTION OF THE DRAWING
[0012] FIG. 1 illustrates an apparatus useful in the invention, not
to scale.
[0013] FIG. 2 illustrates an apparatus useful in the invention
having an electrochemical cell, not to scale.
[0014] FIG. 3 is a flowchart illustrating the present method.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention uses differential electrochemical mass
spectrometry ("DEMS") to analyze one or multiple organic components
in an electroplating solution. This method offers several
advantages over conventional methods of analyzing electroplating
baths. Very low levels of organic species may be determined using
this technique, such as below ppm levels, e.g. .ltoreq.0.5 ppm,
.ltoreq.0.1 ppm, .ltoreq.0.05 ppm and the like. Multiple organic
species in an electroplating bath may be monitored according to the
present invention unlike conventional techniques which analyze only
for a limited number of components, e.g. one or two. The limit on
organic species that can be analyzed is the number of channels
possessed by the mass spectrometer used. The use of a mass
spectrometer provides real-time, multichannel analysis of the
individual species with a typical mass resolution of less than 1
atomic mass unit. The present invention provides highly specific
information about both the mass spectral identity of additives in
the plating bath, but also the time course of their concentrations.
According to the present invention, the spectral identity and
buildup of reaction products of one or more of the organic
additives can be determined while the electroplating bath remains
in operation. Such information is extremely important to the
analysis and control of electroplating baths for use in the
manufacture of electronic devices.
[0016] FIG. 1 illustrates an apparatus useful in the invention, not
to scale. The apparatus has a first chamber 1, a second chamber 11
and a liquid-impermeable, gas-permeable membrane 10 separating the
first and second chambers. The second chamber 11 is connected to a
vacuum pump 12. The vacuum pump reduces the pressure in the second
chamber 11 relative to the first chamber 1 thus producing a gas
flow from the first chamber 1 through the membrane 10 into the
second chamber 11. At least a portion of the gas stream is directed
to a mass selective detector or mass spectrometer 13 The mass
selective detector is used to perform mass spectral analysis of the
components of the gas stream.
[0017] The first chamber holds the solution to be analyzed.
Preferably, the first chamber is constructed of chemically inert,
gas-tight, electrically non-conductive materials. Suitable
materials for the first chamber include polymer resins such as
poly(tetrafluoroethylene) or polyetherketone. The
liquid-impermeable, gas-permeable membrane may be of any suitable
material that does not react with or adversely affect the
components of the solution to be analyzed. The membrane material is
chosen such that it is permeable to the organic components of the
solution to be analyzed. Preferably, the membrane is thin. The
second chamber may be a vessel or a sealed connection between the
membrane and the vacuum system. One or more vacuum pumps may be
successfully utilized and may be connected in series. Preferably, a
high vacuum is applied to the second chamber. Such vacuum reduces
the pressure of the second chamber relative to the first chamber.
Thus, volatile components (i.e. organic additives) of the solution
to be analyzed pass through the membrane to produce a gas stream.
Such gas stream is then directed to the mass selective detector.
Any suitable commercially available mass selective detector may be
used in the present invention such as a quadrupole mass
spectrometer. It will be appreciated that the vacuum system of the
mass selective detector may apply sufficient vacuum to the second
chamber to reduce its pressure relative to the first chamber
without the need for a separate vacuum pump.
[0018] An alternate apparatus having an electrochemical cell useful
in the invention is illustrated in FIG. 2, not to scale. Referring
to FIG. 2, first chamber 1 contains a working electrode 3,
reference electrode 6, auxiliary electrode 8, and membrane 10
separating the first chamber 1 from second chamber 11. Vacuum pump
12 connects the second chamber 11 with a mass selective detector
13. Working electrode 3, reference electrode 6 and auxiliary
electrode 8 are connected to electrical power source 5. Electrolyte
solution enters the first chamber 1 through inlet port 14 and exits
through outlet port 15. Vacuum is applied to the second chamber 11
by vacuum pump 12 thereby reducing the pressure of the second
chamber relative to the first chamber 1. A gas stream is thus
provided passing from the first chamber 1 through membrane 10 into
second chamber 11 and at least a portion of such gas stream is
directed to the mass selective detector 13 for spectral
analysis.
[0019] A wide variety of working electrodes may suitably be used.
The working electrode may be constructed of a noble metal such as
gold or platinum, or the base metal of the electroplating solution
such as copper. The reference electrode has a stable, fixed voltage
and may be used to control the potential of the working electrode
in combination with a potentiostat (power source). The reference
electrode may be made of any suitable material such as an insoluble
metal salt in contact with the same metal. For example, suitable
reference electrodes include the standard calomel electrode,
Hg/HgCl.sub.2 in KCl electrolyte. The auxiliary electrode may be
made of any suitable material such as one of the noble metals
including gold and platinum, or the base metal of the
electroplating solution such as copper. A variety of power sources
are suitable, including a galvanostat or a potentiostat. The inlet
port draws a sample for analysis from an electroplating bath. Such
sampling may be automated or performed manually and the sample
introduced to the first chamber through the inlet port. After the
analysis is performed, the sample exits the first chamber through
the outlet port and the sample may be directed back to the
electroplating bath or to a waste receptacle.
[0020] The present invention provides a method for determining the
level of components in an electroplating bath including the steps
of: a) obtaining a plurality of solutions wherein each solution has
known and different concentrations of an analyte, but where the
quantity of the analyte in each solution differs from the quantity
in the other solutions; b) providing an apparatus having a first
chamber and a second chamber, the first chamber being separated
from the second chamber by a liquid-impermeable, gas-permeable
membrane; c) introducing each solution individually into the first
chamber and carrying out a predetermined sequence of steps
including: i) reducing the pressure in the second chamber relative
to the first chamber to produce a gas stream; ii) directing at
least a portion of the gas stream to a mass spectrometer; iii)
measuring a characteristic mass/charge peak for the analyte; d) for
each solution, correlating the quantity of analyte with the
measurement of the characteristic mass/charge peak; e) introducing
a bath having an unknown quantity of the analyte into the first
chamber; f) performing the predetermined sequence of steps; and g)
choosing from the correlation in step d) a quantity of the analyte
which corresponds to the recorded characteristic mass/charge peak
measurement for the analyte.
[0021] FIG. 3 is a flowchart illustrating the present method. At
step 20, a sample or aliquot is taken from an electroplating bath
containing one or more organic additives and placed in the first
chamber of the apparatus. At this point, the sample may be analyzed
with or without the application of a potential to the first
chamber. Following the first route 22, a reducing potential is
applied to a working electrode in the first chamber prior to
applying a vacuum to the second chamber at step 30. By applying
such reducing potential, the effect of an electroplating bath may
be provided and organic species produced from such electrochemical
operation may be analyzed directly. Alternatively, following route
23, a vacuum is applied to the second chamber at step 30 without
any potential being applied to the working electrode. Applying
vacuum to the second chamber produces a gas stream that is directed
to a mass selective detector. At step 35, the mass spectrum is
swept and the mass/charge spectrum analyzed to identify the organic
components at step 40. A characteristic mass/charge peak, such as a
parent ion peak, is typically monitored for each analyte. The
mass/charge peak intensity is measured at step 45 and the
intensities of selected peaks, such as a characteristic mass/charge
peak, are displayed at step 50. The mass/charge ("m/e") peak
intensity may be measured as peak height or peak area and may be
displayed as either an analog or digital signal, and preferably a
digital signal. Such displayed intensity for each organic additive
of the electroplating bath is then compared to a preset value for
that additive compound. If the displayed intensity falls below the
preset value, the amount of the organic additive in the
electroplating bath may need to be increased. In a fully automated
system, when the intensity of the characteristic peak falls below
the preset value, a computer can be employed to cause an
appropriate amount of organic additive to be added to the
electroplating bath. Following analysis of the solution in the
first chamber, the solution is changed at step 60.
[0022] In the present method, a standard curve is first prepared
for each organic additive, break down product, degradation product
and the like (collectively "analytes") to be monitored. Such
standard curves are obtained by first preparing a series of
solutions containing known, but different amounts of analyte. Each
solution has an amount of analyte that differs from the amount of
analyte in the other solutions. A solution of the analyte is
introduced into the first chamber of the apparatus and the pressure
in the second chamber is then reduced relative to the first
chamber. The reduced pressure produces a gas stream of the volatile
analyte which passes from the solution through the membrane and
into the second chamber. The gas stream is then directed toward the
mass selective detector. The mass spectrum of the analyte is swept
and the intensity of a characteristic mass/charge peak, typically
of the parent ion, is measured. This procedure is then repeated for
each of the analyte solutions of differing concentration. A
correlation (i.e. standard curve, of peak measurement with quantity
of analyte is then prepared. A solution of unknown quantity of
analyte is then introduced into the first chamber of the apparatus
and the above process steps repeated. The measurement of the
characteristic mass/charge peak is then compared to the standard
curve and the quantity of analyte in the solution is
determined.
[0023] In an alternate embodiment, the apparatus may be an
electrochemical cell, such as that shown in FIG. 2. In this
embodiment, after the solution is introduced into the first
chamber, a potential is applied to the working electrode. The
potential is typically sufficient to reduce the metal ions in the
bath to zerovalent metal. After the potential is applied, the
pressure in the second chamber is reduced relative to the first
chamber and the process is as described above. In this alternate
method, a standard curve is first produced and then solutions of
unknown quantities of analyte are analyzed and the characteristic
mass/charge peak measurement is compared to the standard curve and
the quantity of analyte in the solution is determined.
[0024] It will be appreciated by those skilled in the art that the
present invention may be combined with one or more conventional
bath metrology systems that employ techniques such as CVS, CPVS,
OCP, or AC impedance.
[0025] The analysis of very small amounts of material is provided
according to the present invention due to the sensitivity of the
mass selective detector. If a particular component in the bath
sample is present in high amounts, only a portion of the gas stream
produced upon evacuation of the second chamber will be directed to
the detector. If the particular component is present in only very
low amounts, the entire gas stream produced may be directed to the
detector. It will be appreciated by those skilled in the art that
the amount of organic component in the gas stream is related to the
partial pressure of the particular additive. One skilled in the art
can easily determine the amount of the gas stream to be directed
toward the detector.
[0026] The present invention further provides an electroplating
system including an electroplating tank containing an
electroplating bath, the tank having an outlet for directing a
portion of the electroplating bath to an apparatus for determining
the level of components in the electroplating bath, the apparatus
including a first chamber separated from a second chamber by a
liquid-impermeable, gas-permeable membrane, a means for reducing
the pressure in the second chamber relative to the first chamber to
produce a gas stream, and a means for directing at least a portion
of the gas stream to a mass spectrometer.
[0027] A wide variety of electroplating baths may be analyzed
according to the present method to determine the content of organic
components, break down products, degradation products and the like
in such baths. Suitable electroplating baths include, but are not
limited to, those for depositing copper, nickel, chromium, zinc,
tin, gold, silver, and their alloys. A metal electroplating bath
typically contains a source of metal ions and an electrolyte. One
or more organic components may optionally be added to the
electroplating bath. Suitable optional components include, but are
not limited to, halides, accelerators or brighteners, suppressors,
levelers, grain refiners, wetting agents, surfactants, defoamers,
ductilizers, and the like.
[0028] While the present invention may suitably be used with a
variety of electroplating baths, it will be described with
reference to a copper or copper alloy electroplating bath. A
variety of copper salts may be employed in the typical
electroplating solutions, including for example copper sulfates,
copper acetates, copper fluoroborate, and cupric nitrates. Copper
sulfate pentahydrate is a particularly preferred copper salt. A
copper salt may be suitably present in a relatively wide
concentration range in the electroplating compositions of the
invention. Preferably, a copper salt will be employed at a
concentration of from about 1 to about 300 g/L of plating solution,
more preferably at a concentration of from about 10 to about 225
g/L, still more preferably at a concentration of from about 25 to
about 175 g/L. It is preferred that the copper ion is present in
the electroplating bath in an amount of from about 15 to about 50
g/L, and more preferably about 30 to about 45 g/L. The copper
plating bath may also contain amounts of other alloying elements,
such as, but not limited to, tin, zinc, indium, antimony, and the
like. Thus, the copper electroplating baths useful in the present
invention may deposit copper or copper alloy.
[0029] Plating baths useful in the present invention employ an
electrolyte, preferably an acidic electrolyte. When the electrolyte
is acidic, the acid may be inorganic or organic. Suitable inorganic
acids include, but are not limited to, sulfuric acid, phosphoric
acid, nitric acid, hydrogen halide acids, sulfamic acid,
fluoroboric acid and the like. Suitable organic acids include, but
are not limited to, alkylsulfonic acids such as methanesulfonic
acid, aryl sulfonic acids such as phenylsulfonic acid and
tolylsulfonic acid, carboxylic acids such as formic acid, acetic
acid and propionic acid, halogenated acids such as
trifluoromethylsulfonic acid and haloacetic acid, and the like.
Particularly suitable organic acids include
(C.sub.1-C.sub.10)alkylsulfon- ic acids. Preferred acids include
sulfuric acid, nitric acid, methanesulfonic acid, phenylsulfonic
acid, mixtures of sulfuric acid and methanesulfonic acid, mixtures
of methanesulfonic acid and phenylsulfonic acid, and mixtures of
sulfuric acid, methanesulfonic acid and phenylsulfonic acid.
[0030] It will be appreciated by those skilled in the art that a
combination of two or more acids may be used. Particularly suitable
combinations of acids include one or more inorganic acids with one
or more organic acids or a mixture of two or more organic acids.
Typically, the two or more acids may be present in any ratio. For
example, when two acids are used, they may be present in any ratio
from 99:1 to 1:99. Preferably, the two acids are present in a ratio
from 90:10 to 10:90, more preferably from 80:20 to 20:80, still
more preferably from 75:25 to 25:75, and even more preferably from
60:40 to 40:60.
[0031] The total amount of added acid used in the present
electroplating baths may be from about 0 to about 100 g/L, and
preferably from 0 to 50 g/L, although higher amounts of acid may be
used for certain applications, such as up to 225 g/L or even 300
g/L. It will be appreciated by those skilled in the art that by
using a metal sulfate as the metal ion source, an acidic
electrolyte can be obtained without any added acid.
[0032] For certain applications, such as in the plating of wafers
having very small apertures, it is preferred that the total amount
of added acid be low. By "low acid" is meant that the total amount
of added acid in the electrolyte is less than about 0.4 M,
preferably less than about 0.3 M, and more preferably less than
about 0.2 M. It is further preferred that the electrolyte is free
of added acid.
[0033] The electrolyte may optionally contain one or more halides,
and preferably does contain at least one halide. Chloride and
bromide are preferred halides, with chloride being more preferred.
A wide range of halide ion concentrations (if a halide ion is
employed) may be suitably utilized, e.g. from about 0 (where no
halide ion employed) to 100 ppm of halide ion in the plating
solution, preferably from about 10 to about 75 ppm, and more
preferably from about 25 to about 75 ppm. A particularly useful
range of chloride ion is from about 10 to about 35 ppm.
[0034] A wide variety of brighteners and accelerators, including
known brightener agents and accelerators, may be employed in the
copper electroplating compositions of the invention. Typical
brighteners and accelerators contain one or more sulfur atoms, and
typically without any nitrogen atoms and a molecular weight of
about 1000 or less. Brightener and accelerator compounds that have
sulfide and/or sulfonic acid groups are generally preferred,
particularly compounds that comprise a group of the formula
R'--S--R--SO.sub.3X, where R is an optionally substituted alkyl
(which include cycloalkyl), optionally substituted heteroalkyl,
optionally substituted aryl group, or optionally substituted
heteroalicyclic; X is a counter ion such as sodium or potassium;
and R' is hydrogen or a chemical bond (i.e. --S--R--SO.sub.3X or
substituent of a larger compound). Typically alkyl groups will have
from one to about 16 carbons, more typically one to about 8 or 12
carbons. Heteroalkyl groups will have one or more hetero (N, O or
S) atoms in the chain, and preferably have from 1 to about 16
carbons, more typically 1 to about 8 or 12 carbons. Carbocyclic
aryl groups are typical aryl groups, such as phenyl and naphthyl.
Heteroaromatic groups also will be suitable aryl groups, and
typically contain 1 to about 3 N, O or S atoms and 1-3 separate or
fused rings and include e.g. coumarinyl, quinolinyl, pyridyl,
pyrazinyl, pyrimidyl, furyl, pyrrolyl, thienyl, thiazolyl,
oxazolyl, oxidizolyl, triazole, imidazolyl, indolyl, benzofuranyl,
benzothiazol, and the like. Heteroalicyclic groups typically will
have 1 to 3 N, O or S atoms and from 1 to 3 separate or fused rings
and include e.g. tetrahydrofuranyl, thienyl, tetrahydropyranyl,
piperdinyl, morpholino, pyrrolindinyl, and the like. Substituents
of substituted alkyl, heteroalkyl, aryl or heteroalicyclic groups
include e.g. (C.sub.1-C.sub.8)alkoxy; (C.sub.1-C.sub.8)alkyl,
halogen, particularly F, Cl and Br; cyano, nitro, and the like.
[0035] More specifically, useful brighteners and accelerators
include those of the following formulae:
XO.sub.3S--R--SH
XO.sub.3S--R--S--S--R--SO.sub.3X and
XO.sub.3S--Ar--S--S--Ar--SO.sub.3X
[0036] where in the above formulae R is an optionally substituted
alkyl group, and preferably is an alkyl group having from 1 to 6
carbon atoms, more preferably is an alkyl group having from 1 to 4
carbon atoms; Ar is an optionally substituted aryl group such as
optionally substituted phenyl or naphthyl; and X is a suitable
counter ion such as sodium or potassium.
[0037] Some specific suitable brighteners and accelerators include
e.g. n,n-dimethyldithiocarbamic acid-(3-sulfopropyl)ester;
3-mercapto-propylsulfonic acid-(3-sulfopropyl)ester;
3-mercapto-propylsulfonic acid (sodium salt); carbonic
acid-dithio-o-ethylester-s-ester with 3-mercapto-1-propane sulfonic
acid (potassium salt); bissulfopropyl disulfide;
3-(benzthiazolyl-s-thio)propy- l sulfonic acid (sodium salt);
pyridinium propyl sulfobetaine;
1-sodium-3-mercaptopropane-1-sulfonate; sulfoalkyl sulfide
compounds disclosed in U.S. Pat. No. 3,778,357; the peroxide
oxidation product of a dialkyl
amino-thiox-methyl-thioalkanesulfonic acid; and combinations of the
above. Additional suitable brighteners are also described in U.S.
Pat. Nos. 3,770,598, 4,374,709, 4,376,685, 4,555,315, and
4,673,469, all incorporated herein by reference. Particularly
preferred brighteners for use in the plating compositions of the
invention are n,n-dimethyl-dithiocarbamic acid-(3-sulfopropyl)ester
and bis-sodium-sulfonopropyldisulfide.
[0038] The amount of such brighteners or accelerators present in
the electroplating baths is in the range of from about 0.1 to about
1000 ppm. Preferably, such compounds are present in an amount of
from about 0.5 to about 300 ppm, more preferably from about 1 to
about 100 ppm, and still more preferably from about 2 to about 50
ppm.
[0039] The suppressor agents useful in the compositions of the
invention are polymeric materials, preferably having heteroatom
substitution, particularly oxygen linkages. Generally preferred
suppressor agents are generally high molecular weight polyethers,
such as those of the following formula:
R--O--(CXYCX'Y'O).sub.nH
[0040] where R is an aryl or alkyl group containing from about 2 to
20 carbon atoms; each X, Y, X' and Y' is independently hydrogen,
alkyl preferably methyl, ethyl or propyl, aryl such as phenyl;
aralkyl such as benzyl; and preferably one or more of X, Y, X' and
Y' is hydrogen; and n is an integer between 5 and 100,000.
Preferably, R is ethylene and n is greater than 12,000.
[0041] The amount of such suppressors present in the electroplating
baths is in the range of from about 0.1 to about 1000 ppm.
Preferably, the suppressor compounds are present in an amount of
from about 0.5 to about 500 ppm, and more preferably from about 1
to about 200 ppm.
[0042] Surfactants may optionally be added to the electroplating
baths. Such surfactants are typically added to copper
electroplating solutions in concentrations ranging from about 1 to
10,000 ppm based on the weight of the bath, more preferably about 5
to 10,000 ppm. Particularly suitable surfactants for plating
compositions of the invention are commercially available
polyethylene glycol copolymers, including polyethylene glycol
copolymers. Such polymers are available from e.g. BASF (sold by
BASF under TETRONIC and PLURONIC tradenames), and copolymers from
Chemax.
[0043] Levelers may optionally be added to the present
electroplating baths. It is preferred that one or more leveler
components is used in the present electroplating baths. Such
levelers may be used in amounts of from about 0.01 to about 50 ppm.
Examples of suitable leveling agents are described and set forth in
U.S. Pat. Nos. 3,770,598, 4,374,709,4,376,685, 4,555,315 and
4,673,459. In general, useful leveling agents include those that
contain a substituted amino group such as compounds having
R--N--R', where each R and R' is independently a substituted or
unsubstituted alkyl group or a substituted or unsubstituted aryl
group. Typically the alkyl groups have from 1 to 6 carbon atoms,
more typically from 1 to 4 carbon atoms. Suitable aryl groups
include substituted or unsubstituted phenyl or naphthyl. The
substituents of the substituted alkyl and aryl groups may be, for
example, alkyl, halo and alkoxy.
[0044] More specifically, suitable leveling agents include, but are
not limited to, 1-(2-hydroxyethyl)-2-imidazolidinethione;
4-mercaptopyridine; 2-mercaptothiazoline; ethylene thiourea;
thiourea; alkylated polyalkyleneimine; phenazonium compounds
disclosed in U.S. Pat. No. 3,956,084; N-heteroaromatic rings
containing polymers; quaternized, acrylic, polymeric amines;
polyvinyl carbamates; pyrrolidone; and imidazole. A particularly
preferred leveler is 1-(2-hydroxyethyl)-2-imida-
zolidinethione.
[0045] The present invention may be used to analyze or monitor
electroplating baths used for a wide variety of electroplating,
such as plating of printed wiring boards, decorative plating,
functional plating such as for corrosion resistance, plating of
substrates used in the manufacture of integrated circuits, plating
of connectors such as lead frames, plating of multichip modules,
final finish plating and the like. It is preferred that the present
invention is used with electroplating baths for depositing metal on
a printed wiring board or a substrate used in the manufacture of
integrated circuits.
[0046] Additionally, the present invention provides a method for
electrolytically depositing metal on a substrate including the
steps of: a) contacting the substrate with an electroplating bath
including a source of metal ions, and electrolyte and one or more
organic additives; b) subjecting the electroplating bath to
sufficient current density for a period of time sufficient to
deposit a desired thickness of metal on the substrate; and c)
monitoring the one or more organic additives by i) obtaining a
plurality of solutions wherein each solution has known and
different concentrations of an organic additive, but where the
quantity of the organic additive in each solution differs from the
quantity in the other solutions; ii) providing an apparatus having
a first chamber and a second chamber, the first chamber being
separated from the second chamber by a liquid-impermeable,
gas-permeable membrane; iii) introducing each solution individually
into the first chamber and carrying out a predetermined sequence of
steps including: aa) reducing the pressure in the second chamber
relative to the first chamber to produce a gas stream; bb)
directing at least a portion of the gas stream to a mass
spectrometer; cc) measuring a characteristic mass/charge peak for
the organic additive; iv) for each solution, correlating the
quantity of organic additive with the measurement of the
characteristic mass/charge peak; v) introducing a portion of the
electroplating bath having an unknown quantity of the organic
additive into the first chamber; vi) performing the predetermined
sequence of steps; and vii) choosing from the correlation in step
iv) a quantity of the organic additive which corresponds to the
recorded characteristic mass/charge peak measurement for the
organic additive. Preferably, such substrate is a wafer used in
integrated circuit manufacture. Particularly suitable
electroplating baths include copper and copper alloy baths.
* * * * *