U.S. patent application number 10/722174 was filed with the patent office on 2005-05-26 for on-wafer electrochemical deposition plating metrology process and apparatus.
Invention is credited to Han, Jianwen, King, MacKenzie.
Application Number | 20050109624 10/722174 |
Document ID | / |
Family ID | 34591972 |
Filed Date | 2005-05-26 |
United States Patent
Application |
20050109624 |
Kind Code |
A1 |
King, MacKenzie ; et
al. |
May 26, 2005 |
On-wafer electrochemical deposition plating metrology process and
apparatus
Abstract
Electrochemical deposition (ECD) processes and systems used in
the fabrication of products such as semiconductor devices, and more
specifically an on-wafer process and apparatus of such type, in
which the workpiece being plated is utilized as an electrode
element in the monitoring operation, thereby substantially
simplying the analytical monitoring metrology of ECD operation. The
invention is usefully employed in copper electrodeposition
involving control of organic additives concentrations in the copper
plating bath, to achieve highly efficient copper metalizing of
wafer substrates.
Inventors: |
King, MacKenzie; (Southbury,
CT) ; Han, Jianwen; (Danbury, CT) |
Correspondence
Address: |
ATMI, INC.
7 COMMERCE DRIVE
DANBURY
CT
06810
US
|
Family ID: |
34591972 |
Appl. No.: |
10/722174 |
Filed: |
November 25, 2003 |
Current U.S.
Class: |
205/81 |
Current CPC
Class: |
C25D 21/12 20130101;
C25D 7/123 20130101 |
Class at
Publication: |
205/081 |
International
Class: |
C25D 005/00 |
Claims
What is claimed is:
1. A method of controlling copper electrochemical deposition in an
electrochemical deposition system in which a wafer is contacted
with an electrochemical deposition medium including at least one
organic additive, wherein the electrochemical deposition medium has
a plating anode in contact therewith to effect plating of copper on
the wafer, and the electrochemical deposition is characterizable by
at least one dependent variable correlative of efficacy of the
copper electrochemical deposition, said method comprising:
selecting at least one dependent variable correlative of efficacy
of the copper electrochemical deposition; performing a regression
analysis or multivariate calibration modeling of the copper
electrochemical deposition utilizing a wafer-based independent
variable to generate a dependent variable equation for each
selected dependent variable correlative of efficacy of the copper
electrochemical deposition; solving the dependent variable equation
for each selected dependent variable correlative of efficacy of the
copper electrochemical deposition, by regression analysis, to yield
a solution value for each selected dependent variable; and
modulating the copper electrochemical deposition in response to the
solution value for each selected dependent variable.
2. The method of claim 1, wherein the wafer-based independent
variable is selected from the group consisting of plating voltage
output, plating current, electrode size, and wafer preconditioning
pulse.
3. The method of claim 1, wherein the electrochemical deposition
medium includes a copper salt and an inorganic acid.
4. The method of claim 3, wherein the inorganic acid comprises
sulfuric acid.
5. The method of claim 3, wherein the copper salt comprises copper
sulfate.
6. The method of claim 1, wherein the at least one organic additive
includes an organic additive selected from the group consisting of
organic accelerators, organic suppressors and organic levelers.
7. The method of claim 6, wherein the at least one organic additive
includes an organic accelerator, and organic suppressor and an
organic leveler.
8. The method of claim 1, wherein the electrochemical deposition
medium further includes a chloride source.
9. The method of claim 1, wherein the selected at least one
dependent variable includes concentration of at least one component
of the electrochemical deposition medium.
10. The method of claim 9, wherein the selected at least one
dependent variable includes concentration of an organic additive of
the electrochemical deposition medium.
11. The method of claim 9, wherein the selected at least one
dependent variable includes concentration of each organic additive
in the electrochemical deposition medium.
12. The method of claim 9, wherein the selected at least one
dependent variable includes concentration of at least one organic
additive in the electrochemical deposition medium.
13. The method of claim 7, wherein the selected at least one
dependent variable includes concentration of each organic
accelerator, and organic suppressor and an organic leveler.
14. Apparatus for controlling copper electrochemical deposition in
an electrochemical deposition system in which a wafer is contacted
with an electrochemical deposition medium including at least one
organic additive, wherein the electrochemical deposition medium has
a plating anode in contact therewith to effect plating of copper on
the wafer, and the electrochemical deposition is characterizable by
at least one dependent variable correlative of efficacy of the
copper electrochemical deposition, said apparatus comprising: a
computational module constructed and arranged to perform the
following steps: selecting at least one dependent variable
correlative of efficacy of the copper electrochemical deposition;
performing a regression analysis or multivariate calibration
modeling of the copper electrochemical deposition utilizing a
wafer-based independent variable to generate a dependent variable
equation for each selected dependent variable correlative of
efficacy of the copper electrochemical deposition; and solving the
dependent variable equation for each selected dependent variable
correlative of efficacy of the copper electrochemical deposition,
by regression analysis, to yield a solution value for each selected
dependent variable; and means for modulating the copper
electrochemical deposition in response to the solution value for
each selected dependent variable.
15. Apparatus according to claim 14, wherein the wafer-based
independent variable is selected from the group consisting of
plating voltage output, plating current, electrode size, and wafer
preconditioning pulse.
16. Apparatus according to claim 14, wherein the electrochemical
deposition medium includes a copper salt and an inorganic acid.
17. Apparatus according to claim 16, wherein the inorganic acid
comprises sulfuric acid.
18. Apparatus according to claim 16, wherein the copper salt
comprises copper sulfate.
19. Apparatus according to claim 14, wherein the at least one
organic additive includes an organic additive selected from the
group consisting of organic accelerators, organic suppressors and
organic levelers.
20. Apparatus according to claim 19, wherein the at least one
organic additive includes an organic accelerator, and organic
suppressor and an organic leveler.
21. Apparatus according to claim 14, wherein the electrochemical
deposition medium further includes a chloride source.
22. Apparatus according to claim 14, wherein the selected at least
one dependent variable includes concentration of at least one
component of the electrochemical deposition medium.
23. Apparatus according to claim 22, wherein the selected at least
one dependent variable includes concentration of an organic
additive of the electrochemical deposition medium.
24. Apparatus according to claim 22, wherein the selected at least
one dependent variable includes concentration of each organic
additive in the electrochemical deposition medium.
25. Apparatus according to claim 22, wherein the selected at least
one dependent variable includes concentration of at least one
organic additive in the electrochemical deposition medium.
26. Apparatus according to claim 20, wherein the selected at least
one dependent variable includes concentration of each organic
accelerator, and organic suppressor and an organic leveler.
27. Apparatus according to claim 20, wherein said means for
modulating the copper electrochemical deposition in response to the
solution value for each selected dependent variable, comprise a
means selected from the group consisting of: variable output power
supplies arranged to supply power to the electrochemical deposition
system; and variable flow control valves for modulating flow to the
electrochemical deposition medium of one or more components of the
electrochemical deposition medium.
28. Apparatus according to claim 27, wherein said modulating means
comprises a variable output power supply arranged to supply power
to the electrochemical deposition system.
29. Apparatus according to claim 27, wherein said modulating means
comprises variable flow control valves for modulating flow to the
electrochemical deposition medium of one or more components of the
electrochemical deposition medium.
30. Apparatus according to claim 29, wherein the variable flow
control valves are respectively coupled with sources of
accelerator, leveler and suppressor.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to electrochemical deposition
(ECD) processes and systems used in the fabrication of products
such as semiconductor devices, and more specifically to an on-wafer
process and apparatus of such type, in which the workpiece being
plated is utilized as an electrode element in the monitoring
operation, thereby substantially simplying the analytical
monitoring metrology of ECD operation.
[0003] 2. Description of the Related Art
[0004] In the field of semiconductor manufacturing, a wide variety
of unit operations is employed in the fabrication sequence. These
unit operations include chemical vapor deposition, photoresist
patterning, development, etching and residue removal, ion
implantation, etc., as well as electrochemical deposition for
lay-down of copper or other metals on the semiconductor device
substrate.
[0005] In ECD for copper metallization of the substrate article, an
ECD bath is utilized containing an aqueous solution of copper
sulfate containing sulfuric acid and chloride ions as basic
inorganic components, in combination with organic constituents
including accelerators (brighteners), levelers and supressors. The
rigorous control of the relative proportions of the respective
ingredients in the ECD bath is critical to the achievement of
satisfactory results in the rate of metal film formation and the
quality of the film produced on the substrate. During the use of
the plating bath solution, the plating process may be affected by
additive and inorganic depletion and by organic byproduct
formation. Knowing the concentration of these components of the ECD
plating bath is critical to achieving a low defect yield of
metalized products.
[0006] The bath chemistry therefore is conventionally maintained by
periodic replacement of part or all of the plating solution in the
ECD bath. The concentrations of selected components in the ECD bath
may be monitored continuously or periodically, and organic and/or
inorganic components may be added to the bath in response to
monitoring, to maintain the composition of the bath in an effective
state for the electrochemical deposition operation.
[0007] Current methods of analysis of components of the ECD plating
bath include high pressure liquid chromatography (HPLC), cyclic
voltametric stripping (CVS) and pulsed cyclic galvanostatic
analysis (PCGA). Each of these monitoring techniques requires
expensive hardware that uses valuable cleanroom space, and is
susceptible to downtime resulting from monitoring system
malfunction or failure, or from periodic maintenance requirements.
In addition to such cost and reliability issues, none of these
conventional techniques provides a true and accurate indication of
the deposition process on the substrate that is being
metallized.
SMMMARY OF THE INVENTION
[0008] The present invention generally relates to electrochemical
deposition processes and systems used in the fabrication of
products such as semiconductor devices, and more specifically to an
on-wafer process and apparatus of such type.
[0009] The present invention in one aspect relates to a method of
controlling copper electrochemical deposition in an electrochemical
deposition system in which a wafer is contacted with an
electrochemical deposition medium including at least one organic
additive, wherein the electrochemical deposition medium has a
plating anode in contact therewith to effect plating of copper on
the wafer, and the electrochemical deposition is characterizable by
at least one dependent variable correlative of efficacy of the
copper electrochemical deposition, such method including:
[0010] selecting at least one dependent variable correlative of
efficacy of the copper electrochemical deposition;
[0011] performing a regression analysis or multivariate calibration
modeling of the copper electrochemical deposition utilizing a
wafer-based independent variable to generate a dependent variable
equation for each selected dependent variable correlative of
efficacy of the copper electrochemical deposition;
[0012] solving the dependent variable equation for each selected
dependent variable correlative of efficacy of the copper
electrochemical deposition, by regression analysis, to yield a
solution value for each selected dependent variable; and
[0013] modulating the copper electrochemical deposition in response
to the solution value for each selected dependent variable.
[0014] The present invention in another aspect of the invention
relates to an apparatus for controlling copper electrochemical
deposition in an electrochemical deposition system in which a wafer
is contacted with an electrochemical deposition medium including at
least one organic additive, wherein the electrochemical deposition
medium has a plating anode in contact therewith to effect plating
of copper on the wafer, and the electrochemical deposition medium
is characterizable by at least one dependent variable correlative
of efficacy of the copper electrochemical deposition. The apparatus
includes:
[0015] a computational module constructed and arranged to perform
the following steps:
[0016] selecting at least one dependent variable correlative of
efficacy of the copper electrochemical deposition;
[0017] performing a regression analysis or multivariate calibration
modeling of the copper electrochemical deposition utilizing a
wafer-based independent variable to generate a dependent variable
equation for each selected dependent variable correlative of
efficacy of the copper electrochemical deposition; and
[0018] solving the dependent variable equation for each selected
dependent variable correlative of efficacy of the copper
electrochemical deposition, by regression analysis, to yield a
solution value for each selected dependent variable; and
[0019] means for modulating the copper electrochemical deposition
in response to the solution value for each selected dependent
variable.
[0020] Other aspects, features and embodiments of the present
invention will be more fully apparent from the ensuing disclosure
and appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a graph of plating potential E (volts) as a
function of time, in seconds.
[0022] FIG. 2 is a schematic representation of an electrochemical
deposition apparatus according to one embodiment of the
invention.
DETAILED DESCRIPTION OF THE INVENTION, AND PREFERRED EMBODIMENTS
THEREOF
[0023] In the ECD process, the wafer functions as a deposition
electrode due to the thin seed layer of metal thereon as deposited
by chemical vapor deposition or other vapor deposition technique,
with such seed layer functioning as a cathode element of the
electrochemical cell in the aqueous electrolyte medium and a
sacrificial anode element of the metal to be plated forming the
other electrode of the electrochemical circuit. The rate of the
metal deposition on the substrate is determined by the applied
current, and by the concentrations of the suppressor and
accelerator species in the plating bath.
[0024] In order to achieve conformal filling of high aspect ratio
features such as vias and trenches on the substrate, precise
concentrations of suppressor and accelerator components, as well as
chloride, are required in the ECD bath. These components must be
replenished during the use of the bath to compensate for losses
and/or decomposition thereof during processing. Accordingly,
precise and reliable monitoring of bath components is required.
[0025] The present invention utilizes an application of fundamental
modeling concepts to electrochemical signals, to achieve a simply
and highly effective monitoring capability for controlling the ECD
process to yield a uniform plating efficacy that is markedly
superior to conventional HPLC, CVS and/or PCGA analytical
techniques for monitoring ECD plating baths.
[0026] While the ensuing description is directed to an ECD system
involving application of a constant plating current in a copper
sulfate/sulfuric acid solution and measurement of the resulting
potential to provide a signal transient as a unique signature
indicative of the composition of the solution in the ECD bath, it
will be recognized that the methodology and apparatus of the
invention are not thus limited, but rather generally extend to and
encompass the determination of analytes in fluid media. For
example, although the present description is directed primarily to
copper deposition, the invention is readily applicable to other ECD
process applications, including deposition of silver, gold,
iridium, palladium, tantalum, titanium, chromium, cobalt, tungsten,
etc., as well as deposition of alloys and deposition of amalgams
such as solder.
[0027] Examples of additional applications of the invention other
than ECD plating of semiconductor device structures include
analysis of reagents in reaction media for production of
therapeutic agents such as pharmaceutical products, and
biotechnology applications involving the concentrations of specific
analytes in human blood or plasma. It will therefore be appreciated
that the invention is of broad application, and that the ECD system
and method described hereafter is but one of a myriad of potential
uses for which the invention may be employed.
[0028] The present invention in one aspect provides an apparatus
and method for controlling copper electrochemical deposition in an
electrochemical deposition system in which a wafer is contacted
with an electrochemical deposition medium including at least one
organic additive, wherein the electrochemical deposition medium has
a plating anode in contact therewith to effect plating of copper on
the wafer, and the electrochemical deposition medium is
characterizable by at least one dependent variable correlative of
efficacy of the copper electrochemical deposition.
[0029] The approach of the invention includes selecting at least
one dependent variable correlative of efficacy of the copper
electrochemical deposition, and then performing a regression
analysis modeling or a multivariate calibration modeling of the
copper electrochemical deposition utilizing a wafer-based
independent variable to generate a dependent variable equation for
each selected dependent variable correlative of efficacy of the
copper electrochemical deposition. Next, the dependent variable
equation, for each selected dependent variable correlative of
efficacy of the copper electrochemical deposition, is solved by
regression analysis to yield a solution value for each selected
dependent variable.
[0030] The copper electrochemical deposition then may be modulated
in response to the solution value for each selected dependent
variable, so as to carry out the deposition operation in a highly
efficient manner. Such modulation may for example including varying
the output of a power supply that is arranged to supply power to
the electrodes of the electrochemical deposition system. As another
example, the responsive modulation of the process may include
adjustment of flow control valves to vary the flow of ECD solution
components to the ECD bath chamber, so as to maintain an
appropriate concentration of solution species, e.g., accelerator,
suppressor, leveler, chloride anion, acid, metal salt, etc. The
modulation may in like manner involve adjustment of system hardware
components or change of process conditions to maximize the plating
rate, plating uniformity, etc., as desired in a given application
of the invention.
[0031] In an illustrative embodiment, the invention is hereafter
described with reference to an ECD bath for copper plating of a
semiconductor substrate, in which three organic additives, viz.,
the accelerator, suppressor and leveler additives are analyzed. By
measuring a parametric variable such as plating voltage output as a
function of time (or alternatively other parametric variables such
as plating current, electrode size, or a cathode pre-conditioning
pulse), the three organic additives can be determined by simple
modeling approaches, as hereafter more fully described.
[0032] More complex approaches may be carried out in accordance
with the invention, utilizing multivariate calibration techniques,
e.g., chemometrics, for the purpose of principal component analysis
and/or other curve-fitting procedures to provide process models of
appropriate robustness for specific applications of the invention.
Such complex approaches employ a full set of plating information
(as opposed to time cuts that are employed to build a regression
model), to achieve enhanced robustness for signal detection and
increased signal-to-noise.
[0033] The method of the invention may be carried out with any
suitable analytical equipment. For example, in application to the
electrochemical deposition of copper on a semiconductor wafer, the
invention may be practiced with a Sabre.RTM. xT copper
electroplating tool commercially available from Novellus Systems,
Inc. (San Jose, Calif.) or a SlimCell.TM. ECP copper plating tool
commercially available from Applied Materials, Inc. (Santa Clara,
Calif.), which in operation apply a constant current to a wafer in
the copper plating operation. In such operation, the voltage that
develops between the wafer (cathode) and the reference electrode is
indicative of the ECD plating solution composition and deposition
quality. In algorithmically training on the tool of interest, the
potential response of the cathode for several different plating
solution permutations is measured.
[0034] By way of specific example, copper was plated on a 25
micrometer diameter platinum microelectrode. A five-factor,
three-level CCD (central composite design) DOE (design of
experiments) was performed. The five factors were (1) copper
plating current, (2) copper nucleation voltage, (3) suppressor
concentration in the ECD solution, (4) accelerator concentration in
the ECD solution and (5) leveler concentration in the ECD solution.
Because the plating curve voltages were measured over 50 seconds,
it was decided to solve for the three unknowns by selection of
three arbitary times from all plating curves to permit modeling at
5, 10 and 15 seconds. The final model and its coefficients are
shown in Table 1 below.
1TABLE 1 Y-hat Model 50s 10s 5s Factor Name Coeff P(2 Tall) Tol
Active Coeff P(2 Tall) Tol Active Coeff P(2 Tall) Tol Active Const
-0.49700 0.0000 --0.50002 0.0000 --0.50497 0.0000 B Platel 0.00341
0.0000 1 1 0.00505 0.0000 1 2 0.00562 0.0000 1 3 C Acc 0.01884
0.0000 1 4 0.01924 0.0000 1 5 0.01965 0.0000 1 6 D Lev -0.01391
0.0000 1 7 --0.00700 0.0000 1 8 --0.00326 0.0000 1 9 E Supp
-0.00226 0.0001 0.9923 10 --0.00202 0.0003 0.9923 11 --0.00406
0.0000 0.9927 12 CC -0.00128 0.0518 1 13 --0.00815 0.0000 0.9990 14
0.00431 0.0000 0.9929 15 CD -0.00751 0.0000 0.9990 16 17 18 DD
0.00538 0.0000 0.9990 19 0.00151 0.0027 0.9990 20 21 EE 0.00165
0.0032 0.9926 22 0.0009877 0.0614 0.9926 23 24 R.sup.2 0.9627
0.9565 0.9418 Adj R.sup.2 0.9593 0.9531 0.9380 Std Error 0.0045
0.0043 0.0051 F 288.7872 282.8052 245.4038 Slg F 0.0000 0.0000
0.0000 F.sub.LOF 126.5176 89.0144 45.2024 Slg F.sub.LOF 0.0000
0.0000 0.0000 Source SS df MS SS df MS SS df MS Regress- 0.0 8 0.0
0.0 7 0.0 0.0 6 0.0 ion Error 0.0 89 0.0 0.0 90 0.0 0.0 91 0.0
Error.sub.Pure 0.0 73 0.0 0.0 73 0.0 0.0 73 0.0 Error.sub.LOF 0.0
16 0.0 0.0 17 0.0 0.0 18 0.0 Total 0.0 97 0.0 97 0.0 97
[0035] Table 1 shows the coefficient values for the five-factor
analysis, as including the plating current (denoted by Factor
"Const" to reflect its constant value), nucleation voltage (Factor
B), accelerator concentration (Factor C), leveler concentration
(Factor D) and suppressor concentration (Factor E). A Y-hat
regression analysis model was selected, although any other suitable
regression analysis model can be employed. The table includes
goodness of fit of model (R.sup.2) values, adjusted R.sup.2 values,
standard error, F, Sig F, lack of fit F (F.sub.LOF), and lack of
fit Sig F values, as well as regression and error values.
[0036] Using this model, voltage can be measured from a typical
plating curve at the three times (5, 10 and 15 seconds), and
additive concentrations can be determined for the three additives
(suppressor concentration in the ECD solution, accelerator
concentration in the ECD solution and leveler concentration in the
ECD solution).
[0037] FIG. 1 is a graph of plating potential E (volts) as a
function of time, in seconds for copper in sulfuric acid in the
presence of three organic additives (suppressor, accelerator and
leveler).
[0038] Using this data, three equations can be written with three
unknowns, as shown in Table 2 below, and such equations can be
solved for the concentrations of the respective additive components
of the ECD solution.
2 TABLE 2 Left Constant Un-Coded Coefficients Run = 8: V.sub.plate
= EQN # Side Coefficient .DELTA.C .DELTA.D .DELTA.E .DELTA.CC
.DELTA.CD .DELTA.DD .DELTA.EE -0.48846 Eqn 1 (50 s) 0 = -0.01452
0.01714 -0.02622 -0.00886 -0.0008339 -0.0003409 0.00343 0.00165
-0.48773 Eqn 2 (10 s) 0 = -0.04572 0.01728 -0.01046 -0.00597
-0.0009053 0 0.0009696 0.0009877 -0.48783 Eqn 3 (5 s) 0 = -0.06210
0.01808 -0.00261 -0.00442 -0.0009607 0 0 0 Vaiiabie C D E CC CD DD
EE Unique Solution 8.88 5.01 2.16 Actual Conc. 9 3.75 1 Difference
0.12 -1.26 -1.16 % Deviation 1.4% -28.8% -73.6%
[0039] The first three rows in Table 2 represent the coefficients
in the three linear equations that allow a unique solution to the
three unknown concentrations for the respective organic additives,
accelerator (component C in the table), leveler (component D in the
table) and suppressor (component E in the table).
[0040] As shown in Table 2, the only solution that fits all three
linear equations is accelerator concentration=8.88 ml/L, leveler
concentration=5.01 ml/L, and suppressor concentration=2.16
ml/L.
[0041] As is shown by the actual measured values of concentration
of the accelerator, leveler and suppressor components, there was
some deviation for the leveler and suppressor components, but
comparison of the computed and measured values demonstrated the
operability and efficacy of the inventive methodology for
computational determination of additive concentrations.
[0042] It therefore is clear that the plating tool itself can be
the analytical instrument when the factors that affect the plating
potentials are known and accounted for in the computational
methodology.
[0043] The regression analysis software may be of any suitable
type, including for example SAS/STAT.RTM. software (commercially
available from SAS Institute, Cary, N.C., USA), SSPS.TM. data
analysis software commercially available from SSPS, Inc. (Chicago,
Ill., USA), Minitab.RTM. statistical analysis software commercially
available from Minitab Inc. (State College, Pa., USA), NCSS Stat
System statistical analysis software commercially available from
NCSS Statistical Software (Kaysville, Utah, USA), etc.
[0044] Referring now to FIG. 2, there is schematically shown an
electrochemical deposition apparatus 10 according to one embodiment
of the invention.
[0045] The electrochemical deposition apparatus 10 includes an
electrochemical deposition system 12 including an ECD bath. In the
ECD bath, a wafer is contacted with an electrochemical deposition
medium including at least one organic additive. The electrochemical
deposition medium has a plating anode in contact therewith to
effect plating of copper on the wafer, when a suitable voltage is
imposed on the electrochemical cell circuit including the wafer as
the cathode element of the circuit, and the aforementioned anode
element. The electrochemical deposition carried out in the ECD
system 12 is characterizable by at least one dependent variable
correlative of efficacy of the copper electrochemical deposition,
e.g., concentration of one or more of the organic additives, or
plating current, or any other suitable variable.
[0046] The ECD system 12 in the illustrated embodiment is coupled
in power transmission relationship with a power supply 32, by means
of power transmission line 34. The ECD system 12 also is coupled in
feed relationship with organic additive supply vessels 14, 16 and
18, by means of organic additive feed lines 20, 22 and 24 having
flow control valves 26, 28 and 30 therein. The organic additive
supply vessels 14, 16 and 18 may for example contain accelerator,
leveler and suppressor, respectively.
[0047] The ECD system 12 is further coupled in signal processing,
monitoring and control relationship with the computational module
36, which may for example include a programmable general purpose
computer, dedicated microprocessor, programmable logic unit, or any
other suitable computational means effective for the monitoring and
control function. The computational module 36 is coupled with the
ECD system 12 by means of signal transmission cable 38.
[0048] The computational module 36 also is coupled with the flow
control valves 26, 28 and 30 in organic additive feed lines 20, 22
and 24 by means of signal transmission lines 44, 46 and 48,
respectively.
[0049] The computational module 36 is equipped with suitable
regression analysis software, such as SAS/STAT.RTM. software
(commercially available from SAS Institute, Cary, N.C., USA), for
carrying out the regression analysis operations described
hereinafter.
[0050] In operation, the ECD apparatus as shown in FIG. 2 is
operated to produce a copper metalized product wafer 40, with the
power supply being arranged to operatively supply power to ECD
system via power transmission line 34. In the specific embodiment
illustrated, the power supply is arranged to supply a constant
current power signal to the ECD system 12. The organic additives in
organic additive supply vessels 14, 16 and 18 are flowed in
respective lines 20, 22 and 24 to the ECD system 12 for addition to
the plating bath medium (not shown in FIG. 2) therein.
[0051] The voltage that develops between the wafer and the plating
anode in the ECD system under the constant current conditions is
indicative of the solution composition in the plating bath, and is
indicative of the plating quality of the deposited metal, e.g.,
electroplated copper.
[0052] Prior to inception of active operation, the regression
analysis software in the computational module 36 is trained on the
ECD system 12 to measure the voltage response of the cathode for
several different plating solution permutations. The plating
voltages are measure at selected intervals, e.g., at 5, 10 and 50
seconds as described in connection with the discussion of FIG. 1
herein, or, alternatively, all points along the plating curve could
be employed, since each point on the plating curve contains
information reflecting the components and operation of the ECD
system. Plating voltage thus is the selected dependent variable
correlative of the efficacy of the copper electrochemical
deposition.
[0053] The modeling operation is then conducted at the selected
time intervals to establish a model and coefficients, e.g., as
shown in Table 1 hereof. Thereafter, during the plating operation,
the plating voltage can be monitored, and corresponding equations
can be generated for the concentrations of the organic additives,
accelerator, leveler and suppressor, in the supply vessels 14, 16
and 18, respectively. The regression analysis software in the
computational module 36 carries out the regression analysis
operations, and generates a best solution for the concentration
equations for the three organic additives, thereby yielding
concentration data that may be outputted, archived, transmitted,
etc., as necessary or desirable in a given application of the
invention. The concentration data may also include data for
breakdown products of the organic additives in the ECD plating
solution, since such breakdown products affect wafer yields.
[0054] By this sequence of actions, the computational module 36
performs a regression analysis modeling of the copper
electrochemical deposition utilizing a wafer-based independent
variable to generate a dependent variable equation for each
selected dependent variable correlative of efficacy of the copper
electrochemical deposition, and solves the dependent variable
equation for each selected dependent variable correlative of
efficacy of the copper electrochemical deposition, to yield a
solution value for each selected dependent variable.
[0055] The solution value obtained by the computational module 36
then may be employed to modulate the ECD system 12 in a suitable
manner, to ensure continuously optimal performance of the apparatus
10. In the specific embodiment illustrated in FIG. 2, the
computational module generates an output for desired concentration
of each of the organic additives (accelerator, leveler and
suppressor), in the supply vessels 14, 16 and 18. The output from
the computational modules is a control signal in each of signal
transmission lines 44, 46 and 48, which actuates a corresponding
respective flow control valve 26, 28 and 30 in respective lines 20,
22 and 24 to adjust the flow of each respective organic additive to
a flow rate that maintains the ECD system at proper concentration
of the organic additives therein for achievement of high-efficiency
plating operation.
[0056] The present invention thus embodies a useful methodology for
monitoring composition of components in a copper plating bath. The
substrate (wafer) on which copper is being deposited is used as a
cathode element of an electrochemical cell including the copper
source anode as a reference electrode. Constant current is applied
to the electrochemical cell, and voltage is measured as a function
of time.
[0057] Alternatively, if current is time-varying, plating voltage
output could be measured as a function of plating current, or in
other embodiments such plating voltage output could be measured as
a function of electrode size (as the copper source anode is
depleted), or the plating voltage output could be measured as a
function of the cathode pre-conditioning pulse employed to initiate
electrochemical activity.
[0058] In still other embodiments, other combinations of
independent and dependant variables can be employed for the
regression analysis technique, to create a mathematical model that
to predict the value of a dependent variable based on values of an
independent variable.
[0059] In preferred practice, the plating potential is plotted as a
function of time at constant current conditions, to generate a
two-dimensional graph of the type shown in FIG. 1 hereof, in which
the voltage vs. time plot reflects the behavior of the bath
chemistry including the organic additives whose concentrations are
the desired monitored output.
[0060] Then, by selecting values of plating potential at selected
times during the period of measurement, wherein the number of
potential values equals the number of concentration variables,
viz., three in the illustrative example (concentrations of each of
the three organic additives in the ECD bath). Then, by establishing
three linear equations in three unknowns, the data analysis can be
conducted to solve the equations and generate the concentration
values for the respective accelerator, leveler and suppressor
components of the ECD bath.
[0061] The data analysis may be conducted in a computational module
associated with the ECD system, which is programmatically arranged
to sample the plating bath voltage at selected intervals to
generate the coefficients of the linear equations that are then
solved to provide the concentration values of the additives as an
output. The computational module may include a programmable general
purpose computer, dedicated central processing unit (CPU),
microprocessor, integrated circuitry, or other computational device
or system embodying appropriate hardware, firmware and/or software,
for conducting the regression analysis and solution of the
simultaneous equations for the parametric unknowns. Software
employed in the computational module may be of any suitable type,
e.g., of a type as described hereinabove.
[0062] By utilizing a wafer-based electrode parameter as the
sampled variable for regression analysis, e.g., a wafer parameter
such as plating voltage output, plating current, electrode size or
cathode preconditioning pulse (current or voltage), the approach of
the present invention achieves a material simplification in the
monitoring and control infrastructure that is required for the
electrochemical deposition system, relative to prior art approaches
such as HPLC, CVS and PCGS techniques. Specifically, there is no
requirement of ancillary sampling chambers, additional sampling and
reference electrodes, or other indirect measurement means or
methods.
[0063] Additionally, and most importantly, by utilizing the wafer
being plated as an electrode component of an electrochemical cell
providing the sampled variable for regression analysis, the method
of the invention conducts real-time monitoring reflecting
conditions at the wafer, to provide an output indicative of
solution composition in the plating bath. Such on-wafer ECD
metrology embodies a substantial advance in the semiconductor
manufacturing art, and is a preferred embodiment of the present
invention.
[0064] The regression analysis techniques used in the practice of
the invention may be linear or non-linear regression techniques,
depending on the nature of the sampled variable and its
time-varying relationship to concentration parameters.
[0065] The approach of the invention may be applied in a wide
variety of potential applications, including for example: chemical
reaction monitoring and control; fermentation operations or other
operations involving cell culturing in nutrient media; monitoring
of dialysis treatment operations with respect to specific blood
components, e.g., creatinine, urea, etc.; determining the presence
or absence of specific analytes in blood or plasma during
transfusions; monitoring of chemical mechanical polishing
operations in the manufacture of semiconductors; controlled
administration of mixed anaesthesia gases; and other industrial,
biological, and environmental processes in which specific
components may be critical in amount, or in which process
conditions have a critical determinative effect on efficacy or
acceptability of the process operation.
[0066] In application of the regression model in a specific
application, the fit of data points to the best fit line or curve
may be carried out by any suitable fit procedure, e.g., least
squares, residual sum of squares, multiple linear regression matrix
solution or other appropriate technique. The progression from best
fit line or curve to determining the equation for such line or
curve, and the ensuing computational correlation analysis of the
multiple variables, may likewise be carried out in any suitable
manner.
[0067] While the invention has been described herein with reference
to specific aspects, features and embodiments, it will be
recognized that the invention is not thus limited, but rather
extends to and encompasses other variations, modifications and
alternative embodiments. Accordingly, the invention is intended to
be broadly interpreted and construed to encompass all such other
variations, modifications, and alternative embodiments, as being
within the scope and spirit of the invention as hereinafter
claimed.
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