U.S. patent application number 11/347454 was filed with the patent office on 2006-11-30 for method and system for on-line controlling of solder bump deposition.
Invention is credited to Frank Kuechenmeister, Andreas Netz, Niels Rackwitz, Joern Schnapke, Norbert Schroeder.
Application Number | 20060266652 11/347454 |
Document ID | / |
Family ID | 37401763 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060266652 |
Kind Code |
A1 |
Netz; Andreas ; et
al. |
November 30, 2006 |
Method and system for on-line controlling of solder bump
deposition
Abstract
By evaluating a dynamic failure signal, such as a voltage signal
and/or a current signal, obtained during an electroplating
operation for forming solder bumps, an inline control system with a
responsiveness on a substrate basis may be established. Thus, the
electroplating tool may be controlled on a single wafer basis to
improve process uniformity and also significantly reduce yield
loss.
Inventors: |
Netz; Andreas; (Dresden,
DE) ; Rackwitz; Niels; (Dresden, DE) ;
Schnapke; Joern; (Radebeul, DE) ; Kuechenmeister;
Frank; (Dresden, DE) ; Schroeder; Norbert;
(Dresden, DE) |
Correspondence
Address: |
WILLIAMS, MORGAN & AMERSON
10333 RICHMOND, SUITE 1100
HOUSTON
TX
77042
US
|
Family ID: |
37401763 |
Appl. No.: |
11/347454 |
Filed: |
February 3, 2006 |
Current U.S.
Class: |
205/81 ;
257/E21.525 |
Current CPC
Class: |
H01L 22/20 20130101;
H01L 2924/0002 20130101; C25D 21/12 20130101; H01L 2924/00
20130101; H01L 2924/014 20130101; H01L 2924/0002 20130101 |
Class at
Publication: |
205/081 |
International
Class: |
C25D 21/12 20060101
C25D021/12 |
Foreign Application Data
Date |
Code |
Application Number |
May 31, 2005 |
DE |
10 2005 024 910.8 |
Claims
1. A method, comprising: forming a plurality of bumps on a first
substrate by an electrochemical deposition process in an
electroplating tool; obtaining a dynamic status signal during the
processing of said first substrate, said dynamic status signal
representing a dynamic behavior of at least one tool parameter
during the electrochemical deposition process; estimating a current
tool status on the basis of said dynamic status signal; and
releasing said electroplating tool for forming a plurality of bumps
on at least one subsequently processed substrate on the basis of
said estimated tool status.
2. The method of claim 1, wherein estimating said current tool
status comprises providing reference data for at least one
reference status of said electroplating tool and comparing said
dynamic status signal of said first substrate with said reference
data.
3. The method of claim 2, wherein providing said reference data
comprises defining one or more fault conditions for said at least
one process parameter.
4. The method of claim 3, wherein each fault condition is
associated with a specific fault procedure for the further handling
of the electroplating tool.
5. The method of claim 4, wherein each fault procedure comprises
establishing an updated tool status for the processing of said
subsequent substrate by at least one of adapting at least one
manipulated variable of a process recipe to be applied to said
plurality of substrates and initiating a specific maintenance
action.
6. The method of claim 1, further comprising predicting an expected
time to failure of at least one hardware component of said
electroplating tool.
7. The method of claim 1, wherein estimating said current tool
status comprises extracting a plurality of key values from said
dynamic status signal and comparing said key values with reference
key values.
8. The method of claim 7, wherein extracting said plurality of key
values comprises processing raw data of said dynamic status signal
by at least one of compressing said raw data and filtering said raw
data.
9. The method of claim 8, wherein at least some of said key values
are directly calculated from said raw data.
10. The method of claim 1, wherein said dynamic status signal
represents a voltage signal obtained from an anode of said
electroplating tool.
11. The method of claim 1, wherein said dynamic status signal
represents a current flowing through an anode of said
electroplating tool.
12. A method, comprising: processing a first substrate in an
electroplating tool that operates on a single substrate basis;
monitoring a failure status of said electroplating tool on the
basis of a dynamic status signal obtained during the processing of
said first substrate; and comparing said failure status with at
least one reference status prior to processing an additional
substrate.
13. The method of claim 12, further comprising at least one of
releasing said electroplating tool for processing said additional
substrate and initiating a maintenance action on the basis of said
comparison.
14. The method of claim 12, further comprising obtaining reference
data and defining a plurality of reference statuses that represent
one or more fault conditions for at least one tool parameter.
15. The method of claim 14, wherein each fault condition is
associated with a specific fault procedure for the further handling
of the electroplating tool.
16. The method of claim 15, wherein each fault procedure comprises
establishing an updated tool status for the processing of said next
substrate by at least one of adapting at least one manipulated
variable of a process recipe to be applied to said plurality of
substrates and initiating a specific maintenance action.
17. The method of claim 12, further comprising predicting an
expected time to failure of at least one hardware component of said
electroplating tool on the basis of said failure status.
18. The method of claim 12, wherein monitoring said failure status
comprises extracting a plurality of key values from said dynamic
status signal that represent said failure status.
19. The method of claim 18, wherein extracting said plurality of
key values comprises processing raw data of said dynamic status
signal by at least one of compressing said raw data and filtering
said raw data.
20. The method of claim 19, wherein at least some of said key
values are directly calculated from said raw data.
21. The method of claim 12, wherein said dynamic status signal
represents at least one of a voltage signal and a current signal
obtained from an anode of said electroplating tool.
22. The method of claim 12, wherein processing said substrate
comprises forming a plurality of bumps above respective contact
areas, said bumps being configured for a direct contact to contact
regions of a carrier substrate.
23. A system, comprising: an electroplating tool having an anode
assembly; and a failure detection unit connected to said
electroplating tool, said failure detection unit being configured
to indicate a failure status of said electroplating tool for each
process run on the basis of a dynamic status signal.
24. The system of claim 23, wherein said dynamic status signal
represents at least one of a voltage signal and a current signal
obtained from said anode assembly of said electroplating tool.
25. The system of claim 24, wherein said anode assembly comprises a
plurality of anode segments and said dynamic status signal is
obtained from each of said anode segments.
26. The system of claim 23, further comprising a control unit
operatively coupled to said electroplating tool and said failure
detection unit, said control unit being configured to control
operation of said electroplating tool on the basis of said failure
status supplied by said failure detection unit.
27. The system of claim 26, wherein said failure detection unit is
further configured to indicate a type of maintenance action on the
basis of said failure status so as to re-establish a valid tool
status prior to starting a process run.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a process flow for forming
a contact layer including bumps of a contact material, such as
solder, which is used to provide contact areas for directly
attaching an appropriately formed package or carrier substrate to a
die carrying an integrated circuit.
[0003] 2. Description of the Related Art
[0004] In manufacturing integrated circuits, it is usually
necessary to package a chip and provide leads and terminals for
connecting the chip circuitry with the periphery. In some packaging
techniques, chips, chip packages or other appropriate units may be
connected by means of balls of solder or any other conductive
material, formed from so-called solder bumps or bumps that are
formed on a corresponding layer, which will be referred to herein
as a contact layer, of at least one of the units, for instance on a
dielectric passivation layer of the microelectronic chip. In order
to connect the microelectronic chip with the corresponding carrier,
the surfaces of the two respective units to be connected, i.e., a
microelectronic chip comprising, for instance, a plurality of
integrated circuits, and a corresponding package, have formed
thereon adequate pad arrangements to electrically connect the two
units after reflowing the bumps provided at least on one of the
units, for instance on the microelectronic chip. In other
techniques, bumps may have to be formed that are to be connected to
corresponding wires, or the bumps may be brought into contact with
corresponding pad areas of another substrate acting as a heat sink.
Consequently, it may be necessary to form a large number of bumps
that may be distributed over the entire chip area, thereby
providing, for example, the I/O capability required for modern
microelectronic chips that usually include complex circuitry, such
as microprocessors, storage circuits and the like and/or include a
plurality of integrated circuits forming a complete complex circuit
system.
[0005] In order to provide hundreds or thousands of mechanically
well-fastened bumps on corresponding pads, the attachment procedure
of the bumps requires a careful design, since the entire device may
be rendered useless upon failure of only one of the bumps. For this
reason, one or more carefully chosen layers are generally placed
between the bumps and the underlying substrate or wafer including
the pad arrangement. In addition to the important role these
interfacial layers, herein also referred to as underbump
metallization layers, may play in endowing a sufficient mechanical
adhesion of the bump to the underlying pad and the surrounding
passivation material, the underbump metallization has to meet
further requirements with respect to diffusion characteristics and
current conductivity. Regarding the former issue, the underbump
metallization layers have to provide an adequate diffusion barrier
to prevent the solder material or bump material, frequently a
mixture of lead (Pb) and tin (Sn), from attacking the chip's
underlying metallization layers and thereby destroying or
negatively affecting their functionality.
[0006] Moreover, migration of bump material, such as lead, to other
sensitive device areas, for instance into the dielectric, where a
radioactive decay of lead may also significantly affect the device
performance, has to be effectively suppressed by the underbump
metallization. Regarding current conductivity, the underbump
metallization, which serves as an interconnect between the bump and
the underlying metallization layer of the chip, has to exhibit a
thickness and a specific resistance that does not inappropriately
increase the overall resistance of the metallization pad/bump
system.
[0007] In addition, the underbump metallization will serve as a
current distribution layer during electroplating of the bump
material. Electroplating is presently the preferred deposition
technique for solder material, since physical vapor deposition of
solder bump material, which is also used in the art, requires a
complex mask technology in order to avoid any misalignments due to
thermal expansion of the mask while it is contacted by the hot
metal vapors. Moreover, it is extremely difficult to remove the
metal mask after completion of the deposition process without
damaging the solder pads, particularly when large wafers are
processed or the pitch between adjacent solder pads decreases.
[0008] Although a mask is also used in the electroplating
deposition method, this technique differs from the evaporation
method in that the mask is created using photolithography to
thereby avoid the above-identified problems caused by physical
vapor deposition techniques. However, electroplating requires a
continuous and highly uniform current distribution layer adhered to
the substrate that is mainly insulative, except for the pads on
which the bumps have to be formed. Thus, the underbump
metallization also has to meet strictly set constraints with
respect to a uniform current distribution, as any non-uniformities
during the plating process may affect the final configuration of
the bumps and, after reflowing the bumps, of the resulting solder
balls in terms of, for instance, height non-uniformities, which may
in turn translate into fluctuations of the finally obtained
electric connections and the mechanical integrity thereof. Since
the height of the bumps is determined by the local deposition rate
during the electroplating process, which is per se a highly complex
process, any process non-uniformities resulting from irregularities
of the plating tool or any components thereof may also directly
cause corresponding non-uniformities during the final assembly
process. Moreover, since the formation of the bumps is one of the
final steps that is performed on a substrate basis, any variations
of the plating process or even loss of substrates due to tool
failures immensely contributes to increased production costs and
reduced yield.
[0009] Consequently, the metal deposition based on a patterned
photoresist is a key process step with respect to reliability,
yield and production cost, wherein a plurality of process-specific
issues, such as the handling of multiple materials exposed on the
substrate surface, the influence of pattern density at the
substrate, die and feature scale, have to be taken into
consideration to obtain a highly uniform metal deposition.
Particularly, the factors, such as thickness uniformity, deposition
rate and, if an alloy is to be used as the solder or bump material,
the control of the alloy composition, is also an important
criterion, as both the deposition rate and the alloy composition
may strongly be affected by the mass transfer in the electroplating
tool.
[0010] In view of the above-described situation, a need exists for
an enhanced technique that may avoid or at least reduce the effects
of one or more of the problems identified above.
SUMMARY OF THE INVENTION
[0011] The following presents a simplified summary of the invention
in order to provide a basic understanding of some aspects of the
invention. This summary is not an exhaustive overview of the
invention. It is not intended to identify key or critical elements
of the invention or to delineate the scope of the invention. Its
sole purpose is to present some concepts in a simplified form as a
prelude to the more detailed description that is discussed
later.
[0012] Generally, the present invention is directed to a technique
that enables the detection of a failure status of an electroplating
tool on the basis of a dynamic status signal, thereby providing the
potential for rapidly detecting and thus reacting on deviations
from standard situations. For this purpose, a failure data
collection (FDC) technique is provided that may operate on a single
substrate basis, thereby significantly enhancing process control
and production yield.
[0013] According to one illustrative embodiment of the present
invention, a method comprises forming a plurality of bumps on a
first substrate by an electrochemical deposition process in an
electroplating tool. A dynamic status signal is obtained during the
processing of the first substrate, wherein the dynamic status
signal represents a dynamic behavior of at least one tool parameter
during the electrochemical deposition process. Furthermore, a
current tool status is estimated on the basis of the dynamic status
signal and the electroplating tool is released for forming a
plurality of bumps on at least one subsequent substrate on the
basis of the estimated tool status.
[0014] In accordance with another illustrative embodiment of the
present invention, a method comprises processing a first substrate
in an electroplating tool that operates on a single substrate
basis. Furthermore, a failure status of the electroplating tool is
monitored on the basis of a dynamic status signal that is obtained
during the processing of the first substrate. Finally, the failure
status is compared with at least one reference status prior to the
processing of an additional substrate.
[0015] According to yet another illustrative embodiment of the
present invention, a system comprises an electroplating tool having
an anode assembly and a failure detection unit that is connected to
the electroplating tool. The failure detection unit is configured
to indicate a failure status of the electroplating tool for each
process run on the basis of a dynamic status signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The invention may be understood by reference to the
following description taken in conjunction with the accompanying
drawings, in which like reference numerals identify like elements,
and in which:
[0017] FIG. 1a schematically shows a cross-sectional view of a
substrate that receives a plurality of solder bumps during a
specific manufacturing stage;
[0018] FIG. 1b schematically shows a system for forming bumps on a
substrate, such as the substrate of FIG. 1a, by electroplating,
wherein the system comprises a failure detection unit according to
illustrative embodiments of the present invention;
[0019] FIG. 1c schematically represents a graph depicting a voltage
signal as an example for a dynamic signal according to an
illustrative embodiment; and
[0020] FIG. 1d schematically illustrates the failure detection unit
in more detail in accordance with still further illustrative
embodiments of the present invention.
[0021] While the invention is susceptible to various modifications
and alternative forms, specific embodiments thereof have been shown
by way of example in the drawings and are herein described in
detail. It should be understood, however, that the description
herein of specific embodiments is not intended to limit the
invention to the particular forms disclosed, but on the contrary,
the intention is to cover all modifications, equivalents, and
alternatives falling within the spirit and scope of the invention
as defined by the appended claims.
DETAILED DESCRIPTION OF THE INVENTION
[0022] Illustrative embodiments of the invention are described
below. In the interest of clarity, not all features of an actual
implementation are described in this specification. It will of
course be appreciated that in the development of any such actual
embodiment, numerous implementation-specific decisions must be made
to achieve the developers' specific goals, such as compliance with
system-related and business-related constraints, which will vary
from one implementation to another. Moreover, it will be
appreciated that such a development effort might be complex and
time-consuming, but would nevertheless be a routine undertaking for
those of ordinary skill in the art having the benefit of this
disclosure.
[0023] The present invention will now be described with reference
to the attached figures. Various structures, systems and devices
are schematically depicted in the drawings for purposes of
explanation only and so as to not obscure the present invention
with details that are well known to those skilled in the art.
Nevertheless, the attached drawings are included to describe and
explain illustrative examples of the present invention. The words
and phrases used herein should be understood and interpreted to
have a meaning consistent with the understanding of those words and
phrases by those skilled in the relevant art. No special definition
of a term or phrase, i.e., a definition that is different from the
ordinary and customary meaning as understood by those skilled in
the art, is intended to be implied by consistent usage of the term
or phrase herein. To the extent that a term or phrase is intended
to have a special meaning, i.e., a meaning other than that
understood by skilled artisans, such a special definition will be
expressly set forth in the specification in a definitional manner
that directly and unequivocally provides the special definition for
the term or phrase.
[0024] The present invention is generally based on the concept that
a failure data collection approach enables the implementation of a
control strategy for electroplating material, and, in particular
embodiments, for electroplating bumps such as solder bumps, wherein
any misprocessing of substrates is significantly reduced. Moreover,
by using an appropriate failure data collection approach, an
in-line control and associated therewith an automatic failure
detection in the plating process may be accomplished. For this
purpose, an appropriate dynamic failure signal, which is indicative
of the currently prevailing tool and process status, may be
monitored and may be processed to establish the current failure
status of the tool, wherein the further operating mode and/or the
release of the electroplating tool for the next substrate may be
based on the estimated failure state. With reference to the
accompanying drawings, further illustrative embodiments of the
present invention will now be described in more detail.
[0025] FIG. 1a schematically shows a substrate 101 in
cross-sectional view, on which a plurality of semiconductor devices
may be formed which are to receive a contact layer 102 for
providing electrical, thermal and mechanical connection to a
carrier substrate (not shown). The substrate 101 may comprise a
layer 103 having formed therein a plurality of microstructural
features, such as circuit elements of integrated circuits, which,
for convenience, are not shown. Moreover, the layer 103 may
comprise a plurality of contact pads 104, at least some of which
may be in electric contact to any lower-lying circuit elements.
Above the layer 103 there is formed a dielectric layer 105 made of
any appropriate material, wherein respective openings are formed in
the dielectric layer 105 to allow electric contact to at least a
portion of the contact pads 104. Formed on the dielectric layer 105
and the contact pads 104 is an underbump metallization layer 106,
which may typically be comprised of a plurality of specific layers
in order to provide the required functionality, such as diffusion
blocking, adhesion to the contact pads 104, thermal mechanical
characteristics, such as thermal expansion, the current
distribution during a subsequent electroplating process,
appropriately seeding and initializing the electroplating process,
and the like. The substrate 101 further comprises a mask 107, such
as a resist mask, which is patterned in accordance with design
requirements for forming bumps 108, such as solder bumps with a
specified size and especially with a well-defined height, as the
height of the bumps 108 may significantly determine the reliability
and characteristics of contacts to be formed with corresponding
contact areas of the carrier substrate. In some embodiments, the
bumps 108 may be formed by a composition of two or more different
metals. In this case, the composition of the bumps 108 may also
represent an important device feature, since the bumps 108 may have
to consistently melt at a specified temperature during the reflow
process for forming solder balls or for directly contacting
respective contact areas of a carrier substrate. Thus, as
previously pointed out, a precise process control for forming the
bumps 108 is required, in particular as in sophisticated
applications, the pitch between neighboring bumps 108 may
continuously be reduced, while the overall number of bumps 108 per
substrate 101 may steadily increase due to the increasing
requirements with respect to I/O capabilities of sophisticated
semiconductor devices.
[0026] FIG. 1b schematically illustrates a system 100 for
processing substrates which are to receive metal bumps, such as the
bumps 108 of the substrate 101, by an electroplating process. The
system 100 comprises an electroplating tool 110 having a reactor
bowl 111, which is configured to receive and hold an appropriate
electrolyte 112. The reactor bowl 111 further comprises an
electrode assembly 113, which may also be referred to as an anode
assembly, since during an actual deposition process the electrode
assembly 113 provides an averaged positive electric field,
irrespective of whether temporarily a negative voltage is applied
to the electrode assembly 113 during any intermediate time periods.
Thus, it should be understood that the notion "anode assembly" is
to be considered in this general sense. The reactor bowl 111 may
further be configured to receive and hold in place a substrate,
such as the substrate 101, wherein any appropriate means for
electrically contacting the substrate 101 to thereby make the
substrate 101 a counter electrode, are not shown. The system 100
may further comprise a control unit 120, which is configured to
control the operation of the electroplating tool 110, by for
instance coordinating any loading or unloading activity for
conveying the substrate 101 into the reactor bowl 111 after a
previously processed substrate has been removed from the bowl 111.
Moreover, the control unit 120 may be configured to control the
composition and the flow of the electrolyte 112 within the reactor
bowl 111 by controlling appropriate supply tanks and supply lines
(not shown) for replenishing any bath components of the electrolyte
112. Moreover, the relative position of the substrate 101 with
respect to the electrode assembly 113 for establishing a required
distance between the electrode assembly 113 and the counter
electrode, i.e., the surface of substrate 101, and the movement of
the substrate 101 during the actual deposition process may also be
controlled by the control unit 120 by means of corresponding drive
assemblies (not shown).
[0027] Furthermore, the control unit 120 may be configured to
initiate a current flow from the electrode assembly 113 through the
electrolyte 112 and to the substrate 101, thereby depositing metal
on surface portions exposed by the resist mask 107. For this
purpose, the system 100 may comprise or may be connected to a
controllable power supply 121, which is configured to supply power
to the electrode assembly 113 in accordance with specified process
requirements. For example, the controllable power supply 121 may
comprise a controllable current source, which is designed such that
a controllable amount of current may be supplied to the electrode
assembly 113. Based on the adjusted amount of current and the
effective deposition time, the amount of metal deposited on the
substrate 101 may be efficiently controlled for a given bath
composition of the electrolyte 112. The controllable power supply
121 may be configured to be operated in a plurality of operating
modes, such as a pulsed operating mode in which a sequence of
current pulses may be applied, wherein, in intermediate periods,
substantially no current or only a small current, or even an
inverse current, may be generated. It should be noted that in case
of an operating mode with reverse current pulses, the electrode
assembly 113 temporarily acts as a cathode. The controllable power
supply 121 may also be operable in a substantially continuous
constant current mode wherein, however, the magnitude of this
"constant" current may be varied over time. In other embodiments,
the controllable power supply 121 may additionally or alternatively
have implemented therein a constant voltage operating mode, in
which a constant voltage is supplied to the electrode assembly 113,
wherein, similarly as in the constant current operating mode, the
constant voltage may be supplied in pulses or in a substantially
continuous fashion, wherein the plurality of the constant voltage
pulses may even be reversed during certain deposition phases. In
illustrative embodiments, the controllable power supply 121 is
configured to individually operate each of a plurality of anode
segments 113a, 113b, thereby providing the potential for
controlling the deposition profile on the substrate 101, since the
deposition rate may locally be varied by supplying an appropriately
controlled amount of current to each of the anode segments 113a,
113b.
[0028] The system 100 further comprises a failure detection unit
130 which is at least operatively coupled to the electroplating
tool 110 for receiving a dynamic status signal 131a, 131b from the
electroplating tool 110. The dynamic status signal 131a, 131b may
represent a signal that is sensitive to a change of at least one
tool parameter to allow an estimation of the at least one tool
parameter during the processing of a single substrate, such as the
substrate 101, and therefore the signal 131a, 131b may be
considered as a dynamic signal.
[0029] As is previously explained, the electrochemical deposition
process in the tool 110 is a highly complex process, wherein
typically subtle changes of the process output, such as uniformity
of the bumps 108, the material composition thereof, thickness
variation from substrate to substrate, and the like, may be
detected upon processing of a plurality of substrates and
corresponding measurement results may be used for process control
with a significant delay. Consequently, in some embodiments, the
control unit may have implemented therein sophisticated APC
(advanced process control) strategies to provide a certain
predictability in establishing appropriate manipulated variables,
such as values for the current supplied to the assembly 113, the
replenishing of bath components, and the like, on a run-to-run
basis, even for a significant delay of the measurement results of
previously processed substrates. Contrary to the dynamic signal
131a, 131b, such measurement results will be referred to as
post-process data, which are considered as being non-dynamic in the
sense that this data may not be used for qualifying a single
process run of a substrate that is currently being processed.
Similarly, measurement results obtained from one or more of the
substrates 101 prior to being processed in the electroplating tool
110 may also be supplied to the control unit 120, indicated as
pre-process data, so as to determine appropriate values of the
manipulated variables of the process recipe under consideration.
For instance, measurement results relating to the underbump
metallization layer 106 may be used to determine appropriate values
for the manipulated variables. For example, measurement data may
indicate a reduced layer thickness of the underbump metallization
layer 106 so that a reduced deposition rate may be expected due to
the increased resistance of the layer 106, which may require a
higher current and/or an increased deposition time. Also, in this
case, the pre-process data may not be considered as dynamic process
information, since this data may not per se allow extraction of any
information about the actual deposition process for the substrate
under consideration.
[0030] In one illustrative embodiment, the dynamic signal 131a,
131b may represent a voltage determined between the electrode
assembly 113 and an appropriate second point in the electric
circuit formed by the controllable power supply 121, the electrode
assembly 113, the electrolyte 112 and the substrate 101. In one
embodiment, the voltage between the electrode assembly 113 and the
substrate 101, which acts as a counter electrode, may represent the
signal 131a, 131b, which is determined by an appropriate voltage
detector 132. It should be appreciated, however, that any other
"measurement point" within the electric circuit may be selected,
such as an auxiliary electrode (not shown), which may be provided
within the reactor bowl 111. In some illustrative embodiments, when
the electrode assembly 113 comprises the plurality of anode
segments 113a, 113b, the detector 132 may comprise corresponding
detector segments 132a, 132b, to individually establish the
respective dynamic signals 131a, 131b, thereby increasing the
amount of information that may be extracted with respect to the
dynamic behavior within the reactor bowl 111. In this respect, it
is to be noted that the provision of the two anode segments 131a,
131b is of illustrative nature only and in other embodiments the
electrode assembly 113 may comprise any appropriate number of anode
segments, which may be provided in the form of concentric ring
electrodes, in the form of interleaved anode segments, or any other
appropriate arrangement. Moreover, it should be appreciated that in
other embodiments the voltage detector 132 may not necessarily be
directly connected to the electrode assembly 113, although this
arrangement is advantageous, since the dynamic signals 131a, 131b
provided by the detector 132, as shown in FIG. 1b, represent the
voltage drop from the electrode assembly 113 across the electrolyte
112 to the substrate surface of the substrate 101. Consequently,
these voltage signals are based on the "dynamic" behavior of the
reactor bowl 111 during deposition while substantially rejecting
other influences, such as any voltage drops of external components,
such as external connectors, the controllable power supply 121, and
the like.
[0031] In other embodiments it may be considered advantageous to
provide, in addition or alternatively to the electrode assembly 113
as one measurement node, different measurement nodes, such as a
specifically positioned auxiliary electrode, when a certain
location within the reactor bowl 111 has been identified as being
highly sensitive to any changes of a specified tool parameter. For
example, one or more auxiliary electrodes, which may be positioned
between the electrode assembly 113 and the substrate 101, may be
operated continuously or intermittently with an appropriate current
to "probe" the interior of the reactor bowl 111 with a higher
spatial "resolution," at least in the vertical direction, compared
to the arrangement in which the electrode assembly 113 and the
substrate 101 represent the measurement nodes. In such an
arrangement, the auxiliary electrodes may be operated with an
extremely low current so as to not significantly influence the
overall deposition behavior or, in other cases, may be used so as
to provide, in combination with the electrode assembly 113, a
desired deposition profile.
[0032] In still other embodiments, the dynamic signal 131a, 131b
may be supplied by a current measurement detector, which may be
implemented in the controllable power supply 121 or in any other
external device (not shown), wherein optionally the voltage
detector 132 may provide corresponding voltage signals so as to
provide measurement readings of the actual voltage at the electrode
assembly 113, when the controllable power supply 121 is operated in
a constant voltage mode. Similarly, the failure detection unit 130
may be configured to receive corresponding current signals from the
controllable power supply 121, even when it is operated in the
constant current mode so that the unit 130 may have the currently
valid current values, which may be varied by the control unit 120
on the basis of the post-process data and the pre-process data, as
is previously discussed.
[0033] In other embodiments, however, the control unit 120 may be
configured to operate the electroplating tool 110 on the basis of a
predetermined process recipe without any model predictive control
strategy so that constant current values are used for each run. In
this case, the failure detection unit 130 may not receive any
current signals from the controllable power supply 121 and a change
in the dynamic signal 131a, 131b may directly indicate a change in
one or more tool parameters of the tool 110. The failure detection
unit 130 is further configured to estimate the status of the
electroplating tool 110, at least with respect to a failure status,
on the basis of the dynamic signal 131a, 131b. In estimating at
least the failure status of the tool 110, it is to be understood
that the failure detection unit 130 is adapted to recognize at
least an invalid tool status of the tool 110 on the basis of the
signal 131a, 131b, by comparing the signal 131a, 131b with
appropriately defined reference data, wherein the comparison is
performed such that at least the estimation of the tool status is
completed prior to the processing of a subsequent substrate in the
tool 110. In other illustrative embodiments, the failure detection
unit 130 may be configured to perform a more detailed status
analysis on the basis of the signal 131a, 131b, as will be
described in more detail with reference to FIG. 1c.
[0034] During operation of the system 100, a plurality of
substrates 101 are sequentially to be processed in the
electroplating tool 110 in accordance with a specified process
recipe to form the bumps 108 (FIG. 1a) with a desired material
composition and predefined co-planarity. One of the plurality of
substrates 101 is loaded into the reactor bowl 111, wherein an
appropriate substrate holder (not shown) receives the substrate 101
and positions it at a specific operating position, which may have
been defined in a previous calibration procedure or which may be
determined on the basis of manual, semi-automatic and automatic
initialization procedures. It should be appreciated that the
present invention is not restricted to any type of electroplating
reactor and the operating position of the substrate 101 as shown in
FIG. 1b is of illustrative nature only. Thus, any other type of
electroplating reactor, including reactors with a vertically
arranged electrode assembly and substrate, may be used in
combination with the present invention.
[0035] Thereafter, the control unit 120 may establish a current
flow between the electrode assembly 113 and the surface of the
substrate 101 in accordance with the specified process recipe
wherein, as previously explained, a variety of process recipes such
as constant current mode, constant voltage mode, pulsed operation,
continuous operation and any combinations of these different modes,
may have been established so as to obtain, for a valid tool status
of the electroplating tool 110, a highly uniform formation of the
bumps 108. Prior, during or after the creation of a current flow
through the electrolyte 112, the dynamic signal 131a, 131b may be
obtained by the detector 132 and may be supplied to the failure
detection unit 130. As previously explained, the dynamic signal
131a, 131b may be generated by any appropriate mechanism that
allows extraction of information on the presently prevailing status
of the tool 110. For example, if dedicated auxiliary electrodes are
present within the reactor bowl 111, these electrodes may be
operated to establish the signals 131a, 131b. In other embodiments,
as is shown in FIG. 1b, the dynamic signal 131a, 131b may be
obtained upon establishing a current flow through the electrolyte
112, wherein the voltage drop across the reactor bowl 111 may
provide information of the present tool status. In other
embodiments, additionally or alternatively, the current through the
electrode assembly 113, the electrolyte 112 and the substrate 101
may be sampled and may be analyzed by the failure detection unit
130 so as to at least detect whether or not an invalid tool status
has occurred.
[0036] FIG. 1c schematically shows an exemplary wave form of the
signals 131a, 131b when representing a voltage drop measured by the
detector 132, as shown in FIG. 1b. Hereby, it is assumed that the
control unit 120 operates the controllable power supply 121 in a
pulsed constant current mode, wherein a group of current pulses of
identical height and duration is established followed by an
intermediate period with no current supplied. Thereafter, the group
of current pulses may be repeated, followed by a further
deposition-free period. This sequence may be continued until the
current-time integral corresponds to the target value for the
process recipe under consideration. In FIG. 1c, the dashed line may
represent the progression of the current over time supplied to the
electrode assembly 113, while the solid lines may represent the
corresponding voltage signals obtained by the voltage detector 132
as the dynamic signal 131a, 131b. For convenience, only a single
voltage signal is shown in FIG. 1c. It should further be
appreciated that the duration of a single voltage or current pulse
in FIG. 1c may be on the order of magnitude of milliseconds, while
the amount of current per current pulse may range to several tenths
of ampere. Based on the signal 131a, 131b, i.e., in the example of
FIG. 1c, the voltage signal (solid line), the failure detection
unit 130 may correspondingly operate on the data representing the
signal 131a, 131b so as to enable a comparison with appropriately
defined reference data. The reference data may specify a
characteristic status of the tool 110, for instance a valid tool
status, which may represent an operating mode of the tool 110 with
defect-free hardware components, such as the electrode assembly
113, for a given process recipe. Appropriate reference data may be
obtained by gathering one or more of the signals 131a, 131b for a
well-defined tool status of the tool 110.
[0037] In one illustrative embodiment, reference data are gathered
for at least two different tool statuses, which may thus allow a
quantitative estimation of the tool status at least with respect to
one or more specific tool parameters. For instance, the signals 131
a, 131 b may, for otherwise identical operating conditions, be
obtained for an electrode assembly 113 in a valid status and in an
invalid status, wherein, in illustrative embodiments, also a
plurality of intermediate statuses may be investigated to obtain
corresponding reference data. In other cases, various signals
reflecting different tool status with respect to a different
electrolyte composition may be gathered and may correspondingly be
processed to obtain respective reference data. Similarly, reference
data may be obtained for two or more different operating positions
of the substrate 101 to thereby obtain reference data regarding any
mispositioning of the substrate 101. The dynamic signals 131a,
131b, irrespective of whether reference data or actual process data
are considered, may be processed in any appropriate manner to
thereby enable a rapid and reliable comparison of the reference
data with the signals 131a, 131b obtained during an actual
deposition process. In illustrative embodiments, the raw data
representing, for instance, the voltage signals of FIG. 1c, may be
processed to obtain one or more statistically significant values,
which may be referred to as statistical key numbers, which
represent a quantitative measure of at least one quality of the
signals 131a, 131b. For instance, an integration over time of the
raw data, possibly in combination with the current values
corresponding thereto, may provide an "overview" of the global
behavior of the electroplating tool 110. For example, the total
energy supplied by the controllable power supply 121, which is
actually introduced into the reactor bowl 111, may be calculated on
the basis of the time integral of the voltage signal during the
entire deposition process or during a specified part thereof, which
may then be compared with corresponding reference values of the
power for an invalid or a valid reference status to provide a first
criterion for the failure status of the tool 110.
[0038] In addition, or alternatively, appropriate filtering and/or
clipping techniques may be used to significantly reduce the amount
of data or to increase the efficiency of any processes for
extracting information from the signals 131a, 131b. Efficient
filtering techniques, such as high pass filtering, low pass
filtering and band pass filtering, and the like, may be very
efficient in removing unwanted signal components, which may
otherwise compromise or "obscure" the statistical relevance of
extracted values or value ranges. For example, a low pass filter
may remove high frequency components in the signal, thereby
providing a smooth voltage signal so that even individual voltage
pulses may be compared with corresponding reference pulses, by for
instance calculating a corresponding mean value. In other
embodiments, data reduction may be advantageous as, for instance,
the analyzation of reference data may have revealed that only one
or a low number of voltage pulses per each group may suffice to
represent the time progression of the dynamic signal 131a, 131b. It
should be appreciated that corresponding clipping and filtering
criteria may be established on the basis of previously gathered
data, in particular on the basis of previously gathered reference
data for which well-established tool conditions are known.
[0039] Based on the signals 131a, 131b, the failure detection unit
130 may detect at least an invalid tool status by, for instance,
comparing one or more statistical key numbers with corresponding
reference values, and may indicate the corresponding failure state
of the tool 110 prior to the processing of a next one of the
plurality of substrates 101. For this purpose, in some illustrative
embodiments, the failure detection unit 130 may operatively be
coupled to the control unit 120, wherein the control unit 120 is
configured to receive a corresponding failure status indication and
to initiate a corresponding tool activity. For example, when an
invalid tool status is detected by the unit 130, the control unit
120 may instruct the tool 110 to discontinue operation upon
completion of the deposition process presently running in the tool
110. In other embodiments, the failure detection unit 130 may, as
previously discussed, be configured to estimate the tool status in
a more quantitative manner so that the corresponding status
indication may enable an enhanced process control by the control
unit 120. For example, the quantitative measure of the presently
prevailing tool status determined by the failure detection unit 130
may be used as a control variable or as an offset or machine
constant for a model predictive control strategy implemented in the
control unit 120. For instance, based on post-process data and/or
pre-process data, the control algorithm implemented in the control
unit 120 may calculate appropriate manipulated variables for the
plurality of substrates to be processed in the tool 110, wherein
the status indication provided by the unit 130 may be used as
offset values that may provide corrections for each single run,
wherein, in particular, the release of the process tool 110 for the
next substrate is determined by the status indication supplied by
the unit 130.
[0040] In other embodiments, a plurality of predetermined machine
activities may be associated with respective status indications
established by the unit 130. That is, a plurality of status codes
may have been established, for instance on the basis of reference
data and a plurality of well-defined tool conditions, wherein each
failure code is associated with a dedicated tool activity, wherein
corresponding instruction tables and the like may be implemented in
the control unit 120 so as to appropriately respond to the failure
status detected by the unit 130. In some embodiments, the
predefined machine activities may incorporate specific maintenance
actions. In this case, a certain degree of self-diagnosis may be
established in the system 100, thereby significantly enhancing tool
utilization as the tool 110 may be brought back into production
more rapidly compared to conventional electroplating systems.
Moreover, in one illustrative embodiment, the detection unit 130,
possibly in combination with the control unit 120, may provide a
certain predictability of the tool behavior with respect to one or
more tool parameters. For example, a certain criterion may be
established to predict an estimated time period for the replacement
or maintenance of one or more specified hardware components. For
instance, the failure detection unit 130 may recognize a
degradation of a specific component, such as the electrode assembly
113, which may be compensated for automatically by the operational
mode, for instance a constant current mode, substantially without
affecting the quality of the solder bumps 108. Nevertheless, by
providing an estimated time for a replacement of the electrode
assembly 113, the availability of the tool 110 may be estimated
more reliably and therefore process flow management in a
semiconductor facility may significantly be enhanced. For this
purpose, the failure detection unit 130 may indicate to an operator
or to a supervising control system a corresponding predicted time
to maintenance or time to failure of a specific hardware
component.
[0041] FIG. 1d schematically shows the failure detection unit 130
in more detail in accordance with further illustrative embodiments.
The unit 130 may comprise a status signal input 133, which is
configured to receive the dynamic status signals 131a, 131b. For
example, the input 133 may comprise hardware components to receive
the signals 131a, 131b in analogous or digital form, depending on
the configuration of the detector 132. In other embodiments, the
input 133 may have incorporated therein an analog to digital
converter to provide the dynamic status signals 131a, 131b in
digital form for further processing in the unit 130. Moreover, a
data pre-processor 134 may be provided in some embodiments, wherein
the data pre-processor 134 may be configured to operate on the data
received from the input 133 and to provide the data in a format
that allows a rapid and reliable extraction of information. For
instance, the data pre-processor 134 may comprise any filtering and
clipping mechanisms for smoothing the raw data and reducing data
complexity by, for instance, discarding certain raw data outside of
well-defined time slots and/or outside of predefined value
ranges.
[0042] The unit 130 may further comprise a key number extractor 135
that may be coupled to the data pre-processor 134 and the input 133
to operate on the raw data as well as on the pre-processed data of
the signals 131a, 131b. The key number extractor 135 is configured
to reduce the data obtained in a statistically significant manner
to provide "meaningful" numbers or number ranges that allow a rapid
comparison with corresponding reference data. For instance, the key
number extractor 135 may comprise means and components for
integrating and/or differentiating and/or summing and/or
transforming and/or multiplying and/or any combinations of these
processes for operating on the data received. It should be
appreciated that any other data manipulation algorithms may be
implemented in the key number extractor 135 as long as these
algorithms are sufficiently fast to provide the key numbers within
a time period that is comparable to the operation time of a single
substrate in the tool 110.
[0043] The unit 130 may further comprise a comparator 136 that is
configured to compare the dynamic signals 131a, 131b with
appropriately formatted reference data, which may be provided by an
external source or which may be stored in a memory device (not
shown) within the unit 130. It should be appreciated that the
comparator 136 may be designed, depending on the available
computational power, to appropriately compare data as provided by
the input 133 and/or by the data pre-processor 134 with
corresponding reference data. In one particular embodiment, the
comparator is coupled to the key number extractor 135 and compares
reference data, provided in the form of respective reference key
numbers, with the key numbers provided by the extractor 135,
thereby allowing a rapid and reliable estimation of the currently
prevailing failure state of the tool 110. The comparator 136 may be
implemented as a rule based fault classification engine, which may
recognize failure states and classify them in accordance with a
pre-established hierarchical system. For example, the various
failure states recognized by the comparator 136 may represent
elements of different hierarchy levels, which may reflect any
tool-specific activities in response to the recognized failure
status. For example, a highest hierarchy level or fault class may
indicate failure states that require an immediate discontinuation
of the operation of the tool 110 so that the tool 110 will not be
released for the next substrate to be processed. Lower-lying
hierarchy levels may indicate less "dramatic" failure states, which
may in some embodiments be used for enhanced control efficiency in
combination with the APC strategies that may be implemented in the
control unit 120, as is previously described.
[0044] Moreover, the unit 130 may comprise a time-to-failure
predictor 137, which may be configured to provide a prediction for
a time to maintenance or time to failure of one or more specified
hardware components. For example, the predictor 137 may estimate on
the basis of the hierarchy structure, the future behavior of the
tool 110. For this purpose, the predictor 137 may monitor the time
development of the tool status or a portion thereof, i.e., specific
key numbers may represent specified aspects of the total tool
status, wherein the change and the change rate of moving from one
hierarchy level to another may be used in estimating a quantitative
measure for predicting the failure of a specified component. It
should be appreciated that the approach with a hierarchy structure
for predicting the time to failure is of illustrative nature only
and other appropriate algorithms may be used. For instance, one or
more of the statistical key numbers may be analyzed with respect to
their time development without using any hierarchy structure,
wherein the predictor 137 may instead operate on the basis of
corresponding reference data that may have been obtained on the
basis of specifically designed test runs or which may have been
obtained on the basis of empirical data from a large number of
substrates previously processed in the tool 110. Thus, the present
status of the tool 110 may be described more precisely compared to
conventional electroplating systems without failure status
detection, wherein also enhanced process control and/or tool
reliability and availability may be achieved by the predictor
137.
[0045] As a result, the present invention provides a method and a
system that provides significantly increased process reliability by
using a dynamic failure signal during an electroplating process so
as to indicate a tool status and in particular estimate a failure
status prior to processing a subsequent substrate. In particular
embodiments, the dynamic failure signal may be represented by one
or more voltage signals and/or one or more current signals obtained
from "sensitive" areas within the electroplating reactor, such as
the electrode assembly, which therefore implicitly contain
information on the tool condition with respect to the currently
processed substrate, wherein at least a portion of this information
may be extracted and may be used at least for deciding whether or
not the tool is to be released for the processing of the next
substrate. In particular embodiments, in addition to identifying an
invalid tool status, the information extracted from the dynamic
failure signal may also be used in enhancing the control efficiency
for the electroplating tool in that corresponding tool activities
or maintenance activities may be associated with a plurality of
tool states, which may be recognized on the basis of the dynamic
failure signal. Consequently, an inline process control is
established that may operate on a substrate basis, thereby
significantly reducing yield loss during the formation of solder
bumps.
[0046] The particular embodiments disclosed above are illustrative
only, as the invention may be modified and practiced in different
but equivalent manners apparent to those skilled in the art having
the benefit of the teachings herein. For example, the process steps
set forth above may be performed in a different order. Furthermore,
no limitations are intended to the details of construction or
design herein shown, other than as described in the claims below.
It is therefore evident that the particular embodiments disclosed
above may be altered or modified and all such variations are
considered within the scope and spirit of the invention.
Accordingly, the protection sought herein is as set forth in the
claims below.
* * * * *