U.S. patent application number 11/256507 was filed with the patent office on 2006-02-23 for vacuum-processing chamber-shield and multi-chamber pumping method.
This patent application is currently assigned to Tokyo Electron Limited. Invention is credited to Robert F. Foster, Michael J. Lombardi, Glyn J. Reynolds, Robert C. JR. Rowan, Frederick T. Turner.
Application Number | 20060037537 11/256507 |
Document ID | / |
Family ID | 33540203 |
Filed Date | 2006-02-23 |
United States Patent
Application |
20060037537 |
Kind Code |
A1 |
Lombardi; Michael J. ; et
al. |
February 23, 2006 |
Vacuum-processing chamber-shield and multi-chamber pumping
method
Abstract
One or more chambers of a multi-chamber vacuum processing
apparatus are provided with a high gas flow conductance path to an
exhaust volume of the apparatus that is maintained at high vacuum
with a high vacuum pump. Separate pumps for the one or more
chambers are made unnecessary by providing such chambers with a
protective deposition shield or shield set that is configured to
substantially protect walls of the chamber and the gas flow
conductance path from deposition and to partially impede the gas
flow from the chamber through the gas flow conductance path to the
exhaust volume so that the chamber can be operated at a higher
pressure than that of the exhaust volume and the chambers can be
operated at different pressures and without cross-contamination.
Preferably, a nested set of chamber shields is used. A controller
is programmed to control the processing of wafers in the chambers
by controlling the supply of process gas into the chambers.
Inventors: |
Lombardi; Michael J.;
(Phoenix, AZ) ; Reynolds; Glyn J.; (Las Vegas,
NV) ; Foster; Robert F.; (Mesa, AZ) ; Rowan;
Robert C. JR.; (Phoenix, AZ) ; Turner; Frederick
T.; (Sunnyvale, CA) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP (TOKYO ELECTRON)
2700 CAREW TOWER
441 VINE STREET
CINCINNATI
OH
45202
US
|
Assignee: |
Tokyo Electron Limited
|
Family ID: |
33540203 |
Appl. No.: |
11/256507 |
Filed: |
October 21, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10607141 |
Jun 26, 2003 |
|
|
|
11256507 |
Oct 21, 2005 |
|
|
|
Current U.S.
Class: |
118/719 ;
118/504 |
Current CPC
Class: |
H01J 37/32495 20130101;
C23C 14/54 20130101; Y10T 137/0396 20150401; H01J 37/32633
20130101; Y10T 137/0318 20150401; C23C 14/564 20130101; H01J
37/32449 20130101 |
Class at
Publication: |
118/719 ;
118/504 |
International
Class: |
C23C 16/00 20060101
C23C016/00 |
Claims
1. A set of replaceable protective deposition shields for a PVD
processing chamber comprising: an outer shield having a generally
cylindrical portion and a gas outlet opening therethrough and a gas
inlet opening therethrough; an inner shield having a generally
cylindrical portion of a diameter less than that of the generally
cylindrical portion of the outer shield and having an inlet opening
therethrough for alignment with the inlet opening of the outer
shield; and the inner shield being configured to mount in a nested
relationship with the outer so as to form an annular gap between
the inner and outer shields that communicates with the opening and
that extends sufficiently from the opening so as to require at
least three specular reflections off shield surfaces of atoms of
coating material moving from the chamber to the opening when the
set is installed in a process chamber and a PVD process is being
performed in the process chamber.
2. Two sets of replaceable protective deposition shields of claim
1, each set being differently configured so as to differently
impede gas flow from the chambers.
3. A PVD apparatus comprising the protective set of replaceable
deposition shields of claim 1 and further comprising: a plurality
of single-wafer processing chambers; a high vacuum pump; an exhaust
volume communicating with the high vacuum pump; and a gas flow
conductance path extending from at least one of the chambers to the
exhaust volume; and the protective set of replaceable deposition
shields being installed in the at least one of the chambers with
the opening in the outer shield aligned with the gas flow
conductance path.
4. The PVD apparatus of claim 3 further comprising: a processing
gas supply connected to the at least one of the chambers; and a
controller programmed to control the processing of wafers in the
chambers by controlling the supply of process gas into at least
said one of the chambers such that gas flows from the chamber,
through the path and to the exhaust volume, and such that the
chamber is maintained at a controlled processing pressure that is
higher than the pressure at the exhaust volume.
5. The PVD apparatus of claim 3 further comprising: a gas flow
conductance path extending from at least two of the chambers to the
exhaust volume; and a protective set of replaceable deposition
shields being installed in the at least two of the chambers with
the opening in the outer shield of the set aligned with the gas
flow conductance path from the chamber.
6. The PVD apparatus of claim 5 further comprising: a processing
gas supply connected to each of the at least two of the chambers;
and a controller programmed to control the processing of wafers in
the chambers by controlling the supply of process gas into each of
the at least two of the chambers such that gas flows from the
chamber, through the path and to the exhaust volume, and such that
each of the at least two chambers is maintained at a different
controlled processing pressure that is higher than the pressure at
the exhaust volume.
7. A PVD apparatus comprising: a plurality of single-wafer
processing chambers bounded by chamber walls; a high vacuum pump;
an exhaust volume communicating with the high vacuum pump; a gas
flow conductance path extending from at least one of the chambers
to the exhaust volume; a protective deposition shield installed in
the at least one of the chambers configured to substantially
protect walls of the chamber and the gas flow conductance path from
deposition from the chamber, and to partially impede the gas flow
from the chamber through the gas flow conductance path to the
exhaust volume so that the chamber can be operated at a higher
pressure than that of the exhaust volume; and a controller
programmed to control the processing of wafers in the chambers by
controlling the supply of process gas into said one of the chambers
such that gas flows from the chamber, through the path and to the
exhaust volume, and such that the chamber can be maintained at a
controlled processing pressure that is higher than the pressure at
the exhaust volume.
8. The PVD apparatus of claim 7 further comprising: a processing
gas supply connected to the at least one of the chambers; and the
controller being programmed to control the processing of wafers in
the chambers by controlling the supply of process gas into at least
said one of the chambers such that gas flows from the chamber,
through the path and to the exhaust volume, and such that the
chamber is maintained at a controlled processing pressure that is
higher than the pressure at the exhaust volume.
9. The PVD apparatus of claim 7 further comprising: a gas flow
conductance path extending from at least two of the chambers to the
exhaust volume; a protective deposition shield being installed in
the at least two of the chambers configured to substantially
protect walls of the respective chambers and the gas flow
conductance paths from deposition from the chambers, and to
partially impede the gas flow from the chambers through the gas
flow conductance paths to the exhaust volume so that each chamber
can be operated at a higher pressure than that of the exhaust
volume; and the controller being programmed to control the
processing of wafers in the chambers by controlling the supply of
process gas into each of said two of the chambers such that gas
flows from the chamber, through the respective path and to the
exhaust volume, and such that each chamber is maintained at a
different controlled processing pressure that is higher than the
pressure at the exhaust volume.
10. The PVD apparatus of claim 9 further comprising: a plenum
having an index plate lying in a vertical plane and mounted to
rotate on a horizontal axis therein, a plurality of wafer holders
being spaced around the axis on the index plate; the plurality of
single-wafer processing chambers being spaced at intervals around
the plenum for alignment with holders on the index plate; a
plurality of gas flow conductance paths each extending from each of
the at least two of the chambers to the exhaust volume; and each of
the at least two chambers having a protective deposition shield
installed therein configured to substantially protect walls of the
chamber and the gas flow conductance path from deposition from the
chamber, and to partially impede the gas flow from the chamber
through the gas flow conductance path to the exhaust volume so that
the at least two chambers can be operated at different pressures,
at least one being higher than that of the exhaust volume.
11. The PVD apparatus of claim 7 further comprising: a wafer
processing module having the at least one chamber therein; a
transfer module removably connected to the processing module and
having the exhaust volume therein to which the chamber of the
processing module is connected through the flow conductance path;
and the controller being programmed to control the processing of
wafers in the chamber in the processing module by controlling the
supply of process gas into said chamber such that gas flows from
the chamber, through the path and to the exhaust volume, and such
that the chamber is maintained at a controlled processing pressure
that is higher than the pressure at the exhaust volume.
12. The PVD apparatus of claim 11 wherein: the transfer module
includes a transfer arm moveable to pass a wafer between the
transfer module and the processing module through the flow
conductance path; the protective deposition shield being moveable
in response to the controller to so partially impede the gas flow
from the chamber through the gas flow conductance path to the
exhaust volume during processing in the processing module and away
from the gas flow path when a wafer is being passed
therethrough.
13. The PVD apparatus of claim 12 further comprising: a baffle
moveable with the shield into and out of the gas flow path.
14. The PVD apparatus of claim 7 further comprising: at least two
wafer processing modules, each having a chamber therein; a transfer
module removably connected to each processing module and having the
exhaust volume therein; each processing module having a flow
conductance path connecting the chamber thereof to the exhaust
volume; the chamber of each processing module having a shield
therein configured to substantially protect walls of the chamber
and the respective gas flow conductance path from deposition from
the chamber, and to partially impede the gas flow from the
respective chamber through the respective gas flow conductance path
to the exhaust volume; and the controller being programmed to
control the processing of wafers in the chambers in the processing
modules by controlling the supply of process gas into said chambers
such that gas flows from the respective chamber, through the
respective path and to the exhaust volume, and such that the
pressure in one chamber is maintained at a controlled processing
pressure that is higher than the pressure in another chamber.
15. The PVD apparatus of claim 14 further comprising: the transfer
module includes a transfer arm moveable to pass a wafer between the
transfer module and the processing modules through the respective
flow conductance paths thereof; the protective deposition shields
in each processing module being moveable in response to the
controller to so partially impede the gas flow from the chamber
through the gas flow conductance path to the exhaust volume during
processing in the processing module and away from the gas flow path
when a wafer is being passed therethrough; one of the processing
modules being configured to perform a process therein at a pressure
that is higher than that of the other processing module and
provided with a baffle moveable with the shield therein into and
out of the gas flow path.
Description
[0001] This application is a divisional of U.S. patent application
Ser. No. 10/607,141, filed on Jun. 26, 2003, the entirety of which
is incorporated by reference herein.
FIELD OF THE INVENTION
[0002] This application relates to vacuum processes such as
physical vapor deposition processes, and particularly to single
wafer processing modules that may be used for coating semiconductor
wafers. The application particularly relates to the shielding of
processing chamber surfaces and to the maintenance and control of
the vacuum and gas flow in vacuum processing chambers.
BACKGROUND OF THE INVENTION
[0003] A typical physical vapor deposition (PVD) apparatus includes
a processing chamber, a cathode assembly and a substrate support
within the chamber, a vacuum system to maintain the pressure in the
chamber below 100 mTorr and a gas supply system to introduce a
sputtering gas into the chamber. The cathode assembly includes a
target, insulators to electrically isolate that target from the
chamber wall, a power supply to energize the target, and a
magnetron magnet assembly to form a plasma confining magnetic field
close to the target surface. When the substrates being processed by
the PVD apparatus are silicon wafers for integrated circuit
manufacturing, the most commonly encountered PVD apparatus vacuum
systems use high-vacuum cryogenic pumps and several pressure
gauges.
[0004] Because sputtered material is ejected from the target in all
directions in the processing chamber of a PVD apparatus, the whole
chamber, not just the substrate, is exposed to coating material
from the target. Standard practice has been to place physical
barriers known as shields inside the chamber so as to prevent
unwanted deposition on the chamber walls and on various other
components inside the chamber. For example, shields may be used to
protect the dielectric insulator that electrically isolates the
target from the usually grounded metal chamber walls. Shields used
to protect chamber components usually have their surfaces roughened
so that material that is deposited onto the shields adheres better
to the shields and does not spall as it increases in thickness. If
the deposited material does not adhere well to the shields, it can
flake off, causing particles that can land on the substrate. In
integrated circuit manufacturing, these particles can destroy
sensitive devices on the substrate surface. Usually these shields
must be changed on a regular preventive maintenance schedule.
Otherwise the accumulated deposits will become too thick and
stresses will build up that cause the shields to shed
particles.
[0005] For some sensitive applications, a process chamber must be
capable of being evacuated to an ultra-high vacuum (below 10.sup.-8
Torr), and the sputtering gas must be purified before it is
introduced into the process chamber. The equipment required to
achieve these conditions is very expensive. In other semiconductor
PVD applications, such equipment is not required. Some less
critical PVD applications used for integrated circuit manufacture
are extremely sensitive to cost, and call for equipment having a
minimum of expensive components. Some of the most expensive
components of a PVD chamber are those required to achieve
ultra-high vacuum (UHV).
[0006] For silicon wafer processing, the process chamber is most
commonly pumped by a dedicated high vacuum pump, usually a
turbo-molecular or cryopump. However, there are low cost PVD
systems such as the Ulvac SRH-820 and the Sputtered Films, Inc.
(SFI) ENDEAVOR, that use a single, common, centrally located high
vacuum pump to evacuate all PVD process chambers. The lower cost
systems that may be used for less critical applications can achieve
such pumping with less concern for chamber cross-contamination or
interference.
[0007] High end, single wafer, PVD tools such as the Tokyo Electron
Limited ECLIPSE Series, the Applied Materials ENDURA and the
Novellus INOVA, for example, are usually considered too expensive
for dedication to low end foundry packaging applications. Many
foundries are able to use inexpensive, relatively inferior and
lower throughput batch tools for their less critical PVD
applications.
[0008] Single wafer tools have several advantages over batch
machines for silicon wafer processing. Single wafer systems lend
themselves readily to statistical process control, since every
wafer experiences the same process in the same position in a given
process chamber. Also, in the event of wafer breakage, usually all
the wafers in a batch will be scrap due to the particles generated
when a wafer breaks; in a single wafer system, only the wafer that
breaks would be lost. A single wafer tool usually has a higher
throughput for larger wafer sizes. As wafer size increases, the
number of wafers in a batch must decrease correspondingly.
Consequently, there are compelling reasons for current users of
inexpensive batch tools to convert to single wafer machines,
provided that they are sufficiently inexpensive.
[0009] One such inexpensive single wafer tool is the Varian 3180
series tool. This tool is a cassette-to-cassette single wafer PVD
tool, where sputtering takes place in a large plenum with four
sputtering stations. Features of this machine are described in U.S.
Pat. Nos. 4,548,699 and 4,716,815. Each station of this tool is
directly opposed to a sputtering target. The wafers rotate
sequentially from a first station to a last, and may be subjected
to a sputter coating or other process at each of the stations. The
plenum is pumped by a single cryopump. One disadvantage to this
arrangement has been that all sputtering processes take place in a
common ambient, at the same pressure. It is often desirable to
sputter different metals in a stack at different pressures, for
example, to optimize film stress, but this has not been possible
with this kind of common plenum machine. Also, in many of such
machines, there has been no easy way to isolate the sputtering
ambient of the various chambers. In the event that a metal stack
requires reactive sputtering, for example, using a mixture of argon
and nitrogen to deposit titanium nitride, the processes in adjacent
chambers could be contaminated by nitrogen.
[0010] Accordingly, there remains a need for a better way to use a
common vacuum pumping system in a multiple-chamber single-wafer
tool.
SUMMARY OF THE INVENTION
[0011] A primary objective of the present invention is to allow a
PVD system with multiple process chambers that are usually each
pumped by a dedicated high vacuum pump on each process chamber, to
instead be pumped by a single pump located remotely from the
process chambers.
[0012] According to principles of the present invention, a multiple
single-wafer process chamber apparatus is provided with a high
vacuum pump connected to the apparatus via a plenum, a transfer
chamber or other exhaust volume remote from the chambers. A gas
flow conductance path is provided from one or more of the chambers
to the exhaust volume. One or more of such process chambers is
provided with a set of one or more shields that gives line-of-sight
protection from deposition for critical components in the process
chamber, while allowing adequate vacuum conductance from the
chamber through the path to the high vacuum pump. The shield set
for that chamber is configured in such a way that the gas
conductance to the exhaust volume provides a pressure drop that
allows the chamber to be operated at a desired processing pressure
with the pressure of the exhaust volume maintained sufficiently
below the processing pressures of all of the chambers to sustain
the flow of gas from the chambers toward the exhaust volume. The
determination of shield configuration is accompanied by
establishment of a gas flow rate into the chamber so that the
pressure objectives are satisfied.
[0013] Where more than one or all of the chambers of the apparatus
are provided with such shields, one or more of the chambers can be
operated at a pressure that is significantly higher than that of
the exhaust volume, and the operating pressures of different
chambers can be different and controlled by a programmed
controller. With the pressure of each chamber higher than that of
the exhaust volume, cross contamination among the chambers is
reduced significantly so different gases and processes can be used
in the different chambers.
[0014] This may be accomplished, for example, by selecting a shield
set design for the chamber with the highest processing pressure to
provide a relatively low gas conductance to the exhaust volume. The
conductance is chosen that will allow the exhaust volume to
maintain a relatively low pressure that is sufficiently below that
of all of the chambers. The gas flow rate into this high pressure
chamber can be adjusted to optimize the processing pressure in that
chamber. Then the lower pressure chambers are provided with high
conductance shield sets that allow those chambers to operate at
their respectively lower pressures, with the gas flow rates into
those chambers also being adjusted to optimize those pressures.
[0015] Typically, two shield sets may be used, one with relatively
low gas conductance for the higher pressure chambers and one set
with relatively high gas conductance for the lower pressure
chambers. Differences in processing pressures among the lower (or
higher) pressure chambers can be adjusted by varying the flow rates
of processing gas injected into those chambers. Maintaining
sufficiently low pressure into the exhaust volume must take into
account the gases being exhausted into it from all of the
chambers.
[0016] The sets of shields for a PVD system are designed to provide
coverage of the chamber walls and other critical components that
need to be protected from deposition, yet provide a gas conductance
path to a vacuum pump connected to the exhaust volume that is
located remotely from the PVD chamber.
[0017] The configuration of the conductance paths depends on the
apparatus platform architecture. The pumping path can be through a
plenum wall to a common plenum such as exists in the Tokyo Electron
Limited ECLIPSE Series. The pumping path can alternatively be
through a slot in the chamber wall that opens into a central
transfer chamber such as exists in a traditional cluster tool.
[0018] The processing pressure in a chamber equipped with a shield
or shield set according to the present invention is a pressure that
is distinctly higher than that of the exhaust volume. The chamber
is maintained at this distinctly higher pressure by the presence of
a chamber shield to impede the flow of gas from the chamber to the
exhaust volume to the degree that causes a pressure differential
that produces the distinctly higher pressure. As used herein,
"distinctly higher" pressure is a pressure that is adequate for
performance of the process, where the pressure in the exhaust
volume is low enough to insure that there is gas flow from the
chamber to the exhaust volume, typically of a few standard cubic
centimeters per minute (sccm).
[0019] Although two embodiments are specifically described herein,
one that applies to machines such as those of the Tokyo Electron
ECLIPSE type, and the other that applies to the tools of the
generic cluster tool type, those skilled in the art will appreciate
how to use the general principles described herein for other types
of equipment. Such equipment may be used for processing silicon
wafers, or for other substrates, for example, magnetic disks.
[0020] The present invention saves costs by reducing the number of
expensive high-vacuum pumps. In addition, additional savings arise
from the elimination of gate valves, reducing gauging, eliminating
certain regeneration gas and pump out lines in the case of
cryopumps, and eliminating certain fore-lines and backing pumps in
the case of turbo-molecular pumps.
[0021] The invention allows the use of a single high-vacuum pump to
evacuate and maintain process pressure in a single-wafer PVD tool
comprised of several different process stations. This is achieved
without compromising shielding of critical surfaces within the
tool. The nature of the shields, particularly the nested shields of
certain embodiments, allows the conductance between the process
station and vacuum pump to be carefully controlled, thus allowing
different process pressures in adjacent processing chambers.
Furthermore, in a tool design based upon a Tokyo Electron Limited
ECLIPSE or a standard cluster tool, the shields can easily be
replaced with a conventional set of shields suitable for operating
the chambers with separate pumps. High vacuum pumps and isolation
valves can then be added to one or more of the process stations so
that reactive sputtering processes can then be run without major
changes to the tool architecture. This provides flexibility not
possible with machines of the prior art. All the other advantages
of a single wafer PVD tool are retained.
[0022] These and other objectives and advantages of the present
invention will be readily apparent from the following detailed
description of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a cross-sectional view of one of the chambers of a
multi-chamber single-wafer PVD apparatus of the prior art.
[0024] FIG. 2 is a cross-sectional view of a nested chamber shield
installed in the apparatus of FIG. 1 according to one embodiment of
the present invention.
[0025] FIG. 3 is a cross-sectional view of a PVD processing module
of a cluster tool of the prior art.
[0026] FIG. 4 is a cross-sectional view of a nested chamber shield
installed in the apparatus of FIG. 3 according to an embodiment of
the present invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a cross-sectional view through a PVD processing
chamber or pod 10 of a processing apparatus 12. The apparatus 12 is
a semiconductor wafer processing machine of the type described in
U.S. Pat. Nos. 4,909,695; 4,915,564 and 5,516,732, each hereby
expressly incorporated herein by reference. Machines of this type
are marketed under the trademarks ECLIPSE, ECLIPSE MARK II, ECLIPSE
STAR and ECLIPSE MARK IV by Applicant's assignee, Tokyo Electron
Limited.
[0028] In the apparatus 12, five process stations, one of which is
the pod 10, are situated at equal intervals, spaced 72.degree.
apart around a central axis 13. Typically, and in the ECLIPSE-type
machines referred to above, the axis 13 is horizontal. An index
plate 14 is enclosed in a plenum 11 in which it is mounted to
rotate in a vertical plane on the axis 13 to carry five wafer
holders 15, each also spaced at equal 72.degree. intervals around
the axis 13. Each wafer holder 15 is capable of holding a single
semiconductor wafer 16 therein for processing. Rotation of the
index plate 14 indexes the wafer holders 15 through each of the
pods 10 to perform sequential processes on each of the wafers 16.
Each of the wafer holders 15 is supported in an opening in the
index plate 14 by a sealing ring 17. When a wafer holder 15 is
positioned in a pod 10 for processing, a moveable cup-shaped
chamber wall 18 clamps the sealing ring 17 against a wall 19 of the
plenum 11 to form a sealed processing chamber 20 within the pod
10.
[0029] When the processing chamber 20 is sealed, the wafer 16 is
supported so as to face a sputtering target and cathode assembly 21
for the performance of a PVD process on the wafer 16. A chamber
shield 22 is fixed to the plenum wall 19 to shield the walls of the
chamber 10 during the PVD process. A vacuum pump 23 is connected to
the plenum 11 to pump the plenum 11 to a high vacuum, which also
evacuates the pods 10 when the chambers 20 are open to the plenum
11. Each of the pods 10 is itself equipped with a vacuum pump 24 to
pump the respective chamber 20 to a vacuum level as required for
the process being performed in the pod 10. Each pod has a gas inlet
line 25 for introducing processing gas into the chamber 20. The
flow rate of processing gas into the inlet 25 is set by setting the
set point of a mass flow controller (not shown) and a throttle
valve (not shown) at the pump 24 is controlled to maintain an
appropriate pressure and gas flow rate in the chamber 20.
[0030] FIG. 2 is a diagrammatic cross section showing one manner in
which the apparatus 12 of FIG. 1 can be modified according to the
present invention. In FIG. 2, such a modified apparatus 12a is
provided in which a set 30 of nested shields is provided in place
of the shield 22 in the deposition chamber 20 of FIG. 1. The set 30
includes an outer shield 31, which is configured to conform closely
to the pod and plenum wall 19a, and an inner shield 32. The shields
31 and 32 are nested with an annular space or gap 33 maintained
between them. The outer shield 31 may be supported on the chamber
wall 19a and the inner shield 32 may be mounted on standoffs (not
shown) from the outer shield 31 or on alternative structure
supported by the chamber wall 19a.
[0031] A set of one or more slots 34 is cut in the outer shield in
communication with the annular space 33. The shields 31 and 32 are
dimensioned to fit into a modified deposition pod 10a of a tool 12
of the Eclipse type, with the pod 10 modified with a set of slots
36 formed in the plenum wall 19a. The slots 36 align with the slots
34 in the outer shield 31 so that pumping for the deposition pod 10
is effected through the series of circumferential slots 34 and 36,
which may be, for example, about one inch wide, machined into the
wall 19a of the plenum 11 and extending about half way around the
circumference of the chamber to communicate with the vacuum within
the plenum 11. This dimension is nominal, and can be smaller or
larger, depending on the gas flow conductance desired, as explained
below. Examples of slot cross-sectional area are 25 square inches,
50 square inches, or such other larger or smaller areas that are
effective to provide the gas conductance needed to satisfy pressure
criteria as explained herein.
[0032] The outer shield 31 is essentially a "skin," which fits
inside the pod 10a and may conform to or be spaced closely from the
chamber walls 19a. The shield 31 primarily protects all internal
surfaces of the plenum 11 from unwanted deposition. This outer
shield 31 is positioned in the chamber 20 with its slots 34 in
alignment with the pumping slots 36 machined into the plenum wall
19a. The inner shield 32 covers these slots, and extends
sufficiently far up the side of the pod 10a so as to require at
least three specular reflections off shield surfaces before metal
atoms from the target can deposit onto the exposed surface of the
slots 36 in the plenum wall 19a. The slots 34 and 36 allow the pump
23 to be used to maintain a vacuum in the chamber 20, rather than
requiring a dedicated pump such as pump 24 for the chamber 20.
[0033] The spacing 33 between inner shield 32 and outer shield 31
may be maximized as far as the pod and cathode geometry allow.
Nonetheless, the gas flow conductance between the chamber 20 and
the vacuum pump that pumps the chamber is reduced significantly by
the shield set 30 compared to a normal Eclipse set up. The pumping
speed and the reduction thereof, in liters per second (I/s), is gas
dependent, as illustrated in Table I: TABLE-US-00001 TABLE I
PUMPING VIA PLENUM WITH NESTED SHIELDS Ar N.sub.2 H.sub.2O H.sub.2
S.sub.cryo 1,200 1,500 4,000 2,500 U.sub.cryo 3,175 3,795 4,733
14,200 C.sub.valve 2,278 2,723 3,396 10,189 S.sub.net
cryo-to-plenum 1,045 1,298 3,001 2,338 C.sub.nested shield 280 335
418 1,253 S.sub.plenum pump @ process pod 221 265 357 816
.sub.(estimate) Ratio S.sub.pod/S.sub.plenum 3.54 3.61 4.96
2.21
[0034] In Table I, S denotes the pumping speed, U the aperture
conductance, and C the vacuum conductance in molecular flow,
respectively. The last row, ratio S.sub.pod/S.sub.plenum, compares
the pumping speed of a typical apparatus 12 of the ECLIPSE
configuration, where the process pod is pumped by a dedicated
cryopump connected to the pod through a gate valve, to that
obtained when the process pod is pumped with the plenum cryopump
through a set of nested shields as proposed here. The values in the
table are appropriate where the inside diameter of the pod or
chamber is about 14 inches, with the outer shield 31 having a
nominal outside diameter of about 14 inches, the diameter of the
inner shield 32 being about 12 inches, leaving the width of the gap
33 about one inch.
[0035] The net result of using the shield set 30 in the arrangement
detailed in FIG. 2 is to reduce the pumping speed of a typical 1200
l/s (liter per second) cryopump to between 200 and 300 l/s for
argon. This is typical of cryopumps equipped with sputter plates,
which are metal plates with a series of holes that are heat-sunk to
the first stage of the cryopump and provide a reduction in
permanent gas pumping speed, while maintaining full water pumping
speed. Many PVD tool manufacturers use sputter plates to increase
the time between cryopump regenerations, which must occur when
argon ice builds up inside the pump.
[0036] The water pumping speed for the pod 10a of an ECLIPSE type
apparatus 12a that is equipped with a shield set 30, and using the
plenum pump 23 to pump the chamber 20, will be reduced
substantially compared to a machine using a separate pump 24 for
the chamber 20. While this might not be suitable for some
applications, for many packaging applications this will be an
acceptable and economical system.
[0037] To test the effect of reduced water pumping speed on the
properties of a typical UBM stack, a tri-layer stack Cr/CrCu/Cu was
deposited with the pod cryopump throttled so as to simulate the
pumping speed which would result from pumping through the plenum.
The properties of each individual film and the overall stack were
monitored over 100 wafer depositions, and compared to the controls
(films that were deposited with the regular pod pumping speeds). No
discernible differences were observed. The vacuum conditions of
many of the batch tools used to deposit under-bump-metal (UBM)
films are much worse than those observed in pods 10 of the ECLIPSE
type with heavily throttled cryopumps.
[0038] The use of nested shield sets 30 in combination with a
single cryopump in a common location, such as pump 23 connected to
the plenum 11, but with separate control of individual process gas
injection points 25 in each of the individual process pods by a
programmed controller 29, allows different process pressures in
various pods 10a to result with a single pump 23. The process gas
injection into the chambers 20 is controlled by setting the
pressure on a mass flow controller, which may be provided with a
feedback loop to maintain the pressure setting. In this way, films
can be deposited underoptimum pressure conditions often not
practical in batch tools or in the Varian 3180 series. This
requires process pressure control of the gas inlets 25 of each of
the process pods 10. Each of the gas inlets 25 includes an inlet
tube that extends from a gas source (not shown) outside of the
chamber, through the chamber wall and through holes in the shields
31 and 32 into the processing space adjacent the wafer, as shown in
FIG. 2. A pressure sensor 27 is similarly connected through a tube
through holes in the shields 31,32 to sense the pressure directly
from this processing space.
[0039] The operation of pods 10a attached to a common pump 23 at
different pod pressures could lead to possible "cross-talk" between
pods 10a, where gas back-streams from the plenum 11 to one of the
process pods 10a, which could occur when one or more of the common
pods 10 operates at significantly higher pressures than the other
pods. To reduce the possibility of this potential problem,
different sets 30 of shields 31 and 32 are provided for the pods
10a for processes that operate at higher pressures than for
processes that operate at much lower pressures. Such shield sets 30
would be designed to have less gas flow conductance for higher
pressure processes than the nested shield sets 30 for low pressure
processes. The conductance could be reduced for pods 10a used for
higher pressure processes either by reducing the annular gap 33
between inner shield 32 and outer shield 31 or by reducing the
width of the slots 34 in the outer shield 31 to be less than the
slots 36 in the plenum wall 19a. Of these two approaches, reducing
the width of the slots 34 has the advantage of allowing the use of
the same inner shield 32 for both high and low pressure processes,
thereby keeping the process environment similar for all processes,
and thereby reducing the occurrence of subtle effects that might
arise if the inner shield dimensions were different for high and
low pressure processes.
[0040] The process pressure threshold for using the low conductance
shield set may be determined empirically, as could the exact shield
geometry. By using the low conductance shield set, less process gas
would be required to sustain the appropriate process pressure, thus
avoiding any unnecessary pressure rise in the plenum 11. This, in
turn, reduces the potential for back-streaming into those process
pods operating at lower pressures. Because lower conductance shield
sets reduce the effective pumping speed of the process pods
equipped with the low conductance nested shield sets, tests are
used to ascertain which films, if any, are sensitive to further
reductions in effective pumping speed.
[0041] A set of shields may be provided that completely close off
the pumping slots 36 machined into the plenum wall 19a. Then
equipping that pod only with a separate cryopump 24a and isolation
valve 24b would enable the particular pod to be used for reactive
sputtering without risk of contamination of the adjacent sputtering
processes. The implementation of the nested shield sets concept in
the Tokyo Electron ECLIPSE-type machines requires minor
modification to the plenum wall. As noted previously, slots 36 must
be machined to enable the high vacuum pump on the plenum 11 to pump
the process pods 10a.
[0042] FIG. 3 is a cross section of a PVD module 50 of a type found
on a cluster tool. The module 50 is attached to a transport chamber
or module 52 in the configuration of the cluster tool, and a robot
(not shown) loads and unloads wafers from the processing module 50
through a port 53. Usually, the PVD module 50 is isolated from the
transport chamber 52 by a valve 53a at the port 53. The valve 53a
is typically a rectangular gate valve often referred to as a slit
valve. A dedicated high vacuum pump 54, usually a cryopump, pumps
the module 50 to base pressure during wafer processing. This
cryopump is, in turn, isolated from the module by a valve (not
shown), most commonly a gate valve. The pump 54 maintains a vacuum
in the processing chamber 55 during processing.
[0043] The processing chamber 55 is enclosed by a chamber wall 56
that contains an upwardly facing wafer support 57. A chamber shield
assembly 58 protects the chamber wall from deposition from a PVD
source 59 that faces downwardly from the top of the chamber 55.
Processing gas is introduced into the chamber 55 through ports (not
shown) that may be in the source 59 or the chamber wall 56.
[0044] Pumping the process module 50 through the transport module
52, according to the present invention, eliminates the need for a
separate pump 54, as illustrated in FIG. 4. Similarly, isolation
valves 53a at the gate 53 and at the pump 54 on the module 50 can
be eliminated. A nested shield set 60 replaces the shield 58 and is
designed so that an outer shield 61 forms a "skin" that conforms to
the inside of the chamber wall 56 or is spaced closely from it. A
slot 63 is formed in the outer shield 61 that aligns with the gate
opening or slot 53 in the chamber wall 56 that is used by a robot
(not shown) from the transfer chamber 52 to load and unload wafers
to and from the support 57 through the slot 53.
[0045] For 200 mm diameter wafers and larger, the aperture gas flow
conductance of such a slot 53 is sufficient to provide the pumping
speed required for non-critical packaging applications by pumping
the module 50 through the slot 53 with the pump of the transfer
module 52. The shield set 60 includes an inner shield 62 that is
designed so that an annular space 64 between the two nested shields
61 and 62 is sized to provide adequate gas flow conductance for
pumping of the chamber 55 through the slots 63 and 53. The upper
rim of the shield 62 also extends sufficiently past the slot 63 to
ensure that metal atoms sputtered from the target of the source 59
must undergo at least three specular reflections before they can
deposit on any unshielded region of the chamber wall 56 or inside
the slot 53. Depending on the way that wafers are handled in the
PVD module 50, the inner shield 62 may be constructed with a slot
to allow placement of a wafer on the substrate holder 57 by the
robot. Alternatively, the inner shield 62 can be mounted on
actuators 66, as shown, that allow the shield 62 to be moved up and
down to allow placement of the wafer on the substrate holder 57 by
passing it over the top of the shield 62, and to position the
shield 62 relative to the substrate holder 57, which is often
vertically adjustable. In the most common "sputter down" case, the
inner shield 62 is lowered for wafer load and unload to allow robot
access to the substrate holder 57, and raised during processing to
protect the unshielded surfaces of the slot 53 from deposition.
[0046] To add the nested shield set 60 to a generic cluster tool
module 50 so that the module can be pumped by the pump of the
transfer module 52, no modifications are necessary to the hardware
of the module 50. The geometries of the shield set 60 and its
position in relationship to the chamber walls 56 and control of the
flow of injected gas into the chamber 55 allow for regulation of
the pressure in the chamber 55, as with the chamber of the
apparatus of FIG. 2 described above. Different processing pressures
can be accommodated by locating a gas injection port on each of the
individual process modules. If there was a need to run a high
pressure process in one of the modules and to prevent
back-streaming from the transfer chamber 52 to other modules
running at lower processing pressures, the gas flow conductance of
the shield sets 60 can be changed to accommodate this. Restricting
the aperture conductance of the outer shield 61 can be achieved
where it covers the slot 53, provided this can be done without
interfering with the robot arm during wafer load and unload.
Alternatively, the annular gap between the shields can be changed
to adjust gas flow conductance, for example, it can be narrowed to
reduce conductance to allow higher pressure in the chamber 55. This
approach would employ different inner shields 62 for high and low
pressure processes.
[0047] Another approach to reducing gas flow conductance is to
mount a baffle shield 67 on the same actuator 66 that raises and
lowers the inner shield 62. In the raised position of the actuator
66, the baffle shield 67 would cover the pumping slot 53, thus
lowering its conductance to the desired value. The configuration
and position of the baffle for best performance may be determined
empirically.
[0048] To perform reactive sputtering in a cluster tool module 50
that is configured with a nested shield set 60, a separate pump 54
(FIG. 3) could be installed or reinstalled on the module 50, along
with associated isolation valve. In addition, the isolation valve
53a that isolates the chamber 55 from the transfer module 52 would
be reinstalled. No architectural modifications to the module 50
would be necessary. The outer shield 61 would be modified by
forming a hole in the outer shield 61 to align with the cryopump,
so as to allow pumping. The inner nested shield 62 could remain
unchanged.
[0049] From the above description, it will be readily apparent to
those skilled in the art that modifications and additions thereto
can be made without departing from the principles of the present
invention. The concepts can be modified and adapted for use in tool
architectures of various manufacturers.
* * * * *