U.S. patent application number 11/800257 was filed with the patent office on 2007-09-06 for enhanced end effector arm arrangement for cmp pad conditioning.
Invention is credited to Stephen J. Benner.
Application Number | 20070207705 11/800257 |
Document ID | / |
Family ID | 37637845 |
Filed Date | 2007-09-06 |
United States Patent
Application |
20070207705 |
Kind Code |
A1 |
Benner; Stephen J. |
September 6, 2007 |
Enhanced end effector arm arrangement for CMP pad conditioning
Abstract
A CMP conditioning apparatus enhanced end effector arm for
improving the reliability of the apparatus and the quality of the
conditioning and polishing operations includes a conditioner head
with features that provide for simplified alignment/attachment of a
conditioning disk to the arm, while also providing a "quick
release" mechanism for maintenance operations. The enhanced arm
also includes an improved actuator that provides for a static
friction ("stiction")-free movement of the arm and better control
of the downforce applied by the conditioning disk to the polishing
pad. A dual-drive pulley system is used within the enhanced end
effector arm to minimize the tilting of the drive belts within the
effector arm as the arm pivots to follow the contour of an "aging"
polishing pad.
Inventors: |
Benner; Stephen J.;
(Lansdale, PA) |
Correspondence
Address: |
Wendy W. Koba, Esq.
PO Box 556
Springtown
PA
18081
US
|
Family ID: |
37637845 |
Appl. No.: |
11/800257 |
Filed: |
May 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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11484372 |
Jul 10, 2006 |
7217172 |
|
|
11800257 |
May 3, 2007 |
|
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60697893 |
Jul 9, 2005 |
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Current U.S.
Class: |
451/11 |
Current CPC
Class: |
B24B 53/017
20130101 |
Class at
Publication: |
451/011 |
International
Class: |
B24B 51/00 20060101
B24B051/00 |
Claims
1. A conditioner head for use in an end effector arm of a CMP
system, the conditioner head comprising: an abrasive conditioning
disk including a magnetic-filled central aperture; a keyed
alignment/attachment element disposed to contact the abrasive
conditioning disk, the keyed alignment element comprising an
impeller body having a central recessed portion of a known keying
geometry and including at least one magnetic component disposed
within the central recessed portion so as to align with the
magnetic-filled central aperture of the abrasive conditioning disk;
and at least one ejector mechanism disposed at the periphery of the
conditioner head and configured to impart a downward force onto the
abrasive conditioning disk sufficient to break the magnetic
attachment provided by the keyed alignment/attachment element when
needed to remove the abrasive conditioning disk from the
conditioner head.
2. An actuator mechanism for a CMP end effector arm capable of
providing precise control of a downforce applied by a conditioner
head on a polishing pad, the actuator mechanism comprising a piston
and a cylinder for housing the piston, the piston and the cylinder
formed from materials that generate minimal static friction as the
piston is moved within the cylinder.
3. An actuator mechanism as defined in claim 2 wherein the piston
comprises a graphite material and the cylinder comprises a glass
material and the actuator mechanism further comprises: a first
evacuation channel disposed along a top surface thereof; and a
second evacuation channel disposed along an opposing bottom
surface, wherein as vacuum is applied the graphite piston rides
within the glass cylinder and air is evacuated along at least one
of the first evacuation channel and the second evacuation channel
into the end effector arm.
4. A CMP end effector arm including a dual drive belt movement
arrangement disposed between a conditioner head and an actuator
mechanism for translating the actuator mechanism movement into
movement of the conditioner head, the dual drive belt movement
arrangement comprising a first drive belt coupled at a first end to
the conditioner head; a pulley disposed within the end effector arm
and coupled to a second, opposing end of the first drive belt; a
second drive belt coupled at a first end to the actuator mechanism
and at a second, opposing end to the pulley, wherein movement of
the actuator passes through the second drive belt and is thereafter
coupled by the pulley into the first drive belt, thereby resulting
in movement of the conditioner head, the pulley being located along
the end effector arm at a position that minimizes movement of the
pulley during pivoting of the end effector arm.
5. A method for controlling the application of an abrasive
conditioning disk to a polishing pad in a CMP conditioning system
such that zero downforce is applied to the conditioning disk, the
method comprising the steps of: engaging an actuator mechanism to
control movement of an end effector arm, wherein said actuator
mechanism further comprises a piston and a cylinder for housing the
piston and wherein the piston and the cylinder are formed from
materials that generate minimal static friction as the piston is
moved within the cylinder.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 11/484,372, issuing as U.S. Pat. No. 7,217,172 on May 15, 2007,
and claims the benefit of U.S. Provisional Application No.
60/697,893, filed Jul. 9, 2005.
TECHNICAL FIELD
[0002] The present invention relates to conditioning apparatus for
use in a chemical mechanical planarization (CMP) system and, more
particularly, to an improved end effector arm configuration to
provide well-controlled, reliable and efficient movement and
operation of the end effector arm with respect to the polishing pad
surface.
BACKGROUND OF THE INVENTION
[0003] In the field of chemical mechanical planarization (CMP), a
process known as "pad conditioning" or "pad dressing" is used to
restore the surface of the polishing pad and remove surface glazing
by dislodging particulates and spent polishing slurry from the pad.
Pad conditioning also re-planarizes the polishing pad by
selectively removing pad material so as to roughen the
newly-exposed pad surface. Pad conditioning may be performed
"ex-situ" (i.e., conditioning the polishing pad between wafer
polishing cycles) or "in-situ" (i.e., concurrent with, or during, a
wafer polishing cycle). In a typical prior art "in-situ" pad
conditioning process, a fixed abrasive conditioning disk is swept
across the pad surface to remove a small amount of pad material and
accumulated debris, thus creating new asperities in the pad surface
to allow for the free flow of the polishing slurry. The removed pad
material and debris then combine with the used polishing slurry and
are passively carried away from the pad.
[0004] In most typical in-situ conditioning arrangements, the
abrasive conditioning disk is held within a rotatable arm (referred
to as an "end effector arm" or "conditioning arm") that sweeps the
disk across a portion of the polishing pad not currently in use.
One particular arrangement is described in detail in U.S. Pat. No.
7,052,371 issued to S. J. Benner on May 30, 2006, assigned to the
assignee of the present application and herein incorporated by
reference. FIGS. 1 and 2 illustrate an exemplary conditioning
arrangement as taught by Benner, where FIG. 1 illustrates the
arrangement in a top view, and FIG. 2 in a side view. As shown, a
conditioning apparatus 10 (referred to hereinafter as "conditioner
head 10") is mounted on a motorized end effector arm 12 so as to
allow conditioner head 10 to sweep back and forth across the
surface of polishing pad 14 (illustrated by arc AB in FIG. 1). An
abrasive conditioning disk 22, mounted on the bottom of conditioner
head 10, dislodges agglomerated debris as head 10 sweeps across
polishing pad 14. End effector arm 12 is configured to impart a
predetermined downward force (denoted "F" and shown in FIG. 2) and
rotational movement (denoted "R" and shown in FIG. 2) to the
conditioning disk, where a motor 17 is used in this particular
embodiment to both pivot end effector arm 12 in arc AB (or through
any other appropriate translational movement) about a fixed shaft
18, and provide rotational motion R and downward force F to the
conditioning disk. This particular arrangement is considered to be
exemplary only, with other systems utilizing, for example, a
stationary abrasive (in place of a rotating conditioning disk), or
an abrasive structure that covers the full pad radius and thus does
not need to "sweep" across the pad to provide the conditioning
effect.
[0005] In the above-cited Benner arrangement, apertured
conditioning disk 22 is used to both dislodge surface glazing from
the polishing pad and evacuate the dislodged debris through the
application of a vacuum force pulling through and around the
apertures formed in conditioning disk 22. As shown in FIGS. 1 and
2, a vacuum force V pulls debris upward and evacuates the debris
through a channel 25 and away from polishing pad 14. Apertured
conditioning disk 22 itself is attached to conditioner head 10 by
either a mechanical arrangement, or by a magnetic mounting device
24 that is disposed between conditioning disk 22 and conditioner
head 10. It is important to the proper operation of the
conditioning process that the apertured conditioning disk be
properly aligned with the other components in the conditioner head.
During operation, proper alignment between the pad and the removal
features also allows for efficient evacuation of the debris from
the polishing pad surface. Proper alignment is also important for
the resultant planarity of the polishing pad, which is a major
factor in improving wafer polishing uniformity and reducing
defectivity.
[0006] In high volume industrial applications, there is a constant
need to improve the CMP apparatus and processes inasmuch as
planarization of a semiconductor wafer is repeatedly used during
the integrated circuit fabrication process, where there is
significant cost and effort expended before and during each
planarization operation. Any quality problems associated with the
planarization can result in multiple "die" or chips being lost,
with up to an entire wafer needing to be discarded, which is
certainly an undesirable event. While quality issues concerning
conditioning and polishing need to be addressed, the associated
issues of efficiency and expense cannot be ignored, where "quality"
and "expense" are often areas of concern that are in tension.
[0007] For example, in order to remove an abrasive conditioning
disk from the CMP structure (i.e., to replace the disk and
re-qualify the process), the conditioning disk must be unscrewed,
unfastened, and/or grasped by hand and pried away (e.g., with a
blade) in order to break the magnetic or mechanical force and pull
the disk away from the conditioner head. At times, this manual
operation may be cumbersome and may shed unwanted particulates onto
the polishing pad surface. In most cases there is little clearance
between the end effector arm of the conditioner and the polishing
pad itself. Additionally, since any process involving removal of
the conditioning disk is most often carried out in a clean room
environment where the personnel must where gloves (and possibly
other awkward attire) that are cumbersome/clumsy and may lead to
damage or misalignment of the disk, or the remaining components.
Misalignment can lead to chatter, which can cause shedding in
addition to the pad non-uniformity. Slurry build-up due to
misalignment can also lead to large particle (agglomerate)
polishing defects. Radial variations in the polishing pad surface
(a common problem resulting from different wear rates due to
differences in abrasive/pad relative speed differences) are further
exaggerated when the conditioning disk is misaligned with the
conditioner head. The state-of-the-art processing leaves a trough,
or shallow center region, on the polishing pad (due to the
above-described speed differences), which creates high wafer
polishing force in both of the "thicker" regions on the pad (if the
trough is amplified), or laden with particles for the reasons for
the reasons described above, exaggerating wafer polishing defects
and results in non-uniform (edge fast) polishing.
[0008] Another problem area is associated with the translational
movement of the end effector arm itself. In conventional use, end
effector arm 12 translates in the z direction (i.e. "up" and
"down") as it is raised and lowered during the conditioning
process, where this translational movement is controlled by an
actuator 20 located within the end effector arm. The diaphragm, or
piston action of a conventional actuator has been found to be
problematic, with the diaphragm exhibiting poor reliability.
Additionally, conventional air cylinder pistons often require a
force of greater than five p.s.i. to initiate the movement of the
actuator (that is, to break the static force of the assembly and
seal friction). Thus, in most cases, the applied downforce of the
conditioning disk onto the polishing pad must overcome this initial
frictional force, and thereafter provide a corrective force to
bring the system to the proper setpoint. If the setpoint requires
less than 5 p.s.i. to be maintained, the break-away force cannot
easily be achieved. In some equipment, the lifting force is not
supplied by positive pressure, but is instead supplied by a vacuum
(negative force). This configuration cannot be used to reliably
offset the weight of the end effector itself, or frictional
components within the actuator, making low downforce (e.g., less
than two pounds) conditioning impossible. The result of these prior
art actuator problems can be over-conditioning/dressing of the
polishing pad, as a result of the inability to consistently and
repeatedly achieve low abrasive downforces. Alternatively, or
additionally, such prior art systems may require increased
maintenance associated with over-cycling of the actuator in a mode
referred to as "partial pad conditioning". The partial pad
conditioning mode provides the ability to cycle the dressing of the
pad between "on" and "off" phases during a conditioning operation
in an attempt to reduce the pad wear rate. This mode is intended to
compensate for the lack of low downforce, contiguous conditioning.
Partial pad conditioning can also lead to non-uniform dressing as
the start and stop locations of the process are not precisely
controlled. This leads to lesser process capability, poorer quality
control of the polishing operation and potentially to process
control-related down-time.
[0009] Moreover, in swept conditioner applications, as the
polishing pad begins to age and presents an uneven top surface, the
end effector arm will need to pivot slightly or adjust to height
differences as the conditioner head sweeps back and forth. The
pivoting range is desired to be, in most cases, a total of no more
than 10.degree., with the design parameter of "level" defined for
the mid-life thickness of the polishing pad. Any mechanical drive
components within the end effector arm must be able to move through
this range, while maintaining proper alignment/engagement.
Misalignment can lead to a variety of reliability and/or particle
generation (polishing defects) problems.
[0010] Thus, a need remains in the art for an improved conditioning
apparatus and method for use in a CMP system that provides
increased reliability and simplified serviceability to further
improve the overall operation of the CMP system in terms of
polishing/conditioning quality, efficiency and reliability.
SUMMARY OF The INVENTION
[0011] The needs remaining in the prior art are addressed by the
present invention, which relates to conditioning apparatus for use
in a chemical mechanical planarization (CMP) system and, more
particularly, to an improved end effector arm configuration to
provide well-controlled and efficient movement and operation of the
effector arm with respect to the polishing pad surface during
conditioning processes.
[0012] In accordance with the present invention, a conditioning
apparatus end effector arm is formed to include various features
that operate together in a manner that simplifies the maintenance
associated with the conditioning disk itself, while also improving
the precision and control of the downforce applied by the
conditioning disk onto the polishing pad surface. The enhanced end
effector arm of the present invention provides for more consistent
dressing of the polishing pad surface, which results in improving
the quality and efficiency of the associated polishing operation(s)
by limiting the opportunity for variations in the conditioning
process to occur and upset the performance of the polishing
process.
[0013] In an exemplary embodiment of the present invention, a
"quick release" mechanism for removing/replacing the abrasive
conditioning disk is used that eliminates the need for other tools
to be brought into contact with the conditioner head, or for an
individual to physically contact the disk itself. The elimination
of these prior art actions is seen as thus limiting the potential
for contamination of the CMP system, or for breakage to occur as
maintenance operations are performed on the abrasive conditioning
disk. The quick release mechanism takes the form of one or more
ejector mechanism (for example, pins or plungers) that are disposed
through the conditioner head and contact the conditioning disk such
that by depressing the mechanism(s) the disk may be removed.
Further improvement in the reliability of the conditioning disk is
found by having a passive alignment arrangement, in the form of
magnetic locators, disposed within the conditioning disk and the
conditioner head itself, so that the disk will automatically attach
to, and align with, the conditioner head upon replacement.
[0014] In one embodiment of the present invention, a pair of
ejector mechanisms (which would typically be spring-loaded pins)
are disposed at opposing locations on the outer periphery of the
enhanced end effector arm conditioner head in a manner such that
when the mechanisms are pressed downward, they contact the back
surface of the abrasive conditioning disk with a force sufficient
to release the magnetic or mechanical hold between the abrasive
conditioning disk and the conditioner head. Advantageously, the
application of a sufficient balanced force can easily be applied to
the mechanisms by hand to quickly and easily remove the abrasive
conditioning disk without the need for additional tools or physical
handling of the conditioning disk itself.
[0015] Quality improvements associated with controlling the
downforce applied through the conditioning disk to the polishing
pad are achieved in accordance with the enhanced end effector arm
of the present invention through the incorporation of a "static
friction" (stiction)-free actuator for controlling both the
vertical movement of the end effector arm and the downforce applied
by the arm's conditioner head on the CMP polishing pad. In one
embodiment of the present invention, a zero-stiction actuator may
comprise a two-way piston including a glass housing with a graphite
piston. The graphite piston rides within a very closely matched
glass housing allowing for only very slight leakage around the
sides, thus virtually eliminating any perceptible static friction
forces therebetween. The use of a precision pneumatic regulator,
which actively and predictably vents the feedback leakage pressure,
provides for accurate control of the bi-directional movement of the
actuator and a resulting accurate application of downforce to the
conditioning head.
[0016] Quality problems associated with the tilting of the
conditioner head as the polishing pad ages (resulting in a
non-planar polishing pad surface) are addressed in accordance with
the present invention through the use of a dual-drive/intermediate
pulley arrangement within the end effector arm. The use of a pair
of drive belts has been found to minimize the unwanted tilting
movement of the belt drive system as the arm conforms to the uneven
surface of an aging polishing pad. In particular, by using a
"split" dual-drive belt, the span over which the arm must pivot is
cut in half, thus reducing the tilt that the belt must follow as
the polishing pad ages.
[0017] Other and further aspects and advantages of the present
invention will become apparent during the course of the following
discussion and by reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] Referring now to the drawings,
[0019] FIG. 1 is a top view perspective of a prior art conditioning
apparatus;
[0020] FIG. 2 is a side view of the prior art arrangement of FIG.
1;
[0021] FIG. 3 is a cut-away isometric view of an enhanced effector
arm formed in accordance with the present invention;
[0022] FIG. 4 is a detailed, exploded view of the conditioner head
portion of the enhanced effector arm of the present invention;
[0023] FIG. 5 is a further detailed view of the magnetic hex key
configuration within the conditioner head of FIG. 4;
[0024] FIG. 6 is a further detailed view of the conditioning disk
quick-release mechanism within the conditioner head of FIG. 4;
[0025] FIG. 7 is a cut-away side view of a zero-stiction actuator
as used in the enhanced effector arm of FIG. 3;
[0026] FIG. 8 is an enclosed, isometric view of the actuator of
FIG. 7; and
[0027] FIG. 9 is a partial, exploded isometric view of a
split-drive pulley mechanism within the enhanced effector arm of
FIG. 3 as used to control the "tilt" of the conditioner head.
DETAILED DESCRIPTION
[0028] In accordance with the present invention, an enhanced end
effector arm for CMP systems has been developed that provides for
an accurate and well-controlled conditioning process, which thus
results in improving the quality and longevity of the polishing pad
itself and ultimately improves the quality of the
polishing/planarization processes performed by the CMP system.
Inasmuch as the end effector arm is essentially the control
mechanism of the conditioning operation, improvements in the
various aspects of the arm's components are quickly realized in
terms of increased reliability and simplified maintenance of the
CMP apparatus, as well as in terms of improving the quality of the
overall conditioning and polishing processes. The enhanced end
effector arm of the present invention incorporates various features
that function in a cooperative and cumulative manner to improve the
performance and reliability of the arm itself, resulting in also
improving the overall quality of the conditioning and polishing
processes.
[0029] FIG. 3 illustrates, in a cut-away isometric view, an
exemplary enhanced end effector arm 30 as formed in accordance with
the present invention in the manner outlined above. In particular,
enhanced end effector arm 30 includes an improved conditioner head
38 including features to provide simplified alignment/attachment of
an abrasive conditioning disk 36 to conditioner head 38, (shown in
more detail in alignment/attachment mechanism 32 in FIG. 5), as
well as features to provide for simplified removal of the
conditioning disk when desired (for repair, cleaning, replacement,
or the like). The removal features in the inventive enhanced
effector arm comprise a set of quick-release ejector mechanisms 34
(shown in detail in FIG. 6) that break the force (e.g., magnetic
attraction or mechanical coupling through the use of detent
break-away elements, latches, etc.) between abrasive conditioning
disk 36 and conditioner head 38 without the need to use additional
tools or manually pry the disk away from the conditioner head. For
the sake of reference with the following figures, FIG. 3 also shows
a terminating portion 35 of arm 30 to which conditioner head 38 is
attached, where a rotary union 37 associated with the movement of
the conditioning disk is also shown.
[0030] In accordance with the present invention, enhanced end
effector arm 30 further comprises a zero-stiction actuator
mechanism 40 disposed in this particular embodiment within opposing
end portion 42 of enhanced end effector arm 30. Zero-stiction
actuator mechanism 40 comprises a piston and cylinder arrangement
that creates little, if any, static friction as the piston moves
along the cylinder, and as a result provides for the ability to
more accurately control the downforce applied to conditioner head
38 (for example, with a resolution capability of 50 grams or less)
since there is no initial static force ("breakaway force") to
overcome. As will be described in detail hereinbelow, the ability
to so precisely control the applied downforce allows for a
resultant "zero" downforce capability where the conditioner head
may be suspended without any mechanical abrading of the polishing
pad taking place. This precise control of the applied downforce
also allows for variable control of the polishing pad removal rate
during conditioning, most advantageously at varying radial
positions across the polishing pad. Indeed, polishing pads
classically wear faster in the middle, and slower at the center and
edge due to rotation velocity differences. The application of
higher forces at these radial positions allows for the pad removal
rate to be accelerated, and as a result one can control the pad
profile or topography much more precisely, and without reducing
overall pad life. This capability also allows for control at zero
downforce of the dispensing of chemicals or other materials,
relative to the radial position. These advantages were heretofore
unavailable with conventional end effector arm configurations. The
operation and advantages of actuator mechanism 40 will be described
in more detail below in association with FIGS. 7 and 8.
[0031] Also shown in enhanced end effector arm 30 of FIG. 3 is a
dual-drive/intermediate pulley arrangement 80 that has been found
to minimize the unwanted tilting movement of the associated drive
belts as arm 30 pivots by "splitting" essentially in half the span
across which such unwanted movement would occur. These various
aspects of enhanced effector arm 30 will now be described in more
detail hereinbelow.
[0032] FIG. 4 illustrates, in an exploded view, selected components
of conditioner head 38 of inventive enhanced effector arm 30.
Certain elements, not pertinent to the subject matter of this
invention, are not called out or described in detail. Terminating
portion 35 and rotary union 37 of effector arm 30 are also shown in
this view, for the sake of understanding the relationship between
the components of conditioner head 38 and effector arm 30. In
accordance with the present invention, and as shown in an exploded
view in FIG. 4, a pair of ejector mechanisms 34 (in this particular
embodiment illustrated as a pair of pins) is disposed in
conjunction with conditioner head 38 and used to break the magnetic
attraction and quickly release conditioning disk 36 from
conditioner head 38. Also shown in FIG. 4 is magnetic keyed
alignment/attachment arrangement 32, where arrangement 32 is
illustrated and explained below in association with FIG. 5. Other
components of head 38 as shown in FIG. 4 include a vacuum chamber
for pulling debris from the polishing pad surface, the vacuum
chamber comprising a top plate 41, an outer vacuum chamber 43 and
an inner vacuum chamber 45. Evident in the view of FIG. 4 is a
vacuum port 43-P disposed at a predetermined exit location along
outer vacuum chamber 43. As discussed above, the debris from the
conditioning process is pulled away from the polishing pad surface
by applying a vacuum through port 43-P and allowing the debris to
be evacuated through the apertures in conditioning disk 36 and
through channel 25 into a disposal system (not shown).
[0033] Referring to FIG. 5, an exemplary apertured conditioning
disk 36 is shown in association with magnetic keyed
alignment/attachment arrangement 32, where in this particular
embodiment a hexagonally-shaped key is used to create an
anti-rotational alignment arrangement. In accordance with the
present invention, abrasive conditioning disk 36 is configured to
include a central key aperture 42 that is filled with magnetic
material 39. Attachment arrangement 32 is shown as comprising an
impeller body 31 including a central aperture 31-A and a yoke 33
that fits within aperture 31-A. In prior art arrangements, a
separate magnetic disk piecepart (or another mechanical component)
was required to attach the conditioning disk to the conditioner
head, adding to the expense and complexity of the conditioning
apparatus. In accordance with the present invention, the need for
this separate component has been eliminated and the
attachment/alignment process has been significantly simplified by
utilizing a plurality of magnetic elements 44 disposed within
central aperture 31-A of impeller body 31. These magnetic elements
44 are disposed so as to align with magnetic material 39 within key
aperture 42 of conditioning disk 36 and thus provide the desired
attachment and alignment between abrasive conditioning disk 36 and
conditioner head 38. As a result, a conditioning disk may be easily
and repeatedly attached to and aligned with the conditioner head in
a relatively simple manner (each alignment possibly within
60.degree. (hexagonal), typical drive mechanics at 180.degree.
(drive pins)) that improves the overall efficiency and quality of
the CMP conditioning process. It is to be noted that the hexagonal
shape of exemplary yoke 33 and aperture 31-A are considered as
exemplary only, and various other geometries that provide the
desired type of anti-rotational/alignment and drive force
capabilities between rotary union 37 (of FIG. 4), yoke 33 and disk
36 may be used in its place. As will become apparent during the
course of the following discussion, the utilization of
alignment/attachment arrangement 32, in conjunction with the
"back-side"/quick-release mounting of abrasive conditioning disk 36
onto conditioner head 38, provides a system that will efficiently
transfer drive torque from the arm to the disk, while containing
any generated particles and preventing the particles from
contaminating the polishing pad.
[0034] FIG. 6 illustrates, in an exploded view, the details of
inventive quick-release ejector mechanisms 34 of enhanced effector
arm 30 that are used to efficiently disengage conditioning disk 36
from head 38. As mentioned above, prior art effector arm
configurations required that the abrasive conditioning disk be
removed by manually grasping the disk and prying with a blade to
break the magnetic or mechanical force between abrasive
conditioning disk 36 and the conditioner head. This became a
cumbersome task, since in most cases there is little clearance
between the end effector arm of the conditioning apparatus and the
polishing pad itself (see FIG. 2). Moreover, the removal process is
generally carried out in a clean room environment where the
personnel must wear gloves and other awkward attire, increasing the
potential for damage to the disk or the remaining components as the
disk is pried away from the conditioner head. These conventional
manual removal processes also provide an opportunity for
contaminants to enter the environment, for the tool to be damaged,
provide a source of particulate contaminants, associated with the
breaking off of slurry, for example, and/or undesired gouging of
CMP apparatus pieceparts. These particulates can further lead to
wafer scratches and/or problems in re-qualifying the CMP apparatus
for further processing.
[0035] In accordance with the present invention, a "quick release"
arrangement has been developed that utilizes a pair of ejector
mechanisms 34 that effectuate the movement of a pair of pin
elements 50 downward through conditioner head 38 and against the
back surface of conditioning disk 36. While the particular
embodiment of FIG. 6 illustrates the use of "pins" as the ejection
mechanism, it is to be understood that any suitable mechanical
"de-latching" arrangement may be used. For the sake of simplicity,
the remaining discussion will sue the term "ejector pin", where it
is to be understood that the broader definition of "mechanism"
applies as well. Referring to FIG. 6, an exemplary embodiment of an
ejector pin 34 is shown as including an upper housing element 54,
sized to allow for simple movement of the pin elements themselves.
In this particular embodiment, pin element 50 is spring-loaded
within upper housing 54, as evident by a spring 56, so that pin
element 50 returns to its initial position. The use of such
spring-loading, however, is considered optional and other means of
encasing and translating pin element 50 may be used and are
considered to fall within the scope of the present invention. A
lower housing 58 is shown in FIG. 6 to complete the encasing of pin
element 50 while allowing for pin element 50 to exit through
conditioner head 38 and contact the back surface of conditioning
disk 36, breaking the hold between magnetic elements 39 of
conditioning disk 36 and magnetic elements 44 of impeller body 31.
Once conditioning disk 36 has been cleaned, replaced or repaired,
re-attachment is simply provided by bringing disk 36 into the
proximity of impeller body 31, where magnetic elements 44 of
impeller body 31 will attract conditioning disk 36 and
automatically align disk 36 to conditioner head 38 by virtue of the
keyed structure. While the particular embodiment illustrated in
FIG. 6 utilizes a magnetic system to hold conditioning disk 36 in
place, it is to be understood that there are various mechanical
arrangements that also may be used, such as various types of
screws, detents and latching mechanisms. Ejector pins 34 of the
present invention may similarly be used to depress these mechanical
mechanisms so as to effect a release of the abrasive conditioning
disk from the conditioner head.
[0036] As shown by reviewing both FIG. 4 and FIG. 6, ejector pins
34 are located so as to "clear" magnetic key alignment/attachment
arrangement 32 and allow for pin elements 50 to freely move within
conditioner head 38. In a preferred embodiment, a pair of ejector
pins 34 is used, the pins disposed on opposite sides of conditioner
head 38 as shown in FIG. 6 to allow for a balanced ejection force
to be applied against conditioning disk 36.
[0037] Another quality improvement aspect of enhanced end effector
arm 30, as mentioned above, is the utilization of a zero-stiction
actuator to control the "up" and "down" movement of head 38, thus
controlling both the downforce F applied by conditioning disk 36
against the polishing pad surface and the rotational speed of the
conditioning disk itself. In the past, the piston action of a
conventional actuator was problematic, often requiring a force of
greater than five p.s.i. to initiate the movement of the actuator
(referred to as the "breakaway force") as a result of the inherent
static friction between the piston and the housing. Thus, in most
cases, the applied downforce of the conditioning disk to the
polishing pad had to overcome this initial frictional force, and
provide a corrective force to achieve the proper operating
setpoint. Therefore, in situations where the setpoint required less
than five p.s.i. to be maintained, it was often impossible to
achieve the necessary breakaway force. Additionally, some
conventional prior art end effector arm actuators are lifted by the
application of a vacuum, which cannot be used reliably to offset
the weight of the mechanical components, making relatively low
downforce (e.g., less than two pounds) conditioning virtually
impossible.
[0038] In accordance with the present invention, these
actuator-associated problems have been overcome by the
incorporation of "zero stiction" actuator 40 in the enhanced
effector arm (where the term "stiction" is used to define the case
of "static friction"). FIG. 7 illustrates a cut-away view of an
exemplary zero-stiction actuator 40 of the present invention, with
FIG. 8 illustrating an encased isometric view of actuator 40.
Evident in both FIGS. 7 and 8 is an upper evacuation channel 62 and
port 61 formed in a top surface 64 of actuator 40. A lower
evacuation channel 65 and port 66 is formed in the bottom portion
of actuator 40, as shown in FIG. 7. These channels allow for
controlled leakage pressure to be exhausted.
[0039] It has been found that specific material choices for the
piston and housing of the actuator can significantly reduce, if not
eliminate, the static frictional forces that may initially bind the
piston in place. In one particular embodiment of the present
invention, actuator 40 comprises a graphite composite piston 70
that has a diameter closely matched to a glass (for example, a
borosilicate glass (such as a Pyrex.RTM.-brand glass) or an
aluminosilicate glass) cylinder 72, within which piston 70 rides,
as manufactured by Airpot Corporation. The combination of the
graphite piston and glass housing has been found to substantially
reduce the initial "static force" that binds a conventional
pneumatic actuator piston in place and which requires a substantial
initial force to induce movement. In fact, the zero-stiction
actuator arrangement of the present invention has been found to be
able to smoothly move a weight of as little as 50 grams upward and
downward without the need for an initial "impulse" force. Other
combinations of materials that generate little or no static
friction may also be used in the zero-stiction actuator of the
present invention.
[0040] Referring again to FIGS. 7 and 8, as piston 70 is
pressure-controlled to move up and down within cylinder 72, the
displaced air (or gas) is evacuated and directed through upper
channel 62 (or lower channel 65, as the case may be). That is, as
piston 70 moves upward, the air is forced through upper channel 62
and exits at port 61 into the evacuation system of the effector
arm. As piston 70 moves downward, the air will be forced into lower
channel 65 and then through port 66 into the same evacuation
system. In a preferred embodiment of the present invention,
pneumatic regulators are disposed on each side of actuator
mechanism 40 to provide balanced control of piston 70 in either
direction. The evacuation path then proceeds along enhanced
effector arm 30 and away from the conditioning process, so as to
prevent any of the air along this path from contaminating, or
coming in contact with, the various gases and slurries used in the
polishing and conditioning processes themselves.
[0041] The combination of zero-stiction actuator 40 with the
capability of performing precise in-line force measurements (in
terms of both tension and compression) allows for the enhanced end
effector arm of the present invention to operate with extremely
well-controlled downforces, ranging from "zero" downforce to over
forty pounds of downforce. Indeed, the mechanical dead weight of
the end effector itself, coupled with the additive force associated
with the presence of a vacuum and the abrasive conditioning process
can be compensated for by the ability to precisely control the
movement of the actuator and the downforce applied to the
conditioner head. Combining this precise conditioner head control
with the vacuum cleaning capabilities as disclosed in our
co-pending applications allows for the inventive conditioner to
remain in proximity to the pad surface while suspending the
mechanical abrading action (i.e., the sum of all of the existing
forces being a resultant "zero" downforce being applied to the
conditioning disk). The vacuum aperture area is therefore able to
remain stable and the associated flow characteristics of the
various evacuated process wastes to remain equivalent, whether or
not the mechanical abrading action is being used. The ability to so
precisely and accurately control and adjust the downforce on the
conditioning disk with the incorporation of the zero-stiction
actuator allows for independent control of the vacuum and
mechanical aspects of the conditioning process, resulting in a more
effective and efficient conditioning process.
[0042] While the use of a zero-stiction actuator has been found to
improve the force control issues (both vacuum and applied force),
problems remain within the end effector arm as the polishing pad
begins to age and its surface becomes non-planar. As a pad wears,
its cross-section takes on a "bathtub" shape, with thicker regions
in the center and edge of the diameter. These regions are
problematic in that they result in higher forces being transferred
to the wafer surface in the thicker `zone`. These higher pressures
lead to faster localized removal, and higher frequency of scratch,
chatter-type defects at the outer regions of the wafer,
corresponding to the center and edge zones of the pad.
Correspondingly, the end effector arm will need to slightly pivot
(or vertically follow) as the polishing pad begins to age and
present an uneven top surface. This can affect the applied force,
and complicate the force control described earlier (stiction
response). In the pivoting implementation, the pivoting range is
desired to be, in most cases, a total of no more than 10.degree.,
with the design parameter of "level" defined for the mid-life
thickness of the polishing pad. The novel two pulley (dual-drive)
system 80 within enhanced end effector arm 30 of the present
invention has been found to improve the reliability of the rotation
mechanism by transferring the rotational motion from the drive
motors/gearbox so as to minimize the deflection required by the
drive belt.
[0043] FIG. 9 illustrates, in an exploded view, the components of
an exemplary dual-drive arrangement 80 of enhanced effector arm 30.
This particular view illustrates both terminal location 25 of arm
30 (associated with conditioner head 38), as well as the fixed end
portion 42 including actuator 40. Dual drive arrangement 80 is
shown as comprising a first drive belt 82 and a second drive belt
84, both belts 82 and 84 engaged with a pulley 86. First drive belt
82 extends outward toward conditioner head 38 and, as shown, second
drive belt 84 extends inward to engage with actuator 40 and
initiate the desired rotational movement for the conditioning disk
(not shown). In this particular embodiment of the present
invention, first drive belt 82 contacts a lower portion 88 of
pulley 86, with second drive belt 84 engaging an upper portion 90
of pulley 86.
[0044] As shown in FIG. 9, pulley 86 is located just beyond the
up/down pivot point of arm 30, so that its movement during pivoting
is minimized. In accordance with the present invention, the "level"
position is preferably set at mid-life (a typical polishing pad
having a "life" in the range of 0.03'' to 0.05''), since most of
the deflection is experienced when the arm is lifted and the drive
is not loaded. The outer portion of the inventive dual drive
arrangement, comprising first drive belt 82, is thus essentially
"fixed" and remains in alignment regardless of the age of the
polishing pad.
[0045] The present invention has been described in detail with
particular reference to preferred embodiments thereof. However, it
is to be understood that variations and modifications can be
effected within the spirit and scope of the present invention as
defined by claims appended hereto.
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