Information
-
Patent Grant
-
6641462
-
Patent Number
6,641,462
-
Date Filed
Wednesday, June 27, 200123 years ago
-
Date Issued
Tuesday, November 4, 200320 years ago
-
Inventors
-
Original Assignees
-
Examiners
- Hail, III; Joseph J.
- Ojini; Anthony
Agents
- Ingrassia Fisher & Lorenz
-
CPC
-
US Classifications
Field of Search
US
- 451 57
- 451 60
- 451 41
- 451 259
- 451 285
- 451 264
- 451 265
- 451 268
- 451 269
- 451 270
- 451 272
- 451 273
- 451 392
- 451 393
- 451 394
- 451 397
- 451 400
-
International Classifications
-
Abstract
A fluid delivery system is provided for delivering a fluid to a polishing surface of a chemical mechanical polishing tool. The system includes a platen, manifold and slurry delivery conduit. The platen has a plurality of conduits for allowing a fluid to pass to the polishing surface. The manifold, through the use of a plurality of channels, controls the fluid distribution to the conduits in the platen. The channel cross-sectional area at substantially every point is greater than, preferably 1.5 to 2 times, the combined cross-sectional area of all the conduits being serviced by the channel. This results in the conduits being the most restrictive feature and a uniform pressure within the manifold. However, the volume of the channels should also be reduced as this reduces the time necessary for a fluid change over. The slurry delivery conduit communicates fluid from a fluid source to the channels in the manifold.
Description
FIELD OF THE INVENTION
The present invention generally relates to polishing a surface of a workpiece. More particularly, the invention relates to improved methods and apparatus for distributing fluids, for example slurry, to the surface of a polishing pad during chemical mechanical polishing.
BACKGROUND OF THE INVENTION
Chemical mechanical polishing or planarizing a surface of an object may be desirable for several reasons. For example, chemical mechanical polishing is often used in the formation of microelectronic devices to provide a substantially smooth, planar surface suitable for subsequent fabrication processes such as photoresist coating and pattern definition. Chemical mechanical polishing may also be used to form microelectronic features. For example, a conductive feature such as a metal line or a conductive plug may be formed on a surface of a wafer by forming trenches and vias on the wafer surface, depositing conductive material over the wafer surface and into the trenches and vias, and removing the conductive material on the surface of the wafer using chemical mechanical polishing, leaving the vias and trenches filled with the conductive material.
A typical chemical mechanical polishing apparatus suitable for planarizing the semiconductor surface generally includes a wafer carrier configured to support, guide, and apply pressure to a wafer during the polishing process; a polishing compound such as a slurry containing abrasive particles and chemicals to assist removal of material from the surface of the wafer; and a polishing surface such as a polishing pad. In addition, the polishing apparatus may include an integrated wafer cleaning system and/or an automated load and unload station to facilitate automatic processing of the wafers.
A wafer surface is generally polished by moving the surface of the wafer to be polished relative to the polishing surface in the presence of the polishing compound. In particular, the wafer is placed in the carrier such that the surface to be polished is placed in contact with the polishing surface and the polishing surface and the wafer are moved relative to each other while slurry is supplied to the polishing surface.
The distribution of slurry over the polishing surface has been shown to be a critical factor in the chemical mechanical polishing process. The material removal rate across the surface of the wafer is generally related to the amount of slurry received by the polishing surface. Areas on the polishing surface having additional slurry will typically polish the wafer faster than areas on the polishing surface having less slurry. While the material removal rate may be fine tuned by intentionally adjusting the slurry distribution across the polishing surface, it is desirable to have a substantially uniform slurry distribution across the polishing surface.
One approach to distributing slurry across a polishing surface involves depositing the slurry from above in the middle of the polishing surface. Polishing surfaces typically move, for example, in a rotational, orbital or linear motion. The motion, in addition to removing material from the front surface of the wafer, helps to distribute the slurry across the polishing surface. However, this approach leads to a concentration of slurry in the middle of the polishing surface with the concentration of slurry declining in relation to its distance from the middle of the polishing surface.
Another approach to distributing slurry across a polishing surface involves pumping slurry from a cavity below the polishing surface through apertures in a platen and polishing surface to the polishing surface. However, the motions previously mentioned cause the slurry to concentrate along the periphery of the cavity and therefore, when forced to the polishing surface, the slurry is concentrated along the periphery of the polishing surface. As a partial correction for this problem, a cut o-ring has been spirally inserted into the cavity to reduce the concentration of slurry at the periphery of the polishing pad. However, the optimum shape of the cut spiral o-ring is difficult to determine and the optimum shape changes with different slurry delivery rates, speed of motions and types of slurry.
Another problem with using the cavity to distribute the slurry is the time it takes to change from a first slurry reaching the surface of the polishing pad to a second slurry reaching the surface of the polishing pad. Applicant has noticed the delay is caused by the cavity having a volume filled with the first slurry that must be completely replaced by the second slurry. The Applicant has also noticed the problem is compounded by parts of the cavity having no real flow direction resulting in a turbulent fluid motion. The turbulent fluid motion results in a mixing of the slurry and an additional time period when both slurries are delivered to the polishing surface further lengthening the time for a complete slurry change over.
What is needed is a method and apparatus for uniformly delivering a fluid to a polishing surface without being unduly affected by slurry delivery rates, speed of motions or types of slurry. The method and apparatus preferably allow a change in slurry to be quickly accomplished.
SUMMARY OF THE INVENTION
The present invention provides improved methods and apparatus for chemical mechanical polishing of a surface of a workpiece that overcome many of the shortcomings of the prior art. While the ways in which the present invention addresses the drawbacks of the now-known techniques for chemical mechanical polishing will be described in greater detail hereinbelow, in general, in accordance with various aspects of the present invention, the invention provides an improved method and apparatus for controlling the distribution of a fluid across a polishing surface.
The invention is a fluid delivery system for delivering a fluid to a polishing surface for a chemical mechanical polishing tool. The invention includes a platen, manifold and slurry delivery conduit. The platen supports the polishing surface and has a plurality of conduits for allowing a fluid to pass through the conduits in the platen and, preferably, through corresponding conduits in the polishing surface. This allows the fluid to reach the working area of the polishing surface. The platen may comprise several layers for performing additional functions not directly related to fluid distribution to the polishing surface.
The manifold controls the fluid distribution to the conduits to allow the fluid to pass through the platen and polishing pad. The manifold uses a plurality of channels in controlling the fluid distribution to the conduits of the platen. The channels may be formed in the manifold in a variety of ways, including, for example, by removing material from a monolithic manifold by machining or etching.
In one embodiment of the invention, the volume of all the channels is less than a third of the volume of the whole manifold. Reducing the volume of the channels reduces the time for a fluid change over. In another embodiment of the invention the channel cross-sectional area at substantially every point in the channels is greater than, preferably between by 1.5 and 2 times, the combined cross-sectional area of all the conduits being serviced by the channel. This causes the conduits in the platen to be the most restrictive feature in the fluid flow path resulting in a uniform backpressure in the manifold and therefore resulting in a uniform velocity of fluid flow. The cross-section of the channels may be incrementally changed or smoothly tapered.
The slurry delivery conduit communicates fluid from a fluid source to the channels in the manifold. The slurry delivery conduit is preferably in fluid communication with a central area of the manifold that feeds the plurality of channels. The slurry delivery conduit may be in fluid communication with a plurality of fluid sources so that a plurality of different fluids, preferably one at a time, may be communicated to the channels in the manifold as desired.
In operation, a fluid may be distributed across a polishing surface by pumping a fluid from a fluid source to a central area connected to a plurality of channels in a manifold. The fluid is communicated through the plurality of channels in the manifold to a plurality of conduits in a platen. Incrementally changing or tapering the channels as previously described results in a substantially uniform velocity of the fluid throughout the channels. The fluid travels through the conduits in the platen and through the polishing surface, preferably through corresponding conduits in the polishing surface, to reach a working area of the polishing surface.
BRIEF DESCRIPTION OF THE DRAWINGS
A more complete understanding of the present invention may be derived by referring to the detailed description and claims, considered in connection with the figures, wherein like reference numbers refer to similar elements throughout the figures, and:
FIG. 1
illustrates a top cut-away view of a polishing system in accordance with the present invention;
FIG. 2
illustrates a side view of a portion of a clean system for use with the apparatus of
FIG. 1
;
FIG. 3
illustrates a top cut-away view of a polishing system in accordance with another embodiment of the invention;
FIG. 4
illustrates a bottom view of a carrier carousel for use with the apparatus illustrated in
FIG. 3
;
FIG. 5
illustrates a top cut-away view of a polishing system in accordance with yet another embodiment of the invention;
FIG. 6
illustrates a bottom view of a carrier for use with the system of
FIG. 5
;
FIG. 7
illustrates a cross-sectional view of a polishing apparatus in accordance with one embodiment of the invention;
FIG. 8
illustrates a portion of the polishing apparatus of
FIG. 7
in greater detail;
FIGS. 9A and 9B
illustrate a platen including heat exchange channels in accordance with the present invention;
FIG. 10
illustrates a top plan view of a polishing surface, having grooves and apertures, in accordance with the present invention;
FIG. 11
illustrates a top cut-away view of a polishing apparatus in accordance with another embodiment of the invention;
FIG. 12
illustrates a perspective view of a manifold;
FIG. 13
illustrates a fluid transition time for a prior art fluid distribution apparatus;
FIG. 14
illustrates a fluid transition time for a manifold according to this invention; and
FIG. 15
illustrates a flowchart for practicing the invention.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
The following description is of exemplary embodiments only and is not intended to limit the scope, applicability or configuration of the invention in any way. Rather, the following description provides a convenient illustration for implementing exemplary embodiments of the invention. Various changes to the described embodiments may be made in the function and arrangement of the elements described without departing from the scope of the invention as set forth in the appended claims.
FIG. 1
illustrates a top cut-way view of a polishing apparatus
100
, suitable for removing material from a surface of a workpiece, in accordance with the present invention. Apparatus
100
includes a multi-platen polishing system
102
, a clean system
104
, and a wafer load and unload station
106
. In addition, apparatus
100
includes a cover (not illustrated) that surrounds apparatus
100
to isolate apparatus
100
from the surrounding environment. In accordance with a preferred embodiment of the present invention machine
100
is a Momentum machine available from SpeedFam-IPEC Corporation of Chandler, Ariz. However, machine
100
may be any machine capable of removing material from a workpiece surface.
Although the present invention may be used to remove material from a surface of a variety of workpieces such as magnetic discs, optical discs, and the like, the invention is conveniently described below in connection with removing material from a surface of a wafer. In the context of the present invention, the term “wafer” shall mean semiconductor substrates, which may include layers of insulating, semiconducting, and conducting layers or features formed thereon, used to manufacture microelectronic devices.
Exemplary polishing system
102
includes four polishing stations
108
,
110
,
112
, and
114
, which each operate independently; a buff station
116
; a transition stage
118
; a robot
120
; and optionally, a metrology station
122
. Polishing stations
108
-
114
may be configured as desired to perform specific functions; however, in accordance with the present invention, at least one of stations
108
-
114
includes an orbital polish station as described herein. The remaining polishing stations may be configured for chemical mechanical polishing, electrochemical polishing, electrochemical deposition, or the like.
Polishing system
102
also includes polishing surface conditioners
140
,
142
. The configuration of conditioners
140
,
142
generally depends on the type of polishing surface to be conditioned. For example, when the polishing surface comprises a polyurethane polishing pad, conditioners
140
,
142
suitably include a rigid substrate coated with diamond material. Various other surface conditioners may also be used in accordance with the present invention.
Clean system
104
is generally configured to remove debris such as slurry residue and material removed from the wafer surface during polishing. In accordance with the illustrated embodiment, system
104
includes clean stations
124
and
126
, a spin rinse dryer
128
, and a robot
130
configured to transport the wafer between clean stations
124
,
126
and spin rinse dryer
128
. In accordance with one aspect of this embodiment, each clean station
124
and
126
includes two concentric circular brushes, which contact the top and bottom surfaces of a wafer during a clean process.
FIG. 2
illustrates an exemplary clean station (e.g., station
124
) in greater detail. Clean station
124
includes brushes
202
,
204
mounted to brush platens
206
,
208
. Station
124
also includes movable rollers—e.g., capstan rollers
210
,
212
—to keep the wafer in place during the clean process.
In accordance with one embodiment of the invention, during the clean operation, a wafer is placed onto the capstan rollers, and lower clean platen
208
and brush
204
rise to contact and apply pressure to a lower surface of the wafer, while upper platen
206
and brush
202
lower to contact the upper surface of the wafer The brushes are then caused to rotate about their axes to scour the surfaces of the wafer in the presence of a cleaning fluid such as deionized water and/or a NH
4
OH solution.
Wafer load and unload station
106
is configured to receive dry wafers for processing in cassettes
132
. In accordance with the present invention, the wafers are dry when loaded onto station
106
and are dry before return to station
106
.
In accordance with an alternate embodiment of the invention, clean system
104
may be separate from the polishing apparatus. In this case, load station
106
is configured to receive dry wafers for processing, and the wafers are held in a wet (e.g., deionized water) environment until the wafers are transferred to the clean station.
In operation, cassettes
132
, including one or more wafers, are loaded onto apparatus
100
at station
106
. A wafer from one of cassettes
132
is transported to a stage
134
using a dry robot
136
. A wet robot
138
retrieves the wafer at stage
134
and transports the wafer to metrology station
122
for film characterization or to stage
118
within polishing system
102
. In this context, a “wet robot” means automation equipment configured to transport wafers that have been exposed to a liquid or that may have liquid remaining on the wafer and a “dry robot” means automation equipment configured to transport wafers that are substantially dry. Robot
120
picks up the wafer from metrology station
122
or stage
118
and transports the wafer to one of polishing stations
108
-
114
for chemical mechanical polishing.
After polishing, the wafer is transferred to buff station
116
to further polish the surface of the wafer. The wafer is then transferred (optionally to metrology station
122
and) to stage
118
, which keeps the wafers in a wet environment, for pickup by robot
138
. Once the wafer is removed from the polishing surface, conditioners
140
,
142
may be employed to condition the polishing surface. Conditioners
140
,
142
may also be employed prior to polishing a wafer to prepare the surface for wafer polishing.
After a wafer is placed in stage
118
, robot
138
picks up the wafer and transports the wafer to clean system
104
. In particular, robot
138
transports the wafer to robot
130
, which in turn places the wafer in one of clean stations
124
,
126
. The wafer is cleaned using one or more stations
124
,
126
and is then transported to spin rinse dryer
128
to rinse and dry the wafer prior to transporting the wafer to load and unload station
106
using robot
136
.
FIG. 3
illustrates a top cut-away view of another exemplary polishing apparatus
300
, configured to remove material from a wafer surface. Apparatus
300
is suitably coupled to carousel
400
, illustrated in
FIG. 4
, to form an automated chemical mechanical polishing system. A chemical mechanical polishing system in accordance with this embodiment may also include a removable cover (not illustrated in the figures) overlying apparatus
300
and
400
.
Apparatus
300
includes three polishing stations
302
,
304
, and
306
, a wafer transfer station
308
, a center rotational post
310
, which is coupled to carousel
400
, and which operatively engages carousel
400
to cause carousel
400
to rotate, a load and unload station
312
, and a robot
314
configured to transport wafers between stations
312
and
308
. Furthermore, apparatus
300
may include one or more rinse washing stations
316
to rinse and/or wash a surface of a wafer before or after a polishing process and one or more pad conditioners
318
. Although illustrated with three polishing stations, apparatus
300
may include any desired number of polishing stations and one or more of such polishing stations may be used to buff a surface of a wafer as described herein. Furthermore, apparatus
300
may include an integrated wafer clean and dry system similar to system
104
described above.
Wafer transfer station
308
is generally configured to stage wafers before or between polishing processes and to load and unload wafers from wafer carriers described below. In addition, station
308
may be configured to perform additional functions such as washing the wafers and/or maintaining the wafers in a wet environment.
Carousel apparatus
400
includes polishing heads
402
,
404
,
406
, and
408
, each configured to hold a single wafer. In accordance with one embodiment of the invention, three of carriers
402
-
408
are configured to retain and urge the wafer against a polishing surface (e.g., a polishing surface associated with one of stations
302
-
306
) and one of carriers
402
-
408
is configured to transfer a wafer between a polishing station and stage
308
. Each carrier
402
-
408
is suitably spaced from post
310
, such that each carrier aligns with a polishing station or station
308
. In accordance with one embodiment of the invention, each carrier
402
-
408
is attached to a rotatable drive mechanism using a gimbal system (not illustrated), which allows carriers
402
-
408
to cause a wafer to rotate (e.g., during a polishing process). In addition, the carriers may be attached to a carrier motor assembly that is configured to cause the carriers to translate—e.g., along tracks
410
. In accordance with one aspect of this embodiment, each carrier
402
-
408
rotates and translates independently of the other carriers.
In operation, wafers are processed using apparatus
300
and
400
by loading a wafer onto station
308
, from station
312
, using robot
314
. When a desired number of wafers are loaded onto the carriers, at least one of the wafers is placed in contact with a polishing surface. The wafer may be positioned by lowering a carrier to place the wafer surface in contact with the polishing surface or a portion of the carrier (e.g., a wafer holding surface) may be lowered, to position the wafer in contact with the polishing surface. After polishing is complete, one or more conditioners—e.g., conditioner
318
, may be employed to condition the polishing surfaces.
FIG. 5
illustrates another polishing system
500
in accordance with the present invention. System
500
is suitably configured to receive a wafer from a cassette
502
and return the wafer to the same or to a predetermined different location within a cassette in a clean, dry state.
System
500
includes polishing stations
504
and
506
, a buff station
508
, a head loading station
510
, a transfer station
512
, a wet robot
514
, a dry robot
516
, a rotatable index table
518
, and a clean station
520
.
During a polishing process, a wafer is held in place by a carrier
600
, illustrate in FIG.
6
. Carrier
600
includes a receiving plate
602
, including one or more apertures
604
, and a retaining ring
606
. Apertures
604
are designed to assist retention of a wafer by carrier
600
by, for example, allowing a vacuum pressure to be applied to a back side of the wafer or by creating enough surface tension to retain the wafer. Retaining ring limits the movement of the wafer during the polishing process.
In operation, dry robot
516
unloads a wafer from a cassette
502
and places the wafer on transfer station
512
. Wet robot
514
retrieves the wafer from station
512
and places the wafer on loading station
510
. The wafer then travels to polishing stations
504
-
508
for polishing and returns to station
510
for unloading by robot
514
to station
512
. The wafer is then transferred to clean system
520
to clean, rinse, and dry the wafer before the wafer is returned to load and unload station
502
using dry robot
516
.
FIGS. 7
, and
11
illustrate apparatus suitable for polishing stations (e.g., polishing stations
108
-
114
,
302
-
306
, and
504
-
508
) in accordance with the present invention. In accordance with various embodiments of the invention, systems such as apparatus
100
,
300
, and
500
may include one or more of the polishing apparatus described below, and if the system includes more than one polishing station, the system may include any combination of polishing apparatus, including at least one polishing apparatus described herein.
FIG. 7
illustrates a cross-sectional view of a polishing apparatus
700
suitable for polishing a surface of a wafer in accordance with an exemplary embodiment of the invention. Apparatus
700
includes a lower polish module
702
, including a platen
704
and a polishing surface
706
and an upper polish module
708
, including a body
710
and a retaining ring
712
, which retains the wafer during polishing.
Upper polish module or carrier
708
is generally configured to receive a wafer for polishing and urge the wafer against the polishing surface during a polishing process. In accordance with one embodiment of the invention, carrier
708
is configured to receive a wafer, apply a vacuum force (e.g., about 55 to about 70 cm Hg at sea level) to the backside of wafer
716
to retain the wafer, move in the direction of the polishing surface to place the wafer in contact with polishing surface
706
, release the vacuum, and apply a force (e.g., about 0 to about 8 psi.) in the direction of the polishing surface. In addition, carrier
708
is configured to cause the wafer to move. For example, carrier
708
may be configured to cause the wafer to move in a rotational, orbital, or translational direction. In accordance with one aspect of this embodiment, carrier
708
is configured to rotate at about 2 rpm to about 20 rpm about an axis
720
.
Carrier
708
also includes a resilient film
714
interposed between a wafer
716
and body
710
to provide a cushion for wafer
716
during a polishing process. Carrier
708
may also include an air bladder
718
configured to provide a desired, controllable pressure to a backside of the wafer during a polishing process. In this case, the bladder may be divided into plenums or zones such that various amounts of pressure may be independently applied to each zone.
Lower polishing module
702
is generally configured to cause the polishing surface to move by means of motion generator
713
. By way of example, lower modules
702
may be configured to cause the polishing surface to rotate, translate, orbit, or any combination thereof In accordance with one embodiment of the invention, lower module
702
is configured such that platens
704
orbits with a radius of about 0.25 to about 1 inch, about an axis
722
at about 30 to about 340 orbits per minute, while simultaneously causing the platen
704
to dither or partially rotate. In this case, material is removed primarily from the orbital motion of module
704
. Causing the polishing surface to move in an orbital direction is advantageous because it allows a relatively constant speed between the wafer surface and the polishing surface to be maintained during a polishing process. Thus material removal rates are relatively constant across the wafer surface.
Polishing apparatus including orbiting lower modules
702
are additionally advantageous because they require relatively little space compared to rotational polishing modules described below. In particular, because a relatively constant velocity between the wafer surface and the polishing surface can be maintained across the wafer surface by moving the polishing surface in an orbital motion, the polishing surface can be about the same size as the surface to be polished. For example, a diameter of the polishing surface may be about 0.5 inches greater than the diameter of the wafer.
FIG. 8
illustrates a portion of a lower polishing module
800
, including a platen
802
and a polishing surface
804
, suitable for use with polishing apparatus
700
. Platen
802
and polishing surface
804
include conduits
806
and
808
formed therein to allow polishing fluid such as slurry to flow through platen
802
and surface
804
toward a surface of the wafer during the polishing process. Flowing slurry toward the surface of the wafer during the polishing process is advantageous because the slurry acts as a lubricant and thus reduces friction between the wafer surface and polishing surface
804
. In addition, providing slurry through the platen
802
and toward the wafer facilitates uniform distribution of the slurry across the surface of the wafer, which in turn facilitates uniform material removal from the wafer surface. The slurry flow rates may be selected for a particular application; however, in accordance with one embodiment of the invention, the slurry flow rates are less than about 200 ml/minute and preferably about 120 ml/minute.
FIGS. 9A and 9B
illustrate a portion of a lower polish module
900
in accordance with yet another embodiment of the invention. Structure or polish head
900
includes a fluid channel
902
to allow heat exchange fluid such as ethylene glycol and/or water to flow therethrough to cool a surface of a polishing surface
904
such as a polishing pad. Module
900
is suitably formed of material having a high thermal conduction coefficient to facilitate control of the processing temperature.
Lower polish head
900
includes a top plate
906
, channel plate
908
, manifold
919
, and a bottom plate
910
, which are coupled together to form polish head
900
. Top plate
906
includes a substantially planar top surface to which a polishing surface
904
such as a polishing pad is attached—e.g., using a suitable adhesive. Channel section
908
includes channel
902
to allow heat exchange fluid to flow through a portion of polish head
900
. The manifold
919
is designed to distribute slurry through conduits
912
from a slurry delivery tube
922
as more fully explained below. Bottom plate
910
is configured for attachment of the polish head
900
to a shaft. To allow slurry distribution through polish head
900
, top plate
906
, and channel section
908
each include corresponding conduits
912
(similar to channels
806
and
808
, illustrated in FIG.
8
), through which a polishing solution or slurry may flow. In accordance with one exemplary embodiment of the invention, top plate
906
is brazed to channel section
908
and the combination of top plate
906
and channel plate
908
is coupled to bottom plate
910
using clamp ring
926
, or alternatively another suitable attachment mechanism such as bolts.
Heat exchange fluid is delivered to polish head
900
through a fluid delivery conduit
914
and a flexible fluid delivery tube
916
. Fluid circulates through channel
902
and exits at outlet
930
.
In an alternative embodiment, the channel groove is formed in the underside of the cover plate. The channel groove may be sealed by attaching a circular disk having a planar top surface to the underside of the cover plate. The bottom section is attached to the circular disk, or, alternatively, the junction of the circular disk and the bottom section could be combined. In either this case or the illustrated case, a channel groove through which a heat exchange fluid can be circulated is formed beneath the substantially planar surface of the platen assembly.
In accordance with yet another embodiment of the invention, the temperature of the polishing process may be controlled by providing a heat exchange fluid to the backside of a wafer. Apparatus for exposing a heat exchange fluid to the backside of a wafer are well known in the art. For an example of an apparatus configured to regulate the polishing rate of a wafer by backside heat exchange, see U.S. Pat. No. 5,605,488, issued to Ohashi et al. on Feb. 25, 1997, which patent is hereby incorporated by reference.
Fluid, typically slurry or deionized water, may be distributed to lower polish head
900
using a flexible slurry delivery tube
922
and a slurry delivery conduit
920
to deliver the fluid to a manifold
919
. Fluid is then distributed to a top surface of polish head
900
using conduits
912
through the top plate
906
and channel section
908
. The top plate
906
and channel section
908
may be considered the same as a platen
802
as shown in FIG.
8
. The platen
802
supports the polishing surface
804
and has a plurality of conduits
806
for allowing a fluid to pass through the conduits
806
in the platen
802
and, preferably, through corresponding conduits
808
in the polishing surface
804
. This allows the fluid to reach the working area of the polishing surface
804
. The platen
802
may comprise several layers (
906
and
908
in
FIG. 9
) for performing additional functions not directly related to the distribution of fluids to the polishing surface
804
.
Referring to
FIGS. 9
a
and
12
, the manifold
919
controls the fluid distribution to the conduits
912
that allow the fluid to pass through the platen
906
,
908
and the polishing surface
904
. The manifold
919
uses a plurality of channels
1300
in controlling the fluid distribution to the conduits
912
of the platen
906
,
908
. The channels
1300
may be formed by removing material from a monolithic manifold
919
. For example, the channels
1300
may be formed by machining or etching the channels into the manifold
919
.
The volume of the channels is preferably substantially reduced from the volume of the channels in the prior art. As an example for one embodiment of the invention, less than a third, and most preferably less than a tenth, of the top surface area of the manifold
919
is covered by the channels
1300
. Reducing the width and volume of the channels
1300
reduces the time for a fluid change over. In addition, the channels
1300
have a laminar flow compared to the turbulent flow of the prior art, which also assists in reducing the time for a fluid change over. Reducing the fluid change over time improves process flexibility in changing fluids during the planarization process.
FIG. 13
illustrates the results from an experiment for a fluid transition time from one fluid to another fluid using a prior art fluid distribution method.
FIG. 14
illustrates the great reduction in fluid transition time from one fluid to anther fluid using the manifold
919
of the invention.
In another embodiment of the invention the channel cross-sectional area at substantially every point in the channels
1300
is greater than, preferably between 1.1 and 10 times, the combined cross-sectional area of all the conduits
912
being serviced by the channel
1300
. In another embodiment the cross-sectional area for channels
1300
leading to a subgroup of the plurality of conduits
912
is about 1.5 times the cross-sectional area of the combined conduits
912
in the subgroup and the channels
1300
leading to a single conduit
912
are about 2 times the cross-sectional area of the single conduit. The channels
1300
leading to a single conduit
912
are made slightly larger to allow for easier machining of the channels
1300
and to allow particles in the fluid to more easily pass through the channels
1300
. Thus, there is a progressive reduction in channel
1300
cross-sectional area as a channel
1300
feeds fewer and fewer conduits
912
.
The channels
1300
have larger cross sections than the conduits
912
causing the conduits
912
in the platen
906
,
908
to be the most restrictive feature in the fluid flow path. The progressive reduction in channel
1300
size and restrictive conduits
912
assist in producing a more uniform backpressure in the manifold
919
. The uniform backpressure results in a more uniform velocity of fluid flow through the channels
1300
and to the surface of the polishing surface
904
. The substantially uniform fluid velocity throughout the channels
1300
reduce the effect of any motions imparted on the manifold
919
. It should be noted that an equivalent result may be obtained by controlling the cross-sectional area of the conduits in the polishing surface
904
while making the cross-sectional area of the conduits
912
in the platen
906
,
908
larger than the cross-sectional area of the conduits
912
in the polishing surface
904
. This would result in the conduits
912
in the polishing surface
904
being the most restrictive feature in the fluid flow path.
The slurry delivery conduit
920
communicates fluid from a fluid source (not shown) to the channels
1300
in the manifold
919
. The slurry delivery conduit
920
is preferably in fluid communication with a central area
1301
of the manifold
919
that feeds the plurality of channels
1300
. The slurry delivery conduit
920
may be in fluid communication with a plurality of fluid sources so that a plurality of different fluids, preferably one at a time, may be communicated to the channels
1300
as desired.
The manifold
919
may be used in combination with platens that are stationary or that move in a variety of directions. For example, the manifold
919
may be easily used to control the fluid distribution with platens that are rotated or orbited.
With reference to
FIGS. 9
a
,
12
, and
15
, in operation, a fluid may be distributed across a polishing surface
904
by pumping a fluid from a fluid source to a central area
1301
connected to a plurality of channels
1300
in a manifold
919
. (Step
1400
) The fluid is communicated through the plurality of channels
1300
in the manifold
919
to a plurality of conduits
912
in a platen
906
,
908
. (Step
1401
) The fluid travels through the conduits
912
in the platen
906
,
908
and through the polishing surface
904
, preferably through corresponding conduits
912
in the polishing surface
904
, to reach a working area of the polishing surface
904
. (Step
1402
)
The slurry distribution manifold
919
and method of using the slurry distribution manifold
919
produce several advantages over the prior art. The manifold
919
greatly improves the uniformity of slurry delivery to the polishing surface
904
, even under various motions, thereby decreasing wafer non-uniformity. The lower non-uniformity leads to improved die yields. A common problem in the prior art is that additional slurry must be used to insure that all areas of the polishing surface
904
have sufficient slurry. Less slurry may be used by improved control over the slurry distribution resulting in a lower cost of ownership.
Another advantage of the manifold
919
is that greater flexibility in tuning the slurry may be achieved. The channels may be designed to produce uniform slurry delivery or the channels may be designed to direct additional slurry to areas that will benefit the particular polishing process. The slurry delivery may be tuned by plugging holes in the manifold
919
(or platen or polishing surface) or by replacing the manifold
919
with another manifold that has channels that produce the desired slurry distribution. The replacement of one manifold
919
with another manifold is a simple process that requires no other changes to the hardware and allows for easy control over the slurry distribution. A further advantage is that the manifold
919
adds additional rigidity in supporting the polishing surface
904
by replacing the cavity in the prior art with a preferably rigid manifold
919
.
FIG. 10
illustrates a top view of polishing surface
1002
in accordance with the present invention. Polishing surface
1002
includes conduits or apertures
1004
extending through surface
1002
. Apertures
1004
are suitably aligned with conduits formed within a platen (e.g., platen
802
), such that polishing solution may circulate through the platen and polishing surface
1002
as described above in connection with
FIGS. 8
,
9
A, and
9
B. Surface
1000
may also include grooves
1006
. Grooves
1006
are configured to effect transportation of the polishing solution on polishing surface
1002
during a polishing process. Polishing surface
1002
may also be porous, further facilitating transportation of the polishing solution. It will be appreciated that polishing surface
1002
may have any suitably-shaped openings that are configured to produce a uniform or other desired slurry distribution across the surface. For example, grooves
1006
may be configured to facilitate a hydroplaning action such that a wafer floats on polishing solution during a polishing process. In accordance with one exemplary embodiment of the invention, surface
1002
is formed of polyurethane, having a thickness of about 0.050 to about 0.080 inches, and grooves
1006
are formed using a gang saw, such that the grooves are about 0.015 to about 0.045 inches deep, with a pitch of about 0.2 inches and a width of about 0.15 to about 0.30 inches.
FIG. 11
illustrates a cross-sectional view of a polishing apparatus
1100
suitable for polishing a surface of a wafer in accordance with another exemplary embodiment of the invention. Apparatus
1100
includes a lower polish module
1102
, including a platen
1104
and a polishing surface
1106
and an upper polish module
1108
, including a body
1110
and a retaining ring
1112
, which retains the wafer during polishing. Apparatus
1100
may also include a slurry distribution apparatus to supply a polishing fluid to a top surface of lower module
1102
.
Upper module
1108
is configured to cause the wafer to rotate, orbit, translate, or a combination thereof and to retain the wafer. In addition, upper module
1108
is configured to apply a pressure to wafer
1114
in the direction of lower module
1102
, as discussed above in reference to upper module
708
. Lower module is generally configured to move a polishing surface by rotating platen
1104
about its axis.
Although apparatus
1100
may be used to polish wafers in accordance with the present invention, apparatus
1100
generally requires additional space compared to apparatus
700
. In particular, the diameter of polishing surface
1106
is generally about twice the diameter of wafer
1114
, whereas polishing surface
706
of lower module
702
is about the same size as the wafer. Additionally, because lower platen
1100
rotates about an axis, delivery of a polishing solution through platen
1104
may be problematic. Thus, several of the advantages associated with through-platen slurry delivery may be difficult to achieve using a rotational platen system, as illustrated in FIG.
11
.
In operation, a wafer
1114
surface is polished by moving wafer
1114
using upper module
1108
, while simultaneously rotating lower polishing module
1102
and polishing surface
1106
attached thereto. In accordance with one exemplary embodiment of the invention, upper module moves wafer
1114
in both a rotational and a translational direction during the polishing process. In accordance with another embodiment, upper module
1108
orbits about an axis.
Although the present invention is set forth herein in the context of the appended drawing figures, it should be appreciated that the invention is not limited to the specific form shown. Various other modifications, variations, and enhancements in the design and arrangement of the chemical mechanical polishing methods and apparatus as set forth herein may be made without departing from the spirit and scope of the present invention as set forth in the appended claims.
Claims
- 1. An apparatus for planarizing a front surface of a wafer comprising:a) a platen for supporting a polishing surface, said platen having a plurality of conduits adapted for communicating a fluid to said front surface; b) a motion generator for causing relative motion between said wafer and the polishing surface; c) a manifold having a plurality of channels for delivering the fluid to the conduits of the platen, said manifold positioned beneath the platen wherein at least one of said plurality of channels has a progressively reduced cross-section; and d) a slurry delivery conduit adapted for communicating the fluid from a fluid source to the manifold.
- 2. The apparatus of claim 1 wherein the motion generator orbits the polishing surface.
- 3. The apparatus of claim 1 wherein the motion generator rotates the polishing surface.
- 4. The apparatus of claim 1 wherein the channels cover less than a third of the surface area of the manifold.
- 5. The apparatus of claim 1 wherein the channel cross-sectional area at substantially every point in the plurality of channels is between about 1 and 10 times greater than the combined cross-sectional area of all the conduits being serviced by the channel.
- 6. An apparatus according to claim 1 wherein the cross-sectional area of each channel is greater than the combined cross-sectional area of all the conduits being serviced by the channel.
- 7. An apparatus according to claim 1 wherein the cross-sectional area of channels leading to a subgroup of the plurality of conduits is about 1.5 times the cross-sectional area of the combined conduits in the subgroup and the cross-sectional area of the channels leading to a single conduit is about 2 times the cross-sectional area of the single conduit.
- 8. An apparatus for planarizing a front surface of a wafer comprising:a) a platen for supporting a polishing surface, said platen having a plurality of conduits adapted for communicating a fluid to said front surface; b) a motion generator for causing relative motion between said wafer and the polishing surface; c) a carousel apparatus for transporting the wafer to the polishing surface; d) a manifold having a plurality of channels for delivering the fluid to the conduits of the platen, said manifold positioned beneath the platen wherein at least one plurality of channels has a progressively reduced cross-section; and e) a slurry delivery conduit adapted for communicating the fluid from a fluid source to the manifold.
- 9. The apparatus of claim 8 wherein the motion generator orbits the polishing surface.
- 10. The apparatus of claim 8 wherein the motion generator rotates the polishing surface.
- 11. The apparatus of claim 8 wherein the channels cover less than a third of the surface area of the manifold.
- 12. The apparatus of claim 8 wherein the channel cross-sectional area at substantially every point in the plurality of channels is between about 1 and 10 times greater than the combined cross-sectional area of all the conduits being serviced by the channel.
- 13. An apparatus for planarizing a front surface of a wafer comprising:a) a platen for supporting a polishing surface; b) a carrier configured to urge said wafer against the polishing surface, said carrier configured to rotate and including a flexible membrane having a front surface for supporting the wafer and a plurality of plenums for exerting different pressures against different areas on a back surface of the membrane; c) a motion generator for causing relative motion between the wafer and the polishing surface; and d) a manifold positioned beneath the platen, wherein the manifold has a plurality of channels for distributing a fluid to the polishing surface.
- 14. The apparatus of claim 13 further comprising:e) a clean system for cleaning the wafer.
- 15. The apparatus of claim 13 further comprising:e) a polishing surface conditioner.
- 16. The apparatus of claim 13 wherein the motion generator is configured to orbit the platen.
US Referenced Citations (10)
Foreign Referenced Citations (2)
Number |
Date |
Country |
0 774 323 |
May 1997 |
EP |
0 842 738 |
May 1998 |
EP |