U.S. patent application number 11/497545 was filed with the patent office on 2007-02-08 for polishing pad with built-in optical sensor.
This patent application is currently assigned to Strasbaugh. Invention is credited to Gregory L. Barbour, David G. Halley, Benjamin C. Smedley, Stephen H. Wolf.
Application Number | 20070032170 11/497545 |
Document ID | / |
Family ID | 22890065 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070032170 |
Kind Code |
A1 |
Halley; David G. ; et
al. |
February 8, 2007 |
Polishing pad with built-in optical sensor
Abstract
An optical sensor that includes a light source and a detector is
located within a cavity in a polishing pad so as to face the
surface that is being polished. Light from the light source is
reflected from the surface being polished and the detector detects
the reflected light. The electrical signal produced by the detector
is conducted to a hub located at the central aperture of the
polishing pad. The disposable polishing pad is removably connected,
both mechanically and electrically to the hub. The hub contains
electronic circuitry that is concerned with supplying power to the
optical sensor and with transmitting the electrical signal to a
non-rotating station. Several techniques are described for
accomplishing these tasks. The system permits continuous monitoring
of an optical characteristic of a surface that is being polished,
even while the polishing machine is in operation, and permits the
end point of the polishing process to be determined.
Inventors: |
Halley; David G.; (San Luis
Obispo, CA) ; Barbour; Gregory L.; (San Luis Obispo,
CA) ; Smedley; Benjamin C.; (San Luis Obispo, CA)
; Wolf; Stephen H.; (Los Osos, CA) |
Correspondence
Address: |
CROCKETT & CROCKETT
24012 CALLE DE LA PLATA
SUITE 400
LAGUNA HILLS
CA
92653
US
|
Assignee: |
Strasbaugh
|
Family ID: |
22890065 |
Appl. No.: |
11/497545 |
Filed: |
July 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11334148 |
Jan 17, 2006 |
7083497 |
|
|
11497545 |
Jul 31, 2006 |
|
|
|
10850346 |
May 20, 2004 |
6986701 |
|
|
11334148 |
Jan 17, 2006 |
|
|
|
09970252 |
Sep 29, 2001 |
6739945 |
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10850346 |
May 20, 2004 |
|
|
|
60236575 |
Sep 29, 2000 |
|
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Current U.S.
Class: |
451/6 ;
451/526 |
Current CPC
Class: |
B24B 37/205 20130101;
B24B 37/013 20130101; B24B 49/12 20130101 |
Class at
Publication: |
451/006 ;
451/526 |
International
Class: |
B24D 11/00 20060101
B24D011/00; B24B 49/00 20060101 B24B049/00 |
Claims
1. A polishing pad assembly for use in a CMP process, said
polishing pad assembly comprising: a polishing pad sized and
dimension for use on a CMP system; an optical sensor disposed
within the polishing pad; and a means for transferring a signal
indicative of an optical characteristic of a surface of a wafer
from the optical sensor.
2. The polishing pad assembly of claim 1 wherein the means for
transferring the signal is selected from the group consisting of a
radio link, an optical link and an acoustic link.
3. The polishing pad assembly of claim 1 further comprising a means
for supplying electrical power to the optical sensor.
4. The polishing pad assembly of claim 3 wherein the means for
supplying electrical power to the optical sensor is selected from
the group consisting of a battery, a solar cell, a photo voltaic
array, a magneto and a transformer.
5. The polishing pad assembly of claim 1 wherein the optical sensor
is adapted to detect an optical quality in the wafer selected from
the group consisting of reflectivity, polarization, absorptivity
and photoluminescence.
Description
[0001] This application is a continuation of U.S. application Ser.
No. 11/334,148, filed Jan. 17, 2006, now U.S. Pat. No. 7,083,497,
which is a continuation of U.S. application Ser. No. 10/850,346
filed May 20, 2004, now U.S. Pat. No. 6,986,701, which is a
continuation of U.S. application Ser. No. 09/970,252 filed Sep. 29,
2001, now U.S. Pat. No. 6,739,945, which claims priority to U.S.
provisional application 60/236,575 filed Sep. 29, 2000.
FIELD OF THE INVENTIONS
[0002] The present invention is in the field of semiconductor wafer
processing, and more specifically relates to a disposable polishing
pad for use in chemical mechanical polishing. The polishing pad
contains an optical sensor for monitoring the condition of the
surface being polished while the polishing operation is taking
place, thus permitting determination of the endpoint of the
process.
BACKGROUND OF THE INVENTIONS
[0003] In U.S. Pat. No. 5,893,796 issued Apr. 13, 1999 and in
continuation U.S. Pat. No. 6,045,439 issued Apr. 4, 2000, Birang et
al. show a number of designs for a window installed in a polishing
pad. The wafer to be polished is on top of the polishing pad, and
the polishing pad rests upon a rigid platen so that the polishing
occurs on the lower surface of the wafer. That surface is monitored
during the polishing process by an interferometer that is located
below the rigid platen. The interferometer directs a laser beam
upward, and in order for it to reach the lower surface of the
wafer, it must pass through an aperture in the platen and then
continue upward through the polishing pad. To prevent the
accumulation of slurry above the aperture in the platen, a window
is provided in the polishing pad. Regardless of how the window is
formed, it is clear that the interferometer sensor is always
located below the platen and is never located in the polishing
pad.
[0004] In U.S. Pat. No. 5,949,927 issued Sep. 7, 1999 to Tang,
there are described a number of techniques for monitoring polished
surfaces during the polishing process. In one embodiment Tang
refers to a fiber-optic ribbon embedded in a polishing pad. This
ribbon is merely a conductor of light. The light source and the
detector that do the sensing are located outside of the pad.
Nowhere does Tang suggest including a light source and a detector
inside the polishing pad. In some of Tang's embodiments,
fiber-optic decouplers are used to transfer the light in the
optical fibers from a rotating component to a stationary component.
In other embodiments, the optical signal is detected onboard a
rotating component, and the resulting electrical signal is
transferred to a stationary component through electrical slip
rings. There is no suggestion in the Tang patent of transmitting
the electrical signal to a stationary component by means of radio
waves, acoustical waves, a modulated light beam, or by magnetic
induction.
[0005] In another optical end-point sensing system, described in
U.S. Pat. No. 5,081,796 issued Jan. 21, 1992 to Schultz there is
described a method in which, after partial polishing, the wafer is
moved to a position at which part of the wafer overhangs the edge
of the platen. The wear on this overhanging part is measured by
interferometry to determine whether the polishing process should be
continued.
[0006] In earlier attempts to mount the sensor in the polishing
pad, an aperture was formed in the polishing pad and the optical
sensor was bonded into position within the aperture by means of an
adhesive. However, subsequent tests revealed that the use of an
adhesive could not be depended upon to prevent the polishing
slurry, which may contain reactive chemicals, from entering the
optical sensor and from penetrating through the polishing pad to
the supporting table.
[0007] In conclusion, although several techniques are known in the
art for monitoring the polished surface during the polishing
process, none of these techniques is entirely satisfactory. The
fiber optic bundles described by Tang are expensive and potentially
fragile; and the use of an interferometer located below the platen,
as used by Birang et al., requires making an aperture through the
platen that supports the polishing pad. Accordingly, the present
inventor set out to devise a monitoring system that would be
economical and robust, taking advantage of recent advances in the
miniaturization of certain components.
SUMMARY
[0008] The disposable polishing pad described below is composed of
foamed urethane. It contains an optical sensor for monitoring, in
situ, an optical characteristic of a wafer surface being polished.
The real-time data derived from the optical sensor enables, among
other things, the end-point of the process to be determined without
disengaging the wafer for off-line testing. This greatly increases
the efficiency of the polishing process.
[0009] The wafers to be polished are composite structures that
include strata of different materials. Typically, the outermost
stratum is polished away until its interface with an underlying
stratum has been reached. At that point it is said that the end
point of the polishing operation has been reached. The polishing
pad and accompanying optics and electronics is able to detect
transitions from an oxide layer to a silicon layer as well as
transitions from a metal to an oxide, or other material.
[0010] The polishing pad described involves modifying a
conventional polishing pad by embedding within it an optical sensor
and other components. The unmodified polishing pads are widely
available commercially, and the Model IC 1000 made by the Rodel
Company of Newark, N.J., is a typical unmodified pad. Pads
manufactured by the Thomas West Company may also be used.
[0011] The optical sensor senses an optical characteristic of the
surface that is being polished. Typically, the optical
characteristic of the surface is its reflectivity. However, other
optical characteristics of the surface can also be sensed,
including its polarization, its absorptivity, and its
photoluminescence (if any). Techniques for sensing these various
characteristics are well known in the optical arts, and typically
they involve little more than adding a polarizer or a spectral
filter to the optical system. For this reason, in the following
discussion the more general term "optical characteristic" is
used.
[0012] In addition to the optics the disposable pad provides an
apparatus for supplying electrical power to the optical sensor in
the polishing pad.
[0013] The disposable polishing pad also provides an apparatus for
supplying electrical power for use in transmitting an electrical
signal representing the optical characteristic from the rotating
polishing pad to an adjacent non-rotating receiver. The pad is
removably connectable to a non-disposable hub that contains power
and signal processing circuitry.
[0014] An optical sensor that includes a light source and a
detector is disposed within a blind hole in the polishing pad so as
to face the surface that is being polished. Light from the light
source is reflected from the surface being polished and the
detector detects the reflected light. The detector produces an
electrical signal related to the intensity of the light reflected
back onto the detector.
[0015] The electrical signal produced by the detector is conducted
radially inward from the location of the detector to the central
aperture of the polishing pad by a thin conductor concealed between
the layers of the polishing pad.
[0016] The disposable polishing pad is removably connected, both
mechanically and electrically, to a hub that rotates with the
polishing pad. The hub contains electronic circuitry that is
concerned with supplying power to the optical sensor and with
transmitting the electrical signal produced by the detector to
non-rotating parts of the system. Because of the expense of these
electronic circuits, the hub is not considered to be disposable.
After the polishing pad has been worn out from use, it is disposed
of, along with the optical sensor and the thin conductor.
[0017] Electrical power for operating the electronic circuits
within the hub and for powering the light source of the optical
sensor may be provided by several techniques. In one embodiment,
the secondary winding of a transformer is included within the
rotating hub and a primary winding is located on an adjacent
non-rotating part of the polishing machine. In another embodiment,
a solar cell or photovoltaic array is mounted on the rotating hub
and is illuminated by a light source mounted on a non-rotating
portion of the machine. In another embodiment, electrical power is
derived from a battery located within the hub. In yet another
embodiment, electrical conductors in the rotating polishing pad or
in the rotating hub pass through the magnetic fields of permanent
magnets mounted on adjacent non-rotating portions of the polishing
machine, to constitute a magneto.
[0018] The electrical signal representing an optical characteristic
of the surface being polished is transmitted from the rotating hub
to an adjacent stationary portion of the polishing machine by any
of several techniques. In one embodiment, the electrical signal to
be transmitted is used to frequency modulate a light beam that is
received by a detector located on adjacent non-rotating structure.
In other embodiments, the signal is transmitted by a radio link or
an acoustical link. In yet another embodiment, the signal is
applied to the primary winding of a transformer on the rotating hub
and received by a secondary winding of the transformer located on
an adjacent non-rotating portion of the polishing machine. This
transformer may be the same transformer used for coupling
electrical power into the hub, or it can be a different
transformer.
[0019] There must be a viable optical path between the top of the
sensor and the lower side of the wafer. However, a void would not
be acceptable, because it would quickly become filled with
polishing slurry, thereby rendering it incapable of serving as an
optical medium. In addition, a void would present a large
mechanical discontinuity in the otherwise homogenous and uniformly
resilient polishing pad. Further, the components of the optical
sensor must not come into direct mechanical contact with the wafer
that is being polished, to avoid scratching the surface of the
wafer.
[0020] To overcome this problem, the optical sensor is embedded
into the polishing pad using techniques described in detail below.
These techniques have been successful in overcoming the
disadvantages described above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 shows a top view of a chemical mechanical
planarization machine polishing wafers using a polishing pad
embedded with optical sensors.
[0022] FIG. 2 is an exploded view in perspective showing the
general arrangement of the elements of the hub and optical assembly
as placed in a polishing pad.
[0023] FIG. 3 is a front top perspective view of the optical
sensor.
[0024] FIG. 4 is a side elevational diagram showing an optical
sensor without a prism.
[0025] FIG. 5 illustrates an electronics hub using an inductive
coupler.
[0026] FIG. 6 is a diagram showing a cross sectional view of an hub
using a light emitting means to transfer signals to a non-rotating
hub.
[0027] FIG. 7 is a diagram showing a cross sectional view of a hub
utilizing radio emitting means to transfer signals to a
non-rotating hub.
[0028] FIG. 8 is a diagram showing a cross sectional view of a hub
utilizing sound waves to transfer signals to a non-rotating
hub.
[0029] FIG. 9 shows a snap ring disposed in the polishing pad.
[0030] FIG. 10 is a top view of the snap ring, with a contact pad
and conducting ribbon disposed on the bottom of the snap ring.
[0031] FIG. 11 shows a medial cross section of the optical sensor
embedded into the polishing pad.
[0032] FIG. 12 shows a medial cross section of the injection
molding process used to embed the optical sensor shown in FIG.
13.
[0033] FIG. 13 shows a medial cross section of the optical sensor
and hub assembly embedded in a single injection molded pad.
[0034] FIG. 14 shows a medial cross section of the injection
molding process used to embed both the optical sensor and the hub
assembly.
[0035] FIG. 15 shows the polishing pad installed in a CMP
system.
DETAILED DESCRIPTION OF THE INVENTIONS
[0036] FIG. 1 is an overhead view of a chemical mechanical system 1
with the optical port 2 cut into the polishing pad 3. The wafer 4
(or other work piece requiring planarization or polishing) is held
by the polishing head 5 and suspended over the polishing pad 3 from
a translation arm 6. Other systems may use several polishing heads
that hold several wafers, and separate translation arms on opposite
sides (left and right) of the polishing pad.
[0037] The slurry used in the polishing process is injected onto
the surface of the polishing pad through slurry injection tube 7.
The suspension arm 8 connects to the non-rotating hub 9 that
suspends over the electronic assembly hub 10. The electronics
assembly hub 10 is removably attached to the polishing pad 3 by
means of twist lock, detents, snap rings, screws, threaded
segments, or any releasable mating mechanism. The hub 10 is
attached to an electrical conducting assembly located within the
pad where the hub attaches. The electrical conducting assembly can
be either a single contact or a plurality of contacts attached to a
thin, electrically conducting ribbon 11, also known as a flex
circuit or ribbon cable. The ribbon 11 electrically connects an
optical sensing mechanism, located within the optical port 2 and
embedded in the pad 3, to the electronics in the electronics hub
10. The ribbon 11 may also comprise individual wires or a thin
cable.
[0038] The window rotates with the polishing pad, which itself
rotates on a process drive table, or platen 18, in the direction of
arrow 12. The polishing heads rotate about their respective
spindles 13 in the direction of arrows 14. The polishing heads
themselves are translated back and forth over the surface of the
polishing pad by the translating spindle 15, as indicated by arrow
16. Thus, the optical window 2 passes under the polishing heads
while the polishing heads are both rotating and translating,
swiping a complex path across the wafer surface on each rotation of
the polishing pad/platen assembly.
[0039] The optical port 2 and the electrical conducting assembly
(see FIG. 10) always remain on the same radial line 17 as the pad
rotates. However, the radial line translates in a circular path as
pad 3 rotates about the hub 9. Note that the conducting ribbon 11
lies along the radial line 17 and moves with it.
[0040] As shown in FIG. 2, the polishing pad 3 has a circular shape
and a central circular aperture 23. A blind hole 24 is formed in
the polishing pad, and the hole opens upwardly so as to face the
surface that is being polished. An optical sensor 25 is placed in
the blind hole 24 and a conductor ribbon 11, which extends from the
optical sensor 25 to the central aperture 23, is embedded within
the polishing pad 3.
[0041] When the polishing pad 3 is to be used, an electronics hub
is inserted from above into the central aperture 23 and secured
there by screwing a base 26, which lies below the polishing pad 3,
onto a threaded portion of the hub 10. As seen in FIG. 5, the
polishing pad 3 is thus clamped between portions of the hub and
portions of the base 26. During the grinding process, the polishing
pad 3, the hub 10 and the base 26 rotate together about a central
vertical axis 28.
[0042] The non-rotating hub 9 of the polishing machine is located
adjacent and above the hub 10. The non-rotating hub 9 is fixed
during operation to the suspension arm 8.
[0043] FIG. 3 shows the optical sensor 25 in greater detail. The
optical sensor 25 includes a light source 35, a detector 36, a
reflective surface 37 (which could be a prism, mirror, or other
reflective optical component), and the conductor ribbon 11. The
conductor ribbon 11 includes a number of generally parallel
conductors laminated together for the purpose of supplying
electrical power to the light source 35 and for conducting the
electrical output signal of the detector 36 to the central aperture
23. Preferably, the light source 35 and the detector 36 are a
matched pair. In general, the light source 35 is a light emitting
diode and the detector 36 is a photodiode. The central axis of the
beam of light emitted by the light source 35 is directed
horizontally initially, but upon reaching the reflective surface 37
the light is redirected upward so as to strike and reflect from the
surface that is being polished. The reflected light also is
redirected by the reflective surface 37 so that the reflected light
falls on the detector 36, which produces an electrical signal in
relation to the intensity of the light falling on it. The
arrangement shown in FIG. 3 was chosen to minimize the height of
the sensor. The reflective surface 37 may be omitted and instead
the arrangement shown in side view in FIG. 4 may be used.
[0044] The optical components and the end of the conductor ribbon
11 are encapsulated in the form of a thin disk 38 that is sized to
fit snugly within the blind hole 24 of FIG. 2. Note that in the
arrangements of FIGS. 3 and 4 baffles may be used to reduce the
amount of non-reflective light reaching the detector 36. Included
within the conductor ribbon 11 are three conductors: a power
conductor 39, a signal conductor 40, and one or more return or
ground conductors 41.
[0045] FIG. 5 illustrates an electronics hub using an inductive
coupler. The power conductor 39 terminates adjacent the central
aperture 23 of the polishing pad 3 at a power plug 46, and the
signal conductor 40 likewise terminates at a signal plug 49. When
the hub 10 is inserted into the central aperture 23, the power plug
46 makes electrical contact with the power jack 50, and the signal
plug 49 makes electrical contact with the signal jack 51. An O-ring
seal 52 prevents the liquids used in the polishing process from
reaching the plugs and jacks. A ring seal 53 is provided in the
base 26 to further insure that the electronic circuits within the
hub remain uncontaminated.
[0046] An electrical signal produced by the detector and related to
the optical characteristic is carried by the conductor 54 from the
signal jack 51 to a signal processing circuit 55, that produces in
response to the electrical signal a processed signal on the
conductor 56 representing the optical characteristic. The processed
signal on the conductor 56 is then applied to a transmitter 57.
[0047] The process by which the signal is passed from the rotating
hub 10 to the non-rotating hub 9 is referred to as inductive
coupling, or RF coupling. The overall assembly may be referred to
as an inductive coupler or an RF coupler.
[0048] The transmitter 57 applies a time-varying electrical current
to the primary winding 58 of a transformer that produces a varying
magnetic field 59 representative of the processed signal. The
magnetic field 59 extends upward through the top of the hub 10 and
is intercepted by a secondary winding 60 of the transformer which
is located on an adjacent non-rotating portion 9 of the polishing
machine, or on some other non-rotating object. The varying magnetic
field 59 induces a current in the secondary winding 60 that is
applied to a receiver 61 that produces on the terminal 62 a signal
representative of the optical characteristic. This signal is then
available for use by external circuitry for such purposes as
monitoring the progress of the polishing operation or determining
whether the end point of the polishing process has been
reached.
[0049] A similar technique may be used to transfer electrical power
from the adjacent non-rotating portion 9 of the polishing machine
to the rotating hub 10. A prime power source 63 on the non-rotating
portion 9 applies an electrical current to the primary winding 64
of a transformer that produces a magnetic field 65 that extends
downward through the top of the hub 10 and is intercepted by a
secondary winding 66 in which the varying magnetic field induces an
electrical current that is applied to a power receiver circuitry
67. The power receiver 67 applies electrical power on the conductor
68 to the power jack 50, from which it is conducted through the
power plug 46 and the power conductor 46 to the light source. The
power receiver 67 also supplies electrical power to the signal
processing circuit 55 through the conductor 69, and to the
transmitter 57 through the conductor 70. Thus, power for operation
of the LED may also be provided by inductive coupling.
[0050] The winding 58 is the same winding as winding 66, and
winding 60 is the same winding as winding 64. Alternatively, the
windings may be different. The superimposed power and signal
components are at different frequency ranges and are separated by
filtering.
[0051] FIGS. 6 through 8 show other techniques used to transfer
signals from the rotating hub 10 to a non-rotating hub 9 of the
polishing machine, and to transfer electrical power from the
non-rotating portion 9 into the rotating hub 10.
[0052] FIG. 6 shows the transmitter 57 further includes a modulator
75 that applies to a light emitting diode or laser diode 76 a
frequency modulated current representative of the processed signal
that represents the optical characteristic. The light-emitting
diode 76 emits light waves 77 that are focused by a lens 78 onto a
photodiode detector 79. The detector 79 converts the light waves 77
into an electrical signal that is demodulated in the receiver 80 to
produce on the terminal 62 an electrical signal representative of
the optical characteristic.
[0053] The prime source of electrical power is a battery 81 that
supplies power to a power distribution circuit 82 that, in turn,
distributes electrical power to the power jack 50, to the signal
processing circuit 55, and to the transmitter circuit 57. In FIG. 7
the transmitter 57 is a radio transmitter having an antenna 87 that
transmits radio waves 88 through the top of the hub 9. The radio
waves 88 are intercepted by the antenna 89 and demodulated by the
receiver 90 to produce an electrical signal on the terminal 62 that
is representative of the optical characteristic.
[0054] Electrical power is generated by a magneto consisting of a
permanent magnet 91 located in the non-rotating portion 29 and an
inductor 92 in which the magnetic field of the permanent magnet 91
induces a current as the inductor 92 rotates past the permanent
magnet 91. The induced current is rectified and filtered by the
power circuit 93 and then distributed by a power distribution
circuit 94.
[0055] In FIG. 8, the transmitter 57 further includes a power
amplifier 100 that drives a loudspeaker 101 that produces sound
waves 102. The sound waves 102 are picked up by a microphone 103
located in the non-rotating portion 29 of the polishing machine.
The microphone 103 produces an electrical signal that is applied to
the receiver 104 which, in turn, produces an electrical signal on
the terminal 62 that is representative of the optical
characteristic.
[0056] Electrical power is generated in the rotating hub 9 by a
solar cell or solar panel 105 in response to light 106 applied to
the solar panel 105 by a light source 107 located in the
non-rotating portion 29. The electrical output of the solar panel
105 is converted to an appropriate voltage by the converter 108, if
necessary, and applied to the power distribution circuit 94.
[0057] FIGS. 9 through 16 show the hub insertion assembly and the
optical-electrical insertion assembly 25. They also disclose
methods of sealing a snap ring (to releasably attach the
electronics hub) and a optical-electrical assemblies into the
polishing pad. The polishing pads 3 shown in these Figures are
typical polishing pads available in the industry, such as the model
IC 1000 produced by Rodel Co. The model comprises two 0.045 inch
thick layers of foamed urethane bonded face to face by a 0.007 inch
thick layer of adhesive. However, each has been modified to allow
for a conducting ribbon 11, a snap ring 114, and an optical
assembly 25 to be placed into the pad.
[0058] FIG. 9 shows a cross section of a molded insert, comprising
a snap ring, 114 used to fix the electronics hub 10 into the center
aperture of the polishing pad 3. The snap ring 114 is placed inside
the center aperture 23 of the polishing pad 3. An inwardly
extending flange 115, or collar, is cut out of the snap ring 114 so
that the electronics hub 10 will snap securely into place. A guide
pin hole 116 receives an electronics hub guide pin 117 to help
assure proper alignment of the electronics hub 10. The snap ring is
sealed inside of the polishing pad 3 by means of an adhesive or by
a liquid urethane which subsequently dries and solidifies. The
electronics hub 10 has a flange or ridge 118 disposed around its
bottom section 119. This flange 118 is sized to provide a
releasable fit with the molded insert snap ring 114.
[0059] The electrically conducting ribbon 11 conveys electrical
signals and power between the optical assembly 25 and the
electronics hub 10. The terminus of ribbon 11 is disposed on a
contact pad 126 in the bottom of the hub-receiving aperture 120.
The contact pad is provided with contacts for establishing
electrical contact with matching contacts 122 disposed on the hub
10. The contacts 122 are preferably spring loaded or biased
contacts (such as pogo pins). The contacts may be provided in
redundant groups. As shown, three contacts are provided in the
group visible in this view.
[0060] The snap ring assembly 114 is preferably isoplanar with the
polishing pad 3 such that multiple pads may be easily stacked on
top of each other.
[0061] FIG. 10 shows a top view of the snap ring 114. The circular
lip of the snap ring 115, the guide pin hole 116, and the
electrically conducting ribbon 11 are the same as shown in FIG. 9.
Also shown in this Figure are three electrical contacts disposed on
the contact pad 126. Specifically, the three contacts are used for
power conduction (contact 123), signal conduction (contact 124),
and common ground (contact 125), all of which lie on the contact
pad 126. The contact pad 127 is disposed on the bottom inside
surface of the snap ring assembly.
[0062] The electronics hub will snap into place inside the lip 115
of the snap ring 114. Proper alignment of the contacts of the hub
with the contacts of the contact pad 127 is assured by the guide
pin 116. Thus, the contacts of the hub establish electrical contact
with contacts 123, 124, and 125 of the contact pad 126 when the hub
is secured in the snap ring.
[0063] FIGS. 11 and 12 show cross sections of the optical sensor 25
and a method of securing the optical sensor 25 in the optical port
2 into the polishing pad 3. An aperture, or hole, 143 is produced
in the polishing pad. The aperture 143 must be large enough to
accommodate the optical sensor 25. The optical assembly 25 is
placed into an optical assembly puck so that it may be easily
disposed into the aperture. Portions of the aperture adjacent to
the upper surface 144 and lower surface 145 of the polishing pad 3
extend a short distance radially outwardly from the aperture. This
creates a spool-shaped void with the boundaries of the pad.
[0064] A channel is produced in the underside of the upper layer
147 to accommodate the conducting ribbon 11 used to convey
electrical power and signals from the electronics hub 10 to the
optical sensor 25. The conducting ribbon 11 may intrude into the
space generally occupied by the layer of adhesive 148, which
secures the upper layer 147 of the polishing pad to the lower layer
149 of the polishing pad. Alternatively the conducting ribbon 11
may lie above or beneath the adhesive layer 148.
[0065] After the aperture 143 has been formed in the polishing pad
3, the optical sensor 25 and its conductor ribbon 11 are inserted
into their respective places, where they are supported and held in
place by spacers composed of urethane or by portions of the upper
layer 147 and lower layer 149.
[0066] Thereafter, the assembly is placed into a fixture that
includes flat, non-stick surfaces 155 and 156. The non-stick
surfaces 155 and 156 are brought into contact with the. upper pad
surface 144 and lower pad surface 145 and pressed together.
[0067] Next, a liquid urethane is injected by syringe 157 through a
passage 158 in the lower mold plate 159 and into the void
immediately surrounding the optical sensor 25 until the injected
urethane begins to emerge through the vent passage 160 of upper
mold plate 161. During the injection, it is helpful to tilt the
assembly slightly in the clockwise direction so that the liquid is
injected at the lowest point of the void and the vent passage 160
is at the highest point. Tilting the assembly in this manner
prevents air from becoming trapped in the void.
[0068] The injected urethane 162 directly above the optical sensor
25 serves as a window through which the optical sensor 25 can view
the underside of the wafer , which is placed on top of the upper
layer 147. The liquid urethane is a type of urethane that is
optically transparent when it has cured. Because it is chemically
similar to the urethane of the polishing pad 3, it forms a durable,
liquid-proof bond with the material of the polishing pad 3.
[0069] The snap-ring assembly can be inserted into the pad, as
shown in FIG. 9, or formed or integrally with the pad with
injection molding processes. As shown in FIGS. 13 and 14, the
polishing pad 3, including the upper pad layer 147, lower pad layer
149 and adhesive layer 148, has been punched and cut to provide
voids 168 for the optical sensor, ribbon cable and the electrode
pad. The ribbon cable 11, contact pad, and optical sensor 25 are
placed in the corresponding voids in the pad, and a snap-ring hub
mold is inserted into the hub aperture. The electrode pad may be
glued with a weak pressure sensitive adhesive (sticky glue) to the
snap ring mold 169.
[0070] As shown in FIG. 13, an upper mold base 172 and a lower mold
base 173 are pressed against the polishing pad's upper layer 147
and lower 149 layer, respectively. Urethane or other injectable
plastic is then injected through the injection port 174, and the
urethane fills the voids. When the void between the plates is
filled, the liquid urethane 162 will exit through the exit vent
175, signaling that the injection process is complete. As shown in
FIG. 14, the injected urethane 176 forms the snap ring assembly and
fills the ribbon cable channel and the optical sensor assembly
aperture. The injected urethane seals and connects the entire
length of void between the snap ring 114 and the optics insert 25,
and it locks the ribbon cable and the sensor assembly into place
within the pad.
[0071] This process can be accomplished using a snap ring insert as
shown in FIGS. 9 and 10 by sizing the hub aperture in the pad
slightly larger than the snap ring insert, and using the injected
urethane to fix the snap ring insert to the pad.
[0072] FIG. 15 shows a detailed view of the overall polishing pad 3
installed in a CMP system, using the pad design shown in FIGS. 13
and 14. The pad comprises the upper pad layer 147, lower pad layer
149, adhesive layer 148, injected urethane 176, electrically
conductive ribbon 11, optical sensor 25, described in the previous
Figures. The pad is placed on the platen 18. The electronics hub 10
is inserted in to the snap ring, so that the pogo pin electrical
contacts 137 are in contact with the electrodes of the electrode
pad. The non-rotating receiving hub 9 is suspended from the
suspension arm 8 over the rotating electronics hub 10. The
electronics in the rotating electronics hub may be the electronics
shown in FIGS. 5 through 8, inside the box numbered as item 10 in
those drawings, and the non-rotating receiving hub 9 will house the
corresponding electronics in the boxes marked as items 9. After
extended use, the pad will be exhausted and may be removed and
discarded. A new pad may be placed on the platen, and the rotating
hub may be inserted into the snap ring of the new pad.
[0073] It should be noted that the various inventions may be
employed in various combinations. For example, the releasable hub
embodiments, described in connection with inductive couplers and
other non-contacting couplers, can also be employed with slip rings
and other contacting couplers. While urethane has been discussed as
the material to be used as for injection and use as the injected
sealant, other materials may be used, so long as they provide
substantial adhesion and sealing between the several inserts and
the pad. Additionally, while the pad construction has been
discussed in relation to optical sensors, electrical sensors, heat
sensors, impedance sensors and other sensors may be used instead,
and the benefits of the molding and releasable hub still achieved.
Thus, while the preferred embodiments of the devices and methods
have been described in reference to the environment in which they
were developed, they are merely illustrative of the principles of
the inventions. Other embodiments and configurations may be devised
without departing from the spirit of the inventions and the scope
of the appended claims.
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