U.S. patent application number 15/474736 was filed with the patent office on 2018-10-04 for adhesive-less carriers for chemical mechanical polishing.
The applicant listed for this patent is Applied Materials, Inc.. Invention is credited to Rajeev BAJAJ, Niranjan KUMAR, Seshadri RAMASWAMI, Arvind SUNDARRAJAN, Sriskantharajah THIRUNAVUKARASU.
Application Number | 20180281151 15/474736 |
Document ID | / |
Family ID | 63672796 |
Filed Date | 2018-10-04 |
United States Patent
Application |
20180281151 |
Kind Code |
A1 |
RAMASWAMI; Seshadri ; et
al. |
October 4, 2018 |
ADHESIVE-LESS CARRIERS FOR CHEMICAL MECHANICAL POLISHING
Abstract
Embodiments of the disclosure relate to a system, apparatus and
method for polishing thin substrates with high planarity. The
apparatus comprises a chemical mechanical polishing head and a
plate. The polishing head comprises a bottom surface, a retaining
ring, a workpiece-receiving pocket defined between the bottom
surface and the retaining ring, and at least one vacuum port
adapted to provide a vacuum to the workpiece-receiving pocket
through the bottom surface of the polishing head. The plate is
disposed in the workpiece-receiving pocket such that the upper side
of the plate faces the bottom surface of the polishing head and the
lower side of the plate faces away from the bottom surface of the
polishing head. The plate has a geometry or a material property
configured to allow fluid to pass between the upper side and the
lower side of the plate upon application of vacuum in the
workpiece-receiving pocket.
Inventors: |
RAMASWAMI; Seshadri;
(Saratoga, CA) ; BAJAJ; Rajeev; (Fremont, CA)
; KUMAR; Niranjan; (Santa Clara, CA) ;
THIRUNAVUKARASU; Sriskantharajah; (Singapore, SG) ;
SUNDARRAJAN; Arvind; (Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Applied Materials, Inc. |
Santa Clara |
CA |
US |
|
|
Family ID: |
63672796 |
Appl. No.: |
15/474736 |
Filed: |
March 30, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 37/32 20130101;
B24B 41/06 20130101; B24B 37/20 20130101 |
International
Class: |
B24B 37/32 20060101
B24B037/32; B24B 37/20 20060101 B24B037/20; B24B 41/06 20060101
B24B041/06 |
Claims
1. An apparatus for polishing a substrate, the apparatus
comprising: a chemical mechanical polishing (CMP) head comprising:
a bottom surface; a retaining ring; a workpiece-receiving pocket
defined between the bottom surface and the retaining ring; and at
least one vacuum port adapted to provide a vacuum to the
workpiece-receiving pocket through the bottom surface; and a plate
disposed in the workpiece-receiving pocket, an upper side of the
plate facing the bottom surface of the polishing head and a lower
side facing away from the bottom surface of the polishing head, the
plate having a geometry or a material property configured to allow
fluid to pass between the upper side and the lower side of the
plate upon application of the vacuum in the workpiece-receiving
pocket.
2. The apparatus of claim 1, wherein the pressure drop between the
upper side and the lower side of the plate is less than 50% at a
nominal superficial velocity of between one and two meters per
second.
3. The apparatus of claim 1, wherein the plate has porosity between
30-70% and pores less than 200 microns in size.
4. The apparatus of claim 1, wherein the plate has a plurality of
holes fluidly coupling the upper side and the lower side of the
plate.
5. The apparatus of claim 1, wherein the plate has a diameter
substantially similar to a 200 mm semiconductor substrate, 300 mm
semiconductor substrate or a 450 mm semiconductor substrate.
6. The apparatus of claim 1, wherein the plate is fabricated from
at least one of a ceramic material, a conducting material and a
semi-conducting material, the plate comprising a plurality of fine
holes formed therethrough.
7. The apparatus of claim 1, wherein the plate has a thickness of
between 250 microns and 1000 microns.
8. A chemical mechanical polishing (CMP) system comprising: a
rotatable platen; a chemical mechanical polishing (CMP) head
positionable over the platen, the polishing head adapted to urge a
substrate against a polishing pad disposed on the platen for
polishing, the polishing head comprising: a bottom surface; a
retaining ring; a workpiece-receiving pocket defined between the
bottom surface and the retaining ring; and at least one vacuum port
adapted to provide a vacuum to the workpiece-receiving pocket
through the bottom surface; a plate positionable in the
workpiece-receiving pocket, an upper side of the plate facing the
bottom surface of the polishing head and a lower side facing away
from the bottom surface of the polishing head, the plate having a
geometry or a material property configured to allow fluid to pass
between the upper side and the lower side of the plate upon
application of a vacuum in the workpiece-receiving pocket; and a
carrier having an upper mounting surface and a lower mounting
surface, the upper mounting surface configured to mate with the
plate and the lower mounting surface configured secure a substrate,
the carrier having a plurality of vacuum holes extending between
the upper mounting surface and the lower mounting surface.
9. The system of claim 7, wherein the carrier is fabricated from a
ceramic material.
10. The system of claim 7, wherein the carrier is positionable in
the workpiece-receiving pocket below the plate.
11. The system of claim 7, wherein the pressure drop between the
upper side and the lower side of the plate is less than 50% at a
nominal superficial velocity of between one and two meters per
second.
12. The system of claim 7, wherein the plate has porosity between
30-70% and pores less than 200 microns in size.
13. The system of claim 7, wherein the plate is fabricated from
from at least one of a ceramic material, a conducting material and
a semi-conducting material, the plate comprising a plurality of
fine holes formed therethrough.
14. The apparatus of claim 7, wherein the plate and the carrier
have a combined thickness of between 500 microns and 1500
microns.
15. A method of polishing a substrate, the method comprising:
vacuum chucking a substrate through a carrier to a chemical
mechanical polishing (CMP) head by vacuum applied through a plate
disposed between the head and the carrier; and polishing the
substrate chucked to the head on a polishing pad.
16. The method of claim 15 further comprising: electrostatically
chucking the substrate to the carrier.
17. The method of claim 15, wherein vacuum chucking further
comprises: applying vacuum to the substrate through pores formed
through the plate.
18. The method of claim 15 wherein vacuum chucking further
comprises: applying vacuum to the substrate through the holes
formed through the plate and the carrier.
19. The method of claim 15 further comprising: releasing the
substrate and the carrier from the polishing head by removing the
vacuum applied to the substrate while the plate remains in the
polishing head.
20. The method of claim 15 further comprising: releasing the
substrate and the carrier and plate from the polishing head by
removing the vacuum.
Description
BACKGROUND
Field
[0001] Embodiments of the disclosure generally relate to a system,
apparatus and method for polishing thin substrates with high
planarity.
Description of the Related Art
[0002] Semiconductors and microelectronic chips are formed starting
with a substrate, usually made of silicon. The chips are made on
the surface of the substrate using a variety of different
deposition and etch processes. In order to make the chips smaller,
there are efforts to reduce the thickness of the substrate on which
the active circuitry is formed. However, thinner substrates have a
high risk of warping and breaking during the deposition and etching
processes. In order to prevent warpage and breaking, the substrate
is temporarily bonded to a thicker carrier using an adhesive. After
bonding, the substrate is thinned, for example, by mechanical
grinding.
[0003] The ground substrate is then polished using chemical
mechanical polishing (CMP) processes to obtain good total thickness
variation (TTV) and low Ra surfaces. For thin substrates having
thickness in the range of 5-50 microns, the CMP processes exert a
high shear force (lateral force). Adhesive-based temporarily bonded
substrates can be successfully polished down to a thickness in the
range of 20-50 microns. However, these adhesives are unable to
tolerate temperatures greater than 180.degree. C. Therefore, it is
not possible to use thin substrates that are temporarily bonded to
carriers with adhesives for subsequent substrate-to-substrate
bonding at higher temperature (100-400.degree. C.) for
substrate-to-substrate stacking. As a result, the thin substrate is
attached to a carrier without using adhesives so it can withstand
higher temperatures. This can be accomplished through electrostatic
chucking. However, the high lateral forces during polishing can
overcome the electrostatic chucking force and cause the substrate
to slip out from under the carrier. Therefore, there is a need for
an improved way to polish thin substrates attached to a carrier
without an adhesive such that it does not slip out from under the
carrier or get damaged.
SUMMARY
[0004] Embodiments of the disclosure generally relate to a system,
apparatus and method for polishing thin substrates with high
planarity. In one embodiment, an apparatus for polishing a thin
substrate includes a polishing head and a plate. The polishing head
comprises a bottom surface, a retaining ring, a workpiece-receiving
pocket defined between the bottom surface and the retaining ring,
and at least one vacuum port adapted to provide a vacuum to the
workpiece-receiving pocket through the bottom surface of the
polishing head. The plate is disposed in the workpiece-receiving
pocket such that the upper side of the plate faces the bottom
surface of the polishing head and the lower side of the plate faces
away from the bottom surface of the polishing head. The plate has a
geometry or a material property configured to allow fluid to pass
between the upper side and the lower side of the plate upon
application of the vacuum in the workpiece-receiving pocket.
[0005] In another embodiment of the disclosure, a chemical
mechanical polishing (CMP) system is provided that includes a
rotatable platen, a polishing head positionable over the platen, a
plate and a carrier. The polishing head is adapted to urge a
substrate against a polishing pad disposed on the platen for
polishing. The polishing head comprises a bottom surface, a
retaining ring, a workpiece-receiving pocket defined between the
bottom surface and the retaining ring and at least one vacuum port
adapted to provide a vacuum to the workpiece-receiving pocket
through the bottom surface. The plate is disposed in the
workpiece-receiving pocket such that the upper side of the plate
faces the bottom surface of the polishing head and the lower side
of the plate faces away from the bottom surface of the polishing
head. The plate has a geometry or a material property configured to
allow fluid to pass between the upper side and the lower side of
the plate upon application of a vacuum in the workpiece-receiving
pocket. The carrier has an upper mounting surface and a lower
mounting surface, such that the upper mounting surface is
configured to mate with the plate and the lower mounting surface is
configured to secure a substrate. The carrier has a plurality of
vacuum holes extending between the upper mounting surface and the
lower mounting surface.
[0006] Yet another embodiment provides a method for polishing a
substrate. The method includes vacuum chucking a substrate through
a carrier to a polishing head by vacuum applied through a plate
disposed between the head and the carrier, and polishing the
substrate on a polishing pad.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] So that the manner in which the above recited features of
the present disclosure can be understood in detail, a more
particular description of the disclosure, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings. It is to be noted, however,
that the appended drawings illustrate only exemplary embodiments
and are therefore not to be considered limiting of its scope, may
admit to other equally effective embodiments.
[0008] FIG. 1 is a perspective view of a chemical mechanical
polishing (CMP) apparatus used in semiconductor fabrication.
[0009] FIG. 2A is a cross-sectional view of a carrier.
[0010] FIG. 2B is a cross-sectional view of a polishing head.
[0011] FIG. 3A is a schematic representation of a substrate-carrier
combination to be polished.
[0012] FIG. 3B is a schematic representation of the substrate being
polished by a CMP apparatus.
[0013] FIG. 3C is a schematic representation of the substrate
slipping out from under the carrier held by the polishing head.
[0014] FIG. 4A is a schematic representation of a plate disposed
within the polishing head prior to attachment of the
substrate-carrier combination to the polishing head.
[0015] FIG. 4B is a schematic representation of a plate disposed
over the substrate-carrier combination prior to attachment to the
polishing head.
[0016] FIG. 4C is a schematic representation of how the CMP
apparatus in this disclosure prevents the substrate from slipping
out from under the carrier.
[0017] FIG. 5 is a block diagram of a method for polishing a
substrate.
[0018] To facilitate understanding, identical reference numerals
have been used, where possible, to designate identical elements
that are common to the figures. It is contemplated that elements
and features of one embodiment may be beneficially incorporated in
other embodiments without further recitation.
DETAILED DESCRIPTION
[0019] Embodiments of the disclosure generally relate to a system,
apparatus and method for polishing thin substrates with high
planarity.
[0020] Chemical mechanical polishing (CMP) is a method of polishing
or planarization of thin substrates used in fabrication of
semiconductor devices. CMP has become a key technology for removing
irregularities and achieving required planarity, layer and line
width geometries of microelectronic devices, like integrated
circuit chips. An important consideration in the production of
microelectronic devices is process and product stability. To
achieve a high yield, i.e., a low defect rate, each successive
substrate is polished under similar conditions. Each substrate, in
other words, is polished approximately the same amount so that each
semiconductor substrate is substantially identical in planarity.
Disclosed herein are apparatus and techniques that enable robust
polishing of thin substrates while mitigating the potential of
substrate damage due to slippage of the substrate from under the
head of the polishing apparatus while polishing.
[0021] Referring to the drawings, FIG. 1 is a perspective view of a
chemical mechanical polishing (CMP) apparatus 100 suitable for use
in semiconductor fabrication. The CMP apparatus 100 is generally
composed of a polishing head 150, a polishing pad 130 mounted on a
rotatable platen 160 and a fluid delivery arm 140. The fluid
delivery arm 140 dispenses a stream of polishing fluid 145 on the
polishing pad 130 during polishing of a substrate 122. The
polishing fluid, such as but not limited to an abrasive slurry, is
supplied to the polishing surface 135 of the pad 130 to assist
removal of material from the substrate 122 while the substrate 122
is processed against the polishing surface 135.
[0022] The platen 160 is operably coupled to a drive motor (not
shown) that is adapted to rotate the platen 160 about a rotational
axis 110 in a direction shown by the arrow. The platen 160 supports
the polishing pad 130 so that the polishing surface 135 can be in
contact with and process the substrate 122. In some embodiments,
the polishing surface 135 is at least twice the size (i.e.,
diameter) of the substrate 122 that is to be processed on the
polishing pad 130. The polishing pad 130 rotates due to the
rotational motion of the platen 160 during polishing.
[0023] In one embodiment, the polishing material of the polishing
surface 135 may be a commercially available pad material, such as
polymer based pad materials utilized in CMP processes. The polymer
material may be polyurethane, a polycarbonate, fluoropolymers,
polytetrafluoroethylene (PTFE), polyphenylene sulfide (PPS), or
combinations thereof. The polishing material may further comprise
open or closed cell foamed polymers, elastomers, felt, impregnated
felt, plastics, and like materials compatible with the processing
chemistries. In another embodiment, the polishing material is a
felt material impregnated with a porous coating. In other
embodiments, the polishing material includes a material that is at
least partially conductive.
[0024] The fluid delivery arm 140 delivers the polishing fluid 145,
such as but not limited to an abrasive slurry, to the polishing
surface 135 of the polishing pad 130 during polishing. The
polishing fluid 145 may contain abrasive particles, a pH adjuster
and/or chemically active components to enable chemical mechanical
polishing of the substrate 122. The chemistry of the polishing
fluid 145 is selected to polish substrate surfaces and may include
metals, metal oxides, and semimetal oxides, among other materials.
In some embodiments, the polishing fluid may be a chemical
solution, water, a polishing compound, a cleaning solution, or a
combination thereof.
[0025] The CMP apparatus 100 also includes a pad conditioner (not
shown) that is configured to cause a pad conditioning disk (not
shown) to be urged against and sweep across the polishing surface
135 at different times during the polishing process cycle to abrade
and rejuvenate the polishing surface 135 of the polishing pad
130.
[0026] A carrier 124 is utilized to hold a substrate 122 against
the polishing surface 135 of the polishing pad 130. The carrier 124
is retained by the polishing head 150, which is used to urge the
substrate 122 against the polishing pad 130.
[0027] The polishing head 150, as shown in FIGS. 1 and 2B, is
disposed above the polishing surface 135 of the polishing pad 130.
In some embodiments, the polishing head 150 is suspended over the
polishing pad 130 by a support member (not shown) which may be a
carousel, circular or linear track, or other apparatus. The
polishing head 150 is configured to retain the substrate 122 and
controllably urge the substrate 122 towards the polishing surface
135 during polishing. As shown in FIG. 2B, the polishing head 150
has a bottom surface 252, a retaining ring 254 and a
workpiece-receiving pocket 256. The workpiece-receiving pocket 256
is defined as the space between the bottom surface 252 and the
retaining ring 254. The workpiece-receiving pocket 256 has a
diameter selected to receive a substrate having a diameter of 200
mm, 300 mm or 450 mm. The polishing head also has one or more
vacuum ports 258 configured to provide a vacuum from a vacuum
source through the workpiece-receiving pocket 256 to the bottom
surface 252. As the combination of the substrate 122 and the
carrier 124 is placed in connection with the bottom surface 252, it
is supported by the retaining ring 254 and gets disposed within the
pocket 256.
[0028] The polishing head 150 is rotated by a shaft 155 coupled to
an actuator or a motor (not shown). The rotating polishing head 150
in concert with the rotating polishing pad 130 applies a lateral
force to the substrate 122 as it is urged against the polishing pad
130. In other embodiments, the polishing head 150 may have a linear
motion relative to the polishing pad 130. In addition, the
polishing head 150 may be used to move the substrate 122 vertically
towards and against the polishing pad 130. The polishing head 150
may also be moved in a sweeping motion to generate relative motion
between the substrate 122 and the polishing surface 135.
[0029] The polishing head 150 provides a controllable load, i.e.,
pressure, on the substrate 122 to push it vertically down against
the polishing pad 130. In addition, the polishing head 150 rotates
to provide additional motion between the substrate 122 and the
polishing pad 130. The polishing rate (i.e., the rate of removal of
the material from the substrate) is affected by the pressure
applied to the substrate 122 against the polishing pad 130, the
velocity of the polishing pad 130 relative to the substrate 122,
the amount of polishing fluid 145 introduced to the polishing
surface 135, and the condition of the polishing pad 130.
[0030] The thin substrate 122 may be composed of a variety of
different types of materials, such as but not limited to silicon,
gallium arsenide, lithium niobate, etc. The substrate 122 may have
a diameter of 200 mm, 300 mm, 450 mm or other diameter. The
substrate 122 may have a thickness of less than 100 microns. The
substrate 122 is attached to a carrier 124 during the chemical
mechanical polishing process.
[0031] The carrier 124 has the shape of a cylindrical disk and has
a diameter substantially equal to that of the substrate 122 to be
polished. The carrier 124 is positionable in the
workpiece-receiving pocket 256 of the polishing head 150. The
diameter of the pocket 256 is greater than the diameter of the
carrier 124 so that the carrier 124 can be positioned within the
pocket 256. In some embodiments, the carrier 124 may have a
diameter substantially similar to a 200 mm substrate, a 300 mm
substrate or a 450 mm substrate. The carrier 124 may have a
thickness between 400 microns and 1500 microns. The carrier 124 may
be made of a ceramic material, using a rigid dielectric substrate
with conducting electrodes embedded within. Since thin substrates
that are temporarily bonded to carriers with adhesives cannot be
used for subsequent processing at higher temperature
(100-400.degree. C.), the substrate 122 and the carrier 124 are
held together by electrostatic chucking force. The carrier 124 has
a plurality of vacuum holes 226 extending between the upper
mounting surface 124a and the lower mounting surface 124b. The
substrate 122 can be more robustly secured to the carrier 124 while
in the polishing head 150 during polishing by applying vacuum to
the substrate 122 through the vacuum holes 226.
[0032] FIG. 2A shows a cross-sectional view of the carrier 124 that
holds the substrate 122 while in the polishing head 150. The
carrier 124 has an upper mounting surface 124a and a lower mounting
surface 124b. The upper mounting surface 124a is configured to mate
with the lower side 244 of a plate 240. The lower mounting surface
124b is configured to secure an upper surface 122a of the substrate
122, while a lower surface 122b of the substrate 122 is polished.
The lower mounting surface 124b is exposed below the retaining ring
254 (as shown in FIG. 2B).
[0033] In some embodiments, the carrier 124 is an electrostatic
chuck. For example, the carrier 124 may be a bipolar electrostatic
chuck. In the example depicted in FIG. 2A, the carrier 124 has two
chucking electrodes 228a and 228b that can be electrically coupled
to a power source 225 located outside the carrier 124 via the
terminals 227a and 227b respectively. The power source 225 is
configured to provide chucking power to the electrodes 228a, 228b,
such that the substrate 122 can be electrostatically chucked to the
carrier 124, as shown in FIG. 3A. The chucking electrodes 228a,
228b may be an interdigitated mesh that maintains a chucking force
after power is removed from the electrodes 228a, 228b. For example,
when the terminals 227a, 227b are disconnected from the power
source 225, the carrier 124 can freely transport the substrate 122
chucked thereon without the connection to the power source 225. In
an alternative embodiment, a battery power source 229 embedded
within the carrier 124 may be used instead of the power source
225.
[0034] FIG. 3A shows the substrate 122 and the carrier 124
electrostatically chucked together. The carrier 124 is electrically
charged by a power source 225 through the application of voltages
across the embedded chucking electrodes 228a and 228b (shown in
FIG. 2A). The applied voltage from the power source 225 create
localized bipolar electrostatic attraction between the substrate
122 and the carrier 124, resulting in a stacked combination 120 of
the substrate 122 and the carrier 124. The carrier 124 is able to
retain sufficient electrostatic force to process the substrate 122,
after the power source 225 is disconnected. The electrostatic
attraction between the carrier 124 and the substrate 122 can be
released electrically by neutralizing the electrostatic charge that
holds them together. The combination 120 of the carrier 124 and the
substrate 122 has a combined thickness of between 500 microns and
1500 microns.
[0035] FIG. 2B shows a plate 240 disposed within the
workpiece-receiving pocket 256. An upper side 242 of the plate 240
contacts the bottom surface 252 of the polishing head 150. A lower
side 244 of the plate 240 is configured to abut a substrate or a
substrate-carrier combination, as described above. The plate 240
may be made of a ceramic material and has a geometry or a material
property that allows fluid passage between the upper side 242 and
the lower side 244 upon application of vacuum in the
workpiece-receiving pocket 256. The pressure drop between the upper
side 242 and the lower side 244 of the plate 240 (i.e., across the
thickness of the plate 240) is less than about 50% at a nominal
superficial velocity of between one and two meters per second. In
one example, the pressure drop between the upper side 242 and the
lower side 244 of the plate 240 is less than about 10% at a nominal
superficial velocity of between one and two meters per second. In
some embodiments, the plate 240 may be porous in nature so that the
upper side 242 of the plate and the lower side 244 are fluidly
coupled. In other embodiments, the plate 240 may be a porous
ceramic disk with about 30-70% open porosity and has a pore size of
less than 200 microns--for example, ranging between 0.25 to 90
microns. Monolithic, single-grade, aluminum oxide porous ceramic
may have pore sizes of 6, 15, 30, 50, 60 and 120 microns and can be
used for the plate 240. In some alternative embodiments, the plate
240 may also have a predetermined pattern of a plurality of fine
holes 246 (shown in FIG. 2B), having an open area sufficient to
apply the vacuum force to the substrate 122. In those embodiments,
the plurality of fine holes 246 is distributed across the bottom
surface of the plate 240 and each hole has a diameter in the range
of 10-50 microns. In those embodiments, the plate 240 may be made
from a conducting or semi-conducting material.
[0036] The diameter of the plate 240 is substantially similar to a
200 mm substrate, 300 mm substrate or a 450 mm substrate. The
thickness of the plate 240 may be between 250 microns and 1000
microns.
[0037] FIG. 3B is a schematic representation of the substrate 122
being polished while held in the polishing head 150. The polishing
head 150 rotates and pushes down the substrate 122 on the rotating
polishing pad 130. The lower surface 122b of the substrate 122 is
urged against the polishing surface 135 on the polishing pad 130,
thereby polishing the substrate 122. While polishing the substrate
122, the shear force at the interface between the substrate 122 and
the polishing surface 135 may be overcome by the frictional force
holding the substrate 122 to the carrier 124. As a result, the
substrate 122 may slip out from under the carrier 124 and be
damaged. FIG. 3C is a schematic representation of the substrate 122
slipping out from under the carrier 124. The frictional force at
the interface between the substrate 122 and the carrier 124 is a
function of the product of the electrostatic chucking force and the
coefficient of friction. The frictional force remains a constant
for a constant chucking voltage. The shear force at the interface
of the substrate 122 and the polishing surface 135 is inversely
proportional to the thickness of the substrate 122. Therefore, the
surface shear force is higher for thinner substrates than for
thicker substrates, which causes the substrate 122 to be more
likely to slip out from under the carrier 124.
[0038] Advantageously, the CMP apparatus 100 mitigates the
aforementioned problem of the slippage of thin substrates from
under the carrier. The plate 240 disposed within the polishing head
150 with vacuum ports 258 enables active coupling of the substrate
122 through the vacuum holes 226 in the carrier 124 by application
of vacuum. The vacuum force supplements the electrostatic force
between the substrate 122 and the carrier 124, and allows the
combination 120 to successfully withstand the higher shear force
during the polishing process. After the polishing process is
complete, the vacuum is turned off, which releases the combination
120 from the plate 240 and the polishing head 150. The combination
120 is subsequently de-chucked to separate the substrate 122 from
the carrier 124. De-chucking is the process of draining the
accumulated electrostatic charge that holds the substrate 122 to
the carrier 124 by applying a voltage of reverse polarities from
the power source 225 to the chucking electrodes 228a and 228b
(shown in FIG. 2A). The absence of electrostatic force causes the
substrate 122 to be de-chucked from the carrier 124.
[0039] In some embodiments, the plate 240 is first disposed under
the polishing head 150 by a fastener or clamp or by application of
vacuum. The polishing head 150 is moved over the combination 120
and the combination 120 is then secured in the pocket 256 under the
plate 240 by the application of vacuum through the vacuum ports 258
and the holes in the plate 240. The vacuum provides sufficient
suction force to hold the combination 120 to the polishing head
150. The vacuum through the vacuum holes 226 in the carrier 124
also enhances the force holding the substrate 122 to the carrier
124 in addition to the electrostatic chucking force between
them.
[0040] FIG. 4A is a schematic representation of the plate 240
disposed within the polishing head 150 with the combination 120
under the polishing head 150. If the plate 240 is disposed under
the polishing head 150 by application of vacuum, both the
combination 120 and the plate 240 are released when the vacuum is
turned off, after the polishing process is complete. In that case,
the plate 240 is already separated from the combination 120 and a
collection mechanism, such as but not limited to a robot, collects
both the plate 240 and the combination 120. The substrate 122 is
retrieved by de-chucking the electrostatic force between the
carrier 124 and the substrate 122. The plate 240 and/or the carrier
124 may be utilized with subsequent substrates processed in the CMP
apparatus. If the plate 240 is unitarily attached to the polishing
head 150 by a means other than vacuum, only the combination 120 is
released when the vacuum is turned off after the polishing process
is complete. That is, the plate 240 remains attached to the
polishing head 150 after the combination 120 is released and is
utilized in the polishing head 150 to secure the next combination
120 to be polished. The substrate 122 is subsequently retrieved by
de-chucking the electrostatic force between the carrier 124 and the
substrate 122.
[0041] In other embodiments, the plate 240 is disposed over the
combination 120 prior to attachment to the polishing head 150.
Application of vacuum through the vacuum ports 258 provides
sufficient suction force to hold the plate 240 and the combination
120 to the polishing head 150. The holes 246 and/or porosity of the
plate 240 and the vacuum holes 226 in the carrier 124 secure the
plate 240 and the combination 120 to the polishing head 150.
[0042] FIG. 4B is a schematic representation of the plate 240
disposed over the combination 120 prior to attachment to the
polishing head 150. After the polishing process is complete, the
vacuum is turned off to release both the combination 120 and the
plate 240. The plate 240 is already separated from the combination
120 and a collection mechanism collects both the plate 240 and the
combination 120. The substrate 122 is retrieved by de-chucking the
electrostatic force between the carrier 124 and the substrate
122.
[0043] During the polishing process using the CMP apparatus 100,
the substrate 122 is urged against the polishing pad 130 and
rotated about a longitudinal axis 110 (shown in FIG. 1). The shear
force between the substrate 122 and the moving polishing surface
135 cannot overcome the sum of the electrostatic and frictional
forces at the interface between the substrate 122 and the carrier
124, and the suction force due to the vacuum between the substrate
122 and the carrier 124. This prevents the substrate 122 from
slipping out from under the carrier 124. FIG. 4C is a schematic
representation of how the CMP apparatus 100 in this disclosure
prevents the substrate 122 from slipping out from under the carrier
124.
[0044] FIG. 5 is a block diagram of a method for polishing a
substrate described in the embodiments above. The method 500 begins
at block 505 by chucking the substrate 122 to the carrier 124 to
form a substrate-carrier combination. In one example, the substrate
122 is electrostatically chucked to the carrier 124. As mentioned
above, the voltage applied from the power source 225 via terminals
227a and 227b to the chucking electrodes 228a and 228b respectively
in the carrier 124 creates localized bipolar electrostatic
attraction across the substrate 122 and the carrier 124, resulting
in a stacked combination 120 of the substrate 122 and the carrier
124 (shown in FIG. 2A). The power source 225 is disconnected from
the terminals 227a and 227b and the residual electrostatic force
retains the substrate 122 to the carrier 124 as the combination
120.
[0045] At block 510, the combination 120 is chucked to a polishing
head 150 by applying vacuum through the plate 240 disposed over the
combination 120. As described above, the plate 240 has a geometry
or material property which allows fluid to pass between the upper
side 242 and the lower side 244 of the plate 240 upon application
of a vacuum. In one example, as in FIG. 4A, the plate 240 is first
disposed under the polishing head 150 by a means of attachment or
by application of vacuum. The combination 120 is then disposed
under the plate 240 by the application of vacuum through the vacuum
ports 258 and the plate 240, which provides sufficient suction
force to hold the plate 240 and the combination 120 to the
polishing head 150. In another example, the plate 240 is disposed
over the combination 120 prior to attachment to the polishing head
150. Application of vacuum through the vacuum ports 258 provides
sufficient suction force to hold the plate 240 and the combination
120 to the polishing head 150.
[0046] At block 515, the substrate 122 is polished on a polishing
pad, while the combination 120 is disposed within the polishing
head 150. The exposed surface of the substrate 122 is placed
against the rotating polishing pad 130. The polishing head 150
pushes down the bonded combination 120 onto the polishing pad 130
with a lateral pressure in the range of 0.8-4 psi (equivalent to a
force of 110-440 lbf or 50-200 kgf on a 300 mm substrate).
[0047] At block 520, the vacuum is turned off to release the
combination120 . In some embodiments, when the vacuum is turned
off, the plate 240 is retained in the polishing head and is ready
to attach another substrate-carrier combination. In other
embodiments, both the plate 240 and the combination 120 are
released when the vacuum is turned off. A collection mechanism
picks up both the plate 240 and the combination 120. In either
case, the substrate 122 is retrieved by de-chucking the
electrostatic force between the carrier 124 and the substrate 122.
De-chucking is accomplished by applying a voltage of reverse
polarities to drain the accumulated electrostatic charge that holds
the substrate 122 to the carrier 124.
[0048] The method and apparatus described above enables polishing
of thin substrates by preventing slippage of the substrate from
under the carrier and any damage that may be caused to the
substrate subsequently. This method also allows the thin substrate
to endure higher temperature since adhesives, which typically fail
at elevated temperatures are not used for holding the substrate and
the carrier together. Therefore, the processed thin substrates may
have better total thickness variation (TTV) and planarity to enable
successful circuitry design on them. These thin substrates are
expected to meet the future requirements for high-density 3D
Dynamic Random Access Memory (DRAM) applications, image sensors and
emerging market segments.
[0049] While the foregoing is directed to particular embodiments of
the present disclosure, it is to be understood that these
embodiments are merely illustrative of the principles and
applications of the present invention. It is therefore to be
understood that numerous modifications may be made to the
illustrative embodiments to arrive at other embodiments without
departing from the spirit and scope of the present inventions, as
defined by the appended claims.
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