U.S. patent application number 11/466133 was filed with the patent office on 2008-02-28 for apparatus and method for chemical mechanical polishing with improved uniformity.
This patent application is currently assigned to International Business Machines Corporation. Invention is credited to Laertis Economikos, Deok-Kee Kim, Byeongju Park.
Application Number | 20080051008 11/466133 |
Document ID | / |
Family ID | 39197249 |
Filed Date | 2008-02-28 |
United States Patent
Application |
20080051008 |
Kind Code |
A1 |
Economikos; Laertis ; et
al. |
February 28, 2008 |
APPARATUS AND METHOD FOR CHEMICAL MECHANICAL POLISHING WITH
IMPROVED UNIFORMITY
Abstract
A chemical mechanical polishing (CMP) apparatus includes a
workpiece carrier configured for retaining a workpiece thereupon, a
polishing platen configured for retaining a polishing pad
thereupon, and an electromagnetic coil surrounding a periphery of
the workpiece carrier. The electromagnetic coil is configured to
provide a magnetic field of alternating polarity to cause the
rotation of ferromagnetic slurry particles disposed on the
workpiece to facilitate polishing of the workpiece.
Inventors: |
Economikos; Laertis;
(Wappingers Falls, NY) ; Kim; Deok-Kee; (Bedford
Hills, NY) ; Park; Byeongju; (Poughkeepsie,
NY) |
Correspondence
Address: |
CANTOR COLBURN LLP - IBM FISHKILL
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
International Business Machines
Corporation
Armonk
NY
|
Family ID: |
39197249 |
Appl. No.: |
11/466133 |
Filed: |
August 22, 2006 |
Current U.S.
Class: |
451/8 ; 451/285;
451/41 |
Current CPC
Class: |
B24B 37/042 20130101;
B24B 1/005 20130101 |
Class at
Publication: |
451/8 ; 451/41;
451/285 |
International
Class: |
B24B 49/00 20060101
B24B049/00; B24B 7/30 20060101 B24B007/30; B24B 29/00 20060101
B24B029/00 |
Claims
1. A chemical mechanical polishing (CMP) apparatus, comprising: a
workpiece carrier configured for retaining a workpiece thereupon; a
polishing platen configured for retaining a polishing pad
thereupon; and an electromagnetic coil surrounding a periphery of
the workpiece carrier, said electromagnetic coil configured to
provide a magnetic field of alternating polarity to ferromagnetic
slurry particles disposed on the workpiece.
2. The CMP apparatus of claim 1, wherein a longitudinal axis of the
electromagnetic coil is perpendicular to a plane defined by the
surface of contact between the polishing platen and the workpiece
carrier.
3. The CMP apparatus of claim 2, wherein at least one of the
polishing platen and the workpiece carrier has a shaft connected to
the center thereof and is configured for rotational motion around
the shaft.
4. The CMP apparatus of claim 3, wherein the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are coaxial.
5. The CMP apparatus of claim 3, wherein the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are not coaxial and the diameter of the polishing platen is
larger than the diameter of the workpiece carrier.
6. The CMP apparatus of claim 2, further comprising a housing
containing the electromagnetic coil, wherein the housing comprises
a non-rotating part of the polishing platen.
7. The CMP apparatus of claim 6, wherein at least one of the
polishing platen and the workpiece carrier has a shaft connected to
the center thereof and is configured for rotational motion around
the shaft.
8. The CMP apparatus of claim 7, wherein the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are coaxial.
9. The CMP apparatus of claim 7, wherein the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are not coaxial and the diameter of the polishing platen is
larger than the diameter of the workpiece camer.
10. The CMP apparatus of claim 2, further comprising a housing
containing the electromagnetic coil, wherein the housing comprises
a non-rotating part of the workpiece carrier.
11. The CMP apparatus of claim 10, wherein at least one of the
polishing platen and the workpiece carrier has a shaft connected to
the center thereof and is configured for rotational motion around
the shaft.
12. The CMP apparatus of claim 11, wherein the shaft of rotation
for the polishing platen and the shaft of rotation for the
workpiece carrier are coaxial.
13. The CMP apparatus of claim 11, where the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are not coaxial and the diameter of the polishing platen is
larger than the diameter of the workpiece carrier.
14. The CMP apparatus of claim 1, wherein a longitudinal axis of
the electromagnetic coil is within a plane defined by a surface of
contact between the polishing platen and the workpiece carrier.
15. The CMP apparatus of claim 14, wherein the electromagnetic coil
is within a housing enclosing the polishing platen and the
workpiece carrier.
16. The CMP apparatus of claim 14, wherein at least one of the
polishing platen and the workpiece carrier has a shaft connected to
the center thereof and is configured for rotational motion around
the shaft.
17. The CMP apparatus of claim 16, where the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are coaxial.
18. The CMP apparatus of claim 16, where the shaft of rotation for
the polishing platen and the shaft of rotation for the workpiece
carrier are not coaxial and the diameter of the polishing platen is
larger than the diameter of the workpiece carrier.
19. A method for planarizing a workpiece, the method comprising:
disposing a plurality of ferromagnetic slurry particles upon the
polishing platen; affixing the workpiece upon a workpiece carrier;
placing the workpiece carrier upon the polishing platen such that
the ferromagnetic slurry particles contact both the polishing
platen on one side and the workpiece on the other side; and,
subjecting the ferromagnetic slurry particles to a magnetic field
of alternating polarity so as to cause the rotation of the
ferromagnetic slurry particles.
Description
BACKGROUND
[0001] The present invention relates generally to semiconductor
device processing techniques and, more particularly, to an
apparatus and method for chemical mechanical polishing with
improved uniformity.
[0002] Integrated circuits are typically formed on substrates,
particularly silicon wafers, by the sequential deposition of
conductive, semiconductive or insulative layers. After each layer
is deposited, it is patterned by lithographic processes and
subsequently etched to create circuitry features. As a series of
layers are sequentially deposited and etched, the outer or
uppermost surface of the substrate (i.e., the exposed surface of
the substrate) becomes increasingly non-planar; that is, the
topography of the exposed surface contains significant variations
in the height of the surface. This non-planar surface presents
problems in the photolithographic steps of the integrated circuit
fabrication process because the lithographic processes can handle
only limited variations in the height of the surface. Therefore,
there is a need to periodically planarize the substrate
surface.
[0003] Chemical mechanical polishing (CMP) is the most commonly
used process in semiconductor processing for reducing the
aforementioned non-planar topography of the semiconductor surfaces.
In a typical implementation of chemical mechanical polishing, the
substrate is mounted on a carrier head or polishing head. A
polishing pad and retaining ring, typically of a greater diameter
than the wafer, are provided on the opposite side of the carrier.
The polishing pad and wafer are pressed together while both the
carrier head and the polishing pad are rotated. This is achieved by
providing the carrier head with a controllable load (i.e.,
pressure) on the substrate to push it against the polishing pad.
The carrier head and polishing pad may be rotated at different
rates, and with different axes of rotation to help remove the
material uniformly (that is, the average amount of removed material
does not depend on the location within the substrate). The
polishing pad may be either a "standard" pad or a fixed-abrasive
pad. A standard polishing pad has durable roughened surface,
whereas a fixed-abrasive pad has abrasive, submicron particles
(e.g., ceria (CeO.sub.2)) embedded in a containment media. A
polishing slurry, including at least one chemically reactive agent,
and abrasive particles (where a standard pad is used) is supplied
to the surface of the polishing pad.
[0004] With standard pad polishing, the passive motion of the
slurry is caused by mechanical movement of the moving parts (e.g.,
wafer, carrier head, polishing pad, platen, etc.). However, the
mechanical rotation of the moving parts is characterized by a
non-uniform rate of movement of slurry particles in the radial
direction. As such, controlling the rate of polishing becomes a
challenge since the linear velocity of the slurry necessitates a
compensation of the polishing rate with respect to other variables
such as the down force of the polishing pad, and the angular
velocity of the polishing pad and/or chuck. Any polishing mechanism
that provides a higher polishing rate for higher linear velocity of
the polishing slurry faces the challenge of converting uniform
angular velocity of the carrier head and polishing pad into uniform
linear velocity of the polishing slurries across the substrate.
Accordingly, it would be desirable to be able to provide a CMP
mechanism that provides a more uniform polishing rate across a
semiconductor wafer.
SUMMARY
[0005] The foregoing discussed drawbacks and deficiencies of the
prior art are overcome or alleviated by a chemical mechanical
polishing (CMP) apparatus including a workpiece carrier configured
for retaining a polishing pad thereupon, a polishing platen
configured for retaining a workpiece thereupon, an electromagnetic
coil configured to generate a magnetic filed on the workpiece, and
an alternating current supply to provide alternating current
through the electromagnetic coil.
[0006] In one embodiment, the electromagnetic coil surrounds the
periphery of the workpiece carrier. The magnetic field is
substantially perpendicular to the plane of the substrate.
[0007] In another embodiment, the electromagnetic coil is enclosed
within the frame that also contains the polishing pad. The magnetic
field is substantially perpendicular to the plane of the
substrate.
[0008] In still another embodiment, the electromagnetic coil is
embedded in an enclosure in which the polishing pad and polishing
head are contained and either the enclosure or the assembly
containing the polishing pad and polishing head slide in or out to
facilitate the loading and unloading of the substrate. The magnetic
field is substantially within the plane of the substrate.
TECHNICAL EFFECTS
[0009] As a result of the summarized invention, a solution is
technically achieved in which a magnetic slurry is used in
combination with an electromagnetic coil that provides a magnetic
field of alternating polarity. The alternating magnetic field
imparts a spin on the magnetic slurry particles, which in turn
creates additional and more uniform pressure on a workpiece,
thereby enhancing erosion of material during CMP.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] Referring to the exemplary drawings wherein like elements
are numbered alike in the several Figures:
[0011] FIG. 1(a) is a top view of a conventional CMP apparatus
wherein the polishing pad and polishing head are depicted off-axis
to illustrate a typical implementation;
[0012] FIG. 1(b) is a side view of the CMP apparatus of FIG.
1(a);
[0013] FIG. 2(a) is a schematic diagram of a CMP apparatus with
magnetically spinning slurry particles responsive to an alternating
magnetic field, in accordance with a first embodiment of the
invention;
[0014] FIG. 2(b) is a side sectional view of the apparatus shown in
FIG. 2(a);
[0015] FIG. 3(a) is a schematic diagram of a CMP apparatus with
magnetically spinning slurry particles responsive to an alternating
magnetic field, in accordance with a second embodiment of the
invention;
[0016] FIG. 3(b) is a side sectional view of the apparatus shown in
FIG. 3(a);
[0017] FIG. 4(a) is a schematic diagram of a CMP apparatus with
magnetically spinning slurry particles responsive to an alternating
magnetic field, in accordance with a third embodiment of the
invention; and
[0018] FIG. 4(b) is a side sectional view of the apparatus shown in
FIG. 4(a).
DETAILED DESCRIPTION
[0019] Disclosed herein is an apparatus and method for implementing
chemical mechanical polishing with improved uniformity. Briefly
stated, a magnetic slurry is used in combination with an
electromagnetic coil that provides a magnetic field of alternating
polarity. The alternating magnetic field imparts a spin on the
magnetic slurry particles, which in turn creates additional (and
more uniform) pressure on the wafer, thereby enhancing erosion of
material. Consequently, large wafers (e.g., 300 mm or more) may be
polished with a high degree of uniformity, with the polishing rate
less dependent upon the radial distance from the center of the
chuck/pad. Furthermore, the need for radial adjustment of down
force is minimized, and polishing can be carried out at reduced
rotational speeds of the polishing head and/or pad.
[0020] FIG. 1(a) and FIG. 1(b) illustrate a conventional CMP
apparatus 10, in which a carrier head 12 is shown to be carrying a
wafer (or more generally a) substrate 14 (FIG. 1(b)). The surface
of the substrate 14 to be polished faces downward toward a
polishing pad 16 and the slurry 18 disposed thereon. A table 20
(holding pad 16) and a corresponding shaft 22 for the rotation for
the table 20 are also depicted in FIG. 1(b). A shaft 24 for
rotation of the carrier head 12 is shown to be off-axis from with
respect to the axis of rotation of the table 20.
[0021] Referring now to both FIGS. 2(a) and 2(b), there is shown a
schematic diagram of a CMP apparatus 100 with magnetically spinning
slurry particles responsive to an alternating magnetic field, in
accordance with a first embodiment of the invention. As is shown,
the apparatus 100 includes a wafer carrier (chuck) 102 having a
semiconductor wafer (or more generally, a workpiece) 104 held
thereon. In addition, a CMP polishing pad 106 is attached to a
polishing platen (head, table) 108, configured for rotational
motion by means of a shaft 110. The rotating pad 106 is brought
into contact with the wafer 104, which is supplied with magnetic
slurry particles 112 thereon. The slurry particles 112 may include,
for example, a silica or cerium based material along with a
ferromagnetic material as well. Alternatively, the slurry may be
manufactured by coating silica or cerium based material on
spherically shaped ferromagnetic material. Optionally, the carrier
102 (and thus the wafer 104) may also be independently rotated, in
the opposite direction, with respect to the pad 106 and polishing
head 108, as indicated by the shaft 114 shown in dashed lines.
[0022] Although FIGS. 2(a) and 2(b) depict a CMP apparatus with
concentric shafts for the wafer carrier and for the polishing
platen, it is not necessary for both centers to coincide. Nor is it
necessary to limit the size of the polishing platen to that of the
carrier head. In fact, size of the polishing platen may be bigger
than that of the carrier head and the two axes of rotation may be
off-centered as depicted in FIG. 1(a) and FIG. 1(b). This provides
the benefits of a more uniform polishing rate provided by the
conventional (nonmagnetic) component of polishing rate while not
compromising the benefits of the magnetic component of the
polishing rate.
[0023] As further shown in FIGS. 2(a) and 2(b), the apparatus 100
further includes a coil 118 wound around the periphery of the wafer
104, chuck 102 and magnetic slurry particles 112. The coil 118 has
an alternating current (AC) excitation source 120 so as to provide
a magnetic field of varying polarity. In the exemplary embodiment
depicted, the coil 118 is disposed within a housing 122 that is
structurally independent from the rest of the CMP apparatus 100
(i.e., the chuck 102 and polishing head 108), the footprint of
which is generally indicated as 124 in FIG. 2(a). However, as
described herein after, other embodiments contemplate the coil 118
also being incorporated into the chuck 102 and/or polishing head
108 as well.
[0024] In operation, the ferromagnetic slurry particles 112 (in the
presence of an applied magnetic field of alternating polarity
through coil 118) change their orientation so as to align their
internal magnetization with the externally applied magnetic field.
Coupled with a small amount of mechanical rotation (through the
rotating pad 106 and/or chuck 102), the magnetic slurry particles
112 rotate between the pad 106 and the wafer 104. Because the
rotation of the particles 112 is substantially uniform along the
surface of the wafer 104, the resulting amount of energy, force and
pressure applied to the wafer from 104 the spinning slurry
particles 112 is also substantially uniform, thus leading to more
uniform polishing.
[0025] The magnetic potential energy, E, of a solid particle having
a magnetization, M, and a volume, V, is given by the
expression:
E=(-V)MB (eq. 1)
[0026] Wherein B represents the magnetic flux density of an
external applied magnetic field applied to the particle.
[0027] Therefore, if the magnetic particle does not move when the
polarity of the externally applied magnetic field switches from B
to -B, then the energy difference, .DELTA.E, between the two states
becomes:
.DELTA.E=2VMB (eq. 2)
[0028] Because staying in the same magnetic orientation as an
external magnetic field changes direction is not an energetically
"favorable" condition, the particle will, as a result, turn (i.e.,
spin) around in accordance with the least perturbation to the
direction of the particle.
[0029] The volume of an individual slurry particle, having a
radius, R, of about 1 micron is given as follows:
V = 4 / 3 .pi. R 3 = 4 / 3 .pi. ( 10 - 6 m ) 3 = 4 / 3 .pi. 10 - 18
m 3 ( eq . 3 ) ##EQU00001##
[0030] The term "remanence" refers to the residual magnetism left
within a medium after an external magnetic field has been removed.
A typical value of remanence for a ferromagnetic material is on the
order of about M.apprxeq.10,000 gauss (G)=1 tesla (T).
[0031] The magnetic flux density, B, generated by an
electromagnetic coil is given by:
B.apprxeq..mu.NI/L (eq. 4)
[0032] Wherein .mu. is the permeability of free space (air), N is
the number of turns of wire around the electromagnet (e.g.,
100,000), I is the current through the coil (e.g., 10 amperes) and
L is the length of the magnetic circuit (e.g., 1 meter).
[0033] Applying these exemplary values for the coil 118 to equation
4 above, the generated magnetic flux density is approximately:
4.pi.10.sup.-7m.sup.-1(100,000)(10A)/(1
m)=4.pi.10.sup.-1T.apprxeq.1T
[0034] For a magnetic force confined within a high permeability
material, an order of magnitude estimation of force is given
by:
F .apprxeq. E / 2 R = VMB / R .apprxeq. ( 4 / 3 .pi. 10 - 18 m 3 (
1 T ) ( 1 T ) / 10 - 6 m = 4 / 3 .pi. 10 - 12 N ( eq . 5 )
##EQU00002##
[0035] Converting the above to an estimation of force per unit area
(pressure), P, on the wafer yields:
P .apprxeq. F / R 2 = VMB / R = ( 4 / 3 .pi. 10 - 12 N ) / ( 10 - 6
m ) 2 .apprxeq. 4 Pa ( eq . 6 ) ##EQU00003##
[0036] It can thus be seen from the above calculations that the
pressure magnetically generated on the substrate is comparable with
the downward pressure of conventional CMP processing techniques.
Although the polishing pad and the application of some downward
pressure is still used to contain the magnetic slurry between the
wafer and the pad (and to enable contact between the slurry and
wafer), the slurry itself can generate about the same or even more
pressure on the wafer for enhanced erosion of material through its
magnetic coupling with the external magnetic field.
[0037] As stated above, the electromagnetic coil 118 (in addition
to being located within a structurally isolated housing) could also
being incorporated into the chuck 108 and/or polishing platen 102
as well. For example, FIGS. 3(a) and 3(b) illustrate a second
embodiment of a CMP apparatus 200 with magnetically spinning slurry
particles responsive to an alternating magnetic field. As
particularly shown in FIG. 3(b), the polishing platen 202 has a
coil housing 222 integrated into a non-rotating portion therein.
Thus, where the apparatus 200 provides for both a rotating
polishing pad and a rotating carrier head, the coil housing 222 may
be mechanically isolated from a rotating portion of the polishing
platen, as indicated by dashed line 214. The top view of FIG. 3(a)
depicts the relationship between the coil housing 222 of the chuck
202 with respect to the footprint of the carrier head 102,
generally indicated as 224. One skilled in the art will appreciate
that a variant of the second embodiment may be easily constructed
from FIGS. 3(a) and 3(b) where the coil housing is integrated in a
similar manner into the carrier head 102 instead of the integrating
it into the polishing platen as depicted in FIGS. 3(a) and
3(b).
[0038] While not explicitly shown in the figures, one skilled in
the art may easily construct another variant version of the second
embodiment wherein the radius of the polishing platen is greater
than the radius of the carrier head, and the two shafts for the
rotation of the polishing platen and carrier head are off axis as
described in FIG. 1(a) and FIG. 1(b).
[0039] Finally, FIGS. 4(a) and 4(b) illustrate a third embodiment
of a CMP apparatus 300 with magnetically spinning slurry particles
responsive to an alternating magnetic field. Whereas the
longitudinal axis of the coil 118 is along the axis of rotation of
the apparatus in FIGS. 2(a), 2(b), 3(a) and 3(b), the longitudinal
axis of the coil 302 is essentially orthogonal to the axis of
rotation of the apparatus 300. As further shown in FIGS. 4(a) and
4(b), the coil is wound around the entire CMP apparatus, which is
enclosed within a housing 304. The slurry particles 112 are still
caused to spin in accordance with an alternating magnetic field,
but the field in this embodiment alternates in and out of the page
from the perspective of FIG. 4(b), as opposed to in and out of the
page from the perspective of either FIG. 2(a) or FIG. 3(a). In
other words, the direction of the magnetic field is essentially
perpendicular to the surface of the substrate to be polished in the
first and second embodiments while the direction of the magnetic
field is essentially within the plane defined by the hypothetical,
ideally polished substrate. The footprint of the polishing head and
chuck with respect to the housing 304 is indicated at 306 in FIG.
4(a).
[0040] As with the first and second embodiments, one skilled in the
art can easily construct another variant version of the third
embodiment wherein the radius of the polishing platen is greater
than the radius of the carrier head and the two shafts for the
rotation of the polishing platen and carrier head are off axis as
described in FIG. 1(a) and FIG. 1(b).
[0041] While the invention has been described with reference to a
preferred embodiment or embodiments, it will be understood by those
skilled in the art that various changes may be made and equivalents
may be substituted for elements thereof without departing from the
scope of the invention. In addition, many modifications may be made
to adapt a particular situation or material to the teachings of the
invention without departing from the essential scope thereof.
Therefore, it is intended that the invention not be limited to the
particular embodiment disclosed as the best mode contemplated for
carrying out this invention, but that the invention will include
all embodiments falling within the scope of the appended
claims.
* * * * *