U.S. patent application number 11/012396 was filed with the patent office on 2006-06-15 for cmp pad having an overlapping stepped groove arrangement.
Invention is credited to Carolina L. Elmufdi, Gregory P. Muldowney.
Application Number | 20060128290 11/012396 |
Document ID | / |
Family ID | 36576370 |
Filed Date | 2006-06-15 |
United States Patent
Application |
20060128290 |
Kind Code |
A1 |
Elmufdi; Carolina L. ; et
al. |
June 15, 2006 |
CMP PAD HAVING AN OVERLAPPING STEPPED GROOVE ARRANGEMENT
Abstract
A polishing pad (104, 300) having an annular polishing track
(152, 320) and a plurality of groups (160, 308) of grooves (112,
304) repeated circumferentially about the rotational center (128)
of the pad. The plurality of grooves in each group are arranged
along a trajectory (164, 312) in an offset and overlapping manner
so as to provide a plurality of overlapping steps (172, 316) within
the annular polishing track. The groups may be arranged in
spaced-apart or nested relation with one another.
Inventors: |
Elmufdi; Carolina L.; (Glen
Mills, PA) ; Muldowney; Gregory P.; (Earleville,
MD) |
Correspondence
Address: |
Rohm and Haas Electronic Materials;CMP Holdings, Inc.
Suite 1300
1105 North Market Street
Wilmington
DE
19899
US
|
Family ID: |
36576370 |
Appl. No.: |
11/012396 |
Filed: |
December 14, 2004 |
Current U.S.
Class: |
451/527 |
Current CPC
Class: |
B24B 37/26 20130101 |
Class at
Publication: |
451/527 |
International
Class: |
B24D 11/00 20060101
B24D011/00 |
Claims
1. A polishing pad, comprising: a) a polishing layer configured to
polish a surface of at least one of a magnetic, optical or
semiconductor substrate in the presence of a polishing medium, the
polishing layer including a rotational axis and an annular
polishing track concentric with the rotational axis; and b) a
plurality of grooves formed in the polishing layer and arranged
into a plurality of groups of at least three grooves each along a
trajectory that extends through the annular polishing track,
wherein the at least three grooves of the plurality of grooves
within each group form an overlapping stepped pattern of at least
two overlapping steps within the annular polishing track for
forming a discontinuous flow path along the trajectory.
2. The polishing pad according to claim 1, wherein the plurality of
groups ae spaced from one another in a circumferential direction
about the rotational axis.
3. The polishing pad according to claim 1, wherein the plurality of
groups are nested with one another in a circumferential direction
about the rotational axis.
4. The polishing pad according to claim 1, wherein the annular
polishing track has a width and each groove in each of the
plurality of grooves has a length shorter than the width of the
annular polishing track.
5. The polishing pad according to claim 1, wherein the trajectory
of each of the plurality of groups is arcuate.
6. The polishing pad according to claim 5, wherein the polishing
pad has a design rotational direction and the trajectory of each of
the plurality of groups is curved in the design rotational
direction.
7. A polishing pad, comprising: a) a polishing layer configured to
polish a surface of at least one of a magnetic, optical or
semiconductor substrate in the presence of a polishing medium, the
polishing layer including a rotational axis and an annular
polishing track concentric with the rotational axis; and b) a
plurality of grooves formed in the polishing layer and arranged
into a plurality of groups of at least three grooves each along a
trajectory that extends through the annular polishing track,
wherein the at least three grooves (N.gtoreq.3) of the plurality of
grooves within each group form an overlapping stepped pattern of
N-1 steps within the annular polishing track for forming a
discontinuous flow path along the trajectory.
8. The polishing pad of claim 7, wherein ones of the plurality of
grooves within each group form at least two overlapping steps
within the annular polishing track.
9. The polishing pad of claim 7, wherein the pad further comprises
a peripheral edge and the annular polishing track includes an inner
circular boundary, the polishing layer further including a central
region defined by the inner circular boundary of the annular
polishing track, and a peripheral region located between the
annular polishing track and the peripheral edge of the pad, each of
the plurality of groups including an inner groove present only in
the central region and the annular polishing track and an outer
groove present only in the annular polishing track and the
peripheral region.
10. The polishing pad of claim 7, wherein the annular polishing
track has a width and each groove in each of the plurality of
grooves has a length shorter than the width of the annular
polishing track.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention generally relates to the field of
chemical mechanical polishing (CMP). In particular, the present
invention is directed to a CMP pad having an overlapping stepped
groove arrangement.
[0002] In the fabrication of integrated circuits and other
electronic devices, multiple layers of conducting, semiconducting
and dielectric materials are deposited onto and removed from a
surface of a semiconductor wafer. Thin layers of conducting,
semiconducting and dielectric materials may be deposited using a
number of deposition techniques. Common deposition techniques in
modern wafer processing include physical vapor deposition (PVD),
also known as sputtering, chemical vapor deposition (CVD),
plasma-enhanced chemical vapor deposition (PECVD) and
electrochemical plating, among others. Common removal techniques
include wet and dry isotropic and anisotropic etching, among
others.
[0003] As layers of materials are sequentially deposited and
removed, the uppermost surface of the wafer becomes non-planar.
Because subsequent semiconductor processing (e.g., metallization)
requires the wafer to have a flat surface, the wafer needs to be
planarized. Planarization is useful for removing undesired surface
topography and surface defects, such as rough surfaces,
agglomerated materials, crystal lattice damage, scratches and
contaminated layers or materials.
[0004] Chemical mechanical planarization, or chemical mechanical
polishing (CMP), is a common technique used to planarize workpieces
such as semiconductor wafers. In conventional CMP, a wafer carrier,
or polishing head, is mounted on a carrier assembly. The polishing
head holds the wafer and positions the wafer in contact with a
polishing layer of a polishing pad within a CMP apparatus. The
carrier assembly provides a controllable pressure between the wafer
and polishing pad. Simultaneously therewith, a slurry, or other
polishing medium, is flowed onto the polishing pad and into the gap
between the wafer and polishing layer. To effect polishing, the
polishing pad and wafer are moved, typically rotated, relative to
one another. The wafer surface is polished and made planar by
chemical and mechanical action of the polishing layer and polishing
medium on the surface. As the polishing pad rotates beneath the
wafer, the wafer sweeps out a typically annular polishing track, or
polishing region, wherein the wafer surface directly confronts the
polishing layer.
[0005] Important considerations in designing a polishing layer
include the distribution of polishing medium across the face of the
polishing layer, the flow of fresh polishing medium into the
polishing track, the flow of used polishing medium from the
polishing track and the amount of polishing medium that flows
through the polishing zone essentially unutilized, among others.
One way to address these considerations is to provide the polishing
layer with grooves. Over the years, quite a few different groove
patterns and configurations have been implemented. Conventional
groove patterns include radial, concentric-circular, Cartesian-grid
and spiral, among others. Conventional groove configurations
include configurations wherein the depth of all the grooves are
uniform among all grooves and configurations wherein the depth of
the grooves varies from one groove to another.
[0006] It is generally acknowledged among CMP practitioners that
certain groove patterns result in higher slurry consumption than
others to achieve comparable material removal rates. Circular
grooves, which do not connect to the peripheral edge of the
polishing layer, tend to consume less slurry than radial grooves,
which provide the shortest possible path for slurry to reach the
pad perimeter under the forces resulting from the rotation of the
pad. Cartesian grids of grooves, which provide paths of various
lengths to the peripheral edge of the polishing layer, hold an
intermediate position.
[0007] Various groove patterns have been disclosed in the prior art
that attempt to reduce slurry consumption and maximize slurry
retention time on the polishing layer. For example, U.S. Pat. No.
6,241,596 to Osterheld et al. discloses a rotational-type polishing
pad having grooves defining zigzag channels that generally radiate
outward from the center of the pad. In one embodiment, the
Osterheld et al. pad includes a rectangular "x-y" grid of grooves.
The zigzag channels are defined by blocking selected ones of the
intersections between the x- and y-direction grooves, while leaving
other intersections unblocked. In another embodiment, the Osterheld
et al. pad includes a plurality of discrete, generally radial
zigzag grooves. Generally, the zigzag channels defined within the
x-y grid of grooves or by the discrete zigzag grooves inhibit the
flow of slurry through the corresponding grooves, at least relative
to an unobstructed rectangular x-y grid of grooves and straight
radial grooves. Another prior art groove pattern that has been
described as providing increased slurry retention time is a spiral
groove pattern that is assumed to push slurry toward the center of
the polishing layer under the force of pad rotation.
[0008] Research and modeling of CMP to date, including
state-of-the-art computational fluid dynamics simulations, have
revealed that in networks of grooves having fixed or gradually
changing depth, a significant amount of polishing slurry may not
contact the wafer because the slurry in the deepest portion of each
groove flows under the wafer without contact. While grooves must be
provided with a minimum depth to reliably convey slurry as the
surface of the polishing layer wears down, any excess depth will
result in some of the slurry provided to polishing layer not being
utilized, since in conventional polishing layers an unbroken flow
path exists beneath the workpiece wherein the slurry flows without
participating in polishing. Accordingly, there is a need for a
polishing layer having grooves arranged in a manner that reduces
the amount of underutilization of slurry provided to the polishing
layer and, consequently, reduces the waste of slurry.
STATEMENT OF THE INVENTION
[0009] In one aspect of the invention, a polishing pad, comprising:
a) a polishing layer configured to polish a surface of at least one
of a magnetic, optical or semiconductor substrate in the presence
of a polishing medium, the polishing layer including a rotational
axis and an annular polishing track concentric with the rotational
axis; and b) a plurality of grooves formed in the polishing layer
and arranged into a plurality of groups each along a trajectory
that extends through the annular polishing track, wherein ones of
the plurality of grooves within each group form an overlapping
stepped pattern within the annular polishing track.
[0010] In another aspect of the invention, polishing pad,
comprising: a) a polishing layer configured to polish a surface of
at least one of a magnetic, optical or semiconductor substrate in
the presence of a polishing medium, the polishing layer including a
rotational axis and an annular polishing track concentric with the
rotational axis; and b) a plurality of grooves formed in the
polishing layer and arranged into a plurality of groups each along
a trajectory that extends through the annular polishing track,
wherein ones of the plurality of grooves within each group form at
least one overlapping step within the annular polishing track.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a partial perspective view of a chemical
mechanical polishing (CMP) system of the present invention;
[0012] FIG. 2A is a plan view of the polishing pad of FIG. 1 having
a plurality of overlapping stepped grooves arranged in groups that
are spaced from one another in a circumferential direction relative
to the pad; FIG. 2B is a plan view of the polishing pad of FIG. 2A
illustrating one of the spaced apart groups of grooves;
[0013] FIG. 3A is a plan view of an alternative polishing pad of
the present invention having a plurality of overlapping stepped
grooves arranged in groups that are nested with one another in a
circumferential direction relative to the pad; and FIG. 3B is a
plan view of the polishing pad of FIG. 3A illustrating one of the
nested groups of grooves and the nesting of the groups.
DETAILED DESCRIPTION OF THE INVENTION
[0014] Referring now to the drawings, FIG. 1 shows in accordance
with the present invention a chemical mechanical polishing (CMP)
system, which is generally denoted by the numeral 100. CMP system
100 includes a polishing pad 104 having a polishing layer 108 that
includes a plurality of grooves 112 arranged and configured for
improving the utilization of a polishing medium 116 applied to the
polishing pad during polishing of a semiconductor wafer 120 or
other workpiece, such as glass, silicon wafers and magnetic
information storage disks, among others. For convenience, the term
"wafer" is used in the description below. However, those skilled in
the art will appreciate that workpieces other than wafers are
within the scope of the present invention. Polishing pad 104 and
its unique features are described in detail below.
[0015] CMP system 100 may include a polishing platen 124 rotatable
about an axis 128 by a platen driver (not shown). Platen 124 may
have an upper surface on which polishing pad 104 is mounted. A
wafer carrier 132 rotatable about an axis 136 may be supported
above polishing layer 108. Wafer carrier 132 may have a lower
surface that engages wafer 120. Wafer 120 has a surface 140 that
confronts polishing layer 108 and is planarized during polishing.
Wafer carrier 132 may be supported by a carrier support assembly
(not shown) adapted to rotate wafer 120 and provide a downward
force F to press wafer surface 140 against polishing layer 108 so
that a desired pressure exists between the wafer surface and the
polishing layer during polishing.
[0016] CMP system 100 may also include a supply system 144 for
supplying polishing medium 116 to polishing layer 108. Supply
system 144 may include a reservoir (not shown), e.g., a temperature
controlled reservoir, that holds polishing medium 116. A conduit
148 may carry polishing medium 116 from the reservoir to a location
adjacent polishing pad 104 where the polishing medium is dispensed
onto polishing layer 108. A flow control valve (not shown) may be
used to control the dispensing of polishing medium 116 onto pad
104. During the polishing operation, the platen driver rotates
platen 124 and polishing pad 104 and the supply system 144 is
activated to dispense polishing medium 116 onto the rotating
polishing pad. Polishing medium 116 spreads out over polishing
layer 108 due to the rotation of polishing pad 104, including the
gap between wafer 120 and polishing pad 104. The wafer carrier 132
may be rotated at a selected speed, e.g., 0 rpm to 150 rpm, so that
wafer surface 140 moves relative to the polishing layer 108. The
wafer carrier 132 may also be controlled to provide a downward
force F so as to induce a desired pressure, e.g., 0 psi to 15 psi
(0 kPa to 103 kPa), between wafer 120 and polishing pad 104.
Polishing platen 124 is typically rotated at a speed of 0 to 150
rpm. As polishing pad 104 is rotated beneath wafer 120, surface 140
of the wafer sweeps out a typically annular wafer track, or
polishing track 152 on polishing layer 108.
[0017] It is noted that under certain circumstances polishing track
152 may not be strictly annular. For example, if surface 140 of
wafer 120 is longer in one dimension than another and the wafer and
polishing pad 104 are rotated at particular speeds such that these
dimensions are always oriented the same way at the same locations
on polishing layer 108, polishing track 152 would be generally
annular, but have a width that varies from the longer dimension to
the shorter dimension. A similar effect would occur at certain
rotational speeds if surface 140 of wafer 120 were bi-axially
symmetric, as with a circular or square shape, but the wafer is
mounted off-center relative to the rotational center of that
surface. Yet another example of when polishing track 152 would not
be entirely annular is when wafer 120 is oscillated in a plane
parallel to polishing layer 108 and polishing pad 104 is rotated at
a speed such that the location of the wafer due to the oscillation
relative to the polishing layer is the same on each revolution of
the pad. In all of these cases, which are typically exceptional,
polishing track 152 is still annular in nature, such that they are
considered to fall within the coverage of the term "annular" as
this term is used in the appended claims.
[0018] FIGS. 2A and 2B illustrate polishing pad 104 of FIG. 1 in
more detail than FIG. 1. Referring to both FIGS. 2A and 2B, grooves
112 are generally arranged into a plurality of groups 160 that are
distributed in a generally radial manner around rotational axis 128
of polishing pad 104 and are preferably, but not necessarily,
identical to one another. Each group 160 may contain a number N of
grooves 112, wherein N.gtoreq.2. In the present example, each group
160 contains four grooves 112, i.e., N=4. Grooves 112 within each
group 160 are arranged and configured so as to define what may be
described as an "overlapping stepped arrangement" that generally
lies along a trajectory 164. Each groove 112 within a group 160 may
be considered to have a radially inward end 166 and a radially
outward end 168. Consequently, the "overlapping" portion of the
foregoing description refers to the radially inward and radially
outward ends 166, 168 of immediately adjacent grooves 112 being
spaced from one another in a circumferential direction 170 relative
to polishing pad 104 along a nonzero overlap length L. The
"stepped" portion of the foregoing description refers to adjacent
ones of overlapping grooves 112 in each group 160 being spaced, or
offset, from one another by a distance D so as to generally form a
discontinuous polishing medium flow path along trajectory 164. When
traversing each trajectory 164 from one of its ends to the other,
each offset encountered generally has the appearance of a stair
step. Therefore, each of these offsets may be considered to define
a step and, more particularly, an overlapping step 172 having
overlap length L.
[0019] As mentioned above, grooves 112 in each group 160 may be
provided in any number N.gtoreq.2. Consequently, each group 160
will have N-1 overlapping steps 172. For the reasons discussed
immediately below, all overlapping steps 172 should be located
within polishing track 152. Generally, a primary concept underlying
groups 160 is to provide a segmented pathway for a polishing medium
to flow within polishing track 152. When a polishing medium is
present within one of grooves 112, it typically flows within that
groove under the influence of centrifugal force as polishing pad
104 is rotated during polishing. However, the polishing medium
tends to not flow from one groove 112 to an adjacent groove across
the land region 174 therebetween under the influence of this
centrifugal force. Rather, the polishing medium is generally moved
from one groove 112 to a next adjacent groove across land region
174 primarily by the interaction of wafer 120 with the polishing
medium on polishing layer 108 as the wafer is rotated, or rotated
and oscillated, in confrontation with polishing pad 104.
[0020] By providing groups 160 of discontinuous grooves 112, the
polishing medium can be utilized more efficiently than in
conventional polishing pads (not shown) having continuous grooves
extending through their polishing tracks. Generally, this is so,
because the polishing medium advances toward the peripheral edge
176 of polishing pad 104 from one groove 112 to another groove 112
substantially only when wafer 120 is present to move the polishing
medium across the land regions 174. This is in contrast to the
typical situation with continuous grooves (not shown) in which the
polishing medium advances toward the peripheral edge of the
polishing pad even when the wafer is not present simply due to the
rotation of the polishing pad.
[0021] When each group 160 has three or more grooves 112 and,
correspondingly, two or more overlapping steps 172 are located
within polishing track 152, each of a number N-2 of the grooves
will typically have a straight-line end-to-end distance S (i.e.,
distance along a straight line connecting endpoints 166, 168 of the
groove under consideration) less than the width W of polishing
track 152. In exemplary polishing pad 104, the four grooves 112 in
each group 160 provide three overlapping steps 172 located entirely
within polishing track 152. Consequently, two of the four grooves
112 in each group 160 have straight-line distances S shorter than
width W of polishing track 152. In fact, in this example, all four
grooves 112 within each group 160 have straight-line distances S
shorter than width W. It is noted that the relationship S<W will
not hold true for every design. For example, for N=3 with two
overlapping steps 172 within polishing track 152, straight-line
distance S may be equal to or greater than width W, particularly
when trajectory 164 has a relatively large circumferential
component within the polishing track.
[0022] Polishing track 152 will typically have a generally circular
inner boundary 180 spaced from rotational axis 128 of polishing pad
104 and a generally circular outer boundary 184 proximate to, but
spaced from peripheral edge 176 of the pad. Inner boundary 180
typically, but not necessarily, defines a central region 188 of
polishing layer 108. Likewise, outer boundary 184 and peripheral
edge 176 typically define a peripheral region 190. It is noted that
one, the other, or both, of central region 188 and peripheral
region 190 may not be present. Central region 188 would not be
present if inner boundary 180 were coincident with rotational axis
128 of polishing pad 104 or the rotational axis were contained in
polishing track 152. Peripheral region 190 would not be present if
outer boundary 184 were coincident with peripheral edge 176.
[0023] In a CMP system that utilizes polishing pad 104 having
central region 188 and that provides a polishing medium to the pad
in the central region, such as CMP system 100 of FIG. 1, each group
160 of grooves 112 may include a radially innermost groove 192 that
extends from the central region into polishing track 152. In this
manner, grooves 192 can assist in moving the polishing medium from
central region 188 into polishing track 152 during polishing. As
mentioned above, the polishing medium will tend to flow within
grooves 112, including grooves 192, even when wafer 120 is not
present. When grooves 192 are largely radial, the centrifugal
forces caused by rotating polishing pad 104 at a constant speed
will tend to cause the polishing medium within these grooves to
flow toward peripheral edge 176 of the pad.
[0024] When polishing pad 104 includes peripheral region 190, each
group 160 of grooves 112 may contain a radially outermost groove
194 that is present in both polishing track 152 and the peripheral
region. Depending on their orientation relative to the rotational
direction of polishing pad 104, grooves 194 tend to assist in the
transport of the polishing medium out of polishing track 152. Some,
none, or all of radially outermost grooves 194 may extend to
peripheral edge 176, depending upon a particular design. Extending
outermost grooves 194 to peripheral edge 176 tends to move a
polishing medium out of peripheral region 190 and off of polishing
pad 104 at a rate higher than would occur if these grooves were
terminated short of the peripheral edge. For certain orientations,
this is so due to the tendency of the polishing medium to flow
within grooves 194 under the influence of the rotation of polishing
pad 104.
[0025] Trajectory 164 of each group 160 may generally have any
shape desired, such as the arcuate shape shown, any arcuate shape
having a greater or lesser curvature than the curvature shown or a
curvature in the opposite direction from the direction shown,
straight, either in a radial direction or angled thereto, or a wavy
or zigzag shape, among others. Groups 160 may be spaced from one
another in circumferential direction 170 as shown or,
alternatively, may be nested with one another as illustrated in
FIG. 3A as described below. Generally, one group 160 is
"spaced-apart" relative to an immediately adjacent group if an
intermediate line 196 having the same character as trajectory 164
can be drawn midway between the trajectories of the two groups and
all grooves 112 of one group lie on one side of the intermediate
line and all grooves of the other group lie on the other side of
the intermediate line.
[0026] FIGS. 3A and 3B illustrate an alternative polishing pad 300
of the present invention that may be used with a CMP system, such
as CMP system 100 of FIG. 1. As best seen in FIG. 3B, a basic
construct of polishing pad 300 is the arrangement of grooves 304
into a plurality of overlapping stepped groups 308 generally
parallel to trajectories 312 in a manner virtually identical to the
manner grooves 112 of polishing pad 104 of FIGS. 2A and 2B are
arranged in groups 160 along corresponding trajectories 164. For a
detailed description of the arrangement of grooves 304 within each
group 308 of FIGS. 3A and 3B, the foregoing description of the
arrangement of grooves 112 with each group 160 of FIGS. 2A and 2B
may be used by analogy. In exemplary polishing pad 300 of FIGS. 3A
and 3B, each group 308 contains six grooves 304 that provide five
overlapping steps 316 generally parallel to trajectory 312 within
annular polishing region 320. The overlapping stepped arrangement
of grooves 304 provides functionality similar to the functionality
of the groove arrangement described above in connection with FIGS.
2A and 2B. Like groups 160 of FIGS. 2A and 2B, groups 308 of FIGS.
3A and 3B may contain any number N of grooves 304 and a
corresponding number N-1 of overlapping steps 316. Likewise,
trajectories 312 of groups 308 may have any of the shapes described
above relative to the trajectories 164 of FIG. 2B. Also, at least
the N-2 grooves 304 contained entirely within polishing track 320
may each have a straight-line distance S' less than width W' of
polishing track 320.
[0027] Whereas groups 160 of grooves 112 in FIG. 2A are considered
to be spaced-apart from immediately adjacent groups, groups 308 of
FIG. 3A are considered to be nested with adjacent groups. The
nesting of groups 308 is best seen in connection with groups
G.sub.1, G.sub.2, G.sub.3 and G.sub.n of FIG. 3B that are
particularly enumerated as such for convenience of illustration.
Group G.sub.1 contains six grooves G.sub.11, G.sub.12, G.sub.13,
G.sub.14, G.sub.15, G.sub.16. Similarly, groups G.sub.2 and G.sub.3
contains grooves G.sub.21, G.sub.22, G.sub.23, G.sub.24, G.sub.25,
G.sub.26 and grooves G.sub.31, G.sub.32, G.sub.33, G.sub.34,
G.sub.35, G.sub.36, respectively. In a broad sense, the "nesting"
of adjacent groups 308 means that an intermediate line (not shown,
but similar to intermediate line 196 of FIG. 2A) having the same
character as trajectories 312 that lies midway between two adjacent
trajectories does not divide one group from another. Rather,
grooves 304 from each of the two adjacent groups 308, and perhaps
even grooves from other groups, lie on both sides of the
intermediate line. In a particular implementation of nested groups
308, certain ones of grooves 304 from one group are located so that
they align with certain grooves in other groups. This is shown in
FIG. 3A and particularly illustrated in FIG. 3B in connection with
groups G.sub.1, G.sub.2, G.sub.3 and G.sub.n. That said, it is
noted that nesting does not necessarily require that grooves 304 of
group 308 align with any of the grooves of another group.
[0028] Referring particularly to FIG. 3B, it is seen that when
group G.sub.2 is nested with group G.sub.1, groove G.sub.23 of
group G.sub.2 aligns with groove G.sub.11 of group G.sub.1.
Similarly, groove G.sub.24 of group G.sub.2 aligns with groove
G.sub.12 of group G.sub.1. Then, when group G.sub.3 is nested with
groups G.sub.2, and G.sub.1, groove G.sub.36 of group G.sub.3
aligns with grooves G.sub.24 and G.sub.12 of groups G.sub.2 and
G.sub.1, respectively. Similarly, groove G.sub.35 of group G.sub.3
aligns with grooves G.sub.23 and G.sub.11 of groups G.sub.2 and
G.sub.1, respectively. This nesting progresses in circumferential
direction 324 until group G.sub.n ultimately nests with group
G.sub.1 when groove G.sub.n1 aligns with groove G.sub.13, groove
G.sub.n2 aligns with groove G.sub.14, groove G.sub.n3 aligns with
groove G.sub.15 and groove G.sub.n4 aligns with groove G.sub.16.
The nesting provided by the arrangement of grooves G.sub.n1-6 shown
in FIG. 3B enhances slurry movement under the wafer by creating
multiple series and parallel paths for slurry to migrate from one
groove to an adjacent groove, allowing the slurry to advance across
land areas both along a stepped path provided by one group of
grooves and along the smooth segmented path provided collectively
by the ones of the grooves in adjacent nested groups that are
aligned with one another.
* * * * *