U.S. patent application number 11/546366 was filed with the patent office on 2007-02-08 for polishing pad and method of fabricating semiconductor substrate using the pad.
This patent application is currently assigned to TOHO ENGINEERING KABUSHIKI KAISHA. Invention is credited to Tatsutoshi Suzuki.
Application Number | 20070032182 11/546366 |
Document ID | / |
Family ID | 28677621 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070032182 |
Kind Code |
A1 |
Suzuki; Tatsutoshi |
February 8, 2007 |
Polishing pad and method of fabricating semiconductor substrate
using the pad
Abstract
It is provided a polishing pad of novel construction capable of
controlling actively and efficiently a slurry flow during polishing
a surface of a semiconductor substrate, such as a wafer, thus
making it possible to precisely and stably performing a desired
polishing process. Onto a surface of a pad substrate 12 of
synthetic resin material, formed is a groove 16 extending
approximately circumferentially. An inner circumferential wall
surface 20 and an outer circumferential wall surface 22 are made
parallel to each other and slant with respect to a center axis 18
of the pad substrate 12.
Inventors: |
Suzuki; Tatsutoshi;
(Yokkaichi-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
TOHO ENGINEERING KABUSHIKI
KAISHA
YOKKAICHI-SHI
JP
|
Family ID: |
28677621 |
Appl. No.: |
11/546366 |
Filed: |
October 12, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10482740 |
Jan 5, 2004 |
7121938 |
|
|
PCT/JP03/04189 |
Apr 1, 2003 |
|
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11546366 |
Oct 12, 2006 |
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Current U.S.
Class: |
451/527 |
Current CPC
Class: |
B24B 37/26 20130101;
B24D 3/28 20130101 |
Class at
Publication: |
451/527 |
International
Class: |
B24D 11/00 20060101
B24D011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 3, 2002 |
JP |
2002-101945 |
Dec 27, 2002 |
JP |
2002-378965 |
Claims
1. A polishing pad for use in polishing a semiconductor substrate,
comprising: a pad substrate of synthetic resin; and at least one
groove formed in a surface of said pad substrate; wherein: said
groove is at least partially constituted of a slant groove having
two side walls that slant substantially parallel to each other in a
depthwise direction with respect to a center axis of said pad
substrate.
2. A method of producing a polishing pad comprising the step of
cutting into a surface of a pad substrate of synthetic resin a
slant groove having two substantially parallel side walls slant in
a depthwise direction with respect to a center axis of said pad
substrate, with a cutting tool having a cutting part to be placed
in contact on an incline against said surface of said pad substrate
at side faces thereof.
3. A method of producing a polishing pad according to claim 2,
further comprising the step of turning said slant groove so as to
extend substantially circumferentially with said cutting tool
placed against said surface of said pad substrate, while rotating
said pad substrate of synthetic resin about a center axis
thereof.
4. A method of producing a polishing pad according to claim 2,
further comprising the step of cutting said slant groove by
gradually advancing said cutting part of said cutting tool in a
direction of incline against said surface of said pad substrate,
while subjecting a groove producing location on said surface of
said pad substrate to a plurality of repeated cutting cycles.
5. A method of producing a polishing pad according to claim 2,
further comprising the steps of: blowing ionized air from a back of
said cutting part during cutting by said cutting tool said slant
groove into said pad substrate in order to prevent chips from being
charged; and suctioning and collecting said chips forwarded to a
front of said cutting part therefrom.
6. A method of producing a polishing pad according to claim 5,
wherein said ionized air is blown with a slant angle approximately
equal to that of the slant groove.
7. A method of producing a polishing pad according to claim 5,
further comprising the steps of: cutting simultaneously a plurality
of said slant grooves by means of a multi edged tool in which a
plurality of said cutting parts are arranged in series with respect
to a cutting direction; and blowing said ionized air from a back
toward a front of said multi edged tool through gaps between said
plurality of said cutting parts.
Description
TECHNICAL FIELD
[0001] The present invention relates to a polishing pad for use in
a semiconductor fabrication process, for polishing a surface of a
semiconductor substrate, e.g., a semiconductor wafer or a
semiconductor device. The present invention also relates to
techniques associated with the polishing pad, e.g., a method of
fabricating a semiconductor substrate using the polishing pad.
BACKGROUND ART
[0002] In the process of fabricating semiconductor devices such as
LSI devices, conventionally, a lamination of various kinds of thin
layers including metallic layers and insulative layers are formed
on a silicon wafer, for example, through various processing steps.
As one major for polishing or planarizing an outer or upper most
surface of the wafer to obtain a substrate surface having a high
degree of planarity, chemical mechanical polishing (hereinafter
referred to as "CMP") is known, wherein a thin disk-shaped
polishing pad of synthetic resin material or expanded material
thereof may be employed, and the polishing pad and the wafer
(semiconductor substrate) are made to undergo relative rotation
while supplying between the wafer and the pad a slurry consisting
of fine abrasive particles and a suitable kind of liquid, for
effect polishing.
[0003] In order to meet a great demand for a highly integrated,
high-precision semiconductor device, it is required to produce
multiple layers of intricate patterns of extremely fine lines. To
meet this end, the CMP process is required to ensure (a) "polishing
precision", i.e. the ability to polish an entire wafer surface with
highly precise planarization, and (b) "polishing efficiency", i.e.
the ability to polish a wafer with high process efficiency. Higher
circuit densities seen in semiconductor devices in recent years
have raised the bar still further as regards these two
capabilities.
[0004] To meet such requirements, there has been proposed polishing
pads for use in CMP processes, in which the surface of the
polishing pad (i.e. the surface which polishes the wafer) is
provided with a multitude of tiny holes, or with linearly extending
grooves or radially extending grooves. Pads of this kind are
disclosed in Patent Document Nos. 1, 2, 3, for example.
[0005] However, notwithstanding the use of these polishing pads of
conventional design, it is still exceedingly difficult to achieve
both "polishing precision" and "polishing efficiency" at levels
adequate to meet requirements. In the field of super LSI in
particular, metallic interconnect or metallization width of lines
formed on the wafer (line patterns with metal line) is extremely
narrow, i.e., 0.18 .mu.m or smaller, and accordingly the surface
must be polished to a very low degree of surface roughness (Rz),
i.e. 0.25 .mu.m or smaller. Also, the use of recently soft metal
such as cooper and gold for metallization has entered the stage of
research directed to practical application. In view of the above,
still further improvements are required to polishing pads in order
to achieve satisfactory levels of polishing precision and polishing
efficiency.
[0006] As one measures for improving polishing precision in CMP
processes, Patent Document No. 4 teaches a polishing pad having
grooves that, viewed in cross section, expand in dimension toward
the pad surface. According to Patent Document No. 4, the slant side
wall of the groove guides the slurry and polishing residues, thus
improving polishing precision.
[0007] However, research conducted by the inventors has revealed
that when grooves like those taught in Patent Document No. 4 are
formed on a polishing pad surface, polishing performance, which
includes both polishing efficiency and polishing precision is
inconsistent. Therefore, practical use would be extremely
difficult. It is thought that the major reason for this drawback is
the variation in the width dimension of the groove in its depthwise
direction.
[0008] In addition to wear produced in wafer polishing, a polishing
pad is typically subjected to a conditioning process (dressing) by
means of abrading the pad surface at predetermined process time
intervals. However, the grooves taught in Patent Document No. 4
unavoidably experience appreciable change in groove width due to
polishing-induced wear and surface conditioning, and this is
accompanied by significant variation in parameters such as the
distribution of stress. Thus, consistent polishing characteristics
may be not achieved.
(Patent Document No. 1)
[0009] U.S. Pat. No. 5,921,855
(Patent Document No. 2)
[0010] U.S. Pat. No. 5,984,769
(Patent Document No. 3)
[0011] U.S. Pat. No. 6,364,749
(Patent Document No. 4)
[0012] U.S. Pat. No. 6,238,271
DISCLOSURE OF INVENTION
[0013] The present invention has been developed in order to solve
the above-described problems, and it is therefore one object of
this invention to provide a polishing pad of novel construction
whereby the surface of a semiconductor substrate or similar
material can be processed with consistently high levels of
"polishing precision" and "polishing efficiency" using a CMP or
similar process.
[0014] It is another object of the present invention to provide a
novel semiconductor substrate fabrication method employing a
polishing pad, whereby in a semiconductor fabrication process
employing a suitable method such as CMP for polishing the substrate
surface, the object semiconductor substrate may be fabricated with
consistently high levels of "precision" and "efficiency".
[0015] It is yet another object of the present invention to provide
a cutting tool for machining a groove in a polishing pad, which is
capable of producing a polishing pad of novel construction
pertaining to the invention, and a useful production method for the
polishing pad.
[0016] There will be described modes of the invention that have
been developed in an effort to achieve at least one of these
objects of the invention. Every elements employed in the following
modes may be adoptable in any other possible combinations. It is to
be understood that principle or technical features of the invention
are not limited to the following modes of the invention and
combinations of the technical features, but may otherwise be
recognized based on the concepts of the present invention disclosed
in the entire specification and drawings or that may be recognized
by those skilled in the art in the light of the present
disclosure.
(First Mode of the Invention Relating to Polishing Pad)
[0017] A first mode of the invention relating to a polishing pad
provides a polishing pad for use in polishing a semiconductor
substrate, wherein a pad substrate of synthetic resin has at least
one groove formed in a surface thereof, characterized in that the
groove is at least partially constituted of a slant groove having
two side walls that are slant substantially parallel to each other
in a depthwise direction with respect to an center axis of the pad
substrate.
[0018] According to the present invention, the use of the slant
groove having slant side walls permits that centrifugal force
created by rotation of the polishing pad actively acts as a
component force corresponding to the slant angle of the slant
groove on slurry and other material presented in the groove. This
makes it possible to control the flow state of slurry and other
material present between the polishing pad and the wafer or other
semiconductor substrate. In polishing processes such as CMP that
employ specific slurries, a chemical polishing action plays a
significant role in addition to simple mechanical polishing.
Namely, movement of the slurry abrasive grains between the wafer
and polishing pad has a significant effect on the precision and
consistency of polishing. According to the present invention, it is
therefore possible to appropriately establish and adjust polishing
performance, depending upon the polishing pad material or degree of
precision required, for example, by suitably controlling movement
of slurry abrasive grains between the wafer and pad during
polishing, through suitable adjustment of the direction and angle
of incline of the slant groove. Alternatively, through proper
adjustment of the direction and angle of slant of the slant groove,
it is possible to minimize the adverse effects of polishing
residues and other contaminants produced during polishing, as well
as to induce polishing residues or other material entering the
slant groove during polishing to be actively detained within the
slant groove, or conversely to be actively swept out from the slant
groove, through centrifugal action, thereby further improving
consistency in polishing precision.
[0019] According to the polishing pad of this mode, it is
additionally possible to design the groove including the slant
groove with essentially constant width dimension across its
depthwise direction. Thus, if the depth of the groove should change
due to wear of the polishing pad in the course of polishing, or to
dressing of the polishing pad surface, the groove width will
maintained substantially constant so that the desired polishing
performance, including polishing efficiency and polishing
precision, are maintained.
[0020] In the present mode, the material for the pad substrate is
not particularly limited, it being possible to employ appropriately
any number of materials selected with reference to the article
being polished, required polishing parameters, and the like.
Favorable are rigid materials such as expanded or unexpanded
polyurethane resin for use. The polishing pad constructed according
to the present invention may be used for polishing by securing to a
rotating support plate by conventional methods, naturally, the
method of securing to the support plate is not particularly
limited, it being possible to secure the pad juxtaposed directly
onto a support plate of rigid material such as metal, or to secure
it on the support face of the support plate via a suitable
resilient pad.
(Second Mode of the Invention Relating to Polishing Pad)
[0021] A second mode of the invention relating to a polishing pad
provides a polishing pad according to the first mode, wherein the
slant groove is constituted by a circumferential groove extending
substantially in a circumferential direction about the center axis
of the pad substrate. In this mode, the circumferential groove
arrangement for the slant groove further enhances the effect on
slurry and polishing residues present in the slant groove by the
centrifugal force generated through rotation of the polishing pad
about its center axis of rotation.
(Third Mode of the Invention Relating to Polishing Pad)
[0022] A third mode of the invention relating to a polishing pad
provides a polishing pad according to the second mode, wherein the
two side walls of said circumferential groove slant outwardly in
the depthwise direction toward an opening, in a diametrical
direction of the pad substrate. The polishing pad according to this
mode is able to actively cause flow of slurry, polishing residues
and the like present in the slant groove in a direction out from
the slant groove, thereby promoting circulation of slurry supplied
to between the polishing pad and wafer from the central portion of
the polishing pad, and more effectively preventing clogging of the
slant groove due to intrusion of polishing residues, for
example.
(Fourth Mode of the Invention Relating to Polishing Pad)
[0023] A fourth mode of the invention relating to a polishing pad
provides a polishing pad according to the second or third mode,
wherein the circumferential groove is formed in multiple segments
spaced apart at intervals on a diametric line of said pad
substrate, and an slant angle of the two side walls of the
circumferential groove varies depending on a diametric distance
away from the center axis of the pad substrate. The polishing pad
according to this mode enables more varied control of the flow of
slurry etc. across the diameter of the polishing pad. In view of
the fact that consideration the fact that centrifugal force acting
on slurry in the slant groove changes according to the diametric
distance away from the center axis of the pad substrate, it is
possible, by varying gradually or in stepwise fashion the slant
angle of the slant groove side walls, to maintain throughout the
polishing pad as constant a level of centrifugal force as possible
on the slurry in the slant groove over a wide area of the polishing
pad, for example.
(Fifth Mode of the Invention Relating to Polishing Pad)
[0024] A fifth mode of the invention relating to a polishing pad
provides a polishing pad according to any one of first to fourth
modes, wherein the slant groove comprises a plurality of linear
grooves each extending linearly. In the polishing pad according to
this mode as well, slurry or polishing residues present within the
slant grooves can be actively caused to flow or be retained through
the action of centrifugal force produced by rotation of the
polishing pad about its center axis. Also, the flow of slurry etc.
can be controlled through the position and number of slant grooves,
in addition to the slant angle thereof. By combining this mode with
any of the first to fourth modes, combinations of both
circumferential grooves and linear grooves can be produced on the
surface of a single polishing pad.
(Sixth Mode of the Invention Relating to Polishing Pad)
[0025] A sixth mode of the invention relating to a polishing pad
provides a polishing pad according to fifth mode, wherein the
linear grooves are formed as a plurality of groove groupings each
consisting of mutually parallel grooves, with the groove groupings
arranged intersecting one another in a substantially reticulated
arrangement. In the polishing pad according to this mode, the use
of the plurality of groove groupings permits substantially uniform
action of the linear grooves over the entire polishing face of the
polishing pad, thereby affording greater consistency in polishing
precision and polishing efficiency.
(Seventh Mode of the Invention Relating to Polishing Pad)
[0026] A seventh mode of the invention relating to a polishing pad
provides a polishing pad according to sixth mode, wherein the
plurality of the linear grooves making up each of the groove
groupings have placement and incline direction that are
substantially symmetrical to one another to either side of a single
plane that contains the center axis of the pad substrate and
extends parallel to the plurality of linear grooves. In the
polishing pad according to this mode, linear grooves can be made to
produce more uniform action over the polishing face of the
polishing pad. Preferably, the linear grooves extending at
locations diametrically intersection the center axis of the
polishing pad are arranged to be grooves having side walls that
rise parallel to the center axis of the pad substrate.
(Eighth Mode of the Invention Relating to Polishing Pad)
[0027] An eighth mode of the invention relating to a polishing pad
provides a polishing pad according to any one of first to seventh
modes, wherein said slant groove measures 0.005-2.0 mm in width
dimension. In this mode, the slant groove width dimension is made
sufficiently small, making it possible to achieve a high degree of
polishing precision. In this regard, since the side walls of the
slant groove incline, problems tending to occur as a result of the
small-width slant groove, such as retaining of slurry within the
groove or clogging of the groove by polishing residues, can be
effectively avoided, thereby effectively and consistently providing
the desired degree of polishing precision.
[0028] Groove depth dimension and diametric pitch are not
particularly limited, and may be selected appropriately with
reference to the material of the polishing pad, the material being
polished, properties of the slurry being used, the required degree
of polishing precision, and other parameters. The groove depth
dimension is typically 0.1-2.0 mm, and particularly in the case of
substantially circular grooves extending in the circumferential
direction, the slant grooves will be formed substantially parallel
at intervals of 0.1-3.0 mm apart. In the case of linear grooves,
even if grooves are spaced widely away from one another, localized
action on an article being polished due to rotation of the
polishing pad is less intense than with circular grooves extending
in the circumferential direction. Therefore, it is a simple matter
to achieve good polishing characteristics even with larger groove
spacing, which preferably may be appropriately set within a wide
range of 0.1 to 60.0 mm, for example.
(Ninth Mode of the Invention Relating to Polishing Pad)
[0029] A ninth mode of the first aspect of the invention provides a
polishing pad according to any one of first to eighth modes,
wherein the slant groove is provided with a groove dimensional
error of 5% or smaller. According to this mode, the slant groove is
formed with a dimensional accuracy enhanced to a predetermined
value, permitting the polishing pad to polish a semiconductor
substrate with minimized variation in polishing pressure exerted
through the polishing pad on the semiconductor substrate. For
instance, the polishing pad according to this mode is capable of
minimizing variation in polishing pressure to a theoretical target
value, e.g., in an order of 2% or smaller. By the term "groove
dimensional error", meant is not only a groove width, but also a
groove pitch and a groove depth.
(First Mode of the Invention Relating to Method of Fabricating
Semiconductor Substrate)
[0030] A first mode of the invention relating to a method of
fabricating a semiconductor substrate provides a method of
fabricating a semiconductor substrate characterized by the step of
polishing a semiconductor substrate using a polishing pad with a
slant groove constructed according to the present invention
relating to a polishing pad described hereinabove. According to the
method herein, movement of the abrasive particles of a slurry
between the semiconductor substrate and polishing pad can be
controlled by the action of slant grooves like those described
previously formed on the polishing pad surface, on the basis of the
slant groove slant angle, polishing pad rotation speed, and the
like. This enables the target semiconductor substrate to be
fabricated with excellent polishing precision and polishing
efficiency. According to the method herein, semiconductor
substrates having line patterns with metal line widths of not
greater than 0.18 .mu.m can be polished effectively.
(Second Mode of the Invention Relating to Method of Fabricating
Semiconductor Substrate)
[0031] A second mode of the invention relating to a method of
fabricating a semiconductor substrate provides a semiconductor
fabricating method according to first mode, characterized by the
step of polishing the semiconductor substrate under a polishing
pressure whose variation is held in an order of 2% or smaller.
According to this method, since the polishing pressure variation is
in the order of 2% or smaller, semiconductors of ongoing designs
can be fabricated with excellent yield. In particular, the present
method can be advantageously effected by using a polishing pad of
construction according to the ninth mode of the invention relating
to the polishing pad described hereinabove.
(First Mode of the Invention Relating to Polishing Pad Producing
Method)
[0032] A first mode of the invention relating to a polishing pad
producing method provides a method of producing a polishing pad
characterized by the step of cutting into a surface of a pad
substrate of synthetic resin a slant groove having two
substantially parallel side walls slant in a depthwise direction
with respect to a center axis of the pad substrate, with a cutting
tool having a cutting part to be placed in contact on an incline
against the surface of the pad substrate at side faces thereof.
According to the method of this mode, it is easier to produce the
slant groove on the polishing pad surface than would be the case
with, for example, groove machining using a rotary tool, thereby
affording efficient manufacture of a polishing pad with a slant
groove, and having a construction according to the invention
described hereinabove.
(Second Mode of the Invention Relating to Polishing Pad Producing
Method)
[0033] A second mode of the invention relating to a polishing pad
producing method provides a method of producing a polishing pad
according to the first mode herein, characterized by the step of
turning the slant groove so as to extend substantially
circumferentially with the cutting tool placed against the surface
of the pad substrate, while rotating the pad substrate of synthetic
resin about a center axis thereof. According to the method of this
mode, it is a simple matter to produce a plurality of slant grooves
of circular, elliptical or petal shape as disclosed in FIG. 13 of
U.S. Pat. No. 5,984,769, extending concentrically along the
circumference of the polishing pad, or a slant groove extending in
spiral configuration.
(Third Mode of the Invention Relating to Polishing Pad Producing
Method)
[0034] A third mode of the invention relating to a polishing pad
producing method provides a method of producing a polishing pad
according to the first or second mode herein, characterized by the
step of cutting the slant groove by gradually advancing the cutting
part of the cutting tool in a direction of incline against the
surface of the pad substrate, while subjecting a groove producing
location on the surface of the pad substrate to a plurality of
repeated cutting cycles. According to the method of this mode, the
slant groove having smooth inner surfaces can be produced
consistently, enabling the desired slant groove to be formed with
sufficiently small groove width. Where the slant groove being
produced is a linear groove, spiral groove, or other such finite
shape, when performing a plurality of cutting cycles in one
direction or in a reciprocating manner, it is preferable to
increase blade projection stepwise in small increments. More
specifically described, the blade projection may be increased in a
regular increment for each reciprocating cycle, or alternatively
may be increased irregularly in appropriate amounts, for example.
On the other hand, where the slant groove being produced is an
endless shape such as circumferential groove, when performing a
plurality of cutting cycles continuously on a single circuit, the
blade projection may be increased either stepwise in small
increments for each full circuit, or continuously regardless of the
circuit.
(Fourth Mode of the Invention Relating to Polishing Pad Producing
Method)
[0035] A fourth mode of the invention relating to a polishing pad
producing method provides a method of producing a polishing pad
according to any one of first to third modes herein, characterized
by the steps of: blowing ionized air from a back of the cutting
part during cutting by the cutting tool the slant groove into the
pad substrate in order to prevent chips from being charged; and
suctioning and collecting the chips forwarded to a front of the
cutting part therefrom. According to the pad producing method of
this mode, ions, which are adapted to neutralize static electricity
charged in the pad substrate and cut-parts (chips) due to friction
during cutting, are discharged together with compression air toward
the pad substrate from the vicinity of the cutting part of the
cutting tool, thereby preventing the chips from being adhered to
the inside of grooves cut. In addition, the chips neutralized by
the ions and left on the surface of the pad substrate can be
promptly suctioned and removed from the surface of the pad
substrate. The method of this mode can eliminate drawbacks such as
excessively large cutting at walls of the slant groove, which may
be caused by chips adhered to walls or other parts of the slant
groove. This method therefore makes it possible to form onto the
pad substrate the slant groove or the like with high dimensional
accuracy. In this regards, blowing of ionized air and suctioning
and collecting the chips can be effectively performed by means of
known air blowers for use in neutralizing static electrical charge
utilizing Corona Discharge, and known dust collectors or the like,
respectively. Preferably, the ionized air may be blown with a slant
angle approximately equal to that of the slant groove. Hence ions
can be effectively applied even to the inner circumferential
surface and the floor of the slant groove, which provide undercut
formations with respect to the surface of the pad substrate, thus
making it possible to suction and collect the chips adhered to
these inner circumferential surfaces and floor of the slant
groove.
(Fifth Mode of the Invention Relating to Polishing Pad Producing
Method)
[0036] A fifth mode of the invention relating to a polishing pad
producing method provides a method of producing a polishing pad
according to any one of first to fourth modes herein, characterized
by the steps of: cutting simultaneously a plurality of the slant
grooves by means of a multi edged tool in which a plurality of the
cutting parts are arranged in series with respect to a cutting
direction; and blowing the ionized air from a back toward a front
of the multi edged tool through gaps between the plurality of the
cutting parts. According to the method of this mode, the chips can
be forwarded to the front of the multi edged tool by effectively
utilizing the gaps between the plurality of the cutting parts,
making it possible to advantageously prevent the chips from being
adhered to the walls of the grooves even in the case where the
multi edged tool is employed.
(First mode of the Invention Relating to Cutting Tool)
[0037] A first mode of the invention relating to a cutting tool
provides a cutting tool comprising a cutting part for cutting a
groove in a surface of a pad substrate of synthetic resin,
characterized by that the cutting part includes a cutting edge and
two side faces slant in a same lateral direction with respect to
the cutting edge of the cutting part. The cutting tool having
construction according to the present mode is advantageous in
implementing the method of producing the polishing pad according to
the invention described above, and can be used in producing by
means of a cutting process the slant groove whose two side walls
are slant with respect to the center axis of the pad substrate and
whose floor is orthogonal to the center axis of the pad substrate,
as viewed in cross section.
(Second Mode of the Invention Relating to Cutting Tool)
[0038] A second mode of the invention relating to a cutting tool
provides a cutting tool according to the first mode, characterized
by that the cutting tool comprises a multi-edged tool having a
plurality of said cutting parts arranged in series with respect to
a cutting direction in order to enable simultaneous cutting of a
multiplicity of said grooves. This mode affords improved
productivity through the ability to efficiently cut a plurality of
slant grooves.
(Third Mode of the Invention Relating to Cutting Tool)
[0039] A third mode of the invention relating to a cutting tool
provides a cutting tool characterized by that the cutting tool
includes a groove cutting tool for turning a groove extending
substantially circumferentially into said surface of said pad
substrate, while rotating said pad substrate about a center axis
thereof, said groove cutting tool having at least one cutting part
having a tooth width of 0.005-3.0 mm, a wedge angle of 15-35
degrees, and a front clearance angle of 65-45degreee.
[0040] The use of the cutting tool of construction according to the
present mode makes it possible to produce more advantageously a
groove (including a slant groove) into the polishing pad, and to
improve the precision and shape consistency of the inside surfaces
of the groove. Particularly, since the front clearance angle
measures 65-45 degrees, when cutting a groove with a small radius
of curvature sufficiently close to the inner diameter of the pad
substrate, catching of the sides of the cutting part can be reduced
or avoided, so that the outer diameter side of the groove can be
produced with high dimensional precision or accuracy, making it
possible to produce substantially uniform grooves extending
substantially in the circumferential direction over a wide surface
area on the polishing pad with high precision.
[0041] Preferably, the groove-machining cutting tool is arranged to
have a tooth width of 0.005-2.0 mm. Such a narrow tool is employed.
In the groove machining tool according to the present invention, it
is advantageous to employ a multi-edged tool having a plurality of
cutting parts arrayed in the tooth width direction, whereby a
plurality of concentric grooves can be turned efficiently. In the
case of a multi-edged tool having a plurality of cutting parts
arranged in the tooth width direction, the cutting parts may be
arranged at the same pitch as the desired groove pitch (spacing),
or alternatively may be arranged with a wide gap in between by
making the cutting part pitch some suitable multiple (two times or
greater) of the desired groove pitch. The latter multi edged tool
may be used for cutting a plurality of grooves all at once, while
being offset in small increments depending on the groove pitch.
BRIEF DESCRIPTION OF DRAWINGS
[0042] FIG. 1 is a plane view of a polishing pad according to one
embodiment of the invention. FIG. 2 is a plane view of a polishing
pad according to another embodiment of the invention. FIG. 3 is a
fragmentally enlarged cross sectional view showing one preferred
groove construction adapted in the polishing pad of FIG. 1 or 2.
FIG. 4 is a cross sectional view useful for explaining a process of
polishing a substrate with the grooved polishing pad of FIG. 3.
FIG. 5 is a view demonstrating a simulation conducted on a
polishing pad for examining effects of variation in a width
dimension of a groove of the polishing pad on polishing condition.
FIG. 6 is a view demonstrating a simulation conducted on a
polishing pad for examining effects of variation in a slant angle
of a groove of the polishing pad on polishing condition. FIG. 7 is
a graph demonstrating distribution of a contact pressure of the
polishing pad against the wafer as a result of the simulation where
the groove has an slant angle .alpha.: .alpha.=0.degree.. FIG. 8 is
a graph demonstrating distribution of a contact pressure of the
polishing pad against the wafer as a result of the simulation where
the groove has an slant angle .alpha.: .alpha.=-5.degree.. FIG. 9
is a graph demonstrating distribution of a contact pressure of the
polishing pad against the wafer as a result of the simulation where
the groove has an slant angle .alpha.: .alpha.=-10.degree.. FIG. 10
is a graph demonstrating distribution of a contact pressure of the
polishing pad against the wafer as a result of the simulation where
the groove has an slant angle .alpha.: .alpha.=+5.degree.. FIG. 11
is a graph demonstrating distribution of a contact pressure of the
polishing pad against the wafer as a result of the simulation where
the groove has an slant angle .alpha.: .alpha.=+5.degree.. FIG. 12
is a fragmentally enlarged view in cross section of the polishing
pad of FIG. 1 or 2 showing another preferred groove construction
adaptable in the pad. FIG. 13 is a fragmentally enlarged view in
cross section of the polishing pad of FIG. 1 or 2 showing yet
another preferred groove construction adaptable in the pad. FIG. 14
is a fragmentally enlarged view in cross section of the polishing
pad of FIG. 1 or 2 showing still another preferred groove
construction adaptable in the pad. FIG. 15 is a front elevation of
a polishing pad according to yet another preferred embodiment of
the invention. FIG. 16 is a cross sectional view taken along line
16-16 of FIG. 15. FIG. 17 is a plane view of a polishing pad
according to still another preferred embodiment of the invention.
FIG. 18 is a plane view of a polishing pad according to a further
preferred embodiment of the invention. FIG. 19 is a front elevation
of one example of a rotary tool adaptable in producing a polishing
pad of construction according to the present invention. FIG. 20 is
a front elevation of one example of a cutting tool adaptable in
producing a polishing pad of construction according to the present
invention. FIG. 21(a) is a side elevation of the cutting tool of
FIG. 20, and (b) is an enlarged back elevation of a part of FIG. 20
to which a multi-edged tool chip is attached. FIG. 22 is a
fragmentally enlarged view of one example of a cutting tool
suitably adaptable for use in a cutting process for cutting a
groove into a polishing pad according to the present invention.
FIG. 23 is a fragmentally enlarged view of another example of a
cutting tool suitably adaptable for use in a cutting process for
cutting a groove into a polishing pad according to the present
invention. FIG. 24 is a view suitable for explaining a process of
cutting a groove into a pad substrate using the cutting tool shown
in FIG. 22. FIG. 25 is a side elevation of the cutting tool shown
in FIG. 22.
BEST MODE FOR CARRYING OUR THE INVENTION
[0043] There will be described in detail preferred embodiments of
the invention with reference to accompanying drawings in order to
further clarify the present invention.
[0044] Referring first to FIG. 1, shown is a polishing pad 10 of
construction according to a first embodiment of the present
invention. The polishing pad 10 is constituted by a thin disk pad
substrate 12 having a constant thickness dimension T overall. The
pad substrate 12 is advantageously formed of rigid expanded
urethane, for example. The pad thickness dimension is not
particularly limited, and may be selected appropriately depending
not only on the material of the pad substrate 12 but also the
material of the wafer being polished, the required degree of
polishing precision, and the like.
[0045] One surface 14 of the pad substrate 12, serving as a
processed surface, has a groove 16 formed thereon so as to extend
in a circumferential direction about an center axis 18 of the pad
substrate 12, and to be open in the surface 14.
[0046] The groove 16 may be composed of a plurality of circular
grooves 16, 16, 16 . . . each extending about the center axis 18 as
its center of curvature, but at mutually different radii of
curvature, as shown in FIG. 1, or alternatively of a single or
plurality of grooves 16 arranged about the center axis 18 in a
spiral configuration with gradually increasing radius of curvature,
as shown in FIG. 2. Regardless of whether a plurality of grooves
are arranged concentrically as shown in FIG. 1, or one or a number
of grooves are arranged in spiral configuration as shown in FIG. 2,
a diametric pitch, which is defined as the distance between points
of intersection with radial lines of the grooves on a single line
drawn across the diameter, may be constant across the entire
diameter, or change gradually over portions of, or the entirety of,
the surface.
[0047] Here, the groove 16, at least partially across the diameter
of pad substrate 12, is formed as a slant groove(s) having slant
structure according to the invention.
[0048] As a specific example, shown in enlarged longitudinal cross
section in FIG. 3, the groove 16 has an inner diameter side wall
(hereinafter referred to as "inside wall") 20 and an outer diameter
side wall (hereinafter referred to as "outside wall") 22, both of
which are slant faces slant by a predetermined angle .alpha.
(.alpha.=intersect angle with a straight line parallel to the
center axis 18) with respect to the center axis 18 around the
entire circumference. That is, in the groove 16 shown in FIG. 3,
the inside wall 20 and the outside wall 22 are mutually parallel
faces, with the groove 16 having a substantially constant width
dimension B over the entirety of groove 16, not only in the
circumferential direction but also the depthwise direction thereof.
The groove 16 going towards the opening thereof moves gradually
further away toward the outer diameter side from the center axis 18
to open diagonally outward in the diametric direction of pad
substrate 12.
[0049] The floor of the groove 16 is not limited as to shape, and
may curved or flat, for example. In the present embodiment, the
floor of the groove 16 is a flat surface orthogonal to the center
axis 18 of the polishing pad 12. Where the floor of the groove 16
is a flat surface substantially parallel to the surface of the
polishing pad 12, a gap can be effectively maintained at the floor
of the groove 16 even where the groove 16 has a large effective
depth, so that good strength characteristics are achieved.
[0050] Specific design values for the various dimensions, slant
angle etc. for the groove 16 may be selected giving overall
consideration to the material, thickness dimension, and outside
diameter dimension of the pad substrate 12, as well as the material
of the wafer being polished, the configuration and material of
metallization deposited on the wafer, the required polishing
precision and the like, and as such are not particularly limited.
Preferably, however, values for the groove 16, e.g., the groove
width B, depth D, diametric pitch P, and slant angle .alpha. may
fall within the following ranges.
[For Circumferential Groove of Generally Circular Shape]
[0051] 0.005 mm.ltoreq.B.ltoreq.3.0 mm
[0052] 0.1 mm.ltoreq.D.ltoreq.2.0 mm
[0053] 0.1 mm.ltoreq.P.ltoreq.10.0 mm
[0054] 0.5.degree..ltoreq..alpha..ltoreq.30.degree.
[For Linior Groove]
[0055] 0.005 mm.ltoreq.B.ltoreq.3.0 mm
[0056] 0.1 mm.ltoreq.D.ltoreq.2.0 mm
[0057] 0.1 mm.ltoreq.P.ltoreq.60.0 mm
[0058] 0.5.degree..ltoreq..alpha..ltoreq.30.degree.
[0059] More preferably, the above described several values for the
groove 16 may fall within the following ranges.
[For Circumferential Groove of Generally Circular Shape]
[0060] 0.05 mm.ltoreq.B.ltoreq.2.0 mm
[0061] (more preferably: 0.2 mm.ltoreq.B.ltoreq.1.0 mm)
[0062] 0.1 mm.ltoreq.D.ltoreq.1.0 mm
[0063] 0.2 mm.ltoreq.P.ltoreq.5.0 mm
[0064] 1.0.degree..ltoreq..alpha..ltoreq.15.degree.
[For Linior Groove]
[0065] 0.05 mm.ltoreq.B.ltoreq.2.0 mm
[0066] 0.1 mm.ltoreq.D.ltoreq.1.0 mm
[0067] 0.2 mm.ltoreq.P.ltoreq.30.0 mm
[0068] 1.0.degree..ltoreq..alpha..ltoreq.15.degree.
[0069] It should be appreciated that if the groove width B is too
small, it becomes difficult to achieve the slurry flow controlling
action afforded by the groove 16, and the groove 16 will tend to
become clogged with polishing residues and the like, so that
consistent effect is not readily achieved. On the other hand, if
groove width B is too large, the edge portions (edges of the
opening) of the groove 16 will have increased contact pressure
against the wafer, tending to bite into the workpiece during
polishing, making it difficult to achieve consistent polishing.
[0070] If the groove depth D is too small, it becomes difficult to
achieve the slurry flow controlling action afforded by the slant
groove 16, and the excessive rigidity of the surface 14 of the
polishing pad 10 results in uniform contact pressure against the
wafer overall, so that contact pressure against the wafer at the
edge portions of the groove 16 will tend not to be high enough to
conduct polishing effectively. If the groove depth D is too large,
not only is the pad difficult to manufacture, but the surface 14 of
the polishing pad 10 will tend to deform easily, and there is a
risk of stick slip, whereby polishing tends to be inconsistent.
[0071] If the diametric pitch P is too small, the pad becomes
difficult to manufacture, and the surface 14 of the polishing pad
10 will tend to deform or become damaged easily, making it
difficult to achieve consistent polishing. If on the other hand
diametric pitch P is too large, it becomes difficult to achieve the
slurry flow controlling action afforded by the groove 16.
[0072] If the slant angle .alpha. of the inside and outside walls
20, 22 is too small, it likely to become difficult to achieve the
slurry flow controlling action produced by centrifugal force,
described later. On the other hand, if slant angle .alpha. of the
inside and outside walls 20, 22 is too large, not only is the pad
difficult to manufacture, but strength declines at the side walls
of the groove 16, making it difficult to achieve consistent planar
pressure distribution, and possibly suffering from difficulty in
achieving the polishing pad 10 of adequate durability.
[0073] The polishing pad 10 having the groove 16 is used for
polishing a wafer or the like in the conventional manner. More
specifically, as shown in FIG. 4, for example, the polishing pad 10
is arranged on the support face of a rotating plate (support plate)
of a polishing apparatus (not shown), and clamped against the
rotating plate by air-induced negative pressure suction or other
means. Next, while rotating the polishing pad 10 about its center
axis 18, a wafer 24 is juxtaposed against the surface 14 for
polishing. Generally, during this polishing process, an abrasive
liquid (hereinafter referred to as "slurry") 28 is supplied to
opposing the faces, i.e. the surface 14 of the polishing pad 10 and
the process face 26 of the wafer 24, like the conventional manner,
while also rotating the wafer 24 itself about its center axis. The
slurry 28 is supplied, for example, to the surface of the polishing
pad 10 from the vicinity of the central portion of the polishing
pad 10 so as to be spread out over the surface of the polishing pad
10 due to the action of centrifugal force created by rotation of
polishing pad 10 about the center axis 12.
[0074] In the polishing pad 10, since the groove 16 open in the pad
surface 14 gradually slants outwardly in the diametric direction
going from the floor to the opening thereof, rotation of the
polishing pad 10 about its center axis 18 creates centrifugal force
exerted on the slurry 28 present within the groove 16, in turn
creating partial pressure in a direction expelling the slurry 28
from the groove 16, so that force corresponding to the rotational
speed of polishing pad 10 generates flow that actively expels the
slurry 28 from the opening to the outer diameter side while drawing
it between the opposing faces of the polishing pad 10 and the wafer
24. In conjunction with this, at the inner diameter side of the
groove 16, the slurry 28 in an amount corresponding to that
expelled at the outer diameter side of the groove 16 is actively
caused to flow into the groove 16.
[0075] As a result, effective inflow/outflow of the slurry 28 is
created in the groove 16, and active slurry flow is produced
between the opposing faces of the polishing pad 10 and the wafer
24, whereby a chemical polishing action of the slurry 28 as well as
a mechanical polishing action of the slurry 28 may be realized
efficiently and substantially uniformly over the entire interface,
thereby providing consistent, effective polishing.
[0076] A further advantage of employing the slant groove 16
described hereinabove is that simply by making appropriate
adjustments to the slant angle of the groove 16, the flow state of
the slurry 28 during polishing can be actively controlled, so that
optimal polishing conditions may be produced by adjusting the slant
angle of the groove 16 in consideration of the characteristics of
the slurry 28 used, the characteristics of the wafer being
processed, various polishing parameters, and the like. Described
more specifically, as to polishing temperature regulation, the
groove 16 may be slant toward the outside of the pad so as to
increase an amount of slurry flow, whereby the polishing
temperature can be maintained or regulated.
[0077] In the slant groove 16, the two walls 20, 22 are mutually
parallel in the depthwise direction in addition to the
circumferential direction, whereby the width dimension B of the
groove 16 is substantially constant across its entire depth. This
provides the advantage that even if the polishing pad 10 surface
has become worn, or the surface has been ground by means of
dressing, the width dimension of the groove open in the surface 14
will nevertheless remain substantially constant, so that consistent
polishing action is produced over extended periods.
[0078] A simulation was conducted for examining change in polishing
performance by the polishing pad 10 on the wafer 24 in the event of
change in the width dimension B of the groove 16. Results of the
simulation are demonstrated in TABLE 1, following. The simulation
was conducted on a specimen of the polishing pad 10 like that shown
in FIG. 5, having the grooves 16 1.0 mm deep formed extending
parallel to each other at 1.25 mm intervals, with the groove width
dimension B of the groove 16 varied from an initial setting of
B=0.25 mm to -20% (B=0.20 mm), -5% (B=0.2375 mm), +5% (B=0.2625 mm)
and +20% (B=0.30 mm). For the simulation, cross sectional
dimensions of the polishing pad 10 were made rectangular with width
of 3.75 mm and thickness of 2 mm, cross sectional dimensions of the
wafer 24 were made rectangular with width of 3.75 mm and thickness
of 3 mm. The static condition under which the wafer 24 was pressed
against the surface of the polishing pad 10 at a static pressing
load of 5 gf/mm.sup.2 was subjected to stress analysis according to
a finite element method. Each groove 16 in the polishing pad 10 was
of non-slant configuration extending vertically or in a direction
of staking of the polishing pad 10 and the wafer 24. Physical
qualities used for the wafer 24 and the polishing pad 10 are given
in TABLE 2. TABLE-US-00001 TABLE 1 MEAN PRESSURE PEAK PRESSURE
(gf/mm.sup.2) (gf/mm.sup.2) GROOVE WIDTH (RATE OF DEVIATION (RATE
OF DEVIATION ERROR FROM NO ERROR [%]) FROM NO ERROR [%]) -20% 14.26
(-4.40) 5.95(-4.80) -5% 14.81(-0.74) 6.17(-1.30) no error 14.92
6.25 5% 15.03(+0.74) 6.33(+1.30) +20% 15.47(+3.70) 6.58(+5.28)
[0079] TABLE-US-00002 TABLE 2 PHYSICAL PROPERTIES POLISHING PAD 10
WAFER 24 Poisson's Ratio 0.4 0.4 Young's Modulus (gf/mm.sup.2)
2143.0 1.0 .times. 10.sup.7
[0080] As is understood from the results in Table 1, even a slight
change in the width dimension B of the groove 16 is demonstrated to
produce a change on the order of several percent in peak pressure
(pressing force) exerted on the wafer 24 during polishing. The
magnitude of peak pressure exerted on the wafer 24 directly affects
polishing efficiency during wafer polishing, and also significantly
affects polishing precision. This reveals that maintaining as
constant a value as possible for the groove width dimension B is
crucial for the purpose of consistent processing of the wafer 24.
Here, the grooves 16 in the polishing pad 10 of the embodiment
hereinabove are slant, but since the width dimension B thereof is
substantially constant in the depthwise direction, polishing
performance is consistent even in the event that the polishing pad
10 surface has become worn, or the surface has been ground down by
means of dressing. In contrast, where a groove has a cross section
that expands in dimension in the depthwise direction going towards
the pad surface, as taught in the above mentioned U.S. Pat. No.
6,238,271, the width dimension changes in the event that the
polishing pad 10 surface has become worn, or the surface has been
ground by means of dressing. As is readily apparent from the above,
it will be extremely difficult to consistently achieve the desired
polishing of the wafer.
[0081] By slanting the groove 16 with respect to the center axis 18
or polishing pad 10, the component force of centrifugal force
generated depending on the particular slant angle .alpha. improves
the flow of the slurry 28 between the opposing faces of the
polishing pad 10 and the wafer 24, leading to improvement in
polishing efficiency and polishing precision as has been discussed
previously. Apart from the improvement in slurry flow, slanting the
groove 16 has also been shown to increase maximum pressure at the
contact face of the polishing pad 10 against the wafer 24, and to
produce a phenomenon similar to an edge effect, which further
improves polishing efficiency. A further simulation was conducted
for examining this phenomenon. The result of the simulation will be
described in detail.
[0082] As shown in FIG. 6, this simulation was carried out on a
specimen of the polishing pad 10 having grooves 16 1.0 mm deep
formed extending parallel to each other at 1.0 mm intervals. With
the bottom end face of the polishing pad 10 fixed and a pressing
load of 5.0 gf/mm.sup.2 applied to a wafer 24 placed on the surface
14 of the polishing pad 10, a polishing process was simulated
according to a finite element method, by slightly moving the wafer
24 at a relative speed of 583.3 mm/s towards the horizontal
direction (rightward in FIG. 6) with respect to the polishing pad
10. This simulation was conducted with five different values for
groove 16 slant angle .alpha.: .alpha.=0.degree. (opening parallel
to pad center axis); .alpha.=-5.degree. (opening slant towards pad
center axis); .alpha.=-10.degree.; .alpha.=+5.degree. (opening
slant towards pad outer diameter), and .alpha.=+10.degree.. Results
of the simulation are shown in graphs of FIGS. 7-11,
respectively.
[0083] For the simulation, cross sectional dimensions of the
polishing pad 10 were rectangular with width of 4.5 mm and
thickness of 2.5 mm, and cross sectional dimensions of the wafer 24
were rectangular with width of 4.5 mm and thickness of 3.0 mm. Each
groove 16 in the polishing pad 10 had constant width dimension
B=0.5 mm. Physical properties used for the wafer 24 and polishing
pad 10 were in accordance with values of the static simulation
parameters (TABLE 2) relating to groove width change, described
previously.
[0084] As is apparent from the results presented in FIGS. 7-11, by
varying the slant angle of the grooves 16, it is possible to
significantly and efficiently adjust contact pressure of the
polishing pad 10 against the wafer 24 during polishing. Experiments
conducted by the inventors has revealed that the greater the
maximum value for contact pressure, i.e., the more positive the
value of groove 16 slant angle .alpha. within a predetermined range
and the greater the slant towards pad outer diameter, the greater
the improvement in polishing efficiency. This may be attributed to
an edge effect or a bite like function of the polishing pad. Thus,
by adjusting the slant angle of the grooves 16 of the polishing pad
10 in consideration of the polishing pad and wafer material,
required precision, and the like, it is possible to achieve both
suitable polishing precision and polishing efficiency. Also, this
achieved excellent polishing precision and polishing efficiency can
be maintained at consistent level, without being largely diminished
by wear of the polishing pad or by dressing.
[0085] If the slant angle .alpha. of the groove 16 is too large, a
phenomenon similar to stick slip may occur, resulting in
inconsistent polishing. For this reason, the value of slant angle
.alpha. is preferably in the range
-30.degree..ltoreq..alpha..ltoreq.+30.degree., and more preferably
-20.degree..ltoreq..alpha..ltoreq.+20.degree.. In consideration of
effectively in slurry flow through centrifugal force, described
previously, it is preferably that the value of slant angle .alpha.
is arranged to meet the following inequality: 0.degree. <.alpha.
so that the grooves open towards the outer diameter. Further,
polishing efficiency is effectively increased owing to the
above-described edge effect, making it possible to reduce overall
processing pressure of the polishing pad required for achieving a
desired polishing efficiency, in comparison with the conventional
case. Namely, if the processing pressure is too large, the
polishing pad will tend to become dull at its outer circumferential
part, due to resilient elasticity of the material of the polishing
pad. According to the present invention, the desired polishing
efficiency can be achieved not by increase of the processing
pressure, but through the edge effect of the groove 16. Thus, the
groove 16 employed in the invention can eliminate or moderate the
problem of dull at the outer circumferential part of the polishing
pad.
[0086] Referring next to FIGS. 12-18, there will be described
grooves 16 formed in polishing pads according to another specific
embodiments of the invention. In the interest of brevity and
simplification, the same reference numerals as used in the first
embodiment will be used in the following embodiments to identify
the corresponding components, and redundant description of these
components will not be provided.
[0087] Grooves 42 in the polishing pad 41 shown in FIG. 12 have an
inside wall 44 and outside wall 46 that both have slant
configuration extending in the inside diametric direction towards
their openings, as contrasted to the grooves 16 shown in FIG. 3. In
this embodiment, the slant angles .alpha. of inside wall 44 and the
outside wall 46 with respect to center axis 18 are negative and the
same, with grooves 42 extending in the circumferential direction
between their parallel inside and outside walls 44, 46. In other
words, the grooves 42 have substantially constant groove width
dimension B over their entire extension.
[0088] In the grooves 42 shown in FIG. 12, centrifugal force acting
on the slurry 28 entering grooves 42 in association with rotation
of the polishing pad 41 exerts force in a direction tending to push
the slurry 28 into the grooves 42. As a result, outflow of the
slurry 28 from the grooves 42 into the space between the opposing
faces of polishing pad 41 and the wafer 24 is controlled to a
constraining direction, whereby the flow of the slurry 28 diffusing
out from the rotation center of polishing pad 12 towards the outer
diameter under centrifugal force can be regulated.
[0089] In the grooves 42 shown in FIG. 12, polishing residues and
the like entering the grooves 42 can be actively detained on the
floor of the grooves 42, thereby effectively preventing any
problems that could result from polishing residues or the like
entering the space between the opposing faces of the polishing pad
41 and the wafer 24.
[0090] In preferred practice, the slant angle a of the grooves 42
will be set to an absolute value within the same numerical range
recited for slant angle .alpha. of the grooves 16 shown in FIG. 3.
The width dimension, depth dimension, and the diametric pitch of
the grooves 42 will likewise appropriately lie within the numerical
ranges given for the grooves 16 shown in FIG. 3.
[0091] Grooves 52 a polishing pad 50 shown in FIG. 13 and grooves
56 in a polishing pad 54 shown in FIG. 14 are examples of the
grooves 52, 56 having different slant angles .alpha. values in the
diametric direction produced on the surface 14 of a single given
polishing pad 50, 54. FIGS. 13 and 14 are diametric cross sections
showing only the diametric half of the polishing pad 50 lying to
the right of the center axis 18. It is noted that the diametric
left half in the drawing will be symmetrical with the right
diametric half in relation to the center axis 18.
[0092] More specifically described, the inner diameter portion
(closer to center axis 18) and in the medial portion in the
diametric direction, the grooves 52 of the polishing pad 50 shown
in FIG. 13 all slant up (going towards the opening) towards the
outer diameter of the pad, as shown in FIG. 3. However, the slant
angle .alpha. of the grooves 52b in the medial portion is the
diametric direction (located diametrically outward from the grooves
52a in the inner diameter portion) is smaller, and the grooves 52C
formed in the outer diameter portion over an even smalle0 .alpha.
value, namely, approximately 0.degree., so that the inside and
outside walls are all vertical, i.e. rise substantially parallel to
the center axis 18. That is, while the grooves 52 width dimension B
is substantially constant groove 52 slant angle .alpha. becomes
progressively smaller going from the center portion towards the
outer diameter portion.
[0093] With the polishing pad 50 provided with such grooves 52,
differences in the level of centrifugal force exerted on the slurry
28 in the grooves 52, the grooves 52--due to difference in
peripheral speed at points different distances away from the center
axis of rotation 18--can be reduced or eliminated through
adjustment of the slant angle of the grooves 52, so that uniform
effect on the part of slant grooves 52 can be achieved over the
entire surface 14 of the polishing pad 50.
[0094] Grooves 56 in the polishing pad 54 shown in FIG. 14 consist
in the inner diameter portion (closer to center axis 18) of the pad
of the grooves 56a that, moving toward the opening, slant up
towards the outer diameter side as shown in FIG. 3, whereas the
grooves 56b located in the diametric medial portion of the pad
further to the outside of the grooves 56a in the diametric
direction have inside and outside walls that are all vertical, i.e.
rise substantially parallel to the center axis 18, and the grooves
56c formed in the outer diameter portion of the pad farthest away
from the center axis 18 have openings that slant towards the inner
diameter side as shown in FIG. 12. That is, while the groove width
dimension B is substantially constant, groove slant angle .alpha.
changes from positive to negative going from the center portion
towards the outer diameter portion, so as to become progressively
smaller.
[0095] With the polishing pad 54 provided with such grooves 56, in
the inner diameter portion located a small distance from center
axis 18 (center of rotation), flow tending to actively expel is
imparted to the slurry 28 in the grooves 56, whereas in the outer
diameter portion located further away from the center axis 18, flow
tending to restrain outflow is imparted to the slurry 28 in the
grooves 56. This making it possible to control flow of slurry 28
between the opposing faces of the polishing pad 10 and the wafer 24
in consideration of overall flow.
[0096] Grooves 62 in a polishing pad 60 shown in FIG. 15 consists
of a plurality of linear grooves made on the surface 14 of the
polishing pad 60. The plurality of grooves 62 are composed of a
plurality of first grouping grooves 62a extending parallel to one
another, and a plurality of second grouping grooves 62b extending
parallel to one another. The grooves 62a of the first grouping and
the grooves 62b of the second grouping mutually intersect at right
angles on the surface 14 of the polishing pad 60.
[0097] In this embodiment, the plurality of grooves 62, 62b making
up each of the groupings are mutually parallel at substantially
equal distances apart from each other. As a result, the plurality
of grooves 62a and 62b making up the two groupings intersect one
another at substantially right angles, so that the polishing pad 60
surface overall has a multitude of grooves 62 arranged
substantially in a grid pattern.
[0098] As is apparent from the longitudinal sectional view of the
pad shown in FIG. 16, the grooves 62a and the grooves 62b making up
the respective groupings all consist of slant grooves slant in the
depthwise direction with respect to the pad surface 14. In
particular, the grooves 62a and 62b have placement and slant angles
that are (left/right) symmetrical in relation to the center axis 18
and a single plane of symmetry containing a pad diametric line that
is parallel to the grooves 62. In FIG. 16, only the first grouping
grooves 62a are shown, but if a diametric cross section were taken
at a right angle to the cross section shown in FIG. 16, only the
grooves 62b of the second grouping would be shown in a
configuration identical to that in FIG. 16, for example.
[0099] The polishing pad 60 furnished with a multitude of such
linearly extending grooves 62a, 62b, can enjoy the same advantages
of the present invention as described above, when employed for
polishing a wafer by spinning the pad about its center axis 18 as
disclosed in the above mentioned U.S. Pat. Nos. 5,921855, 5,984,769
and 6,364,749, for example. Namely, the polishing pad 60 is able to
effectively produces a flow-accelerating action on the slurry 28 by
means of the slant inside and outside walls 64, 66 of the grooves
62a, 62b, a polishing efficiency regulating action corresponding to
the slant angle of the grooves 62a, 62b, and other actions similar
to that of a polishing pad having circumferential grooves like that
shown in FIG. 1.
[0100] The polishing pad 60 of the present embodiment may be
designed with the grooves 62a, 62b slant such that their openings
face diametrically inward, as with the polishing pad shown in FIG.
12, or with the grooves 62a, 62b having different slant angles
depending on location on the surface 14 of the polishing pad 10, as
with the polishing pad shown in FIGS. 13 or 14. These arrangements
make it possible to control polishing precision and polishing
efficiency of wafers, and to regulate slurry flow conditions and
the like.
[0101] Where a groove pattern composed of a plurality of grooves
extending linearly as exemplified above, the pattern, pitch, number
of lines etc. produced on the polishing pad 10 substrate 12 can be
selected arbitrarily. Specifically, it would be possible as well to
employ first, second, and third groove groupings each composed of a
plurality of grooves 62a, 62b, 62c extending in mutually different
directions, as shown in FIG. 17 and FIG. 18, and the density of the
mesh pattern formed by this plurality of groove groupings can be
selected arbitrarily as will be apparent from FIGS. 17-18. While
not shown in the drawings, a plurality of linear grooves 62
composed of a single or a plurality of groupings may be produced on
the surface of polishing pad 10 in combination with grooves 16
extending in the circumferential direction as shown in FIG. 1 or
2.
[0102] These grooves 16, 42, 52, 56, and 62 having the various
configurations described hereinabove may be produced on the pad
substrate 12 by any of a variety of methods, for example, by
forming the grooves simultaneously with the injection molding
process for the polishing pad 10, or by a cutting process using a
rotary tool 70 (such as a milling cutter) as shown in FIG. 19.
Preferably, these grooves may be formed by a cutting process, using
a cutting tool equipped with a cutting part of shape corresponding
to the groove cross section.
[0103] As specifically illustrated in FIGS. 20-21, the desired
grooves 16, 42, 52, 56, or 62 can be produced using a cutting tool
having a multi-edged tool tip 82 with cutting parts 80
corresponding in shape to the desired grooves arranged at suitable
pitch at the distal edge, for example. This multi-edged tool tip 82
is exchangeably fixed to a suitable tool holder 84, to cut the
surface 14 of the pad substrate 12.
[0104] As shown in FIG. 21(a), the tool holder 84 has an ion
blowing passage 90 straightly extending through an interior part
thereof, while to the front side of the tool holder 84 toward which
the cutting parts 80 protrude, a vacuum suction apparatus 92 may be
attached. Described in detail, The upper end of the ion blowing
passage 90 is connectable to an external air blower for
neutralizing static charge, while the lower end of the ion blowing
passage 90 is open on the back side of the cutting parts 80 in a
direction in which the cutting parts 80 protrude. Ions provided
together with compression air from the external air blower
(hereinafter referred to as "ion blow") are discharged downwardly
with a slant angle substantially equal to that of the cutting parts
80. According to this arrangement, the ion blow is directly
discharged to the pad substrate 12 cut by the cutting parts 80 and
resultant cut-parts (chips), effectively preventing these members
being statically charged, thus advantageously preventing the chips
being adhered to the pad substrate, especially to the walls of the
grooves, due to the static charge. Preferably, the direction of
discharge of the ion blow is slant toward the front in a cutting
direction. Namely, the chips can be transmitted to the front of the
multi edged tool tip 82 through the gaps between blades of the
multi edged tool tip 82, at the same time when the groove is cut
onto the pad substrate. This arrangement permits a further
effective prevention of adhere of the chips to the inside of the
groove. In this regards, a variety of known air blower for
neutralizing static charge may be adoptable as the external air
blower connectable to the ion blowing passage 90.
[0105] The vacuum suction apparatus 92 can be fixed to the tool
holder 84 with its opening portion being open to and located in the
vicinity of the front of the cutting parts 80. This makes it
possible for the vacuum suction apparatus 92 to promptly suction
and collect the chips forwarded to the front of the cutting parts
80 sequentially.
[0106] Additionally, as shown in FIG. 21(b), the lower end portion
of the ion blowing passage 90 is slant with a slant angle
substantially equal to that of the cutting parts 80 with respect to
the center axis 18 of the pad substrate 12. Accordingly, the ion
blow can be effectively applied even to the inner circumferential
surface and the floor of the groove 16, which provide undercut
formations with respect to the surface of the pad substrate 12,
thus making it possible to effectively prevent adhere of the chips
to the surface.
[0107] As shown in FIG. 22 or FIG. 23, the cutting parts 80
projecting from the tool are slant by a predetermined angle,
corresponding to the slant angle .alpha. of the desired grooves 16
etc., with respect to the center axis of the tool holder 84. The
cutting tool having cutting parts 80 projected at a given slant
makes it possible to effectively cut the grooves 16 having the
desired slant angle .alpha. in the manner shown in FIG. 24. Namely,
the cutting part 80 is placed against the pad substrate 12 while
being inclined by a given slant angle .alpha.. Described in detail,
the cutting part 80 includes a cutting edge 81 and two side faces
83, 83 that are slant in a same lateral direction with respect to
the cutting edge 81 of the cutting part 80, by the given slant
angle .alpha.. While being projected out further by a predetermined
distance in the slant projecting direction, the cutting part 80 is
adapted to cut the pad substrate 12, repeating the cutting process
for cutting the same groove so as to trace the same cutting
location. This operation is repeated several times in an
intermittent mode (e.g. reciprocative motion etc.) in the case of a
finite shape such as linear grooves or spiral grooves, or in a
continuous channel mode in the case of an annular circumferential
groove, thus producing the grooves 16 having the desired slant
angle .alpha., effectively. Particularly when performing continuous
cutting in the circumferential direction to form an endless
circumferential groove, a projection height of the cutting part 80
may be increased progressively and continuously, rather than after
each circuit, during cutting. In this case, the cutting part 80
functions as a grooving tool adapted to cut the groove extending
substantially circumferentially onto the surface of the pad
substrate 12.
[0108] When cutting the groove 16 etc. that extends in the
circumferential direction, the desired groove 16 can be produced
efficiently by securing the cutting tool to a lathe, and bringing
the cutting parts 80 of multi-edged tool tip 82 into proximity with
and against the pad substrate 12 while rotating the pad substrate
12 about its center axis 18, to perform cutting in the above
manner. Such a turning process is described in co-pending
Unexamined Japanese Patent Application 2001-18164 filed by the
present Applicant, which is incorporated herein by reference, and
will not be described in detail here.
[0109] A specific exemplary preferred configuration for a cutting
part 80 for use in a cutting process is shown in FIG. 25, wherein a
tooth width is held within the range of 0.005-3.0 mm, corresponding
to the width B of the groove to be produced, a blade angle .beta.
is held within a range of 15-35 degrees, and a front clearance
angle .gamma. is held within a range of 65-45 degrees. Hence, as
the pad substrate 12 is somewhat more elastic than metal or similar
materials, if the front clearance angle .gamma. is less than
45.degree., the back portion of the blade 80 will tend to interfere
with the pad substrate 12 during cutting. This making it difficult
to obtain well-machined groove faces. Particularly when cutting a
circumferential groove as shown in FIG. 1, the back portion of the
blade 80 tends to interfere with the pad substrate 12 during
cutting of the inside diameter portion having a small radius of
curvature, and it will therefore be important to set cutting part
80 the front clearance angle .gamma. to within the range of 65-45
degrees. Where the front clearance angle .gamma. exceeds 65 degrees
or the blade angle .beta. is outside the range of 15-35 degrees, it
becomes difficult to assure an adequate rake angle .theta. of the
blade front surface, making it difficult to achieve good cutting
performance, or to ensure adequate durability and strength.
[0110] While the presently preferred embodiments of this invention
have been described above in detail for the illustrative purpose
only, it is to be understood that the present invention is not
limited to the details of the illustrated embodiments, but may be
otherwise embodied with various other changes, modifications and
improvements, which may occur to those skilled in the art, without
departing from the spirit and scope of the invention defined in the
following claims.
[0111] While a polishing pad of the present invention may be formed
with grooves in various configurations, such as grooves extending
in the circumferential direction or linearly extending grooves
formed in the polishing pad, one or a plurality of portions of a
single groove may be slant to produce a slant groove, or some or
all of a plurality of grooves may be slant over their entire length
to produce slant grooves.
[0112] The two substantially parallel side walls of the slant
groove used in the present invention need not have the same slant
angle in the strict sense, and it is to be understood that the
degree of parallelism of the two side walls of slant grooves has a
permissible range in consideration of the required degree of
polishing precision, the pad substrate material, the wafer material
and other factors. If the two side walls of a slant groove slant in
mutually opposite directions with respect to the center axis of the
pad substrate, there is a risk of significant change in polishing
characteristics occurring with wear of the pad or with dressing. It
is therefore to be understood that excluding such a case, it is
sufficient that the two side walls of the slant groove slant in the
same direction in their depthwise direction with respect to the
center axis of the pad substrate.
[0113] The mode of use of polishing pads of construction according
to the present invention is not limited particularly, and the
polishing pad of the invention may be used in a variety of
different manners, including slurry supply methods, for polishing
of various kinds of workpieces, including semiconductor substrates.
Nor is the polishing pad of the invention limited to use with CMP
processes.
[0114] As is apparent from the foregoing description, the polishing
pad having a construction of this invention is capable of suitably
regulating a polishing condition by controlling a slurry flow
during polishing based on a slant angle of a groove, and
maintaining the polishing condition approximately constantly. This
makes it possible to polish a target-polishing pad of high accuracy
with stability.
[0115] According to a method of the present invention, a
semiconductor substrate, which has been recognized as being
difficult to be polished due to soft or narrow metal lines, for
example, can be effectively and precisely polished with stability,
and accordingly fabricated.
[0116] Further, according to a polishing pad producing method of
the present invention, a polishing pad having construction of the
invention can be stably formed with a groove formed with high
preciseness.
[0117] By using a grooving tool according to the invention, a
groove of the polishing pad can be easily formed by turning with
its inner surface being smoothed, making it possible to effectively
manufacture a polishing pad of construction of the present
invention.
INDUSTRIAL APPLICABILITY
[0118] A polishing pad having construction of the present invention
is applicable to industrial manufacturing processes of
semiconductor substrates, for polishing a semiconductor substrate,
especially to a CMP method. A polishing pad producing process of
the present invention can be effectively executed in industrial
manufacturing processes of polishing pads, and a cutting tool
having a construction of the present invention can be
advantageously used in industrial grooving process of polishing
pads, also. It is accordingly apparent that all of the present
invention are industrially applicable.
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