U.S. patent application number 11/067457 was filed with the patent office on 2006-08-31 for polishing pad for use in polishing work pieces.
Invention is credited to Scott Benjamin Daskiewich, E. Dwaine Halberg, Clifford O. Thomson.
Application Number | 20060194530 11/067457 |
Document ID | / |
Family ID | 36570634 |
Filed Date | 2006-08-31 |
United States Patent
Application |
20060194530 |
Kind Code |
A1 |
Thomson; Clifford O. ; et
al. |
August 31, 2006 |
Polishing pad for use in polishing work pieces
Abstract
A polishing/lapping pad for use in CMP and other polishing and
lapping operations is presented that comprises multiple channels
designed to facilitate in the manipulation of slurry into specific
locations on the wafer being planarized.
Inventors: |
Thomson; Clifford O.;
(Mayer, AZ) ; Daskiewich; Scott Benjamin;
(Oriskany, NY) ; Halberg; E. Dwaine; (Mesa,
AZ) |
Correspondence
Address: |
Dusty Vogelpohl;Snell & Wilmer L.L.P.
One Arizona Center
400 East Van Buren
Phoenix
AZ
85004-2202
US
|
Family ID: |
36570634 |
Appl. No.: |
11/067457 |
Filed: |
February 25, 2005 |
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 for use in supporting work in CMP and similar
polishing and lapping operations, comprising channels cut into the
surface to effect the flow of slurry and characterized by
concentric pad circles having an axis at the axis of rotation of
the rotating pad, improved wherein: said multiple channels are
substantially orthogonal to a first pad circle; and the deviation
of the radial component of any of said multiple channels is
substantially greater than any deviation of the circular component
as said channel extends from the center of the pad outward.
2. The polishing pad of claim 1, wherein at least a subset of said
multiple channels comprise a first end and a second end.
3. The polishing pad of claim 1, wherein at least a portion of the
length of at least one of said multiple channels extends along the
surface of said pad at varying distances from said pad circle.
4. The polishing pad of claim 1, wherein said at least one of said
multiple channels circular component deviates outwardly in the same
direction said pad rotates.
5. The polishing pad of claim 1, further comprising extra channels
to compensate for hotter temperatures on the wafer.
6. A polishing pad comprising: multiple channels; wherein said
channels are positioned in groups of like shapes having common
centers; and wherein said groups are adjacent to at least one other
of said groups, wherein each group has a separate common
center.
7. The polishing pad of claim 6, wherein said shapes are
circles.
8. The polishing pad of claim 7, wherein each of said groups is
adjacent to six other said groups, except at the edges of said
pad.
9. The polishing pad of claim 8, wherein each of said groups is
adjacent to at least three other of said groups
10. The polishing pad of claim 6, wherein said shapes are
hexagons.
11. The polishing pad of claim 6, wherein said shapes are
pentagons.
Description
FIELD OF INVENTION
[0001] The present invention relates, generally, to an improved
polishing/lapping pad for use in polishing various substrates, for
example, during chemical mechanical planarization (CMP) of work
piece surfaces. More particularly, the present invention relates to
an improved channel design on polishing pads to improve the
distribution of slurry during the CMP process.
BACKGROUND OF THE INVENTION
[0002] The production of integrated circuits begins with the
creation of high-quality semiconductor wafers. During the wafer
fabrication process, the wafers may undergo multiple masking,
etching, and dielectric and conductor deposition processes. In
addition, metallization, which generally refers to the materials,
methods and processes of wiring together or interconnecting the
component parts of an integrated circuit located on the surface of
a wafer, is critical to the operation of a semiconductor device.
Typically, the "wiring" of an integrated circuit involves etching
trenches and "vias" in a planar dielectric (insulator) layer and
filling the trenches and vias with a metal.
[0003] In the past, aluminum was used extensively as a
metallization material in semiconductor fabrication due to the
leakage and adhesion problems experienced with the use of gold, as
well as the high contact resistance which copper experienced with
silicon. Other metallization materials have included Ni, Ta, Ti, W,
Ag, Cu/Al, TaN, TiN, CoWP, NiP and CoP. The semiconductor industry
has recently renewed its focus on copper metallization due to
alloying and electromigration problems that are seen with aluminum.
When copper is used as the trench and via filling material,
typically a barrier layer of another material is first deposited to
line the trenches and vias to prevent the migration of copper into
the dielectric layer. After filling, planarization is typically
conducted to remove the extra metal down to the dielectric surface.
Planarization leaves the trenches and vias filled and results in a
flat, polished surface.
[0004] Because of the high degree of precision required in the
production of integrated circuits, an extremely flat surface is
generally needed on at least one side of the semiconductor wafer to
facilitate the fabrication process, as well as to enhance the
accuracy and performance of the microelectronic structures created
on the wafer surface. As the size of the integrated circuits
continues to decrease and the density of microstructures on an
integrated circuit increases, the need for precise wafer surfaces
becomes more important. Therefore, between each processing step, it
is often desirable to polish or planarize the surface of the wafer
to obtain the flattest surface possible.
[0005] Chemical mechanical planarization (CMP) is a technique
conventionally used for planarization of semiconductor wafers.
Typically, a CMP machine includes a wafer carrier configured to
hold, rotate, and transport wafers during the process of polishing
or planarizing the wafer. During a planarization operation, a
pressure applying element (e.g., a rigid plate, a bladder assembly,
or the like) that may be integral to the wafer carrier, applies
pressure to hold the wafer against an opposing polishing surface
with a desired amount of force. The carrier and the polishing
surface are rotated, typically at different rotational velocities,
to produce relative lateral motion between the polishing surface
and the wafer to promote uniform planarization.
[0006] Polishing pads can be formed of various materials, depending
on the nature of the work piece and the process environment, and
are available commercially. For example, a polishing pad may be
blown polyurethane, felt, or stone. The hardness and density of the
polishing pad depend on the material that is to be polished. An
abrasive slurry may also be applied to the polishing surface. The
abrasive slurry acts to chemically weaken the molecular bonds at
the wafer surface so that the mechanical action of the polishing
pad can more effectively liberate the undesired material from the
wafer surface.
[0007] Presently known CMP processes are deficient in several
respects. For example, asymmetrical or otherwise non-uniform
distribution of slurry over the wafer surface, significant slurry
run-off, and maintaining uniform proportionate temperature control
across the wafer surface during the CMP process are common
problems.
[0008] The slurry may be introduced to the CMP system in any
desired manner, for example, at the center of the rotating pad. The
centrifugal forces associated with the rotating pad force the
slurry towards the outer edges of the pad. The slurry, if
unimpeded, will continue to move beyond the outer edge of the wafer
and pad, exiting the system. It is often impractical to reuse this
slurry if, for example, it becomes contaminated. It is therefore
economically advantageous to reduce the amount of slurry
run-off.
[0009] Presently known CMP processes are also deficient in
controlling the asymmetrical or otherwise non-uniform distribution
of slurry across the surface of the wafer being planarized. For
example, as the slurry migrates to the outer edges of the pad, a
much larger pad surface area must be covered with a decreasing
amount of slurry. Many pad designs contain grooves or channels cut
into the surface of the pad that are intended to guide the slurry
during the CMP process. Presently known designs, however, have not
effectively directed the slurry to specific areas of the pad/work
piece.
[0010] During CMP, different locations on a wafer can also get
hotter than other points on the wafer. Therefore, some areas on the
wafer will need more slurry to help regulate the temperature over
the surface of the wafer. As the temperature increases, the
reaction rate between the slurry and wafer generally increases, due
to an increase in the rate constant of the reaction. Therefore,
when there is an increase in temperature at one position of the
wafer, the reaction rate increases, which can cause an asymmetrical
planarization on the wafer. These areas are referred to as "hot
spots."
[0011] Therefore, a need exists for a polishing pad for improving
the planarization of wafers or other work pieces (such as, for
example, LCD glass, optical glass, glass wafers, and float glass
products) during CMP and other polishing processes. More
preferably, a need exists to guide the flow of slurry during CMP,
thereby maximizing the planarization of a wafer or similar work
piece.
SUMMARY OF THE INVENTION
[0012] These and other aspects of the present invention will become
more apparent to those skilled in the art from the following
non-limiting detailed description of preferred embodiments of the
invention taken with reference to the accompanying figures.
[0013] In accordance with an exemplary embodiment of the present
invention, a polishing pad for planarizing a surface of a work
piece is provided. More preferably, a polishing pad that can be
used during CMP is provided.
[0014] As described in greater detail below, each pad comprises a
"pad circle" at each particular radius of the pad. The pad circle
associated with any given point on a pad may be defined as a circle
that has its center at the center of the polishing pad, and a
radius which corresponds to the radius of the polishing pad at that
given radius. Stated another way, a pad circle is a construct or
conceptual tool, wherein each pad circle has the rotational,
vertical axis of the pad as its center and a pad circle radius of
any arbitrary value less than or equal to the radius of the
pad.
[0015] The pad comprises channels that are cut into the pad. These
channels are designed to guide the flow of the slurry used during
CMP. The channels are used to help prevent slurry run-off, provide
a symmetrical distribution of slurry throughout the wafer, and to
direct slurry to specific areas on the wafer where it may be
needed, such as, for example, at a "hot spot."
[0016] Another aspect of one embodiment of the present invention
comprises channels that are substantially orthogonal to any given
pad circle.
[0017] In accordance with another aspect of the present invention,
the polishing pad contains a plurality of channels. Each of the
channels is used to guide the slurry to, or maintain the slurry in,
a particular location on the pad. In one embodiment, each of the
channels has a first end and a second end, the second end having a
greater radius than the first end.
[0018] In accordance with another aspect of the present invention,
each channel has deviation in its radial and circular components.
As you move along a channel from the center of pad the outer edge
of the pad the radial component of the channel gets larger and
larger. The circular component on the other hand, does not deviate
as substantially as the radial component, and in some instances
there may not be any change.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] Exemplary embodiments of the present invention will
hereafter be described in conjunction with the appended drawing
figures, wherein like designations denote like elements, and:
[0020] FIG. 1 is a schematic drawing of a chemical mechanical
polishing apparatus;
[0021] FIG. 2 is a top view of prior art polishing pads;
[0022] FIG. 3 is a top view of prior art polishing pads;
[0023] FIG. 4 is a cross-sectional view of a polishing pad in
accordance with an exemplary embodiment of the present
invention;
[0024] FIG. 5 is a top view of a polishing pad in accordance with
an exemplary embodiment of the present invention;
[0025] FIG. 6 is a top view of a polishing pad in accordance with
an exemplary embodiment of the present invention comparing the
radial and circular deviations of a channel;
[0026] FIG. 7 is a top view of polishing pad in accordance with
another exemplary embodiment of the present invention;
[0027] FIG. 8 is a top view of a polishing pad in accordance with
another exemplary embodiment of the present invention;
[0028] FIG. 9 is a top view of a polishing pad in accordance with
an exemplary embodiment of the present invention;
[0029] FIG. 10 is a top view of a polishing pad in accordance with
an exemplary embodiment of the present invention; and
[0030] FIG. 11 is a top view of a polishing pad in accordance with
an exemplary embodiment of the present invention.
DETAILED DESCRIPTION
[0031] The following description is of exemplary embodiments only
and is not intended to limit the scope, applicability, or
configuration of the invention in any way. Rather, the following
description provides a convenient illustration for implementing
exemplary embodiments of the present invention. Various changes to
the described embodiments may be made in the function and
arrangement of the elements described without departing from the
scope of the invention as set forth in the appended claims.
[0032] With Reference to FIG. 1, a wafer polishing apparatus 100 is
shown. Typical polishing of a work piece involves pressing the work
piece against a polishing pad 20.
[0033] Preferably, pad 20 is rotating about its axis. It should be
noted, however, that pad 20 may also move in a "back and forth"
motion, or alternatively may comprise a continuous belt. In
addition, it is preferable for a carrier element 124 to rotate the
work piece around its axis.
[0034] The carrier element 124 may also oscillate the work piece
back and forth across the rotating pad. During CMP, slurry is added
to the system between pad 20 and the work piece.
[0035] With reference to FIG. 4, the exemplary polishing pad in
accordance with the present invention has a top layer 11, an
adhesive layer 12, and a bottom layer 13. The top layer is
preferably made out of polyurethane, but can be any known or
hereinafter developed material used to planarize a surface. The
bottom layer may comprise polyurethane, polycarbonate, or some type
of "soft" material, such as, for example, a felt pad. It should be
noted that any material now known or hereinafter developed may be
used to make the pad. For optimum planarization it is typical for a
softer pad to be below a stiffer pad. This allows the stiffer pad
to flex over global variations in the wafer, providing a more
uniform surface over the work piece.
[0036] The adhesive layer 12 may comprise a heat sensitive or
pressure sensitive adhesive. In one embodiment of the present
invention the adhesive layer 12 comprises only a single layer of
adhesive. In another embodiment of the present invention, adhesive
layer 12 may comprise a Mylar film positioned between two adhesives
layers on each side of the Mylar film.
[0037] Referring to FIGS. 4 and 5, an exemplary polishing pad in
accordance with the present invention is shown. Preferably,
channels 30 are cut into top layer 11 of pad 20.
[0038] Multiple channels 30 are cut into the polishing surface 22
of pad 20. Each channel 30 has side walls 31 and a bottom wall 32.
As shown in FIG. 5, an exemplary embodiment of the present
invention has walls substantially perpendicular to polishing
surface 22, and a bottom wall that comprises a substantial circular
shape. It should be noted however, that other geometries of channel
30 may be used. For example, the bottom wall 32 may be
perpendicular to the side walls 31. In yet another embodiment, the
channels are substantially cylindrical. In a further embodiment of
the present invention, the channels may be substantially
triangular. Stated in another way, the side walls 31 slant towards
one another and there is a small bottom wall 32, or no bottom wall
at all. Any geometry may be used for the channel shape.
[0039] Preferably, channels 30 are cut into pad 20 with a technique
that allows for incomplete penetration of top layer 11. This
prevents the adhesive layer 12 from contacting slurry, water, or
any other components used in polishing, lapping, or surfacing a
work piece. Examples of such techniques include, but are not
limited to, punching, laser, or CNC methods. It should be noted
that any now known or hereinafter developed technique used to cut
channels into the pads may be used. Upon completion of cutting the
channels into pad 20, the top layer may be sanded down or
treated.
[0040] Each channel has a width W.sub.C and a depth D.sub.C. In an
exemplary embodiment of the present invention, W.sub.C is from
about 0.1 mm and 4 mm. More preferably, W.sub.C is from about 0.3
mm to about 3 mm. Optimally, W.sub.C is from about 0.5 to about 2
mm. DC is from about 0.2 mm to about 4 mm. More preferably, DC is
from about 0.4 to about 3 mm. Optimally, DC is from about 0.5 to
about 2 mm.
[0041] As demonstrated in FIG. 5, it is preferable for a subset of
channels 30 to have a first end 35 and a second end 36.
Furthermore, as demonstrated in FIG. 5, every channel 30 may have a
first end 35 and a second end 36.
[0042] With reference to FIG. 6, each channel has deviation in its
"radial" and "circular" components. Radial refers to the
directional component of a channel that moves directionally from
the center of the pad towards the outer edge or vice versa.
Circular, on the other hand, refers to the directional component of
a channel that moves rotationally around the center axis of the
pad. As a channel moves from one end to the other, the radial
component of the channel will have a large deviation. The circular
component on the other hand, does not deviate as substantially as
the radial component, and in some instances there may be no
deviation. For example, when comparing two separate points along
channel 30, P.sub.1 and P.sub.2, each has a radial component RC and
a circular component .theta.. RC.sub.1 is going be less than
RC.sub.2. The difference between .theta..sub.1 and .theta..sub.2
will not be as great.
[0043] Another preferred aspect of the present invention is that
the deviation of the circular component is related to the direction
of rotation of pad 20. For example, with continued reference to
FIG. 6, pad 20 is rotating in direction 60. Therefore, arrow 65
shows the direction of deviation between the circular components of
P.sub.1 and P.sub.2, which is in the same circular direction as
arrow 60.
[0044] With reference to FIG. 5, for each radius R of pad 20, there
is a corresponding pad circle 40 that has a corresponding radius of
R and has its center at the center of pad 20. Stated another way, a
pad circle is a construct or conceptual tool, wherein each pad
circle has the rotational, vertical axis of the pad as its center
and a pad circle radius of any arbitrary value less than or equal
to the radius of the pad.
[0045] In accordance with one aspect of the present invention,
channel 30 is closer to being orthogonal to any pad circle as
opposed to parallel to it. Furthermore, there is a substantial
amount of deviation between pad circle 40 and channel 30. For
example, as channel 30 extends along the surface of pad 20, there
is a wide range of distances between any pad circle 40 and channel
30. On the other hand, with reference to FIG. 2, the prior art has
practically no deviation between a pad circle and the channel. Any
particular channel of the prior art has a radius, and the pad
circle for that particular radius deviates very little if at all
from the channel.
[0046] With Reference to FIG. 7, an exemplary embodiment of the
polishing pad, more channels 30 can be placed on particular
locations of the pad as needed. For example, due to
non-uniformities of temperature across the surface of the work
piece, it may be necessary to manipulate the slurry to the location
on the work piece that has a higher temperature.
[0047] FIG. 8 demonstrates another exemplary embodiment of the
present invention.
[0048] The pad contains sets of circular channels. Each circular
channel 50 is within a group of circular channels that forms a
circular channel set 55. Each of the circular channels 50 within an
circular channel set 55 has a common center. Each circular channel
set is surrounded by six other circular channel sets, except at the
outer edges of the pad. Similar to prior embodiments described
above, this embodiment helps prevent run-off of slurry. In
addition, the embodiment depicted in FIG. 8 manipulates slurry to
locations on the work piece than may need additional slurry.
[0049] FIG. 9 demonstrates yet another exemplary embodiment of the
present invention.
[0050] Wherever there is a greater need for slurry, a circular
channel set 55 can be placed on the pad to help maintain the proper
uniformity of temperature across the work piece surface. It should
also be noted that shapes other than circles may be used to produce
the same results. For example, FIG. 10 shows hexagons, and FIG. 11
shows pentagons. Any shape can be used in place of circles.
[0051] In the foregoing specification, the invention has been
described with reference to specific embodiments. However, it may
be appreciated that various modifications and changes can be made
without departing from the scope of the present invention as set
forth in the claims below. Accordingly, the specification and
figures are to be regarded in an illustrative rather than
restrictive sense, and all such modifications are intended to be
included within the scope of the present invention.
* * * * *