U.S. patent application number 11/357713 was filed with the patent office on 2006-11-16 for superhard cutters and associated methods.
Invention is credited to Chien-Min Sung.
Application Number | 20060258276 11/357713 |
Document ID | / |
Family ID | 37419762 |
Filed Date | 2006-11-16 |
United States Patent
Application |
20060258276 |
Kind Code |
A1 |
Sung; Chien-Min |
November 16, 2006 |
Superhard cutters and associated methods
Abstract
A cutting device comprises a base having a working side that is
oriented to face a workpiece from which material is to be removed.
A plurality of individual cutting elements are arranged on the
working side of the base, with each cutting element having a peak
that comprises at least one cutting edge that is formed from a
polycrystalline superhard material. The peaks of the cutting
elements are aligned in a common plane.
Inventors: |
Sung; Chien-Min; (Taipei
County, TW) |
Correspondence
Address: |
THORPE NORTH & WESTERN, LLP.
8180 SOUTH 700 EAST, SUITE 200
SANDY
UT
84070
US
|
Family ID: |
37419762 |
Appl. No.: |
11/357713 |
Filed: |
February 17, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60681798 |
May 16, 2005 |
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Current U.S.
Class: |
451/527 ;
51/293 |
Current CPC
Class: |
B24D 7/06 20130101; B24B
7/228 20130101 |
Class at
Publication: |
451/527 ;
051/293 |
International
Class: |
B24D 3/00 20060101
B24D003/00; B24D 18/00 20060101 B24D018/00; B24D 11/00 20060101
B24D011/00 |
Claims
1. A cutting device, comprising: a base having a working side that
can be oriented to face a workpiece from which material is to be
removed; and a plurality of individual cutting elements arranged on
the working side of the base, each cutting element having a peak
that comprises at least one cutting edge that is formed from a
polycrystalline superhard material, the peaks of the cutting
elements being aligned in a common plane.
2. The device of claim 1, wherein the base and each of the cutting
elements are formed from an integral piece of polycrystalline
superhard material.
3. A cutting device, comprising: a base having a working side that
can be oriented to face a workpiece from which material is to be
removed, the base being formed from an integral piece of a
polycrystalline superhard material; and a plurality of individual
cutting elements integrally formed with the working side of the
base, each cutting element having a peak that comprises at least a
tip, the peaks of the cutting elements being aligned in a common
plane.
4. The device of either of claim 2 or claim 3, wherein the
polycrystalline superhard material comprises a polycrystalline
diamond compact.
5. The device of claim 4, wherein the polycrystalline diamond
compact has a diamond grain size of about 50 .mu.m or smaller.
6. The device of claim 5, wherein the polycrystalline diamond
compact has a diamond grain size of about 1 .mu.m to about 10
.mu.m.
7. The device of claim 4, wherein the polycrystalline diamond
compact has a diamond content of about 80% to about 98% by
volume.
8. The device of either of claim 2 or claim 3, wherein the
polycrystalline superhard material comprises a polycrystalline
cubic boron nitride compact.
9. The device of claim 1, wherein the cutting device comprises a
planing device.
10. The device of claim 3, wherein the cutting device comprises a
dressing device.
11. The device of claim 1, further comprising a series of secondary
cutting elements formed on a face of each of the cutting elements,
the secondary cutting elements being configured to maintain a
sharpness of each of the cutting edges during use of the cutting
device.
12. The device of either of claim 1 or claim 3, wherein the peaks
of the cutting element are operable to cut a substantially brittle
material.
13. The device of claim 12, wherein the brittle material is a
member selected from the group consisting of: a metal, a silicon
wafer, a used silicon wafer to be reclaimed by planarization, LCD
glass, an LED substrate, a SiC wafer, a quartz wafer, silicon
nitride, zirconia, sapphire, lithium niobate, lithium titantate,
PZT, gallium arsenide, gallium nitride, indium nitride, boron
phosphate, aluminum nitride and boron nitride.
14. The device of either of claim 1 or claim 3, wherein the peak of
each of the cutting elements includes a plurality of cutting edges
aligned in the common plane.
15. The device of either of claim 1 or claim 3, wherein the peak of
each of the cutting elements includes a shape selected from the
group consisting of: a square, a rectangle, a triangle, a hexagon,
a circle and an oval.
16. The device of either of claim 1 or claim 3, further comprising
a series of secondary cutting elements having at least a tip
aligned in a second common plane, the second common plane being
disposed closer to an opposing side of the base than is the common
plane, the secondary cutting elements being configured to limit a
depth to which the cutting elements can cut into the workpiece.
17. The device of claim 16, wherein the secondary cutting elements
terminate in a planar face.
18. The device of either of claim 1 or claim 3, wherein the peaks
of the cutting elements are leveled relative to the common plane
within about 0.5 .mu.m to about 50 .mu.m.
19. The device of claim 18, wherein the peaks of the cutting
elements are leveled relative to the common plane within about 25
.mu.m.
20. The device of either of claim 1 or claim 3, wherein the common
plane is pitched from about 200 .mu.m to about 2000 .mu.m across
the working side of the cutting device.
21. A method of forming the cutting device as recited in either
claim 2 or claim 3, comprising the step of: providing a
polycrystalline superhard material compact; and removing material
from a working side of a base of the polycrystalline superhard
material compact to form the plurality of individual cutting
elements from the polycrystalline superhard material compact.
22. The method of claim 21, wherein the polycrystalline superhard
material compact comprises a polycrystalline diamond compact.
23. The method of claim 22, wherein the polycrystalline diamond
compact has a diamond grain size of about 50 .mu.m or smaller.
24. The method of claim 23, wherein the polycrystalline diamond
compact has a diamond grain size of about 1 .mu.m to about 10
.mu.m.
25. The method of claim 22, wherein the polycrystalline diamond
compact has a diamond content of about 80% to about 98% by
volume.
26. The method of claim 21, wherein the polycrystalline superhard
material compact comprises a polycrystalline cubic boron nitride
compact.
27. The method of claim 21, further comprising forming a series of
secondary cutting elements on an upper surface of each of the
cutting elements, the secondary cutting elements being configured
to maintain a sharpness of each of the cutting elements during use
of the cutting device.
28. The method of claim 21, wherein cutting edges of the cutting
elements are operable to cut a substantially brittle material.
29. The method of claim 28, wherein the brittle material is a
member selected from the group consisting of: a metal, a silicon
wafer, a used silicon wafer to be reclaimed by planarization, LCD
glass, an LED substrate, a SiC wafer, a quartz wafer, silicon
nitride, zirconia, sapphire, lithium niobate, lithium titantate,
PZT, gallium arsenide, gallium nitride, indium nitride, boron
phosphate, aluminum nitride and boron nitride.
30. The method of claim 21, wherein forming the cutting elements
includes aligning a plurality of cutting edges of each cutting
element in the common plane.
31. The method of claim 21, wherein the peak of each of the cutting
elements includes a shape selected from the group consisting of: a
square, a rectangle, a triangle, a circle and an oval.
32. The method of claim 21, wherein removing material from the
working side of the base includes removing material by a process
selected from the group consisting of: laser ablation,
electro-chemical machining, plasma etching, oxidation and
hydrogenation.
33. The method of claim 21, wherein removing material from the
working side of the base includes removing material by electrical
discharge machining.
34. The method of claim 33, wherein the electrical discharge
machining process utilizes an electrode that includes diamond.
35. The method of claim 34, wherein the electrode is an anode that
includes boron doped diamond.
36. The method of claim 35, wherein the boron doped diamond anode
includes a series of shaped protrusions extending therefrom, the
shaped protrusions being configured to remove material from the
face of the compact in a grooved pattern.
37. The method of claim 34, wherein the electrode is a cathode that
includes boron doped diamond.
38. The method of claim 35, wherein the boron doped diamond cathode
includes a series of shaped protrusions extending therefrom, the
shaped protrusions being configured to remove material from the
face of the compact in a grooved pattern.
39. The method of claim 21, wherein removing material from the face
of the compact further comprises forming a series of secondary
cutting elements having at least a tip aligned in a second common
plane, the second common plane being disposed closer to an opposing
side of the compact than is the common plane, the secondary cutting
elements being configured to limit a depth to which the cutting
elements can cut into the workpiece.
40. The method of claim 39, wherein each of the secondary cutting
elements terminates in a planar face.
41. The method of claim 21, wherein the peaks of the cutting
elements are leveled relative to the common plane within about 0.5
.mu.m to about 50 .mu.m.
42. The method of claim 41, wherein the peaks of the cutting
elements are leveled relative to the common plane within about 25
.mu.m.
43. The method of claim 21, wherein the common plane is pitched
from about 200 .mu.m to about 2000 .mu.m across the face of the
cutting device.
44. A product formed by a process comprising: engaging a surface of
a workpiece with a plurality of individual cutting elements of a
cutting device, the individual cutting elements being integrally
formed from a working side of an integral piece of a
polycrystalline superhard material and each cutting element having
a peak that is aligned in a common plane; and moving the workpiece
and the cutting device relative to one another to thereby remove
material from the workpiece with the cutting elements.
45. The product of claim 44, wherein the polycrystalline superhard
material comprises a polycrystalline diamond compact.
46. The product of claim 45, wherein the polycrystalline diamond
compact has a diamond grain size of about 50 .mu.m or smaller.
47. The product of claim 46, wherein the polycrystalline diamond
compact has a diamond grain size of about 1 .mu.m to about 10
.mu.m.
48. The product of claim 45, wherein the polycrystalline diamond
compact has a diamond content of about 80% to about 98% by
volume.
49. The product of claim 44, wherein the polycrystalline superhard
material comprises a polycrystalline cubic boron nitride
compact.
50. The product of claim 44, wherein each of the plurality of
cutting elements includes a cutting edge aligned in the common
plane.
51. The product of claim 44, wherein the process further comprises
engaging the surface of the workpiece with a series of secondary
cutting elements having at least a tip aligned in a second common
plane, the second common plane being disposed closer to an opposing
side of the polycrystalline superhard material than is the common
plane, to thereby limit a depth to which the cutting elements cut
into the workpiece.
52. The product of claim 51, wherein the secondary cutting elements
terminate in a planar face.
53. The product of claim 44, wherein the peaks of the cutting
elements are leveled relative to the common plane within about 0.5
.mu.m to about 50 .mu.m.
54. The product of claim 44, wherein the peaks of the cutting
elements are leveled within about 15 .mu.m.
Description
PRIORITY DATA
[0001] This application claims priority to copending U.S.
Provisional Patent Application No. 60/681,798, filed May 16, 2005,
which is hereby incorporated herein by reference in its
entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to cutting devices
used to plane workpieces formed of various materials. Accordingly,
the present invention involves the fields of chemistry, physics,
and materials science.
BACKGROUND OF THE INVENTION
[0003] It is estimated that the semiconductor industry currently
spends more than one billion U.S. Dollars each year manufacturing
silicon wafers that exhibit very flat and smooth surfaces.
Typically, chemical mechanical polishing ("CMP") is used in the
manufacturing process of semiconductor devices to obtain smooth and
even surfaced wafers. In a conventional process, a wafer to be
polished is generally held by a carrier positioned on a polishing
pad attached above a rotating platen. As slurry is applied to the
pad and pressure is applied to the carrier, the wafer is polished
by relative movement of the platen and the carrier.
[0004] While this well-known process has been used successfully for
many years, it suffers from a number of problems. For example, this
conventional process is relatively expensive and is not always
effective, as the silicon wafers may not be uniform in thickness,
nor may they be sufficiently smooth, after completion of the
process. In addition to becoming overly "wavy" when etched by a
solvent, the surface of the silicon wafers may become chipped by
individual abrasive grits used in the process. Moreover, if the
removal rate is to be accelerated to achieve a higher productivity,
the grit size used on the polishing pad must be increased,
resulting in a corresponding increase in the risk of scratching or
gouging expensive wafers. Furthermore, because surface chipping can
be discontinuous, the process throughput can be very low.
Consequently, the wafer surface preparation of current
state-of-the-art processes is generally expensive and slow.
[0005] In addition to these considerations, the line wide (e.g.,
nodes) of the circuitry on semiconductors is now approaching the
virus domain (e.g., 10-100 nm). In addition, more layers of
circuitry are now being laid down to meet the increasing demands of
advanced logic designs. In order to deposit layers for making
nanometer sized features, each layer must be extremely flat and
smooth during the semiconductor fabrication. While diamond grid pad
conditioners have been effectively used in dressing CMP pads for
polishing previous designs of integrated circuitry, they have not
been found suitable for making cutting-edge devices with nodes
smaller than 65 nm. This is because, with the decreasing size of
the copper wires, non-uniform thickness due to rough- or
over-polishing will change the electrical conductivity
dramatically. Moreover, due to the use of coral-like dielectric
layers, the fragile structure must be polished very gently to avoid
disintegration. Hence, the pressure used in CMP processes must be
reduced significantly.
[0006] In response, new CMP processes, such as those utilizing
electrolysis (e.g. Applied Materials ECMP) of copper or those
utilizing air film cushion support of wafer (e.g. Tokyo Semitsu),
are being pursued to reduce the polishing pressure on the contact
points between wafer and pad. However, as a consequence of gentler
polishing action, the polishing rate of the wafer will decrease. To
compensate for the loss of productivity, polishing must occur
simultaneously over the entire surface of the wafer. In order to do
so, the contact points between the wafer and the pad must be
smaller in area, but more numerous in quantity. This is in contrast
to current CMP practice in which the contacted areas are relatively
large but relatively few in number.
[0007] Thus, in order to polish fragile wafers more and more
gently, the CMP pad asperities must be reduced. However, to prevent
the polishing rate from declining, more contact points must be
created. Consequently, the pad asperities need to be finer in size
but more in number. However, the more delicate the polishing
process becomes, the higher the risk of scratching the surface of
the wafer becomes. In order to avoid this risk, the highest tips of
all asperities must be fully leveled. Otherwise, the protrusion of
a few "killer asperities" can ruin the polished wafer.
SUMMARY OF THE INVENTION
[0008] Accordingly, the present invention provides a cutting
device, including a base having a working side that can be oriented
to face a workpiece from which material is to be removed. A
plurality of individual cutting elements can be arranged on the
working side of the base. Each cutting element can have a peak that
comprises at least one cutting edge that is formed from a
polycrystalline superhard material. The peaks of the cutting
elements can be aligned in a common plane. The base and each of the
cutting elements can be formed from an integral piece of
polycrystalline superhard material.
[0009] In accordance with another aspect of the invention, a
cutting device is provided, including a base having a working side
that can be oriented to face a workpiece from which material is to
be removed. The base can be formed from an integral piece of a
polycrystalline superhard material. A plurality of individual
cutting elements can be integrally formed with the working side of
the base. Each cutting element can have a peak that comprises at
least a tip. The peaks of the cutting elements can be aligned in a
common plane.
[0010] In accordance with another aspect of the invention, a method
of forming the cutting device above is provided, including the
steps of: providing a polycrystalline superhard material compact;
and removing material from a working side of a base of the
polycrystalline superhard material compact to form the plurality of
individual cutting elements from the polycrystalline superhard
material compact.
[0011] In accordance with another aspect of the invention, a
product is provided that can be formed by the process comprising:
engaging a surface of a workpiece with a plurality of individual
cutting elements of a cutting device, the individual cutting
elements being integrally formed from a working side of an integral
piece of a polycrystalline superhard material and each cutting
element having a peak that is aligned in a common plane; and moving
the workpiece and the cutting device relative to one another to
thereby remove material from the workpiece with the cutting
elements.
[0012] There has thus been outlined, rather broadly, various
features of the invention so that the detailed description thereof
that follows may be better understood, and so that the present
contribution to the art may be better appreciated. Other features
of the present invention will become clearer from the following
detailed description of the invention, taken with the accompanying
exemplary claims, or may be learned by the practice of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1A is a schematic, perspective view of a cutting device
in accordance with an embodiment of the invention;
[0014] FIG. 2 is a side, plan view of the cutting device of FIG.
1;
[0015] FIG. 3 is a schematic, partial side view of a cutting
element cutting a workpiece in accordance with an embodiment of the
invention;
[0016] FIG. 4A is a perspective, more detailed view of a series of
cutting elements in accordance with an embodiment of the
invention;
[0017] FIG. 4B is a perspective view of a cutting device having
arcuate cutting elements in accordance with an embodiment of the
invention;
[0018] FIG. 5 is a sectional view of a pair of cutting elements of
the cutting device of FIG. 1;
[0019] FIG. 6 is a sectional view of a cathode and an anode of an
electrical discharge machining process;
[0020] FIG. 7A is a top view of a cutting device in accordance with
an embodiment of the invention;
[0021] FIG. 7B is a sectional view of a series of cutting elements
of the cutting device of FIG. 7A;
[0022] FIG. 8 is an image of a cutting device with a magnified
image of a cutting element in accordance with an aspect of the
invention; and
[0023] FIG. 9 is an image of a cutting device with a magnified
image of a cutting element in accordance with an aspect of the
invention.
[0024] It will be understood that the above figures are merely for
illustrative purposes in furthering an understanding of the
invention. Further, the figures may not be drawn to scale, thus
dimensions, particle sizes, and other aspects may, and generally
are, exaggerated to make illustrations thereof clearer. Therefore,
departure can be made from the specific dimensions and aspects
shown in the figures in order to produce the cutting devices of the
present invention.
DETAILED DESCRIPTION
[0025] Before the present invention is disclosed and described, it
is to be understood that this invention is not limited to the
particular structures, process steps, or materials disclosed
herein, but is extended to equivalents thereof as would be
recognized by those ordinarily skilled in the relevant arts. It
should also be understood that terminology employed herein is used
for the purpose of describing particular embodiments only and is
not intended to be limiting.
[0026] It must be noted that, as used in this specification and the
appended claims, the singular forms "a," "an" and "the" include
plural referents unless the context clearly dictates otherwise.
Thus, for example, reference to "a cutting element" includes one or
more of such elements and reference to "a brittle material"
includes reference to one or more of such a material.
DEFINITIONS
[0027] In describing and claiming the present invention, the
following terminology will be used in accordance with the
definitions set forth below.
[0028] As used herein, "particle" and "grit" may be used
interchangeably, and when used in connection with a carbonaceous
material, refer to a particulate form of such material. Such
particles or grits may take a variety of shapes, including round,
oblong, square, euhedral, etc., as well as a number of specific
mesh sizes. As is known in the art, "mesh" refers to the number of
holes per unit area as in the case of U.S. meshes. All mesh sizes
referred to herein are U.S. mesh unless otherwise indicated.
Further, mesh sizes are generally understood to indicate an average
mesh size of a given collection of particles since each particle
within a particular "mesh size" may actually vary over a small
distribution of sizes.
[0029] As used herein, "substantial," or "substantially," refers to
the functional achievement of a desired purpose, operation, or
configuration, as though such purpose or configuration had actually
been attained. Therefore, cutting edges that are substantially
aligned in a common plane function as though, or nearly as though,
they were precisely aligned in such a plane.
[0030] Furthermore, when used in an exclusionary context, such as a
material "substantially lacking" or being "substantially devoid of,
or free of" an element, the terms "substantial" and "substantially"
refer to a functional deficiency of the element to which reference
is being made. Therefore, it may be possible that reference is made
to a material in which an element is "substantially lacking," when
in fact the element may be present in the material, but only in an
amount that is insufficient to significantly affect the material,
or the purpose served by the material in the invention.
[0031] As used herein, "working side" refers to the side of a tool
which contacts or is configured to contact material of a workpiece
during a planing or dressing procedure. In some aspects, the
working side may merely face a workpiece to be worked, but may not
actually contact the workpiece.
[0032] As used herein, a "common plane" refers to a profile,
including planar or contoured profiles, above a base surface with
which the peaks of the cutting elements are to be aligned. Examples
of such profiles may include, without limitation, wavy profiles,
convex profiles, concave profiles, multi-tiered profiles, and the
like.
[0033] As used herein, cutting "edge" refers to a portion of a
cutting element that includes some measurable width across a
portion that contacts and removes material from a workpiece. As an
exemplary illustration, a typical knife blade has a cutting edge
that extends longitudinally along the knife blade, and the knife
blade would have to be oriented transversely to a workpiece to
scrape or plane material from the workpiece in order for the
cutting "edge" of the knife blade to remove material from the
workpiece.
[0034] As used herein, "superhard" may be used to refer to any
crystalline, or polycrystalline material, or mixture of such
materials which has a Mohr's hardness of about 8 or greater. In
some aspects, the Mohr's hardness may be about 9.5 or greater. Such
materials include but are not limited to diamond, polycrystalline
diamond (PCD), cubic boron nitride (cBN), polycrystalline cubic
boron nitride (PcBN) as well as other superhard materials known to
those skilled in the art. Superhard materials may be incorporated
into the present invention in a variety of forms including
particles, grits, films, layers, etc.
[0035] As used herein, "vapor deposition" refers to a process of
depositing materials on a substrate through the vapor phase. Vapor
deposition processes can include any process such as, but not
limited to, chemical vapor deposition (CVD) and physical vapor
deposition (PVD). A wide variety of variations of each vapor
deposition method can be performed by those skilled in the art.
Examples of vapor deposition methods include hot filament CVD,
rf-CVD, laser CVD (LCVD), metal-organic CVD (MOCVD), sputtering,
thermal evaporation PVD, ionized metal PVD (IMPVD), electron beam
PVD (EBPVD), reactive PVD, and the like.
[0036] As used herein, "sintering" refers to the joining of two or
more individual particles to form a continuous solid mass. The
process of sintering involves the consolidation of particles to at
least partially eliminate voids between particles. Sintering may
occur in either metal or carbonaceous particles, such as diamond.
Sintering of metal particles occurs at various temperatures
depending on the composition of the material. Sintering of diamond
particles generally requires ultrahigh pressures and the presence
of a carbon solvent as a diamond sintering aid, and is discussed in
more detail below. Sintering aids are often present to aid in the
sintering process and a portion of such may remain in the final
product.
[0037] As used herein, the term "cutting element" refers to a
protrusion or an indentation formed in a cutting device that
includes one or more cutting edges or tips that are configured to
cut or plane material from a surface of a workpiece. While not so
limited, cutting elements described herein can include a frontal
surface and an upper surface that meet at substantially a
90.degree. angle to form the cutting edge. In some cases, cutting
elements of the present invention have a three-dimensional
configuration with relatively substantial width, depth and height.
Each cutting element can include one or more cutting edges that
have a cutting width coinciding with one of the width or depth of
the cutting element.
[0038] As used herein, the term "peak" refers to a relative portion
of a cutting element that extends the greatest distance from a base
of a cutting element. Thus, when oriented to contact a workpiece,
the peaks of cutting elements of a cutting device would contact the
surface of the workpiece prior to any other portion of the cutting
device contacting the workpiece.
[0039] As used herein, a plurality of items, structural elements,
compositional elements, and/or materials may be presented in a
common list for convenience. However, these lists should be
construed as though each member of the list is individually
identified as a separate and unique member. Thus, no individual
member of such list should be construed as a de facto equivalent of
any other member of the same list solely based on their
presentation in a common group without indications to the
contrary.
[0040] Concentrations, amounts, particle sizes, volumes, and other
numerical data may be expressed or presented herein in a range
format. It is to be understood that. such a range format is used
merely for convenience and brevity and thus should be interpreted
flexibly to include not only the numerical values explicitly
recited as the limits of the range, but also to include all the
individual numerical values or sub-ranges encompassed within that
range as if each numerical value and sub-range is explicitly
recited.
[0041] As an illustration, a numerical range of "about 1 micrometer
to about 5 micrometers" should be interpreted to include not only
the explicitly recited values of about 1 micrometer to about 5
micrometers, but also include individual values and sub-ranges
within the indicated range. Thus, included in this numerical range
are individual values such as 2, 3, and 4 and sub-ranges such as
from 1-3, from 2-4, and from 3-5, etc. This same principle applies
to ranges reciting only one numerical value. Furthermore, such an
interpretation should apply regardless of the breadth of the range
or the characteristics being described.
[0042] The Invention
[0043] The present invention provides a cutting device and
associated methods that can be utilized in cutting or otherwise
affecting a workpiece to remove material from the workpiece and
provide a finished, smooth and/or flat surface to the workpiece.
Cutting devices of the present invention can be advantageously
utilized, for example, as planing devices that plane material from
a workpiece, as dressing devices that dress various workpieces, and
as polishing devices that polish various workpieces.
[0044] In the embodiment of the invention illustrated in FIG. 1,
the cutting device 10 can include a base 12 that can have a working
side 14 that faces a workpiece (19 in FIG. 3) to be cut or planed.
A plurality of individual cutting elements 16 can be arranged on
the working side of the base. Each of the cutting elements can
include at least one cutting edge or tip 18, each of which can be
aligned in a common plane 20, shown schematically in FIG. 2. As
discussed in more detail below, the cutting edges can be engaged
with the workpiece 19, and the workpiece and the cutting edges can
be moved relative to one another, to cut, slice, plane or otherwise
remove small pieces or chips from the workpiece to create a surface
on the workpiece that is both very flat and very smooth.
[0045] In one aspect of the invention, each of the cutting elements
16 can include one or a plurality of cutting edges 18 aligned in
the common plane 20. Thus, in the embodiment illustrated in FIG. 1,
each of the cutting elements includes four cutting edges, which can
each serve to cut or plane material from a workpiece. By including
a plurality of cutting elements, each with a plurality of cutting
edges, a total length of cutting edges per cutting element can be
advantageously increased. In addition, since each cutting element
is of substantially the same height, relative to the working
surface of the base, all of the cutting edges from all of the
cutting elements can be aligned in the same common plane. By
aligning each of the cutting edges in a common plane, the cutting
device is substantially self-aligned to shave higher regions of the
workpiece first, then continue cutting until all "high" points on
the workpiece have been reduced, leaving a smooth and flat
workpiece surface.
[0046] The cutting edges 18 of the cutting elements 16 can be
formed from a variety of materials including, in one embodiment, a
polycrystalline superhard material. While not so limited, the
polycrystalline superhard material can be a polycrystalline diamond
compact ("PCD") or a polycrystalline cubic boron nitride compact
("PcBN"). The PCD or PcBN compact can be formed in a variety of
manners, as discussed in more detail below. In the aspect of the
invention shown in FIG. 1, the base 12 and each of the cutting
elements 16 and cutting edges 18 are integrally formed from an
integral piece of polycrystalline superhard material.
[0047] The cutting device of the present invention can be utilized
in a number of applications, and in one embodiment is particularly
well adapted for use in planing substantially brittle materials,
such as silicon wafers, glass sheets, metals, used silicon wafers
to be reclaimed by planarization, LCD glass, LED substrates, SiC
wafers, quartz wafers, silicon nitride, zirconia, etc. In
conventional silicon wafer processing techniques, a wafer to be
polished is generally held by a carrier positioned on a polishing
pad attached above a rotating platen. As slurry is applied to the
pad and pressure is applied to the carrier, the wafer is polished
by relative movements of the platen and the carrier. Thus, the
silicon wafer is essentially ground or polished, by very fine
abrasives, to a relatively smooth surface.
[0048] While grinding of silicon wafers has been used with some
success, the process of grinding materials such as silicon wafers
often results in pieces of the material being torn or gouged from
the body of the material, resulting in a less than desirable
finish. This is due, at least in part, to the fact that grinding or
abrasive processes utilize very sharp points of abrasive materials
(which are often not level relative to one another) to localize
pressure to allow the abrasives to remove material from a
workpiece.
[0049] In contrast to conventional polishing or grinding processes,
the present invention can utilize one or more cutting edges of
cutting elements to cut material from a workpiece to finish or
plane a surface of the workpiece. In general, when a cut is made in
a material, the region of the cut will either deform plastically or
will crack in a brittle manner. If the plastic deformation is
slower than the crack propagation, then the material is known as
brittle. The reverse is true for ductile deformation. However,
under a high pressure, the rate of crack propagation is suppressed.
In this case, a brittle material (e.g. silicon) may exhibit more
ductile characteristics, similar to soft metals. When a sharp
cutting edge of the present invention is pressed against the
surface of brittle silicon, the area of the first contact is
extremely small (e.g. a few nanometers across). Consequently, the
pressure can be very high (e.g. several GPa). Because the cracks
are suppressed, the sharp diamond edge can penetrate silicon
plastically. As a result, the external energy can be transferred to
the very small volume of silicon continually to sustain the ductile
cutting. In other words, the sharp cutting edges can shave or plane
silicon in a manner not previously achieved.
[0050] The PCD or PcBN compacts of the present invention are
generally superhard, resulting in little yielding by the cutting
elements when pressed against a wafer. As hardness is generally a
measure of energy concentration, e.g., energy per unit volume, the
PCD or PcBN compacts of the present invention are capable of
concentrating energy to a very small volume without breaking. These
materials can also be maintained with a very sharp cutting edge due
to their ability to maintain an edge within a few atoms.
[0051] As the ductility of the silicon is maintained by applying
pressure to a very small volume, the penetrating radius is
generally be kept relatively small. This is shown by example in
FIG. 2, where the depth of the cutting elements 16 is shown
generally by the letter "d" and is on the order of about 0.1 mm. In
addition, the shape of the cutting edge must be kept relatively
sharp; in some cases with a radius on the order of 2 nm. In order
to accommodate these dual traits, the material of the cutting edge
of the present invention is hard enough to withstand deformation
during the cutting or planing process. In this manner, both
sharpness and hardness of the cutter is realized to ensure the
ductility of the workpiece. The ductile process of cutting and
removing material from a workpiece is shown schematically in FIG.
3, where cutting edge 18 of cutting element 16 is shown shaving
chip 24 from the workpiece 19.
[0052] Each of the cutting elements 16 can include a substantially
planar face 25 that can define a workpiece contact area. A combined
workpiece contact area of all of the cutting elements can comprise
from between about 5% of a total area of the base to about 20% of a
total area of the base. Thus, in one aspect of the invention, if a
PCD cutter has a diameter of about 100 mm, and the combined contact
areas of the cutting element will be about 10% of that total, then
the total contact area of all cutting elements can be about 7850
mm.sup.2. An edge-to-area ratio of each cutting element can be
about 4/mm, resulting in a total edge length being about 31400
mm.
[0053] The life of the PCD or PcBN cutting devices can often be
limited by the radius of the cutting edge. When the edge becomes
worn such that the radius is increased to about 10 nm, the contact
area may increase up to 100 times. This will reduce the contact
pressure significantly. As a result, the edge will not "bite" into
the silicon but will rather slide against its surface. In this
case, heat will be generated, and the wafer surface might become
thermally damaged. Thus, in it can be important that a sharp edge
be maintained on the cutting edges, less than about 10 nm in radius
for many applications.
[0054] The contact area of a cutting device in accordance with the
present invention will generally determine the pressure applied to
the workpiece. Generally, the larger the area ratio is between the
cutting element contact area and the groove, the smaller the
contact pressure between the cutting element and the workpiece will
be. The contact pressure (P) will determine the penetration depth
(d) as the following expression: d=Pt/B, [0055] where t is the
thickness of the wafer; and B is the bulk modulus of the
workpiece.
[0056] In general, bulk modulus measures the incompressibility of a
material. Its value generally correlates to the pressure to
compress a material completely (zero thickness) at the initial rate
of volume reduction. Bulk modulus of a PCD compact is about 4 Mb
(megabars); the bulk modulus of silicon is about 1 Mb. Thus,
silicon is about four times more compressible than a PCD compact.
When a PCD cutting device or planer is pressed against a silicon
wafer, the relative displacement of the wafer is due primarily to
the sink of silicon wafer surface relative to the PCD surface. A
typical silicon wafer is about 1 mm in thickness, so the shaving
depth may be approximated by:
[0057] d=10.sup.-6 P mm, where P is expressed in bar or atmospheric
pressure.
[0058] If P=1 bar, then the shaving thickness is about 1 nm. This
is about five atomic layers. At this penetration depth, if the
cutting edge is sharp (e.g. radius<1 nm), then the shaving or
cutting is ductile, resulting in a finished, planed surface that is
very smooth, in some cases smoother than a mirror finish. For this
reason, it is important to shave, cut or plane a silicon wafer with
very sharp edge of the PCD planer. If the edge becomes overly dull,
the ductility of silicon can be lost and the resulting brittle
fracturing may destroy the wafer surface.
[0059] The cutting devices of the present invention can be utilized
in either a wet system or a dry system. In a dry application, the
cutting elements can be used to cut or plane chips from a workpiece
without the presence of a liquid slurry. In a typical application,
the cutting device can be mounted to a holder cushion that can be
coupled to a rotatable chuck. The workpiece, for example, a silicon
wafer, can be coupled to a vacuum chuck that provides for rotation
of the workpiece. Both the rotatable chuck and the vacuum chuck can
be rotated in either a clockwise or a counterclockwise direction to
remove material from the workpiece. By changing the rotation of one
element relative to another, more or less material can be removed
in a single rotation of the workpiece. For example, if the
workpiece and planer are rotated in the same direction (but at
different speeds), less material will be removed than if they are
rotated counter to one another.
[0060] In this typical application, a slurry can be applied that
can aid in planing the workpiece surface. The slurry can be either
a water slurry or a chemical slurry. In the case where a chemical
slurry is used, the chemical can be selected to provide cooling or
to react with the surface of the workpiece to soften the workpiece
to provide a more efficient cutting process. It has been found that
the wear rate of a silicon wafer can be dramatically increased by
softening its surface. For example, a chemical slurry that contains
an oxidizing agent (e.g. H.sub.2O.sub.2) may be used to form a
relatively highly viscous oxide that will tend to "cling" on the
wafer surface. In this case, the PCD cutting devices of the present
invention need not necessarily cut the wafer, but rather can scrape
the oxide off the surface of the wafer. Consequently, the sharpness
of the cutting edge becomes less critical. In addition, the service
life of the cutting device can be greatly extended by utilizing a
slurry. For example, a PCD scraper used with a slurry may last 1000
times longer than a PCD cutter.
[0061] Another way to expedite the removal of silicon wafer is by
applying a DC current across the wafer surface. Although diamond is
an insulator, PCD is often electrically conducting due to its
inclusions of metallic cobalt. In this case, the silicon wafer can
be connected to an anode (not shown) and the PCD can be connected
to a cathode (not shown). An electrolytically conducting slurry may
be used to bridge the two electrodes. In this case, the surface of
the silicon may be oxidized by anodation. Furthermore, silicon or
its surface circuitry can be dissolved by electrolysis that will
further accelerate the material removal process.
[0062] Thus, if the cutting device is used to shave or plane in a
dry system, it may last for a few passes on a 12 inch wafer.
However, chemical slurry may increase the scraped surface area by a
thousand times, and if electrical current is applied to assist the
material removal, the cutting device may last an even longer
time.
[0063] FIG. 4A illustrates a variety of cutting elements 16a, 16b,
16c in accordance with an embodiment of the invention. In this
aspect of the invention, the cutting elements can be sized and
shaped with rectangular cross sections, oval cross sections,
circular cross sections, triangular, polygonal, pyramidal cross
sections, etc. The various sized and shaped cutting elements can be
formed by varying locations, and widths, of grooves cut on the
surface of the PCD or PcBN compacts. While not shown in the
figures, the cutting elements can also be formed below the surface
of a PCD or a PcBN compact, such that the cutting elements comprise
inset cavities that include, for example, circular or polygonal
shapes.
[0064] As shown in FIG. 4B, the cutting elements 16d can be formed
in elongate, arcuate fashion, with grooves cut or formed between
the cutting elements. The grooves or depressed regions of the PCD
or PcBN compacts can serve as the reservoirs for slurry used to cut
wafer, as well as for cut debris. The pattern of the network and
the depth of the grooves or recessions can affect the flow for both
slurry and debris. Each PCD cutting element design can be optimized
for the individual process of planarization of a particular
workpiece.
[0065] FIG. 5A illustrates two additional embodiments of the
invention in which cutting element 16 of the cutting device 10 of
FIG. 1 includes a series of secondary cutting elements 40a and 40b
formed on an upper surface or face of the cutting element. In this
aspect of the invention, the secondary cutting elements can be
configured to maintain a sharpness of each of the cutting edges
during use of the cutting device. As shown, the secondary cutting
elements can vary in shape, and can include pyramidal-shaped
cutting elements. The secondary cutting elements can also be formed
in a truncated pyramidal shape (not shown). By utilizing secondary
cutting elements on the primary cutting elements, the total cutting
edge length of the cutting element can be extended by as much as
10,000 times.
[0066] FIGS. 7A and 7B illustrate another embodiment of the
invention in which a plurality of cutting elements 16e and 16f are
formed in a PCD base 12a. As can be appreciated from FIG. 7A, the
present invention can provide for the integral formation from a
superhard polycrystalline material of cutting elements having
differing sizes and configurations. For example, in the embodiment
shown, the larger cutting elements 16e can be used as cutting,
planing or dressing elements while the smaller cutting elements 16f
can be used primarily as "stopping" elements. In other words, the
larger cutting elements can extend further from the base 12a of the
PCD to cut further, or deeper, into the workpiece (not shown in
this figure) on which the PCD is being used.
[0067] When the larger cutting elements 16e extend sufficiently
far, or deep, into the workpiece, the smaller cutting elements can
"bottom out" on the surface of the workpiece to limit further
traveling of the larger elements 16e into the workpiece. To
facilitate this concept, the larger cutting elements can be made
sharper than the smaller cutting elements: for example, they can
terminate in an apex point, while the smaller cutting elements can
terminate in a flat, planar face. In this manner, the larger
cutting elements can more easily cut the workpiece than can the
smaller cutting elements, causing the smaller elements to serve as
depth "stopping" elements. In this manner, the present invention
can provide very accurate control of the depth that the cutting
elements cut into a workpiece (e.g., a PCD pad that is being
dressed).
[0068] FIGS. 8 and 9 present images taken of cutting elements 16g
and 16h, respectively, formed from an integral piece of PCD. As
will be appreciated, the present invention provides a great deal of
flexibility in the shape and size of the cutting elements that can
be formed, with some cutting elements formed in an upright "mesa"
configuration, and others formed in a pyramidal configuration.
[0069] In addition, as the cutting elements of the present
invention can be formed from an integral piece of polycrystalline
superhard material, there generally remains a useful excess portion
of polycrystalline superhard material below the cutting elements on
the base of the cutting device (or that forms the base of the
cutting device). Thus, in one aspect of the invention, once the
cutting elements have become dull or damaged during use, the
cutting device can be sharpened by removing a thin layer of the
superhard material across the entire face of the cutting device in
the same pattern that was originally created on the face of the
device. Cutting devices of the present invention can thus be
relatively easily sharpened or repaired, so long as sufficient
polycrystalline material remains beneath the cutting elements to
allow for further sharpening of the cutting elements.
[0070] The PCD or PcBN compacts utilized in the present can be
formed in a variety of manners. In one embodiment of the invention,
the PCD compact can contain micron (e.g. 1 to 10 .mu.m) diamond,
and can be polished before use. In another aspect, the diamond
grains can be large (e.g. 50 .mu.m) and the surface can be ground
without polishing. In one aspect of the invention, SiC grains can
be mixed with diamond grains as the feed stock for a PCD compact.
The PCD can include a diamond content of about 80% to about 98% by
volume.
[0071] The cutting elements of the present invention can be formed
on or in the polycrystalline superhard material in a variety of
manners. In one aspect, the grooves between the individual cutting
elements can be formed on a PCD surface with electro-chemical
machining, by laser ablation, by plasma etching, by oxidation (to
form carbon dioxide or monoxide gas), hydrogenation (to form
methane gas), etc. Laser beams with relatively longer wavelengths
(e.g. ND:YAG) have been shown to form grooves on PCD effectively.
Laser beams with relatively short wavelengths (e.g. excimers) may
be used to carve out the secondary cutting elements on top of the
primary cutting elements (as shown in FIG. 5). While the latter may
be slower in cutting speed, it is generally more precise due to the
shorter wavelength used. Moreover, the surface damage can be less
with more concentrated energy in higher frequencies. This has been
found suitable for shaving or planing a silicon wafer in accordance
with the present invention.
[0072] In another aspect of the invention, material can be removed
from a polycrystalline superhard material compact to integrally
form the individual cutting elements from the polycrystalline
superhard material compact. In other words, the cutting elements
can be formed by removing the polycrystalline material from around
and about the cutting elements, leaving the cutting elements as the
only remaining material above the base of the cutting device.
[0073] In one aspect of the invention, the material is removed from
the PCD or PcBN compact by electrical discharge machining ("EDM").
In this aspect, the EDM process can utilize one or more electrodes
that include diamond. For example, the cathode used in the EDM
process can be a boron doped diamond material and the anode used in
the EDM process can be the PCD (in this case, the PCD would
generally need to be at least partially electrically conductive).
As current is applied through the boron doped diamond material, the
material of the PCD can be carefully and controllably removed to
form various patterns on the PCD.
[0074] As shown for example in FIG. 6, in one aspect of the
invention, the anode 30 of the EDM process can comprise a portion
of a boron doped diamond ("BDD") material through which current is
applied. The BDD anode can include a series of "V"-shaped
protrusions 31 that, during the EDM process, form a series of
corresponding channels 32 in the PCD compact 34 (which, in turn,
define a plurality of cutting elements in the PCD compact). While
the protrusions are shown as being generally V-shaped, it is of
course contemplated that they can be formed in a variety of shapes
that can be selected to form channels having desired shapes in the
PCD compact. As is known to those having ordinary skill in the art,
the EDM process will generally utilize an insulating liquid such as
oil or deionized water, the details of which are not illustrated in
the drawings.
[0075] It has been found that, while the configuration illustrated
in FIG. 6 (in which the PCD compact serves as the cathode of the
EDM process and the BDD material serves as the anode) performs
well, the reverse configuration can also be used. For example,.in
this aspect of the invention, the BDD material is used as the anode
and the PCD is used as the cathode, resulting in the PCD material
removal rate being relatively fast (note that both the BDD material
and the PCD material will be consumed, at varying rates, during the
EDM process). However, by reversing the polarity (e.g., by using
the BDD as the cathode and the PCD as the anode), the PCD material
removal rate will be slower than in the first configuration but the
surface finish of the PCD will better.
[0076] It is contemplated that the use of an electrically
conducting diamond containing material as an electrode to remove
material from another electrically conducting diamond containing
material (as the other electrode) can be extended to a variety of
applications in addition to those explicitly discussed herein. For
example the diamond-diamond EDM process can be utilized to remove
material from an electrically conductive diamond material that is
used in: abrasive applications, load bearing applications,
protective covering applications, heat spreading applications,
material molding applications, acoustic applications, semiconductor
applications, etc.
[0077] In accordance with another aspect, the present invention
provides a product formed by a process comprising: engaging a
surface of a workpiece with a plurality of individual cutting
elements of a cutting device, the individual cutting elements being
integrally formed from a working side of an integral piece of a
polycrystalline superhard material and each cutting element having
a peak that is aligned in a common plane; and moving the workpiece
and the cutting device relative to one another to thereby remove
material from the workpiece with the cutting elements.
EXAMPLES
[0078] The following examples present various methods for making
the cutting tools of the present invention. Such examples are
illustrative only, and no limitation on present invention is meant
thereby.
Example 1
[0079] A boron doped diamond film ("BDD") having a resistivity of
about 0.001 ohm-cm and a thickness of about 500 .mu.m has a
"zigzag" pattern formed on one edge via a wire EDM process. The
resulting blade is mounted on an EDM machine as a cathode. The
anode is a flat PCD about 100 mm in diameter and about 2 mm in
thickness. The diamond table used is about 500 .mu.m in thickness.
An electrically conducting fluid is used to carry the electricity
between the two electrodes. During the EDM process, the PCD is
gradually traversed across the stationary BDD blade. This process
is repeated while the BDD is gradually descending into the PCD
compact. The portion of the PCD that is brought in close proximity
to the edge of the BDD is selectively eroded away by electrical
discharging, electrolysis, and dissolution.
[0080] In this manner, a corresponding "zigzag" pattern of ridges
is gradually formed on the flat PCD top. When the grooves reach a
predetermined height (e.g., 80 .mu.m), the serrated ridges so
formed are cleaned for measurements of geometry. Subsequently, the
PCD is rotated 90 degrees and the process is repeated such that
pyramid shapes are formed. The angle of the pyramids produced
generally matches the angle of the zigzag pattern on the BDD. The
tips of these pyramids also duplicate the pattern of recesses of
the zigzag pattern on the BDD.
[0081] The PCD planer so formed has improved dimension tolerances
compared to PCD planers formed by metallic electrodes used in an
EDM process. In addition, the consumption rate of BDD blade is much
lower. Also, the voltage (90 V) and current (30 A) utilized are
much lower than metallic electrode processes (e.g. 120 V and 80 A).
During the process of EDM, the pulsation period for EDD (20 micro
seconds on by 20 micro seconds off) can be 10 times longer due to
diamond's exceptional thermal stability, thermal conductivity, and
chemical inertness. It was estimated that the maximum electrode
temperature (about 400.degree. C., compared to oxidation threshold
temperature of 750.degree. C.) during the BDD EDM process was about
200.degree. C. lower than that of the metallic process. The wear
rate of the BDD (0.3%) was also fractional compared to the wear
rate of copper tungsten (30%). The EDM speed (20 microns per
minutes) was twice as fast.
Example 2
[0082] The above example was repeated with the reverse polarity:
e.g., the BDD was positively biased. In this case, the EDM process
was still viable except that the wear rate of the BDD was more than
doubled. However, the surface finish of the ADD improved due to a
slower erosion rate on the surface.
Example 3
[0083] The process of Example 1 was repeated except that the
cathode was replaced by a PCD blank of 1.6 mm in thickness (PCD
table 0.5 mm thick, cemented tungsten carbide 1.5 mm thick). The
PCD used had a 25 .mu.m diamond grain size, it contained 10 wt % of
cobalt and had an electrical resistivity of 0.001 ohm-cm.
Example 4
[0084] BDD grits of 100/120 mesh were used to make a bronzed bonded
grinding wheel. The outside diameter was shaped by a BDD EDM
process to form a zigzag pattern thereon. The BDD wheel was then
used as a cathode for an EDM process performed on a PCD blank.
During the traversing of the PCD surface, the BDD wheel was slowly
turned to uniformly expose the contact edge from which electrical
current was emitted. After the ridges were formed, the PCD was
rotated to traverse in a perpendicular direction until a series of
pyramidal cutting elements were formed on the PCD.
Example 5
[0085] A BDD was formed to an "A" point and used as an anode in an
EDM process. A PCD compact was rotated about the "A" point to
gradually form a V notch in the PCD compact. The V notch was formed
at several radius positions in order to produce concentric ridges
on the PCD surface. The resulting tool can be used as a PCD planer
for truing workpieces.
Example 6
[0086] The process of Example 5 was repeated followed by traversing
the "zigzag"-patterned BDD in three equally spaced directions. The
resulting triangular pyramid formed concentric island chains. The
resulting tool included excellent radial slurry/debris passages as
well as very sharp cutting points.
[0087] It is to be understood that the above-described arrangements
are only illustrative of the application of the principles of the
present invention. Numerous modifications and alternative
arrangements may be devised by those skilled in the art without
departing from the spirit and scope of the present invention and
the appended claims are intended to cover such modifications and
arrangements. Thus, while the present invention has been described
above with particularity and detail in connection with what is
presently deemed to be the most practical and preferred embodiments
of the invention, it will be apparent to those of ordinary skill in
the art that numerous modifications, including, but not limited to,
variations in size, materials, shape, form, function and manner of
operation, assembly and use may be made without departing from the
principles and concepts set forth herein.
* * * * *