U.S. patent application number 09/910907 was filed with the patent office on 2002-02-07 for polishing tool and manufacturing method therefor.
Invention is credited to Hirokawa, Kazuto, Hiyama, Hirokuni, Matsuo, Hisanori, Wada, Yutaka.
Application Number | 20020016139 09/910907 |
Document ID | / |
Family ID | 27344167 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020016139 |
Kind Code |
A1 |
Hirokawa, Kazuto ; et
al. |
February 7, 2002 |
Polishing tool and manufacturing method therefor
Abstract
A polishing tool applicable to various types of polishing
objects is provided that enables to stabilize the polishing speed
and to obtain superior surface details while reducing the formation
of defects such as scratches on the polished surface. The tool is
operated by pressing and sliding on the polishing object in a
swinging motion and the surface is polished with abrasive particles
imbedded in a matrix comprised primarily of a thermoplastic resin
such as butadiene styrene, polybutadiene or MBS resin of acryl
rubber group. The polishing tool includes fixed-abrasive polishing
tool that contains abrasive particles within the polishing tool, or
a polishing pad containing non-fixed-abrasive particles.
Inventors: |
Hirokawa, Kazuto; (Tokyo,
JP) ; Hiyama, Hirokuni; (Fujisawa-shi, JP) ;
Wada, Yutaka; (Tokyo, JP) ; Matsuo, Hisanori;
(Tokyo, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
27344167 |
Appl. No.: |
09/910907 |
Filed: |
July 24, 2001 |
Current U.S.
Class: |
451/54 ;
257/E21.23; 451/527; 451/57; 451/59 |
Current CPC
Class: |
H01L 21/30625 20130101;
B24D 3/346 20130101; B24B 37/24 20130101; B24D 18/00 20130101; B24D
3/32 20130101 |
Class at
Publication: |
451/54 ; 451/57;
451/59; 451/527 |
International
Class: |
B24B 001/00; B24D
011/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 25, 2000 |
JP |
2000-224485 |
Jan 18, 2001 |
JP |
2001-010830 |
Apr 23, 2001 |
JP |
2001-125010 |
Claims
What is claimed is:
1. A polishing tool for polishing an object, wherein the polishing
tool is comprised primarily by a thermoplastic resin.
2. A polishing tool according to claim 1, wherein the polishing
tool is a fixed-abrasive polishing tool that contains abrading
particles within the tool.
3. A polishing tool according to claim 1, wherein the polishing
tool is a non-fixed-abrasive polishing pad.
4. A polishing tool according to claim 2, wherein the abrading
particles include cerium oxide (CeO.sub.2), alumina
(Al.sub.2O.sub.3), silicon carbide (SiC), silicon dioxide
(SiO.sub.2), zirconia (ZrO.sub.2), iron oxides (FeO,
Fe.sub.3O.sub.4), manganese oxide (MnO.sub.2, Mn.sub.2O.sub.3),
magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO),
zinc oxide (ZnO), barium carbonate (BaCO.sub.3), calcium carbonate
(CaCO.sub.3), diamond (C), or a composite material comprised by
those recited above.
5. A polishing tool according to claim 1, wherein the polishing
tool is formed by injection molding to charge a feed material under
pressure into a mold of a specific shape.
6. A polishing tool according to claim 1, wherein a material
comprising the polishing tool further comprises an interface
activation agent.
7. A polishing tool according to claim 1, wherein a material
comprising the polishing tool further comprises a hydrophilic
substance or said material is modified by adding the hydrophilic
substance.
8. A fixed-abrasive polishing tool for polishing an object, said
polishing tool comprising: abrading particles; and a resin for
binding said abrading particles in a matrix of said resin, wherein
said resin comprises thermoplastic resin.
9. A fixed-abrasive polishing tool according to claim 8, wherein
the abrading particles include cerium oxide (CeO.sub.2), alumina
(Al.sub.2O.sub.3), silicon carbide (SiC), silicon dioxide
(SiO.sub.2), zirconia (ZrO.sub.2), iron oxides (FeO,
Fe.sub.3O.sub.4), manganese oxide (MnO.sub.2, Mn.sub.2O.sub.3),
magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO),
zinc oxide (ZnO), barium carbonate (BaCO.sub.3), calcium carbonate
(CaCO.sub.3), diamond (C), or a composite material comprised by
those recited above.
10. A fixed-abrasive polishing tool according to claim 8, wherein a
porosity is formed in said polishing tool.
11. A fixed-abrasive polishing tool according to claim 10, wherein
a range of composition of fixed-abrasives (percentages of abrading
particles (Vg), binder (Vb) and air porosity (Vp)) in volume
percent (vol %) are: 10%<abrading particles (Vg)<50%,
30%<binder (Vb)<80%, and 0%<air porosity (Vp)<40%.
12. A method for making a fixed-abrasive polishing tool comprising:
using abrading particles and a thermoplastic resin as raw
materials; filling a forming fixture with a mixture of abrading
particles and the thermoplastic resin into a mold; and forming the
fixed-abrasive polishing tool.
13. A method according to claim 12, wherein said forming is
performed by heating-cooling the mixture and/or pressing the
mixture.
14. A method according to claim 12, wherein said mixing of the
abrading particles and the thermoplastic resin is carried out prior
to or during filling or after filling a forming fixture with the
raw materials.
15. A method for making a fixed-abrasive polishing tool, said
method comprising: mixing powdery abrading particles or a slurry
and raw materials of the thermoplastic resin to form a dispersion
liquid; polymerizing or manufacturing the thermoplastic resin; and
making a mixture containing the polymerized thermoplastic resin and
the abrading particles in the dispersion liquid during the step of
polymerizing or manufacturing the thermoplastic resin.
16. A method according to claim 15, said method further comprising:
performing a mist drying step of said polymerized mixture.
17. A method according to claim 16, wherein said mist drying step
comprising a spray drying step.
18. A method according to claim 16, wherein said mixture is formed
with particles by the mist drying step and a diameter of the
particles is in a range of 1.about.500 .mu.m.
19. A method for making a fixed-abrasive polishing tool comprising:
mixing abrading particles and a resin in a liquid; drying said
mixed liquid to obtain dried mixed material; and forming said dried
mixed material into the fixed-abrasive polishing tool.
20. A method according to claim 19, wherein said abrading particles
are provided in a state of slurry.
21. A method according to claim 19, wherein said resin is provided
in a state of powder and mixed with abrading particles in water or
a solvent.
22. A method according to claim 19, wherein said resin is provided
in a liquid state where the resin is dispersed or dissolved in
water or a solvent.
23. A method according to claim 19, wherein said drying step
comprises a mist drying step.
24. A method according to claim 23, wherein said mist drying step
is performed by a spray dryer.
25. A method according to claim 19, wherein said polishing tool is
formed by filling the said mixed powder into a mold.
26. A method according to claim 19, wherein pulverizing is
performed to obtain a powder in a range of 1-500 .mu.m during or
after drying said mixed liquid.
27. A method for making a fixed-abrasive polishing tool comprising:
mixing abrading particles and a liquid resin to form a mixed
liquid; drying and comminuting said mixed liquid to obtain dried
mixed material; and forming said dried mixed material into the
fixed-abrasive polishing tool.
28. A method according to claim 27, wherein abrading particles are
provided as a powder or dried slurry.
29. A method according to claim 28, wherein said drying step of
slurry comprises a spray drying step.
30. A method for making a fixed-abrasive polishing tool comprising:
mixing powder of abrading particles and a powder of resin in a
liquid to form a mixed liquid; drying and comminuting said mixed
liquid to obtain dried mixed material; and forming said dried mixed
material into the fixed-abrasive polishing tool.
31. A method according to claim 30, wherein said liquid comprises
water or a solvent.
32. A method according to claim 31, wherein said powder of abrading
particles is obtained by drying slurry.
33. A method according to claim 32, wherein said drying step of
slurry comprises a spray drying step.
34. A method for making a fixed-abrasive polishing tool comprising:
mixing slurry containing abrasive particles and a liquid resin to
form a mixed liquid; drying said mixed liquid to obtain dried mixed
material; and forming said dried mixed material into the
fixed-abrasive polishing tool.
35. A method according to claim 34, wherein said forming is
performed by molding said dried mixed material into a mold.
36. A method according to claim 34, wherein said drying step
comprises a mist drying step.
37. A method according to claim 34, wherein said drying step
comprises a spray drying step.
38. A polishing apparatus for polishing a semiconductor wafer,
comprising: a topring for holding the wafer; and a polishing tool,
said polishing tool comprised primarily by a thermoplastic
resin.
39. A polishing apparatus according to claim 38, wherein said
semiconductor wafer has patterns comprised by high portions and low
portions.
40. A polishing apparatus for polishing a semiconductor wafer,
comprising: a topring for holding the wafer; and a fixed-abrasive
polishing tool, said polishing tool comprising abrading particles
and a resin for binding said abrading particles in a matrix of said
resin, said resin comprises thermoplastic resin.
41. A polishing apparatus according to claim 40, wherein a range of
composition of fixed-abrasive polishing tool (percentages of
abrading particles (Vg), binder (Vb) and air porosity (Vp)) in
volume percent (vol %) are: 10%<abrading particles (Vg)<50%,
30%<binder (Vb)<80%, and 0%<air porosity (Vp)<40%.
42. A polishing apparatus according to claim 40, wherein said
semiconductor wafer has patterns comprised by high portions and low
portions.
43. A polishing apparatus according to claim 40, further
comprising: a dresser for dressing a polishing surface of said
fixed-abrasive polishing tool.
44. A polishing apparatus according to claim 40, wherein said
fixed-abrasive polishing tool is mounted on a base.
45. A polishing apparatus according to claim 44, wherein a
polishing tool comprised by said fixed-abrasive polishing tool and
said base is mounted detachably on a polishing table.
46. A polishing apparatus according to claim 45, wherein said
polishing tool is fixed to said polishing table by clamps.
47. A polishing apparatus for polishing a semiconductor wafer,
comprising: at least one topring for holding the wafer; and at
least two polishing tables providing polishing surfaces
respectively, wherein one of said polishing table having a
fixed-abrasive polishing tool, said polishing tool comprising
abrading particles and a thermoplastic resin for binding said
abrading particles.
48. A method of polishing a substrate comprising: polishing the
substrate firstly by a fixed-abrasive polishing tool, said
polishing tool comprising abrading particles and a thermoplastic
resin for binding said abrading particles; and finishing the
substrate secondly by a finishing pad.
49. A method according to claim 48, wherein said first polishing is
performed by supplying liquid not containing abrading
particles.
50. A method according to claim 48, wherein said first polishing is
performed by supplying water containing additive agent.
51. A method according to claim 48, wherein said finishing step is
performed by supplying water.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing tool and its
manufacturing method, and relates in particular to the structure of
a fixed-abrasive polishing tool or a polishing pad, used to polish
a polishing object such as semiconductor wafers to a flat and
mirror polished surface.
[0003] 2. Description of the Related Art
[0004] In recent years, as semiconductor devices become more highly
integrated, the line width of the circuit is becoming finer and the
dimensions of the integrated devices are becoming finer. In the
process of manufacturing such devices, there is sometimes a need to
remove a film formed on the surf ace of a semiconductor wafer by
polishing so as to planarize the surface, and as a means for such
planarization, chemical mechanical polishing (CMP) is used. The CMP
apparatus of this type has a turntable with a bonded polishing pad
and a topring, and a polishing object is placed between the
turntable and the topring so that both the turntable and the
topring can be rotated while the topring exerts a certain pressure
on the turntable and a slurry is delivered on the polishing pad to
polish the surface of the polishing object flat and in a mirror
polish.
[0005] In the CMP method based on the slurry, there is a problem
that the quality of polish depends on the device pattern, because
polishing is performed using a relatively soft polishing pad while
supplying a slurry containing a large quantity of abrasive
particles. Pattern-dependency means that because the semiconductor
wafer has patterns comprised by high portions and low portions
before it is planarized, the polished surface exhibits mild slopes
even after polishing such that a perfectly flat surface is
difficult to obtain. This is caused by the fact that polishing
speed is fast in regions of finely spaced patterns but the
polishing speed is slow in regions of coarsely spaced patterns,
thereby producing mild slopes between the regions of slow and fast
polishing speeds. And, in the technique based on the polishing pad,
not only the high portions but also the low portions are polished
so that it has been difficult to realize the so-called
self-stopping function in this type of operation, which stops the
polishing automatically when the high portions are completely
removed.
[0006] On the other hand, there has been much study on the
technique of polishing based on the so-called fixed-abrasive
polishing tool in which abrasive particles such as cerium oxide are
fixated using a binder such as phenolic resin. In the technique
based on fixed-abrasive polishing tool, because the polishing
materials are harder than the materials used in the conventional
CMP methods, high portions are more readily removed compared with
the low portions, leading to an advantage that an absolute flatness
is more easily obtained using this technique. Also, depending on
the choice of the composition of the fixed-abrasive polishing tool,
the self-stopping function can be made to operate, in which the
speed of polishing becomes extremely low when the high portions are
removed so that the polishing operation virtually ceases. Also, in
the technique based on fixed-abrasive polishing tool, because
slurry containing a large amount of abrasive particles is not used,
there is an advantage that the technique is environmentally
friendly.
[0007] However, in the technique based on fixed-abrasive polishing
tool, the following problems have been noted. That is, when making
semiconductor devices, the polished surface after the CMP
processing not only must be flat but must also avoid creating
scratches (damage) on the surface. When a polishing pad for CMP
processing is used in polishing an object, it is known that, when
the hardness of the pad is high, the polished surface is vulnerable
to creating scratches, and for this reason, soft materials are used
generally for making pads, and to achieve this end, soft foaming
agents are used in making the pads. On the other hand, using the
fixed-abrasive polishing tools, because the fixed-abrasive
polishing tools are harder than pad materials, many scratches are
created on the polished surface even though high flatness is
achieved.
[0008] Therefore, fixed-abrasive polishing tools for semiconductor
device processing have been used with considerable restrictions,
such as the type of binder or a narrow range of compositions in
which the abrasive particles, binder and porosity have been
optimized. In the meantime, the polishing objects range widely from
silicon substrate, polysilicon films, oxide films, nitride films to
wiring layers comprised by aluminum or copper. For these reasons,
it has been difficult in reality to manufacture fixed-abrasive
polishing tools that can produce stable polishing speed and retain
differences in the pattern level as well as refraining from causing
scratches on the polished surface.
SUMMARY OF THE INVENTION
[0009] The present invention is provided in view of the background
information described above, and an object is to provide a
polishing tool and a method of manufacturing the polishing tool
that exhibits a stable speed of polishing and good surface flatness
and is able to reduce various defects such as scratches created on
the polished surface of a polishing object of various types.
[0010] First aspect of the invention relates to a polishing tool
that polishes an object using a sliding motion while pressing on
the object by abrasive particles, wherein the polishing tool is
comprised primarily by a thermoplastic resin.
[0011] Second aspect relates to a polishing tool that polishes an
object using a sliding motion while pressing on the object by
abrasive particles, wherein the polishing tool is comprised by a
polymer resin to provide a hard matrix and elastic elements having
elastic properties contained in the matrix.
[0012] Third aspect relates to a polishing tool, wherein the
polishing tool is a fixed-abrasive polishing tool that contains
abrasive particles within the tool.
[0013] Fourth aspect relates to a polishing tool, wherein the
polishing tool is a polishing pad.
[0014] Conventional fixed-abrasive polishing tool for semiconductor
wafers is based generally on the use of a thermosetting resin such
as PVA, phenolic resin, or epoxy resin. In the present invention,
instead of thermosetting resin, thermoplastic resin is used, and
elastic bodies (polymer substance) are dispersed within a hard
resin matrix, thereby producing a fixed-abrasive polishing tool
having unique properties that could not be obtained in conventional
fixed-abrasive polishing tools. That is, heat is generated during
polishing of wafers so that, by using a thermoplastic resin in a
fixed-abrasive polishing tool or polishing pad, the generated heat
tends to soften the resin. It enables to polish an object using a
softer abrading surface, thus suppressing the formation of
scratches (damage) on the polished surface. Also, by using a hard
resin matrix containing elastic bodies within, the abrading surface
is hard macroscopically but is soft microscopically, thus enabling
to produce a polished surface of superior flatness as well as
having less scratches.
[0015] Fifth aspect relates to the polishing tool, wherein the
abrasive particles include cerium oxide (CeO.sub.2), alumina
(Al.sub.2O.sub.3), silicon carbide (SiC), silicon dioxide
(SiO.sub.2), zirconia (ZrO.sub.2), iron oxides (FeO,
Fe.sub.3O.sub.4), manganese oxide (MnO.sub.2, Mn.sub.2O.sub.3),
magnesium oxide (MgO), calcium oxide (CaO), barium oxide (BaO),
zinc oxide (ZnO), barium carbonate (BaCO.sub.3), calcium carbonate
(CaCO.sub.3), diamond (C), or a composite material comprised by
those recited above.
[0016] Accordingly, using relatively readily available materials, a
polishing tool is provided that enables a stable polishing speed
with a flat finished surface and create less scratches
(damage).
[0017] Sixth aspect relates to a polishing tool, wherein the
polishing tool is formed by injection molding to charge a feed
material under pressure into a mold of a specific shape. Injection
molding is a process in which a molten feed material is injected
under pressure into a cavity of a metal mold to replicate a solid
product of a conjugate shape to the shape of the cavity.
Accordingly, fixed-abrasive polishing tools can be produced readily
at high productivity.
[0018] Seven aspect relates to a polishing tool, wherein the resin
includes an acryronitrile butadiene styrene resin (known as ABS
resin). ABS resin is a copolymer of acryronitrile, butadiene and
styrene. The structure is comprised by small soft particles of
butadiene rubber nuclei in a hard matrix of AS (acrylonitrile
styrene) resin. A fixed-abrasive polishing tool comprised by ABS
resin is as hard as AS resin from a macroscopic viewpoint so as to
produce high planar surface by polishing on the object, but from a
microscopic viewpoint, shock absorbing action is provided by the
soft butadiene rubber to lead to suppression of scratches (damage)
to enable high quality polishing. A polishing pad comprised by ABS
resin has an abrading surface that is as hard as As resin
macroscopically, but microscopically, soft butadiene rubber
particles provide shock absorbing action so that high quality
polishing is enabled.
[0019] Eighth aspect relates to a polishing tool, wherein the resin
includes a core-shell structure type resin having a core made of an
elastic body containing a rubber material. It is preferable that
the resin is a butadiene styrene, polybutadiene or acrylic rubber
group MBS resin. Use of this resin for making a fixed-abrasive
polishing tool enables highspeed polishing, same as in the case of
ABS resin, and the polishing tool is able to produce extremely low
number of scratches. Other than ABS, MBS resins, resins having a
core-shell structure comprised by a core of an elastic body are
similarly effective.
[0020] Tenth aspect relates to a polishing tool, wherein the
elastic body includes an elastic filler material and the elastic
filler material includes a rubber filler material. In so doing, by
including small and soft rubber particles as a constituting
element, similar effects to ABS resin is obtained such that the
tool acts macroscopically hard, but microscopically the tool act
softly on the polishing surface to enable high quality polishing.
Therefore, even when the tool is used in conjunction with the
slurry polishing technique, less scratches are created and high
quality polishing is enabled.
[0021] Eleventh aspect relates to a polishing tool, wherein a
material comprising the polishing tool further comprises a
surface-active agent. Generally, polymeric materials (resins) have
poor wettability with abrasive particles, and therefore, when a
polishing is made using abrasive particles and binder only, there
is a problem that abrasive particles do not disperse uniformly and
large clusters are formed within the matrix. Extremely small
clusters of particles fall off from the tool during polishing, and
it is known that polishing byproducts and debris are trapped in the
cavities thus generated so as to enable effective polishing action.
However, clusters of the order of several hundred nanometers are
detached from the matrix, immediately resulting in severe
degradation of polishing capability with time and immediate loss of
polishing capability. Further, differences of polishing ability
appear within the polishing surface of the tool and leads to
polishing problems such as non-uniformity of surface finish.
Therefore, when a surface-active agent is added during kneading of
raw material, wettability of the binder with abrasive particles is
assured to produce a fixed-abrasive polishing tool that enables
stable polishing.
[0022] Twelfth aspect relates to a polishing tool, wherein a
material comprising the polishing tool further comprises a
hydrophilic substance. Generally, polymeric materials are
hydrophobic and rejects wetting by a polishing solution so that
solution retaining ability of the polishing pad is low and stable
polishing is difficult. Therefore, by including hydrophilic
material having a large number of hydrophilic bases on its surface,
wettability is assured so that the polishing surface of a polishing
pad can retain the polishing solution uniformly throughout the
polishing surface, and stable polishing is enabled.
[0023] Thirteenth aspect relates to a polishing tool, wherein a
hydrophilic base is further added to modify a material comprising
the polishing tool. Similar to the advantage recited in aspect
twelve, the polishing solution can be retained on the polishing
surface of the tool uniformly throughout to enable stable
polishing.
[0024] Fourteenth aspect relates to a fixed-abrasive polishing tool
that uses a sliding motion to polish an object while pressing on
the object by abrasive particles, wherein the polishing tool
includes a resin containing butadienestyrene group MBS resin,
polybutadiene group MBS resin or an acrylic rubber group MBS
resin.
[0025] MBS resin is a copolymer based on feed materials of
methylmethacrylate and butadiene styrene, so as to form a
core-shell type structure having a core of rubber layer comprised
by a copolymer (SBR) containing butadiene and styrene, and a shell
of a copolymer (MS) containing methylmethacrylate and styrene.
Other than the copolymer (SBR) of butadiene and styrene, MBS resin
comprising polybutadiene group rubber and polyacrylic ester group
rubber may be used.
[0026] The copolymer (MS) of methylmethacrylate and styrene used
for forming the shell structure of MES resin can be softened by
polymerizing polymethylmethacrylate (PMMA) adding styrene.
Polymethylmethacrylate (PMMA) has a high hardness relative to other
plastics and is characterized by its high hardness but suffers from
brittleness, and such characteristics are known to be suitable for
making fixed-abrasive polishing tools. Especially, this resin is
effective for improving scratching property. Further, it is
considered that, by mixing styrene to this material
(methylmethacrylate) for polymerizing, hardness can be lowered and
brittleness can be controlled, and the material cost can be
reduced. MBS resin combining the shell of this material and rubber
layer core has improved shock absorbing quality and is able to
moderate the impact of abrasive particles generated when using the
fixed-abrasive polishing tool. The tool therefore enables high
quality polishing that produces scratch-free polished surface.
[0027] Fifteenth aspect relates to a method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, by filling a mixture of the
feed materials into a forming fixture followed by heating-cooling
and/or a pressing process. In this process, cooling process
includes self-cooling.
[0028] Sixteenth aspect relates to a method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, by mixing the abrasive
particles and the thermoplastic resin, prior to or during filling
or after filling the feed materials into a forming fixture.
[0029] Seventeenth aspect relates to a method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, by mixing abrasive particles
or a slurry in which abrasive particles are dispersed in a liquid
and raw materials for the thermoplastic resin to form a dispersion
liquid, and making a polymerized mixture containing the
thermoplastic resin and abrasive particles in the dispersion
liquid, during the step of polymerizing or manufacturing the
thermoplastic resin.
[0030] Methods for producing particles of a thermoplastic resin
include a suspension polymerization and emulsion polymerization.
According to these methods, spherical polymerized product can be
produced in a dispersion liquid of the raw material (monomer) of a
thermoplastic resin. By mixing abrasive particles or a slurry
(particle dispersion liquid) in such a dispersion liquid, a mixture
of abrasive particles and resin can be obtained during the
polymerizing step.
[0031] Eighteenth aspect relates to a method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, making a dispersion liquid by
mixing abrasive particles or a slurry and raw materials for the
thermoplastic resin, making a polymerized mixture of the
thermoplastic resin and abrasive particles in the dispersion
liquid, and performing a spray drying or other mist drying
process.
[0032] Methods for producing particles of a thermoplastic resin
include a suspension polymerization and emulsion polymerization.
According to these methods, spherical polymerized product can be
produced in a dispersion liquid of the raw material (monomer) of a
thermoplastic resin. By mixing abrasive particles or a slurry
(particle dispersion liquid) in the above dispersion liquid, a
mixture of abrasive particles and resin can be obtained during the
polymerizing step. By drying and particulating the microparticles
of the mixed material, suitable sizes of the feed material for
making the fixed-abrasive polishing tool can be obtained. Further,
it enables to improve the uniformity of distribution of
microparticles of abrasive particles and the resin.
[0033] Nineteenth aspect relates to a method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, wherein during polymerizing
or manufacturing of the thermoplastic resin, a polymerized mixture
containing the thermoplastic resin and abrasive particles of
particle diameter in a range of 1-500 .mu.m is obtained.
[0034] Methods for producing particles of a thermoplastic resin
include a suspension polymerization and emulsion polymerization.
According to these methods, spherical polymerized product can be
produced in a dispersion liquid of the raw material (monomer) of a
thermoplastic resin. By mixing abrasive particles or a slurry
(particle dispersion liquid) in such a dispersion liquid, a mixture
of abrasive particles and resin can be obtained during the
polymerizing step. Further, by obtaining a particle size in a range
of 1-500 .mu.m. which is suitable for making the fixed-abrasive
polishing tool, during the step of obtaining the mixture particles,
the feed material for making a fixed-abrasive polishing tool can be
obtained simply by drying.
[0035] Twentieth aspect relates to the method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, by mixing/dispersing a powder
of abrasive particles or a slurry and a powder of the thermoplastic
resin or an emulsion in a liquid, such as water or a solvent, and
subjecting a resulting liquid to a drying and comminuting process,
before filling into a forming fixture.
[0036] Twenty-first aspect relates to the method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, by drying the powder of
abrasive particles or a slurry, mixing/dispersing an emulsion of a
resulting dried substance and the thermoplastic resin, and
subjecting a resulting liquid to a drying and comminuting process,
before filling into a forming fixture.
[0037] Twenty-second aspect relates to the method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, by drying the powder of
abrasive particles or a slurry, dispersing a resulting dried
substance and a dried product of the thermoplastic resin in a
liquid, such as water or a solvent, and subjecting a resulting
liquid to a drying and comminuting process, before filling into a
forming fixture.
[0038] Twenty-third aspect relates to the method for making a
fixed-abrasive polishing tool using a liquid feed material
containing abrasive particles and a thermoplastic resin, by
applying mist drying during a process of drying the liquid feed
material before filling into a forming fixture.
[0039] Twenty-fourth aspect relates to the method for making a
fixed-abrasive polishing tool using abrasive particles and a
thermoplastic resin as raw materials, during drying of a mixed
matter of a fixed-abrasive polishing tool or after drying,
pulverizing to obtain a powder in a range of 1-500 .mu.m.
[0040] Twenty-fifth aspects relates to a semiconductor wafer
polishing apparatus having a polishing tool recited above.
[0041] Twenty-sixth aspects relates to a method for polishing a
semiconductor wafer using a polishing tool recited above.
[0042] The above and other objects, features, and advantages of the
present invention will be apparent from the following description
when taken in conjunction with the accompanying drawings which
illustrates preferred embodiments of the present invention by way
of example.
BRIEF DESCRIPTION OF THE DRAWINGS
[0043] FIGS. 1A, 1B are schematic diagrams of the fixed-abrasive
polishing tools to show a tool made with a thermoplastic resin in
FIG. 1A, and a tool containing an elastic filler in FIG. 1B;
[0044] FIG. 2 is a diagram to explain injection molding;
[0045] FIGS. 3A, 3B are schematic diagrams of structures of
polishing pads.
[0046] FIG. 4 is a comparison of experimental data of (a) polishing
speed and (b) amount of defects produced by fixed-abrasives made
with various resin materials;
[0047] FIG. 5 is a comparison of experimental data of (a) polishing
speed and (b) amount of defects produced by a polishing pad
containing no abrasive particles;
[0048] FIG. 6 is a diagram to show an example of making particles
using a spray dryer according to a spray drying method;
[0049] FIGS. 7A-7C are diagrams for explaining a method of
manufacturing a fixed-abrasive polishing tool by hot pressing;
[0050] FIG. 8 is an overall plan view of the polishing
facility;
[0051] FIGS. 9A, 9B are a plan view and a cross sectional view of
some key sections of a polishing apparatus;
[0052] FIG. 10 is diagram to show a clamping method of attaching a
fixed-abrasive polishing tool to the fixed disk;
[0053] FIG. 11 is a diagram to show another method of attaching a
fixed-abrasive polishing tool to the fixed disk; and
[0054] FIG. 12 is a schematic diagram to show an example of the
structure of a polishing apparatus based on polishing slurry;
[0055] FIG. 13 is a diagram to show another embodiment of the
polishing apparatus of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0056] In the following, preferred embodiments will be explained
with reference to the drawings.
[0057] FIGS. 1A and 1B are schematic diagrams of a fixed-abrasive
polishing tool of the present invention. The fixed-abrasive
polishing tool 1 shown in FIG. 1A is comprised by the abrasive
particles 5 and porosity or foaming agent 2 with a binder (resin)
4. Here, the binder 4 comprises a thermoplastic resin such as ABS
resin. When such a thermoplastic resin is heated, the binder
becomes soft and exhibits elasticity and acts in a manner similar
to rubber type resins, and is able to reduce damage on the polished
surface such as scratches by contacting the polishing surface of a
polishing object softly during polishing operation. The tool 1
shown in FIG. 1B is comprised by abrasive particles 5, an elastic
filler material 3 such as rubber type particles and porosity or a
foaming agent 2 using a binder (resin). Here, a hard resin is used
as the binder 4. The elastic filler material 3 acts in a similar
manner to rubber type particles, and is able to reduce damage such
as scratches by contacting the polishing surface of a polishing
object softly during polishing operation.
[0058] Conventional fixed-abrasive polishing tools are generally
made by compression forming of a binder feed mixture containing
abrasive particles. In contrast, the present polishing tool
features the use of a thermoplastic material, and accordingly, a
mass production technique such as injection molding, blow forming
and vacuum forming can be used. Because thermoplastic resins are
characterized by its melting behavior when heated to a temperature
beyond a certain temperature, so that it enables to manufacture
various fixed-abrasive polishing tools having characteristics that
have not been demonstrated to date, and enables to manufacture
fixed-abrasive polishing tools having properties that are suitable
for application to various polishing objects. By choosing a
fixed-abrasive polishing tool having an appropriate thermoplastic
resin as its primary component, it is considered that elevated
temperature produced during polishing is localized, and the
abrading surface of the fixed-abrasive polishing tool is made soft
and pliable. Thus, the surface being polished is under a stable
pressing pressure and excessive force is not applied to the
abrasive particles. In other words, abrasive particles which exist
on the surface being polished are being compressed with a softer
tool to enable to reduce scratching (damage) the polishing surface
of the polishing object.
[0059] In the present invention, the resin to serve as the binder
for fixating the particles of the fixed abrasive polishing tool is
comprised primarily of thermoplastic resins. Although it is
permissible to use 100% thermoplastic resin as the binder resin, it
is permissible to use a thermoplastic resin for not less than 90%
of the binder and the remainder may be made of a thermosetting
resin.
[0060] In the following, examples of the materials for comprising
thermosetting resins and thermoplastic resins are shown.
Thermosetting resins include phenol (PF), urea (UF), melamine (MF),
unsaturated polyester (UP), epoxy (EP), silicone (SI), polyurethane
(PUR) and the like, and these substances are hardened by adding a
third substance. And, thermoplastic resins include polyvinyl
chloride (PVC) known as general purpose plastic, polyethylene (PE),
polypropylene (PP), polystyrene (PS), acrylonitrile butadiene
styrene (ABS), butadiene styrene, polybutadiene, or acrylic rubber
group MBS resin (methylmethacrylate butadiene styrene (MBS)), a
copolymer resin of styrene monomer and acrylonitrile (AS, SAN),
polymethylmethacrylate (PMMA), a copolymer of methacrylic methyl
and styrene (MS), polyvinyl alcohol (PVA), polychlorovinyldiene
(PVDC), polyethylene terephthalate (PET), polyamide (PA) known as
an engineering plastic, polyacetal (POM), polycarbonate (PC),
polyphenylene ether (PPE (altered PPO)), polybutylene terephthalate
(PBT), ultra-high-molecular-we- ight polyethylene (UHMW-PE),
polyvinylidene fluoride (PVDF), polysulfone (PSF) known as a super
engineering plastic, polyethersulfone (PES), polyphenylenesulfide
(PPS), polyarylate (PAR), poly(amide-imide) (PAI), polyetheramide
(PEI), polyetheretherkeytone (PEEK), polyimide (PI), liquid crystal
polymer (LCP), polytetrafluoroethylene (PTFE) and the like.
[0061] Thermosetting resins assume a three dimensional structure or
a network structure when heated by itself or with a second
substance and become a non-softening non-melting resin. That is,
once they are hardened they cannot be softened. These resins
activate a chemical reaction at a certain temperature, and begin
crosslinking and hardening, and the hardening process is completed
by continuing to heat at the hardening temperature. Cooling is
performed slowly to attain the hardened state so as to prevent
shape changes and generation of residual internal stresses.
Thermoplastic resins, when subjected to heating and a certain
temperature is exceeded, become soft and flowing without causing a
chemical reaction, and when cooled, it becomes hard, that is, it
returns to its original property.
[0062] FIG. 2 shows a schematic diagram of an injection molding
machine. The injection molding machine has a pressurizing head 19
for injecting a molten material held in a cylinder chamber 16a
inside the cylinder 16 into a metal mold 15. A screw 17 is rotated
by an oil pressure motor 12 to rotate the screw 17 to transfer a
resin feed material poured from a feed opening 18 by pushing it
into a space 16 in front of the pressure cylinder 19. Around the
periphery of the cylinder 16, a heater 13 is disposed, and heats
the feed material while it is being transferred by the screw 17 to
heat to a temperature above its melting point of the resin to
transform the solid resin into a liquid feed material. And, by
pushing the pressuring head 19 towards the mold 15 using the
injecting oil pressure driver 11, the space section 15a of the
metal mold 15 is filled by the liquid feed material.
[0063] That is, the feed granules comprised primarily of abrasive
particles and the resin is poured in from the feed opening 18, and
by rotating the screw 17, it is forwarded from the supply section
18 to the injection section 16a. During this stage, the feed
granules are heated by the heater 13, melted and liquefied. By
reciprocating the pressurizing head 19, the liquid feed material is
injected into the space section 15a of the metal mold 15 and is
made into a product form. After which, it is cooled, removed from
the mold and becomes a product. Injection molding resins include
such general thermoplastic resins as vinyl chloride resin,
vinylidene chloride resin, polystyrene methacrylate resin,
polycarbonate cellulose acetate, polyacetal polyamide,
polypropylene, polyethylene, 3-ethylene fluoride resin, vinylidene
fluoride resin and the like, and it is allowable to use in part
such thermosetting resins as phenol resin, polyester resin,
diarylphalate and the like to enable to use various resins for
forming. Also, many products can be produced in one run, and the
number of processing steps is reduced compared with compression
molding, and the manufacturing time is shortened such that complex
parts can be formed at high precision and high productivity can be
achieved in mass production. Also, by selecting the mixing
proportion of abrasive particles and the grain size of the resin,
it is possible to carry out cold compression molding and hot
compression molding. In this case also, there is no need for high
temperature treatment so that working time is not limited and
handling is facilitated.
[0064] Especially, when ABS resin is used as a binder, it allows
soft polishing due to thermoplastic action of the resin as the
temperature of the polishing object is raised, and furthermore,
because the structure of ABS resin is such that a core-shell
structure is formed by ABS resin surrounding a nucleus of butadiene
rubber so that even when the temperature generated by polishing
action is lower than the softening temperature of the resin,
polishing can be carried out with a lesser degree of scratches
(damage) to enable a high quality planarization process. That is,
ABS resin has an inherent elasticity in its constitution so that it
is as hard as an AS resin from a macroscopic viewpoint so as to
produce high planar surface by polishing the object surface, but
from a microscopic viewpoint, shock absorbing action is provided by
the soft butadiene rubber to lead to suppression of scratches
(damage). Here, in addition to ABS resin, similar elasticized
structure is found by adding methacrylate butadiene styrene(MBS) as
a property modifier to vinyl chloride. By so doing, MBS is made to
act as an elasticizer, so that, similarly, from a macroscopic
viewpoint, the product is hard to produce superior planar surface
during polishing, but from a microscopic viewpoint, it provides a
shock absorbing quality due to the elastic component that behaves
soft and pliable. When the proportion of MBS resin is increased,
i.e., when it forms the main component in the binder, the
fixed-abrasive polishing tool exhibits a highly effective impact
absorbing effect.
[0065] As shown in FIG. 1B, similar effects are obtained when fine
rubber particles are mixed with the abrasive particles and binder
(plastic material). Specific examples of rubber type particles to
be added to plastic materials include natural rubber (NR), styrene
butadiene (SBR), butadiene (BR), chloroprene (CR), butyl (IIR),
nitrile (NBR), ethylenepropylene (EPM, EPDM), chlorosulfone
polystyrene (CSM), acrylic rubber (acrylic esters such as a
copolymer ACM of acrylic alkylester and a bridging monomer, and a
copolymer ANM of acrylic alkylester and acrylonitril), urethane
rubber (U), silicone rubber (SI), fluoro rubber (FKM), high
sulfured rubber (T) and the like. Especially, chlorosulfone
polystyrene (CSM) is highly resistant to weathering, acid,
inorganic chemicals and wear, and acrylic rubber (acrylic esters
such as a copolymer ACM of acrylic alkylester and a bridging
monomer, and a copolymer ANM of acrylic alkylester and
acrylonitril) is highly resistant to heat, and fluoro rubber (FKM)
is resistant to heat, chemicals and weathering, and silicone rubber
(SI) is not only resistant to heat but is useable over a wide range
of temperatures and is suitable for polishing applications because
of it is relatively stable in the polishing environment.
[0066] Also, in addition to rubber type particles, hollow elastic
particles are also effective. For example, hollow particles of
polyacrylonitrile (PAN) are applicable.
[0067] It is noted that to perform high quality polishing, it is
necessary to achieve uniformity of polishing action within the
abrading plane of the fixed-abrasive polishing tool, and for this
reason, it is necessary to provide a uniform distribution of
abrasive particles. Many of the resins are polymers and do not have
good wettability with abrasive particles made of metal oxides, and
they tend to cluster as large clusters within the microstructure of
the polishing tool. For example, when cerium oxide fine particles
are mixed with ABS binder, abrasive particles are not wettable by
the resin well, and clusters of sizes ranging from several hundred
nanometers to several millimeter are found sometimes. The
distribution is improved by adding surface-active agent to enable
high quality polishing. In addition to surface-active agent, it may
be considered that particle distribution can be made more uniform
by kneading well, over a long period of time, but this is time
consuming and is not efficient. By using a surface-active agent,
the surface tension is lowered and uniform distribution of
particles can be obtained. For example, by adding 0.01-0.2%
non-ionic activating agent to urea group resin, it is known that
the surface tension may be lowered from 63 to about 50
dynes/cm.
[0068] Above explanations relate to the examples of the structure
of fixed-abrasive polishing tools, but such examples may be applied
to a polishing pad to be used with a slurry containing a large
amount of abrasive particles. If the polishing pad contains high
hardness resin, flatness of the polishing surface is obtained, but
the surface is vulnerable to severe scratches (damage). Therefore,
as shown in FIG. 3A, while making the polishing pad using a hard
resin 4, soft rubber type particles 6 are mixed within the
structure to prevent the formation of scratches.
[0069] Specific examples of rubber include, similar to the case of
fixed-abrasive polishing tools, natural rubber (NR), styrene
butadiene (SBR), butadiene (BR), chloroprene (CR), butyl (IIR),
nitrile (NBR), ethylenepropylene (EPM, EPDM), chlorosulfone
polystyrene (CSM), acrylic rubber (acrylic esters such as a
copolymer ACM of acrylic alkylester and a bridging monomer, and a
copolymer ANM of acrylic alkylester and acrylonitril), urethane
rubber (U), silicone rubber (SI), fluoro rubber (FKM), high
sulfured rubber (T) and the like. Especially, chlorosulfone
polystyrene (CSM) is highly resistant to weathering, acid,
inorganic chemicals and wear, and acrylic rubber (acrylic esters
such as a copolymer ACM of acrylic alkylester and a bridging
monomer, and a copolymer ANM of acrylic alkylester and
acrylonitril) is highly resistant to heat, and fluoro rubber is
resistant to heat, chemicals and weathering, and silicone rubber
(SI) is not only resistant to heat but is useable over a wide range
of temperatures and is suitable for polishing applications because
of it is relatively stable in the polishing environment. Also, in
addition to rubber type particles, hollow elastic particles are
also effective. For example, hollow particles of polyacrylonitrile
(PAN) are applicable. Resin materials used in the fixed-abrasive
polishing tools can also be used.
[0070] FIG. 3B shows a case of using ABS resin for a polishing pad.
When ABS resin 7 is used for the polishing pad, although the ABS
resin is hard from a macroscopic viewpoint, it contains small and
soft butadiene rubber 8 within its structure. Therefore, the
abrading surface is as hard as an acrylonitrile styrene resin
(AS:SAN) from a macroscopic viewpoint so as to enable to produce a
highly flat surface by polishing, but from a microscopic viewpoint,
shock absorbing effect is provided by the soft butadiene rubber
particles so as to suppress the formation of scratches, thus
enabling to provide high quality polishing action.
[0071] Next, a typical production process of ABS resin based tool
will be explained. ABS resin has a core-shell structure in which
polybutadiene rubber particles are distributed in a AS resin
matrix. A typical method of production is based on emulsion
polymerization that provides relatively easy control over the
interface between the resin phase and the rubber particles or the
rubber phase. Typical production process for ABS resin involves
steps such as, a rubber latex manufacturing process by making
emulsion copolymerization of butadiene to produce polybutadiene
latex; carrying out a graft polymerizing process by adding
acrylonitrile and styrene to the latex solution (or adding abrasive
particles) to carry out graft reaction due to emulsion
polymerization; solidifying the polymer; and dehydrate and drying.
Butadiene latex can be obtained by emulsification by charging
butadiene, water, emulsifying agent, catalyst and polymerization
adjuster in a tank polymerizer with stirring, but fundamentally, it
is the same as emulsion polymerization, and the polymerized
substance thus obtained are controlled by controlling the
polymerization formula and polymerization operation to control the
rubber particle size and the occluded amount of gel (bridging
structure) and the like. In addition to the process of emulsion
polymerization described above, graft blend process is also known
in which an AS copolymer latex body consisting only of
acrylonitrile and styrene is made in a separate process, and it is
mixed with a graft copolymer latex, solidified and dehydrated and
dried.
[0072] Next, fixed-abrasive polishing tools made using butadiene
styrene, polybutadiene or acrylic rubber group MBS resin will be
explained. The MBS resin in a wider context is a graft polymer
having a core-shell structure of a core of butadiene styrene,
polybutadiene or acrylic rubber, and is used primarily as a
property modifier for shock absorbing quality of vinyl chloride
resin or acrylic resin. MBS resin is a thermoplastic copolymer made
of methylmethacrylate and butadiene and styrene as raw materials,
and has the core-shell structure consisting of a core of copolymer
(SBR) containing a rubber layer of butadiene and styrene, and the
shell of copolymer (MS) of methylmethacrylate and styrene.
[0073] Regarding the fixed-abrasive polishing tool based on a
binder made by adding an MBS resin to vinyl chloride or acrylic
resin, and generally, the addition is about several to 20%, and is
designed to emphasize the characteristics of vinyl chloride. In
contrast, if the amount of MBS resin in the binder resin is
increased to over 20%, 50% or even 100% the tool has a very high
shock absorbing property. By using this resin as the binder and
combining with cerium oxide abrasive particles, fixed-abrasive
polishing tools that create very little scratches will be produced.
For example, epoxy resin and MBS resin may be used together as a
binder. That is, the fixed-abrasive polishing tool thus made is
easy to manufacture, because the MBS resin is thermoplastic, and
produce high strength body. When MBS resin is used as the binder,
self-stopping effect is generated, thereby providing fast polishing
rates. For example, compared with the fixed-abrasive polishing tool
based on the binder of conventional epoxy resin, about two times
faster polishing rate can be achieved. Further, because the resin
body itself is shock absorbing, the force acting on the abrasive
particles is moderated (suppressed) to enable to provide
scratch-free polishing, i.e. less defects in the polished product.
It is considered that MBS resin promotes self-generation of
abrasive particles because of the retaining power for the particles
is reduced due to spreading of matrix itself caused by the effects
of absorption of water.
[0074] FIG. 4 shows experimental data of comparison of polishing
results produced by various fixed-abrasive polishing tools made
with various resins in terms of (a) polishing speed and (b) number
of defects. It can be seen that, as shown in FIG. 4A, in
fixed-abrasive polishing tools made with ABS resin, AS resin, and
MBS resin, the polishing speeds are much faster relative to the
fixed-abrasives polishing tools made with phenol resin and epoxy
resin. Also, as shown in FIG. 4B, data show that in the tools made
with ABS resin, AS resin and MBS resin number of defects per unit
area are equal to or less than those made with phenol or epoxy
resin. That is, fixed-abrasives made with thermoplastic resins
generally exhibit higher polishing speed and the number of defects
is lesser. Particulary fixed-abrasives made with ABS resin or MBS
resin exhibit higher polishing speed and less number of defects
such as scratches and adhering matters observed after
polishing.
[0075] FIG. 5 shows the experimental results of comparing with
polishing pad that does not contain abrasive particles in terms of
(a) polishing speed and (b) number of defects. These experimental
results relate to various resins including PC (polycarbonate),
epoxy, phenol, ABS (acrylonitryl butadiene styrene), MBS
(methylmethacrylate butadiene styrene), PE (high density
polyethylene), RB (butadiene rubber), AS (acrylonitryl styrene).
These experimental results also demonstrate that the polishing pads
made with ABS resin or MBS resin exhibit higher polishing speed and
less number of defects.
[0076] Some examples of the structure of the fixed-abrasives by MBS
resin will be explained.
[0077] Ratio of the fixed-abrasive (percentages of abrasive
particles (Vg), binder (Vb) and air porosity (Vp)) in volume
percent (vol %) is, for example:
[0078] abrasive particles (Vg):binder (Vb):air porosity
(Vp)=35:55:10 (vol %).
[0079] This fixed-abrasive polishing tool exhibits faster polishing
speed and produce less defects, compared with the common phenol
epoxy resin bonded polishing tools, so that it is applicable to
semiconductor manufacturing processes that prefer not to create
scratches. For those processes requiring highspeed polishing that
require in-situ dressing, by the use of the common phenol or epoxy
resin bonded polishing tools, the present polishing tool can be
used for such highspeed polishing processes without requiring such
in-situ dressing. Also, because there is no danger of diamond
particles falling from the tool, scratches caused by diamond
particles are not created.
[0080] Next, compositions of the fixed-abrasive polishing tool
based on MBS resin will be explained.
[0081] Composition of fixed-abrasives (percentages of abrasive
particles (Vg), binder (Vb) and air porosity (Vp)) in volume
percent (vol %), are as follows.
[0082] In general, the range is: 10%<abrasive particles
(Vg)<50%,
[0083] 30%<binder (Vb)<80%, and
[0084] 0%<air porosity (Vp)<40%.
[0085] It is preferable that the range be:
[0086] 20%<abrasive particles (Vg)<45%,
[0087] 40%<binder (Vb)<70%, and
[0088] 0%<air porosity (Vp)<20%.
[0089] It is more preferable that the range be:
[0090] 30%<abrasive particles (Vg)<40%,
[0091] 50%<binder (Vb)<60% and
[0092] 5%<air porosity (Vp)<15%.
[0093] Next, a method of making the fixed-abrasive polishing tool
will be explained. First, a dry powder of a mixture of fine cerium
oxide, and butadiene styrene, polybutadiene or acrylic rubber group
MBS resin is prepared. A specific example of the method of
obtaining the dry feed powder will be explained next.
[0094] The first method is to mix a powder of abrasive particles,
and butadiene, polybutadiene or acrylic rubber group MBS resin
powder, and such a mixed powder is easily prepared.
[0095] The second method is to prepare a slurry type polishing
solution made by adding, as necessary, water and/or aqueous
solution and/or solvent and/or binder and/or chemical to the
abrasive particles, and drying the slurry by drying naturally or by
heating or by freeze drying, after which, pulverizing the powder as
required, and mix the powder with butadiene styrene, polybutadiene
or acrylic rubber group MBS resin powder to obtain the dry feed
powder. However, because the abrasive particles are extremely fine,
they tend to agglomerate so that, in order to prepare a powder of
the abrasive particles only, spray drying or other drying method is
used to obtain a powder of average particle size 1-500 .mu.m that
shows weak aggregating force or binding force and exhibits easy
handling quality, or preferably 10-100 .mu.m, or more preferably
30-80 .mu.m range. The binder that shows strong binding force is
not suitable for inclusion in the polishing slurry so that it is
preferable to select a binder that binds due to bridging or
intermolecular forces, or weak binding force (includes resin
binders of weak binding force).
[0096] The third method for obtaining a dry feed powder is to
produce a powder according to the first or second method, and then,
the powder is dispersed in water or an aqueous solution or a
solvent, and then dry the liquid by drying naturally or by heating
or freeze drying or spray drying. This dry feed powder is desirable
because it facilitates mixing of abrasive particles and the resin
powder so that uniform composition is more easily obtained in the
finished fixed-abrasive polishing tool. In this case also, by using
a spray dryer or other mist dryer and selecting the operating
conditions, average particle size and particle distribution can be
controlled to obtain a feed powder that is easy to handle and
suitable for forming operation. For example, the average particle
size should be in a range of 1-500 .mu.m or preferably 10-100 .mu.m
or more preferably 30-80 .mu.m.
[0097] The fourth method is to prepare a slurry type polishing
solution made by adding, as necessary, water and/or an aqueous
solution and/or a solvent and/or a binder and/or a chemical to the
abrasive particles, and adding butadiene styrene, polybutadiene or
acrylic rubber group MBS resin powder to the liquid mixture and
adding, as necessary water or an aqueous solution or a solvent, to
mix or to mix and disperse, and drying the liquid mixture by drying
naturally or by heating or by freeze drying or mist drying
including spray drying to obtain the dry feed powder. In this case
also, average particle size and particle distribution can be
controlled by using spray drying or other mist drying methods so as
to obtain a powder of easy handling and forming qualities. For
example, the average particle size should be in a range of 1-500
.mu.m or preferably 10-100 .mu.m or more preferably 30-80 .mu.m.
The most preferable method of mixing the feed materials is to mix
abrasive particles in a slurry with an MBS resin in a liquid state
(latex), and mist drying the liquid using spray drying to make the
feed particles. this method enables uniform mixing of slurry and
MBS resin. It should be noted that uniform mixing in MBS resin is
possible even if the particles are not supplied in a slurry form,
but are supplied as primary particles obtained beforehand by spray
drying a slurry at a low temperature (room temperature to
200.degree. C).
[0098] The fifth method is used when the butadiene styrene,
polybutadiene or acrylic rubber group MBS resin powder are in a
form of an aqueous solution or an emulsion, the liquid material is
dried first and the dried powder is mixed with abrasive particles
to obtain the feed powder. Also, after dispersing in water or an
aqueous solution or a solvent, a binder and/or a chemical is added,
as necessary, and obtain the feed powder by drying and pulverizing.
This method also facilitates mixing of abrasive particles, resin
powder and additives uniformly. In this case, a desirable feed
powder is obtained that promotes the formation of uniform
composition in the fixed-abrasive thus formed.
[0099] The sixth method is used when the butadiene styrene,
polybutadiene or acrylic rubber group MBS resin powder is in a form
of an aqueous solution or an emulsion, abrasive particles or raw
particle material in a slurry form is mixed or mixed and dispersed
in water or an aqueous solution or a solvent, as necessary, and
after drying, the dried powder is again dispersed in aqueous
solution or solvent, and a binder and/or chemical is added as
necessary, by drying or dry commination processing to obtain the
feed material. In this case also, the feature is that abrasive
particles, the resin and the additives are uniformly mixed, and
that a desirable feed powder is obtained that promotes the
formation of uniform composition in the fixed-abrasive polishing
tool.
[0100] Further, drying and mixing and charging the metal mold with
the feed material can be carried out concurrently in the metal mold
to be used in the method shown next, so that the manufacturing
process is desirably shortened.
[0101] Next, the forming process for the fixed-abrasive polishing
tool involving charging the feed material and heating and press
forming will be explained. Because MBS resin is a thermoplastic
resin that is softened by heating, the polishing tool can be
produced simply by charging the feed material in the metal mold and
heating the mold. In so doing, the metal mold does not need to be
heated, but to control the shape or the amount of porosity in the
formed fixed-abrasive polishing tool, it is preferable to carry out
this process while applying a pressure. In making the
fixed-abrasive polishing tool, in order to obtain a certain size
and amount of porosity in the fixed-abrasive polishing tool, it is
preferable to use a mold having a stopper device so as not to
compress indefinitely to a small volume. The stopper device avoids
a pressure-dependent forming and enables a volume-dependent forming
so as to enable to impart a certain shape and amount of porosity to
the fixed-abrasive polishing tool. After the process of
heating/compaction, the surface and the outer radius are fabricated
and adjusted, and after a desirable shape has been achieved, it is
ready for use in polishing. Also, because the fixed-abrasive
polishing tool is a flat shaped tool, and also, the structural form
and the material are vulnerable to distortion and volume expansion
due to moisture absorption, the fixed-abrasive polishing tool must
be sufficiently wetted during any fabrication process so that the
water content within the tool does not become unbalanced.
[0102] Next, a specific example of manufacturing process for a
fixed-abrasive polishing tool containing cerium oxide particles and
MBS resin binder will be explained. The finished size of the
fixed-abrasive polishing tool is a diameter of 55 cm and a
thickness of 5 mm or more, as an example. The volume ratio of the
abrasive particles and the binder material before the forming
operation is 29-49% (preferably 34-44%)of abrasive particles and
the remainder 51-71% (preferably 56-66%) of binder material. The
fixed-abrasive components may include, in addition to abrasive
particles and binder, additives such as surface-active agent,
polishing promoter and elastic material such as rubber may be added
or more than two kinds of resins may be mixed for use in the feed
material. Then, the volumetric composition of the finished
fixed-abrasive polishing tool is comprised by 25-45% (preferably
30-40%) abrasive particles, 45-65% (preferably 50-60%) binder and
0-20% (preferably 5-15%) porosity, so that a target value may be:
abrasive particles:binder:porosity=35:55:1- 0, for example. MBS
resin is a thermoplastic resin, and it is preferable that the
forming temperature be in a range of 150-200.degree. C.
[0103] Drying treatment can be either natural drying or by heating,
but as shown in FIG. 6, it is preferable to use spray dryer. The
feed material is heated and dried by spray drying, and
thermoplastic MBS resin is melted and is then dried to form
clusters having a spherical shape or cavities. Therefore, the feed
material before and after spray drying is mixed uniformly and its
handling quality is improved. It is preferable to mix all the feed
material before charging the feed material into the metal mold.
[0104] If the mold is charged with a feed material in the liquid
form, when heating and compaction steps are performed, the water
evaporates so that the fixed-abrasive polishing tool is formed with
water inclusions or hollow portions so that a desirable
fixed-abrasive polishing tool of uniform structure is not produced.
Therefore, it is preferable to charge the forming device with dried
feed powder.
[0105] Drying and pulverization process using spray drying is
carried out as follows.
[0106] Spray drying method is carried out by first dispersing the
particles or raw materials such as MBS resin in water or solvent,
and after dispersing the mixture sufficiently by applying
ultrasonic stirring and the like so as to form an emulsion of fine
particles. Then, the emulsion of fine particles is charged into a
spiraling space of hot air. In so doing, the liquid portion of the
emulsion is instantly vaporized, and the fine particles are formed
into agglomerated bodies while increasing the surface area per unit
volume. If, for example, fine particles of 0.3 .mu.m diameter are
used in forming abrasive particles, spherical grains of 5-100 .mu.m
comprised by agglomerated bodies of fine abrasive particles are
produced. According to this spray drying method, a number of
processing steps such as condensing, filtering, pulverizing,
classifying and drying are carried out concurrently, and therefore,
particulate forming process that starts with fine particles and
ends in forming aggregates can be carried out easily. The particle
size of the grains (post-polymerization size) is different for
different forming methods, and for hot pressing, the range is
1-1000 .mu.m, preferably 5-500 .mu.m or more preferably 100-200
.mu.m.
[0107] Here, the particle size can be adjusted when drying and
particulate forming (granulating) are carried out using spray
drying, by adjusting the operating parameters of the spray dryer
such as the temperature of hot air, atomizer shape, atomizer
rotation speed, hot air discharge rate, air temperature, and the
parameters of the liquid to be supplied to the spray dryer such as
viscosity, solid volume and the liquid feed supply rate.
[0108] FIG. 6 shows an example of the spray dryer suitable for use
in the above method. The dryer main body 31 of the spray dryer
receives hot air through a pipe 37, and a spiraling flow 43 is
formed in the dryer main body 31. Air is sent by a blower 34 and is
heated by a heater 35, which supplies hot air into the dryer main
body 31 through the air filter 33. Micro-particle forming apparatus
32 supplies an emulsion of fine particles into the swirling hot
air, thereby forming aggregated abrasive particles. Aggregated
bodies made into grains are either discharged in the vessel 42a
situated below the dryer main body or classified by entering a
cyclone 39 through the pipe 38, and enter either a chamber 42b
situated below or classified by a bag filter 40 and enter a chamber
42c situated below. Hot air passed through the bag filter 40 is
discharged by the discharge fan 41.
[0109] Next, a forming process of a fixed-abrasive polishing tool
will be explained with reference to FIG. 7A, 7B and 7C. First, as
shown in FIG. 7A, after assembling the die 71 and the lower punch
72, the feed powder 73 of mixed powder of abrasive particles and
resin particles is uniformly packed into the mold. Next, as shown
in FIG. 7B, the upper punch 74 is placed on top without loading the
charge or setting a forming fixture with a minimal pressure less
than the forming pressure of the compact, and the compact is heated
to a certain forming temperature (for example, 150-300.degree. C.)
that exceeds the glass transition temperature of the resin but
lower than the temperature that causes thermal decomposition. Then,
this condition is maintained for a period of time sufficient to
homogenize the temperature and to melt the resin uniformly (for
example, 5-30 min). Next, pressure is applied to the upper punch 74
until a target volume is reached. In doing so, as shown in FIG. 7B,
use of a forming fixture having a stopper device 75 enables to
compress to a specified volume.
[0110] The fixed-abrasive while it is being hardened is pressed
from upper portion so that the pressure spreads laterally and the
die contacts the fixed-abrasive feed material intimately. For this
reason, by removing the spacer disposed below the die midway in the
hardening process, the die is able to move as a unit with the
fixed-abrasive feed material so as to prevent distortion of the
peripheries of the fixed-abrasive body, and also, the density of
the fixed-abrasive body is made uniform. Also, the spacer may be
inserted initially under the die 71, and after pressing with
sufficiently small pressure than the forming pressure, and after
removing the spacer, the forming pressure may be applied. Although
the tool may be formed without using the spacer, it is desirable to
use the spacer for the purpose of relieving the internal stresses
in the formed product and to equalize the density. Further,
press-forming may be carried out by controlling the position of the
upper punch 74. After holding for a given period of time, the
compact is preferably cooled naturally, and after cooling down to a
temperature sufficiently lower than the glass transition
temperature, the fixture is removed from the mold to obtain a
fixed-abrasive polishing tool 73. Here, the fixed-abrasive
polishing tool can be manufactured by controlling the time and
pressure without using a forming fixture having the stopper
mechanism illustrated in the diagram.
[0111] After the forming process of the fixed-abrasive polishing
tool, it is subjected to shaping of the external surfaces to
produce a product. Because the fixed-abrasive polishing tool lacks
sufficient strength so that, if it is unsupported, transporting and
attaching to a machine may cause to break or damaged, and
therefore, it is fixed to a holder base. Mounting on the holder
base (by bonding, adhesion or mechanical fixation) can be performed
during the forming process for the tool, but if thermal
coefficients are different or the material is liable to degrade, it
is preferable to do so after the forming process. It is better that
the fixed-abrasive polishing tool has some thickness from the
viewpoint of wear, but if wear is expected to be low during its
use, a thin flat shape may be adopted. When using the
fixed-abrasive polishing tool for polishing, water or a liquid is
often applied during the polishing process. Therefore, there is a
problem of swelling of the fixed-abrasive polishing tool so that
when the tool is to be mounted on a holding base, it is preferable
that the tool be mounted in a slightly swelled condition to
approximate the condition of use. That is, a liquid should be
infiltrated into the interior of the fixed-abrasive polishing tool
so as to simulate the swelled condition in such a way that the size
and shape of the tool are stable, and then to mount the tool on a
holding base, and it is preferable to maintain this condition until
the tool is put to use.
[0112] Typical manufacturing process for the fixed-abrasive
polishing tool is as follows. A dispersion liquid containing a MBS
resin and a slurry containing cerium oxide particles of 0.165 .mu.m
average particle size is prepared. The liquid is dried in the spray
dryer to form particulates having a particle distribution in a
range of 9-200 .mu.m and an average particle size of 45 .mu.m. The
feed powder is charged into a metal mold of about 560 mm diameter,
and hot forming is carried out by hot pressing at a temperature of
about 200.degree. C. Further, after mounting on a holder base
(cartridge plate for attaching to the turntable of a CMP apparatus)
using a bonding agent, outer diameter fabrication and polishing
surface planarization are carried out to produce a fixed-abrasive
polishing tool.
[0113] Next, the glass-transition temperature of thermoplastic
resin will be examined. First, it is necessary that the polishing
tool has sufficient strength during polishing operation. For this
reason, the glass-transition temperature Tg is higher than room
temperature (20-25.degree. C.). And, when the polishing tool is not
in contact with the polishing object, it is necessary that the
polishing tool retain brittleness so that polishing action
pulverizes the resin into fine polishing debris so as not to
interfere with the polishing process. For this reason, it is also
necessary that the glass-transition temperature Tg be above room
temperature. Also, if the resin softens even at room temperature,
when the polishing tool is in contact with a polishing object
(semiconductor wafer, for example), the polishing surface becomes
too soft, and flatness of the polished surface cannot be produced.
Also, there is a problem that the resin tends to agglomerate with
the abrasive particles if the resin has flows too readily.
Therefore, it is preferable that only the topmost layer of the
polishing tool that in contact with the polishing object be in a
softened state. Normally, when polishing the surface of a
semiconductor wafer, the temperature of the surface reaches a
temperature of about 60.degree. C. From such a viewpoint, it is
preferable that the glass-transition temperature of a resin to
comprise the polishing tool be higher than 60.degree. C. From the
viewpoint of formability during manufacturing of the present
polishing tool, if the glass-transition temperature Tg is too low,
it becomes difficult to detach from the mold. From this viewpoint,
it is preferable that the glass-transition temperature be higher
than 50.degree. C. Further, productivity and cost reduction can be
achieved if it is possible to form at a relatively low temperature.
From the viewpoint of manufacturing the polishing tool, it is
preferable that the glass transition temperature be lower than
200.degree. C. From the overall viewpoint based on above
discussion, the glass-transition temperature Tg of the resin to
comprise the present polishing tool should be higher than room
temperature and lower than 200.degree. C.
[0114] However, because resin materials are generally hydrophobic,
it is difficult to retain the slurry on the pad surface. Therefore,
to perform stable polishing operation, it is necessary to perform
an operation called dressing (seasoning). That is, the surface is
lightly abraded using a diamond file, and after removing the debris
and roughing the surface, the surface area is increased so as to
promote retention of slurry on the surface. If the pad itself is
hydrophilic, the extra step of dressing to increase the surface
area is not needed and only the debris must be removed, so that the
dressing cost of the pad is reduced and the pad can be used over a
longer period. Materials that exhibit hydrophilic nature include
all those materials containing hydrophilic base such as --CH--OH,
--OH, --NH.sub.2, --NHCONH.sub.2, --(OCH.sub.2CH.sub.2)N-- among
others. Also, a base containing an element such as oxygen,
nitrogen, sulfur is hydrophilic, and especially if a salt is
formed, it is strongly hydrophilic and is very suitable for this
purpose. Strongly hydrophilic nature is exhibited by such bases as
--SO.sub.3H, --SO.sub.3M, --OSO.sub.3H, --OSO.sub.3M, --COOM,
--NR.sub.3X (where M: an alkaline metal or --NH.sub.4R: alkyl base,
X: halogen). By adding such hydrophilic substances to the resin
forming the polishing pad or to impart hydrophilic property to the
resin itself, that is, to modify its nature, a polishing pad may be
obtained that holds slurry on the surface during polishing.
[0115] The technology for mixing abrasive particles and a resin in
a liquid to achieve uniform mixing is applicable to thermosetting
resins also. As an embodiment, a case of mixing phenol resin liquid
and ceria slurry and a case of mixing phenol resin liquid and
silica slurry will be described.
[0116] If the thermosetting resin is a solid powder, it may be
liquefied by dissolving or forming micro-dispersion in an organic
solvent such as ethanol, methanol and the like. The solvent may
also be water.
[0117] If the viscosity of a resin in the liquid form is high, it
may similarly be dissolved or dispersed in pure water or an organic
solvent such as ethanol. This step is important for obtaining
uniform dispersion in the later operation for mixing the abrasive
particles. In this case, dispersion method used was mechanical
stirring, but other methods such as ultrasonic dispersion method
may be utilized, or a combination of several methods may be
adopted. In general, joint use of both stirring and ultrasonic
dispersion produces superior results.
[0118] Mixing of slurry and liquid resin is performed after
adjusting the viscosity of each material to be the substantially
the same. If the viscosity of one material is higher than that of
the other material, the viscosity should be adjusted before mixing,
by diluting with water or other solvent so as to adjust their
viscosity values are substantially the same, to achieve more
uniform mixing of the abrasive particles and the resin. The liquid
resin is a solution such as emulsion, latex, or suspension in which
resin is dispersed or dissolved in a liquid such as water or other
solvent.
[0119] The thermosetting resin in a liquid form and an abrasive
particle slurry are uniformly mixed and dispersed. In this case
also, joint use of ultrasonic dispersion may be applied as
mentioned above. Also, dispersion treatment does not have to be
applied separately to the thermosetting resin liquid and the
abrasive particle slurry, so that the dispersion treatment may be
applied for the first time when the two materials are mixed.
[0120] The mixed solution produced in the above operation is dried
in the spray dryer or by using other mist drying methods, and after
the drying and granulating operations, a mixed powder material is
produced.
[0121] The mixture obtained in the above step is charged uniformly
in a metal mold and is thermo-pressed to produce a green compact.
In performing such an operation, because the present mixture is a
powder produced by uniformly mixing thermosetting resin and
abrasive particles, there is no change in the mixing ratio of
thermosetting resin, and charging of the powder into the metal mold
is facilitated. The metal mold is comprised by upper and lower dies
and spacers shown in FIG. 7. Because the thermosetting resin
hardens by heat, forming can be carried out at constant pressure.
In this case, after pressing at a lower pressure, the spacers are
removed, so that the dies are floated, and they are pressurized
again. After maintaining this state for a time, it is cooled,
demolded to obtain a fixed-abrasive plate.
[0122] After the molding operation, it is fabricated to form planar
surfaces and outer radius to produce a desired shape for use in
polishing. Also, because the fixed-abrasive polishing tool is made
into a planar shape and the structural body and the material are
susceptible to deformation and expansion due to moisture, it is
important to avoid creating non-uniform moisture distribution in
the tool by providing sufficient water during such fabrication
operations of the fixed-abrasive polishing tool.
[0123] It should be noted that liquid mixing of the abrasive
particles and the resin may be carried out by mixing the powder
abrasives and phenol resin liquid in the liquid, followed by mist
spray drying to produce a mixed powder feed for granulating.
[0124] FIG. 8 shows a plan view of a polishing facility related to
the present invention for primarily polishing semiconductor wafers.
This polishing facility uses the fixed-abrasive polishing tool or
the polishing pad described above.
[0125] The polishing facility shown in FIG. 8 is provided with four
load/unload stages 22, each having a wafer cassette 21 for storing
many waters. Load/unload stage 22 may have an elevator device. A
transport robot 24 having two hands is disposed on a transport
mechanism 23 so that each wafer cassette 21 on the load/unload
stage 22 can be accessed.
[0126] Of the two hands provided for the transport robot 24, the
lower hand is used only when receiving a wafer from the wafer
cassette 21, and the upper hand is used only when returning the
wafer to the wafer cassette 21. This arrangement is chosen so that
the cleaned wafer is placed on top to avoid contaminating the
cleaned wafer. The lower hand is a vacuum suction hand for vacuum
retention of the wafer, and the upper hand is a drop type hand for
supporting the wafer at its periphery. The suction type hand can
carry a wafer correctly regardless of shifting of the wafer inside
the cassette, and the drop type hand can transport the wafer
keeping the back-side of the wafer clean because it does not
collect dust as does the suction type hand. Two cleaning machines
25, 26 are disposed opposite to the wafer cassette 21 about the
transport mechanism 23 of the robot 24 as the symmetry axis. Each
cleaning machine 25 or 26 is disposed so that the hand of the robot
24 can access the machines. Between the two cleaning machines 25,
26, in a location that can be reached by the robot 24, a wafer
station 70 is provided to have four wafer platforms 27, 28, 29, 30.
The cleaning machines 25, 26 have a spin drying capability for
spinning at high-speed to dry the wafers, so that two- or
three-stage cleaning operation can be performed without changing
control modules.
[0127] An isolation wall 84 is provided to isolate the degree of
cleanliness in the region B where the cleaning machines 25, 26 and
the wafer platforms 27, 28, 29, 30 are disposed from the degree of
cleanliness in the region A where the wafer cassette 21 and the
transport robot 24 are disposed, and a shutter 31 is provided in
the opening section of the isolation wall for transporting the
wafers across the two regions. A transport robot 80 having two
hands is disposed in a location that enables the robot 80 to reach
the cleaning machine 25 and the three wafer platforms 27, 29, 30,
and a transport robot 81 having two hands is disposed in a location
that enables the robot 81 to reach the cleaning machine 26 and the
three wafer platforms 28, 29, 30.
[0128] The wafer platform 27 is used to transfer wafers between the
transport robot 24 and the transport robot 80, and is provided with
a wafer-detecting sensor 91. The wafer platform 28 is used to
transfer a wafer between transport robot 24 and transport robot 81
and is provided with a wafer-detecting sensor 92. The wafer
platform 29 is used to transfer a wafer from transport robot 81 to
transport robot 80 and is provided with a wafer-detecting sensor 93
and a rinse nozzle 95 used for wafer drying prevention or wafer
cleaning. The wafer platform 30 is used to transport wafers from
transport robot 80 to transport robot 81 and is provided with a
wafer-detecting sensor 94 and a rinse nozzle 96 used for wafer
drying prevention or wafer cleaning. The wafer platforms 29, 30 are
both disposed inside a common water-proof cover, and a shutter 97
is provided on the opening section of the cover for wafer
transport. The wafer platform 29 is disposed above the wafer
platform 30, and by placing washed wafer on the platform 29 and
placing unwashed wafer on the platform 30, contamination caused by
falling rinse water is prevented. Further, in FIG. 8, the sensors
91, 92, 93, 94, rinse nozzles 95, 96 and shutter 97 are shown
schematically, and their location and shape are not shown
accurately.
[0129] The upper hands of the transport robots 80, 81 are used to
transport a wafer that has been washed once to the cleaning machine
or to the wafer platform on the wafer station, and the lower hands
are used to transport a wafer that has not been washed at all and
an unpolished wafer. By using the lower hands to load or unload a
wafer on the wafer inverter, there is no danger of contaminating
the upper hands by the water dripping from the wall of the upper
section of the wafer inverter.
[0130] The cleaning machine 82 is disposed in a location adjacent
to the cleaning machine 25 so as to enable the hands of the
transport robot 80 to reach it. The cleaning machine 83 is disposed
in a location adjacent to the cleaning machine 26 so as to enable
the hands of the transport robot 81 to reach it.
[0131] The cleaning machines 25, 26, 82, 83, and wafer platforms
27, 28, 29, 30 of the wafer station 70 and the transfer robot 80,
81 are all disposed within region B, and its pressure is adjusted
so that it is lower than the pressure in region A. The cleaning
machines 82, 83 are able to clean front and back surfaces of a
wafer.
[0132] The present polishing facility has a housing 66 so as to
surround the various machines, and the interior of the housing 66
is divided into a plurality of rooms (includes regions A, B) by
means of isolation walls 84, 85, 86, 87 and 67.
[0133] A polishing chamber is separated from the region B by the
isolation wall 87, and the polishing chamber is further divided
into two regions C, D by the isolation wall 67. Inside each of the
two regions C, D, two polishing tables and one topring for holding
one wafer and polishing the wafer while pressing it against the
turntable. That is, polishing tables 54, 56 are disposed inside the
region C and polishing tables 55, 57 are disposed inside the region
D, and topring 52 is disposed inside the region C and topring 53 is
disposed inside the region D. A solution nozzle 60 is provided for
supplying a polishing solution to the polishing table 54 located
inside the region C, also provided is a dresser 58 for dressing the
polishing table 54. A solution nozzle 61 is provided for supplying
a polishing solution to the polishing table 55 located inside the
region D, also provided is a dresser 59 for dressing the polishing
table 55. Also provided are a dresser 68 for dressing the polishing
table 56 in region C, and a dresser 69 for dressing the polishing
table 57 in region D. A wet type wafer film-thickness measuring
device may be provided instead of the polishing tables 56, 57. In
so doing, the thickness of film on a wafer may be measured
immediately after polishing, so that controls can be exercised over
additional material removal for the wafer and setting polishing
parameters for the next wafer.
[0134] A wafer transported to the topring 52 or 53 is vacuum
chucked to the topring, and the wafer is transported in the vacuum
chucked state to the polishing table 54 or 55. Then, the wafer is
polished by the polishing pad of the present invention or by a
polishing surface comprised by the fixed-abrasive polishing tool
installed on the polishing table 54 or 55. Use of the polishing pad
or the fixed-abrasive polishing tool of the present invention
enables to produce superior polished surface having less scratches
even in one-stage polishing. In FIG. 6, the second polishing tables
56, 57 described earlier are disposed in locations that can be
accessed by the toprings 56, 57. Accordingly, after polishing a
wafer in the first polishing table 54 or 55, it may be finished
using a finishing pad bonded to the second table 56 or 57. On the
finish table 56, 57, finishing is carried out by the pure water
method based on supplying pure water to a polishing pad made by
SUBA400 or Polytex (both by Rodel Nitta Co.) or finish polishing is
carried out by supplying a slurry.
[0135] Depending on the type of films deposited on the wafer, after
polishing on the second polishing tables 56, 57, the wafer may
sometimes be processed further on the first polishing tables 54,
55. In this case, because the polishing surface of the second
polishing table is smaller, it is advantageous to carry out rough
polishing using the second polishing table bonded with a
comparatively expensive fixed-abrasive polishing tool relative to
the polishing pad, and then, to carry out finish polishing using
the first polishing table bonded with a polishing pad which has a
comparatively short life relative to the fixed-abrasive polishing
tool. Such a procedure would reduce the operating cost of running
the polishing facility. Accordingly, by assigning a polishing pad
to the first polishing table and assigning a fixed-abrasive
polishing tool to the second polishing table, a low cost polishing
system can be produced. In other words, fixed-abrasive polishing
tools are generally more expensive than polishing pads, and the
larger the diameter the more expensive the tools are. Also, because
the service life of the polishing pad is less than that of the
fixed-abrasive polishing tool, the service life can be extended
when the polishing pad is used under light load. Also, when the
size is large, contacts are spread over a wide area so that the
service life is extended. Therefore, maintenance cycle can be
extended and the productivity is improved.
[0136] FIG. 9 shows a diagram of essential parts of the polishing
apparatus. This polishing apparatus comprises a polishing table 56
(57) having, instead of a polishing pad, a fixed-abrasive polishing
unit 117 consisting of a disk 116 bonded with a fixed-abrasive
polishing tool 115 of a diameter of about 60 cm; and a spray nozzle
110 for supplying, during polishing, water not containing any
abrasive particles or a chemical W. Here, the fixed-abrasive
polishing unit 117 is made by bonding the fixed-abrasive polishing
tool 115 comprised primarily of a thermoplastic resin such as ABS
resin or MBS resin to a metal or ceramic disk 116 using an
adhesive. Then, the fixed-abrasive polishing unit 117 is simply but
firmly attached to the polishing table 56 (57) by means of clamping
devices 118, 119. Wafer polishing parameters are, for example,
planar wafer pressure at 300 g/cm.sup.2; rotational speed of
table/wafer=30/35 min.sup.-1; liquid delivery rate at 200 cc/min;
water as liquid (contains less than 1 weight % of surface-active
agent). The parameters may be modified to: planar wafer pressure at
500 g/cm.sup.2; rotational speed of table/wafer=25/10 min.sup.-1;
liquid delivery rate at 200 cc/min; water as liquid (contains less
than 1 weight % of surface-active agent).
[0137] The structures of the topring 101 that hold other polishing
objects 104 is the same as the structures of other tables 54, 55.
Reasons for supplying a liquid such as water during polishing to
the polishing surface of the fixed-abrasive polishing tool 115 are
to provide lubrication of the polishing surface and to remove heat
that can be generated by polishing action. As an example, in this
example, about 200 mL/min of water is supplied. Ultra-pure water
may also be used. Instead of water, an alkaline solution and other
solutions may be used.
[0138] The wafer 104 as the polishing object is rotated by the
topring 101 through its drive shaft 108 while being pressed on top
of the fixed-abrasive polishing tool 115 with an intervening
elastic mat 102. On the other hand, the polishing table 56 (57)
affixed with the fixed-abrasive polishing tool 115 is independently
rotated, and polishing action is provided by the sliding action of
the fixed-abrasive polishing tool in contact with the surface of
the wafer 104 to be polished.
[0139] The finish process that follows is the buffing process
performed by using pure water and soft polishing pad to carry out
cleaning.
[0140] Next, a specific example is given of affixing the
fixed-abrasive polishing tool to a fixation disk by a clamping
device.
[0141] FIG. 10 shows a clamping method of affixing the
fixed-abrasive polishing tool to the fixation disk. The
fixed-abrasive polishing tool 115 is bonded to a metal disk 116 of
aluminum metal and the like to comprise the fixed-abrasive
polishing unit 117. The polishing table 56 (57) is provided with a
clamping device 118, and the movable section 119 of the clamping
device 118 holds the outer periphery of the fixed-abrasive
polishing unit 117. Therefore, by opening the movable section 119
and placing the fixed-abrasive polishing unit 117 with bonded
fixed-abrasive polishing tool 115 on the polishing table 56 (57)
and then closing the movable section 119, the fixed-abrasive
polishing unit 117 is fixed to the polishing table 56 (57) by means
of a spring mechanism of the movable section. Also, by rotating the
movable section 119 from an open position to a closed position, the
fixed-abrasive polishing unit 117 can be detached from the
polishing table 56 (57).
[0142] FIG. 11 shows another method of affixing the fixed-abrasive
polishing tool to the fixation disk. The fixed-abrasive polishing
tool 115 is fixed by the metal disk 116 with a brim and made of
aluminum and the like to comprise the fixed-abrasive polishing unit
117. The brim section 117A of the fixed-abrasive polishing unit 117
is fixed by bolting the clamps 132 to the polishing table 56 (57).
As shown in the drawing, clamp 132 having an arc-shaped structure
of relatively wide width is used, and the angle of the arc to the
center of both ends is set to 44 degrees, and the brim section 117A
of the fixed-abrasive polishing unit 117 is clamped to the
polishing table 56 (57) using two bolts 133. Therefore, detaching
of the fixed-abrasive polishing unit 117 to and from the polishing
table 56 (57) can be carried out easily by undoing the bolts 133.
The reason for using such a relatively wide brimmed clamp is to
avoid deforming the abrading surface of the fixed-abrasive
polishing tool 115 that can be caused by clamping the outer
periphery of the fixed-abrasive polishing unit 117 to the polishing
table 56 (57).
[0143] Also, a total of four protruded section 135 are provided on
the outer periphery of the brim section 117A of the metal disk
comprising the fixed-abrasive polishing unit 117. The protruded
sections 135 have screw holes 136 so that hanging bolt or push bolt
137 can be coupled. Because the fixed-abrasive polishing unit 117
is fairly heavy so that a hanging bolt 137 is provided to
facilitate handling of the fixed-abrasive polishing unit 117 when
exchanging the unit. And, the screw holes 136 are provided for
inserting the push bolts 137 to detach the fixed-abrasive polishing
unit 117 fixed to the polishing table 56 (57). That is, when the
fixed-abrasive polishing unit 117 is to be detached from intimately
attached polishing table 56 (57), the push bolt 137 is inserted
into the screw hole 136 and rotated, thereby the tip of the push
bolt 137 touches the back surface of the fixation disk and when it
is further rotated, the fixed-abrasive polishing unit 117 can be
detached from the polishing table 56 (57). A groove 138 is provided
to correspond to the location of the screw hole 136 of the
polishing table 56 (57). The groove 138 has a role for
accommodating the tip of the hanging bolt or push bolt 137.
[0144] In this embodiment, four each of the clamps 132 and
protruded section 135 are provided, but considering the service
conditions such as pressing pressure, clamp may be made in a ring
shape and the entire periphery of the fixed-abrasive polishing tool
may be fixated. Also the number of protruded sections may also be
adjusted suitably by considering the weight of the fixed-abrasive
polishing tool and the tightly of fixation to the fixation disk.
The material of the metal disk for bonding the fixed-abrasive
polishing tool may include, in addition to aluminum materials,
stainless steels and titanium materials may also be used, for
example, by considering corrosion resistance characteristics.
[0145] FIG. 12 shows a schematic diagram of an example of the
polishing apparatus based on slurry.
[0146] The apparatus is provided with a polishing table 54 (55)
bonded with a polishing pad 121 made of a thermoplastic resin such
as ABS resin and a topring 101 for holding a polishing object such
as a semiconductor wafer 104. The polishing surface of the wafer
104 is processed to be polished by rotating both of topring and
table over the surface of the polishing pad 121, while it is being
pressed against the polishing pad 121 by the topring 101. A large
volume of slurry Q is supplied on the polishing pad 121 from the
slurry supply line 122. The polishing surface of the wafer 104 is
processed by the sliding action while it is being pressed against
the polishing pad 121 having a slurry containing a large amount of
abrasive particles as described above. Topring 101 is freely
tiltably held on the rotation shaft 108 by way of a ball bearing
111, and topring 101 is rotated at a given speed as the rotation
shaft 108 is driven. The wafer 104 is held within the guide ring
128 disposed around the outer periphery of the topring, and is
pressed against the polishing pad 121 by the topring 101 through
the elastic film 102. Here, because the polishing pad is made of a
thermoplastic resin such as ABS resin or MBS resin, soft polishing
is enabled that does not create scratches caused by a rise in the
interface temperature during the sliding motion. Also, by using a
resin containing elastic elements within the resin, it is possible
to provide superior polishing action that produces stiff action
macroscopically but produces soft action microscopically.
[0147] FIG. 13 shows another polishing apparatus of the present
invention. In this polishing apparatus, a semiconductor wafer 152
as the polishing object is held in a rotating holding section 151,
and a fixed-abrasive polishing tool of a pellet shape that rotates
in a similar manner is made to be in sliding contact therewith. The
pellet-shaped fixed-abrasive polishing tool 155 has a diameter of
20 mm and a thickness of 5 mm, for example, and four such tools are
attached to the rotating holding jig 153. The holding jig 153
rotates about its axis 153c, and polishing action is produced by
pressing the fixed-abrasive polishing tools 155 on the surface of
the semiconductor wafer 152 as the polishing object and sliding the
polishing surface of the fixed-abrasive polishing tools 155 over
the surface of the semiconductor wafer 152. Here, the axis 153c of
the holding jig 153c of the fixed-abrasive polishing tools is
offset by a distance L with respect to the center 151c of the
semiconductor wafer 152 as the polishing object so as to polish the
entire surface of the semiconductor wafer as the polishing object.
In this embodiment, the polishing object of about 150 mm or 200 mm
is targeted and the amount of offset is about 35 mm.
[0148] Next, an outline of an example of the polishing conditions
of this polishing apparatus will be explained. The rotational speed
of semiconductor wafer as the polishing object is 100 min.sup.-1,
and the rotational speed of the fixed-abrasive polishing tool is 25
min.sup.-1. The planar wafer pressure is 390 g/cm.sup.2. In the
case of polishing test using a resin pellet, about 3 cc of a slurry
containing cerium oxide (containing surface-active agent) is
supplied. In the case of fixed-abrasive pellets, about 3 cc of a
pure water (containing surface-active agent) is supplied
similarly.
[0149] In summary, the use of a thermoplastic resin or a resin
having elastic elements in a fixed-abrasive polishing tool or a
polishing pad, high quality polishing is enabled by producing
superior flatness and less scratches (damage).
[0150] It would be noted that "fixed-abrasive polishing tool" may
be also referred to as "bonded-abrasive polishing tool". The
bonded-abrasive polishing tool comprises mixture of abrading
particles and resin material, which are formed into a certain
shape, so that abrading particles are bonded by resin matrix, and
fixedly distributed within a resin matrix.
[0151] Although certain preferred embodiments of the present
invention have been shown and described in detail, it should be
understood that various changes and modifications may be made
therein without departing from the scope of the appended
claims.
* * * * *