The present invention relates to dressers for a polishing
cloth in Chemical and Mechanical Polishing (hereinafter referred to as CMP) and
to manufacturing methods therefor, as per the preamble of claims 1, 2, 5 and 7.
Examples of such dressers and methods are disclosed by
JP 2000 141 204 A
.
In manufacturing highly integrated electronic circuits
such as integrated circuits, CMP processing is generally used to remove surface
defects such as protrusions, crystal lattice defects, scoring, or roughness on a
conductive layer, a dielectric layer or an insulation layer formed on a substrate
or wafer. In CMP processing, a wafer is pressed on an abrasive cloth made of polyurethane
foam or the like by a predetermined load, adhered to a disk surface plate, and the
wafer is polished by rotating both the wafer and the cloth with an abrasive fluid
called a chemical slurry. A preparation in which abrasive particles such as iron
oxide, barium carbonate, cerium oxide, or colloidal silica are suspended in an abrasive
fluid such as potassium hydroxide, dilute hydrochloric acid, aqueous hydrogen peroxide,
or iron nitrate, is used as the chemical slurry, and those are selected as required
according to the polishing speed, the kind of object to be polished, etc.
CMP is performed many times in steps for stacking various
kinds of electronic circuits on a substrate or a wafer. When the number of CMPs
is increased, particles of polishing dust burrows into minute cracks, causing clogging,
and this reduces the polishing rate. Accordingly, an operation by which the surface
of the polishing cloth is replaced to restore the polishing speed, called dressing,
is required to be executed often or regularly. For this operation, an instrument
called a dresser for a CMP polishing cloth is used.
Since diamond grit is an excellent dressing material, a
known dresser for a CMP polishing cloth employs diamond grit. To make the dresser,
a method of electrode depositing the diamond grit on stainless steel by nickel plating
has been proposed. Also, in
Japanese Unexamined Patent Application No. 10-12579
, a method of brazing the diamond grit on the stainless steel by a metallic-brazing
material has been proposed.
However, the nickel plating material or the metallic-brazing
material is dissolved by strongly acidic chemical slurry, and the slurry is contaminated
and the diamond grit is peeled, potentially causing scoring on the surface of the
wafer. Therefore, a dresser for CMP abrasive cloth in which dissolution of metal
or peeling-off of diamond grit will not occur in CMP is desired.
In a conventional dresser for polishing cloth, grit such
as diamond grit is usually randomly arranged.
Japanese Unexamined Patent Application Publication No. 2000-141204
shows an example in which diamond grit is arranged substantially uniformly,
approximate in concentric circles. In this case, the distance between the pieces
of grit is not equal and the grit is arranged irregularly. Therefore, stable polishing
performance cannot be exhibited and a uniform surface of the polishing cloth cannot
be obtained, and furthermore, the polishing speed cannot be adjusted arbitrarily.
For example, if the distance between the pieces grit is small, swarf or polished
particles generated by grinding adhere among the grit and are not discharged, or
a part of the polishing cloth is melted due to frictional heat on grinding, thus
causing clogging, and this causes a decrease in performance of the dresser and the
surface of the polishing cloth becomes a mirror surface resulting in a decrease
in the polishing speed.
Furthermore, with a conventional dresser for a polishing
cloth, as dressing of a polishing cloth and polishing a wafer are always carried
out on the same polishing plate, scraps of the polishing cloth or polished dust
are not sufficiently discharged and so damage is caused on the surface of the wafer
and this causes a decrease in yield.
Furthermore, clogging of the dresser for a polishing cloth
causes application of concentrated stress at the clogged parts, the grit is removed
from a holding part, and scratches are caused on the surface of the wafer resulting
in fatal damage.
It is an object of the invention to provide a dresser for
CMP polishing cloth and a manufacturing method therefor in which bonding material
for holding the diamond grit will not be attacked by the strongly acid chemical
slurry, causing contamination of the slurry by metallic dissolution or peeling off
of the diamond grit CMP.
It is another object of the present invention to provide
a dresser for a polishing cloth and a manufacturing method therefor in which stable
grinding characteristics are maintained, a uniform dressing surface of the polishing
cloth is created, and the polishing speed is always constant.
It is another object of the present invention to provide
a dresser for a polishing cloth and a simple manufacturing method therefor in which,
by correctly adjusting the distance between the pieces of grit, the dresser is suited
to the workpiece and polishing efficiency can be adjusted at will.
A dresser for a polishing cloth according to a first aspect
of the present invention has a dressing face comprising a sintered product obtained
by mixing a bonding material comprising silicon and/or silicon alloy with diamond
grit, and forming and sintering the mixture such that a carbide film generated by
sintering the silicon in the bonding material into the diamond is provided on the
surface of said diamond grit, whereby the diamond grit is firmly bonded with the
bonding material, wherein the sintered product is attached on the surface of a pedestal,
the product is finished into specified size by planarizing and dressing the dressing
surface thereof, and the diamond grit is exposed.
A dresser for a polishing cloth according to a second aspect
of the present invention has a dressing face comprising a sintered product obtained
by mixing a bonding material comprising silicon and/or silicon alloy with diamond
grit coated with a film of a carbide of a metal in the group IV, V or VI of the
periodic table, and forming and sintering the mixture, such that the diamond grit
is firmly bonded with the bonding material with said carbide film, wherein the sintered
product is attached on the surface of a pedestal, the product is finished into specified
size by planarizing and dressing the dressing surface thereof, and the diamond grit
is exposed.
Preferably the sintered product is formed by arranging
each particle on the surface of the bonding member so as to have two-dimensional
regularity, the distance between adjacent pieces of grit on the smallest lattice
constructed by the arrangement is within a range between 10 µm and 3,000 µm
and each piece of grit is arranged in a substantially uniform distribution. These
features help produce a uniform dressing surface.
A first method of making a dresser for a polishing cloth
according to the present invention comprises mixing bonding material comprising
silicon and/or silicon alloy with diamond grit, sintering the mixture such that
a carbide film is generated by sintering the silicon in the bonding material on
the surface of the diamond grit, and the diamond is firmly bonded with the bonding
material by the carbide film, wherein the sintered product is attached on the surface
of a pedestal, the product is finished into specified size by planarizing and dressing
the dressing surface thereof, and the diamond grit is exposed.
In a further manufacturing method according to the present
invention a bonding material comprising silicon and/or silicon alloy is mixed with
diamond grit coated with carbide film of metal in group IV, V or VI of the periodic
table, and the mixture is formed and sintered whereby the diamond grit is firmly
bonded with the bonding material by the carbide film, wherein the sintered product
is attached on the surface of a pedestal, the product is finished into specified
size by planarizing and dressing the dressing surface thereof, and the diamond grit
is exposed.
In a still further optional manufacturing method, adhesive
regions whose size is almost the same as that of the grit are provided on the surface
of the planar bonding material comprising silicon or a silicon alloy or a sheet
placed thereon in positions which are uniformly distributed with two-dimensional
regularity, and after each grit particle is adhered on the adhesive regions, they
are pressed down and sintered. Also in this case, a carbide film is generated on
the surface of the diamond grit by reactive sintering of the diamond and the silicon
in the bonding material, and thus, the diamond grit is firmly bonded to the bonding
material with the carbide film.
When adhering the diamond grit on the adhesive regions,
the diamond grit may be coated with carbide film of a metal in group IV, V, or VI
in the periodic table in advance, and the diamond grit may be firmly bonded to the
bonding material with the carbide film.
Furthermore, the adhesive regions may be formed by non-masked
parts of an adhesive sheet masked with a non-adhesive material.
The bonding material comprising silicon and/or silicon
alloy has excellent acid-resistance in acidic solutions such as nitric acid. As
a result, polishing fluid is not contaminated, and this simplifies the wafer cleaning
step after CMP.
Furthermore, in addition to the above, by arranging the
diamond grit regularly with the appropriate grit distance, stable grinding characteristics
can be maintained, surface roughness on the surface of the polishing cloth creates
a uniform dresser surface, stable polishing can be always carried out with a constant
polishing speed, and the grit distance of the diamond grit or the like which is
arranged with regularity can be appropriately adjusted. Thus, the surface state
of the dresser for the polishing cloth can be created according to a workpiece,
and the polishing efficiency can be adjusted at will.
The invention will now be described by way of example with
reference to the accompanying drawings in which:
- FIG. 1 is a perspective view showing an example of a dresser for a polishing
cloth according to the present invention,
- FIG. 2 is a cross-sectional view showing the main part of the dresser that is
cut at the flat face in parallel to the rotating center of the dresser,
- FIG. 3 is a graph showing the results of an acid resistance test on the dresser
and a comparative example.
- FIG. 4 is an optical microscope photograph of the front surface of the dresser
of Example 1,
- FIG. 5 is an optical microscope photograph of the rear side of the dresser of
Example 1 at the same position as in FIG. 4,
- FIG. 6 is a graph showing the results of an acid resistance test of the dresser
of Example 2,
- FIG. 7 is a detailed cross-sectional view through a flat surface parallel to
the center of rotation of an embodiment of a dresser in which the grit arrangement
is regular showing the main part of the dresser.
- FIG. 8 is an electron micrograph showing the arrangement of the diamond grit
of the dresser of a first embodiment in which the diamond grit distance of the dresser
is set to 0.8 mm.
- FIG. 9 is an electron micrograph showing the arrangement of the diamond grit
on the dresser of a second embodiment in which the diamond grit distance of the
dresser is set to 1.5 mm.
- FIG. 10 is an electron micrograph showing the arrangement of the diamond grit
on the dresser of a comparative example.
In a dresser for a CMP polishing cloth according to the
present invention, the dressing face thereof comprises a sintered product obtained
by mixing a bonding member comprising silicon or silicon alloy with diamond grit
coated with a carbide film generated by the diamond grit or the above-described
metal from the periodic table, and by forming and sintering the mixture. In a preferred
embodiment, the sintered product is adhered to the surface of a pedestal made of
ceramic, plastic or the like, then the dressing face is subjected to planarizing
and dressing processing to finish it into specified size as well as exposing the
diamond grit.
If the sintered product is obtained by mixing the bonding
material comprising silicon or silicon alloy with the diamond grit and forming and
sintering the mixture, a carbide film is formed on the surface of the diamond grit
by sintering of the silicon in the bonding material into the diamond. Thereby, the
diamond grit is bonded firmly with the bonding material.
Referring to the drawings, FIG. 1 and FIG. 2 show embodiments
of a dresser for a CMP polishing cloth according to the present invention. FIG.
1 shows the overall constitution. FIG. 2 shows a cross-section of the dresser that
is sectioned at the face through a central axis of rotation.
In the dresser for a CMP polishing cloth according to the
example, a plurality of sintered products 2 are adhered to the working face 1a of
the cup-shaped pedestal 1 made of metal, ceramic, or plastic. As shown in FIG. 2,
the diamond grit 3 in the sintered product 2 has the carbide film 5 generated on
the surface thereof. The diamond grit 3 is bounded firmly with the bonding material
4 by the carbide film 5.
If the bonding material 4 comprising silicon and/or silicon
alloy is mixed with the diamond grit 3, the mixture is formed and sintered, the
carbide film 5 is generated on the surface of the diamond grit by sintering the
silicon in the bonding material 4 into the diamond grit 3. Also, the carbide film
5 can be formed by coating the surface of the diamond grit 3 with the carbide film
5 of a metal from group IV, V, or VI in the periodic table.
Grain size of the diamond grit 3 is not limited. Generally,
it is preferable that the grit having a grain size of #325/#400 to #30/#40 according
to JIS B4130 be used. If the grain size of the diamond grit is less than #325/400,
exposure amount at the dressing face of the diamond grit is lower, and this cause
imperfect dressing of a CMP polishing cloth or slower dressing speed. If the grain
size of the diamond grit exceeds #30/#40, it might cause a rough face of the CMP
polishing cloth when dressing or cause a lower rate of removal.
If silicon alloy is used as at least a part of the bonding
member 4, preferably it has a silicon content of 15 percent by weight. Metals in
groups IV, V, or VI of the periodic table may be used as alloy metal. In particular,
titanium, chrome, tantalum, tungsten, or molybdenum is preferably used. If the silicon
content is less than 15 percent by weight, the obtained sintered product 2 might
have poor acid-resistance.
As a sintering method employable in the present invention,
there are many methods including hot-pressing using graphite, pressure sintering
with current, pressure sintering with discharge, hot isostatic pressing (HIP), or
sintering with an ultrahigh pressure device. Sintering according to the present
invention is not limited to certain sintering methods, but a preferable sintering
method may be chosen and employed as required.
As a method of coating the carbide film 5 on the diamond
grit 3, there is a PVD method, a CVD method, a plating method, or an immersion method
using a melted salt bath. A preferable method may be chosen and employed as required.
If the sintered product 2 is used as a dresser, as shown
in FIG. 1 and FIG. 2, the sintered product is fixed on the working face 1a around
the pedestal 1 by an adhesive 6, then the dressing face 2a is planarized and is
dressed. Thereby, the product is finished into a specified size and the diamond
grit is exposed for dressing.
Since the dresser for a CMP polishing cloth constituted
accordingly has a bonding material employing acid-resistant silicon or silicon alloy,
metal never dissolves and the diamond grit is never peeled off by strongly acidic
chemical slurry. Therefore, wafer-cleaning steps after CMP processing can be simplified
and scratches on a work surface caused by peeling-off of the diamond grit from the
dressing face 2a can be prevented.
In the above-mentioned dresser for the polishing cloth,
as shown in Fig. 7 to Fig. 9, the sintered body 12 is constructed by arranging each
particle of the diamond grit 13 on the surface of the bonding material 14 so as
to have two-dimensional regularity, the distance between the adjacent pieces of
grit on the smallest lattice constructed by the arrangement is within a range between
10 µm and 3, 000 µm, and each piece of grit is arranged so as to form
a substantially uniform distribution. These features are helpful to obtain a uniform
dressing surface.
In this case, diamond separately classified in some range
is used as the diamond grit 13, and the particle size thereof is not limited. However,
generally speaking, it is preferable to select a grit included within the range
mentioned-above. Also, silicon and/or a silicon alloy is used as the above-mentioned
bonding material 14.
As shown in photographs of Fig. 8 or Fig. 9, each particle
of the grit 13 is arranged to be fixed on the surface of the bonding material with
two-dimensional regularity, the distance between the adjacent pieces of grit on
the smallest lattice constructed by the arrangement is within a range between 10
µm and 3,000 µm, more preferably, the grit 13 has a grain size of #100
to #60 and a distance between the pieces of grit of 100 µm to 2,000 µm,
and each piece of grit is arranged so as to form a substantially uniform distribution.
In this case, the larger the distance of between the grit particles becomes, the
more the polishing speed increases and the larger the roughness of the polishing
cloth becomes. Also, the smaller the distance between the grit particles becomes,
the more the polishing speed decreases, the smaller the roughness of the surface
of the polishing cloth becomes and the more the polishing speed decreases.
When the distance between the pieces of grit 13 is 10 µm
or less, since clogging occurs in the dresser due to a grinding layer of the polishing
cloth or polishing particles, the polishing cloth cannot be uniformly ground. Also,
the distance between the pieces of grit 13 is 3,000 µm or more, a satisfactory
grinding operation cannot be obtained. Therefore, it is preferable to select the
distance between the pieces of grit according to the type of object to be ground
or cost, as required, and the roughness of the polishing cloth or the polishing
speed can be arbitrarily adjusted by adjusting the distance.
The arrangement of the grit 13 will be described more specifically.
The smallest lattice produced by the particles of grit 13 which are adjacent in
a circumferential and radial direction on a pedestal 1 (see Fig. 1 and Fig. 7) is,
in general, a square or a parallelogram (this may be called a triangle formed by
connecting opposing angles). In this case, it is enough for the distance to the
closest adjacent particle of grit in this smallest lattice to be within the range
from 10 µm to 3,000 µm. Meanwhile, although the shape of the lattice is
not limited to the above-mentioned shape, each of the pieces of grit must be arranged
with two-dimensional regularity.
The above-mentioned dresser for a polishing cloth will
be easily manufactured by a method described below.
First, many particles of the grit 13 are held on the planar
surface of the bonding material 14 to be mounted on the dresser for a polishing
cloth with two-dimensional regularity. In this case, it is preferable that an adhesive
part having almost the same size as that of the grit is provided directly on the
surface of the bonding member 14 or via a sheet placed thereon according to the
position of each piece of grit 13 arranged with regularity, and the grit 13 is adhered
and fixed on the adhesive part.
The adhesive part may be formed by a non-masking part in
the adhesive sheet which is masked. In this case, preferably, masking is performed
by forming the non-masking part by making many holes having the same size as that
of the particle size of the grit, and the adhesive part is formed by the non-masking
part. However, the adhesive part may be formed by partial application of the adhesive
using printing techniques. The size of the adhesive part must be almost the same
as the that of the grit in order to adhere and fix each piece of grit 13, and they
must be arranged at regular intervals two-dimensionally according to the holding
position of each piece grit 13.
The grit 13 is sintered and fixed on the surface of the
bonding material 14. In this case, as shown in Fig. 7, the diamond grit 13 is pressed
into the bonding material 14 and sintered. At that time, a carbide film 15 is generated
on the surface of the diamond grit 13 by reactive sintering of the diamond and the
silicon in the bonding material, and thus, the diamond grit 13 is firmly bonded
to the bonding material 14 by the carbide film 15.
Furthermore, grit coated in advance with a carbide film
of a metal in group IV, V or VI in the periodic table is used as the above-mentioned
diamond grit, and the grit is pressed into the bonding material and sintered. In
this way, the diamond grit may be firmly bonded to the bonding material by the carbide
film.
To form the regular two-dimensional arrangement in the
grit 13 or the non-masking part, the following method may be used. Holes whose dimension
is equal to the maximum dimension of the grit distribution are made on a metal plate
with the required arrangement by etching, this metal plate is placed on the surface
of a molded body or a sheet, the grit having a particle size distribution corresponding
to the holes is fitted into the holes while being observed with an microscope, the
grit is pushed into the molded body via a plate placed on the grit after the unnecessary
grit is brushed off with a brush, and then, the metal plate is removed and the object
is sintered under prescribed temperature, pressure, and time conditions.
As shown in Fig. 7, the bonding material 14 holding the
grit 13 with a prescribed arrangement is bonded to a dresser pedestal 1 with an
adhesive 6 such as epoxy resin, and then, the dresser surface is subjected to planarizing
and dressing by shot blasting using unbound grit such as alumina, wrapping or etching
to form a final prescribed dimension, and the grit 13 protrudes at a prescribe height.
In this way, a dresser for a polishing cloth is manufactured.
EXAMPLES
Hereinafter, a further description will be given in detail,
with reference to preferred examples. However, the present invention will not be
limited by these examples.
[EXAMPLE 1]
Diamond grit having a grain size of #100/#200 is mixed
with titanium-silicon alloy powder at 1:1 by weight so as to yield a mixture of
volume ratio of 1:3. Then, an obtained mixed powder is filled in a graphite frame,
and then it is sintered at a sintering temperature of 1,200 degrees Celsius and
under a pressure of 50 Mpa for an hour by hot-pressing. After an obtained sintered
product is adhered on a pedestal (refer to FIG. 1) made from a stainless steel (SUS
316) with an epoxy adhesive, the dressing face of the product is planarized and
dressing-processed by using a GC grinding wheel having a grain size of #240 so that
the thickness of the product and the height of protrusion of the diamond grit from
the matrix may be 2 millimeters and 50 micrometers respectively. This forms a dresser.
The following acid-resistance test and durability test
of grit-peeling-off were carried out on the dresser.
In the acid-resistant test, a sliced sintered product is
dipped in 500 milliliters of ten weight percent of nitric acid water solution for
100 hours, then the rate of change in weight of the product is measured with an
electrobalance (measuring sensitivity 1 mg). FIG. 3 shows the rate of change in
weight (vertical axis) to dipping hours (horizontal axis) . The figure shows that
there was no weight decrease and that the product had superior acid-resistance.
For comparison, a sample in which diamond grit with a grain
size of #100/#120 electroformed with Ni was subjected to the same acid-resistance
test. The result shows that the rate of change in weight after 30 hours was 4 .
0 percent.
In the durability test of peeling-off, the dresser is pressed
on the surface of a CMP polishing cloth made of urethane foam with a face pressure
of 20 kPa, then the dresser was subjected to continuous dressing for 100 hours while
slurry containing 2 weight percent of alumina abrasive grains having a grain size
of #4000 is sprayed at 12 milliliters per minute. The surface of the dresser was
observed with a optical microscope at four points to inspect peeling-off of the
diamond grit and changes in height. FIGs.4 and 5 respectively show the results of
the observation before and after dressing. According to these figures (photographs),
no peeling-off of the diamond is observed. Furthermore, no change in protrusion
of the diamond grit is observed, and the product is confirmed to have durability
and excellent grain retention.
[EXAMPLE 2]
Diamond grit, coated with titanium carbide of about 2 micrometers
by a CVD method, having a grain size of #100/#120 is mixed with titanium-silicon
alloy powder at 1:1 by weight so as to make a mixture having a volume ratio of 1:3.
Then, an obtained mixed powder is filled in a graphite frame, then it is sintered
at a sintering temperature of 1,200 degrees Celsius and a pressure of 50 Mpa for
an hour by hot-pressing. After an obtained sintered product is adhered to a pedestal
1 made from stainless steel (SUS 316) with an epoxy adhesive, the dressing face
of the product is planarized and dressing-processed by using a GC grinding wheel
size of #240 so that the thickness of the product and the height of protrusion of
the diamond grit from matrix may be 2 millimeters and 50 micrometers, respectively.
This becomes a dresser. The following acid-resistance test is a durability test
for grid-peeling-off carried out for the dresser under the same conditions as in
Example 1.
The result of the acid-resistance test is shown in FIG.
6. The figure shows that no increase in weight of the product is seen and the product
has superior acid-resistance. Furthermore, similarly as in the first embodiment,
peeling-off of the diamond grit and change in the height of protrusion are observed
at four points on the dresser before and after dressing. Neither peeling-off of
the diamond grit nor change in the height of the protrusion of the diamond grit
is observed before and after dressing. The product is therefor confirmed to exhibit
superior durability in holding grit.
[EXAMPLE 3]
Tungsten powder and silicon powder are mixed in a ball
mill at a ratio of 1:4 by weight, 20% by volume of paraffin is added to the obtained
mixed powder and mixed, and the obtained mixed powder is filled in a die to fabricate
a planar molded body under a pressure of 50 MPa.
An adhesive sheet having an adhesive applied is masked
by a sheet having a non-masking part formed by making many holes equivalent to the
grit size at two-dimensional regular intervals. The adhesive parts formed by the
non-masking part is 270 µm in size, and they are arranged so that the smallest
lattice formed by the adjacent pieces of grit in the circumferential and radial
directions is a parallelogram and the grit distance in one side thereof is at regular
intervals of 0.8 mm.
Then, classified diamond grit of 150 µm to 250 µm
is adhered and fixed on the non-masking part of the adhesive sheet, the sheet is
placed on the molded body made of the tungsten-silicon mixed powder, the grit is
pressed into the molded body via a plate, and then, the body is hot-press sintered
under a sintering temperature of 1, 200°C and a pressure of 50 MPa for one
hour. In this way, a sintered body comprising grit fixed on the molded body is formed.
The obtained sintered body is bonded with epoxy resin on
a cup-shaped pedestal which is made of stainless steel (SUS 316) and has a diameter
of 100 mm so as to form a ring shape with 10 mm intervals, shot blasting is performed
on the dressing surface of the sintered body by using unbound alumina with #240
particle size, and then, the body is planarized and dressed so that the protrusion
height may be 60 µm to 80 µm. In this way, a dresser for a polishing cloth
is fabricated.
The electron micrograph in Fig. 8 shows the arrangement
of the grit on the dressing surface in the above-mentioned dresser for a polishing
cloth.
The fabricated dresser is pressed on a polishing cloth
made of polyurethane foam, which is rotated at 50 rpm, under a pressure of 19.6
kPa to be ground, while slurry (made by Cabot) containing 2% by volume of fumed
silica is flows at about 15 ml per minute.
The polishing speed and surface roughness (Ra and Rz) of
ten dressers are measured every 1, 2, 3, 5, 10, 15, 20, 25 and 30 hours, and the
results are shown in Table 1.
[Table 1]
Example 2
Example 1
Comparable Example
Grit Distance
1.5mm
0.8mm
Electrode Position
Polishing Speed of Polishing Cloth (Unit: µm/H)
AVE
42.96
15.58
75.6
on-1
2.59
2.80
11.25
Surface Roughness of Polishing Cloth Ra (Unit: µm)
AVE
9.95
3.93
4.33
on-1
0.12
0.12
0.36
Surface Roughness of Polishing Cloth Rz(Unit: µm)
AVE
30.19
24.00
27.46
on-1
1.15
0.96
2.61
[EXAMPLE 4]
As in the case of EXAMPLE 3, a planar sintered body is
fabricated by using mixed powder of tungsten and silicon at a ratio of 1:4 by weight.
Also, as in the case of EXAMPLE 3, an adhesive sheet is
masked by a sheet having a non-masking part, holes having a diameter of about 270
µm forming the non-masking part are arranged so that the smallest lattice formed
by adjacent pieces of grit in the circumferential and radial direction is a parallelogram
and a grit distance in one side thereof is at regular intervals of 1.5 mm, classified
diamond grit of 150 µm to 250 µm is adhered and fixed on the non-masking
part of the adhesive sheet, the sheet is placed on the molded body made of the tungsten-silicon
mixed powder, and the sheet is hot-press sintered. In this way, a sintered body
comprising grit fixed on the molded body is obtained.
The obtained sintered body is bonded with epoxy resin on
the same pedestal as that used in EXAMPLE 1, shot blasting is performed on the operational
surface using unbound alumina with #240 particle size, and then, the protruding
height for a matrix of the diamond grit is adjusted to be 60 µm to 80 µm.
In this way, a dresser for a polishing cloth is fabricated. The electron micrograph
in Fig. 9 shows the arrangement of the grit on the dressing surface of the dresser
for a polishing cloth.
The fabricated dresser is pressed on a polishing cloth
made of polyurethane foam, which is rotating at 100 rpm, under a pressure of 19.6
kPa to be ground, while slurry (made by Cabot) containing 2% by volume of fumed
silica flows at about 15 ml per minute.
The polishing speed and surface roughness (Ra and RZ) of
ten dressers are measured every 1, 2, 3, 5, 10, 15, 25 and 30 hours, and the results
are also shown in Table 1.
[COMPARATIVE EXAMPLE 1]
A polishing cloth made of polyurethane foam is ground under
the same conditions as those in the case of EXAMPLES 3 AND 4 by using the same diamond
grit as that in the case of EXAMPLES 3 and 4. The electron micrograph in Fig. 10
shows the arrangement of the grit on the dressing surface in the above-mentioned
dresser for a polishing cloth. The results after grinding are shown in Table 1 together
with the results of EXAMPLES 3 and 4.
Table 1 shows that, in the dresser for a polishing cloth
in which the diamond grit is regularly arranged at equal intervals in the examples
mentioned above, the surface roughness on the surface of the polishing cloth is
more uniform than that on the surface of a conventional dresser on which grit is
randomly arranged, and the polishing speed of the polishing cloth is very stable.
