U.S. patent application number 11/192846 was filed with the patent office on 2005-11-24 for table of wafer polishing apparatus, method for polishing semiconductor wafer, and method for manufacturing semiconductor wafer.
Invention is credited to Ishikawa, Shigeharu, Jimbo, Naoyuki, Majima, Kazutaka, Okuda, Yuji, Takagi, Hideki, Tsuji, Masahiro, Yasuda, Hiroyuki.
Application Number | 20050260938 11/192846 |
Document ID | / |
Family ID | 27577514 |
Filed Date | 2005-11-24 |
United States Patent
Application |
20050260938 |
Kind Code |
A1 |
Okuda, Yuji ; et
al. |
November 24, 2005 |
Table of wafer polishing apparatus, method for polishing
semiconductor wafer, and method for manufacturing semiconductor
wafer
Abstract
A table for a wafer polishing apparatus having superior
heat-resistant, anti-thermal-shock, and anti-abrasion
characteristics and capable of increasing the diameter of a
semiconductor wafer while improving the quality of the wafer. The
table includes a plurality of superimposed bases each of which is
formed of silicide ceramic or carbide ceramic. The bases are joined
together by an adhesive layer. A fluid passage is formed in a
joining interface between the bases.
Inventors: |
Okuda, Yuji; (Gifu, JP)
; Jimbo, Naoyuki; (Gifu, JP) ; Majima,
Kazutaka; (Gifu, JP) ; Tsuji, Masahiro; (Gifu,
JP) ; Takagi, Hideki; (Gifu, JP) ; Ishikawa,
Shigeharu; (Gifu, JP) ; Yasuda, Hiroyuki;
(Gifu, JP) |
Correspondence
Address: |
SAWYER LAW GROUP LLP
P O BOX 51418
PALO ALTO
CA
94303
US
|
Family ID: |
27577514 |
Appl. No.: |
11/192846 |
Filed: |
July 28, 2005 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11192846 |
Jul 28, 2005 |
|
|
|
10018708 |
Apr 15, 2002 |
|
|
|
10018708 |
Apr 15, 2002 |
|
|
|
PCT/JP00/03899 |
Jun 15, 2000 |
|
|
|
Current U.S.
Class: |
451/285 |
Current CPC
Class: |
B24B 55/02 20130101;
B24B 37/12 20130101; B24B 41/047 20130101; B24B 37/14 20130101;
B24B 37/015 20130101; B24B 37/16 20130101 |
Class at
Publication: |
451/285 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 15, 1999 |
JP |
11-168522 |
Jun 15, 1999 |
JP |
11-168523 |
Jun 30, 1999 |
JP |
11-185333 |
Aug 24, 1999 |
JP |
11-237508 |
Aug 24, 1999 |
JP |
11-237507 |
Aug 24, 1999 |
JP |
11-237509 |
Aug 26, 1999 |
JP |
11-239900 |
Sep 29, 1999 |
JP |
11-277117 |
Sep 29, 1999 |
JP |
11-277118 |
Claims
1. A table having a polishing surface for polishing a semiconductor
wafer held by a wafer holding plate of a wafer polishing apparatus,
wherein the table is formed of a material, the Young's modulus of
which is 1.0 kg/cm.sup.2(.times.10.sup.6) or greater.
2. The table according to claim 1, wherein the material is
ceramic.
3. The table according to claim 1, wherein the material is a
silicon carbide sinter.
4. The table according to claim 3, wherein the silicon carbide
sinter is dense.
5. The table according to claim 3, wherein the Young's modulus of
the silicon carbide sinter is 1.0 to 5.0 kg/cm.sup.2
(.times.10.sup.6).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional of co-pending U.S. patent
application Ser. No. 10/018,708, entitled "Table of Wafer Polishing
Apparatus, Method For Polishing Semiconductor Wafer, And Method for
Manufacturing Semiconductor Wafer", filed Dec. 13, 2001.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to a table of a semiconductor
wafer polishing apparatus, a method for polishing semiconductor
wafers with the polishing apparatus, and a method for manufacturing
a semiconductor wafer with the polishing apparatus.
[0003] These days, most electric products employ a semiconductor
device that includes a fine conductive circuit formed on a silicone
chip. Generally, the semiconductor device is fabricated using a
monocrystal silicon ingot as a starting material in accordance with
the following procedure.
[0004] First, the ingot is sliced into thin pieces. The pieces are
then polished in a lapping step and a polishing step to obtain bare
wafers. The bare wafers include mirror surfaces are thus referred
to as mirror wafers. Also, if the bare wafers are obtained in an
epitaxial growth layer forming step after the lapping step and
before the polishing step, the bare wafers are particularly
referred to as epitaxial wafers.
[0005] In a subsequent wafer treating step, the bare wafers are
repeatedly subjected to oxidation, etching, and impurity diffusion.
Afterwards, the bare wafers are cut into an appropriate size in a
dicing step. This finally completes a desired semiconductor
device.
[0006] In these steps, a device forming side of each semiconductor
wafer needs be polished with a certain means. As an effective
polishing means, various types of wafer polishing apparatuses
(including lapping machines and polishing machines) have been
proposed.
[0007] A typical wafer polishing apparatus includes a table, a
pusher plate, and a cooling jacket. The table is secured to an
upper portion of the cooling jacket. The table and the cooling
jacket are formed of metal such as stainless steel. A passage is
formed in the cooling jacket and coolant water for cooling the
table circulates in the passage. The pusher plate is located above
the table and has a holding side (a lower side) to which a wafer
subject to polishing is adhered by a thermoplastic wax. The pusher
plate rotates to press the wafer, which is held by the pusher
plate, against a polishing side (an upper side) of the table from
above. The wafer thus contacts the polishing side, and one side of
the wafer is uniformly polished. During polishing, heat is
generated on the wafer and is transmitted to the cooling jacket
through the table. The coolant water that circulates in the passage
of the cooling jacket releases the heat from the apparatus.
[0008] The table of the wafer polishing apparatus is often heated
to a high temperature when polishing is performed. It is thus
required that the table be formed of a heat-resistant and
thermal-shock-resistant materials. Further, frictional force
constantly acts on the polishing side of the table. It is thus
required that the material of the table need be resistant to
abrasive wear. In addition, generation of thermal stress that bends
the wafer must be avoided to increase the wafer diameter and
improve the wafer quality. It is thus necessary to minimize
temperature differences in the table. Accordingly, the material of
the table needs to have high heat conductivity.
BRIEF SUMMARY OF THE INVENTION
[0009] It is an objective of the present invention to provide a
table of a wafer polishing apparatus that has superior heat-
resistant, thermal-shock-resistant, and anti-abrasion
characteristics and is capable of increasing the diameter of a
semiconductor wafer while improving the wafer quality.
[0010] It is another objective of the present invention to provide
a method for polishing semiconductor wafers and a method for
manufacturing the semiconductor wafers that are optimal for
uniformly polishing the semiconductor wafers to increase the wafer
diameter and improve the wafer quality.
[0011] To solve the above-described problems in accordance with the
objectives of the present invention, an improved table of a wafer
polishing apparatus is provided. The table has a polishing surface
for polishing a semiconductor wafer held by a wafer holding plate
of the wafer polishing apparatus. The table includes a plurality of
superimposed bases, each base being formed from silicide ceramic or
carbide ceramic. At least one of the bases has a fluid passage
formed in its superimposition interface.
[0012] In a second perspective of the present invention, the table
includes a plurality of superimposed bases, each base being formed
from a silicon carbide sinter. At least one of the bases has a
fluid passage formed in its superimposition interface.
[0013] A third perspective of the present invention is a table
having a polishing surface for polishing a semiconductor wafer held
by a wafer holding plate of a wafer polishing apparatus. The table
is formed of a material, the Young's modulus of which is 1.0
kg/cm.sup.2 (.times.10.sup.6) or greater.
[0014] A fourth perspective of the present invention provides a
method for performing polishing using a table having a polishing
surface for polishing a semiconductor wafer held by a wafer holding
plate of a wafer polishing apparatus. The table includes a
plurality of superimposed bases, each base being formed from
silicide ceramic or carbide ceramic. At least one of the bases has
a fluid passage formed in its superimposition interface. The method
includes the steps of rotating the semiconductor wafer, and
contacting the semiconductor wafer with the polishing surface of
the table while circulating coolant water in the fluid passage.
[0015] A fifth perspective of the present invention provides a
method for manufacturing a semiconductor wafer. The method includes
performing polishing using a table having a polishing surface for
polishing a semiconductor wafer held by a wafer holding plate of a
wafer polishing apparatus. The table includes a plurality of
superimposed bases, each base being formed from silicide ceramic or
carbide ceramic. At least one of the bases has a fluid passage
formed in its superimposition interface. The polishing step
includes the steps of rotating the semiconductor wafer, and
contacting the semiconductor wafer with the polishing surface of
the table while circulating coolant water in the fluid passage.
[0016] A sixth perspective of the present invention is a method for
manufacturing a table having a polishing surface for polishing a
semiconductor wafer held by a wafer holding plate of a wafer
polishing apparatus. The method includes the steps of arranging a
foil-like brazing filler between a plurality of bases, each having
a groove formed in its surface and each formed from a silicon
carbide sinter, and heating each of the bases to braze the bases
together.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a view schematically showing a wafer polishing
apparatus of a first embodiment according to the present
invention;
[0018] FIG. 2 is an enlarged cross-sectional view showing a main
portion of a table used in the apparatus of FIG. 1;
[0019] FIG. 3 is an enlarged view schematically showing a main
portion of a table according to a first modification of the first
embodiment;
[0020] FIG. 4 is an enlarged view schematically showing a main
portion of a table according to a second modification of the first
embodiment;
[0021] FIG. 5 is an enlarged cross-sectional view showing a main
portion of a table according to a third modification of the first
embodiment;
[0022] FIG. 6 is a view schematically showing an apparatus of a
second embodiment according to the present invention;
[0023] FIG. 7 is an enlarged cross-sectional view showing a main
portion of a table used in the apparatus of FIG. 6;
[0024] FIG. 8 is an enlarged cross-sectional view showing a main
portion of a table according to a first modification of the second
embodiment;
[0025] FIG. 9 is an enlarged cross-sectional view showing a main
portion of a table according to a second modification of the second
embodiment;
[0026] FIG. 10 is an enlarged cross-sectional view showing a main
portion of a table according to a third modification of the second
embodiment;
[0027] FIG. 11 is a view schematically showing an apparatus of a
third embodiment according to the present invention;
[0028] FIG. 12 is an enlarged cross-sectional view showing a main
portion of a table used in the apparatus of FIG. 11;
[0029] FIG. 13A is an enlarged cross-sectional view showing a main
portion of a table used in an apparatus of a sixth embodiment
according to the present invention;
[0030] FIGS. 13B and 13C are further enlarged cross-sectional views
each schematically showing an adhering interface of the table;
[0031] FIG. 14 is an enlarged cross-sectional view schematically
showing crystal particles in the adhering interface of the table of
the sixth embodiment;
[0032] FIG. 15 is an enlarged cross-sectional view showing a main
portion of a table according to a first modification of the sixth
embodiment; and
[0033] FIG. 16 is an enlarged cross-sectional view showing a main
portion of a table according to a second modification of the sixth
embodiment.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
First Embodiment
[0034] A wafer polishing apparatus 1 of the first embodiment will
now be described in detail with reference to FIGS. 1 and 2. FIG. 1
schematically shows the wafer polishing apparatus 1 of the first
embodiment. The wafer polishing apparatus 1 includes a disk-like
table 2. A polishing surface 2a, on which a semiconductor wafer 5
is polished, is defined on the upper side of the table 2. A
polishing cloth (not shown) is applied to the polishing surface 2a.
In the first embodiment, a cooling jacket is not employed, and the
table 2 is horizontally and directly secured to an upper end of a
cylindrical rotary shaft 4. Thus, when the rotary shaft 4 is
rotated, the table 2 rotates integrally with the rotary shaft
4.
[0035] As shown in FIG. 1, the wafer polishing apparatus 1 includes
a plurality of wafer holding plates 6 (for the sake of brevity,
only two are shown in FIG. 1). Each plate 6 is formed of, for
example, glass, ceramic such as alumina, or metal such as stainless
steel. A pusher rod 7 is fixed to a middle portion of one side (a
non-holding side 6b) of each wafer holding plate 6. Each pusher rod
7 is located above the table 2 and is connected to a drive means
(not shown). Each pusher rod 7 horizontally supports the associated
wafer holding plate 6. In this state, the holding sides 6a oppose
the polishing surface 2a of the table 2. Further, each pusher rod 7
rotates integrally with the associated wafer holding plate 6 and
moves upward and downward in a predetermined range. In addition to
the upward or downward movement of the plates 6, the table 2 may be
configured to move upward or downward. A semiconductor wafer 5 is
adhered to the holding surface 6a of each wafer holding plate 6 by
an adhesive agent such as thermoplastic wax. The semiconductor
wafers 5 may be vacuumed or electrostatically attracted to the
corresponding holding sides 6a. In this state, a polished surface
5a of each semiconductor wafer 5 must be faced toward the polishing
surface 2a of the table 2.
[0036] If the apparatus 1 is used as a lapping machine, or is used
for polishing the semiconductor wafers 5 after a slicing step of a
bare wafer process is completed, it is preferred that the wafer
holding plates 6 be configured as follows. That is, it is preferred
that each plate 6 allow the corresponding semiconductor wafer 5 to
contact the polishing surface 2a in a state in which a
predetermined pressure is applied to the polishing surface 2a. This
is possible since the wafer 5 does not include an epitaxial growth
layer, which the wafer holding plate 6 (the pusher plate) would
remove from the wafer 5 when applying pressure. It is preferred
that the wafer holding plates 6 be configured in the same manner if
the apparatus 1 is used as a polishing machine for manufacturing
mirror wafers, or is used for polishing the semiconductor wafers 5
without performing an epitaxial growth step after the lapping step
is completed.
[0037] If the apparatus 1 is used as a polishing machine for
manufacturing epitaxial wafers, or is used for polishing the
semiconductor wafers 5 that have been subjected to the epitaxial
growth step after the lapping step, it is preferred that the plates
6 be configured as follows. That is, it is preferred that each
plate 6 have the corresponding semiconductor wafer 5 contact the
polishing surface 2a while applying substantially no pressure to
the polishing surface 2a. This is because a silicone epitaxial
growth layer easily separates compared to monocrystal silicon. It
is preferred that the wafer holding plates 6 be configured
basically in the same manner if the apparatus 1 is used as a
machine for performing chemical mechanical polishing (CMP) after
various layer forming steps.
[0038] The structure of the table 2 will hereafter be described in
detail.
[0039] As shown in FIGS. 1 and 2, the table 2 of the first
embodiment is a superimposed ceramic body that includes a plurality
of (in this embodiment, two) superimposed bases 11A, 11B. Among the
two bases 11A, 11B, grooves 13 having a predetermined pattern are
formed in the upper side of the lower base (hereafter, the lower
base 11B). The bases 11A, 11B are joined together by a brazing
filler layer 14, or a non-organic adhering material layer, thus
forming an integral body. Accordingly, a coolant water passage 12,
or a fluid passage, is formed in the joining interface between the
bases 11A, 11B. That is, the grooves 13 form part of the coolant
water passage 12. A plurality of through holes 15 are formed in the
middle of the lower base 11B. The through holes 15 connect a
passage 4a formed in the rotary shaft 4 to the coolant water
passage 12.
[0040] Each base 11A, 11B is formed from a ceramic material. It is
preferred that the material be ceramic silicide or ceramic carbide.
Particularly, in the first embodiment, the ceramic material is a
dense body that is formed from a silicon carbide sinter (SiC
sinter), the starting material of which is silicon carbide powder.
The dense body has strongly bonded crystal particles and an
extremely small number of pores. The dense body is thus suitable as
the material of the table. Further, compared to other ceramic
sinters, the silicon carbide sinter, the starting material of which
is silicon carbide powder, includes particularly superior heat
conductivity, heat- resistant performance, anti-thermal-shock
performance, and anti-abrasion performance characteristics. In the
first embodiment, the two bases 11A, 11B are formed from the same
material.
[0041] The silicon carbide powder includes a type silicon carbide
powder, .beta. type silicon carbide powder, and amorphous silicon
carbide powder. In this case, one type of powder may be solely
employed. Alternatively, two or more types of powders may be
combined (.alpha. type+.beta. type, .alpha. type+amorphous type,
.beta. type+amorphous type, or .alpha. type+.beta. type+amorphous
type). A sintered formed from .beta. type silicon carbide powder
includes a large number of large plate crystals compared to sinters
of other types of silicon carbide powders. Thus, the sinter formed
from .beta. type silicon carbide powder includes a relatively small
number of grain boundaries in the crystal particles of the sinter
and has particularly superior heat conductivity.
[0042] The density of the bases 11A, 11B is preferred to be 2.7
g/cm.sup.3 or greater, is more preferred to be 3.0 g/cm.sup.3 or
greater, and is especially preferred to be 3.1 g/cm.sup.3 or
greater. If the density is excessively low, the bonding among the
crystal particles of the sintered body is weakened and the number
of the pores increases. This results in the bases 11A, 11B having
unsatisfactory anti-corrosion and anti-abrasion
characteristics.
[0043] It is preferred that the heat conductivity of each base 11A,
11B be 30 W/m.multidot.K or greater and more preferred that the
heat conductivity be 80 W/m.multidot.K to 200 W/m.multidot.K. If
the heat conductivity is excessively low, there is a tendency of
temperature differences being produced in the sinter, thus
hampering the increasing of the diameter of the semiconductor
wafers 5 and improvement of the wafer quality. On the other hand,
although the heat conductivity is preferred to be higher, it
becomes difficult to procure materials inexpensively and stably
when the heat conductivity exceeds 200 W/m.multidot.K.
[0044] The groove 13, which forms part of the coolant water passage
12, is a grounded groove, or is formed by grinding the upper side
of the lower base 11B with a grinder. The groove 13 does not
necessarily have to be ground but may be formed through, for
example, blasting such as sand blasting. As schematically shown in
FIG. 2, the groove 13, which is formed through these processes, has
a relatively round cross-sectional shape. It is preferred that the
depth of the groove 13 be approximately 3-10 millimeters and that
the width of the groove 13 be approximately 5-20 millimeters.
[0045] A procedure for fabricating the table 2 will hereafter be
briefly described.
[0046] First, a small amount of sintering aiding agent is added to
silicon carbide powder and uniformly mixed. Boron, boron compound,
aluminum, aluminum compound, or carbon is selected as the sintering
aiding agent. The addition of the small amount of the sintering
aiding agent increases the crystal growth speed of silicon carbide
such that a resulting sinter is dense and has high heat
conductivity.
[0047] Next, the mixture is molded into disk-like molded products.
The bodies are then calcinated at 1800 to 2400 degrees Celsius to
obtain the two bases 11A, 11B, each of which is a silicon carbide
sinter. If the calcinating temperature is too low, not only does it
become difficult to increase the crystal particle diameter but also
a large number of pores are formed in the sintered body. In
contract, if the calcinating temperature is too high, silicon
carbide starts to decompose lowers the strength of the sintered
body.
[0048] Subsequently, one side of the lower base 11B is
substantially entirely ground with a grinder to form the grooves
13, which have a predetermined width and a predetermined depth.
Further, after applying the brazing filler to on one side of the
upper base 11A, the two bases 11A, 11B are superimposed to arrange
the brazing filler layer 14 and the groove 13 in the interface
between the bases 11A, 11B. In this state, the bases 11A, 11B are
heated to the melting temperature of the brazing filler, thus
brazing the bases 11A, 11B together. Finally, the upper side of the
upper base 11A is polished to form the polishing surface 2a. The
surface polishing step may be performed before the adhesion step or
the groove formation step. The table 2 of the first embodiment is
thus formed in the above-described procedure.
[0049] The following are referential examples of the first
embodiment.
REFERENTIAL EXAMPLE 1-1
[0050] In referential example 1-1, "beta random (trade name)",
product of IBIDEN KABUSHIKI KAISHA, was used as silicon carbide
powder that contained 94.6 weight percent of .beta. type crystals.
The average crystal particle diameter of this powder was 1.3
micrometers. The powder contained 1.5 weight percent of boron and
3.6 weight percent of free carbon.
[0051] First, 5 weight parts of polyvinyl alcohol and 300 weight
parts of water were added to 100 weight parts of the silicon
carbide powder. The mixture was then stirred in a ball mill for
five hours to obtain a uniform mixture. The mixture was dried for a
predetermined time to remove a certain amount of moisture from the
mixture. An appropriate amount of the dry mixture was then sampled
and granulated. Next, the granules of the dry mixture were
subjected to molding with metal press dies at a pressure of 50
kg/cm.sup.2. The density of the resulting molded body was 1.2
g/cm.sup.3.
[0052] Subsequently, the molded body was placed in a graphite
crucible sealed from ambient air. The body was then calcinated
using a Tammann type calcinating furnace. The calcination was
performed in an argon gas atmosphere of one atmospheric pressure.
During the calcination, the heating was increased at a rate of 10
degrees Celsius per minute until reaching a maximum temperature of
2300 degrees Celsius. The maximum temperature was maintained for
two hours. The observation of the resulting bases 11A, 11B
indicated an extremely dense, three-dimensional network structure
in which plate crystals were entangled in multiple directions.
Further, the density of each base 11A, 11B was 3.1 g/cm.sup.3. The
heat conductivity of each base 11A, 11B was 150 W/m.multidot.K.
Each base 11A, 11B contained 0.4 weight percent of boron and 1.8
weight percent of free carbon.
[0053] Afterwards, the grooves 13 were ground to a depth of 5
millimeters and a width of 10 millimeters. The two bases 11A, 11B
were then integrally brazed to each other. The thickness of the
brazing filler layer 14 was about 20 micrometers. Further, the
upper side of the upper base 11A was polished to form the table 2
that had the polishing surface 2a.
[0054] The resulting table 2 of referential example 1-1 was
installed in the aforementioned various types of apparatuses 1. The
semiconductor wafers 5 of different dimensions were then polished
with the apparatuses 1, while the coolant water W was constantly
circulating. As a result, regardless of the type of the apparatus
1, thermal deformations were not found in the table 2. Further,
cracks were not found in the brazing filler layer 14, and a high
bonding strength was maintained in the joining interface between
the bases 11A, 11B. Also, a breakage test was conducted on the
table 2 using a conventional method that complies with JIS R 1624
to measure the flexural strength of the interface. The value was
approximately 15 kgf/mm.sup.2. Further, there was no leakage of the
coolant water W from the joining interface.
[0055] The observation of the semiconductor wafers 5 polished by
the apparatuses 1 indicated that the wafers 5 were not damaged,
regardless of the dimensions of the wafers 5. Further, there was no
significant bending in the wafers 5. In other words, it was
apparent that the semiconductor wafers 5 having extremely high
accuracy and extremely high quality would be obtained by the table
2 of referential example 1-1.
REFERENTIAL EXAMPLE 1-2
[0056] In referential example 1-2, .alpha. type silicon carbide
powder (more specifically, "OY15 (trade name)", product of
YAKUSHIMA DENKO KABUSHIKI KAISHA) was employed in lieu of the
.beta. type. The density of each resulting base 11A, 11B was 3.1
g/cm.sup.3. The heat conductivity of each base 11A, 11B was 125
W/m.multidot.K. Each base 11A, 11B contained 0.4 weight percent of
boron and 1.8 weight percent of free carbon. The heat conductivity
of the bases 11A, 11B in referential example 1-1, in which the
.beta. type powder was the starting material, was approximately 20
percent higher than that of referential example 1-2.
[0057] After the table 2 was obtained through the same procedure as
referential example 1-1, the table 2 was installed in the various
types of apparatuses 1 to polish the semiconductor wafers 5 of
different dimensions. Accordingly, substantially the same
advantageous results as those of referential example 1-1 were
obtained.
[0058] <Conclusion>
[0059] The first embodiment has the following advantages.
[0060] (1) In the table 2 of the wafer polishing apparatus 1, the
coolant water W circulates in the passage 12 located in the
interface between the bases 11A, 11B. Thus, when the polishing of
the semiconductor wafers 5 generates heat, the heat is released
efficiently and directly from the table 2. This ensures the
diffusion of the heat. Accordingly, compared to the prior art in
which the table 2 is mounted on the cooling jacket and indirectly
cooled, the temperature difference of the table 2 is further
decreased. As a result, the apparatus 1 prevents the wafers 5 from
being adversely affected by the heat and enables the diameter of
the wafers 5 to be increased. Further, the wafers 5 are polished
with high accuracy. This improves the quality of the wafers 5.
[0061] (2) The table 2 forms a superimposed structure that includes
the two bases 11A, 11B. Thus, after forming the structure that
functions as the passage 12 (that is, the groove 13) in one surface
of one of the bases 11, the bases 11A, 11B are joined together.
This makes it relatively easy to form the passage 12 in the
interface between the bases 11A, 11B. Thus, the table 2 is
advantageous in that the table 2 is formed relatively easily.
Further, this structure does not need to locate a pipe in the
joining interface between the bases 11A, 11B. This prevents the
structure of the table 2 from becoming complicated and increases in
cost.
[0062] (3) The two bases 11A, 11B of the table 2 are both dense,
sintered silicon carbide bodies, the starring material of which is
silicon carbide powder. The dense bodies are preferred in that
crystal particles are strongly bonded together and the number of
the pores is extremely small. Further, the sintered silicon carbide
body, the starting material of which is silicon carbide powder,
includes superior heat conductivity, heat-resistant,
anti-thermal-shock, and anti-abrasion characteristics compared to
other sintered ceramic bodies. Thus, the table 2 of the bases 11A,
11B enables the diameter of each semiconductor wafer 5 to be
increased and improves the quality of the wafer 5.
[0063] (4) The bases 11A, 11B are securely joined together by the
brazing filler layer 14, or the joining material layer. Thus, as
compared to the case in which the bases 11A, 11B are joined
together without the joining material layer, an increased joining
strength is ensured in the interface between the bases 11A, 11B.
Accordingly, leakage from the joining interface does not occur when
the coolant water W circulates in the passage 12.
[0064] If the joining material layer is the brazing filler layer 14
that has a relatively high heat conductivity, heat resistance is
reduced in the joining material layer, thus making it difficult to
hamper heat transfer between the bases 11A, 11B. This increases
heat radiation from the table 2 and further minimizes the
temperature differences in the table 2. This also contributes to
the increasing of the diameter of each semiconductor wafer 5 and
the improvement of the quality of the wafer 5.
[0065] (5) If the wafer polishing apparatus 1 includes the table 2,
the cooling jacket becomes unnecessary, thus simplifying the entire
structure of the apparatus 1.
[0066] The first embodiment may be modified as follows.
[0067] The joining material layer that joins the bases 11A, 11B
together do not necessarily have to be formed of a non- organic
joining material such as a brazing filler but may be formed of an
organic joining material that contains resin (i.e., an adhesive
agent).
[0068] The bases 11A, 11B do not necessarily have to be joined
together by the joining material layer. For example, in the table 2
of the modification shown in FIG. 3, the joining material layer is
eliminated. Instead, the bases 11A, 11B of the table 2 are fastened
together by a bolt 23 and a nut 24, thus forming an integral body.
Further, a seal member 22, such as a packing, is located in the
interface between the bases 11A, 11B to ensure sufficient seal
performance. It is especially preferred that the seal member 22 be
formed of a material having high heat conductivity. If the
fastening force of the bolt 23 and the nut 24 is strong enough, the
seal member 22 may be eliminated like the further modification
shown in FIG. 4.
[0069] Instead of the double layered structure, the table 2 may be
a triple layered structure like the modification shown in FIG. 5.
Further, the table 3 may include four or more layers.
[0070] As silicide ceramic other than silicon carbide, for example,
silicon nitride (Si.sub.3N.sub.4) or sialon may be selected. It is
preferred that the selected silicide ceramic be a dense body with a
density of 2.7 g/cm.sup.3 or greater.
[0071] As carbide ceramic other than silicon carbide, for example,
boron carbide (B.sub.4C) may be selected. It is preferred that the
selected carbide ceramic be a dense body with a density of 2.7
g/cm.sup.3 or greater.
[0072] In the table 2 of the first embodiment, liquid other than
water may circulate through the passage 12. Also, gas may circulate
through the passage 12.
Second Embodiment
[0073] A wafer polishing apparatus 1 of a second embodiment will
now be described in detail with reference to FIGS. 6 and 7.
[0074] As shown in FIGS. 6 and 7, like the first embodiment, the
table 2 of the second embodiment is a layered ceramic structure
that includes the two superimposed bases 11A, 11B. The grooves 13,
which have a predetermined pattern, are formed in substantially the
entire upper side of the lower base 11B. The bases 11A, 11B are
integrally joined together by an epoxy resin type adhesive agent
layer 14, or an organic joining material layer.
[0075] A pipe made from a material having high heat conductivity is
formed in the interior of the table 2. The coolant water W, or
fluid, circulates in the pipe. More specifically, in the second
embodiment, a copper pipe 16 is located in the joining interface
between the bases 11A, 11B. Copper is selected as the material of
the pipe since it is inexpensive, and easily machined in addition
to having a high heat conductivity.
[0076] The copper pipe 16 has a circular cross-section. The
diameter of the pipe 16 is approximately 5-10 millimeters. The pipe
16 is curved to form a spiral shape as a whole. The adjacent
sections of the pipe 16 at its curved portions are spaced from each
other at an interval of approximately 5-20 millimeters. The curved
pipe 16 is held in the groove 13, which is formed in the upper side
of the lower base 11B. In this state, the bases 11A, 11B are joined
together. The copper pipe 16 occupies substantially the entire
joining interface. Both ends of the pipe 16 are bent downward at a
right angle and are received in the corresponding through holes 15.
The ends of the pipe 16 are thus connected to the corresponding
passages 4a, which extend through the rotary shaft 4.
[0077] It is preferred that the adhesive agent layer 14 for joining
the bases 11A, 11B be formed from an epoxy resin type adhesive
agent. This is because this type of adhesive agent resists heat and
has superior adhering strength. In this case, it is preferred that
the thickness of the adhesive agent layer 14 be approximately 10 to
30 micrometers. Further, it is preferred for the adhesive agent to
have a thermosetting property.
[0078] A procedure for fabricating the table 2 of the second
embodiment will hereafter be described briefly.
[0079] First, like the first embodiment, the two bases 11A, 11B,
each of which is formed by a silicon carbide sinter, are formed
through molding and calcinating, using silicon carbide as a
starting material.
[0080] Subsequently, one side of the lower base 11B is ground with
a grinder to form the grooves 13 with a predetermined width and a
predetermined depth in substantially the entire surface. Further,
the adhesive agent is applied on one side of the upper base 11A,
and the pipe 16 is arranged in the grooves 13. The two bases 11A,
11B are then superimposed. In this state, the bases 11A, 11B are
heated to the hardening temperature of the resin, thus joining the
bases 11A, 11B together. Finally, the upper side of the upper base
11 is polished to form the polishing surface 2a and complete the
table 2.
[0081] The following are referential examples of the second
embodiment.
REFERENTIAL EXAMPLE 2-1
[0082] In referential example 2-1, like referential example 1-1,
the bases 11A, 11B, which were formed of sintered silicon carbide
bodies, were molded, using silicon carbide powder that contained
.beta. type crystals as a starting material, and calcinated.
Further, the copper pipe 16, the diameter of which was 6
millimeters, was prepared and bent into a predetermined shape.
[0083] Next, the groove 13, the depth of which was 10 millimeters
and the width of which was 10 millimeters, was ground in the upper
side of the lower base 11B. The curved portion of the copper pipe
16 was then fitted in the groove 13. In this state, the bases 11A,
11B were integrally adhered together with an epoxy resin type
adhesive agent. The thickness of the adhesive agent layer 14 was
approximately 20 micrometers. Further, the upper side of the upper
base 11A was polished to complete the table 2.
[0084] The resulting table 2 of referential example 2-1 was
installed in the aforementioned various types of apparatuses 1. The
semiconductor wafers 5 of different dimensions were then polished
with the apparatuses 1 with the coolant water W constantly
circulating through the copper pipe 16. Thermal deformations were
not found in the table 2. Further, the adhesive agent layer 14 did
not crack, and the joining strength of the joining interface
between the bases 11A, 11B was high. Also, a breakage test was
conducted on the table 2 using a conventional method complying with
JIS R 1624 to measure the flexural strength of the interface. The
value was approximately 4 kgf/mm.sup.2. Further, no leaks of
coolant water W from the joining interface were noted.
[0085] Observation of the semiconductor wafers 5 polished by the
apparatuses 1 indicated that the wafers 5 were not damaged
regardless of the dimensions of the wafers 5. Further, no
significant bending was found in the wafers 5. In other words, it
was apparent that the table 51 of referential example 2-1
manufactured the semiconductor wafers 5 with extremely high
accuracy and extremely high quality.
REFERENTIAL EXAMPLE 2-2
[0086] In referential example 2-2, like referential example 1-2,
the bases 11A, 11B, which were formed of sintered silicon carbide
bodies, were molded, using silicon carbide powder that contained
.alpha. type crystals as a starting material, and calcinated.
Afterwards, the table 2 was completed by the same procedure as that
of referential example 2-1. The table 2 was then installed in the
aforementioned various types of apparatuses 1 to polish the
semiconductor wafers 5 that had different dimensions. Accordingly,
substantially the same superior results as those of referential
example 2-1 were obtained.
[0087] <Conclusion>
[0088] The second embodiment has the following advantages.
[0089] (1) In the table 2 of the second embodiment, the coolant
water W circulates through the copper pipe 16, which is formed from
a material having highly heat conductivity and which is located in
the joining interface between the ceramic bases 11A, 11B. Thus,
when the polishing of semiconductor wafers 5 generates heat, the
heat is released efficiently and directly from the table 2. This
radiates the heat. Accordingly, compared to the prior art in which
the table 2 is mounted on the cooling jacket to indirectly cool the
table 2, the temperature differences in the table 2 is further
decreased. As a result, the apparatus 1 prevents the wafers 5 from
being adversely affected by the heat and enables the diameter of
the wafers 5 to be increased. Further, the wafers can be polished
with high accuracy, thus improving the quality of the wafers 5.
[0090] (2) In the table 2 of the second embodiment, the coolant
water W circulates in the pipe 16. Thus, the table 2 is
advantageous in that the bases 11 are not exposed directly to the
coolant water W. Further, this structure prevents the coolant water
W from leaking from the joining interface.
[0091] (3) The table 2 employs a layered structure that includes
the two bases 11A, 11B. Thus, after forming the grooves 13 in the
upper surface of the lower base 11B and arranging the pipe 16 in
the grooves 13, the bases 11A, 11B are joined together with the
adhesive agent. This makes it relatively easy to form the coolant
water passage 12 in the interface between the bases 11A, 11B. As a
result, the table 51 is advantageous in that the table is easily
fabricated.
[0092] (4) The two bases 11A, 11B of the table 2 are both dense
bodies formed from silicon carbide sinters, the starting materials
of which are silicon carbide powder. The dense bodies are preferred
in that crystal particles are strongly bonded together and the
number of the pores is extremely small. Further, the sintered
silicon carbide body, the starting material of which is silicon
carbide powder, includes superior heat conductivity,
heat-resistant, anti-thermal-shock, and anti-abrasion
characteristics compared to other sintered ceramic bodies. Thus, by
using the table 2 formed by the bases 11A, 11B to perform
polishing, the diameter of each semiconductor wafer 5 may be
increased while improving the quality of the wafer 5.
[0093] (5) In the table 2, the copper pipe 16 is held in the groove
13. Thus, as shown in FIG. 7, the bases 11A, 11B are adhered
together located close to each other. This reduces the thickness of
the adhesive agent layer 14, thus preventing the adhesive agent
layer 14 from cracking. The joining strength of the adhesive agent
layer 14 thus increases. Accordingly, the table 2 is not easily
damaged by heat.
[0094] (6) In the table 2, the grooves 13 have a round
cross-section, and grooves 13 accommodate the pipe 16, the
cross-section of which is round. This reduces the space formed
between the inner wall of the groove 13 and the outer side of the
pipe 16 when the pipe 16 is accommodated in the groove 13. Thus,
the amount of the adhesive agent layer 14 filling the space between
the inner wall of the groove 13 and the outer side of the pipe 16
is small. This reduces heat resistance of the adhesive agent layer
14 accordingly. As a result, the heat releasing effect is improved,
and the temperature differences in the table 2 are further
decreased.
[0095] (7) In the second embodiment, the pipe material is copper,
which is inexpensive and easy to machine. This decreases the cost
of the table 2. Further, copper has high heat conductivity. Thus,
the copper pipe 16 improves the heat radiating effect and
suppresses the temperature differences in the table 2.
[0096] (8) If the table 2 of the second embodiment is installed in
the wafer polishing apparatus 1, the cooling jacket is not
required. This simplifies the apparatus structure as a whole.
[0097] The second embodiment may be modified as follows.
[0098] In a modification of the table 2, as shown in FIG. 8, powder
formed from a substance having a high heat conductivity is mixed in
the adhesive agent layer 14 at least in the space around the pipe
16 as a filler. It is preferred that a copper powder 17 that has an
average particle diameter of approximately 50 to 200 micrometers is
selected as the powder. It is also preferred that the copper powder
17 be concentrated only around the pipe 16 in the adhesive agent
layer 14, or that the amount of the copper powder 17 in the joining
interface between the bases 11A, 11B be minimal. This increase heat
conductivity of the joining interface between the bases 11A, 11B
and increases the joining strength of the interface.
[0099] Other than the copper powder 17, the powder may be at least
one type of metal powder selected from, for example, gold, silver,
and aluminum. Further, the powder may be a ceramic powder such as
alumina, aluminum nitride, and silicon carbide.
[0100] The table 2, modified as described above, is fabricated by a
procedure in which the grooves are first formed in the upper side
of the lower base 11B, the copper powder 17 is then filled in the
groove 13, and, in this state, adhesive agent is applied to join
the base 11A, 11B together.
[0101] Instead of the table 2 that has the double layered
structure, the table 2 may be formed as a triple layered structure,
as shown in a modification of FIG. 9. Further, the table 2 may be a
structure that has four or more layers.
[0102] In a modification of the table 2, as shown in FIG. 10, the
bases 11A, 11B may be joined together with the copper pipe 16
placed along a flat surface, without forming the groove 13 for
receiving the pipe in the upper side of the lower base 11B.
[0103] The material of the pipe 16 is not restricted to copper, as
indicated in the second embodiment. The pipe material may be made
of other metals that have high heat conductivity, for example,
copper alloy or aluminum.
[0104] A silicide ceramic other than silicon carbide such as
silicon nitride (Si.sub.3N.sub.4) or sialon may be selected. In
this case, it is preferred that the selected silicide ceramic be a
dense body having a density of 2.7 g/cm.sup.3 or greater.
[0105] The carbide ceramic may be, for example, boron carbide
(B.sub.4C), other than silicon carbide. In this case, it is
preferred that the selected carbide ceramic is a dense body with a
density of 2.7 g/cm.sup.3 or greater.
[0106] In the table 2 of the second embodiment, liquid other than
water may circulate in the pipe 16. Further, gas may circulate
through the pipe 16.
Third Embodiment
[0107] In a third embodiment, an improvement is made to further
improve heat uniformity in the tables 2 of the first embodiment and
its modifications (for the sake of brevity, these tables 2 are
hereafter referred to as type A table 2). In the type A table 2,
the grooves 13, which form part of the water passage 12, are formed
in the upper side of the lower base 11B. Thus, the lower side of
the upper base 11A (the heat transmitting surface with respect to
the coolant water W that flows in the water passage 12) is
flat.
[0108] In contrast, in the table 2 of the third embodiment, the
groove 13 is formed in the lower side of the upper base 11A, as
shown in FIGS. 11 and 12. The grooves 13 are not formed in the
upper side of the lower base 11B.
[0109] It is preferred that the depth of the groove 13 is 1/3 to
1/2 of the thickness of the upper base 11A (in the third
embodiment, 3 to 20 millimeters).
[0110] When the groove 13 is not deep enough, the recesses formed
in the lower side of the upper base 11A are small and the heat
transmitting area is insufficient. Further, the flow passage
cross-sectional area is insufficient. This restricts the amount of
the water coolant W that flows in the water passage 12.
Accordingly, the heat uniformity of the table 2 is not sufficiently
improved. In contrast, if the grooves 13 are too deep, the upper
base 11A is partially thin. This would decrease the rigidity of the
upper base 11A. Accordingly, if the material of the upper base 11A
is not optimally selected, the pressing force applied by the plate
6 may damage the upper base 11A.
[0111] As schematically shown in FIG. 12, it is preferred that the
grooves 13 have a rectangular cross-section. More specifically, it
is preferred that the cross-section of each corner of the grooves
13 has an R of 0.3 to 5. If the R is less than 0.3, stress
concentration and machining may form cracks and cause the table 2
to easily break. In contrast, if the R is greater than 5, the flow
passage cross-sectional area would be insufficient, and the heat
uniformity of the table 2 would not be improved.
[0112] Further, it is preferred that the groove 13 be a ground
groove or be formed by grinding the lower side of the upper base
11A with a grinder. If the grooves 13 are formed through grinding,
the grooves 13 would have corners having an R that is included in
the optimal range and would have the preferred cross-sectional
form. In addition, grinding easily forms the deep grooves 13 in a
hard ceramic material such as a silicon carbide sinter.
[0113] The following is a referential example of the third
embodiment.
Referential Example 3-1
[0114] In referential example 3-1, like referential example 1-1,
the bases 11A, 11B, which were formed of silicon carbide sinters,
were molded, using silicon carbide powder as starting material, and
calcinated.
[0115] Next, the groove 13 was formed in the lower side of the
upper base 11A with a grinder such that the groove 13 had a depth
of 5 millimeters and a width of 10 millimeters and each corner of
the groove 13 had an R of one millimeter. The depth of the groove
13 was half of the thickness of the upper base 11A. The upper and
lower bases 11A, 11B were then integrally brazed. After the
brazing, the upper side of the upper base 11A was polished to
produce the table 2 having the polishing surface 2a.
[0116] The resulting table 2 of referential example 3-1 was
installed in the aforementioned various types of apparatuses 1. The
semiconductor wafers (silicon wafers) 5 of different dimensions
were then polished with the apparatuses 1 while constantly
circulating the coolant water W. During the polishing, the
temperature was measured at a number of points on the polishing
surface 2a. The measurement indicated that the temperature
differences in the table 2 were extremely small (more specifically,
within .+-.2 degrees Celsius from 40 degrees Celsius). In other
words, the effect of suppressing the heat variation was improved.
Further, the observation of the wafers 5 polished by the
apparatuses 1 indicated that the wafers 5 were preferably formed,
or were not damaged or bent at all, regardless of the dimensions of
the wafers 5. In other words, it was apparent that the
semiconductor wafers 5 had an extremely high accuracy and high
quality when using the table 2 of referential example 3-1.
[0117] <Conclusion>
[0118] Accordingly, the third embodiment has the following
effects.
[0119] (1) The grooves 13, which form part of the water passage 12
in the table 2, is formed in the lower side of the upper base 11A
of the layered ceramic structure. That is, the lower side of the
upper base 11A includes recesses to ensure sufficient heat
transmitting area. Thus, compared to the first embodiment and its
modifications, heat is transmitted to the water W more efficiently.
This improves the heat uniformity of the table 2, thus making it
relatively easy to control the temperature by supplying fluid.
Accordingly, the wafer 5 is machined with high accuracy such that
the diameter of the wafer 5 is increased and the quality of the
wafer 5 is improved.
[0120] (2) In the table 2, the depth of the groove 13 is included
in the aforementioned preferred range. This maintains the strength
of the table 2 and ensures sufficient heat transmitting area and
sufficient flow passage cross-sectional area. Thus, the durability
of the table 2 and the heat uniformity of the table 2 are
improved.
[0121] (3) In the table 2, each corner of the rectangular cross
section of the groove 13 has an R included in the aforementioned
preferred range. Thus, compared to a groove with a round
cross-sectional shape of the same depth as that of the groove 13,
the groove 13 has a relatively large flow passage cross-sectional
area. This further improves the heat uniformity of the table 2.
[0122] The third embodiment may be modified as follows.
[0123] The bases 11A, 11B do not necessarily have to be joined
together by the brazing filler layer 14. For example, a bolt and a
nut that fasten the bases 11A, 11B together, may replace the
brazing filler layer 14. That is, the aforementioned structures of
FIGS. 3 and 4 may be employed.
[0124] The grooves 13 do not necessarily have to be formed through
grinding but may be formed through blasting such as sand blasting.
Further, the cross-section form of the groove 13 does not have to
be generally rectangular or cornered like in the third embodiment
and may be substantially V-shaped or semicircular.
Fourth Embodiment
[0125] The fourth embodiment employs the following structure to
prevent the type A table 2 from being flexed.
[0126] More specifically, the Young's modulus of the two bases 11A,
11B, which are formed of ceramic, is 1.0 kg/cm.sup.2
(.times.10.sup.6) or greater. It is preferred that the Young's
modulus be 1.0-10.0 kg/cm.sup.2(.times.10.sup.6) and is
particularly preferred that the Young's modulus be 1.0-5.0
kg/cm.sup.2 (.times.10.sup.6). This is because when the Young's
modulus is less than 1.0 kg/cm.sup.2(.times.10.sup.6), the rigidity
of the table 2 would be insufficient. Although a higher Young's
modulus is preferred, it would be difficult to procure material
having a Young's modulus that is greater than 10.0
kg/cm.sup.2(.times.10.sup.6) in an inexpensive and stable
manner.
[0127] The following is a referential example of the fourth
embodiment.
REFERENTIAL EXAMPLE 4-1
[0128] In referential example 4-1, like referential example 3-1,
the bases 11A, 11B, which were formed from a silicon carbide
sinter, were molded, using silicon carbide powder as a starting
material, and calcinated. The Young's modulus of each base 11A, 11B
was 3.5 kg/cm.sup.2(.times.10.sup.6- ). The upper base 11A was then
ground with a grinder, and the bases 11A, 11B were brazed to each
other. After the brazing, the upper side of the upper base 11A was
polished to complete the table 2 provided with the polishing
surface 2a.
[0129] The resulting table 2 of referential example 4-1 was
installed in the aforementioned various types of apparatuses 1. The
semiconductor wafers (silicon wafers) 5 of different dimensions
were then polished with the apparatuses 1 while constantly
circulating the coolant water W. As a result, flexing of the table
2 was not found, and the flatness of the polishing surface 2a was
maintained.
[0130] The flatness of each wafer 5 polished by the apparatus 1 was
also measured. The measurement indicated that the flatness of each
wafer 5 was 2 micrometers or less in 600 millimeters .PHI..
Further, the flatness of the table 2 at 40 degrees Celsius was 5
micrometers or less. The wafers 5 were not damaged. In other words,
it was apparent that the semiconductor wafers 5 had an extremely
high accuracy, high quality, and large diameter when using the
table 2 of referential example 4-1.
[0131] <Conclusion>
[0132] In the fourth embodiment, the bases 11A, 11B, or the
components of the table 2, are formed from a dense silicon carbide
sinter that has a high Young's modulus. The table 2 thus has the
preferred rigidity. Thus, during usage, the table 2 is not flexed
or deformed as a whole even if a pressing force is applied to the
polishing surface 2a. This maintains the flatness of the polishing
surface 2a. Thus, the wafers 5 are polished with high accuracy, and
the flatness of the resulting wafers 5 is increased. Accordingly,
the table 2 enables the diameter of each semiconductor wafer 5 to
be increased and improves the quality of the wafer 5.
[0133] The fourth embodiment may be modified as follows.
[0134] In the fourth embodiment, the table 2 has a double layered
structure. However, the table 2 may have a triple layered
structure. Alternatively, the table 2 may be a multiple layered
structure that includes four or more layers. Further, the water
passage 12 may be eliminated such that the table 2 has a single
layered structure (or a non-layered structure).
[0135] In the fourth embodiment, the groove 13 is formed in only
the upper base 11A. Alternatively, the groove 13 may be formed in
only the lower base 11B or both the upper and lower bases 11A,
11B.
[0136] In the fourth embodiment, the upper base 11A is formed of a
dense silicon carbide sinter, and the lower base 11B is formed of a
porous silicon carbide sinter. However, the bases 11A, 11B are not
restricted to this combination. For example, both the upper and
lower bases 11A, 11B may be formed of dense or porous silicon
carbide sinters.
[0137] A silicide ceramic other than silicon carbide, for example,
silicon nitride or sialon may be selected. A carbide ceramic other
than silicon carbide, for example, boron carbide may be selected.
Further, other than these types, oxide ceramic such as alumina or
metal may be used. In either case, it is preferred Young's modulus
be equal to or greater than 1.0 kg/cm.sup.2(.times.10.sup.6).
Fifth Embodiment
[0138] The fifth embodiment includes the following structure to
improve the heat uniformity and breakage strength of the A type
table 2.
[0139] In the fifth embodiment, the brazing filler layer 14
arranged between the bases 11A, 11B is formed by performing brazing
with a brazing filler that contains silver as a main component
(i.e., a brazing filler which largest component is silver). In this
case, in addition to silver, it is preferred that the brazing
filler contain copper as another main component (i.e., silver being
the largest component and copper being the second largest
component). Representative examples of the brazing filler include
silver brazing fillers such as BAg-1, BAg-1a, and BAg-2 (brazing
fillers that contain silver and copper as main components and zinc
and cadmium in small quantities), which are defined by JIS.
Further, the brazing filler may be BAg-3 (a brazing filler that
contains silver and copper as main components and zinc, cadmium,
and nickel in small quantities), BAg-4 (a brazing filler that
contains silver and copper as main components and zinc and nickel
in small quantities), BAg-5 or BAg-6 (a brazing filler that
contains silver and copper as main components and zinc in a small
quantity), or BAg-7 (a brazing filler that contains silver and
copper as main components and zinc and tin in small quantities).
Further, it is preferred that a brazing filler with a relatively
high melting temperature (for example, BAg-2, BAg-3, BAg-4, BAg-5,
or BAg-6) be selected to enhance the heat resistance of the brazing
portion. In addition, a brazing filler that contains silver and
copper as main components but does not contain zinc or nickel or
tin or cadmium, which are small quantity components in the
aforementioned brazing fillers, may be selected.
[0140] It is further preferred that each of the aforementioned
brazing fillers contains a small quantity of titanium (Ti) in
addition to silver (Ag) and copper (Cu), which are the main
components. Titanium has a large diffusion coefficient with respect
to a sintered silicon carbide body and easily diffuses in the pores
of the sintered body during the brazing. The content of titanium in
the brazing filler is preferably 0.1-10 weight percent, and, more
preferably, 1-5 weight percent.
[0141] It is preferred that the thickness of the brazing filler
layer 14 formed from the aforementioned brazing fillers be
approximately 10-50 micrometers, and, more preferably, 20-40
micrometers, from the viewpoint of joining strength and cost.
[0142] The fifth embodiment also has the following improvement to
prevent the table 2 from being flexed by thermal stress and to
improve the flatness of the wafers 5.
[0143] More specifically, the bases 11A, 11B of the fifth
embodiment have substantially equal thermal expansion coefficients.
That is, the difference of the thermal expansion coefficient
between the bases 11A, 11B is preferably 1.0.times.10.sup.-6/degree
Celsius or smaller, more preferably 0.5.times.10.sup.-6/degree
Celsius or smaller, and, further preferably,
0.2.times.10.sup.-6/degree Celsius or smaller. As the difference
becomes smaller, the thermal stress that would otherwise cause
flexing or cracking is further prevented from being generated.
[0144] The thermal expansion coefficient of each base 11A, 11B at
0-400 degrees Celsius is preferably 8.0.times.10 .sup.-6/degree
Celsius or smaller, more preferably 6.5.times.10.sup.-6/degree
Celsius or smaller, and, most preferably,
5.0.times.10.sup.-6/degree Celsius or smaller. This maximally
suppresses the difference between the thermal expansion coefficient
of silicon, or 3.5.times.10.sup.-6/degree Celsius, and the thermal
expansion coefficient of the table 2. Further, it is preferred that
the thermal expansion coefficient of each base 11A, 11B at 0-400
degrees Celsius be equal to or larger than
2.0.times.10.sup.-6/degree Celsius.
[0145] The fifth embodiment further has the following improvement
to improve the heat uniformity of the table 2.
[0146] More specifically, it is preferred that the heat
conductivity TC1 of the upper base 11A, which is formed from
ceramic, be equal to or larger than the heat conductivity TC2 of
the lower base 11B, which is also formed from ceramic, thus
satisfying the following condition of TC1.gtoreq.TC2. In the fifth
embodiment, a dense body with strongly bonded crystal particles and
an extremely small number of pores is selected as the material of
the upper base 11A. In contrast, a porous body with a large number
of pores is selected as the material of the lower base 11B.
Further, the upper base 11A is thinner than the lower base 11B. The
anti-heat resistance of the upper base 11A is thus lower than that
of the lower base 11B. More specifically, it is preferred that the
thickness of the upper base 11A be 3-20 millimeters and the
thickness of the lower base 11B be 10-50 millimeters.
[0147] If the upper base 11A is formed from a silicon carbide
sinter, it is preferred that the heat conductivity of the upper
base 11A be 40 W/m.multidot.K or higher, and, more preferred that
the heat conductivity be 80-200 W/m.multidot.K. If the heat
conductivity is too low, temperature differences tend to be
produced. This interferes with increasing the diameter and
improving the quality of the semiconductor wafer 5. In contrast,
although it is preferred that the heat conductivity be greater,
material having heat conductivity that is greater than 200
W/m.multidot.K is difficult to procure inexpensively and stably. If
the lower base 11B is formed from a sintered silicon carbide body,
the heat conductivity of the sintered body is preferably 5
W/m.multidot.K or higher, and, more preferably, 10-40
W/m.multidot.K. This prevents heat from being released from an area
lower than the water passage 12, or a cooling portion, thus making
it easy to control the temperature of the polishing surface 2a.
[0148] The following are referential examples of the fifth
embodiment.
REFERENTIAL EXAMPLE 5-1
[0149] To form the upper base 11A, "beta random (trade name)",
product of IBIDEN KABUSHIKI KAISHA, was used as silicon carbide
powder that contained 94.6 weight percent of .beta. type crystals.
The average crystal particle diameter of the powder was 1.3
micrometers. The powder contained 1.5 weight percent of boron and
3.6 weight percent of free carbon.
[0150] First, 5 weight parts of polyvinyl alcohol and 300 weight
parts of water were added to 100 weight parts of the silicon
carbide powder. The mixture was then stirred in a ball mill for
five hours to obtain a uniform mixture. The mixture was dried for a
predetermined time to remove a certain amount of moisture from the
mixture. The dry mixture was then sampled in an appropriate amount.
The sample was granulated. Next, the granules of the dry mixture
were molding with metal press dies at a pressure of 50 kg/cm.sup.2.
The density of the resulting molded body was 1.2 g/cm.sup.3.
[0151] Subsequently, the lower side of the body that forms the
upper base 11A was ground to form the groove 13 having a depth of 5
millimeters and a width of 10 millimeters.
[0152] Next, the molded product was placed in a graphite crucible
sealed from ambient air. The body was then calcinated using a
Tammann type calcinating furnace. The calcination was performed in
an argon gas atmosphere of one atmospheric pressure. During the
calcination, the temperature was increased at a rate of 10 degrees
Celsius per minute to a maximum temperature of 2300 degrees
Celsius. The maximum temperature was maintained for two hours. The
observation of the resulting upper base 11A revealed an extremely
dense, three-dimensional network structure in which plate crystals
were entangled in multiple directions. Further, the density of the
upper base 11A was 3.1 g/cm.sup.3. The heat conductivity (TC1) of
the upper base 11A was 150 W/m.multidot.K. The upper base 11A
contained 0.4 weight percent of boron and 1.8 weight percent of
free carbon. The diameter of the upper base 11A was 600
millimeters, and the thickness of the upper base 11A was 5
millimeters.
[0153] As for the lower base 11B, a commercially available porous
silicon carbide sinter (more specifically, "SCP-5 (trade name)",
product of IBIDEN KABUSHIKI KAISHA) was used. The density of the
sintered body was approximately 1.9 g/cm.sup.3, and the heat
conductivity (TC2) of the sintered body was 30 W/m.multidot.K.
Further, the porosity of the sintered body was 40-45%. The diameter
of the resulting lower base 11B was 600 millimeters, and the
thickness of the base 11B was 25 millimeters. The thermal expansion
coefficient of the upper base 11A at 0-400 degrees Celsius was
4.5.times.10.sup.-6/degrees Celsius, and the thermal expansion
coefficient of the lower base 11B at 0-400 degrees Celsius was
4.4.times.10.sup.-6/degrees Celsius. The difference of the thermal
coefficient between the upper and lower bases 11A, 11B was
0.1.times.10.sup.-6/degrees Celsius.
[0154] The two bases 11A, 11B were then integrally brazed to each
other. A foil-like brazing filler having a thickness of 50
micrometers was used. The brazing filler contained 63 weight
percent of silver, 35 weight percent of copper, and 2 weight
percent of titanium. In other words, the brazing filler contained
silver and copper as main components and titanium in a small
quantity. The heating temperature for brazing was 850 degrees
Celsius, which was the melting temperature of the brazing filler.
The thickness of the brazing filler layer was 20 micrometers.
[0155] After the brazing, the upper side of the upper base 11A was
polished to form the table 2 provided with the polishing surface
2a.
[0156] The resulting table 2 of referential example 5-1 was
installed in the aforementioned various types of apparatuses 1. The
semiconductor wafers (silicon wafers) 5 having different dimensions
were then polished by the apparatuses 1 at a high temperature of
several hundreds of degrees Celsius, while constantly circulating
the coolant water W. As a result, no flexing of the table 2 was
found. Further, no cracks were found in the brazing filler layer
14, and the bonding strength was maintained in the joining
interface between the bases 11A, 11B. Also, a breakage test was
conducted on the table 2 using a conventional method complying with
JIS R 1624 to measure the flexural strength of the interface. The
value was approximately 30 kgf/mm.sup.2. Further, no leaks of
coolant water W from the joining interface were noted.
[0157] The observation of the wafers 5 polished by the apparatuses
1 indicated that the wafers 5 were not damaged, regardless of the
dimensions of the wafers 5. Further, no significant bending was
noted in the wafers 5. More specifically, the flatness of each
wafer 5 was 2 micrometers or less in 600 millimeters .PHI..
Further, the flatness of the table 2 at 40 degrees Celsius was 5
micrometers or less.
[0158] In other words, it was apparent that the semiconductor
wafers 5 produced using the table 2 of referential example 5-1 had
an extremely high accuracy and high quality.
REFERENTIAL EXAMPLE 5-2
[0159] Subsequently, the table 2 like that of referential example
5-1 was fabricated using a general silver brazing filler that
contained no titanium (BAg-6; containing 50 weight percent of
silver, 34 weight percent of copper, and 16 weight percent of
zinc). A breakage test was conducted with the resulting table 2 of
referential example 5-2, and the bending strength of the joining
interface was measured through the method complying with JIS R
1624. The measured value was 10 kgf/mm.sup.2, which is lower that
that of referential example 4-1. In other words, compared to
referential example 5-1, the bonding strength of the joining
interface of the table 2 of referential example 5-2 was lower.
Further, although no cracks were currently found, it was assumed
that the table 2 would be damaged due to cracking if the table 2
was continuously used for a long time.
[0160] <Conclusion>
[0161] Accordingly, the fifth embodiment has the following
effects.
[0162] (1) The brazing filler layer 14 arranged between the bases
11A, 11B contains a predetermined amount of titanium that has an
increased diffusion coefficient with respect to the sintered
silicon carbide body. Thus, during the brazing, titanium diffuses
in the pores of the sintered body, thus ensuring a sufficient
bonding strength in the joining interface between the bases 11A,
11B. Accordingly, regardless of long-term use, damages of the
joining interface caused by cracking are prevented. The strength of
the table 2 is thus improved.
[0163] Further, the brazing filler is a non-organic joining
material. The brazing filler does not deteriorate or change quality
even when exposed to a high temperature of several hundreds of
degrees Celsius. This maintains the bonding strength of the joining
interface. Accordingly, the table 2, formed by such brazing filler,
has improved anti-heat resistance compared to when using an organic
joining material.
[0164] (2) The brazing filler of the table 2 of the fifth
embodiment has a high heat conductivity compared to an organic
joining material such as an adhesive agent. This reduces the
anti-heat resistance in the joining surface. The temperature
differences in the table 2 are thus decreased. Accordingly,
compared to when the table 2 is mounted on a cooling jacket to
indirectly cool the table 2, heat is efficiently released from the
table 2. This further decreases the temperature differences in the
table 2. As a result, the heat uniformity of the table 2 is
improved. Further, this enables the diameter of each semiconductor
wafer 5 to be increased and improves the quality of the wafer
5.
[0165] (3) In the table 2 of the fifth embodiment, the bases 11A,
11B are brazed together by the brazing filler layer 14 that
contains silver and copper as main components. The brazing filler
layer 14 is formed with a relatively inexpensive brazing filler.
This reduces the cost of the table 2. Further, the titanium content
of the brazing filler layer 14 is selected to be in a preferred
range of 0.1-10 weight percent. This further improves the bonding
strength between the bases 11A, 11B.
[0166] (4) The foil-like brazing filler used in the table 2 of the
fifth embodiment is easily handled. This facilitates the brazing,
thus making it easy to fabricate the table 2. Further, the
foil-like brazing filler is arranged in the joining-interface so
that it has a uniform thickness. This increases the joining
strength of the joining interface and seals the joining interface.
Accordingly, when the coolant water W flows in the water passage
12, the water W does not leak from the water passage 12. This
maintains the cooling capability.
[0167] (5) The table 2 is formed by the silicon carbide bases 11A,
11B that have substantially equal thermal expansion coefficients.
Thus, even if the table 2 is exposed to a high temperature,
generation of thermal stress, which otherwise bends the table 2 as
a whole, is suppressed. This prevents the table 2 from being flexed
and increases the flatness of each wafer 5. As a result, the table
2 enables the diameter of each wafer 5 to be increased and improves
the quality of the wafer 5.
[0168] (6) The heat conductivity TC1 of the upper base 11A is
higher than the heat conductivity TC2 of the lower base 11B. Thus,
heat is rapidly transmitted from the polishing surface 2a to the
interior of the table 2 through the upper base 11A, which has the
relatively high heat conductivity. The heat is thus transmitted to
the coolant water W in the water passage 12. Accordingly, compared
to the prior art in which the table 2 is mounted on the cooling
jacket to indirectly cool the table 2, heat is efficiently released
from the table 2. This reduces the temperature differences in the
table 2. As described above, the heat uniformity of the table 2 is
improved. The temperature of the table 2 is controlled relatively
easily and accurately through the fluid supply. This contributes to
increasing the diameter of each wafer 5 and improving the quality
of the wafer 5.
[0169] The fifth embodiment may be modified as follows.
[0170] The brazing filler that joins the bases 11A, 11B together is
not restricted to the brazing fillers containing silver as a main
component like in the fifth embodiment. Other hard brazing fillers,
such as gold brazing fillers, may be used as the brazing filler.
However, in terms of cost, it is preferable to select a brazing
filler that contains silver as a main component.
[0171] In the fifth embodiment, the upper base 11A is formed of a
dense silicon carbide sinter, and the lower base 11B is formed of a
porous silicon carbide sinter. However, the materials of the bases
11A, 11B are not restricted to this combination. Instead, for
example, both the bases 11A, 11B may be formed of dense or porous
silicon carbide sinters.
[0172] As shown in FIG. 5, the table 2 may have a triple layered
structure that includes the bases 11A, 11B, and 11C. In this case,
the heat conductivity TC1 of the base 11A is equal to or greater
than the heat conductivity TC2 of the base 11B. Further, the heat
conductivity TC2 of the base 11B is equal to or greater than the
heat conductivity TC3 of the base 11C. That is, it is preferred
that the following condition be satisfied:
TC1.gtoreq.TC2.gtoreq.TC3. In addition, if the table 2 has four or
more layers, a similar condition must be met.
[0173] Organic joining materials, such as epoxy resin adhesive
agents, may replace the non-organic joining materials, such as the
brazing fillers.
Sixth Embodiment
[0174] A sixth embodiment has the following improvement for further
increasing the joining interface strength of the A type table 2 and
the tables 2 of the second embodiment and its modifications (for
the sake of brevity, these tables 2 are hereafter referred to as a
B type table 2) when an organic joining material is employed.
[0175] As shown in FIG. 13, in the sixth embodiment, the bases 11A,
11B are joined together by the organic adhesive agent layer 14.
Particularly, in this embodiment, the organic adhesive agent layer
14 is formed from an epoxy resin type adhesive agent. More
specifically, the adhesive agent of the adhesive agent layer 14 is
formed from epoxy resin, transformed polyamine, and silicon oxide
(SiO.sub.2) that are mixed in accordance with a predetermined
ratio. This adhesive agent has a preferable property in that it
resists expansion when exposed to water. It is preferred that the
adhesive agent has a thermosetting property. Also, the thickness of
the adhesive agent layer 14 is preferred to be approximately 10-50
micrometers, and, is more preferred to be approximately 20-40
micrometers.
[0176] If the adhesive agent layer 14 is too thin, a sufficient
adhesion strength cannot be obtained and the bases 11A, 11B easily
separate from each other. Further, the modulus of elasticity of the
organic adhesive agent is smaller than that of ceramic.
Accordingly, if the thickness of the adhesive agent layer 14 is
excessively large, cracking easily occurs in the adhesive agent
layer 14 when stress is applied. In addition, the heat conductivity
of the organic adhesive agent is smaller than that of ceramic.
Thus, if the adhesive agent layer 14 is too thick, the heat
resistance of the adhesive agent layer 14 increases and hinders the
improvement of the heat uniformity of the table 2.
[0177] It is preferred that a processed modified layer L1 defined
in a surface layer of the lower surface of the upper base 11A or
the upper surface of the lower base 11B, which function as adhered
surfaces, have a thickness of 30 micrometers or less. It is further
preferred that the thickness be 10 micrometers or less, and
particularly preferred that the thickness be one micrometer or less
(see FIG. 13B). A surface exposing process performed after the
calcinating step produces the processed modified layer L1, which
has a thickness of approximately several tens of micrometers, in
the surface layer of the bases 11A, 11B.
[0178] If the organic adhesive agent is used and the thickness t1
of each zone L1 is greater than 30 micrometers, the processed
modified layers L1 are likely to fall off and the adhering strength
becomes insufficient. If possible, as shown in FIG. 13C, it is
desirable that the processed modified layers L1 be completely
removed. In this case, a grain boundary of crystal particles G1 is
exposed from the surface layer of each base such that the adhesive
agent layer 14 is embedded in the grain boundary, thus presumably
ensuring an extremely high anchoring effect (see FIG. 14).
[0179] It is preferred that the surface roughness Ra of the lower
side of the upper base 11A and the surface roughness Ra of the
upper side of the lower base 11B be 0.01-2 micrometers, and is
particularly preferred to be 0.1-1.0 micrometers. If the organic
adhesive agent is used and Ra is included in the aforementioned
ranges, a preferable anchoring effect is obtained in the surfaces
of ceramic.
[0180] When Ra is less than 0.01 micrometers, the adhered surfaces
of the bases 11A, 11B are smoothened such that there are no pits
and lands. The organic adhesive agent thus cannot be embedded in
the sintered ceramic bodies. In this case, the preferable anchoring
effect cannot be obtained. Further, to make Ra less than 0.01
micrometers, a special process must be performed. This increases
costs and lowers productivity. In addition, if Ra is greater than 2
micrometers, the preferable anchoring effect cannot be
obtained.
[0181] A procedure for fabricating the table 2 will hereafter be
described briefly.
[0182] First, like the first embodiment, disk-like molded products
are molded with metal molds using silicon carbide powder as a
starting material. The grooves 13 are ground in the lower side of a
molded body that forms the upper base 11A. The body is then
calcinated at 1800-2400 degrees Celsius. The bases 11A, 11B formed
of sintered silicon carbide bodies are thus obtained.
[0183] After the calcination, a surface exposing process is
performed to reduce (or completely remove) the processed modified
layers L1 in the lower side of the upper base 11A and the upper
side of the lower base 11B. Examples of a layer thinning process or
a removal processes include a mechanical process such as a surface
grinding using a grinder. A chemical process may be performed
instead of the mechanical process. In the sixth embodiment, the
chemical process is performed by etching with an acid etchant that
melts silicon carbide. More specifically, the etching uses an
etchant formed by adding a predetermined amount of weak acid to
hydrofluoric-nitric acid. The weak acid includes organic acid such
as acetic acid. The weight ratio of the component of
hydrofluoric-nitric-acetic acid, or hydrofluoric acid:nitric
acid:acetic acid, is preferably 1:2:1. As a result of the
processing, the surface roughness Ra of the lower side of the upper
base 11A and the upper side of the lower base 11B is adjusted and
included in a range of 0.01-2 micrometers.
[0184] Subsequently, organic adhesive agent is applied to the upper
side of the lower base 11B. The bases 11A, 11B are then
superimposed. In this state, the bases 11A, 11B are heated to the
hardening temperature of resin, thus adhering the bases 11A, 11B
together. Finally, the upper side of the upper base 11A is polished
to complete the table 2.
[0185] The followings are referential examples of the sixth
embodiment.
REFERENTIAL EXAMPLE 6-1
[0186] In referential example 6-1, "beta random (trade name)",
product of IBIDEN KABUSHIKI KAISHA, was used as silicon carbide
powder that contained 94.6 weight percent of p type crystals.
[0187] First, 5 weight parts of polyvinyl alcohol and 300 weight
parts of water were added to 100 weight parts of the silicon
carbide powder. The mixture was then stirred in a ball mill for 5
hours to obtain a uniform mixture. The mixture was dried for a
predetermined time to remove a certain amount of moisture from the
mixture. An appropriate amount of the dry mixture was then sampled
and granulated. Next, the granules of the dry mixture were molded
with metal press dies at a pressure of 50 kg/cm.sup.2.
[0188] The substantially entire lower side of a molded body that
forms the upper base 11A was then ground to form the grooves 13
having a depth of 5 millimeters and a width of 10 millimeters.
[0189] Subsequently, the molded body was placed in a graphite
crucible sealed from ambient air. The body was then calcinated
using a Tammann type calcinating furnace. The calcination was
performed in an argon gas atmosphere of one atmospheric pressure.
During the calcination, the temperature was increased at a rate of
10 degrees Celsius per minute to a maximum temperature of 2300
degrees Celsius. The heat was maintained for two hours. The density
of each resulting base 11A, 11B was 3.1 g/cm.sup.3. The heat
conductivity of each base 11A, 11B was 150 W/m.multidot.K.
[0190] Next, a surface exposing process was performed using a
conventional method. Afterwards, surface grinding was performed as
the layer thinning process. In this manner, the thickness t1 of the
processed modified layer L1 of the lower side of the upper base 11A
and that of the upper side of the lower base 11B were adjusted to
be approximately one micrometer. Ra was included in the range of
0.01-2 micrometers. Subsequently, the bases 11A, 11B were
integrally adhered to each other by an epoxy resin type adhesive
agent ("EP-169", trade name, product of CEMEDINE). The thickness of
the organic adhesive agent layer 14 was approximately 20
micrometers. The hardening temperature was 160 degrees Celsius, the
hardening time was 90 minutes, and the load applied for adhesion
was 10 g/cm.sup.2.
[0191] Further, the upper side of the upper base 11A was polished
to complete the table 2.
[0192] The resulting table 2 of referential example 6-1 was
installed in the aforementioned various types of apparatuses 1. The
semiconductor wafers 5 of different dimensions were then polished
with the apparatuses 1, while constantly circulating the coolant
water W. As a result, there were no thermal deformations in the
table 2. Further, no cracks were found in the organic agent layer
14, and a high strength was maintained in the joining interface
between the bases 11A, 11B. Also, a breakage test was conducted on
the table 2 using a conventional method complying with JIS R 1624
to measure the bending strength of the interface. The result was
approximately 10 kgf/mm.sup.2. Further, there was no leakage of the
coolant water W from the joining interface.
[0193] The observation of the semiconductor wafers 5 polished by
the apparatuses 1 indicated that the wafers 5 were not damaged,
regardless of the dimensions of the wafers 5. Further, no
significant bending was noted in the wafers 5. In other words, it
was apparent that the semiconductor wafers 5 produced by the table
2 of referential example 6-1 had an extremely high accuracy and
high quality.
REFERENTIAL EXAMPLE 6-2
[0194] In referential example 6-2, a type silicon carbide powder
(more specifically, "OY15 (trade name)", product of YAKUSHIMA DENKO
KABUSHIKI KAISHA) was employed, instead of the P type. The density
of each resulting base 11A, 11B was 3.1 g/cm.sup.3. The heat
conductivity of each base 11A, 11B was 125 W/m.multidot.K. Each
base 11A, 11B contained 0.4 weight percent of boron and 1.8 weight
percent of free carbon. Further, the surface exposing process and
the surface grinding were performed to adjust the thickness t1 of
the processed modified layer L1 of each adhering surface to
approximately 5 micrometers. Ra was included in the range of 0.01-2
micrometers.
[0195] After producing the table 2 through the same procedure as
referential example 6-1, the table 2 was installed in the various
types of apparatuses 1 to polish the semiconductor wafers 5 of
different dimensions. Accordingly, substantially the same
advantageous results as those of referential example 6-1 were
obtained. Further, no cracks were found in the organic adhesive
agent layer 14, and the strength of the adhering interface between
the bases 11A, 11B was high. The measurement of the bending
strength under JIS R 1624 indicated that the average value of the
bending strength was approximately 8 kgf/mm.sup.2. In other words,
referential example 6-2 with the starting material of a type
silicon carbide powder was slightly improved in the adhering
strength, as compared to referential example 6-1 with the starting
material of .beta. type silicon carbide powder.
REFERENTIAL EXAMPLES 6-3, 6-4, 6-5
[0196] In these referential examples, the table 2 was produced
basically through the same procedure as referential example 6-1.
Further, in referential example 6-3, the thickness t1 of each
machining modified zone L1 after the surface grinding was adjusted
to approximately 10 micrometers. In referential example 6-44, the
thickness t1 was adjusted to approximately 20micrometers. In
referential example 6-5, the thickness t1 was adjusted to be
approximately zero micrometers (the processed modified layer L1 was
completely removed). In both referential examples, Ra was included
in the range of 0.01-2 micrometers.
[0197] The resulting table 2 was installed in the aforementioned
various types of polishing apparatuses 1. The semiconductor wafers
5 of different dimensions were then polished. As a result,
substantially the same advantageous effects as those of referential
example 6-1 were obtained. Further, no cracks were noted in the
organic adhesive agent layer 14, and the strength of the adhering
interface between the bases 11A, 11B was high. The measurement of
the bending strength under JIS R 1624 indicated that the averages
of referential examples 6-3, 6-4, and 6-5 were approximately 7
kgf/mm.sup.2, approximately 6 kgf/mm.sup.2, and approximately 12
kgf/mm.sup.2, respectively.
REFERENTIAL EXAMPLES 6-6, 6-7
[0198] In referential example 6-6, the surface exposing process was
performed after the calcination. However, the surface grinding,
which would otherwise be performed after the surface exposing
process, was not performed. The bases 11A, 11B were adhered
together with the epoxy resin type adhesive agent "EP-160".
[0199] In referential example 6-7, the surface exposing process was
performed after the calcination. However, the surface grinding,
which would otherwise be performed after the surface forming
machining, was not performed. The bases 11A, 11B were adhered
together with an epoxy resin type adhesive agent ("CEMEDINE 100",
trade name), which differs from the type used in the aforementioned
referential examples. The thickness of the processed modified layer
L1 of each adhering surface was approximately 35 micrometers and
was much thicker than those of the aforementioned referential
examples. Further, the value Ra of the adhering surface was 3.0
micrometers.
[0200] The measurement of the bending strength under JIS R 1624 was
performed with the resulting table 2. The result indicated that the
average values of referential examples 6-6 and 6-7 were
approximately 4 kgf/mm.sup.2 and approximately 1 kgf/mm.sup.2,
respectively. In other words, the adhering strength was not high
like in referential examples 6-1, 6-2, 6-3, 6-4, and 6-5.
[0201] <Conclusion>
[0202] Accordingly, the sixth embodiment has the following
effects.
[0203] (1) In the bases 11A, 11B of the table 2 of the sixth
embodiment, the thickness t1 of the processed modified layer L1 of
each adhering surface is 30 micrometers or less and Ra of each
adhering surface is included in the range of 0.01 millimeters to 2
micrometers. Accordingly, even though the organic adhesive agent is
used, the organic adhesive agent layer 14 has a sufficient
strength. This suppresses cracking and peeling of the adhering
interface. The table 2 is resists breakage and is practical.
Further, the seal performance of the adhering interface is
maintained to prevent the coolant water W in the water passage 12
from leaking from the adhering interface.
[0204] (2) In the sixth embodiment, the thickness of the organic
adhesive agent layer 14 is selected from a range of 10-50
micrometers. This improves the heat uniformity of the table 2 and
enables the adhering interface to have sufficient strength.
[0205] The sixth embodiment may be modified as follows.
[0206] As shown in FIG. 15, the copper pipe 16 may be located in
the grooves 13. Coolant water may be circulated through the copper
pipe 16.
[0207] As shown in FIG. 16, the powder (for example, the copper
powder) 17, which is formed from a substance having high heat
conductivity, may be mixed as a filler in the organic adhesive
agent 14 at least around the copper pipe 16.
[0208] The present invention is not restricted to the first to
sixth embodiments but may be modified within the scope of the
appended claims.
* * * * *