TECHNICAL FIELD
The present invention relates to a whetstone pellet used
for grinding or polishing glass and metal, a plurality of which is fixed on a pedestal,
a whetstone, and processes for producing them as for example known from document
US-A-6 106 382
.
BACKGROUND ART
The whetstone pellets are fixed on a pedestal with an adhesive
to be used as a whetstone. The whetstone pellet contains abrasive grains bound with
a binder, such as a metallic bond, a resin bond or a vitrified bond.
However, in the conventional technique, for example, even
when it is intended to obtain whetstone pellets having fine abrasive grains mixed
therein for carrying out higher precision processing, the abrasive grains are not
uniformly mixed, and as a result, such a problem arises in that no product available
for practical use can be obtained.
DISCLOSURE OF THE INVENTION
The present invention has been made in view of the conventional
problems, and an object thereof is to provide a whetstone pellet in which distribution
of abrasive grains can be uniformized, a whetstone, processes for producing them,
a process for producing an optical element using the whetstone, and a process for
producing an exposure apparatus.
To this end, the invention provides a process for producing
a whetstone, comprising the features of claim 1. Further, the invention provides
a whetstone pellet, a whetstone, and a process for producing a whetstone pellet,
comprising the features of claims 10, 11, and 12, respectively. Further embodiments
of the invention are described in the dependent claims.
The layer of the plating solution may be either an electrolytic
plated layer or an electroless plated layer. From the view point of production process
and the like, the electroless plated layer is preferred. In the case where the plated
layer is formed by electroless plating, the base body is preferably made of a metal
that functions as a catalyst upon forming the electroless plated layer.
In the case where an electrolytic plating solution is used
as the plating solution in the process for producing a whetstone pellet, it is preferred
that the base body is made of an electroconductive material, the plural base bodies
are electrically connected to each other with an electroconductive material, and
the plural base bodies electrically connected are immersed in an electrolytic plating
solution containing abrasive grains to form the abrasive grain layer on the end
surfaces of the plural base bodies. In the case where the abrasive grain layer is
formed by electrolytic plating in this manner, it is preferred that the abrasive
grain layer is processed to uniformize the thickness of the abrasive grain layer.
In the case where an electroless plating solution is used as the plating solution
in the process for producing a whetstone pellet, it is preferred that the plural
base bodies are fixed on a fixing plate having been prepared, a catalyst layer for
electroless plating is formed on an end surface of the base body opposite to the
end surface to be fixed to the fixing plate before or after fixing the plural base
bodies on the fixing plate, and the plural base bodies fixed on the fixing plate
are immersed in an electroless plating solution to form the abrasive grain layer
on the catalyst layers of the plural base bodies. The abrasive grain layer formed
with an electroless plating solution is almost amorphous.
It is preferred upon fixing the plural base bodies on the
pedestal that an adhesive is applied on the whole surface of the pedestal, and the
plural base bodies are placed on the adhesive to fix the plural base bodies on the
pedestal. In this case, the adhesive also functions as a masking agent against electroless
plating. In the above-described process for producing a whetstone, a plane shape
formed by continuation of the end surfaces of the plural base bodies may be processed
to have an inverse shape of a surface to be processed after fixing the plural base
bodies on the pedestal but before plating the respective end surfaces of the base
bodies.
As described above, according to the whetstone pellet and
the whetstone of the invention, the abrasive grain part is made of the plating layer
containing the abrasive grains formed by mixing the abrasive grains in the plating
solution in a liquid form, whereby the abrasive grains can be uniformly dispersed.
Therefore, the whetstone of the invention is suitably used for superfine processing
which requires abrasive grains of a small particle diameter. Further, since the
plating layer serves as a binder of the abrasive grains, shape retentiveness of
the abrasive grains increases and the binder itself is hard in nature, and therefore
the whetstone lifetime can be prolonged.
In the case where the abrasive grain part is an amorphous
plated layer formed by using electroless plating solution containing abrasive grains,
the thickness of the abrasive grain part can be uniformized since the thickness
of the plated layer on the outer periphery does not increase as differing in electrolytic
plating.
Furthermore, in the whetstone pellet of the invention,
a whetstone having a large size to a certain degree can be obtained since the abrasive
grain part is formed on the base body, therefore the handling quality upon fixing
the whetstone pellet on the pedestal can be improved. Moreover, in order to obtain
a whetstone pellet having a prescribed height, the plating time can be reduced in
comparison with the case of producing a whetstone pellet of a solid plated layer.
BRIEF DESCRIPTION OF DRAWINGS
- Fig. 1 is a perspective view of a whetstone and a whetstone pellet of one embodiment
of the present invention.
- Fig. 2 is an explanatory view showing production procedures of a whetstone pellet
in Example 1 of the present invention.
- Fig. 3 is an explanatory view showing production procedures of a whetstone in
Example 2 of the present invention.
- Fig. 4 is an explanatory view showing production procedures of a whetstone in
a modified version of Example 2 of the present invention.
- Fig. 5 is an explanatory view showing a process for producing an optical element.
- Fig. 6 is an explanatory view showing surface conditions upon grinding fluorite
with a conventional resin-bonded whetstone.
- Fig. 7 is an explanatory view (part 1) showing production procedures of a whetstone
in Example 3 of the present invention.
- Fig. 8 is an explanatory view (part 2) showing production procedures of a whetstone
in Example 3 of the present invention.
- Fig. 9 is a constitutional view of an exposure apparatus of one embodiment.
BEST MODE FOR CARRYING OUT THE INVENTION
Various kinds of embodiments according to the invention
will be described below with reference to the drawings.
First Embodiment
A whetstone pellet as a first embodiment according to the
invention will be described with reference to Figs. 1 and 2.
As shown in Fig. 1, a plurality of whetstone pellets 1
of this embodiment is fixed on a pedestal 9, which is used as a whetstone 10. The
whetstone 10 has a columnar base body 2 and an abrasive grain part 5 formed on one
end surface 3 of the base body 2. The abrasive grain part 5 is formed as an amorphous
plated layer containing abrasive grains by an electroless plating method.
In order to obtain the whetstone pellet 1, the dimensions
of the base body 2 is firstly determined depending upon the required dimensions,
such as the outer diameter, the height and the like, of the whetstone pellet 1.
The material of the base body 2 is preferably such a material that is not easily
corroded by an electroless plating solution and provides good adhesiveness to the
electroless plating layer formed on the surface of the base body 2. Furthermore,
the material of the base body 2 is preferably one capable of maintaining good adhesiveness
with an adhesive which is used to attach the base body 2 to the pedestal 9 of the
whetstone 1, and is most preferably a metal in order to retain mechanical rigidity.
Among metals, metals are suited which have a catalytic function accelerating plating
reaction or metals capable of easily forming a catalyst on the surface of the base
body 2 before plating. The former includes iron and nickel, and the latter includes
stainless steel, aluminum and brass. In particular, stainless steel and aluminum
are preferred since the remaining abrasive grain part can be easily removed upon
reuse of the base body 2.
Because the plane shape of the base body 2 is strictly
reproduced in electroless plating, it is preferred that the surface of the base
body 2 is smoothly finished in advance. In the practical case where the abrasive
grain part 5 is formed by electroless plating, it is preferred to use a fixing plate
capable of fixing plural base bodies 2, 2, ... for producing plural whetstone pellets
1, 1, ... at the same time. The dimension of the fixing plate is determined depending
upon the number of the whetstone pellets 1 to be produced. Such a material should
be selected as the fixing plate for repeated use that is not easily corroded with
a pre-treating solution of electroless plating and with the electroless plating
solution and is not dissolved with a masking agent described later. In the case
where a masking step described later is simplified, the fixing plate made of a resin
is suited. In the case where a large number of base bodies are fixed on the fixing
plate, the fixing plate has to withstand the weight of the base bodies, and in order
to maintain mechanical rigidity, a metal, particularly stainless steel, is preferred,
and as a resin, PTFE (polytetrafluoroethylene) is also preferred.
The plural base bodies 2, 2, ... are fixed on the fixing
plate with an adhesive, and the region on the surface of the base body where no
plating is applied, i.e., the region
where no abrasive grain part 5 is formed, is masked. Before fixing of the base bodies
2, the fixing plate and the base bodies 2 are degreased with a solvent. As an adhesive
for fixing the base bodies 2 to the fixing plate, such one is preferred that can
retain the base bodies 2 during the steps from the pre-treatment of electroless
plating to the electroless plating and has a masking function, but easily releases
the base bodies 2 from the fixing plate after the electroless plating. In other
words, such an adhesive is used for both purposes of fixation and masking of the
base bodies 2. However, the adhesive used for fixing of the base bodies 2 and the
masking agent used for masking the base bodies 2 are not always the same material,
and they may be different materials. However, it is preferred that they are the
same material from the standpoint of simplification of the process.
In the case where the fixing plate is made of a metal,
the plating is also deposited on the fixing plate itself, and thus, the entire exposed
metallic parts immersed in the plating solution are necessarily masked, but in the
case where the fixing plate is made of a resin, no masking of the fixing plate is
necessary. Even in the case where the thickness of the masking film is nonuniform,
no problem arises since an electroless plated layer deposited on the base body has
a uniform thickness owing to the characteristics thereof.
Aftermasking, a catalyst layer for electroless plating
is formed on a region on the surface of the base bodies 2 where no masking film
is formed. In the case where the base body itself has catalytic nature, prescribed
alkali degreasing and activation treatment are carried out to remove an oxide layer
and the like on the surface of the region on the base body where no masking film
is formed, so as to use the region as the catalyst layer. On the other hand, in
the case where the base body itself has no catalytic nature, prescribed alkali degreasing
and activation treatment are carried out, and then a catalyst layer is formed on
the surface of the base body. The formation of the catalyst layer is carried out,
for example, in such a manner in the case where the material of the base body 2
is brass or stainless steel that the base body 2 is immersed in an aqueous solution
containing palladium chloride as a major component to deposit a layer of palladium
to be a catalyst on the surface of the base body. In the case where the material
of the base body 2 is aluminum, the base body 2 is immersed in a zincate conversion
solution to deposit a layer of zinc to be a catalyst on the surface of the base
body. The catalyst accelerating reaction of electroless plating include from metallic
elements of Group 8, such as iron, ruthenium and the like to metallic elements of
Group 10, such as nickel, palladium and the like. While the catalyst layer is formed
on the base body after fixing the base body on the fixing plate herein, it is possible
that the base body is fixed on the fixing plate, after forming the catalyst layer
on the base body.
The formation of the abrasive grain part 5 is carried out
by using an electroless plating solution having good uniform deposition property
as an advantage. As the electroless plating solution, for example, a nickel-phosphorous
plating solution is used. Abrasive grains are mixed in the electroless plating solution.
Commercially available diamond powder, cubic boron nitride (CBN) and the like may
be used as the abrasive grains without limitation in particle diameter, and those
of from approximately 0.1 to 200 µm serve wide ranges of purposes. After putting
the abrasive grains in the plating solution, the base body 2 having the catalyst
layer formed thereon is put in the electroless plating solution under such conditions
that the plating solution is stirred with a stirrer or the like to effect uniform
dispersion of the abrasive grains, whereby a plated layer containing abrasive grains,
having a uniform thickness is formed on the region having the catalyst layer to
constitute an electroless plated layer, i.e., the abrasive grain part 5 using an
amorphous plated layer as a binder. The thickness of the abrasive grain part 5 may
be controlled mainly by the temperature of the plating solution and the plating
time.
After completion of the electroless plating treatment,
the base bodies are detached from the fixing plate, and the masking film is removed
to obtain the whetstone pellets 1.
In the case where an electrolytic plating method is used
instead of the electroless plating method as described above, an electrolytic plated
layer is deposited as concentrated to convex parts, so as to fail to allow the layer
to have a uniform thickness. In the electroless plating method in this embodiment,
on the other hand, it is possible to allow the layer thickness to be uniform without
concentrated deposition of the plated layer on convex parts and peripheral parts
owing to the nature of electroless plating.
In this embodiment, the abrasive grains are uniformly dispersed
in the plated layer thus deposited to be the abrasive grain part 5 because the abrasive
grains are mixed in the plating solution which is a liquid form, and the plating
solution containing the abrasive grains mixed therein is stirred during the deposition
of the plated layer. Accordingly, for example, in the case where a whetstone containing
abrasive grains having a extremely small particle diameter is required to finish
machining, it is significantly effective since the distribution of the abrasive
grains is uniformized even though the diameter of the abrasive grains is small.
Furthermore, the amorphous plated layer formed by the electroless
plating method functions as material for binding the abrasive grains, and thus high
retentivity of the abrasive grains can be obtained to prolong the service life of
the whetstone. Since the amorphous plated layer as a binder material is basically
hard, it suffers less surface denaturation of the abrasive grain layer upon grinding
and polishing, and thus the frequency of repairing the grinding surface or the polishing
surface can be reduced.
In this embodiment, since the abrasive grain part 5 is
formed on the base body 2, such a whetstone pellet 1 can be obtained that has a
certain height without a prolonged period of time for forming the plated layer.
Therefore, the whetstone pellet 1 has a size of good handling to improve the handling
property upon fixing the whetstone pellet 1 on the pedestal 9.
In order to produce a whetstone 10 by using the whetstone
pellets 1 as described above, a pedestal 9 having an inverse shape of a surface
to be processed is prepared, on which the plural whetstone pellets 1 are fixed by
using an adhesive or the like. Thereafter, the plane shape formed by continuation
of the end surfaces of the plural whetstone pellets is finished to become an inverse
shape of a goods' surface to be processed by grinding with a lapping disk or the
like or by subjecting to machining.
Example 1
A specific production process of the whetstone pellet 1
shown in Fig. 1 will be described with reference to Fig. 2.
A base body 2 is made of a stainless steel (SUS 304) material
and formed into a columnar shape having a diameter of 14.4 mm and a height of 3
mm. Among two end surfaces of the base body 2, an end surface 3, on which an abrasive
grain layer 5 is to be formed, is smoothed to Ra of 0.2 by machining.
After degreasing the base body 2 and a fixing plate 11
with a solvent, a masking agent is coated on the fixing plate 11, and the end surface
3 of the base body 2 is placed thereon, so as to apply a masking film 12 to region
on the surface of the base body 2 where no plating is to be applied, as shown in
Fig. 2(a). At this time, the arrangement of the base bodies is arbitrary provided
that attention is paid to prevent the base bodies 2 and 2 from contacting to each
other. As the masking agent, a commercially available plating masking agent, Turco
5980-1A (a trade name, produced by Atofina Chemicals, Inc., U.S.), is used to function
as both the adhesive used for fixing of the base bodies 2 and the masking agent
used for masking the base bodies 2. The fixing plate 11 along with the plural base
bodies 2, 2, ... placed thereon are put in an oven of a temperature increased to
100°C, followed by baking for 1 hour, to cure the masking film 12.
After curing the masking film 12, the base bodies 2, 2,
... placed on the fixing plate 11 are sequentially subjected to alkali degreasing
and activation with an acid and then immersed in an aqueous solution containing
hydrochloric acid and palladium chloride as major components for 60 seconds, so
as to form a palladium layer on the surface of the base body 2 where no masking
film 12 is applied, as shown in Fig. 2 (b) . The palladium layer thus formed becomes
a catalyst layer 4 accelerating electroless plating. In the case where a metal capable
of being a catalyst layer 4, such as iron, is used as material of the base body,
there is no necessity of separate formation of a catalyst layer, but the surface,
on which the catalyst layer is to be formed, is subjected to activation with an
acid to make the surface as the catalyst layer.
After forming the catalyst layer 4, the base bodies 2 placed
on the fixing plate 11 are washed with water, and then they are put in an electroless
nickel-phosphorous plating solution 16 containing abrasive grains 15, as shown in
Fig. 2(c). The electroless nickel-phosphorous plating solution 16 which is containing
0.2 weight percents of the diamond powder having a particle diameter of from 2 to
4 µm, is stirred with a stirrer 17. The content of the abrasive grains 15 in
the plated layer can be adjusted by changing the put amount of the diamond powder
and the stirring conditions, such as the rotation rate of the stirrer 17. The temperature
of the plating solution 16 is 90°C, in which the base bodies 2 are put for
16 hours to deposit an electroless plated layer having a thickness of 0.3 mm. The
electroless plated layer becomes an abrasive grain part 5 formed with an amorphous
plated layer.
Upon depositing the electroless plated layer to a prescribed
thickness, the fixing plate 11 is taken out from the plating bath, and the fixing
plate 11 and the base bodies 2 are washed with water, followed by drying. The base
bodies 2 are detached from the fixing plate 11, and the masking film 12 is removed,
as shown in Fig. 2 (d), whereby whetstone pellets 1 having a diameter of the abrasive
grain part 5 of 15 mm and a total height of 3.3 mm are completed. Upon detaching
the whetstone pellets 1 from the fixing plate 11, the base bodies 2 and the fixing
plate 11 after plating are immersed in a diluent solvent for the masking film 12
as they are, whereby the masking film 12 is dissolved, and the whetstone pellets
1 can easily be detached from the fixing plate 11.
Second Embodiment
A second embodiment according to the invention will be
described.
The outline constitution of a whetstone of this embodiment
is the same as the whetstone 10 described with reference to Fig. 1. That is, plural
base bodies 2 are fixed on a pedestal 9, and an abrasive grain part 5 is formed
on one end surface 3 of the base body 2. However, although the whetstone pellets
1 having been completed are fixed on the pedestal 9 to produce the whetstone 10
in the first embodiment, a whetstone 10 is to be produced through no process step
of completing the whetstone pellets 1 in this embodiment.
Upon producing the whetstone 10, a pedestal 9 having an
inverse shape of an objective surface to be processed is firstly produced. The material
of the pedestal 9 is most suitably a metal since good adhesion adhesiveness to an
adhesive described later is obtained, and a mechanical rigidity can be maintained.
Suitable examples of the metal include aluminum, which can be easily worked by a
casting method or cutting and is lightweight, and iron, which can be worked by a
casting method.
Among the surface of the pedestal 9, the surface on which
the abrasive grain parts are to be formed, maybe roughly finished to improve adhesiveness
to the adhesive, and may be subjected to a roughening treatment, such as a blasting
treatment, depending on necessity. The surface of the pedestal 9, on which the abrasive
grain parts are to be formed, may not be subjected to smooth finish as just described,
and therefore, the processing cost of the pedestal 9 can be suppressed.
The material for making the base body 2 is the same as
in the first embodiment, and the description thereof is omitted herein.
The shape of the base body 2 may be various shapes, such
as a prismatic columnar shape, and a round columnar shape, and it may be formed
into any shape depending on necessity. In the case where a round columnar product
is to be obtained as similar to a resin-bonded pellet or a metal-bonded pellet,
they can be easily obtained with suppressed processing cost by cutting a round bar
at a constant interval. The end surface, which is to be fixed to the pedestal 9,
of the both end surfaces of the base body 2 may be roughly finished to improve adhesiveness
to the adhesive as similar to the pedestal 9, and another end surface, on which
the abrasive grain part 5 is to be formed, may also be roughly finished since it
is separately finished in the later process step. The end surface, which is to be
fixed to the pedestal 9, may be subjected to a roughening treatment, such as a blasting
treatment, as similar to the pedestal 9.
The pedestal 9 and the plural base bodies 2 are thus obtained.
After degreasing them, an adhesive is coated over the entire surface, on which abrasive
grain parts are to be formed, of the pedestal 9, and a necessary number of the base
bodies 2 are placed thereon. Because the surface of the pedestal 9 is a curved surface
but is not a flat surface, the adhesive used herein is preferably one capable of
preventing the base bodies 2 from moving along the curved surface by gravitation,
and an epoxy adhesive having high viscosity is preferred.
It is possible upon fixing the base bodies 2 on the pedestal
9 that a protrusion or a depression is formed on the end surface of the base body
2, and a depression or a protrusion is formed on the pedestal at a position where
the base body 2 is to be fixed, followed by engaging the protrusion or the depression
of the base body 2 with the depression or the protrusion of the pedestal 9. In this
case, an adhesive having low viscosity may be used since the base bodies 2 are not
misaligned with respect to the pedestal 9.
After placing the base bodies 2 on the pedestal 9, a weight
or the like is placed on the base bodies 2 for preventing the base bodies 2 from
lifting from the pedestal 9 by the adhesive. Specifically, in the case where the
surface of the pedestal 9 is a flat surface, it is preferred that the plural base
bodies 2 are placed on a machine platen having a flat surface, and the pedestal
9 having an adhesive coated is placed thereon, so that the pedestal 9 itself is
used as the weight. In the case where the pedestal 9 has a curved surface, it is
preferred that the plural base bodies 2 are placed on the pedestal 9 having an adhesive
applied, and then a lapping disk described later is placed thereon as the weight.
After the plural base bodies 2 are placed on the pedestal
9 having an adhesive applied, and the weight is placed thereon, the assembly is
allowed to stand until the adhesive cures. In the case where the adhesive is of
a thermosetting type, it is preferred that the assembly is placed in an oven or
the like to reduce the curing time.
After curing the adhesive, the end surfaces of the base
bodies 2 are subjected to a grinding process or a cutting process, whereby a plane
shape formed by continuation of the end surfaces of the plural base bodies 2 has
an inverse shape of an objective surface to be processed. A lapping disk having
the same surface shape as the finished surface shape of the material to be processed
is preferably used in the grinding process.
The pedestal 9 having the base bodies attached is then
masked against electroless plating. To the surface of the pedestal 9, on which the
abrasive grain parts are to be formed, the adhesive is applied, which functions
as a masking agent, and therefore no masking is applied to the surface, but the
back surface thereof is masked.
After drying the masking agent to form a masking film 12,
a catalyst layer 4 for electroless plating is formed on a region on the surface
of the base bodies 2, on which no masking film 12 is formed, as similar to the first
embodiment.
After forming the catalyst layer 4, the pedestal 9 having
the base bodies attached is put in an electroless plating solution containing abrasive
grains mixed therein, so as to form an electroless plated layer containing abrasive
grains, i.e., abrasive grain parts 5, on the catalyst layer of the respective base
bodies 2. The electroless plating is carried out in the same manner as in the first
embodiment.
After the thickness of the abrasive grain parts 5 has reached
the objective thickness, the pedestal 9 having the base bodies attached is taken
out from the electroless plating solution and is washed with water, and then the
masking film 12 on the back surface of the pedestal 9 is removed to complete the
whetstone 10.
In this embodiment as described above, the abrasive grain
part 5, which is an electroless plated layer containing abrasive grains, is formed
on the base body 2, and thus the similar effects as in the whetstone pellet 1 in
the first embodiment can basically be obtained.
In this embodiment, furthermore, because the end surfaces
of the base bodies 2 are finished by machining before forming the abrasive grain
part 5 on the base bodies 2, so as to have the shape formed by continuation of the
end surfaces of all the plural base bodies 2 fixed on the pedestal 9 has an inverse
shape of an objective surface to be processed, the machining can be easily carried
out within a short period of time in comparison to the case of the first embodiment,
in which the completed whetstone pellets 1 are fixed on the pedestal 9, and then
the abrasive grain parts 5 of the whetstone pellets 1 are finished by machining.
This is because the target of the machining is not the considerably hard plated
layer containing abrasive grains as in the first embodiment.
It is possible for forming a whetstone that plural grooves
are formed on a pedestal, and protruded regions are used as parts for base bodies.
In the case where grooves are formed on the pedestal, however, the regions of the
grooves are also subjected to plating, and thus the consumption amounts of the plating
solution, the abrasive grains and the like are considerably increased to push up
the costs of the raw materials. In the case where the grooves are to be subjected
to masking as a countermeasure, it requires a complex masking treatment, in which
the grooves are masked while the surfaces of the protruded regions are prevented
from masking. In this embodiment, on the other hand, the adhesive applied on the
entire surface of the pedestal, on which the abrasive grain parts are to be formed,
functions as a masking agent, whereby the consumption amounts of the plating solution,
the abrasive grains and the like can be suppressed, and there is no necessity of
separately masking on the surface of the pedestal, on which the abrasive grain parts
are to be formed.
Example 2
A specific production process of the whetstone 10 described
in the second embodiment will be described with reference to Fig. 3. The whetstone
10 that is to be finally obtained in Example 2 is a whetstone of a spherical surface
having a curvature radius of 197 mm.
The pedestal 9 is a part of an aluminum cast material,
molded into a disk form having a diameter of 300 mm, and the surface thereof, on
which the abrasive grain parts are to be formed, is formed into a spherical surface
having a curvature radius of 200 mm. The surface is not subjected to any particular
roughening treatment. The base bodies 2 are made of aluminum (A5056) and have a
round columnar shape having a diameter of 10 mm and a height of 3 mm. The surface
of the base body 2 is subjected to a shot treatment with glass beads of a grain
size of #100.
After degreasing the pedestal 9 and the base bodies 2 with
a solvent, an epoxy adhesive 12a is coated on the entire spherical surface of the
pedestal 9, on which the abrasive grain parts are to be formed, as shown in Fig.
3 (a). As the adhesive, SC507A/B (a trade name, produced by Sony Chemicals Corp.)
having relatively high viscosity is suitably used. The coated amount of the adhesive
12a is preferably such a thickness that is about half of the height of the base
bodies 2. Subsequently, after placing the plural base bodies 2 on the adhesive 12a,
a lapping disk 19 described later is placed thereon, and the adhesive 12a is cured.
By placing the lapping disk 19 on the base bodies 2 as a weight in this manner,
the base bodies 2 can be prevented from misalignment during the curing process of
the adhesive 12a.
After curing the adhesive 12a, the end surfaces 3 of the
base bodies 2 are ground by using the lapping disk 19 as shown in Fig. 3(b), whereby
the plane shape formed by continuation of the end surfaces 3 of the base bodies
2 is finished to be an inverse shape of a surface to be processed, i.e., the spherical
surface. The lapping is carried out under supplying a mixture of silicon carbide
grinding sand of a grain size of #600 and water to the lapping surface. The curvature
radius of the spherical surface, which is to be obtained in this stage, is 197.3
mm under consideration of the thickness of the plated layer (0.3 mm).
A masking film 13 is then formed on the surface of the
pedestal 9 other than the spherical surface, i.e., on the back surface of the pedestal
9, by using a masking tape or a coating type masking agent (as shown in Fig. 3(c)).
The pedestal 9 having the base bodies attached is sequentially subjected to alkali
degreasing and activation with an acid, and then immersed in a zincate conversion
solution for 30 seconds to form an zinc layer (not shown in the figure) on the side
peripheral surfaces of the plural base bodies 2 and the end surfaces of the base
bodies 2. The zinc layer functions as a catalyst layer for accelerating reaction
of electroless plating.
After forming the catalyst layer, the pedestal 9 having
the base bodies attached is washed with water and then put in an electroless nickel-phosphorous
plating solution 16 containing abrasive grains 15 as shown in Fig. 3(c), so as to
deposit an electroless plated layer having a thickness of 0.3 mm on the end surfaces
3 of the base bodies 2. This is an amorphous plated layer, which is an abrasive
grain part 5 thus formed. The conditions on the electroless plating process are
the same as in Example 1.
After conducting the electroless plating, the pedestal
9 having the abrasive grain layer 5 formed thereon is taken out from the plating
bath and washed with water, followed by drying, and then the masking film 13 attached
to the back surface of the pedestal 9 is removed, so as to complete a whetstone
10 of a spherical surface having a curvature radius of 197 mm.
While the pedestal 9 having a spherical surface is used
in Example 2 in conformity with the plane shape of the surface to be processed,
the pedestal may not be always conformed to the plane shape of the surface to be
processed, but for example, a pedestal 9a having a flat disk shape as shown in Fig.
4(a) may also be used. A production process of a whetstone by using the pedestal
9a will be briefly described below.
After applying the adhesive 12a on the entire surface of
the pedestal 9a in the same manner as in Example 2, plural base bodies 2 having
the same height are placed on the adhesive 12a, and the adhesive 12a is cured. In
this case, the plural base bodies 2 are placed on a machine platen having a flat
surface, and the pedestal 9a having the adhesive applied may be placed thereon,
so that the pedestal 9a itself is used as the weight.
After curing the adhesive 12a, the end surfaces 3 of the
base bodies 2 are ground by using a lapping disk 19 as shown in Fig. 4(b), whereby
the plane shape formed by continuation of the end surfaces 3 of the plural base
bodies 2 is finished to be an inverse shape of a surface to be processed as shown
in Fig. 4(C). Subsequently, the plating process and the like are carried out in
the similar manner as in Example 2 to complete the whetstone.
While the plural base bodies 2 having the same height are
used above, it is possible that the base bodies, the height of which is to be reduced,
i.e., the base bodies attached to the vicinity of the center of the pedestal 9a
in this example, may be those having a smaller height than the other base bodies,
so as to decrease the ground amount with the lapping disk 19.
Performance Test Example 1
Results of the performance test upon grinding quartz glass
by using the whetstone 10 produced in the manner described in the second embodiment
will be described.
In the performance test, quartz glass of high hardness
is processed by using various kinds of whetstones, and the grinding rate, the grinding
accuracy and the like are obtained in the process. The subjects for the test are
the whetstone 10 of the second embodiment, a conventional metal-bonded whetstone
and a conventional resin-bonded whetstone.
The procedures shown in Fig. 5 are generally carried out
in the case where an optical element is produced from a raw material of an optical
element, which is a material to be processed. Specifically, in order to bring the
shape of the raw material of an optical element 25a proximate to the shape of the
desired optical element 25, the raw material 25a is subjected to shape creation
as shown in Fig. 5(a) and 5(b). As shown in Fig. 5(c), the surface of the raw material
25b having been subjected to shape creation is then roughly ground by using a whetstone
26c for rough grinding. Subsequently, as shown in Fig. 5(d), the roughly ground
surface of the raw material 25c is finely ground by using a whetstone 26d for fine
grinding. Finally, as shown in Fig. 5(e), the surface of the raw material 25d finely
ground is polished to obtain an optical element 25 having a desired plane shape
of the processed surface. In Fig. 5, the surface roughness is drawn with exaggeration
for clarifying the change of the surface roughness of the raw material. Furthermore,
while Fig. 5 is drawn such that only one surface of the raw material 25a is processed,
it is needless to say that the other surface is also subjected to the similar processing
in the case where the optical element is a lens. Moreover, while the optical element
as a final product is obtained through the polishing process herein, the polishing
process is not necessarily carried out after the fine grinding process in the case
where the product falls within its specification even when the surface roughness
is certainly large. Therefore, the product having been subjected to the fine grinding
process is an intermediate product in some cases or a final product in other cases.
The test conditions for the performance test are as follows.
- Whetstone of the second embodiment of the invention
- Diameter of base body:
- 10 mm
- Material of abrasive grains:
- diamond
- Particle diameter of abrasive grains :
- 2 to 4 µm (corresponding to mesh size #3500)
- Thickness of abrasive grain layer:
- 0.3 mm
- Conventional metal-bonded whetstone (for rough grinding)
- Diameter of pellets:
- 10 mm
- Material of abrasive grains:
- diamond
- Particle diameter of abrasive grains:
- mesh size of #1500
- Conventional resin-bonded whetstone (for fine grinding)
- Diameter of pellets:
- 10 mm
- Material of abrasive grains:
- diamond
- Particle diameter of abrasive grains:
- mesh size of #3000
- Raw material of optical element: quartz (SiO2) glass
- Shape of optical element: spherical convex lens having an outer diameter of
238 mm and a curvature radius R of 220 mm
- Grinding machine: elliptic movement type, produced by Tateno Co., Ltd.
- Grinding fluid: water soluble concentrated grinding fluid diluted with water
(concentrated grinding fluid/water = 1/15)
The whetstone of the second embodiment used in the test
is composed of a pedestal having base bodies fixed with an interval of 5 mm. In
the whetstones used herein, the distances of the base bodies are retained to a certain
extent to suppress the area of the total grinding surface to 30% or less of the
area of the surface of the pedestal, on which the abrasive grain parts are formed,
whereby the discharge of the grinding dusts is facilitated.
The average grinding rate, the surface roughness of the
raw material and the time required polishing in the polishing process carried out
after the grinding process upon grinding the raw material of an optical element
with the respective whetstones under the foregoing conditions, and the time required
for figuring the whetstone, were those as shown in Table 1 below.
TABLE 1
Whetstone of embodiment of the invention
Metal-bonded whetstone
Resin-bonded whetstone
Average grinding rate
28 µm/min
28 µm/min
5 µm/min
Surface roughness (Ry)
0.47 µm
2.85 µm
0.48 µm
Time required for polishing
90 min
could not be polished
90 min
Time required for figuring whetstone figuring
35 min (10 min + 25 min)
120 min
120 min
It is understood from Table 1 that the average grinding
rate of the whetstone of the second embodiment is 28 µm/min, which is equivalent
to the metal-bonded whetstone as a conventional whetstone for rough grinding and
is considerably superior to the resin-bonded whetstone as a conventional whetstone
for fine grinding. As described herein, the whetstone of the second embodiment contains
abrasive grains having a particle diameter that is far smaller than the conventional
whetstone for rough grinding, but exhibits an average grinding rate equivalent to
the conventional whetstone for rough grinding. It is considered that this is because
of the high retentivity of abrasive grains owing to the use of the plated layer
as a binder material for the abrasive grain layer. The surface roughness after grinding
is 0.47 µm for the whetstone of the second embodiment, which is equivalent
to the resin-bonded whetstone as a conventional whetstone for fine grinding, and
thus, it is far superior to the metal-bonded whetstone as a conventional whetstone
for rough grinding. As described herein, because the surface roughness after grinding
of the whetstone of the second embodiment is equivalent to that of the resin-bonded
whetstone as a conventional whetstone for fine grinding, the time required for polishing
in the polishing process carried out after grinding of the whetstone of the second
embodiment is also equivalent to that of the resin-bonded whetstone as a conventional
whetstone for fine grinding.
That is, the whetstone of the second embodiment is equivalent
in average grinding rate to the metal-bonded whetstone as a conventional whetstone
for rough grinding, and is equivalent in surface roughness and time required for
polishing to the resin-bonded whetstone as a conventional whetstone for fine grounding.
Accordingly, although different whetstones are used in a rough grinding process
and a fine grinding process, respectively, in the conventional technique, basically
the same results as in the conventional technique, i.e., surface roughness and time
required for polishing equivalent to the conventional technique, can be obtained
with the whetstone of the second embodiment without changing the whetstone in the
rough grinding process and the fine grinding process.
Therefore, in the case where grinding is carried out in
such a manner that the grinding amount after the shape creation as shown in Fig.
5(b) is 150 µm, and the surface roughness after the grinding is 0.47 µm,
the conventional technique requires about 5 minutes for the rough grinding process
(≈ 150 µm (grinding amount) / 28 µm per minute), about 5 minutes
for the fine grinding process, and several minutes for an operation time to change
the whetstones, so as to require 10 minutes or more as the total time required for
grinding process. With respect to the whetstone of the second embodiment, on the
other hand, the operation time to change the whetstones is omitted since no change
of whetstones is required between the rough grinding process and the fine grinding
process, and the total time required for the grinding process including the rough
grinding process and the fine grinding process can be suppressed to about 5 minutes
(≈ 150 µm (grinding amount) / 28 µm per minute). The reason why
the fine grinding process in the conventional technique requires about 5 minutes
is that a crack layer (a part of the material that is deteriorated by processing
strain) on the surface of the material formed by the rough grinding to an objective
amount of about 150 µm, is necessarily removed by the fine grinding. On the
other hand, by using the whetstone of the second embodiment, such a crack layer
formed in the rough grinding of the conventional technique does not occur because
the particle diameter of the abrasive grains contained therein is equivalent to
or less than the particle diameter of the abrasive grains contained in the conventional
whetstone for fine grinding.
TABLE 2
Whetstone of Embodiment of the invention
Conventional whetstone
Rough grinding time (min)
5
5
Fine grinding time (min)
5
Time for changing whetstone (min)
0
&agr;
Total grinding time (min)
5
10 + &agr;
The time required for figuring the whetstone, i.e., the
time required for modifying the grinding surface of the whetstone to an inverse
shape of the surface to be processed (optical surface), is 35 minutes for the whetstone
of the second embodiment and 120 minutes for both the conventional metal-bonded
whetstone and resin-bonded whetstone. The reason why the time required for figuring
the whetstone of the second embodiment is shorter is that in the second embodiment,
the end surfaces of the relatively soft base bodies 2 are finished by machining
before forming the abrasive grain part 5 on the base bodies, so that the plane shape
formed by continuation of the end surfaces of all the base bodies 2 fixed on the
pedestal 9 becomes an inverse shape of the desired surface to be processed. The
time required for figuring the whetstone of the second embodiment includes 10 minutes
as a time for processing the end surfaces of the base bodies 2 before forming the
abrasive grain parts 5, and after forming the abrasive grain parts 5, 25 minutes
as a time for finishing the abrasive grain parts 5, so as to take 35 minutes in
total.
Performance Test Example 2
Results of the performance test upon grinding fluorite
by using the whetstone 10 produced in the manner described in the second embodiment
will be described.
In the performance test, fluorite (CaF2) having
a crystalline structure is processed by using either the whetstone of the second
embodiment or a resin-bonded whetstone which is a conventional whetstone for fine
grinding, and the grinding rate, the grinding accuracy and the like are obtained
in the process. Fluorite as a raw material of an optical element has dependency
of processing characteristics on the crystallographic azimuth, and it has been known
that a good plane as a surface to be processed (optical surface) is difficult to
be evenly obtained. In this test, accordingly, such fluorite is used as a grinding
object that is subjected to shape creation in such a manner that the 111 plane,
the 110 plane or the 100 plane thereof is perpendicular to the optical axis.
The test conditions for the performance test are as follows.
- Whetstone of the second embodiment of the invention
- Diameter of base body:
- 6 mm
- Material of abrasive grains:
- diamond
- Particle diameter of abrasive grains :
- 1 to 3 µm (corresponding to mesh size #4000)
- Thickness of abrasive grain layer:
- 0.3 mm
- Conventional resin-bonded whetstone (for fine grinding)
- Diameter of pellets:
- 6 mm
- Material of abrasive grains:
- diamond
- Particle diameter of abrasive grains:
- mesh size of #2000
- Raw material of optical element: fluorite (CaF2)
- Shape of optical element: spherical convex lens having an outer diameter of
39 mm and a curvature radius R of 50 mm
- Grinding machine: Oscar type, produced by Ichimura Seisakusho Co., Ltd.
- Grinding fluid: water soluble concentrated grinding fluid diluted with water
(concentrated grinding fluid/water = 1/15)
The whetstone of the second embodiment used in the test
is composed of a pedestal having base bodies fixed with an interval of 3 mm. In
the whetstones used herein, the distances of the base bodies are retained to a certain
extent to suppress the area of the total grinding surface to 30% or less of the
area of the surface of the pedestal, on which the abrasive grain parts are formed,
whereby the discharge of the grinding dusts is facilitated.
The average grinding rate, the surface condition of the
raw material, the surface roughness of the raw material and the time required for
polishing in the polishing process carried out after the grinding process upon grinding
the raw material of an optical element with the respective whetstones under the
foregoing conditions, and the time required for figuring the whetstone, were those
as shown in Table 3 below.
TABLE 3
Whetstone of embodiment of the invention
Resin-bonded whetstone (conventional whetstone)
Average grinding rate
12 µm/min
10 µm/min
Surface condition
gloss on whole surface
glossy parts and white turbid parts mixed
Surface roughness (Ry)
0.13 µm
0.19 µm for glossy parts
1.11 µm for white turbid parts
Time required for polishing
120 min
≥ 480 min
Time required for figuring whetstone
15 min (5 min + 10 min)
60 min
It is understood from Table 3 that the whetstone of the
second embodiment is somewhat superior to the conventional resin-bonded whetstone
although the abrasive grains thereof are smaller than the abrasive grains of the
conventional resin-bonded whetstone. It is considered that this is because of the
higher retentivity of abrasive grains of the whetstone of the second embodiment
as mentioned in Performance Test Example 1.
In the condition of the surface to be processed after grinding
in the case using the conventional resin-bonded whetstone, the white turbid surface
28 and the glossy surface 29 are mixed in any crystallographic azimuth as shown
in Fig. 6. More specifically, in the case where the fluorite is ground with the
111 plane thereof perpendicular to the optical axis of a lens made by this test
as shown in Fig. 6(a), white turbid surfaces 28 appear by 120° with respect
to the optical axis as the center, in the case where the fluorite is ground with
the 110 plane thereof perpendicular to the optical axis as shown in Fig.6 (b), white
turbid surfaces 28 appear by 180° with respect to the optical axis as the center,
and in the case where the fluorite is ground with the 100 plane thereof perpendicular
to the optical axis as shown in Fig. 6(c), white turbid surfaces 28 appear by 90°
with respect to the optical axis as the center. These are tendencies that appear
on repeated grinding. The reason why the white turbid surface 28 is formed is that
the crack layer described in the foregoing is formed in the white turbid surface
layer part. In the case where the conventional resin-bonded whetstone is used, the
surface roughness after grinding is 0.19 µm on the glossy surface and 1.11
µm for the white turbid surface.
On the other hand, the whetstone of the second embodiment
provides a glossy surface on the entire surface to be processed, which is contrary
to the common knowledge that a good plane as a surface to be processed is difficult
to be evenly obtained, as described in the foregoing. Furthermore, the surface roughness
after grinding is 0.13 µm, which is superior to the conventional resin-bonded
whetstone. The reason why the whetstone of the second embodiment is superior to
the conventional resin-bonded whetstone in surface condition and surface roughness
after grinding as just described is not clear, but it is considered that this is
because of the smaller abrasive grains and the uniform distribution of the abrasive
grains in the whetstone of the second embodiment.
As described in the foregoing, the whetstone of the second
embodiment is superior in surface condition and surface roughness after grinding,
and thus the time required for polishing after the grinding process is 120 minutes,
which is 1/4 of the case using the conventional resin-bonded whetstone. The reason
why the time required for polishing in the case using the conventional resin-bonded
whetstone is significantly prolonged to 480 minutes or more is that the crack layer
forming white turbidity on the processed surface is necessarily removed by polishing.
The time required for figuring the whetstone is 15 minutes
for the whetstone of the second embodiment and 60 minutes for the conventional resin-bonded
whetstone.
It is needless to say that the grinding performance of
the whetstone of the second embodiment is basically equivalent to the grinding performance
of the whetstone of the first embodiment. However, because the first embodiment
is obtained by fixing the whetstone pellets 1 having the abrasive grain layer formed
thereon on the pedestal 9, it is necessary that the hard abrasive grain layers are
directly processed in the figuring operation of the whetstone, and the time required
for figuring is longer than the second embodiment and provides no significant difference
from the conventional technique.
Third Embodiment
A third embodiment according to the invention will be described.
The whetstone of this embodiment has an abrasive grain
layer formed by electrolytic plating but not electroless plating, and other basic
constitutions are the same as the second embodiment.
A pedestal and plural base bodies are firstly prepared
as similar to the second embodiment. However, it is necessary that the pedestal
and the base bodies are made of electroconductive materials, and as such materials,
for example, iron, stainless steel, aluminum and the like are preferred.
After degreasing the pedestal and the base bodies with
a solvent, the necessary number of base bodies are placed on the surface of the
pedestal, on which the abrasive grain parts are to be formed, and then an epoxy
adhesive is applied among the plural base bodies. In other words, the adhesive is
not applied to the end surfaces of the base bodies, but the adhesive is applied
to the side surfaces of the base bodies and a region among base bodies on the surface
of the pedestal, whereby the base bodies are fixed on the pedestal while maintaining
electroconductivity between the base bodies and the pedestal. The reason why the
adhesive is not applied to the end surfaces of the base bodies is to ensure electroconductivity
between the base bodies and the pedestal, and therefore, the adhesive may be applied
to a part of the end surface of the base body. Furthermore, in order to ensure mechanical
connectivity between the base bodies and the pedestal, a protrusion or a depression
may be formed on the end surface of the base body, and a depression or a protrusion
may be formed on the pedestal at a position where the base body is to be fixed,
followed by engaging the protrusion or the depression of the base body with the
depression or the protrusion of the pedestal.
After curing the adhesive, the end surfaces of the base
bodies are ground or cut, whereby the plane shape formed by continuation of the
end surfaces of the base bodies fixed on the pedestal becomes an inverse shape of
the desired surface to be processed, as similar to the second embodiment.
After attaching a cathode for electrolytic plating to the
back surface of the pedestal having the base bodies, the back surface of the pedestal
is masked against electrolytic plating, and the regions that are not masked, i.e.,
the end surfaces of the base bodies and the like, are subjected to pretreatment
for electrolytic plating.
After completing the pretreatment for plating, an anode
is placed in an electrolytic plating solution, and abrasive grains are mixed therein.
The abrasive grains in this case may be diamond powder, cubic boron nitride or the
like, as similar to the first embodiment. The pedestal having the base bodies is
immersed in the electrolytic plating solution having abrasive grains mixed therein,
and an electric current is applied between the anode in the electrolytic plating
solution and the cathode attached to the pedestal under stirring the electrolytic
plating solution, so as to form electrolytic layers containing abrasive grains,
i.e., abrasive grain parts, on the end surfaces of the base bodies.
After completing the formation of the abrasive grain parts,
the pedestal is taken out from the electrolytic plating solution and washed with
water, and then the masking agent on the back surface of the pedestal is removed.
After removing the masking agent, the surfaces of the abrasive grain parts formed
on the end surfaces of the plural base bodies are lapped with a lapping disk or
the like to form a prescribed plane shape, to complete the whetstone. The lapping
is necessarily carried out since the thickness of the plating layer cannot be uniform
by formed due to the concentrated deposition of the electrolytic plated layer to
convex parts and peripheral parts in electrolytic plating process, as described
in the first embodiment.
As described in the foregoing, in this embodiment, because
the abrasive grains are mixed in the plating solution which is a liquid form, the
abrasive grains can be uniformly dispersed in the plated layer thus deposited. Furthermore,
the plated layer formed by the electrolytic plating method is used as a binder material
for the abrasive grains in the plated layer, and thus high retentivity of the abrasive
grains can be obtained to prolong the service life of the whetstone. Since the plated
layer as a binder material is basically hard, it suffers less surface denaturation
of the abrasive grain layer upon grinding and polishing, and thus the frequency
of repairing the grinding surface or the polishing surface can be reduced. Furthermore,
since the adhesive is applied on the surface of the pedestal, on which the abrasive
grain parts are to be formed, among the plural base bodies, the adhesive also functions
as a masking agent, and the plated layer is prevented from forming among the plural
base bodies although masking using another material is not separately carried out.
The grinding performance of the whetstone of this embodiment
is basically equivalent to the grinding performance of the second embodiment. However,
because the whetstone of this embodiment cannot have an abrasive grain layer having
a uniform thickness as described in the foregoing, the time required for figuring
is longer than the second embodiment and provides no significant difference from
the conventional technique.
While the production process of a whetstone has been described,
it is needless to say that a whetstone pellet having an electrolytic plating layer
containing abrasive grains as an abrasive grain part can be produced by using a
fixing plate instead of the pedestal, as in the first embodiment.
Example 3
A specific production process of the whetstone described
in the third embodiment will be described with reference to Figs. 7 and 8.
A pedestal 9b is made of cast iron and has a disk form.
A base body 2b is made of stainless steel (SUS304) and has a columnar form. The
surfaces of the pedestal 9b and the base bodies 2b have been subjected to a shot
treatment with glass beads of a grain size of #100.
After degreasing the pedestal 9b and the base bodies 2b
with a solvent, a necessary number of the base bodies 2b are placed on the pedestal
9b, and then an epoxy adhesive 12b is applied on the surface of the pedestal 9b,
on which abrasive grain parts are to be formed, as shown in Fig. 7 (a). As the adhesive
12b, EP-138 (a trade name, Cemedine Co., Ltd.) and SC507A/B (a trade name, produced
by Sony Chemicals Corp.) used in Example 2 are preferably used. The application
amount of the adhesive 12b is preferably such a thickness that is about half of
the height of the base bodies 2b. After applying the adhesive 12b, a weight is placed
on the plural base bodies 2b, and the adhesive 12b is cured.
After curing the adhesive 12b, the end surfaces 3b of the
base bodies 2b are ground by using the lapping disk 19b as shown in Fig. 7(b), whereby
the plane shape formed by continuation of the end surfaces 3b of the base bodies
2b is finished to be an inverse shape of a surface to be processed. The lapping
is carried out under supplying a mixture of silicon carbide grinding sand of a grain
size of #600 and water to the lapping surface.
After subjecting the pedestal 9b having base bodies to
alkali degreasing and activation with an acid, a cathode 20 for electrolytic plating
is attached to the back surface of the pedestal 9b, and then a masking film 13b
is formed on the back surface of the pedestal 9b by using a masking tape or a coating
type masking agent, as shown in Fig. 7(c). The pedestal 9b having the base bodies
is sequentially subjected to nickel strike plating 4b. In the electrolytic plating
process, an electric current of about 10 A per 100 cm2 of the surface
area is applied for about 2 minutes to form an extremely thin plated film on the
end surface 3b of the base body 2b. The electrolytic plating process is carried
out for electrochemical activation of the surface of stainless steel since the base
bodies 2b is made of stainless steel.
After completing the pretreatment for plating, an anode
21 is placed in an electrolytic plating solution 16b, and abrasive grains 15 are
mixed therein, as shown in Fig. 8(d). In Example 3, a nickel sulfamate plating solution
having a pH of 4 at a temperature of 50°C is used as the electrolytic plating
solution 16b, and diamond powder having a particle diameter of from 2 to 4 µm
is used as the abrasive grains 15. The pedestal 9b having the base bodies is immersed
in the electrolytic plating solution 16b having the abrasive grains 15 mixed therein,
an electric current is applied between the anode 21 in the electrolytic plating
solution 16b and the cathode 20 attached to the pedestal 9b under stirring the electrolytic
plating solution 16b with a stirrer 17, whereby electrolytic plating layers containing
the abrasive grains 15, i.e., abrasive grain parts 5b, are formed on the end surfaces
of the base bodies 2b. In the electrolytic plating process, an electric current
of 5 A per 100 cm2 of the surface area is applied for about 4 hours to
form the abrasive grain parts 5b having a thickness of 0.24 mm.
After completing the formation of the abrasive grain parts
5b, the pedestal 9b having the abrasive grain parts 5b thus formed is taken out
from the electrolytic plating solution 16b and washed with water, and the masking
film 13b on the back surface of the pedestal 9b is removed. Thereafter, lapping
is carried out with a lapping disk 19c as shown in Fig. 8(e), whereby the plane
shape formed by continuation of the surfaces of the abrasive grain parts 5b formed
on the end surfaces of the base bodies 2b fixed on the pedestal 9b is finished to
be an inverse shape of a surface to be processed.
In the case where a fixing plate is used for forming the
whetstone pellets instead of the pedestal, as described in the foregoing, Turco
5980-1A (a trade name, produced by Atofina Chemicals, Inc., U.S.) usedinExample
1 ispreferably used as the adhesive for preliminary fixing the base bodies on the
fixing plate.
Embodiment of Exposure apparatus
An embodiment of an exposure apparatus will be described
with reference to Fig. 9.
The exposure apparatus in this embodiment is to project
a pattern on a silicon wafer 30, and has a light source 31, a condenser lens 32,
an illuminating optical system 33, a projecting optical system 34 and a stage 35,
on which the silicon wafer 30 is placed. A reticle 36 having a pattern formed thereon
corresponding to the processing contents of the silicon wafer 30 is appropriately
arranged between the illuminating optical system 33 and the projecting optical system
34. As the light source 31, an ArF laser emitting light having an extremely short
wavelength or an F2 laser emitting light having a still further short
wavelength is used in this embodiment. The illuminating optical system 33 has such
a function that the distribution of light intensity over the light path is uniformized,
and the projecting optical system 34 has such a function that an image on the reticle
36 is focused on the silicon wafer 30.
It is demanded for the latest exposure apparatus that the
pattern on the reticle 36 is projected by using light having a shorter wavelength
as described in the foregoing in order to project a minute pattern on the silicon
wafer 30. Therefore, in order to deal with light having a short wavelength in this
embodiment, all the condenser lens 32, various lenses in the illuminating optical
system 33 and various lenses in the projecting optical system 34 are made of quartz
or fluorite.
It has been found in the case where fluorite is ground
that good results are obtained when the whetstones of the embodiments of the invention
having been described are used, as described in Performance Test Example 2. In this
embodiment, therefore, the various lenses constituting the optical exposure apparatus
are obtained by grinding fluorite by using one of the whetstones of the embodiments
of the invention as described above, preferably the whetstone of the second embodiment.
The lenses thus obtained can be shape created in a short period of time with high
accuracy for the exposure apparatus, and thus they contribute to reduction of the
production cost of the aligner itself.
