U.S. patent application number 10/229069 was filed with the patent office on 2003-03-06 for metal-less bond grinding stone, and electrolytic dressing grinding method and apparatus using the grinding stone.
This patent application is currently assigned to RIKEN. Invention is credited to Hokkirigawa, Kazuo, Itoh, Nobuhide, Katahira, Kazutoshi, Ohmori, Hitoshi, Ono, Teruko.
Application Number | 20030045222 10/229069 |
Document ID | / |
Family ID | 19093935 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030045222 |
Kind Code |
A1 |
Ohmori, Hitoshi ; et
al. |
March 6, 2003 |
Metal-less bond grinding stone, and electrolytic dressing grinding
method and apparatus using the grinding stone
Abstract
There is here disclosed a metal-less bond grinding stone for
protrusion of grains on the grinding stone by electrolytic
dressing, comprising abrasive grains and a bond portion for holding
the abrasive grains, wherein the bond portion comprises a
carbon-containing nonmetallic material alone. Furthermore, this
metal-less bond grinding stone is used, whereby a current which is
allowed to flow between the grinding stone and the electrode is
controlled within a desired range. In this way, environmental
pollution with a waste liquid containing heavy metal ions and metal
contamination of device wafers can be prevented, and a mirror-like
high-quality level ground surface can be obtained with a
satisfactory efficiency.
Inventors: |
Ohmori, Hitoshi; (Wako-shi,
JP) ; Itoh, Nobuhide; (Hitachi-shi, JP) ;
Katahira, Kazutoshi; (Wako-shi, JP) ; Ono,
Teruko; (Wako-shi, JP) ; Hokkirigawa, Kazuo;
(Sendai-shi, JP) |
Correspondence
Address: |
GRIFFIN & SZIPL, PC
SUITE PH-1
2300 NINTH STREET, SOUTH
ARLINGTON
VA
22204
US
|
Assignee: |
RIKEN
Wako-shi
JP
|
Family ID: |
19093935 |
Appl. No.: |
10/229069 |
Filed: |
August 28, 2002 |
Current U.S.
Class: |
451/546 |
Current CPC
Class: |
B24B 53/001 20130101;
B23H 5/08 20130101; B24B 7/228 20130101 |
Class at
Publication: |
451/546 |
International
Class: |
B24B 001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 4, 2001 |
JP |
JP 2001-267863 |
Claims
What is claimed is:
1. A metal-less bond grinding stone for dressing a ground surface
by electrolytic dressing, comprising: abrasive grains and a bond
portion for holding the abrasive grains, wherein the bond portion
comprises a carbon-containing nonmetallic material alone.
2. The metal-less bond grinding stone according to claim 1, which
comprises a mixture of abrasive grains, carbon powder and resin
powder and which is formed by sintering the mixture under pressure
at a softening temperature lower than a resin melting
temperature.
3. The metal-less bond grinding stone according to claim 2, wherein
a blend ratio of carbon to the resin is about 20% or more and about
30% or less.
4. The metal-less bond grinding stone according to claim 1, which
comprises a mixture of the abrasive grains and carbon-containing
powder and which is obtained by sintering the mixture to impart
conductivity and mechanical strength to the carbon-containing
powder.
5. The metal-less bond grinding stone according to claim 1, which
comprises a mixture of the abrasive grains and resin powder and
which is obtained by sintering the mixture to carbonize at least a
part of the resin powder.
6. An electrolytic in-process dressing grinding method comprising a
step of applying a voltage between a metal-less bond grinding stone
(1) having a bond portion comprising a carbon-containing
nonmetallic material alone and an electrode (2) while a conductive
grinding fluid (3) is allowed to flow between the metal-less bond
grinding stone (1) and the electrode (2), and a step of grinding a
work piece (4) while the grinding stone is subjected to
electrolytic dressing, wherein a current which is allowed to flow
between the grinding stone and the electrode is controlled within a
desired range.
7. An electrolytic dressing grinding apparatus using a metal-less
bond grinding stone, which comprises a metal-less bond grinding
stone (1) having a bond portion comprising a carbon-containing
nonmetallic material alone, a carbon electrode (2) which is located
at a distance from a grinding surface of the metal-less bond
grinding stone (1) and at least whose side opposite to the grinding
stone is made from a carbon material, a grinding fluid supply means
(6) for causing a conductive grinding fluid (3) not containing any
heavy metal ions to flow between the grinding stone and the
electrode, and an power source unit (8) for electrolytic dressing
which applies a voltage between the grinding stone and the
electrode and which controls the current flowing between them
within a predetermined range.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a metal-less bond grinding
stone and an electrolytic dressing grinding method and an apparatus
using the grinding stone.
[0003] 2. Description of the Related Art
[0004] The most common processing means for locations requiring
mirror finish is a polishing work using loose abrasive grains such
as lapping or polishing. However, the polishing work has problems
that (1) efficiency is low because manual operation is normally
made and (2) abrasive grains may bite into a work piece in certain
cases. Accordingly, much attention is paid to a processing means
using fixed abrasive grains typified by a grinding technique.
[0005] On the other hand, in accordance with the background of
processing and the like of semiconductor circuits which become
miniature more and more, demands are placed on development and
commercialization of a ultra-precision grinding technology in which
a processing machine having a high positioning accuracy is combined
a fixed abrasive grain processing technique. The ultra-precision
grinding must satisfy stringent specifications in terms of ground
surface roughness, shape accuracy, and surface quality level.
[0006] As the processing means for overcoming the above problems,
an electrolytic in-process dressing grinding is noticed, in which
the grinding is performed on a work piece with a conductive
grinding stone using fixed abrasive grains while the surface of the
conductive grinding stone is subjected to electrolytic dressing.
This grinding means is hereinafter referred to as the ELID
grinding.
[0007] In the above ELID grinding, a working current of the
electrolytic dressing is relatively high (for example, at about 10
A) at the start of dressing. After a certain dressing time (for
example, 20 to 30 minutes), a metal oxide (non-conductive film) is
formed on the surface of the conductive grinding stone during the
electrolytic dressing, and a thickness of the non-conductive film
is kept almost constant depending on a balance between the grinding
and the electrolytic dressing. Therefore, there is generally shown
a feature that the working current of the electrolytic dressing is
maintained at a relatively low value (for example, about 2 A). In
this stable condition, the fine abrasive grains are properly
projected and held, which makes it possible to usually achieve the
satisfactory ELID grinding. Therefore, the non-conductive film on
the surface of the grinding stone is indispensable in the ELID
grinding. It has been considered that any stable ELID grinding is
not possible unless this film is formed.
[0008] On the other hand, in the ELID grinding, a metal bond
grinding stone in which the abrasive grains are fixed with metal
powder is used as the conductive grinding stone, and cast iron,
cobalt, bronze and the like can be used as the metal powder.
However, in such a case, a problem inconveniently rises. That is to
say, when the conductive grinding stone using such metal powder as
a binder is used in the ELID grinding, heavy metal ions are
dissolved in a grinding fluid during the electrolytic dressing, and
hence, the environment is polluted with a waste liquid containing
these heavy metal ions.
[0009] Particularly, when the conductive grinding stone containing
copper, tin or the like is used for the processing of device wafers
after the formation of devices in a semiconductor wafer
manufacturing field, there has occurred a problem that a device
performance deteriorates owing to the heavy metal ions.
Accordingly, also in order to prevent the contamination of the
device wafers with the metals, demand has been made on a conductive
grinding stone which does not generate the heavy metal ions
(hereinafter referred to as a metal-less bond grinding stone).
SUMMARY OF THE INVENTION
[0010] The present invention has been developed to overcome these
problems. Namely, an object of the present invention is to provide
a metal-less bond grinding stone which can prevent environmental
pollution with a waste liquid containing heavy metal ions and metal
contamination of device wafers and which can achieve a mirror-like
high-quality level ground surface with a satisfactory processing
efficiency, and to provide an electrolytic dressing grinding method
and an apparatus using the grinding stone.
[0011] According to the present invention, a metal-less bond
grinding stone is provided, which is a grinding stone for
electrolytic dressing for protrusion of grains on the grinding
stone by electrolytic dressing and which comprises abrasive grains
and a bond portion for holding the abrasive grains, wherein the
bond portion comprises a carbon-containing nonmetallic material
alone.
[0012] According to the constitution of the present invention, the
bond for holding the abrasive grains of the grinding stone for the
electrolytic dressing comprises the carbon-containing nonmetallic
material alone. Owing to the presence of carbon, the bond portion
becomes conductive, and carbon is liberated during the electrolytic
dressing, whereby the abrasive grains are dressed.
[0013] Furthermore, since a metallic material is not contained at
all in the bond portion, even when the metal-less bond grinding
stone is subjected to the electrolytic dressing, a waste liquid
containing heavy metal ions is not produced, thereby preventing
environmental pollution. Moreover, carbon itself does not affect
the device wafers, metal contamination of the device wafers can be
substantially prevented.
[0014] According to a preferred embodiment of the present
invention, the metal-less bond grinding stone comprises a mixture
of abrasive grains, carbon powder and resin powder, and is formed
by sintering the mixture under pressure at a softening temperature
lower than a resin melting temperature.
[0015] According to this constitution, the metal-less bond grinding
stone of a desired shape can be formed by softening, pressurization
and sintering without melting of a resin. In addition, the bond
portion of this grinding stone comprises carbon and the resin, and
the resin has elasticity to elastically hold the abrasive grains.
In consequence, many abrasive grains act substantially uniformly on
a work piece, which makes it possible to obtain the mirror-like
high-quality level ground surface with a satisfactory processing
efficiency.
[0016] It is recommended that a blend ratio of carbon to the resin
in this metal-less bond grinding stone is about 20% or more and
about 30% or less. Within this carbon ratio range, electrical
resistivity, deflective strength and Young's modules are almost
constant, thereby making it possible to obtain electrical
resistance appropriate to the electrolytic dressing, and strength
and elasticity enough to hold the abrasive grains.
[0017] Another metal-less bond grinding stone is also acceptable
which may comprise a mixture of the abrasive grains and
carbon-containing powder and which may be obtained by sintering the
mixture to impart conductivity and mechanical strength to the
carbon-containing powder. For example, unutilizable resources such
as rice bran may be sintered to provide the conductivity and the
mechanical strength, thereby constituting the metal-less grinding
stone, which makes it possible to obtain the metal-less bond
grinding stone in which the electrical resistance and the
mechanical properties of the bond portion are adequately adjusted
and the bond portion does not contain metallic materials at
all.
[0018] Still another metal-less bond grinding stone is also
acceptable which may comprise a mixture of the abrasive grains and
resin powder and which may be obtained by sintering the mixture to
carbonize at least a part of the resin powder. For example, the
sintering step can be carried out at a high temperature in an
inactive gas atmosphere to carbonize a part of the resin, which
makes it possible to adjust the electrical resistance and the
mechanical properties of the bond portion.
[0019] Furthermore, according to the present invention, there is
provided an electrolytic dressing grinding method which comprises a
step of applying a voltage between a metal-less bond grinding stone
(1) having a bond portion comprising a carbon-containing
nonmetallic material alone and an electrode (2) while a conductive
grinding fluid (3) is allowed to flow between the metal-less bond
grinding stone (1) and the electrode (2), and a step of grinding a
work piece (4) while the grinding stone is subjected to
electrolytic dressing, wherein a current which is allowed to flow
between the grinding stone and the electrode is controlled within a
desired range.
[0020] In the metal-less bond grinding stone having the bond
portion not containing any metallic material, even when the
electrolytic dressing is continued, any non-conductive film is not
formed on the surface thereof, so that an adjustment function of
the working current of the electrolytic dressing by means of a
non-conductive film cannot be obtained. On the other hand, however,
the current which flows between the grinding stone and the
electrode is not affected by the non-conductive film, so that the
current is always maintained at a substantially constant value from
an early stage of the dressing. In consequence, it has
experimentally been confirmed that the electrolytic dressing is
positively controlled by controlling this current within a
predetermined range, so that stable ELID grinding can be
achieved.
[0021] Furthermore, according to the present invention, there is
provided an electrolytic dressing grinding apparatus using a
metal-less bond grinding stone, which comprises a metal-less bond
grinding stone (1) having a bond portion comprising a
carbon-containing nonmetallic material alone, a carbon electrode
(2) which is located at a distance from a grinding surface of the
metal-less bond grinding stone (1) and at least whose side opposite
to the grinding stone is made from a carbon material, a grinding
fluid supply means (6) for causing a conductive grinding fluid (3)
not containing any heavy metal ions to flow between the grinding
stone and the electrode, and an power source unit (8) for
electrolytic dressing which applies a voltage between the grinding
stone and the electrode and which controls the current flowing
between them within a predetermined range.
[0022] The metal-less grinding stone (1) is used as the grinding
stone, the carbon electrode (2) is used as the electrode, and the
conductive grinding fluid (3) which does not contain any heavy
metal ions is used, which makes it possible to fundamentally
prevent environmental pollution with heavy metal ions and
contamination of device wafers with metals.
[0023] In the power source unit (8) for the electrolytic dressing,
the voltage is applied between the grinding stone and the electrode
to control the current between them within the predetermined range,
whereby the electrolytic dressing is positively controlled, which
makes it possible to obtain a mirror-like high-quality finish
surface with a satisfactory processing efficiency.
[0024] The other objects and advantages of the present invention
will be apparent in the following detailed description of
illustrative embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 shows a schematic view of a manufacturing process of
a metal-less bond grinding stone of the present invention.
[0026] FIG. 2 shows a relationship between a blend ratio of carbon
and electrical resistivity.
[0027] FIG. 3 shows a relationship between the blend ratio and
deflective strength and Young's modules.
[0028] FIG. 4 shows a constitutional view of an electrolytic
dressing grinding apparatus of the present invention.
[0029] FIG. 5 shows a relationship between an electrolytic time and
a working current value during initial electrolytic dressing.
[0030] FIG. 6 shows a roughness profile of a surface ground by the
metal-less bond grinding stone.
[0031] FIG. 7 shows a behavior of the working current values of a
conventional grinding stone and the grinding stone of the present
invention during the initial electrolytic dressing.
[0032] FIG. 8 shows a relationship of processing pressure and
processing efficiency between the conventional grinding stone and
the grinding stone of the present invention.
[0033] FIG. 9 shows a relationship of the processing pressure and
surface roughness between the conventional grinding stone and the
grinding stone of the present invention.
[0034] FIG. 10 shows a comparison of a processing efficiency
between presence and absence of ELID of the metal-less bond
grinding stone.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] Recently, solutions of environmental problems are becoming
important more and more in various fields, and a grinding method
which takes the environment into account is also demanded in a
field of machining work. In the future, it is considered that the
importance of such a technique will be increasing more and
more.
[0036] The inventors of the present invention have developed a
metal-less conductive bond grinding stone (hereinafter referred to
as "metal-less bond grinding stone") for ELID grinding using carbon
as a conductive material for the main purposes of reducing the
invasion of heavy metal ions into a grinding fluid to facilitate a
grinding fluid treatment, and reducing the contamination of a work
piece with the metals to facilitate a cleaning treatment, and for
conductivity, strength, initial electrolytic dressing
characteristics and grinding characteristics of the above grinding
stone, various experiments have been conducted.
[0037] Preferred embodiments of the present invention will be
described below together with test results. It is to be noted that
common portions in drawings are indicated by the same symbols.
[0038] 1. Manufacture of a Metal-Less Bond Grinding Stone
[0039] (Grinding Stone Manufacturing Conditions and an Experiment
Method)
[0040] FIG. 1 shows a schematic view of a manufacturing process of
a metal-less bond grinding stone according to the present
invention. As shown in FIG. 1, the grinding stone is manufactured
by mixing abrasive grains, carbon (about 30 .mu.m) and a phenolic
resin, and then sintering the mixture under pressure by a hot
press. The metal-less bond grinding stone according to the present
invention was manufactured at a sintering temperature of
200.degree. C. under a molding pressure of 19.6 kPa (maintained for
40 to 60 minutes). The grinding stones (10.times.4.times.40,
concentration degree=100) were manufactured at carbon blend ratios
of 2%, 5%, 10%, 20% and 30% to the resin, and electrical
resistivity, Young's modules, and deflection strength of the
manufactured wheels were measured.
[0041] (Blend Ratio and Characteristics)
[0042] FIG. 2 shows a relationship between a blend ratio of carbon
and electrical resistivity. With the increase of the carbon blend
ratio, the electrical resistivity tended to decrease. A
substantially constant electrical resistivity of 1 .OMEGA.mm was
achieved at a carbon blend ratio of about 20% or more and about 30%
or less.
[0043] FIG. 3 shows a relationship between a blend ratio,
deflection strength and Young's modules. With the increase of the
blend ratio, the strength tended to decrease. In the case of this
grinding stone, the Young's modules was about 5 GPa regardless of
the blend ratio. In addition, a substantially constant deflection
strength of 10 MPa was obtained at a carbon blend ratio of about
20% or more and about 30% or less.
[0044] (Experimental Manufacturing Conditions of a Grinding
Stone)
[0045] In view of the above results, experimental manufacturing
conditions of a grinding stone were such that a blend ratio of
carbon to a resin was 20%, a concentration degree was 100, a
molding pressure was 19.6 kPa, and a sintering temperature was
200.degree. C. For abrasive grains, diamond of #8000 (average grain
diameter=about 2 .mu.m) was used and shaped into a disk form having
an outside diameter of 250 mm and a grinding stone width of 55 mm.
Evaluation of the experimentally manufactured grinding stone was
made by ELID lap grinding.
[0046] It is to be noted that the metal-less bond grinding stone
according to the present invention is not limited to the above
example, and alternatively, the metal-less bond grinding stone may
be manufactured by sintering a mixture of the abrasive grains and
the carbon-containing powder to impart conductivity and mechanical
strength to the carbon containing powder. For example, unutilizable
resources such as rice bran may be sintered to thereby add the
conductivity and the mechanical strength thereto to constitute the
metal-less grinding stone, whereby the metal-less bond grinding
stone can be obtained in which electric resistance and mechanical
properties of a bond portion are optimally adjusted and any
metallic materials are not contained in the bond portion.
[0047] Furthermore, the metal-less bond grinding stone there may be
manufactured by sintering a mixture of the abrasive grains and the
resin powder to carbonize at least a part of the resin powder. For
example, the sintering step can be carried out at a high
temperature in an inactive gas atmosphere to carbonize a part of
the resin, thereby enabling the adjustment of the electrical
resistance and the mechanical properties of the bond portion.
[0048] 2. Test of Basic Grinding Characteristics
[0049] (Experimental Unit)
[0050] FIG. 4 shows a constitutional view of an electrolytic
dressing grinding unit according to the present invention. In this
experiment, an electrolytic dressing grinding unit of the present
invention was constituted using an ELID lap grinding system, and a
basic test regarding basic grinding characteristics of a metal-less
bond grinding stone was made.
[0051] The system used in this experiment is shown below.
[0052] (a) Grinding machine: An improved version of a single-side
lapping machine (MG773B) was used.
[0053] (b) Grinding stone: A #8000 metal-less bond diamond grinding
stone (metal-less bond grinding stone) was used. The wheel was a
disk having an outside diameter of 250 mm, a grinding stone width
of 55 mm, and a concentration degree of 100 (volume ratio=about
{fraction (1/4)}).
[0054] (c) Grinding fluid: A chemical solution type grinding fluid
(CEM) diluted with tap water 50 times was used.
[0055] (d) Electrolyte power source unit: A high-frequency
electrolyte power source unit (ED630) only for ELID was used.
[0056] (e) Work piece: A monocrystaline silicon (.phi.30) was
used.
[0057] (Procedure of Grinding Experiment)
[0058] The experimentally manufactured grinding stone was applied
to ELID lap grinding to grind the monocrystaline silicon (.phi.30),
and roughness on a ground surface was inspected. Grinding
conditions were that a grinding stone/work piece rotating speed was
about 100 rpm and a grinding pressure was 100 kPa. Moreover,
electrolytic conditions were that an open voltage was 60 V, a
maximum current was 30 A, and a pulse supply/pause interval was 2
.mu.s.
[0059] (Experimental Results)
[0060] FIG. 5 shows a relationship between an electrolytic time and
a working current value during initial electrolytic dressing. Since
a bond material for the metal-less bond grinding stone of the
present invention did not contain any material which brought about
an anodic oxidation reaction, no sudden current value decrease was
observed. Namely, a current which flowed between the grinding stone
and an electrode was not affected by a non-conductive film, and
kept an almost constant value from an initial stage of the
dressing. Therefore, it was experimentally confirmed that the
electrolytic dressing could be positively controlled by controlling
this current within a predetermined range to enable the stable ELID
grinding.
[0061] FIG. 6 shows a roughness profile on a ground surface in the
case that a monocrystaline silicon was ground using the metal-less
bond grinding stone. A mirror surface having a ground surface
roughness of 28 nmRy could be obtained. A ground surface roughness
of 28 nmRy is equivalent to a mirror surface of 10 nm or less under
an average surface roughness Ra.
[0062] Accordingly, it was confirmed from this test that the use of
the metal-less bond grinding stone not only enabled the stable ELID
grinding but also ensured mirror-like high-quality level ground
surface.
[0063] 3. Comparative Test With Metal Bond Grinding Stone
[0064] A comparison test was made on differences in grinding
characteristics between a metal bond grinding conventionally used
as a grinding stone for ELID grinding and a metal-less bond
grinding stone of the present invention.
[0065] (Experimental Unit)
[0066] In this experiment, the same electrolytic dressing grinding
unit as in "2. Basic grinding characteristics test" was used, and
similarly the same grinding fluid, power source and work piece were
used. A #8000 metal-less bond diamond grinding stone (disk having
an outside diameter of 250 mm and a grinding stone width of 55 mm,
and a concentration degree=100) was used together with a #8000
metal-resin bond diamond grinding stone (metal:resin=7:3, and
concentration degree=100) for comparison.
[0067] Moreover, a contact type surface roughness tester (Surf Test
701) was used as an evaluation unit to measure a ground surface
roughness. An EPMA (Electron Probe Micro Analyzer) was used to
evaluate a surface condition.
[0068] (Procedure of the Experiment)
[0069] Grinding stones to be used were trued and their initial
electrolytic dressing characteristics were inspected, followed by a
grinding experiment of a monocrystaline silicon. The grinding
experiment was made at a grinding stone/work piece rotating speed
of 100 rpm by varying a grinding pressure, and differences in a
ground surface roughness and a grinding efficiency were also
inspected. In addition, a state on a ground surface of the work
piece was also measured and observed by the use of EPMA. ELID
electrolytic conditions included an open voltage of 60 V, a maximum
current of 30 A, and a pulse supply/pause interval of 2 .mu.s.
[0070] (Initial Electrolytic Dressing Characteristics)
[0071] FIG. 7 shows a behavior of a working current value during
initial electrolytic dressing of both grinding stones. In the case
of a metal-resin bond grinding stone, a working current value
non-linearly decreased with time and converged to a given value in
about 20 minutes. On the other hand, in the case of the metal-less
bond grinding stone, a slight decrease of the current value was
observed, but a substantially constant value was shown.
[0072] (Grinding Characteristics)
[0073] FIG. 8 shows a relationship between a grinding pressure and
an efficiency. It was observed under the above conditions that the
work efficiency of the metal-less bond grinding stone was lower
than that of the metal-resin bond grinding stone. This is
considered to be due to a difference in a capacity to hold the
abrasive grains. The work efficiency tended to be higher with the
increase in the grinding pressure, which is considered to indicate
the possibility of achieving the stable grinding under the above
conditions.
[0074] FIG. 9 shows a relationship between the grinding pressure
and the ground surface roughness. The ground surface roughness
tended to be worse slightly with the increase of the grinding
pressure, but when the pressure ranged from 75 kPa to 115 kPa,
there was obtained the satisfactory ground surface having a
roughness of about 30 nmRy equivalent to that of a conventional
metal-resin bond grinding stone.
[0075] (Characteristics of a Ground Surface by the Metal-Less Bond
Grinding Stone)
[0076] Using a metal-less bond wheel and a metal-resin bond
grinding stone, a monocrystaline silicon was ground, followed by
the evaluation of characteristics of a ground surface by EPMA. In
the case of the metal-less bond grinding stone, diffraction of the
material of silicon was observed, but no metallic deposit was
found. In the case of the metal-resin bond grinding stone, on the
other hand, no metal component was identified in a satisfactory
ground surface as in the case of the metal-less bond grinding
stone. However, if any scratch mark existed, metallic components of
a bond material were found to deposit around the mark. When
compared with the metal-resin bond grinding stone, the metal-less
bond grinding stone can readily produce the satisfactory ground
surface without metal contamination.
[0077] As described above, the metal-less bond grinding stone was
developed using carbon powder as one means to establish an ELID
grinding technology friendly to environment, and inspection was
made on its characteristics. As a result of the inspection and
review, the following results could be obtained:
[0078] 1) By setting a carbon powder blend ratio to about 20%,
satisfactory conductivity and strength can be secured.
[0079] 2) In the metal-less bond grinding stone, a work efficiency
is lower than in the metal-resin bond grinding stone, but the
equivalent ground surface roughness can be obtained.
[0080] 3) As a result of the evaluation on the ground surface by
EMPA, the satisfactory ground surface without metal contamination
can be produced.
[0081] (Effects on the Work Efficiency by Presence or Absence of
ELID)
[0082] FIG. 10 shows a comparative view of a work efficiency of the
metal-less bond grinding stone by presence or absence of ELID. The
work piece was silicon and the grinding stone was a #8000
metal-less bond grinding stone. As shown in this drawing, the
addition of ELID enables the improvement and maintenance of the
work efficiency.
[0083] In the metal-less bond grinding stone according to the
present invention, the bond portion for holding the abrasive grains
of the grinding stone for the electrolytic dressing comprises a
carbon-containing nonmetallic material alone. Owing to the presence
of carbon, the bond portion becomes conductive, and carbon is
molten during the electrolytic dressing, whereby the abrasive
grains can be protruded.
[0084] Furthermore, the bond portion does not contain metallic
materials at all, and therefore, even if this metal-less bond
grinding stone is subjected to the electrolytic dressing, a waste
liquid containing heavy metal ions is not produced, which makes it
possible to prevent environmental pollution. In addition, since
carbon itself does not adversely affect device wafers, so that
metal contamination of the device wafers can be substantially
prevented.
[0085] Moreover, the current which flows between the grinding stone
and the electrode is not affected by a nonconductive film and
always remains an almost constant value from an initial stage of
the dressing. Therefore, it was confirmed from the experiment that,
by controlling this current within a predetermined range, the
electrolytic dressing can positively be controlled to ensure the
stable ELID grinding.
[0086] Therefore, the metal-less bond grinding stone as well as the
electrolytic dressing grinding method and apparatus using the
grinding stone according to the present invention have excellent
effects, and for example, environmental pollution by a waste liquid
containing heavy metal ions and metal contamination of device
wafers can be prevented, and the mirror-like high-quality level
ground surface can be obtained with a satisfactory efficiency.
[0087] Although some preferable embodiments of the present
invention have been described, it is to be understood that the
rights and scope of this invention are not limited to those
embodiments. Contrary, the rights and scope of this invention
include all of changes, modifications, and equivalent materials
included in the attached claim.
* * * * *