U.S. patent application number 11/499532 was filed with the patent office on 2006-11-30 for filtration apparatus.
This patent application is currently assigned to Sanyo Aqua Technology Co., Ltd.. Invention is credited to Masahiro Iseki, Motoyuki Tsuihiji, Hiroyuki Umezawa.
Application Number | 20060266686 11/499532 |
Document ID | / |
Family ID | 33545455 |
Filed Date | 2006-11-30 |
United States Patent
Application |
20060266686 |
Kind Code |
A1 |
Umezawa; Hiroyuki ; et
al. |
November 30, 2006 |
Filtration apparatus
Abstract
A filtration apparatus is provided which is easy to maintain,
manage and which enables preservation of filtration characteristics
due to the fact that filtration is carried out by use of a
gelatinous filter apparatus. In the filtration apparatus,
filtration characteristics can be maintained by providing a bubble
supplying mechanism for removing a sedimentary layer comprising
removables that is formed on a surface of a filtration film and a
filtration characteristics restoring mechanism for restoring the
filter film clogged by the removables by causing a back-flow of
filtered water accumulated in a cistern. Filtration apparatus
maintenance and management are facilitated by improving recovery
efficiency of the precipitated removables by tapering a lower part
inside a raw water tank and providing a recovery tank for
recovering removables via a valve.
Inventors: |
Umezawa; Hiroyuki; (Gunma,
JP) ; Iseki; Masahiro; (Gunma, JP) ; Tsuihiji;
Motoyuki; (Gunma, JP) |
Correspondence
Address: |
FISH & RICHARDSON P.C.
P.O. BOX 1022
MINNEAPOLIS
MN
55440-1022
US
|
Assignee: |
Sanyo Aqua Technology Co.,
Ltd.
Sanyo electric Co., Ltd.
|
Family ID: |
33545455 |
Appl. No.: |
11/499532 |
Filed: |
August 4, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10831585 |
Apr 23, 2004 |
|
|
|
11499532 |
Aug 4, 2006 |
|
|
|
Current U.S.
Class: |
210/216 |
Current CPC
Class: |
B01D 37/02 20130101;
B01D 63/08 20130101; B01D 29/66 20130101; B01D 65/003 20130101;
B01D 65/02 20130101; B01D 2321/04 20130101; B01D 29/114 20130101;
B01D 61/147 20130101; B01D 29/15 20130101; B01D 2321/185 20130101;
B01D 61/20 20130101; B01D 29/39 20130101 |
Class at
Publication: |
210/216 |
International
Class: |
B01D 33/00 20060101
B01D033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 25, 2003 |
JP |
P. 2003-122583 |
Apr 25, 2003 |
JP |
P. 2003-122584 |
Apr 25, 2003 |
JP |
P. 2003-122585 |
Apr 25, 2003 |
JP |
P. 2003-122586 |
Claims
1.-35. (canceled)
36. A filtration apparatus comprising: a tank for housing a fluid
containing removables, a filter apparatus formed of a first filter
immersed inside the tank and a second filter comprising removables
deposited on a surface of the first filter, a pump connected to the
filter apparatus via a pipe, a peel cistern connected to the pipe
and storing filtered water filtered by the filter apparatus,
wherein the peel cistern is located at a level above a fluid level
of the fluid contained in the tank and when the second filter clogs
and a flow rate of the filtered water decreases, the second filter
is removed by causing the filtered water accumulated in the peel
cistern to flow back in the filter apparatus via the pipe.
37. The filtration apparatus of claim 36, wherein a capacity of the
peel cistern is set to be equal or above the sum of the halves of
the inner product of each filter apparatus immersed in the
fluid.
38. The filtration apparatus of claim 36, wherein upon separation
of the second filter, the pump is halted and a suction pressure
applied to the filter apparatus is cancelled.
39. A filtration apparatus comprises: a tank for housing a fluid
containing colloidal removables, a filter apparatus formed of a
first filter immersed inside the tank and a second filter
comprising a gel film attached to a surface of the first filter, a
pump connected to the filter apparatus via a pipe, a peel cistern
connected to the pipe and storing filtered water filtered by the
filter apparatus, wherein the peel cistern is located at a level
above a fluid level of the fluid contained in the tank and when the
second filter clogs and a flow rate of the filtered water
decreases, the gelatinous second filter is removed by causing the
filtered water accumulated in the peel cistern to flow back to the
filter apparatus the via the pipe
40. The filtration apparatus of claim 39, wherein a capacity of the
peel cistern is set to be equal or above the sum of the halves of
the inner product of each filter apparatus immersed in the
fluid.
41. The filtration apparatus of claim 39, wherein upon separation
of the second filter, the pump is halted and a suction pressure
applied to the filter apparatus is cancelled.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of priority to Japanese
Patent Applications Nos. 2003-122583, 2003-122584, 2003-122585 and
2003-122586 filed on Apr. 25, 2003, contents thereof being hereby
incorporated by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to a filtration apparatus, and
more particularly to a filtration apparatus which is easy to
maintain and manage and which enables preservation of filtration
characteristics.
DESCRIPTION OF THE BACKGROUND ART
[0003] At present, companies are faced with very important and
challenging ecological issues such as reducing industrial waste,
sorting out industrial waste and recycling or avoiding discharge of
industrial waste into the nature. One type of industrial waste
comprises various fluids containing contaminants.
[0004] These fluids have different denominations, such as for
instance sewage water, drainage, effluent, etc., but in the
description to follow, fluids, like for example water, chemicals,
etc. comprising materials which are contaminants are called
wastewater. Such wastewater is filtered using very expensive
filtration apparatuses to remove the contaminants therein. The
resulted clean water is recycled, whereas the separated
contaminants or the residues which could not be filtered are
disposed of as industrial waste. In particular, water is filtered
to a level of purity which meets the environmental standards and is
then discharged into the nature, in rivers, seas, or the like, or
is otherwise recycled.
[0005] However, the usage of these filtration apparatuses is
extremely difficult and becomes an environmental issue in itself
due to a high running cost and equipment cost, etc. of the
filtration process, etc.
[0006] As can be understood from the above, technology and
techniques for wastewater treatment raise an important issue in
terms of environmental pollution and recycling and therefore a
system with a low initial cost and low running cost is promptly
required.
[0007] An example of wastewater treatment in the semiconductor
field is described in the following. When a plate-like metal,
semiconductor or ceramic, etc. is polished or ground, a liquid such
as water, etc. is showered on the polishing (grinding) jig and the
plate due to considerations such as prevention of temperature rise
of the polishing (grinding) jig, etc. caused by friction,
improvement of lubricating property, prevention of polishing waste
or cutting waste adherence, etc. to the plate.
[0008] In more detail, pure water is caused to flow during the
process of dicing or backgrinding a semiconductor wafer comprising
a plate-like semiconductor material. In a dicing apparatus, a flow
of pure water is provided on the semiconductor wafer or pure water
is showered by means of a discharge nozzle such that the blade is
exposed to the pure water in order to prevent a rise in the
temperature of the dicing blade and prevent adherence of dicing
waste to wafer. Pure water is also used due to similar
considerations in a process of thinning the wafer by
backgrinding.
[0009] The wastewater containing polishing waste or grinding waste
discharged from the above dicing apparatus or backgrinding
apparatus is filtered and the clean water obtained thereby is
returned into nature or is recycled, whereas the concentrated
wastewater is recovered.
[0010] At present, two methods are employed in the semiconductor
manufacturing process for the treatment of wastewater containing
contaminants (waste) comprising mainly Si: the flocculation method
and a method combining filter filtration and a centrifugal
separator.
[0011] In the flocculation method, PAC (polychlorinated aluminum)
or Al.sub.2(SO.sub.4).sub.3 (aluminum sulfate), or the like is
mixed in the wastewater as flocculant to generate a reaction with
the Si and filtration is carried out by removing the reaction.
[0012] In the method combining filter filtration and a centrifugal
separator, after the wastewater is filtered, the concentrated
wastewater is fed to the centrifugal separator and silicon waste is
collected as sludge, whereas the clean water resulted from the
filtration process is discharged into the nature or is
recycled.
[0013] For instance, wastewater generated in the dicing process is
collected in a raw water tank 201 and is fed to a filtration
apparatus 203 via pump 202 as shown in FIG. 16. The filtration
apparatus 203 is provided with a ceramic and an organic filter F
and the water filtered thereby is fed to a recycled water tank 205
via a pipe 204, to be further recycled or discharged into the
nature.
[0014] The filtration apparatus 203 is periodically washed due to
clogging of the filter F. The filter F is back-washed with the
water inside the recycled water tank 205 by closing valve B1
provided in the raw water tank 201 and opening valve B3 and valve
B2 which feed washing water from the raw water tank 201. The
wastewater thus generated and having a high concentration of Si
waste mixed therein is returned to the raw water tank 201. The
concentrated water in the concentrated water tank 206 is fed to the
centrifugal separator 209 by means of a pump 208 and the
centrifugal separator 209 separates the sludge and the separate
liquid. The sludge comprising Si waste is collected in a sludge
recovery tank 210, whereas the separate liquid is collected in a
separate liquid tank 211. The wastewater in the separate liquid
tank 211 containing the separate liquid is fed to the raw water
tank 201 by means of a pump 212.
[0015] These methods are also employed when collecting waste
generated during polishing and grinding of, for instance, solids
mainly comprising metal materials such as Cu, Fe, Al, etc., or
solids comprising inorganic materials such as plates, ceramic,
etc., or plates, etc.
[0016] On the one hand, the CMP (Chemical-Mechanical Polishing)
method has emerged as a novel semiconductor process technology. The
CMP technology was brought about by the achievement of plane
insulating film devices and by the implementation of embedded
structures comprising a material different from the material of the
substrate.
[0017] Plane insulating film devices are formed by forming a highly
accurate micropattern using the lithography technology. Together
with the Si wafer attachment technology, etc., this achievement
provides the potential for the implementation of three-dimensional
ICs.
[0018] With respect to the implementation of embedded structures,
conventionally, a technology is used where tungsten (W) is embedded
in the multilayer wiring of an IC. Here, W is embedded in the
grooves of an interlayer film by the CVD method and a surface
thereof is planarized by etch-back. However, recently, the CMP
method is used in the planarization process. The embedding
technology can be applied in the Damascene process and elements
separation. The CMP technology and its applications are described
in detail in "CMP Science" published by Science Forum.
[0019] Next, the mechanism of the CMP technology is described. As
shown in FIG. 17, a semiconductor wafer 252 is placed on an
abrasive cloth 251 provided on a rotating table 250 and the uneven
surface of the wafer 252 is leveled by lapping, polishing and
chemical etching while causing a polishing material (slurry) 253 to
flow. Planarization is obtained by a mechanical polishing process
between a chemical reaction of a solvent included in the polishing
material 253 and a polishing abrasive coating included in the
abrasive cloth and the polishing material. Foamed polyurethane,
non-woven cloth, etc. can be used as the abrasive cloth 251,
whereas the polishing material is a material comprising polishing
abrasive coating such as silica, alumina, etc. mixed with water
comprising a pH adjuster, and is generally known as slurry. Lapping
is carried out by applying a constant pressure while rotating the
wafer 252 in the abrasive coat and causing the slurry 253 to flow.
A dresser 254 has the function of maintaining the polishing
capabilities of the abrasive cloth 251 and always keeps a surface
of the abrasive cloth 251 in a dressed state. Motors 202, 208 and
212 and belts 255, 256 and 257 are also provided.
[0020] The above-described mechanism is constructed as a system, as
shown in FIG. 18. This system can be divided in a wafer cassette
loading/unloading station 260, a wafer reprint mechanical section
261, a polishing mechanical section 262 as described with reference
to FIG. 17, a wafer washing mechanical section 263 and a control
system controlling all these elements.
[0021] First, the cassette 264 comprising wafers is placed in the
wafer cassette loading/unloading station 260 and a wafer inside the
cassette 264 is removed. Next, the wafer reprint mechanical section
261 holds the wafer with, for instance, a manipulator 265 and
places it on the rotating table 250 provided in the polishing
mechanical section 262. Planarization of the wafer is carried out
using the CMP technology. When the planarization process is
finished, the wafer is fed to the washing mechanical section 263 by
the manipulator 266 and is washed in order to wash away the slurry.
The washed wafer is housed in a wafer cassette 266.
[0022] The amount of slurry used in one process is, for instance,
around 500 cc to 1 liter/wafer. Also, pure water is caused to flow
in the polishing mechanical section 262 and wafer washing
mechanical section 263. Thus, the total amount of wastewater, at
drainage, discharged in one planarization process is around 5
liters to 10 liters/wafer. For example, in case of a 3-layered
metal, the planarization process is carried out about 7 times for
metal planarization and interlayer dielectric film planarization,
accordingly, the wastewater amount discharged until one wafer is
completed is 5 to 10 liters multiplied by 7. Thus, it can be
understood that by using the CMP apparatus, the amount of slurry
diluted by pure water and discharged is quite large. The wastewater
is then treated by the flocculation method.
[0023] However, with the flocculation method, chemicals are
injected as flocculants. Nevertheless, it is extremely difficult to
specify the amount of chemicals that fully react and a large amount
of chemicals which do not react is left. By contrast, if the amount
of chemicals is low, not all of the contaminants are coagulated and
are left un-separated. In particular, if the amount of the
chemicals is large, chemicals are left in the clear supernatant
liquid and therefore, because chemicals remain in the filtered
liquid, reuse thereof is impossible at when further chemical
reactions need to be carried out.
[0024] Flocks which are reactions of the chemicals and contaminants
are generated by the suspension of algae. The formation of flocks
requires very strict pH conditions, an agitator, a pH measurement
device, a flocculating agent implantation device, and a controlling
device, for controlling all of these elements, etc. Also, in order
to stabilize and cause precipitation of the flocks, a huge
precipitation tank is required. For instance, for a wastewater
processing capability of 3 m.sup.3/1 h, a tank having about 3
meters in diameter and about 4 meters in depth (around 15 tones) is
needed, so that the entire system becomes a huge system requiring a
compound of about 11 meters by 11 meters.
[0025] However, there are also flocks that keep floating without
precipitating in the precipitation tank. It is therefore possible
that they are discharged to the exterior and recovery thereof is
very difficult. Due to size considerations, initial cost of this
system is expensive, reuse of water is difficult and the running
cost generated by the use of chemicals is very expensive.
[0026] In a method combining filter filtration (5 m.sup.3/1 h) and
a centrifugal separator, as shown in FIG. 16, a filter F (it is
called a UF module and comprises polysulfone fiber or ceramic
filter) is used in the filtration apparatus 203 which enables reuse
of water. Four filters F are attached in the filtration apparatus
203, one filter costing around 50000 yen and having a life span of
no more than a year. Due to the fact that filter F is a pressurized
filtration method, the filter clogs and the load to the motor of
pump 202 increases thus requiring a high-capacity pump 202.
Moreover, 2/3 of the wastewater passing through the filter F are
returned into the raw water tank 201 and because the wastewater
containing removables is supplied using pump 202, the inner walls
of the pump 202 are chipped and the life span of the pump 202 is
extremely short.
[0027] To summarize, running cost, including extremely high power
consumption by the motor, high costs associated with replacement of
the pump P and filter F, becomes extremely high.
[0028] Moreover, with the CMP method, in the dicing process, a very
large amount of wastewater is discharged. Colloid slurry is
distributed in the fluid, but due to a Brownian motion, they do not
precipitate. Particles of the abrasive coating mixed in the slurry
have a diameter of 10 thru 200 nm, in other words, they are very
fine particles. Consequently, when the slurry comprising very fine
abrasive coating is filtered through the filter, particles enter
the holes provided in the filter causing clogging. The filter clogs
very frequently so that it is impossible to filter a large amount
of wastewater.
[0029] As can be understood from the above description, in order to
remove as much as possible all materials that may cause damage to
the environment and to recycle filtered fluid and removables
separated in the filtration process, the wastewater filtration
system becomes a huge system due to various additional apparatuses,
thus triggering extremely high initial cost and running cost.
Accordingly, wastewater treatment apparatuses until now, could not
be easily installed and used for wastewater treatment.
[0030] When using a self-generated film (pre-coat filter) to filter
the wastewater, control of the pump carrying out filtration is very
difficult.
[0031] Furthermore, in order to recover the removables precipitated
at the bottom of the tank, filtration process is temporarily halted
in order to discharge the fluid inside the tank. This led to a
reduction of filtration efficiency.
[0032] Also, when filtration is carried out in a filtration
apparatus having a self-generated filter, there is no appropriate
method of removing the self-generated film which clogged.
SUMMARY OF THE INVENTION
[0033] A first aspect of the present invention thereby provides a
tank for housing a fluid containing removables, a filter apparatus
for filtering the fluid, an air diffuser located under the filter
apparatus and generating air bubbles inside the fluid, an air pump
for supplying gas via an air pipe connected to the air diffuser,
wherein the air pipe is provided with an adjustment valve regulated
in advance so that a predetermined amount of gas is caused to pass,
and a stop valve for blocking or releasing the gas that passes
inside the air pipe.
[0034] A further aspect of the present invention provides a tank
for housing a fluid containing colloidal removables, a filter
apparatus formed of a first filter immersed inside the tank and a
second filter comprising a gel film adhered to a surface of the
first film, an air diffuser located under the filter apparatus and
generating air bubbles inside the fluid, an air pump for supplying
gas via an air pipe connected to the air diffuser, wherein the air
pipe is provided with an adjustment valve regulated in advance so
that a predetermined amount of gas is caused to pass, and a stop
valve for blocking or releasing the gas that passes inside the air
pipe.
[0035] The present invention enables to set the amount of gas
generated from the air pipe to a desired value by using in
combination the adjustment valve having the amount of gas passing
therethrough regulated in advance and the stop valve for blocking
of releasing the gas flow.
[0036] Another aspect of the present invention provides a tank for
housing a fluid containing removables, a filter apparatus formed of
a first filter immersed inside the tank and a second filter
comprising removables deposited on a surface of the first filter, a
pump connected to the filter apparatus via a pipe, wherein the
second filter is formed by the passage of the fluid through the
first filter by applying a suction pressure of the pump and the
filter apparatus thus having the second filter formed filters the
fluid by causing the fluid to pass by applying a suction pressure
of the pump, wherein the suction pressure of the pump in a process
of forming the second filter is larger than in a process of
filtering the fluid.
[0037] A further aspect of the present invention provides a tank
for housing a fluid containing colloidal removables, a filter
apparatus formed of a first filter immersed inside the tank and a
second filter comprising a gel film adhered to a surface of the
first layer, a pump connected to the filter apparatus via a pipe,
wherein the second filter is formed by the passage of the fluid
through the first filter by applying a suction pressure of the pump
and the filter apparatus thus having the second filter formed
filters the fluid by causing the fluid to pass by applying a
suction pressure of the pump, wherein the suction pressure of the
pump in the process of forming the second filter is larger than in
the process of filtering the fluid.
[0038] Accordingly, the present invention enables a smooth
formation of a second filter which is a self-generated film and a
smooth filtration by means of the second filter by regulating the
suction pressure of a pump.
[0039] Another aspect of the present invention provides a tank for
housing a fluid containing removables, a filter apparatus immersed
inside the tank, a recovery tank for removables precipitation which
communicates with a lower part of the tank via a valve, wherein the
recovery tank is detachable from the tank by closing the valve and
detaching the recovery tank from the tank to thus recover
removables precipitated in the recovery tank.
[0040] A further aspect of the present invention provides a tank
for housing a fluid containing colloidal removables, a filter
apparatus formed of a first filter immersed inside the tank and a
second filter comprising a gel film adhered to a surface of the
first filter, a recovery tank for removables precipitation which
communicates with a lower part of the tank via a valve, wherein the
recovery tank is detachable from the tank by closing the valve and
detaching the recovery tank from the tank to thus recover
removables precipitated in the recovery tank.
[0041] Accordingly, in the present invention, a detachable recovery
tank is provided in lower part of a tank carrying out a filtration
process to enable recovery of the precipitated removables by simply
detaching the recovery tank from the tank. It is also possible to
recover the precipitated removables without halting the filtration
operation.
[0042] Another aspect of the present invention provides a tank for
housing a fluid containing removables, a filter apparatus formed of
a first filter immersed inside the tank and a second filter
comprising removables deposited on a surface of the first filter, a
pump connected to the filter apparatus via a pipe, a peel cistern
connected to the pipe and storing filtered water filtered by the
filter apparatus, wherein the peel cistern is located at a level
above the fluid level of the fluid contained in the tank and when
the second filter clogs and the flow rate of the filtered water
decreases, the second filter is removed by causing the filtered
water accumulated in the peel cistern to flow back to the filter
apparatus via the pipe.
[0043] A further aspect of the present invention provides a tank
for housing a fluid containing colloidal removables, a filter
apparatus formed of a first filter immersed inside the tank and a
second filter comprising a gel film adhered to a surface of the
first film, a pump connected to the filter apparatus via a pipe, a
peel cistern connected to the pipe and storing filtered water
filtered by the filter apparatus, wherein the peel cistern is
located at a level above the fluid level of the fluid contained in
the tank and when the second filter clogs and the flow rate of the
filtered water decreases, the gelatinous second filter is removed
by causing the filtered water accumulated in the peel cistern to
flow back in the filter apparatus via the pipe.
[0044] Accordingly, when the second filter which is a
self-generated film clogs, the second filter is removed by causing
the filtered water accumulated in the peel cistern to flow back to
the filter apparatus. Thus, the present structure enables the
removal of the second filter by a very simple structure.
[0045] Typically, in order to remove particles equal to or smaller
than 200 nm like the abrasive coating contained in CMP slurry, a
filter film comprising holes smaller in size than the size of the
particles is generally adopted. However, in the present invention,
a gel film comprising removables is used as a filter and the
numerous spaces formed in the filter are used as passages for the
fluid. Here, the filter itself is an aggregation of removables
particles and filtration characteristics thereof can be preserved
by removing the removables causing the clogging from the filter.
Even if the filter comprising the gel film clogs after prolonged
filtration, the filter is regenerated and filtration can be
continued for a long time.
[0046] With this invention, an air pipe connecting an air diffuser
54 that generates air bubbles inside raw water with an air pump 55
is provided with an adjustment valve and a stop valve. The
adjustment valve is configured so that a desired predetermined
amount of gas is caused to pass therethrough. Accordingly, the
desired amount of gas can be provided to the air diffuser by
opening or closing the stop valve.
[0047] The air pipe is provided with a plurality of paths, each of
the paths being provided with an adjustment valve and a stop valve,
respectively, for allowing a different amount of gas to pass
therethrough. Thus, by opening only one of the stop valves and
closing the other stop valves, a desired amount of gas can be
provided to a raw water tank.
[0048] In a filtration apparatus where filtration is carried out by
using a second filter which is a self-generated film, filtered
water from a filter apparatus 53 is removed by applying the suction
pressure of a pump that has an adjustable motor. In a process of
forming the second filter which is a self-generating film, the
motor is caused to rotate at a high speed, whereas in a process of
filtration using the self-generated film thus formed, the motor can
be caused to rotate at a low speed. Thus, in the process of forming
the second filter, a second filter can be formed promptly, whereas
in the process of filtration, destruction of the second filter by
applying an excessive suction pressure is prevented.
[0049] Furthermore, in case the second filter is a gelatinous
self-generating film, the gel can be kept at a desired degree of
swelling by causing the motor to rotate at a low speed during the
filtration process. Also, the gelatinous second filter can be
prevented from entering in the holes provided in the first
filter.
[0050] Removables concentrated in the filtration process can be
precipitated in a recovery tank 15 which communicates with a lower
part of a raw water tank 50 where filtration is carried out.
Moreover, the recovery tank 15 is detachable from the filtration
apparatus thus enabling recovery of the removables precipitated
inside the recovery tank 15 while he filtration process is
ongoing.
[0051] The raw water tank 50 is formed of a material having
excellent water-shedding qualities and thus, the gelatinous
removables consolidate by a tensile force of a surface thereof and
are moved into the recovery tank 15. The gelatinous removables can
be prevented from adhering to inner walls of the raw water tank
50.
[0052] The filtered water filtered by the filter apparatus 53 is
accumulated in a peel cistern 70 and when the second filter which
is a self-generated film clogs, the second filter is removed by
causing the filtered water from the peel cistern 70 to flow back. A
mechanism is thus provided for removing the second filter without
the need for another pump, etc.
[0053] In order to remove microparticles mainly equal to or smaller
than 0.15 .mu.m like the abrasive coating contained in CMP slurry,
a filter film comprising holes smaller in size than the size of the
microparticles is generally adopted. However, the filtration
apparatus hereby provided forms a gel film filter comprising
removables of a colloidal solution and filtration is carried out
without the need of a filter film comprising mainly holes equal to
or smaller than 0.15 .mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
[0054] FIG. 1 shows a filtration apparatus according to an
embodiment of the invention.
[0055] FIG. 2 shows a filtration apparatus according to an
embodiment of the invention.
[0056] FIG. 3 shows a filtration apparatus according to an
embodiment of the invention.
[0057] FIG. 4 shows a filtration apparatus according to an
embodiment of the invention.
[0058] FIG. 5 shows a concrete filtration apparatus according to an
embodiment of the invention.
[0059] FIG. 6 illustrates the operation of a concrete filtration
apparatus according to an embodiment of the invention.
[0060] FIG. 7 shows a filter apparatus according to an embodiment
of the invention.
[0061] FIG. 8 shows a concrete filter apparatus according to an
embodiment of the invention.
[0062] FIG. 9 illustrates a filter according to an embodiment of
the invention.
[0063] FIG. 10 illustrates the operation principle of the
filter.
[0064] FIG. 11A is a cross-sectional view and FIG. 11B is a
characteristics diagram showing the conditions for the formation of
the second filter film according to an embodiment of the
invention.
[0065] FIG. 12 shows the characteristics of the second filter.
[0066] FIG. 13 shows regeneration of the filter apparatus according
to an embodiment of the invention.
[0067] FIG. 14 shows the operation of a filtration apparatus
according to an embodiment of the invention.
[0068] FIG. 15 shows filtration characteristics according to an
embodiment of the invention.
[0069] FIG. 16 illustrates a conventional filtration system.
[0070] FIG. 17 shows a CMP apparatus.
[0071] FIG. 18 shows a CMP apparatus system.
DETAILED DESCRIPTION OF THE INVENTION
First Embodiment
[0072] Configuration, etc. of a filtration apparatus 20 according
to a first embodiment of the invention is described referring to
FIG. 1. The filtration apparatus 20 comprises a tank 50 for housing
a fluid comprising removables, a filter apparatus 53 for filtering
the fluid, an air diffuser 54 as an air diffusion means, located at
a lower part of the filter apparatus 53 and generating bubbles
inside the fluid, an air pump 55 connected to the air diffuser 54
via an air pipe 40 and supplying gas, wherein the air pipe 40 is
provided with an adjustment valve 41 regulated in advance so that a
predetermined amount of gas is caused to pass, and a stop valve 42
for blocking or releasing the gas that passes inside the air pipe
40. A more detailed description of the configuration of the
filtration apparatus 20 is next provided.
[0073] A raw water tank 50 as shown in FIG. 1 is provided in an
upper part thereof with a pipe 51 as means for supplying
wastewater. The pipe 51 supplies the fluid containing removables to
the tank 50. For instance, to better describe this using
semiconductor-related terms, it is the pipe that supplies
wastewater (raw water) containing removables of a colloidal
solution which flows from dicing apparatuses, backgrinding
apparatuses, mirror polishing apparatuses or CMP apparatuses. A
further description is next given of the wastewater as wastewater
comprising abrasive coating flowing from the CMP apparatus and
waste resulted from polishing or grinding by the abrasive coating.
As shown in FIG. 1, the fluid temporarily stored in a wastewater
reservoir 17 may also be supplied to the raw water tank 50 via the
pipe 51.
[0074] A plurality of filter apparatuses 53 comprising a second
filter are placed in the raw water 52 accumulated in the raw water
tank 50. An air diffuser 54, similar for instance to a bubbling
apparatus used in fish aquariums and having small holes opened in a
pipe thereof, is placed at a lower part of the filter apparatus 53
and the position thereof is adjusted so that air bubbles generated
therefrom can pass through a surface of the filter apparatus 53.
The air diffuser 54 is located along the entire bottom of the
filter apparatus 53 so that air bubbles can be uniformly supplied
in the entire filter apparatus 53. An air pump 55 and the air
diffuser 54 are connected via an air pipe 40.
[0075] The raw water 52 supplied from the pipe 51 is accumulated in
the raw water tank 50 and is filtered by the filter apparatus 53.
The bubbles pass through a surface of a second filter 2 that
adheres to the filter apparatus 53 thus generating a parallel flow
by the climbing power and the burst of the air bubbles, which moves
the gelatinized removables adhered to the second filter 2 so that
they adhere uniformly to the entire filter apparatus 53, thus
preserving filtration capabilities.
[0076] The air pipe 40 connecting the air pump 55 and the air
diffuser 54 is provided with an adjustment valve 41 and a stop
valve 42. The adjustment valve 41 is configured so that a desired
amount of gas is allowed to pass therethrough, for example, a
needle valve, etc. can be adopted as an adjustment valve. The stop
valve 42 controls releasing and blocking of the gas flowing inside
the air pipe 40. More concretely, a valve, etc. using for instance
solenoid, etc., can be employed as the stop valve 42. A desired
amount of gas can be supplied to the air diffuser by using in
combination the adjustment valve 41A and the stop valve 42A, that
is, open only stop valve 42A while fixing an output of the air pump
55.
[0077] Furthermore, a plurality of parallel paths branch off from
the air pipe 40. In more detail, a first path 40A, a second path
40B and a third path 40 C parallel to each other branch off from
the air pipe 40. Each of these paths is provided with adjustment
valve 41 and stop valve 42, respectively.
[0078] A first adjustment valve 41A and a first stop valve 42A are
provided in the first path 40A. The first adjustment valve 41A is
regulated so that an appropriate amount of gas is allowed to pass
during the filtration operation of the filter apparatus 53. During
the filtration process using the filter apparatus 53 or during the
formation process of the gelatinous second filter, the first stop
valve 24A is opened. Also, when the first stop valve 42A is in an
open state, the second stop valve 42B and the third stop valve 42C
are all in a close state. It is thereby possible, in the filtration
process, to supply a moderate amount of gas from the air diffuser
54 via the first adjustment valve 41A thus regulated. Accordingly,
the raw water in the raw water tank 50 is mixed by the air bubbles
rising from the air diffuser 54, thus enabling a smooth
filtration.
[0079] The second adjustment valve 41B and the second stop valve
42B are provided in the second path 40B. The second adjustment
valve 41B is set to allow the passage of a larger amount of gas
than the first adjustment valve 41A. The second stop valve 42B is
opened during the process of removing (regeneration process) the
gelatinous second filter from the first filter, both filters
forming the filter apparatus 53. The second filter can be removed
by supplying a large amount of gas from the air diffuser 54 into
the raw water. When the second stop valve 42B is in an open state,
the first stop valve 42A and the third stop valve 42C are in a
close state.
[0080] The third adjustment valve 41C and the third stop valve 42C
are provided in the third path 40C. The third adjustment valve 41C
is set to allow the passage of a smaller amount of gas than the
first adjustment valve 41A and the second adjustment valve 41B. The
third stop valve 42C is opened when the operation of the entire
filtration apparatus 20 is halted. When the third stop valve 42C is
in an open state, the first stop valve 42A and the second stop
valve 42B are in a close state. Clogging of the air diffuser 54 can
be prevented by maintaining the third stop valve 42C in an open
state when the filtration operation of the entire filtration
apparatus is halted.
Second Embodiment
[0081] Configuration of a filtration apparatus according to a
second embodiment of the invention is basically the same as that
described in the first embodiment, consequently, description is
given only of the differences therebetween.
[0082] FIG. 2A is a schematic diagram of a filtration apparatus 20
according to a second embodiment of the present invention and FIG.
2B is a characteristics diagram showing variation in time of
revolution speed of the motor and the suction pressure inside a
pipe 56.
[0083] The filtration apparatus 20 shown in FIG. 2A comprises a raw
water tank 50 for housing a fluid containing removables, a filter
apparatus 53 comprising a first filter immersed inside the raw
water tank 50 and a second filter comprising removables deposited
on a surface of the first filter, a pump 57 connected to the filter
apparatus 53 via a pipe 56, wherein the second filter is formed by
the passage of the fluid through the first filter by applying a
suction pressure from the pump 57 and the filter apparatus 53 thus
having the second filter formed, filters the fluid by causing the
fluid to pass by applying a suction pressure from the pump 57,
wherein the suction pressure of the pump 57 in the process of
forming the second filter is larger than in the process of
filtering the fluid.
[0084] The pump 57 is coupled with the filter apparatus 53 via the
pipe 56 so that the fluid filtered in the filter apparatus 53 is
discharged to the exterior by the suction power generated by the
pump 57. In the process of forming the second filter or in case the
filtered fluid does not have the desired transparency, the fluid
discharged from the filter apparatus 53 is returned to the raw
water tank 50. In other words, the filtration apparatus 20
according to this embodiment has a process allowing circulation of
filtered water. A barometer 59 for detecting the pressure inside
the pipe 56 is provided therein. The suction pressure of the pump
is controlled by controlling the revolutions of the motor provided
in the pipe, in response to the pressure inside the pipe 56 which
is measured by means of the barometer 59. A peel cistern 70 for
temporarily storing the filtered liquid communicates with the pipe
56.
[0085] Devices comprising an alternating-current motor having a
revolution speed thereof controlled by an inverter circuit, or a
direct-current motor having a revolution speed thereof controlled
by a voltage applied thereto, etc. can be employed as the pump 57.
The use of a motor having a controllable revolution speed enables
variation of the suction pressure applied to the filter apparatus
53 in the second filter formation process and in the filtration
process. Particularly, in the present embodiment, the fluid is
filtered using the gel film formed on the surface of the first
filter. The use of a motor having a controllable revolution speed
enables prevention of the second filter destruction which may be
caused by the gel entering the holes provided in the first filter.
A more detailed description of the gelatinous second filter is
provided later.
[0086] Means other than variation of the motor revolution speed
described above can be used as adjustment means for the suction
pressure applied to the filter apparatus 53. For instance, the
suction pressure applied to the filter apparatus 53 can be adjusted
by fixing the revolution speed of the motor that drives the pump 57
and providing a release valve in the pipe 56. More concretely, the
suction pressure can be decreased by opening the release valve or
can be increased by closing the release valve. The suction pressure
applied to the filter apparatus 53 can also be varied by moving the
position of the pump 57 on a vertical direction.
[0087] Next, the relationship between the suction pressure applied
to the filter apparatus 53 and the revolution speed of the motor
provided in the pump 55 is described with reference to FIG. 2B. The
abscissa axis shows the lapsed time, whereas the vertical axis on
the left shows the suction pressure applied to the filter apparatus
53, in other words, the increase in negative pressure. The vertical
axis on the right shows the revolution speed of the motor operating
the pump 57. The broken line shows the variation of suction
pressure whereas the continuous line shows variation of the motor
revolution speed.
[0088] The filter apparatus 53 is immersed in the raw water 52 and
by operating the pump 57, a second filter which is a self-generated
film is formed on a surface of the first filter. This is the
process in which the second filter is formed. In this process, the
revolution speed of the motor driving the pump 57 is increased as
much as possible in order to allow a prompt formation of the second
filter. Also, here, the discharged filtered water may be returned
into the raw water tank 50.
[0089] In the above process, the second filter which is a
self-generated filter is gradually formed on the surface of the
first filter of the filter apparatus 53. The second filter
comprises removables contained in the fluid and is provided with
very fine holes compared to the holes provided in the first filter.
Along with the formation of the second filter, the suction pressure
gradually decreases. This suction pressure is monitored by the
barometer 59.
[0090] When the suction pressure has reached a predetermined value,
it is determined that the formation of the second filter is
complete and the filtration process is started. The revolution
speed of the motor in the filtration process is slower than the
revolution speed in above process where the second filter is
formed. Accordingly, the suction pressure can be set to be equal or
less than a predetermined value and destruction of the second
filter by applying an excessive suction pressure thereto can be
prevented.
[0091] Filtration capabilities of the second filter decrease with
the progress of the filtration process. The second filter having
decreased filtration capabilities is removed by causing the
filtered water from the peel cistern 70 to flow back into the
filter apparatus 53. The filtered water which is caused to flow
back into the filter apparatus 53 is then returned into the peel
cistern 70 by operating the pump 57. The suction pressure of the
pump 57 at that time is set to be larger compared to that during
the filtration process.
[0092] When the filtration operation is completed, before halting
operation of the filtration apparatus 20, the suction pressure is
reduced compared to that during the filtration process and the pump
is thus operated for a predetermined period of time. The load to
the filtration apparatus 20 when operation thereof is restarted can
thus be reduced.
Third Embodiment
[0093] Configuration of a filtration apparatus according to a third
embodiment of the invention is basically the same as that described
in the first embodiment, consequently, description is given only of
the differences therebetween.
[0094] The configuration, etc. of a filtration apparatus 20
according to a third embodiment of the invention is described with
reference to FIG. 3, where FIG. 3A is a schematic diagram of a
filtration apparatus 20 and FIG. 3B is a cross-sectional enlarged
view of a tapered lower part of a raw water tank 50.
[0095] The filtration apparatus 20 comprises a raw water tank 50
housing a fluid containing removables, a filter apparatus 53
immersed inside the raw water tank 50, a recovery tank 15 that
communicates with a lower part of the raw water tank 50 via a valve
V and where removables precipitate, wherein the recovery tank 15 is
detachable from the raw water tank 50 and the removables
precipitated in the recovery tank 15 are recovered by closing the
valve V and separating the recovery tank 15 from the raw water tank
50.
[0096] The bottom of the raw water tank 50 is tapered and a
lowermost part of the bottom communicates with the recovery tank
15. By forming the bottom of the raw water tank 50 to have a
tapered shape, it is possible to efficiently move the removables
precipitated therein into the recovery tank 15. It is preferable to
employ resins such as polyvinyl chloride, etc. as the material of
the raw water tank 50. The steeper the tapered inclination, the
greater the efficiency in recovering the precipitated removables in
the recovery tank 15. That is, the steeper the tapered inclination,
the easier the removables move below the recovery tank 15 without
adhering to the inner walls of the tapered parts of the raw water
tank 50.
[0097] Air diffusers S are provided in the vicinity of the tapered
inner walls of the raw water tank 50 and are connected with an air
pump 55 via an air pipe 40. An air diffuser 54 has the function of
generating air bubbles inside the raw water tank 52 and is operated
during recovery of the removables accumulated in the recovery tank
15. The removables that adhere to the flat walls of the raw water
tank 50 are removed by the air bubbles generated by the air
diffuser 54 and are moved inside the raw water tank 50.
[0098] The recovery tank 15 communicates with a lower part of the
raw water tank 50 via a valve V. That is, they communicate with
each other when the valve V is in an open state and the
communication thereinbetween is blocked when the valve V is in a
close state.
[0099] A feed section K and a discharge section H are provided in
the recovery tank 15, each being provided with a valve. The feed
section K is used when a large amount of removables are
precipitated inside the recovery tank 15. Air and fluid are
supplied from the feed section K into the recovery tank 15 and the
fluid containing removables can be discharged via the discharge
section H. The valve provided in the discharge section H is opened
to enable recovery of the fluid containing removables.
[0100] While the filter apparatus 53 is operating, the valve V is
in an open state, so that when raw water 52 is supplied in the raw
water tank 50, the inside of the recovery tank 15 is also filled
with raw water 52. The recovery tank 15 may be formed of
transparent materials so that the amount of removables precipitated
inside the recovery tank 15 can be checked visually. The recovery
tank 15 is detachable from the filtration apparatus 20.
[0101] The recovery tank 15 is mounted on a transfer vehicle D,
similar, for instance, to a carriage having wheels.
[0102] An air pump 55 and the air diffuser 54 are connected via an
air pipe 40. The recovery tank 15 communicating with a lower part
of the raw water tank 50 is also provided.
[0103] The pump 57 is coupled with the filter apparatus 53 via pipe
56 so that the suction pressure generated by the pump 57 causes
discharge of the fluid filtered by the filter apparatus 53 to the
exterior.
[0104] The peel cistern 70 is coupled with the pipe 56 that
extracts the filtered fluid from the filter apparatus 53 and stores
it.
[0105] Next, operation of the filtration apparatus 20 according to
this embodiment is described with reference to FIG. 3A and FIG.
3B.
[0106] First, raw water 52 is supplied into the raw water tank 50.
Then, the second filter which is a self-generating film is formed
on the filtration surface of the first filter by allowing the
passage of raw water 52 into the filter apparatus 53 by applying a
suction pressure from the pump 55. At this stage, the fluid that
passes through the pipe 56 is not sufficiently filtered and may
therefore be returned to raw water 52. At this stage, the valve V
is in an open state so that raw water is also supplied in the
recovery tank 15.
[0107] Next, the filtration process of the raw water 52 is started
using the filter apparatus 53 which has a second filter 2
sufficiently formed thereon. At this stage, the filtered water
obtained from the filter apparatus 53 has sufficient transparency
and accordingly, it can be discharged to the exterior of the
filtration apparatus 20. A part of the filtered water is stored in
the peel cistern 70.
[0108] As the filtration process progresses, the second filter 2
gradually clogs and the amount of the filtered water that can be
obtained is reduced. Next, a process of removing the second filter
2 is carried out. First, the pump 55 which applies a suction
pressure to the filter apparatus 53 is halted. Then, the filtered
water accumulated in the peel cistern 70 is caused to flow back to
the filter apparatus 53 via the pump 56. The filtered water is
caused to flow back into center (hollow area) 5 of the filter
apparatus 53 so that the pressure acting from inside to outside is
applied to the filter apparatus 53. This pressure removes the
second filter 2 from the filter 1 and moves it downward. In order
to facilitate the movement of the second filter, a large amount of
air bubbles are generated from the air diffuser 54.
[0109] The removed second filter is moved to the recovery tank 15
via the bottom of the tapered raw water tank 50, as shown in FIG.
3B. As described, the raw water tank 50 is made of a material which
has excellent water-shedding qualities. Accordingly, residues of
the second filter comprising gelatinous removables solidify based
on the surface tensile force. The so-solidified removables are
moved to the recovery tank 15 sliding down the inner walls of the
tapered raw water tank 50.
[0110] When a certain amount of removables are accumulated inside
the recovery tank 15, they are recovered. First, air bubbles are
generated from the air diffusers S to cause removables adhered to
the inner walls of the raw water tank 50 to precipitate in the
recovery tank 15. Next, the valve V is closed and the recovery tank
15 is detached from the raw water tank 50. The recovery tank 15 is
then detached from the filtration apparatus 20 and raw water 52
accumulated therein and containing a large amount of removables is
discharged. After that, the recovery tank 15 is attached to the
filtration apparatus 20 and the valve V is closed so that raw water
inside the raw water tank 50 is supplied inside the recovery tank
15 and the recovery tank 15 is once again filled with raw water 52.
The transfer vehicle D is used to move the recovery tank 15 when
the raw water inside the recovery tank 15 is discharged. The
recovery operation of the removables can be carried out while the
filter apparatus 53 is in operation.
Fourth Embodiment
[0111] Configuration of a filtration apparatus according to a
fourth embodiment of the invention is basically the same as that
described in the first embodiment, consequently, description is
given only of the differences therebetween.
[0112] FIG. 4A is a schematic diagram of a filtration apparatus 20
according to this embodiment and FIG. 4B is a cross-sectional
enlarged view of a filter apparatus.
[0113] The filtration apparatus 20 as shown in FIG. 4A comprises a
raw water tank 50 housing a fluid containing removables, a recovery
tank communicating with a lower part of the raw water tank 50, a
filter apparatus 53 immersed inside the raw water tank 50 and
comprising a first filter and a second filter containing removables
deposited on a surface thereof, a pump 57 connected to the filter
apparatus 53 via a pipe 56, a peel cistern 70 connected with the
pipe 56 and storing filtered water filtered by the filter apparatus
53, wherein the peel cistern 70 is located at a level above the
fluid level of the fluid contained in the raw water tank and when
the second filter 2 clogs and the flow rate of the filtered water
decreases, the second filter 2 is removed by causing the filtered
water accumulated in the peel cistern 70 to flow back into the
filter apparatus 53 via the pipe 56.
[0114] The filter apparatus 53 as shown in FIG. 4B comprises a flat
membrane first filter 1 and a second filter 2 which is a
self-generated film formed on a surface thereof. Here, a fluid
containing very fine colloidal removables is employed as raw water
so that the second filter 2 has a gelatinous aspect. A more
detailed description of the filter apparatus 53 is given later.
[0115] Raw water 52 supplied from a pipe 51 is accumulated in the
raw water tank 50 where it is filtered by the filter apparatus 53.
A parallel flow which is generated by the climbing power and the
bursting of air bubbles passing through a surface of the second
filter 2 attached to the filter apparatus 53, moves the gelatinous
removables adhered to the second filter, thus causing the
removables to attach uniformly the entire filter apparatus 53 so
that filtration capabilities thereof are maintained.
[0116] Pump 57 is connected to the filter apparatus 53 via the pipe
56. The fluid filtered in the filter apparatus 53 is discharged to
the exterior by applying a suction pressure from the pump 57. The
fluid removed from the filter apparatus 53 is returned into the raw
water tank 50 during the second filter formation process or in case
the filtered fluid does not have a desired degree of transparency.
In other words, the filter apparatus 53 of this embodiment has a
process of causing the filtered water to circulate. A cistern 70
for peel purposes temporarily storing filtered fluid is provided so
as to communicate with the pope 56.
[0117] The peel cistern 70 is coupled to the pipe 56 which extracts
filtered fluid from the filter apparatus 53 and stores it. The
capacity of the peel cistern 70 is equal or more than the sum of
the halves of the inner product of each filter apparatus 53
immersed in the raw water 52. More explicitly, in the process of
removing the second filter, the capacity of the peel cistern 70 is
configured so that a quantity of filtered water equal to or larger
than half of the inner product of each filter apparatus 52 can be
caused to flow back to each filter apparatus 53. The peel cistern
70 is located at a level above the fluid level of the raw water 52.
The filtered fluid accumulated in the peel cistern 70 is caused to
flow back inside the filter apparatus 53 by the hydraulic pressure
generated by the positional relationship of the peel cistern 70 and
the raw water 52.
[0118] Next, operation of the filtration apparatus 20 according to
this embodiment is described with reference to FIG. 4A and FIG.
4B.
[0119] First, raw water 52 is supplied into the raw water tank 50.
The second filter 2 which is a self-generated film is formed on the
filtration surface of the first filter 1 by causing the raw water
52 to pass through the filter apparatus 53 by applying a suction
power from the pump 55. At this stage, the fluid that passes
through the pipe 56 is not sufficiently filtered and is therefore
turned to raw water 52. Also, the filtered water at this stage is
not stored in the peel cistern 70.
[0120] Next, the raw water 52 is filtered using the filter
apparatus 53 having a second filter 2 sufficiently formed. At this
stage, the filtered water obtained from the filter apparatus 53 has
a sufficient degree of transparency and can therefore be discharged
outside the filtration apparatus 20. Also, a part of the filtered
water is stored in the peel cistern 70.
[0121] As the filtration process progresses, the second filter 2
gradually clogs, as shown in FIG. 4B, and the amount of filtered
water decreases. A process of removing the second filter 2 is then
carried out. First, the pump 55 which inputs a suction power to the
filter apparatus 53 is halted so that the filtered water stored in
the peel cistern 70 is caused to flow back into the filter
apparatus via the pipe 56. The filtered water is caused to flow
back into center 5 of the filter apparatus 53 so that the pressure
acting from inside to outside is applied to the filter apparatus
53. This pressure removes the second filter 2 from the first filter
1 and moves it downward. In order to facilitate the movement of the
second filter, a large amount of air bubbles are generated from an
air diffuser 54.
[0122] Merits of the above described configuration are described
below. In this embodiment, the peel cistern 70 is positioned at a
level above the liquid level of the raw water 52 where the filter
apparatus 53 is immersed. The filtered water accumulated in the
peel cistern 70 can thus be caused to flow back inside the filter
apparatus 53 by the hydraulic pressure generated by the positional
relationship of the peel cistern 70 and the raw water 52, without
the need to use additional pumps.
[0123] Furthermore, clogging inside the first filter 1 can be
prevented by causing pure filtered water filtered by the filter
apparatus 53 to flow back. The holes provided in the first filter 1
are very fine, therefore, in case tap water or the like is used in
the flow-back process, removables contained in the tap water cause
the first filter 1 to clog from the inside. In this embodiment,
clogging of the first filter 1 during the flow-back process can be
prevented and cost of filtration can be reduced by using, in the
flow-back process, filtered water generated by the filter apparatus
53 itself. Distilled water, etc. can also be supplied into the peel
cistern, instead of filtered water.
Fifth Embodiment
[0124] A concrete example of a filtration apparatus is next
described with reference to FIG. 5, wherein configuration elements
which are same as those of the filtration apparatuses shown in
FIGS. 1 thru 4 are denoted by the same numerical symbols.
[0125] In FIG. 5, a pipe 51 is provided as a means for wastewater
supply above a raw water tank 50. The pipe 51 supplies a fluid
containing removables into the raw water tank 50. For instance, to
better describe this using semiconductor-related terms, it is the
pipe that supplies wastewater (raw water) containing removables of
a colloidal solution which flows from dicing apparatuses,
backgrinding apparatuses, mirror polishing apparatuses or CMP
apparatuses. A further description is next given of the wastewater
as wastewater comprising abrasive coating flowing from the CMP
apparatus and waste resulted from polishing or grinding by the
abrasive coating.
[0126] An adjustment valve 41 and a stop valve 42 are provided in
an air pipe that connects an air pump 55 and an air diffuser 54.
The adjustment valve 41 is configured so that a desired amount of
gas is allowed to pass therethrough, for example, a needle valve,
etc. can be adopted as an adjustment valve. The stop valve 42
controls releasing and blocking of the gas flowing inside the air
pipe 40. More concretely, a valve, etc. using for instance
solenoid, etc., can be employed as the stop valve 42. A desired
amount of gas can thus be supplied to the air diffuser 54 by using
in combination an adjustment valve 41A and the stop valve 42, that
is, only open/close stop valve 42 while fixing an output of the air
pump 55.
[0127] Furthermore, a plurality of parallel paths branch off from
the air pipe 40. In more detail, a first path 40A, a second path
40B and a third path 40 C parallel to each other branch off from
the air pipe 40. Each of these paths is provided with the
adjustment valve 41 and stop valve 42, respectively.
[0128] A first adjustment valve 41A and a first stop valve 42A are
provided in the first path 40A. The first adjustment valve 41A is
regulated so that an appropriate amount of gas is allowed to pass
during the filtration operation of the filter apparatus 53. During
the filtration process using the filter apparatus 53 or during the
formation process of the gelatinous second filter, the first stop
valve 24A is opened. Also, when the first stop valve 42A is in an
open state, the second stop valve 42B and the third stop valve 42C
are both in a close state. It is thereby possible, in the
filtration process, to supply a moderate amount of gas from the air
diffuser 54 via the first adjustment valve 41A thus regulated.
Accordingly, the raw water in the raw water tank 50 is mixed by the
air bubbles rising from the air diffuser 54, so that a smooth
filtration is enabled.
[0129] The second adjustment valve 41B and the second stop valve
42B are provided in the second path 40B. The second adjustment
valve 41B is set to allow the passage of a larger amount of gas
than the first adjustment valve 41A. The second stop valve 42B is
opened during the process of removing (regeneration process) the
gelatinous second filter from the first filter, both filters
forming the filter apparatus 53. The second filter can be removed
by supplying a large amount of gas from the air diffuser 54 into
the raw water. When the second stop valve 42B is in an open state,
the first stop valve 42A and the third stop valve 42C are in a
close state.
[0130] The third adjustment valve 41C and the third stop valve 42C
are provided in the third path 40C. The third adjustment valve 41C
is set to allow the passage of a smaller amount of gas than the
first adjustment valve 41A and the second adjustment valve 41B. The
third stop valve 42C is opened when the operation of the entire
filtration apparatus 20 is halted. When the third stop valve 42C is
in an open state, the first stop valve 42A and the second stop
valve 42B are in a close state. Clogging of the air diffuser 54 can
be prevented by maintaining the third stop valve 42C in an open
state when the filtration operation of the entire filtration
apparatus 20 is halted.
[0131] The pipe 56, wherein filtered fluid filtered in the filter
apparatus 53 flows, is connected to a magnet pump 57 which suctions
via a valve V1. A pipe 58 connects the magnet pump 57 with a valve
V3 and a valve V4 via a control valve CV1. A first barometer 59 is
provided after the valve V1 of the pipe 56 for measuring a suction
pressure Pin. A flowmeter F and a second barometer 60 are provided
after the control valve CV1 of the pipe 58, wherein the flowmeter
61 controls a constant flow rate. A control valve CV2 controls the
flow rate of the air from the air pump 55.
[0132] A plurality of filter apparatuses 53 comprising a second
filter are placed in the raw water 52 accumulated in the raw water
tank 50. An air diffuser 54, similar for instance to a bubbling
apparatus used in fish aquariums and having small holes opened in a
pipe thereof, is placed at a lower part of the filter apparatus 53
and the position thereof is adjusted so that air bubbles generated
therefrom can pass through a surface of the filter apparatus 53. An
air pump 55 supplies gas to an air diffuser 54 via an air flowmeter
69. An air pump 40 connecting the air diffuser 54 and the air pump
55 is provided with the above-described first path 40A, the second
path 40B and the third path 40C. Also, the first stop valve 42A,
the second stop valve 42B and the third stop valve 42C are
electrically connected with the controller 68.
[0133] The pipe 56 fixed in the filter apparatus 53 and circulated
by filtered fluid filtered by the filter apparatus 53 is connected
to the magnet pump 57 which suctions via a valve V1. The pipe 58
connects the magnet pump 57 and valve V3 and valve V4 via the
control valve CV1. A first barometer 59 is provided after the valve
V1 of the pipe 56 for measuring the suction pressure Pin. A
flowmeter 61 and a second barometer 60 are provided after the
control valve CV1 of the pipe 58, wherein the flowmeter 61 controls
a constant flow rate of the filtered water.
[0134] The pipe 58 is connected to an optical sensor 62, and is
conducted to pipes 63 and 64 branching off from the optical sensor
62. Pipes 63 and 64 contain valves V3 and V4, respectively, which
are opened/closed based on a detection signal from the optical
sensor 62, wherein pipe 63 returns filtered water to the raw water
tank 50 and pipe 64 discharges filtered water to the exterior. The
optical sensor 62 monitors the concentration of the microparticles
contained in the filtered water to determine that the mix rate of
the microparticles is smaller than a desired value, after which
filtration is started. When the filtration process is started, the
valve V3 is closed based on a detection signal from the optical
sensor 62 and the valve V4 is opened to discharge pure water to the
exterior.
[0135] The peel cistern 70 is connected to the pipe 58 via a valve
V5 and has a function of storing the filtered water, which, when
exceeding a constant value, overflows and is returned into the raw
water tank 70 via a pipe 71. A valve V2 is provided at a lower part
of the pipe 71 which is connected to the pipe 56. The peel cistern
is positioned about 10 to 20 cm above the fluid surface of the raw
water tank 50 and is used during the regeneration process of the
second filter.
[0136] A pH regulator 65 and a temperature adjusting device 66 are
provided in the raw water tank 70 for adjusting in particular the
pH of the CMP wastewater to a range of 6 to 7 and for adjusting the
temperature of the wastewater for facilitating the gel formation
process. A liquid level meter 67 monitors the level of the
wastewater in the raw water tank 50 to prevent overflow thereof and
adjusts the inlet flow of the wastewater.
[0137] Furthermore, a controlling device 68 for controlling the
operation of the filtration apparatus is provided. This controls
the control valve CV1, the flowmeters 61 and 69, the pump 57, the
barometers 59 and 60, the optical sensor 62, etc. in the processes
where they are used, respectively, as shown by the dashed line.
[0138] In the second filter formation process, the filtration
process, the second filter regeneration process, the re-filtration
process and the maintenance process, the controlling device 68
opens/closes the valves, etc. and controls the operation of the
pump 57, etc. The operation status thereof in each of the processes
is described below. FIG. 6 shows the operation status of the pump
57, the optical sensor 62, the air pump 55 and each of the valves
in each respective process.
[0139] First, wastewater containing removables of a colloidal
solution is supplied into the raw water tank 50 via a pipe 51. A
number of filter apparatuses comprising only a first filter 1
without a second filter 2 formed thereon are immersed in the raw
water tank leaving a space thereamongst so that a desired
filtration flow rate can be obtained. Concretely, figures here do
not illustrate around 10 to 40 filter apparatuses but these
apparatuses are mounted in a support means. The number of the
filter apparatuses 53 differs depending on the filtration surface
of one filter apparatus 53, and the total filtration surface of the
filter apparatuses 53 depends on the size of the raw water tank
50.
[0140] Next, the second filter 2 formation process is carried out.
The wastewater is caused to circulate inside the raw water tank 50
while suctioning with a weak suction pressure from the pump 57 via
the pipe 56. The circulation path includes the filter apparatus 53,
the pipe 56, the valve V1, the pump 57, the pipe 58, the control
valve CV1, the flowmeter 61, the optical sensor 62, and the valve
V3. The wastewater is thereby suctioned from the raw water tank 50
and is returned to the raw water tank. Air bubbles supplied by the
air pump 55 to the air diffuser 54 via the first path 40A rise up
to the surface of the filter apparatus 53. In other words, the
first stop valve 42A is opened so that a desired amount of gas is
supplied to the air diffuser 54 via the first adjustment valve 41A.
At this time, valves V2, V4, V5, V6 and D are closed.
[0141] A second filter 2 is formed in the first filter 1 of the
filter apparatus 53 by causing the wastewater to circulate so that
the removables of a colloidal solution are finally captured (the
concrete principle thereof is further described). When the
wastewater is suctioned by the pump 57 through the first filter 1
using a weak suction pressure, the microparticles of removables are
gelatinized as they get closer to the first filter and adhere to
the surface of the first filter 1. The gelatinous microparticles
which are larger than filter holes 11 provided in the first filter
1 are absorbed thereby and therefore are gradually deposited on the
surface of the first filter 1, thus forming the second filter 2
which is a gel film. Gelatinous microparticles having a smaller
diameter than the filter holes 11 pass through the first filter,
but, together with the formation of the second filter 2, the water
inside the wastewater is suctioned using these spaces as passages,
and then passes through the first filter 1 to be finally discharged
to the outside as filtered, pure water.
[0142] At this time, the optical sensor 62 monitors the
concentration of the microparticles contained in the filtered water
and after it determines that the mix rate of the microparticles is
lower than a desired value, the filtration process is started.
[0143] When the formation of the second filter 2 is completed, the
filtration process is started. The valve V3 is closed based on the
detection signal from the optical sensor 62, the valve V4 is opened
and the above-described circulation path is closed so that filtered
water can be discharged from valve V4. In this process, the
controlling device 68 controls the flowmeter 61 so that a constant
filtration flow rate is set and clogging of the second filter 2 is
prevented, thereby preserving filtration capabilities thereof for a
long time. As shown in FIG. 12, the suction pressure Pin of the
pump 57 is gradually increased to keep a constant filtration flow
rate. The other elements have the same operation as in the filter
formation process. In this process, gas is supplied to the air
diffuser 54 via the first path 40A.
[0144] When the second filter is damaged due to different causes,
the optical sensor 62 detects the mix rate of the microparticles
and the filtered water is returned into the raw water tank 50 by
closing the valve V4 and opening the valve V3. In other words, the
second filter 2 is restored by returning to the filter formation
process and after that, carrying out the re-filtration process.
[0145] The filtration process is continuously carried out and water
inside the wastewater contained in the raw water tank 50 is
discharged to the outside of the raw water tank 50 as filtered
water thus raising concentration of the removables in the
wastewater. More precisely, the colloidal solution is concentrated
and the viscosity thereof is increased. Due to this, wastewater is
supplied into the raw water tank 50 via a pipe 51 in order to
suppress the rise in the wastewater concentration and improve
filtration efficiency. However, a thick gel film adheres to the
surface of the second filter 2 of the filter apparatus 53 and
eventually causes clogging of the second filter 2 thus blocking
filtration.
[0146] When a thick gel film adheres to the surface of the second
filter 2 of the filter apparatus 53, a decrease in the filtration
flow rate is detected at the flowmeter 61 and the process of
regenerating the second filter is started by the controlling device
68.
[0147] In the filter regeneration process, the pump 57 is halted
thus canceling the negative suction pressure applied to the filter
apparatus 53. At the same time, the valve V2 is opened and the
filtered water stored in the peel cistern 70 in advance is sent
back into center 5 of the filter apparatus 53 via valve V1 by
reversing the flow in the pipe 56.
[0148] Consequently, in the filter regeneration process, the weak
suction pressure is stopped, thus returning to atmospheric pressure
and the first filter 1 of the filter apparatus 53 is restored from
a concave shape caused by the suction pressure to its original
shape. The second filter 2 and the gel film adhered to a surface
thereof similarly return to their original shape. As a result, the
suction pressure causing the gel film to adhere disappears, thus
causing the gel film to lose adsorbability to the filter apparatus
53 and to be influenced by a force triggering swelling of the film
towards the exterior. Furthermore, the peel cistern is positioned
at a level above the fluid level in the raw water tank 50 so that a
hydrostatic pressure generated by the difference of elevation
threbetween is applied by the back flow of the filtered water from
the peel cistern 70 so that the first filter 1 and the second
filter 2 of the filter apparatus 53 are caused to swell to the
exterior. Accordingly, the gel film adhered thereto starts
separating from the filter apparatus 53 by its own weight and by
the hydrostatic pressure. Experiments show that separation begins
from a lower end of the filter apparatus 53 and continues with the
separation of the second filter 2 adhered to the surface of the
first filter 1, similar to an avalanche. Separated parts
precipitate to the bottom of the raw water tank 50. Next, water is
caused to circulate in the circulation path described above and the
second filter 2 is re-formed. In this regeneration process, the
second filter 2 is restored to its original state enabling
re-filtration of wastewater. At this time, the valve V2 is closed
and the valve V5 is opened so that filtered water can be
accumulated into the peel cistern 70 in view of the next filter
regeneration process.
[0149] In order to facilitate the removal of the filter, the amount
of air bubbles generated by the air diffuser 54 may be doubled.
More precisely, the second stop valve 42B is opened whereas the
first stop valve 42A and the third stop valve 42C are closed.
[0150] The re-filtration process is then started and wastewater is
filtered again. Operation is similar with the filtration process.
After repeating the filtration process for a number of times while
regenerating the second filter 2, the concentration of the
removables in the wastewater contained in the raw water tank 70
increases and eventually, the wastewater becomes more and more
viscous. When the concentration of the removables of the wastewater
exceeds a desired concentration value, filtration is halted and the
maintenance process is carried out.
[0151] The maintenance process comprises the step of discharging
the filtered water contained in the pipes 56 and 58 and in the peel
cistern 70 and the step of discharging the wastewater contained in
the raw water tank 50 and the gel accumulated at the bottom
thereof. In the former step, pump 57 and air pump 55 are halted and
control valve CV1, valves V1, V2 and V5 are opened so that the
filtered water inside pipes 56 and 58 and in the peel cistern 70 is
discharged to the outside via a discharge valve D provided in the
pipe 56.
[0152] In the latter stage, the concentrated slurry at the bottom
of the raw water tank 50 is left to precipitate for flocculation
purposes and is then recovered by opening valve V6. The
so-recovered concentrated slurry is heat-dried to further
concentrate it by vaporizing the water contained therein.
Consequently, the amount of slurry handled as industrial waste can
be substantially reduced. The supernatant wastewater is similarly
discharged via valve V6 and is fed back to the filtration process
or is returned to the raw water tank 50.
[0153] Next, an embodiment of the filter apparatus 53 as immersed
inside the raw water tank 50 is described with reference to FIG. 7
and FIG. 8.
[0154] A frame 30 having a frame-like shape as shown in FIG. 7A is
provided on both surfaces thereof with filter films 31 and 32 which
form the first filter. Inner spaces 33 surrounded by the frame 30,
the filter films 31 and 32 which filtrate the wastewater by
applying a pressure from the pipe 34. The filtered water is then
discharged via a pipe 34 sealed to the frame 30. The filter films
31 and 32 and the frame 30 are perfectly sealed so that wastewater
does not enter the spaces 33.
[0155] Filter films 31 and 32 shown in FIG. 7A are thin resin films
and may be warped or damaged when suctioned. Thus, in order to
decrease this space as much as possible and increase filtration
capabilities, it is necessary that these spaces 33 be formed
larger. This is solved by the mechanism shown in FIG. 7B. In this
figure, only 9 spaces 33 are illustrated, but in reality, a larger
number of spaces 33 may be formed. Also, the filter film 31
actually used is a polyolefin polymer membrane having a thickness
of about 0.1 mm, as shown in FIG. 7B by the thin pouched filter
film FT. The frame 30 integrated with the pipe 34 is inserted in
the pouched filter FT and these two are then secured together. The
frame having the filter FT attached thereto is held from both sides
by holding support RG Filter FT is exposed from an opening OP
provided in the holding support RG A more detailed description is
provided with reference to FIG. 8.
[0156] FIG. 7C shows a filter apparatus 53 having a cylindrical
shape. The frame attached to the pipe 34 is cylindrical and is
provided on a side surface thereof with openings OP1 and OP2. Due
to the fact that parts of the side surface corresponding to
openings OP1 and OP2 are removed, support SUS is provided between
the openings for supporting the filter film 31. Next, the filter
film 31 is attached to the side surface.
[0157] The filter apparatus 53 illustrated in FIG. 7B is described
in more detail with reference to FIG. 8. A part 30a corresponding
to the frame 30 from FIG. 7B is described referring to FIG. 8A and
FIG. 8B. At a first sight, part 30a is similar to a cardboard. Thin
resin sheets SHT1 and SHT2 having about 0.2 mm each are stacked and
a plurality of sections SC are provided thereinbetween in a
vertical direction so that a space 33 surrounded by the resin films
SHT1, SHT2 and the section SC is formed. The cross-section of this
space 33 is a rectangle sized 3 mm.times.4 mm, in other words, a
plurality of straws having a rectangular cross-section are aligned
and integrated. Part 30a is called a spacer in the description
below because it maintains the filter film FT on both sides at a
certain interval.
[0158] A plurality of holes HL of 1 mm in diameter are provided on
the surface of the thin resin sheet SHT1 and SHT2 forming the
spacer 30a and the filter film FT is attached to the surface.
Accordingly, the filtered water filtered by the filter film FT
passes through the holes HL and the space 33 and is finally
discharged using the pipe 34.
[0159] The filter film FT is also attached to both surfaces SHT1
and SHT2 of the spacer 30a. Surfaces SHT1 and SHT2 of the spacer
30a comprise parts where no holes HL are formed, so that when
filter film FT1 is attached directly thereto, filter film FT1
corresponding to parts where such holes HL are not formed has no
filtration capabilities and therefore does not allow the passage of
wastewater. Consequently, parts which do not capture removables are
formed. In order to prevent this phenomenon, at least 2 filter
films FT are provided. The outermost filter film TF1 is a filter
film that captures removables. A filter film FT2 is also provided
comprising holes which are formed to be larger than the holes
provided in the filter film FT1 as it draws near the surface SHT1
of the spacer 30a. Consequently, the entire filter film FT1 is
enabled with filtration capabilities even in parts where holes HL
of spacer 30 are not formed, because of the existence of filter
film FT2 allowing removables to be captured on the entire surface
of the filter film FT1, so that a second filter film is formed on
the entire surfaces SH1 and SH2 of both surfaces. In this figure,
for the sake of convenience, filter film SHT1 and SHT2 are formed
as a rectangular sheet, but in reality they are pouched as shown in
FIG. 7B.
[0160] Next, a description is given of how the pouched filter films
SHT1, SHT2, the spacer 30a and the holding support RG are attached
referring to FIG. 8A, FIG. 8C and FIG. 8D.
[0161] FIG. 8A is a completion drawing, FIG. 8C is a figure showing
the apparatus described in FIG. 8A along the A-A line, that is from
the head of the pipe 34 in the extending direction (vertical
direction) of the pipe, FIG. 8D is a sectional view taken along the
B-B line, that is, in a horizontal direction of the filter
apparatus 35.
[0162] As can be understood from FIG. 8A, FIG. 8C and FIG. 8D,
spacer 30a inserted in the pouched filter film FT, including the
filter film FT are held on 4 sides thereof by the holding support
RG. The pouched 3 sides and the remaining side are secured by an
adhesive agent AD1 applied to the holding support RG A space SP is
formed between the remaining side (openings) and the holding
support RG so that filtered water generated in the space 33 is
suctioned by the pipe 34 via the space SP. An adhesive AD2 is
applied in the entire opening OP of the holding support RG so that
it is perfectly sealed and fluid is prevented from entering
therein.
[0163] Space 33 communicates with pipe 34, so that when suction is
applied through pipe 34, the fluid passes via the holes of the
filter film Fr and the holes HL of the spacer 30a and is directed
to the spaces 33. The filtered water can then be discharged to the
exterior via the pipe 34.
[0164] The filter apparatus 53 used here has a configuration as the
one described in FIG. 8 and the size of the frame (holding support
RG) for attaching the filter film is A4 size, more precisely, about
19 cm by 28.2 cm, and 5 to 10 mm in thickness. The filter apparatus
53 is actually on both sides of the frame so that the surface
doubles (surface: 0.109 m.sup.2). However, the number and size of
the filter apparatus is freely selected depending on the size of
the raw water tank 50 and on the filtration rate required.
[0165] Next, the principle of filtering raw water using the
gelatinous second filter is described. At first, terms to be used
in the following description are defined.
[0166] A colloidal solution refers to a medium having
microparticles with a diameter of 1 nm to 1 .mu.m dispersed
therein. These microparticles have a Brownian motion and can pass
through a common filter paper but cannot pass through a
semipermeable membrane. Because electrostatic repulsive force works
between very fine particles having an extremely slow coagulation
rate, chances that they come close to each other are reduced.
[0167] Sol is used as a substantial synonym for colloidal solution,
but sol is different from gel in that it is dispersed in the medium
and shows mobility, so that the microparticles have an energetic
Brownian motion.
[0168] Gel refers to the colloidal particles which have lost their
independent mobility and gather together to solidify. For instance,
when agar or gelatin is melted down in warm water, they disperse
and form a gel. When this gel is cooled down, the resulted gel
loses mobility. Some types of gel can include hydrogel comprising a
large amount of liquid and xerogel dried to some degree.
[0169] Removal and drying of water from a dispersion medium,
addition of electrolyte salts to silica slurry (pH 9 to 10) and
adjustment of pH up to pH 6 or 7, loss of mobility due to cooling
down are just a few of the causes leading to gelatinization.
[0170] Slurry refers to the colloidal solution or the sol used in
polishing and contains particles, fluid and chemicals. Abrasives
used in the CMP process described above are called CMP slurry. CMP
slurry is known to include silica abrasive, aluminum oxide
(alumina) abrasive, cerium oxide (ceria) abrasive, etc. The
abrasive used most frequently is silica abrasive, one type thereof
which is largely used is colloidal silica. Colloidal silica refers
to a dispersion liquid, called silica sol, wherein very fine silica
particles with a colloid size of 7 to 30 nm are dispersed
homogeneously in a water or organic liquid medium without
precipitating. Particles of the colloidal silica are monodispersed
in water so that even if the colloidal silica is left unattended
for more than one year, the colloid particles do not precipitate
almost at all due to their mutual force of repulsion.
[0171] The resent invention provides a method of removing
removables from wastewater by filtering the removables from
wastewater which comprises removables in a colloid fluid or
sol.
[0172] Removables are a colloid fluid (sol) containing a large
amount of microparticles having a particle size distribution of 3
nm to 2 .mu.m, such as for example, silica and alumina used in the
CMP process or abrasive coating such as ceria, etc. and
semiconductor material waste, metal waste and/or insulation film
material waste generated by grinding with abrasive coating. Here,
slurry (W 2000) from tungsten polishing from Cabot Micro
Electronics Co. is used as CMP slurry. The slurry mainly comprises
silica having a pH of 2.5 and a particle size distribution of 10 to
200 nm.
[0173] The basic principle of the present invention is described
with reference to FIG. 9. With the present invention, a fluid
(wastewater) containing removables of a colloid solution (sol) is
filtered using a filter comprising a gel film formed of
removables.
[0174] More concretely, a gel film as a second filter 2 is formed
of CMP slurry comprising removables of a colloid solution on a
surface of a first filter 1 formed of organic polymers. Filters 1
and 2 are immersed inside a tank containing fluid 3 where they
carry out filtration of wastewater containing removables.
[0175] Organic polymers or ceramic can be used in principle as
materials for the first filter 1 considering that a gel film is to
adhere thereto. Here, a polyolefin polymer membrane having a
thickness of 0.1 mm and an average hole diameter of 0.25 .mu.m is
used. FIG. 10B shows a picture of a surface of the polyolefin
filter film.
[0176] The first filer 1, which is a flat membrane provided on both
sides of a frame 4, is immersed perpendicularly in the fluid and
wastewater is suctioned by a pump 6 from center 5 of the frame 4.
Filtrate 7 is then discharged.
[0177] Next, a second filter 2, which is a gel film, adheres to the
entire surface of the first filter 1 by suctioning and gelatinizing
the sol containing removables. Typically, a gel film is a gel which
is believed to have no filtration capabilities. However, with this
invention, the gel film is endowed with filtration capabilities by
selecting the gel film formation conditions. These conditions are
described later.
[0178] After the second filter 2 which is a gel film made of
removables of a colloid solution (sol) is formed, filtration of the
removables is carried out. This is described with reference to FIG.
9 and FIG. 10A.
[0179] The first filter 1 is provided with filter holes 11. The
film formed as a layer in the openings of the filter holes 11 and
on the surface of the first filter 1 is a gel film formed of
removables 13. Removables 13 are absorbed via the first filter by
applying a suction pressure from a pump, moisture from the fluid 3
is removed by drying (dehydration) so that microparticles of the
removables from the colloid fluid merge together and gelatinize.
This gel film corresponds to the second filter 2 which cannot pass
through the filter holes 11.
[0180] When the second filter 2 reaches a predetermined film
thickness, spaces are formed therein which do not allow the passage
of gel removables and filtration of removables of colloid substance
is started using this second filter 2. After the filtration process
is performed a number of times while suctioning by pump 6, the gel
film on the surface of the second filter 2 gradually stacks and
thickens, so that eventually the second filter 2 clogs and
filtration is impeded. While the colloid solution is gelatinized,
water from the colloid solution that adhered to the surface of the
second filter passes through the first filter and is discharged as
filtered water.
[0181] FIG. 10A shows wastewater containing colloid fluid with
removables, on one side of the first filter 1 and filtered water
which passed through the first filter 1, on the other side thereof.
Wastewater is suctioned and flows in the direction shown by the
arrows. Microparticles in the colloid solution lose their
electrostatic repulsive force as they get closer to the first
filter 1 and are gelatinized. The second filter 2 is formed by the
gel film comprising some microparticles that merged together and
adheres to the surface of the first filter 1. Wastewater is
filtered by means of the second filter 2 while gelatinizing
removables inside the colloidal solution. Filtered water is
suctioned from the opposite side of the first filter 1.
[0182] The water inside the wastewater is thus discharged by
smoothly suctioning wastewater of the colloid solution via the
second filter 2 and removables are captured to form the gel film by
drying, gelatinizing them so that they stack on the surface of
second filter.
[0183] Next, second filter 2 formation conditions and the
subsequent filtration rate are described with reference to FIG.
11.
[0184] This invention provides a process for forming a second
filter 2 and a process for re-filtration. The purified water
filtration rate during filtration largely varies depending on the
second filter 2 formation conditions. Accordingly, it was
determined that when purification conditions of the second filter 2
are not properly selected, filtration using the gelatinous second
filter 2 is almost impossible. This fact coincides with the
conventional art, where it was known that filtration of colloid
solution is impossible.
[0185] The characteristics shown in FIG. 11B are all proved by
experiments carried out according to the method shown in FIG. 11A.
A first filter 1 is provided at the bottom of a cylindrical
container 21 and a concentrate solution 50 cc of a tungsten
polishing slurry 22 (W 2000) from Cabot Micro Electronics Co. is
supplied thereto. Formation of the gel film is carried out by
varying the suction pressure. Next, the slurry 22 that remained is
removed and after supplying 100 cc of purified water 23, filtration
is carried out at a very low suction pressure. It is thus possible
to determine the filtration characteristics of the gelatinous
second filter 2. The first filter 1 used at this time has a
diameter of 47 mm and has a surface of 1734 mm.sup.2.
[0186] In the gel film formation process shown in FIG. 11B, gel
film characteristics when the suction pressure is varied among -55
cm Hg, -30 cm Hg, -10 cm Hg, -5 cm Hg, -2 cm Hg and the formation
process lasts for 120 minutes were examined. Results show that
filtration rate is best when suction pressure is set to -55H, so
that in 2 hours the filtered amount is 16 cc, then decreasing in
turn to 12.5 cc, 7.5 cc, 6 cc, 4.5 cc.
[0187] Next, purified water is supplied and filtration is carried
out using this gel film. The suction pressure at this time is set
to -10 cm Hg. With the gel film formed at a suction pressure of -55
cm Hg, only 0.75 cc/h can be filtered, with a gel film formed at a
suction pressure of -30 cm Hg, filtration rate is about 1 cc/h.
However, with a gel film formed at -10 cm Hg, filtration rate is 25
cc/h, with a gel film at -5 cm Hg, filtration rate is 3.25 cc/h and
with a gel film at -2 cm Hg, filtration rate is 3.1 cc/h.
Accordingly, even with a gel film formed at a very low suction
pressure, filtration is stable. From these experimental results it
is determined that if the suction pressure in the second filter 2
formation process is set so that the filtration rate is about 3
cc/h, the filtration rate in the subsequent filtration process is
the largest.
[0188] The reason for this is that, if the suction pressure is
strong, the so-formed gel film has a low degree of swelling and
solidifies due to compactness because the film is formed to be
concentrated and thus contains a very small amount of water. This
is probably because paths used by pure water to pass disappear.
[0189] When the suction pressure is decreased, the so-formed gel
film has a high degree of swelling and it is soft due to a
decreased density because the film contains a large amount of water
and is formed in a state of swelling. Thus, a large number of paths
allowing the purified water to pass therethrough can be obtained.
The principle is more easily understood when imagining the snow
powder slowly falling and thickening on the ground. One of the
aspects of this invention is to provide a filtration method using a
gel film formed at a very low suction pressure and having a high
degree of swelling by causing moisture to pass through the gel
film.
[0190] Characteristics of the gel film are described with reference
to FIG. 12. FIG. 12 A shows the relationship between the sol amount
contained in the gel film and the filtration rate. The amount of
removed sol shows the sol amount captured by the first filter from
the filtered amount during the gel film formation process when
purified water having a slurry concentration of 3% is used. It is
believed that the sol amount is an amount that gelatinizes and
adheres as the second filter by drying by suction. It is also
determined that at a very low suction pressure, the amount of sol
during the second filter 2 formation process is very low. That is,
when the filtration rate is 3 cc/h, the sol amount consumed is very
low 0.15 cc, so that the smaller the amount of sol contained in the
second filter 2, the higher the filtration rate. This is an
important aspect of this invention. Accordingly, filtration of
wastewater of colloid fluid can be achieved by forming a second
filter 2 having a sol amount as low as possible.
[0191] FIG. 12 B shows the swelling degree, more precisely, the
density of the sol inside the gel film from the sol amount
described above and the cubic volume of the gel film. Experimental
results show that the second filter 2 film thickness; when the
suction pressure is -30 mm Hg, it is 6 mm, and when -10 mm Hg, it
is 4 mm and that the swelling degree increases from 27 to 30. More
precisely, the greater the suction pressure, the smaller the
swelling degree and the density of the sol amount in the second
filter 2 increases. Also, the smaller the suction pressure, the
thinner the second filter 2 film and the swelling degree increases.
Accordingly, as shown in FIG. 12B, the filtration rate during the
filtration process using the second filter 2 formed by reducing the
suction pressure increases and filtration can be carried out over a
long period of time.
[0192] Consequently, the main point of this invention is that the
ability to filter wastewater of a colloid solution having fine
particles equal to or under 0.15 .mu.m is greatly influenced by the
second filter formation conditions.
[0193] The filter in FIG. 10A illustrates one side of the filter
shown in FIG. 9 and is a pattern diagram showing how the gel film
actually adheres.
[0194] The first filter 1 is immersed perpendicularly in the
wastewater of colloid fluid and wastewater is the colloid fluid
where removables 13 are dispersed. Removables 13 are shown by small
black bullets. When wastewater is suctioned by applying a weak
suction pressure from the pump 6 through the first filter 1 and as
it draws nearer to the first filter, the microparticles of
removables gelatinize and adhere to the surface of the first
filter. The gelatinized microparticles 14 shown by white circles
which are larger than filter holes 11 provided in the first filter
1 gradually adhere and pile up on the surface of the first filter 1
forming a gelatinous second filter 2. The gelatinized
microparticles 14 having a smaller diameter than the filter holes
11 pass through the first filter but in the process of forming the
second filter 2, the filtered water is caused to circulate and is
returned to wastewater. The second filter 2 is formed along a 120
minute period as described above. In this process, the gelatinized
microparticles 14 are suctioned at a very low suction pressure and
thus pile up forming spaces with different shapes thus generating a
second filter 2 with a flexible gel film having a very low degree
of swelling. The water inside the wastewater is absorbed through
this gel film having a high degree of swelling and is discharged as
filtered water after it passes through the first filter.
[0195] More precisely, a gelatinous second filter with a high
degree of swelling is formed by suctioning from the first filter 1
with a weak suction pressure so that the moisture contained in the
gel film which is in contact with the first filter 1 is removed and
the gel film is contracted, whereas moisture from the gel film
contacting the wastewater is supplied and is caused to pass through
the gel film, thus repeatedly causing a swelling of the gel film so
that finally, only moisture is allowed to pass through the second
filter 2.
[0196] Air bubbles 12 are generated from the bottom of the
wastewater and are sent to the first filter 1 flowing parallel to
the surface of the first filter. This is because the second filter
2 adheres uniformly and softly to the entire surface of the first
filter due to the spaces formed therein. More precisely, here air
flow rate is set to 1.8 l/minute, but it is always selected
depending on the nature of the second filter 2.
[0197] In the filtration process, gelatinized microparticles 14
shown by white circles gradually pile up on the surface of the
second filter 2.by suctioning with a weak suction force. At this
time, the purified water passes through the second filter and
further through the gelatinized microparticles 14 piled up thereto
and is then discharged from the first filter 1 as filtered water.
Process waste such as semiconductor material waste, metal waste
and/or insulating resin material waste, etc. generated in the CMP
process by abrasive coating such as silica, alumina, or ceria, etc.
or by grinding with abrasive coating, contained in wastewater, is
captured and gradually piles up as gel on the surface of the second
filter 2 so that water passes through the gel film and is
discharged as filtered water from the first filter 1.
[0198] However, when the filtration process is carried out for a
long period of time as shown in FIG. 11B, a thick gel film adheres
to the surface of the second filter 2 so that the above described
spaces clog and filtered water cannot be obtained any longer. In
order to restore filtration capabilities, it is necessary to remove
this gel film which piled up thereon.
[0199] Next, actual filtration operation using the filtration
apparatus shown in FIG. 5 is described.
[0200] First, wastewater containing removables of a colloid fluid
is supplied into the raw water tank 50 via pipe 51. A filter
apparatus 53 having only the first filter 1 formed thereon, but not
the second filter 2, is immersed into the raw water tank 50 and
wastewater is circulated while applying a weak suctioning pressure
from the pump 57 via pipe 56. The circulation path of the
wastewater includes the filter apparatus 53, pipe 56, valve V1,
pump 57, pipe 58, control valve CV1, flowmeter 61, optical sensor
62, valve V3. The wastewater is suctioned from the raw water tank
50 and is then returned to the raw water tank 50.
[0201] By causing the wastewater to circulate, a second filter 2 is
formed on the surface of the first filter 1 in the filter apparatus
53 so that removables of colloid solution are finally captured.
[0202] More particularly, wastewater is suctioned at a weak suction
pressure by pump 57 via a first filter 1 and as microparticles of
the removables draw nearer to the first filter 1, they are turned
into a gel and adhere to the surface of the first filter. The
gelatinized particles which are larger than filter holes 11
provided in the first filter 1 gradually pile up on the surface of
the first filter thus forming the gelatinous second filter 2.
Gelatinized removables having a smaller diameter than the filter
holes 11 pass through the first filter 1, whereas during the second
filter 2 formation process, water inside the wastewater which is
suctioned through these spaces which function as passages, passes
through the first filter 1 and is then discharged as purified
water.
[0203] Optical sensor 62 monitors the concentration of the
particles contained in the filtered water and when it is determined
that the mix rate of the microparticles is smaller than a desired
value, filtration is started. Before filtration is started, valve
V3 is closed based on a detection signal from the optical sensor 62
and valve V4 is opened so that the circulation path described above
can be closed. Next, purified water is discharged from valve V4.
Air bubbles constantly supplied by the air pump 55 and diffused by
the air diffuser 54 are adjusted by the control valve CV2 and are
supplied to the surface of the filter apparatus 53.
[0204] After filtration is carried out for some time, the water
inside the wastewater contained in raw water tank 50 is discharged
to the outside of the raw water tank 50 as purified water and
accordingly, concentration of the removables inside the wastewater
raises. More precisely, the colloid fluid is concentrated and
viscosity thereof increases. Wastewater is thus supplied into the
raw water tank 50 from pipe 51 in order to suppress the raise in
wastewater concentration and to increase filtration efficiency.
However, a thick gel film adheres to the surface of the second
filter of the filter apparatus 53 eventually causing it to clog and
impeding filtration.
[0205] When the second filter 2 clogs, a process is carried out to
restore filtration capabilities thereof. In this process, pump 57
is halted and the negative suction pressure applied to the filter
apparatus 53 is cancelled.
[0206] The filter regeneration process is next described with
reference to FIG. 13 which shows pattern diagrams. FIG. 13A shows
the status of the filter apparatus 53 during the filtration
process. Center 5 of the first filter 1 has a negative pressure
compared to its exterior, due to a weak suction pressure, so that
it swells towards the inside of the first filter 1. Consequently,
the second filter 2 adhered to a surface thereof also tends to
swell towards the inside, and so does the gel film that gradually
adheres to the surface of the second filter 2.
[0207] In the filter regeneration process as shown in FIG. 13B,
this weak suction pressure is cancelled so that an atmospheric
pressure is restored and the first filter 1 of the filter apparatus
53 returns to its original state and so do the second filter 2 and
the gel film adhered to a surface thereof. As a result, the suction
pressure suctioning the film gel is cancelled so that the gel film
loses its adsorbability towards the filter apparatus 53 and at the
same time is influenced by a force that causes it to swell towards
the exterior. Consequently, the gel film starts separating itself
from the filter apparatus 53 due to its own weight. In order to
facilitate the removal of the gel film, the amount of air bubbles
generated by the air diffuser 54 may be doubled. Experiments show
that separation begins from a lower end of the filter apparatus 53
and continues with the separation of the second filter 2 adhered to
the surface of the first filter 1, similar to an avalanche.
Separated parts precipitate to the bottom of the raw water tank 50.
Next, water is caused to circulate through the circulation path
described above and the second filter 2 is re-formed. In this
regeneration process, the second filter 2 is restored to its
original state enabling re-filtration of wastewater.
[0208] In the filter regeneration process, supplying a back flow of
filtered water to the center 5, firstly, facilitates returning of
the first filter 1 to its original state and due to a hydrostatic
pressure of the filtered water, a force is applied that causes a
swelling to the outside, secondly, the filtered water passes
through the filter holes 11 inside the first filter 1 and seeps at
the boundary of the first filter 1 and second filter 2 thus
facilitating separation of the gel film of the second filter 2 from
the surface of the first filter 1.
[0209] When filtration is continued while the second filter 2 is
regenerated, as described above, the concentration of removables
from the wastewater contained in the raw water tank 50 increases
and eventually so does the viscosity of the wastewater.
Accordingly, if the concentration of the removables in the
wastewater exceeds a certain value, the filtration process is
halted and removables are left to precipitate. As a consequence,
concentrated slurry accumulates at the bottom of the raw water tank
50 and is then recovered by opening valve 64. The recovered slurry
is compressed or heat dried in order to further compress it by
removing water contained therein. Consequently, the amount of
slurry handled as industrial waste can be substantially
reduced.
[0210] The operational status of the filtration apparatus shown in
FIG. 5 is next described with reference to FIG. 14. Here, both
sides (surface: 0.109 m.sup.2) of a filter apparatus 53, size A4,
as described above are used. Initial rate is set to 3 cc/h (0.08
m.sup.3/day), which, as described above, is a good filtration rate,
and the flow rate after filter regeneration is set to the same
value. Air blow rate is set to 1.8 liters/minute during filter
formation and during filtration and to 3 l/minute during filter
regeneration. Pin and re-Pin are suction pressure values and are
measured by the barometer 59. Pout and re-Pout are pressures of
pipe 58 and are measured by barometer 60. The flow rate and re-flow
rate are measured by the flowmeter 61 and show the filtration rate
of the water suctioned from the filter apparatus 53.
[0211] In FIG. 14, the Y-axis on the left side shows negative
pressure (MPa) which increases as drawing closer to the X-axis. The
Y-axis on the right side shows flow rate (cc/minute). The X-axis
shows time elapsed (minutes) from filter formation.
[0212] The point of this invention is that during the second filter
2 formation process, the filtration process and the filtration
process after the filter regeneration process, the flow rate and
re-flow rate are kept at 3 cc/hour. Because of this, in the filter
formation process, Pin is a very weak suction pressure, -0.001 MPa
thru -0.005 MPa so that a second filter 2 is formed by the
adherence of a soft gel film.
[0213] Next, in the filtration process, Pin is gradually increased
from -0.005 MPa and filtration is carried out while maintaining a
constant flow rate. After the filtration process is carried out for
about 1000 minutes, the flow rate eventually starts to decrease,
thus requiring a process of filter regeneration. The reason for
such decrease is the adherence of a thick gel film on the surface
of the second filter 2 causing clogging thereof.
[0214] Furthermore, after the second filter 2 regeneration process
is carried out, the re-filtration operation is started at a
constant re-flow rate while gradually increasing the re-Pin
pressure. The second filter 2 regeneration and the re-filtration
are continued until raw water 52 reaches a predetermined degree of
concentration, more precisely, when the concentration degree
increases from 5 times to 10 times.
[0215] Another filtration method, different from the one described
above, is employed wherein filtration is carried out by setting the
suction pressure to -0.005 MPa to obtain a high filtration rate. In
this case, with the clogging of the second filter 2, the filtration
rate gradually decreases, but filtration time is long and control
of pump 57 is easy. Accordingly, regeneration of the second filter
2 may be carried out when filtration rate is reduced to or below a
constant value.
[0216] FIG. 15A shows the particle size distribution of abrasive
coating contained in the CMP slurry. This abrasive coating is used
in the CMP of interlayer dielectric films comprising Si oxides and
contains Si oxides commonly called silica. The minimum particle
diameter is about 0.076 .mu.m whereas the maximum particle diameter
is about 0.34 .mu.m. These large particles are agglomerated
particles formed by a plurality of particles that agglomerate. The
average particle diameter is 0.1448 .mu.m with a peak distribution
of 0.13 thru 0.15 .mu.m. KOH or NH3 are commonly used as slurry
adjustors and the pH is between 10 and 11.
[0217] More precisely, the CMP abrasive coating mainly comprises
silica, alumina, cerium oxide, diamond, or it may also comprise
chromic oxide, iron oxide, manganese oxide, BaCO.sub.4, antimony
oxide, zirconia, yttria. Silica is used in the planarization of
semiconductor interlayer dielectric films, P--Si, SOI, etc. and in
the planarization of Al/glass disks. Alumina is used in hard disk
polishing, planarization of metals, Si oxide films, etc. Cerium
oxide is used in glass and Si oxides polishing, chromic oxide is
used in the iron and steel mirror surface polishing. Manganese
oxide and BaCO.sub.4 are used in the polishing of tungsten
wiring.
[0218] Colloid-sized fine particles called oxides sol and
comprising metal oxides or partly hydroxides such as silica,
alumina, zirconia, etc. are uniformly dispersed into water or in
fluid. This sol is used in the planarization of interlayer
dielectric films of semiconductor devices and use thereof in
information disks such as Al disks is experimented.
[0219] The data in FIG. 15 shows filtration of CMP wastewater and
capture of the abrasive coating. Concentrate slurry solution is
diluted by pure water 50 times, 500 times, 5000 times and is used
as test solution. As described in the background art, since pure
water is used for wafer wash in the CMP process, wastewater is
believed to be diluted 50 thru 5000 times.
[0220] The light transmission of these three types of test
solution, when examined with light having a wavelength of 400 nm,
is 22.5% in the case of the test solution diluted 50 times, 86.5%
in the case of the test solution diluted 500 times and 98.3% in the
case of the test solution diluted 5000 times. In principle, if the
wastewater does not contain any abrasive coating, light is not
scattered and light transmission is very close to 100%.
[0221] Filters having the second filter film 13 formed thereon are
immersed in the three types of test solutions and after the
solution is filtered, permeability of all three types of test
solutions becomes 99.8%. In other words, abrasive coating can be
captured because light transmission after filtration is greater
than light transmission before filtration. Permeability data of the
50 times diluted test solution does not appear in the figure
because values thereof are too small.
[0222] Based on the above results, it was determined that when the
removables of a colloid fluid discharged from a CMP apparatus are
filtered by use of a second filter comprising a gel film and
provided in a filter apparatus 53 of a filtration apparatus
according to this invention, a permeability value of 99.8% can be
obtained.
[0223] A description was given hereinbefore of a filtration method
of a solution by use of a second filter which is a gelatinous
self-generated film, however, filtration films are not limited to
the gelatinous film. The apparatus and the method according to this
invention can also employ other types of self-generated gels
(pre-coat filters).
* * * * *