JP4535689B2 - Fluid filtration method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a filtration device, and more particularly to a filtration device that can suitably adjust the suction pressure of a pump that takes out filtered water from the filter device.
[0002]
[Prior art]
At present, reducing industrial waste, separating and reusing industrial waste, or not releasing industrial waste to the natural world is an important theme from the viewpoint of ecology and is a corporate issue in the 21st century. Among these industrial wastes, there are various fluids containing the objects to be removed.
[0003]
These are expressed in various words such as sewage, drainage, and waste liquid. Hereinafter, a substance that is a substance to be removed in a fluid such as water or chemicals will be referred to as drainage. These wastewater is treated as industrial waste by removing the object to be removed with an expensive filtration processing device, etc., and draining the wastewater into a clean fluid and reusing it, or separating the object to be removed or unfiltered. ing. In particular, water is returned to the natural world such as rivers and seas by being filtered to be in a clean state that satisfies environmental standards, or reused.
[0004]
However, it is very difficult to adopt these apparatuses due to problems such as equipment costs such as filtration processing, running costs, and the like, which is also an environmental problem.
[0005]
As can be seen from this, the wastewater treatment technique is an important problem from the viewpoint of environmental pollution and from the viewpoint of recycling, and a system with low initial cost and low running cost is urgently desired.
[0006]
As an example, wastewater treatment in the semiconductor field will be described below. In general, when grinding or polishing a plate such as metal, semiconductor, ceramic, etc., prevention of temperature rise of a polishing (grinding) jig due to friction, improvement of lubricity, adhesion of grinding or cutting waste to the plate Therefore, a fluid such as water is showered on a polishing (grinding) jig or a plate-like body.
[0007]
Specifically, a method of flowing pure water when a semiconductor wafer, which is a plate of semiconductor material, is diced or back-ground. In the dicing machine, in order to prevent the temperature of the dicing blade from rising and to prevent dicing debris from adhering to the wafer, a flow of pure water is created on the semiconductor wafer, or the water is discharged so that the pure water hits the blade. A nozzle is installed and showered. Also, when the wafer thickness is reduced by back grinding, pure water is flowed for the same reason.
[0008]
Waste water mixed with grinding or polishing waste discharged from the dicing equipment and back grinding equipment described above is filtered to clean water and returned to nature, or reused, and concentrated waste water is recovered. Yes.
[0009]
In the current semiconductor manufacturing, there are two methods for treating wastewater mixed with removal objects (scraps) mainly composed of Si: a coagulation sedimentation method, and a combination of filter filtration and a centrifugal separator.
[0010]
In the former coagulation-precipitation method, PAC (polyaluminum chloride) or Al2 (SO4) 3 (sulfuric acid band) or the like is mixed in the waste water as a coagulant to generate a reaction product with Si and remove this reaction product. The wastewater was filtered.
[0011]
In the latter method, which combines filter filtration and centrifugation, the wastewater is filtered, the concentrated wastewater is centrifuged and the silicon waste is recovered as sludge, and the clean water produced by filtering the wastewater is returned to nature. It was released or reused.
[0012]
For example, as shown in FIG. 13, waste water generated during dicing is collected in a raw water tank 201 and sent to a filtration device 203 by a pump 202. Since the filter 203 is equipped with a ceramic or organic filter F, the filtered water is sent to the recovered water tank 205 via the pipe 204 and reused. Or released to nature.
[0013]
On the other hand, since the filter F is clogged, the filter 203 is periodically cleaned. For example, the valve B1 on the raw water tank 201 side is closed, the valve B3 and the valve B2 for sending cleaning water from the raw water tank are opened, and the filter F is back-washed with the water of the recovered water tank 205. The waste water mixed with the high-concentration Si waste generated thereby is returned to the raw water tank 201. The concentrated water in the concentrated water tank 206 is transported to the centrifuge 209 via the pump 208 and separated into sludge and sludge by the centrifuge 209. Sludge composed of Si waste is collected in the sludge collection tank 210, and the separation liquid is collected in the separation liquid tank 211. Further, the drainage of the separation liquid tank 211 in which the separation liquid is collected is transported to the raw water tank 201 via the pump 212.
[0014]
These methods occur, for example, when grinding or polishing a solid or plate-like body mainly made of a metal material such as Cu, Fe, or Al, or a solid or plate-like body made of an inorganic substance such as ceramic. It was also used when collecting waste.
[0015]
On the other hand, CMP (Chemical-Mechanical Polishing) has appeared as a new semiconductor process technology. This CMP technology provides (1) realization of a flat device surface shape and (2) realization of an embedded structure of a material different from that of the substrate.
[0016]
{Circle around (1)} is to form a fine pattern with high accuracy using a lithography technique. Further, the combined use of the Si wafer bonding technique brings about the possibility of realizing a three-dimensional IC.
[0017]
(2) enables an embedded structure. Conventionally, a tungsten (W) embedding technique has been adopted for IC multilayer wiring. In this method, W was buried in the groove of the interlayer film by the CVD method, and the surface was etched back to flatten it, but recently it has been flattened by CMP. Applications of this embedding technique include damascene process and element isolation. These CMP techniques and applications are described in detail in “CMP Science” published by Science Forum.
[0018]
Next, the CMP mechanism will be briefly described. As shown in FIG. 14, a semiconductor wafer 252 is placed on a polishing cloth 251 on a rotating platen 250, and is rubbed while flowing an abrasive (slurry) 253, polished, and chemically etched. Is lost. It is flattened by a chemical reaction by the solvent in the abrasive 253 and a mechanical polishing action between the polishing cloth and the abrasive grains in the abrasive. As the polishing cloth 251, for example, foamed polyurethane, non-woven fabric or the like is used. The polishing material is a mixture of abrasive grains such as silica and alumina in water containing a pH adjusting material, and is generally called a slurry. Yes. While flowing the slurry 253, the wafer 252 is rotated against the polishing cloth 251 and rubbed with a certain pressure. Reference numeral 254 denotes a dressing unit that maintains the polishing ability of the polishing pad 251 and always makes the surface of the polishing pad 251 dressed. Reference numerals 202, 208 and 212 denote motors, and 255 to 257 denote belts.
[0019]
The mechanism described above is constructed as a system, for example, as shown in FIG. This system roughly comprises a wafer cassette loading / unloading station 260, a wafer transfer mechanism 261, the polishing mechanism 262 described in FIG. 14, the wafer cleaning mechanism 263, and a system control for controlling them.
[0020]
First, the cassette 264 containing the wafer is placed in the wafer cassette loading / unloading station 260, and the wafer in the cassette 264 is taken out. Subsequently, the wafer is held by a wafer transfer mechanism unit 261, for example, a manipulator 265, placed on a rotating surface plate 250 provided in the polishing mechanism unit 262, and the wafer is flattened using CMP technology. . When the planarization operation is completed, the wafer is transferred to the wafer cleaning mechanism 263 by the manipulator 266 and cleaned in order to clean the slurry. The cleaned wafer is accommodated in a wafer cassette 266.
[0021]
For example, the amount of slurry used in one process is about 500 cc to 1 liter / wafer. Further, pure water is caused to flow through the polishing mechanism 262 and the wafer cleaning mechanism 263. Since these wastewaters are finally combined together at the drain, wastewater of about 5 to 10 liters / wafer is discharged in one flattening operation. For example, in the case of a three-layer metal, about seven times of flattening work is performed by the flattening of the metal and the flattening of the interlayer insulating film, and 5 to 10 liters of seven times drainage is completed until one wafer is completed. Discharged. Therefore, it can be seen that when a CMP apparatus is used, a considerable amount of slurry diluted with pure water is discharged. And these waste water was processed by the coagulation sedimentation method (refer patent document 1).
[0022]
[Patent Document 1]
JP 2001-157894 A
[0023]
[Problems to be solved by the invention]
However, in the coagulation precipitation method, a chemical is input as the coagulant. However, it is very difficult to specify the amount of a chemical that completely reacts, and a large amount of chemical is inevitably added, and an unreacted chemical remains. Conversely, if the amount of chemicals is small, all the objects to be removed are not agglomerated and settled, and the objects to be removed remain without being separated. In particular, when the amount of the chemical is large, the chemical remains in the supernatant. When this is reused, since chemicals remain in the filtered fluid, there is a problem that it cannot be reused for those who dislike chemical reactions.
[0024]
In addition, flocs, which are the reaction product of chemicals and objects to be removed, are generated as if they were floating substances such as algae. The conditions for forming this floc are severe pH conditions, and a stirrer, a pH measuring device, a flocculant injection device, a control device for controlling these, and the like are required. In addition, a large sedimentation tank is required to settle the floc stably. For example, 3 cubic meters (m ^Three ) / 1 hour drainage treatment capacity requires a tank with a diameter of about 3 meters and a depth of about 4 meters (about 15 tons of sedimentation tank). It becomes a large-scale system that is required.
[0025]
Moreover, there are some flocs that do not settle in the sedimentation tank and are floating, and these may flow out of the tank, and it is difficult to collect all of them. In other words, there are problems such as the size of the equipment, the high initial cost of this system, the difficulty of reusing water, and the high running cost generated from the use of chemicals.
[0026]
On the other hand, as shown in FIG. ³ ) / 1 hour filter filtration combined with a centrifuge uses a filter F (referred to as a UF module, made of polysulfone fiber, or a ceramic filter) for the filtration device 203. Reusable. However, four filters F are attached to the filtering device 203. From the life of the filter F, it has been necessary to replace a high-priced filter of about 500,000 yen / piece at least once a year. Moreover, the pump 202 in front of the filtering device 203 is clogged with a filter F because the filter F is a pressurizing type filtration method, and the load on the motor is large, and the pump 202 has a high capacity. Further, about 2/3 of the waste water passing through the filter F was returned to the raw water tank 201. Furthermore, since the waste water containing the object to be removed is transported by the pump 202, the inner wall of the pump 202 is shaved and the life of the pump 2 is very short.
[0027]
To sum up these points, the electric cost of the motor is very high, and the replacement cost of the pump P and filter F is high.
[0028]
Furthermore, in CMP, an amount of waste water that cannot be compared with dicing is discharged. The slurry is colloidally distributed in the fluid and does not settle easily due to Brownian motion. Moreover, the particle size of the abrasive grains mixed in the slurry is extremely fine, 10 to 200 nm. Therefore, when a slurry consisting of fine abrasive grains is filtered with a filter, the abrasive grains enter the pores of the filter, causing immediate clogging and frequent clogging. It was.
[0029]
As can be seen from the above description, wastewater filtration devices are used in various ways to remove as much of the substances that harm the global environment as possible, or to reuse filtration fluids and separated objects. The system becomes a large-scale system, and the initial cost and running cost are enormous. Therefore, the sewage treatment apparatus so far has not been a system that can be adopted at all.
[0030]
Moreover, when the said waste_water | drain is filtered using a self-forming film | membrane (precoat filter), there existed a problem that control of the pump which filters was difficult.
[0031]
[Means for Solving the Problems]
The present invention has been made in view of the above problems, and includes a tank that contains a fluid containing an object to be removed, a first filter that is immersed in the tank, and a second object that is deposited on the surface of the first filter. A filter device formed by a filter and a pump connected to the filter device via a pipe, and the fluid passes through the first filter by a suction pressure of the pump. In the step of forming the second filter, the fluid is filtered by passing the fluid by the suction pressure of the pump through the filter device in which the second filter is formed. The suction pressure of the pump is larger than the step of filtering the fluid.
[0032]
Furthermore, the present invention is formed by a tank in which a fluid containing a colloidal object to be removed is stored, a first filter immersed in the tank, and a second filter composed of a gel film adsorbed on the surface of the first filter. And a pump connected to the filter device via a pipe, and the second filter is formed by the fluid passing through the first filter by the suction pressure of the pump. The fluid is filtered by passing the fluid by the suction pressure of the pump through the filter device in which the second filter is formed. In the step of forming the second filter, the fluid is filtered. The suction pressure of the pump is larger than the step of performing.
[0033]
In the present invention, by adjusting the suction pressure of the pump, the formation process of the second filter which is a self-forming film and the filtration process using the second filter can be performed smoothly.
[0034]
In general, in order to remove particles having a size of 200 nm or less such as abrasive grains mixed in a CMP slurry, it is common to employ a filter film having pores smaller than the particles. However, in the present invention, a gel film made of an object to be removed is used as a filter, and many gaps formed in the filter are used as fluid passages. Further, according to the present invention, since the filter itself is an aggregate of particles of the object to be removed, the object to be removed that causes clogging can be separated from the filter, and the filtration performance can be maintained. Furthermore, even if the filter of the gel membrane is clogged due to continuous filtration, the filter can be regenerated and filtration can be continued for a long time.
[0035]
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIG. 1, the structure of the filtration apparatus 20 of this invention, etc. are demonstrated. FIG. 1 (A) is a schematic configuration diagram of a filtration device 20 according to the present invention, and FIG. 1 (B) is a characteristic diagram showing temporal changes in the rotational speed of the motor and the suction pressure inside the pipe 56.
[0036]
Referring to FIG. 1A, a filtration device 20 according to the present invention includes a tank 50 in which a fluid containing an object to be removed is stored, a first filter immersed in the tank 50, and a substrate deposited on the surface thereof. It has a filter device 53 formed of a second filter made of a removed product, and a pump 57 connected to the filter device 53 via a pipe 56, and the second filter is a first filter by the suction pressure of the pump 57. When the fluid passes through the filter device 53 in which the second filter is formed, the fluid is filtered by the suction pressure of the pump 57 to form the second filter. In this step, the pump 57 has a higher suction pressure than the step of filtering the fluid. Details of the filtration device 20 having such a configuration will be described below.
[0037]
First, an outline of the filtration device 20 will be described with reference to FIG. Reference numeral 50 denotes a raw water tank. Above the tank 50, a pipe 51 is provided as drainage supply means. The pipe 51 introduces the fluid mixed with the object to be removed into the tank 50. For example, in the semiconductor field, wastewater (raw water) mixed with a removal object of a colloidal solution flowing out from a dicing apparatus, a back grinding apparatus, a mirror polishing apparatus or a CMP apparatus is introduced. This waste water will be described as waste water mixed with abrasive grains flowing from the CMP apparatus and scraps polished or ground by the abrasive grains. Moreover, as shown in the figure, the fluid temporarily stored in the drainage receiving tank 17 may be introduced into the raw water tank 50 through the pipe 51.
[0038]
In the raw water 52 stored in the raw water tank 50, a plurality of filter devices 53 in which a second filter is formed are installed. Below this filter device 53, there is provided an air diffuser tube 54, such as a bubbling device used in a fish tank, for example, with a small hole in the pipe, and its position so as to pass through the surface of the filter device 53. Has been adjusted. The air diffuser 54 is arranged over the entire bottom of the filter device 53 so that air bubbles can be uniformly supplied to the entire surface of the filter device 53. 55 is an air pump. The air pump 55 and the diffuser pipe 54 are connected by a pipe-like vent pipe 40.
[0039]
The raw water 52 supplied from the pipe 51 is stored in the raw water tank 50 and filtered by the filter device 53. Bubbles pass through the surface of the second filter 2 attached to the filter device 53 and a parallel flow is generated by the rising force or rupture of the bubbles to move the gelled object to be adsorbed on the second filter. The filter device 53 is uniformly adsorbed on the entire surface and is maintained so that its filtering ability does not decrease.
[0040]
The pump 57 is connected to the filter device 53 via a pipe 56. That is, the fluid filtered by the filter device 53 is released to the outside by the suction force generated by the pump 57. Further, when the step of forming the second filter or the filtrate does not have the desired transparency, the fluid taken out from the filter device 53 is returned to the raw water tank 50. That is, the filtration device 20 of the present invention has a step of circulating filtered water. Further, a pressure gauge 59 for sensing the pressure inside the pipe 56 is provided in the middle of the pipe 56. In response to the pressure inside the pipe 56 measured by the pressure gauge 59, the rotation of the motor of the pump is controlled to control the suction pressure. Further, in the middle of the pipe 56, a peeling water tank 70 in which the filtrate is temporarily stored is provided.
[0041]
As the pump 57, an AC motor whose rotation speed is controlled by an inverter circuit or a DC motor whose rotation is controlled by an applied voltage can be adopted. By adopting the motor capable of controlling the rotation speed in this way, the suction pressure applied to the filter device 53 can be changed between the step of forming the second filter and the step of filtering. In particular, in the present invention, the fluid is filtered using a gel-like film formed on the surface of the first filter. Therefore, by employing a motor capable of controlling the rotation speed, it is possible to prevent the gel from entering the hole of the first filter and destroying the second filter. Details of the gel-like second filter will be described later.
[0042]
Further, as a means for adjusting the suction pressure applied to the filter device 53, not only the above-described change in the rotational speed of the motor but also other means can be employed. For example, the suction pressure applied to the filter device 53 can be adjusted by fixing the rotation speed of the motor that operates the pump 57 and inserting a release valve in the middle of the pipe 56. Specifically, the suction pressure can be reduced by opening the release valve, and the suction pressure can be increased by closing the release valve. Furthermore, the suction pressure applied to the filter device 53 can be changed by moving the position of the pump 55 in the vertical direction.
[0043]
With reference to FIG. 1 (B), the relationship between the suction pressure applied to the filter device 53 and the rotational speed of the motor provided in the pump 55 will be described. The horizontal axis of FIG. The left vertical axis shows the suction pressure applied to the filter device 53, and here shows the increase in negative pressure. The vertical axis on the right side indicates the rotational speed of the motor that operates the pump 57. Furthermore, in the figure, the dotted line shows the change in the suction pressure, and the solid line shows the change in the rotational speed of the motor.
[0044]
First, the filter device 53 is immersed in the raw water 52 and the pump 55 is operated to form a second filter that is a self-forming film on the surface of the first filter. This step is the second filter forming step. In this step, in order to form the second filter at an early stage, the number of rotations of the motor that operates the pump 55 is made as fast as possible. In this step, the taken out filtered water may be returned to the raw water tank 50.
[0045]
Through the above process, a second filter which is a self-forming film is gradually formed on the surface of the first filter of the filter device 53. The second filter is made of an object to be removed contained in the fluid, and its pores are fine compared to the first filter. Accordingly, the suction pressure gradually decreases with the formation of the second filter. The suction pressure is monitored by a pressure gauge 59.
[0046]
When the suction pressure reaches a predetermined value, it is determined that the second filter is formed, and the process proceeds to the filtration step. The rotation speed of the motor in the filtration step is slower than that in the above process. By doing in this way, it is possible to make suction pressure below a predetermined value, and it can prevent destruction of the 2nd filter by excessive suction pressure acting on the 2nd filter.
[0047]
In addition, the filtration capacity of the second filter decreases as the filtration proceeds. Then, the second filter having a reduced filtration capacity is peeled off by causing the filtered water to flow backward from the peeling water tank 70 to the filter device 53. Then, by operating the pump 57 thereafter, the filtered water that has flowed back to the filter device 53 is returned to the peeling water tank 70. At this time, the suction pressure of the pump 55 is set to be larger than that at the time of filtration.
[0048]
Further, when the filtration operation is finished, before the filtration device 20 is stopped, the suction pressure is made smaller than that during filtration and the pump is operated for a predetermined time. By doing in this way, when the filtration apparatus 20 restarts, the load given to the filtration apparatus 20 can be made small.
[0049]
A more specific filter device will be described with reference to FIG. In addition, the same code | symbol was attached | subjected to the same component as the filtration apparatus shown in FIG.
[0050]
In FIG. 2, 50 is a raw water tank. Above the tank 50, a pipe 51 is provided as drainage supply means. The pipe 51 introduces the fluid mixed with the object to be removed into the tank 50. For example, in the semiconductor field, wastewater (raw water) mixed with a removal object of a colloidal solution flowing out from a dicing apparatus, a back grinding apparatus, a mirror polishing apparatus or a CMP apparatus is introduced. This waste water will be described as waste water mixed with abrasive grains flowing from the CMP apparatus and scraps polished or ground by the abrasive grains.
[0051]
An adjustment valve 41 and a stop valve 42 are provided in the middle of the ventilation pipe 40 that connects the air pump 55 and the diffusion pipe 54. The adjustment valve 41 is set to allow a desired amount of gas flow. For example, a needle valve or the like can be employed as the adjustment valve. The stop valve 42 is a valve for opening and shutting off the gas flowing inside the vent pipe 40. Specifically, as the stop valve 42, for example, a valve using a solenoid or the like can be used. In this way, by using the adjustment valve 41A and the stop valve 42 in combination, a desired amount of gas can be supplied to the diffuser tube 54 simply by opening and closing the stop valve 42 while fixing the output of the air pump 55. Can be supplied.
[0052]
In addition, the vent pipe 40 is provided with a plurality of paths that are branched in parallel along the way. Specifically, the first path 40A, the second path 40B, and the third path 40C are branched and parallel. The above-described adjustment valve 41 and stop valve 42 are interposed in each path.
[0053]
A first adjustment valve 41A and a first stop valve 42A are interposed in the first path 40A. The first adjustment valve 41A is adjusted so that an appropriate amount of gas passes when the filter device 53 performs a filtering operation or the like. The first stop valve 42A is opened in a filtration step of filtering with the filter device 53, a step of forming a gel-like second filter, or the like. Further, when the first stop valve 42A is in an open state, the second stop valve 42B and the third stop valve 42C are in a cut-off state. The first adjustment valve 41A adjusted in this way makes it possible to supply an appropriate amount of gas from the diffuser tube 54 during filtration. Therefore, the raw water inside the raw water tank 50 is agitated by the bubbles rising from the air diffuser 54, and the filtration can be performed smoothly.
[0054]
A second adjustment valve 41B and a second stop valve 42B are interposed in the second path 40B. The second adjustment valve 41B is set so that a larger amount of gas passes than the first adjustment valve 41A described above. The second stop valve 42B is opened in a step (regeneration step) of separating the gel-like second filter constituting the filter device 53 from the first filter. The second filter can be detached by supplying a large amount of gas from the air diffuser into the raw water. When the second stop valve 42B is in the open state, the first stop valve 42A and the third stop valve 42C are cut off.
[0055]
A third adjustment valve 41C and a third stop valve 42C are interposed in the third path 40C. The third adjustment valve 41C is set so that less gas flows than the first adjustment valve 41A and the second adjustment valve 41B described above. The third stop valve 42C is opened when the entire filtering device 20 is stopped. 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 cutoff state. Thus, when the filtration device 20 as a whole stops the filtering operation, the diffuser tube 54 can be prevented from being clogged by being in an open state.
[0056]
The pipe 56 is connected to a magnet pump 57 through which the filtered fluid filtered by the filter device 53 flows and sucks through the valve V1. The pipe 58 is connected from the magnet pump 57 to the valve V3 and the valve V4 via the control valve CV1. A first pressure gauge 59 is provided after the valve V1 of the pipe 56 to measure the suction pressure Pin. Further, a flow meter F and a second pressure gauge 60 are provided after the control valve CV1 of the pipe 58, and a flow rate is controlled by a flow meter 61. The air flow rate from the air pump 55 is controlled by the control valve CV2.
[0057]
In the raw water 52 stored in the raw water tank 50, a plurality of filter devices 53 in which a second filter is formed are installed. Below this filter device 53, a diffuser tube 54 is provided over the entire bottom side of the filter device 53, such as a bubbling device used in a fish tank, for example, with a small hole in the pipe. The position is adjusted so as to pass through the surface. 55 is an air pump. Air is supplied from the air pump 55 and guided to the diffuser tube 54 via the air flow meter 69. Further, the above-described first path 40A, second path 40B, and third path 40C are provided in the vent pipe 40 that connects the air diffusion pipe 54 and the air pump 55. Furthermore, the first stop valve 42A, the second stop valve 42B, and the third stop valve 42C provided in each path are electrically connected to the control unit 68.
[0058]
The pipe 56 fixed to the filter device 53 is connected to a magnet pump 57 that carries the suction through the valve V1 through which the filtered fluid filtered by the filter device 53 flows. The pipe 58 is connected from the magnet pump 57 to the valve V3 and the valve V4 via the first control valve CV1. A first pressure gauge 59 is provided after the valve V1 of the pipe 56 to measure the suction pressure Pin. Further, a flow meter 61 and a second pressure gauge 60 are provided after the first control valve CV1 of the pipe 58, and the flow meter 61 controls the flow rate to be constant.
[0059]
The pipe 58 is connected to the optical sensor 62, and is guided from the optical sensor 62 to branched pipes 63 and 64. Valves V3 and V4, which are opened and closed by a detection signal from the optical sensor 62, are inserted into the pipes 63 and 64, the pipe 63 returns filtered water to the tank 50, and the pipe 64 takes out filtered water to the outside. Yes. The optical sensor 62 monitors the concentration of the fine particles contained in the filtered water, confirms that the fine particles are lower than the desired mixing rate, and starts filtration. When the filtration is started, the valve V3 is closed by a detection signal from the optical sensor 62, the valve V4 is opened, and purified water is taken out.
[0060]
Further, the peeling water tank 70 is connected to the pipe 58 by the valve V5 and has a function of storing filtered water. When the amount exceeds a certain amount, it overflows and is returned to the tank 50 by the pipe 71. A valve V <b> 2 is provided at the bottom and connected to the pipe 56. The peeling water tank 70 is provided at a position about 10 to 20 cm higher than the liquid level of the tank 50 and is used in the regeneration process of the second filter.
[0061]
Further, the tank 50 is provided with a pH adjuster 65 and a heating / cooling device 66. In particular, the pH of the CMP waste water is adjusted to about 6 to 7, and the temperature of the waste water is adjusted in order to promote gelation. In order to prevent the drainage from overflowing from the tank 50, monitoring is performed by the liquid level gauge 67 to adjust the inflow amount of the drainage.
[0062]
Further, a control device 68 for controlling the operation of the filtration device is provided. As shown by a dotted line in the figure, a control valve CV1, flow meters 61 and 69, a pump 57, pressure gauges 59 and 60, an optical sensor 62, etc. It is controlled for each process.
[0063]
In the above-described filtration device, in the second filter film forming step, the filtration step, the second filter regeneration step, the refiltration step, and the maintenance step, the valves and the like are opened and closed under the control of the control device 68, and the pump 57 Etc. are controlled. The operation status will be described below for each process. FIG. 3 shows operating states of the pump 57, the optical sensor 62, the air pump 55, and each valve in each process.
[0064]
First, the waste water mixed with the material to be removed of the colloidal solution is put into the raw water tank 50 through the pipe 51. In the tank 50, the filter device 53 of only the first filter 1 in which the second filter 2 is not formed is immersed in a number of sheets that can obtain a desired filtration flow rate. Specifically, about 10 to 40 filter devices 53 are suspended from a support means (not shown). Of course, this number varies depending on the filtration area of one filter device 53, but the total required filtration area of the filter device 53 can be obtained from the size of the tank 50.
[0065]
Next, the process proceeds to the film forming process of the second filter 2. The waste water in the tank 50 is circulated through the pipe 56 while being sucked by the pump 57 with a weak suction pressure. The circulation path is a filter device 53, a pipe 56, a valve V 1, a pump 57, a pipe 58, a control valve CV 1, a flow meter 61, an optical sensor 62, and a valve V 3, and waste water is sucked from the tank 50 and returned to the tank 50. From the air diffuser 54, air bubbles supplied from the air pump 55 through the first path 40A rise and are supplied to the surface of the filter device 53. That is, the first stop valve 42A is opened, and a desired amount of gas is supplied to the diffuser tube 54 by the first adjustment valve 41A. At this time, the other valves V2, V4, V5, V6, and D are closed.
[0066]
By circulating the waste water, the second filter 2 is formed on the first filter of the filter device 53, and finally the object to be removed of the target colloidal solution is captured. (This specific principle will be described later.) That is, when the waste water is sucked through the first filter 1 with a weak suction pressure by the pump 57, the fine particles of the object to be removed become gelled as it approaches the first filter 1. And adsorbed on the surface of the first filter 1. The gelled fine particles larger than the filter holes 11 of the first filter 1 are gradually adsorbed and stacked on the surface of the first filter 1 to form a second filter 2 made of a gel film. The gelled fine particles having a diameter smaller than that of the filter hole 11 pass through the first filter 1, but the water in the drainage is sucked through this gap as the second filter 2 is formed, and the first filter 1. And is taken out as purified water, and the wastewater is filtered.
[0067]
At this time, the concentration of the fine particles contained in the filtered water is monitored by the optical sensor 62, and it is confirmed that the fine particles are lower than the desired mixing rate, and the process proceeds to the filtration step.
[0068]
Subsequently, when the film formation of the second filter 2 is completed, the process proceeds to a filtration step. When filtration is started, the valve V3 is closed by a detection signal from the optical sensor 62, the valve V4 is opened, the above-described circulation path is closed, and filtered water is taken out from the valve V4. In this process, the control device 68 controls the flow meter 61 so as to obtain a constant filtration flow rate, and the second filter 2 is operated so as to prevent clogging as much as possible and to keep the filtration time long. As shown in FIG. 9, the suction pressure Pin of the pump 57 is gradually increased to keep the filtration flow rate constant. The other parts have the same operating conditions as in the film forming process. Also in this step, the gas supplied to the diffuser tube 54 is supplied via the first path 40A.
[0069]
When the second filter 2 is destroyed for some reason, the light sensor 62 detects the entry of fine particles, the valve V4 is closed, and conversely, the valve V3 is opened and the filtered water is returned to the tank 50. That is, the process returns to the film forming process to repair the second filter 2, and when it returns to normal, the process returns to the filtration process again.
[0070]
When the filtration is continued, the water in the waste water from the raw water tank 50 is taken out of the tank 50 as filtered water, so that the concentration of the object to be removed in the waste water increases. That is, the colloidal solution is concentrated to increase the viscosity. For this purpose, the raw water tank 50 is replenished with drainage from the pipe 51 to suppress an increase in the concentration of drainage and increase the efficiency of filtration. However, the gel film is thickly attached to the surface of the second filter 2 of the filter device 53, and eventually the second filter 2 becomes clogged and becomes unable to be filtered.
[0071]
When the gel film of the second filter 2 is adsorbed thickly on the surface of the first filter 1, it is detected by the flow meter 61 as a decrease in the filtration flow rate and is changed from the filtration step to the second filter regeneration step by the control device 68. Transition.
[0072]
First, in the regeneration process, the pump 57 is stopped and the negative suction pressure applied to the filter device 53 is released. At the same time, the valve V2 is opened and the filtered water previously stored in the peeling water tank 70 flows back through the pipe 56 through the valve V1 and is sent to the hollow portion 5 of the filter device 53.
[0073]
Therefore, in the regeneration process, the weak suction pressure is stopped and the pressure returns to almost the atmospheric pressure. Therefore, the first filter 1 of the filter device 53 returns from the depressed state to the original state. As a result, the second filter 2 and the gel film adsorbed on the surface thereof also return in the same manner. As a result, since the suction pressure that first adsorbs the gel film disappears, the gel film loses the adsorbing force to the filter device 53 and simultaneously receives a force that expands outward. Furthermore, since the separation water tank 70 is provided at a position higher than the liquid level of the tank 50, the hydrostatic pressure due to the difference in height is applied by the backflow of the filtered water from the separation water tank 70, and the first filter 1 and the first filter 1 of the filter device 53. The second filter 2 is applied with a force that expands outward. Thereby, the adsorbed gel film starts to be detached from the filter device 53 by its own weight and hydrostatic pressure. According to the experiment, the separation starts from the lower end of the filter device 53, and the gel film of the second filter 2 attached to the surface of the first filter 1 is detached like an avalanche and settles on the bottom surface of the raw water tank 50. . Subsequently, the second filter 2 may be formed by circulating the waste water through the circulation path described above. In this regeneration step, the second filter 2 returns to the original state, returns to a state where the drainage can be filtered, and again filters the drainage. At this time, the valve V2 is closed and the valve V5 is opened, and filtered water is stored in the separation water tank 70 to prepare for the next regeneration step.
[0074]
Furthermore, in order to advance this separation, it is preferable to increase the amount of bubbles from the air diffuser 54 by about twice. Specifically, the second stop valve 42B is opened, and the first stop valve 42A and the third stop valve 42C are shut off.
[0075]
Thereafter, the re-filtration process is started, and drainage filtration is started again. The operating conditions are the same as in the filtration step. If the filtration is continued many times while the second filter 2 is regenerated in this manner, the concentration of the material to be removed from the waste water in the raw water tank 50 increases, and the waste water eventually has a considerable viscosity. Therefore, when the concentration of the object to be removed from the waste water exceeds a predetermined concentration, the filtering operation is stopped and the process proceeds to the maintenance process.
[0076]
The maintenance process includes a step of discharging the filtered water in the pipes 56 and 58 and the peeling water tank 70 and a step of discharging the waste water in the tank 50 and the gel stored in the bottom. In the previous step, the pump 57 and the air pump 55 are stopped, the control valve CV1, the valves V1, V2, and V5 are opened, and the filtered water in the pipes 56 and 58 and the peeling water tank 70 is provided in the pipe 56. To the outside through the valve D.
[0077]
In the subsequent step, the concentrated slurry is allowed to settle at the bottom of the tank 50 for aggregation and precipitation, and the concentrated slurry of the gel is recovered by opening the valve V6. The recovered concentrated slurry is dried by heat to evaporate the water contained therein and further compress the amount. This can greatly reduce the amount of slurry that is treated as industrial waste. The supernatant drainage is likewise discharged from the valve V6 and returned to the tank 50 again in the subsequent filtration step.
[0078]
Here, the filter device 53 described above, specifically, the filter device 53 immersed in the raw water tank 50 will be described with reference to FIGS. 4 and 5.
[0079]
Reference numeral 30 shown in FIG. 4A is a frame having a frame-like shape, and filter films 31 and 32 serving as a first filter are bonded and fixed to both surfaces of the frame 30. Then, the inner space 33 surrounded by the frame 30 and the filter films 31 and 32 is filtered by the filter films 31 and 32 by sucking the pipe 34. Then, filtered water is taken out through a pipe 34 sealed and attached to the frame 30. Of course, the filter membranes 31 and 32 and the frame 30 are completely sealed so that drainage does not enter the space 33 from other than the filter membrane.
[0080]
Since the filter films 31 and 32 in FIG. 4A are thin resin films, if they are sucked, they may warp inward and may be destroyed. Therefore, in order to make this space as small as possible and increase the filtration capacity, it is necessary to make this space 33 large. FIG. 4B shows a solution to this. In FIG. 4B, only nine spaces 33 are shown, but many spaces 33 are actually formed. The filter membrane 31 actually employed is a polyolefin-based polymer membrane having a thickness of about 0.1 mm, and a thin filter membrane is formed in a bag shape as shown in FIG. In B), it is indicated by FT. A frame 30 in which a pipe 34 is integrated is inserted into the bag-like filter FT, and the frame 30 and the filter FT are bonded together. Reference numeral RG denotes pressing means that presses the frame on which the filter FT is bonded from both sides. The filter FT is exposed from the opening OP of the pressing means. Details will be described again with reference to FIG.
[0081]
FIG. 4C shows the filter device 53 itself having a cylindrical shape. The frame attached to the pipe 34 has a cylindrical shape, and openings OP1 and OP2 are provided on the side surfaces. Since the side surfaces corresponding to the openings OP1 and OP2 are removed, support means SUS for supporting the filter film 31 is provided between the openings. Then, the filter film 31 is bonded to the side surface.
[0082]
Further, the filter device 53 of FIG. 4B will be described in detail with reference to FIG. First, a portion 30a corresponding to the frame 30 in FIG. 4B will be described with reference to FIGS. 5A and 5B. The portion 30a is shaped like a cardboard as far as it is seen. Thin resin sheets SHT1 and SHT2 having a thickness of about 0.2 mm are overlapped, and a plurality of sections SC are provided in the vertical direction therebetween, and a space 33 is provided surrounded by the resin sheets SHT1, SHT2 and sections SC. The cross section of the space 33 is a rectangle having a length of 3 mm and a width of 4 mm. In other words, the space 33 has a shape in which many straws having the rectangular cross section are arranged and integrated. Since the portion 30a maintains the filter films FT on both sides at regular intervals, it is hereinafter referred to as a spacer.
[0083]
Many holes HL having a diameter of 1 mm are formed on the surfaces of the thin resin sheets SHT1 and SHT2 constituting the spacer 30a, and a filter film FT is bonded to the surface. Therefore, the filtered water filtered by the filter membrane FT passes through the hole HL and the space 33 and finally exits from the pipe 34.
[0084]
The filter film FT is bonded to both surfaces SHT1 and SHT2 of the spacer 30a. Both surfaces SHT1 and SHT2 of the spacer 30a have a portion where the hole HL is not formed, and when the filter film FT1 is directly attached thereto, the filter film FT1 corresponding to the portion where the hole HL is not formed is filtered. Since there is no function and drainage does not pass, there will be a part where the object to be removed is not captured. In order to prevent this phenomenon, at least two filter films FT are bonded together. The filter film FT1 on the front side is a filter film that captures an object to be removed, and a filter film having a larger hole than the hole of the filter film FT1 is provided from the filter film FT1 toward the surface SHT1 of the spacer 30a. Here, one filter film FT2 is bonded. Therefore, since the filter film FT2 is provided between the portions where the holes HL of the spacer 30a are not formed, the entire surface of the filter film FT1 has a filtering function, and an object to be removed is present on the entire surface of the filter film FT1. The second filter film is captured and formed on the entire front and back surfaces SH1 and SH2. For the convenience of the drawings, the filter films SHT1 and SHT2 are represented as rectangular sheets, but in actuality, they are formed in a bag shape as shown in FIG. 4B.
[0085]
Next, how the bag-like filter films SHT1, SHT2, the spacer 30a, and the pressing means RG are attached will be described with reference to FIGS. 5 (A), 5 (C), and 5 (D). .
[0086]
FIG. 5 (A) is a completed drawing, and FIG. 5 (C) is cut in the extending direction (longitudinal direction) of the pipe 34 from the head of the pipe 34 as shown by the AA line in FIG. 5 (A). FIG. 5D is a cross-sectional view of the filter device 35 cut in the horizontal direction as indicated by the line BB.
[0087]
As can be seen from FIGS. 5A, 5C, and 5D, the spacer 30a inserted into the bag-like filter film FT includes pressing means on the four sides including the filter film FT. It is sandwiched between RG. Then, the three side edges and the remaining one side bound in a bag shape are fixed with an adhesive AD1 applied to the pressing means RG. Further, a space SP is formed between the remaining one side (bag opening) and the pressing means RG, and the filtered water generated in the space 33 is sucked into the pipe 34 through the space SP. In addition, the adhesive AD2 is provided over the entire circumference of the opening OP of the presser fitting RG so that the adhesive AD2 is completely sealed and fluid cannot enter from other than the filter.
[0088]
Therefore, the space 33 and the pipe 34 communicate with each other. When the pipe 34 is sucked, the fluid passes through the hole of the filter film FT and the hole HL of the spacer 30a toward the space 33, and from the space 33 via the pipe 34. The structure is such that filtered water can be transported to the outside.
[0089]
The filter device 53 used here employs the structure shown in FIG. 5, and the size of the frame (holding metal fitting RG) to which the filter membrane is attached is A4 size. Specifically, the length is about 19 cm, and the width is about 28. .8 cm, thickness: 5 to 10 mm. Actually, since the filter device 53 is provided on both sides of the frame, the area twice as described above (area: 0.109 m). ² ) However, the number and size of the filter devices are freely selected depending on the size of the raw water tank 50, and are determined from the required filtration amount.
[0090]
Next, the principle of filtering raw water using a gel-like second filter will be described. First, definitions of terms used in the following explanation are clarified.
[0091]
The colloidal solution refers to a state in which fine particles having a diameter of 1 nm to 1 μm are dispersed in a medium. These fine particles have a Brownian motion and have a property of passing through a normal filter paper but not through a semipermeable membrane. In addition, the property of very slow aggregation speed is thought to reduce the chance of approach because electrostatic repulsion is acting between the fine particles.
[0092]
The sol is used almost synonymously with the colloidal solution. Unlike the gel, the sol is dispersed in a liquid and exhibits fluidity, and the fine particles are actively performing Brownian motion.
[0093]
A gel is a state in which colloidal particles have lost their independent motility and are aggregated and solidified. For example, agar and gelatin are dispersed into a sol when dissolved in warm water, but when cooled, they lose their fluidity and become a gel. Gels include hydrogels with a high liquid content and slightly dry xerogels.
[0094]
Factors for gelation include removing the water of the dispersion medium and drying, adding electrolyte salt to silica slurry (pH 9-10) to adjust pH to pH 6-7, cooling to lose fluidity Etc.
[0095]
Slurry refers to a colloidal solution or sol used for polishing by mixing particles with liquid and chemicals. The above-mentioned abrasive used for CMP is called CMP slurry. As the CMP slurry, a silica-based abrasive, an aluminum oxide (alumina) -based abrasive, a cerium oxide (ceria) -based abrasive, and the like are known. Silica-based abrasives are most often used, and colloidal silica is widely used. Colloidal silica is a dispersion in which ultrafine silica particles having a colloidal size of 7 to 300 nm are uniformly dispersed without being precipitated in water or an organic solvent, and is also called silica sol. Since the colloidal silica has monodispersed particles in water, the colloidal silica hardly settles even when left for more than one year due to the repulsive force of the colloidal particles.
[0096]
First, the present invention provides a method for removing an object to be removed by filtering the object to be removed from waste water in a state where the object to be removed is contained in a fluid as a colloidal solution or a sol.
[0097]
An object to be removed is a colloidal solution (sol) containing a large amount of fine particles having a particle size distribution of 3 nm to 2 μm. For example, a semiconductor generated by grinding with abrasive grains such as silica, alumina or ceria used for CMP and abrasive grains. Material waste, metal waste and / or insulating film material waste. In this example, a slurry for polishing W2000 tungsten manufactured by Cabot was used as the CMP slurry. This slurry is mainly composed of silica having a pH of 2.5 and an abrasive grain distribution of 10 to 200 nm.
[0098]
The basic principle of the present invention will be described with reference to FIG. The present invention removes a fluid (drainage) mixed with an object to be removed of a colloidal solution (sol) with a filter made of a gel film formed from the object to be removed.
[0099]
More specifically, a gel film to be a second filter 2 formed from a CMP slurry that is an object to be removed of a colloidal solution is formed on the surface of the first filter 1 made of organic polymer. It is immersed in the fluid 3 in the tank, and the waste water containing the object to be removed is filtered.
[0100]
The first filter 1 can be either organic polymer type or ceramic type in principle, as long as a gel film can be attached. Here, a polyolefin polymer film having an average pore diameter of 0.25 μm and a thickness of 0.1 mm was employed. A photograph of the surface of the filter membrane made of polyolefin is shown in FIG.
[0101]
Further, the first filter 1 has a flat membrane structure provided on both surfaces of the frame 4, is immersed so as to be perpendicular to the fluid, and is configured to be sucked by the pump 6 from the hollow portion 5 of the frame 4, The filtrate 7 can be taken out.
[0102]
Next, the second filter 2 is a gel film that is attached to the entire surface of the first filter 1 and gels by sucking the sol of the object to be removed. In general, since the gel film is jelly-like, it is considered that there is no function as a filter. However, in this invention, the function of the 2nd filter 2 can be given by selecting the production | generation conditions of this gel film. This generation condition will be described in detail later.
[0103]
Now, referring to FIG. 6 and FIG. 7 (A), the second filter 2 that is the gel film of the object to be removed is formed by the above-described colloidal solution (sol) of the object to be removed, and the filtration for removing the object to be removed is described with reference to FIGS. explain.
[0104]
1 is a first filter and 11 is a filter hole. The film formed in layers on the opening of the filter hole 11 and the surface of the first filter 1 is a gel film of the object 13 to be removed. The removal object 13 is sucked through the first filter 1 by the suction pressure from the pump, and since the moisture of the fluid 3 is sucked off, it is dried (dehydrated) and the fine particles of the removal object of the colloidal solution are gelled. A large gel film that is bonded and cannot pass through the filter hole 11 is formed on the surface of the first filter 1. This gel film forms the second filter 2.
[0105]
Eventually, when the second filter 2 reaches a predetermined film thickness, the second filter 2 forms a gap that does not allow the gel of the object to be removed to pass therethrough, and this second filter 2 is used to filter the object to be removed of the colloidal solution. Is started. Therefore, if the filtration is continued while sucking with the pump 6, the gel film is gradually laminated on the surface of the second filter 2 to become thick, and the second filter 2 is eventually clogged so that the filtration cannot be continued. During this time, the colloidal solution to be removed is gelled and adheres to the surface of the second filter 2 so that the water of the colloidal solution passes through the first filter 1 and is taken out as filtered water.
[0106]
In FIG. 7A, there is a drainage of a colloidal solution mixed with an object to be removed on one side of the first filter 1, and the first filter 1 has passed through the first filter 1 on the opposite side of the first filter 1. Filtered water is generated. The drainage is sucked in the direction of the arrow and flows, and as the fine particles in the colloidal solution approach the first filter 1 due to the suction, the gel film is formed by losing the electrostatic repulsion force and gelling and combining several fine particles. The second filter 2 is formed by being adsorbed on the surface of the filter 1. By the action of the second filter 2, the object to be removed in the colloidal solution is gelled while the waste water is filtered. Filtrated water is sucked from the opposite surface of the first filter 1.
[0107]
By slowly sucking the colloidal solution drainage through the second filter 2 in this way, the water in the drainage can be taken out as filtered water, and the object to be removed is dried and gelled and laminated on the surface of the second filter 2. Then, the object to be removed is captured as a gel film.
[0108]
Next, the generation conditions for the second filter 2 will be described with reference to FIG. FIG. 8 shows the generation conditions of the second filter 2 and the subsequent filtration amount.
[0109]
In the method of the present invention, first, the second filter 2 is formed and filtered. The amount of purified water filtered during filtration varies greatly depending on the production conditions of the second filter 2, and it is apparent that the gel membrane second filter 2 can hardly be filtered unless the purification conditions of the second filter 2 are appropriately selected. It becomes. This is consistent with the fact that it has traditionally been said that filtration of colloidal solutions is impossible.
[0110]
The characteristics shown in FIG. 8B are experimentally obtained by the method shown in FIG. That is, the first filter 1 is provided at the bottom of the cylindrical container 21, and 50 cc of a stock solution of slurry 22 for polishing W2000 tungsten manufactured by Cabot Corporation is added to generate a gel film by changing the suction pressure. Subsequently, the remaining slurry 22 is discarded, 100 cc of purified water 23 is added, and filtration is performed at a very low suction pressure. Thereby, the filtration characteristic of the gel film used as the 2nd filter 2 can be investigated. At this time, the first filter 1 having a diameter of 47 mm is used, and its area is 1734 mm. ² It is.
[0111]
In FIG. 8B, in the gel film generation step, film formation was performed for 120 minutes while changing the suction pressure to −55 cmHg, −30 cmHg, −10 cmHg, −5 cmHg, and −2 cmHg, and the properties of the gel film were examined. As a result, when the suction pressure is set as strong as -55 cmHg, the filtration amount is as large as 16 cc in 2 hours, and becomes 12.5 cc, 7.5 cc, 6 cc and 4.5 cc in order.
[0112]
Next, it replaces with purified water and performs filtration with this gel membrane. The suction pressure at this time is set to -10 cmHg constant. A gel film formed at a suction pressure of −55 cmHg can only filter 0.75 cc / hour. A gel film formed at a suction pressure of −30 cmHg has a filtration rate of about 1 cc / hour. However, the filtration amount is 2.25 cc / hour for a gel membrane with a suction pressure of −10 cmHg, 3.25 cc / hour for a gel membrane with a suction pressure of −5 cmHg, and 3.1 cc / hour for a gel membrane with a suction pressure of −2 cmHg. The gel film formed with the suction pressure can be stably filtered even in the filtration process. From this experimental result, if the suction pressure is set so that the filtration amount of about 3 cc / hour is set in the gel film generation step of the second filter 2, the filtration amount in the subsequent filtration step is the largest. it is obvious.
[0113]
The reason for this is that if the suction pressure is strong, the gel film to be formed has a low degree of swelling, becomes dense and hard, and the gel film is formed in a contracted state with little moisture content, so that purified water penetrates. This is probably because the passage is almost gone.
[0114]
On the other hand, if the suction pressure is weakened, the gel film to be formed has a high degree of swelling, a low density and is soft, and the gel film is formed with a large amount of water swelled and purified water penetrates. Many passages can be secured. It can be easily understood if you think about the situation where powder snow falls slowly. A feature of the present invention resides in that filtration is realized by using a gel film having a high degree of swelling formed with such a weak suction pressure and utilizing the property of moisture permeating into the gel film.
[0115]
The characteristics of the gel film will be described with reference to FIG. FIG. 9A shows the relationship between the amount of sol contained in the gel film and the amount of filtration. The amount of sol removed is obtained from purified water having a slurry concentration of 3% and the amount of sol trapped by the first filter 1 from the amount of filtration during gel film formation. This amount of sol is considered to be the amount of gel attached as the second filter 2 by drying by suction. It becomes clear from this that the amount of sol is smaller as the second filter 2 is formed by weak suction. That is, the amount of sol consumed when the amount of filtration is 3 cc / hour is as extremely small as 0.15 cc, and the amount of filtration increases as the amount of sol contained in the second filter 2 decreases. This suggests an important point of the present invention. By forming the second filter 2 with as little sol as possible, it is possible to filter the drainage of the colloidal solution.
[0116]
FIG. 9B shows the degree of swelling, that is, the density of the sol in the gel film, from the sol removal amount and the volume of the gel film described above. From the experimental results that the film thickness of the second filter 2 when the suction pressure is −30 mmHg is 6 mm and the film thickness of the second filter 2 when the suction pressure is −10 mmHg is 4 mm, the degree of swelling is 27 to 30 It has increased. That is, the greater the suction pressure, the lower the degree of swelling and the higher the sol amount density of the second filter 2. More importantly, the lower the suction pressure is, the thinner the film thickness of the second filter 2 is and the greater the degree of swelling is. Filtration of the second filter 2 formed with the suction pressure shown in FIG. It proves that the amount of filtration at the time is large and it can be filtered for a long time.
[0117]
Therefore, it is clear that the major point where the wastewater of the colloidal solution of fine particles of 0.15 μm or less can be filtered mainly depends on the film forming conditions of the second filter 2 in the present invention.
[0118]
The filter shown in FIG. 7A shows one side of the filter shown in FIG. 6, and is a schematic diagram for explaining how the gel film is actually attached.
[0119]
The first filter 1 is immersed vertically in the colloidal solution wastewater, and the wastewater is a colloidal solution in which the objects to be removed 13 are dispersed. The removal target 13 is indicated by a small black circle. When the drainage is sucked by the pump 6 through the first filter 1 with a weak suction pressure, the fine particles of the object to be removed are gelled and adsorbed on the surface of the first filter 1 as approaching the first filter 1. . The gelled fine particles 14 indicated by white circles are gradually adsorbed and stacked on the surface of the first filter 1 to form the second filter 2 made of a gel film, which is larger than the filter holes 11 of the first filter 1. The gelled fine particles 14 having a diameter smaller than that of the filter hole 11 pass through the first filter 1, but there is no problem because filtered water is circulated again to the drainage in the step of forming the second filter 2. As described above, the second filter 2 is formed by taking about 120 minutes. In this film forming step, the gelled fine particles 14 are stacked while forming gaps of various shapes because they are sucked with a very weak suction pressure, and the second filter is a soft gel film having a very low degree of swelling. 2. The water in the wastewater penetrates through the gel film having a high degree of swelling and is sucked and passes through the first filter 1 to be taken out as filtered water. Finally, the wastewater is filtered.
[0120]
That is, in the present invention, the second filter 2 is formed with a gel film having a high degree of swelling, and moisture contained in the gel film in contact with the first filter 1 is sucked from the first filter 1 with a weak suction pressure. The gel film is contracted by dehydration, and the gel film in contact with the drainage is infiltrated with water, replenished and swollen, and the second filter 2 is infiltrated only with water and filtered.
[0121]
In addition, air bubbles 12 are sent to the first filter 1 from the bottom surface of the drainage, and a parallel flow is formed in the drainage along the surface of the first filter 1. This is because the second filter 2 adheres uniformly to the entire surface of the first filter 1 and forms a gap in the second filter 2 so as to adhere softly. Specifically, the air flow rate is set to 1.8 liters / minute, but it is selected depending on the film quality of the second filter 2.
[0122]
Next, in the filtration step, the gelled fine particles 14 indicated by white circles are gradually stacked on the surface of the second filter 2 while being adsorbed by a weak suction pressure. At this time, the purified water penetrates through the second filter 2 and the gelled fine particles 14 indicated by the white circles to be further laminated, and is taken out from the first filter 1 as filtered water. In other words, in the case of CMP, for example, in the case of CMP, abrasives such as silica, alumina or ceria and scraps of semiconductor material generated by grinding with abrasive grains, metal scraps and / or insulating film material scraps, etc., are treated as gels. Gradually stacked on the surface of the second filter 2 and captured, and water can permeate the gel membrane and be taken out from the first filter 1 as filtered water.
[0123]
However, if filtration is continued for a long time as shown in FIG. 8 (B), the gel film is thickly attached to the surface of the second filter 2, so that the above-mentioned gap eventually becomes clogged, and filtered water cannot be taken out. . For this reason, it is necessary to remove the laminated gel film in order to regenerate the filtration capacity.
[0124]
Next, the actual filtration method will be specifically described using the filtration apparatus shown in FIG.
[0125]
First, the waste water mixed with the material to be removed of the colloidal solution is put into the raw water tank 50 through the pipe 51. The filter device 53 of only the first filter 1 in which the second filter 2 is not formed is immersed in the tank 50, and the waste water is circulated while being sucked with a weak suction pressure by the pump 57 through the pipe 56. . The circulation path is a filter device 53, a pipe 56, a valve V 1, a pump 57, a pipe 58, a control valve CV 1, a flow meter 61, an optical sensor 62, and a valve V 3, and waste water is sucked from the tank 50 and returned to the tank 50.
[0126]
By circulating, the second filter 2 is formed on the first filter of the filter device 53, and finally, the object to be removed of the target colloidal solution is captured.
[0127]
That is, when the pump 57 sucks the waste water through the first filter 1 with a weak suction pressure, the fine particles of the object to be removed are gelled and adsorbed on the surface of the first filter 1 as it approaches the first filter 1. Is done. The gelled fine particles larger than the filter holes 11 of the first filter 1 are gradually adsorbed and stacked on the surface of the first filter 1 to form a second filter 2 made of a gel film. The gelled fine particles having a diameter smaller than that of the filter hole 11 pass through the first filter 1, but the water in the drainage is sucked through this gap as the second filter 2 is formed, and the first filter 1. And is taken out as purified water, and the wastewater is filtered.
[0128]
The concentration of fine particles contained in the filtered water is monitored by the optical sensor 62, and it is confirmed that the fine particles are lower than a desired mixing rate, and filtration is started. When the filtration is started, the valve V3 is closed by a detection signal from the optical sensor 62, the valve V4 is opened, and the above-described circulation path is closed. Therefore, purified water is taken out from the valve V4. Air bubbles constantly supplied from the air pump 55 are adjusted from the air diffusion pipe 54 by the control valve CV2 and supplied to the surface of the filter device 53.
[0129]
If the filtration is continued continuously, the water in the waste water of the raw water tank 50 is taken out of the tank 50 as purified water, so that the concentration of the object to be removed in the waste water increases. That is, the colloidal solution is concentrated to increase the viscosity. For this purpose, the raw water tank 50 is replenished with drainage from the pipe 51 to suppress an increase in the concentration of drainage and increase the efficiency of filtration. However, the gel film is thickly attached to the surface of the second filter 2 of the filter device 53, and eventually the second filter 2 becomes clogged and becomes unable to be filtered.
[0130]
When the second filter 2 of the filter device 53 is clogged, the filtration capacity of the second filter 2 is regenerated. That is, the pump 57 is stopped and the negative suction pressure applied to the filter device 53 is released.
[0131]
The regeneration process will be further described in detail with reference to the schematic diagram shown in FIG. FIG. 10A shows the state of the filter device 53 in the filtration process. Since the hollow portion 5 of the first filter 1 has a negative pressure compared to the outside due to a weak suction pressure, the first filter 1 has a shape recessed inward. Accordingly, the second filter 2 adsorbed on the surface is similarly recessed inward. The same applies to the gel film that is gradually adsorbed on the surface of the second filter 2.
[0132]
However, referring to FIG. 10B, in the regeneration step, the weak suction pressure is stopped and the pressure returns to almost the atmospheric pressure, so that the first filter 1 of the filter device 53 returns to the original state. As a result, the second filter 2 and the gel film adsorbed on the surface thereof also return in the same manner. As a result, since the suction pressure that first adsorbs the gel film disappears, the gel film loses the adsorbing force to the filter device 53 and simultaneously receives a force that expands outward. Thereby, the adsorbed gel film starts to be detached from the filter device 53 by its own weight. Furthermore, in order to advance this separation, it is preferable to increase the amount of bubbles from the air diffuser 54 by about twice. According to the experiment, the separation starts from the lower end of the filter device 53, and the gel film of the second filter 2 on the surface of the first filter 1 is detached like an avalanche and settles on the bottom surface of the raw water tank 50. Thereafter, the second filter 2 may be formed again by circulating the waste water through the circulation path described above. In this regeneration step, the second filter 2 returns to the original state, returns to a state where the drainage can be filtered, and again filters the drainage.
[0133]
Furthermore, when the filtered water is caused to flow back into the hollow portion 5 in this regeneration step, firstly, the first filter 1 is helped to return to its original state, and the hydrostatic pressure of the filtered water is applied to further expand the outside. Second, filtered water oozes out from the inside of the first filter 1 through the filter hole 11 to the boundary between the first filter 1 and the second filter 2, and the second filter 2 from the surface of the first filter 1. Facilitates the release of the gel film.
[0134]
If filtration is continued while regenerating the second filter 2 as described above, the concentration of the material to be removed from the waste water in the raw water tank 50 increases, and the waste water eventually has a considerable viscosity. Therefore, when the concentration of the object to be removed from the wastewater exceeds a predetermined concentration, the filtering operation is stopped and left to settle. Then, the concentrated slurry is stored at the bottom of the tank 50, and the concentrated slurry of the gel is recovered by opening the valve 64. The recovered concentrated slurry is compressed or heat-dried to remove water contained therein and further compressed. This can greatly reduce the amount of slurry that is treated as industrial waste.
[0135]
With reference to FIG. 11, the driving | running state of the filtration apparatus shown in FIG. 2 is demonstrated. The operating condition is one side of the A4 size filter device 53 described above (area: 0.109 m). ² ). As described above, the initial flow rate is 3 cc / hour (0.08 m) with good filtration efficiency. ³ / Day), and the flow rate after regeneration is also set to the same value. The air blow rate is 1.8 L / min during film formation and filtration, and 3 L / min during regeneration. Pin and re-Pin are suction pressures and are measured by a pressure gauge 59. Pout and re-Pout are pressures in the pipe 58 and are measured by the pressure gauge 60. The flow rate and the reflow rate are measured by the flow meter 61 and represent the filtration amount sucked from the filter device 53.
[0136]
In FIG. 11, the left Y-axis indicates pressure (unit: MPa), and the negative pressure increases as the X-axis is approached. The right Y-axis indicates the flow rate (unit: cc / min). The X axis indicates the elapsed time (unit: minutes) from the film formation.
[0137]
As a point of the present invention, the flow rate and reflow rate are controlled to be maintained at 3 cc / hour in the film forming step, the filtering step, and the filtration step after regeneration of the second filter 2. For this reason, in the film forming process, Pin forms the second filter 2 with a gel film that is softly adsorbed with a very weak suction pressure of −0.001 MPa to −0.005 MPa.
[0138]
Next, in the filtration step, Pin is gradually increased from −0.005 MPa, and filtration is continued while ensuring a constant flow rate. Filtration is continued for about 1000 minutes, and the regeneration process is performed when the flow rate begins to decrease over time. This is because the gel film is thickly attached to the surface of the second filter 2 to cause clogging.
[0139]
Further, when the second filter 2 is regenerated, filtration is continued again at a constant reflow rate while gradually increasing the re-Pin. The regeneration and refiltration of the second filter 2 is continued until the raw water 52 has a predetermined concentration, specifically, the concentration is 5 to 10 times.
[0140]
Further, unlike the operation method described above, a method of performing filtration while fixing the suction pressure to −0.005 MPa, which has a large filtration flow rate, can also be employed. In this case, the filtration flow rate gradually decreases as the second filter 2 is clogged, but there is an advantage that the filtration time can be increased and the control of the pump 57 is simplified. Therefore, the regeneration of the second filter 2 may be performed when the filtration flow rate decreases below a certain value.
[0141]
FIG. 12A shows the particle size distribution of abrasive grains contained in the CMP slurry. The abrasive grains are used for CMP of an interlayer insulating film made of Si oxide, and the material is made of Si oxide, which is generally called silica. The minimum particle size was about 0.076 μm, and the maximum particle size was 0.34 μm. These large particles are agglomerated particles made up of a plurality of particles therein. Further, the average particle diameter is about 0.1448 μm, and the distribution has a peak in the vicinity of 0.13 to 0.15 μm. As a slurry adjusting agent, KOH or NH3 is generally used. The pH is between about 10-11.
[0142]
Specifically, the abrasive grains for CMP are mainly silica-based, alumina-based, cerium oxide-based, and diamond-based. Besides, chromium oxide-based, iron oxide-based, manganese oxide-based, BaCO4-based, antimony oxide-based, zirconia-based There is a yttria system. Silica is used for planarization of semiconductor interlayer insulating films, P-Si, SOI, etc., and Al / glass disks. Alumina is used for polishing hard disks, general metals, and planarization of Si oxide films. Further, cerium oxide is used for polishing glass and Si oxide, and chromium oxide is used for mirror polishing of steel. Manganese oxide and BaCO4 are used for polishing tungsten wiring.
[0143]
Furthermore, it is called an oxide sol. This sol is a monolith in which colloidal sized particles consisting of metal oxide or partial hydroxide, such as silica, alumina, zirconia, etc., are uniformly dispersed in water or liquid. It is used for planarization of interlayer insulating films and metals of semiconductor devices, and is also being studied for information disks such as aluminum disks.
[0144]
FIG. 12B shows data indicating that the CMP waste water is filtered and abrasive grains are captured. In the experiment, the above-mentioned slurry stock solution was diluted 50 times, 500 times, and 5000 times with pure water and prepared as a test solution. As described in the prior art, these three types of test solutions were prepared assuming that the drainage was about 50 to 5000 times because the wafer was cleaned with pure water in the CMP process.
[0145]
When the light transmittance of these three types of test solutions is examined with light having a wavelength of 400 nm, the test solution of 50 times is 22.5%, the test solution of 500 times is 86.5%, and the test solution of 5000 times. Is 98.3%. In principle, if abrasive grains are not included in the drainage, light is not scattered and should take a value close to 100%.
[0146]
When the filter on which the second filter film 13 was formed was immersed in these three types of test solutions and filtered, the transmittance after filtration was 99.8%. That is, since the value of the light transmittance after filtration is larger than the light transmittance before filtration, the abrasive grains can be captured. Incidentally, the transmittance data of the 50-fold diluted test solution is not shown in the drawing because the value is small.
[0147]
From the above results, when the removal object of the colloidal solution discharged from the CMP apparatus is filtered by the second filter 2 made of the gel film of the filter apparatus 53 provided in the filtration apparatus of the present invention, the transmittance is 99.8%. It was found that it can be filtered to the extent.
[0148]
In the above description, the fluid filtering method using the second filter which is a gel-like self-forming film has been described. However, the self-forming film is not limited to a gel-like one. The configuration of the present application can also be applied to a filtration apparatus and a filtration method using another type of self-forming film (precoat filter).
[0149]
【The invention's effect】
In the present invention, in the filtration device that performs filtration using the second filter that is a self-forming film, the filtered water is taken out from the filter device 53 using a pump having a motor capable of adjusting the suction pressure. . Therefore, the motor can be rotated at a high speed in the process of forming the second filter which is a self-forming film, and the motor can be rotated at a low speed in the filtration process using the formed self-forming film. Therefore, the second filter can be formed at an early stage in the step of forming the second filter. Furthermore, in the filtration step, it is possible to prevent the second filter from being destroyed by excessive suction pressure.
[0150]
Furthermore, when the second filter is a gel-like self-forming film, the gel can be maintained at a desired degree of swelling by rotating the motor at a low speed in the filtration step. Furthermore, it is possible to prevent the gel-like second filter from entering the hole of the first filter.
[0151]
Further, in order to remove mainly fine particles of 0.15 μm class or less such as abrasive grains mixed in CMP slurry, it is general to employ a filter film having pores smaller than the fine particles. However, the present invention has realized a filtration device that can filter a material to be removed from a colloidal solution by forming a gel membrane filter without using a filter membrane having a small pore size of 0.15 μm or less.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a filtration device according to the present invention.
FIG. 2 is a diagram illustrating a filter device embodied in the present invention.
FIG. 3 is a diagram for explaining an operation state of a further specific filtering device of the present invention.
FIG. 4 is a diagram illustrating a filter device of the present invention.
FIG. 5 is a diagram for explaining a further specific filter device of the present invention.
FIG. 6 is a diagram illustrating a filter according to the present invention.
FIG. 7 is a diagram for explaining the operating principle of the filter of the present invention.
FIG. 8A is a cross-sectional view and FIG. 8B is a characteristic diagram for explaining a film forming condition of a second filter of the present invention.
FIG. 9 is a diagram illustrating characteristics of the second filter of the present invention.
FIG. 10 is a diagram illustrating regeneration of the filter device of the present invention.
FIG. 11 is a diagram for explaining the operating state of the filtration device of the present invention.
FIG. 12 is a diagram illustrating the filtration characteristics of the present invention.
FIG. 13 is a diagram illustrating a conventional filtration system.
FIG. 14 is a diagram illustrating a CMP apparatus.
FIG. 15 is a diagram illustrating a system of a CMP apparatus.
[Explanation of symbols]
1 First filter
2 Second filter
4 frames
5 Hollow part
6 Pump
7 Filtrate
11 Filter hole
40 Ventilation pipe
50 Raw water tank
52 Raw water
53 Filter device
57 pump
61 Flow meter
62 Optical sensor

Claims (4)

A tank in which a fluid containing an object to be removed is stored; a first filter immersed in the tank; and the object to be removed which is deposited on the surface of the first filter by sucking the first filter. A fluid filter that filters the fluid using a filtration device having a filter device formed with a second filter and a pump connected to the first filter for suction. Filtration method,
  The motor provided in the pump is controlled in rotation speed of the motor in response to the pressure inside the pipe,
When forming the second filter, the suction pressure of the pump is larger than when the fluid is filtered,
A fluid filtering method characterized in that the suction pressure of the pump is made smaller when the fluid is filtered than when the second filter is formed. 2. The fluid filtering method according to claim 1, wherein the pump includes an AC motor whose rotation is controlled by an inverter circuit or a DC motor whose rotation is controlled by a voltage. The fluid filtering method according to claim 2, wherein a pressure gauge for measuring the suction pressure is interposed in the pipe. The fluid filtering method according to claim 1, wherein the fluid is a fluid containing a colloidal object to be removed.

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