ABRASIVE RECOVERY METHOD AND ABRASIVE RECOVERY DEVICE

There is provided an abrasive recovery device and an abrasive recovery method capable of recovering a slurry which is condensed until a concentration of its abrasive becomes high while suppressing an increase in pressure loss and a great decrease in a recovery ratio ascribable to membrane clogging. The abrasive recovery device is a device 1 which recovers an abrasive from a used polishing slurry which has been used in a CMP process, the device including a separation membrane 41 having a cylindrical hole passage to which the used polishing slurry is led, wherein an effective filtration part of the hole passage of the separation membrane 41 has a 0.8 m length or less, and the abrasive recovery device 1 condenses the used polishing slurry until a concentration of the abrasive becomes 10 mass % or more.

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Description
CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of prior International Application No. PCT/JP2011/004593 filed on Aug. 16, 2011, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2011-039948 filed on Feb. 25, 2011; the entire contents of all of which are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a recovery method and a recovery device of an abrasive, and more particularly to an abrasive recovery method capable of condensing a used polishing slurry to a high concentration and to a recovery device using the same.

BACKGROUND

A surface of a coating film such as an insulating film or a metal thin film formed on a semiconductor wafer is required to be a surface having high planarity. To meet the requirement, CMP (Chemical Mechanical Polishing) which performs the polishing while a polishing slurry is interposed between a polishing member such as a polishing pad and the semiconductor wafer is adopted.

As an abrasive used in CMP, silica fine particles high in dispersibility and having a uniform particle size, ceria high in polishing speed, alumina having high hardness and stability, and the like are used. These abrasives are provided by makers as slurries in which particles with predetermined particle size are dispersed in water in the predetermined concentration. When supplied to a CMP machine, the slurry is diluted to a predetermined concentration for use according to each site.

Generally, in addition to the abrasive, a pH adjusting agent such as potassium hydroxide, ammonia, organic acid, or amines, a dispersing agent such as a surfactant, an oxidant such as hydrogen peroxide, potassium iodate, or iron nitrate (III), and so on are added to the slurry in advance. Alternatively, these components are added separately to the slurry at the time of the polishing.

The reuse of these polishing slurries is desired in view of that they are used in large amount and are expensive and from a viewpoint of reducing an amount of industrial wastes. However, wastewater of a polishing process is diluted by water and the like in many washing processes and the concentration of the abrasive therein is decreased. In addition, in the wastewater of the polishing process, fine particles produced as a result of breakage of the semiconductor wafer, a material of the coating film, chips of the polishing pad, and the abrasive, solid impurities with a large particle size produced by the flocculation of the abrasive, and so on are mixed. Therefore, if such wastewater of the polishing process is reused as the abrasive without any treatment, a speed of the polishing for flattening is lowered due to the reduction in the concentration of the abrasive, or yields of products lower due to the occurrence of scratches on a surface of the wafer.

Therefore, before the reuse, it is necessary to remove impurities such as coarse solids and salts from the polishing wastewater and further perform the condensation treatment to re-prepare the polishing slurry with a predetermined composition.

Developments of various techniques have been conventionally attempted for the treatment of the wastewater of the CMP process. For example, there has been proposed a method in which wastewater of a CMP process is subjected to membrane treatment by being passed through a separation membrane such as a micro-filtration membrane or an ultra-filtration membrane, a chemical agent and ultra-pure water are added to prepare concentrations of an abrasive and a dispersing agent, and the resultant is reused as a polishing slurry.

A related reference, for instance, discloses a membrane treatment method of CMP wastewater in which, in order to improve a membrane permeation rate, a circulating liquid undergoes membrane separation in a first membrane element while its slurry concentration is maintained at a predetermined value, and thereafter, part thereof is extracted to further undergo membrane separation in a second membrane element.

Another related reference discloses a separation method of a slurried polishing liquid for semiconductor capable of removing a flocculate whose size becomes large due to the flocculation of fine particles and capable of recovering abrasive particles with a desired particle size. In Another related reference, the fine particles are removed by a “1 m” ultra-filtration membrane of a first step and coarse particles causing a polishing scratch are removed by a “2 m” micro-filtration membrane of a second step.

Further, another related reference discloses a method in which abrasive wastewater of a CMP process is condensed so that its specific gravity becomes 0.90 to 0.96 times a specific gravity of an undiluted solution by using a condensation filter such as an ultra-filtration membrane (primary condensation step) and this condensate is further condensed so that its specific gravity becomes 0.99 times to 1.01 times the specific gravity of the undiluted solution (secondary condensation step), whereby an abrasive is recycled.

One of the related references discloses an abrasive recovery device which reduces an amount of water passed through a membrane separation means and an amount of a dispersing agent in wastewater to suppress loading of the membrane at an early stage. In the reference, a condensate having undergone the condensation by a first membrane separation means on a pre-stage is led to a second membrane separation means on a post-stage and coarse solids are removed by the second membrane separation means.

As hollow-fiber separation membranes used in the above-described examples, ultra-filtration membranes are widely used. With respect to the hollow-fiber separation membrane, it is excellent in view of cost as its effective filtration length is longer because the number of modules used is reduced and those with an about 1 m filtration length are widely used in general

On the other hand, in the hollow-fiber separation membrane, as water to be treated has a higher concentration, solid components are deposited as cakes on its inner walls and a thickness of the cakes gradually increases. This results in a decrease in an effective inside diameter of the membrane to cause an increase in pressure loss and the occurrence of clogging of the membrane, which is liable to greatly lower a recovery ratio of the abrasive. Especially in the case of the treatment of wastewater of the CMP process, this tendency becomes conspicuous when the concentration of the abrasive exceeds about several %. Therefore, actually, the condensation up to about several % is a limit. In the arts described in the aforesaid Patent Documents as well, when the water to be treated with a high concentration is passed, it is difficult to sufficiently suppress the loading of the separation membrane and an accompanying reduction in the recovery ratio of the particles of the abrasive.

Generally, in filtration by a separation membrane, a progress speed of loading of the membrane rapidly increases when a concentration of water to be treated exceeds a predetermined value. As previously described, in the case of the polishing slurry, the loading rapidly progresses when the concentration of the abrasive exceeds about several %. Therefore, in conventional arts of wastewater treatment or the like, as the concentration of a solid component, about several % is a limit in practice, and with such a concentration, the reuse directly in the CMP process as a polishing slurry is difficult.

Further, when a hollow-fiber separation membrane is used, if the slurry is condensed until the concentration of the abrasive in the slurry exceeds about several %, the deposition of the cakes gradually progresses in the hollow fibers as previously described. It has been found out that, if the condensation is further continued thereafter, the abrasive turned into a gel state is deposited on a treatment water outlet side of the hollow fibers as shown in FIG. 8. In this state, a condensate cannot be obtained, and further the continuation of the use of the module itself becomes impossible. Further, since the abrasive is deposited in the gel form, a recovery ratio of the abrasive rapidly decreases.

The present invention was made to solve the aforesaid problems, and an object thereof is to provide an abrasive recovery device and an abrasive recovery method capable of suppressing an increase in pressure loss and a great reduction in a recovery ratio ascribable to the clogging of a membrane and capable of condensation so that a concentration of an abrasive becomes high.

As a result of studious studies by the present inventor in order to achieve the above object, it has been found out that whether or not cakes are deposited on filtration surfaces of a separation membrane and whether or not a gelatinous substance of an abrasive is deposited on a treatment water outlet side as described above depend mainly on an effective filtration length of the separation membrane, which has led to the completion of the present invention.

An abrasive recovery device of the present invention is a device which recovers an abrasive from a used polishing slurry in a CMP process, the abrasive recovery device including a separation membrane having a cylindrical hole passage to lead the used polishing slurry, wherein an effective filtration part of the hole passage of the separation membrane has a 0.8 m length or less, and the abrasive recovery device condenses the used polishing slurry until a concentration of the abrasive becomes 10 mass % or more.

The concentration of the abrasive led to the separation membrane depends on a concentration of wastewater of a customer's factory and therefore is not particularly limited, but generally, a used slurry with 0.02 to 5 mass % can be led. A hollow part of the separation membrane is preferably passed through by the used polishing slurry in a cross-flow method. The separation membrane is preferably provided in a membrane separation unit of an internal-pressure type. The separation membrane is preferably a hollow-fiber membrane. An inside diameter of the separation membrane is preferably not less than 0.1 mm nor more than 0.8 mm. A molecular cut-off of the separation membrane is preferably 3,000 to 30,000. The separation membrane is preferably made of any one of polyethylene, tetrafluoroethylene, polyvinylidene difluoride, polypropylene, cellulose acetate, polyacrylonitrile, polyimide, polysulfone, and polyethersulfone.

The abrasive recovery device can have a pre-separation membrane provided on a previous stage of the separation membrane, having a longer effective filtration length than an effective filtration length of the separation membrane, and having a cylindrical hole passage. Namely, An abrasive recovery device of the present invention can include a first separation membrane having a first cylindrical hole passage to lead a used polishing slurry in a CMP process, the first cylindrical hole passage having a first effective filtration part, a second separation membrane provided on a subsequent stage of the first separation membrane, the second separation membrane having a second cylindrical hole passage to lead a condensate from the first separation membrane, the second cylindrical hole passage having a second effective filtration part shorter than the first effective filtration part in length, the second effective filtration part being not longer than 0.8 m, circulation mechanism configured to pass the condensate from the first separation membrane through the second separation membrane sequentially and condense the used polishing slurry until a concentration of the abrasive becomes 10 mass % or more and recover an abrasive from the used polishing slurry.

Preferably, a length L1 of the first effective filtration part is 0.8 to 1.5 m, and a length L2 of the second effective filtration part is 0.2 to 0.8 m or less.

An abrasive recovery method of the present invention includes: passing a used polishing slurry in a CMP process through a separation membrane whose hole passage is cylindrical and whose effective filtration part has a 0.8 m length or less; and condensing the used polishing slurry until a concentration of an abrasive of the used polishing slurry becomes 10 mass % or more. Preferably, a hollow portion of the separation membrane is passed through by the used polishing slurry in a cross-flow method. Further, an inside diameter of the separation membrane is preferably not less than 0.1 mm nor more than 0.8 mm. Further, a circulation flow rate of water to be treated in the effective filtration part of the separation membrane is preferably 0.5 to 2 m/sec.

The method may include: a first filtration step of passing the used polishing slurry in the CMP process through a pre-separation membrane whose hole passage is cylindrical, to condense the used polishing slurry; and a second filtration step of passing a condensate from the first separation membrane through a post-separation membrane whose effective filtration part has a 0.8 m length or less, to condense the condensate, wherein, as the pre-separation membrane, a separation membrane having a longer effective filtration length than an effective filtration length of the post-separation membrane is usable. Namely, the method may include: a first filtration step of passing the used polishing slurry in the CMP process through a first separation membrane having a first cylindrical hole passage, to condense the used polishing slurry, the first cylindrical hole passage having a first effective filtration part; and a second filtration step of passing a condensate from the first separation membrane through a second separation membrane provided on a subsequent stage of the first separation membrane, the second separation membrane having a second cylindrical hole passage, the second cylindrical hole passage having a second effective filtration part shorter than the first effective filtration part in length, the second effective filtration part being not longer than 0.8 m, to condense the condensate until a concentration of an abrasive of the condensate becomes 10 mass % or more.

The concentration depends on an abrasive concentration of wastewater of a customer's factory and therefore is not particularly limited, but in the first filtration step, it is generally preferable that the used polishing slurry with 0.02 to 5 mass % is condensed to 13 mass % at the maximum, more preferably 9 to 10 mass % by the filtration, and in the second filtration step, it is preferable that the condensate with 13 mass % or less obtained in the first filtration step is condensed up to 26 mass % at the maximum, more preferably 20 to 25 mass % by the filtration. Further, the abrasive recovery method preferably uses the above-described abrasive recovery device of the present invention.

According to the used abrasive recovery device of the present invention, the use of the separation membrane whose effective filtration part has a length equal to a predetermined value or less makes it difficult to cause problems such as the deposition of cakes on filtration surfaces and the deposition of a gelatinous abrasive on a treatment water outlet side. This makes is possible to condense the slurry until the abrasive concentration becomes about several ten % or more. Further, with lower energy than is necessary conventionally, it is possible to condense the used polishing slurry having been used in the CMP process to a high concentration, and it is possible to recover the condensed slurry in which the concentration of the abrasive is increased up to a high level enabling the reuse as a product. Further, in spite of the condensation up to such a high concentration, it is possible to suppress an increase in pressure loss inside the membrane and the clogging of the separation membrane, so that the abrasive recovery device can be a device in which a great decrease in a recovery ratio is suppressed.

Further, in the used polishing slurry recovery method of the present invention, it is possible to recover the condensed slurry in which the concentration of the abrasive is increased up to a high level enabling the reuse as a product without causing a great decrease in a recovery ratio. This makes it possible to cut down an amount of a new slurry used in the CMP process by 60% or more.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a schematic structure of an abrasive recovery device according to one embodiment of the present invention.

FIG. 2 is an enlarged view of a cross section of one hollow fiber forming a separation membrane 41.

FIG. 3 is a diagram showing a schematic structure of an abrasive recovery device according to one embodiment of the present invention.

FIG. 4 is a chart showing a relation between a concentration of an abrasive in a treatment tank and an amount of a permeate discharged from a permeate outlet pipe (flux).

FIG. 5 is a chart showing a relation between a concentration of an abrasive in a treatment tank 13 and an amount of a permeate discharged from a first permeate outlet pipe 22 (flux), and a relation between a concentration of the abrasive in a treatment tank 17 and an amount of a permeate discharged from a second permeate outlet pipe 24 (flux), in the recovery device in FIG. 3.

FIG. 6 is a photograph showing a state of an inlet of a membrane separation unit at an instant when a separation membrane is clogged.

FIG. 7 is an enlarged photograph of FIG. 6.

FIG. 8 is a photograph showing a state of an outlet of the membrane separation unit at the instant when the separation

 DETAILED DESCRIPTION

Hereinafter, an abrasive recovery device and an abrasive recovery method of the present invention will be described in detail.

First Embodiment

FIG. 1 is a diagram showing a schematic structure of an abrasive recovery device according to one embodiment of the present invention. In the abrasive recovery device 1 in this embodiment, a guard filter 2 which removes coarse particles contained in a used polishing slurry S which has polished a semiconductor in a CMP process (hereinafter, referred to as the used polishing slurry S), a treatment tank 3 housing water to be treated from the guard filter 2, and a membrane separation unit 4 including a separation membrane 41 which filtrates the used polishing slurry S are installed in sequence along a flow path.

Note that the guard filter 2 captures solid impurities with a large particle size produced by the flocculation of an abrasive, polishing pad chips when a semiconductor wafer is polished, and so on. As the guard filter 2, any filter is usable without any particular limitation, provided that it has a larger pore size than a particle size of particles of the abrasive.

The guard filter 2 and the treatment tank 3 are connected by a pipe 5. The treatment tank 3 and the membrane separation unit 4 are connected by a pipe 6 having a pump P1. Note that the treatment tank 3 is provided with a component concentration meter C1.

A permeate outlet pipe 7 and a condensate outlet pipe 8 having an opening/closing valve B1 are connected to the membrane separation unit 4. The condensate outlet pipe 8 is opened so as to supply a condensate obtained in the membrane separation unit 4 to a condensate recovery tank 9.

Between an upstream portion of the opening/closing valve B1 of the condensate outlet pipe 8 and the treatment tank 3, there is provided a reflux pipe 10 through which the condensate obtained in the membrane separation unit 4 flows back to the treatment tank 3 while the opening/closing valve B1 is closed and the opening/closing valve B2 is opened.

The separation membrane 41 has cylindrical hole passages. The used polishing slurry S is passed inside or outside the hole passages, so that excessive water of the used polishing slurry S is removed, resulting in the condensation.

As the separation membrane 41 having the cylindrical hole passages, a separation membrane of a hollow-fiber type, a tubular type, or a flat-membrane type is applicable, for instance. Among them, the hollow-fiber separation membrane is space-saving and can have a large membrane area and thus is suitably used as the separation membrane 41.

A length L of an effective filtration part of the separation membrane 41 is 0.8 m or less, preferably 0.5 m or less, and more preferably 0.3 m or less depending on a targeted condensation concentration. Generally, in the case of the hollow-fiber separation membrane, for instance, when a high-concentration slurry is passed through the separation membrane, solid components are deposited on filtration surfaces 412 of hollow fibers 410 in a process where the condensate passes through its effective filtration parts. Further continuing the water passage results in the formation of cake layers due to the solid components deposited on the filtration surfaces 412 to cause an increase in their thickness (refer to FIG. 2). The longer the effective filtration length, the more likely the cake layers are formed on the filtration surfaces 412 of the separation membrane 41. The formation of the cake layers narrows an effective inside diameter 410S of the hollow fibers 410, so that a pressure loss increases or the membrane is clogged, which sometimes greatly lowers recovery efficiency of the abrasive. Further, since the cake layers and the gelatinous deposits are formed of abrasive particles, a recovery ratio of the abrasive particles lowers in accordance with the increase of the cake layers and the generation of the gelatinous deposits.

Further, as shown in FIG. 8, the abrasive is deposited in a gel form on a treatment water outlet side of the hollow fibers to make it difficult to continue the filtration. Further, an amount of chemicals required for washing the filtration surfaces and a washing time increase, causing an increase in cost required for the whole abrasive recovery step.

In the abrasive recovery device 1 of the present invention, a separation membrane in which the length L of its effective filtration part is 0.8 m or less, preferably 0.5 m or less, and more preferably 0.3 m or less is used as the separation membrane 41. When a module whose effective filtration length is such a predetermined value or less is used, even the passage of the used slurry with a high concentration does not easily cause loading. Therefore, the growth of the cake layers on the filtration surfaces 412 is suppressed and the gelatinous deposits are not generated.

Therefore, even the passage of high-concentration water to be treated does not easily cause an increase in pressure loss in the separation membrane 41 and the clogging of the separation membrane 41, and a great reduction in the recovery ratio is suppressed in the recovery device 1.

Further, when the cake layers are formed on the filtration surfaces 412 as described above, the coarse particles which are gelated abrasive particles exfoliate from the cake layers and sometimes mix in the water to be treated. The mixture of such coarse particles in the recovered abrasive causes a scratch on a wafer surface when it is reused in the CMP process, causing deterioration in yields of products.

In the abrasive recovery device 1 of the present invention, as the separation membrane 41, a separation membrane in which the length L of its effective filtration part falls within the aforesaid range is used. Therefore, the formation of the cake layers in the separation membrane and the generation of the coarse particles due to the deposition of the gelatinous substances are suppressed, and a mixture amount of the coarse particles in the recovered abrasive is greatly reduced. Therefore, even when it is reused in the CMP process, the abrasive capable of high-precision polishing can be recovered, with almost no scratch or the like being caused on the wafer surface.

When the length L of the effective filtration part of the separation membrane 41 is over 0.8 m, a thickness of the cake layers is likely to increase on the filtration surfaces 412 of the separation membrane 41, and an increase in pressure loss and the clogging of the membrane easily occur due to a decrease in the effective inside diameter.

The length L of the effective filtration part of the separation membrane 41 preferably falls within the aforesaid range and is 0.2 m or more. When the length L of the effective filtration part of the separation membrane 41 is less than 0.2 m, the number of modules of the separation membrane 41 installed in the recovery device 1 increases, which makes it difficult to install an appropriate filtration device. The length L of the effective filtration part of the separation membrane 41 is preferably 0.2 to 0.3 m.

The separation membrane 41 may be an organic membrane made of an organic material or may be an inorganic membrane made of inorganic ceramics.

As the organic membrane, polyethylene (PE), tetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), polypropylene (PP), cellulose acetate (CA), polyacrylonitrile (PAN), polyimide (PI), polysulfone (PS), polyethersulfone (PES), and the like, for instance, are suitably usable.

Further, as the inorganic membrane, a ceramics material of aluminum oxide (Al2O3), zirconium oxide (ZrO2), or titanium oxide (TiO2), stainless steel (SUS), glass (SPG), or the like is usable. Among them, polysulfone (PS) and polyethersulfone (PES) are suitably usable as the separation membrane 41.

The separation membrane 41 may be a micro-filtration membrane or an ultra-filtration membrane, provided that it has a hollow-fiber shape. The ultra-filtration membrane is suitably usable as the separation membrane 41 in view of that it recovers the particles of the abrasive in the recovered condensate most efficiently.

A molecular cut-off of the separation membrane 41 is preferably 3,000 to 30,000. When the molecular cut-off of the separation membrane 41 is less than 3,000, it is necessary to increase a supply pressure to the separation membrane 41 in order to obtain a permeate bypassing the water to be treated through the separation membrane 41. This lowers energy efficiency and may possibly impair the separation membrane 41.

On the other hand, when the molecular cut-off of the separation membrane 41 is over 30,000, part of the particles of the abrasive passes through the separation membrane 41 to move to a permeate side, which is liable to disable the efficiently recovery of the particles of the abrasive. Further, in this case, fine particles having substantially the same diameter as a pore size of the separation membrane 41 are likely to clog the holes of the separation membrane 41, which may cause the loading. The molecular cut-off of the separation membrane 41 is more preferably 6000 to 10000.

When the separation membrane 41 is a hollow-fiber separation membrane or a tubular separation membrane, an inside diameter of each hollow fiber or the like is preferably not less than 0.1 mm nor more than 0.8 mm. When the inside diameter of each hollow fiber or the like of the separation membrane 41 is less than 0.1 mm, a pressure loss of the water to be treated flowing in the hollow portions of the membrane increases, which makes it difficult to obtain appropriate treatment efficiency. Further, in this case, membrane surface strength lowers, which is liable to cause breakage of the membrane in accordance with an increase of the concentration of the water to be treated. On the other hand, when the inside diameter of each hollow fiber or the like of the separation membrane 41 is over 0.8 mm, since a shear speed of the water to be treated flowing in the hollow portions of the membrane is low, the abrasive and other impurities are easily deposited on inner walls of the hollow fibers, which is liable to clog the hollow portions. Further, a large amount of gel of the abrasive is produced, which is liable to lower the concentration of the abrasive in the condensate. In order to increase the shear speed, it is necessary to make the facility large, and a large amount of energy is consumed, which is not preferable. Further, pressure resistance against an external pressure is liable to lower. The inside diameter of each hollow fiber or the like of the separation membrane 41 is more preferably not less than 0.3 mm nor more than 0.8 mm.

The membrane separation unit 4 may be an internal pressure-type separation unit which passes the water to be treated inside the hollow fibers 410 or may be an external pressure-type separation unit which passes the water to be treated outside support layers 411 of the hollow fibers 410. When the membrane separation unit 4 is the internal pressure-type separation unit, the solid components deposited on the filtration surfaces 412 are exfoliated by a shear force of the water to be treated passed in the hollow fibers 410 and the growth of the cake layers can be suppressed, which is preferable.

With such a recovery device 1, it is possible to recover and reuse the permeate obtained from the permeate outlet pipe 7. Concretely, for example, it can be used as raw water of an ultra-pure water device without being treated or after undergoing treatment according to quality of the permeate. Further, it can be used as other utility than in a factory, for example, domestic water, water for cooling tower, or the like.

Second Embodiment

FIG. 3 is a diagram showing a schematic structure of an abrasive recovery device according to one embodiment of the present invention. In the abrasive recovery device 11 in this embodiment, on a subsequent stage of a guard filter 12 which removes coarse particles contained in a used polishing slurry S having polished a semiconductor in a CMP process (hereinafter, referred to as the used polishing slurry S), a pre-treatment tank 13 housing treated water from the guard filter 12 and a pre-membrane separation unit 14 (hereinafter, referred to as the first membrane separation unit 14) including a pre-separation membrane 141 (hereinafter, referred to as the first separation membrane 141) which filtrates the used polishing slurry S are installed in sequence along a flow path.

Note that the guard filter 12 captures solid impurities with a large particle size produced by the flocculation of an abrasive, polishing pad chips when a semiconductor wafer is polished, and so on. As the guard filter 12, any filter is usable without any particular limitation, provided that it has a larger pore size than a particle size of particles of the abrasive. The guard filter 12 and the pre-treatment tank 13 are connected by a pipe 15. The pre-treatment tank 13 and the first membrane separation unit 14 are connected by a pipe 16 having a pump P2. Note that the pre-treatment tank 13 is provided with a component concentration meter C2.

On a subsequent stage of the first membrane separation unit 14, a post-treatment tank 17 housing a condensate separated in the first membrane separation unit 14 (hereinafter, sometimes referred to as the first condensate), a post-membrane separation unit 18 (hereinafter, referred to as the second membrane separation unit 18) including a post-separation membrane 181 (hereinafter, referred to as the second separation membrane 181) which filtrates the first condensate supplied from the post-treatment tank 17, and a recovery tank 19 which recovers a condensate (hereinafter, sometimes referred to as the second condensate) separated in the second membrane separation unit 18 are sequentially installed. Note that the post-treatment tank 17 is provided with a component concentration meter C3.

The first membrane separation unit 14 and the post-treatment tank 17 are connected by a pipe 20 including an opening/closing valve B3. The post-treatment tank 17 and the second membrane separation unit 18 are connected by a pipe 21 including a pump P3.

A first permeate outlet pipe 22 is connected to the first membrane separation unit 14. Further, between a pre-stage of the opening/closing valve B3 of the pipe 20 and the pre-treatment tank 13, there is provided a reflux pipe 23 through which the first condensate obtained in the first membrane separation unit 14 flows back to the pre-treatment tank 13 while the opening/closing valve B3 is closed and the opening/closing valve B4 is opened.

A second permeate outlet pipe 24 and a condensate outlet pipe 25 including an opening/closing valve B5 are connected to the second membrane separation unit 18. The condensate outlet pipe 25 is opened so as to supply the condensate obtained in the second membrane separation unit 18 to the recovery tank 19. Between an upstream portion of the opening/closing valve B5 of the condensate outlet pipe 25 and the post-treatment tank 17, there is provided a reflux pipe 26 through which the second condensate obtained in the second membrane separation unit 18 flows back to the post-treatment tank 17 while the opening/closing valve B5 is closed and the opening/closing valve B6 is opened.

The first separation membrane 141 and the second separation membrane 181 have cylindrical hole passages. The used polishing slurry S is passed inside or outside the hole passages, so that excessive water of the used polishing slurry S is removed, resulting in the condensation. As the first separation membrane 141 having the cylindrical hole passages, a separation membrane of a hollow-fiber type, a tubular type, or a flat-membrane type is applicable, for instance. Among them, the hollow-fiber separation membrane is space-saving and can have a large membrane area and thus is suitably used as the first separation membrane 141 and the second separation membrane 181.

The second separation membrane 181 filtrates and further condenses the condensate from the first separation membrane 141 provided on a previous stage to increase a concentration of its abrasive. A length L2 of an effective filtration part of the second separation membrane 181 is 0.8 m or less, preferably 0.5 m or less, and more preferably 0.3 m or less.

The use of the separation membrane having the aforesaid effective filtration length as the second separation membrane 181 suppresses the growth of cake layers because loading of the membrane does not easily occur even when a high-concentration used slurry is passed therethrough. Therefore, even when the high-concentration water to be treated is passed, an increase in pressure loss in the second separation membrane 181 and the loading of the second separation membrane 181 do not easily occur, which can realize the recovery device 11 in which a great decrease in a recovery ratio is suppressed.

When the length L2 of the effective filtration part of the second separation membrane 181 is over 0.8 m, a thickness of the cake layers is likely to increase on filtration surfaces of the second separation membrane 181, so that an increase in pressure loss and the clogging of the membrane due to the decrease in the effective inside diameter are likely to occur. The length L2 of the effective filtration part of the second separation membrane 181 is especially preferably 0.2 to 0.3 m for the same reason as that for the separation membrane 41 in the first embodiment.

The length L2 of the effective filtration part of the second separation membrane 181 is preferably shorter than the length L1 of the effective filtration part of the first separation membrane 141. That is, the length L1 of the effective filtration part of the first separation membrane 141 is preferably longer than the length L2 of the effective filtration part of the second separation membrane 181.

Consequently, in the first separation membrane 141, the used polishing slurry S low in concentration diluted by a dispersion medium is efficiently filtrated, and in the second separation membrane 181, the first condensate obtained in the first separation membrane 141 is further filtrated. Consequently, with low energy, it is possible to recover the condensed slurry in which a concentration of particles of its abrasive is increased up to a high level enabling the reuse as a product.

In recent years, an amount of a used slurry discharged in a CMP process per day sometimes exceeds 1000 m3. Under such circumstances, there is a demand for a technique which removes and recovers water contained in the slurry and recovers an abrasive component by more efficient treatment.

In this embodiment, the above-described two-stage structure makes it possible to greatly reduce a volume of the water to be treated owing to the first separation membrane 141 with a large membrane area provided on a pre-stage, and to condense the water to be treated to a higher concentration without causing the loading owing to the second separation membrane 181 provided on a post stage. Therefore, it is possible to reduce the number of modules used as compared with the first embodiment.

When the length L2 of the effective filtration part of the second separation membrane 181 is equal to or more than the length L1 of that of the first separation membrane 141, a thickness of the cake layers is likely to increase inside the second separation membrane 181, and an increase in pressure loss and the clogging of the membrane are likely to occur due to a decrease in an effective inside diameter.

The length L1 of the effective filtration part of the first separation membrane 141 is not particularly limited, but is preferably 0.8 to 1.5 m in consideration of a membrane area and the like. When the length L1 of the effective filtration part of the first separation membrane 141 is less than 0.8 m, the number of modules of the separation membrane 141 installed in the recovery device 11 increases and an installation area increases, which makes it impossible to obtain a sufficient effect as the recovery device.

On the other hand, when the length L1 of the effective filtration part of the first separation membrane 141 is over 1.5 m, there occurs a limit to an installation height of the first separation membrane 141 or the separation membrane 141 is liable to be difficult to handle. The length L1 of the effective filtration part of the first separation membrane 141 is more preferably 0.8 to 1.5 m.

The first separation membrane 141 may be a micro-filtration membrane or an ultra-filtration separation membrane, provided that it has cylindrical hole passages, i.e. it has a hollow-fiber shape. Suitably usable is the ultra-filtration membrane which efficiently recovers the particles of the abrasive (abrasive grains), keeps granularity of the abrasive particles in the recovered condensate constant, has a small pore size, and is excellent in energy efficiency.

Further, the second separation membrane 181 may also be a micro-filtration membrane or an ultra-filtration membrane, provided that it has a hollow-fiber shape. The ultra-filtration membrane is suitably usable in view of keeping a recovery ratio of the abrasive particles in the recovered condensate high.

A molecular cut-off of the first separation membrane 141 and the second separation membrane 181 is preferably 3,000 to 30,000. When the molecular cut-off of the first separation membrane 141 and the second separation membrane 181 is less than 3,000, it is necessary to increase a supply pressure to the separation membranes in order to obtain permeates by passing the water to be treated through the separation membranes. Accordingly, energy efficiency lowers and the separation membranes are liable to be damaged.

On the other hand, when the molecular cut-off of the first separation membrane 141 and the second separation membrane 181 is over 30,000, part of the abrasive particles passes through the first separation membrane 141 to move to a permeate side, which may lower recovery efficiency of the abrasive particles. Further, in this case, holes of the separation membrane 141 and the second separation membrane 181 are likely to be clogged by fine particles having substantially the same size as the pore size of the separation membrane 141, which may cause the loading.

When the first separation membrane 141 and the second separation membrane 181 are hollow-fiber separation membranes or tubular separation membranes, an inside diameter thereof is preferably not less than 0.1 mm nor more than 0.8 mm. When the inside diameter of each hollow fiber or the like of the first separation membrane 141 is less than 0.1 mm, a pressure loss of the water to be treated flowing in hollow portions of the membrane increases, which makes it difficult to obtain appropriate treatment efficiency and lowers membrane surface strength of the separation membrane 141, which may lead to a breakage of the membrane in accordance with an increase in the concentration of the water to be treated. On the other hand, when the inside diameter of each hollow fiber or the like of the first separation membrane 141 is 0.8 mm or more, a shear speed of the water to be treated flowing in the hollow portions of the membrane is low and the abrasive and other impurities are easily deposited on inner walls of the hollow portions, which may clog the hollow portions, cause the generation of a large amount of gel produced by the flocculation of the abrasive particles, and lower the concentration of the abrasive in the recovered condensate. The inside diameter of each hollow fiber or the like of the first separation membrane 141 and the second separation membrane 181 is more preferably not less than 0.3 mm nor more than 0.8 mm.

The first separation membrane 141 and the second separation membrane 181 may be organic membranes made of an organic material or may be inorganic membranes made of inorganic ceramics. As the organic membrane, polyethylene (PE), tetrafluoroethylene (PTFE), polyvinylidene difluoride (PVDF), polypropylene (PP), cellulose acetate (CA), polyacrylonitrile (PAN), polyimide (PI), polysulfone (PS), polyethersulfone (PES), and the like, for instance, are suitably usable.

Further, as the inorganic membrane, a ceramics material of aluminum oxide (Al2O3), zirconium oxide (ZrO2), or titanium oxide (TiO2), stainless steel (SUS), glass (SPG), or the like is usable. Among them, polysulfone (PS) and polyethersulfone (PES) are suitably usable as the first separation membrane 141 and the second separation membrane 181.

When the first separation membrane 141 and the second separation membrane 181 are hollow-fiber separation membranes, separation units may be of an internal-pressure type which passes the water to be treated inside the hollow fibers or may be of an external-pressure type which passes the water to be treated outside support layers of the hollow fibers. When the separation unit is of the internal-pressure type, solid components deposited on filtration surfaces are exfoliated by a shear force of the water to be treated passed in the hollow fibers, which is preferable because the growth of cake layers can be suppressed.

In such a recovery device 11, since it is possible to condense a diluted solution of the slurry to a certain degree by the first separation membrane 141, it is possible to efficiently condense a large amount of CMP wastewater. Especially in a semiconductor factory whose production scale is large, an amount of wastewater discharged per day sometimes reaches 1000 tons or more, but providing the first separation membrane 141 makes it possible to reduce such a large amount of the wastewater to about 1/10 to 1/500. Therefore, as compared with the first embodiment without the first separation membrane 141 being provided, it is possible to reduce the number of modules installed as a whole.

In the foregoing, the abrasive recovery device 11 of the present invention is described based on its example, but its structure can be changed as necessary within the limit not contrary to the spirit of the present invention.

Next, an abrasive recovery method using the abrasive recovery device 11 of the present invention will be described based on FIG. 3. Note that this embodiment will describe a case where the abrasive recovery device 11 including ultra-filtration membranes of a hollow-fiber type both as the first separation membrane 141 and the second separation membrane 181 is used. The first separation membrane 141 is not necessarily the hollow-fiber separation membrane, provided that it has cylindrical hole passages, and may be of a tubular type or of a flat membrane type.

The used polishing slurry S to be treated is not particularly limited, provided that it contains an abrasive which has been used in a CMP process (chemical mechanical polishing process). Examples of particles of such an abrasive are silicon particles, cerium particles, and so on. As the particles of the abrasive, those having an average particle size of 0.01 to 1 μm are suitably used in general. The average particle size of the abrasive is appropriately decided depending on the CMP process and is 0.04 to 0.4 μm, for instance.

First, the used polishing slurry S which has been used in the CMP process is supplied to the guard filter 12 via the pipe 15. The used polishing slurry S is stored in the pre-treatment tank 13 after its coarse particles with a particle size of several ten μm or more are removed in a process where it passes through the guard filter 12.

The concentration of the particles of the abrasive in the non-treated used polishing slurry S is not particularly limited because it depends on a customer's factory. The abrasive concentration of the used polishing slurry S in the CMP process is generally 0.02 to 5 mass %.

The used polished slurry S stored in the pre-treatment tank 13 is pressure-fed to the first membrane separation unit 14 including the first separation membrane 141 via the pipe 16 by the pump P2 while the opening/closing valve B3 is closed and the opening/closing valve B4 is opened. The used polishing slurry S is passed inside each hollow fiber of the first separation membrane 141 by the cross-flow method after its coarse particles with a particle size of several ten μm or more are removed in the process where it passes through the guard filter 12, and is condensed with its excessive water being permeated in a process where it passes through the effective filtration part of the first separation membrane 141 (first filtration step). At this time, a dispersion medium and so on of the used polishing slurry S flow out to the permeate outlet pipe 22 via the separation membrane 141, and the particles of the abrasive in the used polishing slurry S remain on the first condensate side being the condensate from the first separation membrane 141.

The first condensate is made to flow back to the pre-treatment tank 13 via the reflux pipe 23. After this step is continued for a predetermined time, the opening/closing valve B3 is opened and the opening/closing valve B4 is closed at a stage when the concentration of the abrasive in the stored water in the pre-treatment tank 13 as measured by the component concentration meter C2 becomes 13 mass % at the maximum, more preferably 9 to 10 mass %, and part of the first condensate is supplied to the post-treatment tank 17 via the pipe 20.

A velocity of the water to be treated (the used polishing slurry S and the first condensate) passing through the effective filtration part of the first separation membrane 141 is preferably 0.5 to 2 m/sec. When the velocity of the water to be treated (the used polishing slurry S and the first condensate) in the effective filtration part of the first separation membrane 141 is less than 0.5 m/sec, the abrasive particles easily adhere onto the filtration surfaces of the separation membrane 141 to sometimes cause a decrease in an amount of the permeate. In this case, it is necessary to increase the number of the separation membranes 141 installed, resulting in an increase in manufacturing cost of the recovery device 11. On the other hand, when the velocity of the water to be treated in the effective filtration part of the first separation membrane 141 is over 2.0 m/sec, an amount of liquid in contact with the membrane surface becomes excessive to sometimes cause heat generation. In this case, the separation membrane 141 and the condensate are both liable to be damaged by the heat to deteriorate. Further, in order to improve the velocity of the water to be treated in the separation membrane 141, it is necessary to increase the sizes of the pipes, the valves, and so on, resulting in an increase in manufacturing cost of the recovery device 11. The velocity of the water to be treated passing through the effective filtration part of the first separation membrane 141 is more preferably 0.55 to 1.5 m/sec.

The first condensate stored in the post-treatment tank 17 is pressure-fed to the second membrane separation unit 18 including the second separation membrane 181 via the pipe 21 by the pump P3 while the opening/closing valve B5 is closed and the opening/closing valve B6 is opened. The second separation membrane 181 has the effective filtration length L2 which is shorter than the effective filtration length L1 of the first separation membrane 141 and is 0.8 m or less, preferably 0.5 m or less, and more preferably 0.3 m or less. In the second separation membrane 181, the first condensate is passed to the hollow portion of each of its hollow fibers by the cross-flow method. The first condensate is condensed with its excessive water being permeated in a process where it passes through the effective filtration part of the hollow fibers (second filtration step). At this time, a dispersion medium and so on of the first condensate flow out to the permeate outlet pipe 24 via the separation membrane 181, and the abrasive particles contained in the first condensate remain in a second condensate side being a condensate from the second separation membrane 181.

A velocity of the water to be treated (first condensate) passing through the effective filtration part of the second separation membrane 181 is preferably 0.5 to 2 m/sec. When the velocity of the water to be treated in the effective filtration part of the second separation membrane 181 is less than 0.5 m/sec, the abrasive particles easily adhere onto the filtration surfaces of the separation membrane 181 to easily cause the clogging of the membrane. On the other hand, when the velocity of the water to be treated in the effective filtration part of the second separation membrane 181 is over 2 m/sec, an excessive amount of energy is given to the abrasive particles, and the particles flocculate to sometimes form coarse particles. When the coarse particles mix in the recovered abrasive, a scratch occurs on the surface of the wafer or the like when the abrasive is recycled in the CMP process, which sometimes lowers yields of products. Further, the generation of such coarse particles causes the formation of cake layers on the filtration surfaces of the separation membrane, which may increase a washing time and an amount of chemicals used. The velocity of the water to be treated passing through the effective filtration part of the second separation membrane 181 is more preferably 0.6 to 1 m/sec.

After the above-described treatment step is continued for a predetermined time, the opening/closing valve B5 is opened and the opening/closing valve B6 is closed at a stage when a concentration of the abrasive of the stored water in the post-treatment tank 17 as measured by the component concentration meter C3 reaches a target concentration, and part thereof is supplied to the recovery tank 19 via the pipe 25. The concentration of the stored water in the post-treatment tank 17 when it is supplied to the recovery tank 19 via the pipe 25 is preferably 10 mass % or more and is 26 mass % at the maximum, and more preferably 20 to 25 mass %.

A pressure loss of the water to be treated on the filtration surfaces of the second separation membrane 181 is preferably 0.1 MPa or less and more preferably 0.08 MPa or less.

In the abrasive recovery method of the present invention, since the second separation membrane 181 having a shorter effective filtration length than the first effective filtration length is used, it is possible to efficiently recover the condensed used polishing slurry S in which the concentration of the abrasive particles is increased up to a high level enabling the reuse as a product while suppressing an increase in pressure loss on the filtration surfaces of the second separation membrane 181 and the clogging of the membrane.

This embodiment shows the filtration method of the internal-pressure type which passes the water to be treated through the hollow portions of the hollow fibers both in the first filtration step and the second filtration step, but the present invention is not necessarily limited to such a form. For example, the filtration may be of an external-pressure type which passes the water to be treated outside the hollow fibers.

The permeates obtained from the first permeate outlet pipe 22 and the second permeate outlet pipe 24 can be recovered to be reused. For example, they are usable as raw water or the like of an ultra-pure water device without being treated or after being treated according to water quality of the permeates. Further, they are also usable as other utility than in a factory, for example, domestic water, cooling tower water, and the like.

EXAMPLES

Hereinafter, the present invention will be described in more detail based on examples and comparative examples.

Example 1

A used slurry in a CMP process was filtrated by using the abrasive recovery device 1 shown in FIG. 1.

As the pump P1 in FIG. 1, a LEVITRO pump “LEV300” (manufactured by Iwaki Co., Ltd, product name) was used, and as the membrane separation unit 4, a hollow-fiber UF membrane module “FB02-VC-FUST653” (Daicen Membrane Systems Ltd., product name) was used. As the treatment tank 3 and the condensate recovery tank 9, a condensation tank (made of PVC) was used. As for the hollow-fiber UF membrane module “FB02-VC-FUST653”, molecular cut-off; 6000, hollow fiber inside diameter; 0.5 mm, membrane area; 0.5 m2, and effective filtration length; 0.26 m.

First, a used polishing slurry solution with an abrasive concentration of about 1 mass % (pH: 9.8) was supplied to the treatment tank 3 via the guard filter 2 through the pipe 5. Next, the used polishing slurry in the treatment tank 3 was passed through the membrane separation unit 4 while the opening/closing valve B1 was closed and the opening/closing valve B2 was opened. A circulation flow rate of the used slurry in each pipe was 8.1 L/min and a linear velocity in the hollow-fiber membrane 41 was 0.55 m/sec. Further, an impellor rotation speed of the pump P1 (LEVITRO pump) and an opening/closing degree of the opening/closing valve B2 on the subsequent stage of the membrane separation unit 4 were adjusted so that a pressure near an inlet of a flow of the used polishing slurry in the hollow-fiber membrane 41 became 0.2 MPa. In this state, the water passage was performed, and a concentration of an abrasive in the treatment tank 3 as measured by the component concentration meter C1 and an amount of a permeate (flux) discharged from the permeate outlet pipe were measured.

Example 2

A used polishing slurry was passed in the same manner as in Example 1 except that as the membrane separation unit 4, a hollow-fiber UF membrane module “M81S60001N” (manufactured by SPECTRUM Laboratories Inc., product name) was used, and a concentration of an abrasive in the treatment tank 3 was measured in the same manner as in Example 1. As for the hollow-fiber UF membrane module “M81S60001N”, hollow-fiber inside diameter; 0.5 mm and effective filtration length; 0.46 m.

Example 3

A used polishing slurry was passed in the same manner as in Example 1 except that as the membrane separation unit 4, a hollow-fiber UF membrane module “KM1S60001N” (manufactured by SPECTRUM Laboratories Inc., product name) was used, and a concentration of an abrasive in the treatment tank 3 was measured in the same manner as in Example 1. As for the hollow-fiber UF membrane module “KM1S60001N”, hollow-fiber inside diameter; 0.5 mm and effective filtration length; 0.63 m.

Comparative Example 1

A used polishing slurry was passed in the same manner as in Example 1 except that as the membrane separation unit 4, a hollow-fiber UF membrane module “KM1S30001N” (manufactured by SPECTRUM Laboratories Inc., product name) was used, and a concentration of an abrasive in the treatment tank 3 was measured in the same manner as in Example 1. As for the hollow-fiber UF membrane module “KM1S30001N”, hollow-fiber inside diameter; 0.5 mm and effective filtration length; 0.81 m.

Comparative Example 2

A used polishing slurry was passed in the same manner as in Example 1 except that as the membrane separation unit 4, a hollow-fiber UF membrane module “AMK-VC-FUST653” (manufactured by Daicen Membrane Systems Ltd., product name) was used, and a concentration of an abrasive in the treatment tank 3 was measured in the same manner as in Example 1. As for the hollow-fiber UF membrane module “AMK-VC-FUST653”, hollow-fiber inside diameter; 0.5 mm, effective filtration length; 1.0 m, and membrane area; 1.5 m2.

A relation between the concentration of the abrasive in the treatment tank 3 as measured by the component concentration meter C1 and the amount of the permeate (flux) discharged from the permeate outlet pipe 7 in Example 1 and the Comparative Example 2 is shown in FIG. 4. Note that in FIG. 4, the broken line represents the amount of the permeate from the permeate outlet pipe 7 in Example 1 and the solid line represents the amount of the permeate from the permeate outlet pipe 7 in Comparative Example 2. Further, Table 1 shows the hollow-fiber inside diameter, the membrane area, the effective filtration length, and the material of the hollow-fiber separation membrane 41, and also the abrasive concentration of the water to be treated at the start of the water passage and the abrasive concentration of the water to be treated at an instant when the condensation became impossible (maximum condensable concentration), in Examples 1 to 3 and Comparative Examples 1 to 2.

TABLE 1 Abrasive Abrasive concen- concen- tration tration of water to of water to Hollow- be treated be treated fiber Mem- Effective (at the start (at the start inside brane filtration of water of water diameter area length Mate- passage) passage) [mm] [m2] [m] rial [mass %] [mass %] E1 0.5 0.50 0.26 PES 1) 1 25 E2 0.5 6.6 0.46 PS 2) 1 22 E3 0.5 8.2 0.63 PS 1 20 CE1 0.5 11.2 0.81 PS 1 17 CE2 0.5 1.5 1.0 PES 1 13 1) Polyethersulfone 2) Polysulfone E1, E2, E3 = Example 1, Example 2, Example 3 CE1, CE2 = Comparative Example 1, Comparative Example 2

As is apparent from Table 1, in the recovery devices of Examples 1 to 3 in which the effective filtration length of the separation membrane 41 is 0.8 m or less, the treated water having the abrasive concentration which is as high as 20 mass % or more is obtained at the instant when the filtration is ended, and it has been confirmed that the maximum condensable concentration becomes larger as the effective filtration length becomes shorter. On the other hand, in the recovery device of Comparative Example 1 having the effective filtration length over 0.8 m, the maximum condensable concentration is less than 20 mass %, and it has been confirmed that the loading easily occurs in a high-concentration region.

Further, as shown in FIG. 4, in the recovery device of Comparative Example 2 using, as the membrane separation unit 4, the separation membrane 41 having the effective filtration length over 0.8 m, the permeate amount (flux) rapidly reduces at an instant when a Si concentration of the water to be treated exceeds 13 mass %, and the further filtration was difficult. On the other hand, in the recovery device of Example 1 using, as the membrane separation unit 4, the separation membrane 41 having the effective filtration length equal to 0.8 m or less, the rapid decrease of the permeate amount did not occur even when the concentration of the water to be treated exceeds 20 mass %, and the stable filtration was possible even when the water to be treated came to have a high concentration.

From the above result, it has been confirmed that, when the separation membrane 41 whose effective filtration length is 0.8 m or less is used as the membrane separation unit 4, it is possible to stably condense the low-concentration used slurry discharged from the CMP process up to a high-concentration range.

Conventionally, due to the need for complying with the emission standard, solid-liquid separation has been performed for wastewater containing abrasive particles such as silica particles. However, even when an ultra-filtration membrane is used for the solid-liquid separation, about several % was a limit for the condensation as a solid component. A polishing slurry, if its abrasive component has about several % concentration, is difficult to reuse in the CMP process, and therefore, the solid component has been usually disposed of as industrial wastes.

In the present invention, as shown in Examples 1 to 3, the wastewater from the CMP process can be condensed so that the concentration of its abrasive becomes about 25% enabling the use as a product, which makes it possible to use the recovered condensate again in the CMP process, enabling high recycling efficiency.

Next, Example 4 to 5 and Comparative Example 3 to 6 were carried out by using the abrasive recovery device 1 used in Example 1, with the pressure at an inlet of the water to be treated in the membrane separation unit 4 being the same as that of Example 1, and with the pressure loss of the separation membrane being varied.

Example 4

A used polishing slurry was passed through the recovery device 1 for filtration, with a linear velocity in the hollow-fiber membrane 41 being 0.6 m/sec, and with other conditions being the same as in Example 1. After this treatment was continued for 80 minutes, a condensate from the membrane separation unit 4 was recovered from the condensate outlet pipe 8 to the condensate recovery tank 9 while the opening/closing valve B1 was opened and the opening/closing valve B2 was closed.

Example 5

The filtration was performed in the same manner as in Example 2 except that the following points were changed, and a condensate from the membrane separation unit 4 was recovered. As the membrane separation unit 4, a hollow-fiber UF membrane module “SLP-1053” (manufactured by Asahi Kasei Chemicals Corporation, product name, hollow-fiber inside diameter 1.4 mm, molecular cut-off: 10000, membrane area: 0.12 m2, effective filtration length 0.20 m, membrane material: polysulfone) was used instead of the hollow-fiber UF membrane module “FB02-VC-FUST653”.

As for a used polishing slurry supplied to the treatment tank 3, an abrasive concentration was set to about 0.8 mass % (pH: 10.5), a circulation flow rate of the used slurry in each pipe was set to 9.0 L/min, a pressure near the inlet of the flow of the used polishing slurry in the hollow-fiber membrane 41 was set to 0.2 MPa, and a linear velocity in the hollow-fiber membrane 41 was set to 0.69 m/sec.

Comparative Example 3

The filtration was performed in the same manner as in Example 2 except that the following points were changed, and a condensate from the membrane separation unit 4 was recovered. As the membrane separation unit 4, a hollow-fiber UF membrane module “AMK-VC-FUS0181” (manufactured by Dicen Membrane Systems Inc., product name, hollow-fiber inside diameter 0.8 mm, molecular cut-off: 10000, membrane area: 0.5 m2, effective filtration length 1 m, membrane material: PES) was used instead of the hollow-fiber UF membrane module “FB02-VC-FUST653”, and a linear velocity in the hollow-fiber membrane 41 was set to 0.55 m/sec.

Comparative Example 4

The filtration was performed in the same manner as in Example 2 except that the following points were changed, and a condensate from the membrane separation unit 4 was recovered. As the membrane separation unit 4, a hollow-fiber UF membrane module “AMK-VC-FUS03C1” (manufactured by Dicen Membrane Systems Inc., product name, hollow-fiber inside diameter 1.2 mm, molecular cut-off: 30000, membrane area: 0.3 m2, effective filtration length 1 m, membrane material: PES) was used instead of the hollow-fiber UF membrane module “FB02-VC-FUST653”, and a linear velocity in the hollow-fiber membrane 41 was set to 0.85 m/sec.

Comparative Example 5

The filtration was performed in the same manner as in Example 2 except that the following points were changed, and a condensate from the membrane separation unit 4 was recovered. As the membrane separation unit 4, “AMK-VC-FUS03C1” (manufactured by Dicen Membrane Systems Inc., product name, hollow-fiber inside diameter 1.2 mm, molecular cut-off: 30000, membrane area: 0.3 m2, effective filtration length 1 m, membrane material: PES) was used instead of the hollow-fiber UF membrane module “FB02-VC-FUST653”, and a linear velocity in the hollow-fiber membrane 41 was set to 1.8 m/sec.

Comparative Example 6

The filtration was performed in the same manner as in Example 2 except that the following points were changed, and a condensate from the membrane separation unit 4 was recovered. As the membrane separation unit 4, “AMK-VC-FUST653” (manufactured by Dicen Membrane Systems Inc., product name. hollow-fiber inside diameter 0.5 mm, molecular cut-off: 6000, membrane area: 1.5 m2, effective filtration length 1 m, membrane material: PES) was used instead of the hollow-fiber UF membrane module “FB02-VC-FUST653”. A linear velocity in the hollow-fiber membrane 41 was the same as that in Example 2.

Regarding Examples 4 to 5 and Comparative Examples 3 to 6, Table 2 shows the abrasive concentration of the condensate recovered into the condensed recovery tank 9 and a recovery ratio of the abrasive. In addition, Table 2 shows an abrasive concentration value in the condensate calculated from the linear velocity in the hollow-fiber membrane 41, the hollow-fiber inside diameter, and a discharge amount of a permeate, regarding Examples 4 to 5 and Comparative Examples 3 to 6.

TABLE 2 Linear Abrasive Abrasive velocity concentra- concentra- Hollow- in tion of tion of Effective fiber hollow- condensate condensate filtration inside fiber (calculated (measured Recovery length diameter membrane value) value) Ratio [m] [mm] [m/sec] [mass %] [mass %] [%] E4 0.26 0.50 0.60 26 25 98 E5 0.2 1.4 0.69 25 22 88 CE3 1.0 0.80 0.55 17 13 76 CE4 1.0 1.2 0.85 22 13 61 CE5 1.0 1.2 1.8 22 13 60 CE6 1.0 0.50 0.60 17 13 79 E4, E5 = Example 4, Example 5 CE3, CE4, CES, CE6 = Comparative Example 3, Comparative Example 4, Comparative Example 5, Comparative Example 6

As is apparent from Table 2, in Example 4 using the separation membrane whose effective filtration length is 0.8 m or less and whose hollow-fiber inside diameter is not less than 0.1 mm nor more than 0.8 mm, the abrasive concentration of the recovered condensate is over 25 mass % and it has been confirmed that a higher recovery ratio can be obtained. Further, in Example 5 in which the effective filtration length is made shorter and a pressure loss is decreased by increasing the hollow-fiber inside diameter as compared with Example 4, a predetermined amount or more of the permeate was obtained until the concentration fell in a relatively high range, but the condensation up to 25 mass % or more was not possible. Further, the concentration of the abrasive contained in the recovered condensate is lower than the abrasive concentration calculated from the permeate amount (calculated value), and it has been confirmed that the recovery ratio of the abrasive slightly decreases in accordance with an increase in the hollow-fiber inside diameter (fiber diameter). This is thought to be because abrasive components (abrasive particles) adhered in the hollow fibers to form cake layers and accordingly the effective inside diameter decreased.

On the other hand, in Comparative Examples 3, 6 using the separation membrane whose effective filtration length is longer than 0.8 m and whose hollow-fiber inside diameter fell within a range from 0.1 to 0.8 mm, the recovery ratio of the abrasive was nearly 76% and the concentration of the abrasive contained in the recovered condensate was lower than the abrasive concentration calculated from the permeate amount (theoretical value). Further, in Comparative Examples 4, 5 in which the inside diameter of the hollow fiber was increased to 1.2 mm, the recovery ratio of the abrasive was further lower. This is thought to be because abrasive components (abrasive particles) adhered in the hollow fibers to form cake layers and accordingly an effective inside diameter decreased.

Comparative Example 7

An ultra-filtration membrane “MLE-7101H” (manufactured by Kuraray Co., Ltd., product name. effective filtration length; 1 m, hollow-fiber inside diameter; 1.2 mm, molecular cut-off; 13000, membrane material; polysulfone) was installed as the membrane separation unit 4 in the recovery device 1 shown in FIG. 1 and the filtration was performed. The filtration was performed by an internal-pressure cross-flow method. A separation membrane was gradually clogged from a stage when a concentration of an abrasive contained in a condensate became 14 mass %. Thereafter, the filtration was continued with a pressure to water to be treated being increased by heightening an output of the pump, but the condensation became impossible at a stage when a Si concentration of the water to be treated became 19 mass %. FIG. 6 shows a state of an inlet of the membrane separation unit 4 at the instant when the filtration became impossible. FIG. 7 shows a part of FIG. 6 being enlarged. FIG. 8 shows a state of an outlet of the membrane separation unit 4 at the same instant in the FIG. 7.

As shown in FIG. 8, on the membrane separation unit at the instant when the condensation became difficult, gelatinous coarse particles being the flocculation of the abrasive were formed in a belt form on a subsequent stage in a water passage direction of the water to be treated (i.e. outlet of the membrane separation unit 4). Consequently, the hollow portions of the separation membrane 41 were clogged, and the continuation of the condensation became difficult.

Example 6

A used slurry in a CMP process was filtrated by using the abrasive recovery device 11 shown in FIG. 3.

A LEVITRO pump “LEV300” (manufactured by Iwaki Co., Ltd, product name) was used as the pumps P2 and P3 in FIG. 3, a hollow-fiber UF membrane module “AMK-VC-FUST653” (manufactured by Daicen Membrane Systems Ltd., product name) was used as the first membrane separation unit 14, and a hollow-fiber UF membrane module “FB02-VC-FUST653” (manufactured by Daicen Membrane Systems Ltd., product name) was used as the second membrane separation unit 18. Further, treatment tanks (made of PE) were used as the treatment tank 13 and the post-treatment tank 17, and a condensation tank (made of PVC) was used as the condensate recovery tank 19.

As for the hollow-fiber UF membrane module “AMK-VC-FUST653” being the first membrane separation unit 14, molecular cut-off; 6000, hollow-fiber inside diameter; 0.5 mm, membrane area; 1.5 m2, and effective filtration length; 1 m, and as for the hollow-fiber UF membrane module “FB02-VC-FUST653” being the second membrane separation unit 18, molecular cut-off; 6000, hollow-fiber inside diameter; 0.5 mm, membrane area; 0.5 m2, and effective filtration length; 0.26 m.

First, a 200 L used polishing slurry solution with an about 1 mass % abrasive concentration (pH: 9.8) was supplied through the pipe 15 via the guard filter 12 to the treatment tank 13. Next, while the opening/closing valve B3 was closed and the opening/closing valve B4 was opened, a used polishing slurry in the treatment tank 13 was passed through the first membrane separation unit 14. A circulation flow rate of the used slurry in the pipes was 8.0 L/min, and a linear velocity in the hollow-fiber membrane 141 was 0.7 m/sec. Further, an impellor rotation speed of the pump P2 (LEVITRO pump) and an opening/closing degree of the opening/closing valve B4 on the subsequent stage of the membrane separation unit 14 were adjusted so that a pressure near an inlet of a flow of the used polishing slurry in the hollow-fiber membrane 141 became 0.2 MPa.

In this state, water passage was performed, and an amount of a permeate (flux) discharged from the permeate outlet pipe 22 was measured until a concentration of an abrasive in the treatment tank 13 as measured by the component concentration meter C2 became 9 mass %. An amount of the used polishing slurry in the treatment tank 13 at this time was about 22 L.

Next, while the opening/closing valve B4 was closed and the opening/closing valve B3 was opened, all the amount of the used polishing slurry in the treatment tank 13 was supplied to the post-treatment tank 17. Next, while the opening/closing valve B5 was closed and the opening/closing valve B6 was opened, the used polishing slurry in the post-treatment tank 17 was passed through the second membrane separation unit 18. A circulation flow rate of the used slurry in the pipes was 8.0 L/m, and a linear velocity in the second separation membrane 181 (the hollow-fiber membrane 181) was 0.7 m/sec. Further, an impellor rotation speed of the pump P3 (LEVITRO pump) and an opening/closing degree of the opening/closing valve B6 on the subsequent stage of the second membrane separation unit 18 were adjusted so that a pressure near an inlet of the flow of the used polishing slurry in the second separation membrane 181 (the hollow-fiber membrane 181) the hollow-fiber membrane 181 became 0.2 MPa. In this state, water passage was performed, and an amount of a permeate (flux) discharged from the permeate outlet pipe was measured until a concentration of an abrasive in the treatment tank 17 as measured by the component concentration meter C3 became 25 mass %.

FIG. 5 shows a relation, in Example 6, between the concentration of the abrasive in the treatment tank 13 as measured by the component concentration meter C2 and the amount of the permeate (flux) discharged from the first permeate outlet pipe 22, and a relation, in Example 6, between the concentration of the abrasive in the treatment tank 17 as measured by the component concentration meter C3 and the amount of the permeate (flux) discharged from the second permeate outlet pipe 24.

Note that in FIG. 5, the solid line represents the permeate from the first membrane separation unit 14, discharged from the first permeate discharge pipe 22 and the broken line represents the permeate from the second membrane separation unit 18, discharged from the second permeate outlet pipe 24.

Based on the measurement data in Example 1 (FIG. 4) and the measurement data of Example 6 (FIG. 5), the abrasive recovery device 1 of Example 1 (first embodiment) and the abrasive recovery device 11 of Example 6 (second embodiment) were designed and fabricated. It was possible to fabricate the abrasive recovery device 11 of the second embodiment, with the number of the hollow-fiber UF membrane modules used being reduced by 87% as compared with the abrasive recovery device 1 of the first embodiment. As a result, effects of the simplification of the pipe structure, a reduction in an installation area, and cost reduction were obtained as the whole recovery device.

Claims

1. An abrasive recovery device, comprising;

a first separation membrane having a first cylindrical hole passage to lead a used polishing slurry in a CMP process, the first cylindrical hole passage having a first effective filtration part,
a second separation membrane provided on a subsequent stage of the first separation membrane,
the second separation membrane having a second cylindrical hole passage to lead a condensate from the first separation membrane,
the second cylindrical hole passage having a second effective filtration part shorter than the first effective filtration part in length,
the second effective filtration part being not longer than 0.8 m,
circulation mechanism configured to pass the condensate from the first separation membrane through the second separation membrane sequentially and condense the used polishing slurry until a concentration of the abrasive becomes 10 mass % or more and recover an abrasive from the used polishing slurry.

2. The abrasive recovery device according to claim 1,

wherein at least one of hollow portions of the first separation membrane and the second separation membrane is passed through by the used polishing slurry in a cross-flow method.

3. The abrasive recovery device according to claim 1,

wherein at least one of the first separation membrane and the second separation membrane is provided in a membrane separation unit of an internal-pressure type.

4. The abrasive recovery device according to claim 1,

wherein at least one of the first separation membrane and the second separation membrane is a hollow-fiber membrane.

5. The abrasive recovery device according to claim 1,

wherein at least one of inside diameters of the first separation membrane and the second separation membrane is not less than 0.1 mm nor more than 0.8 mm.

6. The abrasive recovery device according to claim 1,

wherein at least one of molecular cut-off of the first separation membrane and the second separation membrane is 3,000 to 30,000.

7. The abrasive recovery device according to claim 1,

wherein at least one of the first separation membrane and the second separation membrane is made of any one of polyethylene, tetrafluoroethylene, polyvinylidene difluoride, polypropylene, cellulose acetate, polyacrylonitrile, polyimide, polysulfone, and polyethersulfone.

8. The abrasive recovery device according to claim 1,

wherein a length L1 of the first effective filtration part is 0.8 to 1.5 m, and a length L2 of the second effective filtration part is 0.2 to 0.8 m.

9. An abrasive recovery method comprising:

a first filtration step of passing the used polishing slurry in the CMP process through a first separation membrane having a first cylindrical hole passage, to condense the used polishing slurry, the first cylindrical hole passage having a first effective filtration part; and
a second filtration step of passing a condensate from the first separation membrane through a second separation membrane provided on a subsequent stage of the first separation membrane,
the second separation membrane having a second cylindrical hole passage,
the second cylindrical hole passage having a second effective filtration part shorter than the first effective filtration part in length,
the second effective filtration part being not longer than 0.8 m, to condense the condensate until a concentration of an abrasive of the condensate becomes 10 mass % or more.

10. The abrasive recovery method according to claim 9,

wherein at least one of hollow portions of the first separation membrane and the second separation membrane is passed through by the used polishing slurry in a cross-flow method.

11. The abrasive recovery method according to claim 9,

wherein at least one of inside diameters of the first separation membrane and the second separation membrane is not less than 0.1 mm nor more than 0.8 mm.

12. The abrasive recovery method according to claim 9,

wherein a circulation flow rate of water to be treated in at least one of the effective filtration parts of the first separation membrane and the second separation membrane is 0.5 to 2 m/sec.

13. The abrasive recovery method according to claim 9,

wherein, in the first filtration step, the used polishing slurry is condensed to 13 mass % at the maximum by the filtration, and in the second filtration step, the condensate obtained in the first filtration step is condensed up to 26 mass % at the maximum by the filtration.

14. The abrasive recovery method according to claim 9,

wherein an abrasive concentration of the used polishing slurry led to the first separation membrane is 0.02 to 5 mass %.

15. The abrasive recovery method according to claim 9,

wherein an average particle size of abrasive particles contained in the used polishing slurry is 0.01 to 1 μm.

16. The abrasive recovery method according to claim 9,

wherein a circulation flow rate of water to be treated in the first effective filtration part is 0.55 to 1.5 m/sec.

17. The abrasive recovery method according to claim 9,

wherein a circulation flow rate of water to be treated in the second effective filtration part is 0.6 to 1 m/sec.
Patent History
Publication number: 20130333299
Type: Application
Filed: Aug 21, 2013
Publication Date: Dec 19, 2013
Applicant: NOMURA MICRO SCIENCE CO., LTD. (Atsugi-shi)
Inventors: Keiichiro Ishii (Atsugi-shi), Shoji Hioki (Atsugi-shi)
Application Number: 13/972,364
Classifications
Current U.S. Class: Clay, Silica, Or Silicate (51/308); Serially Connected Distinct Treating With Or Without Storage Units (210/252); Metal Or Metal Oxide (51/309)
International Classification: B24B 57/00 (20060101);