Cleaning method of a slurry concentration device using a separation membrane used for cross-flow filtration

Abstract

To provide a method for cleaning a slurry concentration device capable of simply cleaning a filter unit using a separation membrane used in crossflow filtration having a complicated internal shape.SOLUTION: A method for cleaning a slurry concentration device using a separation membrane used in crossflow filtration forms an air pocket in a flow passage in a concentration device 1, and then passes a gas-liquid mixed fluid containing a slurry or other liquid and air in the air pocket through a filter part 31 and a connection flow passage 32, wherein a filter unit 3 has a plurality of filter parts 31, and the connection flow passage 32 arranged between the adjacent filter parts 31.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for cleaning a slurry concentration device, and more particularly to a method for cleaning a slurry concentration device using a separation membrane used for cross-flow filtration for regenerating used CMP slurry discharged from a CMP process.

Background Art

[0002] In the manufacture of semiconductor integrated circuits, in addition to planarization of the surface of a wafer substrate, in recent years, planarization of conductor metals embedded in a substrate in a damascene method, planarization of an insulating material having a lower relative dielectric constant compared to SiO 2 methods such as planarization of via holes for increasing the number of stacked cells, manufacture of high-density cells, and manufacture of finer patterns of 100 nm or less have become important. Planarization of a wafer and members formed on this substrate is widely adopted by a chemical mechanical polishing method (hereinafter referred to as a CMP process) and has become more important in the semiconductor manufacturing process. As planarization of semiconductor materials becomes more important, the amount of CMP slurry used in the CMP process increases, and the proportion in the manufacturing cost of semiconductor integrated circuits also increases. For this reason, it is required to reduce the price while maintaining the quality of the CMP slurry.

[0003] As one method for reducing the price of CMP slurry, a method for regenerating used CMP slurry is known. As a method for regenerating CMP slurry, for example, a concentration step of removing a part of the dispersion medium from used CMP slurry containing abrasive grains, a dispersion medium, and impurities, a pH adjustment step of adjusting the pH of the concentrated slurry, and a step of recovering abrasive grains and a dispersion medium having a particle size equal to or less than a predetermined particle size from the slurry whose pH has been adjusted are known (Patent Document 1). This Patent Document 1 aims to efficiently recover abrasive grains (abrasives) by solid-liquid separation.

[0004] In addition, as a CMP slurry regeneration method, a method is also known in which the used CMP slurry recovered in a tank is circulated and concentrated while removing water through a cross-flow type ultrafiltration unit, and the pH of the concentrate is adjusted to regenerate the CMP slurry (Patent Document 2). As the ultrafiltration unit, a membrane filter such as a ceramic filter is used.

[0005] When performing circulation concentration using a cross-flow type ultrafiltration unit or the like over a long period of time, contaminants such as aggregates adhere to the filter unit. In such a case, the filter unit is cleaned. The cleaning of the filter unit is performed by disassembling the concentration device to physically remove aggregates and the like adhering to the filter part and the connecting flow path, circulating the cleaning liquid without disassembling the concentration device, or performing backwashing in which the cleaning liquid is flowed from the permeate side to the concentrate side (Patent Document 3). From the viewpoint of the cleaning effect, it is most preferable to disassemble the device for cleaning, but it may require a lot of costs. Therefore, considering the burden and cost required for cleaning, a cleaning method that does not disassemble the device is preferable. However, in the cleaning method performed without disassembling the concentration device, depending on the type and amount of contaminants, the removal may be insufficient.

[0006] Patent Document 4 discloses a method for cleaning a filter unit (hollow fiber membrane module), which includes a first air cleaning step of supplying air to the raw water chamber and discharging air and a part of the water in the raw water chamber from the upper part of the raw water chamber, a backwashing step of pushing the permeated water to the raw water side after the first air cleaning step, and a drainage step of discharging the cleaning wastewater from the lower part of the container after the backwashing step, and it is described that turbidity adhering to the hollow fiber membrane can be evenly and sufficiently removed.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Summary of the Invention

Problems to be Solved by the Invention

[0008] As a cleaning method that does not disassemble the device, air cleaning is known in which a liquid containing air is passed through a filter to remove deposits on the filter surface. However, in order to perform air cleaning, it is necessary to separately provide a gas generator that generates bubbles. This may lead to an increase in device cost and an increase in maintenance burden. In addition, when there are uneven shapes or bent shapes inside the filter unit, or when the inner diameter of the flow path is not constant, aggregates and the like are likely to accumulate, and there is a risk that the cleanability will be insufficient.

[0009] The present invention has been made in view of such circumstances, and an object of the present invention is to provide a cleaning method for a slurry concentration device using a separation membrane used for cross-flow filtration that can easily clean a filter unit having a complex internal shape without adding a special mechanism.

Means for Solving the Problems

[0010] The cleaning method of the present invention is a cleaning method for a slurry concentration device (hereinafter, also simply referred to as "concentration device") including a liquid storage tank, a cross-flow type filter unit through which slurry is passed by a pump from the liquid storage tank, and a circulation flow path that annularly connects the liquid storage tank and the filter unit and enables the slurry to circulate. The filter unit has a plurality of filter parts and a connection flow path disposed between adjacent filter parts. The cleaning method is characterized in that after forming an air pocket in the flow path inside the concentration device, a gas-liquid mixed fluid containing the slurry or other liquid and the air in the air pocket is passed through the filter part and the connection flow path. Hereinafter, the cleaning method of the present invention is also referred to as "the present air cleaning".

[0011] As the slurry, various liquids generally referred to as suspensions can be considered, but it is characterized by being a slurry containing abrasive grains such as silica and ceria used in semiconductor manufacturing processes, or a slurry for manufacturing semiconductor integrated circuits. The slurry is preferably used CMP slurry discharged from a CMP process for manufacturing high-density semiconductor integrated circuits.

[0012] The air pocket is formed by closing at least two valves provided in front of the flow path of the filter unit and extracting the slurry or other liquid between the closed valves. Alternatively, it may be formed by closing a valve provided in front of the flow path of the filter unit and returning all or part of the slurry in the connection flow path, the filter part, and the circulation flow path in the filter unit to the liquid storage tank.

[0013] The filter part is characterized by having a ceramic filter.

[0014] There is no limitation on the shape of the connection flow path, but a bent shape that facilitates the arrangement of a plurality of filter units is often used. When this air cleaning is carried out, the flow velocity inside the connection flow path is likely to change. As a result, the agglomerates adhering to the inner wall of the bent connection flow path such as a U-tube are more likely to peel off, and the cleaning effect is further excellent.

Advantages of the Invention

[0015] In this air cleaning, after forming an air pocket in the internal flow path of the concentration device, a gas-liquid mixed fluid containing slurry or other liquid and the air in the air pocket is passed through the filter part and the connection flow path. Since the filter unit has a plurality of filter parts and a connection flow path arranged between adjacent filter parts, it is possible to effectively clean the entire filter unit without adding a special gas generator. As a result, it is possible to remove the agglomerates adhering to the inside of the filter unit, particularly the bent connection flow path between the filter parts.

[0016] When concentrating and regenerating the used CMP slurry discharged from the CMP process, gels such as pad debris and slurry aggregates tend to accumulate in the connecting flow path in the filter unit. The slurry concentrated by the concentrating device cleaned by this air cleaning is the used CMP slurry discharged from the CMP process for manufacturing semiconductor integrated circuits. In the present invention, it is possible to remove aggregates during the concentration of such used CMP slurry, and it is possible to prevent a decrease in the amount of permeated water when viewed as the entire filter unit. Therefore, the regeneration efficiency of the used CMP slurry can be improved.

[0017] An air pocket is formed by closing at least two valves provided in front of the flow path of the filter unit and extracting the slurry or other liquid between the closed valves. Therefore, an air pocket can be formed in the flow path within the range closed by the valves in front of the flow path of the filter unit without using a special gas generator. Thereby, a gas-liquid mixed fluid for cleaning the filter unit can be easily formed.

[0018] When the filter unit uses a ceramic filter as the separation membrane, it is the most preferable case of the present invention. The strength of the filter part is higher than that when an organic material is used as the material, and there is little risk of pore size change or damage to the filter part even when receiving rapid flow rate changes or pressure changes.

[0019] Although there is no limitation on the shape of the connecting flow path, a bent shape that facilitates the arrangement of a plurality of filter units is often used. When flowing a liquid containing air through the connecting flow path, a change in the flow velocity inside the connecting flow path is likely to occur. As a result, the adhesion of aggregates adhering to the inner wall of the bent connecting flow path such as a U-tube is more likely to peel off, and the cleaning effect is further excellent.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0021] The slurry concentration device to be subjected to this air cleaning will be described. FIG. 1 is a schematic diagram showing an example of a concentration device washed by the cleaning method of the first embodiment of the present invention. In FIG. 1, P01 is a pump for pressurizing to flow a fluid such as slurry, and V01 to V04 are valves for adjusting the flow direction and flow rate of the fluid.

[0022] As shown in FIG. 1, the concentration device 1 includes a liquid storage tank 2, a cross-flow type filter unit 3 through which the slurry sent from the liquid storage tank 2 by the pump P01 flows, and a circulation flow path 4 that annularly connects the liquid storage tank 2 and the filter unit 3 to enable the slurry to circulate. The filter unit 3 has a plurality of filter parts 31 and a connection flow path 32 arranged between adjacent filter parts 31. The concentration device 1 includes a plurality of valves V01 to V04. Note that, in the connection flow path 32 and the circulation flow path 4, a flow path and a pump for leading the slurry out of the concentration device 1 or introducing a cleaning liquid may be separately provided.

[0023] As an example of a method for concentrating a slurry using the above-described concentrating apparatus, a method for concentrating used CMP slurry discharged from a CMP process for manufacturing a semiconductor integrated circuit will be described. In the method for concentrating the CMP slurry, the used CMP slurry is first stored in the liquid storage tank 2. The stored used CMP slurry is fed by the pump P01 and passed through the filter unit 3. The slurry flows in from the inlet 3a of the filter unit 3 and is concentrated (filtered) through a filtration membrane provided on the side wall of the slurry flow path (filter channel) inside each filter section 31. The permeated water that has passed through the filtration membrane is discharged to the outside of the concentrating apparatus 1 from the discharge port 31d. While discharging the permeated water to the outside of the concentrating apparatus 1, the concentrated slurry (outflow liquid) is returned to the liquid storage tank 2. By repeating this circulation, the concentration of the used CMP slurry increases. Note that the above concentration may be performed by a reverse operation in which the slurry is made to flow in from the side of the outlet 3b of the filter unit 3 and flow out from the inlet 3a.

[0024] When the concentration of the slurry as described above is performed over a long period of time, changes in the concentration, acidity, composition, etc. of the slurry may occur, and aggregates in which organic particles and inorganic particles in the liquid have aggregated may be generated. The aggregates may become overly large aggregates (for example, aggregates having a size of 1 μm or more) in which the aggregation has progressed and coarsened. Here, the size of the aggregate refers to the maximum length (major axis) of the aggregate. When the overly large aggregates increase, the possibility of clogging the filter unit increases. In such a case, by using the cleaning method of the present invention, the concentrating apparatus can be easily cleaned, and the possibility of the filter unit being clogged can be reduced.

[0025] Details of implementing the cleaning method of the first embodiment in the forward operation will be described. When performing the forward operation, the valves V02 and V03 are closed in advance, and these valves are maintained in a closed state also during the cleaning of the apparatus. Thereby, according to the opening and closing of the valves V01 and V04, the gas-liquid mixed fluid flows into the filter unit from the inlet 3a and flows out from the outlet 3b, and flows in the forward rotation direction of the circulation flow path 4.

[0026] The operator who performs the cleaning stops the operation of pump P01 and closes valve V04 provided in front of the flow path of filter unit 3 (on the side of inlet 3a). The operator returns a part of the slurry in connecting flow path 32 and filter section 31 in filter unit 3 to liquid storage tank 2 to form an air pocket in the flow path inside concentrator 1. Note that the operator may form an air pocket with valve V04 open. Also, all or part of the slurry in connecting flow path 32, filter section 31, and circulation flow path 4 in filter unit 3 may be returned to liquid storage tank 2. The operator is not limited to returning a part of the slurry to liquid storage tank 2, and may form an air pocket by introducing air generated by a special gas generator or the like.

[0027] Specifically, during the concentration operation of the slurry, the operator stops the operation of pump P01 and returns the slurry inside connecting flow path 32 and filter section 31 in filter unit 3 to liquid storage tank 2 through a recovery flow path (not shown). Thereby, both liquid and air exist in the flow path inside concentrator 1. At this time, valves V01 and V04 may be in either an open state or a closed state. Note that as the recovery flow path, connecting flow path 32 or circulation flow path 4 may be used, or piping separately connected to each part may be used.

[0028] Before forming the air pocket, not limited to the concentration operation of the slurry, cleaning with a liquid may be performed. Therefore, the flow path inside the concentrator may be filled with not only the slurry but also a liquid such as pure water or an alkaline aqueous solution. As the liquid, for example, in the case of a silica abrasive slurry, slurry, pure water, alkaline aqueous solution, tap water, ion-exchanged water, permeated water, etc. are used. From the viewpoint of detergency, pure water, alkaline aqueous solution, ion-exchanged water, and permeated water are preferable, and from the viewpoint of workability, slurry is preferable.

[0029] After the operator forms an air pocket in the internal flow path of the concentrator 1, the gas-liquid mixed fluid containing the slurry and the air in the air pocket is passed through the filter section 31 and the connecting flow path 32. Specifically, the pump P01 is operated again to circulate the gas-liquid mixed fluid through the internal flow path of the concentrator 1. When the valve V04 is closed, the valve is opened. In that case, the valve V04 may be opened before or after the operation of the pump P01. Note that the operator may pass not only the slurry but also a gas-liquid mixed fluid containing other liquid and the air in the air pocket.

[0030] By passing a mixed fluid of air and liquid through the entire filter unit composed of a plurality of filter sections and the connecting flow paths arranged between adjacent filter sections, effective cleaning is performed when passing through the filter unit. As a result, the aggregates (deposits) adhering to the connecting flow path between the filter sections without being able to pass through the filter channels are reduced in particle size and can be removed outside the connecting flow path.

[0031] The cleaning of the concentrator may be performed by a forward operation in which the fluid flows from the side of the inlet 3a of the filter unit to the side of the outlet 3b, or by a reverse operation in which the fluid flows from the side of the outlet 3b to the side of the inlet 3a. From the viewpoint of cleanability, it is preferable to perform cleaning by combining the forward operation and the reverse operation. Further, the cleaning method of the present invention may be combined with a cleaning method by reverse washing in which the fluid flows from the permeate water side to the concentrate side.

[0032] Next, the case of cleaning the device shown in FIG. 1 by reverse operation will be described. In the reverse operation, the valves V02 and V03 that are closed in the forward operation are opened for cleaning. The valves V01 and V04 are closed in advance and these valves are maintained in the closed state even during the cleaning of the device. Other operations can be performed in the same manner as in the forward operation. The forward and reverse operations during cleaning may be alternately operated, or only one of them may be continuously operated. The effect of this air cleaning is very high and it is characterized by being executable in a short time. However, even when the concentration device is continuously operated, sufficient effects can be obtained by performing it once every 1 to 3 months.

[0033] The details of the concentration device shown in FIG. 1 will be described below. The filter unit 3 has three filter parts 31 and two bent connecting channels 32 arranged so as to connect between adjacent filter parts 31. In the filter unit 3, filter parts 31a, 31b, and 31c are arranged in order from the side of the inlet 3a of the filter unit 3 toward the side of the outlet 3b.

[0034] Although there is no limitation on the shape of the connecting channel 32, a bent shape such as a U-shaped tube that facilitates the arrangement of a plurality of filter units is often used. Note that the connecting channel 32 may be a straight tube shape instead of a bent shape. Also, a connecting channel with different diameters having different inner diameters can be used.

[0035] The filter part has a ceramic filter as a filtration membrane inside. Note that the filtration membrane that the filter part has inside is not limited to a ceramic filter and can be freely selected from various filters.

[0036] The filtration membrane used in the concentration device is a separation membrane used for cross-flow filtration. As long as it has a hollow fiber type shape, it may be an ultrafiltration membrane or a reverse osmosis membrane can also be used. When used for the concentration and regeneration of the used CMP slurry, an ultrafiltration membrane can be preferably used from the viewpoint of most efficiently recovering the abrasive particles in the concentrated liquid after recovery.

[0037] The separation membrane used in cross-flow filtration to which this cleaning method is applied may be an organic membrane made of an organic material or an inorganic membrane (ceramic filter) made of an inorganic ceramic. As the organic membrane, it is preferably composed of any one of polyethylene, tetrafluoroethylene, polyvinylidene fluoride, polypropylene, cellulose acetate, polyacrylonitrile, polyimide, polysulfone, or polyethersulfone, aromatic polyamide, or polyvinyl alcohol. As the inorganic membrane, it is preferable to use a ceramic material such as aluminum oxide, zirconium oxide, titanium oxide, stainless steel, glass, or the like.

[0038] A preferable filter membrane for the filter section of the concentration device cleaned by this air cleaning is a ceramic filter. This membrane has about 30 to 40 holes (filter channels) with an inner diameter of 3 mm to 4 mm like lotus roots in one ceramic module, and in an extended form, it has a length of about 1 m. About 20 of them are bundled and housed in the filter section. The flow rate can be freely set. For example, when the liquid flows through the internal flow path of the concentration device at a flow rate of 60 m 3 / h, it flows through the flow path in the filter channel at about 3.4 m / s.

[0039] The number of filter sections is not limited to three, and any number can be provided. The number of filter sections can be, for example, from 1 to 10. From the viewpoints of the concentration processing speed, the cost of the device, the maintenance burden, etc., it is preferable that the number of filter sections is from 2 to 8, and more preferably from 3 to 6.

[0040] Since the filter section has a ceramic filter, the strength of the filter section is higher than when an organic material is used as the material, and even when it is subjected to a rapid change in flow rate or pressure change, there is little risk of a change in the pore diameter of the micropores or damage to the filter section. As a result, a higher pressure can be applied to the filter unit than during normal concentration operation, and a greater cleaning effect can be obtained.

[0041] The gas-liquid mixed fluid flowing into the filter unit permeates through a large number of small-diameter filter channels, and the gas is further divided into finer particles than when it flows in, becoming a gas-liquid mixed fluid containing bubbles of about 0.5 mm to 1 mm. Thereby, it is considered that the deposits adhering to the inside of the connection flow path are more likely to be peeled off and removed.

[0042] Next, the cleaning method according to the second embodiment of the present invention will be described with reference to FIG. 2. Note that detailed descriptions of matters described with reference to FIG. 1 will be omitted.

[0043] FIG. 2 is a schematic diagram showing an example of a concentration device to be cleaned by the cleaning method according to the second embodiment. In FIG. 2, P01 is a pump for pressurizing to flow the fluid, and V01 to V04' are valves for adjusting the flow direction and flow rate of the fluid. As shown in FIG. 2, the circulation flow path 4 extends from the pump P01 toward the filter unit 3 and branches into two. In one of the branched circulation flow paths 4, two valves V04 and V04' are provided on the side of the inlet 3a that becomes the front of the flow path of the filter unit 3 in the case of normal operation. Further, in the other branched circulation flow path 4, two valves V02 and V02' are provided on the side of the outlet 3b that becomes the front of the flow path of the filter unit 3 in the case of reverse operation. Here, the "front of the flow path of the filter unit" is the side where the fluid actually flows in when the fluid flows into the filter unit. In normal operation, the side of the inlet 3a of the filter unit 3 is the front of the flow path of the filter unit, and in reverse operation, the side of the outlet 3b of the filter unit 3 is the front of the flow path of the filter unit.

[0044] In addition, in the second embodiment, when only forward rotation operation is performed, only one valve V02 may be provided on the side of the outlet 3b of the filter unit 3, and when only reverse rotation operation is performed, only one valve V04 may be provided on the side of the inlet 3a of the filter unit 3. When cleaning is performed during forward rotation operation, the two valves V04 and V04' are closed before forming an air pocket and are opened before allowing the gas-liquid mixed fluid to pass through the filter unit. Also, when cleaning is performed during reverse rotation operation, the two valves V02 and V02' are closed before forming an air pocket and are opened before allowing the gas-liquid mixed fluid to pass through the filter unit.

[0045] Details of implementing the cleaning method of the second embodiment during forward rotation operation will be described. When performing forward rotation operation, the valves V02, V02', and V03 are closed in advance, and these valves are maintained in a closed state even during cleaning of the device. Thereby, according to the opening and closing of the valves V01, V04, and V04', the gas-liquid mixed fluid flows into the filter unit from the inlet 3a and flows out from the outlet 3b, flowing in the forward rotation direction of the circulation passage 4.

[0046] The operator performing the cleaning stops the operation of the pump P01, closes the two valves V04 and V04' provided in front of the flow path of the filter unit 3, and extracts the slurry between the closed valves. Thereby, an air pocket is formed in the flow path between the two valves V04 and V04'. Note that the operator may close more valves than the two provided in front of the flow path of the filter unit, and the liquid to be extracted is not limited to slurry and may be a liquid such as pure water or permeated water.

[0047] Specifically, the operator stops the operation of the pump P01 during the concentration operation of the slurry, closes the two valves V04 and V04', and extracts the slurry in the flow path between the two valves V04 and V04' through a recovery flow path (not shown) and returns it to the liquid storage tank 2. Thereby, liquid and air exist in the flow path inside the concentration device 1. At this time, the pump P01 may be stopped or may remain in operation. Also, the extracted slurry does not necessarily need to be returned to the liquid storage tank 2.

[0048] After the operator forms an air pocket in the internal flow path of the concentrator 1, a gas-liquid mixed fluid containing slurry and the air in the air pocket is passed through the filter section 31 and the connecting flow path 32. Specifically, the pump P01 is operated again, and the valves V04 and V04' are opened to circulate the gas-liquid mixed fluid through the internal flow path of the concentrator 1. Note that the valves V04 and V04' may be opened before or after the operation of the pump P01.

[0049] By cleaning in the above-described manner, an air pocket can be formed in the flow path in the range closed by the valve in front of the flow path of the filter unit without providing a special gas generator. Thereby, a gas-liquid mixed fluid for cleaning the filter unit can be easily formed.

[0050] Also, the greater the pressure when the valves V04 and V04' are opened, the more rapid the pressure change occurs, and the greater the vibration and impact received by the flow path in the filter unit. Therefore, from the viewpoint of cleanability, it is preferable to operate the pump P01 simultaneously with opening the valves V04 and V04' that form the air pocket to pressurize the gas-liquid mixed fluid, and it is more preferable to operate the pump P01 from before opening the valves V04 and V04' to pressurize the air pocket. When a rapid pressure change occurs, the gas-liquid mixed fluid rapidly flows into the connecting flow path, and greater vibration and impact are applied to the connecting flow path than when the pump is operated after the valve is opened, so the cleaning effect is more excellent. Note that when the valve V01 is also closed together with the valves V04 and V04', the valve V01 is also opened together with the valves V04 and V04' in order to pass the gas-liquid mixed fluid through the filter section 31 and the connecting flow path 32. When opening a plurality of closed valves, from the viewpoint of causing a rapid pressure change, it is preferable to open the closed valves simultaneously.

[0051] When there is a rapid pressure drop in the flow path inside the concentration device, when using an aqueous liquid as the fluid, so-called cavitation occurs, generating water vapor bubbles. The cleaning method of the present invention can also cause a rapid pressure drop by operating the pump and operating the valve to open and close, and generate bubbles due to this, and use it for cleaning as a gas-liquid mixed fluid.

[0052] In addition, the cleaning method of the second embodiment may be operated in either the forward or reverse direction following the first embodiment. When operating in reverse, the gas-liquid mixed fluid flows into the connecting flow path in the opposite direction to that in the case of forward operation. As a result, vibrations and impacts by the gas-liquid mixed fluid are applied to the connecting flow path from a direction that is less likely to receive the flow from the fluid during normal operation (forward operation), and excellent cleaning effects can be expected.

Examples

[0053] The present invention will be described more specifically with reference to the following examples, but the present invention is not limited by these examples.

[0054] While operating the concentration device shown in FIG. 1 equipped with a ceramic filter in the filter section for 200 days, cleaning tests were conducted using the methods of the examples, comparative examples, and reference examples described below, and the changes in the membrane differential pressure and permeation water volume before and after each cleaning were evaluated. Here, the membrane differential pressure is the pressure difference between the pressure (pressure 1) at the end on the inlet 3a side of the filter section 31a and the pressure (pressure 3) at the end on the outlet 3b side of the filter section 31c (see FIG. 1). The membrane differential pressure in the case of forward operation is pressure 1 - pressure 3, and the membrane differential pressure in the case of reverse operation is pressure 3 - pressure 1. Also, regarding the permeation water volume, the permeation water volume from the filter section 31a is called the F1 permeation water volume, the permeation water volume from the filter section 31b is called the F2 permeation water volume, and the permeation water volume from the filter section 31c is called the F3 permeation water volume.

[0055] [Example] In the concentration device 1 shown in FIG. 1 equipped with a ceramic filter in the filter section, the slurry is about 60m 3During the concentration operation circulating at a flow rate of / h, the operation of pump P01 was stopped. The slurry inside the filter section 31, the connecting flow path 32, and the circulation flow path 4 was returned to the liquid storage tank 2 to form an air pocket in the flow path inside the concentrator 1. At this time, valves V01 and V04 were in the open state. Next, the stopped pump P01 was operated again to circulate and wash a gas-liquid mixed fluid containing slurry and air in the air pocket through the flow path inside the concentrator 1. By forward rotation operation, the flow rate of the slurry was about 30m 3 / h and circulated for 9 hours (air cleaning).

[0056] [Comparative Example] Permeate water was sent from the discharge port 31d provided in the filter section 31 into the filter unit 3 and replaced with slurry to fill the flow path in the concentrator 1 with permeate water. Thereafter, without forming an air pocket, the permeate water was circulated at a flow rate of about 60m 3 / h for 9 hours (liquid cleaning). Here, the permeate water was in a state where the concentration of the contained components was very low and close to pure water.

[0057] [Reference Example] As a conventional cleaning method, the concentrator was disassembled, and internal cleaning of the liquid storage tank, the circulation flow path, and the connecting flow path, replacement of the ceramic filter, etc. were performed (disassembly cleaning).

[0058] Fig. 3 shows the transition of the average value of the membrane differential pressure (pressure 1 - pressure 3) in the forward rotation operation and the membrane differential pressure (pressure 3 - pressure 1) in the reverse rotation operation per day when the concentrator was operated for 200 days. During the concentration operation, the forward rotation operation and the reverse rotation operation were alternately performed approximately every 1 hour. Note that measurements were not taken during the periods when the device was stopped due to cleaning or equipment reasons. Also, Fig. 4 shows the transition of the average value of the permeate water volume per day in the forward rotation operation when the concentrator was operated for 200 days, and Fig. 5 shows the transition of the average value of the permeate water volume per day in the reverse rotation operation. In the figures, the locations shown as the examples, comparative examples, and reference examples indicate the times when cleaning was performed by each cleaning method.

[0059] As shown in Fig. 3, the membrane differential pressure hardly changes during the entire period of both the forward operation and the reverse operation, regardless of the operating conditions and before and after cleaning. The membrane differential pressure during the forward operation is about 430 kPa, while the membrane differential pressure during the reverse operation is about 380 kPa. This is considered to be due to the difference in the positional relationship (distance) of the pipe length, valves, filter units, etc. as viewed from the pump side and the liquid storage tank side.

[0060] Regarding the permeate flow rate, it was confirmed that it recovered after cleaning and gradually decreased over time. In the case of the forward operation, the decrease in the F1 permeate flow rate due to the operation after cleaning was relatively small, while the decrease in the F3 permeate flow rate was significant. Also, not only the F3 permeate flow rate but also the F2 permeate flow rate showed a tendency to gradually decrease with the continuation of the operation (Fig. 4). In the case of the reverse operation, on the contrary to the forward operation, the decrease in the F3 permeate flow rate due to the operation after cleaning was relatively small, and the decrease in the F1 permeate flow rate was the largest. Also, not only the F1 permeate flow rate but also the F2 permeate flow rate showed a tendency to gradually decrease with the continuation of the operation (Fig. 5).

[0061] When comparing the degree of recovery of the permeate flow rate by cleaning with each cleaning method, in the reference example (disassembly cleaning), each member of the concentration device is physically cleaned using cleaning tools and the ceramic filter is also replaced. Therefore, the degree of recovery of the permeate flow rate after cleaning is large and the cleaning effect is significant. In the example (air cleaning), although not as much as the reference example, a significant recovery of the permeate flow rate was confirmed despite not disassembling the concentration device or replacing the filter. In contrast, in the comparative example (liquid cleaning), although a slight recovery of the permeate flow rate was confirmed, the degree of recovery was smaller than that of the example, and a rapid decrease in the permeate flow rate was observed at the initial stage of the operation after cleaning.

[0062] As shown in FIGS. 4 and 5, a decrease in the permeation water volume over time due to long-term concentration operation was confirmed in both the forward operation and the reverse operation. If the slurry stored in the liquid storage tank were pure water without dirt, etc., it would be considered that a decrease in the permeation water volume over time would not occur. However, in reality, it is considered that pad debris generated by CMP polishing, aggregates of particle components in the slurry, or their gelated products, etc. are gradually accumulated, causing a decrease in the permeation water volume.

[0063] Generally, fine pores of about 50 nm formed on the side wall inside the filter channel with an inner diameter of 3 mm of the ceramic filter are likely to cause filter clogging. However, in such a concentration device equipped with a cross-flow type filter unit, a backwashing mode is executed in which permeated water is stored in the backwashing tank every set time during the concentration operation and returned to the filter channel at high pressure to suppress clogging of the fine pores. Therefore, clogging is unlikely to occur during normal concentration operation.

[0064] The F1 permeation water volume, which is the permeation water volume from the filter part on the inlet side during the forward operation, and the F3 permeation water volume, which is the permeation water volume from the filter part on the outlet side during the reverse operation, are both about 20 L / min, and since there was no decrease over time, it is considered that there is no significant difference in clogging of the three ceramic filters themselves.

[0065] When considering factors other than the filter part as the cause of the decrease in the permeation water volume over time, the possibility of aggregates adhering to the connection flow path provided in the filter unit is considered. Since the connection flow path used in this test is a U-shaped tube, the flow inside the tube is likely to be turbulent and it is easy to form places where the flow stagnates. Furthermore, since the inner diameter of the connection flow path is not constant, the flow velocity also varies depending on the location inside the U-shaped tube, and it is considered that aggregates are likely to accumulate in places where the flow velocity of the inner side wall of the tube is slow.

[0066] When the fluid exits the filter section and flows through the connecting flow path into the next adjacent filter section, the flow velocity is slowest in parts with a large pipe diameter or concave parts. For example, in the case of a connecting flow path where the inner diameters at both ends, which are the parts connected to the filter section, are approximately 200 mm and the inner diameter of the middle part is approximately 100 mm, the flow velocity of the fluid passing through the flow paths at both ends is significantly slower, about 1 / 4 of the flow velocity in the middle part. Since the connecting flow path is sandwiched between filter sections equipped with ceramic filters with a channel diameter of 3 mm, when the particle size of the aggregates exceeds 3 mm, they tend to remain and accumulate in the connecting flow path. It is considered that when this deposit accumulates on the surface of the filter housing, it blocks the filter channels.

[0067] Aggregates can also accumulate on the housing surface on the side connected to the circulation flow path of each filter section arranged on the inlet side and outlet side of the filter unit. However, in the backwashing mode regularly performed during the concentration operation, since the liquid is pumped at a flow velocity about 5 times that of the normal concentration operation, even if deposits temporarily occur on the housing surface, they are likely to be washed away by the strong backwashing flow and removed.

[0068] The permeation water volume from each filter section will be described when the fluid flows ideally, such as when there is no deposit or filter clogging immediately after disassembling and cleaning. Under the forward operation conditions, when flowing in at 60 m 3 / h from the inlet, the permeation water volume of F1 is 20 L / min, the permeation water volume of F2 is 19.6 L / min, the permeation water volume of F3 is 19.2 L / min, and it flows out from the outlet at 56.5 m 3 / h. However, in reality, as shown in Fig. 4, only the permeation water volumes (permeation water volume of F2 and permeation water volume of F3) from the two filter sections on the liquid storage tank side showed a decreasing trend over time. This is considered to be because aggregates accumulated in the two U-shaped tubes due to continuous long-term concentration operation, causing an imbalance in the membrane differential pressure of each filter.

[0069] Specifically, the membrane differential pressure ideally applied to each of the three filter units is about 1 / 3 of the membrane differential pressure applied to the entire filter unit. When the concentration operation is performed for a long period and deposits accumulate in the connection flow path, increasing the load required to flow through the connection flow path, it is considered that the downstream filter unit connected to the connection flow path is subjected to the membrane differential pressure in which the above load is lost as pressure loss from the ideal membrane differential pressure. For this reason, although the micropores of each ceramic filter are not clogged, it is considered that the amount of permeate from the two downstream filter units decreases over time.

Industrial Applicability

[0070] The cleaning method of the concentration device of the present invention can easily clean a filter unit having a complex internal shape, so it can be suitably used for cleaning a concentration device used for regenerating the used CMP slurry discharged from the CMP process.

Explanation of Signs

[0071] 1 Concentration device 2 Liquid storage tank 3 Filter unit 3a Inlet 3b Outlet 31, 31a, 31b, 31c Filter part 31d Drain outlet 32 Connection flow path 4 Circulation flow path P01 Pump V01~V04, V02’, V04’ Valve

Claims

1. A cleaning method for a slurry concentrator using a separation membrane used in cross-flow filtration, comprising a liquid storage tank, a cross-flow type filter unit through which slurry is passed from the liquid storage tank by a pump, and a circulation flow path that annularly connects the liquid storage tank and the filter unit to enable circulation of the slurry. The filter unit has a plurality of filter sections and a connecting flow path disposed between adjacent filter sections. The cleaning method is a method of passing a gas-liquid mixed fluid containing the slurry or other liquid and the air in the air pocket through the filter section and the connecting flow path after forming an air pocket in the flow path inside the concentrator. The air pocket is formed by closing at least two valves provided in front of the flow path of the filter unit and extracting the slurry or other liquid between the closed valves. A cleaning method for a slurry concentrator using a separation membrane used in cross-flow filtration, characterized by the above.

2. The cleaning method for a slurry concentrator using a separation membrane used in cross-flow filtration according to Claim 1, wherein the slurry is used CMP slurry discharged from a CMP process for manufacturing a semiconductor integrated circuit.

3. The cleaning method for a slurry concentrator using a separation membrane used in cross-flow filtration according to Claim 1 or Claim 2, wherein the filter section has a ceramic filter.

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