JP4585100B2 - How to recycle polishing used liquid - Google Patents

Description

【００２２】
実施例２
平均粒子径８０ｎｍでシリカ濃度１０重量％のコロイダルシリカ２０ｋｇに、３０ｇのエチレンジアミン四酢酸二カリウム（ＥＤＴＡ−２Ｋ）を加えて溶解し、さらにＰＨが１０．５となるまでＫＯＨを加えて研磨材を作成した。このコロイダルシリカを主成分とする研磨材は、Ｃｕ、Ｚｎ、Ｃｒの含有率がそれぞれ２０ppb、１２ppb、１５０ppbであった。純水に所定濃度のＣｕ、Ｚｎ、Ｃｒ塩を溶解した液を調製し、この液２０ｋｇを前記研磨材に混合し、４０ｋｇの模擬研磨使用済み液を作成した。模擬研磨使用済み液はシリカ濃度５重量％、Ｃｕ、Ｚｎ、Ｃｒの含有率がそれぞれ５０ppb、３０ppb、４００ppbであった。
この模擬研磨使用済み液を下記の第１工程ないし第４工程により再生に施した。
（第１工程） 模擬使用済み液を調製に用いたタンクよりポンプで再生用タンクに圧送し、そのラインの途中には目開き１μの「糸巻きフィルター」を組み込み、全量濾過を行い、全量濾過液を得た。
（第２工程） 第１工程をおわった全量濾過液を、分画分子量１００００の旭化成工業（株）製限外濾過モジュール・マイクローザＳＬＰ−２０５３を使用して循環式濾過で１９ｋｇまで濃縮し、濃縮液を得た。シリカ濃度は比重測定により約１０重量％と測定ができた。
（第３工程） 純水を添加することで液面レベルを一定に保ちつつ前記第２工程の循環式限外濾過を継続し、純水の添加量が１０ｋｇとなったところで濾過を停止し、精製液を得た。
（第４工程） 第３工程で得た精製液を攪拌しながら３０ｇのエチレンジアミン四酢酸二カリウム（ＥＤＴＡ−２Ｋ）を加えて溶解し、さらにｐＨが１０．５となるまでＫＯＨを添加し、再生液を得た。
下記表２に、研磨材、模擬研磨使用済み液、第２工程〜第４工程で得られた液体のの成分組成をそれぞれ示した。このようにして使用前液と同成分の再生液を得ることができた。
【００２３】
【表２】

【００２４】
実施例３
ＢＥＴ法平均１次粒子径３０ｎｍの高純度ヒュームドシリカ４００ｇを１６００ｇの純水に分散し、レーザー法平均２次粒子径１２５ｎｍの高純度シリカ液を作成した。これに５．０ｇのエチレンジアミン四酢酸（ＥＤＴＡ）を加えて溶解し、３．５％過酸化水素水２ｇを添加混合し、全量が２５００ｇとなるよう純水を加えて希釈し、さらにｐＨが１．８となるよう６０％ＨＮＯ₃を加えてシリカ濃度１６重量％の研磨材を作成した。このコロイダルシリカを主成分とする研磨材は、Ｃｕ、Ｎｉ、Ｆｅの含有率がそれぞれ１０ppb、２０ppb、１００ppbであった。純水に所定濃度のＣｕ、Ｎｉ、Ｆｅ塩を溶解した液を調製し、この液２５００ｇを前記研磨材に混合し、５０００ｇの模擬研磨使用済み液を作成した。模擬研磨使用済み液はシリカ濃度８％、Ｃｕ、Ｎｉ、Ｆｅの含有率がそれぞれ５０００ppb、５０００ppb、５０５０ppbであった
この模擬研磨使用済み液を下記の第１工程ないし第４工程により再生に施した。
（第１工程） 模擬使用済み液を調製に用いたタンクよりポンプで再生用タンクに圧送し、そのラインの途中には目開き１μの「糸巻きフィルター」を組み込み、全量濾過を行い、全量濾過液を得た。
（第２工程） 第１工程をおわった全量濾過液を、分画分子量６０００の旭化成工業（株）製限外濾過モジュール・マイクローザＳＩＰ−１０１３を使用して循環式濾過で２０００ｇまで濃縮し、濃縮液を得た。シリカ濃度は比重測定により約２０重量％と測定ができた。
（第３工程） 純水を添加することで液面レベルを一定に保ちつつ循環式限外濾過を継続し、純水の添加量が１１ｋｇとなったところで濾過を停止し、精製液を得た。
（第４工程） 第３工程で得た精製液を攪拌しながら５．０ｇのエチレンジアミン四酢酸（ＥＤＴＡ）を加えて溶解し、３．５％過酸化水素水２ｇを添加混合し、全量が２５００ｇとなるよう純水を加えて希釈し、さらにｐＨが１．８となるよう６０％ＨＮＯ₃を加えてシリカ濃度１６重量％の再生液を得た。
下記表３に、研磨材、模擬研磨使用済み液、第２工程〜第４工程で得られた液体のの成分組成をそれぞれ示した。このようにして使用前液と同成分の再生液を得ることができた。
【００２５】
【表３】

【００２６】
【発明の効果】
本発明によれば、環境への負荷を最小限に抑制することができるとともにコスト的に有利に研磨特性を良好に再生することのできる研磨使用済み液の再生方法が提供される。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a used polishing liquid (usually referred to as a slurry, which is referred to as a “slurry” in this specification after chemical mechanical polishing of a semiconductor substrate or a film formed thereon with an abrasive containing colloidal silica as a main component. ")").
[0002]
[Prior art]
Conventionally, the cost of consumables such as colloidal silica and pads in chemical mechanical polishing has been a problem, and several countermeasures have been proposed.
For example, Japanese Patent Laid-Open No. 8-115589 discloses a polishing in which colloidal silica used for polishing a semiconductor substrate is first subjected to microfiltration to remove coarse impurities by concentrating on the concentrated liquid side, followed by ultrafiltration of the permeate. A method for recovering agent particles is described.
Japanese Patent Laid-Open No. 11-121408 discloses that the waste liquid used for polishing the semiconductor substrate is completely filtered to remove impurities, and then separated into a concentrated liquid and a permeated liquid containing a polishing agent by a membrane separation device. An abrasive slurry recovery device is described in which the liquid is concentrated by a reverse osmosis device, and finally the concentrated solution obtained by the membrane separation device and the concentrated solution obtained by reverse osmosis are mixed.
Further, JP-A-11-277380 discloses a method in which an ion component is removed from a used polishing liquid by an ion exchange method, and then colloidal silica is concentrated and recovered by ultrafiltration, and a new ion component is added and reused. Are listed.
[0003]
[Problems to be solved by the invention]
However, the recovery method described in JP-A-8-115589 can concentrate silica to a reuse concentration, but the concentration of dissolved metal in the solution is not low. In other words, the concentration of dissolved metal is increased, and stable polishing characteristics cannot be maintained.
In addition, the recovery device described in JP-A-11-121408 is good for effective use of resources because it minimizes waste, but does not consider the increase in the concentration of dissolved metal, and the use of a reverse osmosis membrane is a treatment. There is a limit to practical use in terms of ability.
Moreover, although the method of removing an ionic component by the ion exchange method from the used polishing liquid of JP-A-11-277380 is excellent in that the silica component can be recovered with high purity, the cation exchange does not proceed in the acidic solution. Therefore, it cannot be applied to acidic used liquids. In the case of polishing used liquids containing an anionic component other than OH, the cation exchange does not proceed as in the case of acidic liquids. In the spent liquid containing, there are too many problems in practical use, such as carbon dioxide gas is generated as a result of acidity of the liquid when cation exchange occurs, and the inside of the cation exchange tower becomes full of bubbles.
[0004]
Furthermore, the conventional proposals do not pay attention to reducing the concentration of dissolved silica (low molecular weight silica). In particular, in the apparatus described in JP-A-11-121408, the dissolved silica is actively taken into the reuse system. In chemical mechanical polishing, silicon or silicon dioxide is etched with an alkali agent, and the surface of the object to be polished is scraped off with silica particles. Therefore, the concentration of dissolved silica in the polishing liquid is close to saturation when polishing is performed once. It has become. In addition, since a grinding | polishing speed | rate will fall when a melt | dissolution silica density | concentration raises, it adds and reuses an alkali agent. If this is repeated, the alkaline agent in the reuse system will endlessly increase, colloids will aggregate, leading to pad clogging and scratching. In the field, the used polishing liquid is diluted by mixing with cleaning water, and new colloidal silica is added, so that the reuse system has a certain balance. However, if we try to reduce the amount of wastewater and reduce the amount of colloidal silica used, the balance will be lost.
[0005]
Accordingly, an object of the present invention is to provide a method for regenerating a used polishing liquid that can suppress environmental burdens to a minimum and can regenerate the polishing characteristics favorably in terms of cost.
[0006]
[Means for Solving the Problems]
The present invention relates to a method for reclaiming a used polishing liquid generated after chemical mechanical polishing of a semiconductor substrate or a film formed thereon with an abrasive mainly composed of colloidal silica,
A first step for removing the particles used in the chemical mechanical polishing step by filtering the used polishing solution with a filter having an opening of 1 to 10 μm, and the filtrate produced in the first step has a molecular weight cut off of 15000 or less. A second step of ultrafiltration using an ultrafiltration membrane to concentrate the colloidal silica concentration to a concentration higher than necessary for reuse, and a pure solution while maintaining the concentration of the concentrate obtained in the second step. A third step in which ultrafiltration is continued while adding water to lower the dissolved silica concentration and dissolved metal concentration in the solution, and the composition before the polishing is used by adding the lost composition component to the filtrate obtained in the third step. A method for reclaiming a used polishing liquid having a fourth step of returning to the above is provided.
The present invention also provides the above-mentioned method for regenerating a used polishing liquid, wherein a chelating agent for a dissolved metal is added in the third step and / or the fourth step.
The present invention also provides the above-described method for reclaiming used polishing liquid, wherein an oxidizing agent for dissolved metal is added in the third step and / or the fourth step.
Further, the present invention provides the above-mentioned method for regenerating a used polishing liquid, wherein the particle diameter of silica in the colloidal silica after the fourth step is 5 to 150 nm, and the concentration of silica is adjusted to 3 to 60% by weight. Is to provide.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The used polishing liquid regenerated by the present invention is a waste liquid generated after chemical mechanical polishing of a semiconductor substrate or a film formed thereon with an abrasive mainly composed of colloidal silica. Specific examples of objects to be polished include silicon wafers constituting semiconductor elements such as IC and LSI, interlayer insulating films for multilayer wiring formed thereon, buried oxide films for isolating trench elements, and metal films for flat buried wiring When these chemical mechanical polishing is performed, the above-mentioned polishing used liquid is generated.
In addition to the components before use, the polishing spent liquid is mixed with ionic species in which a polishing object is dissolved, dissolved silica, pad wear, pure water used for cleaning, and the like.
[0008]
The abrasive referred to in the present invention is a so-called abrasive slurry or CMP slurry that is mainly composed of colloidal silica. The colloidal silica referred to in the present invention is not only “silica sol” produced from water glass as a raw material, but also a product with less impurities produced from an alkoxide such as ethyl silicate, silicon tetrachloride or the like as a raw material. General products in which fine silica is colloidally dispersed in an aqueous medium, such as a product obtained by dispersing fine powder silica called fumed silica into an aqueous medium.
[0009]
The first step in the present invention is a step of removing the particles mixed in the chemical mechanical polishing step by filtering the polishing spent liquid.
In the first step, it is preferable to remove the particles mixed in the chemical mechanical polishing step by filtering the entire amount of the polishing used liquid. Examples of the filter used here include a filter having an opening of about 1 to 10 μm that is sufficiently larger than the silica particle diameter of colloidal silica. A filter generally referred to as depth filtration can be suitably used. A typical example of this type of filter is a “wound filter” in which a thread made of polypropylene or the like is wound into a cylindrical shape. However, a non-woven fabric, a sponge, a plate, a cloth, etc. There are no particular limitations on the material and shape of the object, and it can be selected as appropriate.
[0010]
The second step in the present invention is a step in which the filtrate produced in the first step is ultrafiltered to concentrate the colloidal silica concentration to a concentration necessary for reuse. As the filter used here, an ultrafilter having an opening of about 1 to 5 nm smaller than the silica particle diameter of colloidal silica can be used. In general, separation using an ultrafiltration membrane is performed with a target particle size of 1 nm to several microns, but since a dissolved polymer substance is also targeted, the filtration accuracy is expressed in the nanometer range by a fractional molecular weight. In the present invention, an ultrafiltration membrane having a molecular weight cut-off of 15000 or less is preferably used. When a film in this range is used, particles of 5 nm or more can be separated. More preferably, an ultrafiltration membrane having a fractional molecular weight of 3000 to 15000 is used. When the membrane is less than 3000, the filtration resistance is too large and the treatment time becomes long, which is uneconomical. When the membrane is 20000 or more, clogging increases and continuous operation is difficult. The material of the membrane includes polysulfone, polyacrylonitrile, sintered metal, ceramic, carbon and the like. Any of them can be used, but polysulfone is easy to use because of its heat resistance and filtration speed. The shape of the membrane includes spiral type, tubular type and hollow fiber type, and any of them can be used, but the hollow fiber type is compact and easy to use.
[0011]
In the third step of the present invention, ultrafiltration is continued while pure water is added while maintaining the concentration of the concentrated solution obtained in the second step, and the dissolved silica concentration and dissolved metal concentration in the solution are set, for example, before use. This is a process to lower the level. According to the third step, the amount of water used can be minimized.
[0012]
A known measurement method can be employed for measuring the dissolved silica concentration. For example, when the silica concentration is on the order of%, the KF addition titration method (described in AM Lowson Anal. Chem., 27, 1810 (1955)) is convenient, and when the silica concentration is on the order of ppm, the ICP (high frequency inductively coupled plasma) method is simple. Any of these methods are suitably used in general.
[0013]
The fourth step in the present invention is a step of adding the lost composition component to the filtrate obtained in the third step to restore the composition before polishing use. In the fourth step, for example, colloidal silica, a pH adjuster, various electrolytes, and the like are added.
[0014]
In addition, the silica particle surface of colloidal silica has high activity, and polyvalent metal ions may be adsorbed and difficult to remove. In such a case, it is preferable to add a chelating agent and / or an oxidizing agent for the dissolved metal.
[0015]
As the chelating agent used in the present invention, any one can be used as long as it binds as a metal multidentate ligand, as long as the effects of the present invention are not impaired. (1) Ethylenediamine Tetraacetate, (2) Hydroxyethylethylenediamine triacetate, (3) Dihydroxyethylethylenediamine diacetate, (4) Diethylenetriamine pentaacetate, (5) Triethylenetetramine hexaacetate, (6) Hydroxyethyliminodiacetic acid It is preferably selected from a salt and (7) gluconate. Specifically, (1) ethylenediaminetetraacetic acid disodium, ethylenediaminetetraacetic acid trisodium, ethylenediaminetetraacetic acid tetrasodium, ethylenediaminetetraacetic acid diammonium, ethylenediaminetetraacetic acid triammonium, ethylenediaminetetraacetic acid tetraammonium, (2) hydroxyethylethylenediamine Trisodium triacetate, triethylammonium hydroxyethylethylenediamine triacetate, (3) disodium dihydroxyethylethylenediaminediacetic acid, diammonium dihydroxyethylethylenediaminediacetic acid, (4) pentasodium diethylenetriaminepentaacetic acid, pentaammonium diethylenetriaminepentaacetic acid, diethylenetriaminepentaacetic acid Disodium iron, diethylenetriaminepentaacetic acid diammonium iron, (5) triethylenetetra Hexasodium acetate, triethylenetetramine hexaacetate hexaammonium, (6) hydroxyethyliminodiacetic acid disodium salt, hydroxyethyliminodiacetic acid diammonium salt, (7) sodium gluconate, potassium gluconate, calcium gluconate, and glucone And acid-6-trisodium phosphate. Glycine and salicylic acid are also suitable.
These chelating agents may contain crystal water or may be anhydrides. Moreover, these chelating agents can use 2 or more types together, In that case, they can be used together in arbitrary ratios.
[0016]
The amount of the chelating agent used in the present invention can be determined based on the amount of metal impurities contained in the used polishing liquid. The amount of the chelating agent varies depending on the type of the chelating agent and the quality of the used polishing liquid. For example, the amount used varies greatly depending on whether or not Al is removed from the dissolved metal. For example, if the object to be polished is a silicon substrate, the chelating agent should be 5 mg equivalent to 1 kg of silica and the chelating agent should be 20 mg equivalent to 1 kg of silica if Al removal is not considered. Amount. In addition, when the object to be polished contains a metal, the amount of chelating agent used should be 5 times or less equivalent to the amount of dissolved metal. In addition, since the equilibrium constant of chelate formation is significantly different depending on pH, there is no limit to adding a large excess exceeding this amount.
[0017]
The oxidizing agent used in the present invention is not particularly limited, but for example, hydrogen peroxide is preferable because it is highly purified and easily available, but generally has an oxidizing action such as permanganic acids, nitric acids, oxygen acids and the like. A substance having the above can be appropriately selected according to the usage form. The amount of the oxidizing agent used can also be determined based on the amount of metal impurities contained in the used polishing liquid. When the object to be polished is a silicon substrate, the amount of oxidizing agent used is generally 0.5 mg equivalent to 10 mg equivalent to 1 kg of silica, but when the object to be polished contains metal, it is 5 times equivalent to the amount of dissolved metal. Use as a guide.
[0018]
Note that it is preferable to use an oxidizing agent and a chelating agent in combination because the removal efficiency of Zn and Cr is increased. Therefore, it is preferable to use together according to the kind of melt | dissolved metal.
A chelating agent and / or an oxidizing agent can also be added in the fourth step. They act to remove metal impurities in the third step during the next regeneration.
[0019]
It is preferable to adjust the particle diameter of silica in the regenerated polishing spent liquid obtained after the fourth step to be 5 to 150 nm. The dispersed state of the particles may be monodispersed or secondary agglomerated, and can be properly used depending on the application. Further, the shape of the particles can be properly used depending on the application, such as a spherical shape or a non-spherical shape. Further, the concentration of the silica is preferably adjusted so as to be 3 to 60% by weight.
[0020]
【Example】
Hereinafter, the present invention will be further described by examples.
Example 1
An example is shown in which bare silicon is polished for 8 hours using 100 L of an abrasive mainly composed of colloidal silica having a silica concentration of 3% by weight. The circulating fluid was continuously measured for pH, and NaOH was added so that the pH was 10.3 of the abrasive before use.
Samples 1 and 2 in Table 1 below show the compositions of the abrasive before use and the used polishing liquid after use, respectively. As can be seen from Table 1, the used polishing liquid is about 200 L containing cleaning water and the like, and the colloidal silica is diluted, but the alkali concentration becomes higher due to pH adjustment, resulting in the dissolved silica. The concentration is high.
This polishing spent solution was subjected to regeneration by the following first to fourth steps.
(First step) Polished spent liquid is pumped from the circulating fluid tank to the regeneration tank with a pump, and a “pound filter” with an opening of 1 μ is installed in the middle of the line, and the whole amount is filtered to obtain the whole amount filtrate. It was.
(2nd process) The whole amount filtrate which finished the 1st process is concentrated to 90L by circulation type filtration using Asahi Kasei Kogyo Co., Ltd. ultrafiltration module Microza AIV-5010 of the molecular weight cut off 6000, A concentrated solution was obtained. The silica concentration was measured to be about 3% by weight by specific gravity measurement.
(Third step) The circulation type ultrafiltration of the second step is continued while keeping the liquid level constant by adding pure water, and the filtration is stopped when the addition amount of pure water reaches 60 L, A purified solution was obtained.
(Fourth step) NaOH was added to the purified solution obtained in the third step while stirring to adjust the pH to 10.3 to obtain a regenerated solution.
The component compositions of the liquids obtained in the second to fourth steps are shown in Sample 3 to Sample 5 in Table 1 below. In this way, a regenerated liquid having the same components as the pre-use liquid could be obtained.
[0021]
[Table 1]

[0022]
Example 2
To 20 kg of colloidal silica having an average particle size of 80 nm and a silica concentration of 10% by weight, 30 g of ethylenediaminetetraacetic acid dipotassium (EDTA-2K) is added and dissolved, and further, KOH is added until the pH becomes 10.5. Created. The abrasives mainly composed of colloidal silica had Cu, Zn, and Cr contents of 20 ppb, 12 ppb, and 150 ppb, respectively. A liquid prepared by dissolving Cu, Zn, and Cr salts at predetermined concentrations in pure water was prepared, and 20 kg of this liquid was mixed with the abrasive to prepare 40 kg of a simulated polishing used liquid. The simulated polishing used liquid had a silica concentration of 5% by weight and Cu, Zn, and Cr contents of 50 ppb, 30 ppb, and 400 ppb, respectively.
This simulated polishing spent solution was subjected to regeneration by the following first to fourth steps.
(First step) Pump the simulated used liquid from the tank used for preparation to the tank for regeneration, and incorporate a “pound filter” with a 1 μ mesh opening in the middle of the line. Got.
(2nd process) The whole amount filtrate which finished the 1st process is concentrated to 19 kg by circulation type filtration using Asahi Kasei Kogyo Co., Ltd. ultrafiltration module Microza SLP-2053 of molecular weight cut off 10,000, A concentrated solution was obtained. The silica concentration was measured to be about 10% by weight by specific gravity measurement.
(Third step) The circulation type ultrafiltration of the second step is continued while keeping the liquid level constant by adding pure water, and the filtration is stopped when the addition amount of pure water becomes 10 kg, A purified solution was obtained.
(Fourth step) While stirring the purified liquid obtained in the third step, 30 g of ethylenediaminetetraacetic acid dipotassium (EDTA-2K) is added and dissolved, and further, KOH is added until the pH becomes 10.5 to regenerate. A liquid was obtained.
Table 2 below shows the component compositions of the abrasive, the simulated polishing used liquid, and the liquid obtained in the second to fourth steps. In this way, a regenerated liquid having the same components as the pre-use liquid could be obtained.
[0023]
[Table 2]

[0024]
Example 3
400 g of high-purity fumed silica having a BET method average primary particle size of 30 nm was dispersed in 1600 g of pure water to prepare a high-purity silica liquid having a laser method average secondary particle size of 125 nm. To this, 5.0 g of ethylenediaminetetraacetic acid (EDTA) is added and dissolved, 2 g of 3.5% hydrogen peroxide water is added and mixed, pure water is added to dilute the total amount to 2500 g, and the pH is 1 An abrasive having a silica concentration of 16% by weight was prepared by adding 60% HNO ₃ so as to be 0.8. The abrasive containing the colloidal silica as a main component had Cu, Ni, and Fe contents of 10 ppb, 20 ppb, and 100 ppb, respectively. A liquid in which Cu, Ni, and Fe salts of predetermined concentrations were dissolved in pure water was prepared, and 2500 g of this liquid was mixed with the abrasive to prepare 5000 g of a simulated polishing used liquid. The simulated polishing used liquid was 8% silica concentration and Cu, Ni, and Fe contents were 5000 ppb, 5000 ppb, and 5050 ppb, respectively. The simulated polishing used liquid was regenerated in the following first to fourth steps. .
(First step) Pump the simulated used liquid from the tank used for preparation to the tank for regeneration, and incorporate a “pound filter” with a 1 μ mesh opening in the middle of the line. Got.
(2nd process) The whole amount filtrate which finished the 1st process is concentrated to 2000g by a circulation type filtration using Asahi Kasei Kogyo Co., Ltd. ultrafiltration module Microza SIP-1013 of the molecular weight cut off 6000, A concentrated solution was obtained. The silica concentration was measured to be about 20% by weight by specific gravity measurement.
(Third step) Circulating ultrafiltration was continued while keeping the liquid level constant by adding pure water, and when the amount of pure water added reached 11 kg, the filtration was stopped to obtain a purified solution. .
(Fourth Step) While stirring the purified liquid obtained in the third step, 5.0 g of ethylenediaminetetraacetic acid (EDTA) is added and dissolved, and 2 g of 3.5% hydrogen peroxide solution is added and mixed, and the total amount is 2500 g. Then, pure water was added to dilute, and 60% HNO ₃ was added so that the pH was 1.8 to obtain a regenerated solution having a silica concentration of 16% by weight.
Table 3 below shows the component compositions of the abrasive, the simulated polishing used liquid, and the liquid obtained in the second to fourth steps. In this way, a regenerated liquid having the same components as the pre-use liquid could be obtained.
[0025]
[Table 3]

[0026]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the reproduction | regeneration method of the polishing used liquid which can suppress the environmental load to the minimum and can reproduce | regenerate the grinding | polishing characteristic favorably economically is provided.

Claims (4)

In a method for reclaiming a used polishing liquid generated after chemical mechanical polishing of a semiconductor substrate or a film formed thereon with an abrasive mainly composed of colloidal silica,
A first step for removing the particles used in the chemical mechanical polishing step by filtering the used polishing solution with a filter having an opening of 1 to 10 μm, and the filtrate produced in the first step has a molecular weight cut off of 15000 or less. A second step of ultrafiltration using an ultrafiltration membrane to concentrate the colloidal silica concentration to a concentration higher than necessary for reuse, and a pure solution while maintaining the concentration of the concentrate obtained in the second step. A third step in which ultrafiltration is continued while adding water to lower the dissolved silica concentration and dissolved metal concentration in the solution, and the composition before the polishing is used by adding the lost composition component to the filtrate obtained in the third step. A method for reclaiming a used polishing liquid, comprising a fourth step of returning to step (b).   The method for regenerating a polishing spent liquid according to claim 1, wherein a chelating agent for dissolved metal is added in the third step and / or the fourth step.   3. The method for regenerating a polishing spent liquid according to claim 1 or 2, wherein an oxidizing agent of a dissolved metal is added in the third step and / or the fourth step.   The polishing according to any one of claims 1 to 3, wherein the particle size of silica in the colloidal silica after the fourth step is 5 to 150 nm and the concentration of silica is adjusted to 3 to 60 wt%. How to recycle spent liquid.