JP2001009721A - Abrasive recovery system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To recover slurry of abrasive particles easily reusable as abrasive slurry from effluent from polishing processes in an easy and effective manner. SOLUTION: This recovery system comprises concentrating means 2 for concentrating effluent from a polishing process, washing means 3 for washing abrasive particles in the concentrate and means for inputting a dispersant into the washing means 3 or an earlier step. In another mode, the recovery system comprises washing and concentrating means 2 for concentrating and washing effluent from a polishing process and means for inputting a dispersant into water introduced into the washing and concentrating means 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to chemical mechanical polishing (CMP) in a semiconductor manufacturing process or the like.
TECHNICAL FIELD The present invention relates to an apparatus for efficiently collecting and reusing abrasive particles from wastewater from a polishing step discharged from a mechanical polishing step.

[0002]

2. Description of the Related Art It is desired that the surfaces of semiconductor wafers and films formed thereon, such as insulating films and metal thin films, be highly flat. 2. Description of the Related Art Conventionally, for planarizing a wafer and a film formed thereon, a method of performing chemical mechanical polishing (CMP) using a slurry of an abrasive has been adopted. In this method, polishing is performed with an abrasive slurry interposed between a polishing member such as a polishing pad and a semiconductor wafer to flatten the surface of a semiconductor wafer or a coating film such as a silicon oxide film or a metal thin film. As the abrasive used in the CMP, silica fine particles (colloidal silica) having good dispersibility and uniform average particle diameter are generally used. In addition, cerium oxide (Ce) having a high polishing rate
O _2), or the like high hardness stable alumina (Al ₂ O ₃₎ are also used. Inorganic oxides such as cerium oxide and alumina are used as a slurry in which particles having an average particle diameter of about 0.05 to 0.5 μm are dispersed in water. Usually, the slurry contains a pH adjuster (KOH , NH ₄ OH, organic acids, amines), surfactants (dispersants), oxidants (H
₂ O ₂ , KIO ₃ , Fe (NO ₃ ) ₃ ) and the like are separately used.

[0003] Since this abrasive slurry is used in a large amount per one wafer and is very expensive, the abrasive is recovered from wastewater discharged from a wafer CMP process, and the recovered abrasive is collected. It is desired to adjust the abrasive slurry having a predetermined composition by using the slurry and reuse the slurry. Such recovery and reuse is also important from the viewpoint of reducing the amount of waste liquid treatment.

However, the wastewater discharged from the CMP process is diluted to lower the concentration of the abrasive, and further, a polishing object such as a semiconductor wafer or a thin film material for forming a coating layer or a polishing pad such as a polishing pad. Impurities such as abrasive chips shaved off, fine particles in which inorganic oxide particles as abrasives are destroyed, and abrasive particles having a large particle diameter caused by aggregation of polished thin film material pieces and abrasive particles. It was mixed. For this reason, if such polishing process wastewater is reused as an abrasive without treatment, scratches are generated on the wafer surface, polishing power is reduced due to accumulation of polishing debris, and polishing due to a decrease in abrasive concentration is further reduced. The polishing process wastewater cannot be circulated and reused as it is because it leads to a reduction in speed. Therefore, in reusing the wastewater from the polishing step, it is necessary to recover the abrasive by performing a process such as removal of impurities and concentration, and to readjust an abrasive slurry having a predetermined composition.

As a technique for recovering and reusing the abrasive from the polishing process wastewater, the present applicant has focused on the fact that abrasive particles such as cerium oxide and alumina have a large specific gravity, and have used a centrifugal separator. A method and an apparatus for recovering an abrasive by concentrating the slurry and performing a water wash to remove impurities such as salts, organic substances, and fine polishing debris from the concentrated slurry after centrifugation have been previously proposed. 11-100034
issue. Hereinafter, it is referred to as “first application”. ). According to the method and the apparatus, it is possible to efficiently collect the slurry of the abrasive particles that can be easily reused as the abrasive from the wastewater of the polishing process.

[0006]

When the abrasive is used, the abrasive is coagulated and dispersed to a predetermined particle size in the slurry.
Its surface is coated with a dispersant. However, when the water washing is performed in the recovery step of the prior application, the concentration of the dispersant decreases, and depending on the time of water washing, the amount of water, the frequency, etc., the dispersant present on or near the abrasive material is washed away. May occur. In particular, if the dispersant on or near the abrasive surface is removed, the abrasive particles are agglomerated and coarse, and it may be difficult or impossible to redisperse the particles to a predetermined particle diameter. Therefore, it is necessary to strictly control the cleaning conditions such as the time, the amount of water and the frequency of the water cleaning so that such a problem does not occur in the recovery technology of the prior application.

The present invention has improved and improved the above-mentioned prior application device,
An object of the present invention is to provide an apparatus for collecting abrasives that can more easily and efficiently collect slurry of abrasive particles that can be easily reused as abrasives from wastewater in a polishing process.

[0008]

According to a first aspect of the present invention, there is provided an apparatus for collecting abrasives from a polishing process wastewater, comprising: a concentration means for concentrating the polishing process wastewater; It is characterized by comprising a washing means for washing a liquid, and a dispersant adding means for adding a dispersant to the washing means or a step before the washing means.

In a fifth aspect of the present invention, there is provided an apparatus for recovering an abrasive from wastewater from a polishing step, wherein the polishing and wastewater is introduced into the cleaning and concentration means for concentrating the wastewater from the polishing step and performing a cleaning treatment. Means for adding a dispersant to water.

In the apparatus for recovering abrasives of the present invention, since the cleaning is performed by adding a dispersant, there is no problem of lowering the concentration of the dispersant and cleaning and removing the coating layer of the dispersant on the surface of the abrasive particles. For this reason, it is possible to omit trouble for re-dispersion of the collected abrasive, and it is not necessary to control conditions in the cleaning step, and the collecting operation can be performed easily and efficiently.

A centrifugal separation means is suitable as the concentration means of the abrasive recovery apparatus of the first aspect. Further, in the abrasive recovery apparatus of the first aspect, the following configuration is specifically adopted as the cleaning means and the dispersant adding means. The washing means is a washing tank provided after the concentration means, and the dispersant adding means is at least one of water introduced into the concentration means, water introduced into the washing tank, and water in the washing tank. Means for adding a dispersant to the mixture. The washing means is a washing tank provided after the concentration means, and the dispersant adding means is a means for adding a dispersant to at least one of water introduced into the washing tank and water in the washing tank. A means is provided for returning a part of the cleaning treatment water in the cleaning tank to the concentration means.

Preferably, the washing and concentrating means comprises a centrifugal separating means and a means for returning a part of the liquid concentrated by the centrifuging means to the centrifugal separating means. Is done.

In the apparatus for recovering abrasives of the present invention, it is preferable that the membrane separation means for removing coarse impurities from the wastewater in the polishing step is provided before or after the concentration means such as the centrifugal separation means or the washing and concentration means. .

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIGS. 1 (a) to 1 (c) are system diagrams showing an embodiment of an apparatus for collecting abrasives according to the present invention.

In the apparatus for collecting abrasives shown in FIG.
The polishing process wastewater containing the abrasive discharged from the polishing process of P is first introduced into a MF (microfiltration) membrane or a UF (ultrafiltration) membrane separation device 1 and the whole amount is subjected to membrane filtration, whereby the polishing process is performed. And impurities having a larger particle size than the abrasive particles, such as polishing pad debris generated in the above step, are removed.

The MF film or the UF film of the membrane separation apparatus 1 only needs to be able to remove such impurities having a large particle diameter.
Generally, those having a pore diameter of about 10 to 100 μm are used. As the MF film material, polypropylene, polycarbonate, cellulose triacetate, polyamide, polyvinyl chloride, polyvinylidene fluoride and the like are used. Also, UF
Examples of the film material include polysulfone, cellulose, cellulose acetate, and polyethylene. In particular, it is preferable to use an MF membrane or a UF membrane having a wind-type filtration element obtained by winding any of these single fibers.

The membrane filtration conditions are basically a total filtration system. During operation, the differential pressure between the inlet and outlet is 1
When the weight becomes kgf / cm ² or more, it is preferable to perform back washing or replace the membrane.

Next, the permeated liquid from the membrane separation device 1 is fed to a centrifugal separator 2 as a concentrating means, where it is centrifuged and concentrated. As the centrifugal separator 2, a general separating means utilizing a centrifugal force, for example, various kinds of centrifuging means such as a separating plate type decanter, a cyclone, and a rotating cylindrical type can be used. The degree of concentration by the centrifugal separator 2 is not particularly limited, but usually, the slurry (SS) in the concentrated liquid is used.
Preferably, the concentration conditions are such that the concentration is about 5 to 50% by weight.

Water (separated liquid) separated by the centrifuge 2
Is discharged outside the system for wastewater treatment. The concentrated liquid is fed to the washing tank 3 and washed by stirring in the washing tank 3. In this abrasive recovery apparatus, the abrasive-containing water introduced into the centrifugal separator 2 (the location in FIG. 1A) and the concentrated liquid concentrated in the centrifuge 2 (the location in FIG. 1A) ) Or a washing tank (at the position shown in FIG. 1A) by adding an aqueous solution of a dispersant and washing with the aqueous solution of the dispersant.

The dispersant used here may be any one generally used as a dispersant for abrasives, and examples thereof include the following dispersants that do not contain metal ions.

Water-soluble organic polymers such as acrylic acid polymers and their ammonium salts, methacrylic acid polymers and their ammonium salts, polyvinyl alcohol, etc. Water-soluble anionic surfactants such as ammonium lauryl sulfate and ammonium polyoxyethylene lauryl ether sulfate Water-soluble nonionic surfactants such as polyoxyethylene lauryl ether and polyethylene glycol monostearate Water-soluble amines such as monoethanolamine and diethanolamine Dispersant aqueous solution as washing water is stored in a chemical storage tank (not shown)
What is necessary is just to add a dispersant adjusted to a predetermined concentration by adding a dispersant to pure water. The concentration of the dispersant in the aqueous solution of the dispersant is not particularly limited, but is usually 10 to 10,000 pp
In the range of m, it is appropriately determined according to the washing temperature, the dispersant concentration required for the recovered slurry, and the like.

The abrasive-containing liquid washed in the washing tank 3 (hereinafter sometimes referred to as “washing slurry”) is then concentrated in the centrifuge 4. Thus, the washing tank 3
The mixture is diluted with an aqueous solution of a dispersant, stirred, and then concentrated by a centrifuge to remove impurities such as salts, organic substances, and fine polishing dust. In this washing,
Since the aqueous solution of the dispersant is used as the washing water, the problems of a decrease in the concentration of the dispersant during washing and peeling of the dispersant from the surface of the abrasive particles are eliminated.

If the amount of the aqueous solution of the dispersant used for this washing is too small, a sufficient washing effect cannot be obtained. Conversely, if the amount is too large, the amount of water used increases and the cost of recovery treatment increases. It is preferable to use a dispersant aqueous solution in an amount of 1 to 10 times the volume of the liquid.

The washing slurry from the washing tank 3 is centrifuged by a centrifugal separator 4.
The washing wastewater generated in the process of feeding and concentrating the wastewater is discharged to the outside of the system for wastewater treatment.

By performing the membrane filtration, centrifugal separation and washing as described above, the abrasive particles from which impurities having a larger particle diameter than the abrasive particles, dissolved components such as salts and organic substances, or impurities such as fine abrasive chips are removed. Slurry (hereinafter “collected slurry”)
It may be called. ) Can be obtained.

In the embodiment shown in FIG. 1A, the size of the recovered slurry is further adjusted by a classifier 5, and fine particles and large particles such as remaining polishing dust are removed to make the particle size more uniform. Then, in the adjusting tank 6, ultrapure water and, if necessary, a pH adjuster such as potassium hydroxide, ammonia, hydrochloric acid, and sulfuric acid, and other agents are added, and the abrasive particle concentration is equivalent to that of the new slurry.
Further, a regenerated slurry is obtained by adjusting the liquid properties to the same as those of the new slurry.

As the centrifugal separator 4, the same centrifugal separator as the centrifugal separator 2, such as a separator type decanter, a cyclone, and a rotating cylindrical type can be used.

Instead of the centrifugal separator 4, a solid-liquid separating means (concentrating means) such as a membrane separating means may be used. As the membrane used here, an MF membrane or a UF membrane having a pore diameter of 0.05 to 1 μm can be generally used, and examples of the MF membrane material include polycarbonate, cellulose triacetate, polyamide, and polyvinyl chloride. Is done. Examples of the UF film material include polysulfone, cellulose, cellulose acetate, and polyethylene.

As the classifier 5 for adjusting the particle size, various types such as a gravity type, a mechanical type, and a hydraulic type can be used.

The apparatus for collecting abrasives shown in FIG. 1B differs from the apparatus for collecting abrasives shown in FIG. 1A in that an aqueous solution of a dispersant is added to a washing tank, and the centrifuge 4 is omitted. The difference is that a part of the washing slurry that has been washed in step 3 is circulated to the centrifugal separator 2, and the other parts have the same configuration.

By circulating a part of the washing slurry and centrifuging the washing slurry, washing and concentration can be performed simultaneously.

Since the washing is carried out with stirring while adding the aqueous dispersant solution and the washing slurry is circulated and concentrated, the impurities can be efficiently discharged out of the system and concentrated. The centrifugal separator 4 after the washing tank 3 shown in FIG. 1A can be omitted. However, also in this case, as shown in FIG. 1A, a centrifugal separator may be provided downstream of the washing tank 3.

1 (b), the introduction of the cleaning slurry from the cleaning tank 3 into the classifier 5 may be continuous or intermittent. The introduction of the polishing process wastewater into the centrifugal separator 2 may be continuous or intermittent. Further, the dispersant may be added to a pipe for introducing the concentrated liquid into the washing tank 3.

The abrasive recovery apparatus shown in FIG. 1C differs from the abrasive recovery apparatus shown in FIG. 1B in that the washing tank 3 is omitted and a dispersant is added at the inlet side of the centrifugal separator 2. The difference is that a part of the concentrated liquid (hereinafter, referred to as “concentrated slurry”) of the centrifuge 2 is circulated to the inlet side of the centrifuge 2, and the other configuration is the same.

By circulating a part of the concentrated slurry while adding the dispersant aqueous solution in this manner, the abrasive can be washed in the same manner as the concentrated by centrifugation in the centrifugal separator 2. Can be omitted.

As shown in FIG. 1 (c), the concentrated slurry is circulated directly from the concentrated slurry discharged from the centrifugal separator 2 by a circulation pipe branched from the concentrated slurry discharge pipe in the abrasive recovery apparatus. In addition, a storage tank may be provided between the centrifuge 2 and the classifier 5, and the concentrated slurry from the storage tank may be circulated.

Even with this abrasive recovery device, FIG.
As in the case of the abrasive recovery device (b), the introduction of the concentrated slurry into the classifier 5 may be continuous or intermittent. The introduction of the concentrated slurry into the classifier 5 depends on the form of discharging the concentrated slurry of the centrifugal separator 2 (intermittent discharge or continuous discharge), but a storage tank is provided between the centrifuge 2 and the classifier 5. If
The introduction of the concentrated slurry into the classifier 5 can be performed without depending on the discharge mode of the centrifugal separator 2 as in the case of FIG. The introduction of the polishing process wastewater into the centrifugal separator 2 may be continuous or intermittent.

Even with this abrasive recovering apparatus, the washing and concentration are performed by circulating the concentrated slurry while adding the aqueous solution of the dispersant, so that the impurities can be efficiently discharged to the outside and concentrated.

The apparatus for collecting abrasives shown in FIGS. 1A to 1C is an example of the embodiment of the present invention, and the present invention is limited to the illustrated embodiment unless it exceeds the gist of the present invention. It is not something to be done. For example, in the apparatus for collecting abrasives shown in FIGS. 1A and 1B, the membrane separation apparatus 1 may be provided at a subsequent stage of the cleaning tank 3. 1C, the membrane separator 1 may be provided after the centrifugal separator 2, and a storage tank is provided between the centrifuge 2 and the classifier 5. In this case, it may be provided at a stage subsequent to the storage tank.

In the present invention, the concentration of the abrasive such as cerium oxide is preferably 1 to 30% by weight, and the particle diameter range of the abrasive is preferably 0.1 to 0.1 by such an abrasive recovery apparatus.
A regenerated slurry having a thickness of about 0.5 μm and a dispersant concentration of 0.01 to 10 parts by weight based on 100 parts by weight of the abrasive is obtained. The concentration of the abrasive in the regenerated slurry is not particularly limited, but is preferably in the range of 1 to 30% by weight from the viewpoint of handleability of the regenerated slurry. The dispersant concentration is preferably in the above range from the viewpoint of the dispersibility of the abrasive particles in the regenerated slurry and the anti-settling property.

[0042]

As described in detail above, according to the apparatus for recovering abrasives of the present invention, since the abrasives are washed with the dispersant, the concentration of the dispersant in the slurry is reduced, and the surface of the abrasives is reduced. There is no problem of peeling of the dispersant covering the surface. For this reason, the process of redispersing the abrasive particles in the recovered slurry can be omitted, and complicated condition management in the cleaning process is not required. Therefore, the time and steps required for reusing the abrasive can be greatly simplified or omitted.

[Brief description of the drawings]

FIG. 1 is a system diagram showing an embodiment of an abrasive recovery apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Membrane separation device 2, 4 Centrifuge 3 Washing tank 5 Classifier 6 Adjustment tank

Claims (7)

[Claims] 1. An apparatus for recovering an abrasive from wastewater from a polishing step, comprising: a concentrating means for concentrating the wastewater from the polishing step; a cleaning means for cleaning a concentrated liquid from the concentrating means; An abrasive collecting apparatus, comprising: a dispersant adding means for adding a dispersant in the previous step. 2. The apparatus according to claim 1, wherein said concentrating means is a centrifugal separating means. 3. The cleaning device according to claim 1, wherein the washing means is a washing tank provided after the concentrating means, and the dispersant adding means is water introduced into the concentrating means, and introduced into the washing tank. A means for adding a dispersant to at least one of the water to be used and the water in the cleaning tank. 4. The cleaning device according to claim 1, wherein the cleaning means is a cleaning tank provided downstream of the concentrating means, and the dispersant adding means includes water introduced into the cleaning tank and water in the cleaning tank. Means for adding a dispersant to any one or more of the water, and means for returning a part of the cleaning treatment water of the cleaning tank to the concentration means are provided. apparatus. 5. An apparatus for recovering an abrasive from wastewater from a polishing step, comprising: a washing / concentrating means for concentrating and washing the wastewater from the polishing step; and a means for adding a dispersant to water introduced into the washing / concentrating means. An abrasive recovery device, comprising: 6. The cleaning and concentrating means according to claim 5, wherein
An abrasive recovery apparatus comprising: a centrifugal separator; and a unit for returning a part of the liquid concentrated by the centrifugal separator to the centrifugal separator. 7. An apparatus for collecting abrasives according to claim 1, further comprising a membrane separation means for removing coarse impurities from waste water in the polishing step.