JP2001198823A - Recovery device for abrasive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturizing the whole device by significantly reducing the amount of cleaning water necessary for removing soluble impurities, fine grinding chips and the like by cleaning, thereby minimizing the capacities of a cleaning water storage tank and a slurry storage tank, in recovering abrasive from grinding process drainage. SOLUTION: This recovery device for abrasive concentrates grinding process drainage with a centrifugal separator 4, wherein switching is conducted between introduction of grinding process drainage into the centrifugal separator 4 and introduction of cleaning water from the cleaning water storage tank 3 to conduct cleaning and concentration with the centrifugal separator 4.

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 the 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.
In this slurry, a pH adjuster (KOH, NH ₄ OH,
Organic acids and amines), a surfactant (dispersant), an oxidizing agent (H ₂ O ₂ , KIO ₃ , Fe (NO ₃ ) ₃ ) and the like are separately added and 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 by its use to reduce the abrasive concentration, and furthermore, a semiconductor wafer to be polished, a thin film material for forming a coating layer, a polishing pad, or the like. Polishing debris from which the polishing member has been scraped, fine particles in which inorganic oxide particles as abrasive have been destroyed, and polishing debris having a large particle diameter caused by agglomeration of the polished thin film material pieces and the polishing particles. It is a mixture of impurities. 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. We have previously proposed a device that concentrates the water and removes impurities such as salts, organic matter, and fine polishing debris from the concentrated slurry after centrifugation, and then recovers the polishing material (Japanese Patent Application No. Hei 10-26139). No. 11-189347, etc., hereinafter referred to as “first application”).

[0006]

According to the device of the prior application,
Abrasive particles that can be easily reused as abrasive can be efficiently recovered from the polishing process wastewater.However, in the device of the prior application, soluble impurities and fine particles contained in the slurry concentrated by the centrifugal separator are used. In order to wash and remove unnecessary polishing debris and the like, the entire amount of the concentrated slurry was diluted and washed with washing water, and then concentrated by circulating through a centrifuge. The method of diluting and washing the entire amount of the concentrated slurry with the washing water as described above requires a large amount of washing water, and therefore requires a large-capacity washing water storage tank for storing the washing water. Also, since the once concentrated slurry is diluted, the concentration rate cannot be increased, and the storage tank for receiving the diluted slurry is also increased in size, resulting in a restriction on the installation area of the apparatus. Was.

SUMMARY OF THE INVENTION The present invention solves such a problem and, when recovering the abrasive from the polishing process wastewater, reduces the amount of cleaning water required for cleaning and removing soluble impurities and fine polishing debris. It is an object of the present invention to provide an abrasive recovery apparatus capable of greatly reducing the size of a washing water storage tank or a slurry storage tank and reducing the size of the entire apparatus.

[0008]

SUMMARY OF THE INVENTION The present invention relates to an apparatus for recovering abrasives from a polishing process wastewater, comprising: a solid-liquid separating means; and a means for introducing the polishing process wastewater to the solid-liquid separating means. A washing water storage tank, a means for introducing the washing water in the washing water storage tank to the solid-liquid separation means, and a switching means for switching between introduction of the polishing process wastewater and introduction of the washing water to the solid-liquid separation means. It is characterized by comprising.

In the apparatus for recovering abrasives of the present invention, the introduction of wastewater from the polishing step and the introduction of washing water into the solid-liquid separation means are switched, and the separated liquid obtained by solid-liquid separation of the wastewater from the polishing step is washed with washing water. By performing the cleaning by replacing, it is possible to efficiently remove soluble impurities and fine polishing debris with a small amount of cleaning water.

In the present invention, it is particularly preferable to use a centrifugal separator as the solid-liquid separator. In this case, when the polishing process wastewater is introduced into the centrifugal separator and centrifuged,
The solids in the wastewater from the polishing process accumulate on the peripheral wall of the rotor of the centrifugal separator, and the separated liquid is collected at the center. In this state, when the liquid to be introduced into the centrifugal separation means is switched from the polishing step wastewater to the washing water by the switching means, the separated liquid is pushed out by the introduced washing water, and contains soluble impurities and fine polishing debris. The separated liquid is replaced with washing water, and a good washing effect is obtained.

[0011]

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

FIG. 1A is a system diagram showing an embodiment of an apparatus for collecting abrasives according to the present invention, and FIG.
It is an enlarged view of the important section (a) (wash water storage tank, centrifuge, and slurry storage tank) of (a).

In the apparatus for recovering abrasives shown in FIG. 1, polishing process wastewater containing abrasives discharged from the CMP polishing step is first introduced into a MF (microfiltration) membrane separation device 2 through a storage tank 1. By performing membrane filtration on the entire amount, impurities having a larger particle size than the abrasive particles, such as polishing pad debris generated in the polishing step, are removed.

The membrane separation apparatus used for removing the impurities is as follows:
Not limited to the MF membrane separator, a UF (ultrafiltration) membrane separator may be used. The MF membrane or the UF membrane to be used only needs to be able to remove such large-diameter impurities, and generally has a pore diameter of 25 to 30 μm. A degree is preferred. As the MF film material, polypropylene, polycarbonate, cellulose triacetate, polyamide, polyvinyl chloride, polyvinylidene fluoride and the like are used. Also, as the UF film material,
Examples thereof 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 whole volume filtration system. During operation, the differential pressure between the inlet and outlet is 1
It is preferable to perform backwashing or exchange the membrane when the weight becomes kgf / cm ² or more.

The membrane separation device for removing the coarse impurities is not always required, and may be provided at the subsequent stage of the next centrifuge 4.

The permeate of the MF membrane separation device 2 (hereinafter sometimes referred to as “pre-treatment slurry” or “raw water”) is then introduced into a solid-liquid separation means such as a centrifuge 4 and concentrated.
As the solid-liquid separation means, any means can be used as long as it can concentrate the polishing process wastewater from which coarse impurities have been removed by the MF membrane separation device 2. In addition to the centrifugal separator 4, an appropriate fractionated molecular weight or pore size should be selected. , A MF or UF membrane separation apparatus can be used, but it is preferable to use a centrifugal separator in that a good washing effect can be obtained by replacing washing water as described below.

In the apparatus for recovering abrasives shown in FIG. 1, concentration is performed using a centrifugal separator 4 as solid-liquid separating means. The washing / concentrating slurry in the slurry storage tank 5 at the subsequent stage is circulated through the centrifugal separator 4.

In the present invention, the introduction of the pretreatment slurry into the centrifugal separator 4 and the introduction of the washing water from the washing water storage tank 3 are switched by opening and closing a valve.

The procedure of the switching operation will be described below.

1. Raw water inlet valve _V 1, _{V 4} to open, the valve _V 2, _{V 3} closed, pump _P 1, _{P 2}
At the stop, the raw water is introduced into the centrifuge 4. At this time, the concentrated water is continuously discharged and stored in the slurry storage tank 5. This raw water introduction step is performed for a preset time or until the slurry storage tank reaches a certain water level, that is, until the level switch detects a predetermined water level.

2. Reconcentrated valve _{V 3} opens, the valve _{V 1, V 2, V 4} closed, pump _{P 1} stop,
In the pump P ₂ starts, to introduce wash thickened slurry in the slurry storage tank 5 to the centrifuge 4. The concentrated water at this time is stored in the centrifuge 4 and is not discharged. Thereby, the washing concentration slurry is re-concentrated.

This re-concentration step is performed until the slurry storage tank 5 becomes empty. Therefore, it is preferable to provide a water level gauge (level switch) in the slurry storage tank 5 so as to detect that the slurry in the slurry storage tank 5 has run out.

3. Washing water introduction valve _{V 2} opens, the valve _{V 1, V 3, V 4} closed, pump _{P 1} starts,
In the pump P ₂ stop, in a centrifuge 4 which cleaning concentrate slurry which is reconcentrated are stored, introducing washing water in the washing water storage tank 3. Thereby, the separated liquid remaining in the centrifugal separator 4 is replaced by the washing water, and the concentrated slurry is washed.
This washing water introduction step is performed for a preset time.

4. When the slurry discharge valves V ₂ and V _{4 are} opened, the valves V ₁ and V _{3 are} closed, the pump P _{1 is} started, and the pump P _{2 is} stopped, the slurry stored in the centrifuge 4 is pushed out into the slurry storage tank 5 by the washing water. . This slurry discharge process is performed until the slurry storage tank 5 reaches a certain water level.
That is, the operation is performed until the level switch detects the predetermined water level.

[5] Repetitive check valve V ₁ ~V ₄ closed, the pump and P _1, P ₂ stop state, adds 1 to the number of repetitions, and a set number of times and repeat count that is set in advance the above step Compare, [Set times]>
In the case of [the number of repetitions], the process returns to the raw water introduction step of 1. If [Set number] = [Repeat number]: Move to the completion step 6 to complete the process.

6. Completion The processing is completed and the number of repetitions is set to 0 (clear).

The operating procedure of the valves and pumps in the above series of steps is summarized in Table 1.

[0029]

[Table 1]

When such a series of processing is automatically controlled, a known control device such as a sequencer is used.
What is necessary is just to carry out a process step or a process jump.

By performing the concentration by the centrifugal separator 4 and the washing and the extrusion by introducing the washing water in this manner, efficient concentration and washing can be performed with a small amount of washing water, and soluble impurities and fine polishing can be performed. Debris is removed.

As the centrifugal separator 4, a general separating means utilizing centrifugal force, for example, a separating plate type decanter,
Various types of centrifugal separation means such as a cyclone and a rotating cylindrical type can be used. The degree of concentration by the centrifugal separator 4 is not particularly limited, but in general, it is preferable to set the concentration conditions such that the concentration of the slurry (SS) in the concentrate is about 5 to 50% by weight.

Water (separated liquid) separated by the centrifuge 4
Is discharged outside the system for wastewater treatment.

In this abrasive recovery apparatus, an aqueous dispersant solution (a dispersant dissolved in ultrapure water as the wash water) is used as the wash water, and washing is performed with the aqueous dispersant solution.

The dispersant used here may be any one generally used as a dispersant for an abrasive, 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 This aqueous dispersant solution is used in a chemical storage tank (not shown) or a washing water storage tank. What is necessary is just to add a dispersant adjusted to a predetermined concentration by adding a dispersant to ultrapure water, and the concentration of the dispersant in the aqueous solution of the dispersant is not particularly limited.
In the range of 0 ppm, it is appropriately determined according to the washing temperature, the dispersant concentration required for the recovered slurry, and the like.

As described above, by using the aqueous solution of the dispersant as the washing water, the problems of the decrease in the concentration of the dispersant during the washing and the peeling of the dispersant on the surface of the abrasive particles are eliminated.

That is, when the abrasive is used, its surface is coated with a dispersant such that the abrasive is coagulated and dispersed to a predetermined particle size in the slurry. However, when the water washing is performed in the recovery step, the concentration of the dispersant decreases, and depending on the time of water washing, the amount of water, the frequency, and the like, the dispersant present on or near the abrasive material may be washed away. Occurs. In particular, if the dispersant on or near the abrasive surface is removed, the abrasive particles are agglomerated and coarsened, and it may be difficult or impossible to redisperse the particles to a predetermined particle diameter. Therefore, in order to avoid such a problem,
It is necessary to strictly control the cleaning conditions such as the time, amount of water, and frequency of water cleaning.

On the other hand, if the washing water contains a dispersant, this problem is solved, and the slurry of the abrasive particles that can be easily reused as the abrasive from the wastewater in the polishing process can be more easily and efficiently. It becomes possible to collect.

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 the recovery treatment increases. It is preferable to use 1 to 100 times the volume of the aqueous dispersant solution with respect to the concentrated liquid of the separator 4.

As described above, the membrane separation of the coarse solids in the MF membrane separation device 2 and the circulating washing and concentration in the centrifugal separator 4 perform impurities, salts and organic substances having a particle size larger than the abrasive particles. It is possible to obtain a slurry of abrasive particles from which impurities such as dissolved components or fine polishing debris have been removed.
The slurry further contains coarse aggregates that are coarsened by reagglomeration of the abrasive particles in the washing and concentration steps.

In the apparatus for collecting abrasives shown in FIG. 1, the slurry containing the coarse aggregates is further separated by a membrane separation apparatus to remove coarse particles still remaining.

In the abrasive recovery apparatus shown in FIG. 1, two MF membrane separators 6 and 7 are installed in series as the membrane separator to perform a two-stage membrane separation process. As described above, the membrane separation devices are provided in multiple stages, and the one having a smaller membrane pore diameter is used in a later stage of the membrane separation device, whereby clogging of the membrane is more effectively prevented and efficient processing is performed. It becomes possible.

In this case, the pore size of the MF membrane is preferably changed in a range of about 1 to 10 μm. For example, as shown in FIG. 1, when the MF membrane separation devices 6 and 7 are arranged in two stages, The pore size of the MF membrane separation device 6 in the former stage is 5 to 10 μm
It is preferable that the pore diameter of the MF membrane separation device 7 in the subsequent stage is about 3 to 5 μm. When the membrane separation devices are arranged in three stages, the MF membrane separation device 7 is further provided with a hole diameter of 1-3.
It is preferable to arrange an MF membrane separation device of about μm.

The material of the MF film is the same as the MF film described above.
What was illustrated as a membrane material of the membrane separation device 2 can be used.

The liquid from which the residual coarse particles have been sequentially removed by the MF membrane separation devices 6 and 7 is mixed with ultrapure water and, if necessary, a pH adjuster such as potassium hydroxide, ammonia, hydrochloric acid, sulfuric acid or the like in an adjustment tank 8.
By adding other chemicals, the reconstituted slurry is obtained by adjusting the abrasive particle concentration to be equal to that of the new slurry and further to the liquid property equivalent to that of the new slurry.

The apparatus for collecting abrasives shown in FIG. 1 is an example of an embodiment of the apparatus for recovering abrasives of the present invention, and the present invention is not limited to the illustrated one unless it exceeds the gist. is not. For example, a classifier may be provided between the MF membrane separation device 7 and the adjusting tank 8 to remove fine particles and large particles such as remaining polishing dust to make the particle size more uniform. In this case, as the classifier for adjusting the particle size, various types such as a gravity type, a mechanical type, and a hydraulic type can be used.

Further, an ultrasonic wave irradiating means is provided in a stage preceding the MF membrane separation device 6, and the slurry from the slurry storage tank 5 is irradiated with ultrasonic waves to re-disperse the coarse aggregates, and then subjected to a membrane separation treatment. Is also good. In this case, there is no particular limitation on the ultrasonic irradiation means, and a device in which a vibrator is immersed in a storage tank, a device in which a vibrator is mounted outside the storage tank, a device in which a vibrator is mounted on the outer periphery of a slurry introduction pipe, or the like is used. Can be used. Further, the frequency of the ultrasonic waves to be irradiated is preferably 20 to 100 kHz, particularly preferably about 40 to 60 kHz, and the irradiation time is appropriately determined so that the effect of re-dispersing the aggregated particles can be sufficiently obtained.

Agglomerated particles are dispersed (redispersed) by such ultrasonic irradiation, and reagglomeration of the abrasive particles is prevented in the subsequent processing, and the clogging of the membranes of the MF membrane separation devices 6 and 7 is prevented. It can be effectively prevented. As a result, the frequency of replacing the membrane is reduced, the running cost is reduced, and the apparatus can be operated stably for a long period of time.

In the present invention, such an apparatus for collecting abrasives preferably has an abrasive concentration of 1 to 30% by weight, an abrasive particle size range of 0.1 to 0.5 μm,
The dispersant concentration is 0.01 to 1 with respect to 100 parts by weight of the abrasive.
A regenerated slurry is obtained which is 0 parts by weight. 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 concentration of the dispersant 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.

[0051]

As described above in detail, according to the apparatus for recovering abrasives of the present invention, when recovering abrasives from wastewater in the polishing step, it is necessary to wash and remove soluble impurities and fine polishing debris. The required amount of washing water can be greatly reduced, the capacity of the washing water storage tank and the slurry storage tank can be reduced, and the size of the entire apparatus can be reduced.

[Brief description of the drawings]

FIG. 1 (a) is a system diagram showing an embodiment of an abrasive recovery apparatus of the present invention, and FIG. 1 (b) is a main part (washing water storage tank, centrifugal separator) of FIG. 1 (a). FIG. 2 is an enlarged view of a machine and a slurry storage tank).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Storage tank 2, 6, 7 MF membrane separation apparatus 3 Washing water storage tank 4 Centrifuge 5 Slurry storage tank 8 Adjustment tank

Claims (2)

[Claims] 1. An apparatus for recovering an abrasive from waste water from a polishing step, comprising: a solid-liquid separating means; a means for introducing the waste water from the polishing step to the solid-liquid separating means; a washing water storage tank; A polishing material collecting apparatus comprising: means for introducing washing water in a washing water storage tank; and switching means for switching between introduction of polishing process wastewater and introduction of washing water to the solid-liquid separation means. . 2. The apparatus according to claim 1, wherein said solid-liquid separation means is a centrifugal separation means.