JP2001198825A - Recovery apparatus for abrasive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To store a membrane separator easily with an apparatus being prevented from being clogged due to membrane by means of valve switching alone, in stopping the operation of the apparatus, provide long stable operation for the membrane separator, and recover and reuse the abrasive with high efficiency stably for a long period. SOLUTION: This recovery apparatus, treating grinding process drainage with the membrane separator 2 and a centrifugal separator 3 for recovery of abrasive, is provided with a circulating means of circulating membrane permeated water in the membrane separator 2 while the operation of the apparatus is stopping.

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.
In this slurry, a pH adjuster (KOH, NH ₄ OH,
Organic acids, 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 abrasives can be efficiently recovered from the polishing process wastewater. However, the apparatus of the prior application uses MF to remove coarse solids such as pad debris contained in the polishing process wastewater. (Microfiltration) Since the separation is carried out by a membrane separation device such as a membrane, the membrane is clogged at an early stage due to coarse solids, and frequent replacement of the membrane is required. As a result, running costs rise and hinder long-term stable operation. Inconvenience was caused. This clogging of the membrane is maintained until the next operation restart, especially after cleaning and replacing the entire recovery system, including the piping, with ultrapure water in order to avoid contamination of impurity ions and maintain cleanliness when the operation of the system is stopped. It turned out to be intense while doing. This is because the dispersant held in the apparatus is replaced by ultrapure water, the dispersibility of the abrasive particles is impaired, the particles become coarse, and the agglomerates themselves are solidified due to the viscosity of the remaining dispersant. It is thought to be due to adhesion to the film. The clogging of the membrane was also severe when the liquid in the membrane separation device was withdrawn and stored.

In order to solve such a problem, the applicant of the present invention has proposed that when the operation of the apparatus is stopped, ultrapure water containing a dispersant or wastewater from a polishing process is stored in a state kept in a membrane separation apparatus. (Japanese Patent Application No. 11-322924)
issue).

According to the present invention, the present invention is further improved, and when the operation of the apparatus is stopped, the membrane separation apparatus can be easily stored only by switching the valve under the condition in which clogging of the membrane is prevented. It is an object of the present invention to provide an abrasive recovery apparatus capable of performing a long-term stable operation, reducing the running cost of the apparatus, and efficiently recovering and reusing the abrasive stably for a long period of time.

[0009]

SUMMARY OF THE INVENTION An abrasive recovery apparatus according to the present invention is a polishing apparatus having a membrane separation means for removing coarse solids in a wastewater from a polishing step, and a solid-liquid separation means for recovering the abrasive. A material recovery apparatus, wherein a circulation means for circulating membrane permeated water to an introduction side of the membrane separation means when the operation of the membrane separation means is stopped is provided.

[0010] The membrane permeated water of the membrane separation means is obtained by subjecting the wastewater from the polishing step to membrane separation, and is a slurry from which coarse solids are removed by membrane separation and which contains a dispersant derived from an abrasive slurry. .

In the present invention, such membrane permeated water is circulated and passed while the operation of the membrane separation means is stopped, so that the membrane is stored under conditions containing a dispersant, thereby preventing clogging of the membrane. be able to.

In the present invention, the solid-liquid separation means is preferably a centrifugal separation means or a membrane separation means.

[0013]

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

FIG. 1 is a system diagram showing an embodiment of an abrasive recovery apparatus according to the present invention. FIGS. 2A and 2B show an embodiment of a means for circulating permeated water of an MF membrane separation apparatus. FIG.

First, the procedure for collecting the abrasive by treating the wastewater in the polishing step by the abrasive collecting apparatus shown in FIG. 1 will be described.

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 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 total 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 permeate from the MF membrane separation device 2 is then introduced into a solid-liquid separation means such as a centrifuge 3 and concentrated. The solid-liquid separation means may be any means capable of concentrating the wastewater from the polishing step from which coarse solids have been removed by the MF membrane separation device 2. In addition to the centrifugal separator 3, an appropriate molecular weight cutoff or pore size is selected. Thus, an MF or UF membrane separation device can be used.

In the apparatus for recovering abrasives shown in FIG. 1, concentration is performed using a centrifugal separator 3 as solid-liquid separating means. In addition, the washing processing liquid in the washing tank 4 at the subsequent stage is circulated through the centrifugal separator 3.

As the centrifugal separator 3, general centrifugal separators utilizing centrifugal force, for example, various types of centrifugal separators such as a separator type decanter, a cyclone, and a rotating cylindrical type can be used. The degree of concentration by the centrifugal separator 3 is not particularly limited, but usually, the slurry (S
S) Preferably, the concentration conditions are such that the concentration is about 5 to 50% by weight.

Water (separated liquid) separated by the centrifuge 3
Is discharged outside the system for wastewater treatment. Further, the concentrated liquid is supplied to the washing tank 4 and washed by stirring with the washing water in the washing tank 4.

In this abrasive recovery device, an aqueous solution of a dispersant (a solution in which the dispersant is dissolved in ultrapure water as washing water) is added to the washing tank 4 and washing is performed with the aqueous solution of the dispersant.

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 polyoxyethylene lauryl ether ammonium 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 converted into ultrapure water in a chemical storage tank (not shown). The concentration of the dispersant in the aqueous solution of the dispersant is not particularly limited, and the washing temperature or the recovery in the range of 10 to 10,000 ppm is usually used. Decide appropriately according to the dispersant concentration required for the slurry Is determined.

A part of the abrasive-containing liquid (hereinafter sometimes referred to as “washing slurry”) that has been washed in the washing tank 4 is circulated to the centrifugal separator 3 and centrifuged.
Washing and concentration are performed simultaneously.

As described above, the diluent is diluted with the aqueous solution of the dispersant in the washing tank 4 and stirred, and then circulated and concentrated in the centrifugal separator 3 to remove impurities such as salts, organic substances, and fine polishing debris. You. And 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.

That is, when the abrasive is used, its surface is coated with a dispersant so 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, the amount of water, the frequency, etc. of the water washing, 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 coarse, 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, the amount of water and the frequency of the water cleaning.

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

If the amount of the aqueous solution of the dispersing agent 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. 1 to 10 for the concentrate from the separator 2
It is preferable to use 0 times the volume of the dispersant aqueous solution.

The washing wastewater generated in the process of concentrating the washing slurry from the washing tank 4 is discharged out of the system as a separated liquid from the centrifuge 3.

By performing the membrane separation, centrifugation, washing and concentration of the coarse solid in the MF membrane separation apparatus 2 as described above, dissolved components such as impurities, salts, organic substances, etc., having a larger particle size than the abrasive particles, or A slurry of abrasive particles from which impurities such as fine abrasive chips have been removed can be obtained, but this slurry further contains coarse solids that have been coarsened by reagglomeration of the abrasive particles in the washing and concentration steps. Have been.

In the abrasive recovery apparatus shown in FIG. 1, the slurry containing the coarse solid is supplied to the ultrasonic irradiation means 5 and irradiated with ultrasonic waves to re-aggregate the aggregated coarse solid.

The ultrasonic irradiation means 5 is not particularly limited, and includes a vibrator immersed in a storage tank, a vibrator mounted outside the storage tank, or a vibrator mounted on the outer circumference of a slurry introduction pipe. Etc. can be used. Also,
The frequency of the ultrasonic wave to be irradiated is 20 to 100 kHz, especially 4
The irradiation time is preferably about 0 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 reaggregation of the abrasive particles is prevented in the subsequent processing.

The liquid subjected to the dispersion treatment of the agglomerated particles by the ultrasonic wave irradiating means 5 is then subjected to membrane separation to remove the remaining coarse solid matter by a membrane separation device.

In the abrasive recovery apparatus shown in FIG. 1, two MF membrane separators 6 and 7 are installed in series as this 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 the 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 solids have been sequentially removed by the MF membrane separators 6 and 7 is subjected to ultrapure water and, if necessary, a pH adjuster such as potassium hydroxide, ammonia, hydrochloric acid, sulfuric acid, etc. By adding the above chemical agent, the abrasive particles concentration is adjusted to the same level as the new slurry, and further, the liquid properties are adjusted to the same level as the new slurry to obtain a regenerated slurry.

A classifier may be provided between the MF membrane separation device 7 and the adjusting tank 8 so as to remove fine particles and large particles such as remaining polishing dust to make the particle size more uniform. . In this case, as a classifier for particle size adjustment, gravity type,
Various types such as a mechanical type and a hydraulic type can be used.

Next, the operation when the operation of such an abrasive recovery apparatus is stopped will be described.

In the abrasive recovery apparatus of the present invention, FIG.
The means for circulating membrane permeated water is provided in the membrane separation device 2 for removing coarse solids as shown in (a) and (b).

The circulation means shown in FIG. 2A includes valves V ₁ , V ₃ , V ₄ provided in a raw water pipe, a permeated water discharge pipe, and a concentrated water discharge pipe of the MF membrane separation device 2, respectively, and a valve V. contact upstream of the _first downstream the valve V _3, composed of a circulation pipe having a pump P and the valve V _2.

Polishing process When treating wastewater, pump P
Stop, valve V₂Closed, valve V₁, V₃, V ₄Open for membrane separation
However, when the operation of the device is stopped, the valve V₁, V₃, V
₄Is closed and the valve V₂Is opened to start the pump P, and the
Of the membrane permeated water in the separation device 2 through a circulation pipe to the inlet of the membrane separation device 2
Circulates to the side.

As a result, the membrane of the membrane separation device 2 is brought into a state in which coarse solids are removed and comes into contact with the permeated water containing the dispersant, thereby preventing clogging of the membrane.

When the membrane permeated water is directly circulated in the circulation pipe as described above, a pipe such as a flow switch for detecting a water flow or a capacitance switch for detecting the presence or absence of water in the pipe is provided at the inlet pipe of the pump P. It is preferable to provide a means for detecting the presence or absence of water in the inside, and in order to protect the pump P (prevent emptying), control is performed so that circulation is not performed when a state without water is detected.

The circulating means shown in FIG. 2 (b) is one of the MF membrane separation devices 2A and 2B which are arranged in series.
Valves V ₁ , V _4A , V _4B respectively provided in the concentrated water discharge piping of each of the membrane separation devices 2A, 2B, and the circulation storage tank 9 provided in the permeated water discharge piping of the membrane separation device 2B.
When, communicating the downstream side of the circulation tank 9 and the valve V _1, composed of a circulation pipe having a pump P and the valve V _2.

Polishing process In treating wastewater, pump P
Stop, the valve _{V 2} is closed, the valve _{V 1,} V _4A, performs membrane separation process in _{V 4B} open, Kyusuru but feeding the overflow water of the circulation reservoir 9 to the subsequent process, when the operation stop of the apparatus, the valve _V 1,
V _4A and V _4B are closed, valve V ₂ is opened to start pump P, and the membrane permeated water in circulation storage tank 9 is circulated to the inlet side of membrane separation device 2A by circulation piping.

As a result, the membranes of the membrane separation devices 2A and 2B are brought into contact with the permeated water containing the dispersant after removing the coarse solids, thereby preventing the membranes from being clogged.

When the circulation storage tank is provided and the membrane permeated water in the circulation storage tank is circulated as described above, the pump P
It is preferable to provide a water level meter (level switch) for preventing the air from being drawn.

The circulation of the membrane permeated water may be performed continuously while the polishing material recovery process is stopped, or may be performed only for a fixed time (for example, 1 to 2 hours) after the recovery process is stopped. But it is good. In consideration of power consumption and the like, the latter method is desirable.

As described above, according to the abrasive recovery apparatus of the present invention which can circulate the membrane permeated water while the operation of the apparatus is stopped, clogging of the membrane can be prevented only by circulating a small amount of the permeated water. And a predetermined amount of permeated water can be stably obtained over a long period of time.

In particular, as shown in FIG. 2, if an abrasive recovery device circulates the membrane permeated water by switching the pump P and the valve, the operation for stopping and storing the device can be performed with extremely simple operation. .

The apparatus for collecting abrasives shown in FIGS. 1 and 2 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 as long as it does not exceed the gist. Not something.

For example, the membrane separation device 2 for removing coarse solids is not limited to the one provided before the centrifugal separator 3 but may be provided after the centrifugal separator 3 or at any other location.

The means for circulating the permeated water as shown in FIGS. 2 (a) and 2 (b) is not limited to the membrane separation device 2 on the preceding stage.
The membrane separation devices 6 and 7 on the subsequent stage may be provided. By doing so, the membrane separation devices 6 and 7 can effectively prevent clogging of the membrane. Also, when the solid-liquid separation means is a membrane separation means, permeated water may be circulated in the same manner, and clogging can be prevented similarly to the above-mentioned membrane.

The aqueous solution of the dispersant may be added to the pipe for introducing the concentrated liquid into the washing tank 4. The aqueous solution of the dispersant is added at the inlet side of the centrifugal separator 3 without the washing tank 4, A part of the concentrated liquid of the separator 3 may be circulated to the inlet side of the centrifuge 3, and the remaining part may be sent to the ultrasonic irradiation means 5. Also in this case, by circulating a part of the concentrated slurry while adding the aqueous dispersant solution, the abrasive can be washed at the same time as the concentration by the centrifugal separation in the centrifugal separator 3. Can be omitted. In this case, the circulation of the concentrated slurry may be directly circulated by a circulation pipe branched from a pipe for discharging the concentrated liquid from the centrifugal separator 3. A storage tank may be provided between the storage tanks to circulate the concentrated liquid from the storage tank.

In the present invention, preferably, the abrasive concentration is 1 to 30% by weight and the abrasive particles have a particle size range of 0.1 to 0.5 μm by such an abrasive recovery apparatus.
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 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.

[0060]

As described in detail above, according to the apparatus for collecting abrasives of the present invention, it is possible to prevent clogging of the membrane of the membrane separation means for removing coarse solids, and therefore, it is necessary to replace the membrane. The frequency can be reduced, the running cost can be significantly reduced, and the abrasive particles with few impurities can be efficiently collected stably over a long period of time.

[Brief description of the drawings]

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

FIG. 2 is a system diagram showing an embodiment of a means for circulating membrane permeated water of the MF membrane separation device.

[Explanation of symbols]

 Reference Signs List 1 storage tank 2, 2A, 2B, 6, 7 MF membrane separator 3 centrifuge 4 washing tank 5 ultrasonic irradiation means 8 adjustment tank 9 circulation storage tank

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3C047 FF08 GG14 GG17 4D006 GA07 JA56A JA70A KA02 KA53 KA63 KA72 KB14 KB20 KB30 KD30 PB08 PB20 PC01 4D037 AA13 AB02 BA28 CA02 CA03

Claims (2)

[Claims] 1. A polishing material recovery apparatus comprising: a membrane separation means for removing coarse solids in a polishing process wastewater; and a solid-liquid separation means for collecting an abrasive. A polishing means for circulating the membrane permeated water to the introduction side of the membrane separation means at the time of a stop; 2. The abrasive recovery device according to claim 1, wherein the solid-liquid separation means is a centrifugal separation means or a membrane separation means.