JP2002018715A - Abrasive recovery device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an abrasive recovery device for recycling by efficiently recovering abrasive grains from polishing process drain containing abrasives drained from a CMP process used in a semiconductor manufacturing plant or the like. SOLUTION: This abrasive recovery device for recovering the abrasives from the CMP process drain containing an organic dispersant is provided with a ceramic film separating means of monolayer honeycomb structure mainly composed of columnar β-type silicon nitride crystal into which the process drain is led.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an apparatus for collecting abrasives. More specifically, the present invention relates to a CMP (Chemical Mechanical Polishing) used in a semiconductor manufacturing plant or the like.
cal Mechanical Polishing) from the polishing process wastewater containing the abrasive discharged from the process,
The present invention relates to an abrasive collection device for efficiently collecting and reusing abrasive particles.

[0002]

2. Description of the Related Art An insulating film formed on a semiconductor wafer,
The surface of a coating such as a metal thin film is required to be a highly flat surface, and as a means for performing polishing, a polishing slurry is interposed between a polishing member such as a polishing pad and a semiconductor wafer. CMP is employed. CM
Examples of the abrasive used in P include silica fine particles having a good dispersibility and uniform particle diameter, ceria having a high polishing rate,
Alumina having high hardness and stable is used. These abrasives are provided by a manufacturer as a slurry in which particles having a predetermined particle size and concentration are dispersed in water, and are diluted to a predetermined concentration when supplied to a CMP machine according to each site. Usually, this slurry contains a pH adjuster such as potassium hydroxide, ammonia, organic acids, and amines, a dispersant such as a surfactant, and an oxidizing agent such as hydrogen peroxide, potassium iodate, and iron (III) nitrate. Or the like is added in advance, or separately added during polishing. It is desired that these polishing slurries be reused from the viewpoint that they are used in large amounts and are expensive, and from the viewpoint of reducing the amount of industrial waste. However, the polishing process wastewater has a reduced abrasive concentration due to dilution. In addition, semiconductor wafers, coating materials, polishing pad debris, fine particles in which the abrasive is broken, and particles generated by agglomeration of the abrasive particles. Solid impurities with a large diameter are mixed. Therefore, if such polishing process wastewater is reused without any treatment as an abrasive, the polishing rate decreases due to a decrease in the concentration of the abrasive, and scratches on the wafer surface are generated. In recent years, in order to maintain the particle size distribution of the abrasive in the slurry within a predetermined range, an organic dispersant has been frequently used. And impurities such as metal ions generated by the process. For this reason, when the recovered slurry is reused, these impurities hinder concentration adjustment, making concentration management difficult. For these reasons, the polishing wastewater cannot be circulated and reused as it is. Therefore, when reusing, it is necessary to remove impurities such as coarse solids and salts from the polishing wastewater, and to perform a concentration treatment to re-prepare a polishing slurry having a predetermined composition. Conventionally, development of various technologies for wastewater treatment in a CMP process has been attempted. For example,
A method has been proposed in which wastewater from the CMP process is treated with a microfiltration membrane to remove coarse solids, then treated with an ultrafiltration membrane, a chemical is added to adjust the concentration, and the slurry is reused as an abrasive slurry. . Even by such a method, it is possible to remove coarse solids, and it is possible to suppress generation of scratches on the wafer surface. However, when the added chemicals and salts remain, new chemicals are added and the abrasive concentration, pH
Since the adjustment is performed, these impurities interfere with the concentration adjustment, and the concentration adjustment cannot be performed properly. In addition, adverse effects on the product such as contamination are caused. In particular, when the particle size distribution of the abrasive in the slurry is controlled uniformly by using an organic dispersant to maintain the particle size distribution within a predetermined range, the effect on the particle size is large. Therefore, it is important to remove these residual drugs and salts. When an organic dispersant is not contained in the wastewater of the CMP process, the treatment can be performed using an organic separation membrane or an inorganic ceramic membrane having a monolith structure such as alumina. However, when an organic dispersant is contained, the flux at the beginning of operation is large, but the viscosity of the dispersant, slurry in which the particles are coarsened by agglomeration, and coarse solids interact with each other to form a film. Clogging is severe, and operation becomes impossible in a short time. During operation, it was necessary to set a high circulation flow rate, which led to a rise in initial capital investment and operation management costs. There is also a problem that the concentration cannot be increased. Further, since the concentration of the abrasive is adjusted in a state where the dispersant, salts, and the like remain, these impurities hinder the concentration adjustment, and the concentration adjustment cannot be performed properly. For this reason, these problems have been solved and CMP containing an organic dispersant has been proposed.
There has been a need for an abrasive recovery device that can efficiently concentrate a slurry of abrasive particles that can be highly concentrated without causing membrane clogging even in process wastewater and that can be easily reused as an abrasive. .

[0003]

SUMMARY OF THE INVENTION The present invention efficiently recovers and reuses abrasive particles from a polishing process wastewater containing an abrasive discharged from a CMP process used in a semiconductor manufacturing plant or the like. The purpose of the present invention is to provide an apparatus for collecting abrasives for the purpose.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have used a ceramic film separating means having a single-layer honeycomb structure mainly composed of columnar β-type silicon nitride crystals. Thereby, continuous operation can be performed for a long time even in the case of wastewater from a CMP step containing an organic dispersant, and the concentrated water obtained by the membrane separation means is washed with washing means, and further from the washing means. It has been found that by adjusting the concentration of the liquid, the abrasive can be recovered as a slurry equivalent to a new one, and the present invention has been completed based on this finding. That is, the present invention provides (1) an apparatus for recovering abrasive from a CMP process wastewater containing an organic dispersant, wherein the single-layer honeycomb structure mainly composed of columnar β-type silicon nitride crystals into which the process wastewater is introduced. 2. The polishing material recovery apparatus according to claim 1, further comprising a ceramic membrane separation means, and (2) washing means for washing the concentrated water obtained by the ceramic membrane separation means with water. 3. The abrasive collecting apparatus according to claim 2, further comprising: a collecting device, (3) a concentration adjusting unit into which the liquid from the cleaning unit is introduced.
And (4) the collection of the abrasive material according to (1) or (3), further comprising a filtration treatment means for removing coarse solids before the ceramic membrane separation means or between the ceramic membrane separation means and the concentration adjustment means. Device.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION An abrasive recovery apparatus according to the present invention is an apparatus provided with a ceramic film separating means having a single-layer honeycomb structure mainly composed of columnar β-type silicon nitride (Si ₃ N ₄ ) crystals. The apparatus of the present invention can be particularly suitably applied to the recovery of an abrasive from a CMP process wastewater containing an organic dispersant. FIG. 1 is a process flow diagram of one embodiment of the abrasive recovery apparatus of the present invention. The abrasive recovery device of this aspect includes a CMP machine unit, a pre-filtration unit, a concentration unit, and a concentration adjustment unit. The CMP machine section includes a slurry supply tank 1 for diluting a new slurry to a predetermined concentration and storing the diluted slurry.
It has a CMP machine 2 for polishing a wafer with a slurry supplied from a slurry supply tank and a waste slurry tank 3 for storing waste slurry after polishing. The front filtration unit is C
A slurry receiving tank 4 for storing waste slurry from the MP machine unit, a filter 5 for filtering and removing coarse solids in waste slurry supplied from the slurry receiving tank, and filtered water from which coarse solids have been removed by the filter. And a filtered water tank 6 for storing the water. The concentrating section has a single-layer honeycomb-structured ceramic membrane separating means 7 mainly composed of columnar β-type silicon nitride crystals for concentrating the filtered water from the pre-filtration section. The concentration adjusting unit includes a concentration adjusting tank 9 in which the dispersant diluted in the dispersant dilution tank 8 is added to the filtered water supplied from the pre-filtration unit, and reaggregated coarse particles in the slurry sent from the concentration adjusting tank. And a slurry stirring tank 11 for storing the recovered slurry. The concentrated water of the ceramic membrane separation means 7 is returned to the filtered water tank 6 via the concentrated water pipe 12.

A ceramic film mainly composed of columnar β-type silicon nitride crystal used in the apparatus of the present invention is formed from a mixture of silicon nitride powder and another additive powder such as a rare earth element compound, and is subjected to a heat treatment at a high temperature. To form a porous body, followed by treatment with an acid and an alkali to dissolve and remove additives other than silicon nitride. Columnar β
A ceramic film having a microstructure in which type silicon nitride crystals are entangled has high porosity and high strength, is excellent in machinability, and can be an element having a single-layer honeycomb structure. In a ceramic film mainly composed of columnar β-type silicon nitride crystals, 50% by volume or more of silicon nitride crystals are β-type silicon nitride crystals, and 80% by volume or more of β-type silicon nitride crystals are columnar particles having an aspect ratio of 3 to 50. Preferably, the volume of the pores is 20 to 75% by volume of the entire porous body, and the average width of the columnar particles is 0.1 to 10 times the average pore diameter of the porous body. The wastewater from the CMP process using an organic dispersant is likely to be clogged by the dispersant and slurry, but has a large porosity and a high flux can be obtained even at a low flow rate. By using the ceramic membrane having the honeycomb structure, the operation can be stably performed for a long time, and the abrasive particles contained in the wastewater of the CMP process can be collected on the concentrated water side. In the case of concentrating the wastewater from the CMP process using a conventional monolithic ceramic membrane, it was necessary to flow the slurry at a high flow rate and concentrate it. However, according to the apparatus of the present invention, high concentration can be performed at a low flow rate.

FIG. 2 is an explanatory view of one embodiment of a ceramic film separating means having a single-layer honeycomb structure mainly composed of columnar β-type silicon nitride crystals, and FIG. 2 (a) is a schematic partial perspective view. FIG. 2B is a schematic cut end view. In the single-layer honeycomb-structured ceramic membrane separation means of the present embodiment, the holes arranged in rows are sealed every other row, the row that is left open is the drainage inlet 13, and the sealed row is the drain side 14. I do. On the side surface on the discharge side, a permeated water discharge port 15 is provided. C flowing from the inlet of the ceramic membrane separation means
The MP process wastewater retains the abrasive particles contained in the concentrated water side without causing clogging of the membrane, and water containing various impurities and ultrafine particles passes through the ceramic membrane 16 and is discharged as permeated water. . A single-layer honeycomb-structured ceramic film mainly composed of columnar β-type silicon nitride crystals has a large mechanical strength and does not require a support layer. Therefore, for example, drainage water flowing from an inlet A located at the center of the element is used. Also permeate the ceramic membrane and pass through the through-hole as shown by arrow A 'and are discharged from the permeate outlet. Therefore, the flow resistance of the permeated water is small, and a large flux can be obtained. In addition, such a mainly columnar β
A ceramic film having a single-layer honeycomb structure made of a type silicon nitride crystal is described in Japanese Patent Application Laid-Open No. 9-110079, Nikkei Mechanical No. 544 (January 2000), and the like.

In the apparatus of the present invention, the discharged slurry containing the abrasive having an average particle diameter of about 0.05 to 0.5 μm discharged from the CMP machine is once received in the slurry receiving tank 4, Is filtered by a filter 5 as a filtration treatment means for removing coarse solids at the preceding stage to remove impurities such as polishing pad debris having a large particle size of about 0.7 to 1.5 μm. By removing the large particle size impurities in the waste slurry, the load on the ceramic membrane separation means can be reduced. When a microfiltration membrane (MF) having a pore size larger than the abrasive and smaller than the polishing debris is used as the filter, a cake layer is formed on the membrane surface, so that even the abrasive having a small particle diameter is captured. The result is severe clogging. Therefore, a microfiltration membrane having openings larger than the polishing pad debris is suitable, and a pore size of 1
A microfiltration membrane of 0 to 100 μm is preferable, and a pore size of 25 to 7
A 5 μm microfiltration membrane is more preferred. The material of the microfiltration membrane is not particularly limited, and examples thereof include polypropylene, polycarbonate, cellulose triacetate, polyamide, polyvinyl chloride, and polyvinylidene fluoride. In particular, it is possible to suitably use a microfiltration membrane having any of these materials and having a multi-layered filtration element whose pores become finer from the primary side to the secondary side.
There are no particular restrictions on the conditions for the filtration treatment using the microfiltration membrane, but it is preferable to filter the entire amount of the waste slurry at a pressure of 0.01 to 0.5 MPa. During operation, the differential pressure between the inlet and outlet is 0.
When the pressure becomes 01 MPa or more, it is preferable to perform back washing or replace the membrane. Further, by providing filters in two or more stages and providing a filter having a large pore size in the first stage and a filter having a small pore size in the second stage, the membrane life can be extended. In the apparatus of the present embodiment, the filter 5 is provided in front of the ceramic membrane separation means to remove coarse solids.
That is, it can be provided between the ceramic membrane separating means and the concentration adjusting means. If a filter as a filtration means is provided at the subsequent stage of the ceramic membrane separation means, the liquid which has been subjected to membrane concentration and whose absolute amount has been reduced is targeted, so that the life of the filter can be extended.

In the apparatus of the present invention, the waste slurry scattered in the polishing section of the CMP machine can be separated and collected and treated as waste water in the CMP process. FIG. 3 is an explanatory diagram of one embodiment of the CMP machine unit. The CMP machine section of this embodiment has a slurry supply pipe 17, a polishing pad 18, a rotating substrate chuck 19, and a collecting means 20 for collecting the scattered waste slurry. The slurry supplied from the slurry supply pipe is scattered by the rotation of the polishing pad, and the scattered waste slurry is collected by a collecting unit. There is no particular limitation on the means of collecting the scattered waste slurry,
For example, as in the embodiment shown in FIG. 3, a waste slurry receiver may be provided around the polishing pad, and the waste slurry may be sucked and sent to the slurry receiving tank 4. Fresh slurries are often provided in concentrations of a few weight percents to tens of weight percents, for example, diluted about 10-fold in a slurry supply tank and used in a CMP process. According to the apparatus of this aspect, the waste slurry having the same concentration as the slurry supplied to the CMP step can be collected. In a normal case, cleaning with pure water or a chemical solution is performed after polishing, so if the drainage generated in all the steps of CMP including the cleaning is collected without separation, the amount of the liquid is 10 times the supplied slurry. And the concentration of the abrasive in the recovery liquid is about one tenth of the concentration of the abrasive in the supply slurry, and the type of contaminants contained in the recovery liquid also increases. According to the apparatus of this aspect, since the waste slurry having the same concentration as the supply slurry scattered in the polishing section of the CMP machine is collected, the amount of the liquid to be processed is smaller than in the case of processing the collected liquid in all the CMP steps. Low, the concentration of the abrasive in the liquid is high, and the tank, pump, piping, processing equipment, etc. in each step can be miniaturized and the abrasive can be efficiently collected. With the apparatus of this embodiment, typically 80
More than% by weight can be recovered. The remaining supply slurry is mixed with the wastewater and sent to a wastewater tank, where the wastewater is treated.

The filtered water treated by the filter 5, which is the filtration means in the former stage, is stored in a filtered water tank 6, and then the ceramic membrane separating means 7 having a single-layer honeycomb structure composed mainly of columnar β-type silicon nitride crystals. Sent to The pore size of the ceramic membrane to be used is not particularly limited, but an ultrafiltration membrane (UF) or a microfiltration membrane (MF) having a pore size of 0.01 to 0.5 μm can be suitably used. Although there is no particular limitation on the degree of concentration in the ceramic membrane separation means, it is usually preferable to set the concentration conditions such that the concentration of the abrasive in the concentrated water is 5 to 50% by weight. The processing conditions are preferably a batch-type or semi-batch-type concentration method using a cross flow in which concentrated water is circulated to the filtrate tank 6 via the concentrated water pipe 12 at a pressure of 0.01 to 0.5 MPa.
The permeated water separated by the ceramic membrane separation means can be discharged to the outside of the system and subjected to wastewater treatment. However, it is preferable to store a part of the permeated water in a pit and use it as backwash water for membrane cleaning.

In the apparatus of this embodiment, the washing means for washing the concentrated water obtained by the ceramic membrane separation means with water is provided by means for supplying washing water to the filtered water tank and means for diluting the concentrated water with the washing water in the filtered water tank. It is configured. Washing can be performed by adding washing water to the concentrated water, diluting and redispersing, and then concentrating by membrane separation.Using ultrapure water for washing effectively removes impurities such as organic substances and salts. And a slurry of a high-purity abrasive can be obtained. The degree of concentration of the concentrated water is monitored by a Coriolis-type concentration meter, level meter, or the like, and the concentrated water concentrated to a predetermined concentration is diluted by supplying washing water by a washing water supply unit and stirring. The concentrated water diluted by the washing water can be circulated between the ceramic membrane separation means 7 and the filtered water tank 6 to perform the concentration and the water washing simultaneously. By this washing, impurities such as organic substances, salts, and fine polishing dust are removed by the ceramic membrane separation means. If the amount of washing water used for water washing is too small, a sufficient washing effect cannot be obtained, and if it is excessively large, the amount of water used increases and the cost of recovery treatment increases. Normally, it is preferable to use about 10 to 100 times by volume of the washing water with respect to the concentrated water, and perform the washing twice. Ultrapure water is usually used as the washing water, but it is preferable to use ultrapure water to which an appropriate amount of a dispersant has been added in order to prevent agglomeration of the abrasive. In the apparatus of the present invention, the cleaning means is not limited to the configuration including the filtered water tank, but may be provided with a concentrated water tank for storing concentrated water at a stage preceding the concentration adjusting tank to supply the cleaning water to constitute the cleaning means. Can also.

The slurry which has been washed and concentrated to a predetermined concentration is introduced from the washing means to a subsequent concentration adjusting tank 9 as a concentration adjusting means, and a dispersant diluted with ultrapure water is supplied to the slurry to obtain a predetermined concentration. Adjusted. According to the apparatus of the present invention, since the organic substances, salts, and the like are removed by washing, the concentration can be easily adjusted, and the impurities such as organic substances and salts are extremely small, and it is possible to collect the slurry as a new slurry. . The density can be detected using a Coriolis type densitometer or the like. The slurry, which has been adjusted to a predetermined concentration, removes the abrasive which has been coarsened by re-aggregation by a filter 10 provided at the subsequent stage of the concentration adjusting tank, and after adjusting to a desired particle size distribution, is stored in a slurry stirring tank 11. And taken out as a recovered slurry. As the filter used here, the same filter as the microfiltration membrane used as the filtration treatment means in the preceding stage of the membrane separation means can be used. The number of filters is not limited to one, but may be two or more. In the apparatus of the present invention, the slurry stirring tank 11 is not always necessary, and the slurry can be returned to the slurry supply tank 1 of the CMP machine directly and recycled.

[0013]

According to the apparatus for recovering abrasives of the present invention, wastewater from a CMP process containing an organic dispersant, which could not be conventionally processed by membrane separation, is processed to enable reusable polishing. The material slurry can be efficiently collected.
In addition, a high flux can be obtained even when the circulation flow rate is reduced, and the pump capacity and the like can be reduced, so that the initial capital investment and operation management costs can be reduced. Furthermore, high concentration is possible even under such conditions. According to the apparatus of the present invention, the impurity is reduced to an extremely low concentration by washing and then the concentration is adjusted, so that an abrasive slurry having the same performance as a new slurry can be recovered. Therefore, according to the apparatus of the present invention, it is possible to reduce the amount of expensive abrasive slurry used in the polishing and kneading of a wafer, and to reduce the slurry cost. Further, since the amount of discharged wastewater decreases, the load on the wastewater treatment system and the like can be reduced, the amount of industrial waste treated can be reduced, and the cost can be reduced.

[Brief description of the drawings]

FIG. 1 is a process flow diagram of one embodiment of an abrasive recovery apparatus of the present invention.

FIG. 2 is an explanatory diagram of one embodiment of a ceramic film separating means having a single-layer honeycomb structure mainly composed of columnar β-type silicon nitride crystals.

FIG. 3 is an explanatory diagram of one embodiment of a CMP machine unit.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Slurry supply tank 2 CMP machine 3 Waste slurry tank 4 Slurry receiving tank 5 Filter 6 Filtration water tank 7 Ceramic membrane separation means 8 Dispersant dilution tank 9 Concentration adjustment tank 10 Filter 11 Slurry stirring tank 12 Concentrated water piping 13 Drainage inlet 14 Discharge side 15 Permeated water discharge port 16 Ceramic film 17 Slurry supply pipe 18 Polishing pad 19 Rotating substrate chuck 20 Collection means

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/304 622 H01L 21/304 622E F-term (Reference) 3C047 FF08 GG14 3C058 AA07 AC04 CB03 CB05 DA17 4D006 GA06 GA07 JA02C JA57A KA01 KA03 KA55 KA57 KA62 KA63 KA72 KB14 KC03 KD01 KD04 KD14 KD17 KD22 KE07Q KE07R MA22 MA40 MB02 MC03 MC18 MC22 MC27 MC29 MC49 MC54 PA04 PB08 PB70 PC01

Claims (4)

[Claims] An apparatus for recovering an abrasive from wastewater from a CMP process containing an organic dispersant, comprising a single-layer honeycomb-structured ceramic membrane mainly composed of columnar β-type silicon nitride crystals into which the wastewater is introduced. An abrasive recovering apparatus, characterized by comprising means. 2. The abrasive recovery apparatus according to claim 1, further comprising a washing means for washing the concentrated water obtained by the ceramic membrane separation means with water. 3. The apparatus for collecting abrasives according to claim 2, further comprising a concentration adjusting means for introducing a liquid from the cleaning means. 4. A method as claimed in claim 1, further comprising a filtration means for removing coarse solids before the ceramic membrane separation means or between the ceramic membrane separation means and the concentration adjusting means. apparatus.