JP2000140861A - Treatment of waste water incorporating fine abrasive grains-dispersed polishing liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely and inexpensively remove suspension particles by successively perform three flocculation treatment processes for performing additions and agitation's of a high polymer flocculant, an inorganic flocculant and another high polymer flocculant into the waste water containing fine abrasive grains-dispersed polishing liquid. SOLUTION: CMP waste water 5 is continuously introduced into a first flocculation tank 1, and is added the high polymer flocculant 6 and is rapidly stirred by a stirrer 7, then a first flocculation treatment is performed. Next, first flocculation treated water 8 is continuously introduced into a second flocculation tank 2 and is added the inorganic flocculant 9 and a pH adjusting agent 10, and is rapidly stirred by a stirrer 11, then a second flocculation treatment is performed. Besides, second flocculation treated water 13 is continuously introduced into a third flocculation tank 3 and is added the high polymer flocculant 14 and slowly stirred with a stirrer 15, then a third flocculation treatment is performed. Like this, suspension particles of abrasive grains, etc., suspended in the waste water, are flocculated, and flocks with large sizes grow further larger to make the flocks easy to sedimentation separation, and the suspension particles can be surely and inexpensively removed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for treating wastewater containing fine abrasive particle-dispersed polishing liquid, and more particularly, to a method for treating CMP wastewater discharged from a CMP (Chemical Mechanical Polishing) step in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In recent years, semiconductor devices have become finer and higher in density, and in the wiring process, it has become necessary to flatten the wiring insulating film. For this planarization, CMP ((Chemical
Mechanical Polishing): Polishing using both chemical and mechanical is being used.

[0003] Examples of the polishing liquid include fine particles of silica (SiO ₂ ), which is generally submicron-order particles, dispersed as abrasive particles in an alkaline aqueous solution.
Alumina (Al ₂ O) which is submicron-order particles
The fine powder of ₃ ) is used as abrasive particles dispersed in an acidic aqueous solution.

[0004] The CMP wastewater discharged from the CMP process in the semiconductor manufacturing process contains not only abrasive particles suspended for polishing, but also polishing debris particles generated by shaving a wafer, a film and a polishing pad. Conventionally, these particles have been removed by coagulation and sedimentation in the treatment process of CMΡ wastewater.

More specifically, after adding an inorganic coagulant such as an aluminum salt or an iron salt to the CMP waste water and rapidly stirring the mixture, a polymer coagulant is added and the mixture is gently stirred. Agglomerates the suspended particles to form flocs,
This is settled and separated. In recent years, CΜP wastewater is often treated by membrane treatment, and membrane permeated water is often reused for process water, etc., and the concentrated CMP wastewater containing high-concentration abrasive particles is discharged from this membrane treatment apparatus. ing. In the treatment of this high-concentration CMP wastewater, the above-mentioned coagulation sedimentation method is applied.

However, in the above-mentioned conventional coagulation and sedimentation method, a large amount of coagulant and neutralizer must be added to the wastewater in order to sufficiently perform coagulation and sedimentation.
There is a problem in that disposal of this large amount of sludge requires a corresponding place and cost.

Further, since a large amount of a coagulant and a neutralizing agent are added to the water to be treated, there is a problem that it is very difficult to reuse the treated water.

[0008]

As described above, according to the conventional method of coagulating and sedimenting waste water containing fine abrasive particle-dispersed polishing liquid, a large amount of coagulant and neutralizing agent are drained to sufficiently coagulate and sediment. In addition, the amount of generated sludge is remarkably increased, and there is a problem that disposal of this large amount of sludge requires a corresponding place and cost.

In addition, since a large amount of a coagulant and a neutralizing agent are added to the water to be treated, there is a problem that it is very difficult to reuse the treated water.

The present invention has been made to solve such a conventional problem, and its main purpose is to reduce the amount of generated sludge and to remove suspended particles such as abrasive particles contained in wastewater reliably and at low cost. It is an object of the present invention to provide a method for treating wastewater containing a polishing slurry in which fine abrasive particles are dispersed. It is another object of the present invention to provide a method for treating wastewater containing fine abrasive particle-dispersed polishing liquid capable of obtaining treated water of easy-to-reuse quality.

[0011]

According to the present invention, there is provided a method of treating waste water containing fine abrasive particle-dispersed polishing liquid, comprising the steps of: A treatment step, a second flocculation treatment step in which an inorganic coagulant is added to the liquid to be treated which has been subjected to the first flocculation treatment step, and stirring, and a liquid to be treated which has been subjected to the second flocculation treatment step. The third flocculation treatment step of adding and stirring the polymer flocculant is sequentially performed to form flocs.

As the wastewater containing the fine abrasive particle-dispersed polishing liquid of the present invention, for example, wastewater containing a CMP polishing liquid is exemplified.

[0013] CMΡ wastewater to be treated in the present invention is:
This is a CMP wastewater using silica, zirconia, selenium, alumina, ceria, manganese oxide, or the like as a CMP polishing agent, and specific examples include a CMP wastewater discharged from a polishing step or a rinsing step of a semiconductor manufacturing process. Can be

As the polymer flocculant used in the present invention, conventionally used polymer flocculants can be used, and polyacrylates, polymethacrylates, polyacrylamides, polyamines, dicyandiamides, polyamine sulfones, chitosans And the like.

The amount of the polymer flocculant to be added to the first flocculation treatment depends on the concentration of suspended particles such as abrasive particles in the raw waste water, but is usually 0.01 ppm to 100 ppm, preferably about 1 ppm to 20 ppm. is there.

As the inorganic coagulant used in the present invention, conventionally used inorganic coagulants can be used, such as polyaluminum chloride (ΡAC), aluminum salts such as sulfuric acid bands, ferrous sulfate, and ferric sulfate. Examples thereof include iron salts such as iron and ferric chloride. The amount of the inorganic coagulant to be added varies depending on the concentration of suspended particles such as abrasive particles in the raw wastewater, but is generally 10 p.
pm to 20,000 ppm, preferably 50 ppm to 10
It is about 00 ppm, more preferably about 100 to 500 ppm.

The amount of the polymer flocculant to be added to the third flocculation treatment varies depending on the concentration of suspended particles such as abrasive particles in the raw waste water, but is usually 0.01 ppm to 50 ppm, preferably 0.05 ppm to 50 ppm. 20 ppm, more preferably about 0.1 to 10 ppm. In the present invention, first, the polymer flocculant is added to the wastewater containing the fine abrasive particle-dispersed polishing liquid and stirred to perform the first flocculation treatment. After the addition of the polymer flocculant, it is desirable to carry out the reaction by rapidly stirring for 1 to 15 minutes. Although the rapid stirring varies depending on the shape and size of the stirring means, it is usually desirable to perform the stirring at about 100 to 200 rpm. By performing the first aggregating treatment in this manner, suspended particles such as abrasive particles suspended in the CMP wastewater aggregate to form extremely fine flocs.

The presence of hydrogen peroxide in the water to be treated hinders the sedimentation and separation of flocs. Therefore, it is preferable to remove them in advance. There is no problem in removing hydrogen peroxide using any known method, and hydrogen peroxide decomposing enzymes, inorganic salts such as sulfurous acid and thiosulfuric acid, and activated carbon towers can be suitably used.

Next, the above-mentioned inorganic coagulant is added to the first coagulation liquid and stirred to perform the second coagulation treatment. In this case, it is preferable to adjust the pH of the water to be treated so as to be pΗ suitable for the inorganic coagulant to be added.

For example, when polyaluminum chloride is used, the pH is 6 to 8, preferably the pH is 6.5 to 7.5.
It is preferred to adjust to. After the addition of the inorganic coagulant,
It is desirable to carry out the reaction by rapidly stirring for 1 to 15 minutes.

The above-mentioned rapid stirring varies depending on the shape and size of the stirring means, but is usually preferably performed at about 100 to 200 rpm. By performing the second aggregation process in this manner, large flocs in which suspended particles such as abrasive particles suspended in the wastewater are further aggregated grow.

Next, the above-mentioned polymer flocculant is added to the second flocculation treatment liquid and stirred to perform the third flocculation treatment. After the addition of the polymer flocculant, it is preferable to carry out the reaction by slowly stirring for 3 to 30 minutes. Although the slow stirring varies depending on the shape and size of the stirring means, it is usually desirable to perform the stirring at about 10 to 100 rpm. By performing the third coagulation treatment in this manner, large flocs in which suspended particles such as abrasive particles suspended in the wastewater are aggregated further grow, and the flocs are easily sedimented and separated.

The flocculation treatment liquid having formed a good floc after the third flocculation treatment is subjected to solid-liquid separation by a usual sedimentation separation operation, filtration separation operation, etc., and the separated liquid is discharged out of the system as treated water. The separated sludge is subjected to a dehydration treatment to form a dewatered cake. The sludge separated at this time may be circulated and reused in the first flocculation treatment.

[0024]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a CM implementing the processing method of the present invention.
It is a P drainage treatment system diagram, code | symbol 1 is a 1st coagulation tank, code | symbol 2
Denotes a second coagulation tank, 3 denotes a third coagulation tank, and 4 denotes a sedimentation tank.

In order to perform wastewater treatment by the apparatus shown in FIG.
The MP wastewater 5 is continuously introduced into the first flocculation tank 1, a polymer flocculant 6 is added, and the mixture is rapidly stirred by a stirrer 7 to perform a first flocculation treatment. Next, the first flocculation treatment water 8 is continuously guided to the second flocculation tank 2, the inorganic flocculant 9 and the pH adjuster 10 are added, and the mixture is rapidly stirred by the stirrer 11 to perform the second flocculation treatment. Do. Reference numeral 12 denotes a pH meter in the second coagulation tank.

Next, the second flocculation treatment water 13 is continuously introduced into the third flocculation tank 3, the polymer flocculant 14 is added, and the mixture is slowly stirred by the stirrer 15 to perform the third flocculation treatment. Thereby, a larger floc is formed.

Finally, the third coagulated water 16 is added to the sedimentation tank 4.
And a solid-liquid separation by sedimentation. The separated liquid is sent to the subsequent stage as treated water 17, and the separated sludge 18 is sent to a sludge treatment process outside the system.

[0028]

Example 1 Simulated CMP wastewater containing silica-based CM polishing liquid was treated. PLA as silica-based CMP polishing liquid
Using NERI @ E-4214 (manufactured by FUJIMI)
Simulated CMP wastewater was obtained by diluting 100 times with ultrapure water. The appearance of this mock CM drainage is milky white, Si
The O ₂ concentration is 0.25% by weight.

500 ml of the simulated CMP waste water was placed in a beaker, and 10 ppm of a polymer flocculant (LTX-10S, manufactured by Konan Chemical Industry Co., Ltd.) was added. The length was 70 mm and the width was 25 m.
m was rotated at 120 rpm and rapidly stirred for 5 minutes (using a JAR-TESTER manufactured by MIYAMO @ O).

Next, polyaluminum chloride (industrial P
AC) was added in the amount shown in Table 1, the pH was adjusted to 6.8 to 7.0 with sodium hydroxide (NaOΗ), and the mixture was rapidly stirred for 5 minutes in the same manner as described above. further,
5 ppm of a polymer pseudo-collector (LTX-10S, manufactured by Konan Chemical Industry Co., Ltd.) was added, and the mixture was slowly stirred at 30 rpm for 10 minutes. Thereafter, the mixture was allowed to stand for 5 minutes, and the turbidity of the supernatant (kaolin particles) and the sedimentation speed of floc were measured. For the sedimentation speed, treatment under the same conditions was performed five times, and the average value was used. Table 1 shows the results.

[0031]

Comparative Example 1 The same procedure as in Example 1 was carried out except that the amount of the polymer coagulant corresponding to the first coagulation treatment was changed to zero. Table 1 shows the results.

[0032]

Comparative Example 2 The same procedure as in Example 1 was carried out except that the amount of the polymer flocculant corresponding to the first flocculation treatment was set to zero and PAC was added so that the turbidity of the treated water supernatant became 0 °. Table 1 shows the results.

[0033]

Comparative Example 3 The same procedure as in Example 1 was carried out except that the amount of the polymer flocculant corresponding to the third flocculation treatment was changed to zero. Table 1 shows the results.

[0034]

[Table 1] In the above embodiments, the first aggregation process, the second aggregation process, and the third aggregation process were each performed using a single tank, but the present invention is not limited to such an example. Instead, the processing may be performed using a plurality of tanks, and another processing tank may be interposed between the tanks.

Furthermore, the example of stirring was described in which a stirrer was inserted into the tank and stirring was performed. In other words, if the added component and the water to be treated can be uniformly mixed within a predetermined time. For example, it is also possible to perform stirring while continuously passing through a pipeline.

[0036]

As described above in detail, according to the method for treating wastewater containing fine abrasive particle-dispersed polishing liquid according to the present invention, the amount of generated sludge is small, and the suspension of the abrasive particles and the like contained in the wastewater is reduced. Particles can be removed reliably and at low cost, and it is possible to obtain treated water of water quality that is easy to reuse.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a processing apparatus used in Example 1 and Comparative Example.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... 1st flocculation tank, 2 ... 2nd flocculation tank, 3 ... 3rd flocculation tank, 4 ... Sedimentation tank 5 ... CMP water flow, 6 ... Polymer flocculant, 7 ... Stirrer, 8 first coagulated water, 9 inorganic coagulant, 10 pH adjuster, 11 stirrer, 1
2 pH meter, 13 second coagulated water, 14 polymer coagulant, 15 stirrer, 16 third coagulated water, 17 treated water, 18 separation Sludge.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4D015 BA03 BA05 BA24 BB09 BB14 CA20 DA04 DA05 DA16 DA17 DB03 DB14 DB19 DB32 EA14 EA32 EA35 4D062 BA03 BA05 BA24 BA24 BB09 BB14 CA20 DA04 DA05 DA16 DA17 DB03 DB14 DB19 DB32 EA14 EA32 EA35

Claims (2)

[Claims] 1. A first coagulation treatment step in which a polymer coagulant is added to waste water containing fine abrasive particle-dispersed polishing liquid and stirred, and an inorganic coagulation treatment is performed on the liquid to be treated which has been subjected to the first coagulation treatment step. A second coagulation treatment step of adding and stirring an agent, and a third coagulation treatment step of adding and stirring a polymer coagulant to the liquid to be treated which has undergone the second coagulation treatment step. A method for treating wastewater containing fine abrasive particle-dispersed polishing liquid, characterized in that flocs are formed by the method. 2. The method for treating wastewater containing fine abrasive particle dispersed polishing liquid according to claim 1, wherein the fine abrasive particle dispersed polishing liquid is a CMP polishing liquid.