JP2002263635A - Method for treating cmp waste water containing suspended silica - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate CMP waste water containing suspended silica into the concentrated water containing all of the suspended materials contained in the CMP waste water and the condensed water of steam vaporized by vaporizing/ concentrating the CMP waste water containing suspended silica while the generation of scale due to silica is controlled and the volume of the concentrated water is reduced. SOLUTION: The pH value of the CMP waste water containing suspended silica is adjusted to 8-10 by adding alkali, which is then introduced into an evaporator. The introduced CMP waste water is circulated between the evaporator and a heating vessel. The water content of the CMP waste water is vaporized in the evaporator by heating the circulated CMP waste water indirectly through the heat transfer surface of the heating vessel so that the CMP waste water in the evaporator is concentrated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for evaporating and concentrating CMP wastewater containing silica-based suspensions among CMP wastewater discharged from a CMP (Chemical Mechanical Polishing) apparatus used in the production of semiconductor components. And a method of processing.

[0002]

2. Description of the Related Art C used in the manufacture of semiconductor components
CMP wastewater discharged from an MP (Chemical Mechanical Polishing) device includes fine abrasive particles mainly composed of silica (SiO ₂ ) and fine particles separated or shaved from the workpiece by the abrasive particles. Since these are suspended, they cannot be discharged to rivers and the like as they are.

Conventionally, in the treatment of the CMP wastewater, there are a method of separating the suspended matter by coagulation sedimentation and a method of separating the suspended matter by filtration.

The former method of coagulation and sedimentation is disclosed, for example, in JP-A-11-33560 and JP-A-11-34756.
No. 9, JP-A-2000-140861 and JP-A-2000-254656, etc., after adding a coagulant to the CMP wastewater and performing a condensation treatment,
This is a method in which a suspension such as silica is precipitated by introducing the suspension into a sedimentation tank, thereby separating the suspension into sediment sludge water containing the suspension and supernatant water containing no suspension.

On the other hand, the latter method using filtration is, for example,
JP-A-7-316846 and JP-A-9-1177
As described in JP-A-63-63, etc., this is a method of separating a suspension by filtering CMP wastewater with a filtration membrane.

[0006]

However, in the former method based on coagulation and sedimentation, a large amount of coagulant must be added to the CMP wastewater in order to coagulate the suspension effectively. Since the amount of the sedimentation sludge later increases only by adding a large amount of the flocculant, the load of the post-treatment such as the drying of the sedimentation sludge afterwards increases, and the cost required for the post-treatment is greatly increased In addition to increasing the sedimentation, there is a problem in that an optimum flocculant and an optimal amount of the flocculant must be selected according to the properties of the CMP wastewater in order to achieve a high precipitation and separation.

[0007] In the latter method of filtration, it is necessary to carefully select the type of filtration membrane according to the properties of the CMP wastewater, and in some cases, a significantly expensive ceramic membrane must be used. Also, in terms of operation management, the frequency of performing a cleaning operation in accordance with the properties of the CMP wastewater, such as removal of a specific substance in the CMP wastewater or the like, depending on the clogging of the filtration membrane. And the setting of the optimum permeation flow velocity are required.

[0008] The present invention relates to a CMP comprising a silica-based suspension.
An object of the present invention is to provide a method for treating wastewater by evaporative concentration without using the conventional coagulation sedimentation method or filtration method.

[0009]

In order to achieve this technical object, claim 1 of the present invention is directed to a method for producing a CMP wastewater containing a suspension of silica, the pH of which becomes 8 to 10 by adding an alkali. And then guided into the evaporator and circulated between the evaporator and the heating can, during which the indirect heating via the heat transfer surface of the heating can causes the evaporator to circulate within the evaporator. Concentration is performed to evaporate the water, and the concentrated water containing the suspension of the silica is separated into condensed water of the evaporated water vapor. "

According to a second aspect of the present invention, in the first aspect, the temperature difference between the heat source side and the CMP wastewater at the time of indirect heating via the heat transfer surface is set to 6 ° C. or less. It is characterized by.

[0011]

Operation and effect of the present invention
Water is evaporated in an evaporator by indirectly heating the wastewater through a heat transfer surface, and the CMP wastewater is separated into the concentrated water and the condensed water of the evaporated water vapor. The water in the CMP wastewater can be recovered as condensed water containing no suspended matter, while the water in the CMP wastewater can be reduced as concentrated water containing all of the suspended matter previously contained in the wastewater.

When the CMP wastewater to be treated is a CMP wastewater containing a silica-based suspension, it is necessary to evaporate the water by indirect heating via a heat transfer surface to concentrate the wastewater.
Since silica scale will adhere to the heat transfer surface, the operation of evaporating and concentrating the silica must be stopped at relatively short intervals to remove the silica scale attached to the heat transfer surface. In addition, the operation for removing the scale must be frequently stopped.

However, as shown in FIG. 3, when the pH of the aqueous solution is 7, the solubility of silica in water increases almost linearly in proportion to the temperature as shown in FIG. The solubility of silica in water when changed to is a value obtained by multiplying the solubility in FIG. 3 by the correction coefficient X obtained from the curve in FIG. 4, and is relatively high when the pH value of the aqueous solution is around 8. It increases gradually, but when it exceeds 10, it is recognized that it increases rapidly.

Therefore, in the present invention, the pH value of the CMP wastewater containing the suspension of silica is adjusted to 8 to 10 by adding an alkali, and then the wastewater is led to the evaporator to evaporate the wastewater. It circulates between the can and the heating can to concentrate water by evaporating water during the circulation, whereby the pH value of the circulating water circulating between the evaporator and the heating can is increased. The pH value exceeds the initially adjusted pH value of 8 to 10 and is further increased by evaporation and concentration, and the solubility of silica is significantly increased, and the scale of silica adhered to the heat transfer surface in the heating can is reliably suppressed. As a result, the time interval during which the evaporative concentration operation must be stopped for the silica scale to adhere to the heat transfer surface can be greatly extended.

In addition, while the solubility of silica in the circulating water circulating between the evaporator and the heating can can be maintained at a remarkably high value, the CM for the purpose of treatment is treated.
It is only necessary to add an alkali up to a pH value of 8 to 10 to the P wastewater. In other words, since the amount of the alkali added can be reduced, the operating cost can be reduced and the alkali is added. For this reason, the increase in the amount of concentrated water containing all of the suspension previously contained in the CMP wastewater to be treated can be suppressed only slightly, and after the concentrated water is dried, etc. Processing load can be reduced.

Further, in the above-mentioned evaporative concentration, as described in the following embodiment, the temperature difference between the heat source side and the indirect heating through the heat transfer surface is reduced by 6%.
By keeping the temperature below ℃, the amount of heat exchanged per unit heat transfer area is reduced, and consequently, when the amount of evaporation per unit heat transfer area is reduced, local excess concentration occurs on the surface of the heat transfer surface. It is possible to prevent that, the scale adheres to the heat transfer surface, since the adhesive force is small, even if the silica scale adheres to the heat transfer surface, the silica scale becomes relatively soft, this silica scale It can be easily removed.

[0017]

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

FIG. 1 shows a first embodiment.

In FIG. 1, reference numeral 1 denotes a supply line 2
Reference numeral 3 denotes an evaporating and concentrating apparatus for the CMP wastewater containing the suspension of silica sent from the company.

The pH adjusting tank 1 is provided with a stirrer, and contains a suspension of silica sent from the pipe 2.
The wastewater is received, and its pH value is adjusted to 8 to 10 by controlling the pH sensor 5 to increase or decrease the amount of alkali such as caustic soda supplied from the pipeline 4.

The pH adjusted CMP wastewater is as follows:
The water is supplied to the lower portion of the evaporator 6 in the evaporator 3 by the pump 7. In this case, a liquid level sensor 8 is provided at a lower portion in the evaporator 6, and the liquid level sensor 8 controls the opening and closing of the CMP wastewater supply valve 9 into the evaporator 6, whereby The lower part is configured to maintain a constant liquid level.

In the upper part of the evaporator 6, a number of horizontally extending heat transfer tubes 10 in the heating can are provided in a multi-stage manner, one end of each of the heat transfer tubes 10 being an inlet header 11 and the other being an outlet header 12. Each of the heat transfer tubes 10 is supplied with steam as a heat source sent from a boiler (not shown) through a pipe line 13 through the inlet header 11.

On the other hand, the CMP wastewater for processing supplied to the inner bottom of the evaporator 6 is pumped out by a circulation pump 14 and is sent to a nozzle 15 disposed above each heat transfer tube 10 in the heating can. After being sent through the passage 16 and sprayed from the nozzle 15 to the outer surface of each of the heat transfer tubes 10, it is circulated again to return to the bottom in the evaporator 6.

By this circulation, in the evaporator 6, the water is evaporated by being indirectly heated by the heat transfer tubes 10.

By this evaporation, CM in the evaporator 6 is
The P wastewater is so-called evaporatively concentrated so that the water evaporates,
The concentrated water having a high concentration of the suspension becomes the concentrated water delivery line 17.
Is discharged from.

On the other hand, the water vapor evaporated in the evaporator 6 is led to a condenser 19 through a duct 18 and becomes condensed water by cooling there, and condensed water together with the condensed water in the outlet header 12. Pumped by pump 20.

In the evaporator 6, a non-condensable gas is extracted from the condenser 19 by a vacuum generator such as a vacuum pump 21 so that the gas is reduced to a pressure lower than the atmospheric pressure (for example, the boiling point is about 80 ° C.). ℃ decompression state)
The above-described evaporation in the evaporator 6 is performed under a reduced pressure state below the atmospheric pressure.

The concentrated water discharged from the concentrated water delivery line 17 contains all of the suspended matter originally contained in the CMP wastewater to be treated, and is sent to a post-processing step such as drying.

On the other hand, the condensed water pumped out by the condensed water pump 20 does not contain any suspended matter.
The condensed water is sent from the condensed water delivery pipe 22 to a reuse point as industrial water or the like.

In the case of this embodiment, a suspended matter concentration sensor 2 such as a hydrometer is provided in the concentrated water delivery line 17.
3, the valve 24 is opened only when the concentration of the suspended solids in the concentrated water becomes a predetermined value or more, and is sent to a post-processing step such as drying. On the other hand, the condensed water delivery line 2
A water quality sensor 25 is provided in the middle of the step 2, and when the water quality of the condensed water is better than a predetermined value, the valve 26 is opened and sent to a reuse point. The valve 26 is closed, the bypass valve 27 is opened, and the fluid is sent to a location other than the reuse location.

In the case of the present embodiment, the circulation line 16 is provided with a scale inhibitor contained in a tank 28 by a valve 29.
In addition to being supplied appropriately at a more appropriate time, the tank 30
The defoamer put in the tank is supplied from the valve 31 at an appropriate time.

Further, in the present embodiment, when the silica scale adheres to the surface of each of the heat transfer tubes 10 to a predetermined value or more, the operation of the evaporation and concentration is stopped,
After discharging the CMP wastewater accumulated in the evaporator 6 and the like, the silica scale is removed by supplying the cleaning agent put in the tank 32 into the evaporator 6 by opening the valve 33 and circulating the same. The cleaning agent that has finished removing the scale
It is configured to be discharged from a discharge valve 34 connected to the condensed water delivery pipe 22.

According to experiments by the present inventors, a facility for processing 144 cubic meters of CMP wastewater containing a suspension of silica per day, and evaporating and concentrating ratio in the evaporating and concentrating device 3 to be 12 times. When the amount of the CMP wastewater to be treated is reduced to 1/12 concentrated water, the pH value of the CMP wastewater to be treated is adjusted to 8 by adding caustic soda in the pH adjusting tank 1, and the water is evaporated. When supplied to the concentrator 3, the evaporative concentrator 3
The pH value of the circulating water at 9.5 to 10 or more.

In the heating can of the evaporating and concentrating apparatus 3, the temperature difference between the inner heating side and the outer heated side of each heat transfer tube 10 increases as the temperature difference per unit heat transfer area increases. Since the amount of heat transfer increases, the heat transfer area can be reduced, and the evaporator can be downsized.

However, according to experiments performed by the present inventors, when the temperature difference exceeds 6 ° C., each of the heat transfer tubes 10
The silica scale that adheres to the outer surface of the
Although a phenomenon was observed in which this could not be easily removed, when the temperature difference was set to 6 ° C. or less, the scale of silica adhering to the outer surface of each heat transfer tube 10 was relatively small. It became soft and could be easily removed by washing with a detergent.

Next, FIG. 2 shows a second embodiment.

In the second embodiment, a vapor compression type evaporating and concentrating apparatus 3 'is used as an evaporating and concentrating apparatus, and the other configuration is the same as that of the first embodiment.

Here, the vapor compression type evaporative concentrator 3 '
After the steam generated in the evaporator 6 is compressed by a blower 36 rotated and driven by an electric motor 35, the steam is supplied into the inlet header 11 of each of the heat transfer tubes 10.
By performing the non-condensable gas from the outlet header 12 of each of the heat transfer tubes 10 by a vacuum generator such as a vacuum pump 21 ′, the evaporation in the evaporator 6 is performed at a reduced pressure below the atmospheric pressure. The steam generated by the evaporation is collected as condensed water at the outlet header 12,
From here, it is pumped by the condensed water pump 20.

According to this structure, the current in the electric motor decreases in inverse proportion to the adhesion of the silica scale to the outer surface of each of the heat transfer tubes 10, and the current in the electric motor is detected by the ammeter 37. By doing so, it is possible to know when to remove the scale from the current value.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of the present invention.

FIG. 2 is a diagram showing a second embodiment of the present invention.

FIG. 3 is a graph showing the solubility of silica in water.

FIG. 4 is a diagram showing a correction coefficient of solubility of a silica aqueous solution depending on pH.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 pH adjustment tank 2 CMP waste water supply line containing suspension of silica 3, 3 Evaporation concentrator 6 Evaporator 10 Heat transfer tube 14 Circulation pump 17 Concentrated water delivery line 19 Condenser 20 Condensed water pump 21 Condensed water delivery tube Road

Claims (2)

[Claims] 1. The CMP waste water containing a suspension of silica is adjusted to have a pH value of 8 to 10 by adding an alkali, and then is introduced into an evaporator. During the circulation, concentration is performed by evaporating water in the evaporator by indirect heating through the heat transfer surface of the heating can, and concentrated water containing a suspension of the silica, A method for treating CMP wastewater containing a silica-based suspension, wherein the wastewater is separated into condensed water of steam. 2. The silica suspension according to claim 1, wherein the temperature difference between the indirect heating through the heat transfer surface and the heat source side is maintained at 6 ° C. or less. A method for treating CMP wastewater, comprising: