JPS61111199A - Method for producing washing water for semiconductor wafer of chip - Google Patents

Abstract

PURPOSE:To produce titled washing water without propagating bacteria in an active carbon filtration column by treating previously mixed water composed of waste water formed in washing chips, etc. and feed water in a cation exchange column to obtain acidic water then treating the acidic water in the active carbon filtration column. CONSTITUTION:The waste water 5 formed in washing the semiconductor wafers or chips is recovered and is mixed with the feed water 1. The mixed water is treated in the cation exchange resin column, the active carbon filtration column 8, an anion exchange resin column 9 or a mixed bed column. contg. a cation exchange resin and anion exchange resin and a reverse osmosis membrane device 10 in this order. As a result the ultra-pure water ideal for washing the semiconductor wafers is obtd. without propagating the bacteria in the active carbon filtration column. An extra operation for sterilizing the active carbon layer is not required and since no extra drugs are used at all, the supply of the ultra-pure water at the low cost is made possible.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is used in the electronics industry that produces LSIs and VLSIs to produce cleaning water for semiconductor wafers or chips (hereinafter referred to as semiconductor wafers), which are intermediate products thereof. It is about the method.

<Prior art> In the electronics industry that produces LSIs and VLSIs, when cleaning semiconductor wafers, which are intermediate products, in order to improve the yield, not only the amount of ions is reduced to ppb order, but also T.

0.0, C (total organic carbon) is reduced to several tens of ppb, and the number of viable bacteria is reduced to 10-1 cells/ml, so-called ultrapure water is required. On the other hand, due to recent water shortages and restrictions on wastewater discharge, in recent years, a portion of the semiconductor wafer cleaning wastewater has been recovered and mixed with raw water to produce ultrapure water.

When processing such mixed water to produce ultrapure water, it is essential to add an activated carbon filtration tower to remove organic matter from the washing wastewater. ), the filtered water is treated with a sand filtration tower, the washing wastewater is mixed with the filtered water, and the mixed water is then mixed with an activated carbon filtration tower, a cation exchange resin tower, a decarboxylation tower, and an anion exchange resin tower. Demineralized water is obtained by sequential treatment with a reverse osmosis membrane device, and ultrapure water is produced by subjecting the demineralized water to a hotbed polisher, ultraviolet treatment, etc., and the ultrapure water is used as water for cleaning the semiconductor wafer.

<Problems with the prior art> However, the above-mentioned prior art has the following problems.

In other words, activated carbon filtration towers fully demonstrate their ability to remove organic matter from water, but the activated carbon layer tends to become a breeding ground for bacteria, and when mixed water is treated with activated carbon filtration towers, the amount of organic matter in the treated water is significantly reduced. However, the disadvantage is that the number of viable bacteria increases significantly. In particular, as mentioned above, the cleaning wastewater from cleaning semiconductor wafers contains various organic substances suitable for the propagation of bacteria, and the increase in the number of viable bacteria is greater than in activated carbon filtration towers in ordinary water treatment.

The treated water from the activated carbon filtration tower is then treated with a pure water production device, a reverse osmosis membrane device, etc., but as the number of viable bacteria increases, the number of viable bacteria in the terminal pure water also increases, and semiconductor wafers are This makes it undesirable as cleaning water.

It is also possible to sterilize the activated carbon filtration tower in which such bacteria have grown by periodically washing it with hot water or various disinfectants, but this would be complicated and
In addition, when hot water is used, the tower and piping must be made heat-resistant, which increases equipment costs.When using disinfectants, treatment costs increase and the amount of organic matter adsorbed by activated carbon is reduced. This is undesirable because there are problems such as the disinfectant being contaminated or the disinfectant leaking into the water.

<Purpose of the Invention> The present invention solves the drawbacks of conventional semiconductor wafer cleaning water and performs periodic sterilization without using any hot water or sterilizers. The purpose is to prevent bacterial growth in activated carbon filtration towers at a lower cost.

Means for Solving Problems> The growth of microorganisms is affected by the pH of the environment, and each microorganism has its preferred pH range for growth. For example, it is said that bacteria have an optimal pH range between neutral and slightly alkaline (pH 7-8), and yeast and mold have an optimal pH range between slightly acidic (pH 6-7). Furthermore, as the pH shifts from the optimum pH range to the acidic or alkaline side, the growth of microorganisms is gradually suppressed.
It is said that it will die if it is chased. Therefore, the lower the pH, the more inhibited the growth of normal bacteria.
I'm going to growl.

The present invention was made in view of this point, and since the treated water of the cation exchange resin tower is usually acidic with a pH of around 3, the mixed water is first treated in the cation exchange resin tower, and the acidic treated water is By passing water through the activated carbon filtration tower, organic matter is removed and the proliferation of bacteria in the activated carbon filtration tower is effectively prevented, and then the filtered water is passed through an anion exchange resin tower or a mixed bed of cation exchange resin and anion exchange resin, The present invention relates to a method for producing cleaning water for semiconductor wafers, which is characterized by processing with a reverse osmosis membrane device.

The drawing is an explanatory diagram of a flow showing an example of an embodiment of the present invention. Raw water 1 is first passed through a coagulation sedimentation device 2 and a sand filter tower 3.
The filtered water is treated to remove suspended solids, organic matter, colloidal silica, etc. contained in the raw water, and the filtered water is supplied to the storage tank 4. Note that depending on the quality of the raw water 1, the coagulation-sedimentation device 2 may be omitted, or microfloc filtration may be performed in which a coagulant or the like is added to the inlet water of the sand filtration tower 3.

On the other hand, the waste water 5 for cleaning semiconductors is supplied to the storage tank 4, and the sand filtered water and the waste water 5 for cleaning are mixed in the storage tank 4.

Next, the mixed water in the storage tank 4 is treated in the cation exchange resin column 6. The cation exchange resin column 6 is a multi-layer bed filled with an H-type weakly acidic cation exchange resin or an H-type weakly acidic cation exchange resin and a strongly H-swelled acidic cation exchange resin. Ion exchange to H ions.

Therefore, the treated water contains CI ions, S
Mineral acids corresponding to mineral acid ions such as 04 ions are produced, and HCO3 ions contained in the water become free carbonic acid, and its pH usually exhibits acidity of around 3. Next, the acidic soft water is subjected to a decarboxylation tower 7 treatment.

The decarboxylation tower 7 is one in which acidic soft water flows down from the upper part of a packed bed such as a Raschig ring, and gases such as air and nitrogen are introduced from the bottom of the packed bed, or the inside of the decarboxylation tower 7 is depressurized. Free carbonic acid in the acidic soft water is removed by such gas-liquid contact or depressurization treatment using a so-called vacuum deaerator that removes dissolved gases. Note that if the acidic soft water contains volatile organic substances, the organic substances can also be removed here. Therefore, if the cleaning wastewater 5 contains volatile organic matter, it is effective for removing this.

In the present invention, the decarbonated water from the decarbonation tower 7 is then passed through the activated carbon filtration tower 8 to remove organic substances from the decarbonated water.

The activated carbon filtration tower 8 is filled with granular activated carbon, and in the present invention, acidic water with a pH of around 3 is always in contact with the packed bed, so that it effectively prevents bacteria from propagating in the packed bed. be able to. In addition, among the organic substances generally contained in water, hydrophilic organic acids are
It is said that when H becomes acidic, its solubility decreases, and as a result, its affinity for water decreases and it is better adsorbed by activated carbon. Therefore, in the present invention, the removal effect of these hydrophilic organic acids is improved. It is also effective.

Activated carbon filtration tower 8 from which organic matter has been removed through such treatment
The treated water is then passed through an anion exchange resin tower 9, where mineral acid ions, silica, residual free carbonic acid, residual organic matter, etc. are adsorbed to obtain demineralized water. Note that instead of the anion exchange resin column 9, this portion may be used as a mixed bed column of cation exchange resin and anion exchange resin. In short, an ion exchange column capable of removing anion components such as mineral acid ions, silica, and residual free carbonate may be used after the activated carbon filtration column 8.

The demineralized water is then treated in a reverse osmosis membrane device 10 to obtain permeated water from which residual ions, silica, and colloidal substances have been removed. Processed with 11,
Further, ultrapure water is obtained by ultraviolet treatment (not shown).

In the present invention, since Ca ions, Mg ions, SO4 ions, silica, organic substances, etc. that contaminate the reverse osmosis membrane are removed at the front stage of the reverse osmosis membrane device 10, the permeated water of the reverse osmosis membrane device 10 is recovered. It is possible to obtain ultrapure water suitable for cleaning semiconductor wafers by increasing the efficiency as much as possible, reducing the overall processing cost. Note that the non-permeated water of the reverse osmosis membrane device 10 can also be collected into a storage tank (not shown) for raw water.

<Effects of the Invention> As explained above, in the present invention, mixed water is first treated in a cation exchange resin tower to obtain acidic water, and the acidic water is then treated in an activated carbon filtration tower, so that bacteria do not breed in the activated carbon filtration tower. It is possible to obtain ultrapure water, which is ideal for cleaning semiconductor wafers, without causing any damage.

In addition, the present invention does not require any extra operations to sterilize the activated carbon layer, and does not use any unnecessary chemicals.
Ultra-pure water can be supplied at low cost.

Examples will be described below to clarify the effects of the present invention.

EXAMPLE As an example of the present invention, first, mixed water with a pH of 5.4 to 6.2, which was a 1:1 mixture of sand filtered water and semiconductor wafer cleaning waste water, was treated in a cation exchange resin tower and a decarboxylation tower. As a result, acidic soft water with a pH of 2.7 to 2.9 was obtained. This acidic soft water is passed through an activated carbon filter tower.

As a result of water flow operation for 3,000 hours under the condition of 20 m / hr, the number of viable bacteria that leaked into the treated water was 4 to 4 at the beginning of operation.
12 pieces/m1! , mid-term operation 3-8 pieces/m I! ,
3,000 hours - 10 cells/ml, and there was no increase in the number of viable bacteria that leaked into the treated water. Note that the number of viable bacteria in the mixed water was 11 to 18 cells/ml.

After treating this activated carbon-treated water with an anion exchange resin tower,
When treated with a low-pressure reverse osmosis membrane device and the number of viable bacteria in the permeated water was measured, it was less than 1 cell/m1.

On the other hand, for comparison, the same pH as used in the examples of the present invention was used.
The mixed water of 5.4 to 6.2 was first filtered to LV and 2 in an activated carbon filtration tower.
As a result of water flow operation for 3,000 hours under the condition of 0 m/hr, the number of viable bacteria that leaked into the treated water was 5 to 11 per hour at the initial stage of operation.
ml, middle stage of operation 92-180 pieces/ml, 3.00
After 0 hours, the number of viable bacteria leaked into the treated water was 210 to 290 cells/ml, which greatly increased.

The number of viable bacteria in the mixed water was 11 to 1, which is the same as in the example of the present invention.
8 pieces/m I! It is.

After this activated carbon-treated water was treated with a cation exchange resin tower, a decarboxylation tower, and an anion exchange resin tower, it was treated with the same reverse osmosis membrane device as in the example of the present invention, and the number of viable bacteria in the permeated water was measured. 18-28 pieces/m after 3,000 hours
It was e.

[Brief explanation of the drawing]

The drawing is an explanatory diagram of a flow showing an example of an embodiment of the present invention. 1...Raw water 2...Coagulation sedimentation device 3...
・Sand filter tower 4...Storage tank 5...Washing wastewater
6...Cation exchange resin tower 7...Decarboxylation tower
8...Activated carbon filtration tower 9...Anion exchange resin tower 10...Reverse osmosis membrane device 11...Mixed bed polisher 12...Non-permeated water

Claims (1)

[Claims] Semiconductor wafer or chip cleaning wastewater is collected and mixed with raw water, and the mixed water is passed through a cation exchange resin tower, an activated carbon filtration tower, an anion exchange resin tower, a mixed bed tower of cation exchange resin and anion exchange resin, or a reverse osmosis membrane device. A method for producing cleaning water for semiconductor wafers or chips, comprising processing in the following order.