JP2003334550A - Ultrapure water and production method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide ultrapure water which contains only a trace of impurities and controls the adhesion of impurities to a semiconductor material, and a method for producing the ultrapure water. <P>SOLUTION: In the ultrapure water, the content of substances having a positive zeta potential is 0.3 ppb or below. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to ultrapure water and a method for producing the same. More specifically, it relates to high-purity pure water suitable for use in the electronic industry such as washing water used in the manufacturing process of VLSI and the like, and a method for manufacturing this pure water using an ion exchange resin. is there.

[0002]

2. Description of the Related Art As is well known, ion exchange resins are widely used in the fields of desalting water, refining solutions and the like. Currently, the most commonly used anion exchange resins are
It is a strongly basic anion exchange resin obtained by halomethylating a styrene-divinylbenzene cross-linked copolymer and then reacting this halomethyl group with a tertiary amine, or an anion exchange resin having a spacer group structure. On the other hand, as the strongly acidic cation exchange resin, a sulfonated product of a styrene-divinylbenzene cross-linked copolymer is used as an ion exchange resin for producing ultrapure water.

In the production process of ultrapure water, in the final production process, a so-called (cartridge) polisher in which a strongly acidic cation exchange resin and a strongly basic anion exchange resin are mixed is used, and an extremely small amount of metal ions and carbonates are added. In addition to ions, hydrogencarbonate ions, and silica ions, the eluate from the other ion exchange resin is captured.

At present, resistivity, TOC, fine particles, metal ion concentration, etc. are used as a scale for expressing the water quality of this ultrapure water. It is said that the improvement of these scientific indicators has led to the improvement of the yield of semiconductors. However, due to advances in silicon wafer miniaturization technology, it has become clear that such scientific indicators are not sufficient.

[0005] As the requirement level for removing impurities increases, it is becoming difficult to meet this requirement with the water quality of conventional ultrapure water. For example, it has been said that it is important to reduce TOC in ultrapure water in order to improve the yield of semiconductor manufacturing. However, since the semiconductor manufacturing process is complicated, the scientific basis for the causal relationship was not clear.

When forming the mixed bed type ion exchange resin bed according to the present invention, the mixing ratio of the anion exchange resin and the cation exchange resin is usually 1: 1 in terms of exchange capacity ratio. Furthermore, as one of the methods for producing ultrapure water, a strong basic anion exchange resin is placed in front of the cartridge polisher to capture the organic acid and inorganic acid components oxidatively decomposed in the previous TOC-UV step. It is also known. However, no attention has been paid to substances having a positive zeta potential derived from a strongly basic anion exchange resin, and no measures have been taken to reduce leakage of these substances.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide ultrapure water used for semiconductor manufacturing and the like, and ultrapure water in which impurities are hardly attached during cleaning and a method for producing the same.

As a result of intensive studies made by the present inventors in view of the above problems, a substance having a positive zeta potential is significantly related to the defective rate of products in semiconductor manufacturing, and the positive zeta potential in ultrapure water is high. The inventors have found that the yield rate of semiconductors can be improved by reducing the leakage of substances having the properties as much as possible, and reached the present invention.

[0009]

The summary of the present invention is as follows.
The content of substances having a positive zeta potential is 0.3 ppb
It exists in ultrapure water characterized by the following. Further, another gist of the present invention is an anion exchange resin having a repeating unit represented by the following general formula (1) and a general formula (2) below.
A method for producing ultrapure water is characterized in that raw water is passed through a mixed bed type ion exchange resin obtained by mixing a cation exchange resin having a repeating unit represented by

[0010]

[Chemical 3] (In the general formula (1), A represents an alkylene group having 1 or 3 to 8 carbon atoms or an alkyleneoxymethyl group having 4 to 8 carbon atoms, and R ₁ , R ₂ and R ₃ each independently have a carbon number. 1 to
6 represents an alkyl group having 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms, and X ⁻ represents a counter anion. )

[0011]

[Chemical 4] (In the general formula (2), Y ⁺ represents a counter cation.)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION TOC (total organic carbon content), specific resistance, metal concentration, fine particles and the like are used as a scale for expressing the water quality of ultrapure water. However, TOC is expressed as the total amount of organic carbon, but not all of them have an adverse effect on the manufacturing process of silicon wafers, but a certain specific component of the yield of the product in the manufacturing process of semiconductor silicon wafers and devices. We believe that there is a strong correlation with the decline.

It is known that both a bare silicon wafer and an oxide film silicon wafer have a negative zeta potential in most pH regions (Clean Technology 1996, Vol. 6, P30, Otsuka Electronics Co., Ltd.). ) Refer to the home page). This suggests that the organic compound component having a positive zeta potential contained in ultrapure water is likely to adhere to bare silicon or an oxide film silicon wafer.

Among the positively charged substances in ultrapure water, the inventors of the present invention, as a substance contaminating a semiconductor silicon wafer, have a polystyrene compound having an ammonium group derived from an anion exchange resin, or a strong acidic cation. Attention was focused on the ion complex of polystyrene sulfonate derived from the exchange resin. And, it has been found that controlling the substances whose zeta potential is positively charged is an important factor for reducing the contamination of the semiconductor silicon wafer.

On the basis of such a background, the ultrapure water of the present invention contains 0.3 p of the substance having a positive zeta potential.
It is characterized in that it is pb or less. by this,
In particular, when used for cleaning the semiconductor material, the adhesion of impurities onto the semiconductor material is small, and the contamination of the semiconductor material can be effectively reduced.

The content of the substance having a positive zeta potential in the ultrapure water of the present invention is usually 0.3 ppb or less as described above, but it is preferably 0.1 ppb or less. This further reduces the deposition of impurities on the semiconductor material, leading to a further reduction of contamination of the semiconductor material.

Further, the substance having a positive zeta potential contained in the ultrapure water of the present invention is a polystyrene compound having a trimethylammonium group, and the possibility that it is adsorbed on a silicon wafer is more remarkable. Here, the number average molecular weight of the polystyrene compound having a trimethylammonium group is preferably in the range of 400 or more and 100,000 or less.

On the other hand, in the present invention, in order to produce the ultrapure water of the present invention having the above characteristics, raw water is passed through a mixed bed type ion exchange resin obtained by mixing an anion exchange resin and a cation exchange resin. A liquid manufacturing method is used. Here, in this specification, raw water refers to water that is a material for producing ultrapure water. There are no particular restrictions on the type of raw water, and various types of water may be used depending on the situation, such as water that has not been purified and water that has been purified (primary purified) in the previous stage.

Here, in the method for producing pure water of the present invention, a polystyrene compound having a repeating unit represented by the following general formula (1) is used as the anion exchange resin constituting the mixed bed type ion exchange resin.

[0020]

[Chemical 5]

In the above general formula (1), A is a linear or branched alkylene group having 1 or 3 to 8 carbon atoms or an alkyleneoxymethylene group having 4 to 8 carbon atoms. It is bonded to the benzene ring at a part. Among them, A is a linear or branched alkylene group having 3 to 8 carbon atoms, or an alkyleneoxymethyl group having 4 to 8 carbon atoms, which is bonded to the benzene ring at the portion of the methylene group. Is preferred. Examples of the alkylene group represented by A include a trimethylene group, a tetramethylene group, and a hexamethylene group. Further, examples of the alkyleneoxymethylene group include a tetramethyleneoxymethylene group and a hexamethyleneoxymethylene group.

The substituent represented by R ₁ , R ₂ and R ₃ which is bonded to the nitrogen atom is a hydrogen atom, an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms. , A hydrogen atom, an alkyl group having 1 to 4 carbon atoms, 1 to 4 carbon atoms
A hydroxyalkyl group of 4 is preferred. Furthermore, when the portion of the ammonium group excluding the substituent A is specifically mentioned,
Trimethylammonium group, triethylammonium group,
Examples thereof include a dimethyl hydroxyethyl ammonium group and a dimethyl hydroxypropyl ammonium group. Of these, a trimethylammonium group or a dimethylhydroxyethylammonium group is particularly preferable.

The anion exchange resin used in the mixed bed type ion exchange resin bed in the present invention is essentially composed of the repeating unit represented by the above general formula (1) and a crosslinking group. The most common bridging group is the divinylbenzene unit. When a divinylbenzene unit is used as a crosslinking group, the anion exchange resin used in the present invention usually contains 1 to 99 mol% of repeating units represented by the general formula (1) and 0.1 to 50 mol of divinylbenzene units. It consists essentially of% and. Generally, it is preferable that the neutral salt decomposing ability is large, and therefore, it is preferable that the proportion of the repeating unit represented by the general formula (1) is as large as possible.

The anion exchange resin used in the present invention is
When it essentially consists of a repeating unit having a quaternary ammonium group as an anion-exchange group and a divinylbenzene unit, its neutral salt decomposing ability is usually the dry resin 1
The OH form is preferably 0.1 to 5.0 meq, and more preferably 2.5 to 4.5 meq, per g. The neutral salt decomposition capacity per 1 mL of wet resin is usually 0.1 to 2.
It is 0 meq, but preferably 0.5 to 1.5 meq.

On the other hand, in the method for producing pure water of the present invention, as the cation exchange resin constituting the mixed bed type ion exchange resin,
A polystyrene compound having a repeating unit represented by the following general formula (2) is used.

[0026]

[Chemical 6] (In the general formula (2), Y ⁺ represents a counter cation.)

Examples of Y include hydrogen ion, sodium ion, magnesium ion, calcium ion and the like. Further, since the strongly acidic cation exchange resin captures metal ions, Fe ions, Ni ions, C
Metal ions such as o ion, Zn ion, Al ion,
As an example of Y. When the cation exchange resin represented by the general formula (2) is used as the resin for polisher, the counter cation Y ⁺ is preferably a hydrogen ion type.

The cation exchange resin used in the present invention is also
It essentially consists of a repeating unit represented by the general formula (2), a divinylbenzene unit, and a crosslinking group. The most common bridging group is the divinylbenzene unit. When a divinylbenzene unit is used as a crosslinking group, the cation exchange resin used in the present invention usually contains 1 to 99 mol% of repeating units represented by the general formula (1),
Although it is essentially composed of 0.1 to 50 mol% of divinylbenzene units, it is generally preferable that the ion exchange capacity is large, and therefore the ratio of the repeating unit represented by the general formula (2) is preferably as large as possible. preferable.

The neutral salt decomposing ability of the cation exchange resin used in the present invention is usually 0.1 to H type per 1 g of dry resin.
It is 5.0 meq and preferably 3.0 to 4.5 meq. The neutral salt decomposing capacity per 1 mL of the wet resin is usually 0.1 to 2.0 meq, but 0.8 to 1.
It is preferably 9 meq.

Generally, the eluate derived from the ion exchange resin is mainly the eluate produced by the production process immediately after the resin is produced, but after the resin is sufficiently washed, it is derived from the linear polymer from the resin. Is believed to be. Examples of the substance having a positive zeta potential derived from the anion exchange resin include trimethylamine, dimethylamine, ammonia derived from the anion exchange group, polytrimethylbenzylammonium salt derived from the polymer skeleton of the anion exchange resin, and polytrimethylstyrylalkylammonium. salt,
Examples include polydimethylbenzylamine, polydimethylstyrylalkylamine, and salts thereof.

Examples of the counter ion of ammonium salt include halide ions such as hydroxide ion, chloride ion, bromide ion, fluoride ion, hydrogen carbonate ion, carbonate ion, sulfate ion, nitrate ion, silica ion and the like. To be Among these, hydroxide ions are particularly likely to contaminate the silicon wafer.

The styrene polymer having an ammonium group includes not only a single molecule but also a high molecular weight substance. The impurities eluted from the anion exchange resin differ depending on the degree of crosslinking of the anion exchange resin, but the molecular weight of the ammonium salt polymer is 400 or more and 100,000 or less. The molecular weight of the ammonium salt polymer is TOF-M.
Measured by S.

Among these eluates derived from ion-exchange resins, among others, ammonium salt polymers such as polytrimethylbenzylammonium salt and polytrimethylstyrylalkylammonium salt (hereinafter, PSQ may be abbreviated as a generic term for ammonium salt polymers). .) Does not volatilize even after adhering to the silicon wafer, and is apt to cause contamination.

When the anion exchange resin is used in a single bed,
The ammonium salt polymer is dissolved alone in pure water, depending on its concentration. On the other hand, when used in a mixed bed with a cation exchange resin, it is considered that polystyrene sulfonic acid (hereinafter sometimes abbreviated as PSA) and PSQ form an ionic complex. In either case, the polymer containing PSQ may adhere to the silicon wafer and cause contamination. Contamination of the silicon wafer by this complex depends on the ratio of the cation exchange resin and the anion exchange resin, and when the ratio of PSA derived from the cation exchange resin in the complex is high, it is difficult to adhere to the silicon wafer.

The molecular weight of PSA to be eluted also differs depending on the degree of crosslinking of the cation exchange resin, the production method and the use conditions. Also,
Generally, the higher the molecular weight of the both and the higher the concentration of the solution, the easier the ionic complex is formed. Both linear polymers each form a complex complex and grow large. Its size reaches several nm to several 100 nm. The composition ratio of both linear polymers varies depending on the composition ratio of both ion exchange resins of the cartridge polisher and the elution property from the resin.

The contamination property of a silicon wafer greatly depends on the processing temperature. A substance having a positive zeta potential has a high temperature (specifically, usually 30 ° C or higher, further 50 ° C or higher,
In particular, when it contacts a silicon wafer at a temperature of 70 ° C. or higher), it is likely to adhere. Therefore, it is desirable to treat the silicon wafer with pure water whose temperature is as low as possible without impairing the cleaning property. The temperature of the water is usually 30 ° C. or lower, preferably 20 ° C. or lower, more preferably 15 ° C. or lower,
It is usually 1 ° C or higher.

Ultrapure water for semiconductors is usually produced by producing primary pure water, passing through a TOC-UV step, passing a mixed bed resin (cartridge polisher), and finally microfiltration with a UF membrane. Has been done. The organic matter oxidatively decomposed in the TOC-UV step is captured by the mixed bed resin as organic acid, carbon dioxide gas, hydrogen carbonate ion, and sulfate ion. There is also a manufacturing method in which a single bed of anion exchange resin is arranged in the front stage or the upper layer of this mixed bed resin. The eluate from the strongly basic anion exchange resin often leaks, including the case where the anion exchange resin is placed in front of the mixed bed resin, which may cause contamination of the silicon wafer.

Based on such a background, in the present invention, from the viewpoint of suppressing the leakage of the linear polymer derived from the anion exchange resin as much as possible in the final stage of purification with the secondary ion exchange resin, the cation exchange resin / anion exchange resin is used. The mixing ratio of the resins is preferably in the range of 1.1 to 3.0 in terms of neutral salt decomposing ability. In the mixed bed resin,
It is preferable that the particles of the cation exchange resin and the particles of the anion exchange resin are present in a state of being mixed as uniformly as possible.
By doing so, the ion exchange reaction close to an infinite stage is repeated in the ion exchange resin bed, and impurities are removed to the utmost limit.

Further, in order to capture the eluate derived from the anion exchange resin as much as possible, it is preferable to dispose a mixed bed resin having a high exchange ratio of the strongly acidic cation exchange resin in the lower layer or the latter stage of the cartridge polisher. Also,
It is preferable to prepare a mixed bed resin of a cation exchange resin / anion exchange resin so that the ratio of neutral salt decomposing ability is usually in the range of 1.1 or more and 3 or less, particularly 1.2 or more and 2 or less. As a result, the elution amount of the linear polymer from the anion exchange resin was decreased, so that the elution amount from the cation exchange resin was increased, but it was found that the influence on the contamination property of the silicon wafer was extremely small. The physical structure of the cation exchange resin and the anion exchange resin used here may be a gel type resin or a porous type resin, but it is a resin structure capable of capturing a linear polymer for as long as possible. Is desirable.

Here, the silicon wafer includes a bare wafer in which an oxide film is dissolved by cleaning (sulfuric acid, nitric acid, hydrogen peroxide solution, HF, ammonia water, etc.) and an oxide wafer in which an oxide film is formed. Since both wafers have a negative zeta potential in the entire pH range, positively charged substances are likely to adhere to the silicon wafer. However, since the oxide film wafer is generally more hydrophilic, the ammonium salt polymer is more likely to adhere to the oxide film wafer. Therefore,
Since the silicon wafer on which the oxide film is formed is easily contaminated, care must be taken when cleaning with ultrapure water.

It has been found that a method of producing ultrapure water at a low temperature is effective as a method of reducing the amount of eluate from the anion exchange resin and a method of preventing the silicon wafer from being contaminated.

Normally, ultrapure water is produced at room temperature / air conditioning temperature, so the water temperature of ultrapure water is around 25.degree. On the other hand, when the anion exchange resin represented by the general formula (1) and the cation exchange resin represented by the general formula (2) are used at a lower temperature than at room temperature, The amount of eluate is small and TOC can be reduced more effectively. Suitable temperature is usually 20 ° C. or lower, further 15 ° C. or lower, especially 10 ° C. or lower, and usually 1
℃ or above.

When the liquid is passed at a low temperature, the water to be passed may be cooled in advance, or an ion exchange device equipped with an ion exchange resin (usually a column packed with the ion exchange resin) may be cooled. Alternatively, the water may be cooled during the passage. Even when the water to be passed is not cooled in advance, it is preferable that the temperature is 1 ° C. or higher and 15 ° C. or lower at least at the outlet of the apparatus.

The cation exchange resin which forms the mixed bed type ion exchange resin bed used in the method for producing ultrapure water of the present invention in combination with the above-mentioned anion exchange resin is represented by the above general formula (2). It has a unit. This is a sulfonated product of a copolymer of styrene and a crosslinking agent, usually divinylbenzene. The proportion of the cross-linking agent in the copolymer is usually in the range of 1 to 50% by weight, and preferably in the range of 3 to 30% by weight.

As the water-soluble polymer having a dissociative group,
Usually, the number average molecular weight by gel permeation chromatography or the molecular weight by TOF-MS is 4 × 1.
A material having a range of 0 ² to 1 × 10 ⁶ is used. Of this range, the range is preferably 1 × 10 ^{3 to} 5 × 10 ⁵ , and particularly preferably 4 × 10 ³ to 1 × 10 ⁵ . When the molecular weight of the water-soluble polymer is too small, the water-soluble polymer that should originally neutralize the surface charge diffuses into the ion exchange resin, which is not preferable. On the contrary, if the molecular weight is too large, the diffusion of ions is hindered, which is not preferable.

The concentration of alkylamine in water at the outlet of the column largely changes depending on the water flow rate (space velocity) and the water flow temperature. Here, the space velocity (hereinafter abbreviated as SV) is a parameter indicating how many times the resin volume of the solution is passed in one hour. Generally, the water flow rate when producing ultrapure water is
SV10 to SV1000. More preferably, S
V50 to SV500. The larger SV dilutes the eluate from the resin, particularly the substance having a positive zeta potential. Therefore, it is important to set SV as large as possible.

[0047]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to the following examples, and various modifications may be made without departing from the scope of the invention. It is possible to

[Example 1] It was verified by Example 1 that PSQ (polytrimethylbenzylammonium salt) contaminating PSQ, which is a typical eluate of anion exchange resin, contaminates silicon wafers.

<Preparation of Ultrapure Water for Testing> The ultrapure water used here was used as a resin for polisher, Diaion ^R
(Diaion is a registered trademark of Mitsubishi Chemical) SMT1200
Was used. Raw water obtained by using a known anion exchange resin for this resin was passed through SV800. Specific resistance 18.2
The concentration of the compound having 4 MΩ · cm, TOC of 0.1 ppb, the number of fine particles of 0.05 μm or more is 1 / mL or less, and the compound having a positive zeta potential is 0.05 ppb. The TOC of this ultrapure water was measured online using an Anatel TOC meter. Further, a compound having a positive zeta potential is T
It was measured by an OF-MS and a laser surface inspection device.

A bare wafer and an oxide film silicon wafer were prepared by the following processing. <Wafer Pretreatment> As a silicon wafer, a 4-inch silicon wafer (manufactured by Sumitomo Sitix, SC2 cleaning product) was used, and the following treatments were performed and then used in the experiment. The oxide film wafer was prepared by the following method. A predetermined number of silicon wafers are arranged on a PFA carrier, washed with the above ultrapure water for 10 minutes, and SC1 (water: H ₂ O ₂ : NH ₄ OH =
It was immersed in a 5: 1: 1 cleaning solution) for 10 minutes, and then further washed with ultrapure water for 10 minutes, and used for the experiment. The bare wafer was prepared by the following method. In the same manner as for the oxide film wafer, the above-mentioned ultrapure water was washed for 10 minutes, immersed in SC1 for 10 minutes, washed with ultrapure water for 10 minutes, and then washed with 0.5% H
What was washed with F aqueous solution for 5 minutes and washed with ultrapure water for 10 minutes was used for the experiment.

<Forced Contamination Experiment> An aqueous solution of PSQ used in the forced contamination experiment was prepared by the following method. As PSQ, Mitsubishi Chemical's PSQ-A (molecular weight about 10,000)
The counter ion was converted to the OH form in a 5.6% aqueous solution of. A predetermined amount of the above-mentioned ultrapure water was placed in a quartz container equipped with a thermometer and a heater, and the PSQ aqueous solution was added thereto to a desired concentration, and the liquid temperature was adjusted to 25 ° C. A predetermined number of pretreated silicon wafers were arranged on a PFA carrier and immersed in a PSQ aqueous solution for 10 minutes. P
The concentration of SQ is 0.1ppm, 1.0ppm, 10pp
m. After dipping the wafer in the PSQ aqueous solution, 1
It was washed for 0 minutes, dried using a spin drier, and surface-analyzed. To evaluate the contamination of silicon wafers,
Hitachi Electronic Engineering's laser surface inspection equipment:
LS-5000 was used. The number of deposits having a size of 0.2 μm or more was measured to evaluate the contamination property. The results are shown in Table 1 below.

[0052]

[Table 1] The concentrations in Table 1 above are expressed as the concentration per N atom.
The PSQ reveals that the silicon wafer is contaminated.

Example 2 Evaluation of PSQ Contamination Property In Example 2, the silicon wafer was contaminated under the same conditions as in Example 1 except that the contact temperature with the PSQ aqueous solution was raised from 25 ° C. to 70 ° C. The sex was evaluated. The results are shown in Table 2 below.

[0054]

[Table 2] The concentrations in Table 2 above are also expressed as the concentration per N atom.
In addition, the fact that measurement is impossible in Table 2 above means that PSQ has adhered to the entire surface of the silicon wafer and cannot be detected as particles,
As a result, it means that it cannot be measured. It can be seen that the silicon wafer is more contaminated due to the increase in the contact temperature with the PSQ aqueous solution.

Example 3 Verification of Contamination Property of PSA (Polystyrene Sulfonic Acid) PSA which is also a typical eluate of anion exchange resin.
It was verified according to Example 3 whether or not it would contaminate the silicon wafer. The experiment was performed under the same conditions as in Example 1 except that PSQ was replaced with PSA. As the PSA, a product obtained by converting the counter ion into H form in a 20% aqueous solution of PS-1 (molecular weight of about 10,000) manufactured by Tosoh Corporation was used. The results are shown in Table 3 below.

[0056]

[Table 3] The concentrations in Table 3 above are expressed as the concentration per S atom. P
It can be seen that the silicon wafer is contaminated by PSA as well as SQ.

Example 4 Verification of Contamination Property in PSQ / PSA Mixing System It was verified in Example 4 whether PSQ and PSA were mixed to contaminate a silicon wafer. The experiment is
Same as Example 1 except that the contact temperature with the solution was 70 ° C., and that the PSA aqueous solution was added to the PSQ aqueous solution and the immersion of the silicon wafer was started after stirring for 5 minutes. It was performed under the conditions. As the respective aqueous solutions of PSQ and PSA, those similar to those in Examples 1 and 2 and Example 3 were used. The results are shown in Table 4 below.

[0058]

[Table 4] The concentrations in Table 4 above represent the concentration per N atom in the case of PSQ and the concentration per S atom in the case of PSA. PSQ
It can be seen that the silicon wafer is contaminated even if PSA and PSA are mixed.

Example 5 Comparison of Contamination between Polytrimethylbenzylammonium Salt (PSQ) and Polytrimethylstyrylbutylammonium Salt (PBSQ) PBSQ manufactured by Mitsubishi Chemical was used. Example 5 was carried out under the same conditions as in Example 1 except that PSQ and PBSQ were respectively added after the temperature of the solution was raised to 70 ° C., and immersion of the silicon wafer was started after 5 minutes had elapsed. It was An oxide film wafer was used as the silicon wafer. The results are shown in Table 5 below.

[0060]

[Table 5] The concentrations in Table 5 above are expressed as the concentration per N atom in both PSQ and PBSQ. It can be seen that PBSQ has less contamination than PSQ.

[0061]

The present invention provides ultrapure water with less contamination of silicon wafers in semiconductor manufacturing. INDUSTRIAL APPLICABILITY The present invention improves the yield of products and greatly improves the productivity in semiconductor manufacturing applications that require high-quality ultrapure water. This effect is remarkable.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshimune Aozaki             1-1 Kurosaki Shiroishi, Hachiman Nishi Ward, Kitakyushu City, Fukuoka Prefecture               Within Mitsubishi Chemical Corporation F-term (reference) 4D025 AA04 AB08 AB14 AB38 BA09                       BA14 BB04 BB07 CA08 CA10

Claims (11)

[Claims] 1. Ultrapure water, characterized in that the content of a substance having a positive zeta potential is 0.3 ppb or less. 2. The ultrapure water according to claim 1, wherein the content of the substance having the positive zeta potential is 0.1 ppb or less. 3. The substance having the positive zeta potential is:
The ultrapure water according to claim 1 or 2, which is a polystyrene compound having a trimethylammonium group. 4. The number average molecular weight of the polystyrene compound having a trimethylammonium group is 400 or more and 1 or more.
The ultrapure water according to any one of claims 1 to 3, characterized in that the ultrapure water is in a range of 0,000 or less. 5. The ultrapure water according to claim 1, which contains a polystyrene compound having a sulfonic acid group. 6. A mixed bed system comprising a mixture of an anion exchange resin having a repeating unit represented by the following general formula (1) and a cation exchange resin having a repeating unit represented by the following general formula (2). A method for producing ultrapure water, which comprises passing raw water through an ion exchange resin. [Chemical 1] (In the general formula (1), A represents an alkylene group having 1 or 3 to 8 carbon atoms or an alkyleneoxymethyl group having 4 to 8 carbon atoms, and R ₁ , R ₂ and R ₃ are each independently a hydrogen atom. ,
It represents an alkyl group having 1 to 6 carbon atoms or a hydroxyalkyl group having 1 to 6 carbon atoms, and X ⁻ represents a counter anion. ) [Chemical 2] (In the general formula (2), Y ⁺ represents a counter cation.) 7. The ultrapure water according to claim 6, wherein A in the general formula (1) represents an alkylene group having 3 to 8 carbon atoms or an alkyleneoxymethyl group having 4 to 8 carbon atoms. Manufacturing method. 8. An anion exchange resin having a repeating unit represented by the general formula (1) and a cation having a repeating unit represented by the general formula (2) in a lower layer of the mixed bed type ion exchange resin. The method for producing ultrapure water according to claim 6 or 7, wherein the mixed bed ratio of the exchange resin is in the range of 1.1 or more and 3.0 or less in terms of exchange capacity ratio. 9. The temperature of the raw water passing through the mixed bed type ion exchange resin is in the range of 1 ° C. or higher and 15 ° C. or lower, according to claim 6. Method for producing ultrapure water. 10. The ultrapure water according to claim 6, wherein the raw water is passed through the mixed bed type ion exchange resin under conditions of a space velocity SV of 100 or more. Manufacturing method. 11. The ultrapure water according to claim 6, wherein the raw water is passed through the mixed bed type ion exchange resin under conditions of a space velocity SV of 300 or more. Manufacturing method.