JP2008145384A - Method for evaluating ion-exchange resin - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an evaluation method for simple, easy and high-sensitivity selection of ion-exchange resin, that is suitable for manufacturing ultrapure water for reducing the degree of etching on the surface of a silicon material, when the ultrapure water, used as cleaning water, is to be produced during the manufacturing of semiconductor or liquid crystals. <P>SOLUTION: After the extra-pure water passes through a column filled with the ion-exchange resin and is brought into contact with the silicon material, by comparing the concentration of silica contained in the ultrapure water and the concentration of silica contained in the ultrapure water, obtained by bringing the ultrapure water into contact with the silicon material, without making the ultrapure water pass through the column filled, with the ion-exchange resin, ion-exchange resin which is suitable for manufacturing the ultrapure water for cleaning the silicon material is selected. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for evaluating an ion exchange resin, and more particularly, to a method for evaluating an ion exchange resin for production of ultrapure water that evaluates the elution of amines that cause etching of a silicon wafer.

  Ultrapure water is used in semiconductor manufacturing processes such as IC and LSI, liquid crystal manufacturing processes, pharmaceutical manufacturing processes, and the like. Ultrapure water used in such fields usually produces primary pure water in a primary pure water production system containing an ion exchange resin, and the obtained primary pure water is ion exchange resin, ultraviolet oxidation, Impurities are further removed to achieve a high purity by treatment in a secondary pure water production system including reverse osmosis membrane treatment.

  In such ultrapure water, particularly as ultrapure water used as cleaning water in the semiconductor manufacturing process, the impurities contained therein are maintained at a very low concentration as the degree of integration of semiconductor integrated circuits increases and miniaturization progresses. It has been sought to do. As impurities contained in such ultrapure water, it is known that there are organic substances as well as fine particles, bacteria, metal elements and the like. Among these, with respect to metal elements such as iron and zinc, recent ultrapure water is required to be 1 ng / L or less. The organic matter is measured as total organic carbon (TOC), but in recent years, the TOC concentration is required to be 1 μg / L or less.

  As shown in the International Semiconductor Manufacturing Technology for Semiconductor Roadmap (ITRS), in the semiconductor manufacturing process, as the definition of semiconductor devices increases, maintaining the cleanliness of the silicon wafer surface, Maintaining flatness is becoming important.

  It has long been known that the surface of a silicon wafer is etched in the presence of certain amines (eg, RM Finne and DL Klein, A Water-Amine-Complexing Agent System For Etching). (Silicon, J. Electrochemical Soc .: SOLID STATE SCIENCE, p965, September 1967, etc.), and further, it is known that surface roughness of the silicon wafer due to amines becomes a problem in manufacturing semiconductor devices (Japanese Patent Laid-Open No. 2003-2003). 142447). Therefore, in the semiconductor manufacturing process, it is necessary to use water with less roughness on the surface of the silicon wafer when cleaning with ultrapure water, and it is determined whether the water used is water that etches the silicon wafer surface or not. It is extremely important industrially. Therefore, a method for evaluating the quality of ultrapure water using the degree of influence of ultrapure water on a silicon wafer has also been proposed (Japanese Patent Laid-Open No. 2006-29880).

On the other hand, depending on the method for producing ultrapure water, amines eluted from an ion exchange resin or the like may be mixed during the production process. It is also known that when a silicon wafer is cleaned using ultrapure water mixed with amines, an undesirable etching action is caused in the rinsing process. Therefore, conventionally, as an evaluation method for selecting an ion exchange resin suitable for producing ultrapure water, resistance of treated water flowing out of the column by passing ultrapure water through a column packed with ion exchange resin is used. The ratio, TOC concentration, and low molecular weight amine concentration such as trimethylamine were measured, and those having lower concentrations were judged to be better quality ion exchange resins.
JP 2003-142447 A JP 2006-29880 A

  Even if the concentrations of TOC and amines eluted from the ion exchange resin for the evaluation of the ion exchange resin were measured, it was unclear what kind of trouble occurred in semiconductor manufacturing when these impurity concentrations were high. . Also, when problems such as product performance degradation occur in the semiconductor manufacturing process, even if you try to find the cause by measuring the impurity concentration in ultrapure water, the causal relationship between impurities and performance degradation is unknown, There were many cases that could not be solved.

  Under the circumstances, the present invention is an ion exchange resin used for producing ultrapure water used as cleaning water for manufacturing semiconductors and liquid crystals, in particular, using the degree of influence on a silicon wafer as an index. It aims at providing the evaluation method for selecting the ion exchange resin suitable for ultrapure water manufacture simply and with high sensitivity.

  Therefore, as a result of intensive studies on the relationship between the etching property of silicon and the concentration of eluted silica by utilizing an analysis method of extremely small amount of silica in water, the inventor has found that water in which a silicon wafer is brought into contact with water that can easily etch silicon. The silica concentration in the water was relatively high and the silica elution into water with little etching was found, and the present invention was completed based on this finding.

  The present invention is the following ion exchange resin evaluation method.

  (1) After passing ultrapure water through a column packed with an ion exchange resin and then bringing the ultrapure water into contact with a silicon substance, the silica concentration contained in the ultrapure water and the ion exchange resin After bringing ultrapure water into contact with the silicon substance without passing through the packed column, the silica concentration contained in the ultrapure water is determined, and the quality of the ion exchange resin is determined based on the difference in the silica concentration. An evaluation method of an ion exchange resin characterized by evaluating.

  (2) In the above (1), the silicon substance to be contacted with ultrapure water is a silicon wafer, a piece or powder of silicon wafer, granular silicon, a piece of silicon crystal, or a combination of these. The evaluation method of the ion exchange resin of description.

  That is, if silica in a high concentration is contained in water in contact with silicon, it can be determined that the water can etch the silicon surface and damage the flat wafer surface.

  Therefore, ultrapure water that has been passed through a column filled with ion exchange resin is brought into contact with the silicon substance as described above, and the silica concentration in the water at this time is measured. In the same way, the silica concentration in water measured by contacting ultrapure water with a silicon substance is compared, and when the difference between them is large, it can be determined that a large amount of the substance that etches silicon is eluted from the ion exchange resin. it can. By contacting ultrapure water with a silicon substance in this way and measuring the concentration of the eluted silica, whether the ultrapure water is likely to etch silicon, that is, a substance that causes problems in semiconductor manufacturing is ion-exchanged. It is possible to provide a method for determining whether or not it is eluted from the resin and contained in water.

  According to the method for evaluating an ion exchange resin of the present invention, ultrapure water is passed through an ion exchange resin column and then contacted with a silicon substance to measure the silica concentration in the ultrapure water. Since it is possible to easily determine whether ultrapure water in contact with the resin has the property of etching the silicon wafer surface, select an ion exchange resin for producing ultrapure water that does not easily elute substances that etch the silicon wafer surface. It becomes possible. By selecting and using an ion exchange resin suitable for ultrapure water production, it is extremely effective in preventing the occurrence of defects in semiconductor production.

Since silicon is etched with an alkali and alkaline when an amine is present in water, etching of the silicon surface due to the presence of an amine is considered to be an alkali etching. Silicon dissolved by alkali elutes in water in the form of Si (OH) ₄ , which dissociates and exists as ionic silica (usually expressed as SiO ₂ ).

Ionic silica SiO _{2 in} water reacts with molybdate ions to form a molybdate complex, which absorbs light having a wavelength of about 440 nm, or that this reductant absorbs light of about 880 nm. It is used for analysis of silica concentration.

  Therefore, after passing ultrapure water through the ion exchange resin column, measure the silica concentration in the ultrapure water in contact with the silicon substance such as silicon wafer or silicon crystal fragments, By comparison, the silica concentration increased by contact with the ion exchange resin can be measured. As the amine concentration in the water in contact with the silicon material increases, the amount of silicon that elutes, ie the silica concentration in the water, also increases, so water can be passed through the silicon by monitoring the silica concentration periodically or continuously. Changes in water quality can be monitored in the form of the degree of etching into silicon. In addition, by making the contact condition with silicon constant, it is possible to compare and compare the degree of etching of silicon into a plurality of water.

The silica concentration to be detected is not necessarily the SiO ₂ concentration, and any physical quantity (for example, light absorbance (absorbance), etc.) that can detect the change in silica concentration described above may be used. As long as it is constant, a physical property value such as electrical resistance may be used.

  In the method for evaluating an ion exchange resin of the present invention, as a method for bringing ultrapure water into contact with the ion exchange resin, any container provided with an inlet and an outlet of ultrapure water is filled with the ion exchange resin, and ultrapure water is used. As long as the ultrapure water can be taken out from the container after contacting with the ion exchange resin, various containers can be used. Considering efficient contact between the ultrapure water and the ion exchange resin and a small amount of amine concentration eluted from the ion exchange resin, a method of passing ultrapure water through the column filled with the ion exchange resin is desirable.

  The ultrapure water that passes through the ion-exchange resin can be used as long as the silica concentration is low enough to detect the silica concentration eluted from the subsequent silicon material, but the silica concentration is extremely low and other impurities can be used. It is desirable to use ultrapure water that contains almost no water. Such ultrapure water preferably has a specific resistance of 18 megohm · centimeter or more and a silica concentration of 1 μg / L or less.

  As the silicon substance that contacts the ultrapure water that has passed through the ion exchange resin column, it is only necessary to determine whether or not the ultrapure water has the property of etching the silicon wafer. A small piece of silicon, a powder of silicon wafer, granular silicon, a small piece of silicon crystal, or a combination of these can be suitably used. It is preferable to use high purity silicon. In addition to a single crystal, a silicon polycrystal can be used as the silicon crystal. A silicon wafer is preferably used as the high purity silicon material. Moreover, it is desirable that the silicon material used for the evaluation of the ion exchange resin of the present invention is used after removing the natural oxide film formed on the surface of the silicon material. For this purpose, a natural oxide film formed on the surface can be removed by immersing a silicon substance in dilute hydrofluoric acid prepared to a concentration of 0.1 to 1.0% by weight.

  As a method of bringing ultrapure water into contact with the silicon material as described above, it is only necessary to put the silicon material into a container and pass ultrapure water therethrough, and various methods can be used, but simple and efficient. In order to make contact, a method of passing ultrapure water through a column filled with a silicon substance is preferable. In this case, there is no particular limitation on the size of the silicon substance packed in the column. However, considering the contact efficiency and pressure loss, it is usually 0.1 to 5 mm, preferably 0.3 to 1 mm. it can. Moreover, the column length is usually 20 to 200 mm, preferably 50 to 150 mm. The flow rate of ultrapure water through the column filled with the silicon substance is usually 10 to 200 ml / min, preferably 50 to 150 ml / min.

  As a method for detecting the silica concentration in ultrapure water contacted with a silicon substance, in addition to the silica concentration measurement method based on the absorbance of the molybdate complex, concentration analysis by ion chromatography, inductively coupled plasma-mass spectrometry (ICP-) MS), atomic absorption spectrophotometry such as graphite furnace atomic absorption spectrophotometry (GF-AA), and other methods capable of detecting silica (silicon oxide) in water are applicable.

  By utilizing the present invention as described above, ultrapure water capable of keeping the silicon wafer surface flat can be produced. In other words, it becomes possible to compare and examine ion exchange resins that are less likely to elute substances that etch the silicon wafer surface, and it is possible to easily select ion exchange resins for ultrapure water production that do not cause problems during semiconductor or liquid crystal production. become able to.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited to these examples.

[Example 1]
In FIG. 1, the aspect of one Example of the silicon substance contact apparatus 1 used for evaluation of the ion exchange resin of this invention is shown. A fluororesin column 6 having an inner diameter of 8 mm and a length of 10 cm is packed with about 5 ml of silicon particles 7 having a diameter of about 0.5 mm, and the ends of the fluororesin column 6 are removed using tube joints 4 and 5. Fluororesin tubes 8 and 9 having a diameter of 6 mm were connected. Cocks 2 and 3 were attached to the inlet and outlet sides of the column 6 so that they could be closed.

  Ultra pure water is supplied to the silicon substance contact device 1 using a small flow pump (not shown), air is removed from the inside of the fluororesin column 6 filled with silicon particles 7, and then a plastic syringe is used. Then, 5 ml of diluted hydrofluoric acid prepared to a concentration of 0.5% by weight was injected. After injecting dilute hydrofluoric acid, it was allowed to stand for 2 minutes to remove the natural oxide film on the surface of the silicon particles. Thereafter, 15 ml of ultrapure water was injected to remove dilute hydrofluoric acid inside the column.

  Using a small flow rate pump, 200 ml of ultrapure water was supplied to the column 6 at a rate of 100 ml per minute, and the water discharged from the fluororesin tube 9 provided on the outlet side of the column was received in a clean container. As a result of analyzing the silica concentration using the silica analysis method by molybdenum blue described in JIS K-0101 Industrial Water Test Method, this discharged water showed a concentration of 80 μg / L.

  On the other hand, two acrylic columns having an inner diameter of 50 mm and a length of 1 m were prepared, one of which was filled with 1 L of brand A anion exchange resin, and the other column was filled with 1 L of brand B anion exchange resin. . Ultrapure water was passed through each of the two acrylic columns filled with these resins at a flow rate of 1 L / min for 5 hours, and the column outlet water after 5 hours was collected.

  In the same manner as described above, a column of silicon material contact apparatus in which silicon particles are packed in a fluororesin column and the natural oxide film on the surface of the silicon particles is removed with dilute hydrofluoric acid. 200 ml of outlet water was passed. The silica concentration of the discharged water obtained from the column packed with silicon particles was analyzed by the silica analysis method described in JIS K-0101. As a result, 140 μg / L was passed through the treated water of the brand A anion exchange resin through the silicon particle packed column, and the treated water of the brand B anion exchange resin was passed through the silicon particle packed column. 95 μg / L of silica was detected in the other discharged water. The results are summarized in Table 1.

この結果から、銘柄Ａの陰イオン交換樹脂処理水のシリカ濃度は、超純水（ブランク）を通水したシリカ濃度に比べて６０μｇ／Ｌ増加し、銘柄Ｂの陰イオン交換樹脂処理水のシリカ濃度は１５μｇ／Ｌ増加したことがわかる。つまり、銘柄Ｂの陰イオン交換樹脂に比べて銘柄Ａの陰イオン交換樹脂の方がシリコン表面をエッチングする成分がより多く溶出したということがわかる。これより、銘柄Ｂの陰イオン交換樹脂を使用して超純水を製造することによって、銘柄Ａを使用した時よりもシリコンウエハ表面へのダメージが少ない超純水を製造することができると判断される。

From this result, the silica concentration of the anion exchange resin treated water of the brand A is increased by 60 μg / L compared with the silica concentration of the ultrapure water (blank) passed through, and the silica of the anion exchange resin treated water of the brand B It can be seen that the concentration increased by 15 μg / L. In other words, it can be seen that the anion exchange resin of brand A eluted more of the components that etch the silicon surface than the anion exchange resin of brand B. From this, it is determined that by producing ultrapure water using the anion exchange resin of brand B, ultrapure water can be produced with less damage to the silicon wafer surface than when brand A is used. Is done.

It is the aspect of one Example of the silicon substance contact apparatus used for evaluation of the ion exchange resin of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Silicon substance contact apparatus 2 Inlet side cock 3 Outlet side cock 4, 5 Tube joint 6 Fluororesin column 7 Silicon particle 8, 9 Fluororesin tube

Claims (2)

  Ultrapure water is passed through a column filled with an ion exchange resin, and then the ultrapure water is brought into contact with a silicon substance, and then the silica concentration contained in the ultrapure water and the column filled with the ion exchange resin are filled. After bringing ultrapure water into contact with a silicon substance without passing through the water, the silica concentration contained in the ultrapure water is obtained, and the quality of the ion exchange resin is evaluated based on the difference in the silica concentration. Evaluation method of ion exchange resin characterized by this.   2. The ion exchange according to claim 1, wherein the silicon substance brought into contact with the ultrapure water is a silicon wafer, a piece or powder of silicon wafer, granular silicon, a piece of silicon crystal, or a combination thereof. Evaluation method of resin.

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