JP2007170863A - Water-quality evaluation method, ultrapure water evaluation device using the same and ultrapure water producing system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a water-quality evaluation method for readily evaluating the etching functionality of ultrapure water used as washing water for manufacturing a semiconductor or a liquid crystal, using the degree of effects with respect to a silicon substance as an index, an ultrapure water evaluation device that uses it, and an ultrapure water producing system equipped with the ultrapure water evaluation device. <P>SOLUTION: Sample water, such as ultrapure water manufactured by an ultrapure water producing apparatus is brought into contact with the silicon substance, the concentration of dissolved hydrogen in the sample water, after the contact with the silicon substance has been measured, the amount of rising corresponding to the concentration of the dissolved hydrogen in the sample water, before the contact with the silicon substance, is calculated, and on the basis of the amount corresponding to the rise in the concentration of the dissolved hydrogen, it is decided whether the sample water has properties for etching silicon surface. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a water quality evaluation method. More specifically, a water quality evaluation method for evaluating water quality such as etching properties of ultrapure water used as cleaning water for manufacturing semiconductors and liquid crystals in a simple and highly sensitive manner using the influence on silicon substances as an index, The present invention relates to an ultrapure water evaluation apparatus and an ultrapure water production system to be used.

  Ultrapure water used for manufacturing semiconductors and liquid crystals needs to stably supply water having an extremely low impurity concentration. For this purpose, sample water is collected and the concentration of impurities is measured using a highly sensitive analyzer to confirm the water quality.

  Conventionally, water quality is monitored by installing an item that can measure and index impurities in ultrapure water using an electrical method and a water quality monitor that can analyze impurities directly at the outlet of ultrapure water production equipment. Yes. For example, measuring instruments such as a resistivity meter (specific resistance meter), a TOC meter, and a silica meter have been used. However, in order to accurately measure the impurity concentration contained in water with extremely low impurity concentration such as recent ultrapure water, a conventional water quality monitor is insufficient, and high sensitivity analysis by sampling is indispensable. For example, the concentration of metal elements such as Na and Fe needs to be measured at an extremely low concentration of 1 ppt, and there is no water quality monitor that can cope with this, so sampling and high sensitivity analysis must be performed.

  On the other hand, depending on the method for producing ultrapure water, amines eluted from ion exchange resins and separation membranes may be mixed during the production process. It is known that when a silicon wafer is cleaned using ultrapure water mixed with amines, an undesirable etching action is caused in the rinsing process. Conventionally, in order to confirm this etching action, for example, a method of observing the surface of a silicon wafer with a scanning electron microscope after being immersed in ultrapure water to be evaluated has been used. However, in this method, there is a problem that a high technique for handling a scanning electron microscope is required and that it takes too much time for measurement.

Japanese Patent Laid-Open No. 2001-208748 discloses a method for evaluating the quality of ultrapure water used for cleaning silicon wafers by bringing a silicon wafer into contact with sample water, causing impurities in the sample water to adhere to the wafer, and removing the adhered impurities. A water quality evaluation method for elution and analyzing the impurities has been proposed. However, this method is intended to measure fine particles or metal impurities in the sample water, and cannot evaluate the etchability of the sample water.
JP 2001-208748 A

  In the semiconductor manufacturing process, it is important to maintain the cleanliness and flatness of the silicon surface as the semiconductor devices become more precise. In the process of manufacturing high-definition semiconductors, ultrapure water that dissolves even a small amount of silicon on the surface can cause surface roughness associated with surface etching, and as a result, electrical characteristics are degraded. Cause problems.

  Therefore, in the semiconductor manufacturing process, it is necessary to use water with little roughness on the silicon surface when cleaning with ultrapure water, and it is an industrial matter to determine whether the water used has the property of etching the silicon surface. This is an extremely important issue.

  Under such circumstances, the present invention is simple and highly sensitive, particularly with respect to the water quality such as etching properties of ultrapure water used as cleaning water for manufacturing semiconductors and liquid crystals, using the degree of influence on the silicon substance as an index. The purpose is to provide a water quality evaluation method. Furthermore, this invention is made | formed for the purpose of providing the ultrapure water evaluation apparatus using the said water quality evaluation method, and the ultrapure water manufacturing system provided with this ultrapure water evaluation apparatus.

  Therefore, as a result of intensive studies on the relationship between the etching of the silicon surface and the concentration of dissolved hydrogen in the sample water after contact with the silicon, the inventor found that when the silicon wafer was brought into contact with water that was easy to etch the silicon surface, In the case where the dissolved hydrogen concentration of the water is relatively large and the degree of etching of the silicon surface is small, the relationship is found that the dissolved hydrogen concentration contained in the water is also reduced, and the present invention is completed based on this finding. It came to.

  That is, the present invention contacts sample water with a silicon substance, measures the dissolved hydrogen concentration, which is a physical property value correlated with the silica concentration contained in the sample water after contact with the silicon substance, and makes contact with the silicon substance. The present invention provides a water quality evaluation method characterized by evaluating the quality of sample water based on the increased dissolved hydrogen concentration. Furthermore, this invention provides the ultrapure water evaluation apparatus which uses the said water quality evaluation method, and the ultrapure water manufacturing system provided with this ultrapure water evaluation apparatus.

As described above, if a substance that easily etches silicon, such as amines, is mixed in the sample water, etching occurs on the silicon surface when the sample water is brought into contact with the silicon substance, and silicon is contained in the sample water. Elute. The eluted silicon reacts with OH ^- ions or water molecules to form ionic silica (silicate ion) (SiO ₃ ^2- ), while the remaining hydrogen is considered to exist as dissolved hydrogen in water. It is done. Therefore, since the dissolved hydrogen concentration has a correlation with the silica concentration, it is possible to evaluate whether the sample water is water quality that causes etching in silicon by monitoring the increase in the dissolved hydrogen concentration.

  Regarding the increase in dissolved hydrogen concentration, dissolved hydrogen concentration in ultrapure water after contact with silicon materials such as silicon wafer debris or silicon crystals, spherical silicon particles, etc. by using the dissolved hydrogen concentration analysis method and its analyzer If the concentration is measured and compared with the dissolved hydrogen concentration before contact with the substance, the dissolved hydrogen concentration increased by contact with the substance can be measured. In addition to the silicon single crystal, a silicon polycrystal can be used as the silicon material. The silicon substance is not particularly limited, but it is preferable to use high-purity silicon such as a silicon wafer, crushed particles thereof, or single crystal silicon particles.

  Then, by measuring or monitoring the dissolved hydrogen concentration directly or continuously, it is possible to monitor the quality of water such as ultrapure water, particularly the etching property. Further, by making the contact condition with silicon constant, it is possible to relatively compare and compare the etching ability of a plurality of types of sample water with respect to silicon.

  Further, the method for analyzing the concentration of dissolved hydrogen contained in the sample is not particularly limited, but an electrochemical measurement method using a diaphragm is the simplest and preferable.

  In the water quality evaluation method of the present invention described above, the ultrapure water etches the silicon wafer surface by contacting sample water, particularly ultrapure water, with a silicon substance and measuring the dissolved hydrogen concentration in the ultrapure water. Since it can be easily determined whether or not it has properties, it is extremely effective in preventing the occurrence of defects in semiconductor manufacturing.

  The ultrapure water evaluation apparatus using the water quality evaluation method of the present invention described above has a sample water passage opening and a sample water discharge opening, a contact container loaded with a silicon substance inside, and a sample discharged from the discharge opening And a dissolved hydrogen concentration measuring device for measuring a dissolved hydrogen concentration in water.

  The above-described ultrapure water evaluation apparatus of the present invention includes, for example, an ultrapure water feed pipe from the ultrapure water production apparatus to the use point and a water path at an arbitrary position in the ultrapure water return pipe from the use point. , A silicon contact container for water quality evaluation and a dissolved hydrogen concentration measuring device can be connected.

  The dissolved hydrogen concentration measuring device may be connected to a silicon contact vessel, and sample water that is in contact with silicon in the silicon contact vessel may be introduced into the dissolved hydrogen concentration measuring device to measure the dissolved hydrogen concentration. Prepare a concentration measuring device in a place separate from the silicon contact container, take the sample water that has contacted the silicon in the silicon contact container to the water sampling container, carry it to the place where the dissolved hydrogen measuring device is located, and measure with the dissolved hydrogen concentration measuring device You may do it. Moreover, when measuring the dissolved hydrogen concentration before making it contact with silicon, the sample water on the upstream side of the silicon contact vessel may be introduced and supplied to the dissolved hydrogen concentration measuring device.

  Here, in the above embodiment, the silicon contact vessel constituting the ultrapure water evaluation apparatus is not limited. After the sample water is brought into contact with the semiconductor substrate, impurities in the sample water are detected or measured by analyzing the surface of the substrate. Although the holding | maintenance container of the semiconductor substrate used with the evaluation method of the water quality to be used can also be used, it is preferable to use the column filled with the particulate silicon or silicon substrate crushed material with a larger contact surface area.

  The ultrapure water evaluation apparatus of the present invention is suitably used in an ultrapure water production processing apparatus including a subsystem that further purifies pure water supplied from a primary pure water production apparatus and supplies the purified water to a use point. The primary pure water production apparatus constituting the ultrapure water production treatment apparatus includes a condensation precipitation apparatus, a sand filter, an activated carbon filter, a reverse osmosis membrane apparatus, an ultraviolet irradiation apparatus, vacuum degassing or nitrogen gas degassing. An apparatus, a catalyst degassing apparatus, a non-regenerative ion exchange apparatus, and the like are appropriately selected according to the quality of raw water and are arranged in an arbitrary order. The subsystem is formed by appropriately combining an ultraviolet sterilizer, a mixed bed desalting apparatus, an ultrafiltration membrane (UF) apparatus, and the like.

  A branch pipe is provided in a necessary place in the ultrapure water circulation pipe in advance, for example, immediately after the exit of the ultrapure water production apparatus, near the use point, or at any position such as a position returning from the use point to the ultrapure water production apparatus. Install one or more tubes. In order to fully demonstrate the effects of the present invention, it is preferable to provide three or more branch pipes. The ultrapure water evaluation apparatus of the present invention can be attached to the branch pipe every time the water quality is evaluated. However, it is preferable that the apparatus is permanently installed so that the water quality can be immediately evaluated in an emergency.

  The contact between the sample water and the silicon substance is, for example, by continuously supplying the sample water into the contact container loaded with the silicon substance, and then supplying the supplied sample water to the dissolved hydrogen measuring device connected to the contact container or It can be carried out by supplying the water collection container continuously or intermittently. The contact conditions in this case can be arbitrarily set, and predetermined contact conditions such as the filling amount of silicon substance or the number of filling silicon wafers, the surface area of the silicon, the amount of water per unit time, and the contact time are set. be able to. For example, it is preferable to supply sample water such as ultrapure water at 1 L / min to one 6-inch silicon wafer.

  The water quality is evaluated by contacting the sample water with a silicon substance based on the preset contact conditions, measuring the increase in dissolved hydrogen concentration of the sample water, and comparing it with a predetermined allowable increase value. Determine if it is possible or if some action should be taken. For example, in the evaluation of the quality of ultrapure water produced by a certain ultrapure water production device, the conditions are first set as described above, and ultrapure water is used as the standard water with acceptable water quality under the same conditions as those set forth above. Measure the dissolved hydrogen concentration of the sample water every time, using the dissolved hydrogen concentration as a reference, and if there is a case where the dissolved hydrogen concentration rises above the allowable increase value, Judged as ineligible as water. Further, by making the contact condition between the sample water and the silicon substance constant, it is possible to evaluate each of the ultrapure water supplied from the ultrapure water production apparatus provided at different locations.

  The increase value of the dissolved hydrogen concentration can be obtained as an increase in the dissolved hydrogen concentration by measuring the dissolved hydrogen concentration before and after contact with silicon and from the difference between the dissolved hydrogen concentrations before and after the contact. In this case, when the dissolved hydrogen concentration of ultrapure water at normal times is known, the measurement of the dissolved hydrogen concentration before contact can be omitted. The allowable increase value of the dissolved hydrogen concentration varies depending on the contact conditions and the purpose of use of the ultrapure water. However, when the increase value of the dissolved hydrogen concentration exceeds 0.5 ppb, measures should be taken.

  As a countermeasure, if the increase in dissolved hydrogen concentration exceeds the allowable increase, a warning is issued, the use of the ultra pure water is stopped, and the cause of water quality deterioration in the ultra pure water production equipment is eliminated. Do. For example, it is considered that amine mixed in ultrapure water is eluted from an ion exchange resin or the like, so that the water quality can be recovered by replacing it with an ion exchange resin or the like that has been prevented from being eluted. In addition, the quality evaluation of ultrapure water using the ultrapure water evaluation apparatus of the present invention can be performed not only periodically, for example, at a frequency of about once / month, but also at any time when trouble occurs. Although it is possible to directly measure the silica concentration by the absorbance, it is generally necessary to provide a sample water concentration step separately in the high-precision measurement of the silica concentration. Is more preferable.

  The water quality evaluation method of the present invention and the ultrapure water evaluation apparatus using the water quality evaluation method are obtained by contacting sample water, particularly ultrapure water, with a silicon substance and measuring the dissolved hydrogen concentration in the ultrapure water. Since it can be easily determined whether or not ultrapure water has the property of etching the surface of a silicon wafer, it is extremely effective in preventing the occurrence of defects in semiconductor manufacturing.

  The ultrapure water evaluation apparatus of the present invention is a water quality evaluation using a silicon substance, which is equipped with an instrument for sampling at any position, such as the ultrapure water production apparatus immediately, in the production apparatus, in the middle of supply piping to the factory, etc. Can be performed quickly, which helps to elucidate the causes of semiconductor manufacturing defects and their sources, and greatly contributes to the solution.

  Further, according to the ultrapure water production system provided with the ultrapure water evaluation apparatus of the present invention, the index of the increase in dissolved hydrogen concentration in the ultrapure water is used as an index for the produced ultrapure water. Semiconductor operation can be stably maintained by managing the operation so as to be within a certain numerical range. In addition, when an abnormality occurs in the water quality, it can be detected before the result is obtained in the actual process, and measures can be taken before the damage increases.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic diagram of an ultrapure water production system according to an embodiment of the present invention, and FIG. 2 is a diagram of a silicon contact container constituting an ultrapure water evaluation apparatus incorporated in the ultrapure water production system of FIG. It is sectional drawing.

  The ultrapure water production system 1 in FIG. 1 includes an ultrapure water production apparatus composed of a primary pure water production apparatus and subsystems, a use point of ultrapure water, and an ultrapure water feed from the ultrapure water production apparatus to the use point. It consists of pipes and ultrapure water return pipes from use points. In the ultrapure water production system 1 described above, sample water outlets are attached to three locations before and after the final outlet of the subsystem and the use point, and each of the sample water outlets is provided with clean branch pipes 4a, 4b, and 4c. The ultrapure water evaluation devices 2a, 2b, and 2c comprising the silicon contact container of the invention and the dissolved hydrogen measurement device were connected to enable sample water to be constantly supplied to each ultrapure water evaluation device. In FIG. 1, a known pure water production apparatus is used as the primary pure water production apparatus constituting the ultrapure water production system, and the subsystem in FIG. 1 includes an ultraviolet oxidation apparatus and an ultrafiltration membrane apparatus. The ion exchange resin towers are sequentially combined.

  2 constitutes the ultrapure water evaluation devices 2a, 2b, and 2c incorporated in the ultrapure water production system 1 of FIG. 1, respectively, and includes a column 12 for filling a silicon substance, and a column 12 Is composed of an eye ring 11 with a mesh sandwiched from both ends, and an O-ring provided at the joint between the column 12 and the eye dish 11. The column 12 is filled with a predetermined amount of particulate silicon substance, sample water is supplied from above the packing, and the sample water that has been contacted is discharged from below the packing. The main constituent material of the silicon contact container is not particularly limited as long as it is a material that has very little eluate even when it comes into contact with water.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
[Example 1]
Whether or not the ultrapure water produced by the ultrapure water production system of FIG. 1 has the property of etching the surface of the silicon wafer was evaluated by the following method.

  First, 200 ml of particulate single crystal silicon was prepared, and the silicon was washed with a 0.5% concentration dilute hydrofluoric acid aqueous solution to remove the natural oxide film formed on the surface of the particulate silicon. Next, after filling the silicon contact container of FIG. 2 with the particulate silicon from which the natural oxide film has been removed, the ultra pure water produced by the ultra pure water production system of FIG. 1 is flowed at a flow rate of 1 L / min. Water was passed through. The ultrapure water (hereinafter referred to as “sample water for analysis”) that has passed through the silicon contact container of FIG. 2 is passed through a diaphragm electrode type dissolved hydrogen concentration meter connected to the discharge port of the silicon contact container. Measurements were performed.

The dissolved hydrogen concentration contained in the sample water for analysis, that is, the sample water after contact with the particulate silicon was 0.51 ppb. With respect to the ultrapure water before contact with the particulate silicon, the dissolved hydrogen concentration was measured in the same manner as in the above measurement method, and found to be 0.02 ppb. From this result, it can be seen that the ultrapure water produced increased the dissolved hydrogen concentration by 0.49 ppb due to the particulate silicon contact.
[Comparative Example 1]
In the same manner as in Example 1, particulate single crystal silicon washed with a 0.5% dilute hydrofluoric acid aqueous solution was placed in the silicon contact container of FIG. Next, tetramethylammonium hydroxide was added to the ultrapure water produced by the ultrapure water production system of FIG. 1 to prepare sample water so that the tetramethylammonium hydroxide concentration was 5 ppb. The sample water was passed through the silicon contact vessel and passed through a diaphragm electrode type dissolved hydrogen concentration meter connected to the discharge port of the silicon contact vessel, and measurement was performed. With respect to the sample water for analysis, when the dissolved hydrogen concentration was measured in the same manner as in Example 1, it was found that the dissolved hydrogen concentration increased by 5.05 ppb due to the particulate silicon contact.
[Comparative Example 2]
In the same manner as in Example 1, particulate single crystal silicon washed with a 0.5% dilute hydrofluoric acid aqueous solution was placed in the silicon contact container of FIG. Next, tetramethylammonium hydroxide was added to the ultrapure water produced by the ultrapure water production system in FIG. 1 to prepare sample water so that the tetramethylammonium hydroxide concentration was 10 ppb. The sample water was passed through the silicon contact vessel and passed through a diaphragm electrode type dissolved hydrogen concentration meter connected to the discharge port of the silicon contact vessel, and measurement was performed. With respect to the sample water for analysis, when the dissolved hydrogen concentration was measured in the same manner as in Example 1, it was found that the dissolved hydrogen concentration increased by 8.10 ppb due to contact with particulate silicon.

When the silicon wafer used in each evaluation test of Example 1 and Comparative Examples 1 and 2 was observed at a magnification of 30000 times using a scanning electron microscope (SEM), the silicon wafer used in Example 1 was observed. The surface was flat. However, it was observed that the surface of the silicon wafer used in Comparative Examples 1 and 2 was uneven, and the surface was considerably rough. Thus, for sample water such as ultrapure water, the allowable range for etching properties is the range where the increase in dissolved hydrogen concentration is 0.5 ppb or less, and the increase in dissolved concentration after contact with a silicon substance. When the value exceeded 0.5 ppb, it was confirmed that it was better to take measures.
[Example 2]
Whether or not the ultrapure water produced by the ultrapure water production system has the property of etching the silicon wafer surface was evaluated by the following method.

  First, silicon wafer fragments crushed to about 1 mm to 10 mm were filled in an acrylic column as a silicon contact container to a thickness of about 50 mm. Next, a 0.5% concentration dilute hydrofluoric acid aqueous solution is passed through the acrylic column to clean the filled silicon wafer fragments, and a natural oxide film formed on the surface of the silicon wafer fragments And the inside of the acrylic column was sufficiently washed by passing ultrapure water through the acrylic column.

  Next, in a state where the ion exchange resin has not been exchanged for 12 months from the start of use, ultrapure water is produced using the ultrapure water production system shown in FIG. The concentration of dissolved hydrogen was continuously measured using the ultrapure water evaluation apparatus constituting the water production system. As a result, it was found that the produced ultrapure water has a high dissolved hydrogen concentration of 0.5 to 1.1 ppb. In this case, it is desirable to take measures.

  Therefore, the ultra-pure water was produced by replacing the ion exchange resin of the ultra-pure water production system with a new one. About the produced ultrapure water, when the dissolved hydrogen concentration was continuously measured using the ultrapure water evaluation apparatus constituting the ultrapure water production system, the dissolved hydrogen concentration of the produced ultrapure water was: It was found to be stable at a low level of 0.01 to 0.02 ppb. In this case, the upper limit value of the dissolved hydrogen concentration was small, and the increased value of the dissolved hydrogen concentration after contact with the silicon substance was 0.5 ppb or less. From this, it can be seen that, when a high dissolved hydrogen concentration is measured, replacing the ion exchange resin with a new one is extremely effective in improving the etching property of the ultrapure water produced. . In addition, according to the water quality evaluation method of the present invention and the ultrapure water evaluation apparatus using the water quality evaluation method, it is possible to know the replacement time of the ion exchange resin with high accuracy, which is extremely effective in preventing the occurrence of problems in semiconductor manufacturing. It turns out that it is.

It is a schematic diagram of the ultrapure water manufacturing system which concerns on embodiment. It is sectional drawing of the silicon contact container which comprises the ultrapure water evaluation apparatus integrated in the ultrapure water manufacturing system of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Ultrapure water production system 2a, 2b, 2c Ultrapure water evaluation apparatus 3 (Ultrapure water) circulation piping 4a, 4b, 4c Branch pipe 10 O-ring 11 Eye plate 12 Column

Claims (5)

  The sample water is brought into contact with the silicon substance, the dissolved hydrogen concentration contained in the sample water after contact with the silicon substance is measured, and the quality of the sample water is determined based on the dissolved hydrogen concentration increased by the contact with the silicon substance. Water quality evaluation method characterized by evaluating water.   The water quality evaluation method according to claim 1, wherein a silicon single crystal or a silicon polycrystal is used as the silicon material.   3. The water quality evaluation method according to claim 1, wherein the sample water brought into contact with the silicon substance is ultrapure water.   A sample vessel having a sample water passage and a sample water discharge port, and a contact container in which a silicon substance is loaded; and a dissolved hydrogen measuring device for measuring a dissolved hydrogen concentration in the sample water discharged from the discharge port. The ultrapure water evaluation apparatus used for the water quality evaluation method in any one of Claims 1-3 characterized by the above-mentioned. The ultrapure water production apparatus, the ultrapure water use point, the ultrapure water feed pipe from the ultrapure water production apparatus to the usepoint, and the ultrapure water return pipe from the usepoint, The ultrapure water production system according to claim 4, wherein the ultrapure water evaluation device according to claim 4 is provided at any position of the final outlet, the ultrapure water feed pipe, or the ultrapure water return pipe.

Images