JP2016162963A - Measuring method and measuring apparatus of concentration of metal ion in liquid and cleaning system of electronic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a measuring method and a measuring apparatus of the concentration of metal ions in a liquid, such as a sulphuric acid-based chemical, used for cleaning an electronic device capable of measuring the concentration in a process in real time, and to provide a cleaning method and a cleaning system of an electronic device using the same.SOLUTION: In a method of measuring the concentration of metal ions in a sample liquid, containing one kind or more of ions of metal elements in the third through sixth periods of a periodic table and having an electric conductivity exceeding 0.33 S/cm, by plasma emission spectrometry, preprocessing for preparing an adjustment liquid, where the electric conductivity of the sample liquid has been adjusted to 0.33 S/cm or less, is performed before the concentration of metal ions in the liquid is measured for the adjustment liquid. A cleaning method of an electronic device for measuring the concentration of metal ions in the cleaning liquid for cleaning the electronic device is also provided.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and an apparatus for measuring a metal ion concentration in a liquid. The method and apparatus for measuring the concentration of metal ions in the liquid of the present invention are contained as impurities in a sulfuric acid-based cleaning chemical for cleaning and removing unnecessary materials such as residual metals from an electronic device such as a silicon wafer in an electronic device manufacturing process. This is useful in an electronic device cleaning system that measures the concentration of metal ions to be collected in the cleaning process and collects and reuses the cleaning liquid based on the result.

  In a semiconductor manufacturing process, concentrated sulfuric acid and hydrogen peroxide mixed solution (SPM) or a solution in which ozone gas is blown into concentrated sulfuric acid (SPM) in a plurality of cleaning steps for stripping and cleaning resist residues, fine particles, metals, natural oxide films, etc. SOM) is frequently used as a cleaning liquid. Since these sulfuric acid-based cleaning chemicals lose their activity as chemicals in a high sulfuric acid concentration state, the amount of sulfuric acid used and the amount of waste liquid in semiconductor factories are very large.

  In order to improve this situation, a technique for recovering and reusing waste sulfuric acid on-site and regenerating it by refining or adjusting components is being studied. For example, Patent Documents 1 and 2 propose a method of separating and recovering sulfuric acid and impurities using a two-stage distillation method and Patent Document 3 using a vacuum distillation method. Patent Document 4 proposes a method of recovering sulfuric acid by using electrodialysis and further reusing it by adding an oxidizing substance by electrolysis.

  When these techniques are applied, it is necessary to measure and manage the impurity concentration in sulfuric acid in order to determine whether or not the recovered and regenerated sulfuric acid can be reused. There is no description of impurity measurement and management methods.

  On the other hand, in order to reduce the amount of sulfuric acid waste solution, a washing method in which electrolytic sulfuric acid containing an oxidizing substance such as persulfuric acid obtained by electrolysis of sulfuric acid is used as a washing solution, and the used sulfuric acid is electrolyzed again and circulated For example, Patent Documents 5 and 6 propose a cleaning system. This electrolytic sulfuric acid system can obtain a high cleaning effect while reducing the amount of chemical solution used and the amount of waste liquid. However, there is no mechanism for removing inorganic impurities, and when inorganic impurities are contained in the object to be treated, this accumulates in the liquid over time. For this reason, the only way to determine how much recycling is possible is to make a prediction based on the amount of accumulated impurities calculated from the number of wafers processed.

As an impurity concentration measurement method in sulfuric acid, elemental analysis such as an analysis method described in JIS K8951, atomic absorption spectrometer, inductively coupled plasma emission spectrometer, inductively coupled plasma mass (ICP-MS) analyzer, etc. There is a method of analyzing using an apparatus. However, all of these methods sample the sulfuric acid to be reused, perform pretreatment such as concentration and dilution, and then measure various impurity concentrations with an analyzer. There is a problem in that the predetermined time until obtaining is long.
Therefore, it may be reused without being able to immediately grasp that impurities are mixed in the recovered sulfuric acid to an abnormal concentration due to a trouble with the recovery device. Product defects may occur due to wafer contamination.

  Regarding the technique for analyzing metal impurities in the field of electronic device manufacturing, Patent Document 7 discloses a technique for measuring the metal contamination concentration on the surface of a silicon wafer in a semiconductor manufacturing process by plasma emission analysis. A technique for quantifying metals by plasma emission analysis has been proposed. However, there are no known methods for analyzing metal impurities in sulfuric acid-based cleaning chemicals or cleaning waste liquids in the field of electronic device manufacturing.

  The liquid electrode plasma emission analysis (LEP-AES analysis) used in the present invention quantifies the spectrum unique to each element using plasma generated in a sample solution under an appropriate voltage. This is a technique for measuring the concentration of contained substances by detecting them manually, and a handy type analyzer (MH-5000, Microemission Co., Ltd.) that requires little installation space has been put into practical use ( Non-patent document 1). In addition, although it has been reported that heavy metals in a solution can be measured using this analyzer (Non-patent Document 2), the metal ion concentration in a liquid such as a sulfuric acid chemical solution used for cleaning an electronic device is also reported. There is no report that it is applied to the quantification.

  In addition, this analyzer can quantitatively analyze any element that emits plasma, but in the case of a liquid with low electrical conductivity such as pure water, current does not flow and plasma emission does not occur. In the case of a solution containing an electrolyte at a high concentration, electrolysis easily occurs, so that plasma emission can be suppressed. Therefore, in this case, pretreatment such as addition of electrolyte or dilution with pure water is required. For this reason, even if the plasma emission analysis is applied to the determination of the metal ion concentration in a liquid such as a sulfuric acid chemical solution used for cleaning an electronic device, the metal ion concentration may not be measured as it is.

JP-A-9-48603 JP-A-9-278424 Japanese Patent No. 3507317 Japanese Patent No. 3383334 JP 2006-114880 A JP 2006-278687A JP-A-6-230002 JP 2010-54423 A

Yamamoto et al. 32-36, (2009) Kumai et al., Analytical Chemistry, Vol. 58, no. 6, pp. 561-567, (2009)

  The present invention relates to a method and an apparatus for measuring a metal ion concentration in a liquid capable of instantaneously measuring a metal ion in a liquid such as a sulfuric acid chemical solution used for cleaning an electronic device in a process, It is an object of the present invention to provide an electronic device cleaning method and an electronic device cleaning system using the above.

As a result of intensive studies to solve the above problems, the present inventor performed pretreatment so that measurement by plasma emission analysis is possible, and by performing plasma emission analysis on the liquid subjected to this pretreatment, It has been found that the concentration of metal ions contained as an impurity in a cleaning solution such as a sulfuric acid chemical solution used in a device cleaning process can be measured immediately in the cleaning process.
The present invention has been achieved based on such findings, and the gist thereof is as follows.

[1] A method in which the concentration of metal ions in a sample solution having an electrical conductivity of more than 0.33 S / cm, including one or more types of metal element ions in the third to sixth periods of the periodic table, is measured by plasma emission analysis. A metal in the liquid, characterized in that a pretreatment for preparing an adjustment liquid in which the electric conductivity of the sample liquid is adjusted to 0.33 S / cm or less is prepared, and the adjustment liquid is measured by plasma emission analysis. Ion concentration measurement method.

[2] In [1], the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 80 wt% or more and a solution temperature of more than 80 ° C., and the pretreatment cools the solution temperature of the sample solution to 80 ° C. or less. A method for measuring a metal ion concentration in a liquid, characterized by being a treatment.

[3] In [1], the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 70% by weight to less than 80% by weight and a liquid temperature of more than 35 ° C., and the pretreatment is previously stored in association with the sulfuric acid concentration. A method for measuring a metal ion concentration in a liquid, characterized in that the liquid temperature of the sample liquid is cooled to the lower limit set value or less based on a lower limit set value of the liquid temperature.

[4] In [2] or [3], the sulfuric acid chemical solution is electrolytic sulfuric acid, a mixed solution of sulfuric acid and hydrogen peroxide, or a solution obtained by blowing ozone into sulfuric acid. Concentration measurement method.

[5] The method for measuring a metal ion concentration in a liquid according to any one of [1] to [4], wherein the sample liquid is a cleaning liquid used for cleaning an electronic device in an electronic device manufacturing process.

[6] The method for measuring a metal ion concentration in a liquid according to [5], wherein the cleaning removes residual metal on the electronic device with the cleaning liquid.

[7] The method for measuring the concentration of metal ions in the liquid according to [5] or [6], wherein the cleaning waste liquid after the cleaning is reused as it is or after being recycled.

[8] A method for measuring a metal ion concentration in a liquid according to [7], wherein the metal ion concentration is measured using the cleaning liquid separated from the circulation system as the sample liquid.

[9] The method for measuring a metal ion concentration in a liquid according to [8], wherein the sample liquid after the measurement is returned to the circulation system.

[10] A method for cleaning an electronic device, wherein the concentration of metal ions in the cleaning liquid is measured according to the method according to any one of [1] to [9].

[11] An apparatus for measuring the concentration of metal ions in a sample liquid having an electrical conductivity of more than 0.33 S / cm by plasma emission analysis, including one or more kinds of ions of metal elements in the third to sixth periods of the periodic table. A pretreatment means for preparing an adjustment liquid in which the electric conductivity of the sample liquid is adjusted to 0.33 S / cm or less, and a plasma emission analyzer for supplying the adjustment liquid as the sample liquid. An apparatus for measuring the concentration of metal ions in a liquid.

[12] In [11], the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 80% by weight or more and a solution temperature of more than 80 ° C., and the pretreatment means cools the solution temperature of the sample solution to 80 ° C. or less. An apparatus for measuring the concentration of metal ions in a liquid, characterized by being a cooling means.

[13] In [11], the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 70% by weight or more and less than 80% by weight and a liquid temperature of more than 35 ° C., and the pretreatment unit stores the pretreatment means in association with the sulfuric acid concentration in advance. An apparatus for measuring the concentration of metal ions in a liquid, which is cooling means for cooling the liquid temperature of the sample liquid below the lower limit set value based on the lower limit set value of the liquid temperature.

[14] The metal ion in the liquid according to [12] or [13], wherein the sulfuric acid chemical liquid is electrolytic sulfuric acid, a mixed liquid of sulfuric acid and hydrogen peroxide solution, or a liquid obtained by blowing ozone into sulfuric acid. Concentration measuring device.

[15] The apparatus for measuring a metal ion concentration in a liquid according to any one of [11] to [14], wherein the sample liquid is a cleaning liquid used for cleaning an electronic device in an electronic device manufacturing process.

[16] Cleaning means for cleaning the electronic device with the cleaning liquid, recovery means for recovering the cleaning waste liquid from the cleaning means, circulation means for circulating the cleaning waste liquid recovered by the recovery means as the cleaning liquid to the cleaning means, A cleaning system for an electronic device having a metal ion concentration measuring means for extracting a part of the circulating liquid from the circulation system by the circulation means and measuring a metal ion concentration of the circulating liquid, the metal ion concentration measuring means comprising: An electronic device cleaning system comprising a plasma emission analyzer.

[17] In [16], the metal ion concentration measuring unit includes a circulating liquid cooling unit, and the circulating liquid cooled by the cooling unit is measured by the plasma emission analyzer. Electronic device cleaning system.

[18] In [17], the cleaning liquid is a sulfuric acid chemical solution having a sulfuric acid concentration of 80% by weight or more and a liquid temperature of over 80 ° C., and the cooling means is means for cooling the liquid temperature of the cleaning liquid to 80 ° C. or lower. An electronic device cleaning system, comprising:

[19] In [17], the cleaning liquid is a sulfuric acid chemical solution having a sulfuric acid concentration of 70 wt% or more and less than 80 wt% and a liquid temperature of more than 35 ° C., and the cooling means is stored in advance in association with the sulfuric acid concentration. An electronic device cleaning system, characterized in that it is means for cooling the liquid temperature of the cleaning liquid below the lower limit set value based on a lower limit set value of the liquid temperature.

[20] The electronic device cleaning system according to [18] or [17], wherein the sulfuric acid chemical solution is electrolytic sulfuric acid, a mixed solution of sulfuric acid and hydrogen peroxide solution, or a solution obtained by blowing ozone into sulfuric acid. .

[21] Cleaning means for cleaning the electronic device with the cleaning liquid, recovery means for recovering the cleaning waste liquid from the cleaning means, circulation means for circulating the cleaning waste liquid recovered by the recovery means as the cleaning liquid to the cleaning means, A cleaning system for an electronic device having a metal ion concentration measuring means for extracting a part of the circulating liquid from the circulation system by the circulation means and measuring a metal ion concentration of the circulating liquid, the metal ion concentration measuring means comprising: [11] A cleaning system for an electronic device comprising the apparatus for measuring a metal ion concentration in a liquid according to any one of [15] to [15].

[22] The electronic device cleaning system according to any one of [16] to [21], wherein the cleaning means is means for cleaning and removing residual metal on the electronic device with the cleaning liquid.

[23] In any one of [16] to [22], the circulation system has a regenerating means for purifying or adjusting the components of the cleaning waste liquid, and a part of the regenerated liquid regenerated by the regenerating means is extracted. The electronic device cleaning system is characterized in that the metal ion concentration is measured by the metal ion concentration measuring means.

[24] The electronic device according to any one of [16] to [23], further comprising a liquid return means for returning the liquid after the metal ion concentration measurement by the metal ion concentration measurement means to the circulation system. Cleaning system.

[25] The electronic device cleaning system according to any one of [16] to [24], wherein the cleaning liquid is a sulfuric acid-based cleaning chemical and further includes a measuring device for the sulfuric acid concentration of the circulating liquid.

  According to the plasma emission analysis, it is possible to measure the concentration of ions of the metal elements in the third to sixth periods of the periodic table in the liquid, but the electrical conductivity of the sample liquid exceeds 0.33 S / cm. If so, plasma is not generated and measurement is impossible. In the present invention, the metal ion concentration can be measured by plasma emission analysis by performing a pretreatment for adjusting the electric conductivity of the sample solution to 0.33 S / cm or less.

  The technique for measuring the concentration of metal ions in a liquid according to the present invention is, for example, a chemical liquid in the case where a sulfuric acid chemical liquid used in a manufacturing process of an electronic device is used as a cleaning liquid or the like and then recycled or recycled for reuse. It is useful as a means of measuring the concentration of metal ions contained as impurities in the process. By measuring the impurity concentration of cleaning chemicals immediately in the process by plasma emission analysis, the possibility of reuse of chemicals can be determined in a short time. It becomes possible to judge. Also, by detecting the impurity concentration in the chemical solution, if the impurity concentration exceeds the set value, it is discharged out of the system, or the regeneration conditions are changed, so that the wafer etc. caused by the impurity in the chemical solution can be changed. Contamination of electronic devices can be suppressed, and product defects can be prevented.

It is a systematic diagram which shows an example of embodiment of the washing | cleaning system of the electronic device of this invention. It is a systematic diagram which shows the other example of embodiment of the washing | cleaning system of the electronic device of this invention. It is a systematic diagram which shows another example of embodiment of the washing | cleaning system of the electronic device of this invention. It is a chart which shows the LEP-AES spectrum of sulfuric acid aqueous solution with a sulfuric acid concentration of 85 weight% and a liquid temperature of 30 degreeC. It is a chart which shows the LEP-AES spectrum of an arsenic containing sulfuric acid solution. It is a graph which shows the relationship between the emitted light intensity of an EP-AES spectrum of an arsenic containing sulfuric acid solution, and an arsenic density | concentration.

  Embodiments of the present invention are described in detail below.

<Sample solution>
The sample liquid to be measured in the method and apparatus for measuring the concentration of metal ions in the liquid of the present invention contains one or more kinds of ions of metal elements in the third to sixth periods of the periodic table, and has an electric conductivity of 0. More than 33 S / cm. In plasma emission analysis, ions of metal elements in the third to sixth periods of the periodic table can be analyzed. Therefore, in the present invention, a liquid containing such metal ions is used as a sample liquid.
Note that the sample solution may contain only one kind of metal element ions in the third to sixth periods of the periodic table, or two or more kinds. That is, in the case of plasma emission analysis, since the emission peak wavelength of the LEP-AES spectrum differs depending on the type of metal ions, even a sample solution containing two or more types of metal ions can be quantitatively analyzed for each metal ion. .

  In addition, if the liquid has an electric conductivity of 0.33 S / cm or less, it can be analyzed by plasma emission analysis without performing pretreatment. Therefore, in the present invention, the electric conductivity exceeds 0.33 S / cm. This solution is used as a sample solution.

In the present invention, the sample liquid to be measured is not particularly limited as long as it satisfies the above-mentioned conditions, but the present invention is used as a cleaning liquid for an electronic device, particularly in the manufacturing process of the electronic device. Concentration of metal ions contained as impurities in sulfuric acid chemicals with a sulfuric acid concentration of 80% by weight or more and a liquid temperature exceeding 80 ° C, or sulfuric acid concentrations with a sulfuric acid concentration of 70% to less than 80% by weight and a liquid temperature of over 35 ° C It can be suitably applied to the analysis.
Examples of such a sulfuric acid-based chemical solution include electrolytic sulfuric acid in which an oxidizing substance such as persulfuric acid is generated by the above-described electrolysis, a mixed solution of sulfuric acid and hydrogen peroxide, or a solution in which ozone is blown into sulfuric acid.

  The sulfuric acid concentration of these sulfuric acid chemical solutions is usually about 70 to 96% by weight, the solution temperature is about 35 to 80 ° C., and the electric conductivity is about 0.1 to 2 S / cm. In the sulfuric acid chemical solution, impurities derived from the material of the electronic device to be cleaned include impurities such as transition metals such as As, Ti, Fe and Co, alkali metals such as Na and K, alkaline earth metals such as Ca and Ba, Metal ions such as noble metals such as Pt are included.

  If the sulfuric acid concentration is less than 70% by weight, as shown in Experimental Example 1 described later, no plasma is generated even when the liquid temperature is lowered, and it is difficult to measure the metal ion concentration by plasma emission analysis. For this reason, when cleaning is performed by mixing hydrogen peroxide with sulfuric acid solution as in the electronic device cleaning system shown in FIGS.

<Pretreatment>
In the present invention, pretreatment is performed to adjust the electrical conductivity of the sample solution as described above to 0.33 S / cm or less.
The pretreatment means is not particularly limited as long as the electrical conductivity of the sample solution can be 0.33 S / cm or less, and dilution with pure water can be adopted. Since the liquid composition does not need to be changed, the liquid after measurement can be used as it is, and it is preferable in that it can be easily performed using a cooling means such as a general heat exchanger.

For example, in the case of the above-described sulfuric acid chemical solution, as shown in Experimental Example 1 described later, when the sulfuric acid concentration is in the range of 70 to 96% by weight, the higher the sulfuric acid concentration, the lower the electric conductivity, and the plasma emission. Is more likely to occur.
However, the lower the liquid temperature, the lower the electric conductivity. Therefore, the sample liquid is cooled until the electric conductivity is reduced to 0.33 S / cm or less, for example, about 0.03 to 0.33 mS / m. Plasma emission can be obtained.

  The sample liquid cooling means is not particularly limited, and a general heat exchanger using cooling water or air as a cooling medium can be used.

<Application to electronic device manufacturing process>
The method and apparatus for measuring the concentration of metal ions in a liquid according to the present invention is particularly applicable to a cleaning liquid used for cleaning an electronic device in an electronic device manufacturing process as a sample liquid, and the concentration of metal ions contained as impurities in the cleaning liquid. It is useful as a measuring method and apparatus.

For example, when residual metal on a semiconductor substrate, which is an electronic device, is removed by washing with a cleaning solution, and the cleaning waste solution used for cleaning is reused as a cleaning solution as it is or after reprocessing such as purification or component adjustment. According to the invention, the impurity metal ion concentration in the cleaning waste liquid and the reclaimed liquid is measured, and based on the measurement result, it is determined whether or not the cleaning waste liquid and the regenerated liquid can be reused as the cleaning liquid. In such a case, it is sent to the cleaning process, and when it is judged that it cannot be reused, it is discharged out of the system or by taking measures such as changing the regeneration conditions, the contamination of the cleaning liquid is detected at an early stage. It is possible to prevent secondary contamination of the semiconductor substrate due to contamination of the cleaning liquid.
That is, a cleaning solution such as a sulfuric acid chemical solution used for cleaning an electronic device is a high concentration and high temperature chemical solution having a sulfuric acid concentration of about 70 to 96% by weight and a liquid temperature of 100 to 180 ° C., and its electric conductivity is Usually, the metal ion concentration cannot be measured by plasma emission analysis at 0.4 to 1.5 S / cm.
According to the present invention, it is possible to accurately measure the metal ion concentration contained in the cleaning liquid for such an electronic device.

  Embodiments of an electronic device cleaning system to which a method and apparatus for measuring a metal ion concentration in a liquid according to the present invention are applied will be described below with reference to the drawings. However, the electronic device cleaning system of the present invention is not limited to the one shown in FIGS. 1 to 3 below, and the method and apparatus for measuring the metal ion concentration in the liquid of the present invention is an electronic device cleaning system. It is not limited to what is applied to.

<Embodiment I>
FIG. 1 is a system diagram showing an electronic device cleaning system that cleans an electronic device (semiconductor substrate such as a silicon wafer) with a sulfuric acid chemical solution, collects and recovers the cleaning waste liquid, and recycles the recycled liquid. is there.

Reference numeral 1 denotes a single-wafer type electronic device cleaning apparatus, in which a sulfuric acid solution in a high-concentration sulfuric acid storage tank 2 and a hydrogen peroxide solution in a hydrogen peroxide storage tank 3 are respectively connected to a pipe 11 and a pump P having a pump P _{1. 2} is supplied via a pipe 12 and a pipe 13 provided with ₂ , and the electronic device is cleaned with a mixed solution of sulfuric acid and hydrogen peroxide. Washing waste liquid after washing is fed from the pipe 14 to the sulfuric acid waste liquid collecting tank 4 is fed to a sulfuric acid refining playback device 5 via a pipe 15 with a pump P _3.

  As the sulfuric acid refining and regenerating apparatus 5, a conventional one by a conventional method can be used, for example, a two-stage distillation method, a vacuum distillation method, an electrodialysis method or the like described in Patent Documents 1 to 4 described above is adopted. can do.

Regeneration liquid regenerated with sulfuric acid refining reproducing apparatus 5 is fed to a high concentration sulfuric acid storage tank 2 via a pipe 16 from the reproduction sulfate bath 6 in the device 5 comprises a pump P _4, it is circulated and reused as washing liquid.

In the electronic device cleaning system of FIG. 1, the liquid in the regenerated sulfuric acid tank 6 is extracted from a pipe 17 provided with a pump P ₅ , cooled by a heat exchanger 7 that is a cooling device, and then liquid that is an impurity monitor from a pipe 18. The sample was introduced into an electrode plasma emission analyzer (hereinafter referred to as “LEP-AES analyzer”) 8 and the metal ion concentration was measured by plasma emission analysis with the LEP-AES analyzer 8. return.

  In the LEP-AES analyzer 8, as shown in Examples 1 and 2 to be described later, the metal ion concentration in the sample liquid is determined based on the emission peak wavelength of the metal ion to be measured that has been obtained in advance by plasma emission analysis. Can be sought. Therefore, when the emission intensity at the emission peak wavelength is lower than the set value, it is determined that the metal ion concentration as an impurity is low and can be reused for cleaning, and the liquid circulation from the regenerated sulfuric acid tank 6 to the high concentration sulfuric acid storage tank 2 is performed. However, if it is above the set value, it is determined that the regenerated liquid in the regenerated sulfuric acid tank 6 is contaminated with impurities and cannot be recycled and reused as a cleaning liquid, and the liquid in the regenerated sulfuric acid tank 6 is discharged from a discharge pipe (not shown). A new sulfuric acid solution is introduced into the high-concentration sulfuric acid storage tank 2 from outside the system.

By performing on-line analysis in this way, it is possible to prevent in-system contamination of the cleaning liquid due to circulation and reuse of the cleaning liquid, and secondary contamination of the electronic device due thereto.
In addition, the time required to measure the impurity concentration at that time is significantly shortened compared to the offline analysis, and the residence time in the regenerated sulfuric acid tank can be shortened. Is also possible.

  Also in the electronic device cleaning system of FIG. 1, as shown in FIGS. 2 and 3, which will be described later, a sulfuric acid concentration meter for measuring the sulfuric acid concentration may be further provided to measure the sulfuric acid concentration of the regenerated solution. Examples of the sulfuric acid concentration meter include those that use ultrasonic waves, those that use electrical conductivity, those that use absorbance, and those that use specific gravity. For example, what can be confirmed online is 70% by weight or more.

  In addition, an electric conductivity meter for measuring the electric conductivity of the sample liquid of the LEP-AES analyzer can be provided. However, since the electric conductivity of the sulfuric acid solution is determined by the sulfuric acid concentration and the liquid temperature, the liquid temperature is determined in advance. The electrical conductivity can be obtained from the sulfuric acid concentration and the measurement of the electrical conductivity in the electronic device cleaning system can be made unnecessary.

<Embodiment II>
The electronic device cleaning system shown in FIG. 1 includes a purification / regeneration device for sulfuric acid waste solution used for cleaning, but there is no purification / regeneration device, and the treatment effect as a cleaning chemical solution is lost without regenerating the sulfuric acid waste solution. It may be a cleaning system for electronic devices that is circulated and reused as it is.
FIG. 2 shows an embodiment of such an electronic device cleaning system. 2, parts having the same functions as those of the electronic device cleaning system of FIG.

In the electronic device cleaning system 2 extracts through a pipe 17 by the pump P ₅ sulfuric acid waste liquid of the sulfuric acid waste liquid collection tank 4, after cooling in the heat exchanger 7, sulfuric acid in a sulfuric acid concentration meter 9 via a pipe 18a The concentration is measured, the metal ion concentration as an impurity is measured by the LEP-AES analyzer 8 through the pipe 18 b, and returned to the sulfuric acid waste liquid recovery tank 4 through the pipe 19.
When the measurement results of the sulfuric acid concentration meter 9 and the LEP-AES analyzer 8 satisfy the preset condition values, the liquid in the tank is extracted from the sulfuric acid waste liquid recovery tank 4 by the pump P ₆ and the high concentration sulfuric acid storage tank 2 through the pipe 16. Then, when the sulfuric acid concentration is lower than the set value or when the impurity concentration is higher than the set value, it is discharged out of the system from the pipe 20.

  The destination of the liquid in the sulfuric acid waste liquid recovery tank 4 is a switching valve (not shown) provided at the branch point of the pipe 16 and the pipe 20, and the measurement value of the sulfuric acid concentration meter 9 and the measurement value of the LEP-AES analyzer 8 are input. It can be automatically performed by performing switching control with a control device incorporating a calculation means for analyzing these measured values.

<Embodiment III>
FIG. 3 shows a method for measuring the concentration of metal ions in a liquid according to the present invention, in a cleaning system for an electronic device in which the sulfuric acid solution is electrolyzed to generate persulfuric acid (peroxodisulfuric acid). It is a systematic diagram which shows the example which applied the measuring apparatus.

  In FIG. 3, 30 is a single-wafer electronic device cleaning apparatus, 31 is a sulfuric acid waste liquid storage tank, 32 is a sulfuric acid solution storage tank, and 33 is an electrolytic apparatus.

The sulfuric acid solution in the storage tank 32 is supplied to the electrolysis device 33 through the pipe 41 provided with the pump P ₇ and the cooler 34, and persulfuric acid is generated by electrolysis in the electrolysis device 33. It is circulated to the sulfuric acid solution storage tank 32 through a pipe 42 provided with a liquid separator 35. The sulfuric acid solution storage tank 32 is provided with a pure water supply pipe 43 and a concentrated sulfuric acid supply pipe 44.

Electrolytic sulfuric acid storage tank 32 is withdrawn from the pipe 45 with a pump _{P 8,} the filter 36, pipe 46, heater 37, is fed to the cleaning device 30 through the pipe 47. Sulfuric acid waste liquid used in the cleaning device 30 for cleaning electronic device is returned to the sulfuric acid waste liquid tank 31 by the pump P _9, filter 38, it is recycled to the sulfuric acid waste liquid tank 32 via a pipe 49 having a cooler 39.

Some of the sulfuric acid waste in sulfuric acid waste liquid tank 31 is withdrawn through a pipe 17 by the pump P _5, after being cooled in the heat exchanger 7, the sulfuric acid concentration is measured via a pipe 18a at a sulfuric acid concentration meter 9 The impurity metal ion concentration is measured by the LEP-AES analyzer 8 through the pipe 18b and returned to the sulfuric acid waste liquid storage tank 31 through the pipe 19.

When the measurement results of the sulfuric acid concentration meter 9 and the LEP-AES analyzer 8 satisfy the condition values set in advance, the sulfuric acid solution is extracted from the sulfuric acid waste liquid storage tank 31 by the pump P _{9 and the} liquid in the tank passes through the filter 38 and the cooler 39. When the sulfuric acid concentration is lower than the set value or when the impurity concentration is higher than the set value, it is discharged out of the system through the pipe 50.

  The destination of the liquid in the sulfuric acid waste liquid storage tank 31 is a switching valve (not shown) provided at the branch point of the pipe 49 and the pipe 50, and the measurement value of the sulfuric acid concentration meter 9 and the measurement value of the LEP-AES analyzer 8 are input. These can be automatically performed by switching control with a control device incorporating means for analyzing the measured values.

  According to the electronic device cleaning system of FIGS. 1 to 3, when the cleaning liquid is circulated and reused, the impurity concentration in the reused cleaning liquid is accurately grasped in a short time, and the impurity concentration does not exceed the control value. To prevent the occurrence of product defects in advance by controlling the contamination of electronic devices to be cleaned by stopping the circulation and discharging the contaminated cleaning liquid out of the system. Can do.

  Hereinafter, the present invention will be described more specifically with reference to examples.

[Example 1]
A sulfuric acid concentration of 85% by weight, a liquid measured using an analyzer “MH-5000” (Micro Emission Co., Ltd.) (hereinafter referred to as “MH-5000”) based on liquid electrode plasma emission analysis. The LEP-AES spectrum of the sulfuric acid aqueous solution of temperature 30 degreeC is shown in FIG. As shown in FIG. 4, when plasma is generated, emission peaks derived from O, H, and S elements contained in sulfuric acid are detected from the LEP-AES spectrum.

  Table 1 shows the results of testing the presence or absence of plasma generation by variously changing the sulfuric acid concentration and the liquid temperature of the sulfuric acid aqueous solution by using MH-5000.

Table 1 shows the following.
When the sulfuric acid concentration was 50 to 60% by weight, the electric conductivity was high even when the liquid temperature was lowered to room temperature, and the plasma was not generated or was not generated. On the other hand, when the sulfuric acid concentration was 80% by weight or more, plasma was stably generated by setting the liquid temperature to 80 ° C. or lower. Plasma was generated stably by adjusting the temperature to 40 ° C. or less at 70 wt% and 50 ° C. or less at 75 wt%.

[Example 2]
In the cleaning system shown in FIG. 1, a simulated contamination test using As was performed to determine whether the apparatus for measuring the concentration of metal ions in the liquid of the present invention can serve as a monitor for managing the impurity concentration.
Here, the sulfuric acid waste liquid recovery tank 4 and the sulfuric acid refining and regenerating apparatus 5 are not installed, but a sulfuric acid storage tank corresponding to the regenerated sulfuric acid tank 6 is installed, and in this storage tank, 30 L of 95% by weight sulfuric acid aqueous solution for electronic industry is heated to 90 ° C. Warmed up.
The electrical conductivity of a 95% by weight aqueous sulfuric acid solution at 90 ° C. is 0.35 S / cm.

MH-5000 is used as the LEP-AES analyzer 8 of the impurity concentration management monitor, and the sulfuric acid aqueous solution in the sulfuric acid storage tank is cooled by the heat exchanger 7 so that the liquid temperature becomes 40 ° C. at a flow rate of 10 mL / min. The solution was passed through 5000 and measured, and then returned to the sulfuric acid storage tank.
Here, the electrical conductivity of the 95 wt% sulfuric acid aqueous solution at 40 ° C. is 0.16 S / cm.

An arsenic-containing aqueous solution in which arsenic ions used as an ion implantation material for silicon wafers are selected as simulated contaminants and diarsenic pentoxide (As ₂ O ₅ ) is added to a concentration of about 10,000 mg / L Was added to the sulfuric acid storage tank at 200 mL / min.
In addition, using a sulfuric acid solution containing arsenic at a known concentration in advance, the LEP-AES spectrum shown in FIG. 5 was obtained, and the peak wavelength of arsenic to be measured was confirmed. As shown in FIG. The relationship of concentration was grasped.

  Based on this, the peak wavelength of arsenic is selected to be 228.8 nm, and when the emission intensity at the wavelength of 228.8 nm is less than 2000 (As concentration is about 120 mg / L or less), a high concentration is obtained from the sulfuric acid storage tank assumed to be a regenerated sulfuric acid tank. A sulfuric acid solution in the tank was transferred to the sulfuric acid storage tank 2 at 500 mL / min, and when the emission intensity was 2000 or more, a control program for stopping this transfer was set up.

As a result, when the arsenic-containing aqueous solution was added to the sulfuric acid storage tank for 2 minutes simultaneously with the start of the operation of the system, the transfer pump stopped because the emission peak at 228.8 nm exceeded 2000. At this time, the transfer amount of the sulfuric acid solution from the sulfuric acid storage tank to the high concentration sulfuric acid storage tank 2 was 1 L, and the sulfuric acid concentration was 94.2% by weight. Moreover, as a result of sampling the sulfuric acid solution in a sulfuric acid storage tank and measuring As concentration with an ICP-MS analyzer, As concentration was 120 mg / L.
Thus, by using the apparatus for measuring the concentration of metal ions in the liquid of the present invention, it is possible to detect on-time that the sulfuric acid solution in the regenerated sulfuric acid tank is contaminated with As, and minimize the diffusion of contamination. To the limit.

[Example 3]
In the cleaning system using the electrolytic sulfuric acid apparatus shown in FIG. 3, a simulated contamination test with Na was performed.
Electrolysis was performed by adjusting the sulfuric acid concentration to 85 wt%, and electrolytic sulfuric acid containing 20 to 30 mM of an oxidizing agent (persulfuric acid) was heated to 140 ° C. and supplied to the cleaning device 30. The electric conductivity of this electrolytic sulfuric acid is 0.60 S / cm. In the cleaning apparatus 30, a 300 mmφ silicon wafer having a silicon oxide film formed on the surface thereof was installed, and an electrolytic sulfuric acid solution was supplied to the wafer surface at 1 L / min. The electrolytic sulfuric acid solution supply time at the time of washing was 5 minutes, and then rinse washing with pure water for 2 minutes was performed. This operation was repeated every 10 minutes, and after 2 hours, 8 wafers were cleaned. The electrolytic sulfuric acid solution used for wafer cleaning was recovered in the sulfuric acid waste liquid storage tank 31 and returned to the sulfuric acid solution storage tank 32, and subjected to electrolytic treatment to contain an oxidizing agent to a predetermined concentration.

  MH-5000 is installed as a LEP-AES analyzer 8 for monitoring the impurity concentration of sulfuric acid waste liquid, and the heat in the sulfuric acid waste liquid storage tank 31 is adjusted to a liquid temperature of 40 ° C. at a flow rate of 10 mL / min. After cooling and passing through the solution, the solution after measurement was returned to the sulfuric acid waste liquid storage tank 31. The electrical conductivity of the sulfuric acid waste liquid cooled to 40 ° C. is 0.15 S / cm.

Here, Na ions were selected as a simulated contaminant, and an aqueous solution containing Na having a sodium concentration of about 1,000 mg / L with sodium sulfate (Na ₂ SO ₄ ) was used as the contaminated solution.
In addition, it confirmed from the LEP-AES spectrum by the high concentration sulfuric acid solution to which sodium sulfate was added beforehand that Na had a strong luminescence peak at a wavelength of 498.3 nm, and when the luminescence intensity was 1000 or more, to the sulfuric acid solution storage tank 32. It partnered the control program of the transfer pump P ₉ so as not to run.

Two hours after starting the operation of the test apparatus, 100 mL of the Na-containing aqueous solution was added to the sulfuric acid waste liquid storage tank 31. One minute later, since the emission peak at 498.3 nm exceeded 1000, the liquid in the sulfuric acid waste liquid storage tank 31 was discharged out of the system without transfer, and the system was restarted when cleaning was completed.
Thereafter, it was operated for 1 hour to clean four wafers. When the amount of Na deposited on the silicon oxide film surface was measured with a VPD / ICP-MS analyzer on the processed wafer, it was 1 × 10 ¹⁰ atoms / cm ² or less, which was the management reference value.

[Comparative Example 1]
A simulated contamination test with As was performed under the same conditions as in Example 1. Here, the impurity concentration monitor was not used, the sulfuric acid solution was sampled from the high concentration sulfuric acid storage tank, and the As concentration was measured with an ICP-MS analyzer. As a result, the As concentration was not detected in the solution immediately after the start of liquid feeding from the sulfuric acid recovery tank, but the As concentration was 3.8 g / L 1 hour after the transfer was completely completed. Thus, in the management method of sampling and applying to the analyzer, it takes several hours to obtain the measurement result, so that it is understood that the entire apparatus is contaminated with impurities at a high concentration.

[Comparative Example 2]
A simulated contamination test with Na was performed under the same conditions as in Example 2. The Na-containing aqueous solution was added 2 hours after the operation of the apparatus. This apparatus was continuously operated for 3 hours to obtain 12 cleaning wafers. When the Na adhesion amount on the silicon oxide film surface was measured with the VPD / ICP-MS analyzer for the processed wafer, the wafer from the operation of the apparatus to 2 hours was set as a management reference value of 1 × 10 ¹⁰ atoms / cm ^2. As described below, the amount of Na deposited on the four wafers that started processing two hours after the addition of the Na-containing aqueous solution increased to 1 × 10 ¹¹ to 1 × 10 ¹² atoms / cm ² .
As described above, in the cleaning system that circulates and reuses the cleaning liquid, it is understood that there is a possibility that the cleaning target object may be contaminated when the impurity contamination of the cleaning liquid is not measured online.

DESCRIPTION OF SYMBOLS 1 Cleaning apparatus 2 High concentration sulfuric acid storage tank 3 Hydrogen peroxide water storage tank 4 Sulfuric acid waste liquid recovery tank 5 Sulfuric acid refinement | purification reproduction apparatus 6 Regenerated sulfuric acid tank 7 Heat exchanger 8 LEP-AES analyzer 9 Sulfuric acid concentration meter 30 Cleaning apparatus 31 Sulfuric acid waste liquid storage tank 32 Sulfuric acid solution storage tank 33 Electrolyzer 34, 39 Cooler 35 Bubble separator 37 Heater

Claims (25)

A method for measuring the concentration of metal ions in a sample liquid having an electrical conductivity of more than 0.33 S / cm by plasma emission analysis, which includes one or more kinds of ions of metal elements in the third to sixth periods of the periodic table,
A pretreatment for preparing an adjustment liquid in which the electrical conductivity of the sample liquid is adjusted to 0.33 S / cm or less is performed, and the adjustment liquid is subjected to measurement by plasma emission analysis. Measuring method. In Claim 1, the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 80% by weight or more and a liquid temperature of more than 80 ° C.
The method for measuring a metal ion concentration in a liquid, wherein the pretreatment is a process of cooling the liquid temperature of the sample liquid to 80 ° C. or lower. The sample solution according to claim 1, wherein the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 70% by weight or more and less than 80% by weight and a liquid temperature of more than 35 ° C.
In the liquid, the pretreatment is a process of cooling the liquid temperature of the sample liquid to the lower limit set value or less based on the lower limit set value of the liquid temperature stored in advance associated with the sulfuric acid concentration. Method for measuring metal ion concentration.   4. The method for measuring a metal ion concentration in a liquid according to claim 2, wherein the sulfuric acid chemical solution is electrolytic sulfuric acid, a mixed solution of sulfuric acid and hydrogen peroxide solution, or a solution obtained by blowing ozone into sulfuric acid.   5. The method for measuring a metal ion concentration in a liquid according to claim 1, wherein the sample liquid is a cleaning liquid used for cleaning an electronic device in an electronic device manufacturing process.   6. The method for measuring a concentration of metal ions in a liquid according to claim 5, wherein the cleaning removes residual metal on the electronic device with the cleaning liquid.   7. The method for measuring a metal ion concentration in a liquid according to claim 5, wherein the cleaning waste liquid after the cleaning is reused as it is or after being recycled.   8. The method for measuring a metal ion concentration in a liquid according to claim 7, wherein the metal ion concentration is measured using the cleaning liquid separated from the circulation system as the sample liquid.   9. The method for measuring a metal ion concentration in a liquid according to claim 8, wherein the sample liquid after the measurement is returned to the circulation system.   A method for cleaning an electronic device with a cleaning liquid, wherein the metal ion concentration in the cleaning liquid is measured according to the method according to any one of claims 1 to 9. An apparatus for measuring the metal ion concentration of a sample liquid having an electric conductivity of more than 0.33 S / cm by plasma emission analysis, including one or more kinds of ions of metal elements in the third to sixth periods of the periodic table,
Pretreatment means for preparing an adjustment liquid in which the electric conductivity of the sample liquid is adjusted to 0.33 S / cm or less;
An apparatus for measuring the concentration of metal ions in a liquid, comprising: a plasma emission analyzer to which the adjustment liquid is supplied as a sample liquid. In Claim 11, the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 80 wt% or more and a liquid temperature of more than 80 ° C.
The apparatus for measuring a metal ion concentration in a liquid, wherein the pretreatment means is a cooling means for cooling the liquid temperature of the sample liquid to 80 ° C. or lower. In Claim 11, the sample solution is a sulfuric acid chemical solution having a sulfuric acid concentration of 70% by weight or more and less than 80% by weight and a liquid temperature of more than 35 ° C.
A liquid characterized in that the pretreatment means is a cooling means for cooling the liquid temperature of the sample liquid below the lower limit set value based on a lower limit set value of the liquid temperature stored in advance associated with the sulfuric acid concentration. Measuring device for metal ion concentration inside.   14. The apparatus for measuring a metal ion concentration in a liquid according to claim 12, wherein the sulfuric acid chemical liquid is electrolytic sulfuric acid, a mixed liquid of sulfuric acid and hydrogen peroxide solution, or a liquid in which ozone is blown into sulfuric acid.   The apparatus for measuring a metal ion concentration in a liquid according to any one of claims 11 to 14, wherein the sample liquid is a cleaning liquid used for cleaning an electronic device in an electronic device manufacturing process. Cleaning means for cleaning the electronic device with a cleaning liquid;
A recovery means for recovering cleaning waste liquid from the cleaning means;
A circulation means for circulating the cleaning waste liquid recovered by the recovery means to the cleaning means as a cleaning liquid;
An electronic device cleaning system comprising metal ion concentration measuring means for extracting a part of the circulating fluid from the circulation system by the circulating means and measuring the metal ion concentration of the circulating fluid,
The electronic device cleaning system, wherein the metal ion concentration measuring means includes a plasma emission analyzer.   17. The electronic device according to claim 16, wherein the metal ion concentration measuring unit includes a circulating liquid cooling unit, and the circulating liquid cooled by the cooling unit is measured by the plasma emission spectrometer. Cleaning system. The cleaning liquid according to claim 17, wherein the cleaning liquid is a sulfuric acid chemical solution having a sulfuric acid concentration of 80% by weight or more and a liquid temperature exceeding 80 ° C.
The electronic device cleaning system, wherein the cooling means is means for cooling the liquid temperature of the cleaning liquid to 80 ° C. or lower. The cleaning liquid according to claim 17, wherein the cleaning liquid is a sulfuric acid chemical solution having a sulfuric acid concentration of 70 wt% or more and less than 80 wt%, and a liquid temperature exceeding 35 ° C.
Cleaning the electronic device, wherein the cooling means is means for cooling the liquid temperature of the cleaning liquid below the lower limit set value based on a lower limit set value of the liquid temperature stored in advance associated with the sulfuric acid concentration. system.   18. The electronic device cleaning system according to claim 18 or 17, wherein the sulfuric acid chemical solution is electrolytic sulfuric acid, a mixed solution of sulfuric acid and hydrogen peroxide solution, or a solution obtained by blowing ozone into sulfuric acid. Cleaning means for cleaning the electronic device with a cleaning liquid;
A recovery means for recovering cleaning waste liquid from the cleaning means;
A circulation means for circulating the cleaning waste liquid recovered by the recovery means to the cleaning means as a cleaning liquid;
An electronic device cleaning system comprising metal ion concentration measuring means for extracting a part of the circulating fluid from the circulation system by the circulating means and measuring the metal ion concentration of the circulating fluid,
An electronic device cleaning system, wherein the metal ion concentration measuring means includes the apparatus for measuring a metal ion concentration in a liquid according to any one of claims 11 to 15.   22. The cleaning system for electronic devices in liquid according to claim 16, wherein the cleaning means is means for cleaning and removing residual metal on the electronic device with the cleaning liquid.   23. The method according to any one of claims 16 to 22, further comprising a regenerating unit for purifying or adjusting a component of the cleaning waste liquid in the circulation system, wherein a part of the regenerated liquid regenerated by the regenerating unit is extracted. An electronic device cleaning system, wherein a metal ion concentration is measured by a metal ion concentration measuring means.   24. The electronic device cleaning system according to any one of claims 16 to 23, further comprising liquid returning means for returning the liquid after the metal ion concentration measurement by the metal ion concentration measuring means to the circulation system.   25. The electronic device cleaning system according to any one of claims 16 to 24, wherein the cleaning liquid is a sulfuric acid-based cleaning chemical, and further includes a measuring device for the sulfuric acid concentration of the circulating liquid.

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