Method for measuring number of fine particles

Abstract

To provide a method for measuring the number of fine particles capable of accurately measuring the number of fine particles in a liquid by eliminating the influence of air bubbles by a simple means.SOLUTION: The method for measuring the number of fine particles in a liquid includes the following steps: (1) A step of filling a vessel with a liquid such that a length from a spout for pouring the liquid into the vessel to an inner face of the vessel (drop length of the liquid) is in a range of 30 to 90mm and a Reynold's number (Re) satisfies 2200 ≤ Re ≤ 3200. (2) A step of allowing the container filled with the liquid to stand for 1 hour or more. (3) A step of passing water through the pipe from the liquid injection port to the particle size detection unit to wash the 750ml or more in the fine particles counter. (4) A step of sending the liquid allowed to stand in the step (2) from the liquid injection port of the fine particle counter to the particle detection unit, and measuring the number of fine particles in the liquid in the particle detection unit.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for measuring the number of particles in a liquid. [Background technology]

[0002] In recent years, with the increase in the degree of integration of semiconductor circuits, there has been a stricter demand for reducing impurities and particles in chemicals and ultrapure water used in semiconductor manufacturing processes.

[0003] In particular, with regard to microparticles, requirements regarding not only the number but also the size have become stricter in recent years. For example, in the case of ultrapure water, ultrapure water was previously managed based on microparticles of 50 nm or larger, but in recent years there has been a demand for management based on microparticles of the 10 nm level (IRDS: International Roadmap for Devices and Systems).

[0004] Product inspection of particles in chemicals and ultrapure water initially employed the so-called direct inspection method using optical microscopes or scanning electron microscopes. This method involves filtering the chemicals through a filter, capturing the particles in the liquid on the filter, and then directly observing them. However, this method has many drawbacks, such as cumbersome pre-processing, a high susceptibility to contamination during handling, and the long measurement time required. For this reason, detailed particle measurement and analysis using direct microscopy is performed only as needed, and for routine particle management, it is common to use a light-scattering liquid particle counter (LPC) to directly pass the chemical solution through a measurement cell and perform measurements (see, for example, Patent Documents 1 and 2).

[0005] To properly manage particles using LPC, it is necessary to improve the reliability of LPC measurement results. However, LPC has the drawback that if there are factors that scatter light, such as the refractive index of the liquid or air bubbles, it can be measured as if particles are present even when they are not, resulting in a higher reading than that obtained by direct detection. It is known that such errors become more pronounced immediately after a container filled with a chemical solution is transported by truck or other means.

[0006] This is because air entrained during filling or gas generated from the chemical solution dissolves in the liquid and becomes bubbles due to factors such as temperature changes and external impacts, causing the actual measured value to be larger than the true value when measuring particles using the light scattering method by the amount of the bubbles.

[0007] Known methods for removing bubbles from such chemical solutions include leaving the solution to stand for a long period of time, treating the solution under reduced pressure or pressure, removing bubbles by centrifugal force, and contacting the solution with a porous material to capture the bubbles. However, simply leaving the solution to stand for a long period of time is not time-efficient, and reduced pressure or pressure treatment is not effective enough. Furthermore, when centrifugal force is used, there are problems with the maintenance and inspection of the centrifugal device, and when porous materials are used, there is the problem of impurities being mixed in, so these methods are not necessarily satisfactory treatment methods.

[0008] As a means for solving these problems, a method is known in which the number of particles is measured with high accuracy by removing bubbles through a combination of heating / cooling or decompression / pressurization of the chemical solution and ultrasonic cavitation (see, for example, Patent Documents 3 and 4).

[0009] However, although the methods proposed in Patent Documents 3 and 4 are effective for measuring the number of particles targeting particles with a particle diameter of several hundred nanometers, there is no mention of their effectiveness for measuring the number of particles targeting particles with a particle diameter of several tens of nanometers.

[0010] Another known method involves flowing a liquid containing particles and bubbles through a flow cell, irradiating it with laser light, and detecting the resulting scattered light and fluorescence using a spectral analyzer to distinguish between particles and bubbles and measure the number of particles in the water (see, for example, Patent Documents 5 and 6).

[0011] The above-mentioned Patent Documents 5 and 6 require a spectrum analyzer for spectrally analyzing the fluorescence generated when the sample liquid is irradiated with laser light, which poses a problem of expensive measurement equipment. [Prior art documents] [Patent documents]

[0012] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-170406 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-226642 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-121315 [Patent Document 4] Japanese Patent Application Laid-Open No. 2009-31173 [Patent Document 5] Japanese Patent Application Laid-Open No. 2001-4523 [Patent Document 6] Japanese Patent Application Laid-Open No. 2001-74644 Summary of the Invention [Problem to be solved by the invention]

[0013] The object of the present invention is to provide a method for measuring the number of particles in a liquid by eliminating the influence of bubbles using simple means and by which the number of particles in a liquid can be measured with high accuracy. [Means for solving the problem]

[0014] As a result of extensive research into methods for measuring the number of particles in a liquid, the inventor discovered that the number of particles in a liquid can be measured with high accuracy by using a method for filling a specific liquid into a container, and arrived at this invention.

[0015] That is, the embodiments of the present invention are [1] to [5] shown below. [1] A method for measuring the number of particles in a liquid through the following steps: (1) A process of filling a container with liquid so that the distance from the outlet through which the liquid is poured into the container to the inner surface of the container (the liquid dripping distance) is in the range of 30 to 90 mm and the Reynolds number (Re) is 2200≦Re≦3200. (2) A process of leaving the container filled with liquid undisturbed for at least one hour. (3) In the particle counter, a process of washing the inside of the pipe from the liquid inlet to the particle size detection unit with 750 ml or more of liquid. (4) A step of sending the liquid that has been left to stand in step (2) to a particle detection section through the liquid inlet of the particle counter, and measuring the number of particles in the liquid in the particle detection section. [2] The method for measuring the number of microparticles described in [1] above, wherein the minimum particle diameter of the microparticles that can be measured is 20 nm. [3] The method for measuring the number of particles according to [1] or [2] above, wherein the liquid is ultrapure water. [4] The method for measuring the number of particles according to any one of [1] to [3] above, wherein six or more containers are used. [5] The method for measuring the number of fine particles according to any one of the above [1] to [4], wherein the container is a hollow container in the shape of a bottle.

[0016] An embodiment of the present invention will be described below.

[0017] In this embodiment, when evaluating the number of particles in a liquid in a container, four steps are performed: a filling step in which the container is filled with liquid, a settling step in which precipitates and deposits on the container are dispersed in the liquid, a cleaning step in which water is passed through the pipe from the liquid inlet of the liquid-borne particle counter (LPC) to the particle size detection unit to clean the piping, tubes, and particle size detection unit within the device, and a measurement step in which the LPC is used to send the settling liquid from the liquid inlet of the LPC to the particle detection unit, and the particle detection unit measures the number of particles in the liquid. The filling step, settling step, cleaning step, measurement step, and the container and liquid used are described below.

[0018] [1] Filling process In the method for measuring the number of fine particles of the present invention, the filling step is a step of filling a container with liquid. When filling a container with liquid, the distance from the spout through which the liquid is poured into the container to the inner surface of the container is preferably in the range of 30 to 90 mm, more preferably 40 to 80 mm. If the distance from the spout to the inner surface of the container is less than 30 mm, stress caused by the liquid colliding with the inner surface of the container propagates across the liquid surface, creating unevenness on the surface of the liquid column. Air enters these uneven areas, causing bubbles to become mixed into the liquid, thereby degrading the accuracy of measuring the number of fine particles. Furthermore, if the distance from the spout to the inner surface of the container is longer than 90 mm, the contact area with air increases until the container is filled, increasing the likelihood of air bubbles becoming mixed in.

[0019] Furthermore, the Reynolds number (Re) of the liquid when filling the container is 2200≦Re≦3200, and more preferably 2600≦Re≦3000. If Re is less than 2200, the liquid will not be able to maintain a stable liquid column from the outlet until it reaches the inner surface of the container, and air bubbles will become mixed in the uneven parts caused by turbulence in the liquid column. If Re is greater than 3200, a liquid film will form from the jet surface, causing the liquid column to break up into liquid chunks, increasing the possibility of air bubbles being mixed in.

[0020] The amount of liquid to be filled into the container is preferably 90 to 100% of the volume. A filling amount of 90% or more of the volume is preferable because it facilitates dispersion of precipitates from the container and deposits on the container walls into the liquid. Furthermore, by increasing the filling amount, reducing the container headspace, and reducing the liquid-air interface, the possibility of air bubbles being mixed into the liquid when the container is physically vibrated after filling is reduced.

[0021] [2] Standing process The standing step is a step of dispersing precipitates from the container and deposits on the container wall into the liquid. The standing time of the container in this standing step is preferably 1 hour or more, more preferably 2 hours or more, and even more preferably 4 hours or more, so that the eluted substances and deposits from the container are sufficiently dispersed in the liquid and air bubbles mixed in the liquid disappear.

[0022] The temperature during the standing step must be set within a range that prevents the liquid from boiling and maintains the shape of the container. When ultrapure water is used as the liquid, the standing temperature (water temperature) is preferably in the range of 10 to 80°C, more preferably 20 to 40°C. When the temperature is 10°C or higher, the saturated dissolved oxygen concentration decreases, making it possible to suppress the generation of bubbles due to dissolved gas. When the temperature is 60°C or lower, the generation of water vapor can be suppressed, making it possible to prevent eluted materials and adhered materials from dissipating on the container along with the water vapor.

[0023] [3] Cleaning process The cleaning process is a process in which water is passed through the pipes from the liquid inlet of the liquid-borne particle counter (LPC) to the particle size detection unit to wash away particles generated from the piping, tubing, and particle size detection unit within the device until they are no longer detectable. The liquid used in the cleaning process is preferably the same liquid as the liquid used for particle measurement.

[0024] For example, when cleaning with ultrapure water containing 10 particles / ml of particles with a particle size of 20 nm or more, the liquid is purged until the number of particles detected by LPC reaches 10 ± 1 particles / ml. The amount of this purge is preferably 750 ml or more, as this reduces the number of particles generated by the device and stabilizes the measured particle count. If the purge volume is less than 750 ml, not only will the number of particles of 20 nm or larger generated from the device increase, but the number of particles detected by LPC will range from 20 to 100 particles / ml, resulting in large measurement variations, which is undesirable.

[0025] [4] Measurement process The measuring step is a step in which the liquid that has been left to stand in the standing step is sent to a particle detection section from a liquid inlet of the particle counter, and the number of particles in the liquid is measured in the particle detection section.

[0026] LPC is used to measure fine particles. The LPC used may be any of the light scattering method, the agglutination particle counter (CPC) method, and the ultrasonic method. Among the light scattering method, the CPC method, and the ultrasonic method, the light scattering method is preferred because it is easy to measure and has high reproducibility.

[0027] Specific examples of light scattering LPCs include KS-20F, KS-19F, KS-17B, KS-18F, KS-18FX, KS-16 / KS16F, KS-41a, KS-41B, KS-42a / 42F, KS-42B / 42BF, KS-42C, KS-42D, KL-30AX, KL-30B, KL-30, and XP-65 manufactured by RION Corporation; Hslis M50e, Ultra DI50, Ultra Chem 40, Ultra DI20, and Chem20 manufactured by Spectris; and Nanocount 25, Nanocount 30, and Nanocount 50+ manufactured by Lighthouse.

[0028] In the method of the present invention, there is no upper limit to the particle size to be measured as long as it is 20 nm or more, and the number of fine particles of multiple particle sizes may be measured simultaneously in any particle size range within the range that can be set by the device.

[0029] For example, when measuring the number of particles in ultrapure water with a particle size range of 20 nm or more, the number of particles belonging to each of the following ranges may be simultaneously measured: 20 nm or more, 30 nm or more, 40 nm or more, 50 nm or more, 60 nm or more, 70 nm or more, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, and 130 nm or more.

[0030] When measuring the number of particles through the above-mentioned filling, settling, washing, and measurement steps, for example, when measuring the number of particles with a particle diameter of 20 nm or more, it is preferable to measure six or more samples in the same container and use the average value as the number of particles in the container. When the number of samples is six or more, the average value is equivalent to a 95% confidence value, which is preferable because it allows the calculation of a value close to the true value. Furthermore, it is preferable if the standard deviation is 10 particles / ml or less, as this increases the accuracy of the average value.

[0031] [5] Container The containers used in the filling, settling, washing, and measuring steps can be any bottle-shaped hollow container with a storage space for holding a liquid. Examples include hollow containers with a container body having a mouth that opens into the storage space, a cap that can be attached to the mouth, a cylindrical body with a larger diameter than the mouth, and a bottom that connects to the lower end of the body. The diameters of the body and mouth of the container can be the same or different. There are no particular restrictions on the material of the container. Examples include borosilicate glass, tetrafluoroethylene (PFA), high-density polyethylene (HDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), polytetrafluoroethylene (PTFE), and polypropylene (PP). Borosilicate glass hollow containers, in particular, are suitable for analyzing particles in liquids because they exhibit low particle and metal elution. The container and cap can be made of the same or different materials.

[0032] [6]Liquid The liquid used in the filling, standing, cleaning, and measuring steps is not particularly limited in type, as long as the number of particles contained therein is equal to or less than the maximum particle number concentration measured by a liquid particle counter. Examples of suitable liquids include ultrapure water, sulfuric acid, hydrochloric acid, nitric acid, hydrofluoric acid, ammonium fluoride, hydrogen peroxide, isopropyl alcohol, xylene, TMAH (tetramethylammonium hydroxide), methanol, acetic acid, phosphoric acid, aqueous ammonia, PGMEA (propylene glycol methyl ether acetate), DMSO (dimethyl sulfoxide), and NMP (N-methyl-2-pyrrolidone), which are used in the electronics industry for wafer cleaning and etching, wiring and insulating film etching, jig cleaning, developing solutions, resist dilutions, resist strippers, drying, and the like.

[0033] Among these, ultrapure water is a preferred liquid for particle analysis because it is a clean liquid from which particles, organic matter, and trace ions have been removed, and it is stable at room temperature and pressure, causes little damage to the container, and can be stored for long periods of time.

[0034] Here, the term "ultrapure water" refers to any ultrapure water that is considered ultrapure. Among these, ultrapure water with a resistivity of 18.0 MΩ·cm or higher and a TOC (Total Organic Carbon) of 100 ppb or lower is preferred, as it has a particularly low amount of eluted metals and particle count, allowing for reproducible measurement of particle counts. More preferably, the resistivity is 18.2 MΩ·cm or higher and the TOC is 10 ppb or lower. When the resistivity is 18.0 MΩ·cm or higher, the ultrapure water contains few low-molecular-weight electrolytes (inorganic ions) and their sources, trace metals, and metal oxides. This reduces the likelihood of metals from the ultrapure water being mixed in with eluates and deposits from the container, allowing for reproducible measurement of particle counts.

[0035] When the TOC level is 100 ppb or less, the amount of organic matter contained in the ultrapure water is small, so there is little chance that organic matter originating from the ultrapure water will be mixed in with the eluate and deposits from the container, making it possible to measure the number of particles with good reproducibility.

[0036] It is preferable to carry out these steps of filling, standing, washing, and measuring in a clean environment, since this reduces the possibility of particles in the air being mixed into the liquid and improves the reproducibility of the measurements. The cleanliness of the clean environment is preferably class 3 or higher, more preferably class 2 or higher, and even more preferably class 1 or higher, according to the cleanliness classes defined in ISO 14644-1:2015. [Example]

[0037] The present invention will be described below with reference to examples and comparative examples, but the present invention is not limited to these examples at all.

[0038] The containers used were commercially available borosilicate glass containers (Premium Bottle Duran R 500 ml, manufactured by Shibata Scientific Co., Ltd.) and tetrafluoroethylene containers (PFA wide-mouth bottle 500 ml, F-1005-04, manufactured by Flon Industries Co., Ltd.).

[0039] Using the method of the present invention, a container was filled with ultrapure water in a clean room (Class 1 (ISO 14644-1:2015)), the container was left to stand, and then the liquid-borne particle counter was washed with ultrapure water and the number of particles was measured. The number of particles is expressed in particles / ml.

[0040] The ultrapure water and liquid-borne particle counter used in the examples and comparative examples are as follows: (1) Ultrapure water Ultrapure water (resistivity 18.2 MΩ·cm, TOC: 2 ppb) produced from industrially pure water using an ultrapure water production system (Organo Corporation, Puric FP-0500XU-0T0) was used. (2) Liquid-borne particle counter Rion Co., Ltd. Particle Sensor KS-20F (Controller KE-40B1) Example 1 Six borosilicate glass containers were prepared, and each was filled with 450 ml of ultrapure water in a clean room at a drip distance of 30 mm and a Reynolds number of 2900. The containers filled with ultrapure water were then left to stand at 23°C for 1 hour. Regarding the dripping distance, in this example, to prevent the water level from rising during filling of the container and shortening the dripping distance, the container was fixed at an angle (60° from the horizontal), and the filling operation was carried out so that the liquid flowed from the top of the container along the inner wall surface of the container and accumulated at the bottom of the container. In addition, the Reynolds number was calculated by dividing the inertial force (ρvL) by the viscous force (μ), assuming that the liquid poured onto the inner surface of the container from the outlet maintains the properties of a liquid column and regarding the liquid column as a liquid flowing inside an invisible pipe.

[0041] where ρ is the density of the fluid (kg / m 3 ), v is the flow velocity (m / s), L is the diameter of the liquid column (m), and μ is the viscosity coefficient of the liquid (Pa·s). The liquid-borne particle counter was purged with 750 ml of ultrapure water containing 8.2 particles / ml of particles 20 nm or larger, and the apparatus was then cleaned. The liquid-borne particle counter was then used to measure the number of particles 20 nm or larger in the ultrapure water filled in the six containers, and the average number and standard deviation of the particle counts in the six containers were calculated. The results are shown in Table 1.

[0042] The average number of microparticles was 24.9 / ml with a standard deviation of 7.2 / ml, demonstrating that the measurement method had excellent measurement accuracy.

[0043] Example 2 Except for the fact that the dropping distance during filling was 90 mm, the number of particles was measured using the same container and method as in Example 1. The average number of particles was 23.5 particles / ml, with a standard deviation of 5.1 particles / ml, demonstrating that the measurement method had excellent measurement accuracy.

[0044] Example 3 The number of particles was measured in the same manner and in the same container as in Example 2, except that the Reynolds number of the liquid at the time of filling was 2200. The average number of particles was 25.9 particles / ml, with a standard deviation of 4.4 particles / ml, demonstrating that this measurement method had excellent measurement accuracy.

[0045] Example 4 The number of particles was measured in the same manner and in the same container as in Example 2, except that the Reynolds number of the liquid at the time of filling was 3200. The average number of particles was 25.1 particles / ml, with a standard deviation of 5.2 particles / ml, demonstrating that this measurement method had excellent measurement accuracy.

[0046] Example 5 Except for using a tetrafluoroethylene container (PFA wide-mouth bottle 500 ml F-1005-04, manufactured by Flon Kogyo Co., Ltd.), the number of particles was measured using the same container and method as in Example 2. The average number of particles was 48.1 particles / ml, with a standard deviation of 2.9 particles / ml, demonstrating that this measurement method had excellent measurement accuracy.

[0047] Comparative Example 1 The number of particles was measured using the same container and method as in Example 2, except that the dropping distance during filling was 10 mm. The average number of particles was 71.9 particles / ml, with a standard deviation of 13.4 particles / ml, indicating that this measurement method had poor measurement accuracy.

[0048] Comparative Example 2 The number of particles was measured using the same container and method as in Example 2, except that the dropping distance during filling was 130 mm. The average number of particles was 251.9 particles / ml, with a standard deviation of 16.2 particles / ml, indicating that this measurement method had poor measurement accuracy.

[0049] Comparative Example 3 The number of particles was measured in the same manner and in the same container as in Example 2, except that the Reynolds number of the liquid at the time of filling was 1380. The average number of particles was 242.4 particles / ml, with a standard deviation of 21.5 particles / ml, indicating that this measurement method had poor measurement accuracy.

[0050] Comparative Example 4 The number of particles was measured in the same manner and in the same container as in Example 2, except that the Reynolds number of the liquid at the time of filling was 13600. The average number of particles was 903.4 particles / ml, with a standard deviation of 50.2 particles / ml, indicating that the measurement method had poor measurement accuracy.

[0051] Comparative Example 5 Except for the fact that the purging volume in the cleaning step was 125 ml, the number of particles was measured using the same container and method as in Example 2. The average number of particles was 50.1 particles / ml, with a standard deviation of 26.4 particles / ml, indicating that this measurement method had poor measurement accuracy.

[0052] [Table 1]

Claims

1. A method for measuring the number of particles in a liquid, which involves the following steps: (1) A process of filling a container with liquid so that the distance from the outlet through which the liquid is poured into the container to the inner surface of the container (the liquid dripping distance) is in the range of 30 to 90 mm and the Reynolds number (Re) is 2200≦Re≦3200. (2) A step of leaving the container filled with the liquid undisturbed for at least one hour. (3) A step of passing water through the tube from the liquid inlet to the particle size detection unit in the particle counter, and washing the tube with at least 750 ml of water. (4) A step of sending the liquid that has been left to stand in step (2) to a particle detection section through a liquid inlet of the particle counter, and measuring the number of particles in the liquid in the particle detection section.

2. 2. The method for measuring the number of fine particles according to claim 1, wherein the minimum particle size of the fine particles that can be measured is 20 nm.

3. 2. The method for measuring the number of particles according to claim 1, wherein the liquid is ultrapure water.

4. The method for measuring the number of particles according to claim 1, wherein six or more containers are used.

5. 2. The method for measuring the number of particles according to claim 1, wherein the container is a hollow container in the shape of a bottle.

Images