JPH07167852A - Filter device for measuring number of fine particles in ultra-pure water, and filter membrane therefor - Google Patents

Abstract

PURPOSE:To accurately perform an idle inspection by a constitution wherein a part of a filter membrane is a non-penetration region for the idle inspection. CONSTITUTION:A filter membrane 1 consists of a filter region 2 and a non- penetration region 3 and the region 2 filters ultra-pure water to capture fine particles. The region 3 is for the use of an idle inspection and does not filter the ultra-pure water so that the fine particles are not captured. Therefore, particles that are detected in the region 3 have been on a face of the membrane from the beginning. After the filtering operation, the fine particles are counted so that the correction of the particles that have been there from the beginning can be carried out. The surface of the membrane after the filtering is subjected to a prescribed treatment and photographs of the surface are taken by means of a scanning microscope by moving the field-of-view and the image processing thereof is carried out to count the number of fine particles on the surface. At that time, the counted result of the region 3 corresponds to the result of the idle inspection. On the basis of those results, it is possible to calculate the number of fine particles in the ultra-pure water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a filtration device for measuring the number of fine particles in ultrapure water and a filtration membrane for measuring the number of fine particles.

[0002]

2. Description of the Related Art In the ultrapure water used as water for various processes in the semiconductor industry, with the recent rapid increase in the required water quality, it has become possible to obtain a high degree of purity for measuring the minute amount of impurities contained in them. Analytical technology is required.

Among the measurement items of these impurities, the number of fine particles in ultrapure water is mentioned as a particularly important item. This is because fine particles in ultrapure water cause pattern defects in the exposure-etching process.

As a method for measuring the number of fine particles in ultrapure water, an online method applying laser scattering or sound waves and ultrapure water are captured by a filtration membrane and the membrane surface is observed by an optical microscope or a scanning electron microscope. There is a direct microscopic method for counting the number of fine particles.

FIG. 8 shows a conventional measuring method by direct microscopy. A filtration device 10 in which ultrapure water is supplied from a supply pipe 7 through which ultrapure water is passed through a sample introduction pipe 9 provided with a valve 8 and a filtration membrane 1 is held inside a holder 20.
To the normal temperature (25
The sample water is filtered at a constant temperature (.degree. C.) to capture the fine particles in the ultrapure water.

FIG. 7A is a sectional view for explaining the outline of the inside of the filtration device. The filtration membrane 1 is supported by a filtration membrane support 5 having a porous disk made of ceramics, sintered metal or the like, or a large number of flow paths such as holes and slits formed over almost the entire surface, and is an ultrapure sample. Water is filtered by the filtration membrane, and the fine particles 4 in the ultrapure water are captured on the surface of the filtration membrane. As shown in FIG. 7 (B), the filtration is performed on almost the entire surface of the filtration membrane 1 excluding the peripheral portion.

After filtration, the surface of the filtration membrane is subjected to a certain treatment,
Photographing or image processing is performed by an optical microscope or a scanning electron microscope to count the number of fine particles on the filtration membrane. As shown in FIG. 6, observation of the film surface with an optical microscope or a scanning electron microscope is performed by moving the visual field 11. The number of visual fields to be observed is determined from the area of one visual field so that approximately 0.01% of the effective filtration area can be observed.

However, 10 ⁵ to 10 ⁶ fine particles are originally present on the surface of a commonly used filtration membrane,
The measured fine particles are the total of the fine particles in the ultrapure water captured by filtration, the fine particles attached to the surface of the membrane before the measurement, and the fine particles attached by the operation necessary for the measurement.

Therefore, it is necessary to correct the measured number of fine particles only to the number of fine particles in the ultrapure water captured by the filtration membrane. In order to make a correction, before and after the filtration of the actual test as a blank test, another filtration membrane is used without filtration or a small amount (for example, 10 L) of filtration is performed, and then the number of fine particles on the filtration membrane surface is measured. The number of fine particles only in the ultrapure water captured by filtration is calculated by correcting the measured value. Further, as shown in FIG. 9, there is also a method in which a filtration device 10a for an actual test and a filtration device 10b for a blank test are mounted, filtration is started at the same time, and the filtration of the blank test is finished first.

After the actual test and the blank test are performed to measure the number of fine particles, the number of fine particles in the ultrapure water is calculated by making a correction by the following equation (1).

[0011]

[Equation 1]

[0012]

However, the conventional direct microscopy method has the following problems.

That is, the number of fine particles originally present on the filtration membrane differs for each filtration membrane, and even the filtration membranes of the same lot may vary by one digit or more. Therefore,
It was hard to say that the measurement results of the number of fine particles in ultrapure water always had satisfactory reliability even after correction by blank test.

In addition, since ultrapure water used in the manufacture of VLSIs in recent years has very few fine particles present, few fine particles are captured by filtration. Therefore, the measurement of the number of fine particles is strongly affected by the variation in the number of fine particles originally existing in the filtration membrane.

An object of the present invention is to provide a filtration device for measuring the number of fine particles and a filtration membrane for measuring the number of fine particles, which can accurately measure the number of fine particles.

[0016]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies to improve the accuracy of measuring the number of fine particles in ultrapure water, and as a result, permeate ultrapure water onto a single filtration membrane. The area for capturing ultrafine particles and a part of the filtration membrane for the blank test are made impermeable,
The inventors have found that a blank test can be performed with high accuracy by devising a filtration device or a filtration membrane itself so that a region where fine particles are not captured occurs, and have completed the present invention.

That is, according to the present invention, (1) in a filtration device for measuring the number of fine particles in ultrapure water, which comprises a filtration membrane and a filtration membrane support, a part of the filtration membrane is used as an impermeable region for a blank test. A filtration device for measuring the number of fine particles in ultrapure water, characterized in that (2) a part of the filtration membrane by applying a waterproof resin or attaching a sheet-shaped waterproof member to the back surface of the filtration membrane. Is a non-permeable region, and (3) a part of the filtration membrane support is impermeable, thereby making a part of the filtration membrane a non-permeable region. (4) The filtration device according to item (1), wherein (4) a sheet-shaped water-resistant member is inserted between the filtration membrane and the filtration membrane support to make a part of the filtration membrane an impermeable region. Features (1)
(5) Fine particles in ultrapure water in which a part of the filtration membrane is made into an impermeable region by coating a water-resistant resin or attaching a sheet-shaped water-resistant member to the back surface of the filtration membrane (5) The gist is a filtration membrane for number measurement.

[0018]

The present invention will be described in detail below.

FIG. 1 is a plan view of a filtration membrane used in the filtration device of the present invention. Reference numeral 1 is a filtration membrane, 2 is a filtration area for capturing fine particles, and 3 is an impermeable area for blank test.
In the example of FIG. 1, the area of the impermeable region 3 where no filtration is performed is shown as about 50% of the filtration membrane area, but the present invention is not limited by this ratio.

The filtration membrane used in the filtration device of the present invention is
Since one filtration membrane is provided with a filtration region 2 for filtering ultrapure water to capture fine particles and an impermeable region 3 for blank test, the filtration region 2 through which ultrapure water permeates fine particles. Although captured, the ultrapure water is not substantially permeated in the impermeable region 3, so that the fine particles in the ultrapure water are not captured. Therefore,
The fine particles on the impermeable region 3 are not the fine particles present in the ultrapure water, but the fine particles originally present on the surface of the filtration membrane. By measuring the fine particles in the impermeable region 3 after the filtration operation, The fine particles originally existing on the surface of the filtration membrane can be accurately corrected. In principle, the same filtration membrane is used for the actual test and the blank test, so the correction can be performed completely, but in reality, even on the same filtration membrane surface, there are variations in the originally existing fine particles. , Some errors will occur.

The surface of the membrane after filtration is subjected to a certain treatment, and then, as shown in FIG. 5, the field of view 11 is moved to perform photography, image processing, etc. using a scanning electron microscope or the like. Measure the number of fine particles on the film surface. As described above, the ratio of the surface actually observed is about 0.01%, so even if the filtration area is reduced by providing the impermeable region, if the movement interval at the time of observation is made small, it will be the same as the conventional method. The filtration membrane surface can be observed at the same rate. In FIG. 5, the measurement result of the filtration region 2 corresponds to the sample of the conventional method, and the measurement result of the impermeable region 3 corresponds to the result of the blank test. Based on the measurement results obtained in this way, the filtration amount V _{b in the} blank test is calculated by the formula (1).
The number of fine particles in ultrapure water is calculated with 0 as zero.

FIG. 2 is a sectional view of an embodiment for providing an impermeable region in a part of the filtration membrane. Reference numeral 1 is a filtration membrane, and 5 is a filtration membrane support. The filtration membrane support 5 is not particularly limited as long as it has a structure that supports the filtration membrane and allows the passage of ultrapure water. For example, a porous ceramic or a large number of flow channels including holes and slits are formed. It was done. The example in Figure 2
In order to make a part of the filtration membrane an impermeable region, the back surface of the filtration membrane 1 is coated with a water resistant resin 3a. In addition to applying the waterproof resin, a sheet-shaped waterproof member such as a waterproof polymer sheet may be attached to the back surface of the filtration membrane 1. When ultrapure water is passed through the filtration membrane 1, the ultrapure water is filtered in the area that has not been subjected to the impermeable treatment and the fine particles 4 are captured on the surface of the filtration membrane. Since the particles are not substantially filtered, ultrapure water particles are not trapped on the filtration membrane surface in the impermeable region.

FIG. 3 is an explanatory view of another embodiment for providing an impermeable region in a part of the filtration membrane. In the example of FIG. 3, the filtration membrane 1 is not treated to make it impermeable, and a part of the filtration membrane support 5 is used as the impermeable structure 5a, so that the filtration membrane portion in contact with this portion is substantially This is to prevent ultrapure water from being filtered. As a method of making a part of the filtration membrane support an impermeable structure, for example, a structure in which a water channel as described above is formed in about half of the filtration membrane support and no channel is formed in the other half Alternatively, a method of injecting the water-resistant resin as described above into a part of the flow path of the filtration membrane support to close it may be mentioned.

FIG. 4 is an explanatory view of still another embodiment for providing an impermeable region in a part of the filtration membrane. The filtration membrane 1 and the filtration membrane support 5 were not subjected to the impermeability treatment, and the sheet-shaped water resistant member 6 was inserted between the filtration membrane 1 and the filtration membrane support 5.

The filtration device of the present invention may be connected to a supply pipe through which ultrapure water is passed through a sample introduction pipe provided with a valve, as in the conventional filtration device. When measuring fine particles in ultrapure water using the filtration device of the present invention, a pump or a gas pressurizing means or the like may be provided between the supply pipe and the filtration device for measuring the number of fine particles, if necessary. By reducing the pressure of the liquid after filtration, the filtration rate can be increased and the filtration time can be shortened.

[0026]

【Example】

Example 1 An experiment was conducted using an ultrapure water supply line of Organo Research Institute. As a filtration membrane for measuring the number of fine particles, Nuclelipa (effective filtration area: 320 mm ² ) having a pore size of 0.1 μ was used. In order to make a part of the filtration membrane an impermeable region, a commercially available water-resistant adhesive tape was attached to 50% of the back surface of the filtration membrane. After filtering 50 liters of ultrapure water, the filter membrane was subjected to sputtering treatment, and fine particles were measured with a scanning electron microscope. The number of fine particles on the filtration region was measured as an actual test, and the number of fine particles on the impermeable region was measured as a blank test, and the number of fine particles in the ultrapure water was calculated by the formula (1) (where V _b = 0. Calculated as). The test was repeated 5 times, and the average value and standard deviation of the number of fine particles were obtained. The results are shown in Table 1.

Comparative Example 1 As a comparative example, the fine particles in the same ultrapure water line as in Example 1 were measured by the conventional method. That is, after using a filtration membrane having the same pore size as that used in Example 1 and conducting an actual test as in Example 1 (however, the amount of filtered water of ultrapure water was 100 liters), the filtration membrane was replaced. As a blank test, 5 liters of ultrapure water was filtered to obtain the measurement value of the blank test. The number of fine particles in the ultrapure water was calculated by the equation (1). The test was repeated 5 times, and the average value and standard deviation of the number of fine particles were obtained. The results are shown in Table 1.

[0028]

[Table 1]

As is clear from Table 1, in the conventional method, there is a large variation in the number of fine particles even if correction is performed by a blank test. On the other hand, according to the results of the present invention, although the measured values have some fluctuations, the variation in the calculated number of fine particles is far smaller than that of the conventional method.

The large variation in the number of fine particles in the conventional example is considered to occur because the actual test and the blank test differ in the contamination state of the surface of the filter. That is, the surface of the filtration membrane is contaminated at the time of membrane formation and at the subsequent steps such as packaging. The degree is not constant from film to film. Therefore, even if the blank test is corrected using two films, a large error is included. This possibility is high especially when the number of fine particles in water is small.

On the other hand, when the correction is performed with one film as in the present invention, there is a difference in the contamination due to the portion of the one film, but the difference in the contamination state between the films does not cause an error. Therefore, it is possible to measure the number of fine particles with much higher accuracy.

Further, conventionally, two filtration operations were required to remove the influence of fine particles adhering to the filtration membrane by the operation required for measurement, but according to the present invention, one filtration operation is required. There are advantages such as goodness.

[0033]

According to the present invention, the accuracy of measuring the number of fine particles in ultrapure water is improved, and the actual test and the blank test can be performed in one operation, so the work required for measuring the number of fine particles is reduced. To do.

[Brief description of drawings]

FIG. 1 is a plan view of a filtration membrane used in a filtration device of the present invention.

FIG. 2 is a sectional view for explaining one embodiment of the filtration device and the filtration membrane of the present invention.

FIG. 3 is a cross-sectional view for explaining another embodiment of the filtration device of the present invention.

FIG. 4 is a cross-sectional view for explaining another embodiment of the filtration device of the present invention.

FIG. 5 is an explanatory view of a microscopic method of a filtration membrane when the filtration device of the present invention is used.

FIG. 6 is an explanatory view of a microscopic method of a filtration membrane when a conventional filtration device is used.

7A is a cross-sectional view for explaining a conventional filtration device, and FIG. 7B is a plan view of a filtration membrane used in the conventional filtration device.

FIG. 8 is an explanatory view of a conventional method for measuring fine particles in ultrapure water.

FIG. 9 is an explanatory view of a conventional method for measuring fine particles in ultrapure water.

[Explanation of symbols]

 1 Filtration Membrane 2 Filtration Area 3 Impermeable Area 3a Water-Resistant Resin 4 Fine Particles 5 Filtration Membrane Support 6 Sheet-shaped Water-Resistant Member 7 Ultra Pure Water Supply Pipe 8 Valve 9 Ultra Pure Water Introducing Tube 10 Filtration Device 11 Field of View

Claims (5)

[Claims] 1. A filtration device for measuring the number of fine particles in ultrapure water, comprising a filtration membrane and a filtration membrane support, wherein a portion of the filtration membrane is used as an impermeable region for a blank test. A filtration device for measuring the number of fine particles in the product. 2. The filtration membrane according to claim 1, wherein a part of the filtration membrane is made an impermeable region by applying a water-resistant resin or adhering a sheet-shaped water-resistant member to the back surface of the filtration membrane. Filtration device. 3. The filtration device according to claim 1, wherein a part of the filtration membrane is made impermeable so that a part of the filtration membrane becomes an impermeable region. 4. The filtration device according to claim 1, wherein a part of the filtration membrane is made an impermeable region by inserting a sheet-shaped water resistant member between the filtration membrane and the filtration membrane support. . 5. A filtration for measuring the number of fine particles in ultrapure water in which a part of the filtration membrane is made an impermeable region by coating a water-resistant resin or attaching a sheet-shaped water-resistant member to the back surface of the filtration membrane. film.