JPH1063810A - Method for evaluating content of particulate in liquid - Google Patents

Abstract

PROBLEM TO BE SOLVED: To filter liquid efficiently in a short time and to perform speedy evaluation by filtering the liquid by a filter which has a hole diameter larger than specific particle size, counting particulates sticking on the filter, and estimating the number of particulates of larger than the specific particle size on the basis of the count value. SOLUTION: Even if the filter having the hole diameter larger than the specific particle size, i.e., particle sizes of particulates to be counted when the particles in the liquid are collected through the filter, the particulates approach the filter to a short distance in passing through holes of the filter and an attractive force operate between the particulates and filter, so that the particulates stick on the filter surface. Those particulates are magnified through an electron microscope, etc., and counted. Consequently, even when extremely small particulates are counted, the use of the filter having the diameter larger than the particulates to be counted does not make the filtering time extremely long and the filtering is carried out in a short time to enable efficient evaluation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for evaluating the content of fine particles in a liquid, and more particularly to a method for evaluating the content of fine particles in ultrapure water for cleaning a silicon wafer used in a semiconductor integrated circuit manufacturing process. The present invention relates to a method for evaluating the content of fine particles in a liquid.

[0002]

2. Description of the Related Art In a manufacturing process of a semiconductor integrated circuit,
For the purpose of highly cleaning the surface of the silicon wafer, a step of repeatedly cleaning with ultrapure water is incorporated, and a large amount of ultrapure water is used for cleaning. The silicon wafer is subjected to fine processing on its surface to form wiring and insulating parts,
At this time, if fine particles adhere to the surface of the silicon wafer, wiring and insulating portions cannot be formed correctly. Therefore, it is necessary to control the concentration of fine particles contained in chemicals used for cleaning the silicon wafer and ultrapure water to a predetermined concentration or less. There is. Generally, the particles to be controlled are based on design rules (minimum wiring width).
Is 1/10 or more of the particle size. Therefore, when cleaning the silicon wafer, it is contained in ultrapure water,
It is necessary to count the number of fine particles having a particle size equal to or more than 1/10 of the design rule and determine whether or not the fine particles are suitable as ultrapure water for cleaning.

In recent years, as the degree of integration of integrated circuits has increased, processing performed on silicon wafers has been further miniaturized, and the design rules of integrated circuits have become smaller. Therefore, at present, the particle size of the fine particles to be counted is also becoming smaller.

Conventionally, as a means for counting the number of fine particles contained in a liquid, a method of irradiating a liquid with a laser light to obtain the number of fine particles from the scattered light by utilizing the principle that laser light is scattered when fine particles are present is used. Automatic counting devices have been put to practical use. However, the particle size of the fine particles to be counted in recent ultrapure water for cleaning is much smaller than the wavelength of light, and the intensity of scattered light is also very small. Cannot count.

Therefore, in order to accurately count ultrafine particles having a particle diameter of 0.1 μm or less, ultrapure water is filtered through a filter to capture the contained particles on the filter surface, and this is captured by an electron microscope. For example, a method of directly counting the data by enlarging the data is used.

[0006]

However, the method of capturing and counting fine particles with a filter has the drawback that the filtration speed when filtering ultrapure water with a filter is very slow and the efficiency is low.

That is, when filtering the fine particles, a filter having the same pore size as the fine particles to be counted is used, and all the fine particles larger than the pore size of the filter are captured. In this method, for example, when filtering ultrapure water with a filter having such a very small pore size in order to capture extremely fine particles having a particle size of 0.1 μm or less, the filtration speed is extremely low. In addition, the time required for filtration becomes very long.

As shown in Table 1 below, if the pore size of the filter is reduced to 1/2, the time required for filtering the same ultrapure water is increased by a factor of five.

The present invention solves the above-mentioned conventional problems, and captures fine particles by filtration with a filter, counts them, and evaluates the content of the fine particles in the liquid. It is an object of the present invention to provide a method that enables efficient filtration in a short period of time, even when minute particles are to be counted, and provides a quick evaluation method.

[0010]

The method for evaluating the content of fine particles in a liquid according to the present invention is a method for evaluating the content of fine particles having a predetermined particle size or more in a liquid, wherein the pore size is larger than the predetermined particle size. And filtering the liquid with a filter having the following formula, counting the number of fine particles attached to the filter, and estimating the number of fine particles having the predetermined particle size or more based on the counted value.

The fine particles in the liquid generate a suction force with another solid surface due to factors such as the surface potential and Van der Waals force, and adhere to the solid surface. Therefore, when filtering and trapping fine particles in the liquid, the fine particles pass through the pores of the filter even if the filter has a predetermined particle size, that is, a filter having a pore size larger than the particle size of the fine particles to be counted. At this time, the fine particles approach the filter to a very short distance, and a suction force acts between the fine particles and the filter, so that the fine particles adhere to the filter surface.

The present invention utilizes such a phenomenon. The present invention utilizes a filter having a pore size larger than the particle size of the fine particles to be counted, and filters the fine particles smaller than the filter. The particles adhered to the filter are enlarged and counted by an electron microscope or the like.

According to the present invention, since a filter having a pore size larger than that of the microparticles to be counted is used, the filtration time does not become excessively slow even when ultrafine microparticles are to be counted, and the filtration can be performed in a short time. To conduct efficient evaluations.

[0014]

Embodiments of the present invention will be described below.

In the following, a method for evaluating the content of fine particles in ultrapure water according to the method of the present invention will be described. However, the method of the present invention has high purity and adheres to the filter by filtration. Any liquid capable of counting fine particles can be applied, and the target liquid is not limited to ultrapure water at all.

In the method of the present invention, first, a filter having a pore size larger than a predetermined particle size, that is, a particle size of fine particles to be counted (hereinafter, simply referred to as “predetermined particle size”) is used. Filter the water.

If the pore size of the filter used is too large,
Since the fine particles do not adhere to the filter due to the above-described suction force, the pore size of the filter must be within a range where the fine particles near the holes can be suctioned by the filter and adhere to the filter during filtration. is important. Also,
Even if the pore size of the filter is too small, the effect of shortening the filtration time according to the present invention cannot be sufficiently obtained.

In the normal case, the pore size of the filter is preferably 2 to 10 times, more preferably 2 to 5 times the predetermined particle size.

The material of the filter is preferably a material exhibiting a zeta (ζ) potential, particularly a material exhibiting a positive potential because fine particles in ultrapure water are considered to exhibit a negative potential. Examples include polycarbonate, polyester, nylon, polysulfone, polyamide, polyetherimide, polyvinyl chloride, cellulose, polytetrafluoroethylene, ceramics, and metals.

The filtration by this filter is 0.0
Pressure filtration at 1 to ²⁰ kg / cm ² is preferred.

After filtering the ultrapure water, the number of fine particles adhering to the filter is counted according to a conventional method.

That is, first, in order to make it possible to observe the filter to which the fine particles have adhered with an electron microscope, Pt is used as a pretreatment.
A filter is vapor-deposited with, for example, Au, carbon, or the like to impart conductivity to the surface. This allows observation with a scanning electron microscope. This is observed with a scanning electron microscope at a magnification of several thousand to tens of thousands, and the number of fine particles in the observation visual field is counted.

If necessary, the number of fine particles contained in a predetermined amount (for example, 1 liter) of ultrapure water is calculated from the counted value, the number of observation fields, the observation field area, the filtration area, and the amount of filtered water. Is determined, and this value is used as an evaluation reference value for the content of fine particles having a predetermined particle size or more in ultrapure water.

In the present invention, the content of fine particles in ultrapure water is evaluated from such a count value and an evaluation reference value according to, for example, the following method.

In advance, with respect to ultrapure water having various fine particle contents, filtration and counting are performed in the same manner as described above using a filter having a predetermined particle diameter to obtain a fine particle content of a predetermined particle size or more. If there is a predetermined relationship (for example, a proportional relationship) between this value and the count value or the evaluation reference value according to the present invention,
Based on the relationship, the count value or the evaluation reference value is corrected using a correction coefficient to determine the content of fine particles. For example, from the results of Example 1 and Comparative Example 1 described below, the value according to the present invention is multiplied by 7/6 to obtain the content of fine particles.

With respect to ultrapure water having various particle contents in advance, filtration and counting are performed in the same manner as described above using a filter having a pore diameter of a predetermined particle size to obtain a particle content of a predetermined particle size or more. A calibration curve is prepared with the count value or the evaluation reference value according to the present invention, and the fine particle content is determined by applying the above-mentioned count value or evaluation reference value to the calibration curve.

The evaluation is directly performed using the above-mentioned count value or evaluation reference value. For example, with respect to the count value or the evaluation reference value according to the present invention, a set value for evaluating the suitability of the ultrapure water for cleaning is provided in advance, and the set value is compared with the set value.

[0028]

The present invention will be described more specifically below with reference to examples and comparative examples.

Example 1, Comparative Example 1 The pore size and filtration flow of a polycarbonate membrane filter (trade name “Polycarbonate type membrane filter” manufactured by Advantech Toyo Co., Ltd.) conventionally used for counting the number of fine particles are conventionally used. Bundle (0.7 kg / cm ²
The filtration time required for filtering 10 liters of water with a filter having a diameter of 25 mm is as shown in Table 1.

As can be seen from Table 1, as the pore size decreases, the filtration flux decreases significantly, and the filtration time increases significantly.

[0031]

[Table 1]

The ultrapure water was filtered using the filters having the pore diameters of 0.2 μm (Example 1) and the pore diameter of 0.1 μm (Comparative Example 1), and the number of fine particles was counted and contained in the ultrapure water. The number of fine particles having a particle size of 0.1 μm or more was determined.

That is, each filter has an effective filtration area of about 9 cm.
Attached to the ^second filter holder, ultrapure water from the sampling valve fitted in the pipe of the final treated water directly introduced to the pressure of the ultrapure water production system (0.7 kg / cm ²⁾ and filtered.
Table 2 shows the time required for filtration of 100 liters of ultrapure water.

Further, the filter after filtration is taken out, subjected to pre-treatment after drying (gold deposition treatment), and then observed with a scanning electron microscope at a magnification of 8000 times. The number was counted. The number of counted particles,
The number of fine particles contained in one liter of ultrapure water was calculated from the number of observation visual fields, the visual field area, the filtration area, and the amount of filtered water, and the results are shown in Table 2.

[0035]

[Table 2]

As is clear from Table 2, the pore size is 0.2 μm.
In Example 1 using the filter of Example 1, the filtration time was significantly reduced as compared with Comparative Example 1 using a filter having a pore size of 0.1 μm.

Comparative Example 1 using a filter having a pore size of 0.1 μm is a result of counting fine particles having a particle size of 0.1 μm or more in ultrapure water by a filter and counting the number of particles. The pore size was 0.2μ for 1400
The result of Example 1 using the filter of m is not much different from the result of 1200 pieces / liter even though the pore diameter of the filter is doubled.

From these results, it can be seen that the number of fine particles in ultrapure water can be easily and accurately evaluated in a short period of time based on the results of Example 1 in accordance with the above-mentioned methods.

[0039]

As described in detail above, according to the method for evaluating the content of fine particles in a liquid of the present invention, the content of fine particles in a liquid can be quickly and accurately evaluated.

The method of the present invention is particularly effective for evaluating the content of fine particles in ultrapure water for cleaning silicon wafers used in the manufacturing process of semiconductor integrated circuits, and for evaluating the suitability of ultrapure water for cleaning. The time required can be greatly reduced.

Claims (2)

[Claims] 1. A method for evaluating the content of fine particles having a predetermined particle size or more in a liquid, comprising: filtering the liquid with a filter having a pore size larger than the predetermined particle size; And estimating the number of fine particles having a particle diameter equal to or larger than the predetermined particle diameter based on the counted value. 2. The method according to claim 1, wherein the liquid is ultrapure water.
The method for evaluating the content of fine particles in a liquid, wherein the pore size of the filter is 2 to 10 times the predetermined particle size.