JP3171633B2 - Analysis and quantification of nonvolatile impurities in ultrapure water - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing and quantifying impurities in pure water, and more particularly, to a method for removing a very small amount of non-volatile impurities in ultrapure water (including ultrapure chemicals) from the surroundings. The present invention relates to a method for concentrating without receiving contamination and performing component analysis and quantification.

[0002]

2. Description of the Related Art In recent years, with the progress of the degree of integration and miniaturization of semiconductors, contamination from the surrounding environment (contamination) has greatly affected the reliability and yield of products. Therefore, in the semiconductor manufacturing process, for example, the concentration of metal impurities on the wafer surface is reduced to 10 ¹⁰ atm / cm ^{2 to} 10 ⁷ at.
Wafers are required to be kept clean, for example, reduced to m / cm ² , and therefore, the demand for water quality is becoming higher even in ultrapure water used for cleaning wafers.

As described above, the necessity of analyzing and quantifying a trace amount of impurities for the purpose of controlling the quality of ultrapure water and the like has been increasing in recent years, and the analysis sensitivity (concentration of impurities that can be analyzed) has also been increasing. It is required to increase from about 100 ppt to a level of 1 ppq or less. In order to perform such high-sensitivity analysis and quantification, methods such as maintenance of the surrounding environment and development of high-sensitivity analytical instruments are conceivable.
It is expected to be quite difficult to implement.

[0004] Therefore, conventionally, ultrapure water has been concentrated by the method described below to increase the impurity concentration and then analyzed or quantified. That is, a method of analyzing or quantifying the water of an ultrapure water sample placed in a sample container or a dedicated container by using a rotary evaporator, or by irradiating an infrared lamp or heating a hot plate, and then using various devices is performed. ing. In particular, in the analysis and quantification of metal impurities on semiconductor wafers, hydrogen fluoride gas is sprayed on the wafer surface,
Alternatively, a method of contacting a small amount of a hydrofluoric acid solution, concentrating a metal impurity in a hydrofluoric acid solution or the like, and then analyzing and quantifying the same is adopted.

[0005]

However, in such a method for concentrating, analyzing and quantifying impurities, there are problems such as contamination from outside and low analytical accuracy in a trace amount range. That is, when concentrating impurities, it is necessary to increase the concentration magnification as much as possible without receiving contamination from the surroundings. However, the above-described conventional method cannot sufficiently satisfy the requirements, and the concentration is not sufficient. It was difficult to accurately analyze and quantify the impurities.

SUMMARY OF THE INVENTION The present invention has been made to solve such problems, and all impurities other than low-boiling organic substances and dissolved oxygen, such as ions, fine particles, viable bacteria, organic substances, and silica in ultrapure water, have been developed. The purpose of the present invention is to provide a method capable of concentrating ultrapure water at a high magnification without being contaminated by the surroundings and analyzing and quantifying its components and concentrations with high sensitivity and high accuracy. And

[0007]

SUMMARY OF THE INVENTION According to the present invention, there is provided a method for analyzing and quantifying non-volatile impurities in ultrapure water, which comprises spraying ultrapure water into clean air or an inert gas to form polydisperse droplets. And evaporating the water content of the generated droplets with clean air or an inert gas heated at a high temperature to convert non-volatile impurities into dry particles, and collecting the dry particles by a membrane filter. And a step of analyzing and measuring the surface of the membrane filter that has collected the dried particles by spectroscopic analysis means. In the method of the present invention, as a medium (gas) for atomizing ultrapure water into droplets, an ultra-high-speed air filter or the like is used to remove air of impurity particles to the utmost and to purify air. Is used. Also,
In addition to such clean air (clean air), an inert gas such as ultrapure nitrogen or argon can be used.

In the method of the present invention, the step of generating polydisperse droplets from ultrapure water and the step of evaporating the water content of the generated droplets to convert non-volatile impurities as evaporation residues into dry particles include, for example, High Pure Monitor (Nomura Micro
The measurement is performed by a total evaporation residue meter such as a product name of Science Co., Ltd.). FIG. 1 schematically shows the structure of the high-pure monitor.

This apparatus comprises an atomizer 4 which sprays ultrapure water 1 into clean air 2 to form polydisperse droplets 3,
Introduce clean hot air 5 ° C and atomizer 4
And an evaporating drying tube 6 for evaporating the water content of the droplets 3 sent from the apparatus. Non-volatile impurities in the ultrapure water 1 become dry particles 7 in the following process. That is, the ultrapure water 1 continuously sampled from the supply line 8 is quantitatively supplied by using the negative pressure generated inside the atomizer 4, and is sprayed into the clean air 2 by the atomizer 4 to be polydispersed. The droplet 3 is obtained. Among the droplets 3 that are continuously generated in this manner, droplets having a certain particle size or more are removed by an impactor (not shown), and only droplets 3 having a particle size smaller than that are transferred to the evaporative drying tube 6. Sent. Then, in the evaporative drying tube 6, the moisture of the droplets 3 is completely evaporated by the clean hot air 5 having a high temperature of 120 ° C., and the non-volatile impurities as evaporation residues become dry particles 7. Further, the evaporative drying tube 6
In the lower part, the dry particles 7 are mixed and diluted with the clean air 2 so that the pressure is equal to or lower than the saturated steam pressure even when the temperature drops to room temperature.

In the present invention, the membrane filter (membrane filter) for collecting the dried particles of the non-volatile impurities thus generated has a pore size (size of mesh) of 0.01.
It is preferable to use one having a thickness of 10 μm.

Further, as a method for analyzing and measuring the surface of such a membrane filter that has collected the dried particles, any surface analysis technique such as a spectroscopic analysis shown in the following table can be used. In other words, by irradiating the surface of the membrane filter with radiation such as electrons, ions, neutral particles, and X-rays, and by detecting and measuring various kinds of radiation generated secondarily, the components of the filter and the collected dry particles are detected. An analysis can be performed.

[0012]

[Table 1] Still further, in the present invention, for samples of ultrapure water adjusted to various impurity concentrations, analysis and measurement are performed using the above-described spectroscopic means, and the peak sizes and the like of the obtained spectra are compared. By the method, it is also possible to carry out a quantitative measurement.

[0013]

In the method for analyzing and quantifying non-volatile impurities in ultrapure water according to the present invention, ultrapure water is first sprayed into air or ultrapure inert gas that has been cleaned through a filter or the like in a spraying step. By this, it becomes a polydisperse droplet,
Then, by being heated by high-temperature air, etc.,
The water content of the droplet is completely evaporated. As a result of such evaporation, only the nonvolatile impurities in the ultrapure water remain, and the evaporation residue becomes extremely fine dry particles and floats in the gas. Next, the entire amount of the dried particles thus generated is collected or captured on the membrane filter. Then, the surface of the membrane filter that has collected the dried particles is analyzed and measured by a spectroscopic method, and the components of the dried particles, the weight thereof, and the like are obtained.

In this way, the trace amount of non-volatile impurities contained in the ultrapure water is concentrated and collected in a very clean state without being contaminated by the surrounding environment, and its components and concentrations are reproducible and stable. It is well analyzed and measured. In addition, the analysis accuracy is good, and high-sensitivity analytical measurement is possible.

[0015]

Embodiments of the present invention will be described below.

EXAMPLE Ultrapure water was continuously supplied to the high-purity monitor, and a 0.4 μm mesh Nuclepore membrane filter was installed at the outlet of the evaporative drying tube. Then, the dried residual particles (non-volatile impurities) in the ultrapure water were collected on the membrane filter for about one month.

Next, the dried residual particles thus collected on the membrane filter were photographed using an electron microscope. From this photograph, it was found that the dried particles were almost spherical and had a particle size of about 10 to 100 nm.

Further, the component analysis of the dried particles on the filter was performed using a scanning micro Auger electron spectrometer. The measurement results are shown in FIGS.

In the electron spectroscopy spectrum of the membrane alone (blank) shown in FIG. 2, peaks of C and O, which are components of the membrane, are observed, whereas in the spectrum shown in FIG. As a result, the peak of O becomes larger and the peak of Si appears. From these measurement results, it was found that the component of the dried particles collected on the membrane was considered to be SiO _2, and silica accounted for most of the nonvolatile impurities in the ultrapure water.

[0020]

As described above, according to the method of the present invention, a very small amount of non-volatile impurities in ultrapure water are concentrated into dry particles without being contaminated from the surroundings, and the components and the concentration of the dry particles are determined. Can be analyzed and measured with high sensitivity and quantified with high precision.

Therefore, it is extremely useful in managing the quality of ultrapure water in response to recent developments in the semiconductor industry and the like.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing the structure of a high-pure monitor used in the present invention.

FIG. 2 is an electron spectrum of a membrane filter used in an example, measured by a scanning micro Auger electron spectrometer.

FIG. 3 is an electron spectrum of the dried residual particles collected by the membrane filter, obtained in the example, as measured by a scanning micro Auger electron spectrometer.

[Explanation of symbols]

 1 Ultrapure water 2 Clean air 3 Droplets 4 Atomizer 5 Clean hot air 6 Evaporation drying tube 7 Dry particles 8 Supply line

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-195340 (JP, A) JP-A-1-195341 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 23/227 G01N 1/28 G01N 33/18

Claims (1)

(57) [Claims] 1. A step of spraying ultrapure water into clean air or an inert gas to form polydisperse droplets, and removing the water content of the formed droplets to high-temperature heated clean air or inert gas. Evaporating with an active gas to convert non-volatile impurities into dry particles, collecting the dry particles with a membrane filter, and analyzing and measuring the surface of the membrane filter that has collected the dry particles by spectroscopic means And a method for analyzing and quantifying non-volatile impurities in ultrapure water.