JP2001141721A - Analytical method of trace metallic impurity - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analytical method capable of quickly and precisely analyzing a trace metallic impurity in a sample such as an aqueous solution dissolving an easily thermally decomposable compound, easily volatile compound, extrapure water or the like. SOLUTION: In this method of analyzing a trace metallic impurity of a sample solution, the sample solution is put in a vertically long vessel consisting of a microwave transmitting material and placed in the chamber of a microwave generating device, and the gas generated in the vessel is eliminated by a gas eliminating means allowing the vertically long vessel to communicate with the outside of the chamber in the state where the vessel is sealed to the inside of the chamber while working a microwave to heat the content, and the resulting residue is taken out and analyzed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel method for analyzing trace metal impurities in a sample obtained by dissolving a thermally decomposable compound in a solvent. Specifically, it is an analysis method capable of analyzing trace metal impurities in the above sample quickly and accurately.

[0002]

2. Description of the Related Art Chemicals used in the semiconductor industry include sodium, potassium, iron, cobalt, nickel, copper, silver, lead, etc. in order to improve the yield of semiconductor substrates.
It is required to reduce the concentration of metal impurities such as tin. For this evaluation, various trace metal analysis methods developed in recent years can be used. For example, inductively coupled plasma emission method,
A typical example is inductively coupled plasma mass spectrometry.

In these cases, the sample is generally introduced into the measuring apparatus as a solution. However, a large amount of purification is required because the solute in the sample often interferes with detection of metal impurities. A method of diluting with water or removing the main component before introducing it into an apparatus is often employed.

[0004] For example, in the case of sulfuric acid used in the semiconductor industry, Semiconductor Equipment & Materials Internatio
The nal (SEMI) standard describes a method in which sulfuric acid is evaporated to dryness on a hot plate, the remaining residue is dissolved in nitric acid, and metal impurities are measured by flameless atomic absorption spectrometry or inductively coupled plasma mass spectrometry. .

Further, tetramethylammonium hydroxide (hereinafter abbreviated as TMAH), which is used as a developing solution for a photoresist for forming an integrated circuit pattern, is heated to a temperature of 120 ° C. or more to form volatile trimethylamine,
Utilizing the property of decomposing into dimethyl ether, TM
A method has been proposed in which an aqueous solution of AH is heated at a temperature of 220 ° C. or more and 500 ° C. or less for several hours to evaporate and decompose water and a main component to remove it, and dissolve the obtained residue in nitric acid to measure metal impurities. (JP-A-10-38873).

[0006] According to these methods, metal impurities can be highly concentrated by removing the compound of the main component as a solute, and the accuracy and sensitivity of analysis can be remarkably improved as compared with the dilution method.

[0007]

However, the problems of this method are that there is a concern that the sample is heated at a high temperature for a long time in an open system, and that the sample is contaminated by the external atmosphere, that the sample is contaminated from the container, and that the decomposition time is high. Takes a long time, it is not suitable for the analysis for daily quality control of the solution or the like as the sample in a production facility or a use facility.

Accordingly, it is an object of the present invention to quickly remove the solvent and the easily decomposable compound which is a main component as a solute in a sample while suppressing contamination of the sample, and to remove trace metals in the sample. An object of the present invention is to provide an analysis method capable of detecting impurities with high accuracy.

[0009]

Means for Solving the Problems The present inventors have conducted intensive studies to achieve the above object, and as a result, heating a sample solution such as the solution containing TMAH by microwaves in an extremely short time. By decomposing and concentrating the sample solution to obtain a residue, and by using a container of a specific shape in this treatment and employing a specific gas exclusion means, the contamination of the residue can be extremely effectively performed. It has been found that the metal impurities in the sample solution can be analyzed with extremely high reliability, and the present invention has been completed.

That is, the present invention provides a method for analyzing trace metal impurities in a sample solution, wherein the sample solution is placed in a microwave-transparent vertical container, placed in a chamber of a microwave generator, and then placed in a microwave generator. While heating the contents by applying waves, the gas generated in the container is
A method for analyzing trace metal impurities, comprising removing a residue obtained after removing the vertically elongated container and the outside of the chamber by gas removing means communicating with the inside of the chamber in a state where the inside of the container is sealed with respect to the chamber, and analyzing the residue. It is.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The sample solution to be analyzed by the method of the present invention is not particularly limited as long as it can be concentrated by heating. In particular, a sample solution containing an easily thermally decomposable compound such as TMAH is dissolved. It is effective for the used solution. That is, heating by microwaves can directly heat the target compound, and can complete the thermal decomposition in a shorter time than conventional external heating.

The above thermally decomposable compound is 500 ° C. or less,
A water-soluble compound that thermally decomposes at a temperature of 300 ° C. or less is preferable, and specific examples include the above-mentioned TMAH and ammonium fluoride. The solvent constituting the sample solution is not particularly limited as long as it can be heated by microwaves. In the case of an ionic compound, water, which is a good solvent, is preferably used.

In the present invention, a vertical container is used as a container in which the sample solution is allowed to exist, and the vertical container is configured to communicate with the outside of the microwave generator in a state where the container is sealed with respect to the chamber. In order to prevent the analysis accuracy from lowering due to the entrapment of metal impurities, which are the object of the analysis, with the evaporating substance, is important.

That is, the heating by microwaves does not substantially heat the container itself, so that the upper inner wall of the container is kept at a relatively low temperature. Therefore, by using a vertically long container, the metal impurities entrained together with the vaporized and decomposed gas easily condense on the inner wall during the process of ascending the inside of the container and easily stop, so that the analysis accuracy can be maintained at a high level.

Further, the inside of the chamber of the microwave generator has a very high metal ion concentration, and by providing a means for removing gas from the container in a state where the gas is sealed in the chamber, such contamination is significantly reduced. Reduced.

FIG. 1 shows a typical embodiment of the apparatus used in the present invention.

In the present invention, the shape of the vertically long container 1 is not particularly limited as long as it is vertically long, that is, a shape having a large height with respect to the diameter, but it is preferably a cylindrical body, and particularly preferably a cylindrical shape. Are preferred in terms of detergency. Further, it is preferable to set the length to be longer than the diameter of the cylinder in order to capture metal impurities accompanying the mist generated by heating the sample solution on the inner wall and improve the analysis accuracy. A suitable ratio (L / D) of the length to the diameter of the container is 1.5 or more, preferably 2 to 10, and more preferably 2 to 5.

As the material of the vertical container 1, a material having microwave permeability is used without any particular limitation, but a material having heat resistance to heating and chemical resistance to the sample is preferable. It is. Among them, quartz having a low content of metal impurities and fluororesins such as PFA and PTFE are particularly preferable.

Further, in the present invention, as the mode of providing the gas removing means, a mode in which a solvent gas, a decomposition gas or a volatile gas generated by heating by microwaves can be removed by suction is not particularly limited. For example, in FIG. 1 described above, a carrier gas pipe 3 is connected to the upper part of the vertically long container 1 via a joint portion 2, and the gas is sucked from the vertically long container 1 by a flushing effect by flowing the gas through the carrier gas pipe. An embodiment in which this is performed will be described. A clean gas having no reactivity with the decomposition gas as the carrier gas;
For example, a high-purity gas such as nitrogen or helium can be suitably used. As another aspect, there is an aspect in which the vertically long container is connected to an exhaust pump to suck and exhaust the gas.However, if the suction is performed too strongly, the metal to be analyzed is entrained by the gas and is lost. When the residue is taken out or the outside air is sucked into the container or the like, there is a possibility of causing contamination. Therefore, the embodiment shown in FIG. 1 is preferable.

When a suction means is employed, it is preferable that the degree of pressure reduction be kept at about -40 Pascal, and control is performed so that the inside of the container is at normal pressure when heating is completed.

In the present invention, the heating of the sample solution in the vertical container is performed by placing the vertical container 1 in which the sample solution 6 is present in the chamber 12 of the microwave heating device 11 as shown in FIG. Gas removing means is applied (in the figure, the carrier gas pipe 3 having the carrier gas inlet 4 and the carrier gas outlet 5 is connected to the microwave heating device 11).
This is a mode in which the piercing is provided. ), While irradiating with microwaves.

In the heating by the microwave, the wavelength and intensity of the microwave may be appropriately selected according to the amount and type of the sample. Generally, the wavelength of about 2450 MHz used for a cooking microwave oven is preferable. Can be used for In general, the intensity of microwave is 1 to 1 ml of sample.
It is preferable to select in the range of 0 to 60W. In other words, when the microwave is too weak, the processing takes time. On the other hand, when the microwave is too strong, a large amount of mist is generated due to rapid evaporation of the solvent in the sample, which flows out to outside through the gas suction means, and the loss of metal impurities. And the accuracy of the analysis decreases.

Since the components in the sample solution generate heat by the heating by applying the microwave as described above, the time required for evaporation, thermal decomposition, etc., is much shorter than that required by heat conduction or radiation. Moreover, as described above, since the container itself is not substantially heated, the upper inner wall of the container is kept at a relatively low temperature, so that metal impurities entrained together with evaporation and decomposition gas condense on the inner wall of the container. And the accuracy of the analysis can be kept high.

In order to sufficiently exhibit such an effect, the amount of the sample to be present in the container 1 is preferably 50% or less of the capacity of the container, more preferably 5 to 40%.
%, Particularly preferably 10 to 30%.

In addition, by performing processing in the chamber of the microwave generator and in the vertically long container which is cut off from the outside air, contamination of the sample by the outside air during heating is almost completely prevented, and the analysis accuracy is improved. Can be significantly improved.

Further, the contamination of the contents of the sample from the container progresses as the sample and the container come into contact with each other at a high temperature for a long time. However, according to the heating by the microwave, the container is not substantially heated. Since the temperature does not rise above the heating temperature of the sample, the sample can be processed in a state where the wall surface temperature of the container is low. Therefore, heating by microwaves
There is also an advantage that metal contamination from the container can be reduced.

In the present invention, the heating by microwave is preferably performed until most of the solvent and the easily decomposable compound in the sample solution are removed.

The residue thus obtained is supplied by dissolving a small amount of a solvent in a vertically long container, and is then taken out.
Then, by measuring this with a known metal analysis method, trace metal impurities contained in the sample solution can be analyzed with high accuracy.

As the above analysis method, flameless atomic absorption spectrometry, inductively coupled plasma emission method, inductively coupled plasma mass spectrometry, etc. can be preferably used.

The solvent for dissolving the residue may be any solvent that completely dissolves the residue and is suitable for the measuring device. For example, an aqueous solution such as nitric acid or hydrochloric acid can be particularly preferably used.

It is preferable that the smaller the amount of the solvent is, the higher the concentration rate of the sample is, and it is preferable that the amount be determined in consideration of the amount required for the measurement.

[0032]

According to the present invention, it is possible to concentrate a sample solution in a short period of time and very effectively prevent contamination due to various factors. Can be analyzed.

[0033]

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

Example 1 A 20-wt% TMAH aqueous solution (25 ml) was placed in a vertically long container composed of a 100-ml PFA container (L / D = 2.5).
As shown in (1), the microwave oven was set with a lid having a connection pipe and a carrier gas pipe connected to the side of the connection pipe. 10 L / liter of filtered nitrogen gas as carrier gas
Microwave for 30 minutes while flowing at a flow rate of
The MAH aqueous solution was evaporated and pyrolyzed.

At this time, the wavelength of the microwave is 2450 MHz.
z, strength was 500W. Immediately after completion, the lid was removed, the container was taken out, and the residue was dissolved with 10 ml of a 0.1 M nitric acid aqueous solution, and this was measured by inductively coupled plasma mass spectrometry. The decomposition temperature measured at this time was a maximum of 160 ° C, and the decomposition rate was 99.
9% or more. The results are shown in Table 1. These operations were all performed in a clean room.

Example 2 50 ml of a 20% by weight aqueous solution of TMAH was placed in a vertically long container similar to that in Example 1, and a lid having a connecting pipe as shown in FIG. And set it in the microwave generator. While flowing a filtered nitrogen gas at a flow rate of 10 L / min as a carrier gas, a microwave was irradiated for 60 minutes to evaporate and thermally decompose the TMAH aqueous solution.

At this time, the wavelength of the microwave is 2450 MHz.
z, strength was 500W. Immediately after completion, the lid was removed, the container was taken out, and the residue was dissolved with 10 ml of a 0.1 M nitric acid aqueous solution, and this was measured by inductively coupled plasma mass spectrometry. The decomposition temperature measured at this time was a maximum of 160 ° C, and the decomposition rate was 99.
9% or more. The results are also shown in Table 1. These operations were all performed in a clean room.

Example 3 In a vertically long container similar to that of Example 1, 50 ml of a 20% by weight aqueous solution of TMAH was put, and a lid having a connection pipe as shown in FIG. 1 and a carrier gas pipe connected to the side thereof was provided. And set it in the microwave generator. While flowing filtered nitrogen gas as a carrier gas at a flow rate of 10 L / min, microwave irradiation was performed for 30 minutes to evaporate and thermally decompose the TMAH aqueous solution.

At this time, the wavelength of the microwave is 2450 MHz.
z, strength was 1000W. Remove the lid immediately after the end,
The container was taken out and the residue was dissolved in 10 ml of a 0.1 M aqueous nitric acid solution, and this was measured by inductively coupled plasma mass spectrometry.
The decomposition temperature measured at this time was a maximum of 160 ° C, and the decomposition rate was 9
It was 9.9% or more. The results are also shown in Table 1. These operations were all performed in a clean room.

[0040]

[Table 1] Comparative Example 1 <Method by Dilution> 2 in 100 ml PFA volumetric flask
25 ml of a 0 wt% TMAH aqueous solution and 5 ml of 10 M nitric acid were added, and the mixture was made up to 100 ml with purified water. This was measured by inductively coupled plasma mass spectrometry. The results are shown in Table 2. These operations were all performed in a clean room.

From Table 2, it can be seen that when no concentration is performed, the analysis accuracy is extremely low.

Comparative Example 2 <Method by Hot Plate Heating>
25% by weight of a TMAH aqueous solution was put in, placed on a hot plate, and heating was started.
After the temperature reached 80 ° C., the temperature was raised at a rate of 2 ° C./min, and when the temperature reached 330 ° C., heating was performed for 4 hours while maintaining this temperature. After cooling, the residue was dissolved in 10 ml of a 0.1 M aqueous nitric acid solution, and the residue was measured by inductively coupled plasma mass spectrometry. At this time, the TMAH decomposition rate was 99.9% or more. The results are also shown in Table 2. These operations were all performed in a clean room.

It is apparent from Table 2 that the value of a specific metal component in the analysis value has increased due to contamination during concentration.

[0044]

[Table 2]

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a typical embodiment of an apparatus used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical container 2 Joint part 3 Carrier gas piping 4 Carrier gas inlet 5 Carrier gas outlet 6 Sample solution 11 Microwave heating device 12 Chamber

Claims (7)

[Claims] In a method for analyzing trace metal impurities in a sample solution, the sample is placed in a vertically long container made of a microwave-permeable material, placed in a chamber of a microwave generator, and then the microwave is applied. While heating and heating the contents, the gas generated in the container is eliminated by gas elimination means communicating the vertically long container and the outside of the chamber in a state where the inside of the container is sealed with respect to the chamber, A method for analyzing trace metal impurities, wherein the obtained residue is taken out and analyzed. 2. The analysis method according to claim 1, wherein the amount of the sample solution to be present in the vertically long container is 50% or less of the volume of the container. 3. The analysis method according to claim 1, wherein the gas removing means is constituted by connecting a pipe above the vertically long container, and connecting the other end of the pipe to a side of the pipe of the carrier gas. 4. The analysis method according to claim 1, wherein the intensity of the microwave is 10 to 60 W per ml of the sample solution. 5. The analysis method according to claim 1, wherein the sample solution contains a thermally decomposable compound. 6. The method according to claim 5, wherein the easily thermally decomposable compound is tetramethylammonium hydroxide. 7. The method according to claim 1, wherein the residue is dissolved in a small amount of a solvent and taken out of the vertically long container.