JP2002005799A - Analytical method for trace metal impurities - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an analytical method capable of quickly, accurately analyzing trace metal impurities in a sample of, for example, an aqueous solution in which an easily heat decomposable compound or an easily volatile compound is dissolved, or ultra-pure water. SOLUTION: In the analytical method of the trace metal impurities in a sample solution 15, the sample solution is put into a longitudinally long container made of a microwave permeable material, the container is put in a chamber having a usual heating means such as a microwave generating device 13 and a hot air generating device 14, heating by microwaves and the wall surface heating of the sample container are simultaneously or sequentially conducted to vaporize and/or decompose the sample solution, and the obtained 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 an evaporable solution sample or 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. For example, in the case of sulfuric acid used in the semiconductor industry, Semiconductor Equipment &
The Materials International (SEMI) standard describes a method of evaporating sulfuric acid on a hot plate to dryness, dissolving the remaining residue in nitric acid, and measuring metal impurities by flameless atomic absorption spectrometry or inductively coupled plasma mass spectrometry. I have.

As described above, a method of analyzing the remaining trace metal impurities by removing the main components in the sample by heating is not limited to the above-mentioned sulfuric acid. It can be applied to the analysis of impurities. As an example of this, an aqueous solution of tetramethylammonium hydroxide (hereinafter abbreviated as TMAH) used as a developing solution for a photoresist for forming an integrated circuit pattern is placed in a heat-resistant container at a temperature of 220 ° C. or more and 500 ° C. or less. There has been proposed a method of heating for several hours to evaporate and decompose water and main components to remove them, dissolve the residue in nitric acid, and measure metal impurities. (JP-A-10-38873) According to this method,
The solute main component is completely removed to eliminate the interference of detection of metal impurities by the main component, and the metal impurities can be highly concentrated, thereby significantly improving the accuracy and sensitivity of analysis compared to the dilution method. Can be improved.

[0005]

However, as a problem of this method, there is a concern that contamination by an external atmosphere due to heating the sample at a high temperature for a long time in an open system, contamination from a container, etc. Is not suitable for analysis for performing daily quality control of the solution or the like as the sample in a production facility or a use facility.

An object of the present invention is to quickly evaporate and / or decompose and remove a solvent and a compound which is a main component as a solute in a sample while suppressing contamination of the sample to remove trace metal impurities in the sample. An object of the present invention is to provide an analytical method that can be detected with high accuracy and that can be used for daily quality control.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found that evaporable solution samples or samples in which a thermally decomposable compound is dissolved in a solvent are used. Simultaneous or sequential heating of the microwave and heating of the wall surface of the sample container can completely evaporate and / or decompose the sample solution in a very short time to obtain a residue. By using a container of the above type and employing a specific gas elimination means, the loss of trace metal impurities in the sample can be reduced and the contamination can be suppressed very effectively, and the metal impurities can be extremely highly reliable. And found that the present invention was completed.

That is, according to the present invention, in a method for analyzing trace metal impurities in a sample solution, the sample solution is placed in a vertically long container made of a microwave-permeable material and placed in a chamber of a microwave generator. Then, the gas generated in the vertical container by heating is removed by the microwave of the sample solution while gas is removed by gas removing means communicating the vertical container and the outside of the chamber in a state where the vertical container is sealed in the chamber. A method for analyzing trace metal impurities in a sample solution, wherein heating and wall heating of a vertically long container are performed simultaneously or sequentially to evaporate and / or decompose a sample solution, and take out and analyze the obtained residue. .

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION The sample solution to be analyzed by the present invention is not particularly limited as long as it can be evaporated and / or decomposed by heating. It is effective for a solution in which an active compound is dissolved. The solvent constituting the sample solution is not particularly limited as long as it can be heated by microwaves. However, when the main component as a solute is an ionic compound, water as 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. It is important to provide such a gas exclusion means in order to analyze metal impurities as an object of analysis with extremely high reliability.

That is, trace metal impurities in the sample are contained in the mist accompanying the solvent gas, the decomposition gas, or the volatile gas generated when the sample solution is evaporated by heating. Therefore, it is necessary to minimize the loss of mist from the container. In the case of a vertically long container, the mist condenses on the wall surface of the container and is collected, so that the loss of the mist is suppressed. However, if the container is not vertically long, mist is discharged from the container along with the gas, and the reliability of analysis is reduced.

Further, the inside of the chamber of the microwave generating apparatus is made of metal, and there is a concern that metal contamination will occur as it is. However, such contamination is significantly reduced by providing a means for removing the gas in the container from the evaporation and / or decomposition of the sample solution while keeping the gas sealed in the chamber.

FIG. 1 shows a typical embodiment of the instrument 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 relative to the diameter, but it is preferably a cylindrical body, and particularly preferably a cylindrical shape. Are preferred in terms of detergency. In addition, in order to capture the metal impurities entrained in the mist generated by heating the sample solution on the inner wall and improve the analysis accuracy, the height ratio (L / D) to the diameter of the vertically long container may be set to be large. preferable. A suitable ratio of height to diameter (L / D) of the container is 1.5 or more, preferably 2 to 10, 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, a fluororesin such as quartz or PFA or PTFE having a low content of metal impurities is particularly preferable.

In the present invention, a mode in which the above-mentioned gas removing means is provided is not particularly limited, and a mode in which a solvent gas, a decomposition gas or a volatile gas generated by heating can be removed by suction is adopted. For example, in FIG. 1 described above, a gas discharge pipe 3
Is connected to the side of the carrier gas pipe 4, and the gas is sucked from the vertically long container 1 by a flushing effect by flowing the gas through the carrier gas pipe.
As the carrier gas, a clean gas having no reactivity with the decomposition gas, for example, a high-purity gas such as nitrogen or helium can be suitably used.

As another mode, there is a mode in which the vertical container is connected to an exhaust pump to suck and exhaust the gas, but if the suction is performed too strongly, the metal to be analyzed is accompanied by the gas. When the residue is taken out or the residue is taken out, contamination may be caused due to the outside air being sucked into the container. Therefore, the embodiment shown in FIG. 1 is preferable. Further, a purge gas pipe 5 for purging a solvent gas, a decomposition gas or a volatile gas remaining in the vertically long container 1 after the processing is completed is connected to the joint portion 2.

In the present invention, the microwave heating of the sample solution and the wall heating of the vertically long container may be performed simultaneously or sequentially. At this time, a normal heating means is used without any particular limitation for the method of heating the wall surface, but a radiation method using an electric heater or a hot air heating method is preferable from the viewpoint of operability.

As shown in FIG. 2, the microwave heating of the sample solution in the vertically long container and the wall heating of the vertically long container are performed by combining the vertically elongated container 1 in which the sample solution 15 is present with the microwave generator 13 and the hot air generator. 14 is placed in the chamber 12 of the heating device 11 and a gas elimination means is applied (in the figure, a carrier gas inlet 16 and a carrier gas outlet 1
This is an embodiment in which a carrier gas pipe 4 having a through hole 7 is provided through the heating device 11. However, it is common practice to simultaneously or sequentially perform microwave heating and wall heating with hot air.

In the heating by microwaves, the wavelength and intensity of the microwaves may be appropriately selected according to the amount and type of the sample. Generally, those having a wavelength of about 2450 MHz used in a microwave oven for cooking are preferred. 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.

The temperature of the wall heating performed simultaneously or sequentially with the microwave heating needs to be higher than the boiling point or decomposition temperature of the sample solution, but if it is too high, the container may be damaged. In particular, when a fluorocarbon resin such as PFA or PTFE is used as a sample container, the maximum operating temperature is 260 ° C. When these containers are used, it is necessary to use a heating temperature lower than this. Elution of contaminants from the sample container is more likely to occur at higher temperatures. From this point, it is preferable that the wall heating temperature is in a range exceeding the boiling point or the decomposition temperature and not more than the boiling point or the decomposition temperature + 40 ° C.

The microwave heating and the wall heating may be performed simultaneously or sequentially. By simultaneously or sequentially performing the microwave heating and the wall heating, the sample solution can be completely evaporated and / or decomposed in a short time as compared with heating the sample solution on a heating body such as a hot plate.

When heating is performed sequentially, microwave heating is first performed to evaporate and / or decompose most of the sample solution, and then the remaining sample solution is completely evaporated and / or decomposed by wall heating. Is preferred, but the opposite is not expected to be effective. In addition, it is more preferable to perform the heating at the same time because the wall heating can enhance the effect of the microwave heating, and the processing time can be shortened as compared with the case where the heating is performed sequentially.

The amount of the sample solution to be present in the container 1 is preferably 50% or less, more preferably 5 to 40% of the volume of the container in order to suppress the loss of trace metal impurities due to the generation of mist. And particularly preferably, 10 to 30
%.

As described above, by treating the sample solution in the chamber of the heating device and in the vertical container which is shut off from the outside air, contamination of the sample solution by the outside air during heating is almost completely prevented, and the analysis accuracy is remarkably improved. Can be improved.

Further, the contamination of the sample solution, which is the content, from the container progresses as the sample solution and the container come into contact with each other at a high temperature for a long time. However, simultaneous and / or sequential microwave heating and wall heating are required. Thereby, the contact time between the container wall surface, which has become hot, and the sample solution can be remarkably shortened to perform the treatment. Therefore, simultaneous and / or sequential execution of the microwave heating and the wall heating also has an advantage that metal contamination from the container can be reduced.

In the present invention, the microwave heating and the wall heating are preferably performed until the solvent and the easily decomposable compound in the sample solution are completely removed.

A solvent gas, a decomposition gas or a volatile gas remains in the sample container after the evaporation and / or decomposition treatment.
Since these gases may be harmful to the human body or have an odor, it is desirable to replace them with an inert gas.As a means for this, a purge gas pipe is provided in the sample container, and an inert gas is supplied from the pipe. Preferably, the gas can be blown.

The residue thus obtained is dissolved and taken out by supplying a small amount of solvent into a vertically long container. 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 can completely dissolve 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.

The smaller the amount of the solvent is, the higher the concentration of the sample is, and the more preferable it is. The amount may be determined in consideration of the amount required for the measurement.

[0033]

According to the present invention, evaporation of a sample solution and / or
Alternatively, the decomposition can be performed in a short time while preventing contamination due to various factors extremely effectively, and the metal impurities can be analyzed with high sensitivity and high accuracy.

[0034]

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 In a vertically long container composed of a 100 ml PFA container (L / D = 2.5), 25 ml of a 20% by weight aqueous solution of TMAH was placed, and FIG.
As shown in (1), the heating apparatus was set with a lid having a gas discharge pipe connected to the side of the carrier gas pipe. While flowing a filtered nitrogen gas as a carrier gas at a flow rate of 10 L / min, a microwave was irradiated at a wavelength of 2450 MHz and an intensity of 500 W for 30 minutes to evaporate and thermally decompose the TMAH aqueous solution.

Subsequently, TMAH is completely decomposed,
After heating with hot air at a set temperature of 170 ° C. for 20 minutes, nitrogen gas was introduced into the vertically long container through the purge gas pipe 5, and the gas in the container was completely purged. TMAH at this time
Was 100%, and was completely decomposed.
The decomposition rate was determined by a gravimetric method.

After the above operation is completed, the container is taken out, and the container is set at 0.
The residue was dissolved in 10 ml of a 1M aqueous nitric acid solution, and this was measured by inductively coupled plasma mass spectrometry.

The results of the analysis are shown in Table 1. These operations were all performed in a clean room.

Example 2 In a vertically long container similar to that in Example 1, 25 ml of a 20% by weight aqueous solution of TMAH was placed, and as shown in FIG. 2, a lid having a gas discharge pipe connected to the side of a carrier gas pipe was placed. And set in a heating device. The wavelength is 2450 M while flowing the filtered nitrogen gas as a carrier gas at a flow rate of 10 L / min.
TMAH was decomposed by heating with hot air at a set temperature of 170 ° C. for 30 minutes while irradiating microwaves at a frequency of 500 W with a frequency of 500 W, and nitrogen gas was introduced through a purge gas pipe 5 to completely purge the gas in the container. TMAH at this time
Was 100%, and was completely decomposed.
The decomposition rate was determined by a gravimetric method.

After the above operation is completed, the container is taken out, and the container is set to 0.
The residue was dissolved in 10 ml of a 1M aqueous nitric acid solution, and this was measured by inductively coupled plasma mass spectrometry.

The results of the analysis are shown in Table 1. These operations were all performed in a clean room.

Example 3 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 gas discharge pipe connected to the side of a carrier gas pipe was used as shown in FIG. And set in a heating device. The wavelength is 2450 M while flowing the filtered nitrogen gas as a carrier gas at a flow rate of 10 L / min.
TMAH was decomposed by heating with hot air at a set temperature of 170 ° C. for 50 minutes while irradiating microwaves at a frequency of 500 W at a frequency of 500 Hz, and nitrogen gas was introduced through a purge gas pipe 5 to completely purge the gas in the container. TMAH at this time
Was 100%, and was completely decomposed.
The decomposition rate was determined by a gravimetric method.

After the above operation is completed, the container is taken out, and the container is set at 0.
The residue was dissolved in 10 ml of a 1M aqueous nitric acid solution, and this was measured by inductively coupled plasma mass spectrometry.

The results of the analysis are shown in Table 1. These operations were all performed in a clean room.

[0045]

[Table 1]

Comparative Example 1 (Method by heating on a hot plate)
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., the mixture was heated for 4 hours while maintaining this temperature, and then allowed to cool. At this time, the decomposition rate of TMAH was 100.
%, And had been completely decomposed. The decomposition rate was determined by a gravimetric method. Thereafter, the residue was dissolved in 10 ml of a 0.1 M aqueous nitric acid solution, and measured by inductively coupled plasma mass spectrometry. The results are shown in Table 2. These operations were all performed in a clean room.

Comparative Example 2 (Method by Dilution)
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.

Comparative Example 3 (Method using stock solution) A 20% by weight aqueous TMAH solution was directly 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 heated on a hot plate, evaporation and / or decomposition takes a long time, and the value of a specific metal component in the analytical value increases due to contamination during heating. Is evident. In addition, when the sample solution is directly analyzed, the analysis is impossible because TMAH as the main component interferes, and when the analysis is performed after dilution, the analysis accuracy is remarkably low.

[0050]

[Table 2]

[0051]

[Brief description of the drawings]

FIG. 1 is a schematic view showing a typical embodiment of a vertically long container used in the present invention.

FIG. 2 is a schematic diagram showing a typical embodiment of the apparatus used in the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Vertical container 2 Joint part 3 Gas discharge piping 4 Carrier gas piping 5 Purge gas piping 11 Heating device 12 Chamber 13 Microwave generator 14 Hot air generator 15 Sample solution 16 Carrier gas inlet 17 Carrier gas outlet 18 Purge gas inlet

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G01N 31/00 G01N 1/28 K

Claims (3)

[Claims] In a method for analyzing trace metal impurities in a sample solution, the sample solution is placed in a vertically long container made of a microwave-permeable material, placed in a chamber of a microwave generator, and then heated. While the gas generated in the vertical container is excluded by gas exclusion means communicating the vertical container and the outside of the chamber in a state where the vertical container is sealed with respect to the inside of the chamber, heating of the sample solution by microwave and vertical container And / or sequentially performing the heating of the wall surface to evaporate and / or decompose the sample solution, and take out and analyze the obtained residue to analyze trace metal impurities in the sample solution. 2. The analysis method according to claim 1, wherein the vertical container has a height ratio to the diameter of the container of 1.5 or more. 3. After evaporating and / or decomposing the sample solution, the residual gas in the vertical container is discharged with an inert gas, the inside of the vertical container is replaced with an inert gas, and the obtained residue is taken out and analyzed. The analysis method according to claim 1, wherein: