JPH10231108A - Preparation of sample for analysis of impurity in phosphoric acid, and analysis of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to quantitatively analyze a sample, specially polonium(Po) impurities, in shorter time, by coprecipitating Po with a substance coprecipitable with Po and concentrating them after they are separated. SOLUTION: This sample for analysis of impurities in phosphoric acid is prepared by treating the phosphoric acid sample with a substance coprecipitable with polonium(Po) contained in the acid. The substances coprecipitable with Po include sulfides (e.g. hydrogen sulfide), hydroxides (e.g. nickel hydroxide), metallic deposits (e.g. tellurium deposited in phosphoric acid), metallic complexes [e.g. cobalt-(α-nitroso-β-naphthol)], and phosphate deposits (e.g. iron phosphate). The sample for impurity analysis, separated from the phosphoric acid sample by coprecipitation with the above substances and concentrated, can be swiftly analyzed for the Po impurities by analyzing α rays radiated from the sample fixed on a substrate for analysis.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for preparing a sample for analyzing trace impurities required for producing and controlling phosphoric acid of high purity, and a method for analyzing such trace impurities. More specifically, the present invention relates to a method for preparing an analytical sample for quantitatively analyzing a trace amount of radioactive impurities contained in phosphoric acid, and a method for analyzing such trace impurities.

[0002]

2. Description of the Related Art Phosphoric acid is one of the chemical substances widely used in various industrial fields. For example, in the semiconductor industry, phosphoric acid is used for integrated circuits (ICs), large-scale integrated circuits (LSs).
It is often used as an etching agent in the semiconductor device manufacturing process such as I). For example, wet etching using phosphoric acid as a treatment liquid is used to selectively remove an insulating film formed on a semiconductor substrate, for example, a thin film of silicon nitride.

[0003] By the way, phosphoric acid contains various impurities, as in the case of general substances. The control of impurities in phosphoric acid is usually performed by the phosphate reagent manufacturer in terms of impurity control items and control levels (content,
ppm).

[0004]

[Table 1]

As is clear from this table, the impurities contained in phosphoric acid are about 22.3 ppm. For comparison, the results of the present inventors' analysis of impurities with respect to other acids show that <0.28 pp for hydrochloric acid (20% aqueous solution).
b, <0.36 ppb for nitric acid (68% aqueous solution), <0.42 ppb for hydrofluoric acid (38% aqueous solution),
And the analysis result of impurities about the ammonia water (20% aqueous solution) was <0.33 ppb. in this way,
The impurity control level of phosphoric acid is on the order of ppm, whereas the impurity control level of hydrochloric acid, nitric acid, hydrofluoric acid, aqueous ammonia and the like is on the order of ppb. Therefore, it can be said that phosphoric acid has lower purity than other chemicals.

On the other hand, it is clear from the literature that the impurity control level of sulfuric acid is of the order of ppb, similar to hydrochloric acid and nitric acid other than phosphoric acid (Donald Potter et al., "
Ultra Trace Analysis of Semiconductor Grade Reagen
ts by ICP-MS ", ANALYTICALSCIENCES VOL.7, SUPPLEME
According to NT 1991, pp 467-470, the total amount of impurities in sulfuric acid is reported to be 0.902 ng / g = 0.902 ppb). In other words, it is clear that the analysis of impurities in phosphoric acid involves difficulties and the purification of phosphoric acid is not easy even in comparison with sulfuric acid. According to the understanding of the present inventors, it is difficult to analyze impurities in phosphoric acid and to purify phosphoric acid as described above. Due to the physicochemical properties of high viscosity and high viscosity (phosphoric acid is 85%
Boiling point of 158 ° C.
Kinematic viscosity at 28 ° C. is 28 centistokes).

In addition, phosphoric acid is ²¹⁰ Po (half-life =
(138.4 days) as trace impurities. Therefore, during treatment with phosphoric acid in the semiconductor industry, ²¹⁰ Po may be adsorbed on a silicon substrate or deposited by electroless plating. ²¹⁰ Po thus deposited on the silicon substrate is
After a series of semiconductor device manufacturing steps are completed, α-rays are emitted, which may cause a soft error (memory error) in an electronic device such as a semiconductor memory. To avoid soft errors, the concentration of a polonium isotope radioactive substance such as ²¹⁰ Po in phosphoric acid should be, for example, 10 ⁻³ B
It is believed that it is desirable to be less than q / ml.

[0008] The reason why ²¹⁰ Po is contained in phosphoric acid is mainly due to the composition of the phosphate rock used as a starting material in the production process. That is, phosphoric acid can be prepared by a wet method (phosphoric acid is converted to sulfuric acid, as described in, for example, Keiichiro Kubo, “Inorganic Industrial Chemistry,” pp. 121-129, Asakura Shoten (issued October 5, 1972). Decomposition to obtain phosphoric acid) or dry method (reducing phosphate ore to obtain phosphorus, oxidizing this phosphorus to phosphorus pentoxide, and dissolving this phosphorus pentoxide in water to obtain phosphoric acid) However, the radioactive impurities contained in the raw phosphate rock are
It remains in the produced phosphoric acid without being removed in the process of producing phosphoric acid. The occurrence of the soft error in the electronic device is not limited to ²¹⁰ Po described above, and it is considered that other radioactive impurities contained in phosphoric acid also participate. Accordingly, there is a need in the semiconductor industry in particular to eliminate the adverse effects of such radioactive impurities contained in phosphoric acid.

[0009] From this background, it is necessary to know the amount of radioactive impurities in phosphoric acid in detail. As is well known, the quantification of ²¹⁰ Po is usually performed by measuring the α-ray emitted when it decays, and
^To separate the polonium element containing ²¹⁰ Po from other elements, 1) a precipitation method, 2) an electrodeposition method, 3) a volatilization method, 4) an ion exchange resin method, 5) a solvent extraction method and the like are used. The most reliable method is to electrodeposit on a metal plate and then volatilize in a vacuum.

[0010] In the prior art, α present in a liquid
As a method for analyzing a radiation emitting nuclide, for example, Japanese Patent Laid-Open
No. 8645 discloses a method for analyzing an α-ray emitting nuclide present in a liquid such as wastewater discharged from a nuclear facility to the environment. According to the analysis method described in this publication, after a cathode electrodeposition plate serving also as a bottom plate is attached to an electrodeposition cell made of a resin material such as tetrafluoroethylene resin, a sample liquid and an electrolyte solution are injected into the electrodeposition cell. Then, while controlling the temperature of the mixed liquid by immersing the anode in the mixed liquid and inserting the lower part of the electrodeposition cell into a temperature-controlled medium,
It energizes between the electrodes. After the α-ray emitting nuclide in the sample liquid is electrodeposited on the electrodeposited plate, the nuclide can be analyzed by passing the electrodeposited plate through an α-ray measuring device such as an α-ray wave height analyzer. In addition, in order to improve the accuracy of the analysis or to correct the analysis, it is also possible to add a known amount of a different α-ray nuclide before the analysis. However, according to the analysis method described in this publication, ²¹⁰ Po contained in phosphoric acid is used.
No mention is made of the above-mentioned undesired effects on radioisotopes, etc., nor is the analysis of such radioisotopes discussed.

Many related techniques are known from US patent specifications, such as a method for detecting radioisotopes, a method for recovering an actinide element (uranium and the like) from a phosphoric acid effluent by a wet method, and a method for regenerating a phosphoric acid effluent. For example, US Pat. No. 4,336,451
In the specification, uranium series and thorium series radioactive isotopes are eluted from a leaching solution (acid solution such as nitric acid, hydrochloric acid, etc.) on a metal plate, or electroless plating, electrolytic plating And then detecting radiation decay. But,
The U.S. patent does not mention the analysis of polonium in phosphoric acid at all. Also, US Patent No. 3
In the description of the prior art, it is described in Japanese Patent No. 983219 that it was possible to deposit ²¹⁰ Po from a 4 to 8 N nitric acid solution on a platinum cathode by an electrolytic method.

Regarding a method for purifying phosphoric acid, for example, US Pat. No. 4,450,142 and US Pat.
No. 0, No. 4200620, and No. 5316748
In the specification. Further, a method for regenerating a phosphoric acid waste liquid is disclosed in, for example, US Pat. Nos. 4,749,455 and 4,615,776.

As will be understood from the above description, in order to quantitatively analyze impurities in phosphoric acid, particularly radioactive impurities, down to a trace amount region, it is necessary to quantitatively separate impurities from phosphoric acid as a matrix. In order to improve the quantitative accuracy, it is necessary to prepare a measurement sample, preferably in the form of a thin film, so as to be convenient for measurement with an α-ray measuring device.

As a technique for meeting such a demand, an alkali is added to phosphoric acid, which is a strong acid, to form a weakly acidic aqueous solution, and this aqueous solution is energized to deposit impurities on the cathode in a thin film by electrolysis. Separating impurities,
The measurement of radiation emitted from these impurities is described in Japanese Patent Application No. 8-64635.

[0015]

SUMMARY OF THE INVENTION This Japanese Patent Application No. 8-646 is disclosed.
The method described in the specification of JP-A No. 35 makes it possible to prepare a sample for quantitatively analyzing radioactive impurities in phosphoric acid with high sensitivity and to analyze impurities with high sensitivity.
However, since the concentration of radioactive impurities in phosphoric acid is very small, the amount of impurities to be analyzed contained in the analytical sample produced by this method is also very small.
^{To determine 210} Po to a concentration of, for example, 10 ⁻⁵ Bq / ml, a measurement time of about one week or more is required.

The present invention has been made in view of the fact that such a long time measurement is required when quantifying a trace amount of radioactive impurities in phosphoric acid, especially polonium, and therefore, an analysis sample which enables quantification in a shorter time. It is an object of the present invention to provide a method for producing the same. Another object of the present invention is to provide a method capable of analyzing impurities in a short time using such an analysis sample.

[0017]

According to the method for preparing a sample for analyzing impurities in phosphoric acid of the present invention, polonium in phosphoric acid is co-precipitated using a substance capable of co-precipitation with polonium, whereby polonium is removed from phosphoric acid. It is characterized by separating and concentrating impurities.

In the method for analyzing impurities in phosphoric acid according to the present invention, polonium in phosphoric acid is coprecipitated using a substance capable of coprecipitating with polonium, whereby polonium impurities are separated and concentrated from phosphoric acid. The method is characterized in that the obtained analysis sample is attached to an analysis support, and the α-ray emission of the sample attached to the support is measured.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the method for preparing an analytical sample of the present invention, it is important to coprecipitate polonium in phosphoric acid using a substance capable of coprecipitating with polonium. Examples of those effective as a substance capable of coprecipitating with polonium in the present invention include sulfides, hydroxides, metal precipitates, metal complexes,
Phosphate deposits and the like.

An example of a sulfide that can be coprecipitated with polonium is arsenic sulfide. When co-precipitating polonium in phosphoric acid using arsenic sulfide, for example, sodium arsenite and sodium sulfide are added to a phosphoric acid sample, and polonium can be co-precipitated together with arsenic sulfide generated thereby. Thereby, the polonium as the analyte is separated from the phosphoric acid and concentrated at the same time. Other than arsenic sulfide that can be used as a sulfide in the present invention, mercury sulfide, antimony sulfide, bismuth sulfide, tin sulfide, cadmium sulfide, lead sulfide, zinc sulfide, cobalt sulfide, nickel sulfide, and the like can be given. . In the case where these sulfides are used, a substance that generates the sulfide may be added to phosphoric acid as in the case of arsenic sulfide described above.

Examples of hydroxides that can be coprecipitated with polonium include nickel hydroxide, copper hydroxide, aluminum hydroxide, beryllium hydroxide, manganese hydroxide, zinc hydroxide,
Cobalt hydroxide, chromium hydroxide and the like can be mentioned. In the case of using nickel hydroxide as an example, nickel hydroxide can be generated by adding, for example, nickel chloride to a phosphoric acid sample and adding an alkali to make the sample alkaline.

As an example of a metal precipitate that can be coprecipitated with polonium, tellurium can be mentioned. In the case where tellurium is used as an example of a metal precipitate, tellurium can be deposited by adding, for example, tellurium chloride to a phosphoric acid sample and further adding tin (II) chloride as a reducing agent.

An example of a metal complex that can be coprecipitated with polonium is cobalt- (α-nitroso-β-naphthol). Cobalt- (α-nitroso-β-
Taking naphthol as an example, this complex can be formed by adding cobalt chloride and α-nitroso-β-naphthol to a phosphoric acid sample.

An example of a phosphate precipitate that can be coprecipitated with polonium is iron phosphate. In the case of iron phosphate, the phosphoric acid sample contains iron (III) chloride.
Can be added to adjust the pH to cause precipitation of iron phosphate.

The sample for impurity analysis according to the present invention obtained by coprecipitating from a phosphoric acid sample using a suitable substance capable of coprecipitating with polonium and separating and concentrating the same is as follows:
By attaching the sample to the support for analysis and measuring the α-ray emission of the sample attached to the support, the polonium impurities can be analyzed much faster than in the past.

The support to which the analytical sample obtained by the method for preparing a sample for analyzing impurities in phosphoric acid of the present invention is to be attached in order to measure the emission of α-rays is used for the measurement of α-rays after attaching the analytical sample. Anything you can get.
Preferable examples of such a support include a support made of a silver or nickel material capable of spontaneously depositing polonium from a solution in which an analysis sample obtained by the method of the present invention is dissolved, and an electrode. This is a support made of a metal material such as stainless steel on which polonium can be deposited by deposition. In addition, a filter to which the coprecipitate adhered in the filtration operation for separating the coprecipitate containing polonium co-precipitated by the method of the present invention from phosphoric acid can also be used as the support in the present invention.

The case where the polonium impurities separated and concentrated from phosphoric acid are attached to a support made of silver material will be described. The coprecipitate containing polonium from phosphoric acid is filtered,
This coprecipitate is dissolved in hydrochloric acid, and hydrosilamine hydrochloride and ascorbic acid are added to the solution, and then a support made of a silver material, such as a silver plate, is added to the solution, and polonium is spontaneously deposited on the surface. Can be done. Techniques for spontaneously depositing polonium in a hydrochloric acid solution on a silver support surface are well known and need not be described in further detail here.

When polonium is deposited on a metal support by electrodeposition, the precipitate containing polonium separated from phosphoric acid by filtration is dissolved in an appropriate solvent, and then the coprecipitated component and the polonium are separated by a solvent extraction technique. Then, if electrodeposition is performed in an electrodeposition cell containing an electrolytic solution in which polonium is dissolved, polonium is deposited in the form of polonium oxide on a cathode (for example, a stainless steel electrode plate). Electrodeposition is also a well-known technique and need not be described in further detail here.

As described above, the polonium deposited on various supports can be easily quantified in a phosphoric acid sample by measuring the concentration of a radioactive substance such as ²¹⁰ Po by a normal α-ray measuring method. be able to. In the present invention, since polonium is concentrated in the phosphoric acid sample, ²¹⁰ Po is reduced to 10 ⁻⁵ Bq / p by the conventional method.
Whereas it took about one week or more to measure the amount to the milliliter, the present invention enables the same level of measurement in one day.

[0030]

Next, the present invention will be further described with reference to examples.
Of course, the invention is not limited to these examples.

Example 1 0.1 g of sodium arsenite was added to a phosphoric acid sample (50 ml), and the pH of the solution was adjusted to 7 with ammonia. 0.1 g of sodium sulfide was added to this solution to cause precipitation of arsenic sulfide, and together with the precipitation, co-precipitation of polonium in the phosphoric acid sample. After aging the precipitate, it was filtered. The precipitate was dissolved in aqua regia, evaporated to dryness, and further dissolved in hydrochloric acid. Next, hydroxylamine hydrochloride and ascorbic acid were added to this hydrochloric acid solution, and then a silver plate was put therein, and polonium was spontaneously deposited on the surface. The silver plate on which the polonium was deposited was used as a measurement sample, and an α-ray spectrometer (ORTEC) was used.
²¹⁰ Po was quantified to 10 ⁻⁵ Bq / ml. The time required for this quantification was one day.

Example 2 0.1 g of nickel chloride was added to a phosphoric acid sample (50 ml), and the pH was adjusted with ammonia.
Was adjusted to 9 to cause precipitation of nickel hydroxide. After aging the precipitate, it was filtered. The precipitate was dissolved in aqua regia, evaporated to dryness, and further dissolved in hydrochloric acid. After adding hydroxylamine hydrochloride and ascorbic acid to this hydrochloric acid solution, a silver plate was put therein, and polonium was spontaneously deposited on the surface. The silver plate on which the polonium was precipitated was used as a measurement sample, and ²¹⁰ Po was added to 10 ⁻⁵ Bq / m in the same manner as in Example 1.
l. The time required for the quantification was also one day.

Example 3 Salt of phosphoric acid sample (50 ml)
0.1 g of tellurium chloride and tin (II) chloride
Tellurium was deposited. Dissolve the precipitate in hydrochloric acid after filtration.
And add hydroxylamine hydrochloride and as
After adding corbic acid, put a silver plate and polonium on the surface
Was spontaneously deposited. Using this measurement sample,
In the same way ²¹⁰Po 10^-FiveIt was quantified to Bq / ml.
The time required for the quantification was also one day.

Example 4 0.1 g of cobalt chloride was added to a phosphoric acid sample (50 ml), and the pH was further adjusted with ammonia.
Was adjusted to 8. Α-Nitroso-β-naphthol was added to this solution to cause precipitation. After aging the precipitate,
This was filtered. This precipitate was dissolved in a mixture of nitric acid and perchloric acid, and hydrochloric acid was added to make a hydrochloric acid acidic solution. Then, after adding hydroxylamine hydrochloride and ascorbic acid to this solution, a silver plate was put therein, and polonium was spontaneously deposited. Using the silver plate on which the polonium was deposited as a measurement sample, ²¹⁰ Po was quantified to 10 ^-5 Bq / ml in the same manner as in Example 1. The time required for the quantification was also one day.

Example 5 0.1 g of iron (III) chloride was added to a phosphoric acid sample (50 ml), and the pH was adjusted with ammonia.
Was adjusted to 8 to cause precipitation of iron phosphate. After aging this precipitate, it was filtered. This precipitate was then dissolved in hydrochloric acid. After adding hydroxylamine hydrochloride and ascorbic acid to this solution, a silver plate was put therein, and polonium was spontaneously deposited. The silver plate on which the polonium was precipitated was used as a measurement sample, and ²¹⁰ Po was added to 10 ^{−5 in the same} manner as in Example 1.
It was quantified to Bq / ml. The time required for the quantification was also one day in this example.

[0036]

As described above, according to the prior analysis method, one week or more was required for measurement after preparation of an analysis sample, but according to the present invention, analysis is performed with the same level of sensitivity or more in one day. Now you can do it.

Claims (15)

[Claims] 1. An impurity analysis in phosphoric acid, comprising: coprecipitating polonium in phosphoric acid using a substance capable of coprecipitating with polonium, thereby separating and concentrating polonium impurities from phosphoric acid. Sample preparation method. 2. The method according to claim 1, wherein the substance coprecipitable with polonium is a sulfide. 3. The method of claim 2, wherein the sulfide is a sulfide of arsenic, mercury, antimony, bismuth, tin, cadmium, lead, zinc, cobalt, or nickel. 4. The method of claim 1, wherein the coprecipitable substance with polonium is a hydroxide. 5. The method of claim 4, wherein said hydroxide is a hydroxide of nickel, copper, aluminum, beryllium, manganese, zinc, cobalt or chromium. 6. The method of claim 1, wherein the substance co-precipitable with polonium is a metal precipitate. 7. The method of claim 6, wherein said metal deposit is tellurium precipitated in phosphoric acid. 8. The method according to claim 1, wherein the substance coprecipitable with polonium is a metal complex. 9. The method of claim 8, wherein said metal complex is cobalt- (α-nitroso-β-naphthol). 10. The method according to claim 1, wherein the substance co-precipitable with polonium is a phosphate precipitate. 11. The method of claim 10, wherein said phosphate precipitate is iron phosphate. 12. A sample for analysis obtained by coprecipitating polonium in phosphoric acid with a substance capable of coprecipitating with polonium, thereby separating and concentrating polonium impurities from phosphoric acid, and attaching the sample to an analysis support. And measuring the α-ray emission of the sample attached to the support. 13. The method according to claim 12, wherein the support is a filter used for filtering a precipitate co-precipitated with polonium impurities. 14. The method according to claim 12, wherein the support is made of a nickel or silver material, and polonium is deposited on a surface of the support in a solution in which the sample for analysis is dissolved. 15. The support according to claim 1, wherein the support is made of a metal material, and polonium is separated from the sample for analysis, and the polonium is adhered to the surface of the support by electrodeposition.
2. The method according to 2.