JPH0989841A - Method for determining phosphorus in hydrofluoric acid solution - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a determination method for analyzing a trace of phosphorus in a solution containing hydrofluoric acid. SOLUTION: Silicon is added at mole ratio of 1/100 or more to fluoride ions contained in a sample solution 11a by applying thermal evaporation introduction-ICP mass spectrometry 10. Silicon is added by previously admixing a solution containing silicon to a sample solution or admixing a solution containing silicon to a sample solution introduced into a graphite tube 14.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for quantifying phosphorus in a hydrofluoric acid solution by heating vaporization introduction-ICP mass spectrometry.

[0002]

2. Description of the Related Art With the high integration of electronic circuits such as LSIs, impurities on the surface of a silicon wafer cause an increase in junction leakage current, disconnection, etc., which causes a problem that electrical characteristics are deteriorated. There is.

Usually, in order to remove the contamination on the surface of a silicon wafer generated in the LSI manufacturing process, sulfuric acid / hydrogen peroxide solution (representing a mixed solution of sulfuric acid and hydrogen peroxide; hereinafter the same), ammonia / hydrogen peroxide solution, A method of removing impurities in the oxide film on the surface of a silicon wafer using a hydrofluoric acid solution after removing organic substances, particles, impurity elements, etc. adhering to the surface with a cleaning solution such as hydrochloric acid / hydrogen peroxide solution. Is taken. Therefore, the hydrofluoric acid solution to be finally used must have impurities removed as much as possible. In particular, since phosphorus is a dopant element and greatly affects the electrical characteristics of LSI, it is necessary to reduce the content of phosphorus contained in hydrofluoric acid to 0.1 μg / liter or less. Therefore, it is necessary to quantify a very small amount of phosphorus.

Further, phosphorus in the silicon wafer, quartz,
Since phosphorus contamination from the jig of the LSI manufacturing equipment such as silicon carbide or alumina affects the electrical characteristics of the LSI, phosphorus mixed in the material forming the jig of the silicon wafer or the LSI manufacturing equipment is minimized. Need to reduce.
Therefore, it is necessary to quantify a small amount of phosphorus contained in these materials, but if phosphorus is contained in hydrofluoric acid used during analysis, it will cause an error in the analytical value, so the phosphorus content It is necessary to use low hydrofluoric acid, which requires the determination of trace amounts of phosphorus in hydrofluoric acid.

On the other hand, graphite furnace atomic absorption spectrometry and ICP mass spectrometry have been applied to the determination of trace metal impurities in hydrofluoric acid solutions. Further, ICP emission spectrometry or a method of quantifying phosphoric acid using ion chromatography is applied to quantify a small amount of phosphorus.

In addition to the above method, as a highly sensitive analytical method,
"Heating vaporization introduction-IC
"P mass spectrometry" is also considered to be a promising method for the determination of trace phosphorus.

However, all of these methods have the following problems.

[0008]

The graphite furnace atomic absorption spectrometry is a highly sensitive method for the determination of metallic elements, but even if this method is used for the determination of phosphorus, the atomic ratio of phosphorus is low. Therefore, highly sensitive analysis is difficult. Therefore, a method of adding molybdenum and antimony to the sample solution, extracting the phosphorus-molybdenum-antimony complex in butyl acetate, quantifying molybdenum in the complex, and calculating the phosphorus amount from the composition ratio of each element in the complex is a method. Attempted (analytical chemistry,
30 (1981) p164). However, in this method, the detection limit of phosphorus is 3.6 μg / liter, and in order to apply it to the determination of a trace amount of phosphorus in hydrofluoric acid, the sample solution is heated in advance or a large amount of phosphorus-molybdenum is used. -Phosphorus must be concentrated by extracting the antimony complex into butyl acetate, but there is a problem in that heating and concentration require a long time, and phosphorus contamination occurs during the concentration operation, resulting in an error in the analytical value. It was On the other hand, concentration by solvent extraction has a problem that the operation is complicated, and phosphorus is mixed from a reagent such as butyl acetate used in the extraction operation, and an error is likely to occur in the analysis value.

[0009] ICP mass spectrometry is also a highly sensitive method for the determination of metal elements, but when phosphorus in a hydrofluoric acid solution is determined by this method, the hydrofluoric acid contained in the solution is In order to dissolve glass parts such as nebulizers and torches, it is necessary to remove hydrofluoric acid by heating in advance. Therefore, there is a problem that analysis takes a long time, and phosphorus is mixed in at the time of heat removal to easily cause an analysis error. Furthermore, ¹⁴ N ¹⁶ generated due to water in the solution
There is also a problem that a minute amount of phosphorus cannot be quantified because O ¹ H ⁺ raises the background of 31 which is the measured mass number of phosphorus.

Also in the ICP emission analysis method, since hydrofluoric acid dissolves glass parts such as a nebulizer and a torch, it is necessary to remove the hydrofluoric acid by heating, and it takes a long time for analysis and contamination is caused. There was a problem of easy occurrence. Therefore, a method of quantifying phosphorus using ICP emission spectrometry has been attempted by heating and vaporizing a sample solution on a platinum filament and introducing vaporized phosphorus into Ar plasma at the same time (Anal. Chem. 5).
5 (1983) p802). However, in this method, the detection limit of phosphorus is 10 μg / liter, and the sensitivity is insufficient for application to the determination of a trace amount of phosphorus in hydrofluoric acid. Therefore, although it is necessary to concentrate the sample solution by heating it in advance, there is a problem that the heating concentration requires a long time and phosphorus is mixed in the process, and an analysis error is likely to occur.

In ion chromatography, phosphorus can be concentrated in a measuring system using a concentration column (Semiconductor World, 11 (1)).
989) p198). However, in order to quantify 0.1 μg / liter of phosphorus, it is necessary to introduce a large amount of sample solution into the concentration column to concentrate phosphorus, and therefore there is a problem that the concentration operation takes a long time.

On the other hand, in the heating vaporization-introduction-ICP mass spectrometry method, the sample solution is heated and vaporized in a graphite tube, and the vapor is Ar.
Water and hydrofluoric acid can be removed by heating in a graphite tube by measuring the amount of the ionized element to be analyzed by introducing it into plasma. Therefore, it is possible to dissolve glass parts and to remove ¹⁴ N ¹⁶ O ¹ H ⁺ There is an advantage that it is possible to avoid an increase in the background at the mass number of 31, that is, the background of ³¹ P ⁺ .

Therefore, if the heat vaporization-introduction-ICP mass spectrometry is used, it is not necessary to remove hydrofluoric acid and water by heating in advance, and it is possible to shorten the analysis time and eliminate phosphorus contamination during the heating removal operation. Therefore, it is considered that the trace amount of phosphorus in the hydrofluoric acid solution can be easily quantified with high sensitivity and accuracy.

However, in practice, heating vaporization introduction-I
When the solution containing hydrofluoric acid was measured by the CP mass spectrometry method, the following problems occurred.

FIG. 1 shows a background signal at a mass number of 31 when an aqueous solution containing 50 v / v% hydrofluoric acid was introduced into a graphite tube, heated and vaporized at 120 ° C., and then heated to 2600 ° C. FIG. In FIG. 1, for example, 5 μl (microliter) HF is 50
This means that v / v% HF was introduced into a 5 μl graphite tube. As is clear from this result, as the amount of hydrofluoric acid introduced into the graphite tube increases, the background of mass number 31 significantly increases. It is considered that this is because ¹² C ¹⁹ F ⁺ was generated in Ar plasma due to the reaction between the fluoride ions and the graphite tube material, and the background at the mass number 31 was increased.

As a method of reducing the background at such a mass number of 31, a method of using platinum or tungsten, which is a material other than graphite and has heat resistance, as a heating furnace is considered. However, platinum is extremely expensive, and tungsten forms a compound with phosphorus, so vaporization of phosphorus is hindered, and phosphorus cannot be quantified accurately.

The present invention has been made in view of the above problems, and by applying the heat vaporization introduction-ICP mass spectrometry, a trace amount of phosphorus in a solution containing hydrofluoric acid can be easily and highly sensitively and highly sensitive. It is an object of the present invention to provide a quantification method that enables accurate analysis.

[0018]

[Means for Solving the Problems] A problem in applying the heat vaporization-introduction-ICP mass spectrometry to the determination of a small amount of phosphorus in a solution containing hydrofluoric acid is that the background in the above-mentioned mass number 31 is a problem. Is the rise of. As a result of repeated studies to solve this problem, the present inventor has found that the background can be reduced by adding silicon to the hydrofluoric acid-containing solution.

The present invention has been made based on this finding, and the gist thereof is the following method for quantifying phosphorus.

A method for quantifying phosphorus in a hydrofluoric acid solution by heating vaporization introduction-ICP mass spectrometry, wherein the molar ratio to the fluoride ion contained in the sample solution is 1/100 or more. A method for quantifying phosphorus in a hydrofluoric acid solution, characterized by containing silicon.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION The phosphorus quantification method of the present invention will be described in detail below.

FIG. 2 is a diagram schematically showing a part of the steps (procedures) of the method for quantifying phosphorus in a hydrofluoric acid solution, which is carried out using the heating vaporization introduction-ICP mass spectrometer 10.

In FIG. 2, an analytical solution 11 (for example, a silicon wafer cleaning solution) containing a trace amount of phosphorus and hydrofluoric acid is sampled by an auto sampler 12 (this is referred to as a sample solution 11a), and the sample solution is introduced. Mouth 13
Is introduced into the graphite tube 14 (FIG. 2 (a)). Then
By heating the graphite tube 14 with electricity, the sample solution 11a
The hydrofluoric acid, water, etc. contained therein are vaporized, and the generated hydrofluoric acid vapor and water vapor are introduced together with Ar gas introduced from both ends of the graphite tube 14 from the sample solution inlet 13 to the graphite tube 1.
4 is discharged to the outside (FIG. 2B). Subsequently, after closing the sample solution introduction port 13 with the graphite shield rod 15, the graphite tube 14 is heated to a high temperature to vaporize phosphorus, and the valve 16 is switched to connect to the graphite tube 14 and the Ar plasma 17. When connected to 16 ', phosphorus vapor is introduced into Ar plasma 17 together with Ar gas (Fig. 2).
(C)). Phosphorus vapor is ionized in Ar gas, and the generated ions are guided to the mass spectrometer 19 through the sampling cone 18, and the amount thereof is measured.

In the method for quantifying phosphorus according to the present invention, silicon is contained in the sample solution 11a introduced into the graphite tube 14 in the above step. As a result, as shown in FIG. 3 described below, the background at the mass number of 31,
That is, the background of ³¹ P ⁺ is significantly reduced.

In FIG. 3, 5 μl of a 50 v / v% aqueous solution of hydrofluoric acid was prepared using the heat vaporization introduction-ICP mass spectrometry method.
(Microliter), and a mass number 3 of 5 μl of a 50 v / v% hydrofluoric acid aqueous solution to which 50 μg of silicon was added
It is the figure which showed the result of having measured the background signal in 1 respectively. In the figure, the broken line labeled "HF + Si" corresponds to an aqueous solution of hydrofluoric acid containing silicon. As is clear from this figure, the background at the mass number 31 is significantly reduced by adding silicon.

This is because the addition of silicon to the hydrofluoric acid solution produced SiF ₄ and SiC, and suppressed the production of ¹² C ¹⁹ F ⁺ , which causes the background at the mass number 31. Conceivable. As a result, phosphorus in the hydrofluoric acid solution can be accurately quantified.

The amount of silicon contained in the hydrofluoric acid solution (sample solution) is 1/100 or more in terms of molar ratio with respect to the fluoride ions contained in this solution. Since the fluoride ion reacts with silicon to form SiF ₄ and vaporizes, it is necessary from the chemical formula that the molar ratio is 1/4 with respect to the fluoride ion. Most of the hydrofluoric acid volatilizes when the tube is electrically heated, so the fluoride ions that generate ¹² C ¹⁹ F ⁺ due to the reaction with graphite are converted to the fluoride ions in the sample solution before heating. On the other hand, it is only 1/100 at most. Therefore, if the amount of silicon contained in the sample solution is 1/100 or more in terms of the molar ratio to the fluoride ion as described above, the production of ¹² C ¹⁹ F ⁺ can be sufficiently suppressed.

As a method of adding silicon to the sample solution, a silicon-containing solution is added to the sample solution in advance and mixed, or a silicon-containing solution is added to and mixed with the sample solution introduced into the graphite tube. Can be used.

The phosphorus quantification method of the present invention has a remarkable effect when applied to the quantification of phosphorus contained in an aqueous solution having a hydrofluoric acid concentration of 1 v / v% or more. This is because generation of ¹² C ¹⁹ F ⁺ is recognized when the concentration of hydrofluoric acid is 1 v / v% or more, and the influence of the background at the mass number 31 on the analytical value becomes significant.

[0030]

EXAMPLES Assuming that the method for quantifying phosphorus according to the present invention is applied to the quantification of phosphorus in a 50 v / v% hydrofluoric acid solution used for cleaning silicon wafers, the concentration of phosphorus is known for analysis. The solution was checked for accuracy of analysis. The analysis was performed using a heating vaporization introduction-ICP mass spectrometer according to the step shown in FIG. 2 (however, silicon was added to the sample solution in the middle of the step).

50 v / v% hydrofluoric acid aqueous solution 10 m
Using a solution for analysis in which a known amount of phosphorus was gradually added to 1 l, 10 μl of the solution was introduced as a sample solution into a graphite tube using an autosampler. Then, silicon 100
After introducing 10 μl of a solution containing μg into the graphite tube using an auto sampler, the graphite tube was heated at 120 ° C. for 30 minutes.
The sample solution was dried by heating for 2 seconds. When heating,
To prevent bumping of the sample solution, from room temperature to 120 ° C 2
The temperature was raised over 0 seconds.

Next, after closing the sample solution inlet with a graphite shield rod, it was heated to 2600 ° C. to vaporize phosphorus. The vapor containing phosphorus generated at this time was introduced into Ar plasma, and phosphorus was quantified by the calibration curve method.

The results are shown in Table 1 as an example. The indicated addition amount of phosphorus is the addition amount to 10 ml of a 50 v / v% aqueous solution of hydrofluoric acid. In Table 1, as a comparative example, the results obtained by measuring phosphorus by ion chromatography after further concentrating phosphorus 10 times by a concentration column of a solution obtained by concentrating 10 times by heating the analytical solution are also shown. Indicated. Here, the relative standard deviation is the standard deviation of the analysis values for seven samples divided by the analysis value and expressed as a percentage.

As is clear from the results shown in Table 1, the method for quantifying phosphorus of the present invention has less variation in measurement as compared with the conventional ion chromatography. Further, by using the quantification method of the present invention, it is possible to quantify phosphorus in an aqueous solution of hydrofluoric acid quickly and with high accuracy, because heating concentration of an analytical solution and phosphorus concentration operation in a concentration column are unnecessary. .

The detection limit of phosphorus in the aqueous solution of hydrofluoric acid was determined by applying the phosphorus determination method of the present invention.
It was 01 μg / liter, and it was found that it is possible to measure a very small amount of phosphorus. The detection limit is
It was set to 3 times the standard deviation of the analytical value of the blank test solution.

[0036]

[Table 1]

[0037]

The method for quantifying phosphorus according to the present invention is a method for quantifying phosphorus dissolved in a solution containing hydrofluoric acid by using heat vaporization introduction-ICP mass spectrometry. In this method, ³¹ P ⁺ due to ¹² C ¹⁹ F ⁺ generated in Ar plasma due to reaction between fluoride ions and graphite tube material.
Since the background can be reduced by including silicon in the sample solution, phosphorus in the solution containing hydrofluoric acid can be easily quantified with high sensitivity and accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a background signal at a mass number of 31 of an aqueous hydrofluoric acid solution when quantifying phosphorus in an aqueous hydrofluoric acid solution by a heating vaporization introduction-ICP mass spectrometry method.

FIG. 2 is a step (procedure) of a method for quantifying phosphorus in a hydrofluoric acid solution using a heating vaporization introduction-ICP mass spectrometer.
It is the figure which showed a part of model typically.

FIG. 3 Reduction of background signal at mass number 31 of hydrofluoric acid aqueous solution by containing silicon in a sample solution when quantifying phosphorus in hydrofluoric acid aqueous solution by heating vaporization introduction-ICP mass spectrometry method. It is a figure which shows an effect.

[Explanation of Codes] 10: Heat vaporization introduction-ICP mass spectrometer 11: Analytical solution 11a: Sample solution 12: Autosampler 13: Sample solution inlet 14: Graphite tube 15: Graphite shield rod 16: Valve, 16 ': Pipeline 17: Ar plasma 18: Sampling cone 19: Mass spectrometer

Claims (1)

[Claims] 1. A method for quantifying phosphorus in a hydrofluoric acid solution by heating vaporization-introduction-ICP mass spectrometry, which comprises a sample solution containing 1 / molar ratio of fluoride ion contained in the solution. A method for quantifying phosphorus in a hydrofluoric acid solution, which comprises containing 100 or more silicon.