JPH10267836A - Method for analyzing microelement - Google Patents

Abstract

PROBLEM TO BE SOLVED: To analyze a trace of silicon in a solution including fluorine with high sensitivity, by adding boron as a modification agent when a sample is analyzed by a frameless atomic absorption spectrometer. SOLUTION: For instance, hydrofluoric acid is added to a trace of silicon of a cleaning chemical solution on a wafer surface, which is separated and condensed, thereby obtaining a sample solution including fluorine. When the silicon in the sample solution is to be analyzed by frameless atomic absorption spectrometry, preferably, an aqueous solution of boron is added to an atomization part and dried hard beforehand, and then boron is added to the sample before the sample is measured. The boron is used generally in a form of the aqueous solution and the amount of boron added to the atomization part is generally approximately 0.4 μg. An addition concentration to the sample is required to be 0.25 times or more a concentration of the fluorine in the sample. Although the effect may be insufficient if the boron is added too small, an excessive amount is not preferable. According to the method, the silicon is prevented from volatilizing when a solvent evaporates in the presence of the fluorine, thus enabling analyses with high sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a technique for analyzing silicon in a solution containing fluorine by flameless atomic absorption spectrometry.

[0002]

2. Description of the Related Art In a semiconductor manufacturing process, as the degree of integration increases, it is increasingly important to reduce metal contamination on the wafer surface. Therefore, the metal impurity element in the chemical solution for cleaning the wafer surface is required to have a level of 0.1 ppb. As a method for analyzing silicon, a means for measuring by a molybdenum blue colorimetric method is generally used. However, this method is insufficient in sensitivity for the analysis of a highly clean sample as described above.

[0003] For this reason, a method of adding hydrofluoric acid, separating and concentrating the solution and measuring it by ICP mass spectrometry can be considered as a highly sensitive analysis method, but a satisfactory lower limit of detection has not yet been obtained. The reason for this is that in the case of quadrupole ICP mass spectrometry, a quartz torch is generally used for the sample introduction part, a silicon background occurs in the measurement, and the detection sensitivity is significantly deteriorated due to the overlap of molecular ions. Is mentioned.

[0004] In the ICP mass spectrometry using the heat vaporization introduction method, since the solvent can be removed by preheating, the molecular ion peak derived from the solvent is reduced and high sensitivity can be expected. However, also in this case, a background of silicon is generated from the quartz torch, and the silicon in the measurement solution is volatilized as silicon fluoride in the solvent evaporation stage, so that it cannot be analyzed.

[0005] In the flameless atomic absorption spectrometry, no quartz background is used because no quartz is used in the sample introduction part, but it cannot be analyzed because silicon is volatilized in the solvent evaporation stage as in the case of the heat vaporization ICP mass spectrometry. . As described above, in a semiconductor process that will be increasingly integrated in the future, the present situation in which silicon impurities in cleaning chemicals cannot be analyzed with high sensitivity is a serious problem.

[0006]

DISCLOSURE OF THE INVENTION In view of the above background, an object of the present invention is to provide a method for separating and concentrating silicon in a chemical solution as a fluoride with high sensitivity using a flameless atomic absorption apparatus without loss of silicon. It is to propose a new elemental analysis method capable of performing silicon analysis.

[0007]

The above object can be attained by adding boron as a modifier when analyzing a sample with a flameless atomic absorption spectrometer.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
The trace silicon in the present invention specifically refers to silicon in an amount of 100 ppb or less. For silicon of 100 ppb or more, it corresponds by dilution measurement. In the present invention, the silicon introduced into the atomized portion is not particularly limited as long as it is dissolved or uniformly dispersed. Examples of the silicon form include silicate ions, silicofluoride ions, and colloidal silicon.

The flameless atomic absorption spectrometry according to the present invention is an apparatus for detecting absorption of a wavelength specific to metal atoms atomized in a heated vaporizing section. The present device evaporates the solvent component in advance by preheating, and then evaporates the target element, and the target element must not volatilize during the evaporation / ashing. The form of boron added in the present invention is not particularly limited, but is usually added as an aqueous boric acid solution. Since the added boron is used for trace analysis, it is required to have a high purity, and a purity of 99.99% or more is preferable.

In the method of adding boron in the present invention, boron may be added to the sample, or an aqueous boron solution may be added to the atomized portion in advance. Preferably, after adding an aqueous boron solution to the atomized portion in advance and drying it, a sample obtained by adding boron to the sample is added. In the present invention, the added amount of the boron aqueous solution to be added to the atomization part in advance is 4 ng or more as a boron atom, and usually about 0.4 μg is added.
The concentration of boron added to the sample must be at least 0.25 times the amount of fluorine in the sample, and if too small, the effect may not be sufficient. On the other hand, when the addition of boron is excessively large, the blank value due to the silicon impurity in the boron solution becomes large, and a problem of a decrease in sensitivity due to self-absorption occurs.
pm or less, more preferably 100 ppm by weight or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. In the following Examples, the absorbance at a wavelength of 251.6 nm was measured using GFAAS4100ZL manufactured by Perkin-Emmer Co., Ltd. as a flameless atomic absorption device. Reference Example First, in order to obtain a calibration curve, a Na ₂ SiO ₃ is silicon concentration 30n
0.1% NH ₄ OH containing g / g was prepared, and this was used as a sample and measured with a flameless atomic absorption spectrometer.
It was 050. From this, the original absorbance at a silicon concentration of 30 ng / g could be determined to be 0.050.

Comparative Example 1 0.1% containing H ₂ SiF ₆ at a silicon concentration of 30 ng / g
When an aqueous solution of NH ₄ OH was prepared and used as a sample and measured under the same conditions as in the Reference Example, the absorbance was 0.003, and sufficient silicon could not be detected. Comparative Example 2 H ₂ SiF ₆ having a silicon concentration of 30 ng / g and HF having a fluorine concentration of 10 wt.
Prepare an aqueous solution of 0.1% NH ₄ OH containing to be ppm,
When this was measured as a sample under the same conditions as the reference example,
The absorbance was 0.000, and no silicon could be detected.

Example 1 H ₂ SiF ₆ has a silicon concentration of 30 ng / g and HF has a fluorine concentration of 10 wt.
ppm, and prepared an aqueous solution of 0.1% NH ₄ OH containing boric acid so that the boron concentration becomes 10 wt ppm, and when this was measured as a sample under the same conditions as in the reference example, the absorbance was 0.030.
It became possible to detect silicon.

Example 2 An aqueous boric acid solution was prepared so that the boron concentration became 10 ppm by weight, and introduced into a heating furnace. After water evaporation, the sample prepared in Example 1 was introduced and measured under the same conditions as in Reference Example.
The absorbance was 0.053, and quantitative measurement of silicon was possible. Example 3 The sample prepared in Example 1 was introduced into a heating furnace, and after water evaporation,
When the boric acid aqueous solution prepared in Example 2 was introduced and measured under the same conditions as in Reference Example, the absorbance was 0.049, and quantitative measurement of silicon was possible.

Example 4 The boric acid aqueous solution prepared in Example 2 was introduced into a heating furnace, and after water evaporation, the sample prepared in Example 1 was introduced. After water evaporation, the above boric acid aqueous solution was introduced. When measured under the same conditions as in the Reference Example later, the absorbance was 0.043, and it was possible to detect silicon.

The results of Reference Example, Comparative Examples 1 and 2, and Examples 1 to 4 are summarized in Table 1.

[0017]

[Table 1]

[0018]

According to the present invention, highly sensitive analysis of a trace amount of silicon becomes possible.

Claims (6)

[Claims] 1. A method according to claim 1, wherein a trace amount of silicon in a solution containing fluorine is
A method for analyzing trace elements, characterized by adding boron as a modifier when analyzing by flameless atomic absorption spectrometry. 2. The method according to claim 1, wherein boric acid is used as the boron source. 3. The analysis method according to claim 1, wherein the method of adding boron is a method of introducing boron before introducing a measurement sample into a heating furnace. 4. The analysis method according to claim 3, wherein the boron concentration is 0.1 ppm or more. 5. The analysis method according to claim 1, wherein the method of adding boron is a method of mixing a measurement sample and boron and introducing the mixture into a heating furnace. 6. The method according to claim 5, wherein the amount of boron is at least 0.25 times the amount of fluorine.