JP3266431B2 - Simple analysis method for alkali metals in high dielectric materials - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for analyzing an alkali metal in a high dielectric material, and more particularly, to a method for analyzing a high dielectric material containing a trace amount of an alkali metal used for a capacitor insulating film of a DRAM. To an alkali metal analysis method.

[0002]

2. Description of the Related Art In recent years, DR
As one of the dielectric materials having a high dielectric constant instead of SiO ₂ for the dielectric of the AM capacitor cell, titanates made of Ba, Sr and the like have been attracting attention. In this type of dielectric material, it is desired that alkali metals such as Na and K reduce the insulation resistance as much as possible, for example, because they reduce the yield of products in a semiconductor manufacturing process. . Therefore, as an evaluation method, specifically, a quantitative method capable of analyzing a sub-ppm order alkali metal at a raw material stage is required.

Hitherto, this type of analysis method has hardly been developed. However, as an analysis method for a dielectric material for a temperature sensor or a constant-temperature heating element, flame atomic absorption analysis, ICP-emission analysis, etc. However, these methods are melted with lithium tetraborate for sample pretreatment, and the melt is heated and dissolved with hydrochloric acid for measurement. Application to the analysis of alkali metals is not possible. As described above, at present, it has not been developed an appropriate method for analyzing a required sub-ppm order alkali metal in a high dielectric material.

[0004]

Under such circumstances, the present inventors have used a flameless atomic absorption spectrometer which can sufficiently perform background correction and which is highly sensitive to the analysis of alkali metals, in the sub-ppm order in a short time. Investigating a method to analyze the alkali metals in the sample, using hydrochloric acid and hydrogen peroxide, for which high-purity reagents are easily available, as sample decomposers, completely dissolving the sample, and separating the standard without separating the matrix. The present inventors have found a simple analysis method using an addition calibration curve method and have reached the present invention.

[0005] That is, the present invention relates to BaTiO ₃ , Sr
Hydrochloric acid and hydrogen peroxide are added to at least one compound selected from the group consisting of TiO ₃ and (Ba, Sr) TiO ₃ and dissolved by heating. The diluted solution is subjected to a parallel magnetic field type AC Zeeman by a standard addition calibration method. This is a simple method for analyzing alkali metals in a high dielectric material, characterized by performing a quantitative analysis by a flameless atomic absorption method.

In the present invention, it is needless to say that the analysis of alkali metals having a high concentration exceeding the order of ppm can be carried out more easily. Therefore, in the present invention, the analysis of alkali metals in the sub-ppm order will be described. I do.

That is, in order to carry out the present invention, it is necessary to sufficiently consider contamination from the environment, contamination from the analysis container, and contamination from the reagent, and to minimize these. The capability of the parallel magnetic field type AC Zeeman flameless atomic absorption spectrometer itself is expressed as the lower limit of absolute detection, Na: 0.3 pg, K: 0.
5 pg, and the lower limit of relative detection when measuring a 25 μl collection solution as in this method is Na: 0.012 ppb,
K: 0.02 ppb. Therefore, when analyzing the sample, it is necessary to suppress the contamination amount to several tens of ppt on the measurement stage.

First, in order to suppress contamination from the environment, sample pretreatment is performed using a clean bench in a clean room, and a parallel magnetic field type AC Zeeman flameless atomic absorption apparatus is also installed and used in the clean room. There is a need.

Regarding contamination from the reagent, it is preferable to use a reagent purified by a non-boiling distillation method as a reagent for precision analysis, and use a commercially available hydrochloric acid and hydrogen peroxide according to this method. In the measurement stage, the amount of each alkali metal can be reduced to the order of sub-ppt.

With respect to contamination from a container, after the heat treatment with an acid, acid washing and ultrapure water washing are performed for a long time or repeatedly, so that the amount of each alkali metal can be removed to the extent that it does not affect the analysis. As described above, by suppressing various contamination sources as much as possible, the reagent blank value can be reduced, so that the analysis of sub-ppm-order alkali metals can be sufficiently performed.

The analysis method according to the present invention comprises the steps of:
The amount of the sample to be used for the measurement to avoid the interference of the matrix and the items of the parallel magnetic field type AC Zeeman flameless atomic absorption measurement by the standard addition calibration method are described in detail according to the items.

First, the solution of the sample is dissolved. When the content of alkali metals such as Na and K is on the order of sub-ppm, the amount of the sample to be collected is determined by the solubility of the sample, the parallel magnetic field type AC Zeeman flameless atomic absorption spectrometer. Considering the measurement sensitivity, interference of the matrix during measurement, etc., it is desirable to dissolve about 0.5 g in 100 ml of solvent. When the content is large, the amount of the collected sample may be small.

When the sample is 0.5 g, it is first correctly weighed to three decimal places in a PFA container (internal volume: 150 ml), added with 30 ml of 20% wt hydrochloric acid, and heated on a Teflon heater. The heating temperature at this time is 120
~ 140 ° C, and the heating time is preferably about 40 minutes. During the heating process, hexachlorotitanic acid once shows a yellow color, but at this point it can be easily melted by adding warm water immediately. Next, this is allowed to cool, 0.25 ml of 30% wt hydrogen peroxide is added, and the mixture is further heated for about 10 minutes. In the above sample dissolving operation, in order to completely dissolve the sample and maintain the solution for a long period of time, it is necessary to add hydrogen peroxide as a hydrolysis inhibitor and to make the titanium component in the sample a peroxo complex ion. . Failure to do so may result in the formation of a precipitate over time. Next, this solution was treated with ultrapure water for 100 hours.
Make up to a constant volume in ml, and use this as the test solution for analysis.

Next, from this test solution, 5 μl was used to make a total volume of 25 μl with water, that is, a 1000-fold diluted solution of the sample was measured by a standard addition method using a parallel magnetic field type AC Zeeman flameless atomic absorption apparatus. Sub pp
Quantitative analysis of m-order Na and K with high accuracy is possible. Here, the dilution ratio of the sample and the measurement result at the time of measurement are described. When a diluted solution exceeding 100,000 times is measured, the standard addition calibration curve gradient of the sample {excluding K of (Ba, Sr) TiO ₃ } is as follows. The calibration curve gradient of the standard solution is almost approached, and the interference of the matrix is almost eliminated. However, measurement at these dilution rates is not possible for analysis on the order of sub-ppm due to insufficient measurement sensitivity. Conversely, when the dilution ratio is lowered, that is, when the amount of matrix is increased, chemical interference is recognized, negative interference appears, and the calibration curve gradient of the standard addition method tends to decrease. The ground interference cannot be completely corrected, and therefore the calibration curve by the standard addition method cannot be correctly created and cannot be used for analytical quantification. Next, regarding the dilution ratio and the measurement result of the reagent blank that has undergone exactly the same operation as the sample, when a solution diluted 100 times or more is measured, the standard addition calibration curve gradient is:
Almost identical with the calibration curve gradient of the standard solution, and there is no matrix interference.

1 to 6 show the matrix amount (dilution ratio:
5 shows the gradient and accuracy of the calibration curve by the standard addition method at a change of 500 to 100,000 times (the dilution ratio of the reagent blank in FIGS. 1 to 6 is 1000 times).

From the above results, in the present method, the sensitivity at the time of the measurement of the standard solution was lowered (Na: 1/5,
K: 1/10, relative detection lower limit: Na: 0.06 ppb,
K: 0.2 ppb), but the background interference was completely corrected, and the correlation coefficient of the calibration curve was good and close to that of the standard solution. did. That is, from the standard blank calibration curve of the reagent blank and sample diluted 1000-fold,
Quantitative analysis on the order of pm is possible.

[0017]

EXAMPLES The present invention will be described below in detail with reference to examples, but the present invention is not limited to these examples.

Embodiment 1 1. Metal standard solution: A standard reagent for atomic absorption is diluted with ultrapure water and used. 2. Hydrochloric acid, hydrogen peroxide: a reagent purified by a non-boiling distillation method is used. 3. In the embodiment of the present invention, the specific resistance value is 18 MΩ / c.
m (25 ° C) or higher. 4. Sample decomposition container: A PFA-made total volume 150 ml with a marked line is used. 5. Heater: Use one coated with Teflon. 6. Flameless atomic absorption spectrometer: Perkin-Elmer parallel magnetic alternating current Zeeman flameless atomic absorption spectrometer 4100, which is installed in a clean room of class 1000 or less. 7. Clean bench: Use equipment of class 100 or less.

(Operation) Approximately 0.5 g of SrTiO _{3 of the} sample was placed in a PFA container (internal volume 150 ml) to three decimal places.
Then, 30 ml of 20% wt hydrochloric acid is added thereto, and the mixture is heated at a heating temperature of 120 to 140 ° C. on a Teflon heater. Approximately 20 ml of warm water immediately when it turns yellow
And continue heating for about 40 minutes. After cooling, 3
Add 0.25 ml of 0% wt hydrogen peroxide and heat for about another 10 minutes. After standing to cool, ultrapure water is added to make a total volume of 100 ml, which is used as a test solution.

Next, a test solution, a 5 ppb standard solution, and ultrapure water are taken in each cell for the autosampler of the flameless atomic absorption spectrometer, and set in the autosampler. From these solutions, 5 μl of the test solution and 20 μl of ultrapure water are first automatically injected into a tube, and the absorbance of only the sample is measured by a flameless atomic absorption method under a predetermined measurement condition shown in Table 1 for a total volume of 25 μl.

That is, under the measurement conditions of Na, the temperature is raised from room temperature to 120 ° C. in 1 second in drying 1 and then kept at 120 ° C. for 30 seconds. The Ar gas flow rate at this time is 250 m
1 / min. In drying 2, 120 ° C to 140 ° C
After the temperature was raised for 10 seconds, the temperature was maintained at 140 ° C. for 40 seconds, and the Ar gas flow rate at this time was 250 ml / min. In incineration 1, after the temperature was raised from 140 ° C. to 400 ° C. for 1 second, the temperature was maintained at 400 ° C. for 10 seconds, and the Ar gas flow rate at this time was 250 ml / min. In incineration 2, 40
After the temperature was raised from 0 ° C. to 700 ° C. for 10 seconds, the temperature was maintained at 700 ° C. for 30 seconds, and the Ar gas flow rate at this time was 250 ml.
/ Min. In the atomization, the temperature is maintained at 1700 ° C. for 4 seconds, and no Ar gas is supplied at this time. For cleaning, 1
After the temperature was raised from 700 ° C. to 2400 ° C. for 1 second, the temperature was maintained at 2400 ° C. for 2 seconds, and the Ar gas flow rate at this time was 250 ° C.
ml / min. Table 1 also shows measurement conditions for K.

Next, 5 pp was added to 5 μl of the test solution in the same manner.
b. The standard solution is added stepwise, and the absorbance of each of the 1 ppb standard addition solution, the 2 ppb standard addition solution, and the 3 ppb standard addition solution is measured, and a standard addition calibration curve is prepared. Next, a standard addition calibration curve is created for a reagent blank that has undergone exactly the same operation as the sample. The amount of each metal in the sample and the reagent blank is determined from these calibration curves, and the content (X) of each metal in the sample is calculated from the following formula (I).

Formula (I): X (ppb) = {amount of each metal in sample (ng / ml) −amount of each metal in reagent blank (ng / ml)} × 100 × 5
/ Sample collection amount (g) The results are shown in Table 2. Table 2 shows examples of reagent blank values after all operations, standard deviation values in actual sample analysis, and samples (A, B, C, D) having different contents. Regarding the lower limit of the analysis and quantification of the actual sample, the sample analysis value / reagent blank analysis value = 3 in consideration of each measurement error.
I decided to adopt.

Example 2 Except that BaTiO ₃ was used instead of SrTiO ₃ ,
The same operation as in Example 1 was performed. Table 2 also shows the results
It was shown to.

Example 3 The same operation as in Example 1 was carried out except that (Ba, Sr) TiO ₃ was used instead of SrTiO ₃ . The results are also shown in Table 2.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

According to the analytical method of the present invention, SrTi
Sub-ppm quantitative analysis of alkali metals in high dielectric materials such as O ₃ , BaTiO _3, and (Ba, Sr) TiO ₃ can be easily and accurately analyzed, supporting research on the production of high dielectric materials. This is an extremely useful analysis method.

[Brief description of the drawings]

FIG. 1 SrTi during flameless atomic absorption measurement
FIG. 3 is a graph showing changes and variations in the slope of a standard addition calibration curve depending on the dilution ratio (matrix amount) of Na in O ₃ .

FIG. 2 shows BaTi during flameless atomic absorption measurement.
FIG. 3 is a graph showing changes and variations in the slope of a standard addition calibration curve depending on the dilution ratio (matrix amount) of Na in O ₃ .

FIG. 3 shows (Ba,
Sr) Dilution ratio of Na in TiO ₃ (matrix amount)
1 shows changes and variations in the slope of the standard addition calibration curve due to the above.

FIG. 4 shows SrTi during flameless atomic absorption measurement
FIG. 4 shows changes and variations in the slope of a standard addition calibration curve depending on the dilution ratio (matrix amount) of K in O ₃ .

FIG. 5: BaTi during flameless atomic absorption measurement
FIG. 4 shows changes and variations in the slope of a standard addition calibration curve depending on the dilution ratio (matrix amount) of K in O ₃ .

FIG. 6 shows (Ba,
Sr) Changes in the slope of the standard addition calibration curve and variations in the dilution ratio (matrix amount) of K in TiO ₃ are shown.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-91570 (JP, A) Zh Anal. Khim, Russia, Vol. 47, No. 5 (1992), p896-900 (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 21/00-21/01 G01N 21/17-21/61 JICST file (JOIS) Practical file (PATOLIS) Patent file (PATOLIS)

Claims (1)

(57) [Claims] 1. A method according to claim 1, wherein BaTiO ₃ , SrTiO ₃ , (Ba,
Sr) After adding hydrochloric acid and hydrogen peroxide to at least one compound selected from the group of TiO ₃ and dissolving by heating,
A simple analysis method for alkali metals in a high-dielectric material, characterized by performing a quantitative analysis by a standard addition calibration curve method using a parallel magnetic field type AC Zeeman flameless atomic absorption spectrometer.