JPH11211662A - Quick analytical method for trace amount of phosphorus in silicon material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a quick analytical method in which a trace amount of phosphorus in a high-purity silicon material used for a solar cell, a semiconductor, an electronic material or the like can be quantitatively analyzed in a short time and quickly by a method wherein the silicon material is inserted directly into a plasma so as to be excited to emit light and the luminous intensity of the phosphorus is measured. SOLUTION: A silicon material which is housed in a sample cup such as a graphite cup or the like is inserted directly into a high-temperature plasma so as to be excited to emit light, and the luminous intensity of phosphorus is measured. The obtained luminous intensity of the phosphorus is converted into the concentration of the phosphorus in the silicon material by using a working curve obtained by using a silicon material whose concentration of silicon is known. In addition, regarding the silicon material, the luminous intensity of silicon is measured, and the concentration of the phosphorus in the silicon material is found by using a working curve which expresses a correlation between [the luminous intensity of the phosphorus/the luminous intensity of the silicon] (intensity ratio) obtained by using the silicon material whose concentration of silicon is known and the concentration of the silicon. Thereby, the analytical accuracy of a trace amount of phosphorus can be enhanced.

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 phosphorus in a silicon material such as a high-purity silicon material used for solar cells, semiconductors, and electronic materials, and more particularly, to a method for rapidly quantifying a trace amount of phosphorus in a silicon material. The present invention relates to a rapid analysis method for trace amounts of phosphorus in a silicon material.

[0002]

2. Description of the Related Art Phosphorus has higher excitation energy and ionization energy than other metal elements.
The analytical sensitivity of the ICP analysis method is poor, and direct analysis cannot be applied to trace levels below the ppm level. The same applies to the analysis of phosphorus in silicon materials.For example, despite the high analysis requirements for phosphorus as an element that has a significant effect on product characteristics in silicon wafers and solar cells, the proposed high-sensitivity analysis method is Few.

[0003] As a method for analyzing phosphorus in silicon material,
Infrared absorption method [BOKolb
esen: Appl. Phys. Letters, 27,353 (1975)] and the photoluminescence method [Michio Tajima: Applied Physics, 47, 376 (1978)]
The quantitative method has been studied and established, but the former requires complicated and time-consuming preparation of the sample to finish the light input / output surface of the sample flat and smooth, while the latter requires a large-scale apparatus itself. However, there is a problem that the analysis requires a long time of about half a day.

[0004] Therefore, the present inventors decomposed silicon with an acid vapor under a pressurized state, and formed phosphorus with the molybdic acid in the decomposition residue to form a complex with a cationic surfactant to form an ion pair. After that, Mo was collected and measured, and a method for indirectly quantifying phosphorus with high sensitivity and high precision was provided (Japanese Patent Application No. 9-15001: Method for analyzing phosphorus in silicon material). According to the above-described analysis method, trace amounts of ppb-level phosphorus in high-purity silicon can be easily analyzed with high accuracy, and further, the analysis has been significantly speeded up.

However, it takes several hours for sample decomposition (unmanned operation), and in order to respond to a rapid analysis request such as on-site analysis at a production site, the time required for analysis including sample preparation to analysis is further increased. It has been desired to develop a method for analyzing a trace amount of phosphorus in a silicon material that is short, highly accurate, and can be easily analyzed. On the other hand, IC which is usually a solution analysis method
A method has been studied and reported in which a sample placed in a graphite cup is directly inserted into the plasma of P emission spectrometry to quickly analyze impurity elements therein [EDSalin, G. Horli
ck: Anal. Chem., 51, 13 (1979)].

The solid sample used in this report is a standard sample in which each element is attached to the surface of a graphite powder.
Excitation of the analysis element, not a sample in which the analysis element is actually taken into the solid itself, is much easier than that of an actual solid sample, and is not affected by fluctuations in the evaporation amount of the matrix itself. Also, the environmental sample of NBS, which is another solid sample used in the above report, is an organic matrix, so that only the matrix can be selectively removed by preheating in the low temperature part of the plasma.

That is, ICP emission analysis is not applied as a direct analysis of trace elements in a metal sample such as a silicon material, that is, a direct analysis of trace elements in a matrix. As another application example of the direct sample insertion method to a solid sample, there is an application example to a trace element analysis method in Al [G. Zaray, P. Burba, JACB Roekaert, F. Lei
s: Spectrochim. Acta, 43B, 255 (1988)], which uses a sample after preconcentration with cellulose using an acid and alkali solution to which a chelating agent has been added. Application of ICP emission spectrometry to material analysis has not been studied.

As described above, despite the high demand for analysis of phosphorus as an element that greatly affects product characteristics in, for example, silicon wafers and solar cells, the time required for analysis from sample preparation to analysis is short. A rapid analysis method for trace amounts of phosphorus in a silicon material that can be easily analyzed with high accuracy has not been found.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems of the prior art and removes a trace amount of phosphorus in a silicon material such as a high-purity silicon material used for solar cells, semiconductors and electronic materials for a short time. It is an object of the present invention to provide a rapid analysis method for a trace amount of phosphorus in a silicon material, which can be quickly and quantitatively analyzed by using the method.

[0010]

Means for Solving the Problems In the course of intensive studies to solve the above-mentioned problems, the present inventors have found that high-boiling silicon, which is a matrix of silicon material, is sufficiently vaporized and excited in plasma. We studied the possibility that phosphorus in the matrix, which is an element to be analyzed, would sublimate and excite.

As a result, the silicon material is directly inserted into the plasma to excite and emit light, and the emission intensity of phosphorus is measured, whereby a trace amount of phosphorus of sub-ppm level or less in high purity silicon is analyzed with high accuracy. It has been found that this is possible and led to the present invention. That is, the first invention is
A silicon material is directly inserted into a high-temperature plasma and excited to emit light, the emission intensity of phosphorus is measured, and the obtained emission intensity of phosphorus and a calibration curve obtained using a silicon sample with a known phosphorus concentration. The method for rapid analysis of a trace amount of phosphorus in a silicon material is characterized in that the concentration of phosphorus in the silicon material is determined from the following formula.

According to a second aspect of the present invention, a silicon material is directly inserted into a high-temperature plasma to excite and emit light, and the luminescence intensity of phosphorus and silicon is measured to obtain the intensity ratio. Determining the phosphorus concentration in the silicon material from a calibration curve showing the correlation between the phosphorous concentration and the emission intensity ratio of phosphorus and silicon obtained using a silicon sample with a known phosphorus concentration; This is a method for rapid analysis of phosphorus.

[0013] In the above-described first and second inventions, the method for rapidly analyzing a trace amount of phosphorus in a silicon material comprises the following steps: (1) a sample storage section; Diameter d of a shaft portion which is a support member of the sample storage unit
A sample cup comprising a shaft portion having a diameter equal to or smaller than 1/2 of the diameter D of the lower end of the sample storage portion, or (2) a shaft using a non-heat-conductive material which is a support member of the sample storage portion and the sample storage portion. Or (3) a sample storage portion, and a diameter d of a shaft portion, which is a support member of the sample storage portion, is a diameter D of a lower end of the sample storage portion.
It is preferable to use a sample cup which is not more than 1/2 of the above and which comprises a shaft portion using a non-heat-conductive material.

[0014] The first invention described above, the plasma in the second invention, Ar generated by radio wave or microwave discharge, it is preferable to use a high-frequency plasma of He or N _2. In addition, it is preferable to use ceramics, which is a nonmetallic inorganic material, as the non-heat-conducting material in the preferred embodiments of the first and second inventions described above.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the present invention, a silicon material contained in a sample cup such as a graphite cup is directly inserted into high-temperature plasma to excite and emit light, and the emission intensity of phosphorus is measured. The emission intensity of the obtained phosphorus is converted into the phosphorus concentration in the silicon material by a calibration curve obtained using a silicon sample having a known phosphorus concentration.

Further, according to the present invention, the luminescence intensity of silicon is measured simultaneously with phosphorus with respect to the silicon material, and [luminescence intensity of phosphorus / luminescence intensity of silicon] (intensity) obtained using a silicon sample having a known phosphorus concentration. The analysis accuracy can be further improved by determining the phosphorus concentration in the silicon material using a calibration curve representing the correlation between the ratio) and the phosphorus concentration.

Furthermore, according to the present invention, as a sample cup for inserting a sample into the plasma, (1) the diameter d of the shaft portion, which is a support member of the sample storage portion, is set to be smaller than the diameter D of the lower end of the sample storage portion. Or (2) a sample cup in which the material of the shaft, which is the support member of the sample storage unit, is a non-heat-conductive material, or (3) a diameter d of the shaft, which is the support member of the sample storage unit. Of the silicon material to be analyzed is efficiently vaporized and atomized by using a sample cup having a diameter smaller than the diameter D of the lower end of the sample storage part and having a shaft made of a non-heat-conductive material. Thus, highly sensitive analysis of phosphorus in a silicon material was made possible.

In the ICP emission spectrometry (ICP emission spectrometry) based on the ordinary solution introduction method, the efficiency of sample introduction into plasma is several percent, which is a major factor that limits the analysis sensitivity. . In addition, when a solid sample is to be analyzed, it takes a long time to convert the sample into a solution, and it is not possible to cope with a demand for rapid analysis such as on-site analysis at a production site.

In addition, in the case of solution, it is unavoidable that the analysis sensitivity and the analysis accuracy are reduced due to the decrease in the content of impurities to be analyzed in the sample. Therefore, the present inventors have paid attention to a method of directly emitting a solid sample into plasma for excitation light emission in ICP emission spectrometry. In the case of the above method, several mg ~
By inserting several hundred mg of a solid sample directly into the plasma for thermal decomposition and vaporization, and then exciting and emitting light in the plasma, the amount of impurities that are the target components to be introduced into the plasma can be compared with the solution introduction method. , Can be dramatically increased.

For example, 0.5 g of a solid sample having an impurity concentration of 1 ppm
Is dissolved to prepare a 100 ml solution, the amount of impurities inserted into the plasma is only 0.05 ng when the sample suction volume is 1 ml / min, 20 sec integration, and the introduction efficiency is 3%. In the case of the sample direct insertion method, the amount of impurities inserted into the plasma is 20 ng for a sample amount of 20 mg, and an improvement in relative sensitivity of about 400 times is expected.

The present inventors have found that the temperature inside a graphite cup inserted into a normal ICP plasma (output 1.2 kW) is about 3000
Since the boiling point of the silicon material to be analyzed is 2360 ° C and the phosphorus of the element to be analyzed sublimates at 431 ° C, it is considered that vaporization and excitation can be sufficiently performed even in ICP plasma. Thus, when the emission intensity of phosphorus in silicon having different phosphorus concentrations was actually measured by the present method, it was found that a good correlation was obtained between the emission intensity of phosphorus and the concentration at a high frequency output of 0.6 kW or more.

Furthermore, it has been found that the analysis accuracy can be further improved by using the ratio of the luminescence intensity of phosphorus to the luminescence intensity of silicon detected simultaneously with phosphorus. Phosphorus emission analysis lines (: measurement wavelength) are less affected by the emission intensity of silicon, such as PI
A wavelength such as 178.29 nm or 177.44 nm is preferred.

As the silicon emission analysis line (measurement wavelength) used for the internal standard correction, it is more effective to use an analysis line whose behavior in the plasma is similar to that of phosphorus. In the case where is used, an atomic beam is used, and in the case where an ion beam is used, the correction effect is larger when an ion beam is used.
Further, the specification of the sample cup for inserting the sample into the plasma greatly affects the vaporization and excitation of the sample.

For this reason, the shaft portion, which is a support member of the sample storage section in the sample cup, is made thinner or a non-conductive material is used as a material of the shaft section to transfer heat from the sample storage section to the shaft section. By suppressing or combining the above and the above, the temperature of only the sample storage section is efficiently raised, thereby making it possible to greatly improve the analysis sensitivity. That is, in the analysis method of the present invention, as the sample cup for inserting the sample into the plasma, (1) the sample storage portion, and the diameter d of the shaft portion, which is a support member of the sample storage portion, is set at the lower end of the sample storage portion. A sample cup comprising a shaft portion having a diameter equal to or less than 1/2 of the diameter D of the sample container, or (2) a sample comprising a sample storage portion and a shaft portion using a non-heat-conductive material as a support member of the sample storage portion. Cup or (3) the diameter d of the sample storage part and the shaft part which is a support member of the sample storage part is １ ／ of the diameter D of the lower end of the sample storage part.
It is preferable to use a sample cup comprising the following and a shaft portion using a non-heat-conductive material.

It should be noted that the diameter d of the above-mentioned sample storage part and the shaft part which is a support member of the sample storage part is the diameter D of the lower end of the sample storage part.
The diameter D of the lower end of the sample storage unit in the sample cup consisting of a shaft portion that is not more than 1/2 of the diameter of the sample storage unit indicates the outer diameter of the lower end of the sample storage unit if the sample storage unit is a hollow cylinder. If it is not circular, it indicates the equivalent circle diameter of the bottom surface. Also,
Similarly, the diameter d of the shaft portion indicates the diameter or the outer diameter of the shaft portion if the shaft portion is a column or a cylinder, and indicates the equivalent circle diameter of the cross section of the shaft portion if the shaft portion is not a column or a cylinder.

The non-heat-conductive material described above includes:
It is preferable to use a heat-resistant ceramic which is a nonmetallic inorganic material, and the heat-resistant ceramic is preferably
Examples include ZrO ₂ and ThO ₂ , but are not particularly limited. According to the analysis method of the present invention described above, it has become possible to easily and quickly analyze phosphorus in a high-purity silicon to a sub-ppm level.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below more specifically based on embodiments. (Example 1) FIG. 3 shows the sample directly inserted / used in this example.
The plasma torch part and the sample cup of the ICP emission spectrometry (: inductively coupled plasma emission spectrometry) are shown in a sectional view.

In FIG. 3, reference numeral 1 denotes a plasma torch unit;
Is ICP (high frequency inductively coupled plasma), 3 is sample cup,
Reference numeral 4 denotes a sample storage unit (a sample atomization unit) of the sample cup 3 and 5
Denotes a shaft portion of the sample cup 3, 6 denotes an Ar gas, 7 denotes a carrier gas, d denotes a diameter of the shaft portion 5, D denotes a diameter of a lower end of the sample storage portion 4, and f denotes a moving direction of the sample cup 3. As the plasma torch part, an open type was used in the lower part, and the sample cup 3 was directly inserted into the plasma from the lower part with the plasma turned on.

The material of the sample storage section 4 is graphite, and the shaft section 5 is made of graphite.
Is hollow, the outer diameter of the hollow cylindrical sample storage unit 4 is 5 mm, and the cross-sectional diameter of the shaft 5 is 1.5 mmφ. Sample volume is 20
mg was used. The sample storage unit 4 of the sample cup 3 is positioned at a fixed position near the high-frequency coil, that is, at the bottom (:
The bottom of the cup was stopped at a position where it overlapped the center of the high-frequency coil, and the emission intensity of phosphorus and silicon emitted after vaporization, excitation, and emission in plasma were measured.

The measurement wavelength was PI 178.29 nm, SI 251.61 nm, and the photometry was performed at 10 mm on a high frequency coil. FIG.
FIG. 7 shows an example of the emission intensity (: emission signal) obtained when high-purity silicon having a phosphorus content of 0.9 ppm was inserted into plasma by the method described above. After inserting the sample into the plasma, the signal almost returned to the baseline within a few ten seconds, indicating that phosphorus was vaporized and emitted light in the plasma in a very short time.

The same operation was repeated for samples having different phosphorus contents.
The luminescence signal from seconds to 15 seconds was integrated. FIG. 2 shows an example of a calibration curve prepared by plotting the obtained integrated intensity against the phosphorus content. The unit of the P emission intensity on the vertical axis in FIG. 2 is an arbitrary unit. In preparing the above-mentioned calibration curve, in order to reduce the influence of segregation in the sample, each sample of samples having different phosphorus contents was analyzed three times, and the average value was used.

As shown in FIG. 2, the phosphorus content was 1 pp.
The linearity of the calibration curve is good even in a trace area of less than m, indicating that the analysis method of the present invention is extremely useful as a rapid analysis method of trace phosphorus in high-purity silicon. Next, using the calibration curve described above, the phosphorus content was 0.2 ppm (: wet analysis value).
Table 1 shows the results of quantifying the phosphorus in the actual sample.

As shown in Table 1, according to the analysis method of the present invention, a sample having a phosphorus content of 0.2 ppm can be quantified with a standard deviation σ = 0.07 ppm. In addition, in order to further improve the analysis accuracy of the analysis method of the present invention, at the same time as phosphorus, the intensity of the atomic line of silicon whose emission behavior in plasma is similar to that of phosphorus is measured and corrected with the emission intensity of silicon. did.

The results obtained are shown in Table 1. As shown in Table 1, according to the analysis method of the present invention, by using the ratio between the emission intensity of phosphorus and the emission intensity of silicon as a matrix, fluctuations in the amount of evaporation, the amount of atomization, and the like in the plasma are achieved. Was reduced, and the analysis accuracy was improved more than twice. Note that all of the above results were obtained by using the sample cup 3 in which the shaft portion as shown in FIG. 3 was thinned to increase the temperature rising rate of the sample storage section 4 (: sample atomization section) (: cup section). Things.

On the other hand, instead of the sample cup 3 described above,
When a shaft and a sample storage part that are commercially available for DC discharge emission analysis are molded integrally, and the shaft part uses a neck electrode with the same diameter as the sample storage part as a sample cup, the vaporization of silicon is 5 times. The above time was required, and only a signal of 1/10 or less of the luminescence intensity (: signal) of FIG. 1 was obtained, and it could not be applied to the quantification of a trace region of sub-ppm or less.

Further, the time required for analysis by the analysis method of the present invention is less than one minute per sample, and even if the measurement is repeated several times to reduce the influence of segregation in the sample and improve the accuracy. It has become possible to analyze extremely quickly and easily.

[0037]

[Table 1] (Example 2) As the sample cup 3 shown in FIG.
Except that the material of the sample storage part 4 was graphite, the material of the shaft part 5 was ZrO ₂ , the outer diameter of the sample storage part 4 which was a hollow cylinder was 5 mm, and the cross-sectional diameter of the shaft part 5 was 1.5 mmφ. In the same manner as in Example 1, the emission intensity of high-purity silicon having a phosphorus content of 0.9 ppm was measured.

As a result, after inserting the sample into the plasma, 10
In a few seconds, the signal almost returned to the baseline, and it was found that phosphorus was vaporized and emitted in a very short time in the plasma, and the method for rapid analysis of trace amounts of phosphorus in the silicon material according to the present invention relates to the above-described present invention. It has been found preferable to use a sample cup.

[0039]

As described above, according to the present invention, it has become possible to analyze a trace amount of phosphorus of sub-ppm level or less in high-purity silicon with high accuracy and extremely quickness by a simple method. In other words, the quantitative analysis of trace phosphorus in high-purity silicon, which has been difficult and traceable in the past, can now be performed simply and extremely quickly. Analysis and reaction control of the silicon manufacturing process used for solar cells and the like can be performed accurately and quickly, and significant effects are expected in terms of product quality improvement and stable production.

[Brief description of the drawings]

FIG. 1 is a graph showing an example of a luminescence signal obtained when high-purity silicon having a phosphorus content of 0.9 ppm is inserted into plasma.

FIG. 2 is a graph showing an example of a calibration curve according to the present invention.

FIG. 3 is a cross-sectional view showing a plasma torch part and a sample cup in direct sample insertion / ICP emission spectrometry.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Plasma torch part 2 ICP (high frequency induction coupling plasma) 3 Sample cup 4 Sample storage part of sample cup (: sample atomization part) 5 Shaft part of sample cup 6 Ar gas 7 Carrier gas d Diameter of shaft part D Sample storage part Bottom diameter f Moving direction of sample cup

Claims (3)

[Claims] 1. A method in which a silicon material is directly inserted into a high-temperature plasma to cause excitation and emission, and the emission intensity of phosphorus is measured.
A rapid analysis method for a trace amount of phosphorus in a silicon material, wherein a phosphorus concentration in the silicon material is obtained from a light emission intensity of the obtained phosphorus and a calibration curve obtained using a silicon sample having a known phosphorus concentration. 2. A method in which a silicon material is directly inserted into a high-temperature plasma to excite and emit light, and the emission intensity of phosphorus and silicon is measured to obtain an intensity ratio.
Determining the phosphorus concentration in the silicon material from a calibration curve showing the correlation between the phosphorous concentration and the emission intensity ratio of phosphorus and silicon obtained using a silicon sample with a known phosphorus concentration; Rapid analysis method for phosphorus. 3. The method for rapidly analyzing a trace amount of phosphorus in a silicon material according to the above method, wherein the sample cup for inserting a sample into the plasma includes: (1) a sample storage portion and a shaft serving as a support member of the sample storage portion. A sample cup comprising a shaft portion having a diameter d of the portion being equal to or less than 1/2 of a diameter D of the lower end of the sample storage portion, or
(2) a sample cup comprising a sample storage portion and a shaft portion using a non-heat-conductive material as a support member of the sample storage portion, or
(3) a sample storage portion, and a shaft portion which is a support member of the sample storage portion, wherein a diameter d of the shaft portion is equal to or less than の of a diameter D of a lower end of the sample storage portion, and a shaft portion using a non-heat-conductive material. 3. The rapid analysis method for trace amounts of phosphorus in a silicon material according to claim 1, wherein a sample cup comprising: