JP4992996B2 - Nitrogen concentration measurement method and calculation method of proportional conversion factor for nitrogen concentration measurement - Google Patents

Description

  The present invention relates to a method for measuring a nitrogen concentration and a method for calculating a proportional conversion coefficient for measuring the concentration of nitrogen.

  Silicon devices are manufactured using a silicon wafer cut out from a silicon ingot pulled up by the Czochralski method. At that time, the concentration of impurities such as nitrogen in the silicon wafer to be used is known in advance. It is necessary to keep.

In particular, in recent years, nitrogen is doped to reduce void defects, COP, or vacancy defects such as LSTD, and to enhance the gettering action by promoting oxygen precipitation. (For example, refer to Patent Document 1).

  Therefore, conventionally, a wafer manufacturer was requested to supply a wafer having a desired nitrogen concentration, and a nitrogen concentration test measurement for confirming the supplied wafer was performed.

  In this case, if a SIMS (secondary ion mass spectrometer) is used, it is possible to measure the nitrogen concentration precisely, but there is a problem that the measurement is expensive, and therefore a simple measurement method using infrared rays is required. It has been.

  Therefore, the present inventors have already developed a technique for quantifying the impurity nitrogen concentration in the silicon crystal pulled up by the Czochralski method by infrared absorption measurement (see Japanese Patent Application No. 2001-259446 if necessary). Therefore, the outline of the method is shown below.

First, when infrared absorption measurement is performed on the supplied nitrogen-added CZ-Si crystal sample, infrared absorption line peaks due to two types of nitrogen-related defects are observed. One of these two types of defects is a defect consisting of impurity nitrogen between the lattices of silicon atoms and impurity nitrogen between the lattices of silicon atoms within the fourth proximity of the impurity nitrogens, so-called NN pairs. This is a defect having an absorption peak at a wave number of 963 cm ⁻¹ . The “fourth adjacent silicon atom from the impurity nitrogen” means a silicon atom bonded through three connectors counted from the nearest Si lattice position of one N of the NN pair.

Another has defects consisting of impurity oxygen is between N-N from the pair of silicon atoms is within a fourth proximity grating, the absorption peak at a wavenumber of 996cm ^-1 and 1026cm ^-1 which so-called N-O complex It is a defect.

  When the present inventors hold a nitrogen-added CZ-Si crystal sample at a temperature higher than 600 ° C. for about 2 hours or more, the defect reaction between the N—N pair and the N—O complex reaches a thermal equilibrium at this time scale. We have succeeded in finding a quasi-thermal equilibrium state where the density is constant.

In this quasi-thermal equilibrium state, the density ratio of the N—N pair and the N—O complex is also constant, so that the sample reaches a quasi-thermal equilibrium state and has at least wave numbers of 963 cm ⁻¹ , 996 cm ⁻¹ , and 1026 cm ⁻¹ . By obtaining the intensity of the absorption peak appearing at one position, the intensity of the three peaks can be determined. The total impurity nitrogen concentration can be determined by using a proportional conversion coefficient prepared in advance.

  As described above, when the absorption due to impurity atoms is evaluated by infrared absorption measurement, it is common to use a difference spectrum from a crystal containing impurities, using a crystal containing no impurities as a reference.

  For example, the well-known quantification of impurity oxygen in CZ-Si uses a silicon crystal prepared by a floating zone method that does not contain oxygen as a reference. In general, an infrared absorption difference spectrum with a crystal containing impurity nitrogen is used with a sample containing no nitrogen as a reference.

JP 2000-332074 A

However, infrared absorption lines due to the nitrogen-related defects, such as N-N pair or N-O complex, 963cm ^-1 as described above, 996cm ^-1 and has a peak at 1026cm ^-1, which is at room temperature This corresponds to the base of large absorption of interstitial oxygen having a peak at 1106 cm ⁻¹ .

  In addition, since the concentration of impurity nitrogen is a few percent of impurity oxygen and the absorption is negligible, when obtaining the infrared absorption difference spectrum, not only the oxygen concentration with the reference but also the sample thickness and the amount of impurity doping other than nitrogen are aligned However, there is a problem that there is a slight difference between them and the absorption of nitrogen cannot be detected just by changing the baseline. Therefore, the biggest challenge is how to align factors other than nitrogen in the measurement sample and reference. is there.

  The most important thing in practical use is how accurately a nitrogen-added wafer having a thickness of 1 mm or less can be measured. This is because, in addition to the concentration of nitrogen contained in silicon being smaller than the concentration of other impurities, if the thickness of the sample to be measured is thin, such as a wafer, impurities contained in the wafer through which infrared light passes This is because the absolute amount of nitrogen is reduced, so that the peak intensity of infrared absorption due to impurity nitrogen is also reduced. Therefore, the demand for the reference becomes more severe.

  The only way to eliminate such inconsistencies in the oxygen concentration, sample thickness, and impurity doping amount other than nitrogen in the measurement crystal and reference crystal is to use the same crystal for both the measurement sample and the reference crystal. If the same sample is used, even the impurity nitrogen concentration matches, so there is a problem that it does not play a role in determining the nitrogen concentration.

  Accordingly, an object of the present invention is to precisely measure the nitrogen concentration in a silicon wafer by a simple infrared absorption difference spectrum without requiring a separate reference.

  From one aspect disclosed, a first step of heating a silicon crystal to 600 ° C. to reach a quasi-thermal equilibrium state, a second step of measuring a first infrared absorption spectrum of the silicon crystal, A third step of heating the silicon crystal at a temperature higher than 600 ° C. to reach a quasi-thermal equilibrium state, a fourth step of measuring a second infrared absorption spectrum of the silicon crystal, and the first infrared ray A fifth step of obtaining an infrared absorption difference spectrum between an absorption spectrum and the second infrared absorption spectrum, obtaining an intensity of an absorption peak corresponding to a defect caused by nitrogen, and based on the intensity of the absorption peak, the silicon And a sixth step of determining the nitrogen concentration in the crystal. A method for measuring the nitrogen concentration is provided.

  From another viewpoint to be disclosed, a step of preparing a plurality of silicon crystals cut out from one silicon mother crystal, and a first silicon crystal among the plurality of silicon crystals is heated at 600 ° C. A first step of reaching a thermal equilibrium state; a second step of measuring a first infrared absorption spectrum of the first silicon crystal; and a second silicon crystal of the plurality of silicon crystals at 600 ° C. A third step of heating at a higher temperature to reach a quasi-thermal equilibrium state, a fourth step of measuring a second infrared absorption spectrum of the second silicon crystal, and the first infrared absorption spectrum And an infrared absorption difference spectrum between the second infrared absorption spectrum and the fifth step for determining the intensity of an absorption peak corresponding to a defect caused by nitrogen, based on the intensity of the absorption peak, Nitrogen concentration measurement method characterized in that it comprises a sixth step of obtaining the nitrogen concentration of the serial silicon crystal, is provided.

  From another point of view, a silicon crystal whose nitrogen concentration has been measured in advance is heated at 600 ° C. to reach a quasi-thermal equilibrium state, and a first infrared absorption spectrum of the silicon crystal is measured. The silicon crystal is heated at a temperature higher than 600 ° C. to reach a quasi-thermal equilibrium state, a second infrared absorption spectrum of the silicon crystal is measured, and the first infrared absorption spectrum and the second infrared absorption spectrum are measured. An infrared absorption difference spectrum with an absorption spectrum is obtained, an intensity of an absorption peak corresponding to a defect caused by nitrogen is obtained, and calculated based on the obtained intensity of the absorption peak and the previously measured nitrogen concentration. A characteristic method for calculating a proportional conversion factor for measuring nitrogen concentration is provided.

  According to the disclosed nitrogen concentration measurement method and the calculation method of the proportional conversion coefficient for nitrogen concentration measurement, the infrared absorption difference spectrum after heat-treating a semiconductor crystal cut from the same semiconductor mother crystal such as a CZ-silicon wafer at different temperatures is obtained. Since it is used, it is possible to determine the concentration of added impurities in impurity-doped semiconductor crystals such as nitrogen-doped silicon wafers by a simple method called infrared absorption measurement, which in turn greatly contributes to improving the reliability of semiconductor devices. .

It is explanatory drawing of the correlation of the light absorbency and heat processing temperature in three infrared absorption peaks when a silicon crystal reaches a quasi-thermal equilibrium state. It is explanatory drawing of the infrared absorption difference spectrum in each heat processing temperature. It is a flowchart of the determination method of the nitrogen concentration in the silicon crystal of Example 1 of this invention. It is a flowchart of the determination method of the nitrogen concentration in the silicon crystal of Example 2 of this invention.

  Here, an embodiment of the present invention will be described. In the present invention, one or more silicon crystals for infrared absorption measurement cut out from one silicon mother crystal are prepared, the silicon crystals are heated at different temperatures, and the infrared absorption spectrum of the silicon crystal after heating is measured. Measure and obtain the intensity of the absorption peak corresponding to the defect caused by nitrogen from the infrared absorption difference spectrum.

  When heat treatment is performed at a specific heat treatment temperature and a quasi-thermal equilibrium state is reached, each peak intensity ratio corresponding to defects caused by specific impurities such as nitrogen is constant regardless of the impurity concentration and each peak at each heat treatment temperature. Since the intensity reflects the impurity concentration, one or more infrared absorption measurement silicon crystals cut out from one silicon mother crystal are heated at different temperatures, so that nitrogen does not need a separate reference. It becomes possible to determine the concentration of specific impurities such as. Note that this phenomenon does not depend on the base crystal material and the specific impurity, and is a phenomenon determined thermodynamically, and thus is commonly applied to various semiconductor crystals and impurities.

  In this case, the same silicon crystal may be heated twice at different temperatures, or two silicon crystals may be heated at different temperatures, and when the same silicon crystal is used, Since the original impurities are the same, the background can be accurately removed, and when two silicon crystals are used, heat treatment can be performed simultaneously using a plurality of heat treatment apparatuses. Therefore, the measurement time can be shortened.

  The heat treatment time is within the range of the measurement error of the infrared absorption difference spectrum, for example, the variation of the defect form and density caused by the specific impurity, for example, 2 hours to 15 hours, more preferably 2 hours to 8 hours. It is desirable to be. If the time exceeds 15 hours, the internal structure changes due to oxygen precipitation, making it difficult to measure with high accuracy.

  Further, as such a silicon mother crystal, a silicon crystal containing impurity oxygen, particularly a silicon ingot pulled up by the Czochralski method is typical.

Next, with reference to FIG.1 and FIG.2, the measurement principle of the addition nitrogen concentration in this invention is demonstrated. 1, the inventors have found, 963cm ^-1 of silicon crystal of impurity nitrogen concentration of ^{3.2 × 10 15 cm -3, 996cm} -1, and the nitrogen-related defects having a peak at 1018 cm ^-1 It is a figure which shows the heat treatment temperature dependence of the light absorbency when permeate | transmitting to a quasi-thermal equilibrium state. Note that the impurity concentration in this case is accurately determined in advance by SIMS (secondary ion mass spectrometry) or radiochemical analysis.

As shown, when the heat treatment prescribed time to fix the heat treatment temperature, since the reaction of the nitrogen-related defects reaches a quasi-thermal equilibrium, 963cm ^-1, 996cm ^-1, and, in proportion to the density of each defect in the 1018 cm ^-1 The peak intensity ratio is constant regardless of the impurity nitrogen concentration.

Therefore, when attention is paid to any one of the peaks of 963 cm ⁻¹ , 996 cm ⁻¹ , and 1018 cm ⁻¹ , the difference in absorbance at different heat treatment temperatures is uniquely determined according to the impurity nitrogen concentration.

FIG. 2 shows that five silicon chips cut out from one CZ-silicon wafer are heat-treated at 600 ° C., 700 ° C., 750 ° C., 800 ° C., and 900 ° C. to reach a quasi-thermal equilibrium state. It is a later infrared absorption spectrum, a difference spectrum with a silicon chip heat-treated at 600 ° C. as a reference, a peak is observed in the difference spectrum at 963 cm ⁻¹ , and in particular, there is a difference from a silicon chip heat-treated at 800 ° C. It is understood that it will be the largest. In addition, the underline of the straight line in each curve is a line for determining the magnitude | size of the peak of 963 cm < ^-1 >.

As background of the above, the impurity nitrogen concentration measured in advance by SIMS of nitrogen added CZ- silicon crystals A and N _A, where, for example, the N-N pair with a peak at 963cm ^-1 peak is observed in the difference spectrum Focus only on the resulting absorption.

  First, the silicon crystal A is heat treated at 600 ° C. to reach the quasi-thermal equilibrium state, and then the reference crystal is used as the reference crystal. The measured crystal is used as a measurement crystal, and the difference spectrum with respect to the reference crystal is measured.

In this case, the true absolute value of the absorbance of each of the measurement crystal and the reference crystal is unknown, and only the difference between the absorbances is known.
This is represented by α _A (800-600).

However, the absolute value alpha _A of the absorbance _(800-600) is proportional to the impurity concentration of nitrogen contained in the silicon crystal, the relation of the following equation using a fixed proportionality conversion factor κ and impurity nitrogen concentration N _A obtained It is done.
_{α A (800-600) = κ ·} N A ··· (1)

Thus, alpha _A a _(800-600) was determined from the infrared absorption measurement, the total impurity nitrogen concentration N _A by leaving measured by secondary ion mass as described above analyzes or activation analysis or the like, a proportional conversion factor κ Is uniquely determined. Note that the transition to the quasi-thermal equilibrium state due to the heat treatment of defects derived from such impurity nitrogen is determined by the thermodynamic requirements, so the proportional conversion factor κ is not limited to the growth method but is a silicon crystal containing oxygen. Is common.

Next, the silicon crystal B whose impurity nitrogen concentration is unknown is subjected to a heat treatment at 600 ° C. to reach a quasi-thermal equilibrium state, and then infrared absorption measurement is performed as a reference crystal, and the absorbance of the 963 cm ⁻¹ peak including the background is measured. Obtain α ₆₀₀ .

Next, the same silicon crystal B was subjected to a heat treatment at 800 ° C. to reach a quasi-thermal equilibrium state, and then infrared absorption measurement was performed as a measurement crystal to obtain an absorbance α ₈₀₀ of a 963 cm ⁻¹ peak including the background. The difference α _B (800−600) = α ₈₀₀ −α ₆₀₀ is obtained.

As described above, the proportional conversion coefficient κ for the difference in absorbance α (800−600) between the quasi-thermal equilibrium state by the heat treatment at 600 ° C. and the quasi-thermal equilibrium state by the heat treatment at 800 ° C. is constant regardless of the crystal. From equation (1)
α _B (800−600) = κ · N _B
It becomes.

Therefore, impurity nitrogen concentration N _B of the silicon crystal B has already a proportional conversion factor κ as determined by silicon crystal A which had been accurately measured impurity nitrogen concentration by SIMS or the like, in a silicon crystal B of impurity nitrogen concentration is unknown From the measured difference infrared absorbance α _B (800-600),
N _B = α _B (800−600) / κ (2)
As required.

  In this way, once the accurate impurity nitrogen concentration is measured by SIMS etc. once and the proportional conversion coefficient κ is obtained, the impurity nitrogen concentration contained in various silicon crystals is accurately determined only by simple infrared absorption measurement. It becomes possible to evaluate to.

  Further, since the same sample is heat-treated a plurality of times, the difference between the measurement sample and the reference as described in the problem to be solved by the above invention does not substantially occur. Although the impurity concentration slightly changes due to out-diffusion or the like by heat-treating the same sample a plurality of times, there is no problem because the change in absorbance due to the change is smaller than the measurement error of the infrared absorption difference spectrum.

Based on the above measurement principle, Example 1 of the present invention will now be described with reference to FIG. FIG. 3 is a flowchart of a method for quantifying the nitrogen concentration in the silicon crystal of Example 1 of the present invention.
a. One sample piece for infrared absorption measurement is cut out from one silicon wafer cut out from a silicon ingot pulled up by the Czochralski method.

Then
b. The cut out sample piece for infrared absorption measurement is subjected to heat treatment in a nitrogen atmosphere at 600 ° C. for 2 to 15 hours, for example, 2 hours.
In this heat treatment, the sample piece for infrared absorption measurement reaches a quasi-thermal equilibrium state. Then
c. An infrared absorption spectrum is acquired for the heat-treated sample piece for infrared absorption measurement.

Then
d. The same sample piece for infrared absorption measurement is subjected to heat treatment in a nitrogen atmosphere at 800 ° C. for 2 to 15 hours, for example, 2 hours.
In this heat treatment, the sample piece for infrared absorption measurement reaches another quasi-thermal equilibrium state again. Then
e. An infrared absorption spectrum is obtained again for the sample piece for infrared absorption measurement subjected to the second heat treatment.

Then
f. An absorbance α (800-600) in a difference spectrum at a peak of 963 cm ⁻¹ between an infrared absorption spectrum obtained after heat treatment at 600 ° C. and an infrared absorption spectrum obtained after heat treatment at 800 ° C. is obtained.

Then
g. Based on the above equation (2), using a silicon chip with a known impurity nitrogen concentration, using a proportional conversion coefficient κ related to the difference absorbance α (800-600) obtained by heat treatment at 800 ° C. and 600 ° C. obtained in advance. Nitrogen concentration N
N = α (800−600) / κ
Asking.

  As described above, in Example 1 of the present invention, the same chip is heat-treated twice, so that the infrared absorption spectrum obtained by the first heat-treatment is used as a reference, so a separate reference chip is not required. Therefore, since the oxygen concentration, the concentration of impurities other than nitrogen, and the thickness of the chip are constant, there is no problem when using a separate reference chip as in the prior art.

Next, Embodiment 2 of the present invention will be described with reference to FIG. FIG. 4 is a flowchart of a method for quantifying the nitrogen concentration in the silicon crystal of Example 2 of the present invention.
a. Two sample pieces for infrared absorption measurement are cut out from one silicon wafer cut out from a silicon ingot pulled up by the Czochralski method.

Then
b. The two cut infrared specimens for measuring infrared absorption were respectively used with different heat treatment apparatuses, and one of them was subjected to heat treatment for 2 to 15 hours, for example, 2 hours at 600 ° C. in a nitrogen atmosphere to reach a quasi-thermal equilibrium state. The other sample piece for infrared absorption measurement is subjected to a heat treatment in a nitrogen atmosphere at 800 ° C. for 2 to 15 hours, for example, 2 hours to reach another quasi-thermal equilibrium state.

Then
c. An infrared absorption spectrum is acquired for each of the two sample pieces for infrared absorption measurement subjected to heat treatment.
Then
d. The absorbance α (800-600) in the difference spectrum at the 963 cm ⁻¹ peak of the two infrared absorption spectra is determined.

Then
e. Based on the above equation (2), using a silicon chip with a known impurity nitrogen concentration, using a proportional conversion coefficient κ related to the difference absorbance α (800-600) obtained by heat treatment at 800 ° C. and 600 ° C. obtained in advance. Nitrogen concentration N
N = α (800−600) / κ
Asking.

  Thus, in Example 2 of the present invention, two chips cut out from the same wafer are heat-treated at the same time, so that the time required for heat treatment is only once, so that the time required for measurement is greatly reduced. Can do. Although the oxygen concentration and the concentration of impurities other than nitrogen in the two chips may be slightly different, there is no substantial problem by cutting out the two chips from areas adjacent to each other.

  Although the embodiment and each example of the present invention have been described above, the present invention is not limited to the configurations and conditions described in the embodiment and each example, and various modifications can be made. For example, in each of the above embodiments, the difference spectrum between the infrared absorption spectrum after the heat treatment at 800 ° C. and the infrared absorption spectrum after the heat treatment at 600 ° C. is used, but the difference spectrum between other temperatures is used. Is also good.

  In each of the above embodiments, the infrared absorption spectrum after the heat treatment at 600 ° C. is used as the reference. However, the infrared absorption spectrum after the heat treatment at 600 ° C. is not necessarily required. An absorption spectrum may be used. In that case, the second heat treatment may be performed at 700 ° C. or higher. However, in that case, it is necessary to set the heat treatment temperature of the reference to 700 ° C. when κ is acquired in advance.

  In Example 2 above, heat treatment is performed simultaneously using two heat treatment apparatuses, but a temperature gradient may be provided in the same heat treatment furnace, and heat treatment may be performed simultaneously in the same heat treatment furnace. Only one heat treatment device is needed.

  Alternatively, the heat treatment may be performed separately using the same heat treatment furnace, and in this case, variations in the impurity concentrations in the two chips are somewhat problematic, but on the contrary, compared to Example 1. Thus, it is not affected by the fluctuation of the impurity concentration due to the out diffusion due to the difference in the heat treatment time.

Further, in the above-mentioned embodiments, although the peak at 963cm ^-1 measured, it is permissible using a peak of 996cm ^-1 and 1018 cm ^-1.

  In each of the above embodiments, the CZ-silicon crystal is an object to be measured. However, the present invention is not limited to the CZ-silicon crystal, and silicon that contains at least oxygen and nitrogen added by other growth methods. If it is a crystal, a similar quasi-thermal equilibrium state exists, so that it is applied.

  Furthermore, oxygen does not necessarily need to be included. If attention is paid to the NN pair, the present invention can also be applied to an ingot grown by a floating zone method that substantially does not contain oxygen.

  In each of the above embodiments, the impurity to be measured is nitrogen. However, since the quasi-thermal equilibrium state used in the present invention is a phenomenon that is established in the crystal by a thermodynamic phenomenon, it depends on the type of impurity. Therefore, the present invention is not limited to nitrogen, but can be applied to the measurement of the concentration of carbon (C), which is an impurity that promotes the precipitation of oxygen as in the case of nitrogen.

  In addition, as described above, the quasi-thermal equilibrium state used in the present invention is a phenomenon that is established in the crystal due to a thermodynamic phenomenon, and thus is a phenomenon that does not depend on the base material of the crystal, and is therefore limited to the silicon crystal. However, it is also applied to other group IV crystals such as SiGe crystals or Ge crystals, or other semiconductor crystals such as III-V group compound semiconductors such as GaAs, and a quasi-thermal equilibrium state is obtained in each crystal. It is only necessary to find the heat treatment conditions that can be obtained.

Claims (13)

A first step of heating the silicon crystal to 600 ° C. to reach a quasi-thermal equilibrium state;
A second step of measuring a first infrared absorption spectrum of the silicon crystal;
A third step of heating the silicon crystal at a temperature higher than 600 ° C. to reach a quasi-thermal equilibrium state;
A fourth step of measuring a second infrared absorption spectrum of the silicon crystal;
A fifth step of determining an infrared absorption difference spectrum between the first infrared absorption spectrum and the second infrared absorption spectrum, and determining an intensity of an absorption peak corresponding to a defect caused by nitrogen;
A sixth step of determining a nitrogen concentration in the silicon crystal based on the intensity of the absorption peak;
The nitrogen concentration measuring method characterized by having. 963cm ^-1 as an absorption peak corresponding to the defects due to the nitrogen, 996cm ^-1, the nitrogen concentration measuring method according to claim 1, wherein the use of what appears to any one of wave numbers of 1018 cm ^-1.   The nitrogen concentration measuring method according to claim 1 or 2, wherein the sixth step calculates the nitrogen concentration based on an intensity of the absorption peak and a predetermined proportional conversion factor.   The nitrogen concentration measurement method according to any one of claims 1 to 3, wherein the temperature higher than 600 ° C is 800 ° C. Preparing a plurality of silicon crystals cut out from one silicon mother crystal;
A first step of heating the first silicon crystal of the plurality of silicon crystals at 600 ° C. to reach a quasi-thermal equilibrium state;
A second step of measuring a first infrared absorption spectrum of the first silicon crystal;
A third step of heating the second silicon crystal of the plurality of silicon crystals at a temperature higher than 600 ° C. to reach a quasi-thermal equilibrium state;
A fourth step of measuring a second infrared absorption spectrum of the second silicon crystal;
A fifth step of determining an infrared absorption difference spectrum between the first infrared absorption spectrum and the second infrared absorption spectrum, and determining an intensity of an absorption peak corresponding to a defect caused by nitrogen;
A sixth step of determining a nitrogen concentration in the silicon crystal based on the intensity of the absorption peak;
The nitrogen concentration measuring method characterized by having.   6. The nitrogen concentration measuring method according to claim 5, wherein the silicon mother crystal is a silicon wafer cut out from a silicon ingot pulled up by the Czochralski method. Nitrogen concentration according to 963cm ^-1, 996cm ^-1, claim 5 or claim 6, characterized in that used as appearing in any of the wave number of 1018 cm ^-1 as an absorption peak corresponding to the defects due to the nitrogen Measuring method.   The said 6th process calculates | requires the said nitrogen concentration based on the intensity | strength of the said absorption peak and a predetermined proportional conversion factor, The any one of Claim 5 to 7 characterized by the above-mentioned. Nitrogen concentration measurement method.   The nitrogen concentration measurement method according to any one of claims 5 to 8, wherein the temperature higher than 600 ° C is 800 ° C. A silicon crystal whose nitrogen concentration has been measured in advance is heated at 600 ° C. to reach a quasi-thermal equilibrium state, and a first infrared absorption spectrum of the silicon crystal is measured,
The silicon crystal is heated at a temperature higher than 600 ° C. to reach a quasi-thermal equilibrium state, and a second infrared absorption spectrum of the silicon crystal is measured,
Obtaining an infrared absorption difference spectrum between the first infrared absorption spectrum and the second infrared absorption spectrum, obtaining an intensity of an absorption peak corresponding to a defect caused by nitrogen,
A method for calculating a proportional conversion coefficient for measuring nitrogen concentration, wherein the calculation is based on the obtained intensity of the absorption peak and the previously measured nitrogen concentration. As the absorption peak corresponding to the defects due to the nitrogen, 963cm ^-1, 996cm ^-1, proportional terms for nitrogen concentration measurement according to claim 10, wherein the use of what appears to any one of wave numbers of 1018 cm ^-1 Coefficient calculation method.   12. The proportional conversion coefficient for measuring a nitrogen concentration according to claim 10, wherein the silicon crystal is obtained by measuring the nitrogen concentration in advance by secondary ion mass spectrometry or radiochemical analysis. Calculation method.   The method for calculating a proportional conversion coefficient for measuring nitrogen concentration according to any one of claims 10 to 12, wherein the temperature higher than 600 ° C is 800 ° C.

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