JPH06194310A - Method and equipment for automatically measuring substitutional carbon concentration in silicon single crystal - Google Patents

Abstract

PURPOSE:To provide a method and equipment for measuring the substitutional carbon concentration in a silicon single crystal accurately and automatically. CONSTITUTION:When the substitutional carbon concentration in a silicon single crystal is measured using FT-IR method (Fourier Transform Infrared spectrometry), a differential coefficient is calculated basing on the infrared absorbance spectrum obtained from a sample, i.e., a silicon single crystal, and that obtained from a non-carbon silicon single crystal (reference) having substantially identical free carrier absorbance produced by same method as the sample. The differential coefficient is employed in the determination of a differential absorbance spectrum from both infrared absorbance spectrums. Substitutional carbon concentration in the sample is then determined basing on the distance between a base line and a local oscillation absorption peak of the substitutional carbon in the differential absorbance spectrum.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a carbon analysis method by the FT-IR method, more specifically, using a reference,
The present invention relates to a method of measuring the substitutional carbon concentration in a silicon single crystal by the T-IR method, and the like.

[0002]

[Prior art]

Carbon impurities in a wafer made of a silicon single crystal are important factors that control the quality of the wafer together with oxygen impurities, and the FT-IR method is widely adopted to measure the carbon concentration in the silicon wafer. ing.

FIG. 9 shows the F used in this FT-IR method.
2 shows a T-IR optical system. In this FT-IR optical system, the divergent light emitted from the infrared continuous light source 1 is collimated by the collimator mirror 3 through the aperture 2, enters the Michelson interferometer 4, and enters the beam splitter 5. The infrared light that has entered the beam splitter 5 is split into reflected light and transmitted light. Of this, the reflected light is reflected by the fixed mirror 6 and returns to the beam splitter 5, and the transmitted light is reflected by the movable mirror 7 and beamed. Return to splitter 5. Then, the beams splitter 5 combines the two lights and interferes with each other, and the interference light is reflected by the concave mirror 8.
The light is collected at, passes through the sample 9, passes through the aperture 10, and enters the detector 11. The interferogram detected by the detector 11 is digitally converted and then Fourier-transformed to obtain an infrared absorption spectrum of the sample 9. The infrared absorption spectrum of the reference is obtained by the same method. An example of the infrared absorption spectrum of the silicon single crystal sample (p-type 10 Ωcm) obtained by the CZ method and the reference (p-type 2000 Ωcm) of the silicon single crystal obtained by the FZ method is shown in FIG.
0 and FIG. 11 respectively.

The order of measurement of the sample and the reference is often the reverse of the above. Usually, the reference measurement is performed in advance and the infrared absorption spectrum data thereof is stored. ing.

When the infrared absorption spectra of both the sample and the reference are obtained for the substitutional carbon in the silicon single crystal wafer in this way, the difference coefficient f is determined to obtain the difference absorption spectrum, and the difference coefficient f is determined. By subtracting the infrared absorption spectrum multiplied by the difference coefficient f from the infrared absorption spectrum of the sample,
Obtain the differential absorbance spectrum. An example of the difference absorbance spectrum obtained from the both infrared absorbance spectra of FIG. 10 and FIG. 11 is shown in FIG.

[0007] If the difference absorbance spectrum as described above is obtained, in the differential absorbance spectrum, for example from 595 cm ^-1 and baseline drawn between 615 cm ^-1, the substitutional carbon Cs appearing at 605 cm ^-1 The substitutional carbon concentration is quantified from the distance from the localized vibration absorption peak, that is, the peak height. When the concentration with the substitutional carbon Cs was quantified from the differential absorbance spectrum shown in FIG. 12, the value was 0.
It is 5 ppma. The lower limit of detection of the substitutional carbon concentration in this case is about 0.05 ppma according to the standard of ASTM designation: F123-81.

[0008]

By the way, there are roughly two methods for producing a silicon single crystal wafer which is a material for producing a semiconductor device. One is to put raw material polysilicon in a quartz crucible, melt the polysilicon with a carbon heater, immerse a seed crystal that is single crystal silicon in the surface of the melt, and pull up while rotating the seed crystal. CZ for growing silicon single crystal
The other is the FZ method (floating zone method) in which a silicon single crystal is grown by melting a part of a raw material polysilicon rod with a melting coil and moving this zone. .

Comparing the silicon single crystals produced by these two methods, the CZ method silicon single crystal contains a relatively large amount of carbon impurities and oxygen impurities. It is considered that the carbon impurities are mixed from a carbon heater or the like for melting the raw material polysilicon, and the oxygen impurities are mixed from a quartz crucible holding a melt of the raw material polysilicon. On the other hand, it was said that the FZ method silicon single crystal contained almost no carbon impurities and oxygen impurities.

Therefore, in the conventional method, it has been considered that the FZ method silicon single crystal is effective as a reference for measuring the carbon concentration and the oxygen concentration in the CZ method silicon single crystal.

However, when the FZ method silicon single crystal is used as a reference, the researches by the present inventors have revealed the following problems.

That is, the localized vibration absorption peak of the substitutional carbon Cs in the silicon single crystal appears at 605 cm ^-1 , so that it overlaps with the strong absorption peak of phonon of silicon, as shown in FIG. Looking at the shape of the phonon absorption peak of this silicon, the shape changes depending on the free carrier absorption by the dopant when the resistivity is 3 Ωcm and when the resistivity is 20 Ωcm as shown in FIG.

Therefore, in order to accurately extract the localized vibration absorption peak of the substitutional carbon Cs as the difference absorption spectrum from both the infrared absorption spectra of the sample and the reference, the locality of the substitutional carbon Cs between the sample and the reference should be measured. It is necessary to minimize the effects of differences other than the local vibration peak, especially the effects of absorption by silicon's strong phonons and the effects of free carriers. For that purpose, it is necessary to use a reference in which the phonon absorption of silicon and the free carrier absorption of the dopant, which overlap with the absorption peak of carbon, are almost the same.

However, in almost all cases, the sample CZ method silicon single crystal has a resistivity of 20 Ωcm.
On the contrary, the FZ method silicon single crystal for reference has a resistivity of 1000 Ωcm or more because it is usually manufactured without adding a doping agent. Therefore,
A large difference occurs in free carrier absorption of the dopant between the sample and the reference.

Moreover, the FZ method silicon single crystal has a much lower concentration of oxygen impurities than the CZ method silicon single crystal as described above. Therefore, the shapes of the phonon absorption peaks of silicon are further different between the sample and the reference. As a result, 0.
At a low carbon concentration of 1 ppma or less, the carbon absorption peak of the obtained differential absorption spectrum was deformed, and it was difficult to accurately obtain the substitutional carbon concentration.

Further, there is a problem in the conventional method of determining the difference coefficient related to the measurement accuracy.

That is, the FT-IR commercially available in the past
In the case of the method carbon concentration quantification device, the difference coefficient f is calculated by measuring the infrared absorbance (As (κ)) of the sample at a specific wave number κ.
And a simple ratio of the reference infrared absorbance (Ar (κ)) ([Equation 1]), or in a continuous wave number region, the infrared absorbance (A
s (κ)), and the infrared absorbance of the reference (Ar
This is performed by comparing the integrated values of (κ)) ([Equation 2]).
However, in the case of [Equation 2], the wave number κ is practically measured with a certain resolution, so that it is not a continuous value but a discontinuous value κ _n : n =
1, 2, 3, ...), the formula is as shown in [Equation 3].

[0018]

[Equation 1]

[Equation 2]

[Equation 3]

However, when the difference coefficient f is obtained by the method of [Equation 1], [Equation 2] or [Equation 3], and the difference absorbance spectrum is obtained by the difference coefficient f, the change over time of the apparatus itself, the sample The influence of the difference in the reference state (difference in thickness, resistivity, etc.) could not be minimized, and the influence remained. As a result, problems such as poor repeatability for each measurement and a large difference between models have occurred. However, in today's high-purity silicon single crystal wafers, due to stricter quality requirements associated with higher device integration and accompanying higher purification of device processes, the required concentration of carbon impurities is
It has reached the level of 0.05ppma or less,
The accuracy required for measurement is becoming severe.

The present invention has been made in view of the above points, and an object of the present invention is to provide a method and an automatic measuring apparatus capable of accurately measuring the concentration of substitutional carbon in a silicon single crystal.

[0021]

The measuring method according to claim 1 is the same manufacturing method as the sample as a reference in measuring the substitutional carbon concentration in a silicon single crystal sample by using the FT-IR method. A silicon single crystal that is manufactured by, and has substantially the same free carrier absorption and is substantially carbon-free.

That is, in the measuring method according to claim 1, the infrared absorption spectrum of the sample is measured, and the sample is manufactured by the same manufacturing method as that of the sample. An infrared absorption spectrum of a carbon reference is measured, and a differential absorption spectrum obtained from the above infrared absorption spectra by the above calculation formula ([Equation 1], [Equation 2] or [Equation 3]) is obtained. Then, the concentration of the substitutional carbon in the sample is quantified from the distance between the localized vibration absorption peak of the substitutional carbon and the baseline in this difference absorbance spectrum.

As a concrete example, in the conventional method, p-type CZ having a resistivity of 10 Ωcm and a carbon concentration of about 0.05 ppma is used.
Method Silicon single crystal as a sample, resistivity 2000Ωc
Using the p-type FZ method silicon single crystal of m as a reference,
The differential absorbance spectrum is obtained by using the calculation formula ([Equation 1], [Equation 2] or [Equation 3]). An example of the differential absorbance spectrum obtained by this conventional method is shown in FIG.

On the other hand, in claim 1 of the present invention, the resistivity of the same sample as in FIG.
Using a p-type CZ method silicon single crystal having substantially no carbon in cm as a reference, the differential absorption spectrum is obtained by using the above calculation formula ([Equation 1], [Equation 2] or [Equation 3]). An example of the differential absorbance spectrum obtained by the present invention is shown in FIG. According to FIG. 2, it is understood that the localized vibration absorption peak of the substitutional carbon Cs can be clearly observed.

According to the measuring method of claim 2, in obtaining the differential absorbance spectrum of claim 1, [Formula 1],
Without using the formula of [Equation 2] or [Equation 3], from the infrared absorption spectra of both the sample and the reference, in the wavenumber region before and after the localized vibration absorption peak of the substitutional carbon, the wavenumber of the difference absorbance spectrum and the red The differential absorption coefficient is calculated by the method of least squares so that the relational expression with the external absorbance is closest to the linear expression or the quadratic expression, and the differential absorption spectrum is obtained using the difference coefficient.

As described above, the difference absorbance spectrum is calculated by subtracting the difference obtained by multiplying the reference infrared absorbance spectrum by the difference coefficient f from the sample infrared absorbance spectrum. Therefore, the shape of the differential absorbance spectrum changes greatly depending on how the difference coefficient f is selected. FIG. 3 shows an example of the shape change of the difference absorbance spectrum when the difference coefficient f is changed. Here, the sample has a resistivity of 10 Ωcm and a carbon concentration of about 0.05 ppma.
The p-type CZ method silicon single crystal is used as a reference and a substantially carbon-free p-type CZ method silicon single crystal having a resistivity of 20 Ωcm is used. Then, the difference coefficient f is set to f = 0.97.
5, f = 0.985, f = 0.995, f = 1.00
5, f = 1.015, f = 1.025. In this case, the difference coefficient f most suitable for quantifying the carbon concentration is f = where the curves on the high wave number side and the low wave number side of the localized vibration absorption peak of the substitutional carbon Cs are the most flat.
This is the case of 0.955. However, in the case of a commercially available line measuring instrument for measuring a large amount of samples, since the difference coefficient f is calculated by the above calculation formula ([Equation 1], [Equation 2] or [Equation 3]), f = The optimum difference coefficient f such as 0.995 cannot be calculated. Nevertheless, when the substitutional carbon concentration exceeds 0.1 ppma, the quantified value was relatively stable due to the large localized vibration absorption peak, but in the case of the low carbon concentration sample of 0.1 ppma or less, a large quantified value was obtained. It causes an error. Therefore, the present inventor has found the method according to claim 2 as a method for calculating the optimum difference coefficient f = 0.995.

That is, conventionally, the difference coefficient f is given by [Equation 1],
The difference coefficient f is calculated by the calculation formula of [Formula 4], although the calculation is performed by the calculation formula of [Formula 2] or [Formula 3]. As a result, the differential absorption spectrum becomes almost flat in the wave number region before and after the localized vibration absorption peak of the substitutional carbon Cs. However, in the case of [Equation 4], since the wave number κ is practically measured at a certain resolution, it is not a continuous value, but a discontinuous value κ _n : n = 1, 2, 3, ...
・), So the formula becomes [Equation 5].

[0028]

[Equation 4]

[Equation 5]

To calculate the difference coefficient f using the formula of [Equation 5], the wavenumbers from κ = κ _l1 to κ = κ _h1 are set as the region on the low wavenumber side of the localized vibration absorption peak of the substitutional carbon Cs. Area
The wave number region from κ = κ _l2 to κ = κ _h2 is set as the region on the high wave number side, and in these two regions, the difference absorbance spectrum is closest to the linear equation of the first order with respect to the wave number κ ], The difference coefficient f is calculated. In particular,
550 to 595 cm ^-1 (that is, κ _l1
= 550, κ _h1 = 595), and 615 as a high wavenumber region
~ 660cm ^-1 (ie κ _l2 = 615, κ _h2 = 660)
Is used.

In FIG. 3, a reference whose conductivity type is the same as that of the sample and whose resistivity is almost the same is used, but when the resistivity of the sample becomes lower, there is a baseline in the differential absorption spectrum. It becomes a curve with curvature.

In such a case, it is not a method of approximating with a linear expression like [Equation 4] or [Equation 5], but
An appropriate difference coefficient f can be calculated by using a method of approximating with a quadratic expression as in [Equation 6]. However, in the case of [Equation 6], since the wave number κ is practically measured with a certain resolution,
Not continuous value but discontinuous value κ _n : n = 1, 2, 3, ...
・), So the formula becomes like [Equation 7].

[0032]

[Equation 6]

[Equation 7]

For comparison with FIG. 3, FIG. 4 shows the differential absorbance spectra obtained by the methods of [Equation 1] and [Equation 2] for the same sample and reference. In FIG. 4, the broken line is based on [Equation 1] and the solid line is based on [Equation 2]. It can be seen from FIG. 4 that the localized vibration absorption peak of the substitutional carbon Cs does not appear in either case.

The measuring apparatus according to claim 3 obtains a difference absorption spectrum of infrared absorption from both infrared absorption spectra of the sample and the reference obtained by using the FT-IR method, and from this difference absorption spectrum, silicon is obtained. The measuring device is configured to quantify the concentration of substitutional carbon in a single crystal. This measuring device is provided with a storage unit capable of recording and holding an infrared absorption spectrum, and this storage unit records and holds infrared absorption spectrum data of a plurality of substantially carbon-free reference infrared carriers having different free carrier absorptions. The infrared absorption spectrum data of the reference having the same free carrier absorption as that of the sample can be selected. Further, the substitutional carbon concentration is quantified by the method according to claim 1 or 2 from the infrared absorption spectrum data of the selected reference and the infrared absorption spectrum data of the sample. Further, in the present measuring apparatus, a differential absorption spectrum is obtained from both infrared absorption spectra of the CZ method silicon single crystal (sample) obtained by using the FT-IR method and the reference, and the substitutional carbon concentration is obtained from this differential absorption spectrum. A series of operations for quantifying is automated.

[0035]

According to the above means, as a reference,
Since a silicon single crystal which is manufactured by the same manufacturing method as the sample and has the same free carrier absorption and no carbon is used, the localized vibration absorption peak of the substitutional carbon Cs is extracted between the sample and the reference. Other than the localized vibration absorption peak of the substitutional carbon Cs can be made approximately the same.

This will be described with reference to FIG. 1 (using a FZ method silicon single crystal as a reference) and FIG. 2 (using a CZ method silicon single crystal as a reference). In FIG. Localized vibration absorption peak (shaded area)
Clearly appears, whereas in FIG. 1, it is understood that the localized vibration absorption peak does not appear. The cause is that in the method according to claim 1, the same p-type silicon single crystal as the sample is used as a reference, and the resistivity difference is F
Compared with the case of using the Z method silicon single crystal, there is not much difference, so that the free carrier absorption is about the same, and furthermore, since the reference is substantially carbon-free, localized vibration absorption of substitutional carbon Cs in the sample is achieved. The peak is emphasized. Thus, as a reference, C with substantially the same free carrier absorption and substantially carbon-free
It can be seen that a clear peak can be obtained by using the Z method silicon single crystal.

According to the measuring method of claim 2,
Even if the carbon concentration is as low as 0.1 ppma or less, it is possible to reduce the influence of the difference in the state (thickness or resistivity) between the sample and the reference.

That is, in the result (FIG. 4) of calculating the differential absorbance spectrum by the commercially available FT-IR method carbon concentration determination quantitative software by the method of [Equation 1] or [Equation 2], the method of [Equation 1] is shown. The influence of the silicon absorption peak remains in both (dashed line data) and the method (solid line data) according to [Equation 2],
The localized vibration absorption peak of the substitutional carbon Cs is buried in it. On the other hand, in the method of calculating the difference coefficient f found by the present inventors ([Equation 5], when the difference absorbance spectrum is obtained using the same sample and reference, the localized vibration absorption of the substitutional carbon Cs is It can be seen that the peak can be accurately extracted, and thus the carbon concentration can be accurately determined (FIG. 5).

According to the measuring device of the third aspect,
Since it is possible to select and calculate the optimum reference infrared absorption spectrum from the infrared absorption spectra of multiple carbon-free silicon single crystal references with different free carrier absorption, even with commonly used line measuring devices, A highly accurate measurement method can be applied.

[0040]

EXAMPLES Examples of the method and apparatus for measuring the substitutional carbon concentration in a silicon single crystal according to the present invention will be described below.

The measuring device used in this embodiment is FT
The infrared absorption spectrum is obtained from the infrared absorption spectrum of both the sample and the reference obtained by using the IR method, and the substitutional carbon concentration is quantified from the difference absorption spectrum. It is equipped with a storage unit capable of recording and holding spectra.
Infrared absorption spectrum data of various references are recorded and held.

When a sample is a silicon single crystal wafer by the CZ method, which is a mainstream method for producing a silicon single crystal, a CZ method silicon single crystal with extremely few carbon impurities is used as a reference. In the CZ method silicon single crystal, raw material polysilicon is melted by a carbon heater in a quartz crucible, and a seed crystal is immersed in the silicon melt,
Since it is manufactured by pulling up the seed crystal, the raw material polysilicon and carbon derived from the carbon heater are taken in. The carbon uptake in this case gradually increases toward the tail of the silicon rod due to segregation. Therefore, if a silicon single crystal obtained by slicing a portion close to a seed crystal of a silicon single crystal rod pulled up using carefully selected raw material polysilicon having a minute carbon concentration is used, CZ that is substantially carbon-free is obtained. A silicon single crystal reference is obtained. In the storage unit,
The infrared absorption spectrum data of the carbon-free CZ method silicon single crystals thus obtained, which have different free carrier absorptions, are recorded and held in advance.

After such preparation, infrared absorption spectra of various samples are obtained by the same method, reference data having similar free carrier absorption to that of the sample is selected from the data in the storage section, and the obtained data A differential absorption spectrum is obtained from the infrared absorption spectrum data of the sample.

In obtaining this difference absorbance spectrum, from the above both data, the relational expression between the wave number and the absorbance in the difference absorbance spectrum in the wave number region before and after the localized vibration absorption peak of the substitutional carbon Cs is a linear expression or 2 The difference coefficient is calculated by the method of least squares so as to be closest to the following equation, and the difference absorbance spectrum is obtained from the difference coefficient.

Specifically, as shown in FIG. 6, the localized vibration absorption peak of the substitutional carbon Cs appears at 605 cm ⁻¹ , so that the wave number range is 550 to 595 cm ⁻¹ as a region lower than the wave number region of the Cs peak. 615 as the high wavenumber region
Set to ~ 660 cm ^-1 . For example, in [Equation 4], κ _l1 = 550 cm ⁻¹ , κ _l1 = 595 cm ⁻¹ , κ _l2 = 61
5cm ^-1, and κ _h2 = 660cm ^-1. Next, as a sample, the resistivity is 10 Ωcm and the carbon concentration is about 0.05 ppma.
The p-type CZ method silicon single crystal is used as a reference and a carbon-free p-type CZ method silicon single crystal having a resistivity of 20 Ωcm is used, and infrared absorption spectra of both silicon single crystals are obtained. The infrared absorbance spectra of this sample and reference are shown in FIG.

From the above data, when the difference coefficient f is calculated using [Equation 5], f = 0.9764 is lost, and the difference absorbance spectrum is calculated using this difference coefficient. The differential absorbance spectrum thus obtained is shown in FIG. Figure 8
From 595 cm ⁻¹ and 615 cm ⁻¹ as baselines, the carbon concentration was quantified based on ASTM designation: F123-81, [Cs] = 0.09 ppma.

Although the measuring method of the embodiment of the present invention has been described above, the present invention is not limited to the embodiment and various modifications can be made without departing from the scope of the invention.

For example, in the above embodiment, the carbon concentration of the p-type CZ method silicon single crystal was described, but it is needless to say that the carbon concentration of the n-type CZ method silicon single crystal can also be measured. However, in that case, it is necessary to use, as a reference, a CZ method silicon single crystal that has almost the same free carrier absorption as the sample. Further, not only the CZ method silicon single crystal but also the FZ method silicon single crystal can be applied. However, in that case, a substantially carbon-free FZ method silicon single crystal may be used as a reference.

[0049]

According to the present invention, in measuring the substitutional carbon concentration in a silicon single crystal by using the FT-IR method, an infrared absorption spectrum obtained from a silicon single crystal sample and the above-mentioned sample Free carrier absorption produced by the same production method is similar, and a difference coefficient is calculated from an infrared absorption spectrum obtained from a substantially carbon-free silicon single crystal reference, and the difference coefficient is used to calculate the difference. Obtaining the difference absorbance spectrum from both infrared absorbance spectra, from the distance between the localized vibration absorption peak of the substitutional carbon in this difference absorbance spectrum and the baseline, so that the concentration of the substitutional carbon in the sample was quantified, Compared with the conventional method, the localized vibration absorption peak of substitutional carbon can be extracted more accurately, and the carbon concentration can be obtained more accurately. Further, it is possible to reduce the repeatability in the measurement and thus the difference between the devices. Specifically, according to a test conducted using several devices owned by the present inventors,
The repeatability could be tripled and the difference between the devices could be reduced to 1/3.

[Brief description of drawings]

FIG. 1 is an FZ of a conventional CZ silicon single crystal sample.
It is a figure showing the difference light absorption spectrum by the method silicon single crystal reference.

FIG. 2 is a diagram showing a differential absorption spectrum of a CZ method silicon single crystal sample of the method of the present invention by a CZ method silicon single crystal reference.

FIG. 3 is a diagram showing a change in shape of a difference absorbance spectrum when a difference coefficient is changed.

FIG. 4 is a diagram showing a differential absorbance spectrum calculated by commercially available FT-IR software.

FIG. 5 is a diagram showing a differential absorbance spectrum calculated by the method of the present invention.

FIG. 6 is a diagram illustrating an example of quantitative determination of carbon concentration from a differential absorption spectrum by the method of the present invention.

FIG. 7 is a diagram showing infrared absorption spectra of a sample and a reference in an example of the method of the present invention.

FIG. 8 is a diagram showing an example of calculating a differential absorbance spectrum in the example of the present invention.

FIG. 9 is a diagram showing an FT-IR optical system.

FIG. 10 is a diagram showing an infrared absorption spectrum of a CZ method silicon single crystal.

FIG. 11 is a diagram showing an infrared absorption spectrum of an FZ method silicon single crystal.

FIG. 12 is a diagram showing a differential absorption spectrum obtained from a conventional CZ method silicon single crystal sample and an FZ method silicon single crystal reference.

FIG. 13 is a diagram showing an infrared absorption spectrum of CZ method silicon single crystal samples having different resistivities in a conventional method.

[Explanation of symbols]

 4 Michelson interferometer 9 samples (or reference)

Claims (3)

[Claims] 1. Fourier transform infrared spectroscopy (hereinafter referred to as F
In measuring the substitutional carbon concentration in the silicon single crystal by using the T-IR method), an infrared absorption spectrum obtained from the silicon single crystal that is the object to be measured (hereinafter referred to as a sample), Substantially carbon-free silicon single crystal produced by the same production method as that of the sample and having substantially the same free carrier absorption (hereinafter referred to as a reference)
The difference coefficient is calculated from the infrared absorption spectrum obtained from, the difference absorption spectrum is obtained from the both infrared absorption spectra using this difference coefficient, and the localized vibration absorption peak of the substitutional carbon in the difference absorption spectrum is obtained. The method for measuring the concentration of substitutional carbon in a silicon single crystal, characterized in that the concentration of substitutional carbon in the sample is quantified from the distance from the baseline. 2. In obtaining the difference absorbance spectrum, the relational expression between the wave number and the infrared absorbance is 1 in the wave number region before and after the localized vibration absorption peak of the substitutional carbon from both the infrared absorbance spectra of the sample and the reference. 2. The silicon single crystal according to claim 1, wherein a difference coefficient is calculated by a least square method so as to be closest to the following equation or a quadratic equation, and the difference absorbance spectrum is obtained from the difference coefficient. Method for measuring substitutional carbon concentration. 3. A differential absorption spectrum of infrared absorption is obtained from both infrared absorption spectra of a sample and a reference obtained by the FT-IR method, and the substitutional carbon in the silicon single crystal is obtained from this differential absorption spectrum. In a measuring device configured to quantify the concentration, a storage unit capable of recording and holding an infrared absorption spectrum is provided, and in this storage unit, a plurality of substantially carbon-free reference reds having different free carrier absorptions are stored. The infrared absorbance spectrum data is recorded and retained, and reference infrared absorbance spectrum data having a similar free carrier absorption to that of the sample is selected from the data, and the data and the infrared absorbance spectrum data of the sample are selected. Alternatively, the method according to claim 2 is configured to quantify the substitutional carbon concentration. Characteristic automatic measuring device for substitutional carbon concentration in silicon single crystal.