JP2014092411A - EVALUATION METHOD OF SiC SINGLE CRYSTAL AND METHOD FOR MANUFACTURING SiC SINGLE CRYSTAL USING THE SAME - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an evaluation method of a SiC single crystal, capable of non-destructively estimating nitrogen concentration of the SiC single crystal including nitrogen at a concentration of 5×10atom/cmor more in the crystal, and a method for manufacturing the SiC single crystal.SOLUTION: The evaluation method of a SiC single crystal comprises: contacting an optical medium having a refractive index higher than that of the SiC single crystal to a surface of the SiC single crystal; irradiating an interface between the SiC single crystal and the optical medium with an infrared ray; obtaining intensity of an absorption peak having a peak value of an absorption wave number varied in a range of 966-971 cmfrom an obtained infrared spectrum; and estimating a nitrogen concentration in the SiC single crystal on the basis of the obtained absorption peak intensity. A method for manufacturing the SiC single crystal includes the evaluation method.

Description

  The present invention relates to a method for evaluating a SiC single crystal and a method for producing a SiC single crystal to which the SiC single crystal is applied, and more particularly, an evaluation of a SiC single crystal capable of nondestructively evaluating the concentration of nitrogen as an impurity in the SiC single crystal. The present invention relates to a method and a method for producing a SiC single crystal to which the method is applied.

  SiC single crystal is very stable thermally and chemically, excellent in mechanical strength, resistant to radiation, and excellent in breakdown voltage and high thermal conductivity compared to Si (silicon) single crystal. It has physical properties and can easily control p-type and n-conductivity type electrons by adding impurities, and has a wide forbidden band width (about 3.3 eV for 4H-type SiC single crystal, about 3.3 eV for 6H-type SiC single crystal). 0 eV). For this reason, it is possible to realize high temperature, high frequency, withstand voltage and environmental resistance that cannot be realized with existing semiconductor materials such as Si single crystal and GaAs (gallium arsenide) single crystal. It is growing.

This SiC single crystal often contains nitrogen as a donor impurity, and since the nitrogen concentration of the SiC single crystal affects the characteristics of the device, an evaluation method that can evaluate the nitrogen concentration in the SiC single crystal Is required.
Conventionally, FTIR (Fourier Transform Infrared Spectroscopy) is known as a method for measuring impurities at the interface of a SiC single crystal. However, the presence or absence of impurities can be analyzed, but it is a qualitative analysis. The concentration of nitrogen as an impurity cannot be evaluated.
In addition, the measurement of the amount of nitrogen in the SiC single crystal is performed by highly sensitive SIMS (Secondary Ion Mass Spectrometry) or XPS (X-ray Photoelectron Spectroscopy, X-ray photoelectron spectroscopy). In the former, the sample used for evaluation cannot be used as a substrate, and the latter is limited to the measurement of the crystal surface.

ICP-MS (Inductively Coupled Plasma Mass Spectrometry) and GC-MS (Gas Chromatograph-Mass Spectrometry) are used to evaluate SiC single crystals containing impurities at high concentrations. However, all of them are not suitable for measuring nitrogen, which is a light element, because they are measured by melting a sample.
On the other hand, a SiC single crystal for semiconductor materials, particularly as an SiC single crystal of an epitaxial layer, is about 5 × 10 ¹⁵ atoms / cm ³ , and an SiC single crystal as a substrate for forming this epitaxial film is nitrogen which is an impurity of about 10 ¹⁹ atoms / cm ^3. There is a need for crystals having a concentration. For this reason, the evaluation of SiC single crystal containing nitrogen at a high concentration of about 5 × 10 ¹⁵ atoms / cm ³ or more, particularly 10 ^{18 to} ax10 ¹⁹ atoms / cm ³ (a = 1 to 5) in a SiC single crystal substrate. There is a need for an evaluation method that can be performed non-destructively.
The necessity for nondestructively evaluating impurities in the single crystal is the same for other semiconductor materials such as silicon, and various studies have been made.
In the impurity analysis and concentration analysis method using the infrared absorption method, since a large amount of light absorption can be obtained, the transmission method is generally used, and standardized by SEMI, JEITA, and the like. For example, Japanese Patent Laid-Open No. 2002-350331 describes a method for measuring a silicon single crystal by a transmission method. On the other hand, the method using reflection is at the research stage and is not standardized.

For example, in Patent Document 1, a prism having a refractive index larger than that of the substrate is brought into contact with the surface of the substrate, and light is totally reflected on the surface of the prism that is in contact with the substrate. A method for evaluating a substrate to be evaluated is described. As a specific example, a spectrum is shown in which a silicon substrate containing oxygen, carbon, and nitrogen is irradiated with infrared light using a germanium prism and measured with an infrared light wave number of 900 to 1300 cm ⁻¹ .

  Patent Document 2 discloses that a plurality of semiconductor silicon crystals having different oxygen concentrations are irradiated with light, and a dielectric function real part having an arbitrary wave number at each oxygen concentration based on an amplitude ratio and a phase difference of the reflected light with respect to the irradiated light. Describes a method for evaluating the oxygen concentration of a semiconductor silicon crystal, in which the correlation between the oxygen concentration at the wave number and the real part of the dielectric function is obtained in advance. As a specific example, an example in which the silicon crystal is directly irradiated with light and the reflected light is measured to determine the oxygen concentration is shown.

  Patent Document 3 discloses an internal reflection element including a contact area between a light source and a sample, and light toward the contact area so that an incident angle at the front surface of the element is not less than a critical angle of the element and is totally reflected. , A spectroscopic device including a detector that collects reflected light from a contact area, and forms an image of the reflected light, and a method for obtaining a spectral absorption image are described. And the spectrum measurement value is shown about the epoxy resin fiber as an example which can use germanium, a silicon | silicone, zinc selenide, or a diamond as an internal reflection element.

  Furthermore, in Patent Document 4, ultraviolet light is irradiated on the surface of a nitrogen-doped 4H type silicon carbide bulk single crystal substrate, and photoluminescence light obtained by emitting light from the substrate is applied to the 4H type silicon carbide bulk single crystal substrate. A defect inspection method for a silicon carbide bulk single crystal substrate for discriminating included 6H type stacking faults is described.

JP 7-297247 A Japanese Patent Laid-Open No. 11-14543 Japanese Patent Laid-Open No. 11-132941 JP 2011-220744 A

However, it is impossible to quantitatively evaluate the nitrogen concentration, which is an impurity in the SiC single crystal, nondestructively by the techniques described in these known documents.
Accordingly, an object of the present invention is to provide a method for evaluating a SiC single crystal capable of nondestructively evaluating the nitrogen concentration of a SiC single crystal containing nitrogen at a concentration of 5 × 10 ¹⁵ atoms / cm ³ or more in the crystal. .
Another object of the present invention is to provide a SiC single crystal for nondestructively evaluating the nitrogen concentration of a SiC single crystal containing nitrogen at a concentration of 5 × 10 ¹⁵ atoms / cm ³ or more after the SiC single crystal is grown. It is to provide a manufacturing method.

The inventors of the present invention have completed the present invention as a result of intensive studies to achieve the above object.
The present invention is a method for evaluating a SiC single crystal for evaluating the nitrogen concentration in a crystal,
(1) An optical medium having a refractive index higher than that of the SiC single crystal is brought into contact with the surface of the SiC single crystal,
(2) irradiating the interface between the SiC single crystal and the optical medium with infrared rays;
(3) Obtain the absorption peak intensity at which the peak value of the absorption wave number changes in the range of 966 to 971 cm ⁻¹ from the obtained infrared spectrum,
(4) Evaluating the nitrogen concentration in the SiC single crystal based on the obtained absorption peak intensity,
It relates to said method.

The present invention is also a method for producing a SiC single crystal,
A step of growing a SiC single crystal, and a step of evaluating the nitrogen concentration in the obtained SiC single crystal by the evaluation method,
The method.
In the present invention, the above-mentioned absorption peak intensity is a range of 966 to 971 cm ⁻¹ in an infrared absorption spectrum by Fourier transform infrared (FTIR) measurement measured by a measurement method described in detail in the column of Examples described later. It is a numerical value based on the absorption peak signal.
In the present invention, the higher refractive index than the SiC single crystal means that the refractive index is at least in the range of 966 to 971 cm ⁻¹ .
Moreover, nondestructive evaluation in this specification means evaluating without destroying the SiC single crystal whose nitrogen concentration is unknown.

According to the present invention, it is possible to nondestructively evaluate the nitrogen concentration of a SiC single crystal containing nitrogen in the crystal at a concentration of 5 × 10 ¹⁵ atoms / cm ³ or more, preferably 2 × 10 ¹⁶ atoms / cm ³ or more.
Further, according to the present invention, the nitrogen concentration of the SiC single crystal nondestructively evaluated by nitrogen ^5x10 15 atom / cm ³ or more in the crystal, SiC containing preferably at a concentration of ^2x10 16 atom / cm ³ or more A single crystal can be easily obtained.

FIG. 1 shows the absorption peak intensities of Fourier transform infrared absorption (FTIR) measurement data in the embodiment of the present invention for 4H-SiC single crystals whose nitrogen concentration was previously measured and 4H-SiC single crystals whose nitrogen concentration was unknown. It is a corrected infrared absorption spectrum. FIG. 2 shows the intensity of the absorption peak of the Fourier transform infrared absorption (FTIR) measurement data in the embodiment of the present invention for a 4H—SiC single crystal whose nitrogen concentration was previously measured and a 4H—SiC single crystal whose nitrogen concentration was unknown. It is a graph which shows the correlation with the absorption intensity calculated | required as the height of the absorption peak of the corrected infrared absorption spectrum, and the nitrogen concentration in a 4H-SiC single crystal. FIG. 3 shows a fixed value obtained according to a known document [Journal of The Electrochemical Society 147 (6) 2324-2327 (2000)] for a 4H—SiC single crystal whose nitrogen concentration was previously measured by an evaluation method outside the scope of the present invention. It is a graph which shows the correlation with the absorption peak intensity | strength by the fixed wave number equivalent to 980cm < ^-1 > which is a signal, and the nitrogen concentration in 4H-SiC single crystal. FIG. 4 is an infrared absorption spectrum in which the absorption peak intensities measured for three types of 4H—SiC single crystals having different nitrogen concentrations are not corrected. FIG. 5 is an infrared absorption spectrum in which the absorption peak intensity measured by the measurement method of the embodiment of the present invention and the conventional method is not corrected for a SiC single crystal containing nitrogen as an impurity. FIG. 6 is a graph showing the wave number dependence of the refractive index when a single crystal of SiC is irradiated with light in a measurement method outside the scope of the present invention. FIG. 7 is a graph showing the wave number dependence of the refractive index when an SiC single crystal is irradiated with light in the measurement method of the present invention. FIG. 8 is a schematic diagram showing a state in which infrared rays are applied to the interface between the SiC single crystal and the optical medium in the example.

In particular, in the present invention, the following embodiments can be mentioned.
1) The evaluation method described above, wherein the absorption peak intensity is obtained by (1) to (3) for a plurality of SiC single crystals having known nitrogen concentrations and different concentrations, and the correlation between the nitrogen concentration and the absorption peak intensity is obtained in advance. .
2) The evaluation method, wherein the infrared spectrum is a spectrum of reflected light obtained by totally reflecting infrared rays at the interface.
3) The evaluation method described above, wherein the optical medium is selected from As ₂ Se ₃ , Si and Ge.
4) The above evaluation method, wherein the SiC single crystal is bulk.
5) The said evaluation method whose said SiC single crystal is 4H type.
6) The manufacturing method described above, wherein the SiC single crystal is grown by a solution method.

In the method for evaluating a SiC single crystal according to an embodiment of the present invention,
(1) An optical medium having a refractive index higher than that of the SiC single crystal is brought into contact with the surface of the SiC single crystal,
(2) irradiating the interface between the SiC single crystal and the optical medium with infrared rays;
(3) Obtain the absorption peak intensity at which the peak value of the absorption wave number changes in the range of 966 to 971 cm ⁻¹ from the obtained infrared spectrum,
(4) Evaluating the nitrogen concentration in the SiC single crystal based on the obtained absorption peak intensity,
Thus, the nitrogen concentration of the SiC single crystal containing nitrogen in the crystal at a concentration of 5 × 10 ¹⁵ atoms / cm ³ or more, preferably 2 × 10 ¹⁶ atoms / cm ³ or more is quantitatively evaluated nondestructively. can do.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
As shown in FIG. 1, the infrared absorption spectrum in the embodiment of the present invention is obtained by irradiating infrared rays by the evaluation method of the embodiment of the present invention on a plurality of 4H—SiC single crystals having different nitrogen concentrations measured in advance. Infrared absorption spectrum in which the Fourier transform infrared absorption (FTIR) measurement is performed and the obtained absorption peak intensity is corrected, the vertical axis is the normalized absorption intensity and the horizontal axis is the logarithmic wave number, 966 It has a peak value of absorption wave number in a range of ˜971 cm ⁻¹ .
Then, as shown in FIG. 2, the absorption intensity of the infrared absorption spectrum of a plurality of 4H—SiC single crystals having different nitrogen concentrations measured in advance is plotted against the nitrogen concentration in the 4H—SiC single crystal. By doing so, one curve can be created.
Then, using this curve as a calibration curve, 4H-SiC single crystal with unknown nitrogen concentration was subjected to Fourier transform infrared absorption (FTIR) measurement by the evaluation method of the embodiment of the present invention, and from the obtained absorption peak intensity, The nitrogen concentration in the 4H—SiC single crystal can be determined.

In an embodiment of the present invention, (1) an optical medium having a refractive index higher than that of the SiC single crystal is brought into contact with the surface of the SiC single crystal, and (2) an interface between the SiC single crystal and the optical medium. Irradiation with infrared rays (3) By obtaining the absorption peak intensity at which the peak value of the absorption wave number changes in the range of 966 to 971 cm ⁻¹ from the obtained infrared spectrum, as shown in FIG. 2, in the 4H—SiC single crystal It is possible to obtain a calibration curve or correlation equation that is a correlation in which the nitrogen concentration uniquely corresponds to each value of the absorption peak intensity. Based on this correlation, the nitrogen concentration of the SiC single crystal is quantitatively evaluated nondestructively using the absorption peak intensities obtained by the above (1) to (3) for the SiC single crystal whose nitrogen concentration is unknown. It can be done.

On the other hand, the infrared absorption spectra of a plurality of 4H-SiC single crystals having different nitrogen concentrations measured in advance by the evaluation methods outside the scope of the present invention, for example, (1) and (2) above. When the absorption intensity (peak intensity) at a fixed wave number corresponding to 980 cm ⁻¹ described in a known document [Journal of The Electrochemical Society 147 (6) 2324-2327 (2000)] is plotted against the nitrogen concentration, As shown in FIG. 3, one curve is created. However, in the obtained curve, two nitrogen concentrations correspond to each value of the absorption peak intensity in the 4H—SiC single crystal in a wide nitrogen concentration range. That is, according to the evaluation method outside the scope of the present invention, the nitrogen concentration of the SiC single crystal cannot be uniquely determined using the absorption peak intensity.

The infrared absorption spectrum in the embodiment of the present invention obtained by satisfying the above (1) to (3) is a Fourier transform infrared absorption (FTIR) by irradiating the 4H-SiC single crystal with infrared rays as described above. ) This is an infrared absorption spectrum in which the absorption peak intensity obtained by measurement is peak-separated by a Vogt function and the intensity is corrected, as shown in the Examples section below.
The infrared absorption spectrum before peak separation and intensity correction giving the infrared absorption spectrum shows data of absorption intensity obtained by Fourier transform infrared absorption (FTIR) measurement. As shown in FIG. It has a minute peak in the range of 971 cm ⁻¹ . 4A shows a nitrogen concentration measured by SIMS of 1.5 × 10 ¹⁹ atoms / cm ³ , and FIG. 4B shows a nitrogen concentration measured by SIMS of 7.0 × 10 ¹⁸ atoms / cm ³ , FIG. ) Is an infrared absorption spectrum of each 4H-SiC single crystal having a nitrogen concentration measured by SIMS of 7.6 × 10 ¹⁷ atoms / cm ³ before the peak separation and before intensity correction.

The above requirement (1) Even if the 4H-SiC single crystal is irradiated with infrared rays without bringing the optical medium having a refractive index higher than that of the SiC single crystal into contact with the surface of the SiC single crystal, the transmission method uses FIG. As shown in FIG. 5, in the reflection method, as shown in FIG. 5B, anomalous dispersion in which distortion occurs in the base line occurs, and the infrared absorption spectrum of the target 4H—SiC single crystal cannot be obtained.
Moreover, the SiC single crystal has a large light absorption in the infrared light region. Therefore, for a thick substrate having a bulk single crystal, a method using reflection can be suitably employed because it is affected by light absorption by the SiC single crystal.
According to the evaluation method of the embodiment of the present invention, the above requirement (1) an optical medium having a refractive index higher than that of the SiC single crystal is brought into contact with the surface of the SiC single crystal, and (2) the 4H-SiC single crystal and the optical medium In the reflection method, as shown in FIG. 5C, the baseline distortion is eliminated and the 4H—SiC single crystal red showing a peak based on nitrogen, which is the target impurity, is irradiated in the reflection method. An external absorption spectrum can be obtained.

In the evaluation method according to the embodiment of the present invention, the 4H-SiC single crystal exhibiting a peak based on nitrogen, which is the target impurity, by eliminating the distortion of the baseline by satisfying the above requirements (1) to (2) Although the theoretical elucidation that can obtain the infrared absorption spectrum is not sufficiently made, it can be considered as follows. For example, when an infrared ray is irradiated with the incident medium as the atmosphere without contacting an optical medium having a higher refractive index than that of the SiC single crystal, the refractive index of the 4H—SiC single crystal suddenly changes with respect to the refractive index of air in the vicinity of 1000 cm ⁻¹ ( n = 2.0 → 0.05), and the magnitude relationship of the refractive index is reversed. This causes baseline distortion (anomalous dispersion) in the infrared absorption spectrum, as shown in FIG. On the other hand, when an optical medium having a higher refractive index than that of the SiC single crystal is brought into contact, it is considered that this sudden change in the refractive index does not occur and the baseline distortion is eliminated as shown in FIG.

The high optical medium refractive index than the SiC single crystal, having a refractive index higher than the refractive index of the SiC single crystal at 1000 cm ^-1 vicinity, at least 966~971cm ^-1 (2.0~0.05) As ₂ Se ₃ , (refractive index = 3.15), Si (refractive index = 4.40), and Ge (4.00).
In the evaluation method of the embodiment of the present invention, when irradiating infrared rays to the interface between the SiC single crystal containing nitrogen as an impurity and the optical medium, the intensity of the absorption peak is preferably achieved by totally reflecting the infrared rays at the interface. Can ask for. In the infrared irradiation described above, the incident angle varies depending on the type of the high refractive index medium, but can usually be 45 ° to 85 °.

In the embodiment of the present invention, for the Fourier transform infrared measurement data obtained, for example, in the observation range of 920 to 1000 cm ⁻¹ as described above, the absorption peak intensity at 966 to 971 cm ⁻¹ is measured by infrared absorption measurement. The peak can be separated by a Vogt function generally used in the above and the intensity can be corrected.
As the absorption peak intensity, the peak value of the peak signal (peak height) or the integrated intensity of the peak signal, preferably the peak value of the peak signal (peak height) can be used.

Examples of the SiC single crystal in the present invention include bulk, homoepitaxial, and SiC epitaxial thin films on a SiC substrate.
The evaluation method of the present invention can be applied to any type of SiC single crystal, but is preferably applicable to a 4H-SiC single crystal that is 4H type.
The SiC single crystal contains nitrogen (N) which is a donor element when the SiC single crystal is grown, and is grown by any growth method for growing the SiC single crystal, for example, a solution method or a vapor phase method. It can be obtained by a method of growing a SiC single crystal.
As the seed crystal in the SiC single crystal growth method, it is preferable to use an SiC bulk single crystal having the same crystal structure as the crystal to be grown. For example, in the solution method, a 4H—SiC single crystal is used.
In the solution method described above, a crucible for accommodating a Si-containing melt provided in a growth furnace via a heat insulating material, and provided around the growth furnace for heating the melt to maintain a constant temperature. A SiC single crystal can be grown using a SiC single crystal growth apparatus based on a solution method in which a high frequency coil and a support rod capable of moving up and down are provided and a seed crystal is placed at the tip of the support rod.

As the Si-containing melt, a Si melt is used, carbon (C) is supplied from a crucible, and N ₂ gas is supplied into the furnace to obtain an N-added SiC single crystal.
In the above growth method, the concentration of nitrogen as an impurity in the SiC single crystal can be changed by changing the amount of nitrogen in the melt within a range of 0.01 to 0.5 atm% with respect to SiC. it can.

The temperature is controlled by high-frequency induction heating, for example, by observing the temperature of the melt surface with a radiation thermometer and / or a thermocouple installed inside a supporting part (for example, a carbon rod), for example, W-Re (tungsten / lenium). ) It can be performed by the temperature controller based on the measured temperature obtained by measuring the temperature using a thermocouple.
In the method of growing a SiC single crystal using the SiC single crystal production apparatus by the solution method, a growth method known per se in the solution method, for example, the shape of the graphite crucible, the heating method, the heating time, the atmosphere, the temperature rising rate The crystal can be grown by applying a cooling rate.
For example, the heating time by high-frequency induction heating (approximately the time from the preparation of raw materials to the SiC saturation concentration) is about 30 minutes to 200 hours (for example, about 3 to 10 hours), depending on the size of the crucible, The atmosphere includes a rare gas, for example, an inert gas such as He, Ne, Ar, or a part of them replaced with N ₂ . Further, a part of the inert gas may be replaced with methane gas.
The growth temperature in the crystal growth is preferably performed in a melt heated to a temperature of 1800 to 2100 ° C.

In the sublimation method, for example, a seed crystal is attached to the inner surface of a graphite crucible lid filled with SiC powder as a sublimation raw material in a graphite crucible, placed inside a quartz tube, Ar gas and N ₂ Gas is allowed to flow inside the double quartz tube so that the SiC powder has a temperature of, for example, 2300 ° C. or higher, for example, 2300 ° C., and the SiC single crystal substrate has a temperature of 2200 ° C. or higher, for example, 2200 ° C. Thus, a SiC single crystal can be grown on the seed crystal. The raw material may further contain Ga, In, Ge, or Te.
As for the SiC single crystal with N added, as described above, the 4H-SiC single crystal grown by the solution growth method or the sublimation method is CVD (chemical vapor deposition), and the Si raw material is monosilane or monomethyl. By using propane, methane, or the like as the silane and C raw materials, and introducing these raw materials into a reaction furnace heated to 1400 to 2000 ° C. with a carrier gas such as H _2, N _{2 serving as the} N raw material is introduced together with soot. A SiC single crystal film to which N is added can be obtained.

The production method of the present invention is a method for producing a SiC single crystal, comprising the steps of growing the SiC single crystal and evaluating the nitrogen concentration in the obtained SiC single crystal by the evaluation method.
By the manufacturing method, the nitrogen concentration of the SiC single crystal is evaluated nondestructively, and nitrogen is contained in the crystal at 5 × 10 ¹⁵ atoms / cm ³ or more, preferably 2 × 10 ¹⁶ atoms / cm ³ or more, particularly 10 ^{18 to} ax10 ^19. An SiC single crystal containing a high concentration of atom / cm ³ (a = 1 to 5) can be easily obtained.

Examples of the present invention will be described below.
The measurement methods shown below are examples, and measurement methods considered equivalent to those skilled in the art can be used as well.
In each of the following examples, the infrared absorption spectrum of the SiC single crystal is obtained by bringing an optical medium having a high refractive index into contact with the SiC single crystal and performing the irradiation method shown in FIG. The interface was irradiated with infrared rays, and Fourier transform infrared (FTIR) measurement was performed.
Measuring device: Fourier transform infrared spectrophotometer Bio-Rad FTS 5 as measuring device
75c
Optical medium: Ge (germanium)
Measurement method: Total reflection method Irradiation condition: Incident angle 85 °
Measurement conditions: resolution 4 cm ⁻¹ , integration count 128 times, gain 1, aperture: open,
Measurement temperature: room temperature, measurement wavenumber region: 600-1200 cm ⁻¹

Moreover, in each of the following examples, the intensity of the absorption peak for each SiC single crystal was acquired between 600 and 1200 cm ⁻¹ as described above. For Fourier transform infrared measurement data obtained in the observation range of 920 to 1000 cm ⁻¹ , the intensity of the absorption peak signal in the range of 966 to 971 cm ⁻¹ is the Vogt generally used for infrared absorption measurement. The intensity was corrected by the function and obtained from the peak value of the peak signal.

Example 1
1. Growth of 4H-SiC single crystal containing nitrogen as an impurity In 4H-SiC single crystal growth using a solution growth method, Si as a raw material is 60 atm%, Cr is 40 atm%, and N is supplied to SiC (total amount is supplied as nitrogen gas) 0.02. ˜0.2 atm% is put into a graphite crucible, and 4H—SiC single crystal is immersed as a seed crystal in a melt heated to a growth temperature of 2010 ° C. for 1 to 200 hours to grow the crystal for about 10 hours. It was.
The obtained SiC single crystal had the following N concentration.
N concentration 7.0 × 10 ^{17 to} 1.5 × 10 ¹⁹ atoms / cm ⁻³
Further, in the growth method of 4H—SiC single crystal thin film using CVD, monosilane 10 ccm (cm ³ / min.), Propane 5 ccm, N ₂ gas 20 to 250 ccm, and carrier gas are used in a hot wall type CVD apparatus. and _{H 2} flow 25Lm as, by heating for about one hour at a growth temperature of 1500 ° C., the thickness 10μm of the single-crystal thin film of 4H-SiC in the foregoing solution process growth 4H-SiC substrate and sublimation growth 4H-SiC substrate Formed. The N concentration was 2.0 × 10 ^{16 to} 3.0 × 10 ¹⁷ atoms / cm ⁻³ .

2.4 Evaluation of Single Crystal of H-SiC The nitrogen concentration was 1.5x10 ¹⁹ atom / cm ³ and 7.0x10 ¹⁸ atom / cm ³ , respectively, which were grown by the above method and evaluated by SIMS in advance. , 7.6 × 10 ¹⁷ atoms / cm ³ and 2.0 × 10 ¹⁶ atoms / cm ³ of 4 types of 4H—SiC single crystals were irradiated with infrared rays under the above conditions to be totally reflected to obtain infrared absorption spectra. .
The obtained infrared absorption spectrum is shown in FIG.
A calibration curve is created by correlating the relationship between the absorption peak intensity and the nitrogen concentration of each SiC single crystal with the absorption intensity on the vertical axis and the nitrogen concentration on the horizontal axis in logarithmic form, and is shown in FIG.

On the other hand, 4H-SiC single crystal with unknown nitrogen concentration was irradiated with infrared rays under the same conditions as described above and totally reflected to obtain an infrared absorption spectrum.
The obtained infrared absorption spectrum is shown as point a in FIG.
The intensity of the absorption peak of this 4H—SiC single crystal was 0.0527.
From the calibration curve in FIG. 2, the nitrogen concentration was estimated to be 7 × 10 ¹⁸ atoms / cm ³ .

Comparative Example 1
SIMS to evaluate in advance the nitrogen concentration in the nitrogen concentration respectively ^1.5x10 19 atom ^/ cm ³ to, 7.0x10 ¹⁸ atom ^{/ cm 3,} is 7.6x10 17 atom / cm ³ and ^2.0x10 16 atom / cm ³ For four types of 4H—SiC single crystals, infrared absorption spectra were obtained in the same manner as in Example 1. From the infrared absorption spectrum, the absorption intensity (peak intensity) at a fixed wave number corresponding to 980 cm ⁻¹ was plotted against the nitrogen concentration. The results are shown in FIG.
From FIG. 3, it is clear that the nitrogen concentration cannot be uniquely evaluated even if the intensity of the absorption peak of the 4H—SiC single crystal whose nitrogen concentration is unknown is obtained.

Comparative Example 2
The 4H-SiC single crystal whose nitrogen concentration was evaluated in advance by SIMS and the nitrogen concentration was 1.5 × 10 ¹⁹ atoms / cm ³ was the same as in Example 1 except that air was used instead of Ge as the optical medium. Infrared absorption spectrum was obtained. This infrared absorption spectrum is shown in FIG.
From FIG. 5B, in this evaluation method, anomalous dispersion in which distortion occurs in the baseline occurs, and an infrared absorption spectrum showing a peak based on impurities cannot be obtained, and the nitrogen concentration in the 4H—SiC single crystal is evaluated. Obviously you can't.

By the method for evaluating a SiC single crystal of the present invention, the nitrogen concentration of a SiC single crystal containing nitrogen at a concentration of 5 × 10 ¹⁶ atoms / cm ³ or more can be evaluated nondestructively.
Further, according to the manufacturing method of the present invention, it is possible to easily obtain a SiC single crystal in which the nitrogen concentration of the SiC single crystal is evaluated nondestructively and nitrogen is contained in the crystal at a concentration of 5 × 10 ¹⁶ atoms / cm ³ or more. it can.

Claims (8)

A method for evaluating a SiC single crystal for evaluating a nitrogen concentration in a crystal,
(1) An optical medium having a refractive index higher than that of the SiC single crystal is brought into contact with the surface of the SiC single crystal,
(2) irradiating the interface between the SiC single crystal and the optical medium with infrared rays;
(3) Obtain the absorption peak intensity at which the peak value of the absorption wave number changes in the range of 966 to 971 cm ⁻¹ from the obtained infrared spectrum,
(4) Evaluating the nitrogen concentration in the SiC single crystal based on the obtained absorption peak intensity,
Said method.   The absorption peak intensity is obtained by the above (1) to (3) for a plurality of SiC single crystals having a known nitrogen concentration and different concentrations, and a correlation between the nitrogen concentration and the absorption peak intensity is obtained in advance. Evaluation method.   The evaluation method according to claim 1, wherein the infrared spectrum is a spectrum of reflected light obtained by totally reflecting infrared rays at the interface. The evaluation method according to claim 1, wherein the optical medium is selected from As ₂ Se ₃ , Si, and Ge.   The evaluation method according to claim 1, wherein the SiC single crystal is bulk.   The evaluation method according to claim 1, wherein the SiC single crystal is a 4H type. A method for producing a SiC single crystal, comprising:
A step of growing a SiC single crystal, and a step of evaluating the nitrogen concentration in the obtained SiC single crystal by the evaluation method according to any one of claims 1 to 6,
Said method.   The manufacturing method according to claim 7, wherein the SiC single crystal is grown by a solution method.

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