WO2023112171A1 - Method for forming silicon boride film - Google Patents

Abstract

The present disclosure provides a method for forming a silicon boride film by using CVD, which is one of film forming techniques widely applied in industries. A method for forming a silicon boride film according to the present disclosure comprises: preparing a Si (100) substrate, and removing a native oxide film formed on the surface of the Si (100) substrate; installing the Si (100) substrate in a chamber, and evacuating the inside of the chamber; introducing disilane gas and diborane gas into the chamber, heating the Si (100) substrate to 600 °C, and forming a Si buffer layer on the Si (100) substrate; irradiating light or generating plasma in the chamber and forming a silicon boride film on the Si (100) substrate; and removing, from the chamber, a laminate in which silicon boride is formed on the Si (100) substrate, and performing post-annealing on the laminate at 900 °C to crystallize silicon boride.

Description

Method for forming silicon boride film

The present disclosure relates to a method for forming a silicon boride film.

Silicon boride (hereinafter referred to as SiB) is a compound of silicon (Si) and boron (B), and is a compound material for which stable phases have been reported in various composition ratios. Typical stable phases of SiB include SiB ₃ and SiB ₆ , which have already been put to practical use as thermoelectric conversion devices and refractory materials.

Existing techniques for forming SiB include, for example, a method of melting a mixture of Si and B powders as raw materials at high temperature (see, for example, Non-Patent Documents 1 and 2), and a method of pressing at high pressure (for example, Non-Patent Document 3) and the like are known. However, such a forming method usually requires a high temperature environment of 1200° C. or more, and in addition, there is a problem that only a powdery SiB crystal can be formed. On the other hand, SiB is required to be a thin film from the viewpoint of industrial applications such as thermoelectric conversion devices.

On the other hand, B is also a typical p-type dopant for Si crystals, and Si crystals doped with a small amount of B are applied to devices such as photodiodes and CMOS transistors as p-type semiconductors. As a method of manufacturing a device using such a B-doped Si crystal, for example, in a silicon process for LSI, a method of irradiating (ion-implanting) B ions accelerated in an electric field to a Si crystal is known. . However, when the concentration of B doped into Si exceeds 6×10 ²⁰ cm ⁻³ , which is considered to have no effect on the crystal structure of Si, the presence of excess B atoms disturbs the crystal structure of Si. Further, it is considered that the above-mentioned SiB is generated in the Si crystal when the concentration of B is further increased. However, at present, no report has been found in which Si is doped with such a high concentration of B in a silicon process and a B-doped Si crystal formed is investigated in detail.

In order to form a thin film of SiB (hereinafter referred to as a SiB film), it is desirable to apply a semiconductor process such as the silicon process described above instead of a solid-phase reaction. However, as described above, the introduction of B at a high concentration in the silicon process for LSI has not been carried out until now. The reason for this is that diborane (B ₂ H ₆ ) gas, commonly used as a source of B, is not sufficiently decomposed in the thermal excitation process. Therefore, there have been no reports of SiB films formed by a film forming technique widely used in industry, such as chemical vapor deposition (hereinafter referred to as CVD). That is, from the viewpoint of industrial use such as application to thermoelectric conversion devices, there is a problem that an effective film forming technique for forming a SiB film has not been established.

D. Eklof, A. Fischer, A. Ektarawong, A. Jaworski, A. J. Pell, J. Grins, S. I. Simak. B. Alling, Y. Wu, M. Widom, W. Scherer and U. Haussermann, ACS Omega 4, 18741-18759, 2019 J. Wu, W. Ma, B. Yang, D. Liu and Y. Dai, Silicon 4, 289-295, 2012 X. Liang, A. Bergara, Y. Xie, L. Wang, R. Sun, Y. Gao, X.-F. Zhou, B. Xu, J. He, D. Yu, G. Gao and Y. Tian , Phys. Rev. B 101, 014112, 2020 D. E. Aspnes and A. A. Studna, Surf. Sci., 96, 294, 1980 O. Cojocaru-Miredin, D. Mangelinck and D. Blavette, J. Appl. Phys., 106, 113525, 2009

The present disclosure has been made in view of the above problems, and the purpose thereof is to form a SiB film using CVD, which is one of the film formation techniques widely applied in industry. It is to provide a method.

In view of the above problems, the present disclosure provides a method for forming a silicon boride film by chemical vapor deposition, in which a Si (100) substrate from which a natural oxide film has been removed is placed in a chamber, and the chamber is evacuated. heating the Si(100) substrate to 600° C. while introducing disilane gas and diborane gas into the chamber to form a Si buffer layer on the Si(100) substrate; Irradiation or plasma generation to form a film of silicon boride on a Si (100) substrate, and post-annealing at 900° C. a laminate in which the silicon boride film is formed on the Si (100) substrate. and crystallizing the silicon boride by subjecting it to a method of forming a silicon boride film.

1 is a flow chart illustrating a method 10 of forming a SiB film according to the present disclosure; FIG. 4 is a diagram schematically showing the aspect of forming a SiB film by optical CVD in the first embodiment of the present disclosure; , a Si(100) substrate with a buffer layer formed thereon, a SiB film after deposition by CVD, a SiB film after post-annealing, and aB pseudo-dielectric response function spectra; FIG. ) shows the real part of the pseudo-dielectric response function, and FIG. 3(b) shows the imaginary part of the pseudo-dielectric response function. FIG. 4 is a diagram showing trajectories of ellipsometric angles (Ψ, Δ) of each sample shown in FIG. 3; It is a diagram showing the results of fitting the pseudo-dielectric response function spectrum assuming various single-layer models to the pseudo-dielectric response function of the SiB film after CVD film formation shown in FIG. The spectrum of the real part is shown, and FIG. 5(b) shows the spectrum of the imaginary part. It is a diagram showing the substrate temperature dependence during film formation of the pseudo-dielectric response function spectrum of the a-SiB film after film formation, FIG. A spectrum at a temperature of 400° C. is shown, respectively. FIG. 7 shows the results of fitting the pseudo-dielectric response function spectra of various single-layer models to the pseudo-dielectric response function of the SiB film after post-annealing shown in FIG. 7B shows the spectrum of the imaginary part, respectively. FIG. 8 is a diagram showing the disilane gas flow rate ratio dependence of the trajectory of the ellipsometric angle (Ψ−Δ) obtained using spectroscopic ellipsometry with respect to the growth surface of the SiB film during film formation by CVD, and FIG. FIG. 8B shows the trajectory when the incident light energy used for measurement is 3.4 eV, and FIG. 8B shows the trajectory when the incident light energy used for measurement is 1.5 eV. FIG. 9 is a diagram showing the pseudo-dielectric response function spectrum of a SiB film deposited at a disilane flow rate of 0.2 sccm, FIG. 9A shows the spectrum of the real part, and FIG. showing. FIG. 10 is a diagram schematically showing the aspect of forming a SiB film by plasma CVD in the second embodiment of the present disclosure;

Various embodiments of the present disclosure will be described in detail below with reference to the drawings. Identical or similar reference numerals indicate identical or similar elements and redundant description may be omitted. The following description is an example, and part of the configuration may be omitted or modified, or implemented with additional configuration, as long as it does not deviate from the gist of the embodiments of the present disclosure.

As mentioned above, the reason why the formation of SiB films using CVD has not been realized so far is that the reaction gas diborane gas is not sufficiently decomposed in the thermal excitation process. However, if the energy source for exciting the diborane gas is a higher energy medium (eg, light or plasma), it is believed that the diborane gas can be decomposed into active species (eg, radicals) capable of forming a film by CVD. In particular, in the case of optical CDV in which the medium for exciting the reaction gas is light, if the excitation light is vacuum ultraviolet light (ultraviolet light with a wavelength shorter than 200 nm), diborane gas can be efficiently decomposed into radicals. This is because diborane has a large excitation cross section under vacuum ultraviolet light irradiation. Focusing on these points, the present disclosure uses disilane gas and diborane gas as reactive gases, and a method of forming a SiB film by CVD (optical CVD or plasma CVD) in which light or plasma is applied to the excitation medium of these reactive gases. I will provide a.

However, as will be described later, when the SiB film is formed by photo-CVD using vacuum ultraviolet light as excitation light, the formed SiB film is amorphous in the state after film formation. On the other hand, when assuming application to the above-mentioned thermoelectric conversion device and the like, the SiB film is preferably crystalline. Therefore, the method for forming a SiB film according to the present disclosure transforms amorphous SiB (hereinafter referred to as a-SiB) deposited by photo-CVD or plasma CVD into crystallized SiB (hereinafter referred to as c-SiB). including methods. Specifically, after the film formation by CVD is completed, the layered body in which the a-SiB film is formed on the substrate is taken out from the chamber and post-fired (post-annealed).

FIG. 1 is a flowchart illustrating a method 10 of forming a SiB film according to the present disclosure. A method 10 for forming a SiB film according to the present disclosure includes preparing a Si(100) substrate, removing a native oxide film formed on the surface of the Si(100) substrate (step 11), and placing Si(100) in a chamber. After placing the substrate, the chamber is evacuated (step 12), and the Si(100) substrate is heated to 600° C. while introducing reaction gases such as disilane gas and diborane gas into the chamber. forming a buffer layer of Si on the substrate (step 13); irradiating light or generating plasma in the chamber to form a SiB film on the Si (100) substrate (step 14); 100) removing the stack having SiB deposited on the substrate from the chamber and subjecting it to post-annealing at 900° C. to crystallize the SiB (step 15).

In step 11, the method of removing the natural oxide film can be pickling, which removes the natural oxide film by immersing the Si (100) substrate in dilute hydrofluoric acid, for example.

In step 13, the Si buffer layer is formed on the Si (100) substrate by utilizing thermal growth of disilane gas introduced into the chamber as a reaction gas. As will be described later, the purpose of forming this buffer layer is to flatten the top surface of the Si (100) substrate at the atomic level.

By using such a method, it becomes possible to form a c-SiB film on Si (100). Since the method of forming the SiB film according to the present disclosure does not require a high temperature environment of 1200° C. or higher as in the conventional technology, the process is a lower temperature process than the conventional one, and in terms of manufacturing cost and energy saving, it is lower than the conventional technology. Are better.

(First embodiment)
A first embodiment of the present disclosure will be described in detail below with reference to the drawings. The present embodiment relates to a method of forming a SiB film by optical CVD and crystallizing SiB by post-annealing.

FIG. 2 is a diagram schematically showing the aspect of forming a SiB film by optical CVD in the first embodiment of the present disclosure. As shown in FIG. 2, in forming the SiB film in this embodiment, a Si (100) substrate 23 is placed on a substrate heater 22 placed in a chamber 21 . Then, in a high vacuum environment, a disilane gas 24 with a purity of 100% and a diborane gas 25 diluted to 1% with helium (He) are introduced at predetermined flow rates, respectively, and excitation light 26 is irradiated. Here, the excitation light 26 is vacuum ultraviolet/soft X-ray white excitation light with photon energies in the range of 100-1000 eV. By being irradiated with this excitation light 26, the disilane gas 24 and the diborane gas 25 are decomposed into chemically active radicals (SiHx, BHx). is deposited. As shown in FIG. 2, disilane gas 24 and diborane gas 25 are preferably flowed toward Si(100) substrate 23 and then Si(100) substrate 23 is irradiated with excitation light 26 .

As described above, a Si buffer layer is formed on the Si (100) substrate 23 . In this embodiment, the heat generated by operating the substrate heater 22 is used as an energy source to deposit a buffer layer from the disilane gas 24 onto the Si(100) substrate. Since the Si (100) substrate 23 is a single crystal, the buffer layer is epitaxially grown, and thus becomes Si (100) itself. As a result, the outermost surface of the Si(100) substrate (that is, the interface with the SiB film) becomes flat Si(100) at the atomic level.

The substrate temperature during film formation is 300-400° C., the flow rate of disilane gas 24 is 0.1-0.2 sccm, and the flow rate of diborane gas is 0.1 sccm.

In this way, the laminate in which SiB is formed on the Si (100) substrate using optical CVD is post-annealed to crystallize the formed SiB film. Post-annealing is performed by holding at a predetermined temperature, for example, using an electric furnace. The post-annealing temperature in this embodiment is 900.degree.

Such a method makes it possible to form a SiB film. As described above, conventional methods for forming SiB require a high temperature environment of 1200° C. or higher, but the method according to the present disclosure can form a SiB film at a lower temperature than that.

The mechanism by which the SiB film is formed by the method described above will be described below. This mechanism is based on the results of evaluating the pseudo-dielectric response function (ε=ε ₁ +iε ₂ ) by spectroscopic ellipsometry for SiB films and Si(100) substrates before film formation, after film formation, and after post-annealing. there is

Analysis using spectroscopic ellipsometry in the present embodiment is performed on a Si (100) substrate before film formation by CVD (that is, immediately after step 13 described above), and after film formation by CVD (that is, after step 14 above). ) and the SiB film after post-annealing (that is, immediately after step 15 described above). In the analysis, the temperatures of the Si(100) substrate and the SiB film were room temperature. In-situ observation in the chamber was used for the analysis before and after the CVD film formation.

Usually, the evaluation of the pseudo-dielectric response function by spectroscopic ellipsometry consists of measuring the change in polarization by irradiating the sample surface with incident light and analyzing the reflected light, performing regression analysis with an assumed model, It includes comparing and evaluating the measurement results and the analysis results. In this embodiment, the energy of the incident light in the measurement was 1.5-5.0 eV. On the other hand, in the analysis, crystalline silicon (hereinafter referred to as c-Si), amorphous silicon (hereinafter referred to as a-Si), amorphous boron (hereinafter referred to as aB), vacancies (hereinafter referred to as void ) was assumed as a component, and Bruggeman's effective medium approximation was applied. For the dielectric response functions of c-Si and a-Si, Aspnes values were used based on existing reports (see, for example, Non-Patent Document 4). For the dielectric response function of aB, the value of a thick film of aB separately formed on a Si (100) substrate with only borane gas was used. Also, the void dielectric response function was assumed to match the vacuum dielectric response function (1+i0). Under these conditions, the optimum values were determined by changing the volume fraction and film thickness of each component as parameters, and performing fitting so that the difference between the measured spectrum and the spectrum obtained by analysis was minimized. .

FIG. 3 shows pseudodielectric response function spectra of a Si (100) substrate on which a buffer layer is formed, a SiB film after deposition by CVD, a SiB film after post-annealing, and aB. 3(a) shows the real part of the pseudo-dielectric response function, and FIG. 3(b) shows the imaginary part of the pseudo-dielectric response function. The aB spectrum is the result of using a sample of a thin film separately formed by CVD using only diborane gas, and is also plotted for comparison. Note that the substrate temperature during film formation of each sample is 300° C. here. As shown in FIG. 3, the spectrum of aB is in a saturated state showing a substantially constant value in the region of 2 eV or more, so it can be regarded as showing the bulk dielectric response function of aB. On the other hand, the SiB film formed by CVD contains Si having a larger mass number than B, so the dielectric response is enhanced in the region of 2 eV or more compared to aB. Furthermore, it can be seen that the spectrum of the imaginary part of the SiB film after post-annealing changes to have a peak around 3.4 eV, as shown in FIG. 3(b). This indicates that the atoms forming the a-SiB bulk diffused to stable sites due to the thermal energy of the post-annealing, resulting in microcrystals.

FIG. 4 is a diagram showing the trajectory of the ellipsoid angle (Ψ, Δ) of each sample shown in FIG. Here, the energy of incident light is 3.4 eV. The origin O shown in FIG. 4 corresponds to the Si (100) substrate having the buffer layer formed on the outermost surface before film formation. The change in the ellipsoidal angle on the locus O→A is due to the growth of the SiB film on the Si(100) substrate, indicating that the growth was terminated at A. The locus A→B corresponds to the process in which the substrate temperature cools down to room temperature after the film formation is finished. Even in this process, the ellipsoid angle changes slightly, but this is due to the temperature dependence of the optical constant, suggesting that the state of the deposited SiB is changing. isn't it. The locus B→C corresponds to the process of post-annealing the stack of the SiB film and the Si(100) substrate taken out from the chamber at 900.degree. As shown in FIG. 4, the ellipsoid angle changes with heating in this process, and the change in the ellipsoid angle becomes steady at 900°C. The change in the ellipsoidal angle due to heating is thought to indicate that the SiB film, which was a-SiB immediately after film formation, was transformed into microcrystalline c-SiB. In other words, since the change in the ellipsoidal angle became steady at 900° C., it is understood that the post-annealing temperature must be 900° C. in order to form c-SiB.

From the above, when photo-CVD using vacuum ultraviolet light/soft X-ray as excitation light is used, the SiB film formed at a substrate temperature of 300° C. is amorphous SiB (hereinafter referred to as a-SiB). , the a-SiB film is post-annealed at 900° C. to form a crystalline SiB (hereinafter referred to as c-SiB) film. This interpretation is supported by the evaluation results of the pseudo-dielectric response function spectra assuming various monolayer models, as described below.

FIG. 5 is a diagram showing the result of fitting the pseudo-dielectric response function spectrum assuming various single-layer models to the pseudo-dielectric response function of the SiB film after CVD deposition shown in FIG. (a) shows the spectrum of the real part, and FIG. 5(b) shows the spectrum of the imaginary part. Three single layer models were assumed here: (c-Si+a-Si+a-B), (c-Si+a-B+void), and (a-Si+a-B+void). FIG. 5 also shows the spectrum of the pseudo-dielectric response function of the SiB film obtained by actual measurement. The reason why the single layer model is adopted is to evaluate the volume fraction including the whole while ignoring the layer structure such as the internal structure and surface roughness of the film. When the (c-Si+a-B+void) and (a-Si+a-B+void) models were assumed, the volume fraction of the void component converged to zero no matter what initial parameters were chosen. The void component effectively corresponds to the surface roughness, since it is unlikely that there are pores in the film. That is, it suggests that the SiB film surface is flat at the atomic level. For the (c-Si+a-B+void) model, the singularity structure at 3.4 eV, 4.3 eV corresponding to the _E1 and _E2 interband transitions of the Si crystal is emphasized in the imaginary dielectric response function spectrum. there is This is because the amplitudes of the dielectric response functions of aB and void are small, so when trying to reproduce the amplitude of the dielectric response function spectrum of the imaginary part of 20-25 eV, the volume fraction of the c-Si component is inevitably large. This is due to the fact that there is no On the other hand, the (a-Si+a-B+void) model reproduces the characteristics of the maximum amplitudes of 3 eV and 3.7 eV, and shows the spectrum closest to the measured value of a-SiB. The volume fraction corresponding to this case was 80% a-Si, 20% aB, 0% void, and the film thickness was 212 angstroms. Assuming that the volume fraction of the void component is zero, the model can be substantially regarded as the (a-Si+a-B) model. From the above, the composition obtained using the volume fraction of the film evaluated based on the dielectric response is Si ₄ B. The reason why the volume fraction of a-Si is four times higher than the volume fraction of a-B even though the flow rate of both disilane and diborane is set to 0.1 sccm is that Si atoms are incorporated into the film. probability is greater than that of the B atom incorporation. Also, since the spectrum of the measured values of a-SiB is well reproduced by the analysis, it is considered appropriate to apply the effective medium approximation. In other words, it was suggested that the a-SiB film formed by the method according to the present embodiment is a film having a-Si and aB as domains or an assembly of clusters. In other words, it is considered that the solid phase of c-SiB in which Si atoms and B atoms are combined is not formed. In fact, according to existing reports, it is known that B atoms form clusters when a high concentration of B exists in a Si crystal (see, for example, Non-Patent Document 5).

FIG. 6 is a diagram showing the dependence of the pseudo-dielectric response function spectrum of the a-SiB film after film formation on the substrate temperature during film formation. FIG. b) shows the spectrum at a substrate temperature of 400° C., respectively. Here, the analysis spectrum assuming the (a-Si+a-B+void) model, which shows the spectral shape closest to the actual measurement in FIG. 5, is also shown. As shown in FIGS. 6A and 6B, even when the substrate temperature during film formation is 350° C. and 400° C., the spectrum of the pseudo-dielectric response function of the formed a-SiB film is the measured value. and the analytical values are in good agreement. The parameters (volume fraction and film thickness) at this time were 74% a-Si, 26% aB, 0% void, and 217 Å film thickness at a substrate temperature of 350°C. . On the other hand, at a substrate temperature of 400.degree. That is, it was found that the composition of a-SiB formed at a substrate temperature of 350° C. corresponds to Si ₃ B, and the composition of a-SiB formed at a substrate temperature of 400° C. corresponds to Si ₂ B.

FIG. 7 shows the results of fitting the pseudo-dielectric response function spectra of various single-layer models to the pseudo-dielectric response function of the post-annealed SiB film shown in FIG. shows the spectrum of the real part, and FIG. 7(b) shows the spectrum of the imaginary part. Here, four models of (c-Si+a-Si+void), (c-Si+a-Si+a-B), (c-Si+a-B+void), and (a-Si+a-B+void) were assumed for the analysis. As a result, (c-Si + a-Si + void) shows a spectrum shape closest to the measured value, and the parameters (volume fraction and film thickness) at this time are 10% for c-Si, 62% for a-Si, The void was 28% and the film thickness was 187 angstroms. From this, it is considered that the SiB film after post-annealing is a film having slightly crystallized Si as a domain. It is considered that the fact that the void volume fraction is not zero corresponds to the surface roughness.

From the above, in the method according to the present disclosure, when forming an a-SiB film on a Si (100) substrate by CVD, if the substrate temperature is 300 to 400 ° C., a Si-rich amorphous film is formed. found to be formed. Furthermore, it was confirmed that post-annealing this amorphous a-SiB film at 900° C. transformed it into a microcrystalline c-SiB film.

FIG. 8 is a diagram showing the disilane gas flow ratio dependence of the trajectory of the ellipsometric angle (Ψ−Δ) obtained using spectroscopic ellipsometry with respect to the growth surface of the SiB film during film formation by CVD. (a) shows the trajectory when the energy of the incident light used for the measurement is 3.4 eV, and FIG. 8(b) shows the trajectory when the energy of the incident light used for the measurement is 1.5 eV. Here, the diborane gas flow rate was fixed at 0.1 sccm, and the disilane gas flow rate ratio was varied from 0.2 to 1.0 sccm. The substrate temperature during the film formation is constant at 300.degree. As shown in Fig. 8(a), when monitored with incident light of 3.4 eV, which is strongly absorbed by Si, the initial stages of the trajectories corresponding to 0.7 and 1 sccm are generally overlapped, and the convergence points are also close to each other. I understand. When the spiral trajectory of one rotation is drawn and converged, it indicates that the dielectric response has already reached saturation and does not change any more even if the film thickness increases. On the other hand, as shown in FIG. 8(b), at 1.5 eV where absorption by Si is small, it can be seen that the destination of the Ψ-Δ trajectory varies depending on the disilane flow rate. This indicates that the optical constant of the SiB film differs depending on the flow rate ratio of disilane and diborane, and the composition changes continuously.

9A and 9B are diagrams showing the pseudo-dielectric response function spectrum of the SiB film formed at a disilane flow rate of 0.2 sccm, FIG. 9A shows the spectrum of the real part, and FIG. Spectra are shown, respectively. Three types of models were assumed here: (a-Si+a-B+void), (c-Si+a-Si+a-B), and (c-Si+a-B+void). In the case of the disilane flow rate of 0.1 sccm shown in FIG. 5, the (a-Si+a-B+void) model showed the best agreement. On the other hand, the (c-Si+a-Si+a-B) model shows generally better agreement than the (a-Si+a-B+void) model, which showed the best agreement at a disilane flow rate of 0.1 sccm. This result suggests that a region exhibiting a crystal structure appears by increasing the disilane flow ratio. It is considered that this is because the area in contact with smooth and highly crystalline Si (100) increased due to the increase in the amount of Si. From the above, it is believed that a c-SiB film can be formed by the method according to the present disclosure if the disilane flow ratio is in the range of 0.1-0.2 sccm.

(Second embodiment)
A second embodiment of the present disclosure will be described in detail below with reference to the drawings. This embodiment relates to a method of forming an a-SiB film by plasma CVD and forming c-SiB by post-annealing.

FIG. 10 is a diagram schematically showing the aspect of forming an a-SiB film by plasma CVD in the second embodiment of the present disclosure. As shown in FIG. 10, in forming the a-SiB film in the second embodiment, a Si (100) substrate 23 is placed on a substrate heater 22 placed in a chamber 21 . Then, in a high vacuum environment, disilane gas 24 and diborane gas 25 diluted with helium (He) are introduced at predetermined flow rates, respectively, and voltage is applied to electrode 102, which serves as a cathode, using power supply 101. FIG. Here, the power source 101 is a high frequency power source. Then, electrons generated by natural radiation or the like existing in the chamber are accelerated by the electric field around the electrode 102, and inelastic collisions with the reaction gas (disilane gas and diborane gas) in the chamber generate plasma. As this process becomes steady, part of the disilane gas and diborane gas is decomposed into chemically active radicals (SiHx, BHx), and these radicals impinge on the Si (100) substrate 23, resulting in a-SiB is deposited.

A buffer layer of Si is formed on the Si (100) substrate 23 in the same manner as in the first embodiment. In this embodiment, the heat generated by operating the substrate heater 22 is used as an energy source to cause thermal growth on the Si (100) substrate by the disilane gas 24 . As a result, the outermost surface of the Si (100) substrate (interface with a-SiB) is flattened at the atomic level.

The substrate temperature during film formation is 300-400° C., the flow rate of the disilane gas 14 is 0.1-0.2 sccm, and the flow rate of the diborane gas is 0.1 sccm.

In this way, the laminate in which a-SiB is formed on the Si (100) substrate using plasma CVD is post-annealed to crystallize the a-SiB film into a c-SiB film. Post-annealing is performed by holding at a predetermined temperature, for example, using an electric furnace. The post-annealing temperature in this embodiment is 900.degree.

A SiB film can be formed by such a method as in the first embodiment. As described above, conventional methods for forming SiB require a high temperature environment of 1200° C. or higher, but the method according to the present disclosure can form a SiB film at a lower temperature than that.

The method of forming a SiB film according to the present disclosure realizes the formation of a SiB film, which has not been established in the past, by CVD and post-annealing, which are widely used in industry. Therefore, it contributes to the miniaturization of thermoelectric conversion elements, etc., and is expected to be put into practical use as a manufacturing method for thermoelectric conversion.

Claims (4)

A method for forming a silicon boride film by chemical vapor deposition, comprising:
placing a Si (100) substrate from which a natural oxide film has been removed in a chamber and evacuating the chamber;
heating the Si(100) substrate to 600° C. while introducing disilane gas and diborane gas into the chamber to form a buffer layer of Si on the Si(100) substrate;
irradiating light or generating plasma in the chamber to form a film of silicon boride on the Si (100) substrate;
crystallizing the silicon boride by performing post-annealing at 900° C. on the laminate in which the silicon boride is formed on the Si (100) substrate;
A method for forming a silicon boride film, comprising: the disilane gas has a flow rate of 0.1 sccm or more and 0.2 sccm or less;
2. The method of forming a silicon boride film according to claim 1, wherein the diborane gas has a flow rate of 0.1 sccm. 3. The method of forming a silicon boride film according to claim 1, wherein the temperature of the Si(100) substrate is 300[deg.] C. or more and 400[deg.] C. or less in the film formation of the silicon boride. The method for forming a silicon boride film according to any one of claims 1 to 3, wherein the light is excitation light that has a photon energy of 100 eV or more and 1000 eV or less and is a mixture of vacuum ultraviolet light and soft X-rays.

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