Semiconductor substrate and method for manufacturing the same

Abstract

The objective is to provide semiconductor substrates in which high-quality GaO2 is grown on large-diameter Si substrates. [Solution] A semiconductor substrate and a method for manufacturing the same, characterized by having a Si substrate with a main surface orientation of (111), a 3C-SiC layer on the Si substrate, and a GaO2 layer on the 3C-SiC layer.

Description

Technical Field

[0001] The present invention relates to a semiconductor substrate and a method for manufacturing the same.

Background Art

[0002] The need for power devices has been increasing in a very wide range, including the fields of automotive electrification and FA (Factory Automation). In addition, energy loss in power semiconductors has become significant, and research on structures with good energy efficiency has been conducted and has achieved great results.

[0003] In this application, power MOSFETs and IGBTs based on silicon are dominant. However, the bandgap of silicon is 1.1 eV, and there is an inherent limit to the breakdown voltage due to the material.

[0004] Therefore, the use of materials other than silicon has been studied. In addition to wide bandgap materials such as GaN, SiC, and diamond, which have a large bandgap, there are also oxide semiconductors such as GaO2 and GeO2.

[0005] Among them, α-type GaO2 has a very large bandgap of 5.3 eV, has a high breakdown voltage, high radiation resistance performance, and is suitable for use in harsh environments (Non-Patent Document 1).

[0006] In addition, in Non-Patent Document 1, the lattice constant of α-type GaO2 is reported to be 4.8. This value is very close to 4.35 of 3C-SiC, and heteroepitaxial growth is possible.

Prior Art Documents

Patent Documents

[0007]

Patent Document 1

Non-Patent Documents

[0008] [Non-Patent Document 1] M. Biswas et.al., “Thermodynamically metastable α-,ε-(or κ-),and γ-Ga2O3:From material growth to device applications”, APL Materials,10,060701(2022) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, when forming 3C-SiC on a Si(111) substrate, it is believed that there remain challenges in the quality of the 3C-SiC surface for GaO2 growth due to lattice mismatch between Si and 3C-SiC. This is because the lattice constant of Si(111) is 3.84, resulting in a large difference in lattice constant between it and 3C-SiC. For these reasons, it is also considered difficult to increase the diameter.

[0010] This invention was made to solve the above problems and aims to provide a semiconductor substrate in which high-quality GaO2 is grown on a large-diameter Si substrate. [Means for solving the problem]

[0011] The present invention has been made to achieve the above objective and provides a semiconductor substrate having a Si substrate with a main surface orientation of (111), a 3C-SiC layer on the Si substrate, and a GaO2 layer on the 3C-SiC layer.

[0012] Such a semiconductor substrate suppresses the degradation of crystal quality due to lattice mismatch, resulting in a semiconductor substrate in which GaO2 is grown on a large-diameter Si substrate.

[0013] In this case, the Si substrate may have voids at the interface between the Si substrate and the 3C-SiC layer.

[0014] This makes it possible to further relax the stress generated by lattice mismatch.

[0015] At this time, a carbon-doped Si layer can be further provided between the Si substrate and the 3C-SiC layer.

[0016] This suppresses deterioration of crystal quality due to lattice mismatch more effectively, and results in a semiconductor substrate in which GaO₂ is grown on a large-diameter Si substrate.

[0017] At this time, the carbon-doped Si layer can have voids at the interface between the carbon-doped Si layer and the 3C-SiC layer.

[0018] This makes it possible to further relax the stress generated by lattice mismatch.

[0019] The present invention is also made to achieve the above object, and includes a step of removing a natural oxide film on the surface of a Si substrate having a plane orientation of (111) on the main surface by hydrogen baking, a step of forming a 3C-SiC layer on the Si substrate using a source gas containing carbon and silicon, and a step of forming a GaO₂ layer on the 3C-SiC layer, and provides a method for manufacturing a semiconductor substrate.

[0020] According to such a semiconductor substrate, deterioration of crystal quality due to lattice mismatch can be suppressed, and a semiconductor substrate in which GaO₂ is grown on a large-diameter Si substrate can be manufactured.

[0021] At this time, between the step of removing the natural oxide film by hydrogen baking and the step of forming the 3C-SiC layer, a step of forming a carbon-doped Si layer on the Si substrate using a source gas containing carbon and silicon can be further included.

[0022] This suppresses deterioration of crystal quality due to lattice mismatch more effectively, and results in a semiconductor substrate in which GaO₂ is grown on a large-diameter Si substrate.

Effects of the Invention

[0023] As described above, according to the semiconductor substrate of the present invention, deterioration of crystal quality due to lattice mismatch is suppressed, and a semiconductor substrate in which GaO₂ is grown on a large-diameter Si substrate is obtained. Further, according to the method for manufacturing a semiconductor substrate of the present invention, it is possible to manufacture a semiconductor substrate in which deterioration of crystal quality due to lattice mismatch is suppressed and GaO₂ is grown on a large-diameter Si substrate.

Brief Description of the Drawings

[0024] [Figure 1] An example of a cross-sectional structure of a semiconductor substrate according to the first embodiment of the present invention is shown. [Figure 2] An example of a cross-sectional structure of a semiconductor substrate according to the second embodiment of the present invention is shown. [Figure 3] An example of a process flow of a method for manufacturing a semiconductor substrate according to the first embodiment of the present invention is shown. [Figure 4] An example of a process flow of a method for manufacturing a semiconductor substrate according to the second embodiment of the present invention is shown.

Modes for Carrying Out the Invention

[0025] Hereinafter, the present invention will be described in detail, but the present invention is not limited thereto.

[0026] As described above, there has been a demand for a semiconductor substrate in which high-quality GaO₂ is grown on a large-diameter Si substrate.

[0027] As a result of intensive studies on the above problems, the present inventors have found that a semiconductor substrate having a Si substrate with a (111) plane orientation on the main surface, a 3C-SiC layer on the Si substrate, and a GaO₂ layer on the 3C-SiC layer suppresses deterioration of crystal quality due to lattice mismatch and becomes a semiconductor substrate in which GaO₂ is grown on a large-diameter Si substrate, and thus completed the present invention.

[0028] The inventors have also conducted extensive research on the above-mentioned problems and have found that a semiconductor substrate manufacturing method comprising the steps of removing a native oxide film on the surface of a Si substrate with a main surface orientation of (111) by hydrogen baking, forming a 3C-SiC layer on the Si substrate using a source gas containing carbon and silicon, and forming a GaO2 layer on the 3C-SiC layer, can suppress the deterioration of crystal quality due to lattice mismatch and manufacture a semiconductor substrate on which GaO2 has been grown on a large-diameter Si substrate, thus completing the present invention.

[0029] In other words, the present invention relates to a gallium oxide substrate which is a wide-bandgap semiconductor, and more specifically, to a virtual gallium oxide substrate having a single crystal 3C-SiC on a silicon substrate, with gallium oxide formed on top of it.

[0030] Embodiments of the present invention will be described below with reference to the drawings.

[0031] [Semiconductor substrates] Figure 1 shows an example of the cross-sectional structure of a semiconductor substrate according to the first embodiment of the present invention. As shown in Figure 1, the semiconductor substrate 1 according to the first embodiment of the present invention is a semiconductor substrate having a Si substrate (Si(111) substrate) 2 with a main surface orientation of (111), a 3C-SiC layer 4 on the Si(111) substrate 2, and a GaO2 layer 5 on the 3C-SiC layer 4.

[0032] The Si(111) substrate 2 can be a Si substrate with a diameter of 300 mm, but is not limited to this, and may be a Si substrate with a diameter of 300 mm or more.

[0033] The semiconductor substrate 1 may further include a Si(111) substrate 3 having vacancies intentionally formed at the interface between the Si(111) substrate 2 and the 3C-SiC layer 4. This allows for greater relaxation of stresses caused by lattice mismatch.

[0034] Figure 2 shows an example of a cross-sectional structure of a semiconductor substrate according to the second embodiment of the present invention. As shown in Figure 2, the semiconductor substrate 10 according to the second embodiment of the present invention is a semiconductor substrate having a Si(111) substrate 2, a 3C-SiC layer 4, and a GaO2 layer 5, and may further have a carbon-doped Si layer 6 between the Si(111) substrate 2 and the 3C-SiC layer 4.

[0035] This further suppresses the degradation of crystal quality due to lattice mismatch, and results in a semiconductor substrate in which GaO2 is grown on a large-diameter Si substrate.

[0036] The semiconductor substrate 10 may further have a carbon-doped Si layer 7 having vacancies intentionally formed at the interface between the carbon-doped Si layer 6 and the 3C-SiC layer 4. This further reduces the stress caused by lattice mismatch. Note that the carbon-doped Si layer 6 may contain vacancies smaller than those in the carbon-doped Si layer 7.

[0037] The thickness of each of the above layers, the carbon concentration of the carbon-doped Si layer, etc., will be described in detail in the semiconductor substrate manufacturing method described later.

[0038] [Manufacturing method for semiconductor substrates] Next, the method for manufacturing a semiconductor substrate according to the present invention will be described. Figure 3 shows an example of a process flow for manufacturing a semiconductor substrate according to the first embodiment of the present invention. As shown in Figure 3, the method for manufacturing a semiconductor substrate according to the first embodiment of the present invention includes a step (S1) of removing the native oxide film on the surface of a Si substrate (Si(111) substrate) 2 with a main surface orientation of (111) by hydrogen baking, a step (S2) of forming a 3C-SiC layer 4 on the Si(111) substrate 2 using a source gas containing carbon and silicon, and a step (S3) of forming a GaO2 layer 5 on the 3C-SiC layer 4. In this case, during the process using a reduced-pressure CVD apparatus, it becomes possible to form vacancies in the Si(111) substrate 2 at the interface between the Si(111) substrate 2 and the 3C-SiC layer 4 (forming a Si(111) substrate (with vacancies) 3).

[0039] (Step to remove the native oxide film by hydrogen baking: S1) First, a single-crystal silicon substrate (Si(111) substrate) 2 is placed in a reduced-pressure (RP-)CVD apparatus, and the native oxide film on the surface is removed by hydrogen baking (H2 annealing).

[0040] By removing the amorphous silicon oxide film on the outermost surface of the Si(111) substrate 2, it becomes possible to grow a carbon-doped silicon epitaxial layer on the Si(111) substrate 2. The H2 annealing at this stage is preferably performed at a temperature between 1000°C and 1200°C. Within this temperature range, the occurrence of slip dislocations can be effectively suppressed, and the residue of the native oxide film can be prevented with an efficient processing time. Furthermore, there are no particular restrictions on the pressure or time of the H2 annealing at this stage; it is sufficient to remove the native oxide film.

[0041] (Step to form the 3C-SiC layer: S2) Next, the 3C-SiC layer 4 is grown on the Si(111) substrate 2 by controlling the gas type, gas flow rate, and temperature. Specifically, the Si(111) substrate 2 is preferably set to a temperature of 300°C to 1100°C, and a source gas containing carbon and silicon, such as monomethylsilane or trimethylsilane, is introduced as a raw material gas for SiC to form SiC nucleation. Compared to Si, C atoms are smaller and more easily vaporized, so trimethylsilane is easier to adjust the growth conditions for when considering raw material efficiency.

[0042] SiC nucleation can be performed on the surface of the Si(111) substrate 2 at a pressure of 100 Torr (13332 Pa) or less and a temperature of 300°C or higher. However, since epitaxial growth of SiC is promoted at temperatures of 800°C or higher, it is more preferable to set the SiC nucleation temperature to 800°C or higher so that SiC nucleation and the formation of the 3C-SiC layer 4 can be performed under the same conditions. Furthermore, at temperatures of 1100°C or lower, polycrystallization and the adhesion of by-products to the inner wall of the CVD apparatus can be effectively suppressed. This is presumed to be because at high temperatures, molecules adsorbed on the substrate surface desorb before epitaxial growth occurs, causing a gas-phase reaction.

[0043] Furthermore, the growth pressure during the formation process of the 3C-SiC layer (3C-SiC single crystal film) 4 is preferably 100 Torr or less. If the growth pressure is 100 Torr or less, polycrystallization of 3C-SiC can be effectively prevented. If the pressure is 10 Torr (1333 Pa) or less, and more preferably 1 Torr (133 Pa) or less, vacancies will be formed directly beneath the 3C-SiC layer 4, and the effect of relaxing the stress on the entire epitaxial layer can be obtained.

[0044] Since the film thickness of the 3C-SiC layer 4 depends on pressure and temperature, the film deposition time can be appropriately set based on the pressure and temperature conditions set to achieve the desired film thickness. Preferably, the film thickness of the 3C-SiC layer 4 can be between 100 nm and 1000 nm. With a thickness in this range, 3C-SiC can be grown in an efficient amount of time, and a sufficient amount of pores can be formed at the interface between the Si(111) substrate 2 and the 3C-SiC layer 4.

[0045] Furthermore, during the epitaxial growth of the 3C-SiC layer 4, silicon used for 3C-SiC growth is supplied from the Si(111) substrate 2 in addition to the gas used for epitaxial growth, resulting in the formation of voids in the Si(111) substrate 2.

[0046] (Step to form the GaO2 layer: S3) Finally, a GaO2 film is deposited on the 3C-SiC layer 4 to form a GaO2 layer 5. There are no restrictions on the film deposition method, but techniques such as mist CVD are commonly used for the production of oxide semiconductors. Here, for example, reference can be made to Patent Document 1, etc.

[0047] There are no particular restrictions on the thickness of the GaO2 layer 5; it is determined by the thickness required to withstand the actual pressure of the device.

[0048] Figure 4 shows an example of a process flow for a semiconductor substrate manufacturing method according to the second embodiment of the present invention. As shown in Figure 4, the semiconductor substrate manufacturing method according to the second embodiment of the present invention further includes a step (S1a) of forming a carbon-doped Si layer 6 on a Si(111) substrate 2 using a source gas containing carbon and silicon, between the step (S1) of removing the native oxide film by hydrogen baking and the step (S2) of forming a 3C-SiC layer 4. In this case, during the process using a reduced-pressure CVD apparatus, it becomes possible to form vacancies in the carbon-containing silicon layer and the carbon-containing silicon layer at the 3C-SiC interface (forming a carbon-doped Si layer (with vacancies) 7).

[0049] (Step to remove the native oxide film by hydrogen baking: S1) The step of removing the native oxide film by hydrogen baking (S1) is the same as in the third embodiment, so the explanation will be omitted.

[0050] (Step to form a carbon-doped Si layer: S1a) Next, a carbon-doped Si layer 6 is formed on the Si(111) substrate 2 under reduced pressure using a vacuum CVD apparatus, controlling the gas type, gas flow rate, and temperature. Specifically, for example, the carbon-doped Si layer 6 is epitaxially grown using a gas mixture of trimethylsilane, monomethylsilane, or monosilane gas with a carbon source. At this time, by forming the film at a growth temperature preferably in the range of 700°C to 900°C, and more preferably in the range of 730°C to 750°C, it is possible to obtain a carbon-doped epitaxial layer with fewer defects.

[0051] The amount of carbon doping is 1 × 10⁻⁶20 ~4×10 21 atoms / cm 3 This can be achieved. Within this range of carbon concentration, the effect of doped carbon is more reliably exerted, and the 3C-SiC layer 4 can be single-crystallized more effectively.

[0052] The thickness of the carbon-doped Si layer 6 is not particularly limited and can be changed at any time, but it is preferably between approximately 1 nm and 1000 nm. With a film thickness in this range, the film can be formed in an efficient time, and the carbon can escape from the substitution site, allowing for more effective vacancy formation.

[0053] This makes it possible to further suppress the degradation of crystal quality due to lattice mismatch and to manufacture semiconductor substrates in which GaO2 is grown on large-diameter Si substrates.

[0054] (Step to form the 3C-SiC layer: S2) Regarding the step (S2) for forming the 3C-SiC layer, explanations of the same aspects as those for the semiconductor substrate manufacturing method according to the first embodiment (source gas type, growth temperature, growth pressure, film thickness, etc.) will be omitted.

[0055] SiC nucleation can be performed on the surface of the carbon-doped Si layer 6 at a pressure of 100 Torr (13332 Pa) or less and a temperature of 300°C or higher. However, since epitaxial growth of SiC is promoted at temperatures of 800°C or higher, it is more preferable to set the SiC nucleation temperature to 800°C or higher so that SiC nucleation and the formation of the 3C-SiC layer 4 can be performed under the same conditions. Furthermore, at temperatures of 1100°C or lower, polycrystallization and the adhesion of by-products to the inner wall of the CVD apparatus can be effectively suppressed. This is presumed to be because at high temperatures, molecules adsorbed on the substrate surface desorb before epitaxial growth, causing a gas-phase reaction.

[0056] During the epitaxial growth of the 3C-SiC layer 4, numerous tiny vacancies are formed as carbon atoms in the carbon-doped Si layer 6 escape from their substitution positions. Furthermore, silicon is supplied to the 3C-SiC layer 4 during its growth not only from the gases used during epitaxial growth but also from the carbon-doped Si layer 6, leading to the formation of vacancies in the carbon-doped Si layer 6. In other words, vacancies of different sizes and densities are formed by these two effects.

[0057] In other words, the vacancies formed in the carbon-doped Si layer (with vacancies) 7 are created by using the silicon of the substrate as the silicon source when growing 3C-SiC, and by the removal of carbon at substitution sites in the carbon-doped silicon layer during the heat treatment process during 3C-SiC epitaxial growth.

[0058] (Step to form the GaO2 layer: S3) The process of forming the GaO2 layer (S3) is the same as the method for manufacturing a semiconductor substrate according to the first embodiment, so its explanation will be omitted. [Examples]

[0059] The present invention will be described in detail below with reference to examples, but this is not intended to limit the present invention.

[0060] (Example 1) A 300 mm diameter, (111) orientation, boron-doped high-resistance single-crystal silicon substrate was prepared. The silicon substrate was placed on a susceptor in the reactor of a reduced-pressure CVD apparatus, and H2 annealing was performed at 1080°C for 1 minute.

[0061] Next, trimethylsilane gas was introduced at a growth temperature of 900°C and a growth pressure of 5 Torr to perform SiC nucleation and grow a 3C-SiC single crystal film. After 60 minutes of growth, a 3C-SiC single crystal film with a thickness of 200 nm was grown.

[0062] Next, GaO2 was grown to a thickness of 1 μm by mist CVD to obtain the semiconductor substrate of the desired first embodiment.

[0063] XRD (X-ray Diffraction) measurement of the GaO2 layer of the obtained semiconductor substrate revealed that it was a high-quality single-crystal GaO2 layer.

[0064] (Example 2) A 300 mm diameter, (111) orientation, boron-doped high-resistance single-crystal silicon substrate was prepared. The silicon substrate was placed on a susceptor in the reactor of a reduced-pressure CVD apparatus, and H2 annealing was performed at 1080°C for 1 minute.

[0065] Next, using trimethylsilane as the source gas, carbon is converted to 4 × 10¹⁶ carbon atoms at 700°C and 10 Torr. 21 atoms / cm 3 A doped Si layer was grown to a wavelength of 500 nm.

[0066] Next, trimethylsilane gas was introduced at a growth temperature of 900°C and a growth pressure of 5 Torr to perform SiC nucleation and grow a 3C-SiC single crystal film. After 60 minutes of growth, a 3C-SiC single crystal film with a thickness of 200 nm was grown.

[0067] Next, GaO2 was grown to a thickness of 1 μm by mist CVD to obtain the semiconductor substrate of the desired second embodiment.

[0068] XRD (X-ray Diffraction) measurement of the GaO2 layer of the obtained semiconductor substrate revealed that it was a high-quality single-crystal GaO2 layer.

[0069] As described above, according to the embodiments of the present invention, it was possible to manufacture a semiconductor substrate in which a high-quality GaO2 layer was formed on a Si substrate. This indicates that the lattice mismatch of the semiconductor substrate was mitigated. Furthermore, it was possible to manufacture a semiconductor substrate in which GaO2 was grown on a large-diameter (300 mm diameter) Si substrate.

[0070] This specification includes the following embodiments: [1]: A semiconductor substrate having a Si substrate with a main surface orientation of (111), a 3C-SiC layer on the Si substrate, and a GaO2 layer on the 3C-SiC layer. [2]: The semiconductor substrate according to [1], wherein the Si substrate has vacancies at the interface between the Si substrate and the 3C-SiC layer. [3]: The semiconductor substrate according to [1] or [2], further comprising a carbon-doped Si layer between the Si substrate and the 3C-SiC layer. [4]: The semiconductor substrate according to [1], [2], or [3], wherein the carbon-doped Si layer has vacancies at the interface between the carbon-doped Si layer and the 3C-SiC layer. [5] A method for manufacturing a semiconductor substrate, comprising the steps of: removing a native oxide film on the surface of a Si substrate having a main surface orientation of (111) by hydrogen baking; forming a 3C-SiC layer on the Si substrate using a source gas containing carbon and silicon; and forming a GaO2 layer on the 3C-SiC layer. [6]: A method for manufacturing a semiconductor substrate according to [5], further comprising the step of forming a carbon-doped Si layer on the Si substrate using a source gas containing carbon and silicon, between the step of removing the native oxide film by hydrogen baking and the step of forming the 3C-SiC layer.

[0071] It should be noted that the present invention is not limited to the embodiments described above. The embodiments described above are illustrative, and any configuration that is substantially identical to the technical idea described in the claims of the present invention and achieves similar effects is included within the technical scope of the present invention. [Explanation of Symbols]

[0072] 1…Semiconductor substrate according to the first embodiment, 2…Single-crystal silicon substrate (Si(111) substrate), 3…Si(111) substrate (with voids), 4…3C-SiC layer, 5…GaO2 layer, 6...Carbon-doped Si layer, 7...Carbon-doped Si layer (with voids), 10…A semiconductor substrate according to the second embodiment.

Claims

1. A Si substrate with a main surface orientation of (111), a 3C-SiC layer on the Si substrate, and GaO on the 3C-SiC layer. ２ A semiconductor substrate characterized by having layers.

2. The semiconductor substrate according to claim 1, characterized in that the Si substrate has vacancies at the interface between the Si substrate and the 3C-SiC layer.

3. The semiconductor substrate according to claim 1 or 2, characterized in that it further has a carbon-doped Si layer between the Si substrate and the 3C-SiC layer.

4. The semiconductor substrate according to claim 3, characterized in that the carbon-doped Si layer has vacancies at the interface between the carbon-doped Si layer and the 3C-SiC layer.

5. A step of removing the native oxide film on the surface of a Si substrate with a main surface orientation of (111) by hydrogen baking, A step of forming a 3C-SiC layer on the Si substrate using a source gas containing carbon and silicon, GaO on the 3C-SiC layer ２ A method for manufacturing a semiconductor substrate, characterized by including a step of forming a layer.

6. The method for manufacturing a semiconductor substrate according to claim 5, further comprising a step of forming a carbon-doped Si layer on the Si substrate using a source gas containing carbon and silicon, between the step of removing the native oxide film by hydrogen baking and the step of forming the 3C-SiC layer.

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