Manufacturing method for SiC semiconductor device and SiCMOSFET

Abstract

This SiC semiconductor element manufacturing method comprises: a step for etching the surface of an SiC substrate 1 using H2 gas, under an Si-excess atmosphere and in a temperature range of 1000°C to 1350°C; a step for depositing an SiO2 film 2 on the SiC substrate 1 using the CVD method and at a temperature at which the SiC substrate 1 is not oxidized; and a step for heat-treating the SiC substrate 1 on which the SiO2 film has been deposited, in an NO gas atmosphere and in a temperature range of 1150°C to 1350°C.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a SiC (silicon carbide) semiconductor device, and to a SiCMOSFET. [Background technology]

[0002] In MOS transistors (SiCMOSFETs) using SiC substrates, when an SiO2 film (gate insulating film) is formed on the surface of the SiC substrate by thermal oxidation, there is a problem that the defect density at the interface between the SiO2 film and the SiC substrate is very high. If the interface defect density is high, it is difficult to obtain sufficient characteristics such as channel mobility of the SiCMOSFET.

[0003] As a method for reducing the interface defect density, Patent Document 1 discloses a method in which, instead of forming an SiO2 film directly on the surface of a SiC substrate by thermal oxidation, a Si thin film is deposited on the surface of the SiC substrate and then the Si thin film is oxidized to form an SiO2 film.

[0004] Furthermore, Non-Patent Document 1 discloses a method (interface nitridation) in which an SiO2 film is formed on the surface of a SiC substrate by thermal oxidation, and then heat treatment is performed in an NO (nitric oxide) gas atmosphere to nitride the interface between the SiO2 film and the SiC substrate.

[0005] However, although these methods can reduce the defect density at the interface between the SiO2 film and the SiC substrate, the interface defect density is still high, significantly limiting the characteristics of SiCMOSFETs.In addition, the method of nitriding the interface between the SiO2 film and the SiC substrate by NO heat treatment not only nitrids the interface but also promotes oxidation, so the interface defect density may not be sufficiently reduced.

[0006] As another method for reducing the interface defect density, Non-Patent Document 2 discloses a method in which the surface of a SiC substrate is etched with high-temperature H2 gas, an SiO2 film is formed on the SiC substrate, and then the SiC substrate with the SiO2 film formed thereon is heat-treated in a high-temperature N2 gas atmosphere. Here, the SiO2 film is formed by depositing a Si thin film on the SiC substrate and then thermally oxidizing this Si thin film at a temperature that does not oxidize the SiC substrate. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 11-067757 [Non-patent literature]

[0008] [Non-Patent Document 1] GY Chung et al., IEEE Electron Device Lett., vol.22, 176(2001) [Non-patent document 2] T. Kobayashi et al., Appl. Phys. Express, vol.13, 091003 (2020) Summary of the Invention [Problem to be solved by the invention]

[0009] According to the method disclosed in Non-Patent Document 2, the defect density at the interface between the SiO2 film and the SiC substrate can be significantly reduced. However, when this method is used to form a gate insulating film made of an SiO2 film on a SiC substrate to form a SiCMOSFET, high channel mobility is obtained, but the threshold voltage is likely to be a negative normally-on characteristic.

[0010] The present invention has been made in view of the above points, and a main object of the present invention is to provide a manufacturing method for a SiC semiconductor element that can realize a SiC MOSFET having high channel mobility and normally-off characteristics. [Means for solving the problem]

[0011] The method for manufacturing a SiC semiconductor device according to the present invention includes the steps of etching the surface of a SiC substrate with H2 gas in a Si-rich atmosphere at a temperature ranging from 1000°C to 1350°C, depositing an SiO2 film on the SiC substrate by a CVD method at a temperature that does not oxidize the SiC substrate, and heat-treating the SiC substrate on which the SiO2 film has been deposited in an NO gas atmosphere at a temperature ranging from 1150°C to 1350°C. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a method for manufacturing a SiC semiconductor device that can realize a SiC MOSFET having high channel mobility and normally-off characteristics. [Brief explanation of the drawings]

[0013] [Figure 1] 1(A) to 1(C) are diagrams illustrating a method for manufacturing a SiC semiconductor device according to one embodiment of the present invention. [Figure 2] 1 is a graph showing the defect density at the interface between an SiO 2 film and an SiC substrate. [Figure 3] FIG. 1 is a cross-sectional view showing the structure of an n-channel MOSFET. [Figure 4] 1 is a graph showing the drain current-gate voltage characteristics of an n-channel MOSFET. [Figure 5] 1 is a graph showing the channel mobility of an n-channel MOSFET. [Figure 6] 1 is a graph showing the nitrogen atom density in an SiO 2 film and at the SiO 2 film / SiC substrate interface. [Figure 7]1 is a graph showing the correlation between the nitrogen atom density in the SiO 2 film and the effective fixed charge density at the SiC substrate / SiO 2 film interface. [Figure 8] 10 is a graph showing the dependency of channel mobility on the temperature of NO heat treatment. [Figure 9] 10 is a graph showing the hydrogen etching temperature dependence of channel mobility. [Figure 10] 1 is a graph showing the dependency of channel mobility on the acceptor density of a p-type epitaxial growth layer. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following embodiment. Furthermore, appropriate modifications are possible within the scope of the effects of the present invention.

[0015] 1(A) to 1(C) are diagrams illustrating a method for manufacturing a SiC semiconductor device according to one embodiment of the present invention.

[0016] As shown in FIG. 1(A), the surface of a SiC substrate 1 is etched with high-temperature H2 gas in a Si-rich atmosphere. During this process, several (1 to 3) ultrathin Si films are formed on the SiC substrate 1. The high-temperature H2 gas etching is performed with the addition of a small amount of SiH4 gas. The high-temperature H2 gas etching can be performed, for example, under the following conditions: H2 flow rate: 5000 sccm, SiH4 flow rate: 0.2 sccm, temperature: 1300°C, pressure: 13 kPa, and time: 15 minutes. The high-temperature H2 gas etching is preferably performed at a temperature range of 1000°C to 1350°C. However, the optimal gas flow rate, pressure, and time depend on the equipment used for this process. Similar effects can be achieved by forming several ultrathin Si films on a SiC substrate using Si-containing gases such as SiH2Cl2 and SiH3Cl instead of SiH4.

[0017] The SiC substrate 1 may be a SiC substrate 1 having a SiC epitaxial layer (not shown) formed thereon. When fabricating a MOSFET on the SiC epitaxial layer, it is preferable to oxidize the surface of the SiC epitaxial layer and then remove the oxide film.

[0018] 1(B), an SiO2 film 2 is deposited on the SiC substrate 1 by plasma CVD. The SiO2 film 2 can be deposited at a temperature that does not oxidize the SiC substrate 1, for example, under the following conditions: TEOS (tetraethoxysilane) flow rate: 0.3 sccm, O2 flow rate: 450 sccm, temperature: 400°C, pressure: 43 Pa, high-frequency power: 100 W, and time: 30 minutes. The SiO2 film 2 is preferably deposited at a temperature in the range of 300°C to 450°C.

[0019] The SiO2 film 2 may be deposited by thermal CVD under the following conditions: SiH4 flow rate: 5 sccm, N2O flow rate: 300 sccm, N2 flow rate: 3000 sccm, temperature: 720°C, pressure: 15 kPa, and time: 4 minutes.

[0020] Next, as shown in FIG. 1(C), the SiC substrate 1 on which the SiO2 film 2 has been deposited is heat-treated in an NO gas atmosphere. The heat treatment may be performed under the following conditions: NO flow rate: 300 sccm, N2 flow rate: 2700 sccm, temperature: 1250°C, pressure: 1 atmosphere, and time: 60 minutes. The heat treatment in the NO gas atmosphere is preferably performed in a temperature range of 1150°C to 1350°C. Here, "NO gas atmosphere" also includes an atmosphere in which NO gas is diluted with a diluent gas such as N2 gas. For example, in this embodiment, the heat treatment is performed in an atmosphere in which NO gas is diluted with N2 gas (NO flow rate: 10%; N2 flow rate: 90%) in order to reduce the amount of toxic NO gas used.

[0021] (Analysis of interface defect density) Using the method shown in Figures 1(A) to (C), a MOS capacitor was fabricated on an SiO2 film 2 deposited on an SiC substrate 1, and the defect density (interface state density) at the interface between the SiO2 film 2 and the SiC substrate 1 was determined by analyzing the CV characteristics (High-Low method). The SiC substrate 1 was an n-type 4H-SiC (0001) substrate, and the donor concentration of the SiC epitaxial growth layer was set to 5 × 10 15 cm -3 The thickness of the SiO2 film 2 was set to about 30 nm.

[0022] For comparison, a sample was also prepared by using the method disclosed in Non-Patent Document 2 to form an SiO2 film 2 on the SiC substrate 1, which had been subjected to high-temperature H2 etching on the surface of the SiC substrate 1, and then heat-treating the SiC substrate 1 in a high-temperature N2 gas atmosphere. Another sample was also prepared by forming an SiO2 film 2 on the surface of the SiC substrate 1 by thermal oxidation, and then heat-treating the SiC substrate 1 in a high-temperature NO gas atmosphere.

[0023] Figure 2 shows the results of this graph, with the horizontal axis representing the conduction band edge (E C ) from the energy (E T ), and the vertical axis represents the interface state density. The graph indicated by A shows the results of a sample in which an SiO2 film 2 was deposited on an SiC substrate 1 by the method shown in Figures 1(A) to 1(C), and then the SiC substrate 1 was heat-treated in a high-temperature NO gas atmosphere. The graph indicated by B shows the results of a sample in which an SiO2 film was formed on an SiC substrate by the method disclosed in Non-Patent Document 2, and then the SiC substrate was heat-treated in a high-temperature N2 gas atmosphere. The graph indicated by C shows the results of a sample in which an SiO2 film was formed on the surface of an SiC substrate by thermal oxidation, and then the SiC substrate was heat-treated in a high-temperature NO gas atmosphere.

[0024] As shown in Figure 2, the interface state density of the samples (graphs A and B) in which the SiC substrate was etched with high-temperature H2 gas in a Si-rich atmosphere as a pretreatment before forming an SiO2 film on the SiC substrate was significantly reduced compared to the sample (graph C) in which high-temperature H2 gas etching was not performed as a pretreatment.

[0025] From these results, it can be seen that many defects remain on the surface of the SiC substrate 1 after the oxide film has been removed after the surface has been sacrificially oxidized. In order to efficiently remove these defects, the surface of the SiC substrate 1 is etched using high-temperature H gas in a Si-excess atmosphere, thereby significantly reducing the interface state density.

[0026] (SiCMOSFET characteristic evaluation) 1(A) to 1(C), an n-channel MOSFET was fabricated on an SiO2 film 2 deposited on an SiC substrate 1, and the transistor characteristics were evaluated. For comparison, a sample was also fabricated by forming an SiO2 film on an SiC substrate using the method disclosed in Non-Patent Document 2, and then heat-treating the SiC substrate in a high-temperature N2 gas atmosphere.

[0027] 3 is a cross-sectional view showing the structure of the fabricated n-channel MOSFET. - A type SiC epitaxial growth layer 10A is formed, and an n-type SiC epitaxial growth layer 10A is formed on the surface of the epitaxial growth layer 10A. + A source region 11 and a drain region 12 of a type are formed on the epitaxial growth layer 10A. A gate insulating film 20 made of an SiO2 film is formed on the surface of the epitaxial growth layer 10A between the source region 11 and the drain region 12. A source electrode 30, a drain electrode 31, and a gate electrode 32 are formed on the source region 11, the drain region 12, and the gate insulating film 20, respectively.

[0028] In addition, p - The acceptor concentration of the SiC epitaxial growth layer 10A is 1×10 15 cm -3 The donor concentration of the source region 11 and the drain region 12 is 8×10 19 cm -3 The thickness of the gate insulating film 20 was set to 30 nm.

[0029] (A) Drain current-gate voltage characteristics 4 is a graph showing the drain current-gate voltage characteristics of the fabricated n-channel MOSFET. Graph A shows the results when a gate insulating film 20 is formed by the method shown in FIGS. 1(A) to 1(C) and then the SiC substrate is heat-treated in a high-temperature NO gas atmosphere. Graph B shows the results when a gate insulating film 20 is formed by the method disclosed in Non-Patent Document 2 and then the SiC substrate is heat-treated in a high-temperature N gas atmosphere.

[0030] As shown in Figure 4, both samples showed high drain currents, but the sample in which the SiC substrate was heat-treated in a high-temperature NO gas atmosphere (graph A) exhibited normally-off characteristics (positive threshold voltage), whereas the sample in which the SiC substrate was heat-treated in a high-temperature N2 gas atmosphere (graph B) exhibited normally-on characteristics (negative threshold voltage).

[0031] (B) Channel mobility 5 is a graph showing the channel mobility of the fabricated n-channel MOSFET. Graph A shows the results when a gate insulating film 20 is formed by the method shown in FIGS. 1A to 1C, and then the SiC substrate is heat-treated in a high-temperature NO gas atmosphere. Graph B shows the results when a gate insulating film 20 is formed by the method disclosed in Non-Patent Document 2, and then the SiC substrate is heat-treated in a high-temperature N gas atmosphere.

[0032] As shown in Figure 5, both samples exhibited high channel mobility, but the sample in which the SiC substrate was heat-treated in a high-temperature NO gas atmosphere (graph A) exhibited normally-off characteristics (positive threshold voltage), while the sample in which the SiC substrate was heat-treated in a high-temperature N2 gas atmosphere (graph B) exhibited normally-on characteristics (negative threshold voltage). Note that graph B shows a decrease in channel mobility at high gate voltages.

[0033] From these results, it has been found that a MOSFET having a high drain current and channel mobility as well as normally-off characteristics can be obtained by etching the SiC substrate 1 with high-temperature H2 gas in a Si-rich atmosphere before depositing the SiO2 film 2 on the SiC substrate 1, and then heat-treating the SiC substrate 1 in a high-temperature NO gas atmosphere after depositing the SiO2 film 2.

[0034] (Nitrogen atom density in the SiO2 film and at the SiO2 film / SiC interface) 6 is a graph showing the results of measuring the nitrogen atom density in the SiO2 film 2 and at the interface between the SiO2 film 2 and the SiC substrate 1 using SIMS (secondary ion mass spectrometry). The horizontal axis indicates the position in the film thickness direction, with zero indicating the interface between the SiO2 film 2 and the SiC substrate 1, the positive side indicating the position within the SiC substrate 1, and the negative side indicating the position within the SiO2 film 2. The vertical axis indicates the nitrogen atom density.

[0035] Graph A shows the results of a sample in which an SiO2 film 2 was deposited on an SiC substrate 1 by the method shown in Figures 1(A) to 1(C), and then the SiC substrate 1 was heat-treated in a high-temperature NO gas atmosphere. Graph B shows the results of a sample in which an SiO2 film 2 was formed on an SiC substrate 1 by the method disclosed in Non-Patent Document 2, and then the SiC substrate 1 was heat-treated in a high-temperature N2 gas atmosphere.

[0036] 6, it can be seen that in both samples, a sufficient density of nitrogen atoms is introduced at the interface between the SiO2 film 2 and the SiC substrate 1. This is thought to have sufficiently reduced the defect density at the interface between the SiO2 film 2 and the SiC substrate 1.

[0037] On the other hand, in the sample (graph A) in which the SiC substrate 1 was heat-treated in a high-temperature NO gas atmosphere, the nitrogen atom density in the SiO2 film 2 is very low, whereas in the sample (graph B) in which the SiC substrate 1 was heat-treated in a high-temperature N2 gas atmosphere, a high density of nitrogen atoms is present in the SiO2 film 2.

[0038] (Correlation between nitrogen atom density in SiO2 film and effective fixed charge density at the interface) Figure 7 is a graph showing the correlation between the nitrogen atom density in the SiO2 film 2 and the effective fixed charge density at the interface between the SiO2 film 2 and the SiC substrate 1. Here, the nitrogen atom density in the SiO2 film 2 indicates the average nitrogen atom density in the SiO2 film 2 in a region 5 to 20 nm from the interface. The effective fixed charge density at the interface was calculated from the voltage shift from the theoretical characteristics in the measured capacitance-voltage characteristics of the MOS capacitor. The square dots in the graph indicate the results for a sample in which the SiC substrate 1 was heat-treated in a high-temperature NO gas atmosphere. The round dots in the graph indicate the results for a sample in which the SiC substrate 1 was heat-treated in a high-temperature N2 gas atmosphere. The numerical values ​​at each point indicate the heat treatment temperature.

[0039] As shown in Figure 7, the sample (circle points) heat-treated in a high-temperature N2 gas atmosphere where the nitrogen atom density in the SiO2 film 2 is high has a high effective fixed charge density at the interface, whereas the sample (square points) heat-treated in a high-temperature NO atmosphere where the nitrogen atom density in the SiO2 film 2 is low has a low effective fixed charge density at the interface.

[0040] From these results, it is considered that when the nitrogen atom density in the SiO2 film 2 is excessively high, nitrogen atoms bond with impurity atoms, generating positive fixed charges in the SiO2 film 2, which causes the MOSFET to have normally-on characteristics, and conversely, when the nitrogen atom density in the SiO2 film 2 is low, positive fixed charges are less likely to be generated in the SiO2 film 2, causing the MOSFET to have normally-off characteristics. Note that the impurity atoms that bond with nitrogen atoms may be, for example, hydrogen introduced in a heat treatment process (hydrogen sintering process) performed in a hydrogen-containing atmosphere in the final stage of MOSFET formation.

[0041] As shown in Figure 7, when the nitrogen atom density in the SiO2 film 2 is low, the effective fixed charge at the interface between the SiO2 film 2 and the SiC substrate 1 may be negative or positive. This is thought to be due to the following reasons.

[0042] The effective fixed charge density at the interface between the SiO2 film 2 and the SiC substrate 1 is expressed as the sum of the positive charge due to impurities and defects in the SiO2 film 2 (near the interface with the SiC substrate 1) and the negative charge due to electrons trapped in the interface states. When the NO treatment temperature is low, the positive charge is low because the nitrogen atom density in the SiO2 film 2 is low, but the interface state density is slightly high, so the negative charge is relatively high. As a result, the effective fixed charge expressed as the difference is negative.

[0043] On the other hand, when the NO treatment temperature is high, the density of nitrogen atoms in the SiO2 film 2 increases, resulting in an increase in positive charges, but the interface state density decreases, resulting in a relatively small amount of negative charges. As a result, the effective fixed charge becomes positive.

[0044] When the effective fixed charge density is negative and has a large value, it means that there are a large number of interface states, which is undesirable as it reduces the current of the SiC semiconductor device. On the other hand, when the effective fixed charge density is positive and has a large value, it means that there is a large amount of nitrogen in the SiO2 film 2, which is undesirable as it is likely to result in normally-on characteristics (negative threshold voltage) due to the influence of this high positive charge density.

[0045] As shown in Figure 7, in order for the MOSFET to have normally-off characteristics, the absolute value of the effective fixed charge density at the interface between the SiO2 film 2 and the SiC substrate 1 must be 4 × 10 11 cm -2 It is preferable that:

[0046] (Dependence of channel mobility on NO heat treatment temperature) 8 is a graph (shown as graph A) showing the results of measuring channel mobility when the temperature at which the SiC substrate 1 is heat-treated in a high-temperature NO gas atmosphere is changed in the range of 1100°C to 1350°C when fabricating an n-channel MOSFET using an SiO2 film 2 deposited on an SiC substrate 1 as the gate insulating film 20 by the method shown in Figures 1(A) to 1(C). Graph B shows the results when etching the SiC substrate 1 with high-temperature H2 gas is not performed in a Si-excess atmosphere, without adding a trace amount of SiH4 gas.

[0047] 8, when etching the SiC substrate 1 with high-temperature H2 gas, the channel mobility is high when the etching is performed in an Si-rich atmosphere (graph A), whereas the channel mobility is low when the etching is not performed in an Si-rich atmosphere (graph B). This is thought to be due to the following reasons.

[0048] That is, etching the SiC substrate 1 with high-temperature H2 gas before forming the SiO2 film 2 on the SiC substrate 1 is expected to reduce the interface defect density between the SiO2 film 2 and the SiC substrate 1. However, when depositing the SiO2 film 2 on the SiC substrate 1 by CVD, the reactive gas contains O2 gas and N2O gas, so the surface of the SiC substrate 1 may be slightly oxidized at the beginning of deposition. However, even in such cases, by performing the etching with high-temperature H2 gas in a Si-rich atmosphere, an ultrathin Si layer of about 1 to 3 layers is formed on the surface of the SiC substrate 1. Therefore, oxidation of this ultrathin Si layer is limited to preventing oxidation of the surface of the SiC substrate 1. This is thought to have significantly reduced the interface defect density between the SiO2 film 2 and the SiC substrate 1, resulting in high channel mobility.

[0049] On the other hand, if etching with high-temperature H2 gas is not performed in a Si-rich atmosphere, even if an SiO2 film is subsequently deposited under conditions considered to be optimal and a high-temperature NO heat treatment is performed, an ultrathin Si film is not formed on the surface of the SiC substrate 1, and the surface of the SiC substrate 1 is oxidized in the early stage of depositing the SiO2 film. As a result, the interface defect density between the SiO2 film 2 and the SiC substrate 1 cannot be sufficiently reduced, resulting in low channel mobility.

[0050] 8, it can be seen that high channel mobility can be obtained by performing the NO heat treatment on the SiC substrate 1 in the temperature range of 1150°C to 1350°C. If the NO heat treatment temperature is too low below 1150°C, nitrogen atoms are not introduced at a sufficient density at the interface between the SiO2 film 2 and the SiC substrate 1, and therefore the interface nitriding process is insufficient, and the effect of reducing the interface defect density is not obtained, which is undesirable. Also, if the NO heat treatment temperature exceeds 1350°C, the oxidation of the SiC substrate by the NO gas progresses, which generates new interface defects, which is undesirable.

[0051] (Dependence of channel mobility on hydrogen etching temperature) FIG. 9 is a graph showing the results of measuring the channel mobility when the temperature for hydrogen etching the SiC substrate 1 in a Si-rich atmosphere before forming the SiO2 film 2 is changed in the range of 900°C to 1400°C when fabricating an n-channel MOSFET using an SiO2 film 2 deposited on an SiC substrate 1 as the gate insulating film 20 by the method shown in FIGS. 1(A) to 1(C).

[0052] 9, it can be seen that high channel mobility can be obtained by performing hydrogen etching of the SiC substrate 1 in the temperature range of 1000°C to 1350°C. If the hydrogen etching temperature is too low below 1000°C, the surface of the SiC substrate 1 cannot be sufficiently cleaned, and the effect of reducing the interface defect density cannot be obtained, which is undesirable. On the other hand, if the hydrogen etching temperature exceeds 1400°C, which is close to the melting point of Si (1420°C), it becomes difficult to form an ultrathin Si film on the surface of the SiC substrate 1, and the effect of reducing the interface defect density cannot be obtained, which is undesirable.

[0053] As described above, the method for manufacturing a SiC semiconductor device in this embodiment includes the steps of etching the surface of the SiC substrate 1 with H2 gas in a Si-excess atmosphere at a temperature in the range of 1000°C to 1350°C, depositing the SiO2 film 2 on the SiC substrate 1 by a CVD method at a temperature that does not oxidize the SiC substrate 1, and heat-treating the SiC substrate 1 on which the SiO2 film 2 has been formed in a NO gas atmosphere at a temperature in the range of 1150°C to 1350°C. This significantly reduces the defect density at the interface between the SiO2 film 2 and the SiC substrate 1, and when a SiC MOSFET is fabricated using this SiO2 film as the gate insulating film 20, it exhibits high channel mobility and normal off It is possible to realize a SiC MOSFET having the above characteristics.

[0054] In the above embodiment, an example of a MOSFET fabricated on the 4H—SiC (0001) plane has been described. However, it is generally known that when a SiC MOSFET is fabricated on a non-basal plane such as the (11-20) plane or the (1-100) plane, better characteristics can be obtained than when fabricated on the (0001) plane.

[0055] In fact, when a MOSFET was fabricated by forming a gate insulating film 20 by the method shown in FIGS. 1(A) to 1(C) and then heat-treating the SiC substrate in an NO gas atmosphere at 1250°C, the MOSFET fabricated on the (11-20) plane exhibited a channel mobility of 164 cm 2 / Vs, threshold voltage 1.21V, and channel mobility 158cm for MOSFETs fabricated on the (1-100) plane. 2 / Vs and a threshold voltage of 1.28V. Thus, the present invention is effective on many crystal planes of SiC substrates used in practical applications. The acceptor density of the p-type SiC epitaxial growth layer 10A in the MOSFET fabricated here was 1×10 16 cm -3 It was decided.

[0056] In addition, it is known that in SiC power MOSFETs, trench-type MOSFETs, in which the MOS channel is formed on the trench sidewall, are advantageous for achieving extremely low on-resistance. In this case, since the SiC substrate surface is the (0001) plane, the MOS channel must be formed on the sidewall surface, which is the (11-20) plane (A-plane) or the (1-100) plane (M-plane). In addition, in actual SiC power MOSFETs, the acceptor density of the p-type epitaxial growth layer is 10 17 ~10 18 cm -3 A relatively high value of the degree is used.

[0057] Therefore, in order to verify whether the present invention is also effective for trench-type SiC power MOSFETs, we used SiC substrates with surfaces of (11-20) and (1-100) planes, and increased the acceptor density of the p-type epitaxial growth layer to 10 17 ~10 18 cm -3 MOSFETs with the structure shown in Figure 3 were fabricated by changing the orientation within the range of (11-20) and (1-100) planes, and the channel mobility was measured. As a comparative example, MOSFETs were fabricated by forming a gate insulating film (SiO2 film) 20 on the SiC substrate 1 by thermal oxidation, and then heat-treating the SiC substrate 1 in a high-temperature NO gas atmosphere. Here, the thickness of the gate insulating film was set to 30 nm.

[0058] FIG. 10 is a graph showing the results, with the vertical axis representing the channel mobility and the horizontal axis representing the acceptor density of the p-type epitaxial growth layer (p-type region).

[0059] As shown in the graph of A1, in the MOSFET formed on the (11-20) plane, the acceptor density is 10 17 ~10 18 cm -3 In the range of about 130 cm 2 As shown in graph A2, even in the MOSFET formed on the (1-100) plane, the acceptor density was 10 17 ~10 18 cm-3 In the range of 80-110cm 2 In both MOSFETs, the higher the acceptor density of the p-type epitaxial growth layer, the larger the difference in channel mobility became compared to the MOSFETs formed by the conventional method shown in B1 and B2, reaching 1×10 18 cm -3 At this acceptor density, we achieved extremely high channel mobilities, 6 to 80 times higher than those achieved by conventional methods.

[0060] Furthermore, according to the present invention, excellent MOS interface characteristics can be obtained, and therefore the present invention is also effective in fabricating other SiC devices that use a MOS interface, such as insulated gate bipolar transistors (IGBTs).

[0061] While the present invention has been described above using preferred embodiments, these descriptions are not limiting and various modifications are possible. For example, in the above embodiment, a SiC epitaxial layer is formed on the surface of a SiC substrate, and a SiO2 film is formed on the SiC epitaxial layer. However, a SiO2 film may be formed directly on the SiC substrate.

[0062] In addition, in the above embodiment, a SiC substrate was used in which the oxide film was removed after the surface was sacrificially oxidized, but the manufacturing method of the present invention can also be applied to a SiC substrate that has not been subjected to sacrificial oxidation.

[0063] In the above embodiment, the SiO2 film 2 is deposited on the SiC substrate 1 by CVD. Alternatively, a thin Si film may be deposited by CVD and then thermally oxidized at a temperature that does not oxidize the SiC substrate 1 to form the SiO2 film. In this case, since the thin Si film is formed on the surface of the SiC substrate 1 before the SiO2 film 2 is formed, the high-temperature H2 etching of the SiC substrate 1 performed as a pretreatment does not need to be performed in a Si-excessive atmosphere. The high-temperature H2 etching of the SiC substrate 1 is preferably performed in a temperature range of 1200°C to 1350°C. [Explanation of symbols]

[0064] 1. SiC substrate 2 SiO2 film 10 p-type SiC substrate 10A p - Type SiC epitaxial growth layer 11 Source Area 12 Drain region 20 Gate insulating film 30 Source electrode 31 Drain electrode 32 gate electrode

Claims

1. The surface of the SiC substrate is annealed in a Si-rich atmosphere at a temperature range of 1000°C to 1350°C using H ２ A step (A) of etching with a gas; SiO is deposited on the SiC substrate by a CVD method at a temperature that does not oxidize the SiC substrate. ２ (B) depositing a film; The SiO ２ Step (C) of heat-treating the SiC substrate on which the film has been deposited in an NO gas atmosphere at a temperature range of 1150°C to 1350°C; A method for manufacturing a SiC semiconductor element, comprising:

2. 2. The method for manufacturing a SiC semiconductor device according to claim 1, wherein in the step (A), one to three Si layers are formed on the surface of the SiC substrate.

3. The step (A) is H ２ Gas containing SiH ４ The method for manufacturing a SiC semiconductor device according to claim 1 , wherein the method is carried out in an atmosphere to which a gas or a gas containing Si atoms is added.

4. 2. The method for manufacturing a SiC semiconductor device according to claim 1, further comprising, before step (A), the step of sacrificially oxidizing the SiC substrate and then etching away an oxide film formed on the surface of the SiC substrate.

5. The method for manufacturing a SiC semiconductor device according to claim 1 , wherein the SiC substrate includes a SiC substrate having a SiC epitaxial layer formed on a surface thereof.

6. The SiO ２ The absolute value of the effective fixed charge density at the interface between the film and the SiC substrate is 4×10 １１ cm －２ The method for manufacturing a SiC semiconductor device according to claim 1 , wherein:

Images