Method for manufacturing a laminate containing nitrogen at the SiO2 / SiC interface, the laminate, and a metal oxide film semiconductor field-effect transistor element.

Abstract

This invention provides a method for manufacturing a laminate that introduces nitrogen into the SiO2 / SiC interface at a lower temperature than conventional technologies, a standard apparatus, and a MOSFET element. [Solution] A method for manufacturing a laminate having an SiO2 layer on a SiC layer and containing nitrogen at the SiO2 / SiC interface, comprising the step of heat-treating a substrate made of SiC in a mixed gas, wherein the mixed gas is a mixture of NO and N2 containing 200 ppm to 20000 ppm of O2, and the heat treatment temperature is 900°C to 1200°C.

Description

[Technical Field]

[0001] This disclosure relates to a method for manufacturing a laminate containing nitrogen in the SiO2 / SiC interface, a laminate having a specific SiO2 / SiC interface structure, and a metal oxide semiconductor field-effect transistor element having a specific nitrogen concentration at the interface between a field oxide film and a SiC semiconductor. [Background technology]

[0002] To address global challenges such as the depletion of fossil fuels and global warming, highly efficient use of electricity, the most readily available energy source, is essential. Therefore, improving the performance of power devices that convert and control electricity is crucial. In recent years, silicon carbide (SiC) semiconductor devices, which can reduce energy loss compared to conventional silicon (Si), have attracted significant attention. SiC has a wider bandgap and higher dielectric breakdown field strength than Si, enabling higher efficiency and higher voltage resistance in power devices.

[0003] SiC MOS (Metal-Oxide-Semiconductor) transistors, key components of inverters for low power consumption, consist of three terminals: gate, source, and drain. The gate plays a role in controlling the flow of current by providing a channel through which current flows between the source and drain. An insulator such as SiO2 is placed at the gate, with metal placed on top of it. When a voltage is applied to the gate, electrons or holes accumulate beneath the insulator between the gate and source, forming a channel through which current flows between the source and drain. The formation of this channel makes it possible to control the current between the source and drain by the gate voltage (Figure 1).

[0004] SiC MOS transistors are already installed in some railway vehicles and electric vehicles, and are expected to become even more widespread in the future. However, current SiC MOS transistors are not performing to their full potential (performance predicted from the physical properties of SiC). For example, in a 1.2kV class SiC MOS transistor, the channel resistance accounts for nearly half of the conduction resistance (on-resistance). One reason why current SiC MOS transistors are not performing to their full potential is the interface state density (D) of the SiO2 / SiC interface. it ) is D at the SiO2 / Si interface it The channel mobility is thought to be reduced because it is one to four orders of magnitude higher (i.e., high-density interface defects are present). In other words, the channels that conduct / block current are located near the interface with SiO2 within SiC, and it is thought that conduction is hindered because electrons or holes are trapped and scattered by high-density interface defects present at the SiO2 / SiC interface.

[0005] D at the SiO2 / SiC interface it To reduce (i.e., improve the quality of the SiO2 / SiC interface), commercially available SiC MOS transistors are typically manufactured by first forming an SiO2 film on the surface of a SiC substrate, and then introducing nitrogen into the SiO2 / SiC interface. Generally, the SiO2 film is formed by thermal oxidation in an oxygen atmosphere or deposition by chemical vapor deposition. The introduction of nitrogen into the SiO2 / SiC interface is generally carried out by heat-treating the substrate in a nitric oxide (NO) or nitrous oxide (N2O) atmosphere. [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Jia, Y., Lv, H., Tang, X. et al.Influence of various NO annealing conditions on N-type and P-type 4H-SiC MOS capacitors. J Mater Sci: Mater Electron 30, 10302-10310 (2019). https: / / doi.org / 10.1007 / s10854-019-01368-z [Non-Patent Document 2] Haasmann, Daniel, et al. “Dipole Type Behavior of NO Grown Oxides on 4H-SiC.” Materials Science Forum, vol. 858, Trans Tech Publications, Ltd., 24 May 2016, pp. 453-456. doi:10.4028 / www.scientific.net / msf.858.453. [Non-Patent Document 3] N. Yasuda, H. Ota, T. Horikawa, T. Nabatame, H. Satake, A. Toriumi, Y. Tamura, T. Sasaki, F. Ootsuka. Reliable Extractions of EOT and Vfb in Poly-Si Gate High-k MISFETs through Advanced Modeling of Gate and Substrate Capacitances. Extended Abstracts of the 2005 International Conference on Solid State Devices and Materials, Kobe, 2005, pp.250-251. [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] Heat treatment for introducing nitrogen into the SiO2 / SiC interface is typically performed at a high temperature of around 1250°C. Non-patent document 2 also describes heat treatment of a SiC substrate in 100% NO at 1250°C for 20 hours.

[0008] On the other hand, the heat resistance temperature of quartz, which is commonly used in silicon (Si) semiconductor device manufacturing equipment, is lower than 1250°C. Therefore, conventionally, it was not possible to introduce nitrogen into the SiO2 / SiC interface using widely available Si semiconductor device manufacturing equipment. Heating SiC required expensive equipment made from materials with higher heat resistance than quartz. Furthermore, the energy required to create a high-temperature environment of approximately 1250°C was enormous. In other words, conventional nitrogen introduction into the SiO2 / SiC interface required heat treatment at a high temperature of approximately 1250°C, necessitating expensive manufacturing equipment with high heat resistance, as well as enormous energy. Consequently, the manufacturing of SiC semiconductor devices was significantly more expensive than that of Si semiconductor devices.

[0009] In view of the above circumstances, the present inventor's main objective was to provide a technology that can introduce nitrogen into the SiO2 / SiC interface at a lower temperature than the conventional technology. [Means for solving the problem]

[0010] The inventors discovered the possibility of introducing nitrogen into the SiO2 / SiC interface at a lower temperature than conventional techniques by heat-treating a SiC substrate in a mixed gas atmosphere of NO and N2 containing 200 ppm to 20,000 ppm of O2. Further improvements led to the completion of this disclosure.

[0011] This disclosure includes, for example, the following subjects: Section 1. A method for manufacturing a laminate having an SiO2 layer on a SiC layer and containing nitrogen at the SiO2 / SiC interface, The process includes heat treatment of a substrate made of SiC in a mixed gas, The mixed gas is a mixed gas of NO and N2 containing 200 ppm to 20,000 ppm of O2, A method for manufacturing a laminate, characterized in that the heat treatment temperature is 900 °C to 1200 °C. Item 2. The manufacturing method according to item 1, characterized in that the substrate to be treated substantially does not have a SiO2 layer before performing the heat treatment step. Item 3. The nitrogen concentration at the SiO2 / SiC interface of the laminate is 3×10 20 atoms / cm 3 or more, and the manufacturing method according to item 1 or 2. Item 4. In the SiO2 layer of the laminate, the nitrogen concentration at a portion 15 nm away from the SiO2 / SiC interface is 5.5×10 18 atoms / cm 3 or less, and the manufacturing method according to any one of items 1 to 3. Item 5. The manufacturing method according to any one of items 1 to 4, characterized in that the volume of NO in the entire mixed gas is 5 to 20%. Item 6. The manufacturing method according to any one of items 1 to 5, including a step of further depositing SiO2 on the SiO2 layer generated by the heat treatment step after the heat treatment step. Item 7. A laminate having a SiO2 layer on a SiC layer and containing nitrogen at the SiO2 / SiC interface portion, wherein the nitrogen concentration at the SiO2 / SiC interface is 3×10 20 atoms / cm 3 or more, and in the SiO2 layer, the nitrogen concentration at a portion 15 nm away from the SiO2 / SiC interface is 5.5×10 18 atoms / cm 3 or less. Item 8. A metal oxide semiconductor field effect transistor (MOSFET) device, characterized in that the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor is 1 / 2 or less of the nitrogen concentration at the interface between the gate oxide film and the SiC semiconductor. [Effects of the Invention]

[0012] According to this disclosure, nitrogen can be introduced to the SiO2 / SiC interface at a lower temperature than in conventional techniques during the manufacturing of SiC semiconductor devices. This makes it possible to manufacture SiC semiconductor devices using less expensive and more widely available Si semiconductor device manufacturing equipment. Furthermore, the energy costs required for heat treatment can be significantly reduced.

[0013] Furthermore, the SiO2 / SiC interface obtained by the technology of this disclosure may have excellent interfacial properties. Therefore, according to this disclosure, high-performance SiC semiconductor devices can be provided. [Brief explanation of the drawing]

[0014] [Figure 1] A simplified schematic diagram of a SiC MOS transistor is shown. In the diagram, the arrow pointing from the source electrode to the drain electrode indicates the channel. [Figure 2] This graph, from Jia et al., 2019 (Non-Patent Literature 1), shows the relationship between the distance from the SiO2 / SiC interface and the nitrogen concentration when nitrogen is introduced at different temperatures. The vertical axis (left) shows the nitrogen concentration (atoms / cm3), and the horizontal axis shows the distance from the SiO2 / SiC interface (nm). On the horizontal axis, a negative value indicates that the distance is on the SiO2 layer side of the interface, and a positive value indicates that the distance is on the SiC layer side of the interface. [Figure 3]An outline of a process for obtaining a laminate using conventional technology and an example of a process for obtaining a laminate using the technology of this disclosure are shown. In Conventional Technology 1 shown in the figure, an SiO2 layer is formed on SiC by thermal oxidation, and then nitrogen is introduced to the SiO2 / SiC interface by heat treatment at approximately 1250°C in an NO atmosphere. In Conventional Technology 2 shown in the figure, an SiO2 layer is formed on SiC by chemical vapor deposition, and then nitrogen is introduced to the SiO2 / SiC interface by heat treatment at approximately 1250°C in an NO atmosphere. On the other hand, in the technology of this disclosure, it is presumed that the heat treatment process in a mixed gas containing NO causes both a reaction in which the surface of SiC is oxidized and an SiO2 film is formed (i.e., a laminated structure having an SiO2 layer on a SiC layer is formed), and a reaction in which nitrogen is introduced to the SiO2 / SiC interface created by the oxidation reaction. In the technology of this disclosure, after the heat treatment process, SiO2 may be further deposited on the SiO2 layer by chemical vapor deposition or the like, as is optional. In the figure, nitrogen atoms introduced to the SiO2 / SiC interface are shown as circles. [Figure 4] This is a diagram illustrating the nitrogen distribution near the SiO2 / SiC interface in a laminate obtained by a conventional technique and a laminate obtained by the technique of this disclosure. In the diagram, nitrogen atoms introduced at the SiO2 / SiC interface are indicated by circles. [Figure 5] A schematic diagram of the SiC-MOS capacitor fabricated in the test example is shown. [Figure 6] The CV curve measured for a SiC-MOS capacitor fabricated using a sample heat-treated at 1100°C for 3 hours in Test Example 1.1 is shown. In the figure, the measured values ​​are plotted as circles, and the ideal value (value when there are no interface defects) is shown as a solid line. [Figure 7] The CV curve measured for a SiC-MOS capacitor fabricated using a sample heat-treated at 1150°C for 1 hour in Test Example 1.1 is shown. In the figure, the measured values ​​are plotted as circles, and the ideal value (value when there are no interface defects) is shown as a solid line. [Figure 8]The CV curves measured for SiC-MOS capacitors fabricated in Test Example 1.2. are shown, which were prepared using samples heat-treated at 1100°C for 1 hour in a 10% NO / N2 mixed gas containing oxygen at concentrations of 393-442 ppm (400 ppm), 970-1060 ppm (0.1%), or 1800-2070 ppm (0.2%). In the figure, the curves for 0.1% oxygen concentration and 0.2% oxygen concentration almost overlap. [Figure 9] The following shows an outline of the preparation process for each sample described in Test Example 1.3. In the figure, nitrogen atoms introduced at the SiO2 / SiC interface are indicated by circles. [Figure 10] Left figure: Shows the CV curve measured in Test Example 1.3. i), ii), and iii) shown in the figure correspond to i), ii), and iii) in Figure 9 (and so on). Right figure: Shows the interface state density (Dit) measured in Test Example 1.3. [Figure 11] The CV curve measured in Test Example 1.4 is shown. The conditions for the NO oxynitriding process and the thickness of the SiO2 film are shown on the right side of the graph. [Figure 12] The CV curves (left) and interface state density (Dit) (right) measured for SiC-MOS capacitors fabricated by NO oxynitriding under conditions i), ii), iii), v), vi), and viiii) are shown. [Figure 13] In Test Example 1.6, the N1s spectra measured by X-ray photoelectron spectroscopy using substrates obtained by heat treatment at 900°C, 950°C, 1000°C, or 1050°C for 1 hour are shown. [Figure 14] In Test Example 1.7, the nitrogen concentration at the SiO2 / SiC interface was measured by secondary ion mass spectrometry using substrates heat-treated at 1000°C (NO-ox@1000°C) and substrates heat-treated at 1100°C (NO-ox@1100°C). [Figure 15] The CV curve measured for a SiC-MOS capacitor fabricated using a sample heat-treated at 1300°C for 2 minutes in a CO2 atmosphere is shown in the reference example. In the figure, the measured values ​​are plotted as circles, and the ideal value (value when there are no interface defects) is shown as a solid line. [Figure 16]The CV curve for a SiC-MOS capacitor fabricated using a sample heat-treated at 1300°C for 30 minutes in a CO2 atmosphere is shown in the reference example. In the figure, the measured values ​​are plotted as circles, and the ideal value (value when there are no interface defects) is shown as a solid line. [Figure 17] The following shows the electrical characteristics of a SiC-MOS capacitor fabricated using a sample heat-treated at 1300°C for 5 minutes or 15 minutes in a CO2 atmosphere, or for 2 minutes in an O2 (0.1 atm) atmosphere, as shown in the reference example. Left figure: CV curve. Right figure: Interface state density (Dit) measured by the conductance method. [Figure 18] This diagram shows a schematic representation of the process of introducing nitrogen atoms into the SiO2 / SiC interface of a MOSFET element using conventional technology. In the diagram, downward arrows indicate the introduction of nitrogen atoms. The nitrogen atoms introduced into the SiO2 / SiC interface are indicated by circles. [Figure 19] This diagram shows a schematic representation of the process for introducing nitrogen atoms into the SiO2 / SiC interface of a MOSFET device using the technology disclosed herein. In the diagram, downward arrows indicate the introduction of nitrogen atoms. Nitrogen atoms introduced into the SiO2 / SiC interface are indicated by circles. [Figure 20] A schematic diagram of the cross-sectional structure of a DMOSFET, an example of a MOSFET element, is shown. In the diagram, * indicates the field oxide film. Note that nitrogen atoms introduced at the interface are not shown in this diagram. [Modes for carrying out the invention]

[0015] The embodiments included in this disclosure will be described in more detail below. This disclosure preferably includes, but is not limited to, a method for manufacturing a laminate containing nitrogen at the SiO2 / SiC interface, a laminate having a specific SiO2 / SiC interface structure, and a MOSFET element having a specific nitrogen concentration at the interface between the field oxide film and the SiC semiconductor. This disclosure includes everything disclosed herein and recognizable to those skilled in the art.

[0016] A method for manufacturing a laminate as encompassed in this disclosure is a method for manufacturing a laminate having an SiO2 layer on a SiC layer and containing nitrogen at the SiO2 / SiC interface, and is characterized by comprising a step of heat-treating a substrate made of SiC in a mixed gas, wherein the mixed gas is a mixed gas of NO and N2 containing 200 ppm to 20000 ppm of O2, and the heat treatment temperature is 900°C to 1200°C. Hereinafter, the manufacturing method as encompassed in this disclosure may be referred to as the "manufacturing method of this disclosure".

[0017] I. Substrate to be treated using SiC as the material SiC crystals exist in a variety of crystalline polymorphisms, including hexagonal 2H-SiC, cubic 3C-SiC, hexagonal 4H-SiC, hexagonal 6H-SiC, hexagonal 8H-SiC, hexagonal 10H-SiC, and rhombohedral 15R-SiC. In the technology of this disclosure, the crystalline polymorphism of the SiC constituting the substrate to be treated is not particularly limited. That is, in the technology of this disclosure, a substrate to be treated made of SiC of any crystalline polymorphism can be used. Although not particularly limited, it is preferable to use a substrate to be treated made of at least one selected from the group consisting of 3C-SiC, 4H-SiC, and 6H-SiC, and it is particularly preferable to use a substrate to be treated made of 4H-SiC.

[0018] More specifically, in a preferred embodiment of the present disclosure, the substrate to be treated, made of SiC, is, for example, a substrate to be treated obtained by growing an epitaxial layer on a 4H-SiC(0001) substrate (off-angle 0 to 8°, preferably off-angle 4°).

[0019] While not particularly limited, in the technology of this disclosure, it is preferable that the substrate to be treated, which is made of SiC, be cleaned before being subjected to the heat treatment step described later. This cleaning step can remove oxide films and the like from the surface of the substrate. The specific method of the cleaning step is not particularly limited, and methods known in the art or methods that can be easily conceived from methods known in the art can be used. Specifically, for example, the cleaning step can be performed by washing the substrate to be treated with a mixed solution of sulfuric acid and hydrogen peroxide (H2SO4 + H2O2), rinsing with ultrapure water, washing with about 10% dilute hydrofluoric acid (HF), rinsing again with ultrapure water, and then drying. Alternatively, the cleaning step may be performed by heat treating the substrate in a hydrogen atmosphere.

[0020] In the technology disclosed herein, it is preferable that the substrate to be treated, made of SiC, substantially does not have an SiO2 layer before being subjected to the heat treatment process described later. Although not particularly limited, for example, the SiO2 layer that the substrate to be treated before heat treatment may have can be removed by performing the cleaning process described above. Alternatively, the SiO2 layer that the substrate to be treated before heat treatment may have can be removed by polishing. Note that "substantially does not have an SiO2 layer" does not exclude embodiments in which an unavoidable SiO2 layer may be present (for example, a trace amount of SiO2 that may be generated by spontaneous oxidation between the cleaning process and the heat treatment process).

[0021] II. Heat Treatment Process As described above, the SiC substrate is heat-treated at a temperature of 900°C to 1200°C in a mixed gas of NO and N2 containing 200 ppm to 20000 ppm of O2. In this disclosure, this heat treatment process in the mixed gas may be referred to as "NO oxynitriding". The upper or lower limits of the O2 concentration in the mixed gas are 200, 250, 300, 350, 400, 450, 500, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2100, 2200, 2300, 2400, 2500, and 30000 ppm. The concentrations may be 0, 3500, 4000, 4500, 5000, 5500, 6000, 6500, 7000, 7500, 8000, 8500, 9000, 9500, 10000, 10500, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, or 20000 ppm. While not particularly limited, the concentration of O2 in the mixed gas is preferably 300 ppm to 11000 ppm, more preferably 350 ppm to 10000 ppm, even more preferably 400 ppm to 6000 ppm, particularly preferably 400 ppm to 4000 ppm, and most preferably 400 ppm to 3000 ppm. In this disclosure, the concentration of a gas is expressed as a value based on the volume of the gas mixture (i.e., volume of the gas / volume of the gas mixture).

[0022] The specific concentration of NO in the mixed gas is not particularly limited as long as the desired effect is obtained. Note that as the concentration of NO increases, the amount of O2 produced by the decomposition of NO tends to increase as well; therefore, the concentration of NO can be selected so that the amount of O2 in the mixed gas is within the desired range. The specific concentration of NO in the mixed gas is not particularly limited, but for example, it may be 1-50%, preferably 2-40%, more preferably 3-30%, even more preferably 5-20%, particularly preferably 5-15%, and most preferably 10%. Note that in the context of gas concentrations, "%" represents "v / v%" unless otherwise specified.

[0023] The specific concentration of N2 in the mixed gas is not particularly limited as long as the desired effect is obtained. For example, the mixed gas can be prepared by selecting the concentrations of O2 and NO that give the desired effect, and making the remainder N2. The specific concentration of N2 in the mixed gas is not particularly limited, but may be, for example, 50-99%, preferably 60-98%, more preferably 70-97%, even more preferably 80-95%, particularly preferably 85-95%, and most preferably 90%.

[0024] While not particularly limited, it is preferable that the mixed gas in the art of this disclosure substantially contains no gases other than O2, NO, and N2. Here, "substantially containing no gases other than O2, NO, and N2" means that no gases other than O2, NO, and N2 are intentionally included when preparing the mixed gas. In other words, "substantially containing no gases other than O2, NO, and N2" does not exclude the possibility that the mixed gas may contain trace amounts of gases that are inevitably present in it (e.g., water vapor).

[0025] One embodiment of the mixed gas used in the technology of this disclosure is a mixed gas containing 200 ppm to 20,000 ppm of O2, 1 to 50% of NO, and N2, and substantially free of gases other than O2, NO, and N2. A preferred embodiment of the mixed gas used in the technology of this disclosure is a mixed gas containing 200 ppm to 11,000 ppm of O2, 2 to 40% of NO, and N2, and substantially free of gases other than O2, NO, and N2. A more preferred embodiment of the mixed gas used in the technology of this disclosure is a mixed gas containing 300 ppm to 10,500 ppm of O2, 3 to 30% of NO, and N2, and substantially free of gases other than O2, NO, and N2. A more preferred embodiment of the mixed gas used in the art of this disclosure is a mixed gas containing 350 ppm to 10,000 ppm of O2, 5 to 20% of NO, and N2, and substantially free of gases other than O2, NO, and N2. A particularly preferred embodiment of the mixed gas used in the art of this disclosure is a mixed gas containing 400 ppm to 6,000 ppm of O2, 5 to 15% of NO, and N2, and substantially free of gases other than O2, NO, and N2. A most preferred embodiment of the mixed gas used in the art of this disclosure is a mixed gas containing 400 ppm to 4,000 ppm of O2, 10% of NO, and N2, and substantially free of gases other than O2, NO, and N2.

[0026] The heat treatment in the above mixed gas is carried out at a temperature of 900°C to 1200°C. Although not particularly limited, the temperature of the heat treatment may be 950°C to 1200°C, 1000°C to 1200°C, preferably 1020 to 1180°C, more preferably 1050 to 1180°C, even more preferably 1080 to 1180°C, and particularly preferably 1100 to 1150°C. The upper or lower limit of the range may be 900, 910, 920, 930, 940, 950, 960, 970, 980, 990, 1000, 1010, 1020, 1030, 1040, 1050, 1060, 1070, 1080, 1090, 1100, 1110, 1120, 1130, 1140, 1150, 1160, 1170, 1180, 1190, or 1200°C.

[0027] As mentioned above, in conventional technology, the heat treatment for introducing nitrogen into the SiO2 / SiC interface is performed at a high temperature of approximately 1250°C. Since the heat resistance temperature of quartz, which is commonly used in widely available Si semiconductor device manufacturing equipment, is lower than 1250°C, heat treatment of SiC required the use of expensive equipment made of materials with higher heat resistance than quartz. Furthermore, the energy required to create a high-temperature environment of approximately 1250°C was enormous. On the other hand, according to the technology disclosed herein, nitrogen can be introduced into the SiO2 / SiC interface with heat treatment at 900°C to 1200°C, thereby significantly reducing the manufacturing cost of SiC semiconductor devices in terms of both equipment and energy.

[0028] The heat treatment time is not particularly limited as long as the desired effect is obtained. For example, it may be 5 minutes to 10 hours, 10 minutes to 8 hours, preferably 30 minutes to 5 hours, more preferably 45 minutes to 4 hours, and particularly preferably 1 hour to 3 hours. The heat treatment time can be appropriately adjusted depending on the composition of the mixed gas and the heat treatment temperature. Generally, it is presumed that the higher the heat treatment temperature and the longer the heat treatment time, the thicker the SiO2 film will be, as described later.

[0029] III. Laminates The laminate obtained by the technology of this disclosure has an SiO2 layer on a SiC layer and contains nitrogen at the SiO2 / SiC interface. In this disclosure, the term "SiO2 / SiC interface" refers to the region near the SiO2 / SiC interface, including the interface itself. More specifically, in this disclosure, "SiO2 / SiC interface" refers to the region within 15 nm of the SiO2 / SiC interface. Furthermore, in this disclosure, "SiO2 / SiC interface" is defined as the surface where the carbon (C) signal intensity is half that of SiC in the profile obtained by secondary ion mass spectrometry (SIMS).

[0030] In the technology of this disclosure, it is presumed that the process of heat-treating a substrate made of SiC in a mixed gas causes both a reaction in which the surface of SiC is oxidized and an SiO2 film is formed (i.e., a laminated structure having an SiO2 layer on a SiC layer is formed), and a reaction in which nitrogen is introduced into the SiO2 / SiC interface formed by the oxidation reaction. Although not particularly limited, in the technology of this disclosure, it is preferable that the SiO2 layer is formed on the (0001) plane of the SiC layer.

[0031] According to the technology of this disclosure, a laminate can be obtained in which the nitrogen concentration at the SiO2 / SiC interface is relatively high, and the nitrogen concentration in the portion away from the SiO2 / SiC interface is relatively low. Specifically, the laminate obtained by the technology of this disclosure has, for example, a nitrogen concentration of 3 × 10⁻¹⁶ at the SiO2 / SiC interface. 20 atoms / cm 3 The above, or 3.5 × 10 20 atoms / cm 3 It may be more than 4 × 10 20 atoms / cm 3 The above, or 4.5 × 10 20 atoms / cm 3 It is preferable that the above is true, 5 × 10 20 atoms / cm 3 The above is 5.5 × 10 20 atoms / cm 3 The above 6 x 10 20 atoms / cm 3 The above, or 6.5 × 10 20 atoms / cm 3 More preferably, the above is true, 7 × 10 20 atoms / cm 3 The above is 7.5 x 10 20 atoms / cm 3 The above 8 x 10 20 atoms / cm 3 The above, or 8.5 × 10 20 atoms / cm 3 It is even more preferable that the above be the case, 9 × 10 20 atoms / cm 3 The above is 9.5 x 10 20 atoms / cm 3The above, or 1 x 10 21 atoms / cm 3 The above is particularly preferable. The higher the nitrogen concentration at the SiO2 / SiC interface, the higher the interface state density (D it It is predicted that the ) will decrease (i.e., the interface quality will improve). In this disclosure, the nitrogen concentration in the laminate refers to the value measured by secondary ion mass spectrometry (SIMS).

[0032] There is no particular upper limit to the nitrogen concentration at the SiO2 / SiC interface, for example, 1 × 10⁻⁶ 23 atoms / cm 3 The following is also acceptable: 5 × 10 22 atoms / cm 3 The following is also acceptable: 2 × 10 22 atoms / cm 3 The following is also acceptable: 1 × 10 22 atoms / cm 3 The following is also acceptable: 5 × 10 21 atoms / cm 3 The following is also acceptable: 2 × 10 21 atoms / cm 3 The following is also acceptable.

[0033] The nitrogen concentration at the SiO2 / SiC interface of the laminate obtained by the technology of this disclosure is, for example, 3 × 10⁻¹⁴. 20 ~1 × 10 23 atoms / cm 3 , or 3.5 × 10 20 ~1 × 10 23 atoms / cm 3 It may also be 4 x 10 20 ~5×10 22 atoms / cm 3 , or 4.5 × 10 20 ~5×10 22 atoms / cm 3 Preferably, 5 × 10 20 ~5×10 22 atoms / cm 3 , 5.5×10 20 ~5×1022 atoms / cm 3 、6×10 20 ~2×10 22 atoms / cm 3 、 or 6.5×10 20 ~2×10 22 atoms / cm 3 is more preferable, 7×10 20 ~1×10 22 atoms / cm 3 、7.5×10 20 ~1×10 22 atoms / cm 3 、8×10 20 ~5×10 21 atoms / cm 3 、 or 8.5×10 20 ~5×10 21 atoms / cm 3 is even more preferable, 9×10 20 ~5×10 21 atoms / cm 3 、9.5×10 20 ~2×10 21 atoms / cm 3 、 or 1×10 21 ~2×10 21 atoms / cm 3 is particularly preferable.

[0034] In the laminate obtained by the technology of the present disclosure, the nitrogen concentration at a portion 15 nm away from the SiO2 / SiC interface in the SiO2 layer is 5.5×10 18 atoms / cm 3 or less, or 5×10 18 atoms / cm 3 or less is preferable, 4.5×10 18 atoms / cm 3 or less, or 4×10 18 atoms / cm 3 or less is more preferable, 3.5×10 18 atoms / cm 3 or less, or 3×10 18 atoms / cm 3 or less is even more preferable, 2.5×1018 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable. Note that when measuring nitrogen concentration by secondary ion mass spectrometry, approximately 2 × 10⁻⁶ 18 atoms / cm 3 This is the detection limit. In other words, it is most preferable that the laminate obtained by the technology of this disclosure has a nitrogen concentration in the SiO2 layer at a distance of 15 nm from the SiO2 / SiC interface that is below the detection limit by secondary ion mass spectrometry.

[0035] The laminate obtained by the technology disclosed herein has a nitrogen concentration of 5.5 × 10⁻¹⁰ in the SiO2 layer at a distance of 10 nm from the SiO2 / SiC interface. 18 atoms / cm 3 The following, or 5 x 10 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0036] The laminate obtained by the technology disclosed herein has a nitrogen concentration of 5.5 × 10⁻¹⁰ in the SiO2 layer at a distance of 8 nm from the SiO2 / SiC interface. 18 atoms / cm 3 The following, or 5 x 10 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0037] The laminate obtained by the technology disclosed herein has a nitrogen concentration of 5.5 × 10⁻¹⁰ in the SiO2 layer at a distance of 5 nm from the SiO2 / SiC interface. 18 atoms / cm 3 The following, or 5 x 10 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0038] It is known that SiC MOS transistors with nitrogen introduced exhibit a significant threshold voltage shift due to positive / negative bias voltage stress. Bias voltage stress is a phenomenon in which the source and drain current values ​​decrease over time when the voltage is kept constant. In this case, the initial current value cannot be obtained unless an even higher threshold voltage (gate voltage) is applied. Therefore, a significant threshold voltage shift due to positive / negative bias voltage stress can hinder the stable operation of SiC MOS transistors. It has been suggested that one of the causes of this threshold voltage shift (BR>L) is the incorporation of nitrogen atoms into the SiO2 insulator (Non-Patent Literature 1). Therefore, from the viewpoint of suppressing the threshold voltage shift, it is preferable to have a low nitrogen concentration in the SiO2 layer away from the SiO2 / SiC interface.

[0039] As mentioned above, the higher the nitrogen concentration at the SiO2 / SiC interface, the higher the interface state density (D it It is predicted that the nitrogen concentration will decrease (i.e., the interface quality will improve), and the lower the nitrogen concentration in the portion of the SiO2 layer away from the SiO2 / SiC interface, the more the threshold voltage shift due to positive / negative bias voltage stress will be suppressed. Therefore, as a preferred embodiment of the laminate obtained by the technology of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is 4 × 10⁻¹⁰. 20 atoms / cm 3 The above, or 4.5 × 10 20 atoms / cm 3 The above conditions are met, and the nitrogen concentration in the SiO2 layer at a distance of 15, 10, 8, or 5 nm from the SiO2 / SiC interface is 5.5 × 10⁻¹⁰. 18 atoms / cm 3 The following, or 5 x 10 18 atoms / cm 3 The following are examples of laminates. In a more preferred embodiment of the laminate obtained by the technology of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is 5 × 10 20 atoms / cm 3 The above, or 5.5 × 10 20 atoms / cm 3Furthermore, the nitrogen concentration in the SiO2 layer at a distance of 15, 10, 8, or 5 nm from the SiO2 / SiC interface is 4.5 × 10⁻¹⁰. 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 The following are examples of laminates. In a more preferred embodiment of the laminate obtained by the technology of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is 6 × 10 20 atoms / cm 3 The above, or 7 x 10 20 atoms / cm 3 Furthermore, the nitrogen concentration in the SiO2 layer at a distance of 15, 10, 8, or 5 nm from the SiO2 / SiC interface is 3.5 × 10⁻¹⁰. 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 The following are examples of laminates. In one particularly preferred embodiment of a laminate obtained by the technology of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is 8 × 10 20 atoms / cm 3 The above conditions are met, and the nitrogen concentration in the SiO2 layer at a distance of 15, 10, 8, or 5 nm from the SiO2 / SiC interface is 2.5 × 10⁻¹⁰. 18 atoms / cm 3 The following are examples of laminates. In one of the most preferred embodiments of a laminate obtained by the art of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is 9 × 10 20 atoms / cm 3 The above conditions are met, and the nitrogen concentration in the SiO2 layer at a distance of 15, 10, 8, or 5 nm from the SiO2 / SiC interface is 2 × 10⁻¹⁰. 18 atoms / cm 3 The following are examples of laminates.

[0040] Furthermore, the thickness of the SiO2 film formed on the SiC surface by the heat treatment process described above may be less than 15 nm. In this case, "nitrogen concentration at a distance of 15 nm from the SiO2 / SiC interface" refers to the value measured when further SiO2 is deposited on the SiO2 layer formed by the heat treatment process, and the thickness of the SiO2 layer becomes 15 nm or more. In this embodiment, if SiO2 that has not undergone nitrogen introduction treatment is used as the SiO2 to be deposited later, the nitrogen concentration at a distance of 15 nm from the SiO2 / SiC interface should be below the detection limit. Similarly, if the thickness of the SiO2 film formed on the SiC surface by the heat treatment process is less than 10 nm, the "nitrogen concentration at a distance of 10 nm from the SiO2 / SiC interface" refers to the value measured when further SiO2 is deposited on the SiO2 layer formed by the heat treatment process, resulting in a thickness of 10 nm or more. If the thickness of the SiO2 film formed on the SiC surface by the heat treatment process is less than 8 nm, the "nitrogen concentration at a distance of 8 nm from the SiO2 / SiC interface" refers to the value measured when further SiO2 is deposited on the SiO2 layer formed by the heat treatment process, resulting in a thickness of 8 nm or more. If the thickness of the SiO2 film formed on the SiC surface by the heat treatment process is less than 5 nm, the "nitrogen concentration at a distance of 5 nm from the SiO2 / SiC interface" refers to the value measured when further SiO2 is deposited on the SiO2 layer formed by the heat treatment process, resulting in a thickness of 5 nm or more.

[0041] As described above, in the technology of this disclosure, after the heat treatment step, further SiO2 may be deposited on the SiO2 layer produced by the heat treatment step. The method for further depositing SiO2 on the SiO2 layer is not particularly limited, and conventionally known methods or methods that can be easily conceived from conventionally known methods can be used. Specifically, examples include sputter deposition, chemical vapor deposition (CVD), atomic layer deposition (ALD), etc.

[0042] If further SiO2 is deposited on the SiO2 layer formed by the heat treatment process, a subsequent heat treatment in a CO2 atmosphere may be optionally performed. This process may improve the quality of the SiO2. The temperature when performing heat treatment in a CO2 atmosphere is not particularly limited and may be, for example, around 1000°C to 1300°C, around 1000°C to 1200°C, or around 1050°C to 1150°C.

[0043] This disclosure relates to a laminate having an SiO2 layer on a SiC layer, with nitrogen contained in the SiO2 / SiC interface, wherein the nitrogen concentration at the SiO2 / SiC interface is 3 × 10⁻¹⁴ 20 atoms / cm 3 Furthermore, the nitrogen concentration in the SiO2 layer at a distance of 15 nm from the SiO2 / SiC interface is 5.5 × 10⁻¹⁰. 18 atoms / cm 3 This also includes laminates, which may be referred to as "the laminates of this disclosure." The matters described in this disclosure relating to the manufacturing method shall be appropriately incorporated into the laminates of this disclosure. Furthermore, the matters described in this disclosure relating to the laminates shall be appropriately incorporated into the manufacturing method of this disclosure.

[0044] In the laminate of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is 3 × 10⁻¹⁰ 20 atoms / cm 3 The above, or 3.5 × 10 20 atoms / cm 3 It may be more than 4 × 10 20 atoms / cm 3 The above, or 4.5 × 10 20 atoms / cm 3 It is preferable that the above is true, 5 × 10 20 atoms / cm 3 The above is 5.5 × 10 20 atoms / cm 3 The above 6 x 10 20 atoms / cm 3 The above, or 6.5 × 10 20 atoms / cm 3 More preferably, the above is true, 7 × 10 20 atoms / cm 3The above is 7.5 x 10 20 atoms / cm 3 The above 8 x 10 20 atoms / cm 3 The above, or 8.5 × 10 20 atoms / cm 3 It is even more preferable that the above be the case, 9 × 10 20 atoms / cm 3 The above is 9.5 x 10 20 atoms / cm 3 The above, or 1 x 10 21 atoms / cm 3 It is especially preferable that the above conditions are met.

[0045] In the laminate of the present invention, the upper limit of the nitrogen concentration at the SiO2 / SiC interface is not particularly limited, for example, 1 × 10 23 atoms / cm 3 The following is also acceptable: 5 × 10 22 atoms / cm 3 The following is also acceptable: 2 × 10 22 atoms / cm 3 The following is also acceptable: 1 × 10 22 atoms / cm 3 The following is also acceptable: 5 × 10 21 atoms / cm 3 The following is also acceptable: 2 × 10 21 atoms / cm 3 The following is also acceptable.

[0046] In the laminate of this disclosure, the nitrogen concentration at the SiO2 / SiC interface is, for example, 3 × 10⁻¹⁴. 20 ~1 × 10 23 atoms / cm 3 , or 3.5 × 10 20 ~1 × 10 23 atoms / cm 3 It may also be 4 x 10 20 ~5×10 22 atoms / cm 3 , or 4.5 × 10 20 ~5×10 22 atoms / cm 3 Preferably, 5 × 10 20~5×10 22 atoms / cm 3 , 5.5×10 20 ~5×10 22 atoms / cm 3 , 6×10 20 ~2×10 22 atoms / cm 3 , or 6.5 × 10 20 ~2×10 22 atoms / cm 3 It is more preferable that it be 7 × 10 20 ~1 × 10 22 atoms / cm 3 , 7.5×10 20 ~1 × 10 22 atoms / cm 3 , 8×10 20 ~5×10 21 atoms / cm 3 , or 8.5 × 10 20 ~5×10 21 atoms / cm 3 It is even more preferable that it be 9 × 10 20 ~5×10 21 atoms / cm 3 , 9.5×10 20 ~2×10 21 atoms / cm 3 , or 1 × 10 21 ~2×10 21 atoms / cm 3 It is particularly preferable that this be the case.

[0047] In the laminate disclosed herein, the nitrogen concentration in the SiO2 layer at a distance of 15 nm from the SiO2 / SiC interface is 5 × 10 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0048] In the laminate of this disclosure, the nitrogen concentration in the SiO2 layer at a distance of 10 nm from the SiO2 / SiC interface is 5 × 10 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0049] In the laminate disclosed herein, the nitrogen concentration in the SiO2 layer at a distance of 8 nm from the SiO2 / SiC interface is 5 × 10⁻¹⁰. 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0050] In the laminate disclosed herein, the nitrogen concentration in the SiO2 layer at a distance of 5 nm from the SiO2 / SiC interface is 5 × 10⁻¹⁰. 18 atoms / cm 3 Preferably, it is 4.5 × 10 18 atoms / cm 3 The following, or 4 x 10 18 atoms / cm 3 It is more preferable that the following conditions apply: 3.5 × 10 18 atoms / cm 3 The following, or 3 × 10 18 atoms / cm 3 It is even more preferable that the following conditions apply: 2.5 × 10 18 atoms / cm 3 The following, or 2 × 10 18 atoms / cm 3 The following is particularly preferable:

[0051] The laminate of this disclosure can be manufactured by the manufacturing method of this disclosure. Furthermore, the laminate of this disclosure can be used in the manufacture of, for example, semiconductor devices, insulated gate semiconductor devices, metal-oxide-semiconductor field-effect transistor (MOSFET) elements, etc.

[0052] IV. Estimation Mechanism Conventionally, when forming an SiO2 layer on SiC by thermal oxidation, it was known that performing thermal oxidation at a higher temperature resulted in a higher quality SiO2 layer. Furthermore, when attempting to form an SiO2 layer on SiC by thermal oxidation after introducing nitrogen to the SiC surface, at least a portion of the nitrogen introduced to the SiC surface may be removed. For this reason, conventional techniques typically involve forming an SiO2 layer on SiC by thermal oxidation or chemical vapor deposition, and then introducing nitrogen to the SiO2 / SiC interface (Figure 3).

[0053] Nitrogen introduction into the SiO2 / SiC interface is generally performed by heat-treating the substrate in a nitric oxide (NO) or nitrous oxide (N2O) atmosphere. It has been reported that higher heat treatment temperatures for nitrogen introduction into the SiO2 / SiC interface result in a larger amount of nitrogen introduced into the interface, but also a larger amount of nitrogen diffusing into the SiO2 layer away from the interface. On the other hand, it has been reported that lower heat treatment temperatures result in less nitrogen diffusing into the SiO2 layer away from the interface, but also less nitrogen introduced into the interface, which is insufficient to fill interface defects (Non-Patent Literature 1, Figure 2).

[0054] While we do not wish to be bound by any theory, in the technology of this disclosure, it is presumed that the process of heat-treating a substrate made of SiC in a mixed gas causes both a reaction to occur in which the surface of SiC is oxidized to form an SiO2 film (i.e., a laminated structure having an SiO2 layer on a SiC layer is formed), and a reaction to which nitrogen is introduced into the SiO2 / SiC interface created by the oxidation reaction (Figure 3). In this disclosure, the process in which both the oxidation reaction and the nitrogen introduction reaction occur may be referred to as "NO oxynitriding".

[0055] The heat treatment process is carried out at a temperature of 900°C to 1200°C, which is lower than the temperature used in conventional techniques for forming an SiO2 layer on SiC by thermal oxidation and for introducing nitrogen. Based on the conventional level of technology, it was predicted that if an SiO2 layer was formed on a SiC layer at a relatively low temperature of 900°C to 1200°C and nitrogen was introduced into the SiO2 / SiC interface, the quality of the SiO2 would be low, and the amount of nitrogen atoms present at the SiO2 / SiC interface would be insufficient, resulting in a laminate with a low-quality SiO2 / SiC interface.

[0056] Surprisingly, however, the laminate obtained by the present disclosure exhibited excellent interfacial properties, with a capacitance-voltage (CV) curve that closely matched the ideal value and remarkably few interfacial defects (Figures 6 and 7). While we do not wish to be bound by any theory, the surface of SiC is expected to be highly reactive, and in the present disclosure, it is presumed that the reaction in which the SiC surface is oxidized to form an SiO2 film and the reaction in which nitrogen is introduced into the SiO2 / SiC interface proceed almost simultaneously. For this reason, even at relatively low temperatures, nitrogen atoms are expected to be incorporated at a high concentration at the newly formed SiO2 / SiC interface, and the diffusion of nitrogen atoms into the SiO2 layer is expected to be suppressed due to the relatively low temperature. As a result, a high concentration of nitrogen atoms is specifically present at the SiO2 / SiC interface, and it is thought that a laminate with a high-quality SiO2 / SiC interface can be obtained (Figure 4).

[0057] Furthermore, the technology disclosed herein allows for the formation of a high-quality SiO2 layer even at lower temperatures than conventional technologies. Although the reason is not entirely clear, it is possible that trace amounts (200 ppm to 20,000 ppm) of O2 contained in the mixed gas subjected to heat treatment contribute to the formation of a high-quality SiO2 layer at relatively low temperatures.

[0058] V. MOSFET elements of the present disclosure Furthermore, the technology of this disclosure makes it possible to obtain a metal-oxide-semiconductor field-effect transistor (MOSFET) element in which the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor is significantly lower than the nitrogen concentration at the interface between the gate oxide film and the SiC semiconductor. Such a MOSFET element may be referred to as the "MOSFET element of this disclosure." This disclosure also includes the MOSFET element of this disclosure and methods for manufacturing the MOSFET element of this disclosure.

[0059] In this disclosure, "gate oxide" means an insulating layer of SiO2 formed between the gate electrode and the SiC substrate in a MOSFET device. The gate oxide plays a role in controlling the electric field when a voltage is applied from the gate electrode and controlling the operation of charge carriers in the channel region. In this disclosure, "field oxide" means an insulating layer of SiO2 formed in the field region other than the channel region in a MOSFET device. The field oxide has the function of improving the breakdown voltage characteristics and electrical insulation of the entire device.

[0060] Both the gate oxide film and the field oxide film are insulating layers of SiO2, but the field oxide film is thicker, usually having a thickness of several hundred nanometers or more. The interface between the gate oxide film and the SiC semiconductor, and the interface between the field oxide film and the SiC semiconductor, are both SiO2 / SiC interfaces. As mentioned above, the "SiO2 / SiC interface" is defined as the surface where the carbon (C) signal intensity is half that of SiC in the profile obtained by secondary ion mass spectrometry (SIMS).

[0061] In the MOSFET device of this disclosure, the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor may be, for example, 1 / 2, 1 / 3, 1 / 4, 1 / 5, or 1 / 6 of the nitrogen concentration at the interface between the gate oxide film and the SiC semiconductor, preferably 1 / 7 or 1 / 8, more preferably 1 / 9 or 1 / 10, and even more preferably 1 / 15 or 1 / 20.

[0062] The MOSFET device of this disclosure is obtained by heat-treating a SiC semiconductor having a field oxide film before gate oxide film formation using the method described in section II. Heat Treatment Process. The portion of the MOSFET device of this disclosure that includes the gate oxide film, the interface between the gate oxide film and the SiC semiconductor, and the SiC semiconductor that shares the interface with the gate oxide film has the structure and properties described in section III. Laminate. The matters described in sections I. Substrate to be processed using SiC as the material, II. Heat Treatment Process, III. Laminate, and IV. Estimated Mechanism are appropriately incorporated into the MOSFET device of this disclosure and the method for manufacturing the MOSFET device of this disclosure.

[0063] Schematic diagrams of the process for introducing nitrogen atoms to an interface using the prior art and the technology of this disclosure are shown in Figures 18 and 19. In the figures, nitrogen atoms introduced to the interface are represented as dots. In the prior art, in order to perform NO heat treatment at high temperatures, approximately the same amount of nitrogen was introduced to both the interface between the field oxide film and the SiC semiconductor, and the interface between the gate oxide film and the SiC semiconductor. The high nitrogen concentration at the interface between the field oxide film and the SiC semiconductor could adversely affect the electrical properties of the entire device. On the other hand, in the technology of this disclosure, NO heat treatment is performed at low temperatures, and the formation of the gate oxide film and introduction of nitrogen are performed in one step, thereby introducing a high concentration of nitrogen at the interface between the gate oxide film and the SiC semiconductor while reducing the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor.

[0064] Figure 20 shows a schematic cross-sectional diagram of a DMOSFET, which is an example of a MOSFET element. In Figure 20, * indicates the field oxide film. Note that nitrogen atoms introduced at the interface are not shown in this figure.

[0065] In this specification, the term “comprising” includes not only “containing” but also “essentially consisting of” and “consisting of.” Furthermore, this disclosure encompasses all combinations of the constituent elements described herein.

[0066] Furthermore, the various characteristics (properties, structure, numerical values, functions, etc.) described for each embodiment of this disclosure described above may be combined in any way to identify the subject matter covered by this disclosure. In other words, this disclosure covers all subject matter consisting of any combination of the combinable characteristics described herein. [Examples]

[0067] The embodiments of this disclosure will be described in more detail below with examples, but the embodiments of this disclosure are not limited to the examples below.

[0068] 1. Example Test 1.1. A 4H-SiC(0001) 4°-off substrate with a w / n type epitaxial layer was used as the substrate to be treated. This was washed in a mixed solution of sulfuric acid and hydrogen peroxide (H2SO4 + H2O2) for 10 minutes, and then thoroughly rinsed with ultrapure water. Subsequently, it was washed again with 10% hydrofluoric acid (HF) for 10 minutes, thoroughly rinsed with ultrapure water, and dried.

[0069] The cleaned substrate was heat-treated in a mixed gas of 10 v / v% NO and N2 (10% NO / N2). The heat treatment was carried out at 1100°C for 3 hours or at 1150°C for 1 hour. The mixed gas subjected to the heat treatment contained 400-600 ppm of oxygen. Furthermore, the mixed gas substantially contained no gases other than NO, N2, and oxygen. In this disclosure, the fact that the gas other than NO and oxygen is substantially all N2 is indicated by " / N2".

[0070] A SiC-MOS capacitor was fabricated by forming an aluminum (Al) gate electrode on a heat-treated substrate (Figure 5), and capacitance-voltage (CV) measurements were performed at a frequency of 1 MHz. Furthermore, the thickness of the SiO2 film formed on the SiC was calculated using a capacitance-voltage characteristic simulator, following the method described in Non-Patent Document 3. The results are shown in Figures 6 and 7. In these results, measured values ​​are plotted as circles, and ideal values ​​(values ​​when interface defects are zero) are shown as solid lines.

[0071] The SiO2 film thickness was 3.1 nm after heat treatment at 1100°C for 3 hours. The SiO2 film thickness was 2.8 nm after heat treatment at 1150°C for 1 hour. As shown in Figures 6 and 7, the CV curves measured for the samples prepared in this test example were in almost agreement with the ideal values. These results suggest that, according to the technology of this disclosure, a laminate having an SiO2 / SiC interface with significantly fewer interface defects and excellent interface properties can be obtained by heat treatment at a lower temperature than the conventional technology.

[0072] 1.2. Next, the inventors fabricated a SiC-MOS capacitor in the same manner as in 1.1, except that it was heat-treated at 1100°C for 1 hour in a 10% NO / N2 mixed gas containing 393-442 ppm (400 ppm), 970-1060 ppm (0.1%), or 1800-2070 ppm (0.2%) of oxygen. Capacitance-voltage (CV) measurements were performed on the SiC-MOS capacitor using the method described in 1.1, and the thickness of the SiO2 film formed on the SiC was calculated. The results are shown in Figure 8.

[0073] The SiO2 film thickness was 2.6 nm at an oxygen concentration of 400 ppm, and 2.9 nm at oxygen concentrations of 0.1% and 0.2%. As shown in Figure 8, the CV curve showed a steep rise at oxygen concentrations of 0.1% and 0.2%, similar to that at an oxygen concentration of 400 ppm. These results suggest that even when the oxygen concentration during heat treatment is increased to around 0.1% or 0.2%, laminates with excellent electrical properties, similar to those in 1.1., can be obtained.

[0074] 1.3. Next, the inventors formed an SiO2 / SiC interface using the technique of the present disclosure and then deposited further SiO2 on the SiO2 layer. Specifically, heat treatment was performed in the same manner as in 1.1, except that the heat treatment was performed at 1100°C for 1 hour in a 10% NO / N2 mixed gas containing 400 ppm oxygen. Then, further SiO2 was deposited on the SiO2 layer by chemical vapor deposition at 400°C to a thickness of approximately 50 nm for the SiO2 film. After that, heat treatment was performed at 1100°C in a CO2 atmosphere (Figure 9, upper panel). Using the substrate subjected to the above treatment, a SiC-MOS capacitor was fabricated using the method described in 1.1 (hereafter, the data measured for this capacitor may be represented as "i)").

[0075] Furthermore, for comparison, a SiC-MOS capacitor was fabricated using a substrate treated by a conventional method. Specifically, the substrate to be treated was cleaned using the method described in 1.1, and then a SiO2 film of approximately 50 nm was deposited at 400°C by chemical vapor deposition. Subsequently, heat treatment was performed at 1250°C for 1 hour in an NO atmosphere to introduce nitrogen into the SiO2 / SiC interface. After that, heat treatment was performed at 1100°C in a CO2 atmosphere (middle panel of Figure 9). Using the substrate treated above, a SiC-MOS capacitor was fabricated using the method described in 1.1 (hereafter, the data measured for this capacitor may be represented as "ii)").

[0076] As another point of comparison, a SiC-MOS capacitor was fabricated using a substrate that had not undergone heat treatment in NO (no NO oxynitriding). Specifically, the substrate to be treated was cleaned using the method described in 1.1, and then a SiO2 film of approximately 50 nm was deposited at 400°C by chemical vapor deposition. After that, heat treatment was performed at 1100°C in a CO2 atmosphere (Figure 9, bottom). Using the substrate that had undergone the above treatment, a SiC-MOS capacitor was fabricated using the method described in 1.1 (hereafter, the data measured for this capacitor may be referred to as "iii)").

[0077] For each SiC-MOS capacitor fabricated as described above, capacitance-voltage (CV) measurements were performed using the method described in 1.1, and the interface state density (D) was measured using the conductance method. it The following was measured. The results are shown in Figure 10.

[0078] As shown in Figure 10 (left), the SiC-MOS capacitors fabricated using this method have interface characteristics equivalent to those of SiC-MOS capacitors fabricated using conventional methods, and clearly exhibit superior interface characteristics compared to SiC-MOS capacitors without NO oxynitriding. Furthermore, as shown in Figure 10 (right), the SiC-MOS capacitors fabricated using this method have interface state densities (D) equivalent to or lower than those of SiC-MOS capacitors fabricated using conventional methods. it ) possessed.

[0079] 1.4. Next, the inventors analyzed the effects of temperature and oxygen concentration on the interfacial properties during the NO oxynitriding process. Specifically, the following conditions were considered: iv) 500 ppm O2, 1100℃, 1h; v) 500 ppm O2, 1050℃, 1h; vi) 500 ppm O2, 1000℃, 1h; vii) 0.5% O2, 1100℃, 1h; viii) 1.0% O2, 1100℃, 1h (Under each condition, gases other than oxygen are 10% NO / N2) A SiC-MOS capacitor was fabricated using the same method as in 1.1, except for the heat treatment. CV measurements were performed, and the thickness of the SiO2 film formed on the SiC was calculated. The results are shown in Figure 11.

[0080] The SiO2 film thicknesses were iv) 2.9 nm, v) 2.4 nm, vi) 2.4 nm, vii) 3.6 nm, and viiii) 3.7 nm, respectively. As shown in Figure 11, it was revealed that an SiO2 film was formed even when the heat treatment temperature was 1000°C (vi)), and moreover, the interfacial properties (slope of the rise of the CV curve) were equivalent to those of the higher temperatures of iv) and v).

[0081] Furthermore, comparisons of iv), vii), and viii) revealed that while the SiO2 film formed becomes thicker with increasing oxygen concentration, the interfacial properties remain equivalent. These results suggest that increasing the oxygen concentration may shorten the heat treatment time.

[0082] 1.5.Summary CV curves and interface state density (D) measured for SiC-MOS capacitors fabricated by NO oxynitridation under conditions i), ii), iii), v), vi), and viiii). it Figure 12 shows the laminates obtained by the present disclosure, despite being heat-treated at a lower temperature than the conventional technology, all of them had interface properties equivalent to or better than those of laminates obtained by the conventional technology.

[0083] 1.6. Furthermore, the inventors analyzed the effect of the heat treatment temperature in the NO oxynitriding process on the introduction of nitrogen into the SiO2 / SiC interface. Specifically, substrates were obtained by heat treatment in the same manner as in 1.1, except that heat treatment was performed at 900°C, 950°C, 1000°C, or 1050°C for 1 hour. For each obtained substrate, the N1s spectrum originating from nitrogen atoms was obtained by X-ray photoelectron spectroscopy. The results are shown in Figure 13.

[0084] As shown in Figure 13, the peak intensities of the N1s spectra for each substrate (900°C, 950°C, 1000°C, 1050°C) are similar, confirming that nitrogen is introduced into the SiO2 / SiC interface at each heat treatment temperature, and that its abundance is similar.

[0085] 1.7. Next, the inventors measured the nitrogen concentration at the SiO2 / SiC interface when SiO2 was deposited after the SiO2 / SiC interface was formed. Specifically, heat treatment was performed in the same manner as in 1.1, except that heat treatment was performed at 1000°C for 1 hour or 1100°C for 1 hour. Then, SiO2 was further deposited on the SiO2 layer by chemical vapor deposition to a thickness of approximately 50 nm for the SiO2 film. Using the substrate that underwent the above treatment, the nitrogen concentration at the SiO2 / SiC interface was measured by secondary ion mass spectrometry. The results are shown in Figure 14.

[0086] As shown in Figure 14, the substrates obtained by heat treatment at 1000°C using this method (NO-ox@1000°C) and the substrates obtained by heat treatment at 1100°C (NO-ox@1100°C) showed that nitrogen was introduced at a similar concentration at the SiO2 / SiO interface even at lower heat treatment temperatures below 1200°C compared to the substrates obtained by heat treatment at 1250°C using the conventional method (NO-POA@1250°C). Furthermore, the substrate produced by this method originates from the raw materials used in chemical vapor deposition, resulting in a rising baseline on the SiO2 side. It is presumed that the nitrogen concentration, after removing the influence of these raw materials, will be equivalent to or lower than that of the substrate obtained by conventional methods.

[0087] 1.8. Furthermore, the inventors measured the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor in the MOSFET device of this disclosure. Specifically, a SiC semiconductor having a field oxide film before gate oxide film formation was heat-treated at 900°C for 1 hour in the same mixed gas as in 1.1. to fabricate a MOSFET device (Figure 19).

[0088] For comparison, a SiC semiconductor having a gate oxide film and a field oxide film was heat-treated in an NO atmosphere at 1250°C for 1 hour to create a MOSFET device (Figure 18).

[0089] For each MOSFET element fabricated as described above, the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor was measured.

[0090] Measurement results showed that in MOSFET devices fabricated using the technology of this disclosure, the nitrogen concentrations at the interface between the field oxide or gate oxide and the SiC semiconductor were 1.62 × 10⁻¹⁰. 14 cm -2 and 4×10 14 cm -2 Therefore, the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor was less than half the nitrogen concentration at the interface between the gate oxide film and the SiC semiconductor. In MOSFET devices fabricated using conventional technology, the nitrogen concentrations at the interface between the field oxide film or the gate oxide film and the SiC semiconductor were both 4 × 10⁻¹⁰. 14 cm -2 The nitrogen concentration at the interface between the field oxide film and the SiC semiconductor was equivalent to the nitrogen concentration at the interface between the gate oxide film and the SiC semiconductor.

[0091] 2.Reference example As a reference example, the electrical characteristics when nitrogen is not introduced to the SiO2 / SiC interface are shown. In this reference example, a 4H-SiC(0001) 4°-off substrate with a w / n type epitaxial layer was used as the substrate to be treated, similar to the test example. The cleaning procedure before heat treatment was also performed in the same manner as the test example. The heat treatment was performed in a CO2 atmosphere or O2 (0.1 atm) atmosphere that did not contain NO and N2O, at the temperature and time shown in the figure. Although an SiO2 film is formed on the SiC by this heat treatment, nitrogen is not introduced to the SiO2 / SiC interface. After heat treatment, a SiC-MOS capacitor was fabricated in the same manner as the test example, and capacitance-voltage (CV) measurements were performed at a frequency of 1 MHz. The film thickness of the SiO2 film formed on the SiC was also calculated in the same manner as the test example. The results are shown in Figures 15 to 17. In Figures 15 and 16, the measured values ​​are plotted as circles, and the ideal values ​​(values ​​when there are no interface defects) are shown as solid lines.

[0092] Figures 15 and 16 show the results of heat treatment at 1300°C for 2 minutes or 30 minutes in a CO2 atmosphere. The SiO2 film thickness after heat treatment in a CO2 atmosphere for 2 minutes was 1.9 nm. The SiO2 film thickness after heat treatment in a CO2 atmosphere for 30 minutes was 3.3 nm. As shown in Figures 15 and 16, the CV curve when nitrogen was not introduced to the SiO2 / SiC interface deviated significantly more from the ideal value than in Figures 6 and 7. This result indicates that the SiO2 / SiC interface without nitrogen introduction has many interface defects and is of low quality.

[0093] Figure 17 shows the results of heat treatment at 1300°C for 5 minutes or 15 minutes in a CO2 atmosphere, or for 2 minutes in an O2 (0.1 atm) atmosphere. The SiO2 film thickness after heat treatment in a CO2 atmosphere for 5 minutes was 2.3 nm. The SiO2 film thickness after heat treatment in a CO2 atmosphere for 15 minutes was 3.1 nm. The SiO2 film thickness after heat treatment in an O2 (0.1 atm) atmosphere for 2 minutes was 3.1 nm. The left side of Figure 17 shows the measured CV curve. The right side of Figure 17 shows the interface state density (D) measured by the conductance method. it ) indicates.

Claims

1. SiO on SiC layer ２ It has a layer, SiO ２ A method for manufacturing a laminate containing nitrogen in the SiC interface, The process includes heat treatment of a substrate made of SiC in a mixed gas, The mixed gas contains 200 ppm to 20,000 ppm of O. ２ NO and N ２ It is a mixed gas, A method for manufacturing a laminate, characterized in that the heat treatment temperature is 900°C to 1200°C.

2. The substrate to be treated is substantially SiO before the heat treatment process. ２ The manufacturing method according to claim 1, characterized in that it does not have a layer.

3. The SiO of the laminate ２ The nitrogen concentration at the SiC interface is 3 × 10 ２０ atoms / cm ３ The manufacturing method according to claim 1 or 2, characterized in that it is as described above.

4. In the SiO layer of the laminate ２ layer, the nitrogen concentration at a position 15 nm away from the SiO ２ / SiC interface is 5.5×10 １８ atoms / cm ３ or less. The manufacturing method according to claim 3, characterized in that

5. The manufacturing method according to claim 1 or 2, characterized in that the volume of NO relative to the total mixed gas is 5 to 20%.

6. After the heat treatment step, the SiO generated by the heat treatment step ２ Further SiO on top of the layer ２ A manufacturing method according to claim 1 or 2, comprising the step of depositing.

7. SiO on SiC layer ２ It has a layer, SiO ２ / A laminate containing nitrogen in the SiC interface, SiO ２ The nitrogen concentration at the SiC interface is 3 × 10 ２０ atoms / cm ３ That is all, and The SiO ２ In the layer, SiO ２ The nitrogen concentration at a distance of 15 nm from the SiC interface is 5.5 × 10⁻⁶. １８ atoms / cm ３ The following is a laminate.

8. A metal oxide semiconductor field-effect transistor (MOSFET) element characterized in that the nitrogen concentration at the interface between the field oxide film and the SiC semiconductor is less than or equal to half the nitrogen concentration at the interface between the gate oxide film and the SiC semiconductor.

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