Sic polycrystalline substrate, sic bonded substrate, and method for producing sic polycrystalline substrate

Abstract

To provide an SiC polycrystalline substrate in which variation in electrical characteristics due to position on the same surface is suppressed when a semiconductor device is produced, an SiC bonded substrate, and a method for producing an SiC polycrystalline substrate.　This SiC polycrystalline substrate is characterized by comprising: a first portion which has a surface resistivity within a first range and which is arranged so as to include the central part of the entire surface; and a second portion which has a surface resistivity within a second range that is larger than the first range and which is arranged so as to surround the periphery of the first portion. In the method for producing an SiC polycrystalline substrate, a support substrate 200 arranged in a film deposition furnace 1010 is rotated with a first direction perpendicular to the film deposition surface 201 of the support substrate 200 as the central axis Y, and a raw material gas is circulated along the first direction (arrow F direction) to perform chemical vapor deposition on the film deposition surface 201.

Description

SiC polycrystalline substrate, SiC bonded substrate, and method for manufacturing a SiC polycrystalline substrate

[0001] This invention relates to a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC polycrystalline substrate.

[0002] Silicon carbide (SiC), used as a material for polycrystalline substrates, is a compound semiconductor material composed of silicon and carbon. It boasts superior dielectric breakdown field strength (10 times that of silicon) and a band gap (3 times that of silicon). Furthermore, it allows for a wide range of control over p-type and n-type characteristics necessary for device fabrication, making it a promising material for power devices that surpasses the limitations of silicon.

[0003] Furthermore, SiC is characterized by its ability to achieve high voltage resistance even at thinner thicknesses, resulting in semiconductors with low ON resistance and low loss when constructed thinly. However, compared to widely used Si semiconductors, SiC semiconductors are difficult to mass-produce and are expensive due to the difficulty in obtaining large-area wafers and the complexity of the manufacturing process.

[0004] Therefore, various measures have been taken to reduce the cost of SiC semiconductors. For example, Patent Document 1 discloses a method for manufacturing a SiC substrate, characterized in that the density of micropipes is at least 30 units / cm³. ２ The following describes a process for manufacturing a substrate in which a SiC single crystal layer is formed on a SiC polycrystalline substrate by bonding a SiC single crystal substrate and a SiC polycrystalline substrate together, and then thinning the SiC single crystal substrate.

[0005] Patent Document 1 further describes a method for manufacturing an SiC substrate, wherein, before the step of bonding the SiC single crystal substrate and the SiC polycrystalline substrate, a step of implanting hydrogen ions into the SiC single crystal substrate to form a hydrogen ion implanted layer is performed, after the step of bonding the SiC single crystal substrate and the SiC polycrystalline substrate, heat treatment is performed at a temperature of 350°C or less before the step of thinning the SiC single crystal substrate, and the step of thinning the SiC single crystal substrate is a step of mechanically peeling it off at the hydrogen ion implanted layer.

[0006] This method has made it possible to obtain more SiC wafers from a single SiC single-crystal ingot, accelerating device development. In addition, taking advantage of the fact that SiC polycrystalline substrates can be made with lower resistance than SiC single-crystal substrates, SiC bonded substrates, which are formed by bonding a SiC single-crystal substrate and a SiC polycrystalline substrate, are attracting attention in the development of vertical devices that require low resistance.

[0007] Japanese Patent Publication No. 2009-117533

[0008] However, as device development using SiC bonded substrates, which are formed by bonding a SiC single-crystal substrate and a SiC polycrystalline substrate, progresses, it has been frequently observed that the electrical properties vary depending on the location on the same surface of the same semiconductor device. Therefore, the present invention aims to provide a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC polycrystalline substrate in which variations in electrical properties depending on the location on the same surface are suppressed when manufacturing semiconductor devices.

[0009] The present inventors conducted diligent research to solve the above problems and discovered that variations in the distribution of resistivity (resistivity) of the SiC substrate used on the film deposition surface cause variations in electrical properties depending on the position on the film deposition surface when semiconductor devices are fabricated using this substrate. This led to the invention of the SiC polycrystalline substrate according to the present invention.

[0010] Furthermore, it was considered that the reason for the variation in the distribution of resistivity on the film deposition surface was that when the support substrate was placed in the manufacturing chamber of the CVD (chemical vapor deposition) manufacturing apparatus for film deposition, the temperature distribution and the concentration gradient of the raw material gas within the deposition furnace were affected by these factors depending on the position of the support substrate.

[0011] Therefore, the present inventors conducted further intensive research and discovered that when depositing a SiC polycrystalline film on the film deposition surface of a support substrate by the CVD method, if the support substrate is rotated about a first direction perpendicular to the film deposition surface, and the raw material gas is flowed along the first direction to perform chemical deposition on the film deposition surface, the position of the support substrate will not be constant with respect to the flow of the raw material gas. As a result, a SiC polycrystalline substrate with suppressed variation in properties on the film deposition surface can be obtained. This led to the invention of the SiC polycrystalline substrate, SiC bonded substrate, and method for manufacturing the SiC polycrystalline substrate according to the present invention. That is, the embodiments of the present invention are as follows.

[0012] <1> A SiC polycrystalline substrate comprising: a first portion including the central part of the film-forming surface and having a resistivity within a first range; and a second portion surrounding the first portion on the film-forming surface and having a resistivity within a second range greater than the first range. <2> The SiC polycrystalline substrate according to <1>, wherein the average resistivity, which is the average value of the resistivity of the film-forming surface, is 25 mΩcm or less. <3> The SiC polycrystalline substrate according to <2>, wherein the average resistivity is determined as the average of the resistivity of multiple points on the film-forming surface, and the resistivity of the multiple points is within ±20% of the average resistivity. <4> A SiC bonded substrate comprising: the SiC polycrystalline substrate according to <1> and a SiC single crystal substrate bonded to the film-forming surface. <5> A method for manufacturing a SiC polycrystalline substrate, in which a support substrate placed in a film-forming furnace is rotated about a first direction perpendicular to the film-forming surface of the support substrate as the central axis, and a raw material gas is flowed along the first direction to perform chemical deposition on the film-forming surface. <6> The method for manufacturing a SiC polycrystalline substrate according to <5>, wherein the raw material gas is rectified before it reaches the film deposition surface. <7> The method for manufacturing a SiC polycrystalline substrate according to <5>, wherein a plurality of support substrates are arranged in the film deposition furnace.

[0013] According to the present invention, it is possible to provide a SiC polycrystalline substrate, a SiC bonded substrate, and a method for manufacturing a SiC polycrystalline substrate in which variations in electrical properties due to the position on the surface are suppressed when semiconductor devices are fabricated.

[0014] This is an example of a resistivity distribution mapping diagram for a SiC polycrystalline substrate according to the present invention. This is a schematic cross-sectional view showing an example of a SiC polycrystalline substrate deposition apparatus that can be used in the deposition process of the SiC polycrystalline substrate manufacturing method according to the embodiment. This is an enlarged perspective view of the substrate holder and drive device in the deposition apparatus shown in Figure 2. This is a plan view showing the measurement points in the plane of the SiC polycrystalline substrate where resistivity was measured in the example. This is a mapping diagram of the actual resistivity distribution in the SiC polycrystalline substrate of Example 1. This is a mapping diagram of the actual resistivity distribution in the SiC polycrystalline substrate of Example 2. This is a mapping diagram of the actual resistivity distribution in the SiC polycrystalline substrate of Comparative Example 1. This is a mapping diagram of the actual resistivity distribution in the SiC polycrystalline substrate of Comparative Example 2.

[0015] The following describes exemplary embodiments of the present invention in detail with reference to the drawings, but the present invention is not limited to these embodiments.

[0016] [SiC Polycrystalline Substrate] The SiC polycrystalline substrate of the embodiment is characterized by comprising, on the film-forming surface which is the surface on which a SiC polycrystalline film is formed, a first portion which includes the central part of the entire surface and has a resistivity in a first range on the surface, and a second portion which surrounds the first portion and has a resistivity in a second range which is greater than the first range on the surface.

[0017] The "first range" and "second range" of resistivity do not refer to specific ranges, but rather it is sufficient that the "first range" includes the resistivity of the central part of the entire surface of the SiC polycrystalline substrate, and that the resistivity of the "second range" is greater than that of the "first range". Therefore, the above characteristic refers to the fact that the resistivity distribution is low in the central part of the entire surface, and high in the surrounding region, forming a so-called donut shape. In particular, it is preferable that the entire first part, which is the first range with low resistivity, is surrounded by the second part, which is the second range with higher resistivity than the first range, that is, that the entire area of ​​the first part is included inside the second part. The central part of the film-forming surface may be not only a precise geometric center point, such as the center position when the film-forming surface is circular, but also a point that is shifted by about 5% from the geometric center point, such as the center of a circle, by the diameter when the film-forming surface is circular, or the length of the long side or diagonal when it is a polygon such as a rectangle, etc.

[0018] Figure 1 shows an example of a mapping diagram on the surface of a SiC polycrystalline substrate. The mapping diagram shown in Figure 1 is actually for a SiC polycrystalline substrate according to Example 1, which will be described later. The mapping diagram in Figure 1 shows lines (hereinafter referred to as "equiresistivity lines") connecting positions where the surface resistivity is 0.0125 Ωcm, 0.0130 Ωcm, and 0.0135 Ωcm. Although the SiC polycrystalline substrate and its deposition surface shown in Figure 1 are exemplified as having an orientation flat to indicate the crystal orientation of the SiC polycrystalline substrate, substrates and deposition surfaces having a circular shape without an orientation flat, or notches instead of an orientation flat, or polygonal shapes such as rectangles are also acceptable. Furthermore, even with a SiC polycrystalline substrate having an orientation flat as exemplified in the embodiment, it is preferable to determine the position of the central part of the deposition surface based on a circular shape without an orientation flat.

[0019] As shown in Figure 1, the region where the resistivity is less than 0.0125 Ωcm is defined as Region A, the region where the resistivity is 0.0125 Ωcm or more and less than 0.0130 Ωcm is defined as Region B, the region where the resistivity is 0.0130 Ωcm or more and less than 0.0135 Ωcm is defined as Region C, and the region where the resistivity is 0.0135 Ωcm or more is defined as Region D.

[0020] Region A includes the central part X of the entire surface of the SiC polycrystalline substrate (the center point of the circle that becomes the film deposition surface in this embodiment), so region A can be considered as the "first range" of resistivity. On the other hand, regions B, C, and D all have resistivity greater than the "first range," so they can all be considered as the "second range" of resistivity. Both ranges of regions B and C, both ranges of regions C and D, and even the entire range of all three regions B, C, and D can each be considered as the "second range."

[0021] Furthermore, regarding the "first range," not only region A, but also both regions A and B, and even the entire range of all three regions A, B, and C, can be considered as the "first range" because they all include the central part X. In these cases, the outer regions of each "first range" become the "second range."

[0022] As described above, regardless of the specific value or range of resistivity, if the SiC polycrystalline film exists on the deposition surface in regions that can be considered as the "first range" and the "second range" (hereinafter referred to as the "doughnut-shaped region of resistivity"), it corresponds to the SiC polycrystalline substrate of the present invention.

[0023] As described above, in a SiC polycrystalline substrate having a donut-shaped region of resistivity, it is inferred that the source gas is in uniform contact with the film-forming surface of the supporting substrate when the SiC polycrystalline film is formed on the film-forming surface by CVD, which inevitably suppresses variations in resistivity on the surface. Therefore, according to the SiC polycrystalline substrate of the embodiment, when a semiconductor device is manufactured, variations in electrical characteristics depending on the position on the same surface are suppressed. Furthermore, it is possible to reduce variations in the electrical characteristics of a semiconductor device manufactured from a bonded SiC substrate obtained by bonding using the SiC polycrystalline substrate of the embodiment. That is, it is possible to increase the yield of semiconductor devices and reduce manufacturing costs.

[0024] In the SiC polycrystalline substrate according to the embodiment, the average resistivity of the film-forming surface on which the SiC polycrystalline film is formed (hereinafter may be simply referred to as "average resistivity") is preferably 25 mΩcm or less, more preferably 20 mΩcm or less. If the average resistivity is extremely high, it exceeds the resistance value of a SiC single crystal substrate, so the advantage of low resistance that is a characteristic of a bonded SiC substrate cannot be utilized. In view of productivity and other factors, it is considered preferable that the average resistivity is 0.5 mΩcm or more.

[0025] The average resistivity of the film-forming surface can be obtained, for example, by averaging the resistivity at a plurality of points on the film-forming surface. The "plurality of points on the film-forming surface" (hereinafter may be referred to as "plurality of measurement points") are a plurality of positions set on the film-forming surface on which the SiC polycrystalline film is formed on the SiC polycrystalline substrate. The plurality of measurement points are preferably a plurality of points (positions) dispersed as evenly as possible. For example, a total of 5 points can be used: one point at the center, and four points spaced 90° apart at equal intervals in the circumferential direction on the outer peripheral side separated by a predetermined distance in the radial direction from the center of the film-forming surface. A value obtained by averaging the resistivities respectively measured at such a plurality of measurement points can be used as the average resistivity. The resistivity is preferably measured at 20 or more points (positions) on the film-forming surface, more preferably 30 or more points. For example, in the examples described later, 37 points are measured.

[0026] It is preferable that the resistivity distribution at a plurality of measurement points falls within ±20% of the average resistivity. A SiC polycrystalline substrate in which the resistivity distribution at a plurality of measurement points is leveled within 20% above and below the average resistivity can suppress variation in electrical characteristics depending on the position on the same surface when a semiconductor device is manufactured using the same.

[0027] The phrase "the resistivity distribution at a plurality of measurement points falls within ±20% of the average resistivity" means that the following formulas (1) and (2) are satisfied when the average resistivity is denoted as Ra, the maximum resistivity at the plurality of measurement points is denoted as Rmax, and the minimum resistivity at the plurality of measurement points is denoted as Rmin. Ra × (100% + 20%) / 100% ≧ Rmax … Formula (1) Ra × (100% - 20%) / 100% ≦ Rmin … Formula (2) Hereinafter, the left-hand side of formula (1) is R （ａ＋２０％） , the left-hand side of formula (2) is R （ａ－２０％） and expressed as such.

[0028] Furthermore, in the SiC polycrystalline substrate of the embodiment, it is preferable that the resistivity distribution at a plurality of measurement points falls within ±20% of the average resistivity, more preferably within ±15%, even more preferably within ±10%, and the closer to 0% the more preferable. By further leveling the resistivity distribution at a plurality of measurement points, variation in electrical characteristics depending on the position on the same surface when manufacturing a semiconductor device can be further suppressed.

[0029] In a SiC polycrystalline substrate, in order to suppress variation in resistivity distribution on the film formation surface on which a SiC polycrystalline film is formed, it is effective to manufacture the substrate by the method for manufacturing a SiC polycrystalline substrate according to the embodiment described later. That is, according to the method for manufacturing a SiC polycrystalline substrate according to the embodiment described later, the SiC polycrystalline substrate of the present invention can be suitably manufactured, variation in film thickness on the film formation surface 101 of the support substrate 200 is suppressed, and as a result, variation in resistivity distribution is suppressed.

[0030] The resistivity required to determine the average resistivity and resistivity distribution in a SiC polycrystalline substrate can be measured, for example, by a method conforming to the Japanese Industrial Standard JIS R1637 "Test Method for Resistivity of Fine Ceramic Thin Films - 4. Measurement Method by Probe Method".

[0031] According to the method for manufacturing a SiC polycrystalline substrate as described in the embodiment later, variations in the resistivity distribution of the film-forming surface of the SiC polycrystalline film are suppressed. However, because chemical deposition is performed while rotating the support substrate 200 with a rotation axis 200 perpendicular to the film-forming surface 101, the distribution of positions with the same range of resistivity within the plane tends to become ring-shaped, centered on a single point. This ring-shaped distribution is synonymous with the previously described "donut-shaped region of resistivity."

[0032] The distribution of locations with the same resistivity range on the film deposition surface of a SiC polycrystalline substrate can be mapped by measuring at the center point of the SiC polycrystalline substrate and several points radially extending outward from the center point. After inferring the change between each measurement point from the measured values, multiple lines (i.e., "isoresistivity lines") are drawn connecting points with the same resistivity. In the example described later, measurements are taken at the center point of the SiC polycrystalline substrate and at six points on a line with a diameter W in six directions, each shifted by a central angle of 30°, with three points at regular intervals in both directions from the center point (a total of 37 points including the center point) (see Figure 4). Note that the "center point" at the measurement point and the "central part X" in the phrase "central part X on the entire surface of the SiC polycrystalline substrate" do not need to coincide exactly.

[0033] [SiC Bonded Substrate] The SiC bonded substrate of this embodiment comprises the SiC polycrystalline substrate described above and a SiC single crystal substrate bonded to the film deposition surface.

[0034] [Method for Manufacturing a SiC Polycrystalline Substrate] A method for manufacturing a SiC polycrystalline substrate suitable for manufacturing the SiC polycrystalline substrate described above will be described below. The method for manufacturing a SiC polycrystalline substrate according to this embodiment mainly includes a film formation step, an exposure step, and a burn removal step, and may also include a polishing step and other steps as needed. Among these steps, the method for manufacturing a SiC polycrystalline substrate according to this embodiment is particularly characterized by the film formation step.

[0035] (Film Formation Process) The method for manufacturing a SiC polycrystalline substrate according to this embodiment includes a film formation process in which, in a film formation furnace for chemical deposition, the support substrate to be formed is rotated with a central axis perpendicular to the film formation surface on the support substrate, and the raw material gas is flowed from a direction intersecting the film formation surface to perform chemical deposition and form a film.

[0036] The support substrate, which is the substrate to be deposited on, is not particularly limited, but examples include silicon support substrates and carbon support substrates. The shape of the support substrate can be, for example, a thin film in the form of a circular wafer with a diameter of approximately 4 to 8 inches.

[0037] The film to be deposited is not particularly limited, but examples include films of SiC, titanium nitride, aluminum nitride, titanium carbide, or diamond-like carbon. Furthermore, either a single-crystal film or a polycrystalline film may be deposited.

[0038] The film deposition process will be described by giving an example of a crystalline film deposition apparatus that can be used in the film deposition process of the SiC polycrystalline substrate manufacturing method according to the above embodiment. Figure 2 shows a schematic cross-sectional view of the crystalline film deposition apparatus 1000.

[0039] The film deposition apparatus 1000 includes a film deposition furnace 1010 for depositing a crystalline film on a support substrate 200, a supply port 1020 for introducing a gas containing raw material gas and carrier gas (hereinafter referred to as "supply gas") into the film deposition furnace 1010, an exhaust port 1030 for exhausting the supply gas (hereinafter referred to as "exhaust gas") discharged from the film deposition furnace 1010 to the outside of the film deposition apparatus 1000, an exhaust gas introduction chamber 1040 for introducing the exhaust gas discharged from the film deposition furnace 1010 into the exhaust port 1030, a box 1050 covering the exhaust gas introduction chamber 1040, a heater 1060 for controlling the temperature inside the film deposition furnace 1010 from outside the box 1050, and a water-cooled stainless steel housing (not shown) located outside the heater 1060 and forming the exterior of the film deposition apparatus 1000.

[0040] Inside the film deposition furnace 1010, there is a substrate holder 1080 that holds the support substrate 200 and a drive device 1090 that rotates it. On the support substrate 200, one or both sides are the film deposition surface 201, and the film deposition surface 201 is oriented toward the supply port 1020 side (the upstream side of the supply gas flow). The support substrate 201 is rotated by the rotating substrate holder 1080 with a first direction perpendicular to the film deposition surface 201 (the direction in which the dashed line of symbol Y in Figure 2 extends) as the center (hereinafter referred to as the "center axis Y").

[0041] Figure 3 is an enlarged perspective view of the substrate holder 1080 and drive unit 1090 in the film deposition apparatus 1000 shown in Figure 2. The substrate holder 1080 has an annular turntable 1083, four columns 1081 erected on the turntable 1083, and a mounting section 1082 on which the support substrate 200 is placed. The mounting sections 1082 are provided at equal intervals in the vertical direction of each column 1081 and are used to position the support substrate 200 in the film deposition furnace 1010 while keeping it horizontal.

[0042] A gear 1083a is formed on the side surface of the rotating base 1083 of the substrate holder 1080, and a drive device 1090 that rotates a gear (not shown) that meshes with this gear allows the substrate holder 1080 and the support substrate 200 to rotate horizontally (with the first direction perpendicular to the film deposition surface 201 as the central axis Y).

[0043] Further, in FIG. 2, arrow F indicates the directions in which the supply gas and the exhaust gas flow. In FIG. 2, the flow direction of the supply gas is a direction orthogonal to the film formation surface 201 (a direction that coincides with a first direction perpendicular to the film formation surface 201), and the film formation surface 201 faces the upstream side in the flow direction of the supply gas. Note that the flow direction of the supply gas does not need to be a direction exactly orthogonal to the film formation surface 201 (a direction that exactly coincides with the first direction perpendicular to the film formation surface 201), and may be any direction along the first direction perpendicular to the film formation surface 201. The angle formed between the flow direction of the supply gas and the central axis Y is preferably 20° or less, more preferably 15° or less, still more preferably 10° or less, and particularly preferably close to 0°.

[0044] The raw material gas used is not particularly limited as long as a film can be produced, and generally used raw material gases can be used. For example, in the case of producing a SiC polycrystalline film, in addition to a binary gas using a Si-based raw material gas and a C-based raw material gas, a monocomponent gas containing both Si and C in one molecule may be used.

[0045] As the Si-based raw material gas, for example, silane (SiH ４ ), and SiH ３ Cl, SiH ２ Cl ２ , SiHCl ３ , SiCl ４ and other chlorine-based Si raw material-containing gases (chloride-based raw materials) containing Cl that has an etching effect can also be used. As the C-based raw material gas, for example, methane (CH ４ ), propane (C ３ H ８ ), acetylene (C ２ H ２ ), or the like can be used.

[0046] Furthermore, a carrier gas may be entrained in the raw material gas. Any commonly used carrier gas can be used as long as the raw material gas can be spread onto the support substrate 200 without hindering the film manufacturing process. For example, when manufacturing a SiC polycrystalline film as in this embodiment, hydrogen (H), which has excellent thermal conductivity and etching properties for SiC, can be used. ２ ) can be used as a carrier gas.

[0047] Furthermore, along with these raw material gases and carrier gases, a third gas, an impurity doping gas, can also be supplied simultaneously. For example, if the conductivity type is n-type, nitrogen (N) can be used. ２ ), if the p-type is used, trimethylaluminum (TMA) can be used as the third gas.

[0048] Furthermore, along with these raw material gases and carrier gases, a third gas, an impurity doping gas, can also be supplied simultaneously. For example, if you want to make the conductivity type n-type, nitrogen (N) can be supplied. ２ ), if you want to make it p-type, you can use trimethylaluminum (TMA).

[0049] The rotation speed of the support substrate 200 during the film deposition process is not particularly limited, but can be set to, for example, 0.1 to 30 rpm (revolutions / minute). If the rotation speed is too slow, the effect of leveling the thickness of the deposited film may be insufficient, and if it is too fast, the support substrate 200 may fall off or the substrate holder 1080 may be damaged, or airflow due to rotation may occur, potentially causing manufacturing problems.

[0050] Furthermore, inside the film deposition furnace 1010, in order to supply the gas supplied from the supply port 1020 for introducing the raw material gas and carrier gas to the support substrate 200 as uniformly as possible, a flow straightening plate 1070 with multiple holes is installed in the flow path of the raw material gas before it reaches the film deposition surface 201 on the support substrate 200 in the rotationally symmetric substrate group 400, thereby straightening the raw material gas before it reaches the film deposition surface 201.

[0051] The rectifier plate 1070 is a component designed to temporarily trap the gas supplied from the supply port 1020, which has a relatively small opening area, and then discharge it as uniformly as possible through multiple holes provided at roughly equal rates over a relatively wide area where the support substrate 200 is located. In addition to a simple structure with circular, polygonal, or other types of holes, it may also have a mesh-like, fin-like, slit-like, or curved structure, and various structures can be adopted, such as stacking these rectifier plates of the same or different structures.

[0052] The supply gas that has passed through the rectifier plate 1070 is rectified and flows upward in an advective region up to the region where it reaches the support substrate 200. On the other hand, around the support substrate 200, the supply gas remains stagnant and flows in a diffusive region. The support substrate 200, located in the diffusive region, is less affected by the advective gas flow, making it easier to obtain a crystalline film with a relatively uniform thickness.

[0053] In this embodiment, the support substrate 200 is rotated around a first direction perpendicular to the film deposition surface 201 while chemical vapor deposition is performed to deposit the film. As a result, variations in the thickness of the crystal film due to the position on the plane of the support substrate 200 are suppressed, and consequently, the resistivity distribution within the plane is suppressed. When a SiC polycrystalline substrate is manufactured by the manufacturing method of this embodiment, a donut-shaped region of resistivity is formed, and a SiC polycrystalline substrate with a suppressed resistivity distribution within the plane is obtained. As a result, variations in the electrical properties of semiconductor devices made from SiC bonded substrates obtained by bonding these substrates are reduced. Thus, according to the manufacturing method of the SiC polycrystalline substrate of this embodiment, variations in properties due to the position on the film deposition surface can be suppressed not only for SiC polycrystalline substrates but also for various polycrystalline substrates and single crystal substrates.

[0054] Furthermore, the side of the support substrate 200 closest to the supply port 102, facing the supply port 1020, is susceptible to the influence of advection-like gas flow, and the crystalline film tends to become thicker on this side compared to the other film-forming surfaces 201. For this reason, a dummy plate may be placed on the mounting section 1082 closest to the supply port 102 instead of the support substrate 200.

[0055] In the film deposition apparatus 1000 shown in Figure 2, the rectifier plate 1070 and the support substrate 200 are in close proximity. By ensuring a sufficient distance between them, when the supplied gas reaches the periphery of the support substrate 200, it is possible to create a region where the gas loses its advect-like properties and exhibits more diffusive properties.

[0056] (Exposure Process) The exposure process is a process in which any part of the support substrate, on which a crystal film has been formed by the film formation process, is exposed. By exposing the support substrate through the exposure process, it is possible to facilitate the vaporization of the support substrate in the combustion removal process described later.

[0057] One example of an exposure process is a step in which the edges of the crystal film formed on the surface of a support substrate (e.g., a carbon support substrate) obtained by the above film formation process are removed to expose the support substrate (e.g., carbon).

[0058] Since a crystalline film is formed on the sidewall of the support substrate during the film deposition process, the support substrate can be exposed by, for example, feeding it into an end-face processing device and grinding approximately 2 to 4 mm inward from the end face of the deposited crystalline film. However, if the outer periphery of the support substrate is masked with a ring-shaped graphite or the like before the crystalline film is manufactured, end-face processing is unnecessary, and in this case, the exposure process involves removing the mask.

[0059] Alternatively, the carbon support substrate, which has a crystalline film deposited on its surface, can be drilled out using a core drill or the like to achieve a desired diameter (for example, 6 inches in diameter), thereby exposing the carbon support substrate on its outer periphery. In this case, the drilling process becomes the exposure process.

[0060] (Combustion Removal Process) The combustion removal process is a process in which a SiC polycrystalline substrate is obtained by burning and removing the support substrate. An example of the combustion removal process is a process in which the support substrate after the exposure process is held for 100 hours or more in an atmospheric atmosphere under conditions of a pressure of 1 atmosphere and a temperature of 800°C.

[0061] (Polishing Process) In the method for manufacturing a SiC polycrystalline substrate according to this embodiment, a polishing process may be included after the combustion removal process to polish the surface of the manufactured crystal film. If the SiC polycrystalline substrate is to be used as a substrate for semiconductor manufacturing, a surface accuracy that can be used in the semiconductor manufacturing process is required. Therefore, it is preferable to smooth the surface of the SiC polycrystalline substrate by this polishing process.

[0062] One example of a polishing process involves lapping a SiC polycrystalline substrate with a diamond slurry, hard polishing it with a mixed slurry of diamond and alumina, and then polishing it with a silica slurry (colloidal silica, pH 11). Through these processes, the surface of the SiC polycrystalline substrate can be smoothed.

[0063] (Other steps) The method for manufacturing a SiC polycrystalline substrate according to this embodiment may include other steps in addition to those described above. For example, a cleaning step to remove any deposits from the substrate due to the polishing step may be included.

[0064] The following provides a detailed explanation with reference to examples and comparative examples. Here, we will describe an example in which a carbon support substrate is used as the support substrate for film deposition, and a SiC polycrystalline film is deposited on the carbon support substrate. However, the present invention is not limited to the examples described below.

[0065] (Example 1) In the example, the film deposition apparatus 1000 shown in Figure 2 was used to manufacture the SiC polycrystalline film. However, in the film deposition apparatus 1000 shown in Figure 2, four mounting sections 1082 are provided in the vertical direction of each column 1081 so that the substrate holder 1080 can hold four support substrates 200, but in this example, 20 sections are provided so that 20 support substrates 200 can be held.

[0066] As the film deposition apparatus 1000, a hot-wall type thermal CVD apparatus was used, which introduced the raw material gas from the bottom side of the film deposition furnace 1010 and discharged it from the ceiling. As the support substrates 200, wafer-shaped carbon support substrates with a thickness of 5 mm and a diameter of 151 mm were used. Twenty support substrates 200 were placed on the substrate holder 1080 of the film deposition furnace 1010. The distance between adjacent support substrates 200 was set to be 20 mm, ensuring equal spacing. The film deposition surface 201 of the support substrates 200 was the side facing upwards (the back surface of the side facing the supply port 1020).

[0067] The inside of the film deposition furnace 1010 was evacuated using an exhaust pump (not shown) to create a reduced pressure state. Then, Ar gas was introduced to return the pressure inside the film deposition furnace 1010 to atmospheric pressure, and the inside of the film deposition furnace 1010 was heated to 1400°C while the Ar gas flowed through it. SiCl was used as the raw material gas. ４ ,CH ４ Using H as the carrier gas ２ Using N as the impurity doping gas, ２ SiCl was used. ４ :CH ４ : H ２ : N ２ The supply gas was provided at a flow rate ratio of 1:1:30:10.

[0068] The substrate holder 1080 was rotated at a rotational speed of 1 rpm (revolutions / minute) while chemical vapor deposition was performed on both sides of the support substrate 200 for 3000 minutes (film deposition process). During this time, the pressure inside the film deposition furnace 1010 was controlled to 20 kPa.

[0069] After the film deposition process was completed, the support substrate 200 with the SiC polycrystalline film deposited on it was removed from the deposition furnace 1010 along with the substrate holder 1080. The support substrate 200 was then removed from the substrate holder 108, and a portion of the edges of the deposited SiC polycrystalline film was removed to expose the carbon support substrate 200 (exposure process). Subsequently, the substrate was heated in an air atmosphere at 800°C for more than 100 hours to burn off the carbon support substrate (burn-off process). Through these operations, a total of 20 substrates were obtained per batch.

[0070] The thickness of all 20 obtained substrates was measured at five points. The thinnest point was 1157 μm, and the thickest point was 1290 μm. The obtained substrates were ground and polished to produce a 450 μm thick SiC polycrystalline substrate of Example 1. The resistivity on the surface of the film-deposited surface of the obtained SiC polycrystalline substrate of Example 1 was measured. The resistivity on the surface was measured at 37 points in the plane according to JIS R1637, and the average resistivity and resistivity distribution in the plane were determined.

[0071] Figure 4 shows a plan view of the measurement points in the plane of the SiC polycrystalline substrate where resistivity was measured in the examples and comparative examples. The 37 in-plane measurement points are the 37 measurement points P shown in Figure 4, which are located on the center point X of the SiC polycrystalline substrate 500 and on lines of diameter W in six directions with a central angle shifted by 30° each. There are 3 points at 20 mm intervals in both directions from the center point X, for a total of 37 points (= 1 (center point) + 6 (6 lines of diameter) × 6 (6 points on each line)). The results are summarized in Table 1 below.

[0072] As shown in Table 1, the SiC polycrystalline substrate of Example 1 had an average resistivity Ra of 0.0131 Ωcm (13.1 mΩcm), a maximum value Rmax of 0.0139 Ωcm (13.9 mΩcm) at 37 points in the plane, and a minimum value Rmin of 0.0124 Ωcm (12.4 mΩcm). Therefore, R （ａ＋２０％） is 0.01572, R （ａ－２０％） The result was 0.01048, and it was confirmed that equations (1) and (2) were satisfied, as shown below. Therefore, the resistivity distribution at multiple points in the SiC polycrystalline substrate of Example 1 falls within ±20% of the average resistivity.

[0073] Regarding equation (1) R （ａ＋２０％） = 0.01572 ≥ 0.0139 • Regarding equation (2) R （ａ－２０％） = 0.01048 ≤ 0.0124

[0074] Figure 5 shows an actual mapping diagram of the resistivity distribution on the surface of the SiC polycrystalline substrate of Example 1. The resistivity distribution mapping diagram shown in Figure 5 represents isoresistivity lines, and the numbers on the vertical and horizontal axes represent the distance from the center point X of the SiC polycrystalline substrate (one is denoted as + and the other as -), and the numbers in the figure represent the resistivity (Ωcm) of each isoresistivity line. The same applies to the resistivity distribution mapping diagrams in Figures 6 to 8.

[0075] As can be seen in Figure 5, by rotating the support substrate around a first direction perpendicular to the film deposition surface and flowing the raw material gas along this first direction during film deposition, a donut-shaped region of resistivity is formed. This trend was the same for all 20 substrates in one batch, resulting in SiC polycrystalline substrates with similar resistivity distribution patterns. When fabricating devices, it is desirable for the resistivity distribution pattern to not change between substrates.

[0076] (Example 2) In Example 1, the flow rate ratio of the supply gas was changed to SiCl ４ :CH ４ : H ２ : N ２ Except for setting the ratio to 1:1:30:17, the SiC polycrystalline substrate of Example 2 was fabricated by performing each step under the same conditions as in Example 1. The average resistivity and resistivity distribution on the film-deposited surface of the obtained SiC polycrystalline substrate of Example 2 were determined in the same manner as in Example 1. The results are summarized in Table 1 below.

[0077] As shown in Table 1, the SiC polycrystalline substrate of Example 2 had an average resistivity Ra of 0.0017 Ωcm (1.7 mΩcm), a maximum value Rmax of 0.0018 Ωcm (1.8 mΩcm), and a minimum value Rmin of 0.0016 Ωcm (1.6 mΩcm). Therefore, R （ａ＋２０％） is 0.00204, R （ａ－２０％） The value is 0.00128, and in Example 2, the resistivity distribution at multiple points of the SiC polycrystalline substrate falls within ±20% of the average resistivity.

[0078] Furthermore, Figure 6 shows an actual mapping of the resistivity distribution on the film-deposited surface of the SiC polycrystalline substrate of Example 2. As can be seen from Figure 6, the SiC polycrystalline substrate of Example 2, like Example 1, has a donut-shaped resistivity distribution. This trend was the same for all 20 substrates in one batch, and SiC polycrystalline substrates with similar resistivity distribution patterns were obtained. When fabricating devices, it is desirable for the resistivity distribution pattern to not change between substrates.

[0079] (Comparative Example 1) A SiC polycrystalline substrate of Comparative Example 1 was fabricated by performing each step in the same manner and under the same conditions as in Example 1, except that the substrate holder 1080 was not rotated and the rectifier plate 1070 was removed. The average resistivity and resistivity distribution on the film deposition surface of the obtained SiC polycrystalline substrate of Comparative Example 1 were determined in the same manner as in Example 1. The results are summarized in Table 1 below.

[0080] As shown in Table 1, the SiC polycrystalline substrate of Comparative Example 1 had an average resistivity Ra of 0.0132 Ωcm (13.2 mΩcm), which is almost the same as that of Example 1, but the maximum value Rmax was 0.0181 Ωcm (18.1 mΩcm) and the minimum value Rmin was 0.0114 Ωcm (11.4 mΩcm). Therefore, R （ａ＋２０％） is 0.01584, R （ａ－２０％） The value was 0.01056, confirming that the resistivity distribution at multiple points in the SiC polycrystalline substrate of Comparative Example 1 did not fall within ±20% of the average resistivity, indicating a large variation in resistivity within the plane.

[0081] Furthermore, Figure 7 shows the actual mapping of the resistivity distribution in the SiC polycrystalline substrate of Comparative Example 1. As can be seen from Figure 7, the actual resistivity distribution of the SiC polycrystalline substrate of Comparative Example 1 is biased, and is significantly different from the distribution of Examples 1 and 2, in which a donut-shaped resistivity region was formed.

[0082] In Comparative Example 1, the resistivity distribution on the film-forming surfaces of the 20 SiC polycrystalline substrates was not the same as in Example 1; each of the 20 substrates had a different resistivity distribution. This is presumed to be due to the distribution corresponding to the temperature and gas flow at the location where the support substrate 200 was placed in the film-forming furnace 1010. Therefore, in the 20 SiC polycrystalline substrates of Comparative Example 1, there is a high probability that variations in electrical performance within the plane will occur when fabricating devices.

[0083] (Comparative Example 2) A SiC polycrystalline substrate of Comparative Example 2 was fabricated by performing each step in the same manner and under the same conditions as in Example 2, except that the substrate holder 1080 was not rotated and the rectifier plate 1070 was removed. The average resistivity and resistivity distribution on the film deposition surface of the obtained SiC polycrystalline substrate of Comparative Example 2 were determined in the same manner as in Example 1. The results are summarized in Table 1 below.

[0084] As shown in Table 1, the SiC polycrystalline substrate of Comparative Example 2 had an average resistivity Ra of 0.0018 Ωcm (1.8 mΩcm), which is almost the same as that of Example 2, but the maximum value Rmax was 0.0020 Ωcm (2.0 mΩcm) and the minimum value Rmin was 0.0014 Ωcm (1.4 mΩcm). Therefore, R （ａ＋２０％） is 0.00216, R （ａ－２０％） The value was 0.00144, and it was confirmed that the resistivity distribution at multiple points in the SiC polycrystalline substrate of Comparative Example 2 did not fall within ±20% of the average resistivity, indicating a large variation in resistivity within the plane.

[0085] Furthermore, Figure 8 shows an actual mapping diagram of the resistivity distribution on the surface of the SiC polycrystalline substrate of Comparative Example 2. As can be seen from Figure 8, the actual resistivity distribution of the SiC polycrystalline substrate of Comparative Example 2 is biased, and is significantly different from the distribution of Examples 1 and 2, in which a donut-shaped resistivity region was formed.

[0086] In Comparative Example 2, the resistivity distribution on the film-forming surfaces of the 20 SiC polycrystalline substrates was not uniform, unlike in Example 2; each of the 20 substrates had a different resistivity distribution. This is presumed to be due to the same reasons as in Comparative Example 1, and it is highly probable that variations in electrical performance within the plane will occur when fabricating the device.

[0087]

[0088] In Table 1, the underlined values ​​are those that fall outside the ±20% range of the average resistivity Ra.

[0089] (Discussion of Results) As described above, in Examples 1 and 2, it is possible to manufacture SiC polycrystalline substrates with little variation in resistivity on the surface. In the examples, we introduced the case of depositing a SiC polycrystalline film on a carbon substrate as one example, but the effects of the embodiments can be similarly expected not only in this case, but also when manufacturing single crystal films or polycrystalline films of SiC, titanium nitride, aluminum nitride, titanium carbide, or diamond-like carbon on carbon substrates, silicon substrates, etc.

[0090] 200: Support substrate, 201: Film deposition surface, 1000: Film deposition apparatus, 1010: Film deposition furnace, 1020: Supply port, 1030: Exhaust port, 1040: Exhaust gas introduction chamber, 1050: Box, 1060: Heater, 1070: Rectifier plate, F: Direction of raw material gas flow, P: Measurement point, W: Diameter, X: Center, Y: Central axis

Claims

1. A SiC polycrystalline substrate comprising: a first portion including the central part of the film-forming surface and having a resistivity within a first range; and a second portion surrounding the first portion on the film-forming surface and having a resistivity greater than the first range.

2. The SiC polycrystalline substrate according to claim 1, wherein the average resistivity, which is the average value of the resistivity of the film-forming surface, is 25 mΩcm or less.

3. The SiC polycrystalline substrate according to claim 2, wherein the average resistivity is determined as the average of the resistivity of multiple points on the film-forming surface, and the resistivity of the multiple points is within ±20% of the average resistivity.

4. A SiC bonded substrate comprising: a SiC polycrystalline substrate according to claim 1; and a SiC single crystal substrate bonded to the film-forming surface.

5. A method for manufacturing a SiC polycrystalline substrate, comprising rotating a support substrate placed in a film deposition furnace around a first direction perpendicular to the film deposition surface of the support substrate as the central axis, and flowing a raw material gas along the first direction to perform chemical deposition on the film deposition surface.

6. The method for manufacturing a SiC polycrystalline substrate according to claim 5, wherein the raw material gas is rectified before it reaches the film deposition surface.

7. The method for manufacturing a SiC polycrystalline substrate according to claim 5, wherein a plurality of support substrates are arranged in the film deposition furnace.

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