Method for forming silicon carbide polycrystalline film and method for manufacturing silicon carbide polycrystalline substrate

Abstract

To provide a deposition method for a silicon carbide polycrystalline film and a production method for a silicon carbide polycrystalline substrate, wherein: an SiC polycrystalline film is deposited by CVD with a nitrogen doping gas on a carbon support substrate, and the SiC polycrystalline film is separated from the carbon support substrate with reduced warpage, thereby solving the problem of worsened yield, cost, productivity in the process and production of an SiC polycrystalline substrate, resulting in a high-conductivity SiC polycrystalline substrate with reduced warpage.SOLUTION: A deposition method for a silicon carbide polycrystalline film includes a deposition step in which the CVD is used to, with a nitrogen gas, silicon gas, and carbon gas, deposit a silicon carbide polycrystalline film of 300 μm-1200 μm thick on a carbon support substrate of 300 μm-10 mm thick. In the deposition step, an average deposition rate is 200 μm / h or less in depositing the silicon carbide polycrystalline film. The carbon support substrate satisfies αv / αp=2.5-4.0 where αp is a thermal expansion coefficient in a direction parallel with the thickness direction and αv is a thermal expansion coefficient in a direction orthogonal to the thickness direction.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a method for forming a silicon carbide polycrystalline film and a method for manufacturing a silicon carbide polycrystalline substrate, and in particular to a method for forming a silicon carbide (hereinafter sometimes referred to as "SiC") polycrystalline film on a carbon support substrate by chemical vapor deposition (hereinafter sometimes referred to as "CVD method"), and a method for manufacturing a SiC polycrystalline substrate, which subsequently involves burning and removing the carbon support substrate to obtain a SiC polycrystalline substrate. [Background technology]

[0002] SiC is a compound semiconductor material composed of silicon (hereinafter sometimes referred to as "Si") and carbon. Not only is SiC superior, with a dielectric breakdown field strength 10 times that of Si and a band gap three times that of Si, but it also allows for a wide range of control over the p-type and n-type required for device fabrication, making it a promising material for power devices that surpasses the limitations of Si.

[0003] However, compared to the widely used Si semiconductors, it is not possible to obtain large-area SiC single crystal substrates and the manufacturing process is complicated, making mass production of SiC semiconductors difficult and expensive compared to Si semiconductors.

[0004] Various efforts have been made to reduce the cost of SiC semiconductors. For example, Patent Document 1 describes a method for manufacturing a SiC substrate, in which the density of micropipes is at least 30 pieces / cm 2 It describes a method of preparing a SiC single crystal substrate and a SiC polycrystalline substrate as described below, performing a process of bonding the SiC single crystal substrate and the SiC polycrystalline substrate together, and then performing a process of thinning the SiC single crystal substrate, thereby manufacturing a substrate in which a SiC single crystal layer is formed on a SiC polycrystalline substrate.

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

[0006] This method makes it possible to produce more SiC substrates from one SiC single crystal ingot. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2009-117533 A [Patent Document 2] Japanese Patent Application Publication No. 10-251062 Summary of the Invention [Problem to be solved by the invention]

[0008] However, most of the SiC substrates manufactured by the above-described method are polycrystalline substrates. Therefore, the magnitude of warpage of the SiC substrate obtained by bonding a SiC single crystal substrate and a SiC polycrystalline substrate is dominated by the magnitude of warpage of the SiC polycrystalline substrate. Therefore, in the device manufacturing process after bonding the SiC polycrystalline substrate and the SiC single crystal substrate, if the SiC substrate has a large warpage, problems such as poor pattern formation in the photolithography process and non-uniform ion penetration depth in the ion implantation process occur. Therefore, it is required that the SiC polycrystalline substrate has a small warpage.

[0009] In response to the problem of large warpage of such SiC polycrystalline substrates, for example, Patent Document 2 proposes that the thermal expansion coefficient of the carbon support substrate used in forming the SiC polycrystalline film by the CVD method is (3.0 to 5.0) × 10-6 ( / K), and the thermal expansion coefficient of the SiC polycrystalline film is (4.3 to 4.5) × 10 -6 A method has been shown to obtain a SiC polycrystalline film with reduced warping by applying a carbon support substrate with a thermal expansion coefficient close to that of the SiC polycrystalline film ( / K), which can be caused by the difference in thermal expansion coefficients, thereby reducing the difference in volumetric shrinkage between the carbon support substrate and the SiC polycrystalline film during the process of cooling the carbon support substrate after the SiC polycrystalline film is formed, and by reducing the stress generated in the SiC polycrystalline film due to the difference in volumetric shrinkage.

[0010] However, it has been found that factors that cause warping of the SiC polycrystalline film are not only the difference in volumetric shrinkage during the cooling process due to the difference in thermal expansion coefficient between the carbon support substrate and the SiC polycrystalline film, but also the state of the crystal orientation of each crystal grain constituting the SiC polycrystalline film (for example, the orientation of the (0001) plane, etc.). In other words, if the crystal orientation of each crystal grain is in a non-uniform state, the SiC polycrystalline film grown on the carbon support substrate side is less able to reduce the stress perpendicular to the growth direction of the SiC polycrystalline film, which is received due to the difference in volumetric shrinkage during the cooling process, by the plastic structural transformation within each crystal grain, and as a result, the residual stress of the SiC polycrystalline film grown on the carbon support substrate side is greater than that of the surface of the SiC polycrystalline film.

[0011] On the other hand, the SiC polycrystalline film on the growth end side (hereinafter sometimes referred to as the "growth surface side"), which is the surface of the SiC polycrystalline film that is less likely to be restrained by the volumetric change of the carbon support substrate, is less susceptible to stress due to the volumetric shrinkage of the carbon support substrate than the carbon support substrate side when it shrinks in volume during the cooling process, and the residual stress on the growth surface side is smaller than that on the carbon support substrate side. The magnitude of the difference in the residual stress inherent in the carbon support substrate side and the growth surface side of the SiC polycrystalline film is the main factor that determines the magnitude of warping of the SiC polycrystalline film obtained after removing the carbon support substrate. Therefore, if the crystal orientation of each crystal grain is non-uniform, the warping of the SiC polycrystalline film after removing the carbon support substrate becomes large, and thereafter, in the process of processing the SiC polycrystalline film into a SiC polycrystalline substrate, even if the portion where the grain size changes in the SiC polycrystalline film is scraped off, the degree of warping does not become sufficiently small.

[0012] In addition, in the process of processing the SiC polycrystalline film into a SiC polycrystalline substrate, in processes such as surface grinding and surface polishing for adjusting the SiC polycrystalline film to a specified thickness and flatness, the large warpage of the SiC polycrystalline film causes many processing defects such as poor thickness, flatness, or warpage, which is also a factor in reducing the yield in the processing process into a SiC polycrystalline substrate. In addition, if the thickness of the SiC polycrystalline film is increased by deposition using a CVD method, for example, in order to improve these processing defects, the amount of raw material gas, carrier gas, etc. used increases and the deposition time becomes longer, resulting in a deterioration in the manufacturing cost and productivity of the SiC polycrystalline film.

[0013] On the other hand, the difference in residual stress inherent in the SiC polycrystalline film on the carbon support substrate side and the growth surface side, which is the main factor that determines the degree of warping of the SiC polycrystalline film mentioned above, also depends on the difference in the size of the polycrystalline grains grown by the film formation process, and generally, the SiC polycrystalline grains that start growing on the surface of a support substrate made of a material other than SiC, such as carbon, are small, and if the subsequent growth conditions are not appropriate, the polycrystalline grains will gradually expand as they grow. Under such inappropriate growth conditions, even if a carbon support substrate with an appropriate thermal expansion coefficient is used, it may not be possible to sufficiently reduce the warping of the SiC polycrystalline film.

[0014] The present invention has been made in view of these problems, and an object of the present invention is to provide a method for forming a silicon carbide polycrystalline film and a method for manufacturing a silicon carbide polycrystalline substrate, which solves the problems of deterioration in yield, cost, and productivity when processing and manufacturing SiC polycrystalline substrates by forming a SiC polycrystalline film together with nitrogen doping gas on a carbon support substrate by a CVD method and mitigating warping of the SiC polycrystalline film separated from the carbon support substrate, and can provide a SiC polycrystalline substrate with high conductivity and reduced substrate warping. [Means for solving the problem]

[0015] As a result of intensive research by the inventors to solve the above problems, they have discovered that in a process of depositing a SiC polycrystalline film by a CVD method by introducing a raw material gas together with a nitrogen doping gas onto a carbon support substrate, warping of the SiC polycrystalline film can be reduced by using a carbon material with large structural anisotropy for the support substrate, in which the ratio αv / αp of the thermal expansion coefficient αp in the parallel direction to the SiC film deposition direction of the carbon support substrate and the thermal expansion coefficient αv in the perpendicular direction to the SiC film deposition direction is within a predetermined range, and by growing the SiC polycrystalline film at a predetermined film deposition rate.

[0016] In order to solve the above problems, the present invention provides a method for forming a silicon carbide polycrystalline film, comprising: a deposition step of depositing a silicon carbide polycrystalline film having a thickness of 300 μm to 1200 μm on a carbon support substrate having a thickness of 300 μm to 10 mm by chemical vapor deposition using nitrogen gas, a silicon-based gas, and a carbon-based gas, wherein the average deposition rate of the silicon carbide polycrystalline film in the deposition step is 200 μm / hour or less, and the carbon support substrate has a thermal expansion coefficient of αv / αp=2.5 to 4.0, where αp is a thermal expansion coefficient parallel to the thickness direction and αv is a thermal expansion coefficient perpendicular to the thickness direction.

[0017] The a p is 1.0 × 10 -6 ( / K)~6.0×10 -6 ( / K), and αv is 1.0×10 -6 ( / K)~6.0×10 -6 ( / K) is also acceptable.

[0018] The silicon carbide polycrystalline film may be formed at a film formation temperature of 1200 to 1500°C in the film formation step.

[0019] In order to solve the above-mentioned problems, the method for producing a silicon carbide polycrystalline substrate of the present invention includes a combustion removal step of burning and removing the carbon support substrate from a laminate including the carbon support substrate and the silicon carbide polycrystalline film obtained by the method for forming a silicon carbide polycrystalline film of the present invention.

[0020] The method may include a polishing step of polishing the surface of the silicon carbide polycrystalline film after the burning and removing step. Effect of the Invention

[0021] According to the method for forming a silicon carbide polycrystalline film and the method for manufacturing a silicon carbide polycrystalline substrate of the present invention, a SiC polycrystalline film is formed on a carbon support substrate together with a nitrogen doping gas by a CVD method, and warping of the SiC polycrystalline film separated from the carbon support substrate is mitigated, thereby solving the problems of deterioration in yield, cost, and productivity when processing and manufacturing SiC polycrystalline substrates, and a SiC polycrystalline substrate with reduced substrate warping and high conductivity can be obtained. [Brief description of the drawings]

[0022] [Figure 1] 1 is a schematic diagram showing a cross-sectional side view of a carbon support substrate and a silicon carbide polycrystalline film when a method for forming a silicon carbide polycrystalline film of the present invention is carried out; [Diagram 2] 1 is a schematic diagram showing a cross-sectional side view of a carbon support substrate and a silicon carbide polycrystalline film when a film formation method different from the silicon carbide polycrystalline film formation method of the present invention is carried out. FIG. [Diagram 3] FIG. 2 is a schematic diagram showing a cross-sectional side view of one crystal grain of a carbon support substrate and the orientation of its internal crystal structure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Hereinafter, an embodiment of the present invention will be described in detail, but the present invention is not limited to this embodiment.

[0024] [Method of forming silicon carbide polycrystalline film] The method for forming a silicon carbide polycrystalline film of the present invention includes the film forming steps described below.

[0025] <Film formation process> This process is a process of forming a silicon carbide polycrystalline film having a thickness of 300 μm to 1200 μm on a carbon support substrate having a thickness of 300 μm to 10 mm by chemical vapor deposition using nitrogen gas, silicon-based gas, and carbon-based gas.

[0026] For example, a carbon support substrate is fixed in a reaction furnace of a film forming apparatus, and the inside of the furnace is heated to a reaction temperature while flowing an inert gas such as Ar under reduced pressure. When the reaction temperature is reached, the inert gas is stopped, and raw material gases such as silicon-based gas and carbon-based gas, and nitrogen gas and carrier gas as dopant gas are supplied into the furnace, and a chemical reaction is carried out on the surface of the carbon support substrate and in the gas phase for a predetermined period of time under atmospheric pressure, thereby forming a silicon carbide polycrystalline film.

[0027] (raw gas) The source gas is not particularly limited as long as it can form a SiC polycrystalline film, and generally used Si-based source gas or C-based source gas can be used. As the Si-based source gas, for example, silane (SiH4) can be used, and chlorine-based Si source-containing gas (chloride source) containing Cl having an etching effect, such as monochlorosilane (SiH3Cl), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), and tetrachlorosilane (SiCl4), can also be used. As the C-based source gas, for example, hydrocarbon gas such as methane (CH4), propane (C3H8), and acetylene (C2H2) can be used. In addition to the above, gases containing both Si and C, such as trichloromethylsilane (CH3Cl3Si), trichlorophenylsilane (C6H5Cl3Si), dichloromethylsilane (CH4Cl2Si), dichlorodimethylsilane ((CH3)2SiCl2), and chlorotrimethylsilane ((CH3)3SiCl), can also be used as source gases.

[0028] (Nitrogen gas) In addition, an impurity doping gas is supplied simultaneously with these source gases in an amount appropriate for the target conductivity. For example, nitrogen (N2) gas can be used to make the conductivity type n-type, and trimethylaluminum (TMA) gas can be used to make the conductivity type p-type. In the present invention, nitrogen gas can be used.

[0029] (Carrier gas) Furthermore, a carrier gas can be used together with these source gases and nitrogen gas. As the carrier gas, any commonly used carrier gas can be used as long as it can spread the source gas onto the carbon support substrate without impeding the formation of the silicon carbide polycrystalline film. For example, hydrogen (H2), which has excellent thermal conductivity and an etching effect on silicon carbide, can be used.

[0030] (Average deposition rate) In the film formation step, the average film formation speed of the silicon carbide polycrystalline film is 200 μm / hour or less. For example, the average film formation speed can be adjusted by changing the flow rate of a source gas such as a Si-based source gas or a C-based source gas to control the growth speed of the SiC polycrystalline film.

[0031] By using carbon having a structural anisotropy in the range of αv / αp=2.5-4.0 as the carbon support substrate and setting the average film formation speed to 200 μm / hour, it is possible to uniform the crystal orientation and crystal grain size of the silicon carbide polycrystalline film to be grown to a certain degree. If the silicon carbide polycrystalline film has a uniform crystal orientation and crystal grain size, the stress that the silicon carbide polycrystalline film receives due to the volumetric shrinkage of the carbon support substrate, which occurs when the carbon support substrate on which the silicon carbide polycrystalline film is formed after the film formation process is cooled, can be alleviated to the same degree in the polycrystalline grains on the support substrate side and the growth surface side by plastic structural transformation in the crystal grains in the film. This alleviation can reduce the residual stress difference between the support substrate side and the growth surface side of the silicon carbide polycrystalline film, and as a result, it is possible to reduce the warpage of the silicon carbide polycrystalline film that occurs after the carbon support substrate is burned and removed.

[0032] (Film forming temperature) In the film forming step, the film forming temperature for forming the silicon carbide polycrystalline film is not particularly limited as long as it is within a temperature range in which crystal grains having a uniform crystal orientation of the silicon carbide polycrystal can be formed so as not to cause significant warping. For example, in order to sufficiently suppress warping of the silicon carbide polycrystalline film, it is preferable to set the film forming temperature to 1200 to 1500°C, at which silicon carbide crystal grains having a cubic crystal structure with a (111) growth surface are easily formed.

[0033] (Thickness of film) The thickness of the silicon carbide polycrystalline substrate may be 350 μm as a standard, and in consideration of this, the silicon carbide polycrystalline film may be formed to a thickness of 300 μm to 1200 μm in the film forming process. For example, to obtain a silicon carbide polycrystalline substrate with a thickness of 350 μm, the thickness of the silicon carbide polycrystalline film to be formed may be 400 μm, taking into consideration that the thickness will be thinned by polishing and grinding in the polishing process and surface grinding process. If the thickness is less than 300 μm, the warping of the silicon carbide polycrystalline film may be large due to the influence of internal stress. In addition, if the thickness is thicker than 1200 μm, the polishing amount and grinding amount may be large in the polishing process and surface grinding process in the processing and manufacturing process of the silicon carbide polycrystalline substrate, and the material loss may be large.

[0034] Carbon support substrate Hereinafter, with reference to FIGS. 1 to 3, the carbon support substrate used in the present invention, the cause of warping in the formed silicon carbide polycrystalline film, and the reason why the present invention can reduce the warping will be described.

[0035] 3 is a schematic diagram showing a cross-sectional side view of one crystal grain of a carbon support substrate and the orientation of its internal crystal structure. The vertical lines on the cross-section of the carbon crystal grain 10 indicate the crystal orientation direction 50, and a number of crystal grains 10 with different orientation directions 50 come together to form the carbon support substrate 100 or 150.

[0036] 1 is a schematic diagram showing a cross-sectional side view of a carbon support substrate and a silicon carbide polycrystalline film when the silicon carbide polycrystalline film forming method of the present invention is carried out. A silicon carbide polycrystalline film 200 is formed on a carbon support substrate 100 with the direction indicated by arrow A as the film formation direction. The carbon support substrate 100 is a substrate obtained by processing anisotropic graphite with a strong vertical orientation, with the majority of crystal grains 11 having an orientation direction 50 facing the vertical direction, and a small number of crystal grains 12 facing diagonally to the right and crystal grains 13 facing diagonally to the left. Such anisotropic graphite can be obtained, for example, by an extrusion method or the like.

[0037] The carbon support substrate 100 obtained from anisotropic graphite has a different thermal expansion coefficient depending on the direction of the substrate. In the present invention, when the thermal expansion coefficient in a direction parallel to the deposition direction A of the silicon carbide polycrystalline film (parallel to the thickness direction of the carbon support substrate 100) is αp and the thermal expansion coefficient in a direction perpendicular to the deposition direction A (direction perpendicular to the thickness direction of the carbon support substrate 100) is αv, the carbon support substrate 100 used has structural anisotropy such that αv / αp=2.5 to 4.0.

[0038] By using a support substrate made of a carbon material having such a structural anisotropy in the range of αv / αp=2.5 to 4.0, it becomes possible to align the crystal orientation 210 of the silicon carbide polycrystalline film 200 to be grown in a certain direction to some extent, and in Fig. 1, the crystal orientation 210 is aligned mainly in the film formation direction. In this way, when the laminate of the carbon support substrate 100 and the silicon carbide polycrystalline film 200 is cooled after the film formation process, the silicon carbide polycrystalline film 200 with the aligned crystal orientation 210 relaxes the stress caused by the volumetric contraction of the carbon support substrate 100 by the plastic structural transformation in the crystal grains 220 of the silicon carbide polycrystalline film 200, thereby reducing the residual stress difference between the support substrate 230 side and the growth surface 240 side of the silicon carbide polycrystalline film 200, and thus it becomes possible to reduce the warpage of the silicon carbide polycrystalline film 200 that occurs after the carbon support substrate 100 is burned and removed.

[0039] 2 is a schematic diagram showing a cross-sectional side view of a carbon support substrate and a silicon carbide polycrystalline film when a film formation method different from the silicon carbide polycrystalline film formation method of the present invention is carried out. As in the case of FIG. 1, a silicon carbide polycrystalline film 250 is formed on a carbon support substrate 150 with the direction indicated by the arrow A as the film formation direction. The carbon support substrate 150 is a substrate obtained by processing isotropic graphite, in which crystal grains 14 to 16 whose orientation direction 50 faces the up-down direction, the right diagonal direction, and the left diagonal direction are present at the same level. Such isotropic graphite can be obtained, for example, by a hydrostatic pressure method or the like.

[0040] The carbon support substrate 150 obtained from isotropic graphite does not have a thermal expansion coefficient that differs depending on the direction of the substrate, as compared with the carbon support substrate 100. In FIG. 2, a substrate that does not fall within the range of αv / αp=2.5 to 4.0 and satisfies αv / αp≈1.0 is used as the carbon support substrate 150.

[0041] When such a carbon support substrate 150 is used, the crystal orientation 260 of the silicon carbide polycrystalline film 250 to be grown is not aligned in a certain direction but is irregularly oriented. In this way, when the laminate of the carbon support substrate 150 and the silicon carbide polycrystalline film 250 is cooled after the film formation process, it is difficult to alleviate the stress caused by the volumetric contraction of the carbon support substrate 150 by plastic structural transformation in the crystal grains 270 of the silicon carbide polycrystalline film 250, and it is not possible to reduce the residual stress difference between the support substrate 280 side and the growth surface 290 side of the silicon carbide polycrystalline film 250, making it difficult to reduce the warpage of the silicon carbide polycrystalline film 250 that occurs after the carbon support substrate 150 is burned and removed.

[0042] At present, a carbon support substrate 100 with αv / αp exceeding 4.0 is not available, and the behavior of such a support substrate cannot be confirmed.

[0043] In the present invention, a carbon support substrate having a thickness of 300 μm to 10 mm is used. If the carbon support substrate is too thin, less than 300 μm, the carbon support substrate itself may warp, which may cause the silicon carbide polycrystalline film to warp to an extent that it cannot be corrected. On the other hand, if the carbon support substrate is too thick, more than 10 mm, it may take a long time to burn and remove the carbon support substrate, which may reduce the manufacturing efficiency of the silicon carbide polycrystalline substrate.

[0044] The thermal expansion coefficient of the carbon support substrate is α p is 1.0 × 10 -6 ( / K)~6.0×10 -6 When αp is in this range, a carbon support substrate made of particles having a single crystal structure is easily obtained, and a silicon carbide polycrystalline film with uniform crystal orientation is easily produced. In particular, when α p is 1.0×10 -6 ( / K)~2.0×10 -6 ( / K), this tendency becomes more pronounced. Also, when αp is 1.0×10 -6 ( / K)~6.0×10 -6 If the ratio ( / K) is outside this range, it may be difficult to obtain a carbon support substrate made up of particles having a single crystal structure, and it may be difficult to produce a silicon carbide polycrystalline film with uniform crystal orientation.

[0045] Also, αv is 1.0×10 -6 ( / K)~6.0×10 -6 ( / K). When α is in this range, a carbon support substrate composed of particles having a single crystal structure is easily obtained, and a silicon carbide polycrystalline film with uniform crystal orientation is easily produced. In particular, when α is 2.5×10 -6 ( / K)~5.0×10 -6 ( / K), this tendency becomes more pronounced. Also, when αv is 1.0×10 -6 ( / K)~6.0×10 -6 If the ratio ( / K) is outside this range, it may be difficult to obtain a carbon support substrate made up of particles having a single crystal structure, and it may be difficult to produce a silicon carbide polycrystalline film with uniform crystal orientation.

[0046] (Other processes) The method for forming a silicon carbide polycrystalline film of the present invention may include other steps in addition to the above-mentioned film formation step, such as a step of setting a plurality of carbon support substrates on a substrate holder in a film formation apparatus, a step of heating the set carbon support substrates, a step of circulating an inert gas such as argon in order to make the substrate under an inert atmosphere so that no reaction that would inhibit the formation of a silicon carbide polycrystalline film occurs in the carbon support substrate before chemical vapor deposition, and a cooling step of stopping the supply of the source gas, doping gas, and carrier gas after the film formation step and cooling the inside of the furnace of the film formation apparatus to room temperature.

[0047] [Method for manufacturing silicon carbide polycrystalline substrate] Next, one embodiment of a method for producing a silicon carbide polycrystalline substrate of the present invention will be described. The method includes a burning and removing step as described below.

[0048] <Combustion removal process> This step is a step of burning and removing the carbon support substrate from the laminate including the carbon support substrate and the silicon carbide polycrystalline film obtained by the above-mentioned method for forming a silicon carbide polycrystalline film. As a result, the carbon support substrate disappears and the silicon carbide polycrystalline film with suppressed warpage remains, which becomes the silicon carbide polycrystalline substrate.

[0049] The carbon support substrate can be removed by burning using an appropriate method such as heating in air, for example, at about 1000° C. in an air atmosphere.

[0050] <Polishing process> The method for producing a silicon carbide polycrystalline substrate of the present invention may include a polishing step of polishing the surface of the silicon carbide polycrystalline film after the burnt removal step. If the silicon carbide polycrystalline substrate is to be used as a substrate for semiconductor manufacturing, for example, it needs to have a surface precision that can be used in the semiconductor manufacturing process. Therefore, it is preferable to smooth the surface of the silicon carbide polycrystalline film by this step.

[0051] For example, the surface of a silicon carbide polycrystalline substrate can be smoothed by lapping a silicon carbide polycrystalline film 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).

[0052] (Other processes) The method for producing a silicon carbide polycrystalline substrate of the present invention may include other steps in addition to the steps described above. For example, in order to burn and remove the carbon support substrate completely covered with the silicon carbide polycrystalline film, an exposure step of removing a part of the silicon carbide polycrystalline film attached to the side surface of the carbon support substrate to expose the carbon support substrate before the burning and removing step, and a cleaning step of cleaning the silicon carbide polycrystalline substrate after the polishing step may be included. In addition, a surface grinding step may be included to adjust the silicon carbide polycrystalline film to a predetermined thickness.

[0053] Specifically, the exposure process can involve cutting off a portion of the outer peripheral edge of the silicon carbide polycrystalline film with a single wire saw using diamond or C-BN (cubic BN) abrasive grains, or by scraping off a portion of the outer peripheral edge of the silicon carbide polycrystalline film with a grinding wheel, thereby exposing the carbon substrate.

[0054] The method for forming a silicon carbide polycrystalline film of the present invention can provide a silicon carbide polycrystalline substrate with reduced warpage, and therefore, in the polishing step or surface grinding step in the processing and manufacturing process of the silicon carbide polycrystalline substrate, the uniformity of thickness, flatness, or warpage caused by the large warpage of the silicon carbide polycrystalline film does not deteriorate, and it becomes possible to process and manufacture the silicon carbide polycrystalline substrate into a silicon carbide polycrystalline substrate with small warpage and high conductivity. EXAMPLES

[0055] Examples of the present invention will be specifically described below with reference to comparative examples, but the present invention is not limited to these examples.

[0056] [Example 1] (Deposition of silicon carbide polycrystalline film) In the reaction tube of a thermal CVD apparatus used for chemical vapor deposition, a total of four carbon support substrates 100 with different conditions of αv / αp=2.5, 3.0, 3.5, and 4.0, each with a diameter of 6 inches and a thickness of 500 μm, were fixed, and the inside of the furnace was depressurized by an exhaust pump while Ar gas was flowed into the furnace at a flow rate of 20 L / min, and then the furnace was heated to 1200° C., and then the Ar gas was stopped. Next, SiCl4 at a flow rate of 1 L / min (gas equivalent, 25° C.), CH4 at a flow rate of 1 L / min, N2 at a flow rate of 50 L / min as a doping gas, and H2 at a flow rate of 10 L / min as a carrier gas were flowed into the carbon support substrate 100, and a silicon carbide polycrystalline film 200 with a thickness of about 1000 μm was formed on both the front and back surfaces of the carbon support substrate 100 by film formation with a flow time of the raw material gases, etc. being 20 hours. The average deposition rate in the deposition process was 50 μm / hr. After that, the inflow of the source gas, doping gas, and carrier gas was stopped, and the inside of the furnace was cooled to room temperature.

[0057] (Manufacturing of silicon carbide polycrystalline substrates) Only the silicon carbide polycrystalline film formed on the outer periphery of the side of the carbon support substrate 100 was ground to expose the side of the carbon support substrate 100, and then the carbon support substrate 100 was heated under a temperature condition of approximately 1000°C in an atmospheric air to burn and remove it, and the carbon support substrate 100 and the silicon carbide polycrystalline film 200 were separated to obtain a total of eight silicon carbide polycrystalline substrates, two for each of the conditions of αv / αp = 2.5, 3.0, 3.5, and 4.0.

[0058] (Measurement of warpage of silicon carbide polycrystalline substrate) The center line of the surface of the growth surface 240 of the silicon carbide polycrystalline substrate was measured by an oblique incidence type optical measuring device, and the difference between the maximum and minimum values ​​of the obtained measurements was taken as the warpage, and the average of the warpage of two substrates was calculated for each of the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0. The measurement was performed at five points, including the center, the circumferential edge, and a point between the center and the circumferential edge that was the same distance from the center as it was from the circumferential edge. As a result, the average warpage of the silicon carbide polycrystalline substrate obtained under each of the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Example 1 was 110 μm to 130 μm.

[0059] Table 1 shows the measurement results of the thermal expansion coefficients (αp, αv), αv / αp, the deposition temperature of the silicon carbide polycrystalline film, and the warpage of the silicon carbide polycrystalline substrates of the four carbon support substrates 100 in Example 1. Other examples are similarly shown in Tables 1 and 2, and comparative examples are similarly shown in Table 3.

[0060] [Example 2] Except for changing the inflow rates of the source gases SiCl4 and CH4 and setting the average film formation rate to 100 μm / hr, film formation, grinding, and firing were performed under the same conditions as in Example 1 to obtain silicon carbide polycrystalline substrates. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Example 2 was 120 μm to 140 μm.

[0061] [Example 3] Except for changing the inflow rates of the source gases SiCl4 and CH4 to set the average film formation rate to 200 μm / hr, film formation, grinding, and firing were performed under the same conditions as in Example 1 to obtain silicon carbide polycrystalline substrates. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Example 3 was 170 μm to 190 μm.

[0062] [Comparative Example 1] Except for changing the inflow rates of the source gases SiCl4 and CH4 to set the average film formation rate to 300 μm / hr, film formation, grinding, and firing were performed under the same conditions as in Example 1 to obtain silicon carbide polycrystalline substrates. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Comparative Example 1 was 300 μm to 350 μm.

[0063] [Comparative Example 2] Except for changing the inflow rates of the source gases SiCl4 and CH4 and setting the average film formation rate to 500 μm / hr, film formation, grinding, and firing were performed under the same conditions as in Example 1 to obtain silicon carbide polycrystalline substrates. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Comparative Example 2 was 450 μm to 480 μm.

[0064] [Example 4] Silicon carbide polycrystalline substrates were obtained by film formation, grinding, and firing under the same conditions as in Example 1, except that the film formation temperature was 1500° C. The silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Example 4 had an average warpage of 110 μm to 130 μm.

[0065] [Example 5] Silicon carbide polycrystalline substrates were obtained by film formation, grinding, and firing under the same conditions as in Example 2, except that the film formation temperature was 1500° C. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Example 5 was 130 μm to 140 μm.

[0066] [Example 6] Silicon carbide polycrystalline substrates were obtained by film formation, grinding, and firing under the same conditions as in Example 3, except that the film formation temperature was 1500° C. The silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Example 6 had an average warpage of 180 μm to 200 μm.

[0067] [Comparative Example 3] Silicon carbide polycrystalline substrates were obtained by film formation, grinding, and firing under the same conditions as in Comparative Example 1, except that the film formation temperature was 1500° C. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Comparative Example 3 was 440 μm to 470 μm.

[0068] [Comparative Example 4] Silicon carbide polycrystalline substrates were obtained by film formation, grinding, and firing under the same conditions as in Comparative Example 2, except that the film formation temperature was 1500° C. The average warpage of the silicon carbide polycrystalline substrates obtained under the conditions of αv / αp=2.5, 3.0, 3.5, and 4.0 in Comparative Example 4 was 630 μm to 660 μm.

[0069] [Table 1]

[0070] [Table 2]

[0071] [Table 3]

[0072] [summary] As described above, the present invention solves the problems of the deterioration of yield, cost, and productivity when processing and manufacturing a silicon carbide polycrystalline substrate, and can obtain a silicon carbide polycrystalline substrate with high conductivity and reduced warpage of the substrate. In particular, since the warpage of the silicon carbide polycrystalline substrate can be reduced, it can be used in a device manufacturing process as a silicon carbide substrate for horizontal and vertical diodes. In addition, it is possible to suppress pattern formation defects in a photolithography process and non-uniformity of ion penetration depth in an ion implantation process, and thus an improvement in yield can be expected. [Explanation of symbols]

[0073] 10 Grains 11 Crystal grains 12 Grains 13 Crystal grains 14 Grains 15 Grains 16 Grains 50 Orientation 100 Carbon support substrate 150 Carbon support substrate 200 Silicon carbide polycrystalline film 210 Crystal Orientation 220 Grains 230 Support Substrate 240 Growth aspect 250 Silicon carbide polycrystalline film 260 Crystal Orientation 270 Grains 280 Support Substrate 290 Growth aspect A Arrow

Claims

1. The method includes a film formation step of forming a silicon carbide polycrystalline film having a thickness of 300 μm to 1200 μm on a carbon support substrate having a thickness of 300 μm to 10 mm by a chemical vapor deposition method using nitrogen gas, a silicon-based gas, and a carbon-based gas; an average film formation speed of the silicon carbide polycrystalline film in the film formation step is 200 μm / hour or less; the thermal expansion coefficient of the carbon support substrate in a direction parallel to the thickness direction is αp and the thermal expansion coefficient of the carbon support substrate in a direction perpendicular to the thickness direction is αv, where αv / αp=2.5 to 4.0; The method for forming a silicon carbide polycrystalline film, wherein the αp is 1.0×10 −6 ( / K).

2. 2. The method for forming a silicon carbide polycrystalline film according to claim 1, wherein the silicon carbide polycrystalline film is formed at a film formation temperature of 1200 to 1500° C. in the film formation step.

3. 2. A method for producing a silicon carbide polycrystalline substrate, comprising: a burning and removing step of burning and removing the carbon support substrate from a laminate including the carbon support substrate and the silicon carbide polycrystalline film obtained by the method for forming a silicon carbide polycrystalline film according to claim 1.

4. 4. The method for producing a silicon carbide polycrystalline substrate according to claim 3, further comprising a polishing step of polishing a surface of the silicon carbide polycrystalline film after the burning and removing step.

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