JP7600612B2 - Method for forming silicon carbide polycrystalline film and method for manufacturing silicon carbide polycrystalline substrate - Google Patents

Description

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"), and a method for manufacturing a SiC polycrystalline substrate, which subsequently burns and removes the carbon support substrate to obtain a SiC polycrystalline substrate.

SiC is a compound semiconductor material composed of silicon (hereafter 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.

However, compared to the widely used Si semiconductors, it is difficult 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.

Various efforts have been made to reduce the cost of SiC semiconductors. For example, Patent Literature 1 describes a method for manufacturing a SiC substrate, which includes at least preparing a SiC single crystal substrate and a SiC polycrystalline substrate having a micropipe density of 30 pieces/cm2 or ^less, performing a step of bonding the SiC single crystal substrate and the SiC polycrystalline substrate, and then performing a step of thinning the SiC single crystal substrate, thereby manufacturing a substrate in which a SiC single crystal layer is formed on the SiC polycrystalline substrate.

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 a step of mechanically peeling it off at the hydrogen ion implanted layer.

This method makes it possible to produce many more SiC substrates from a single SiC single crystal ingot.

JP 2009-117533 A Japanese Patent Application Publication No. 10-251062

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

In response to the problem of significant warping of such SiC polycrystalline substrates, for example, Patent Document 2 discloses a method of obtaining a SiC polycrystalline film with reduced warping by using a carbon support substrate used in depositing a SiC polycrystalline film by CVD with a thermal expansion coefficient in the range of (3.0 to ^5.0 ) x ^10-6 (/K) and using a carbon support substrate with a thermal expansion coefficient close to that of the SiC polycrystalline film, which is (4.3 to 4.5) x 10-6 (/K), 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 depositing the SiC polycrystalline film, which may occur due to the difference in thermal expansion coefficients, and reducing the stress generated in the SiC polycrystalline film due to the difference in volumetric shrinkage.

However, it has been found that the 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 that constitutes the SiC polycrystalline film (for example, the orientation of the (0001) plane). In other words, if the crystal orientation of each crystal grain is non-uniform, 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 due to the difference in volumetric shrinkage during the cooling process through 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.

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 restricted 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 residual stress inherent in the carbon support substrate side and the growth surface side of this 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 areas where the grain size changes in the SiC polycrystalline film are scraped off, the degree of warping does not become sufficiently small.

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 to adjust the SiC polycrystalline film to a specified thickness and flatness, processing defects such as poor thickness, flatness, or warping due to the large warping of the SiC polycrystalline film occur frequently, 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 and carrier gas used increases and the deposition time becomes longer, resulting in a deterioration in the manufacturing cost and productivity of the SiC polycrystalline film.

The present invention was made with a focus on these problems, and its objective 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 the deterioration of yield, cost, and productivity when processing and manufacturing a SiC polycrystalline substrate by forming a SiC polycrystalline film together with nitrogen doping gas on a carbon support substrate by a CVD method and mitigating the warping of the SiC polycrystalline film separated from the carbon support substrate, thereby obtaining a SiC polycrystalline substrate with high conductivity and reduced substrate warping.

The inventors conducted extensive research to solve the above problems, and discovered that in the process of depositing a SiC polycrystalline film by CVD 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 of the carbon support substrate to the direction of SiC film deposition and the thermal expansion coefficient αv in the perpendicular direction is within a predetermined range.

In order to solve the above problems, the method for forming a silicon carbide polycrystalline film of the present invention includes a deposition process in which a silicon carbide polycrystalline film having a thickness of 300 μm to 1200 μm is formed 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, and the carbon support substrate has a thermal expansion coefficient of αv/αp = 2.5 to 4.0, where αp is the thermal expansion coefficient parallel to the thickness direction and αv is the thermal expansion coefficient perpendicular to the thickness direction.

The α p may be in the range of 1.0×10 ⁻⁶ (/K) to 6.0×10 ⁻⁶ (/K), and the α v may be in the range of 1.0×10 ⁻⁶ (/K) to 6.0× ^{10 −6} (/K).

The film formation temperature for forming the silicon carbide polycrystalline film in the film formation process may be 1200 to 1500°C.

In order to solve the above problem, the method for producing a silicon carbide polycrystalline substrate of the present invention includes a burning and removing 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 method for forming a silicon carbide polycrystalline film of the present invention.

After the burning and removing process, a polishing process may be included in which the surface of the silicon carbide polycrystalline film is polished.

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 by CVD together with nitrogen doping gas, 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 highly conductive SiC polycrystalline substrate with reduced substrate warping can be obtained.

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; 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. 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.

The following describes in detail an embodiment of the present invention, but the present invention is not limited to this embodiment.

[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.

<Film formation process>
This process is a process for 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.

For example, a carbon support substrate is fixed in the reactor of a film-forming device, and the temperature inside the reactor is raised to the 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 gases are supplied into the reactor, and a chemical reaction is carried out on the surface of the carbon support substrate and in the gas phase at atmospheric pressure for a predetermined period of time, thereby forming a silicon carbide polycrystalline film.

(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 (SiH ₄ ) can be used, and chlorine-based Si source-containing gas (chloride source) containing Cl having an etching effect, such as monochlorosilane (SiH ₃ Cl), dichlorosilane (SiH ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ), and tetrachlorosilane (SiCl ₄ ), can also be used. As the C-based source gas, for example, hydrocarbon gas such as methane (CH ₄ ), propane (C ₃ H ₈ ), and acetylene (C ₂ H ₂ ) 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.

(Nitrogen gas)
In addition, an impurity doping gas is supplied simultaneously with these source gases in an amount appropriate for the desired 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.

(Carrier gas)
Furthermore, a carrier gas can be used together with the source gas and the 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 (H ₂ ), which has excellent thermal conductivity and an etching effect on silicon carbide, can be used.

In the film formation process, the film formation 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 with a certain degree of alignment in the crystal orientation of the silicon carbide polycrystals can be produced so that significant warping does not occur. For example, in order to sufficiently suppress warping of the silicon carbide polycrystalline film, it is preferable to set the temperature at 1200 to 1500°C, at which silicon carbide crystal grains with a cubic crystal structure whose growth surface is the (111) plane are likely to be produced.

(Thickness of film)
The silicon carbide polycrystalline substrate may have a standard thickness of 350 μm, 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 formation process. For example, to obtain a silicon carbide polycrystalline substrate having 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 is reduced 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. If the thickness is greater 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 loss of material may be large.

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.

Figure 3 shows a schematic diagram of a side cross section of one crystal grain of a carbon support substrate, showing the orientation of the crystal's internal structure. The vertical straight lines on the cross section of the carbon crystal grain 10 indicate the crystal orientation direction 50, and multiple crystal grains 10 with different orientation directions 50 come together to form the carbon support substrate 100 or 150.

Figure 1 shows a schematic diagram of a side cross section of a carbon support substrate and a silicon carbide polycrystalline film when the silicon carbide polycrystalline film formation 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 up and down, 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.

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 (perpendicular to the thickness direction of the carbon support substrate 100) is αv, the carbon support substrate 100 used has a structural anisotropy such that αv/αp = 2.5 to 4.0.

By using a carbon support substrate having such structural anisotropy in the range of αv/αp = 2.5 to 4.0, it is possible to align the crystal orientation 210 of the silicon carbide polycrystalline film 200 to a certain extent in a certain direction, 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 is able to reduce 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, thereby reducing the warping of the silicon carbide polycrystalline film 200 that occurs after the carbon support substrate 100 is burned and removed.

Figure 2 shows a schematic diagram of 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 Figure 1, a silicon carbide polycrystalline film 250 is formed on a carbon support substrate 150 with the direction indicated by arrow A as the film formation direction. The carbon support substrate 150 is a substrate obtained by processing isotropic graphite, in which crystal grains 14-16 with orientation directions 50 facing up and down, right diagonal directions, and left diagonal directions are present at the same level. Such isotropic graphite can be obtained, for example, by a hydrostatic pressure method.

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 to 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 for which αv/αp ≈ 1.0 is used as the carbon support substrate 150.

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 fixed 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 shrinkage of the carbon support substrate 150 through plastic structural transformation within 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 warping of the silicon carbide polycrystalline film 250 that occurs after the carbon support substrate 150 is burned and removed.

Note that carbon support substrates 100 with αv/αp exceeding 4.0 are currently unavailable, and the behavior of such support substrates cannot be confirmed.

In addition, 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, warping may occur in the carbon support substrate itself, causing the warping of the silicon carbide polycrystalline film to become too large to be corrected. On the other hand, if the carbon support substrate is too thick, exceeding 10 mm, it may take a long time to burn and remove the carbon support substrate, reducing the manufacturing efficiency of the silicon carbide polycrystalline substrate.

In addition, in the thermal expansion coefficient of the carbon support substrate, α p may be 1.0×10 ⁻⁶ (/K) to 6.0× ^{10 −6} (/K). When α p 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 having uniform crystal orientation is easily generated. In particular, when α p is 1.0×10 ⁻⁶ (/K) to 2.0× ^{10 −6} (/K), this tendency becomes remarkable. Also, when α p is out of the range of 1.0×10 ⁻⁶ (/K) to 6.0× ^{10 −6} (/K), it may be difficult to obtain a carbon support substrate composed of particles having a single crystal structure, and it may be difficult to generate a silicon carbide polycrystalline film having uniform crystal orientation.

Also, αv may be 1.0×10 ⁻⁶ (/K) to 6.0× ^{10 −6} (/K). When αv 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 having uniform crystal orientation is easily produced. In particular, when αv is 2.5×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K), this tendency becomes remarkable. When αv is out of the range of 1.0×10 ⁻⁶ (/K) to ^{6.0×10 −6} (/K), it may be difficult to obtain a carbon support substrate composed of particles having a single crystal structure, and it may be difficult to produce a silicon carbide polycrystalline film having uniform crystal orientation.

(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.

[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.

<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.

The carbon support substrate can be removed by burning using an appropriate method such as heating in air. Heating conditions include, for example, heating to about 1000°C in an air atmosphere.

<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.

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).

(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.

Specifically, the exposure process can involve cutting off part of the outer 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 part of the outer edge of the silicon carbide polycrystalline film with a grinding wheel to expose the carbon substrate.

The method for forming a silicon carbide polycrystalline film of the present invention makes it possible to obtain a silicon carbide polycrystalline substrate with reduced warping. Therefore, in the polishing process and surface grinding process in the processing and manufacturing of silicon carbide polycrystalline substrates, the uniformity of thickness, flatness, or warping caused by the large warping of the silicon carbide polycrystalline film does not deteriorate, making it possible to process and manufacture a silicon carbide polycrystalline substrate with low warping and high conductivity.

The following describes the examples of the present invention in detail with comparative examples. Note that the present invention is not limited to these examples.

[Example 1]
(Deposition of silicon carbide polycrystalline film)
Ten carbon support substrates 100 with a diameter of 6 inches, a thickness of 500 μm, and thermal expansion coefficients of αp = 1.0 × 10 ^-6 (/K), αv = 2.5 ^{× 10 -6} (/K), and αv/αp = 2.5 were fixed in the reaction tube of a thermal CVD apparatus used for chemical vapor deposition, and the pressure inside the furnace was reduced using an exhaust pump while Ar gas was flowed into the furnace at a flow rate of 20 L/min.The furnace was then heated to 1400°C, and the Ar gas was then 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 for 20 hours to form a silicon carbide polycrystalline film 200 having a thickness of about 1000 μm on both the front and back surfaces of the carbon support substrate 100. Thereafter, the flow of the raw material gas, doping gas, and carrier gas was stopped, and the inside of the furnace was cooled to room temperature.

(Production of silicon carbide polycrystalline substrate)
Only the silicon carbide polycrystalline film formed on the outer periphery of the side surface of the carbon support substrate 100 was ground to expose the side surface of the carbon support substrate 100, and then the carbon support substrate 100 was heated under a temperature condition of about 1000° C. in an air atmosphere to burn and remove the silicon carbide polycrystalline film 200, and the carbon support substrate 100 and the silicon carbide polycrystalline film 200 were separated to obtain 20 silicon carbide polycrystalline substrates.

(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. Measurements were performed at five points, at the center, the circumferential edge, and points between the center and the circumferential edge that were the same distance from the center and the circumferential edge. As a result, the warpage of the silicon carbide polycrystalline substrate obtained by Example 1 was 100 μm on average for 20 substrates. Table 1 shows the measurement results of αv/αp, the deposition temperature of the silicon carbide polycrystalline film, and the warpage of the silicon carbide polycrystalline substrate.

[Example 2]
Except for using a carbon support substrate having thermal expansion coefficients of αp=1.0× ¹⁰⁻⁶ (/K), αv= ^3.2×10−6 (/K), and αv/αp=3.2, film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 1. The warpage of the silicon carbide polycrystalline substrate obtained in Example 2 was 80 μm.

[Example 3]
Except for using a carbon support substrate having thermal expansion coefficients of αp=1.0× ¹⁰⁻⁶ (/K), αv= ^4.0×10−6 (/K), and αv/αp=4.0, film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 1. The warpage of the silicon carbide polycrystalline substrate obtained in Example 3 was 60 μm.

[Example 4]
Except for the temperature during film formation being 1200° C., film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 1. The warpage of the silicon carbide polycrystalline substrate obtained in Example 4 was 140 μm.

[Example 5]
The film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 2, except that the film formation temperature was 1200° C. The warpage of the silicon carbide polycrystalline substrate obtained in Example 5 was 120 μm.

[Example 6]
The film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 3, except that the film formation temperature was 1200° C. The warpage of the silicon carbide polycrystalline substrate obtained in Example 6 was 110 μm.

[Example 7]
Except for the temperature during film formation being 1500° C., film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 1. The warpage of the silicon carbide polycrystalline substrate obtained in Example 7 was 150 μm.

[Example 8]
The film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 2, except that the film formation temperature was 1500° C. The warpage of the silicon carbide polycrystalline substrate obtained in Example 8 was 130 μm.

[Example 9]
The film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 3, except that the film formation temperature was 1500° C. The warpage of the silicon carbide polycrystalline substrate obtained in Example 9 was 120 μm.

[Comparative Example 1]
Except for using a carbon support substrate having thermal expansion coefficients of αp=1.0× ¹⁰⁻⁶ (/K), αv= ^1.0×10−6 (/K), and αv/αp=1.0, film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 1. The warpage of the silicon carbide polycrystalline substrate obtained in Comparative Example 1 was 460 μm.

[Comparative Example 2]
Except for using a carbon support substrate having thermal expansion coefficients of αp=2.0× ¹⁰⁻⁶ (/K), αv= ^3.6×10−6 (/K), and αv/αp=1.8, film formation, grinding, firing, and warpage measurement were performed under the same conditions as in Example 1. The warpage of the silicon carbide polycrystalline substrate obtained in Comparative Example 2 was 220 μm.

[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.

10 Crystal grain 11 Crystal grain 12 Crystal grain 13 Crystal grain 14 Crystal grain 15 Crystal grain 16 Crystal grain 50 Orientation direction 100 Carbon support substrate 150 Carbon support substrate 200 Silicon carbide polycrystalline film 210 Crystal orientation 220 Crystal grain 230 Support substrate 240 Growth surface 250 Silicon carbide polycrystalline film 260 Crystal orientation 270 Crystal grain 280 Support substrate 290 Growth surface A Arrow

Claims (4)

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;
wherein the carbon support substrate has a thermal expansion coefficient αv/αp=2.5 to 4.0, where αp is a thermal expansion coefficient parallel to a thickness direction and αv is a thermal expansion coefficient perpendicular to the thickness direction, αp is 1.0×10 ^-6 (/K) (room temperature to 450° C.) to 2.0 ×10 ^-6 (/K) (room temperature to 450° C.) , and αv is 2.5×10 ^-6 (/K) (room temperature to 450° C.) to 6.0×10 ^-6 (/K) (room temperature to 450° C.) . The method for forming a silicon carbide polycrystalline film according to claim 1, wherein the film forming temperature for forming the silicon carbide polycrystalline film in the film forming step is 1200 to 1500°C. 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 or 2. The method for producing a silicon carbide polycrystalline substrate according to claim 3, further comprising a polishing step of polishing the surface of the silicon carbide polycrystalline film after the burning and removing step.

Images