JP7163756B2 - LAMINATED PRODUCT, METHOD FOR MANUFACTURING LAMINATED BODY, AND METHOD FOR MANUFACTURING SILICON CARBIDE POLYCRYSTALLINE SUBSTRATE - Google Patents

Description

The present invention relates to a laminate, a laminate manufacturing method, and a silicon carbide polycrystalline substrate manufacturing method.

Silicon carbide (hereinafter sometimes referred to as "SiC") is a compound semiconductor material composed of silicon (hereinafter sometimes referred to as "Si") and carbon. SiC not only has a dielectric breakdown field strength 10 times that of Si and a bandgap 3 times that of Si, but it is also possible to control the p-type and n-type necessary for device fabrication in a wide range. Therefore, it is expected as a material for power devices exceeding the limit of Si.

However, SiC semiconductors cannot be obtained in large-area SiC single-crystal substrates and require more complicated processes than Si semiconductors, which are widely used. rice field.

Various efforts have been made to reduce the cost of SiC semiconductors. For example, Patent Literature 1 discloses a method for manufacturing a SiC substrate, wherein at least a SiC single crystal substrate and a SiC polycrystalline substrate having a micropipe density of 30/cm ² or less are prepared, and the SiC single crystal substrate and the SiC polycrystalline substrate are prepared. It is possible to manufacture a substrate in which a SiC single crystal layer is formed on the SiC polycrystalline substrate by performing a step of bonding the SiC polycrystalline silicon carbide substrate and then performing a step of thinning the SiC single crystal substrate. Have been described.

Furthermore, in Patent Document 1, before the step of bonding the SiC single crystal substrate and the SiC polycrystalline substrate together, 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 crystal substrate and the SiC polycrystalline substrate together and before the step of thinning the SiC single crystal substrate, heat treatment is performed at a temperature of 350° C. or less to thin the SiC single crystal substrate. A method for manufacturing a SiC substrate is described in which a step of mechanically exfoliating an ion-implanted layer is used.

Such a method has made it possible to obtain a larger number of SiC substrates from one SiC single crystal ingot.

JP 2009-117533 A

However, most of the SiC substrates manufactured by the method described above are SiC polycrystalline substrates. Therefore, the magnitude of the warpage of the SiC substrate obtained by bonding the SiC polycrystalline substrate and the SiC single crystal substrate together is predominantly the magnitude of the warpage of the SiC polycrystalline substrate. Therefore, if the SiC polycrystalline film separated from the carbon support substrate has a large warp, the yield due to the warp deteriorates when such a SiC polycrystalline film is used in the device manufacturing process of diodes and transistors. Further, in the device manufacturing process after bonding the SiC polycrystalline substrate and the SiC single crystal substrate together, if the SiC substrate has a large warp, the pattern formation is defective in the photolithography process and the ion penetration depth is insufficient in the ion implantation process. Problems such as uniformity arise. Therefore, the warpage of the SiC polycrystalline film is required to be small.

The present invention has been made with a focus on such problems, and an object of the present invention is to provide a carbon supporting substrate by, for example, a chemical vapor deposition method (hereinafter sometimes referred to as a "CVD method"). In a method of manufacturing a SiC polycrystalline substrate by forming a SiC polycrystalline film thereon with a nitrogen doping gas and then separating the SiC polycrystalline film from a carbon supporting substrate, the thermal expansion coefficient of the SiC polycrystalline film (4. 3 to 4.5)×10 ⁻⁶ (/K), a carbon supporting substrate having a coefficient of thermal expansion different from 10 −6 (/K) is used. By solving the problem that the warpage of the SiC polycrystalline substrate increases due to the stress imbalance generated in the SiC polycrystalline film due to the difference in volume shrinkage, a highly conductive SiC polycrystalline substrate with reduced warpage can be manufactured. to provide.

In order to solve the above problems, the present inventors conducted intensive research and found that the thermal expansion coefficient of the SiC polycrystalline film (4.3 ∼4.5) × 10 ^-6 (/K), even if a carbon supporting substrate having a different thermal expansion coefficient is used, it is possible to form a carbon film having a predetermined thickness or more after forming a SiC polycrystalline film. , and found that the warpage of SiC polycrystalline substrates can be reduced, and have arrived at the present invention.

In order to solve the above problems, the laminate of the present invention has a thickness of 300 μm to 10 mm and a coefficient of thermal expansion of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K). a silicon carbide polycrystalline film having a thickness of 300 μm to 700 μm formed on the carbon substrate; and a silicon carbide polycrystalline film having a thickness of 50 μm to 200 μm and having a thermal expansion coefficient of 4. and a carbon film of .0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K).

In order to solve the above problems, the method for producing a laminate of the present invention has a thickness of 300 μm to 10 mm and a coefficient of thermal expansion of 4.0×10 ⁻⁶ (/K) ^to 5.0×10 −6 . A first film forming step of forming a silicon carbide polycrystalline film having a thickness of 300 μm to 700 μm on a carbon substrate of ⁶ (/K) by chemical vapor deposition, and forming a silicon carbide polycrystalline film having a thickness of 50 μm by chemical vapor deposition. a second film forming step of forming a carbon film having a thickness of up to 200 μm and a thermal expansion coefficient of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K).

Further, in order to solve the above problems, a method for manufacturing a silicon carbide polycrystalline substrate of the present invention burns and removes the carbon substrate and the carbon film of the laminate manufactured by the method for manufacturing the laminate described above. including a burn-out step.

After the burning and removing step, a polishing step of polishing the surface of the polycrystalline silicon carbide substrate may be included.

ADVANTAGE OF THE INVENTION According to the laminated body, the manufacturing method of a laminated body, and the manufacturing method of the silicon carbide polycrystalline substrate of this invention, the curvature of a SiC polycrystalline substrate can be reduced, without impairing high electrical conductivity. Therefore, in addition to the horizontal SiC substrate for diodes, it can be used as a vertical SiC substrate for diodes in the device manufacturing process. Non-uniformity of ion penetration depth in the ion implantation process can be suppressed, and an improvement in yield can be expected.

1 is a schematic cross-sectional view of a laminate 100, which is an example of the laminate of the present invention; FIG. FIG. 2 is a schematic cross-sectional view of a laminate 110 that is an example of the laminate of the present invention different from FIG. FIG. 4 is a schematic cross-sectional view of a warped carbon substrate on which a silicon carbide polycrystalline film is formed.

Embodiments of the present invention will be described in detail below, but the present invention is not limited to these embodiments.

[Laminate]
A laminate of the present invention includes a carbon substrate, a silicon carbide polycrystalline film, and a carbon film, which will be described below.

<Carbon substrate>
The carbon substrate has a thickness of 300 μm to 10 mm and a coefficient of thermal expansion of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K). By using carbon as the substrate, the SiC polycrystalline film does not warp during film formation because it does not soften or change its shape due to heat during the chemical vapor deposition process, unlike the Si substrate. Moreover, if carbon is used, the SiC polycrystalline film can be easily separated by combustion.

If the thickness of the carbon substrate is less than 300 μm, the SiC polycrystalline film formed on the carbon substrate may warp due to the internal stress of the formed SiC polycrystalline film, which may cause problems. be. Further, if the thickness is greater than 10 mm, the number of substrates that can be placed in the chamber of the film forming apparatus is reduced, so the number of carbon substrates that can be chemically vapor-deposited with a SiC polycrystalline film in one film forming process is small. resulting in a decrease in productivity. If the thickness of the substrate is 300 μm to 10 mm, the above warpage does not occur and productivity can be maintained.

Further, when the thermal expansion coefficient of the carbon substrate is less than 4.0×10 ⁻⁶ (/K), the graphite as the carbon substrate is no longer isotropic graphite, and has orientation dependence and expansion. There is a possibility that the shape of the carbon substrate itself may be changed due to the deformation, and the SiC polycrystalline film may be cracked. Further, if the coefficient of thermal expansion exceeds 5.0×10 ⁻⁶ (/K), there is a risk that the formed SiC polycrystalline film will be greatly warped or cracks will occur. Since the carbon substrate has a coefficient of thermal expansion of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K), cracks, warping, and cracking of the SiC polycrystalline film occur. can be suppressed.

<Silicon carbide polycrystalline film>
The silicon carbide polycrystalline film is a film with a thickness of 300 μm to 700 μm formed on a carbon substrate. For example, a SiC polycrystalline film can be formed on a carbon substrate by chemical vapor deposition using a laminate manufacturing method described later.

The thickness of the silicon carbide polycrystalline film is a general polycrystalline film used for SiC substrates. There is a possibility that problems may arise in thinning. In addition, the film thickness of the polycrystalline silicon carbide film is also required by the device manufacturing process. Further, when the silicon carbide polycrystalline film is thick, there is a possibility that the amount of processing is large when removing the unnecessary polycrystalline film after the device is manufactured, resulting in poor economy.

<Carbon film>
The carbon film is formed on the silicon carbide polycrystalline film, has a thickness of 50 μm to 200 μm, and a thermal expansion coefficient of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K). membrane. By sandwiching the SiC polycrystalline film between the carbon substrate and the carbon film, the warping of the SiC polycrystalline film after the carbon substrate is separated due to the difference in thermal expansion coefficient between the carbon substrate and the SiC polycrystalline film is alleviated. can be done. Moreover, if it is a carbon film, the SiC polycrystalline film can be easily separated by burning, like the carbon substrate.

If the thickness of the carbon film is less than 50 μm, the effect of alleviating the warpage of the SiC polycrystalline film may not be sufficiently obtained. On the other hand, if the thickness is more than 200 μm, it takes a long time to form the carbon film, and there is a risk that the productivity will decrease, and that the SiC polycrystalline film will warp due to the excessive thickness of the carbon film. If the thickness of the carbon film is 50 μm to 200 μm, warping of the SiC polycrystalline film can be sufficiently alleviated, and productivity can be maintained.

Also, the carbon film has a coefficient of thermal expansion substantially the same as that of the carbon substrate. That is, the thermal expansion coefficient of the carbon film is set to 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K), and the SiC polycrystalline film is sandwiched between carbon films having approximately the same thermal expansion coefficient. As a result, warpage of the SiC polycrystalline film after separation of the carbon substrate can be reduced.

The plane size of the SiC polycrystalline film in the laminate may be either 4 inches or 6 inches in diameter. For example, such a SiC polycrystalline film can be obtained by depositing a SiC polycrystalline film on a carbon substrate having a diameter of 4 inches or 6 inches by chemical vapor deposition in a method for manufacturing a laminate, which will be described later.

(Other configurations)
The laminate of the present invention can have other configurations in addition to those described above. For example, on the condition that it can be installed in a furnace for burning a carbon substrate or a carbon film, not only one layer but also two layers, three layers, four layers or more of composite layers composed of a SiC polycrystalline film and a carbon film, Multiple layers may be provided repeatedly.

[Laminate production method]
Next, one aspect of the manufacturing method of the laminate of the present invention described above will be described. This manufacturing method includes a first film forming process and a second film forming process, which will be described below.

<First film formation step>
In this process, a carbon substrate having a thickness of 300 μm to 10 mm and a coefficient of thermal expansion of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K) is applied to a carbon substrate having a thickness of 300 μm by chemical vapor deposition. This is a step of forming a silicon carbide polycrystalline film of up to 700 μm. The thickness of the carbon substrate, the coefficient of thermal expansion, and the thickness of the SiC polycrystalline film are as described in the item of the laminate.

A SiC polycrystalline film is formed by chemical vapor deposition using a CVD method. For example, a carbon substrate is fixed in a reaction furnace of a film forming apparatus, and the inside of the furnace is heated to the reaction temperature while an inert gas such as Ar is flowed under reduced pressure. When the reaction temperature is reached, the inert gas is stopped and the source gas, carrier gas, etc. are allowed to flow, whereby a SiC polycrystalline film formed on the carbon substrate can be obtained.

More specifically, a mixed gas such as a raw material gas containing components of the SiC polycrystalline film and a carrier gas heated to a temperature of 1200 to 1700° C. is applied to a heated carbon substrate having a coefficient of thermal expansion different from that of the SiC polycrystalline film. is supplied, and a chemical reaction is performed on the surface of the carbon substrate or in the gas phase under atmospheric pressure for a predetermined time to deposit a SiC polycrystalline film.

(raw material gas)
The raw material gas is not particularly limited as long as a SiC polycrystalline film can be formed, and a generally used Si-based raw material gas or C-based raw material gas can be used. As the Si-based source gas, for example, silane (SiH ₄ ) can be used, as well as monochlorosilane (SiH ₃ Cl), dichlorosilane (SiH ₂ Cl ₂ ), trichlorosilane (SiHCl ₃ ), tetrachlorosilane (SiCl ₄ ). ), a chlorine-based Si raw material-containing gas (chloride-based raw material) containing Cl having an etching action can also be used. Hydrocarbon gases such as methane (CH ₄ ), propane (C ₃ H ₈ ) and acetylene (C ₂ H ₂ ) can be used as the C source gas. In addition to the above, trichloromethylsilane (CH ₃ Cl ₃ Si), trichlorophenylsilane (C ₆ H ₅ Cl ₃ Si), dichloromethylsilane (CH ₄ Cl ₂ Si), dichlorodimethylsilane ((CH ₃ ) ₂ SiCl ₂ ), chlorotrimethylsilane ((CH ₃ ) ₃ SiCl), and other gases containing both Si and C can also be used as source gases.

(carrier gas)
As the carrier gas, any commonly used carrier gas can be used as long as the source gas can be spread over the substrate without interfering with the film formation. For example, hydrogen (H ₂ ), which has excellent thermal conductivity and an etching effect on SiC, can be used.

(other gases)
Also, an impurity doping gas can be supplied as a third gas at the same time as these raw material gas and carrier gas in an amount corresponding to the target conductivity. For example, nitrogen (N ₂ ) gas can be used for n-type conductivity, and trimethylaluminum (TMA) gas can be used for p-type conductivity.

<Second film formation step>
In this step, a silicon carbide polycrystalline film is formed by chemical vapor deposition to have a thickness of 50 μm to 200 μm and a thermal expansion coefficient of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K). is a step of forming a carbon film. The thickness and thermal expansion coefficient of the carbon film are as described in the item of the laminate.

A carbon film is formed by chemical vapor deposition by a CVD method. For example, a carbon substrate on which a SiC polycrystalline film is formed 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 the raw material gas, carrier gas, etc. are allowed to flow, whereby a carbon film formed on the SiC polycrystalline film can be obtained.

More specifically, to the carbon substrate on which the heated SiC polycrystalline film is formed, a mixed gas such as a raw material gas and a carrier gas containing components of the carbon film heated to a temperature of 1200 to 1700° C. is supplied. , a method of depositing a carbon film by performing a chemical reaction on the surface of a SiC polycrystalline film or in a gas phase under atmospheric pressure for a predetermined time.

For example, the carbon substrate on which the SiC polycrystalline film is formed by the first film forming process can be fixed in the reaction furnace of the film forming apparatus, and the second film forming process can be started. Further, by stopping the supply of the Si-based raw material gas under the conditions of the first film forming process, the second film forming process can be performed continuously from the first film forming process.

(raw material gas)
The raw material gas is not particularly limited as long as it can form a carbon film, and a generally used C-based raw material gas can be used. For example, hydrocarbon gases such as methane ₍ CH4), propane _{( C3H8} ) and acetylene _{( C2H2} ) can be used.

(carrier gas)
As the carrier gas, any commonly used carrier gas can be used as long as the raw material gas can be developed into the SiC polycrystalline film without interfering with the formation of the carbon film. For example, hydrogen (H ₂ ) can be used as in the first film formation step.

(other gases)
In addition to these raw material gas and carrier gas, a third gas such as HCl gas can be used as an etching gas. When forming a SiC polycrystalline film, if the types and ratios of the raw material gas and carrier gas are not appropriate, some Si grains may be generated and a single SiC polycrystalline film may not be formed. The etching gas can be supplied simultaneously with the raw material gas and the carrier gas at a suitable ratio so as not to generate the etching gas.

<Other processes>
The method for manufacturing a laminate of the present invention can include other steps in addition to the steps described above. For example, in the process of setting a plurality of carbon substrates on a substrate holder in the deposition apparatus, in the process of heating the set carbon substrates, and in the carbon substrates before chemical vapor deposition, there are and a step of circulating an inert gas such as argon so as to place the substrate in an inert atmosphere.

[Manufacturing method of polycrystalline silicon carbide substrate]
Next, one aspect of the method for manufacturing a silicon carbide polycrystalline substrate of the present invention will be described. Such a manufacturing method includes a combustion removal step described below.

<Combustion removal process>
This step is a step of burning and removing the carbon substrate and the carbon film of the laminate manufactured by the method for manufacturing the laminate described above. As a result, the carbon substrate and the carbon film disappear and the silicon carbide polycrystalline film remains, which becomes the silicon carbide polycrystalline substrate.

Burning removal of the carbon substrate and the carbon film can be performed by an appropriate method such as heating in the air. Heating conditions include, for example, heating to about 1000° C. in an air atmosphere.

<Polishing process>
The method for manufacturing a polycrystalline silicon carbide substrate of the present invention may include a polishing step of polishing the surface of the polycrystalline silicon carbide substrate after the removal by burning. If the polycrystalline silicon carbide substrate is to be used, for example, in the manufacture of semiconductors, it must have surface accuracy that can be used in the semiconductor manufacturing process. Therefore, it is preferable to smooth the surface of the polycrystalline silicon carbide substrate by this step.

For example, a polycrystalline silicon carbide substrate is lapped with a diamond slurry, hard-polished with a mixed slurry of diamond and alumina, and then polished with a silica slurry (colloidal silica, pH 11). The surface can be smoothed.

(Other processes)
The method for manufacturing a polycrystalline silicon carbide substrate of the present invention can include other steps in addition to the steps described above. For example, in order to burn off the carbon substrate completely covered with the polycrystalline silicon carbide film, an exposing step of removing part of the polycrystalline silicon carbide film to expose the carbon substrate before the burning removal step, or a polishing step. A cleaning step for cleaning the silicon carbide polycrystalline substrate afterward, and the like are included.

Specifically, the exposure step includes a method of cutting a part 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, and a method of carbonizing with a polishing wheel. The carbon substrate can be exposed by scraping off a portion of the outer peripheral edge of the silicon polycrystalline film.

1 to 3, a description will be given of the factors that cause the SiC polycrystalline substrate to warp, and the reason why the warping can be reduced by the present invention.

FIG. 3 is a schematic cross-sectional view of a carbon substrate on which a polycrystalline silicon carbide film is formed. The carbon substrate 200 is obtained by depositing the SiC polycrystalline film 20 on the carbon substrate 10 by the above-described CVD method or the like. After forming the SiC polycrystalline film 20, when the carbon substrate 200 is cooled to room temperature, the carbon substrate 200 may be deformed under the influence of volume shrinkage. For example, since the coefficient of thermal expansion of the carbon substrate 10 and the coefficient of thermal expansion of the SiC polycrystalline film 20 are different, the internal stress in the direction in which the side surface of the carbon substrate 10 is compressed inward is greater than that of the SiC polycrystalline film 20. may also grow. As in this case, if the volume contraction rate of the carbon substrate 10 is larger than that of the SiC polycrystalline film 20, the surface 11 of the carbon substrate 10 is recessed inward, and the surface 21 of the SiC polycrystalline film 20 protrudes outward. There is a case where a warp such as deformation occurs (Fig. 3(a)). If the carbon substrate 10 is burned off in this state by the burning removal process, the remaining SiC polycrystalline film 20 may not completely recover from the warpage, resulting in a warped SiC polycrystalline substrate.

On the other hand, since the coefficient of thermal expansion of the carbon substrate 10 and the coefficient of thermal expansion of the SiC polycrystalline film 20 are different, the internal stress in the direction in which the SiC polycrystalline film 20 is compressed inward on the side surface is greater than that of the carbon substrate 10. may be larger than As in this case, when the SiC polycrystalline film 20 has a larger volume contraction rate than the carbon substrate 10, the surface 11 of the carbon substrate 10 protrudes outward and the surface 21 of the SiC polycrystalline film 20 dents inward. In some cases, a warp that deforms into a shape may occur (Fig. 3(b)). If the carbon substrate 10 is burned off in this state by the burning removal process, the remaining SiC polycrystalline film 20 may not completely recover from the warpage, resulting in a warped SiC polycrystalline substrate.

FIG. 1 is a schematic cross-sectional view of a laminate 100, which is an example of the laminate of the present invention. The laminated body 100 is formed by depositing the SiC polycrystalline film 20 on the carbon substrate 10 by the above-described CVD method or the like, and further depositing the carbon film 30 on the SiC polycrystalline film 20 . The layered body 100 is also affected by volumetric shrinkage when the layered body 100 is cooled to room temperature after the carbon film 30 is formed. However, since the carbon substrate 10 and the carbon film 30 have substantially the same coefficient of thermal expansion, it is possible to suppress or alleviate the occurrence of warpage during cooling.

For example, since the coefficient of thermal expansion of the carbon substrate 10 and the coefficient of thermal expansion of the SiC polycrystalline film 20 are different, the internal stress in the direction in which the side surface of the carbon substrate 10 is compressed inward is greater than that of the SiC polycrystalline film 20. may also grow. As in this case, even if the volume shrinkage ratio of the carbon substrate 10 is larger than that of the SiC polycrystalline film 20, the internal stress in the direction in which the side surfaces of the carbon film 30 are compressed inwardly causes the SiC polycrystalline film 20 to , the stresses of the carbon substrate 10 and the carbon substrate 30 on both sides of the SiC polycrystalline film 20 can be balanced. As a result, it is possible to suppress or mitigate the occurrence of warping such that the surface 11 of the carbon substrate 10 is deformed inwardly. Therefore, even if the carbon substrate 10 and the carbon film 30 are burnt off by the burn-off process, the remaining SiC polycrystalline film 20 will not be in such a warped state as to affect the subsequent process.

In addition, since the coefficient of thermal expansion of the carbon substrate 10 and the coefficient of thermal expansion of the SiC polycrystalline film 20 are different, the internal stress in the direction in which the side surfaces of the SiC polycrystalline film 20 are compressed inward is greater than that of the carbon substrate 10. may also grow. In this case as well, even if the SiC polycrystalline film 20 has a larger volumetric contraction rate than the carbon substrate 10, the internal stress in the direction in which the side surfaces of the carbon film 30 are compressed inwardly causes the SiC polycrystalline film to Since it is smaller than that of 20, the carbon substrate 10 and the carbon substrate 30 on both sides of the SiC polycrystalline film 20 can balance the stress. As a result, it is possible to suppress or alleviate the occurrence of warpage that deforms the surface 11 of the carbon substrate 10 to protrude outward. Therefore, even if the carbon substrate 10 and the carbon film 30 are burnt off in the burn-off process, the remaining SiC polycrystalline film 20 will not be warped significantly to affect the subsequent process.

FIG. 2 is a schematic cross-sectional view of a laminate 110, which is an example of the laminate of the present invention different from that of FIG. Laminate 110 is obtained by forming SiC polycrystalline film 20 on the entire surface of carbon substrate 10 by the above-described CVD method or the like, and further forming carbon film 30 on the entire surface of SiC polycrystalline film 20 . (Fig. 2(a)). On the other hand, the laminated body 110 shown in FIG. 2B is obtained by removing the outer peripheral edge of the SiC polycrystalline film 20 through the exposure process to expose the carbon substrate 10 .

Even if the SiC polycrystalline film 20 is formed on both the front surface and the back surface of the carbon substrate 10 as in the laminate 110 and the carbon film 30 is further formed, the laminate 100 Similarly, by balancing the stresses of the carbon substrate 10 and the carbon film 30, the occurrence of warpage can be suppressed or alleviated. Therefore, even if the carbon substrate 10 and the carbon film 30 are burnt off by the burn-off process, the remaining SiC polycrystalline film 20 will not be in such a warped state as to affect the subsequent process.

In the case of FIG. 3, if there is no large difference in thermal expansion coefficient between the carbon substrate 10 and the SiC polycrystalline film 20, and no stress imbalance occurs, large warpage will not occur even when cooling after film formation. does not occur. Similarly, in the case of FIGS. 1 and 2, if the thermal expansion coefficients of the carbon substrate 10, the SiC polycrystalline film 20, and the carbon film 30 do not differ greatly, and stress imbalance does not occur, cooling is performed after film formation. Large warpage does not occur even when

EXAMPLES The present invention will now be described more specifically with reference to examples and comparative examples. It should be noted that the present invention is not limited by these examples and comparative examples.

[Example 1]
Carbon substrates 10 each having a diameter of 4 inches or 6 inches, a thickness of 500 μm, and a coefficient of thermal expansion of 4.9×10 ⁻⁶ (/K) were fixed in a reaction tube of a thermal CVD apparatus, and Ar gas was introduced into the furnace. After reducing the pressure in the furnace with an exhaust pump while heating, the furnace was heated to 1350° C., and then the Ar gas was stopped. Next, a mixed gas obtained by mixing SiCl ₄ and CH ₄ as raw material gases, N ₂ as doping gas, and H ₂ as carrier gas is flowed into the reaction tube for a predetermined time at a flow rate of 190 l/min to perform chemical vapor deposition. , a SiC polycrystalline film 20 having a thickness of about 500 μm was formed (first film forming step).

Next, the mixed gas in which the flow of only SiCl ₄ among the raw material gases is stopped and the flow of the other gases is maintained is flowed into the reaction tube at a flow rate of 190 l/min for a predetermined time, thereby forming a polycrystalline SiC film. A carbon film 10 having a thickness of about 50 μm was formed on the substrate 20 to obtain a laminate 110 (second film forming step). After that, all the inflow of gas was stopped and it was cooled.

The thermal expansion coefficient of the obtained carbon film was measured with a laser thermal dilatometer and found to be 5.0×10 ⁻⁶ (/K). Further, the outer peripheral end portion of the SiC polycrystalline film 20 was removed to expose the carbon substrate 10, thereby forming a laminate 110 shown in FIG. 2(b) (exposure step). After that, the carbon substrate 10 and the carbon film 30 of the laminated body 110 are burned off at about 1000° C. in an air atmosphere (burning removal step), thereby separating the SiC polycrystalline film 20 and obtaining the SiC polycrystalline substrate. got The warpage of the SiC polycrystalline substrate was measured on the center line of the surface of the SiC polycrystalline substrate with an oblique incidence type optical measuring instrument, and the difference between the maximum and minimum values of the measured values was defined as the amount of warpage. Five points were measured: the center, the edge of the circumference, and the point between the center and the edge of the circumference, the distance from the center being the same as the distance from the edge of the circumference. As a result, the amount of warp was 33 μm for the 4-inch SiC polycrystalline substrate and 41 μm for the 6-inch SiC polycrystalline substrate.

[Example 2]
Film formation was carried out under the same conditions as in Example 1, except that the thermal expansion coefficient of the carbon substrate 10 was set to 4.8×10 ⁻⁶ (/K) and the film thickness of the carbon film 30 was set to about 80 μm. A laminate 110 was obtained. The thermal expansion coefficient of the obtained carbon film 30 was 4.8×10 ⁻⁶ (/K). Moreover, the amount of warpage of the SiC polycrystalline substrate obtained by the same process as in Example 1 was 36 μm for the 4-inch SiC polycrystalline substrate and 45 μm for the 6-inch SiC polycrystalline substrate.

[Example 3]
Film formation was carried out under the same conditions as in Example 1, except that the thermal expansion coefficient of the carbon substrate 10 was set to 5.0×10 ⁻⁶ (/K) and the film thickness of the carbon film 30 was set to about 100 μm. A laminate 110 was obtained. The thermal expansion coefficient of the obtained carbon film 30 was 4.8×10 ⁻⁶ (/K). Moreover, the amount of warpage of the SiC polycrystalline substrate obtained by the same process as in Example 1 was 31 μm for the 4-inch SiC polycrystalline substrate and 39 μm for the 6-inch SiC polycrystalline substrate.

[Comparative Example 1]
Film formation was carried out under the same conditions as in Example 1, except that the thermal expansion coefficient of the carbon substrate 10 was set to 4.8×10 ⁻⁶ (/K) and the film thickness of the carbon film was set to about 10 μm. A laminate was obtained in which the SiC polycrystalline film and the carbon film were formed on the front surface and the back surface of the carbon substrate 10 in the same manner as the laminate 110 . The thermal expansion coefficient of the obtained carbon film was 4.9×10 ⁻⁶ (/K). Moreover, the amount of warpage of the SiC polycrystalline substrate obtained by the same process as in Example 1 was 140 μm for the 4-inch SiC polycrystalline substrate and 190 μm for the 6-inch SiC polycrystalline substrate.

[Comparative Example 2]
Film formation was carried out under the same conditions as in Example 1, except that the thermal expansion coefficient of the carbon substrate 10 was set to 4.9×10 ⁻⁶ (/K) and the film thickness of the carbon film was set to about 30 μm. A laminate similar to that of Comparative Example 1 was obtained. The thermal expansion coefficient of the obtained carbon film was 4.8×10 ⁻⁶ (/K). Moreover, the amount of warpage of the SiC polycrystalline substrate obtained by the same process as in Example 1 was 80 μm for the 4-inch SiC polycrystalline substrate and 120 μm for the 6-inch SiC polycrystalline substrate.

[Comparative Example 3]
Film formation was carried out under the same conditions as in Example 1, except that the thermal expansion coefficient of the carbon substrate 10 was set to 3.5×10 ⁻⁶ (/K) and the film thickness of the carbon film was set to about 50 μm. A laminate similar to that of Comparative Example 1 was obtained. The thermal expansion coefficient of the obtained carbon film was 4.9×10 ⁻⁶ (/K). The amount of warpage of the SiC polycrystalline substrate obtained by the same process as in Example 1 was 190 μm for the 4-inch SiC polycrystalline substrate and 250 μm for the 6-inch SiC polycrystalline substrate.

[Comparative Example 4]
Film formation was performed under the same conditions as in Example 1, except that the thermal expansion coefficient of the carbon substrate 10 was set to 5.5×10 ⁻⁶ (/K) and the film thickness of the carbon film was set to about 50 μm. A laminate similar to that of Comparative Example 1 was obtained. The thermal expansion coefficient of the obtained carbon film was 4.8×10 ⁻⁶ (/K). The amount of warpage of the SiC polycrystalline substrate obtained by the same process as in Example 1 was 220 μm for the 4-inch SiC polycrystalline substrate and 310 μm for the 6-inch SiC polycrystalline substrate.

Table 1 shows the results of the carbon substrate, the SiC polycrystalline film, the thermal expansion coefficient of the carbon film, the thickness of the carbon film, and the amount of warpage of the SiC polycrystalline substrate in Examples 1 to 3 and Comparative Examples 1 to 4. shown in The reason why the coefficient of thermal expansion of the SiC polycrystalline substrate in Table 1 has a range is that the value varies depending on the direction in which the coefficient of thermal expansion is measured due to the orientation of the crystal grains.

In the device manufacturing process after bonding the SiC polycrystalline substrate and the SiC single crystal substrate together, considering the pattern formation in the photolithography process and the uniformity of the ion penetration depth in the ion implantation process, warping of the SiC polycrystalline substrate Preferably, the amount is 50 μm or less. From the results of Examples 1 to 3, by setting the thickness and thermal expansion coefficient of the carbon substrate, the SiC polycrystalline substrate, and the carbon film within a predetermined range, SiC polycrystalline substrates of either size of 4 inches or 6 inches can be obtained. Also, the amount of warpage could be suppressed to 50 μm or less.

On the other hand, from the results of Comparative Examples 1 to 4, when the thermal expansion coefficient of the carbon substrate does not fall within the range of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K), When the thickness of the carbon film is thin, the warpage of the SiC polycrystalline substrate cannot be sufficiently suppressed.

[summary]
As described above, according to the present invention, warpage of the SiC polycrystalline substrate can be reduced, so that it can be used in the device manufacturing process as a horizontal and vertical SiC substrate for diodes. In addition, pattern formation defects in the photolithography process and non-uniform ion penetration depth in the ion implantation process can be suppressed, and an improvement in yield can be expected.

REFERENCE SIGNS LIST 10 carbon substrate 11 surface of carbon substrate 20 silicon carbide polycrystalline film (SiC polycrystalline film)
21 Surface of silicon carbide polycrystalline film 20 30 Carbon film 100 Laminate 110 Laminate 200 Carbon substrate on which polycrystalline silicon carbide film is formed

Claims (4)

a carbon substrate having a thickness of 300 μm to 10 mm and a coefficient of thermal expansion of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K);
a silicon carbide polycrystalline film having a thickness of 300 μm to 700 μm formed on the carbon substrate;
a carbon film having a thickness of 50 μm to 200 μm and a thermal expansion coefficient of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K), which is formed on the silicon carbide polycrystalline film; ,
A laminate comprising: A carbon substrate having a thickness of 300 μm to 10 mm and a thermal expansion coefficient of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K) is carbonized to a thickness of 300 μm to 700 μm by chemical vapor deposition. a first film forming step of forming a silicon polycrystalline film;
A carbon film having a thickness of 50 μm to 200 μm and a thermal expansion coefficient of 4.0×10 ⁻⁶ (/K) to 5.0×10 ⁻⁶ (/K) is formed on the silicon carbide polycrystalline film by chemical vapor deposition. A second film forming step of forming a film of
A method of manufacturing a laminate, comprising: 3. A method for manufacturing a polycrystalline silicon carbide substrate, comprising a burning removal step of burning and removing said carbon substrate and said carbon film of said laminate manufactured by the manufacturing method according to claim 2. 4. The method of manufacturing a polycrystalline silicon carbide substrate according to claim 3, further comprising a polishing step of polishing a surface of said polycrystalline silicon carbide substrate after said burning and removing step.

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