JP7081453B2 - Graphite substrate, silicon carbide film formation method and silicon carbide substrate manufacturing method - Google Patents

Description

The present invention relates to a graphite substrate, a method for forming a silicon carbide film, and a method for manufacturing a silicon carbide substrate.

Silicon carbide is a wide bandgap semiconductor having a wide forbidden bandwidth of 2.2 to 3.3 eV, and because of its excellent physical and chemical properties, for example, high frequency electronic devices, high withstand voltage and high output electronic devices, Research and development of devices (semiconductor devices) using silicon carbide (SiC), including short-wavelength optical devices from blue to ultraviolet, are being actively carried out. In order to promote the practical use of SiC devices, it is required to manufacture a large-diameter silicon carbide substrate for high-quality SiC epitaxial growth. Currently, most of them are manufactured by a sublimation recrystallization method (called an improved Rayleigh method, an improved Rayleigh method, etc.) using a seed crystal, a CVD method, or the like.

In the method of manufacturing a silicon carbide substrate using a CVD method (chemical vapor deposition method), a raw material gas is subjected to a gas phase reaction to precipitate a silicon carbide product on the surface of the substrate to form a film, and then the substrate is formed. It is possible to obtain a dense and high-purity silicon carbide substrate. Further, the base material is removed by cutting, polishing, or the like, but if a carbon material is used for the base material, it can be removed by heat treatment in the air, so that there is an advantage that the process can be simplified.

As a method for manufacturing a silicon carbide substrate by the CVD method, a silicon carbide film is formed on the surface of a base material by a chemical vapor deposition method, and then the silicon carbide film is further formed on both surfaces of the silicon carbide substrate obtained by removing the base material. A method for manufacturing a silicon carbide substrate by a chemical vapor deposition method, which is characterized by forming a silicon carbide substrate, has been proposed (Patent Document 1).

Further, in a method for producing a silicon carbide substrate by forming a silicon carbide film on the surface of a substrate by a chemical vapor deposition method and then removing the substrate, a silicon carbide layer is formed by a chemical vapor deposition method, and then the substrate is formed. By repeating the step of flattening the surface of the silicon carbide layer a plurality of times, the silicon carbide layer having a thickness of 100 μm or less is laminated to a desired thickness or more, and then the base material is removed by a chemical vapor deposition method. A method for manufacturing a silicon carbide substrate has been proposed (Patent Document 2).

Further, a disk-shaped graphite material having a convex upper surface and a lower surface and having grooves formed along the circumferential direction on the side surface is used as a base material, and silicon carbide is deposited and adhered to the surface of the base material by a CVD method. A method for manufacturing a silicon carbide substrate (Patent Document 3) has been proposed in which a base material is burned and removed after the silicon carbide is formed.

Japanese Unexamined Patent Publication No. 8-188408 Japanese Unexamined Patent Publication No. 8-188468 Japanese Unexamined Patent Publication No. 10-251062

However, the manufacturing methods of Patent Document 1 and Patent Document 2 are methods in which the SiC film formed by the CVD method is not formed at once to a desired film thickness, but is formed a plurality of times until the desired film thickness is reached. Further, there is a problem that the process such as the flattening process becomes complicated and the manufacturing efficiency is lowered.

Further, in the manufacturing method of Patent Document 3, it takes time to burn the base material of the graphite material. Therefore, in order to burn and remove the substrate in a short time, it is necessary to cut the substrate horizontally, for example, at the groove portion to expose the graphite. In this case, there may be a problem that the silicon carbide film formed at the time of cutting is cracked or the end portion of the silicon carbide film is chipped.

Further, as disclosed in Patent Document 3, in a graphite material having grooves formed along the circumferential direction on the side surface portion, the width of the grooves must be at least twice the thickness of the formed silicon carbide film. There is a possibility that the silicon carbide film formed on the upper surface of the graphite material and the silicon carbide film formed on the lower surface may be connected. Then, if the end portion of the graphite material is polished and removed in order to divide the connected silicon carbide film, the end portion of the graphite material may be chipped, which makes it difficult to use a thin graphite material. be.

In view of the above problems, in the present invention, the silicon carbide film formed by chemical vapor deposition does not crack or chip, has less warpage, and has a smooth surface, without requiring a complicated process. It is an object of the present invention to provide a graphite substrate, a method for forming a film of silicon carbide, and a method for producing a silicon carbide substrate, which can efficiently produce a silicon substrate.

In order to solve the above problems, the graphite base material of the present invention has a semi-elliptical first curved surface protruding outward and a surface opposite to the first curved surface, and has the same diameter. , The diameter of the semi-elliptical second curved surface protruding outward is the same as the diameter of the first curved surface and the second curved surface, and the circumference of the first curved surface and the circumference of the second curved surface are defined as each other. A disk-shaped surface portion comprising a columnar side surface portion to be connected and an annular convex portion that circulates around the side surface portion and projects outward, and the side surface portion includes a gap having a plurality of openings that open to the outside. It is a graphite base material.

The annular convex portion may have a peripheral groove larger than the diameter of the first curved surface and capable of breaking the annular convex portion.

The radius of curvature of the first curved surface and the second curved surface may be 5000 mm to 11000 mm.

The graphite substrate may have a thickness of 1.4 mm to 3.1 mm.

The number of the voids may be 3 to 5.

The graphite base material has a first curved surface as a surface, a planar first back surface having the same diameter as the diameter of the first curved surface, and the same diameter as the diameters of the first curved surface and the first back surface. A first graphite material having a columnar first side surface portion connecting the circumference of the first curved surface and the circumference of the first back surface, and the diameter of the second curved surface having the second curved surface as a surface. A planar second back surface having the same diameter as the above, and having the same diameter as the diameters of the second curved surface and the second back surface, and the circumference of the second curved surface and the circumference of the second back surface. The side surface portion of the graphite base material is provided with a second graphite material having a columnar second side surface portion to be connected, and a bonding layer bonded to the first back surface and the second back surface and having the annular convex portion. May have the first side surface portion, the first back surface portion, the bonding layer, the second back surface portion, and the second side surface portion.

The coefficient of thermal expansion of the first graphite material and the second graphite material may be 3.0 × 10 ⁻⁶ / ° C. to 6.0 × 10 ⁻⁶ / ° C.

The bonding layer may be bonded to the first back surface and the second back surface with a carbon adhesive.

The thickness of the first side surface portion and the second side surface portion may be 0.2 mm to 0.6 mm.

The thickness of the bonding layer may be 0.8 mm to 1.8 mm.

Further, in order to solve the above problems, the silicon carbide film forming method of the present invention includes a film forming step of forming silicon carbide on the surface of the graphite substrate by chemical vapor deposition.

Further, in order to solve the above problems, the method for manufacturing a silicon carbide substrate of the present invention is the annular convex portion of the graphite substrate on which the silicon carbide is formed on the surface obtained by the film forming method. It includes an exposure step of removing at least a part of the graphite base material to expose the graphite base material, and a combustion removal step of burning and removing the graphite base material after the exposure step.

The annular convex portion may have a peripheral groove larger than the diameter of the first curved surface and may have a peripheral groove capable of breaking the annular convex portion, and the method for manufacturing a silicon carbide substrate is the peripheral in the exposure step. The groove may be cut off to expose the graphite substrate.

After the combustion removal step, a polishing step of polishing the surface of the formed silicon carbide may be included.

According to the present invention, it is possible to manufacture a silicon carbide substrate having a small amount of warpage, excellent flatness, and no cracks or chipping at the edges. Therefore, it is extremely useful in the manufacture of various members used in the manufacture of semiconductors such as wafers for device fabrication and epitaxial growth wafers and susceptors, and industrial materials that require heat resistance and corrosion resistance.

It is a figure which shows the graphite base material 100 as an example of the graphite base material of this invention. It is a graph which shows the result of having calculated the influence which the thickness of a graphite base material has on the number of layers of a graphite base material. It is a figure explaining the stress generated when the silicon carbide film is formed on the graphite base material. It is a figure explaining the stress different from FIG. It is a figure which shows the graphite base material 110 as an example of the graphite base material of this invention. It is a figure which looked at the bonding layer 40 obtained by processing the sheet material made of graphite from the top. It is sectional drawing for demonstrating the process of manufacturing the silicon carbide substrate using a graphite base material 110. It is a figure which shows the graphite base material 120 as an example of the graphite base material of this invention. It is sectional drawing for demonstrating the process of manufacturing the silicon carbide substrate using the graphite base material 130 without an annular convex portion 31.

Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

[Graphite substrate]
The graphite substrate of the present invention includes a first curved surface, a second curved surface, a side surface portion, and an annular convex portion. A graphite base material is used because it is a base material for forming a silicon carbide film on the surface by chemical vapor deposition, and the base material is burned and removed after the silicon carbide is formed. FIG. 1 shows a view of the graphite base material 100 from above (FIG. 1 (a)) and a side view of the graphite base material 100 (FIG. 1 (b)) as an example of the graphite base material of the present invention. The graphite base material 100 has a disk shape, is circular when viewed from above (FIG. 1 (a)), and has a certain thickness when viewed from the side surface (FIG. 1 (b)). The diameter D of the circumference 11 of the first curved surface 10 of the graphite base material 100 is not particularly limited, but is usually about 4 to 6 inches (about 100 to 150 mm).

(Thickness)
The thickness T of the graphite base material 100 is preferably 1.4 mm to 3.1 mm. In FIG. 2, assuming that the height of the accommodating portion for accommodating the graphite substrate 100 in the CVD apparatus is 250 mm, the thickness T of the graphite substrate 100 when the graphite substrate 100 is laminated at intervals of 10 mm in this accommodating portion is The result of calculating the influence on the number of laminated graphite base material 100 is shown. When the thickness T is 3 mm, 20 graphite base materials 100 can be laminated, but when the thickness T exceeds 3.2 mm, the number of laminateable graphite base materials 100 is reduced by one, and when the thickness T is 4 mm. It can be seen that the number of the graphite base materials 100 that can be laminated is reduced to 18 sheets. Therefore, the upper limit of the thickness T is preferably 3.1 in consideration of the number of graphite substrates 100 that can be laminated. Further, when the thickness T is less than 1.4 mm, it becomes difficult to set the thickness of the first side surface portion and the second side surface portion to be described later and the thickness of the bonding layer within a preferable range, and the graphite base material 100 is good. It may be difficult to make a good disk shape.

<First curved surface>
The first curved surface 10 is a semi-elliptical curved surface protruding outward. When silicon carbide is deposited on the surface of a graphite base material by chemical vapor deposition to form a silicon carbide film, the graphite base material and the silicon carbide film have different coefficients of thermal expansion, so that the graphite base material and the silicon carbide film have internal stress. Accumulate. Therefore, in the cooling process from the high temperature at which the silicon carbide film is formed to the completion of film formation and removal from the film forming apparatus, the silicon carbide film may be cracked or warped due to internal stress. be.

For example, assuming a case where a silicon carbide film 600 is formed by chemical vapor deposition on a flat plate-shaped graphite base material 500 as shown in FIGS. 3 and 4 (FIGS. 3 (a) and 4 (a)), the graphite base material is assumed. The coefficient of thermal expansion of 500 is α1, the coefficient of thermal expansion of the columnar structure 610 of the silicon carbide film 600 is α2-L, and the coefficient of thermal expansion of the fine structure 620 of the silicon carbide film 600 is α2-S.

In the process of forming the silicon carbide film 600 by chemical vapor deposition, first, silicon carbide nuclei are formed on the graphite substrate 500, and an amorphous or fine-grained polycrystal fine structure 620 grows, and further becomes a crystal structure of a columnar structure 610. It continues to grow and the silicon carbide film 600 is formed. After the film formation, the coefficient of thermal expansion of the graphite base material 500 becomes larger than that of the silicon carbide film 600, and internal stress may act in the direction in which the graphite base material 500 is compressed inward on the side surface. The surface 550 of the graphite base material 500 is recessed inward, and the surface 650 of the silicon carbide film 600 is warped so as to be deformed so as to protrude outward (FIG. 3 (b)).

FIG. 3C shows a case where the silicon carbide film 600 is formed and the graphite base material 500 is removed by combustion or the like. Since the coefficient of thermal expansion α2-S of the fine structure 620 of the silicon carbide film 600 in contact with the graphite base material 500 is smaller than the coefficient of thermal expansion α2-L of the columnar structure 610 of the silicon carbide film 600, the graphite base material After the 500 is removed, the microstructure 620 of the silicon carbide film 600 is subjected to internal stress in the direction of being pulled outward on the side surface, and the columnar structure 610 of the silicon carbide film 600 is stressed in the direction of being compressed inward on the side surface. Works. As a result, the surface 650 of the columnar structure 610 of the silicon carbide film 600 may be dented, and the surface 660 of the microstructure 620 of the silicon carbide film 600 may be warped so as to be deformed into a protruding state (FIG. 3 (c)). ..

Further, unlike the case of FIG. 3, after the silicon carbide film 600 is formed, the coefficient of thermal expansion of the graphite base material 500 becomes smaller than that of the silicon carbide film 600, and the silicon carbide film 600 is compressed inward on the side surface. Internal stress may act in the direction (Fig. 4 (b)). In this case, the surface 550 of the graphite base material 500 protrudes outward, and the surface 650 of the silicon carbide film 600 is warped so as to be deformed inward (FIG. 4B).

FIG. 4C shows a case where the graphite base material 500 is removed from the warped state shown in FIG. 4B after the silicon carbide film 600 is formed by combustion or the like. The coefficient of thermal expansion α2-S of the fine structure 620 of the silicon carbide film 600 in contact with the graphite base material 500 is smaller than the coefficient of thermal expansion α2-L of the columnar structure 610 of the silicon carbide film 600. Therefore, even after the graphite base material 500 is removed, internal stress acts in the direction of being pulled outward on the side surface of the microstructure 620 of the silicon carbide film 600, and inside the columnar structure 610 of the silicon carbide film 600 on the side surface. Stress acts in the direction of being compressed to. As a result, as shown in FIG. 3, the warp is not reversed by removing the graphite base material 500, the surface 650 of the columnar structure 610 of the silicon carbide film 600 is dented, and the surface 660 of the fine structure 620 of the silicon carbide film 600 is protruding. Warpage that deforms to the surface may occur (FIG. 4 (c)).

As shown in FIG. 1 (b), the graphite base material 100 of the present invention has a semi-elliptical curved surface (first curved surface 10, second curved surface 20) in which the shapes of the upper surface and the lower surface project outward. By forming the silicon carbide film in a convex shape on this curved surface, the degree of warpage of the concave shape can be alleviated even if a force in the concave direction acts on the silicon carbide film due to internal stress.

(curvature radius)
The radius of curvature of the first curved surface 10 is preferably 5000 mm to 11000 mm. When the radius of curvature is within this range, the silicon carbide film formed on the first curved surface 10 can alleviate the warp generated by removing the graphite base material 100 and suppress the occurrence of cracks. .. If the radius of curvature is less than 5000 mm or more than 11000 mm, the warp may increase or cracks may occur.

<Second curved surface>
The second curved surface 20 is a surface opposite to the first curved surface 10 and has the same diameter as the diameter of the first curved surface 10 (same as the diameter D), and is a semi-elliptical curved surface protruding outward. Is. Since a silicon carbide film may be formed on both sides of the graphite base material 100, the second curved surface 20 is opposite to the first curved surface so that the first curved surface 10 and the second curved surface 20 have a relationship of both sides. It becomes the surface of. Then, by forming the second curved surface 20 into a semi-elliptical shape protruding outward, a silicon carbide film is formed in a convex shape on this curved surface, and a concave force acts on the silicon carbide film due to internal stress. Even so, the degree of warpage of the concave shape can be alleviated. If the second curved surface 20 has the same shape as the first curved surface 10, the film forming conditions for silicon carbide are the same. Therefore, the same quality silicon carbide is formed on both the first curved surface 10 and the second curved surface 20. Will be done.

(curvature radius)
The radius of curvature of the second curved surface 20 is preferably 5000 mm to 11000 mm. When the radius of curvature is within this range, the silicon carbide film formed on the first curved surface 10 can alleviate the warp generated by removing the graphite base material 100 and suppress the occurrence of cracks. .. If the radius of curvature is less than 5000 mm or more than 11000 mm, the warp may increase or cracks may occur.

<Side part>
The side surface portion 30 has the same diameter as the diameters of the first curved surface 10 and the second curved surface 20, and is a columnar shape connecting the circumference 11 of the first curved surface 10 and the circumference 21 of the second curved surface 20 to form a void. Be prepared.

(Gap)
The side surface portion 30 includes a gap 32 having a plurality of openings 32a and 32b that open to the outside. The presence of the voids 32 facilitates the burning and removal of the graphite base material 100 by causing fire to circulate in the voids 32. Further, since there are a plurality of openings for one void 32 (32a, 32b), the void 32 penetrates the graphite base material 100, so that it becomes easier for the fire to circulate in the void 32, and the graphite base material 100. The effect of removing combustion is higher. Since the supply of the raw material gas for chemical vapor deposition is small in the gap 32, it is difficult to form a silicon carbide film inside the gap 32. Therefore, when the graphite base material 100 is burnt and removed after the silicon carbide film is formed, the voids 32 are exposed to oxygen, and the graphite base material 100 is more easily burned.

The number of voids 32 is preferably 3-5. If the number of voids 32 is 2 or less, the effect of burning and removing the graphite base material 100 may be reduced. Further, if the number of voids 32 is 6 or more, the strength of the graphite base material 100 may decrease. The width w of the void 32 in the circumferential direction is preferably 0.8 mm to 3 mm from the viewpoint of the combustion removing effect of the graphite base material 100. If the width w is less than 0.8 mm, it may take time to remove the graphite base material by burning. Further, if the width w is larger than 3 mm, the strength of the graphite base material 100 may decrease.

<Circular convex part>
The annular convex portion 31 has a shape that goes around the side surface portion 30 and projects outward. In the graphite base material 100, the annular convex portion 31 protrudes from the other portions, which simplifies the treatment of the end portion of the silicon carbide film 600 after the film is formed. For example, in the case of a graphite base material having grooves recessed along the circumferential direction on the side surface as in Patent Document 3, if the width of the grooves is not sufficient, a film is formed on the upper surface and the lower surface of the film. The silicon carbide film may be connected and integrated in the groove. In this case, it is necessary to perform a treatment such as polishing removal on the end portion of the integrated silicon carbide film to separate the silicon carbide film formed on the upper surface and the lower surface. Chips such as chipping may occur at the edges of the film.

However, by providing the annular convex portion 31 as in the present invention, in the process of forming the silicon carbide film 600 on the surfaces of the first curved surface 10 and the second curved surface 10, the surface of the annular convex portion 31 is formed. Although the silicon carbide film 600 forms a film, if the silicon carbide film 600 cuts and trims only the annular convex portion 31 after the film formation, the carbonization formed on the surfaces of the first curved surface 10 and the second curved surface 10 is performed. It becomes easy to separate the silicon film 600. Further, in the case of trimming, it is possible to prevent chipping or the like from being chipped at the end of the silicon carbide film 600.

As shown in the graphite base material 120 of FIG. 8, the annular convex portion 31 has a diameter D larger than that of the first curved surface 10 and has peripheral grooves 31a and 31b capable of breaking the annular convex portion 31. good. The presence of the peripheral grooves 31a and 31b facilitates trimming of the annular convex portion 31 by folding off the annular convex portion 31 at this portion, and the first curved surface 10 is not chipped at the end portion of the silicon carbide film 600. And it becomes easier to separate the silicon carbide film 600 formed on the surface of the second curved surface 10. For example, the annular convex portion 31 can be broken off by applying a disk punching cutter or the like to the peripheral grooves 31a and 31b. The peripheral groove may be provided on both the upper surface and the lower surface of the annular convex portion 31, but the peripheral groove 31a on the upper surface may be used alone, or the peripheral groove 32a on the lower surface alone may be used to break off the annular convex portion 31. ..

As the graphite substrate of the present invention, for example, one graphite block may be processed into the shape of the graphite substrate 100, but as in the graphite substrate 110 shown in FIG. 5, the first graphite material 15 and the second graphite substrate are used. A graphite base material may be formed by combining several parts such as the graphite material 25 and the bonding layer 40. By assembling the graphite base material by combining some parts in this way, the shape of the graphite base material is stabilized and the production becomes easy.

(1st graphite material)
The first graphite material 15 has a first curved surface 10 as a front surface, and has a planar first back surface 12 having the same diameter as the diameter D1 of the first curved surface 10. Then, a columnar first side surface portion 14 having the same diameter as the diameter D1 of the first curved surface 10 and the first back surface 12 and connecting the circumference 11 of the first curved surface 10 and the circumference 13 of the first back surface 12 is formed. Be prepared. Since the first back surface 12 is planar, it is easy to join with the bonding layer 40 described later.

(Second graphite material)
The second graphite material 25 has a second curved surface 20 as a front surface, and has a planar second back surface 22 having the same diameter as the diameter D2 of the second curved surface 20. Then, a columnar second side surface portion 24 having the same diameter as the diameter D2 of the second curved surface 20 and the second back surface 22 and connecting the circumference 21 of the second curved surface 20 and the circumference 23 of the second back surface 22 is formed. Be prepared. Since the second back surface 22 is planar, it is easy to join with the bonding layer 40 described later.

The thickness t1 of the first side surface portion 14 and the thickness t2 of the second side surface portion 24 are preferably 0.2 mm to 0.6 mm. With a thickness in this range, it is possible to maintain the strength of the graphite material and keep the thickness to a level that allows a large number of graphite base materials 110 to be formed at one time. If the thicknesses t1 and t2 are less than 0.2 mm, the strength of the first graphite material 15 and the second graphite material 25 may be insufficient. Further, when the thicknesses t1 and t2 exceed 0.6 mm, the thickness of the graphite base material 110 becomes thick and the number of films that can be formed as a base material at one time decreases, which is not preferable. If the first graphite material 15 has the same shape as the second graphite material 25, the film forming conditions for silicon carbide are the same, so that silicon carbide of the same quality is formed.

(Joining layer)
The bonding layer 40 is a layer for bonding the first back surface 12 of the first graphite material 15 and the second back surface 22 of the second graphite material 25. Similar to the first graphite material 15 and the second graphite material 25, the material may be graphite, and a plate-shaped or sheet-shaped material may be used as the bonding layer 40. FIG. 6 shows a top view of the bonding layer 40 obtained by processing a graphite sheet material. When it is difficult to process the first graphite material 15 and the second graphite material 25 to provide voids, the sheet material may be cut out in a circular shape and then cut to provide voids 32 in the bonding layer 40. can.

The thickness t3 (FIG. 5 (b)) of the bonding layer 40 is preferably 0.8 mm to 1.8 mm. Since a silicon carbide film of about 0.4 mm may be formed by chemical vapor deposition, if the thickness t3 is less than 0.8 mm, the voids 32 are blocked by the silicon carbide film, and the graphite substrate 110 is formed. It may be difficult to remove by burning. Further, if the thickness t3 exceeds 1.8 mm, the thickness T of the graphite base material 110 may exceed 3.1 mm, and the number of graphite base materials 110 that can be laminated on the film forming apparatus is reduced, so that the film formation is formed. Efficiency may be reduced.

Further, since the bonding layer 40 has an annular convex portion 31, it has a diameter larger than that of the first graphite material 15 and the second graphite material 25, and has a diameter larger by about 2 mm to 10 mm, whereby the first graphite material 15 is formed. It is preferable that the graphite material 25 protrudes from the side surface thereof with a width b of 1 mm to 5 mm (FIG. 5 (b)). In the case of chemical vapor deposition, the film thickness of the silicon carbide film 600 tends to increase at the end of the graphite base material 110. Therefore, when the width b is less than 1 mm, the silicon carbide film 600 may be thickly formed on the annular convex portion 31 and it may be difficult to break it off. Further, when the width b exceeds 5 mm, a large portion is removed by breaking off the annular convex portion 31, and a film is formed on this portion as well, which not only results in wasteful film formation but also increases the film formation area. The increase may slow down the film formation speed.

In the graphite base material 110, the side surface portion 30 has a first side surface portion 14, a first back surface portion 12, a bonding layer 40, a second back surface portion 22, and a second side surface portion 24. Further, when the carbon adhesive 50 described later is used for adhering the first graphite material 15 and the bonding layer 40 and the second graphite material 25 and the bonding layer 40, this is also included in the configuration of the side surface portion 30. ..

In the graphite base material 110, the thickness T is the thickness t1 of the first side surface portion 14, the thickness t2 of the second side surface portion 24, and the thickness t3 of the bonding layer 40, as well as the thickness s1 of the first curved surface portion 10 and the thickness s1 of the second curved surface portion 20. It is the sum of the thicknesses s2 of. When the carbon adhesive 50 described later is used, this thickness is also taken into consideration. Hereinafter, the thickness s1 and s2 are set to the same value, and the thickness s will be described. The thickness s can be calculated from the diameter W of the graphite base material 110 and the radius of curvature r of the first curved surface (the same applies to the second curved surface) by the following equations (1) and (2).

[Number 1]
W = 2 * r * sin (θ / 2) (1)
s = r * (1-cos (θ / 2)) (2)

Table 1 shows the results of calculating the thickness s when the diameter W of the graphite base material 110 is 100 mm and 150 mm and the radius of curvature is 3000 to 12000 mm. For example, under the condition that the diameter W is 150 mm, the thickness s is 0.563 mm when the radius of curvature is 5000 mm, and the thickness s is 0.281 mm when the radius of curvature is 10000 mm.

Table 1 shows the results of calculating the minimum and maximum values of the thickness T of the graphite base material 110. The thickness T can be calculated by the following equation (3).

[Number 2]
T = t1 + t2 + t3 + s1 + s2 (3)
(If t1 and t2 are equal (let's say t) and s1 and s2 are equal (let's say s), T = 2 × (t + s) + t3 can also be calculated)

For example, under the condition that the diameter W is 100 mm and the radius of curvature is 3000 mm, the minimum value of the thickness T is 2 × (0.417 + 0.2) + 0.8 = 2.034, and the maximum value of the thickness T is. 2 × (0.417 + 0.6) +1.8 = 3.834.

(Coefficient of thermal expansion)
The coefficient of thermal expansion of the first graphite material 15 and the second graphite material 25 varies depending on the raw material coke of the graphite material, manufacturing conditions, etc., but as a graphite material, it is 3.0 × 10 ^-6 / ° C. to 6.0 × 10 ^-6 . It is preferably in the range of / ° C (room temperature to 450 ° C). When the coefficient of thermal expansion is less than 3.0 × 10 ^-6 / ° C, graphite as a graphite material is not isotropic graphite and has orientation dependence, and the shape of the graphite base material itself changes due to expansion. , The silicon carbide film may crack. Further, if the coefficient of thermal expansion exceeds 6.0 × 10 ⁻⁶ / ° C., the formed silicon carbide film may be warped significantly or cracks may occur. It should be noted that, for example, graphite powder having an orientation larger than 3.0 × 10 ^-6 / ° C and a small orientation can be solidified with an isotropic press (CIP) and sintered to produce isotropic graphite. It is possible, and this isotropic graphite can be used as a graphite material.

(glue)
The bonding layer 40 is preferably bonded to the first back surface 12 and the second back surface 22 with a carbon adhesive 50 having good adhesiveness even in a high temperature state. By using the carbon adhesive 50 having good adhesiveness up to a high temperature, the first graphite material 15 and the second graphite material 25 can be more firmly bonded to the bonding layer 40.

The carbon adhesive 50 is not particularly limited, and examples thereof include a carbon adhesive "ST-201" manufactured by Nisshinbo Co., Ltd. and a carbon adhesive "Resbond 931" manufactured by COTRONICS.

The carbon adhesive 50 is applied to, for example, both sides of the bonding layer 40, pressed against the first graphite material 15 and the second graphite material 25 so as to be bonded to the first back surface 12 and the second back surface 22, and then dried. By curing, the first graphite material 15 and the second graphite material 25 can be adhered to the bonding layer 40. The temperature condition for curing may be a temperature range in which a normal phenol resin is cured, and is not particularly limited, but for example, curing is preferably performed in a temperature range of about 60 to 250 ° C.

After adhering the first graphite material 15 and the second graphite material 25 to the bonding layer 40, the carbon adhesive 50 is carbonized by heating the carbon adhesive 50 in an inert gas or vacuum to carbonize the carbon adhesive 50. It is a carbon material composed of only one, and moreover, the first graphite material 15 and the second graphite material 25 and the bonding layer 40 can be firmly adhered to each other. The temperature for carbonization is not particularly limited as long as it is within the temperature range that the carbon material can withstand.

When the above-mentioned graphite substrate of the present invention is set in a film forming apparatus for chemical vapor deposition and a film forming process is performed, a silicon carbide film is uniformly formed on the first curved surface 10, the second curved surface 20, and the side surface portion 30. To.

Since it is difficult to supply the raw material gas and the carrier gas to the voids 32 during the film forming process, it is difficult for the silicon carbide film to be deposited in this portion, and the graphite base material is not covered and the exposed state is maintained. Can be done. Therefore, the voids 32 of the graphite base material after the film forming treatment are exposed to oxygen and easily burned, so that the base material can be easily removed.

[Silicon carbide film formation method]
Next, one aspect of the silicon carbide film forming method of the present invention will be described. Such a film forming method includes a film forming step of forming silicon carbide on the surface of the graphite substrate of the present invention by chemical vapor deposition. By this step, a polycrystalline film of silicon carbide can be formed on the surface of the graphite base material.

<Film formation process>
As an example of the film forming process, a mixed gas such as a raw material gas or a carrier gas containing a component of the silicon carbide film 600 heated to a temperature of 1200 to 1700 ° C. is supplied onto the heated graphite base material 110 to provide an atmospheric pressure. Below, a method of depositing the silicon carbide film 600 by carrying out a chemical reaction on the surface of the graphite base material 110 or in a gas phase for a predetermined time can be mentioned (FIG. 7A). Here, the silicon carbide film 600 is formed on the surface of the graphite base material 110, but since it is difficult for the raw material gas and the carrier gas to reach the voids 32, the silicon carbide film 600 may or may not be formed on these portions. Even if the film is formed, the amount is small, and the graphite base material 110 can be maintained in an exposed state. If the number of graphite substrates installed at the time of film formation is increased, the distance between the graphite substrates becomes shorter, and the difference in the amount of raw material supplied between the edge of the graphite substrate and the graphite substrate becomes large. Therefore, as the number of graphite substrates to be formed in one treatment increases, the film thickness at the edges of the graphite substrate, which has a large supply of raw materials, becomes thicker, and the center of the graphite substrate becomes thinner. It is preferable to adjust.

(Raw material gas)
As long as the silicon carbide film can be formed, the raw material gas that is generally used is not particularly limited and can be used. For example, trichloromethylsilane, trichlorophenylsilane, dichloromethylsilane, dichlorodimethylsilane, chlorotrimethylsilane, etc., or tetrachlorosilane (SiCl ₄ ), SiCl ₂ and methane, propane, acetylene, or other hydrocarbon gas is used as the raw material gas. Can be done.

(Carrier gas)
If the raw material gas can be developed on the substrate without inhibiting the film formation, a commonly used carrier gas can be used. For example, H ₂ gas or the like can be used as the carrier gas.

<Other processes>
The silicon carbide film forming method of the present invention can include other steps in addition to the film forming step. For example, a step of setting a plurality of graphite base materials 110 in the substrate holder in the film forming apparatus, a step of heating the set graphite base material 110, and a step of inhibiting film formation on the graphite base material 110 before chemical vapor deposition. Examples thereof include a step of circulating an inert gas such as argon so that the graphite substrate 110 is placed in an inert atmosphere so that some reaction does not occur.

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

<Exposure process>
As an example of the exposure step, the annular convex portion with respect to the graphite base material 110 having the silicon carbide film 600 formed on the surface obtained by the above-mentioned method for forming the silicon carbide film of the present invention (FIG. 7A). A step of removing at least a part of 31 to expose the graphite base material 110 can be mentioned (FIG. 7 (b)). By this step, the side surface 35 of the graphite base material 110 is exposed at the portion where the annular convex portion 31 is located, and the graphite base material 110 is easily burned.

Specifically, a method of cutting the annular convex portion 31 and the silicon carbide film 630 formed on the annular convex portion 31 with a single wire saw using diamond or C-BN (cubic BN) abrasive grains, or an annular convex portion with a polishing wheel. The graphite base material 110 can be exposed by scraping off the portion 31 and the silicon carbide film 600 formed therein.

Further, when the annular convex portion 31 has a peripheral groove 31a or 31b larger than the diameter of the first curved surface and capable of breaking off the annular convex portion as in the graphite base material 120 (FIG. 8 (b). )), The graphite base material 120 can be exposed by breaking off the annular convex portion 31 together with the silicon carbide film 600 formed therein in the peripheral grooves 31a, 31b, or both in the exposure step. For example, the annular convex portion 31 can be broken off by applying a disk punching cutter or the like to the peripheral grooves 31a and 31b. The peripheral groove may be provided on both the upper surface and the lower surface of the annular convex portion 31, but the peripheral groove 31a on the upper surface may be used alone, or the peripheral groove 32a on the lower surface alone may be used to break off the annular convex portion 31. ..

<Combustion removal process>
As an example of the combustion removing step, there is a step of burning and removing the graphite base material 110 after the exposure step (FIG. 7 (c)). By this step, the graphite base material 110 disappears, and the silicon carbide film 600 remains, which becomes the silicon carbide substrate 700.

Combustion removal of the graphite base material 110 can be performed by an appropriate method such as heating in air. Examples of the heating conditions include conditions for heating to about 1000 ° C. in an atmospheric atmosphere.

<Polishing process>
The method for manufacturing a silicon carbide substrate of the present invention may include a polishing step of polishing the surface of the formed silicon carbide film 600 after the combustion removing step. If the silicon carbide substrate is a substrate used for semiconductor manufacturing, surface accuracy that can be used in the semiconductor manufacturing process is required. Therefore, it is preferable to smooth the surface of the silicon carbide substrate 700 by this step.

For example, the surface of the silicon carbide substrate 700 is subjected to a step of wrapping the silicon carbide substrate 700 with a diamond slurry, hard polishing with a mixed slurry of diamond and alumina, and then polishing with a silica slurry (coloidal silica, pH 11). Can be smoothed.

<Other processes>
The method for manufacturing a silicon carbide substrate of the present invention can include other steps in addition to the above steps. For example, a cooling step of cooling the silicon carbide substrate 700 after the combustion removal step can be mentioned.

According to the method for forming a silicon carbide film and the method for manufacturing a silicon carbide substrate of the present invention, after forming a silicon carbide film on the first curved surface and the second curved surface having a convex curved surface shape, an annular convex portion is formed. Since the graphite substrate is burnt and removed after cutting, the internal stress of the silicon carbide film acting in the concave direction can be skillfully relieved. Further, since the presence of the voids can prevent the silicon carbide film from being integrally formed on the entire surface of the graphite base material, it is possible to manufacture a silicon carbide substrate having less warpage and cracks.

Hereinafter, the present invention will be described in more detail based on Examples. However, the present invention is not limited to the contents of the following examples.

[Examples 1 to 6, Comparative Examples 1 and 2]
(Manufacturing of graphite base material 120)
By processing graphite materials having different coefficients of thermal expansion, the diameters D1 and D2 are 150.6 mm, the thickness t1 of the first side surface portion 14 and the thickness t2 of the second side surface portion 24 are 0.2 mm, the first curved surface 10 and the second surface portion 24 and the second. The first graphite material 15 and the second graphite material 25 having a radius of curvature of the curved surface 20 of 7,000 mm were produced. As the bonding layer 40, a carbon sheet (PF-UHPL manufactured by Toyo Carbon Co., Ltd.) was cut out on a disk having a diameter of 158 mm so as to be larger than the diameters D1 and D2 in order to form the annular convex portion 31, and FIG. As shown, when the void with a width w of 20 mm is orthogonal to the opening direction of the void and is the intersection point C1 and C2 between the straight line C passing through the center of the carbon sheet and the circumference of the carbon sheet, it is 24.5 mm from C1. , C1 to 69 mm and C2 to 24.5 mm. Further, circular grooves 31a and 31b were formed with a compass so as to have a diameter of 153 mm. Then, the carbon adhesive 50 (Nisshinbo ST-201) was used to bond the first graphite material 15 and the second graphite material 25 to the bonding layer 40.

After bonding, heat curing was performed in the air at 80 ° C. for 4 hours, 120 ° C. for 4 hours, and 200 ° C. for 1 hour, and then in a nitrogen atmosphere at a heating rate of 0.8 ° C./min at 1000 ° C. The temperature was raised to the above, and the adhesive was carbonized. The thickness t3 of the bonding layer 40 was set to 0.8 mm. Table 2 shows the coefficients of thermal expansion of the first graphite material 15 and the second graphite material 25 used for the graphite base materials 120 of Examples 1 to 6 and Comparative Examples 1 and 2, and the curvatures of the first curved surface 10 and the second curved surface 20. Indicates the radius. In each Example and each Comparative Example, the first graphite material 15 and the second graphite material 25 had the same coefficient of thermal expansion.

(Manufacturing of Silicon Carbide Substrate 700)
Using the prepared graphite base material 120 as a substrate, silicon carbide was formed on the surface thereof by chemical vapor deposition. Specifically, five substrates are set in the quartz reaction tube of the film forming apparatus so as to be laminated at intervals of 10 mm, and a mixed gas of trichloromethylsilane and hydrogen (trichloromethylsilane) is set at a reaction temperature of 1400 ° C. under atmospheric pressure. (Concentration of 7.5 vol%) was sent into the quartz reaction tube at a flow rate of 190 l / min, and a chemical vapor deposition reaction was carried out for 40 hours to deposit and deposit silicon carbide, and the thickness at the center of the substrate was 0.7 mm. The silicon carbide film 600 of the above was formed (FIG. 7 (a)). The total thickness E of the annular convex portion 31 and the silicon carbide film 600 formed therein was 1.3 mm. The coefficient of thermal expansion of the silicon carbide film 600 was 4.4 × 10 ^-6 / ° C.

Next, the side surface 35 of the graphite base material 120 was exposed by cutting the annular convex portion together with the silicon carbide film 600 formed therein with an ultrasonic cutter along the grooves 31a and 31b (exposure step FIG. 7 (exposure step FIG. 7). b)). After that, the graphite base material 120 is heated in air to be burned and removed (combustion removal step), and both sides of the silicon carbide film 600 are polished (polishing step) to form a flat plate having a diameter of 150 mm and a thickness of 0.5 mm. Silicon Carbide Substrate 700 was manufactured (FIG. 7 (c)).

(Evaluation of Silicon Carbide Substrate 700)
The amount of warpage of the silicon carbide substrate 700 thus obtained was measured using a three-dimensional shape measuring machine. In addition, the state of occurrence of cracks on the surface of the silicon carbide substrate 700 and chipping on the side surfaces was observed with a microscope. The obtained results are shown in Table 2 together with the mechanical properties (hardness, Young's modulus) of graphite. The hardness is the hardness measured by an instruction type tester based on "JIS Z-2246 Shore hardness test-test method".

From the results in Table 2, the carbonization obtained by the thermal expansion coefficients of the first graphite material 15 and the second graphite material 25 being 3.8 × 10 ^-6 / ° C to 5.6 × 10 ^-6 / ° C. The silicon substrate 700 had little warpage, and no cracks or chippings were observed (Examples 1 to 6). On the other hand, when the coefficient of thermal expansion was small, the warp of the obtained silicon carbide substrate 700 was large, and the occurrence of cracks was observed (Comparative Examples 1 and 2). In Table 2, in Examples 1 and 2 in which the amount of warpage is negative, the silicon carbide substrate 700 protrudes inward and warps, contrary to the protruding state of the first curved surface 10 and the second curved surface 20. It is in a state. Further, in Examples 3 to 6 and Comparative Examples 1 and 2 in which the amount of warpage is positive, the silicon carbide substrate 700 protrudes outward and warps in the same manner as in the protruding state of the first curved surface 10 and the second curved surface 20. It is in a state of being.

[Examples 7 to 9, Comparative Examples 3 to 5]
Using a graphite material having the same coefficient of thermal expansion as in Example 4, a graphite base material 120 having a radius of curvature of 2000 to 12000 mm changed every 2000 mm was produced by the same method as in Example 4. Next, a flat plate-shaped silicon carbide substrate 700 was manufactured by the same method as in Example 4. With respect to the silicon carbide substrate 700 thus obtained, the amount of warpage was similarly measured using a three-dimensional shape measuring machine, and the state of occurrence of cracks on the surface and chipping of the side surface of the silicon carbide substrate 700 was observed with a microscope. .. Table 3 shows the evaluation results of the amount of warpage and the occurrence of cracks in the silicon carbide substrate 700 together with the radius of curvature and the thickness T of the graphite base material 120.

From the results in Table 3, since the radius of curvature of the graphite base material 120 was 6000 mm to 10000 mm, the obtained silicon carbide substrate 700 had little warpage, and no cracks or chippings were observed (Examples 7 to 9). ). On the other hand, when the radius of curvature of the graphite base material 110 is 2000 to 4000 mm or 12000 mm, the obtained silicon carbide substrate 700 warps significantly and cracks are observed (Comparative Examples 3 to 3). 5).

[Comparative Examples 6 to 8]
The diameter of the bonding layer 40 is 150.6 mm, which is the same as the diameters D1 and D2, and the graphite substrate 130 (FIG. 9) without the annular protrusion 31 is used. A silicon film 600 was formed (FIG. 9 (a)). The silicon carbide substrate 600 formed on the first curved surface 140 and the second curved surface 150 of the graphite substrate 130 is integrated to form an outer peripheral end portion, and the graphite substrate 130 is completely covered with combustion removal. Since it became impossible to do so, the outer peripheral side surface 640 of the silicon carbide film 600 was cut off to expose the side surface 36 of the graphite base material 130 (FIG. 9 (b)). Then, the graphite base material 130 was burnt off and removed by the same method as in Examples 7 to 9 to obtain a silicon carbide substrate 710 (FIG. 9 (c)). With respect to the silicon carbide substrate 710 thus obtained, the amount of warpage was similarly measured using a three-dimensional shape measuring machine, and cracks on the surface of the silicon carbide substrate 710 and chipping on the surface of the end portion 720 were generated by a microscope. I observed the situation. Table 4 shows the evaluation results of the amount of warpage, cracks, and chipping of the silicon carbide substrate 710, as well as the radius of curvature and the thickness T of the graphite base material 130.

From the results in Table 4, since the graphite base material 130 without the annular convex portion 31 was used, the formed silicon carbide substrate 600 was integrated and completely covered the graphite base material 130. In order to burn and remove the base material 130, a step of cutting and removing the outer peripheral side surface 640 of the silicon carbide film 600 was required. As a result, chipping occurred in the silicon carbide film 600 by this cutting and removing step, and among the 10 silicon carbide substrates 710, there were 3 or more of the 10 silicon carbide substrates 720 in which the end portion 720 was finely chipped.

[summary]
From the above, according to the present invention, it is possible to easily manufacture a silicon carbide substrate having a small amount of warpage, excellent flatness, and no cracks or cracks. Further, since the graphite base material has voids and is easily removed by combustion, it is not necessary to cut the graphite base material in the transverse direction and divide the graphite base material into upper and lower parts. It is possible to prevent the occurrence of cracks. Therefore, according to the present invention, it is possible to easily manufacture a silicon carbide substrate having high purity, excellent density, corrosion resistance, etc., and having no warp or crack, for example, a silicon carbide substrate useful as a wafer for manufacturing a device. Therefore, it is industrially useful.

10 1st curved surface 11 Circumference 12 1st back surface 13 Circumference 14 1st side surface part 15 1st graphite material 20 2nd curved surface 21 Circumference 22 2nd back surface 23 Circumference 24 2nd side surface part 25 2nd graphite material 30 Side surface Part 31 Circular convex part 31a Circumferential groove 31b Circumferential groove 32 Void 32a Opening 32b Opening 35 Side 36 Side 40 Bonding layer 50 Carbon adhesive 100 Graphite base material 110 Graphite base material 120 Graphite base material 130 Graphite base material 140 1st Curved surface 150 Second curved surface 500 Graphite base material 550 Surface 600 Silicon carbide film 610 Columnar structure 620 Fine structure 630 Silicon carbide film 640 Outer peripheral side surface 650 Surface 660 Surface 700 Silicon carbide substrate 710 Silicon carbide substrate 720 End b Width C Straight line C1 Intersection point C2 Intersection D Diameter D1 Diameter D2 Diameter E Total thickness r Radical radius s Thickness s1 Thickness s2 Thickness T Thickness t1 Thickness t2 Thickness t3 Thickness α1 Thermal expansion coefficient α2-L Thermal expansion coefficient α2-S Thermal expansion coefficient w Width W Diameter

Claims (14)

A semi-elliptical first curved surface protruding outward,
A semi-elliptical second curved surface that is opposite to the first curved surface and has the same diameter and protrudes outward.
A columnar side surface portion having the same diameter as the diameters of the first curved surface and the second curved surface and connecting the circumference of the first curved surface and the circumference of the second curved surface.
It is provided with an annular convex portion that circulates around the side surface portion and projects outward.
The side surface portion is a disk-shaped graphite base material having voids having a plurality of openings that open to the outside. The graphite base material according to claim 1, wherein the annular convex portion is larger than the diameter of the first curved surface and has a peripheral groove in which the annular convex portion can be cut off. The graphite substrate according to claim 1 or 2, wherein the first curved surface and the second curved surface have a radius of curvature of 5000 mm to 11000 mm. The graphite substrate according to any one of claims 1 to 3, which has a thickness of 1.4 mm to 3.1 mm. The graphite substrate according to any one of claims 1 to 4, wherein the number of voids is 3 to 5. The first curved surface is a front surface, and the first back surface is a plane having the same diameter as the diameter of the first curved surface, and the diameter is the same as the diameters of the first curved surface and the first back surface. A first graphite material having a columnar first side surface portion connecting the circumference of the curved surface and the circumference of the first back surface,
The second curved surface is a front surface, and the diameter is the same as the diameters of the second curved surface and the second back surface, which are planar and have the same diameter as the diameter of the second curved surface. A second graphite material having a columnar second side surface portion connecting the circumference of the curved surface and the circumference of the second back surface, and
A bonding layer that is bonded to the first back surface and the second back surface and has the annular convex portion is provided.
The aspect according to any one of claims 1 to 5, wherein the side surface portion of the graphite substrate has the first side surface portion, the first back surface portion, the bonding layer, the second back surface portion, and the second side surface portion. Graphite substrate. The graphite substrate according to claim 6, wherein the first graphite material and the second graphite material have a coefficient of thermal expansion of 3.0 × 10 ^-6 / ° C to 6.0 × 10 ^-6 / ° C. The graphite base material according to claim 6 or 7, wherein the bonding layer is bonded to the first back surface and the second back surface with a carbon adhesive. The graphite base material according to any one of claims 6 to 8, wherein the thickness of the first side surface portion and the second side surface portion is 0.2 mm to 0.6 mm. The graphite base material according to any one of claims 6 to 9, wherein the thickness of the bonding layer is 0.8 mm to 1.8 mm. A method for forming silicon carbide, which comprises a film forming step of forming silicon carbide on the surface of the graphite substrate according to any one of claims 1 to 10 by chemical vapor deposition. An exposure step obtained by the film forming method according to claim 11, wherein at least a part of the annular convex portion of the graphite substrate having the silicon carbide deposited on the surface is removed to expose the graphite substrate. ,
A method for manufacturing a silicon carbide substrate, which comprises a combustion removing step of burning and removing a graphite base material after the exposure step. The annular convex portion is larger than the diameter of the first curved surface and has a peripheral groove capable of breaking the annular convex portion. In the exposure step, the peripheral groove is broken to expose the graphite base material. The method for manufacturing a silicon carbide substrate according to claim 12. The method for manufacturing a silicon carbide substrate according to claim 12 or 13, further comprising a polishing step of polishing the surface of the formed silicon carbide after the combustion removing step.

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