JP7413768B2 - Method for manufacturing polycrystalline substrate - Google Patents

Description

The present invention relates to a method for manufacturing a polycrystalline substrate.

Silicon carbide (SiC) is a compound semiconductor material composed of silicon (Si) and carbon (C). Silicon carbide has a dielectric breakdown field strength ten times that of silicon and a band gap three times that of silicon, making it excellent as a semiconductor material. Furthermore, since it is possible to control p-type and n-type over a wide range, which is necessary for device fabrication, it is expected to be a material for power devices that exceeds the limits of silicon.

However, compared with silicon carbide semiconductors, which have been widely used in the past, it is difficult to obtain a silicon carbide single crystal substrate with a large area, and the manufacturing process is also complicated. For these reasons, silicon carbide semiconductors are difficult to mass produce and are expensive compared to silicon semiconductors.

Various efforts have been made to reduce the cost of silicon carbide semiconductors. For example, Patent Document 1 discloses a method for manufacturing a silicon carbide substrate, in which at least a silicon carbide single crystal substrate and a silicon carbide polycrystalline substrate having a density of micropipes of 30 pieces/cm ² or less are prepared, and the silicon carbide A step of bonding a single crystal substrate and the silicon carbide polycrystalline substrate is performed, and then a step of thinning the single crystal substrate is performed to form a substrate with a single crystal layer formed on the polycrystalline substrate (hereinafter referred to as "silicon carbide bonded"). It is described that the manufacturing method is sometimes referred to as "laminated substrate").

Furthermore, Patent Document 1 discloses that before the step of bonding the single crystal substrate and the polycrystalline substrate, a step of implanting hydrogen ions into the single crystal substrate to form a hydrogen ion implantation layer is performed, and the single crystal substrate and the polycrystalline substrate are bonded together. After the process of bonding with the crystal substrate and before the process of thinning the single crystal substrate, heat treatment is performed at a temperature of 350°C or less, and the process of thinning the single crystal substrate is mechanically performed using a hydrogen ion implantation layer. A method for manufacturing a silicon carbide substrate is described, which includes a step of peeling off the substrate.

With this method, more silicon carbide bonded substrates can be obtained from one silicon carbide single crystal ingot.

JP2009-117533A

For example, in the manufacturing process of silicon carbide semiconductors, most of the silicon carbide bonded substrates manufactured by the method of Patent Document 1 are polycrystalline substrates, and in the manufacturing process of silicon carbide polycrystalline substrates, chemical vapor deposition After forming a silicon carbide polycrystalline film on a graphite support substrate at a high temperature of about 800°C or higher by (chemical vapor deposition method, CVD method), the silicon carbide polycrystalline film is further baked to vaporize the graphite support substrate. A silicon carbide polycrystalline substrate was obtained by removing part or all of the support substrate from a laminate of the substrate and silicon carbide polycrystalline film.

However, polycrystalline film substrates such as silicon carbide obtained in this way sometimes warp due to internal stress generated due to the difference in coefficient of thermal expansion between the graphite support substrate and the polycrystalline film during cooling. . In order to use it for applications such as manufacturing bonded substrates made of silicon carbide, etc., it is necessary to increase the flatness of the polycrystalline substrate. The amount of grinding during grinding increases, which causes a decrease in manufacturing yield.

Therefore, the present invention focuses on the above-mentioned problems, and an object of the present invention is to provide a method for manufacturing a polycrystalline substrate that can suppress the occurrence of warpage of the polycrystalline substrate.

The method for manufacturing a polycrystalline substrate of the present invention includes a film forming step of forming a polycrystalline film on a support substrate made of graphite by chemical vapor deposition, and heating a laminate of the support substrate and the polycrystalline film. and a removing step of burning and removing the support substrate, wherein the heating temperature of the laminate in the removing step is from −50° C. to the film forming temperature of the polycrystalline film in the film forming step. +50°C.

Furthermore, in the method for manufacturing a polycrystalline substrate of the present invention, in the film forming step, the polycrystalline film may be formed on both surfaces of the support substrate as film-forming target surfaces.

Further, in the method for manufacturing a polycrystalline substrate of the present invention, between the film forming step and the removing step, at least a part of the polycrystalline film at an outer peripheral end of the laminate is removed, and the supporting substrate is It may further include an exposing step of exposing at least a portion of the.

The method for manufacturing a polycrystalline substrate of the present invention may further include a polishing step of polishing the surface of the polycrystalline film after the removal step.

Further, in the method for manufacturing a polycrystalline substrate of the present invention, the polycrystalline film may be a silicon carbide polycrystalline film, and the film forming temperature may be 1200°C to 1700°C.

With the method for manufacturing a polycrystalline substrate of the present invention, it is possible to suppress the occurrence of warpage of the polycrystalline substrate. This reduces the burden on post-processes such as increasing flatness, and improves yield and cost.

1 is a cross-sectional view schematically showing an example of a film forming apparatus used in a method for manufacturing a polycrystalline substrate according to an embodiment of the present invention. FIG. 2 is a cross-sectional view schematically showing a support substrate, a polycrystalline film, and a polycrystalline substrate in each step of a method for manufacturing a polycrystalline substrate according to an embodiment of the present invention.

A method for manufacturing a polycrystalline substrate according to an embodiment of the present invention will be described with reference to the drawings. The method for manufacturing a polycrystalline substrate of this embodiment includes a film forming step of forming a polycrystalline film on a support substrate made of graphite by chemical vapor deposition, and a laminate of the support substrate and the polycrystalline film. The method includes a removing step of heating and burning away the supporting substrate. As a result of intensive research and repeated trial and error, the inventors of the present invention have discovered that the method for manufacturing a polycrystalline substrate of this embodiment allows a polycrystalline substrate without warping to be obtained. The method for manufacturing a polycrystalline substrate of this embodiment can be applied to, for example, manufacturing a silicon carbide (SiC) polycrystalline substrate or a silicon (Si) polycrystalline substrate. In the following embodiments, a case where a silicon carbide polycrystalline substrate is manufactured as a polycrystalline substrate will be exemplified and explained.

Next, the method for manufacturing a polycrystalline substrate according to the present embodiment will be described in the order of a film formation process and a removal process.

(Film forming process)
The film forming process will be explained with reference to the drawings. The following description is an example of a film forming process, and conditions such as temperature and pressure, procedures, etc. may be changed within a range that causes no problems.

The film forming process of this embodiment is a process of forming a silicon carbide polycrystalline film 200 (polycrystalline film) on a support substrate 100 made of graphite by a chemical vapor deposition method. When forming the silicon carbide polycrystalline film 200, the film formation temperature of the silicon carbide polycrystalline film can be set to 1200° C. to 1700° C., which is a general film forming temperature of silicon carbide polycrystalline film. . For example, it can be performed using a film forming apparatus 1000 (FIG. 1) described below. As the support substrate 100, a support substrate made of graphite can be suitably used, which prevents softening, shape deformation, etc. even in the chemical vapor deposition method in which a silicon carbide polycrystalline film is deposited under high temperature conditions. Hard to occur. Further, the shape of the support substrate 100, such as the thickness and the size of the surface to be film-formed, is not particularly limited, and a support substrate 100 that matches the desired silicon carbide polycrystalline substrate 500 can be used. Note that there is no particular limitation on whether the polycrystalline silicon carbide film 200 is formed on both sides or one side of the support substrate 100. By targeting both sides of support substrate 100 for film formation, two silicon carbide polycrystalline substrates can be obtained from one support substrate 100, and production efficiency can be improved. In this embodiment, a method for manufacturing a silicon carbide polycrystalline substrate will be described with film formation being performed on both sides of the support substrate 100.

Film forming apparatus 1000 can be used to form silicon carbide polycrystalline film 200 on support substrate 100 by chemical vapor deposition. The film forming apparatus 1000 includes a housing 1100 serving as an exterior of the film forming apparatus 1000, a film forming chamber 1010 for forming a silicon carbide polycrystalline film 200 on a supporting substrate 100, and a source gas discharged from the film forming chamber 1010. An exhaust gas introduction chamber 1040 that introduces carrier gas into a gas exhaust port 1030 (described later), a box 1050 that covers the exhaust gas introduction chamber 1040, and a carbon heater 1060 that heats the inside of the film forming chamber 1010 from outside the box 1050. A gas inlet 1020 that is provided at the lower part of the film forming chamber 1010 and introduces a source gas and a carrier gas into the film forming chamber 1010, a gas exhaust port 1030, and a substrate holder 1070 that holds the support substrate 100. Further, the substrate holder 1070 includes two pillars 1071 and a mounting section 1072 provided on the pillars 1071 on which the supporting substrate 100 is horizontally mounted.

Prior to film formation, the support substrate 100 is held in the film formation chamber 1010 in advance, and is heated to a reaction temperature for film formation under a reduced pressure state (for example, about 25 kPa) or a low oxygen partial pressure using an exhaust pump. Preferably, the support substrate 100 is heated by the heater 1060. At this time, the support substrate 100 is placed in an inert atmosphere so that a reaction that would inhibit the formation of the silicon carbide polycrystalline film 200 does not occur on the support substrate 100 before the silicon carbide polycrystalline film is deposited. It is preferable to use an atmosphere of an inert gas such as Ar. When the reaction temperature for film formation is reached, the supply of inert gas is stopped, and a raw material gas, a carrier gas, and a doping gas containing the components of the silicon carbide polycrystalline film 200 are supplied into the film formation chamber 1010 to start the film formation process. conduct.

The source gas is not particularly limited as long as it can form the silicon carbide polycrystalline film 200, and Si-based source gas or C-based source gas that is generally used for forming a silicon carbide polycrystalline film is used. be able to. 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 It is also possible to use a chlorine-based Si raw material-containing gas (chloride-based raw material) containing Cl, which has an etching effect such as ). Further, as the C-based raw material gas, for example, hydrocarbon gas such as methane (CH ₄ ), propane (C ₃ H ₈ ), acetylene (C ₂ H ₂ ), etc. can be used. 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 A gas containing both Si and C, such as SiCl ₂ ) or chlorotrimethylsilane ((CH ₃ ) ₃ SiCl), can also be used as the raw material gas.

Further, as the carrier gas, a commonly used carrier gas can be used as long as it can spread the raw material gas to the support substrate 100 without inhibiting the formation of the silicon carbide polycrystalline film 200. For example, hydrogen (H ₂ ), which has excellent thermal conductivity and has an etching effect on SiC, can be used. Further, an impurity doping gas can be supplied as a third gas simultaneously with these source gas and carrier gas. For example, nitrogen (N ₂ ) gas can be used when the conductivity type is n-type, and trimethylaluminum (TMA) gas can be used when the conductivity type is p-type.

When forming silicon carbide polycrystalline film 200, the above gases are appropriately mixed or individually supplied into film forming chamber 1010. Specifically, a mixed gas such as a raw material gas and a carrier gas containing the components of the silicon carbide polycrystalline film 200 is supplied to the heated support substrate 100 at a temperature of 1200 to 1700° C., and the mixture is heated under reduced pressure (for example, about 25 kPa). ), a silicon carbide polycrystalline film 200 is obtained by depositing a silicon carbide polycrystalline film 200 by performing a chemical reaction on the surface of the silicon dioxide film of the supporting substrate 100 or in the gas phase for a predetermined period of time. Furthermore, depending on the desired properties of polycrystalline silicon carbide film 200, conditions such as the gas mixture ratio and supply amount may be changed within the above conditions during the film forming process.

Here, when forming a silicon polycrystalline film on the support substrate, the raw material gas is typically silane (SiH ₄ ), trichlorosilane (SiHCl ₃ ), etc. Any gas used can be used. Further, the film forming temperature can be, for example, about 800°C to 1000°C.

Silicon carbide polycrystalline film 200 can be formed on heated support substrate 100 by a chemical reaction on the surface of support substrate 100 or in the gas phase. As a result, as shown in FIG. 2(B), a laminate 300 of the support substrate 100 and the silicon carbide polycrystalline film 200, in which the silicon carbide polycrystalline film 200 is formed on the support substrate 100, is obtained. After that, the supply of the gas supplied during film formation and the exhaust pump are stopped, and then an inert gas such as Ar is supplied into the film formation chamber 1010 under reduced pressure or in a state where the oxygen partial pressure is low. While cooling to room temperature. The laminate 300 formed as described above is cooled to about room temperature and then subjected to a removal process.

(Removal process)
Next, the laminate 300 obtained by the film forming process is subjected to a removing process. The removal step is a step of removing support substrate 100 from laminate 300 of support substrate 100 and silicon carbide polycrystalline film 200 .

Between the film forming step and the removing step, the method further includes an exposing step of removing at least a portion of the silicon carbide polycrystalline film 200 at the outer peripheral end of the laminate 300 to expose at least a portion of the supporting substrate 100. You can stay there. That is, at least a portion of the support substrate 100 (this embodiment In this step, the side surface 110) of the support substrate 100 is exposed to obtain a laminate 300A of the support substrate 100 and the main body portion 200B of the silicon carbide polycrystalline film 200 (FIG. 2(C)). This exposes the side surface 110 of the support substrate 100 made of graphite, making it easier to vaporize the support substrate 100 made of graphite during the removal process. Note that by masking the outer peripheral edge of the support substrate 100 with ring-shaped graphite or the like, forming the silicon carbide polycrystalline film 200, and then removing the silicon carbide polycrystalline film 200 together with the masked material, The support substrate 100 may be exposed. Note that, even if the silicon carbide polycrystalline film 200 is formed on the ring-shaped graphite, it can be easily removed by forming a gripping part such as a tab on the ring-shaped graphite. is preferred. Furthermore, when a polycrystalline silicon carbide film is formed on one side of the support substrate 100, a part of the support substrate may be exposed by removing the polycrystalline silicon carbide deposited on the back side. . Further, the support substrate 100 can be removed by heating the stacked body 300A and burning the support substrate 100. The heating temperature ranges from -50°C (50°C lower than the film forming temperature) to the film forming temperature of the silicon carbide polycrystalline film 200 in the film forming process to +50°C (50°C higher than the film forming temperature). shall be. The combustion time can be, for example, about 10 hours. For the step of removing the support substrate 100 by combustion, for example, a combustion furnace or the like equipped with a heater made of molybdenum disilicide can be used. First, the stacked body 300A is held in a combustion furnace, and while supplying an oxidizing gas such as O ₂ or air into the combustion furnace, the heater is used to Heat the inside. In addition, when raising the temperature inside the combustion furnace to the heating temperature, an inert gas such as Ar gas is supplied into the combustion furnace under reduced pressure or in a state where the oxygen partial pressure is low to bring the inside of the combustion furnace into an inert condition. It is preferable to do so. By heating, only the support substrate 100 is burned, and a silicon carbide polycrystalline film from which the support substrate 100 has been removed is obtained, which is used as a silicon carbide polycrystalline substrate 500 as shown in FIG. 2(D).

In addition, the surface of the silicon carbide polycrystalline film after the removal process is polished as necessary to adjust the thickness and surface roughness, and to increase flatness. The silicon carbide polycrystalline substrate 500 may be obtained by further performing a polishing step. If the silicon carbide polycrystalline substrate 500 is to be used as a substrate for manufacturing semiconductors, it needs to have a surface precision that can be used in semiconductor manufacturing processes. Therefore, it is preferable to smooth the surface of the silicon carbide polycrystalline film after removing the support substrate 100 by a polishing process. For example, after removing the supporting substrate 100, the silicon carbide polycrystalline film is lapped with diamond slurry, hard polished with a mixed slurry of diamond and alumina, and then polished with silica slurry (colloidal silica, pH 11). Through this process, a smoothed silicon carbide polycrystalline substrate 500 can be obtained.

Further, the method for manufacturing a silicon carbide polycrystalline substrate according to the present embodiment may include other steps in addition to the steps described above. Other steps include, for example, a cleaning step for removing deposits that have adhered to the surface of the silicon carbide polycrystalline substrate after the polishing step in the silicon carbide substrate after the polishing step.

In the method for manufacturing a silicon carbide polycrystalline substrate of the present embodiment, the heating temperature of the laminate in the removal step is from −50° C. to the film forming temperature in the film forming step to +50° C. above the film forming temperature. In the step of forming a polycrystalline silicon carbide film, when the stack of support substrate 100 and polycrystalline silicon carbide film 200 is in the film formation temperature range, the sizes of the polycrystalline silicon carbide film and the support substrate do not match. There will be no warping.

In conventional methods of manufacturing silicon carbide polycrystalline substrates, the combustion temperature of the support substrate is often lower, for example, by about 200° C. or more, than the film formation temperature of the silicon carbide polycrystalline film. Here, when a polycrystalline silicon carbide film is formed on one side of the support substrate, in the cooling process after the polycrystalline silicon carbide film is formed, if the thermal expansion coefficients of silicon carbide and graphite, which is the material of the support substrate, differ. , a difference occurs in the amount of shrinkage between the silicon carbide polycrystalline film and the graphite support substrate, and warpage may occur in the laminate. If the support substrate is burned and removed with the laminate in a warped state, the warp will be fixed on the silicon carbide substrate, so the obtained silicon carbide substrate will also be warped. In addition, when a polycrystalline silicon carbide film is formed on both sides of the support substrate, in the cooling process after forming the polycrystalline silicon carbide film, shrinkage occurs due to the difference in the amount of shrinkage due to the difference in coefficient of thermal expansion between graphite and silicon carbide. Although no warpage occurs, stress is generated inside each layer. If the supporting substrate is burned and removed in this state, the silicon carbide substrate may warp due to internal stress.

On the other hand, as in the method for manufacturing a silicon carbide polycrystalline substrate of the present embodiment, the heating temperature of the laminate 300A in the removal step is set to the film-forming temperature in the film-forming step -50° C. to the film-forming temperature +50° C. By burning and removing 100, even if warpage occurs during cooling after film formation, the laminate is heated to a temperature comparable to the film formation temperature, resulting in a laminate with almost no warpage. Furthermore, even if stress is generated inside, the generated stress is canceled out by being heated to a temperature comparable to the film forming temperature. Since supporting substrate 100 is burned and removed in this state, silicon carbide polycrystalline substrate 500 with small warpage can be obtained.

With the method for manufacturing a polycrystalline substrate of this embodiment, it is possible to suppress the occurrence of warpage of the polycrystalline substrate. This reduces the burden on post-processes such as increasing flatness, and improves yield and cost.

In addition, the best configuration, method, etc. for carrying out the present invention have been disclosed in the above description, but the present invention is not limited thereto. That is, although the present invention has been specifically described mainly with respect to specific embodiments, there may be changes in shape, material, quantity, Various modifications can be made by those skilled in the art in other detailed configurations. Therefore, the descriptions that limit the shapes, materials, etc. disclosed above are provided as examples to facilitate understanding of the present invention, and do not limit the present invention. Descriptions of names of members that exclude some or all of the limitations such as these are included in the present invention.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples of the present invention, but the present invention is not limited to these Examples in any way.

In this example, after performing a film formation step of forming a silicon carbide polycrystalline film on a support substrate made of graphite using the film formation apparatus 1000, an exposure step and a support substrate removal step are performed to form a polycrystalline silicon carbide film. An example in which a polycrystalline substrate was obtained will be illustrated and explained.

(Example 1)
[Manufacture of silicon carbide polycrystalline substrate]
A support substrate made of graphite with a diameter of 6 inches and a thickness of 0.6 mm was held in the film forming chamber of the film forming apparatus 1000 of the embodiment described above, and a film forming process was performed. First, while flowing Ar gas into the film forming chamber 1010, the pressure inside the film forming chamber 1010 is reduced to 25 kPa using an exhaust pump (not shown), and then heated to 1350°C. After reaching 1350°C, Ar gas is supplied. has been stopped. SiCl ₄ gas and CH ₄ gas were introduced at 800 sccm each (standard cc/min, 1 atm, gas flow rate converted to the value at 0°C) as raw material gases, and hydrogen gas was introduced at 5000 sccm as a carrier gas. A silicon carbide polycrystalline film was formed by performing film formation for several hours.

After forming the silicon carbide polycrystalline film, the outer periphery of the silicon carbide polycrystalline film was polished using an end face processing device to expose the side surface of the graphite support substrate. After that, the temperature in the combustion furnace was raised to the heating temperature while the pressure inside the combustion furnace was reduced, and then the pressure was 1 atm and the heating temperature was maintained at 1350°C for 10 hours in an O ₂ atmosphere. The laminate with the crystal film was burned and the supporting substrate was completely removed to obtain a silicon carbide polycrystalline substrate.

[Evaluation of silicon carbide polycrystalline substrate]
The center line of the surface of the silicon carbide polycrystalline substrate was measured using an oblique incidence type optical measuring device, and the difference between the maximum value and the minimum value of the obtained measurement values was defined as the amount of warpage. Measurements were made at five points: the center, the circumferential end, and a point between the center and the circumferential end, the distance from the center being the same as the distance from the circumferential end. When the amount of warpage was 50 μm or less, it was evaluated as ◎, when it was 150 μm or less, it was evaluated as ◯, and when it was larger than 150 μm, it was evaluated as ×. The results are shown in Table 1. Table 1 also shows the film forming temperature, heating temperature, and temperature difference (heating temperature - film forming temperature (°C)).

(Example 2, Example 3, Comparative Examples 1 to 4)
A silicon carbide polycrystalline substrate was manufactured in the same manner as in Example 1, except that the heating temperature in the removal step was variously changed. Table 1 shows the heating temperature in the removal process and the evaluation results of the silicon carbide polycrystalline substrate.

In exemplary embodiments 1 to 3 of the present invention, when the amount of warpage of the silicon carbide polycrystalline substrate was confirmed, the amount of warpage was was 50 μm or less, and a substrate with a very small amount of warpage was obtained. In addition, in Example 2 (heating temperature is 50°C lower than the film-forming temperature) and Example 3 (heating temperature is 50°C higher than the film-forming temperature), the amount of warpage is 150 μm or less, and the substrate has a small amount of warpage. was gotten. In addition, in the silicon carbide polycrystalline substrates of Comparative Examples 1 to 4 (in each case, the heating temperature was lower than the film-forming temperature -50°C or higher than the film-forming temperature +50°C), the amount of warpage was 150 μm. It was bigger than Therefore, with the polycrystalline substrate manufacturing method of the present invention, it is possible to suppress the occurrence of warpage of the polycrystalline substrate, reduce the burden on post-processes such as increasing flatness, and improve yield and cost. It was shown that it is possible.

100 Support substrate 200 Silicon carbide polycrystalline film (polycrystalline film)
300 Laminated body 500 Silicon carbide polycrystalline substrate (polycrystalline substrate)

Claims (4)

A film forming step of forming a polycrystalline film on a support substrate made of graphite with a thickness of 0.6 mm by chemical vapor deposition method;
a removing step of heating the laminate of the support substrate and the polycrystalline film to burn and remove the support substrate,
The heating temperature of the laminate in the removing step is from -50° C. to the film forming temperature of the polycrystalline film in the film forming step +50° C.,
In the film forming step, the polycrystalline film is formed using both sides of the support substrate as film formation target surfaces,
The polycrystalline film is a silicon carbide polycrystalline film,
A method for producing a polycrystalline substrate having a warpage of 150 μm or less, wherein the film forming temperature is 1200° C. to 1700° C. Between the film forming step and the removing step, the method further includes an exposing step of removing at least a portion of the polycrystalline film at an outer peripheral end of the laminate to expose at least a portion of the supporting substrate. The method for manufacturing a polycrystalline substrate according to claim 1 . 3. The method for manufacturing a polycrystalline substrate according to claim 1 , further comprising a polishing step of polishing the surface of the polycrystalline film after the removal step. The film forming temperature is 1350°C,
The method for manufacturing a polycrystalline substrate according to any one of claims 1 to 3, wherein the heating temperature of the laminate in the removing step is 1350°C.

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