SiC Device and Method of Manufacturing SiC Device

Abstract

To provide an SiC device with a low boron content.SOLUTION: The SiC device comprises a SiC substrate, and an epitaxial layer of SiC laminated on the SiC substrate. The epitaxial layer contains impurities that determine the conductivity type, and boron that has a different conductivity type from the impurities. The concentration of the boron as measured by secondary ion mass spectrometry is less than 5.0×1012 cm-3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a SiC device and a method for manufacturing a SiC device.

Background Art

[0002] Silicon carbide (SiC) has a breakdown electric field that is one order of magnitude larger, a bandgap that is three times larger, and a thermal conductivity that is about three times higher than that of silicon (Si). Silicon carbide (SiC) is expected to be applied to power devices, high-frequency devices, high-temperature operation devices, etc.

[0003] To promote the practical application of SiC devices, the establishment of high-quality SiC epitaxial wafers and high-quality epitaxial growth technologies is required.

[0004] SiC devices are formed on SiC epitaxial wafers. The SiC epitaxial wafer includes a SiC substrate and an epitaxial layer laminated on the SiC substrate. The SiC substrate is obtained by processing a bulk single crystal of SiC grown by a sublimation recrystallization method or the like. The epitaxial layer is formed by a chemical vapor deposition (CVD) method or the like and becomes the active region of the device.

[0005] The epitaxial layer may have an impurity that determines the conductivity type of the epitaxial layer and boron having a conductivity type different from that of the impurity (for example, Patent Documents 1 to 3). Boron may reduce the effective carrier concentration in the drift layer and cause a short carrier lifetime in bipolar devices.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] Since boron is contained in members used in manufacturing, etc., it is difficult to completely remove it, but further reduction of boron concentration is required.

[0008] The present invention has been made in view of the above problems, and an object thereof is to obtain a SiC epitaxial wafer with a low boron content and a method for manufacturing the same.

Means for Solving the Problems

[0009] The present invention provides the following means for solving the above problems.

[0010] (1) The SiC epitaxial wafer according to the first aspect includes a SiC substrate and a SiC epitaxial layer laminated on the SiC substrate. The epitaxial layer contains an impurity that determines the conductivity type and boron having a conductivity type different from that of the impurity. The concentration of boron at the center of the epitaxial layer is less than 5.0×10 12 cm -3 less than.

[0011] (2) The SiC epitaxial wafer according to the above aspect may have a diameter of 150 mm or more.

[0012] (3) The SiC epitaxial wafer according to the above aspect may have a diameter of 200 mm or more.

[0013] (4) The manufacturing method of the SiC epitaxial wafer according to the second aspect has a film forming step of forming an epitaxial layer of SiC on a SiC substrate using a vertical furnace having a gas supply port above the placement surface of the SiC substrate. The film forming step has a temperature rising step of raising the temperature to the film forming temperature while changing the temperature rising rate in the order of a first temperature rising rate, a second temperature rising rate, and a third temperature rising rate. The first temperature rising rate is faster than the second temperature rising rate, the second temperature rising rate is faster than the third temperature rising rate, and the first temperature rising rate is 100 ° C / min or more. In the film forming step, the temperature of the gas supply port and an upstream member in the middle of the gas flow path from the gas supply port to the placement surface is set to 1200 ° C or less.

[0014] (5) In the manufacturing method of the SiC epitaxial wafer according to the above aspect, the gas supply port and the upstream member may be a carbon member on which a plurality of SiC layers are laminated.

[0015] (6) In the manufacturing method of the SiC epitaxial wafer according to the above aspect, the height position of the center of the placement surface of the SiC substrate at the film forming temperature may be 30 μm or more higher than the height position of the outer periphery.

[0016] (7) The time required for the temperature rising step of the manufacturing method of the SiC epitaxial wafer according to the above aspect may be 300 seconds or more and 750 seconds or less.

[0017] (8) In the manufacturing method of the SiC epitaxial wafer according to the above aspect, the temperature when the SiC substrate is transported to the vertical furnace may be 500 ° C or more.

[0018] (9) In the film forming step of the manufacturing method of the SiC epitaxial wafer according to the above aspect, purge gas may be supplied from the back surface of the SiC substrate. The purge gas is supplied, for example, from 20 mm or more inside the outer periphery of the SiC substrate.

Advantages of the Invention

[0019] The SiC epitaxial wafer according to the above aspect has a low boron content and can extend the carrier lifetime of the device. Further, the method for manufacturing the SiC epitaxial wafer according to the above aspect can reduce the boron content.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Modes for Carrying Out the Invention

[0021] Hereinafter, this embodiment will be described in detail with appropriate reference to the drawings. The drawings used in the following description may show, for the sake of clarity, the characteristic parts enlarged for convenience, and the dimensional ratios of the respective components may be different from the actual ones. The materials, dimensions, etc. exemplified in the following description are merely examples, and the present invention is not limited thereto, and can be appropriately changed and implemented without departing from the gist thereof.

[0022] FIG. 1 is a cross-sectional view of the SiC epitaxial wafer 10 according to the first embodiment. FIG. 2 is a plan view of the SiC epitaxial wafer 10 according to the first embodiment. The SiC epitaxial wafer 10 has a SiC substrate 1 and an epitaxial layer 2. The SiC epitaxial wafer 10 is, for example, a disk with a diameter of 150 mm or more. The diameter of the SiC epitaxial wafer 10 may be 200 mm or more.

[0023] The SiC substrate 1 is, for example, cut out from a SiC ingot. The SiC ingot grows on a SiC seed crystal using, for example, the sublimation method. The SiC substrate 1 has, for example, a plane parallel to the (0001) plane offset by an angle in the <11-20> direction as the growth plane. The SiC substrate 1 contains impurities. The impurities are, for example, nitrogen.

[0024] The planar shape of the SiC substrate 1 is, for example, circular. The diameter of the SiC substrate 1 is, for example, 150 mm or more. A part of the circle of the SiC substrate 1 may be cut out. The cut-out part is called an orientation flat OF. The orientation flat OF is used to confirm the orientation of the SiC substrate 1.

[0025] The epitaxial layer 2 is laminated on the SiC substrate 1. The epitaxial layer 2 is formed, for example, by chemical vapor deposition (CVD method). The epitaxial layer 2 is a single crystal film of SiC. The epitaxial layer 2 may be composed of, for example, a plurality of layers. For example, the epitaxial layer 2 may be composed of a plurality of SiC single crystal films with different impurity concentrations.

[0026] The epitaxial layer 2 contains an impurity that determines the conductivity type and boron. The impurity that determines the conductivity type is, for example, nitrogen. The conductivity type of nitrogen is n-type. The impurity concentration that determines the conductivity type in the epitaxial layer 2 is, for example, 1.0×10 14 cm -3 or more and 3.0×10 16 cm -3 or less, preferably 1.0×10 14 cm -33.0×10 or less as described above. 15 cm -3 Specifically, the in-plane uniformity of the impurity concentration that determines the conductivity type in the epitaxial layer 2 is preferably, for example, within 20%, more preferably 10% or less. The in-plane uniformity of the impurity concentration that determines the conductivity type is obtained, for example, from the results of 10 or more measurement points in the radial direction passing through the center of the SiC epitaxial wafer. The in-plane uniformity of the impurity concentration is a value obtained by dividing the difference between the maximum value and the minimum value of the impurity concentration among a plurality of measurement points by the average value of the impurity concentrations of the plurality of measurement points. The measurement points may be arranged in a direction parallel to the orientation flat OF, in a direction perpendicular to the orientation flat OF, or in both a direction parallel and a direction perpendicular to the orientation flat OF.

[0027] Boron exhibits a conductivity type different from that of nitrogen. The conductivity type of boron is p-type. Boron is not intentionally doped into the epitaxial layer 2, but is a contaminant mixed as an impurity from components included in the film-forming apparatus such as a susceptor during the film formation of the epitaxial layer 2. Boron is a cause of a decrease in the effective carrier concentration and can also be a cause of suppressing the conductivity modulation effect of bipolar devices. Although it is preferable that the boron concentration in the epitaxial layer 2 is low, it is difficult to completely remove it.

[0028] The concentration of boron at the center p1 of the epitaxial layer 2 is 5.0×10 12 cm -3 or less. The boron concentration at the point p2 on the outer peripheral side of the epitaxial layer 2 is preferably less than 1.0×10 14 cm -3 The point p2 is a point 5 mm inside from the outer periphery of the epitaxial layer 2. The range of 5 mm from the outer periphery may not be regarded as an effective region of the device. Therefore, the range of 5 mm from the outer periphery is often negligible.

[0029] The impurity and boron concentrations of each layer can be measured, for example, by a mercury probe (Hg-CV) method, secondary ion mass spectrometry (SIMS), or the like.

[0030] The Hg-CV method measures the difference (N d - N a ) between the donor concentration N d and the acceptor concentration N a as the n-type impurity concentration. When the acceptor concentration is sufficiently smaller than the donor concentration, these concentration differences can be regarded as the n-type impurity concentration.

[0031] Secondary ion mass spectrometry (SIMS) is a method of performing mass spectrometry on the ejected secondary ions while shaving layers in the thickness direction. The doping concentration can be measured from the mass spectrometry.

[0032] Next, a method for manufacturing a SiC epitaxial wafer according to the first embodiment will be described. First, a SiC substrate 1 is prepared. The SiC substrate 1 can be obtained by cutting a SiC ingot to a predetermined thickness. The SiC substrate 1 may be purchased as a commercially available product.

[0033] Next, a film formation step of forming an epitaxial layer 2 on the SiC substrate 1 is performed. The epitaxial layer 2 is formed by, for example, the CVD method.

[0034] FIG. 3 is a schematic diagram of an example of a film formation apparatus 100 for a SiC epitaxial wafer 10 according to the first embodiment. The film formation apparatus 100 includes, for example, a chamber 20, a support 30, a susceptor 40, a lower heater 50, and an upper heater 60. FIG. 3 shows a state in which the SiC substrate 1 is placed on the susceptor 40. The film formation apparatus 100 is a vertical furnace having a gas supply port 22 above the placement surface of the SiC substrate 1.

[0035] The chamber 20 has, for example, a main body 21, a gas supply port 22, and a gas discharge port 23. The main body 21 surrounds the film formation space S. The gas supply port 22 is an inlet for supplying the film formation gas G to the film formation space S. The gas supply port 22 is the portion of the gas supply pipe that is exposed to the film formation space S. The gas supply port 22 is, for example, above the placement surface of the SiC substrate 1. The gas discharge port 23 is an outlet for discharging the film formation gas G and the like that has stayed in the film formation space S. The gas discharge port 23 is, for example, below the placement surface of the SiC substrate 1. The film formation gas G is, for example, an Si-based gas, a C-based gas, a purge gas, or a dopant gas.

[0036] The Si-based gas is a source gas containing Si in its molecule. The Si-based gas is, for example, silane (SiH4), dichlorosilane (SiH2Cl2), trichlorosilane (SiHCl3), tetrachlorosilane (SiCl4), etc. The C-based gas is, for example, propane (C3H8), ethylene (C2H4), etc. The dopant gas is a gas containing an element that serves as a carrier. The dopant gas is, for example, nitrogen, ammonia, etc. The purge gas is a gas that transports these gases to the SiC substrate 1 and is, for example, hydrogen that is inert to SiC.

[0037] The gas supply port 22 includes, for example, a carbon member and an SiC or TaC layer that coats its surface. By coating the surface with SiC or TaC, the release of boron from the gas supply port 22 can be suppressed. It is more preferable that the gas supply port 22 is a carbon member on which a plurality of SiC layers are laminated. Each of the plurality of SiC layers is preferably an epitaxial layer of SiC. Each of the plurality of SiC layers is preferably formed under the same conditions as those for forming the epitaxial layer 2. When a plurality of SiC layers are formed on the surface of the carbon member, the release of boron from the member can be further suppressed.

[0038] The support 30 supports the SiC substrate 1. The support 30 is rotatable about the axis center. The SiC substrate 1 is placed on the support 30, for example, with the SiC substrate 1 placed on the susceptor 40. The susceptor 40 is transported into the chamber 20 with the SiC substrate 1 placed thereon. The support 30 and the susceptor 40 can be made of, for example, the same material as the gas supply port 22. The lower heater 50 is, for example, inside the support 30 and heats the SiC substrate 1. The upper heater 60 heats the upper part of the chamber 20.

[0039] The film formation process is performed, for example, in a vertical furnace shown in FIG. 3. First, the SiC substrate 1 is transported to the film formation space S. The SiC substrate 1 is transported, for example, while placed on the susceptor 40. The temperature when transporting the SiC substrate 1 into the film formation apparatus 100 is preferably 500°C or higher. By maintaining a high transport temperature of the SiC substrate 1, the time required for the entire film formation can be shortened.

[0040] Next, an epitaxial layer 2 is formed on the SiC substrate 1 after transportation. FIG. 4 is an example of a manufacturing process of the SiC epitaxial wafer 10 according to the first embodiment. The film formation process includes a temperature rising process RS of raising the temperature to the film formation temperature T1. After the temperature rising process, the film formation temperature T1 is maintained and the epitaxial layer 2 is formed. The film formation temperature T1 is, for example, 1500°C or higher.

[0041] The time required for the temperature rising process RS is, for example, 300 seconds or more and 750 seconds or less. If the time required for the temperature rising process RS is short, the distortion of the SiC substrate 1 and the susceptor 40 becomes large, and the in-plane uniformity of the epitaxial layer 2 deteriorates. Also, if the time required for the temperature rising process RS is short, the film formation gas is re-circulated due to convection caused by the in-plane temperature difference of the susceptor 40, etc., and the boron released from the susceptor 40 is taken into the wafer. If the time required for the temperature rising process RS is long, the amount of boron released from the members used in the film formation apparatus 100 increases.

[0042] The temperature increase process RS has, for example, a first temperature increase process S1, a second temperature increase process S2, and a third temperature increase process S3. The first temperature increase process S1, the second temperature increase process S2, and the third temperature increase process S3 each have a different temperature increase rate. The temperature increase process RS only needs to change the temperature increase rate two or more times, and may have further processes with different temperature increase rates such as a fourth temperature increase process and a fifth temperature increase process.

[0043] The first temperature increase process S1 increases the temperature at the first temperature increase rate. The first temperature increase rate is 100 °C / min or more. The first temperature increase rate is faster than the second temperature increase rate in the second temperature increase process S2. In the first temperature increase process S1, for example, the temperature is raised to about 1200 °C.

[0044] The second temperature increase process S2 is performed after the first temperature increase process S1 and before the third temperature increase process S3. The second temperature increase process S2 is performed at the second temperature increase rate. The second temperature increase rate is slower than the first temperature increase rate and faster than the third temperature increase rate. The second temperature increase rate is, for example, 90% or less of the first temperature increase rate. In the second temperature increase process S2, for example, the temperature is raised to about 1400 °C.

[0045] The third temperature increase process S3 is performed after the second temperature increase process S2. The third temperature increase process S3 is performed at the third temperature increase rate. The third temperature increase rate is slower than the second temperature increase rate. The third temperature increase rate is, for example, 90% or less of the second temperature increase rate.

[0046] By increasing the first temperature increase rate, the time required for the entire temperature increase process RS can be shortened. When the time required for the entire temperature increase process RS is shortened, the amount of boron released from the film forming apparatus 100 decreases. Also, by gradually decreasing the temperature increase rate, it is possible to suppress the distortion of the SiC substrate 1 and the susceptor 40 from becoming too large.

[0047] Next, after reaching the film formation temperature T1, an epitaxial layer 2 is formed on the SiC substrate 1. When forming the film, the temperature of the gas supply port 22 is set to 1200°C or lower, preferably 1100°C or lower. The temperature of the gas supply port 22 can be realized, for example, by adjusting the outputs of various heaters such as an upper heater and a lower heater. In addition, it may be realized by utilizing physical property values such as the structure and emissivity of the members constituting the furnace interior. The temperature of the gas supply port 22 can be measured, for example, using a thermocouple. Also, the simulation results by a computer may be used. The amount of boron released from the member increases as the temperature is higher. By lowering the temperature of the gas supply port 22, the amount of boron released can be reduced.

[0048] Further, FIG. 5 is an enlarged view of the vicinity of the SiC substrate 1 of the film formation apparatus for SiC epitaxial wafers according to the first embodiment. The SiC substrate 1 is placed on the susceptor 40. The susceptor 40 has, for example, a support portion 41, an outer peripheral portion 42, and a through hole 43.

[0049] The SiC substrate 1 is placed on the support portion 41. The outer peripheral portion 42 prevents the SiC substrate 1 from protruding outward during film formation. The outer peripheral portion 42 may be, for example, a ring-shaped separate member. The ring-shaped separate member is more preferably a carbon member in which a plurality of SiC layers are laminated. Each of the plurality of SiC layers is preferably an epitaxial layer of SiC. Each of the plurality of SiC layers is preferably formed under the same conditions as those for forming the epitaxial layer 2. When a plurality of SiC layers are formed on the surface of the carbon member, boron release from the member can be more suppressed. The through hole 43 is a hole connecting the upper surface and the lower surface of the support portion 41.

[0050] The difference between the height position at the center of the mounting surface of the SiC substrate 1 and the height position at the outermost periphery is referred to as the height difference Δh. The height difference Δh can be measured, for example, by a laser displacement meter. First, a measurement port and a laser displacement meter are installed at the center and the outer peripheral part of the susceptor at the upper part of the furnace respectively, and the warp of the susceptor is measured by obtaining the difference in height between the center part and the outer peripheral part at the film formation temperature without installing the wafer. Next, the wafer is installed on the susceptor, and the height difference Δh can be measured by measuring under the same conditions as when measuring the warp without installing the wafer. By forming a film while measuring the height difference Δh, an arbitrary height difference Δh can be maintained. Also, by selecting the wavelength of the laser light source, it is possible to measure the warp of the susceptor with the wafer installed. For example, in the case of a SiC wafer, when the wavelength of the laser light source is 600 nm or more, the laser transmits through the SiC wafer, so the warp of the susceptor can be measured with the wafer installed. The height difference Δh during film formation is preferably 30 μm or more. That is, at the film formation temperature T1, it is preferable that the height position at the center of the mounting surface of the SiC substrate 1 is 30 μm or more higher than the height position at the outermost periphery. Also, the height difference Δh at the film formation temperature T1 is preferably 100 μm or less.

[0051] The above range of the height difference Δh only needs to be satisfied at the film formation temperature T1, and it does not need to be satisfied at room temperature. Also, in the case where there is an outer peripheral part 42, the boundary between the outer peripheral part 42 and the mounting surface is the outer periphery of the mounting surface.

[0052] The height difference Δh can be controlled, for example, by the film formation conditions. When the heating rate is high, the height difference Δh tends to be large. In addition, the height difference Δh may be adjusted by the material constituting the susceptor 40. For example, when the susceptor 40 is made of two or more materials having different coefficients of thermal expansion, the height difference Δh may be adjusted by utilizing the difference in the coefficient of thermal expansion.

[0053] If the height difference Δh increases, a flow of the film-forming gas G from the center of the SiC substrate 1 toward the outside can be formed near the upper surface of the SiC substrate 1, and it is possible to prevent the occurrence of a rollback or the like of the film-forming gas G. The rollback of the film-forming gas G causes boron released from the member to be taken into the epitaxial layer 2 again. When a flow of the film-forming gas G from the center of the SiC substrate 1 toward the outside can be formed near the upper surface of the SiC substrate 1, the boron concentration in the epitaxial layer 2 decreases. Also, if the height difference Δh is within a predetermined range, the difference in film-forming conditions between the center and the outer peripheral portion of the epitaxial layer 2 is small, and the in-plane uniformity of the epitaxial layer 2 is enhanced.

[0054] Also, during film formation, gas may be supplied to the back surface of the SiC substrate 1 through the through hole 43. The gas supplied to the back surface side of the SiC substrate 1 prevents the film-forming gas G from flowing around to the back surface of the SiC substrate 1. The gas supplied to the back surface is an inert purge gas with respect to SiC.

[0055] The purge gas is preferably supplied toward the back surface of the SiC substrate 1 from 20 mm or more inside the outermost periphery of the SiC substrate 1. For example, the distance d between the through hole 43 and the outermost periphery is preferably 20 mm or more. When the supply position of the purge gas to the back surface of the SiC substrate 1 satisfies the above conditions, it is possible to suppress the flow of the film-forming gas G from being disturbed by the purge gas from the back surface, and it is possible to suppress the rollback of the film-forming gas G to the SiC substrate 1.

[0056] The film-forming method of the SiC epitaxial wafer 10 according to the present embodiment uses a vertical furnace and defines a temperature-raising process, thereby controlling the flow of the film-forming gas G and preventing the rollback of the unreacted gas to the epitaxial layer 2. Also, the film-forming method of the SiC epitaxial wafer 10 according to the present embodiment can reduce the amount of boron released from the member itself by defining the temperature of the gas supply port 22. As a result, the film-forming method of the SiC epitaxial wafer 10 according to the embodiment can reduce the boron concentration at the center of the epitaxial layer 2 to less than 5.0×10 12 cm -3 less than. Also, the boron concentration at the outer periphery of the epitaxial layer 2 is 1.0×1014 cm -3 It can be as follows.

[0057] Since boron becomes a lifetime killer, in order to obtain a sufficient conductivity modulation effect in a bipolar device, the concentration of boron must be less than 5.0×10 12 cm -3 less. In the SiC epitaxial wafer 10 according to the present embodiment, since the concentration of boron at the center of the epitaxial layer 2 is less than 5.0×10 12 cm -3 less, in a bipolar device, a sufficient conductivity modulation effect can be obtained. That is, when the SiC epitaxial wafer 10 according to the present embodiment is used, a high-quality device can be fabricated.

[0058] In the epitaxial layer 2, the lower the impurity concentration that determines the conductivity type, the greater the influence of the boron concentration on the carrier concentration uniformity. This is because the lower the nitrogen concentration in the epitaxial layer 2, the relatively higher the ratio of boron to nitrogen contained in the epitaxial layer 2. In other words, in the epitaxial layer 2 with a low impurity concentration that determines the conductivity type, a low boron concentration is valuable.

[0059] As described above, the preferred embodiments of the present invention have been described in detail. However, the present invention is not limited to specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention described in the claims.

[0060] For example, FIG. 6 is a schematic diagram of another example of a film forming apparatus for fabricating the SiC epitaxial wafer according to the first embodiment. The film forming apparatus 101 shown in FIG. 6 is different from the film forming apparatus 100 according to FIG. 3 in that there is an upstream member 70 in the middle of the gas flow path from the gas supply port 22 in the film forming space S to the mounting surface of the SiC substrate 1. In the description of the film forming apparatus 101, the same components as those of the film forming apparatus 100 are denoted by the same reference numerals. When the film forming apparatus 101 is used, the epitaxial layer 2 is formed in the same manner as the film forming apparatus 100.

[0061] The upstream member 70 is a member within the film formation space S and is located between the gas supply port 22 and the mounting surface of the SiC substrate 1 in the gas flow direction. The upstream member 70 is, for example, a reflector that reflects radiation from a heater, a taper member that controls the gas flow, or the like.

[0062] The upstream member 70 includes, for example, a carbon member and a SiC or TaC layer that coats its surface. By coating the surface with SiC or TaC, the release of boron from the upstream member 70 can be suppressed.

[0063] Even in this modification, by using a vertical furnace and defining a temperature rising process, the flow of the film formation gas G can be controlled, and the return of unreacted gas to the epitaxial layer 2 can be prevented. Also, by defining the temperatures of the gas supply port 22 and the upstream member 70 in the middle of the gas flow path in the film formation space S, the amount of boron released from the member itself can be reduced. As a result, even in this modification, the concentration of boron at the center of the epitaxial layer 2 can be made less than 5.0×10 12 cm -3 and the concentration of boron at the outer periphery of the epitaxial layer 2 can be made 1.0×10 14 cm -3 or less.

Example

[0064] (Example 1) A SiC substrate with a diameter of 150 mm was prepared. An epitaxial layer 2 was formed on the SiC substrate 1 using a vertical furnace similar to the film formation apparatus 100 shown in FIG. 3. For the outer peripheral portion 42, a ring-shaped separate member in which a plurality of SiC layers were laminated was used. The temperature rising process was divided into three stages, and the temperature rising rate was changed twice. The first temperature rising rate (the first temperature rising rate) was set to 100°C / min or more. The second temperature rising rate (the second temperature rising rate) was set to less than 80% of the first temperature rising rate. The third temperature rising rate (the third temperature rising rate) was set to less than 80% of the second temperature rising rate. The film formation temperature was set to 1600°C or more and less than 1700°C. The time required for temperature rising was 350 seconds or more and less than 750 seconds.

[0065] When forming the epitaxial layer 2, a purge gas was supplied from the back side of the SiC substrate 1. The purge gas was supplied so as to hit a position 20 mm or more inside from the outer periphery of the SiC substrate 1. Also, in the temperature range of 1600 °C or more and less than 1700 °C, the height position of the center of the mounting surface of the SiC substrate 1 was made 30 μm or more higher than the height position of the outermost periphery. Further, the temperature of the gas supply port 22 during film formation was 1100 °C or less.

[0066] And, after production, the boron concentration at the center p1 of the SiC epitaxial wafer 10 was measured. The boron concentration at the center p1 of Example 1 was 2.0×10 12 cm -3 It was.

[0067] (Comparative Example 1) A SiC substrate with a diameter of 150 mm was prepared. In Comparative Example 1, a horizontal furnace having a gas supply port on the side of the SiC substrate was used. A part of the members constituting the furnace used a carbon member not covered with a SiC epitaxial layer. Then, using the horizontal furnace, an epitaxial layer 2 was formed on the SiC substrate 1. The temperature rising process was in one stage, and the temperature rising rate was not changed. The temperature rising rate was 100 °C / min or less. The film formation temperature was 1600 °C or more and less than 1700 °C. The time required for temperature rising was 750 seconds or more.

[0068] In Comparative Example 1, a purge gas was not supplied to the back side of the SiC substrate 1. Also, since the temperature rising rate was gentler than that of the example, in the temperature range of 1600 °C or more and less than 1700 °C, the height position of the center of the mounting surface of the SiC substrate 1 was less than 30 μm higher than the height position of the outer periphery.

[0069] And, after production, the boron concentration at the center p1 of the SiC epitaxial wafer of Comparative Example 1 was measured. The boron concentration at the center p1 of Comparative Example 1 was 1.7×10 14 cm -3 It was.

Explanation of symbols

[0070] 1…SiC substrate, 2…epitaxial layer, 10…SiC epitaxial wafer, 20…chamber, 21…body, 22…gas supply port, 23…gas discharge port, 30…support, 40…susceptor, 41…support part, 42…outer peripheral part, 43…through hole, 50…lower heater, 60…upper heater, 70…upstream member, 100…film forming apparatus, G…film forming gas, RS…heating-up process, S1…first heating-up process, S2…second heating-up process, S3…third heating-up process, T1…film forming temperature, Δh…height difference, d…distance, p1…center, p2…point

Claims

1. A SiC substrate and an epitaxial layer of SiC laminated on the SiC substrate, the epitaxial layer includes an impurity that determines a conductivity type and boron having a conductivity type different from that of the impurity; The boron concentration measured by secondary ion mass spectrometry was 5.0×10 １２ cm －３ The SiC device is less than

2. The SiC device of claim 1 which is a power device.

3. The SiC device of claim 1 which is a high frequency device.

4. The SiC device of claim 1 which is a high temperature operating device.

5. The SiC device of claim 1 which is a bipolar device.

6. The method includes a step of manufacturing a SiC device using a SiC epitaxial wafer in which a SiC epitaxial layer is formed on a SiC substrate, the epitaxial layer includes an impurity that determines a conductivity type and boron having a conductivity type different from that of the impurity; The SiC epitaxial wafer has a boron concentration of 5.0×10 at the center of the epitaxial layer as measured by secondary ion mass spectrometry. １２ cm －３ A method for manufacturing a SiC device, comprising the steps of:

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