JP2023072238A - Method for manufacturing silicon carbide single crystal, and silicon carbide single crystal - Google Patents

Abstract

To provide a method for manufacturing a silicon carbide single crystal, capable of preventing cracks from being generated while enhancing electrical resistivity, and the silicon carbide single crystal.SOLUTION: A method for manufacturing a silicon carbide single crystal comprises: heating a silicon carbide crystal to a first temperature; cooling the silicon carbide crystal at a first cooling rate from the first temperature to a second temperature after heating a silicon carbide crystal to a first temperature; and cooling the silicon carbide crystal at a second cooling rate from the second temperature to a third temperature. The first cooling rate is larger than 50°C/minute; the second cooling rate is 20°C/minute or less; the first temperature is 2000°C or more; the second temperature is 1300°C or more and 1500°C or less; the third temperature is 900°C or more and 1100°C or less; and the electrical resistivity of the silicon carbide crystal cooled from the third temperature to 27°C is 1×107 Ωcm.SELECTED DRAWING: Figure 7

Description

The present disclosure relates to a method for producing a silicon carbide single crystal and a silicon carbide single crystal.

Japanese National Publication of International Patent Application No. 2005-531145 (Patent Document 1) discloses a method for producing a semi-insulating silicon carbide single crystal. A method for manufacturing a semi-insulating silicon carbide single crystal includes the steps of heating the silicon carbide crystal to a temperature of 2000° C. or more and 2400° C. or less, and cooling the silicon carbide crystal at a cooling rate of 30° C./min or more and 150° C./min or less. ing.

Japanese Patent Publication No. 2005-531145

An object of the present disclosure is to provide a method for manufacturing a silicon carbide single crystal and a silicon carbide single crystal capable of suppressing the occurrence of cracks while increasing electrical resistivity.

A method for manufacturing a silicon carbide single crystal according to the present disclosure includes the following steps. A silicon carbide crystal is heat-treated to a first temperature. The silicon carbide crystal is heat-treated to a first temperature and then cooled from the first temperature to the second temperature at a first cooling rate. The silicon carbide crystal is cooled from the second temperature to the third temperature at the second cooling rate. The first cooling rate is greater than 50°C/min. The second cooling rate is 20° C./min or less. The first temperature is 2000° C. or higher. The second temperature is 1300° C. or higher and 1500° C. or lower. The third temperature is 900° C. or higher and 1100° C. or lower. The electrical resistivity of the silicon carbide crystal cooled from the third temperature to 27° C. is 1×10 ⁷ Ωcm or more.

The diameter of the silicon carbide single crystal according to the present disclosure is 100 mm or more. The thickness of the silicon carbide single crystal is 30 mm or more. The electrical resistivity of the silicon carbide single crystal is 1×10 ⁷ Ωcm or more. The silicon carbide single crystal does not contain cracks having a length of 10 mm or more.

Advantageous Effects of Invention According to the present disclosure, it is possible to provide a method for manufacturing a silicon carbide single crystal and a silicon carbide single crystal capable of suppressing the occurrence of cracks while increasing electrical resistivity.

FIG. 1 is a schematic side view showing the configuration of a silicon carbide single crystal according to this embodiment. FIG. 2 is a schematic plan view showing the configuration of the silicon carbide single crystal according to this embodiment. FIG. 3 is a schematic plan view showing measurement positions of impurity atom concentrations. FIG. 4 is a schematic plan view showing measurement positions of electrical resistivity. FIG. 5 is a schematic partial cross-sectional view showing the configuration of the silicon carbide single crystal manufacturing apparatus according to the present embodiment. FIG. 6 is a flow diagram schematically showing a method for manufacturing a silicon carbide single crystal according to this embodiment. FIG. 7 is a schematic diagram showing the relationship between temperature and elapsed time. FIG. 8 is a schematic diagram showing the relationship between power and elapsed time.

[Description of Embodiments of the Present Disclosure]
First, an outline of the embodiments of the present disclosure will be described.

(1) A method for manufacturing silicon carbide single crystal 10 according to the present disclosure includes the following steps. Silicon carbide crystal 20 is heat-treated to first temperature C1. Silicon carbide crystal 20 is heat-treated to first temperature C1 and then cooled from first temperature C1 to second temperature C2 at a first cooling rate. Silicon carbide crystal 20 is cooled from second temperature C2 to third temperature C3 at the second cooling rate. The first cooling rate is greater than 50°C/min. The second cooling rate is 20° C./min or less. The first temperature C1 is 2000° C. or higher. The second temperature C2 is 1300° C. or higher and 1500° C. or lower. The third temperature C3 is 900° C. or higher and 1100° C. or lower. Silicon carbide crystal 20 cooled from third temperature C3 to 27° C. has an electrical resistivity of 1×10 ⁷ Ωcm or more.

(2) According to the method for manufacturing silicon carbide single crystal 10 according to (1) above, silicon carbide crystal 20 may have a diameter of 100 mm or more.

(3) According to the method for manufacturing silicon carbide single crystal 10 according to (1) or (2) above, silicon carbide crystal 20 may have a thickness of 30 mm or more.

(4) According to the method for manufacturing silicon carbide single crystal 10 according to any one of (1) to (3) above, the first cooling rate may be 80° C./min or more.

(5) According to the method for manufacturing silicon carbide single crystal 10 according to any one of (1) to (4) above, the second cooling rate may be 10° C./min or less.

(6) Silicon carbide single crystal 10 according to the present disclosure has a diameter of 100 mm or more. Silicon carbide single crystal 10 has a thickness of 30 mm or more. Silicon carbide single crystal 10 has an electrical resistivity of 1×10 ⁷ Ωcm or more. Silicon carbide single crystal 10 does not include cracks having a length of 10 mm or more.

(7) Silicon carbide single crystal 10 according to (6) above may contain nitrogen. The concentration of nitrogen in silicon carbide single crystal 10 may be 5×10 ¹⁵ atoms/cm ³ or more and 1×10 ¹⁶ atoms/cm ³ or less.

(8) Silicon carbide single crystal 10 according to (6) or (7) above may contain boron. Silicon carbide single crystal 10 may have a boron concentration of 1×10 ¹⁵ atoms/cm ³ or more and 5×10 ¹⁵ atoms/cm ³ or less.

(9) Silicon carbide single crystal 10 according to any one of (6) to (8) above may contain aluminum. The concentration of aluminum in silicon carbide single crystal 10 may be 1×10 ¹⁴ atoms/cm ³ or more and 5×10 ¹⁴ atoms/cm ³ or less.

[Details of Embodiments of the Present Disclosure]
Hereinafter, details of an embodiment of the present disclosure (hereinafter also referred to as the present embodiment) will be described based on the drawings. In the drawings below, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated. In the crystallographic descriptions in this specification, individual orientations are indicated by [], aggregated orientations by <>, individual planes by (), and aggregated planes by {}. Also, for negative exponents, a "-" (bar) is added above the number in terms of crystallography, but in this specification, a negative sign is added before the number.

(Structure of silicon carbide single crystal)
First, the structure of the silicon carbide single crystal according to this embodiment will be described. FIG. 1 is a schematic side view showing the configuration of a silicon carbide single crystal according to this embodiment. As shown in FIG. 1 , silicon carbide single crystal 10 according to the present embodiment mainly has first main surface 1 , second main surface 2 , and first outer peripheral surface 8 . The second major surface 2 is opposite the first major surface 1 . The second main surface 2 is convex outward. First main surface 1 is, for example, a flat surface. The first outer peripheral surface 8 continues to each of the first main surface 1 and the second main surface 2 . Silicon carbide single crystal 10 according to the present embodiment has a substantially cylindrical shape. Silicon carbide single crystal 10 is used, for example, as a substrate of a high frequency device such as a gallium nitride high electron mobility transistor (GaN HEMT).

In a direction perpendicular to first main surface 1, silicon carbide single crystal 10 has a thickness (hereinafter referred to as first thickness H1) of, for example, 30 mm or more and 60 mm or less. Although the lower limit of the first thickness H1 is not particularly limited, it may be, for example, 35 mm or more, or 40 mm or more. Although the upper limit of the first thickness H1 is not particularly limited, it may be, for example, 55 mm or less, or 50 mm or less.

A silicon carbide single crystal is made of, for example, hexagonal silicon carbide. A polytype of hexagonal silicon carbide is, for example, 4H. First main surface 1 is, for example, the {0001} plane or a plane inclined in the off direction with respect to the {0001} plane. Specifically, first main surface 1 may be, for example, the (000-1) plane or a plane inclined in the off direction with respect to the (000-1) plane. The off direction is, for example, the <11-20> direction. The tilt angle (off angle) with respect to the {0001} plane is, for example, 8° or less.

FIG. 2 is a schematic plan view showing the configuration of the silicon carbide single crystal according to this embodiment. As shown in FIG. 2 , silicon carbide single crystal 10 has a substantially circular shape when viewed in a direction perpendicular to first main surface 1 . Silicon carbide single crystal 10 has a diameter (hereinafter referred to as first diameter D1) of, for example, 110 mm. The first diameter D1 is, for example, 100 mm or more. Although the lower limit of the first diameter D1 is not particularly limited, it may be, for example, 125 mm or more, or 150 mm or more. The upper limit of the first diameter D1 may be, for example, 200 mm or less.

Silicon carbide single crystal 10 does not include cracks having a length of 10 mm or more. The crack has an elongated shape when viewed in a direction perpendicular to the surface on which the crack is formed. The length of the crack in the longitudinal direction is, for example, at least three times the length of the crack in the lateral direction. The lower limit of the crack length is not particularly limited, but may be, for example, 5 mm or longer, or 1 mm or longer. In this specification, the length of the crack means the length in the longitudinal direction seen from the direction perpendicular to the surface on which the crack is formed. Specifically, when the crack is formed on the first main surface, the length of the crack is the length in the longitudinal direction of the crack as seen from the direction perpendicular to the first main surface 1 . When the crack is formed on the first outer peripheral surface 8 , the length of the crack is the length of the crack when viewed from the radial direction of the first outer peripheral surface 8 .

Silicon carbide single crystal 10 does not include cracks having a depth of 10 mm or more. The lower limit of the crack depth is not particularly limited, but may be, for example, 5 mm or more, or 1 mm or more. In this specification, the crack depth means the maximum depth of the crack in the direction perpendicular to the surface on which the crack is formed. Specifically, when a crack is formed on the first main surface, the depth of the crack is the maximum depth of the crack in the direction perpendicular to the first main surface 1 . When a crack is formed on the first outer peripheral surface 8 , the depth of the crack is the maximum depth of the crack in the radial direction of the first outer peripheral surface 8 .

(Concentration of impurity atoms in silicon carbide single crystal)
Silicon carbide single crystal 10 contains impurity atoms. Silicon carbide single crystal 10 contains nitrogen as an n-type impurity, for example. The concentration of nitrogen in silicon carbide single crystal 10 is, for example, 5×10 ¹⁵ atoms/cm ³ or more and 1×10 ¹⁶ atoms/cm ³ or less. The lower limit of the nitrogen concentration in silicon carbide single crystal 10 is not particularly limited, but may be, for example, 6×10 ¹⁵ atoms/cm ³ or more, or may be 7×10 ¹⁵ atoms/cm ³ or more. The upper limit of the nitrogen concentration in silicon carbide single crystal 10 is not particularly limited, but may be, for example, 9×10 ¹⁵ atoms/cm ³ or less, or may be 8×10 ¹⁵ atoms/cm ³ or less.

Silicon carbide single crystal 10 contains, for example, boron as a p-type impurity. The concentration of boron in silicon carbide single crystal 10 is, for example, 1×10 ¹⁵ atoms/cm ³ or more and 5×10 ¹⁵ atoms/cm ³ or less. The lower limit of the boron concentration ⁱⁿ silicon carbide single crystal 10 ^is not ^particularly limited ^. good. ^The upper limit of the boron concentration ⁱⁿ silicon carbide single crystal 10 is ^not particularly limited ^. good.

Silicon carbide single crystal 10 contains, for example, aluminum as a p-type impurity. The concentration of aluminum in silicon carbide single crystal 10 is, for example, 1×10 ¹⁴ atoms/cm ³ or more and 5×10 ¹⁴ atoms/cm ³ or less. The lower limit of the aluminum concentration in silicon carbide single crystal 10 is not particularly limited, but may be, for example, 1.5×10 ¹⁴ atoms/cm ³ or more, or may be 2×10 ¹⁴ atoms/cm ³ or more. good. Although the upper limit of the aluminum concentration in silicon carbide single crystal 10 is not particularly limited, it may be, for example, 4.5×10 ¹⁴ atoms/cm ³ or less, or 4×10 ¹⁴ atoms/cm ³ or less. good.

In silicon carbide single crystal 10, the absolute value of the difference between the n-type impurity concentration and the p-type impurity concentration is, for example, 7×10 ¹⁵ atoms/cm ³ or less. The upper limit of the absolute value of the difference between the n-type impurity concentration and the p-type impurity concentration is not particularly limited, but may be, for example, 6×10 ¹⁵ atoms/cm ³ or less, or 5×10 ¹⁵ atoms/cm ³ . It may be below. When silicon carbide single crystal 10 contains two or more types of n-type impurities, the sum of the concentrations of the two or more types of n-type impurities is taken as the n-type impurity concentration. Similarly, when silicon carbide single crystal 10 contains two or more types of p-type impurities, the sum of the concentrations of the two or more types of p-type impurities is taken as the p-type impurity concentration. As the absolute value of the difference between the n-type impurity concentration and the p-type impurity concentration decreases, the carrier concentration in silicon carbide single crystal 10 decreases.

Next, a method for measuring the concentration of impurity atoms will be described. The impurity atom concentration is measured, for example, by secondary ion mass spectrometry (SIMS). For SIMS, for example, IMS7f, which is a secondary ion mass spectrometer manufactured by Cameca, can be used. As the measurement conditions in SIMS, for example, the measurement conditions that the primary ions are O ₂ ⁺ and the primary ion energy is 8 keV can be used.

FIG. 3 is a schematic plan view showing measurement positions of impurity atom concentrations. Silicon carbide wafer 11 is manufactured by slicing silicon carbide single crystal 10 in a direction parallel to first main surface 1 . Silicon carbide wafer 11 has a third main surface 3 and a second outer peripheral surface 9 . The second outer peripheral surface 9 has an orientation flat portion 6 and an arcuate portion 7 . The arcuate portion 7 continues to the orientation flat portion 6 . The direction in which orientation flat portion 6 extends is, for example, the <11-20> direction. A point located at the center of the arcuate portion 7 and located on the third main surface 3 is defined as a center point 41 . The concentration of impurity atoms at the center point 41 is measured by SIMS. The concentration of impurity atoms measured as described above is defined as the concentration of impurity atoms in silicon carbide single crystal 10 .

(Electrical resistivity of silicon carbide single crystal)
Silicon carbide single crystal 10 according to the present embodiment is semi-insulating. Specifically, silicon carbide single crystal 10 has an electrical resistivity of 1×10 ⁷ Ωcm or more. The lower limit of electrical resistivity of silicon carbide single crystal 10 is not particularly limited, but may be, for example, 1×10 ⁸ Ωcm or more, 1×10 ⁹ Ωcm or more, or 1×10 ¹⁰ Ωcm. or more. The upper limit of electrical resistivity of silicon carbide single crystal 10 may be, for example, 1×10 ¹² Ωcm or less.

Next, a method for measuring electrical resistivity will be described. The electrical resistivity can be measured using, for example, COREMA-WT, an electrical resistivity measuring device manufactured by Semimap. Specifically, an electrode is used to apply a voltage without contacting the object to be measured. As a result, the charge on the object to be measured increases over time. Measure the charge of the part to which the voltage is applied in the device under test. Specifically, the charge of the object to be measured immediately after the voltage is applied and the charge of the object to be measured after a certain period of time has passed since the voltage is applied are measured. Furthermore, the relaxation time of the electric charge of the part to which the voltage is applied in the object to be measured is measured. Thereby, the electrical resistivity of the object to be measured is measured. As the measurement condition for the measurement of electrical resistivity, for example, the measurement condition that the voltage applied to the object to be measured is 5.0 V can be used.

FIG. 4 is a schematic plan view showing measurement positions of electrical resistivity. Electrical resistivity is measured on third main surface 3 of silicon carbide wafer 11 manufactured using silicon carbide single crystal 10 . As shown in FIG. 4 , a plurality of measurement points 42 are located on the third main surface 3 . A plurality of measurement points 42 are positioned in a lattice at intervals of 6 mm, for example. The number of measurement points 42 is 200, for example. Let the average value of the electrical resistivity values at each of the plurality of measurement points 42 be the electrical resistivity of silicon carbide single crystal 10 .

(Silicon carbide single crystal manufacturing apparatus)
Next, the configuration of the silicon carbide single crystal manufacturing apparatus according to the present embodiment will be described.

FIG. 5 is a schematic partial cross-sectional view showing the configuration of the silicon carbide single crystal manufacturing apparatus according to the present embodiment. As shown in FIG. 5 , silicon carbide single crystal manufacturing apparatus 100 mainly includes crucible 30 and induction heating coil 13 . The crucible 30 has a housing portion 32 and a lid portion 31 . The lid portion 31 is positioned on the housing portion 32 . The induction heating coil 13 is positioned so as to surround the outer periphery of the housing portion 32 . The crucible 30 is heated by supplying power to the induction heating coil 13 . The atmospheric gas pressure in crucible 30 is maintained at, for example, about 90 kPa. Atmospheric gas includes inert gas such as argon gas, helium gas, or nitrogen gas.

(Method for producing silicon carbide single crystal)
Next, a method for manufacturing silicon carbide single crystal 10 according to the present embodiment will be described.

As shown in FIG. 5 , silicon carbide crystal 20 is arranged in accommodating portion 32 . Silicon carbide crystal 20 is produced, for example, using a sublimation method. Silicon carbide crystal 20 may be produced without actively supplying a dopant. From another point of view, silicon carbide crystal 20 may contain unavoidable impurities. When silicon carbide crystal 20 is arranged in accommodating portion 32 , the temperature of silicon carbide crystal 20 may be room temperature (eg, 27° C.). When silicon carbide crystal 20 is arranged in accommodating portion 32, the electrical resistivity of silicon carbide crystal 20 is, for example, 1×10 ⁴ Ωcm or less. In other words, when silicon carbide crystal 20 is arranged in accommodating portion 32, silicon carbide crystal 20 is not semi-insulating.

Silicon carbide crystal 20 has a fourth main surface 4 and a fifth main surface 5 . The fifth major surface 5 is opposite the fourth major surface 4 . The fourth main surface 4 is in contact with the housing portion 32 . The fourth main surface 4 is, for example, the {0001} plane or a plane inclined in the off direction with respect to the {0001} plane. The fifth main surface 5 is arranged to face the lid portion 31 .

Silicon carbide crystal 20 has a diameter (hereinafter referred to as second diameter D2) of, for example, 110 mm. The second diameter D2 is, for example, 100 mm or more. Although the lower limit of the second diameter D2 is not particularly limited, it may be, for example, 125 mm or more, or 150 mm or more. The upper limit of the second diameter D2 may be, for example, 200 mm or less.

Silicon carbide crystal 20 has a thickness (hereinafter referred to as second thickness H2) of, for example, 30 mm. The second thickness H2 is, for example, 30 mm or more and 60 mm or less. Although the lower limit of the second thickness H2 is not particularly limited, it may be, for example, 35 mm or more, or 40 mm or more. Although the upper limit of the second thickness H2 is not particularly limited, it may be, for example, 55 mm or less, or 50 mm or less.

FIG. 6 is a flow diagram schematically showing a method for manufacturing silicon carbide single crystal 10 according to the present embodiment. As shown in FIG. 6, the method for manufacturing silicon carbide single crystal 10 according to the present embodiment mainly includes a heat treatment step (S10), a first cooling step (S20), and a second cooling step (S30). have in

FIG. 7 is a schematic diagram showing the relationship between temperature and elapsed time. In FIG. 7, the vertical axis indicates temperature and the horizontal axis indicates elapsed time. In FIG. 7, each of a first graph G1 and a second graph G2 shows changes in temperature of silicon carbide crystal 20 with respect to elapsed time. A first graph G1 shows changes in temperature in the method for manufacturing silicon carbide single crystal 10 according to the present embodiment. A second graph G2 shows changes in temperature in the method for manufacturing silicon carbide single crystal 10 according to the comparative example. The details of the method for manufacturing silicon carbide single crystal 10 according to the comparative example will be described later.

FIG. 8 is a schematic diagram showing the relationship between power and elapsed time. In FIG. 8, the vertical axis indicates power and the horizontal axis indicates elapsed time. In FIG. 8, each of a third graph G3 and a fourth graph G4 shows changes in supplied power with respect to elapsed time. In this specification, the power supplied means the power supplied to the induction heating coil 13 . A third graph G3 shows changes in electric power in the method for manufacturing silicon carbide single crystal 10 according to the present embodiment. In FIG. 8, a fourth graph G4 shows changes in electric power in the method for manufacturing silicon carbide single crystal 10 according to the comparative example.

As shown in the first graph G1 in FIG. 7, in the heat treatment step (S10), from the first time T1 to the second time T2, the temperature of the silicon carbide crystal 20 inside the crucible 30 rises to the first temperature C1 up to

The first temperature C1 is 2550° C., for example. The first temperature C1 is 2000° C. or higher. The lower limit of the first temperature C1 is not particularly limited, but may be, for example, 2300° C. or higher, 2400° C. or higher, or 2500° C. or higher. The first temperature C1 is, for example, 2600° C. or lower. Although the upper limit of the first temperature C1 is not particularly limited, it may be, for example, 2580° C. or lower or 2560° C. or lower.

As shown in the third graph G3 in FIG. 8, in the heat treatment step (S10), power is supplied to the induction heating coil 13 from the first time point T1 to the second time point T2. Power may be supplied to the induction heating coil 13 before the first time T1. In other words, silicon carbide crystal 20 may be heated before first time point T1. In the heat treatment step (S10), the supplied power may fluctuate over time with the first power E1 as the center. In other words, in the heat treatment step (S10), the supplied power is substantially the first power E1. The first electric power E1 is, for example, 28 kW. In the heat treatment step (S10), the supplied power fluctuates, for example, within a range of 20 kW or more and 35 kW or less.

The time from the first time point T1 to the second time point T2 is, for example, 5 minutes. In other words, silicon carbide crystal 20 is heat-treated, for example, for 5 minutes. As described above, in the heat treatment step (S10), silicon carbide crystal 20 is heated to first temperature C1.

Next, a first cooling step (S20) is performed. As shown in the first graph G1 in FIG. 7, in the first cooling step (S20), silicon carbide crystal 20 is cooled from first temperature C1 to second temperature C2 from second time point T2 to third time point T3. be.

The second temperature C2 is 1370° C., for example. The second temperature C2 is 1300° C. or higher and 1500° C. or lower. Although the lower limit of the second temperature C2 is not particularly limited, it may be, for example, 1325° C. or higher, or 1350° C. or higher. Although the upper limit of the second temperature C2 is not particularly limited, it may be, for example, 1475° C. or lower or 1450° C. or lower.

A cooling rate of the silicon carbide crystal 20 in the temperature range from the second temperature C2 to the first temperature C1 is defined as a first cooling rate. The first cooling rate is, for example, 91°C/min. The first cooling rate is greater than 50°C/min. In other words, the cooling rate of silicon carbide crystal 20 in the first cooling step (S20) is higher than 50° C./min. The first cooling rate is a value obtained by dividing the temperature obtained by subtracting the second temperature C2 from the first temperature C1 by the time from the second time T2 to the third time T3. Although the lower limit of the first cooling rate is not particularly limited, it may be, for example, 65° C./min or higher, or 80° C./min or higher. The first cooling rate is, for example, 135° C./min or less. Although the upper limit of the first cooling rate is not particularly limited, it may be, for example, 120° C./min or less, or 105° C./min or less.

As shown in the third graph G3 in FIG. 8, the power supply to the induction heating coil 13 is stopped from the second time T2 to the third time T3 in the first cooling step (S20). Therefore, silicon carbide crystal 20 is cooled by heat transfer. In the first cooling step (S20), the supplied power may be 0 kW.

The time from the second time T2 to the third time T3 is, for example, 13 minutes. In other words, in the first cooling step (S20), silicon carbide crystal 20 is cooled at the first cooling rate for 13 minutes, for example. As described above, in the first cooling step (S20), silicon carbide crystal 20 is cooled from first temperature C1 to second temperature C2 at the first cooling rate.

Next, a second cooling step (S30) is performed. As shown in the first graph G1 in FIG. 7, in the second cooling step (S30), silicon carbide crystal 20 is cooled from second temperature C2 to third temperature C3 from third time point T3 to fourth time point T4. be. The third temperature C3 is 1000° C., for example. The third temperature C3 is 900° C. or higher and 1100° C. or lower. Although the lower limit of the third temperature C3 is not particularly limited, it may be, for example, 925° C. or higher, or 950° C. or higher. Although the upper limit of the third temperature C3 is not particularly limited, it may be, for example, 1075° C. or lower or 1050° C. or lower.

A cooling rate of silicon carbide crystal 20 in a temperature range in which the temperature of silicon carbide crystal 20 is equal to or higher than third temperature C3 and lower than second temperature C2 is defined as a second cooling rate. The second cooling rate is, for example, 6°C/min. The second cooling rate is 20° C./min or less. In other words, the cooling rate of silicon carbide crystal 20 in the second cooling step (S30) is 20° C./min or less. The second cooling rate is a value obtained by dividing the temperature obtained by subtracting the third temperature C3 from the second temperature C2 by the time from the third time T3 to the fourth time T4. The upper limit of the second cooling rate is not particularly limited, but may be, for example, 15° C./min or less, or 10° C./min or less.

As shown in the third graph G3 in FIG. 8, electric power is supplied to the induction heating coil 13 from the third time point T3 to the fourth time point T4 in the second cooling step (S30). In the second cooling step ( S<b>30 ), induction heating coil 13 reduces the cooling rate of silicon carbide crystal 20 by heating silicon carbide crystal 20 .

Power supply is controlled such that the cooling rate of silicon carbide crystal 20 is the second cooling rate. Specifically, manufacturing apparatus 100 measures the temperature of silicon carbide crystal 20 . Manufacturing apparatus 100 controls power supply based on the measured temperature of silicon carbide crystal 20 . Therefore, the supplied power fluctuates over time. As the temperature of silicon carbide crystal 20 decreases, the supplied power substantially decreases. Specifically, in the second cooling step (S30), the supplied power substantially decreases from the second power E2 to the third power E3 while fluctuating.

The second power E2 is, for example, 10 kW. The third electric power E3 is, for example, 5 kW. The second power E2 is, for example, less than half the first power E1. In other words, the power supplied in the second cooling step (S30) is, for example, substantially half or less of the power supplied in the heat treatment step (S10). In the second cooling step (S30), the supplied power is reduced substantially by 0.1 kW every minute, for example. In the second cooling step (S30), the supplied power is, for example, 15 kW or less.

The time from the third time T3 to the fourth time T4 is, for example, 52 minutes. In other words, in the second cooling step (S30), silicon carbide crystal 20 is cooled at the second cooling rate for 52 minutes, for example. The time from the third time T3 to the fourth time T4 is longer than the time from the second time T2 to the third time T3. In other words, the time for cooling silicon carbide crystal 20 at the second cooling rate is longer than the time for cooling silicon carbide crystal 20 at the first cooling rate. The time from the third time T3 to the fourth time T4 is, for example, three times or more the time from the second time T2 to the third time T3. As described above, in the second cooling step (S30), silicon carbide crystal 20 is cooled from second temperature C2 to third temperature C3 at the second cooling rate.

After the second cooling step (S30), silicon carbide crystal 20 is cooled from third temperature C3 to 27°C. In other words, after the second cooling step (S30), silicon carbide crystal 20 is cooled from third temperature C3 to room temperature. Silicon carbide crystal 20 cooled from third temperature C3 to 27° C. has an electrical resistivity of 1×10 ⁷ Ωcm or more. The lower limit of the electrical resistivity of silicon carbide crystal 20 is not particularly limited, but may be, for example, 1×10 ⁸ Ωcm or more, 1×10 ⁹ Ωcm or more, or 1×10 ¹⁰ Ωcm or more. may be The upper limit of electrical resistivity of silicon carbide crystal 20 may be, for example, 1×10 ¹² Ωcm or less. In other words, silicon carbide crystal 20 cooled from third temperature C3 to 27° C. after the second cooling step (S30) is semi-insulating.

As described above, silicon carbide single crystal 10 is produced. Fourth main surface 4 of silicon carbide crystal 20 corresponds to first main surface 1 of silicon carbide single crystal 10 . Fifth main surface 5 of silicon carbide crystal 20 corresponds to second main surface 2 of silicon carbide single crystal 10 .

(Effect)
Next, the effects of silicon carbide single crystal 10 and the method for manufacturing silicon carbide single crystal 10 according to the present embodiment will be described.

Electric resistance in silicon carbide single crystal 10 produced by heating silicon carbide crystal 20 to a temperature of 2000° C. or more and then cooling silicon carbide crystal 20 at a cooling rate of 30° C./min or more and 150° C./min or less rate increases. However, by cooling silicon carbide crystal 20 at a cooling rate of 30° C./min or more and 150° C./min or less, cracks may occur in manufactured silicon carbide single crystal 10 . Specifically, as shown in the second graph G2 in FIG. 7 and the fourth graph G4 in FIG. 8, after the heat treatment step (S10), power supply to the induction heating coil 13 is stopped, Cooling silicon carbide crystal 20 from first temperature C1 to third temperature C3 sometimes caused cracks in manufactured silicon carbide single crystal 10 .

As a result of detailed investigation of the cause of the above phenomenon, the inventors found that, for example, when the second diameter D2 is 100 mm or more, or the second thickness H2 is 30 mm or more, if the silicon carbide crystal 20 is rapidly cooled, the above I found that the phenomenon occurs. In this specification, rapid cooling means stopping the supply of electric power to induction heating coil 13 and cooling silicon carbide crystal 20 by heat transfer. In the process of cooling silicon carbide crystal 20, the temperature of the surface of silicon carbide crystal 20 first decreases. Thereafter, the heat at the central portion of silicon carbide crystal 20 is transferred to the surface, and the temperature at the central portion of silicon carbide crystal 20 decreases. Therefore, in the process of cooling silicon carbide crystal 20 , a temperature difference is generated between the surface and the center of silicon carbide crystal 20 . As second diameter D2 or second thickness H2 increases, heat from the central portion of silicon carbide crystal 20 is less likely to be conducted to the surface. Therefore, the temperature difference between the surface and the central portion of silicon carbide crystal 20 increases. As the temperature difference between the surface and center of silicon carbide crystal 20 increases, the thermal stress generated in silicon carbide crystal 20 increases. Therefore, when second diameter D2 was 100 mm or more, or when second thickness H2 was 30 mm or more, it is believed that rapid cooling caused silicon carbide crystal 20 to generate a large thermal stress and cracks.

As a result of intensive studies on the cause of crack generation, the inventor obtained the following knowledge and found a method for manufacturing silicon carbide single crystal 10 according to the present embodiment. Specifically, it was found that rapid cooling of silicon carbide crystal 20 causes cracks in a temperature range equal to or higher than third temperature C3 and lower than second temperature C2. In the temperature range equal to or higher than second temperature C2, silicon carbide crystal 20 is plastically deformed by thermal stress, so crack generation is suppressed. On the other hand, since silicon carbide crystal 20 is hardly plastically deformed in a temperature range lower than second temperature C2, cracking is accelerated. In addition, in the temperature range below third temperature C3, the temperature difference between silicon carbide crystal 20 and the outside air is relatively small. As a result, even when silicon carbide crystal 20 is rapidly cooled, the cooling rate is relatively low, thereby suppressing the occurrence of cracks. On the other hand, in the temperature range equal to or higher than third temperature C3, the cooling rate in the case of rapidly cooling silicon carbide crystal 20 is relatively high, thus promoting crack generation. Therefore, it is considered that the cracks were generated by rapidly cooling the silicon carbide crystal 20 in the temperature range equal to or higher than the third temperature C3 and lower than the second temperature C2.

Furthermore, the inventors found that the electrical resistivity of silicon carbide crystal 20 is sufficiently increased by rapidly cooling silicon carbide crystal 20 in the temperature range between second temperature C2 and first temperature C1. In other words, it was found that rapid cooling in a temperature range lower than second temperature C2 has little effect on the electrical resistivity of silicon carbide crystal 20 . When the temperature of silicon carbide crystal 20 rises to first temperature C1, intrinsic defects such as carbon vacancies are formed. Intrinsic defects trap carriers in silicon carbide crystal 20 . Therefore, the electrical resistivity of silicon carbide crystal 20 increases. In the temperature range from second temperature C2 to first temperature C1, atoms in silicon carbide crystal 20 have high energy. Therefore, when the silicon carbide crystal 20 is slowly cooled in the temperature range between the second temperature C2 and the first temperature C1, recovery of intrinsic defects is promoted. When the intrinsic defects are recovered, the electrical resistivity of silicon carbide crystal 20 decreases. On the other hand, when the silicon carbide crystal 20 is rapidly cooled, the time during which the temperature of the silicon carbide crystal 20 is in the temperature range equal to or higher than the second temperature C2 and equal to or lower than the first temperature C1 is shortened. Therefore, recovery of intrinsic defects is suppressed. As a result, it is considered that the electrical resistivity of silicon carbide crystal 20 increases as compared with the case where silicon carbide crystal 20 is not rapidly cooled. On the other hand, in the temperature range below the second temperature C2, since the energy possessed by the atoms in the silicon carbide crystal 20 is low, recovery of intrinsic defects is suppressed. Therefore, a decrease in electrical resistivity of silicon carbide crystal 20 is suppressed in a temperature range lower than second temperature C2. As a result, in the temperature range below the second temperature C2, it is considered that the effect of rapid cooling on the electrical resistivity was reduced.

Based on the above findings, the inventor has conceived of suppressing the occurrence of cracks while increasing the electrical resistivity of silicon carbide crystal 20 by switching the cooling rate of silicon carbide crystal 20 at second temperature C2.

According to the method for manufacturing silicon carbide single crystal 10 according to the present embodiment, silicon carbide crystal 20 is heat-treated to first temperature C1 and then cooled from first temperature C1 to second temperature C2 at the first cooling rate. be done. Silicon carbide crystal 20 is cooled from second temperature C2 to third temperature C3 at the second cooling rate. The first cooling rate is greater than 50°C/min. The second cooling rate is 20° C./min or less. The first temperature C1 is 2000° C. or higher. The second temperature C2 is 1300° C. or higher and 1500° C. or lower. The third temperature C3 is 900° C. or higher and 1100° C. or lower. Thereby, generation of cracks in silicon carbide single crystal 10 can be suppressed while increasing the electric resistivity of silicon carbide single crystal 10 .

Furthermore, according to the method for manufacturing silicon carbide single crystal 10 according to the present embodiment, the first cooling rate may be 80° C./min or more. Thereby, the electrical resistivity of silicon carbide single crystal 10 can be increased more effectively.

Furthermore, according to the method for manufacturing silicon carbide single crystal 10 according to the present embodiment, the second cooling rate may be 10° C./min or less. Thereby, generation of cracks in silicon carbide single crystal 10 can be suppressed more effectively.

Furthermore, according to the method for manufacturing silicon carbide single crystal 10 according to the present embodiment, silicon carbide crystal 20 has a diameter of 100 mm or more. Further, the diameter of silicon carbide single crystal 10 according to the present embodiment is 100 mm or more. Thus, crack generation can be suppressed even in silicon carbide single crystal 10 having a large diameter.

Further, according to the method for manufacturing silicon carbide single crystal 10 according to the present embodiment, silicon carbide crystal 20 has a thickness of 30 mm or more. Moreover, the thickness of silicon carbide single crystal 10 according to the present embodiment is 30 mm or more. Thus, crack generation can be suppressed even in thick silicon carbide single crystal 10 .

Furthermore, silicon carbide single crystal 10 according to the present embodiment does not include cracks having a length of 10 mm or more. Thereby, the reliability of a silicon carbide semiconductor device produced using silicon carbide single crystal 10 according to the present embodiment can be improved.

Furthermore, according to silicon carbide single crystal 10 according to the present embodiment, the absolute value of the difference between the n-type impurity concentration and the p-type impurity concentration is, for example, 7×10 ¹⁵ atoms/cm ³ or less. Therefore, the concentration of free electrons or holes in silicon carbide single crystal 10 is reduced. Thereby, the electrical resistivity of silicon carbide single crystal 10 can be increased more effectively.

(Example)
(Sample preparation)
Next, a test using samples will be described. First, silicon carbide single crystals 10 according to samples 1 to 10 were prepared. Samples 1, 6, 8 and 10 are comparative examples. Samples 2 through 5, 7 and 9 are examples. Silicon carbide single crystals 10 according to samples 1 to 10 were produced using the manufacturing method according to the present embodiment described above. In the production of silicon carbide single crystals 10 according to samples 1 to 10, first temperature C1 was set to 2550.degree. The third temperature C3 was set to 1000°C. The second diameter D2 was set to 110 mm. The second thickness H2 was set to 30 mm. The atmospheric gas pressure in the crucible 30 was set to 90 kPa.

As shown in Table 1, in manufacturing silicon carbide single crystals 10 according to samples 1 to 6, second temperature C2 was varied between 1600°C and 1200°C. In the first cooling step (S20), the cooling rate becomes slower as the temperature of silicon carbide crystal 20 becomes lower. Therefore, in samples 1 to 6, when the second temperature C2 was changed, the first cooling rate was also changed. In other words, in Samples 1 to 6, the power supplied in the first cooling step (S20) was 0 kW. In the production of silicon carbide single crystals 10 according to samples 4, 7, and 8, the power supplied in the first cooling step (S20) was controlled to set the first cooling rate from 91°C/min to 50°C/min. changed between In producing silicon carbide single crystals 10 according to samples 4, 9, and 10, the second cooling rate was varied between 6° C./min and 25° C./min.

(Measuring method)
All the samples were measured for electrical resistivity and checked for cracks. Specifically, silicon carbide wafers 11 were produced for all samples, and the electrical resistivity was measured. As shown in FIG. 4 , electrical resistivity was measured at a plurality of measurement points 42 located on third main surface 3 of silicon carbide wafer 11 . The number of measurement points 42 is 200. The interval between adjacent measurement points 42 was 6 mm. An average value of electrical resistivities at a plurality of measurement points 42 was taken as the electrical resistivity of silicon carbide wafer 11 . Cracks were identified visually. Cracks having a length of 10 mm or more when viewed in a direction perpendicular to the surface on which the crack is formed were identified as cracks.

(Measurement result)

Comparing the electrical resistivities of samples 1 to 6, it was confirmed that the electrical resistivity was less than 1×10 ⁷ Ωcm when the second temperature C2 exceeded 1500°C. On the other hand, when comparing the presence or absence of cracks in samples 1 to 6, it was confirmed that cracks occurred when the second temperature C2 was lower than 1300°C.

Comparing the electrical resistivities of samples 4, 7 and 8, it was found that the electrical resistivity was less than 1×10 ⁷ Ωcm when the first cooling rate was 50° C./min or less.

Comparing the presence or absence of cracks in samples 4, 9 and 10, it was confirmed that cracks occurred when the second cooling rate exceeded 20°C/min.

In order to suppress the occurrence of cracks while increasing the electrical resistivity to 1×10 ⁷ Ωcm or more, the second temperature should be 1300° C. or higher and 1500° C. or lower, and the first cooling rate should be higher than 50° C./min. Moreover, it was confirmed that the second cooling rate is preferably 20° C./min or less.

The embodiments and examples disclosed this time are illustrative in all respects and should not be considered restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above-described embodiments, and is intended to include meanings equivalent to the scope of the claims and all modifications within the scope.

1 First main surface 2 Second main surface 3 Third main surface 4 Fourth main surface 5 Fifth main surface 6 Orientation flat portion 7 Circular portion 8 First outer peripheral surface 9 Second outer peripheral surface 10 Silicon carbide single crystal 11 Carbonization Silicon wafer 13 Induction heating coil 20 Silicon carbide crystal 30 Crucible 31 Lid 32 Housing 41 Center point 42 Measuring point 100 Manufacturing equipment C1 First temperature C2 Second temperature C3 Third temperature D1 First diameter D2 Second diameter E1 First Power E2 Second power E3 Third power G1 First graph G2 Second graph G3 Third graph G4 Fourth graph H1 First thickness H2 Second thickness T1 First time point T2 Second time point T3 Third time point T4 Fourth time point

Claims (9)

heat-treating the silicon carbide crystal to a first temperature;
cooling the silicon carbide crystal from the first temperature to the second temperature at a first cooling rate after the step of heat-treating the silicon carbide crystal to the first temperature;
cooling the silicon carbide crystal from the second temperature to the third temperature at a second cooling rate;
wherein the first cooling rate is greater than 50°C/min;
The second cooling rate is 20° C./min or less,
The first temperature is 2000° C. or higher,
the second temperature is 1300° C. or higher and 1500° C. or lower;
the third temperature is 900° C. or higher and 1100° C. or lower;
The method for producing a silicon carbide single crystal, wherein the silicon carbide crystal cooled from the third temperature to 27° C. has an electrical resistivity of 1×10 ⁷ Ωcm or more. 2. The method for manufacturing a silicon carbide single crystal according to claim 1, wherein said silicon carbide crystal has a diameter of 100 mm or more. 3. The method for producing a silicon carbide single crystal according to claim 1, wherein said silicon carbide crystal has a thickness of 30 mm or more. The method for producing a silicon carbide single crystal according to any one of claims 1 to 3, wherein said first cooling rate is 80°C/min or higher. 5. The method for producing a silicon carbide single crystal according to claim 1, wherein said second cooling rate is 10[deg.] C./min or less. The diameter is 100 mm or more,
The thickness is 30 mm or more,
The electrical resistivity is 1×10 ⁷ Ωcm or more,
A silicon carbide single crystal containing no cracks having a length of 10 mm or more. containing nitrogen,
The silicon carbide single crystal according to claim 6, wherein the concentration of nitrogen is 5 x ¹⁰¹⁵ atoms/cm3 ^or more and 1 x ¹⁰¹⁶ atoms/ ^cm3 or less. containing boron,
8. The silicon carbide single crystal according to claim 6, wherein the concentration of boron is 1×10 ¹⁵ atoms/cm ³ or more and 5×10 ¹⁵ atoms/cm ³ or less. contains aluminium,
The silicon carbide single crystal according to any one of claims 6 to 8, wherein the concentration of aluminum is 1 x ¹⁰¹⁴ atoms/ ^cm3 or more and 5 x ¹⁰¹⁴ atoms/ ^cm3 or less.

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