WO2019044029A1

WO2019044029A1 - Silicon carbide epitaxial substrate and production method for silicon carbide semiconductor device

Info

Publication number: WO2019044029A1
Application number: PCT/JP2018/016565
Authority: WO
Inventors: 洋典伊東; 勉堀
Original assignee: 住友電気工業株式会社
Priority date: 2017-09-01
Filing date: 2018-04-24
Publication date: 2019-03-07
Also published as: JP7415558B2; JPWO2019044029A1

Abstract

This silicon carbide epitaxial substrate has a silicon carbide substrate (10) and a silicon carbide epitaxial film (20). The silicon carbide epitaxial film includes a first layer (21) and a second layer (22). The concentration of n-type impurities contained in the first layer is lower than the concentration of n-type impurities contained in the silicon carbide substrate, and is higher than the concentration of n-type impurities contained in the second layer. The silicon carbide substrate has a main surface (12) which has a basal plane dislocation having a first surface density. The silicon carbide epitaxial film has a main surface (14) having a basal plane dislocation having a second surface density lower than the first surface density. The value obtained by dividing the second surface density by the first surface density is 1/1000 or less. The main surface of the silicon carbide epitaxial film is sloped with respect to the (000-1) plane or the (000-1) plane at an off-angle of 8° or less.

Description

Silicon carbide epitaxial substrate and method of manufacturing silicon carbide semiconductor device

The present disclosure relates to a silicon carbide epitaxial substrate and a method of manufacturing a silicon carbide semiconductor device. This application claims priority based on Japanese Patent Application No. 2017-168252, which is a Japanese patent application filed on September 1, 2017. The entire contents of the description of the Japanese patent application are incorporated herein by reference.

JP-A-2014-170891 (Patent Document 1) discloses a method of epitaxially growing a silicon carbide layer on a silicon carbide single crystal substrate.

JP, 2014-170891, A

A silicon carbide epitaxial substrate according to the present disclosure includes a silicon carbide substrate and a silicon carbide epitaxial film. The silicon carbide epitaxial film is on a silicon carbide substrate. The polytype of the silicon carbide substrate and silicon carbide epitaxial film is 4H. The silicon carbide epitaxial film includes a first layer in contact with the silicon carbide substrate, and a second layer on the first layer and constituting the main surface of the silicon carbide epitaxial film. The silicon carbide substrate, the first layer, and the second layer contain n-type impurities. The concentration of n-type impurities contained in the first layer is lower than the concentration of n-type impurities contained in the silicon carbide substrate and higher than the concentration of n-type impurities contained in the second layer. The main surface of the silicon carbide substrate has basal plane dislocations having a first surface density. The main surface of the silicon carbide epitaxial film has basal plane dislocations having a second surface density lower than the first surface density. The value obtained by dividing the second area density by the first area density is 1/1000 or less. The main surface of the silicon carbide epitaxial film is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane.

A silicon carbide epitaxial substrate according to the present disclosure includes a silicon carbide substrate and a silicon carbide epitaxial film. The silicon carbide epitaxial film is on a silicon carbide substrate. The polytype of the silicon carbide substrate and silicon carbide epitaxial film is 4H. The silicon carbide epitaxial film includes a first layer in contact with the silicon carbide substrate, and a second layer on the first layer and constituting the main surface of the silicon carbide epitaxial film. The silicon carbide substrate, the first layer, and the second layer contain n-type impurities. The concentration of n-type impurities contained in the first layer is lower than the concentration of n-type impurities contained in the silicon carbide substrate and higher than the concentration of n-type impurities contained in the second layer. The main surface of the silicon carbide substrate has basal plane dislocations having a first surface density. The main surface of the silicon carbide epitaxial film has basal plane dislocations having a second surface density lower than the first surface density. The value obtained by dividing the second area density by the first area density is 1/1000 or less. The main surface of the silicon carbide epitaxial film is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane. The maximum diameter of the main surface of the silicon carbide epitaxial film is 150 mm or more. The thickness of the first layer is 0.5 μm or more and 2 μm or less. The thickness of the second layer is 5 μm or more and 30 μm or less. The concentration of the n-type impurity contained in the first layer is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less. The concentration of the n-type impurity contained in the second layer is 1 × 10 ¹⁵ cm ⁻³ or more and 1 × 10 ¹⁶ cm ⁻³ or less.

FIG. 1 is a schematic plan view showing the configuration of the silicon carbide epitaxial substrate according to the present embodiment. FIG. 2 is a schematic cross-sectional view showing the configuration of the silicon carbide epitaxial substrate according to the present embodiment. FIG. 3 is a partial cross-sectional schematic view showing the configuration of the apparatus for manufacturing a silicon carbide epitaxial substrate according to the present embodiment. FIG. 4 is a flow chart schematically showing a method of manufacturing a silicon carbide epitaxial substrate according to the present embodiment. FIG. 5 is a schematic cross sectional view showing a first step of the method for manufacturing the silicon carbide epitaxial substrate according to the present embodiment. FIG. 6 is a schematic cross sectional view showing a second step of the method for manufacturing a silicon carbide epitaxial substrate according to the present embodiment. FIG. 7 is a diagram showing the manufacturing conditions of the silicon carbide epitaxial substrate according to the present embodiment. FIG. 8 is a flow chart schematically showing a method of manufacturing a silicon carbide semiconductor device according to the present embodiment. FIG. 9 is a schematic cross sectional view showing a first step of a method of manufacturing a silicon carbide semiconductor device according to the present embodiment. FIG. 10 is a schematic cross sectional view showing a second step of the method for manufacturing the silicon carbide semiconductor device according to the present embodiment. FIG. 11 is a schematic cross-sectional view showing the configuration of the silicon carbide semiconductor device according to the present embodiment. FIG. 12 is a diagram showing the manufacturing conditions of the silicon carbide epitaxial substrate according to Sample 2. As shown in FIG.

Overview of Embodiments of the Present Disclosure
First, an outline of an embodiment of the present disclosure will be described. In the crystallographic description of the present specification, an individual orientation is indicated by [], a collective orientation is indicated by <>, an individual plane is indicated by (), and a collective plane is indicated by {}. The fact that the crystallographic index is negative is usually expressed by adding a "-" (bar) above the numbers, but in the present specification the crystallography is indicated by putting a negative sign before the numbers. Express the negative index above.

(1) A silicon carbide epitaxial substrate 100 according to the present disclosure includes a silicon carbide substrate 10 and a silicon carbide epitaxial film 20. Silicon carbide epitaxial film 20 is on silicon carbide substrate 10. The polytype of silicon carbide substrate 10 and silicon carbide epitaxial film 20 is 4H. Silicon carbide epitaxial film 20 includes a first layer 21 in contact with silicon carbide substrate 10, and a second layer 22 which is on first layer 21 and which constitutes main surface 14 of silicon carbide epitaxial film 20. Silicon carbide substrate 10, first layer 21, and second layer 22 contain n-type impurities. The concentration of n-type impurities contained in the first layer 21 is lower than the concentration of n-type impurities contained in the silicon carbide substrate 10 and higher than the concentration of n-type impurities contained in the second layer 22. Main surface 12 of silicon carbide substrate 10 has basal plane dislocation 1 having a first surface density. Main surface 14 of silicon carbide epitaxial film 20 has basal plane dislocation 1 having a second surface density lower than the first surface density. The value obtained by dividing the second area density by the first area density is 1/1000 or less. Main surface 14 of silicon carbide epitaxial film 20 is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane.

(2) In the silicon carbide epitaxial substrate 100 according to the above (1), a value obtained by dividing the second area density by the first area density may be 1/2000 or less.

(3) In silicon carbide epitaxial substrate 100 concerning the above (1) or (2), maximum diameter 111 of main surface 14 of silicon carbide epitaxial film 20 may be 100 mm or more.

(4) In the silicon carbide epitaxial substrate according to (3), the maximum diameter 111 of the main surface 14 of the silicon carbide epitaxial film 20 may be 150 mm or more.

(5) The silicon carbide epitaxial substrate 100 according to the present disclosure includes the silicon carbide substrate 10 and the silicon carbide epitaxial film 20. Silicon carbide epitaxial film 20 is on silicon carbide substrate 10. The polytype of silicon carbide substrate 10 and silicon carbide epitaxial film 20 is 4H. Silicon carbide epitaxial film 20 includes a first layer 21 in contact with silicon carbide substrate 10, and a second layer 22 which is on first layer 21 and which constitutes main surface 14 of silicon carbide epitaxial film 20. Silicon carbide substrate 10, first layer 21, and second layer 22 contain n-type impurities. The concentration of n-type impurities contained in the first layer 21 is lower than the concentration of n-type impurities contained in the silicon carbide substrate 10 and higher than the concentration of n-type impurities contained in the second layer 22. Main surface 12 of silicon carbide substrate 10 has basal plane dislocation 1 having a first surface density. Main surface 14 of silicon carbide epitaxial film 20 has basal plane dislocation 1 having a second surface density lower than the first surface density. The value obtained by dividing the second area density by the first area density is 1/1000 or less. Main surface 14 of silicon carbide epitaxial film 20 is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane. Main surface 14 of silicon carbide epitaxial film 20 is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane. The maximum diameter 111 of the main surface 14 of the silicon carbide epitaxial film 20 is 150 mm or more. The thickness of the first layer 21 is 0.5 μm or more and 2 μm or less. The thickness of the second layer 22 is 5 μm or more and 30 μm or less. The concentration of the n-type impurity contained in the first layer 21 is 1 × 10 ¹⁷ cm ⁻³ or more and 1 × 10 ¹⁹ cm ⁻³ or less. The concentration of the n-type impurity contained in the second layer 22 is 1 × 10 ¹⁵ cm ⁻³ or more and 1 × 10 ¹⁶ cm ⁻³ or less.

(6) The method for manufacturing the silicon carbide semiconductor device 300 according to the present disclosure includes the following steps. The silicon carbide epitaxial substrate 100 according to any one of the above (1) to (5) is prepared. Silicon carbide epitaxial substrate 100 is processed.

Details of Embodiments of the Present Disclosure
Hereinafter, details of the embodiment of the present disclosure will be described. In the following description, the same or corresponding elements are denoted by the same reference numerals, and the same description will not be repeated.

(Silicon carbide epitaxial substrate)
As shown in FIGS. 1 and 2, silicon carbide epitaxial substrate 100 according to the present embodiment includes silicon carbide substrate 10 and silicon carbide epitaxial film 20. Silicon carbide epitaxial film 20 is on silicon carbide substrate 10. Silicon carbide substrate 10 has a first main surface 11 and a first main surface 12 opposite to first main surface 11. The silicon carbide epitaxial film 20 is in contact with the first major surface 11. Silicon carbide epitaxial film 20 has a third main surface 13 in contact with first main surface 11 and a second main surface 14 opposite to third main surface 13. The polytype of silicon carbide substrate 10 and silicon carbide epitaxial film 20 is 4H. As shown in FIG. 1, the silicon carbide epitaxial substrate 100 may be provided with a first flat 16 extending in the first direction 101. Silicon carbide epitaxial substrate 100 may be provided with a second flat (not shown) extending in second direction 102.

The second direction 102 is, for example, a <1-100> direction. The first direction 101 is a direction parallel to the second major surface 14 and perpendicular to the second direction 102. The first direction 101 is, for example, a direction including a <11-20> direction component. As shown in FIG. 1, the maximum diameter 111 (diameter) of the second main surface 14 is, for example, 100 mm or more. The maximum diameter 111 may be 150 mm or more, 200 mm or more, or 250 mm or more. The upper limit of the maximum diameter 111 is not particularly limited. The maximum diameter 111 may be, for example, 300 mm or less.

Silicon carbide substrate 10 is formed of, for example, a silicon carbide single crystal. Silicon carbide substrate 10 contains an n-type impurity such as nitrogen (N), for example. The conductivity type of silicon carbide substrate 10 is, for example, n-type. The first major surface 11 is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane. When the first major surface 11 is tilted with respect to the (000-1) plane, the tilt direction of the first major surface 11 is, for example, the <11-20> direction. The thickness of silicon carbide substrate 10 is, for example, not less than 350 μm and not more than 500 μm.

As shown in FIG. 2, silicon carbide epitaxial film 20 is on first main surface 11 of silicon carbide substrate 10. Silicon carbide epitaxial film 20 is an epitaxial layer. Silicon carbide epitaxial film 20 is in contact with first main surface 11. Silicon carbide epitaxial film 20 contains an n-type impurity such as nitrogen, for example. The conductivity type of silicon carbide epitaxial film 20 is, for example, n-type. The second main surface 14 is a surface inclined at an off angle θ of 8 ° or less with respect to the carbon surface or the carbon surface. In other words, the second major surface 14 is a surface inclined at an off angle θ of 8 ° or less with respect to the (000-1) plane or the (000-1) plane. The off direction is, for example, the <11-20> direction. The off direction is not limited to the <11-20> direction. The off direction may be, for example, a <1-100> direction or a direction having a <1-100> direction component and a <11-20> direction component.

The off angle θ is an angle at which the second major surface 14 is inclined to the (000-1) plane. The off angle θ is, for example, greater than 0 ° and not more than 8 °. The off angle θ may be 1 ° or more, or 2 ° or more. The off angle may be 7 ° or less or 6 ° or less.

The surface described by a broken line in FIG. 2 is, for example, a {0001} surface. The third direction 103 is a direction perpendicular to the {0001} plane. The third direction 103 is, for example, the [000-1] direction. The fourth direction 104 is a direction perpendicular to the third direction 103. The fourth direction 104 is, for example, the <11-20> direction. The fourth direction 104 is, for example, the off direction. The normal direction of the second major surface 14 is the fifth direction 105. The fifth direction is a direction inclined by an off angle θ in the off direction with respect to the [000-1] direction, for example.

As shown in FIG. 2, silicon carbide epitaxial film 20 includes a first layer 21 and a second layer 22. The first layer is, for example, a buffer layer. The second layer 22 is, for example, a drift layer. The first layer 21 is in contact with the first major surface 11. First layer 21 is in contact with silicon carbide substrate 10. The first layer 21 constitutes a third major surface 13. The second layer 22 is on the first layer 21. The second layer 22 constitutes a second major surface 14. The thickness of the first layer 21 is, for example, 0.5 μm or more and 2 μm or less. The thickness of the first layer 21 may be 0.7 μm or more, or may be 1.0 μm or more. The thickness of the first layer 21 may be 1.8 μm or less, or 1.5 μm or less. The thickness of the second layer 22 is, for example, 5 μm or more and 30 μm or less. The thickness of the second layer 22 may be 7 μm or more, or 10 μm or more. The thickness of the second layer 22 may be 25 μm or less, or 20 μm or less.

Each of the first layer 21 and the second layer 22 contains an n-type impurity such as nitrogen, for example. The concentration of the n-type impurity contained in the first layer 21 is, for example, not less than 1 × 10 ¹⁷ cm ^{−3 and not} more than 1 × 10 ¹⁹ cm ⁻³ . The concentration of the n-type impurity contained in the first layer 21 may be 3 × 10 ¹⁷ cm ⁻³ or more, or 5 × 10 ¹⁷ cm ⁻³ or more. The concentration of the n-type impurity contained in the first layer 21 may be 7 × 10 ¹⁸ cm ⁻³ or less, or 5 × 10 ¹⁸ cm ⁻³ or less. The concentration of the n-type impurity contained in the second layer 22 is, for example, not less than 1 × 10 ¹⁵ cm ^{−3 and not} more than 1 × 10 ¹⁶ cm ⁻³ . The concentration of the n-type impurity contained in the second layer 22 may be 2 × 10 ¹⁵ cm ⁻³ or more, or 3 × 10 ¹⁵ cm ⁻³ or more. The concentration of the n-type impurity contained in the second layer 22 may be 9 × 10 ¹⁵ cm ⁻³ or less, or 8 × 10 ¹⁵ cm ⁻³ or less.

The concentration of n-type impurities contained in the first layer 21 is lower than the concentration of n-type impurities contained in the silicon carbide substrate 10 and higher than the concentration of n-type impurities contained in the second layer 22. The concentration of the n-type impurity is measured, for example, by a mercury probe type CV measurement device. The area of the probe is, for example, 0.005 cm ² .

As shown in FIG. 2, silicon carbide substrate 10 and silicon carbide epitaxial film 20 have basal plane dislocation 1. The basal plane dislocation 1 is exposed, for example, to both the first major surface 11 and the first major surface 12. The basal plane dislocations 1 extend in a direction parallel to the {0001} plane. The basal plane dislocation 1 has, for example, a first basal plane dislocation 25, a second basal plane dislocation 26, and a third basal plane dislocation 27. Silicon carbide epitaxial film 20 has, for example, second basal plane dislocations 26, third basal plane dislocations 27, and threading edge dislocations 2. The third basal plane dislocations 27 and the threading edge dislocations 2 are exposed to the second main surface 14. The threading edge dislocation 2 has, for example, a first threading edge dislocation 35 and a second threading edge dislocation 36. The first threading edge dislocations 35 are dislocations formed by converting the first basal plane dislocations 25. Similarly, the second threading edge dislocations 36 are dislocations formed by converting the second basal plane dislocations 26. The threading edge dislocations 2 extend along a third direction 103 substantially perpendicular to {0001}.

When basal plane dislocation 1 is present in silicon carbide epitaxial substrate 100, for example, the reliability of the gate insulating film formed on silicon carbide epitaxial substrate 100 is degraded. On the other hand, the threading edge dislocations 2 hardly affect the reliability of the gate insulating film formed on the silicon carbide epitaxial substrate, even if they are present in the silicon carbide epitaxial substrate. Therefore, it is desirable to convert basal plane dislocations 1 present in silicon carbide substrate 10 into threading edge dislocations 2 and reduce the number of basal plane dislocations 1 in silicon carbide epitaxial film 20.

In silicon carbide epitaxial substrate 100 according to the present embodiment, on first main surface 12 of silicon carbide substrate 10, there is basal plane dislocation 1 having a first surface density. The second main surface 14 of the silicon carbide epitaxial film 20 has a basal plane dislocation 1 having a second surface density lower than the first surface density. The value obtained by dividing the second area density by the first area density is 1/1000 or less. In other words, the rate (conversion rate) of conversion from basal plane dislocation 1 to threading edge dislocation 2 is 99.9% or more. The value obtained by dividing the second area density by the first area density may be, for example, 1/2000 or less. In other words, the ratio (conversion ratio) of conversion from basal plane dislocation 1 to threading edge dislocation 2 is 99.95% or more.

The second area density is, for example, 10 cm ⁻² or less. The second area density may be, for example, 6 cm ⁻² or less, or 2 cm ⁻² or less. In the silicon carbide epitaxial film 20, the surface density of the basal plane dislocation is low, but the surface density of the threading edge dislocation is high. The surface density of threading edge dislocations on the second main surface 14 of the silicon carbide epitaxial film 20 may be, for example, higher than 3990 cm ⁻² . But the lower limit of the first surface density is limited, the first surface density may be for example 2000 cm ^-2 or more, or may be 2500 cm ^-2 or more. Although not limit the first surface density is limited, the first surface density may be for example 6000 cm ^-2 or less, or may be 5500Cm ^-2 or less.

(Method of measuring the surface density of basal plane dislocations)
Next, a method of measuring the surface density of basal plane dislocation will be described. For observation of basal plane dislocation, for example, a photoluminescence imaging apparatus (model number: PLIS-100) manufactured by Photon Design Co., Ltd. is used. When excitation light is irradiated to the measurement region of the silicon carbide epitaxial substrate, photoluminescence light is observed from the measurement region. For example, a mercury xenon lamp is used as an excitation light source. Excitation light from a light source passes through a band pass filter of 313 nm and is then irradiated to the measurement area. The photoluminescence light passes through, for example, a low pass filter of 750 nm and then reaches a light receiving element such as a camera. As described above, the photoluminescence image of the measurement area is taken. The measurement temperature is room temperature.

For example, while the silicon carbide epitaxial substrate is moved in a direction parallel to the main surface (specifically, second main surface 14 or first main surface 12) of the silicon carbide epitaxial substrate, a photoluminescence image of the main surface is photographed. . Thereby, the photoluminescence image in the whole area of the main surface is mapped. The basal plane dislocations are identified in the acquired photoluminescence image, and the total number of the basal plane dislocations is calculated. The surface density of basal plane dislocations is calculated by dividing the total number of basal plane dislocations by the total measurement area.

In silicon carbide epitaxial substrate 100 according to the present embodiment, first main surface 12 is a surface inclined at an off angle of 8 ° or less with respect to the (0001) plane or the (0001) plane. The calculation of the surface density of the basal plane dislocation on the first main surface 12 may be performed, for example, by counting the pits generated using a potassium hydroxide (KOH) melt. Specifically, the first major surface 12 is etched using a KOH melt. The temperature of the KOH melt is, for example, about 500 ° C. or more and about 550 ° C. or less. The etching time is, for example, about 5 to 10 minutes. After etching, the first major surface 12 is observed by a normal ski differential interference microscope. The basal plane dislocations are etched by the KOH melt to form pits. The surface density of basal plane dislocations is calculated by dividing the total number of pits by the total measurement area. The threading edge dislocations also form pits in the same manner as the basal plane dislocations. The pits derived from threading edge dislocations and the pits derived from basal plane dislocations are distinguished as follows. Rounded hexagonal pits are derived from threading edge dislocations, and elliptical pits are derived from basal plane dislocations.

(Production apparatus for silicon carbide epitaxial substrate)
Next, the structure of the manufacturing apparatus 200 of the silicon carbide epitaxial substrate 100 which concerns on this embodiment is demonstrated.

As shown in FIG. 3, the manufacturing apparatus 200 for the silicon carbide epitaxial substrate 100 is, for example, a hot wall type horizontal CVD (Chemical Vapor Deposition) apparatus. The manufacturing apparatus 200 mainly includes a reaction chamber 201, a heating element 203, a quartz tube 204, a heat insulating material 205, and an induction heating coil 206.

The heat generating body 203 has, for example, a cylindrical shape, and forms a reaction chamber 201 inside. The heating element 203 is made of, for example, graphite. The heat insulating material 205 surrounds the outer periphery of the heating element 203. The heat insulating material 205 is provided inside the quartz tube 204 so as to be in contact with the inner circumferential surface of the quartz tube 204. The induction heating coil 206 is wound, for example, along the outer peripheral surface of the quartz tube 204. The induction heating coil 206 is configured to be able to supply an alternating current by an external power supply (not shown). Thereby, the heating element 203 is induction-heated. As a result, the reaction chamber 201 is heated by the heating element 203.

The reaction chamber 201 is a space formed by being surrounded by the heating element 203. In reaction chamber 201, silicon carbide substrate 10 is arranged. Reaction chamber 201 is configured to be able to heat silicon carbide substrate 10. In reaction chamber 201, a susceptor 210 for holding silicon carbide substrate 10 is provided. The susceptor 210 is configured to be capable of rotating around the rotation shaft 212.

The manufacturing apparatus 200 has a gas inlet 207 and a gas outlet 208. The gas exhaust port 208 is connected to an exhaust pump (not shown). Arrows in FIG. 6 indicate the flow of gas. The gas is introduced into the reaction chamber 201 through the gas inlet port 207 and exhausted through the gas exhaust port 208. The pressure in the reaction chamber 201 is adjusted by the balance between the gas supply amount and the gas discharge amount.

The manufacturing apparatus 200 includes, for example, a gas supply unit (not shown) configured to be able to supply a mixed gas containing silane, ammonia, hydrogen, and propane to the reaction chamber 201. Specifically, the gas supply unit may have a gas cylinder capable of supplying propane gas, a gas cylinder capable of supplying hydrogen gas, a gas cylinder capable of supplying silane gas, and a gas cylinder capable of supplying ammonia gas. Good.

In the axial direction of the reaction chamber 201, the winding density of the induction heating coil 206 may be changed. The winding density [times / m] is the number of turns of the coil per unit length in the axial direction of the device. For example, the winding density of the induction heating coil 206 on the upstream side may be higher than the winding density of the induction heating coil 206 on the downstream side in order to effectively thermally decompose ammonia on the upstream side.

(Method of manufacturing silicon carbide epitaxial substrate)
Next, a method of manufacturing the silicon carbide epitaxial substrate according to the present embodiment will be described.

First, a silicon carbide single crystal substrate preparation step (S11: FIG. 4) is performed. For example, a silicon carbide single crystal of polytype 4H is manufactured by a sublimation method. Next, silicon carbide substrate 10 is prepared by slicing a silicon carbide single crystal with, for example, a wire saw. Silicon carbide substrate 10 contains an n-type impurity such as nitrogen, for example. The conductivity type of silicon carbide substrate 10 is, for example, n-type.

As shown in FIG. 5, silicon carbide substrate 10 has a first main surface 11 and a first main surface 12 opposite to first main surface 11. The first major surface 11 is a surface inclined in the off direction by, for example, the off angle θ with respect to the (000-1) plane. The off direction is, for example, the <11-20> direction. The maximum diameter of first main surface 11 of silicon carbide substrate 10 is, for example, 100 mm or more. For example, a plurality of basal plane dislocations 1 exist in silicon carbide substrate 10. The basal plane dislocations 1 extend in a direction parallel to the {0001} plane. The basal plane dislocation 1 has, for example, a first basal plane dislocation 25, a second basal plane dislocation 26, and a third basal plane dislocation 27.

Next, silicon carbide substrate 10 is arranged on susceptor 210 in reaction chamber 201 (see FIG. 3). Silicon carbide substrate 10 is arranged in reaction chamber 201 under atmospheric pressure (time T0). Next, the pressure in the reaction chamber 201 is reduced. As shown in FIG. 7, the pressure in the reaction chamber 201 is reduced from atmospheric pressure to about 1 × 10 ⁻⁴ Pa from time point T1 to time point T2.

Next, the temperature raising step is performed. From time T2 to time T3, the temperature of the silicon carbide substrate 10 rises from room temperature to about 1100 ° C. in a state where the pressure in the reaction chamber 201 is about 1 × 10 ^-4 Pa. Next, from time T3 to time T4, the temperature of silicon carbide substrate 10 is maintained at 1100 ° C. for a fixed time. The temperature of silicon carbide substrate 10 rises from 1100 ° C. to 1630 ° C. from time point T4 to time point T5. At time point T4, hydrogen (H ₂ ) gas is introduced into the reaction chamber 201. The flow rate of hydrogen gas is, for example, 100 slm. The pressure in the reaction chamber 201 is, for example, about 10 kPa. Thus, a hydrogen etching process is performed. While the temperature of silicon carbide substrate 10 is maintained at 1630 ° C. from time T5 to time T6, the surface of silicon carbide substrate 10 is etched by hydrogen gas.

Next, a buffer layer formation step (S12: FIG. 4) is performed. Specifically, the source gas, the dopant gas and the carrier gas are supplied to the reaction chamber 201. For example, a mixed gas containing silane (SiH ₄ ), propane (C ₃ H ₈ ), ammonia (NH ₃ ) and hydrogen is supplied to the reaction chamber 201. As shown in FIG. 7, silicon carbide substrate 10 is maintained at about 1630 ° C. from time point T6 to time point T7. In the reaction chamber 201, the respective gases are thermally decomposed to form the buffer layer 21 on the silicon carbide substrate 10 (see FIG. 6). In the process of forming the buffer layer 21, the susceptor 210 may rotate around the rotation axis 212. Silicon carbide substrate 10 may revolve around rotation axis 212 (see FIG. 3).

In the step of forming the buffer layer, the flow rates of silane and propane are adjusted so that the growth rate is, for example, 5 μm / h. Specifically, the flow rate of the silane gas is adjusted to, for example, 46 sccm. The flow rate of propane gas is adjusted to, for example, 29 sccm. The flow rate of ammonia gas is adjusted to, for example, 1.5 sccm. The flow rate of hydrogen gas is adjusted to be 100 slm. The thickness of buffer layer 21 is, for example, 1 μm. The pressure in the reaction chamber 201 is, for example, 10 kPa. The C / Si ratio is, for example, 1.9.

As shown in FIG. 6, a part of the plurality of basal plane dislocations 1 present in silicon carbide substrate 10 are converted into threading edge dislocations. For example, the first basal plane dislocations 25 are converted into first penetrating edge dislocations 35. For example, the second basal plane dislocations 26 and the third basal plane dislocations 27 are not converted into threading edge dislocations, but propagate in the buffer layer 21 as basal plane dislocations.

Next, the drift layer forming step (S13: FIG. 4) is performed. Specifically, a mixed gas containing silane, propane, ammonia and hydrogen is supplied to the reaction chamber 201. Between time point T6 and time point T7, silicon carbide substrate 10 is maintained at 1630.degree. In the reaction chamber 201, each gas is thermally decomposed to form the drift layer 22 on the buffer layer 21 (see FIG. 2). In the process of forming the drift layer 22, the susceptor 210 may rotate around the rotation axis 212. Silicon carbide substrate 10 may revolve around rotation axis 212 (see FIG. 3).

In the step of forming the drift layer, the flow rates of silane and propane are adjusted such that the growth rate is, for example, 25 μm / h. Specifically, the flow rate of the silane gas is adjusted to, for example, 115 sccm. The flow rate of propane gas is adjusted to, for example, 57.6 sccm. The flow rate of ammonia gas is adjusted to, for example, 2.5 × 10 ⁻² sccm. The flow rate of hydrogen gas is adjusted to be 100 slm. The thickness of drift layer 22 is, for example, 10 μm. The pressure in the reaction chamber 201 is, for example, 10 kPa. The C / Si ratio is, for example, 1.5. As described above, by increasing the growth rate of the drift layer 22 of the silicon carbide epitaxial film to about 25 μm / h, the rate (conversion rate) of conversion of basal plane dislocations into threading edge dislocations can be improved.

Next, a cooling process is performed. As shown in FIG. 7, the temperature of silicon carbide substrate 10 is reduced from 1630 ° C. to room temperature from time point T8 to time point T9. At time T9, the supply of hydrogen introduced into the reaction chamber 201 is stopped, and the pressure in the reaction chamber 201 returns to atmospheric pressure. As described above, silicon carbide epitaxial substrate 100 is manufactured.

(Method of manufacturing silicon carbide semiconductor device)
Next, a method of manufacturing the silicon carbide semiconductor device 300 according to the present embodiment will be described.

The method for manufacturing a silicon carbide semiconductor device according to the present embodiment mainly includes an epitaxial substrate preparation step (S10: FIG. 8) and a substrate processing step (S20: FIG. 8).

First, an epitaxial substrate preparation step (S10: FIG. 8) is performed. Specifically, silicon carbide epitaxial substrate 100 is prepared by the method for manufacturing a silicon carbide epitaxial substrate described above (see FIG. 2).

Next, a substrate processing step (S20: FIG. 8) is performed. Specifically, a silicon carbide semiconductor device is manufactured by processing a silicon carbide epitaxial substrate. "Processing" includes, for example, various processes such as ion implantation, heat treatment, etching, oxide film formation, electrode formation, dicing and the like. That is, the substrate processing step may include at least one of ion implantation, heat treatment, etching, oxide film formation, electrode formation, and dicing.

Below, the manufacturing method of MOSFET as an example of a silicon carbide semiconductor device is explained. The substrate processing step (S20: FIG. 8) includes, for example, an ion implantation step (S21: FIG. 8), an oxide film forming step (S22: FIG. 8), an electrode forming step (S23: FIG. 8) and a dicing step (S24: FIG. 8). )including.

First, an ion implantation step (S21: FIG. 8) is performed. A p-type impurity such as aluminum (Al) is implanted into second main surface 14 on which a mask (not shown) having an opening is formed. Thus, a body region 132 having p-type conductivity is formed. Next, an n-type impurity such as phosphorus (P) is implanted at a predetermined position in body region 132, for example. Thus, a source region 133 having n-type conductivity is formed. Next, p-type impurities such as aluminum are implanted into predetermined positions in the source region 133. Thereby, a contact region 134 having p type conductivity is formed (see FIG. 9).

In the second layer 22 of the silicon carbide epitaxial film 20, portions other than the body region 132, the source region 133, and the contact region 134 become the drift region 131. Source region 133 is separated from drift region 131 by body region 132. The ion implantation may be performed by heating the silicon carbide epitaxial substrate 100 to approximately 300 ° C. or more and 600 ° C. or less. After ion implantation, activation annealing is performed on silicon carbide epitaxial substrate 100. The activation annealing activates the impurities implanted in the silicon carbide epitaxial film 20, and carriers are generated in each region. The atmosphere for activation annealing is, for example, an argon (Ar) atmosphere. The temperature of activation annealing is, for example, about 1800.degree. The activation annealing time is, for example, about 30 minutes.

Next, an oxide film formation step (S22: FIG. 8) is performed. For example, oxide film 136 is formed on second main surface 14 by heating silicon carbide epitaxial substrate 100 in an atmosphere containing oxygen (see FIG. 10). Oxide film 136 is made of, for example, silicon dioxide or the like. The oxide film 136 functions as a gate insulating film. The temperature of the thermal oxidation treatment is, for example, about 1300.degree. The time of thermal oxidation treatment is, for example, about 30 minutes.

After the oxide film 136 is formed, heat treatment may be further performed in a nitrogen atmosphere. For example, heat treatment is performed at about 1100 ° C. for about one hour in an atmosphere of nitrogen monoxide. Thereafter, heat treatment is performed in an argon atmosphere. For example, heat treatment is performed in an argon atmosphere at about 1100 ° C. or more and about 1500 ° C. or less for about one hour.

Next, an electrode formation step (S23: FIG. 8) is performed. Specifically, gate electrode 141 is formed on oxide film 136. Gate electrode 141 is formed, for example, by a CVD method. Gate electrode 141 is formed of, for example, polysilicon having conductivity. The gate electrode 141 is formed at a position facing the source region 133 and the body region 132.

Next, an interlayer insulating film 137 covering the gate electrode 141 is formed. Interlayer insulating film 137 is formed, for example, by the CVD method. Interlayer insulating film 137 is made of, for example, silicon dioxide or the like. Interlayer insulating film 137 is formed to be in contact with gate electrode 141 and oxide film 136. Next, portions of oxide film 136 and interlayer insulating film 137 are removed by etching. Thus, source region 133 and contact region 134 are exposed from oxide film 136.

Next, the source electrode 142 is formed on the exposed portion, for example, by sputtering. Source electrode 142 is made of, for example, titanium, aluminum, silicon or the like. After source electrode 142 is formed, source electrode 142 and silicon carbide epitaxial substrate 100 are heated, for example, at a temperature of about 900 ° C. or more and about 1100 ° C. or less. Thereby, source electrode 142 and silicon carbide epitaxial substrate 100 come into ohmic contact with each other. Next, the wiring layer 138 is formed in contact with the source electrode 142. Wiring layer 138 is made of, for example, a material containing aluminum. Next, the drain electrode 143 is formed on the third major surface 13. Drain electrode 143 is made of, for example, an alloy (eg, NiSi or the like) containing nickel and silicon.

Next, a dicing step (S24: FIG. 8) is performed. For example, silicon carbide epitaxial substrate 100 is divided into a plurality of semiconductor chips by dicing silicon carbide epitaxial substrate 100 along dicing lines. Thus, silicon carbide semiconductor device 300 is manufactured (see FIG. 11).

Although the method of manufacturing the silicon carbide semiconductor device according to the present disclosure has been described above by exemplifying the MOSFET, the method of manufacturing the present disclosure is not limited thereto. The manufacturing method according to the present disclosure is applicable to silicon carbide semiconductor devices such as IGBTs (Insulated Gate Bipolar Transistors), SBDs (Schottky Barrier Diodes), thyristors, GTOs (Gate Turn Off thyristors), PiN diodes, and the like.

Next, functions and effects of the silicon carbide epitaxial substrate and the method for manufacturing a silicon carbide semiconductor device according to the present embodiment will be described.

When the basal plane dislocation 1 is present in the silicon carbide epitaxial substrate 100, the basal plane dislocation 1 may be expanded to become a stacking fault at the time of energization. In that case, for example, the gate insulating film formed on silicon carbide epitaxial substrate 100 may be damaged, which may cause a decrease in withstand voltage of silicon carbide semiconductor device 300. As a result, the reliability of silicon carbide semiconductor device 300 may be reduced. On the other hand, the threading edge dislocations 2 hardly affect the reliability of the silicon carbide semiconductor device 300 even if they are present in the silicon carbide epitaxial substrate 100. Therefore, in order to enhance the reliability of silicon carbide semiconductor device 300, it is desirable to convert basal plane dislocations 1 into threading edge dislocations 2 to reduce the number of basal plane dislocations 1. It is also difficult to reduce basal plane dislocation 1 on the carbon surface as compared to the silicon surface.

According to silicon carbide epitaxial substrate 100 in accordance with the present embodiment, the surface density (second surface density) of basal plane dislocation 1 in second main surface 14 can be compared to the surface density of basal plane dislocation 1 in first main surface 12 (first The value divided by 1) is 1/1000 or less. The second main surface 14 is a surface inclined at an off angle of 8 ° or less with respect to the carbon surface or the carbon surface. That is, according to silicon carbide epitaxial substrate 100 according to the present embodiment, the basal plane of second main surface 14 of silicon carbide epitaxial film 20 is obtained by converting most of basal plane dislocations 1 in silicon carbide substrate 10 into threading dislocations. Dislocation 1 can be reduced. Therefore, the reliability of silicon carbide semiconductor device 300 including silicon carbide epitaxial substrate 100 having second main surface 14 inclined at an off angle of 8 ° or less with respect to the carbon surface or the carbon surface can be improved.

Next, an example will be described. First, silicon carbide substrates according to

samples

1 and 2 were prepared. The basal plane dislocation (BPD) on the main surface of the silicon carbide substrate according to

Samples

1 and 2 was 4000 cm.sup.- ² . The largest diameter of the main surface of the silicon carbide substrate according to

Samples

1 and 2 was 150 mm. Next, a silicon carbide epitaxial film was grown on the silicon carbide substrate according to

Samples

1 and 2.

For the silicon carbide substrate according to Sample 1, a silicon carbide epitaxial film was formed using the method for manufacturing a silicon carbide epitaxial substrate according to the present embodiment. That is, for the silicon carbide substrate according to sample 1, a silicon carbide epitaxial film was formed using the temperature profile shown in FIG. Specifically, the growth rate of the buffer layer was 5 μm / h. The growth rate of the drift layer was 25 μm / h. The thickness of the buffer layer was 1 μm. The carrier concentration of the buffer layer was set to 1 × 10 ¹⁸ cm ⁻³ . The thickness of the drift layer was 10 μm. The carrier concentration of the drift layer was 7 × 10 ¹⁵ cm ⁻³ .

For the silicon carbide substrate according to sample 2, a silicon carbide epitaxial film was formed using the temperature profile shown in FIG. Specifically, the growth rate of the buffer layer was 5 μm / h. The growth rate of the drift layer was 10 μm / h. The thickness of the buffer layer was 1 μm. The carrier concentration of the buffer layer was set to 1 × 10 ¹⁸ cm ⁻³ . The thickness of the drift layer was 10 μm. The carrier concentration of the drift layer was 7 × 10 ¹⁵ cm ⁻³ .

The method of manufacturing a silicon carbide substrate according to sample 2 is different from the method of manufacturing a silicon carbide substrate according to sample 1 in the drift layer forming step, and the other steps are the same as the method of manufacturing a silicon carbide substrate according to sample 1 is there. In the step of forming the drift layer of the silicon carbide substrate according to sample 2, the flow rate of the silane gas was adjusted to, for example, 69 sccm. The flow rate of propane gas was adjusted to, for example, 43.5 sccm. The flow rate of ammonia gas was adjusted to be, for example, 1.0 × 10 ⁻² sccm. The C / Si ratio was 1.9.

As described above, the silicon carbide epitaxial substrates according to

Samples

1 and 2 were manufactured. Next, the areal densities of basal plane dislocations on the first main surface 12 and the second main surface 14 of the silicon carbide epitaxial substrate according to

Samples

1 and 2 were measured. The areal density of basal plane dislocations was measured using the measurement method described above.

Table 1 shows the surface density (first surface density) of the basal plane dislocation (BPD) of the first main surface 12 of the silicon carbide substrate and the plane of the basal surface dislocation (BPD) of the second main surface 14 of the silicon carbide epitaxial film The density (second surface density), the value obtained by dividing the second surface density by the first surface density, and the conversion ratio from basal plane dislocation to threading edge dislocation are shown. As shown in Table 1, a value obtained by dividing the areal density of basal plane dislocations on the second main surface 14 of the silicon carbide substrate epitaxial substrate according to

Samples

1 and 2 by the areal density of basal plane dislocations on the first main surface 12 Of 0.0005 and 0.01045, respectively. In the silicon carbide substrate epitaxial substrate according to

Samples

1 and 2, the conversion ratio determined as the value obtained by subtracting the second surface density from the first surface density divided by the first surface density is 99.95% and 98, respectively. It was .955%.

From the above results, in the case of manufacturing a silicon carbide epitaxial substrate using the manufacturing conditions of FIG. 7, the basal plane dislocation is penetrated like dislocation as compared to the case of manufacturing a silicon carbide epitaxial substrate using the manufacturing conditions of FIG. As a result, it has been confirmed that the surface density of basal plane dislocations in a silicon carbide epitaxial film can be reduced.

The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the embodiments described above but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

1 basal plane dislocation, 2 threading edge dislocation, 10 silicon carbide substrate, 11 first main surface, 12 first main surface, 13 third main surface, 14 second main surface, 16 first flat, 20 silicon carbide epitaxial film 21 first layer (buffer layer) 22 second layer (drift layer) 25 first basal plane dislocation 26 second basal plane dislocation 27 third basal plane dislocation 35 first threading edge dislocation 36 third 2 threading edge dislocation, 100 silicon carbide epitaxial substrate, 101 first direction, 102 second direction, 103 third direction, 104 fourth direction, 105 fifth direction, 111 maximum diameter, 131 drift region, 132 body region, 133 Source region, 134 contact region, 136 oxide film, 137 interlayer insulating film, 138 wiring layer, 141 gate electrode, 142 source electrode, 1 Reference Signs List 3 drain electrode, 200 manufacturing apparatus, 201 reaction chamber, 203 heating element, 204 quartz tube, 205 heat insulator, 206 induction heating coil, 207 gas inlet, 208 gas outlet, 210 susceptor, 212 rotating shaft, 300 silicon carbide semiconductor apparatus.

Claims

A silicon carbide substrate,
And a silicon carbide epitaxial film on the silicon carbide substrate,
The polytype of the silicon carbide substrate and the silicon carbide epitaxial film is 4H,
The silicon carbide epitaxial film includes a first layer in contact with the silicon carbide substrate, and a second layer on the first layer and constituting the main surface of the silicon carbide epitaxial film.
The silicon carbide substrate, the first layer, and the second layer contain an n-type impurity,
The concentration of the n-type impurity contained in the first layer is lower than the concentration of the n-type impurity contained in the silicon carbide substrate, and higher than the concentration of the n-type impurity contained in the second layer.
There is a basal plane dislocation having a first surface density on the main surface of the silicon carbide substrate,
The main surface of the silicon carbide epitaxial film has a basal plane dislocation having a second surface density lower than the first surface density,
A value obtained by dividing the second area density by the first area density is 1/1000 or less,
The silicon carbide epitaxial substrate, wherein the main surface of the silicon carbide epitaxial film is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane.
The silicon carbide epitaxial substrate according to claim 1, wherein a value obtained by dividing the second area density by the first area density is 1/2000 or less.
The silicon carbide epitaxial substrate according to claim 1 or 2, wherein the largest diameter of the main surface of said silicon carbide epitaxial film is 100 mm or more.
The silicon carbide epitaxial substrate according to claim 3, wherein the largest diameter of the main surface of said silicon carbide epitaxial film is 150 mm or more.
A silicon carbide substrate,
And a silicon carbide epitaxial film on the silicon carbide substrate,
The polytype of the silicon carbide substrate and the silicon carbide epitaxial film is 4H,
The silicon carbide epitaxial film includes a first layer in contact with the silicon carbide substrate, and a second layer on the first layer and constituting the main surface of the silicon carbide epitaxial film.
The silicon carbide substrate, the first layer, and the second layer contain an n-type impurity,
The concentration of the n-type impurity contained in the first layer is lower than the concentration of the n-type impurity contained in the silicon carbide substrate, and higher than the concentration of the n-type impurity contained in the second layer.
There is a basal plane dislocation having a first surface density on the main surface of the silicon carbide substrate,
The main surface of the silicon carbide epitaxial film has a basal plane dislocation having a second surface density lower than the first surface density,
A value obtained by dividing the second area density by the first area density is 1/1000 or less,
The main surface of the silicon carbide epitaxial film is a surface inclined at an off angle of 8 ° or less with respect to the (000-1) plane or the (000-1) plane,
The largest diameter of the main surface of the silicon carbide epitaxial film is 150 mm or more,
The thickness of the first layer is 0.5 μm or more and 2 μm or less,
The thickness of the second layer is 5 μm or more and 30 μm or less,
The concentration of the n-type impurity contained in the first layer is 1 × 10 17 cm −3 or more and 1 × 10 19 cm −3 or less.
The silicon carbide epitaxial substrate, wherein the concentration of the n-type impurity contained in the second layer is 1 × 10 15 cm −3 or more and 1 × 10 16 cm −3 or less.
Preparing a silicon carbide epitaxial substrate according to any one of claims 1 to 5;
And b. Processing the silicon carbide epitaxial substrate.