Epitaxial silicon carbide substrate and method for fabricating a silicon carbide semiconductor device

Abstract

Epitaxial silicon carbide substrate (100) comprising: a silicon carbide single crystal substrate (10) with a first principal surface (11); and a silicon carbide layer (20) on the first principal surface (11), wherein the silicon carbide layer (20) has a surface in contact with the silicon carbide single-crystal substrate (10) and a second principal surface (12) opposite the surface, the silicon carbide layer (20) comprises a buffer layer (21) in contact with the first principal surface (11), the nitrogen concentration contained in the buffer layer (21) is 5 × 10¹⁷ cm⁻³ or more and 1 × 10¹⁹ cm⁻³ or less, the second principal surface (12) is a plane inclined at a dislocation angle in a dislocation direction relative to a {0001} plane, the second principal surface (12) has defects, and assuming that a defect satisfying the relations of Formula 1 and Formula 2 is a first defect (1), wherein the dislocation angle is θ°,a thickness of the silicon carbide layer in a direction perpendicular to the second principal surface (12) is W µm, a width of the defect in a direction parallel to a direction obtained by projecting the dislocation direction onto the second principal surface (12) is L µm, and a width of the defect in a direction perpendicular to the dislocation direction and parallel to the second principal surface (12) is Y µm, and assuming that a defect with an elongated shape considered in the direction perpendicular to the second principal surface (12) and satisfying the relations of formula 3 and formula 4 is a second defect (2) where a width of the defect in a longitudinal direction of the defect is A µm and a width of the defect in a short direction of the defect is B µm when considered in the direction perpendicular to the second principal surface (12), then a value iswhich is obtained by dividing a number of the second defect (2) by a sum of a number of the first defect (1) and the number of the second defect (2), greater than 0.5: LY≦10.8xWtanθ <L<1.2xWtanθ3<ABL<Wtan θ,

Description

TECHNICAL AREA

[0001] The present invention relates to an epitaxial silicon carbide substrate and a method for fabricating a silicon carbide semiconductor device. This application claims priority from Japanese patent application No. 2017-015502, filed on January 31, 2017, the entire contents of which are incorporated herein by reference. STATE OF THE ART

[0002] Japanese patent application no. 2014-170891 (PTL1) discloses a process for epitaxial growth of a silicon carbide layer on a silicon carbide single crystal substrate. LIST OF CITINGS PATENT LITERATURE

[0003] PTL1: Japanese Disclosure No. 2014-170891 SUMMARY OF THE INVENTION

[0004] An epitaxial silicon carbide substrate according to the present invention comprises: a silicon carbide single-crystal substrate with a first principal surface; and a silicon carbide layer on the first principal surface. The silicon carbide layer comprises a surface in contact with the silicon carbide single-crystal substrate and a second principal surface opposite the first principal surface. The second principal surface is a plane inclined at a dislocation angle in a dislocation direction relative to a {0001} plane. The second principal surface has defects. Assuming that a defect satisfying the relationships of Formulas 1 and 2 is a first defect where the dislocation angle is θ°, the thickness of the silicon carbide layer in a direction perpendicular to the second principal surface is Wµm is the width of the defect in a direction parallel to a direction obtained by projecting the dislocation direction onto the second main surface, L µm and a width of the defect in a direction perpendicular to the dislocation direction and parallel to the second main surface. Y µm, and assuming that a defect with an elongated shape, when viewed in the direction perpendicular to the second principal surface and satisfying the relationships of formulas 3 and 4, is a second defect in which a width of the defect in the longitudinal direction of the defect A µm and a width of the defect in a short direction of the defect B is µm when viewed in the direction perpendicular to the second main surface, then a value greater than 0.5 is obtained by dividing a number of the second defect by a sum of a number from the first defect and a number of the second defect: L Y ≦ 1 0.8 × W tan θ < L < 1.2 × W tan θ 3 < A B L< W tan θ List of characters Fig. Figure 1 is a schematic planar view showing a configuration of an epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 2 is a schematic sectional view along a line II-II in Fig. 3 and in view along the direction of the arrows. Fig. Figure 3 is a schematic planar view showing a configuration of a first section of a second main surface of the epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 4 is a schematic planar view showing a configuration of a second section of the second main surface of the epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 5 is a schematic sectional view along a line V-V in Fig. 4 and in the direction of the arrows. Fig. Figure 6 is a schematic partial sectional view showing a configuration of a device for producing the epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 7 is a flowchart that schematically shows a process for producing the epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 8 is a schematic sectional view showing a first step of the process for producing the epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 9 is a schematic sectional view showing a second step of the process for producing the epitaxial silicon carbide substrate according to the present embodiment. Fig. Figure 10 is a flowchart that schematically shows a method for manufacturing a silicon carbide semiconductor device according to the present embodiment. Fig. Figure 11 is a schematic sectional view showing a first step of the method for manufacturing the silicon carbide semiconductor device according to the present embodiment. Fig. Figure 12 is a schematic sectional view showing a second step of the method for manufacturing the silicon carbide semiconductor device according to the present embodiment. Fig. Figure 13 is a schematic sectional view showing a configuration of the silicon carbide semiconductor device according to the present embodiment. DETAILED DESCRIPTION [Summary of the embodiment of the present invention]

[0005] First, a summary of one embodiment of the present invention is provided. With regard to crystallographic information, an individual orientation is represented by [], a group orientation by <>, an individual plane by (), and a group plane by {}. Although a crystallographically negative index is normally expressed by a number with a dash “-” above it, here a negative sign precedes a number to indicate a crystallographically negative index. (1) An epitaxial silicon carbide substrate 100 According to the present invention, comprising: a silicon carbide single-crystal substrate 10 with a first main surface 11 ; and a silicon carbide layer 20 on the first main surface 11The silicon carbide layer 20 includes a surface 14 in contact with the silicon carbide single crystal substrate 10 and a second main surface opposite the surface 12 The second main area 12 is a plane inclined at a dislocation angle in a dislocation direction relative to a {0001} plane. The second principal surface 12 exhibits defects. Assuming that a defect satisfying the relationships of Formula 1 and Formula 2 is a first defect 1 is, where the dislocation angle θ° is, a thickness of the silicon carbide layer 20 in a direction perpendicular to the second main surface is 12 W µm, a width of the defect in a direction parallel to a direction determined by projecting the dislocation direction onto the second main surface 12 will be received Lµm, and a width of the defect in a direction perpendicular to the dislocation direction and parallel to the second main surface 12 Y µm, and assuming that a defect has an elongated shape when it is in the direction perpendicular to the second principal surface 12 Considered and fulfilling the relationships of formula 3 and formula 4, a second defect is one in which the width of the defect is in a longitudinal direction of the defect. A µm and a width of the defect in a short direction of the defect B µm is the value when they are in the direction perpendicular to the second main surface 12 If considered, then a value is obtained by taking a number of the second defects. 2 by a sum of a number from the first defect 1 and the number of the second defect 2The division is greater than 0.5. As a result, a two-dimensional extent of a defect can be suppressed. (2) In the epitaxial silicon carbide substrate 100 according to (1) above, the thickness of the silicon carbide layer can be determined. 20 at least 5 µm and at most 100 µm. (3) In the epitaxial silicon carbide substrate 100 According to (1) or (2) above, the dislocation angle can be greater than 0° and less than or equal to 8°. (4) In the epitaxial silicon carbide substrate 100 after one of ( 1 ) to (3) above, the value obtained by dividing by the number of the second defect 2 by the sum of the number of the first defect 1 and the number of the second defect 2 The result obtained will be greater than 0.6. (5) In the epitaxial silicon carbide substrate 100 according to ( 4 ) above, the value obtained by dividing by the number of the second defect2 by the sum of the number of the first defect 1 and the number of the second defect 2 The result obtained will be greater than 0.7. (6) In the epitaxial silicon carbide substrate 100 according to ( 5 ) above, the value obtained by dividing by the number of the second defect 2 by the sum of the number of the first defect 1 and the number of the second defect 2 The result obtained will be greater than 0.8. (7) In the epitaxial silicon carbide substrate 100 according to ( 6 ) above, the value obtained by dividing by the number of the second defect 2 by the sum of the number of the first defect 1 and the number of the second defect 2 The result obtained will be greater than 0.9. (8) A method for manufacturing a silicon carbide semiconductor device 300According to the present invention, the following steps are required. An epitaxial silicon carbide substrate is prepared. 100 according to one of ( 1 ) until ( 7 ) prepared above. The epitaxial silicon carbide substrate 100 is being processed. [Details of the embodiment of the present invention]

[0006] The details of the embodiment of the present invention are described below. In the following description, the same or corresponding elements are designated with the same symbols, and the same description is not repeated. (Silicon Carbide Epitaxy Substrate)

[0007] According to the presentation in the Fig. 1 and Fig. 2 features an epitaxial silicon carbide substrate 100 according to the present embodiment, a silicon carbide single crystal substrate 10 and a silicon carbide layer 20 on. The silicon carbide single-crystal substrate10 has a first main area 11 and a third main area 13 opposite the first main surface 11 on. The silicon carbide layer 20 includes a fourth main area 14 , which are based on the silicon carbide single crystal substrate 10 is in contact, and a second main area 12 , which is the fourth main area 14 opposite. According to the representation in Fig. 1. The epitaxial silicon carbide substrate 100 with an initial flattening 16 be provided which in a first direction 101 extends. The epitaxial silicon carbide substrate 100 may be provided with a second flattening (not shown) that extends in a second direction 102 extends.

[0008] The first direction 101 is a direction parallel to the second main surface 12 and perpendicular to the second direction 102The second direction 102 For example, a <1-100> direction. According to the representation in Fig. 1 represents a maximum diameter 111 (Diameter) of the second main surface 12 For example, 100 mm or more. The maximum diameter 111 It can 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 upper limit of the maximum diameter 111 It could be, for example, 300 mm.

[0009] The silicon carbide single crystal substrate 10 It is formed from a silicon carbide single crystal. This silicon carbide single crystal exhibits, for example, a 4H-SiC polytype. 4H-SiC is superior to other polytypes with respect to electron mobility, dielectric strength, and the like. The silicon carbide single-crystal substrate 10 includes an n-type impurity, such as nitrogen ( NThe conductivity type of the silicon carbide single-crystal substrate 10 The n-type is one example. The first main surface 11 is a plane inclined at an angle of 8° or less relative to a {0001} plane. If the first principal surface 11 inclined relative to the {0001} plane, is a direction of inclination of the normal to the first principal surface 11 for example, an <11-20> direction.

[0010] According to the representation in Fig. The silicon carbide layer is located in position 2. 20 on the first main surface 11 of the silicon carbide single crystal substrate 10 The silicon carbide layer 20 is an epitaxial layer. The silicon carbide layer 20 stands with the first main surface 11 in contact. The silicon carbide layer 20 includes an n-type impurity, such as nitrogen. The conductivity type of the silicon carbide layer.20 The second principal surface is, for example, the n-type. The second principal surface is a plane inclined at a dislocation angle θ (°) in a dislocation direction relative to the {0001}-plane. In particular, the second principal surface can be 12 a plane inclined by 8° or less in a dislocation direction relative to a (0001) plane. Alternatively, the second principal surface 12 A dislocation direction is a plane inclined by 8° or less in a dislocation direction relative to a (000-1) plane. The dislocation direction is, for example, the <11-20> direction. The dislocation direction is not limited to the <11-20> direction. For example, the dislocation direction could be the <1-100> direction or a direction with a <1-100> directional component and a <11-20> directional component.

[0011] The displacement angle θ is an inclination angle of the second principal surface relative to the {0001} plane. The dislocation angle θ In other words, is an angle of inclination of the normal to the second principal surface relative to a <0001> -Direction. The displacement angle θ For example, it is greater than 0° and less than or equal to 8°. The displacement angle θ can be at least 1° or at least 2°. The opening angle can be at most 7° or at most 6°.

[0012] A line drawn with a dotted line in Fig. 2 designated level 15 For example, the {0001} plane. A third direction 103 is a direction perpendicular to the plane 15 The third direction 103 For example, is the <0001> -direction. A fourth direction 104 is a direction perpendicular to the third direction 103 The fourth direction 104 For example, the <11-20> direction. The fourth direction 104 is the direction of displacement. A direction of the normal to the second principal surface. 12 is a fifth direction105 The fifth direction is a direction that is offset by an angle of displacement. θ in the direction of displacement relative to the <0001> -direction is inclined.

[0013] The silicon carbide layer 20 includes a buffer layer 21 and a drift layer 22 The buffer layer 21 stands with the first main area 11 in contact. The buffer layer 21 forms the fourth main area 14 the silicon carbide layer 20 The drift layer 22 is located on the buffer. The drift layer 22 forms the second main surface 12 the silicon carbide layer 20 The buffer layer 21 includes an n-type impurity, such as nitrogen. The concentration of this impurity in the buffer layer 21 The amount of n-type impurity contained is, for example, 1 × 10 18 cm -3 The concentration of the substance in the buffer layer 21The contained n-type impurity can, for example, be 5 × 10 17 cm -3 or more and 1 × 10 19 cm -3 or less. For example, the concentration of an n-type impurity contained in the drift layer is 3 × 10 15 cm -3 The concentration of n-type contamination in the drift layer 22 The concentration contained is lower than the concentration of the n-type impurity in the buffer layer. 21 is contained. The concentration of the n-type impurity in the buffer layer 21 The concentration of the n-type impurity contained in the silicon carbide single crystal substrate may be lower than the concentration of the n-type impurity. 10 is included.

[0014] According to the representation in Fig. 3 can be the second main surface 12 a first defect 1 exhibit the first defect 1For example, a triangular defect. According to the illustration in the Fig. 2 and Fig. 3 is the first defect 1 a defect that satisfies the relationships of the aforementioned formula 1 and the aforementioned formula 2, where the dislocation angle θ (°) is the thickness of the silicon carbide layer in the fifth direction 105 perpendicular to the second main surface is 12 W (µm), the width of the defect in the first direction 101 , which is obtained by projecting a direction parallel to the dislocation direction onto the second main surface, is L (µm) and is the width of the defect in the second direction 102 perpendicular to the direction of displacement and parallel to the second main surface Y (µm). The thickness W of the silicon carbide layer is, for example, 5 µm or more and 100 µm or less. The lower limit of the thickness WThe thickness of the silicon carbide layer is not particularly limited and can, for example, be 10 µm or 20 µm. The upper limit of the thickness W The thickness of the silicon carbide layer is not particularly limited and can be, for example, 80 µm or 50 µm.

[0015] According to the presentation in the Fig. 2 and Fig. The first defect dates back to 3. 1 for example, from a threaded screw misalignment 25 and extends in the first direction 101 Viewed in a direction perpendicular to the second main surface 12 the first defect extends 1 , so that it covers a range within ± 45° relative to the first direction 101 covers. Viewed in the direction perpendicular to the second main surface. 12 The first defect indicates 1 for example, a triangular shape. The polytype of silicon carbide, which exhibits the first defect. 1forms, differs from the polytype that forms the silicon carbide layer 20 forms. The polytype that forms the first defect 1 The resulting structure can be, for example, 3C or 8H. The surface of the first defect 1 , those of the first direction 101 Facing towards, can lead to the second main surface 12 be aligned. The surface of the first defect 1 , those of the first direction 101 Conversely, it can have a lower height than the second main surface. 12 exhibit the second main surface 12 Ideally, it has no initial defect. 1 on.

[0016] According to the representation in Fig. 4 shows the second main surface 12 one or more second defects 2 on. According to the representation in Fig. 4 shows the second defect 2 in view in the direction perpendicular to the second main surface 12an elongated shape. Viewed in the direction perpendicular to the second main surface. 12 is the second defect 2 One defect has a rectangular shape. The second defect 2 satisfies the relationship of formula 3, where in view in perpendicular direction to the second main surface 12 the width of the second defect 2 in the longitudinal direction of the second defect 2 A (µm) and the width of the second defect 2 in the short direction of the second defect 2 B (µm).

[0017] The longitudinal direction of the second defect 2 is a direction in which the second defect 2 has a maximum dimension when it is in the direction perpendicular to the second main surface 12 The short direction of the second defect is viewed in the direction perpendicular to the second main surface. 12a direction perpendicular to the longitudinal direction. A value obtained by dividing by A through B in view in the direction perpendicular to the second main surface 12 The amount obtained can be at least 4 or at least 5. According to the representation in the Fig. 4 and Fig. 5 is the second defect 2 a defect that satisfies the relationship of formula 4, where the dislocation angle θ (°) is the thickness of the silicon carbide layer 20 in the fifth direction 105 perpendicular to the second main surface is 12 W (µm) and the width of the defect in the first direction 101 , which are projected onto the second main surface in a direction parallel to the dislocation direction 12 is obtained L (µm).

[0018] According to the representation in Fig. 4. The second defect can occur. 2 in view in the direction perpendicular to the second main surface 12a portion of an area within ± 45° relative to the first direction 101 occupy. In a view in the direction perpendicular to the second direction, the second defect can be seen. 2 extend in a direction that is in relation to the first direction 101 on one side of the second direction 102 is inclined at 45°, or can extend in a direction which is in relation to the first direction 101 on one side opposite the second direction, inclined at 45°. The silicon carbide polytype, which contains the second defect 2 forms, differs from the polytype of silicon carbide that forms the layer 20 forms. The polytype of silicon carbide, which forms the second defect 2 The resulting structure can be, for example, 3C or 8H. The first direction 101 facing surface of the second defect 2 can lead to the second main surface 12 be aligned. Those of the first direction101 opposite surface of the second defect 2 can have a lower height than the second main surface 12 exhibit. In view in the direction perpendicular to the second main surface. 12 is the second defect 2 smaller in area than the first defect 1 .

[0019] It is desirable to reduce the number of initial defects. 1 to reduce and the number of second defects 2 on the second main surface 12 of the silicon carbide epitaxy substrate 100 to increase. According to the silicon carbide epitaxy substrate 100 According to the present embodiment, a value is obtained by dividing the number of second defects. 2 by the sum of the number of first defects 1 and the number of second defects 2is obtained, greater than 0.5. For example, if the number of first defects is one and the number of second defects is in the second main surface 12 nine is the value obtained by the number of second defects. 2 by the sum of the number of first defects 1 and the number of second defects 2 Dividing by the number of second defects, 9 / (1 + 9) = 0.9. 2 by the sum of the number of first defects 1 and the number of second defects 2 The result obtained can be greater than 0.6, greater than 0.7, greater than 0.8 or greater than 0.9. (Method for measuring the number of defects)

[0020] The number of initial defects 1 and the second defect 2 can be achieved by observing the second main surface 12 of the epitaxial silicon carbide substrate 100The number of defects can be measured using a defect detection device, such as a confocal differential interference microscope. For example, the WASAVI "SICA 6X" series from Lasertec Corporation can be used as a defect detection device comprising the confocal differential interference microscope. The objective lens has a 10x magnification. A threshold for the detection sensitivity of this defect detection device is determined using a standard sample. With this defect detection device, the number of initial defects can be determined. 1 and the second defect 2 to be quantitatively evaluated.

[0021] In particular, the second main surface 12First, the area is divided into a multitude of observed regions. For example, an observed region might be a square area measuring 1.3 mm × 1.3 mm. Images of all observed regions are captured. The image of each observed region is processed using a prescribed procedure to identify defects in the image. Based on the dimensions of the defects, the identified defects are categorized into a first defect category. 1 , second defect 2 and other defects classified. The number of first defects 1 and the second defect 2 in each of the observed areas of the second main surface 12 calculated to determine the number of first defects 1 and the second defect 2 in the entire second main area 12 to determine. (Device for producing a silicon carbide epitaxy substrate)

[0022] Next, a configuration of a device will be performed.200 for the production of a silicon carbide epitaxy substrate 100 as described in the present embodiment.

[0023] According to the representation in Fig. 6 is the device 200 for the production of the epitaxial silicon carbide substrate 100 For example, a CVD (Chemical Vapor Deposition) device of the lateral hot-wall type. The manufacturing device 200 mainly features a reaction chamber 201 , a heating element 203 , a quartz tube 204 , a thermal insulator 205 and an induction heating coil 206 on.

[0024] The heating element 203 For example, it has a cylindrical shape and forms the reaction chamber within it. 201 The heating element 203 It consists, for example, of graphite. The thermal insulator 205 surrounds the outer circumference of the heating element 203 The thermal insulator 205is inside the quartz tube 204 designed to be used with an inner circumferential surface of the quartz tube 204 to come into contact. The induction heating coil 206 is, for example, along an outer circumferential surface of the quartz tube. 204 wound. The induction heating coil 206 is configured to be powered by alternating current from an external power supply (not shown). The heating element 203 This causes it to be inductively heated. As a result, the reaction chamber 201 through the heating element 203 heated.

[0025] The reaction chamber 201 is a space formed by the fact that it is separated from the heating element 203 is surrounded. The silicon carbide single-crystal substrate 10 is in the reaction chamber 201 arranged. The reaction chamber 201 is designed to support the silicon carbide single crystal substrate 10 to heat up. The reaction chamber 201is equipped with a susceptor 210 equipped to process the silicon carbide single crystal substrate 10 to hold. The susceptor 210 is configured so that it rotates around an axis of rotation 212 turns.

[0026] The manufacturing device 200 has a gas inlet opening 207 and a gas outlet opening 208 open. The gas outlet opening 208 is connected to an air release pump (not shown). In Fig. 6 give arrows 6 a gas flow. Gas enters through the gas inlet opening. 207 into the reaction chamber 201 introduced and through the gas outlet opening 208 expelled. Pressure in the reaction chamber 201 is established by an equilibrium between the amount of gas supplied and the amount of gas expelled.

[0027] The manufacturing device 200features a gas supply unit (not shown) designed to supply a gas mixture comprising, for example, silane, ammonia, hydrogen and propane to the reaction chamber 201 to supply. In particular, the gas supply unit may include 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 or a gas mixture of ammonia gas and nitrogen gas.

[0028] In an axial direction of the reaction chamber 201 can the winding density of the induction heating coil 206 The turns density [number / m] refers to the number of turns of the coil per unit length in the axial direction of the device. For example, the turns density of the induction heating coil 206 on the upstream side be higher than the winding density of the induction heating coil206 on the downstream side, in order to effectively thermally decompose ammonia on the upstream side. (Method for the production of a silicon carbide epitaxy substrate)

[0029] Next, a method for producing the epitaxial silicon carbide substrate according to the present embodiment is described.

[0030] First, a preparatory step is performed for a silicon carbide single crystal substrate ( S11 : Fig. 7) is carried out. For example, a silicon carbide single crystal with a polytype of 4H is prepared by sublimation. Then the silicon carbide single crystal is cut, for example, with a wire saw, thereby revealing the silicon carbide single crystal substrate. 10 is produced. The silicon carbide single-crystal substrate 10 includes an n-type impurity, such as nitrogen. The conductivity type of the silicon carbide single-crystal substrate. 10is, for example, of the n-type.

[0031] According to the representation in Fig. 8 shows the silicon carbide single crystal substrate 10 a first main area 11 and a third main area 13 on, which of the first main area 11 opposite. The first main area 11 is a plane that is inclined, for example, at a dislocation angle θ in a dislocation direction relative to the {0001} plane 15. The dislocation direction is, for example, the <11-20> direction. A maximum diameter of the first principal surface 11 of the silicon carbide single crystal substrate 10 For example, 150 mm or more. A threaded screw offset 25 or a carbon inclusion can, for example, be found in the silicon carbide single crystal substrate 10The thread screw dislocation or carbon inclusion often serves as the origin of the first defect, such as a triangular defect. The thread screw dislocation 25 extends in the direction 103 perpendicular to the {0001} plane 15.

[0032] Next, a surface treatment step ( S12 : 7) is carried out. First, the silicon carbide single-crystal substrate is prepared. 10 on the susceptor 210 in the reaction chamber 201 arranged (see Fig. 6) The pressure in the reaction chamber 201 For example, a vacuum pump is used to reduce the pressure from atmospheric pressure to approximately 1 × 10 -3 Pa on 1 × 10 -6 Pa is reduced. After the residual gas, such as atmospheric components and moisture, has entered the reaction chamber... 201 The reduced temperature of the silicon carbide single crystal substrate increases the temperature of the silicon carbide single crystal substrate. 10The reaction chamber is started. Then hydrogen gas is introduced into the reaction chamber. 201 initiated. This, for example, initiates the first main surface. 11 of the silicon carbide single crystal substrate 10 etching is carried out by hydrogen gas. In particular, hydrogen etching is performed, for example, under conditions of a hydrogen gas flow rate of 150 slm, a temperature of 1600°C, and a pressure of 1 × 10 4 Pa and a holding time of 20 minutes. This can remove a pit, which is a threaded screw displacement located in the first main surface. 11 exposed. Instead of or in addition to hydrogen etching, CMP (chemical-mechanical polishing) can be applied to the first main surface. 11 This can be carried out. This can determine the flatness of the first main surface. 11 improve. In particular, the arithmetic mean roughness (Ra) of the first main surface can be improved. 11for example, smaller than 0.1 nm.

[0033] Next, a buffer layer formation step (S13: 7) is performed. After the temperature of the silicon carbide single-crystal substrate 10 Once the temperature has reached at least 1600°C, the reaction chamber 201 For example, a starting material gas, a doping gas, and a carrier gas are supplied. In particular, a gas mixture comprising silane and propane, ammonia, and hydrogen is introduced into the reaction chamber. 201 The respective gases are introduced into the reaction chamber. 201 thermally decomposed, thereby disrupting the buffer layer 21 on the silicon carbide single crystal substrate 10 is formed (see Fig. 9) In the step of forming the buffer layer 21 The susceptor rotates 210 around the axis of rotation 212 The silicon carbide single-crystal substrate 10 rotates around the axis of rotation 212 (see Fig. 6).

[0034] In the buffer layer formation step, the flow rates of ammonia, silane, and propane are adjusted to achieve a (C+N) / Si ratio of 1.0 or less. Specifically, the silane flow rate is set to 96 sccm, for example. The propane flow rate is set to 30.3 sccm, for example. The ammonia flow rate is set to 0.25 sccm. In this case, (C+N) / Si = (30.3 × 3 + 0.25) / 96 = approximately 0.95 is obtained. The concentration of the carbon in the buffer layer is then determined by the specific gravity of the carbon. 21 The number of nitrogen atoms contained is approximately 1×10 18 cm -3 The thickness of the buffer layer 21 For example, it is 0.5 µm. In this way, the buffer layer 21 on the silicon carbide single crystal substrate 10 formed by epitaxial growth.

[0035] Ammonia gas is more likely to undergo thermal decomposition than nitrogen gas, which has a triple bond. Ammonia gas is more likely to be incorporated into silicon carbide than nitrogen gas. If the buffer layer 21 When a similar concentration of nitrogen atoms is formed using nitrogen gas instead of ammonia gas, the nitrogen gas must have a flow rate of approximately 50 sccm. In this case, (C+N) / Si = (30.3 × 3 + 50 × 2) / 96 = approximately 1.99 is obtained.

[0036] The next step involves forming a drift layer ( S14 : Fig. 7) is carried out. A gas mixture comprising silane, propane, ammonia, and hydrogen is introduced into the reaction chamber. 201 supplied while the temperature of the silicon carbide single crystal substrate 10 for example, it is kept at approximately 1640°C. The respective gases are in the reaction chamber. 201thermally decomposed, causing the drift layer 22 on the buffer layer 21 is formed (see Fig. 2 and Fig. 5) In the step of forming the drift layer 22 The susceptor rotates 210 around the axis of rotation 212 The silicon carbide single-crystal substrate 10 rotates around the axis of rotation 212 (see Fig. 6).

[0037] In the drift layer formation step, the flow rates of ammonia, silane, and propane are adjusted to achieve a (C+N) / Si ratio of approximately 1.35. Specifically, the silane flow rate is set to, for example, 140 sccm. The propane flow rate is set to, for example, 63 sccm. The ammonia flow rate is set to 0.07 sccm. In this case, (C+N) / Si = (63 × 3 + 0.07) / 140 = approximately 1.35 is obtained. The concentration in the drift layer 22The number of nitrogen atoms contained is approximately 3 × 10 15 cm -3 The thickness of the drift layer 22 For example, it is 30 µm. In this way, the drift layer 22 on the buffer layer 21 formed by epitaxial growth, resulting in the epitaxial silicon carbide substrate 100 is manufactured.

[0038] If the buffer layer 21 When a similar concentration of nitrogen atoms is formed using nitrogen gas instead of ammonia gas, the nitrogen gas must have a flow rate of approximately 15 sccm. In this case, (C+N) / Si = (63 × 3 + 15 × 2) / 140 = approximately 1.56 is obtained. (Mechanism for suppressing the spread of a defect)

[0039] Next, an estimation mechanism for suppressing the extent of a defect is described.

[0040] During the epitaxial growth of a silicon carbide layer, it is assumed that a nitrogen atom whose size is closer to that of a carbon atom than to that of a silicon atom is more likely to enter a carbon site than a silicon site. A silicon atom, radical, or precursor, compared to a carbon or nitrogen atom, has the property of migrating more easily on a growth surface during step-flow growth. Accordingly, if epitaxial growth is carried out under conditions of a higher ratio of silicon atoms to carbon and nitrogen atoms, satisfactory step-flow growth can be achieved, resulting in a flat growth surface.Conversely, if epitaxial growth is carried out under the condition of a lower ratio of Si atoms to C atoms and N atoms, it is difficult to achieve satisfactory step-flow growth, and it is assumed that step clustering on the growth surface is likely to occur as a result.

[0041] Since ammonia gas, as described above, is more likely to undergo thermal decomposition than nitrogen gas, which has a triple bond, it is probable that nitrogen atoms will be incorporated into a silicon carbide layer. In the case of ammonia gas, a silicon carbide layer with the same nitrogen atom concentration can be formed at a flow rate of approximately one-hundredth that of nitrogen gas. Thus, a higher ratio of silicon atoms to carbon and nitrogen atoms can be achieved when using ammonia gas than when using nitrogen gas. It is therefore assumed that satisfactory step-flow growth can be achieved when using ammonia gas.

[0042] It is assumed that a two-dimensional defect, such as a triangular defect, arises due to a screw dislocation, carbon inclusion, or similar feature. Specifically, the following mechanism is thought to operate: Silicon (Si atoms alone or a radical with Si and hydrogen bonded together) diffuses onto an epitaxial layer surface during film formation, resulting in screw dislocations on the surface. The diffusion of Si at the screw dislocations is inhibited by C and / or N atoms, leading to bonding through interaction. Such bonding does not form 4H-SiC, but rather defects such as 3C-SiC, and these defects each form the core of a two-dimensional defect. That is, each of these defects can contribute to the formation of a triangular defect.By using ammonia gas in the step of forming the buffer layer in an early growth phase (early stage of crystal growth), a buffer layer with a high N atom concentration of about 1 × 10 can be obtained. 11 cm -3The buffer layer can be formed even if the ratio of (C+N) / Si is reduced to approximately 1.0 or less. In other words, the buffer layer can be formed using ammonia gas in a Si-rich state. Thus, satisfactory step-flow growth can be implemented at an early stage of crystal growth, suppressing the two-dimensional expansion of a defect originating from a threaded screw dislocation, carbon inclusion, or the like, present in a silicon carbide single-crystal substrate.Consequently, it is assumed that the probability of a threaded screw dislocation, carbon inclusion, or the like growing into the first defect with a large two-dimensional extent can be reduced, and the probability of a threaded screw dislocation, carbon inclusion, or the like growing into the second defect with a small two-dimensional extent can be increased.

[0043] It is desirable to perform a surface treatment such as hydrogen etching on the surface of the silicon carbide single-crystal substrate before the buffer layer is formed. This can remove a pit originating from a threaded screw dislocation or carbon inclusion that is exposed on the surface of the silicon carbide single-crystal substrate. Consequently, this can further suppress the two-dimensional expansion of a defect originating from a threaded screw dislocation, carbon inclusion, or the like. (Method for the production of a silicon carbide semiconductor device)

[0044] Next, a method for manufacturing a silicon carbide semiconductor device will be described. 300 as described in the present embodiment.

[0045] The method for manufacturing the silicon carbide semiconductor device according to the present embodiment mainly comprises an epitaxial substrate preparation step ( S10 : 10) and a substrate processing step ( S20 : 10) on.

[0046] First, the epitaxial substrate preparation step ( S10 : 10). In particular, the epitaxial silicon carbide substrate is 100 produced using the above-described method for the preparation of the epitaxial silicon carbide substrate (see Fig. 7).

[0047] Next comes the substrate processing step ( S20: 10) is carried out. In particular, the epitaxial silicon carbide substrate is processed, thereby producing a silicon carbide semiconductor device. The "processing" includes various types of processing, such as ion implantation, heat treatment, etching, oxide film formation, electrode formation, and sawing. That is, the substrate processing step can include at least one of the processing types, including ion implantation, heat treatment, etching, oxide film formation, electrode formation, and sawing.

[0048] The following describes a method for fabricating a MOSFET (metal oxide semiconductor field-effect transistor) as an example of a silicon carbide semiconductor device. The substrate processing step ( S20 : Fig. 10) includes an ion implantation step ( S21 : Fig. 10), an oxide film formation step ( S22 : Fig. 10), an electrode formation step ( S23 : Fig. 10) and, for example, a cutting step ( S24 : Fig. 10).

[0049] First, the ion implantation step ( S21 : 10). A p-type impurity such as aluminum (Al) is incorporated into the second main surface. 12 implanted, on which a mask with an opening (not shown) was formed. Consequently, a body area 132 with a p-type conductivity. Then an n-type impurity such as phosphorus (P) is moved to a prescribed position within the body area. 132 implanted. Consequently, a source area is created. 133 with n-type conductivity. Then, a p-type impurity, such as aluminum, is placed in a prescribed position within the source region. 133 implanted. Consequently, a contact area is created. 134 formed with a p-type conductivity (see Fig. 11).

[0050] In the silicon carbide layer20 A different section than the body area serves this purpose 132 , the source area 133 and the contact area 134 as a drift area 131 The source area 133 is through the body area 132 from the drift area 131 separated. Ion implantation can be performed while the epitaxial silicon carbide substrate is in place. 100 It is heated to approximately 300°C or more and 600°C or less. After ion implantation, the epitaxial silicon carbide substrate 100 The anneal is subjected to an activation anneal. The activation anneal activates the silicon carbide layer. 20Implanted impurities are used to create a carrier in each area. The activation anneal is performed, for example, in an argon atmosphere (Ar atmosphere). The activation anneal is performed, for example, at a temperature of approximately 1800°C. The activation anneal is performed, for example, for a period of approximately 30 minutes.

[0051] Next comes the oxide film formation step ( S22 : 10). The epitaxial silicon carbide substrate 100 For example, it is heated in an oxygen-containing atmosphere, resulting in an oxide film. 136 on the second main surface 12 is formed (see Fig. 12) The oxide film 136 It consists, for example, of silicon dioxide. The oxide film 136It acts as a gate insulating film. The thermal oxidation treatment is carried out, for example, at a temperature of approximately 1300°C. The thermal oxidation treatment is carried out, for example, for a period of approximately 30 minutes.

[0052] After the oxide film 136 Once the coating has formed, the heat treatment can continue in a nitrogen atmosphere. For example, heat treatment is carried out in a nitrogen monoxide atmosphere at approximately 1100°C for about one hour. Subsequently, the heat treatment is carried out in an argon atmosphere. For example, heat treatment is carried out in an argon atmosphere at approximately 1100 to 1500°C for about one hour.

[0053] Next comes the electrode formation step ( S23 : 10). A first electrode 141 is applied to the oxide film 136 formed. The first electrode 141acts as a gate electrode. The first electrode 141 is formed, for example, by CVD. The first electrode 141 It consists, for example, of polysilicon with conductivity. The first electrode 141 is trained in a position that corresponds to the source area 133 and the body area 132 is turned towards.

[0054] Next, an insulating intermediate film is applied. 137 formed to form the first electrode 141 to cover. The insulating intermediate film 137 It is formed, for example, by CVD. The insulating interlayer film 137 It consists, for example, of silicon dioxide. The insulating intermediate film 137 comes into contact with the first electrode 141 and the oxide film 136 formed. Then the oxide film is formed. 136 and the insulating intermediate film 137at a prescribed position, it is removed by etching. Consequently, the source area is 133 and the contact area 134 from the oxide film 136 exposed.

[0055] Next, a second electrode will be inserted. 142 formed on this exposed section, for example, by sputtering. The second electrode 142 acts as the source electrode. The second electrode 142 It consists, for example, of titanium, aluminum, and silicon. After the second electrode 142 Once formed, the second electrode is used. 142 and the epitaxial silicon carbide substrate 100 For example, heated to a temperature of approximately 900°C or more and 1100°C or less. Consequently, the second electrode 142 and the epitaxial silicon carbide substrate 100 They are brought into ohmic contact with each other. Then a wiring layer is formed. 138 in contact with the second electrode 142formed. The wiring layer 138 It consists, for example, of a material that includes aluminum.

[0056] Next, a third electrode will be added. 143 on the third main surface 13 formed. The third electrode 143 The third electrode acts as a drain electrode. 143 consists of a compound that includes, for example, nickel and silicon (e.g., NiSi).

[0057] Next comes the division step ( S24 : Fig. 10) carried out. The epitaxial silicon carbide substrate 100 For example, it is cut along the dividing lines, thereby exposing the epitaxial silicon carbide substrate 100 is divided into a large number of semiconductor chips. In this way, the silicon carbide semiconductor device 300 manufactured (see Fig. 13).

[0058] Although the method for fabricating the silicon carbide semiconductor device according to the present invention was described above with reference to a MOSFET as an example, the fabrication method according to the present invention is not limited as such. The fabrication method according to the present invention can be applied to silicon carbide semiconductor devices such as an IGBT (insulated-gate bipolar transistor), an SBD (Schottky barrier diode), a thyristor, a GTO (gate-off thyristor), and a PiN diode.

[0059] It is understood that the embodiment disclosed herein is in every respect illustrative and not limiting. The scope of the present invention is defined by the terms of the claims and not by the embodiment described above, and is intended to include all modifications within the scope and meaning that correspond to the terms of the claims. Reference symbol list

[0060] 1: First defect; 2: Second defect; 10: Silicon carbide single-crystal substrate; 11: First principal face; 12: Second principal face; 13: Third principal face; 14: Fourth principal face; 15: {0001} plane; 16: First flat; 20: Silicon carbide layer; 21: Buffer layer; 22: Drift layer; 25: Threaded screw dislocation; 100: Epitaxial silicon carbide 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: Swell region; 134: Contact region; 136: Oxide film; 137: Insulating interlayer film; 138: Wiring layer; 141 First electrode; 142 Second electrode; 143 Third electrode; 200 Manufacturing apparatus; 201 Reaction chamber; 203 Heating element; 204: Quartz tube; 205: Thermal insulator; 206 Induction heating coil; 207: Gas inlet opening; 208: Gas outlet opening; 210: Susceptor; 212: Rotation axis; 300: Silicon carbide semiconductor device. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] JP 2017015502

[0001]

Claims

[1] Epitaxial silicon carbide substrate comprising: a silicon carbide single-crystal substrate with a first principal surface; and a silicon carbide layer on the first main surface, wherein the silicon carbide layer has a surface in contact with the silicon carbide single crystal substrate and a second main surface opposite the surface, the second principal surface is a plane inclined at a dislocation angle in a dislocation direction relative to a {0001} plane, the second main area has defects and Assuming that a defect satisfying the relations of Formula 1 and Formula 2 is a first defect, where the dislocation angle is θ°, the thickness of the silicon carbide layer in a direction perpendicular to the second principal surface is W µm, the width of the defect in a direction parallel to a direction obtained by projecting the dislocation direction onto the second principal surface is L µm, and the width of the defect in a direction perpendicular to the dislocation direction and parallel to the second principal surface is Y µm, and assuming that a defect with an elongated shape when viewed in the direction perpendicular to the second principal surface and satisfying the relations of Formula 3 and Formula 4 is a second defect, where the width of the defect in a longitudinal direction of the defect is A µm and the width of the defect in a short direction of the defect is B µm,When viewed in the direction perpendicular to the second main surface, then a value obtained by dividing a number of the second defect by a sum of a number of the first defect and the number of the second defect is greater than 0.5: , L Y ≦ 1 0.8 × W tan θ < L < 1.2 × W tan θ 3 < A B L < W tan θ [2] Epitaxial silicon carbide substrate according to claim 1, wherein the thickness of the silicon carbide layer is at least 5 µm and at most 100 µm. [3] Epitaxial silicon carbide substrate according to claim 1 or 2, wherein the dislocation angle is greater than 0° and less than or equal to 8°. [4] Epitaxial silicon carbide substrate according to any one of claims 1 to 3, wherein the value obtained by dividing the number of the second defect by the sum of the number of the first defect and the number of the second defect is greater than 0.

6. [5] Epitaxial silicon carbide substrate according to claim 4, wherein the value obtained by dividing the number of the second defect by the sum of the number of the first defect and the number of the second defect is greater than 0.

7. [6] Epitaxial silicon carbide substrate according to claim 5, wherein the value obtained by dividing the number of the second defect by the sum of the number of the first defect and the number of the second defect is greater than 0.

8. [7] Epitaxial silicon carbide substrate according to claim 6, wherein the value obtained by dividing the number of the second defect by the sum of the number of the first defect and the number of the second defect is greater than 0.

9. [8] Method for manufacturing a silicon carbide semiconductor device, the method comprising: a production of the epitaxial silicon carbide substrate according to any one of claims 1 to 7; and a machining of the epitaxial silicon carbide substrate.