JP2020090436A - Silicon carbide epitaxial substrate and method of manufacturing silicon carbide semiconductor device - Google Patents

Abstract

To provide a silicon carbide epitaxial substrate in which uniformity of carrier concentration in a silicon carbide layer and uniformity of thickness of the silicon carbide layer are improved.SOLUTION: There is provided a silicon carbide epitaxial substrate 100 in which: a silicon carbide layer 20 includes a second principal plane 30 on the side opposite to a surface 14 in contact with a silicon carbide single-crystal substrate 10; the second principal plane 30 has an outer peripheral region 32 which is 5 mm or less away from an outer edge 31 and a center region 33 which is surrounded with the outer peripheral region 32; the silicon carbide layer 20 has a center surface layer 25; an average value of carrier concentration in the center surface layer 25 is 1×10cmto 5×10cm; circumferential uniformity of the carrier concentration is 2% or less; in-plane uniformity of carrier concentration is 10% or less; an average value of thickness of a part 27 of the silicon carbide layer sandwiched between the center region 33 and silicon carbide single-crystal substrate 10 is 5 μm or larger; and circumferential uniformity of thickness is 1% or less and in-plane uniformity of thickness is 4% or less.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a silicon carbide epitaxial substrate and a method for manufacturing a silicon carbide semiconductor device.

Japanese Patent Laying-Open No. 2014-170891 (Patent Document 1) discloses a method of forming a silicon carbide layer on a silicon carbide single crystal substrate by epitaxial growth.

JP, 2014-170891, A

A silicon carbide epitaxial substrate according to the present disclosure includes a silicon carbide single crystal substrate and a silicon carbide layer. The silicon carbide single crystal substrate includes a first main surface. The silicon carbide layer is on the first main surface. The silicon carbide layer includes a second main surface opposite to the surface in contact with the silicon carbide single crystal substrate. The maximum diameter of the second main surface is 100 mm or more. The second main surface has an outer peripheral area within 5 mm from the outer edge of the second main surface and a central area surrounded by the outer peripheral area. The silicon carbide layer has a central surface layer including a central region. The average value of carrier concentration in the central surface layer is 1×10 ¹⁴ cm ⁻³ or more and 5×10 ¹⁶ cm ⁻³ or less. The circumferential uniformity of carrier concentration is 2% or less, and the in-plane uniformity of carrier concentration is 10% or less. The average value of the thickness of the portion of the silicon carbide layer sandwiched between the central region and the silicon carbide single crystal substrate is 5 μm or more. The circumferential uniformity of thickness is 1% or less, and the in-plane uniformity of thickness is 4% or less. The circumferential uniformity of carrier concentration is the ratio of the absolute value of the difference between the maximum and minimum carrier concentrations of the central surface layer in the circumferential direction to the average value of the carrier concentration of the central surface layer in the circumferential direction. The in-plane uniformity of carrier concentration is the ratio of the absolute value of the difference between the maximum value and the minimum value of the carrier concentration of the central surface layer in the entire central region to the average value of the carrier concentration of the central surface layer in the entire central region. .. The circumferential uniformity of thickness is the ratio of the absolute value of the difference between the maximum value and the minimum value of the thickness of the portion in the circumferential direction to the average value of the thickness of the portion in the circumferential direction. The in-plane uniformity of thickness is the ratio of the absolute value of the difference between the maximum value and the minimum value of the thickness of the portion in the entire central region to the average value of the thickness of the portion in the entire central region.

It is a plane schematic diagram which shows the structure of the silicon carbide epitaxial substrate which concerns on this embodiment. It is a cross-sectional schematic diagram which shows the structure of the silicon carbide epitaxial substrate which concerns on this embodiment. It is a plane schematic diagram which shows the measurement position of carrier concentration. It is a figure which shows the method of calculating|requiring carrier concentration by CV method. It is a partial cross section schematic diagram which shows the structure of the susceptor plate of the manufacturing apparatus of the silicon carbide epitaxial substrate which concerns on this embodiment. It is a functional block diagram which shows the structure of the manufacturing apparatus of the silicon carbide epitaxial substrate which concerns on this embodiment. FIG. 2 is a schematic plan view showing the configuration of gas ejection holes of the silicon carbide epitaxial substrate manufacturing apparatus according to the present embodiment. It is a figure which shows the relationship between the rotation speed of a susceptor plate, and time. 7 is a flowchart showing an outline of a method for manufacturing a silicon carbide semiconductor device according to the present embodiment. It is a cross-sectional schematic diagram which shows the 1st process of the manufacturing method of the silicon carbide semiconductor device which concerns on this embodiment. It is a cross-sectional schematic diagram which shows the 2nd process of the manufacturing method of the silicon carbide semiconductor device which concerns on this embodiment. It is a cross-sectional schematic diagram which shows the 3rd process of the manufacturing method of the silicon carbide semiconductor device which concerns on this embodiment.

[Description of Embodiments of the Present Disclosure]
First, an embodiment of the present disclosure will be described. In the following description, the same or corresponding elements will be denoted by the same reference symbols, and the same description will not be repeated. In the crystallographic description of the present specification, individual orientations are indicated by [], collective orientations are indicated by <>, individual planes are indicated by (), and aggregate planes are indicated by {}. The fact that the crystallographic index is negative is usually expressed by adding a "-" (bar) over the number, but in the present specification, the crystallographic index is indicated by adding a negative sign in front of the number. Express the negative index above.

(1) Silicon carbide epitaxial substrate 100 according to the present disclosure includes silicon carbide single crystal substrate 10 and silicon carbide layer 20. Silicon carbide single crystal substrate 10 includes a first main surface 11. Silicon carbide layer 20 is on first main surface 11. Silicon carbide layer 20 includes a second main surface 30 opposite to surface 14 in contact with silicon carbide single crystal substrate 10. The maximum diameter 111 of the second main surface 30 is 100 mm or more. The second main surface 30 has an outer peripheral region 32 within 5 mm from the outer edge 31 of the second main surface 30, and a central region 33 surrounded by the outer peripheral region 32. Silicon carbide layer 20 has a central surface layer 25 including central region 33. The average value of the carrier concentration in the central surface layer 25 is 1×10 ¹⁴ cm ⁻³ or more and 5×10 ¹⁶ cm ⁻³ or less. The circumferential uniformity of carrier concentration is 2% or less, and the in-plane uniformity of carrier concentration is 10% or less. The average value of the thickness of the portion 27 of the silicon carbide layer sandwiched between central region 33 and silicon carbide single crystal substrate 10 is 5 μm or more. The circumferential uniformity of thickness is 1% or less, and the in-plane uniformity of thickness is 4% or less. The circumferential uniformity of carrier concentration is the ratio of the absolute value of the difference between the maximum and minimum carrier concentrations of the central surface layer 25 in the circumferential direction to the average value of the carrier concentration of the central surface layer 25 in the circumferential direction. .. The in-plane uniformity of the carrier concentration is the ratio of the absolute value of the difference between the maximum value and the minimum value of the carrier concentration of the central surface layer 25 in the entire central region to the average value of the carrier concentration of the central surface layer 25 in the entire central region. Is. The circumferential uniformity of thickness is the ratio of the absolute value of the difference between the maximum value and the minimum value of the thickness of the portion 27 in the circumferential direction to the average value of the thickness of the portion 27 in the circumferential direction. The in-plane uniformity of thickness is the ratio of the absolute value of the difference between the maximum value and the minimum value of the thickness of the portion 27 in the entire central region to the average value of the thickness of the portion 27 in the entire central region.

When forming the silicon carbide layer by epitaxial growth, the silicon carbide layer is formed on the silicon carbide single crystal substrate while rotating the silicon carbide single crystal substrate. The silicon carbide layer is formed at a high temperature of about 1600° C., for example. Therefore, it is not possible to employ a mechanism that mechanically rotates silicon carbide single crystal substrate 10 by using a metal such as stainless steel. Therefore, in the epitaxial growth of the silicon carbide layer, a gas foil method is used in which a gas such as hydrogen is used to float the susceptor plate holding the silicon carbide single crystal substrate while rotating the susceptor plate. ..

However, in the case of the gas foil method, for example, deposits such as silicon carbide may adhere to the vicinity of gas ejection holes for ejecting gas onto the susceptor plate. As a result, the gas flow direction, speed, etc. change, and the number of revolutions of the susceptor plate changes. Also, if the shape of the susceptor plate is distorted, the rotation speed will not be stable. Further, as the silicon carbide layer is deposited on the silicon carbide single crystal substrate and the susceptor plate with the lapse of time, the total weight changes, which may change the rotation speed. For the above reasons, it is considered that the rotation speed is not stable in the case of the gas foil method. It is presumed that this is the cause of large variations in the thickness of the silicon carbide layer and the carrier concentration in the silicon carbide layer in the circumferential direction of the silicon carbide single crystal substrate.

Therefore, the inventors have found that it is possible to suppress fluctuations in the rotation speed by monitoring the rotation speed of the silicon carbide single crystal substrate and performing feedback control of the gas flow rate based on the rotation speed. This can improve the uniformity of carrier concentration in the silicon carbide layer and the uniformity of thickness of the silicon carbide layer in the circumferential direction of the silicon carbide single crystal substrate. As a result, the in-plane uniformity of the carrier concentration in the silicon carbide layer and the in-plane uniformity of the thickness of the silicon carbide layer can be improved.

(2) In silicon carbide epitaxial substrate 100 according to (1) above, the maximum diameter may be 150 mm or more.

(3) In silicon carbide epitaxial substrate 100 according to (1) or (2) above, the average value of carrier concentration may be 1×10 ¹⁵ cm ⁻³ or more and 1×10 ¹⁶ cm ⁻³ or less.

(4) In silicon carbide epitaxial substrate 100 according to any of (1) to (3) above, the circumferential uniformity of carrier concentration may be 1% or less.

(5) In silicon carbide epitaxial substrate 100 according to any of (1) to (4) above, the in-plane uniformity of carrier concentration may be 5% or less.

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

[Details of the embodiment of the present disclosure]
Hereinafter, one embodiment of the present disclosure (hereinafter, also referred to as “this embodiment”) will be described. However, the present embodiment is not limited to these.

(Silicon carbide epitaxial substrate)
As shown in FIGS. 1 and 2, silicon carbide epitaxial substrate 100 according to the present embodiment has a silicon carbide single crystal substrate 10 and a silicon carbide layer 20. Silicon carbide single crystal substrate 10 includes a first main surface 11 and a third main surface 13 opposite to first main surface 11. Silicon carbide layer 20 includes a fourth main surface 14 in contact with silicon carbide single crystal substrate 10 and a second main surface 30 opposite to fourth main surface 14. As shown in FIG. 1, silicon carbide epitaxial substrate 100 may have a first flat 5 extending in first direction 101. Silicon carbide epitaxial substrate 100 may have a second flat (not shown) extending in second direction 102. The first direction 101 is, for example, the <11-20> direction. The second direction 102 is, for example, the <1-100> direction.

Silicon carbide single crystal substrate 10 (hereinafter sometimes abbreviated as “single crystal substrate”) is made of silicon carbide single crystal. The polytype of the silicon carbide single crystal is, for example, 4H—SiC. 4H-SiC is superior to other polytypes in electron mobility, breakdown electric field strength, and the like. Silicon carbide single crystal substrate 10 contains an n-type impurity such as nitrogen. The conductivity type of silicon carbide single crystal substrate 10 is, for example, n-type. The first main surface 11 is, for example, a {0001} surface or a surface inclined by 8° or less from the {0001} surface. When the first principal surface 11 is inclined from the {0001} plane, the inclination direction of the normal to the first principal surface 11 is, for example, the <11-20> direction.

Silicon carbide layer 20 is an epitaxial layer formed on silicon carbide single crystal substrate 10. Silicon carbide layer 20 is on first main surface 11. Silicon carbide layer 20 is in contact with first main surface 11. Silicon carbide layer 20 contains an n-type impurity such as nitrogen (N). The conductivity type of silicon carbide layer 20 is, for example, n-type. The concentration of n-type impurities contained in silicon carbide layer 20 may be lower than the concentration of n-type impurities contained in silicon carbide single crystal substrate 10. As shown in FIG. 1, the maximum diameter 111 (diameter) of the second main surface 30 is 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 upper limit of the maximum diameter 111 may be 300 mm, for example.

The second main surface 30 may be, for example, a {0001} surface or a surface inclined by 8° or less from the {0001} surface. Specifically, the second main surface 30 may be a (0001) surface or a surface inclined by 8° or less from the (0001) surface. The inclination direction (OFF direction) of the normal line of second main surface 30 may be, for example, the <11-20> direction. The inclination angle (off angle) from the {0001} plane may be 1° or more, or 2° or more. The off angle may be 7° or less, or 6° or less.

As shown in FIG. 1, the second main surface 30 has an outer peripheral region 32 and a central region 33 surrounded by the outer peripheral region 32. The outer peripheral region 32 is a region within 5 mm from the outer edge 31 of the second main surface 30. In other words, the distance 112 between the outer edge 31 and the boundary between the outer peripheral region 32 and the central region 33 in the radial direction of the second main surface 30 is 5 mm.

As shown in FIG. 2, silicon carbide layer 20 has a buffer layer 21 and a drift layer 24. The concentration of the n-type impurity contained in the drift layer 24 may be lower than the concentration of the n-type impurity contained in the buffer layer 21. The drift layer 24 includes a surface layer region 23 and a deep layer region 22. The surface area 23 constitutes the second major surface 30. The surface layer region 23 has a central surface layer 25 and an outer peripheral surface layer region 19. The central surface layer 25 constitutes the central region 33. The outer peripheral surface area 19 constitutes an outer peripheral area 32. The central surface layer 25 is surrounded by the outer peripheral surface layer region 19 when viewed from a direction perpendicular to the second main surface 30. The central surface layer 25 is an area within 5 μm from the central area 33 toward the first main surface.

The deep region 22 has a central deep region 18 and an outer peripheral deep region 17. When viewed from the direction perpendicular to the second main surface 30, the central deep layer region 18 is surrounded by the outer peripheral deep layer region 17. Similarly, the buffer layer 21 has a central buffer area 16 and an outer peripheral buffer area 15. The central buffer area 16 is surrounded by the outer peripheral buffer area 15 when viewed from the direction perpendicular to the second main surface 30. The central deep region 18 is sandwiched between the central buffer region 16 and the central surface layer 25. Similarly, the outer peripheral deep region 17 is sandwiched between the outer peripheral buffer region 15 and the outer peripheral surface region 19.

Silicon carbide layer 20 is formed of a central silicon carbide region 27 and a peripheral silicon carbide region 26. Central silicon carbide region 27 is composed of central surface layer 25, central deep region 18, and central buffer region 16. Similarly, outer peripheral silicon carbide region 26 is formed of outer peripheral surface layer region 19, outer peripheral deep layer region 17, and outer peripheral buffer region 15.

(Uniformity of carrier concentration in the circumferential direction and in-plane uniformity)
Silicon carbide layer 20 contains, for example, nitrogen as a dopant. According to silicon carbide epitaxial substrate 100 according to the present disclosure, the average value of carrier concentration in central surface layer 25 is 1×10 ¹⁴ cm ⁻³ or more and 5×10 ¹⁶ cm ⁻³ or less. In the central surface layer 25, the carrier concentration uniformity in the circumferential direction is 2% or less, and the carrier concentration in-plane uniformity is 10% or less. Regarding the circumferential uniformity and the in-plane uniformity, the smaller the value, the more uniformly the carrier concentration is distributed. The carrier concentration in this application means the effective carrier concentration. For example, when the silicon carbide layer contains a donor and an acceptor, the effective carrier concentration is calculated as an absolute value (|N _d −N _a |) of the difference between the donor concentration (N _d ) and the acceptor concentration (N _a ). To be done. The method for measuring the carrier concentration will be described later.

In the central surface layer 25, the average value of carrier concentration may be 2×10 ¹⁶ cm ⁻³ or less, or 9×10 ¹⁵ cm ⁻³ or less. The average value of the carrier concentration may be, for example, 1×10 ¹⁵ cm ⁻³ or more, or 5×10 ¹⁵ cm ⁻³ or more.

In the central surface layer 25, the uniformity of carrier concentration in the circumferential direction may be 1.5% or less, 1% or less, or 0.5% or less. The in-plane uniformity of carrier concentration in the central surface layer 25 may be 8% or less, 5% or less, or 3% or less.

Next, a method for measuring the carrier concentration will be described. The carrier concentration is measured by, for example, a mercury probe type CV measuring device. Specifically, one probe is arranged at the measurement position of the central region 33, which will be described later, and the other probe is arranged on the third main surface 13. The area of one probe is, for example, 0.01 cm ² . A voltage is applied between one probe and the other probe and the capacitance between the one probe and the other probe is measured.

As shown in FIG. 3, a plurality of concentric circles 34 centering on the center 35 of the second main surface 30 are assumed. Each of the plurality of concentric circles 34 has a common center 35. As shown in FIG. 3, the measurement position of the carrier concentration can be the hatched position. Specifically, the measurement position of the carrier concentration passes through the center 35, on the straight line 4 parallel to the first direction 101, on the straight line 3 passing through the center 35 and parallel to the second direction 102, and through the center 35. And on a straight line 6 that divides the angle formed by the straight line 4 and the straight line 3 into two equal parts. A line segment that connects the intersection of the straight line 3 with the boundary line between the outer peripheral region 32 and the central region 33 and the center 35 is divided into approximately five equal parts. The position of the intersection of the straight line 3, the straight line 4, and the straight line 6 with the five concentric circles 34 passing through the respective positions where the line segment is divided into five and centered on the center 35 may be the measurement position. As shown in FIG. 3, the carrier concentration is measured at a total of 31 measurement positions in the central region.

As shown in FIG. 3, the outer edge 31 includes the arc portion 7 and the linear first flat 5. The center of a circumscribed circle of a triangle formed by any three points on the arc portion 7 may be the center 35 of the second principal surface 30.

The circumferential uniformity of carrier concentration is the ratio of the absolute value of the difference between the maximum and minimum carrier concentrations of the central surface layer 25 in the circumferential direction to the average value of the carrier concentration of the central surface layer 25 in the circumferential direction. .. Specifically, the average value, the maximum value, and the minimum value of the carrier concentration at eight measurement positions on one concentric circle 34 are obtained, and the circumferential uniformity of the carrier concentration is calculated. According to the silicon carbide epitaxial substrate of the present disclosure, the uniformity of the carrier concentration in the circumferential direction is 2% or less in each of the five concentric circles 34. For example, the average value of the carrier concentration at the above eight measurement positions is 1.00×10 ¹⁶ cm ⁻³ , the maximum value is 1.01×10 ¹⁶ cm ⁻³ , and the minimum value is 0.99×10. ^{In the} case of ¹⁶ cm ⁻³ , the carrier concentration circumferential uniformity is (1.01×10 ¹⁶ cm ⁻³ −0.99×10 ¹⁶ cm ⁻³ )/1.00×10 ¹⁶ cm ⁻³ =2 %.

The in-plane uniformity of the carrier concentration is the ratio of the absolute value of the difference between the maximum value and the minimum value of the carrier concentration of the central surface layer 25 in the entire central region to the average value of the carrier concentration of the central surface layer 25 in the entire central region. Is. Specifically, the average value, the maximum value, and the minimum value of the carrier concentration at the 31 measurement positions are calculated, and the in-plane uniformity of the carrier concentration is calculated. According to the silicon carbide epitaxial substrate of the present disclosure, the in-plane uniformity of carrier concentration is 10% or less. For example, the average value of carrier concentration at the 31 measurement positions is 1.00×10 ¹⁶ cm ⁻³ , the maximum value is 1.05×10 ¹⁶ cm ⁻³ , and the minimum value is 0.95×10 6. ^{In the} case of ¹⁶ cm ⁻³ , the in-plane uniformity of carrier concentration is (1.05×10 ¹⁶ cm ⁻³ −0.95×10 ¹⁶ cm ⁻³ )/1.00×10 ¹⁶ cm ⁻³ =10 %.

As shown in FIG. 4, the vertical axis represents 1/C (reciprocal number of capacitance), the horizontal axis represents V (voltage), and the measurement data 41 is plotted. As the voltage increases, the reciprocal of the capacitance decreases as shown in FIG. The carrier concentration is obtained from the slope of the straight line of the measurement data 41. The larger the absolute value of the slope of the measurement data 41, the higher the carrier concentration. In FIG. 4, the carrier concentration of the substrate indicated by the straight line measurement data 41 is higher than the carrier concentration of the substrate indicated by the broken line measurement data 42. The measurement depth of the carrier concentration depends on the applied voltage. In the present embodiment, the voltage is swept from 0 V to 5 V (voltage V1 in FIG. 4), for example. Thus, the carrier concentration in the central surface layer 25, which is within about 5 μm from the central region 33 toward the first major surface 11, is measured. When the voltage becomes higher than the voltage V1, the carrier concentration in the deeper region is measured.

(Uniformity of thickness of silicon carbide layer in the circumferential direction and in-plane uniformity)
The average value of thickness 113 of the portion of the silicon carbide layer sandwiched between central region 33 and silicon carbide single crystal substrate 10 (that is, central silicon carbide region 27) is 5 μm or more. The average value of the thickness 113 may be 10 μm or more, or 15 μm or more. The circumferential uniformity of thickness is 1% or less, and the in-plane uniformity of thickness is 4% or less. The circumferential uniformity of thickness is the ratio of the absolute value of the difference between the maximum and minimum values of the thickness of central silicon carbide region 27 in the circumferential direction to the average value of the thickness of central silicon carbide region 27 in the circumferential direction. The in-plane uniformity of the thickness is the ratio of the absolute value of the difference between the maximum value and the minimum value of the thickness of central silicon carbide region 27 in the entire central region to the average value of the thickness of central silicon carbide region 27 in the entire central region. is there.

The measurement position of the thickness may be the same as the measurement position of the carrier concentration described above. Specifically, as shown in FIG. 3, the average value, the maximum value, and the minimum value of the thickness of central silicon carbide region 27 at the eight measurement positions on one concentric circle 34 are obtained, The circumferential uniformity of the thickness of central silicon carbide region 27 is calculated. According to the silicon carbide epitaxial substrate of the present disclosure, in each of the five concentric circles 34, the circumferential uniformity of thickness is 1% or less. For example, when the average value of the thickness of central silicon carbide region 27 at the above-mentioned 8 measurement positions is 10.00 μm, the maximum value is 10.05 μm, and the minimum value is 9.95 μm, the thickness is uniform in the circumferential direction. The sex is (10.05 μm-9.95 μm)/10 μm=1%. Similarly, the average value, the maximum value, and the minimum value of the thickness of central silicon carbide region 27 at the above 31 measurement positions are obtained, and the in-plane uniformity of the thickness of central silicon carbide region 27 is calculated. .. When the average value of the thickness of the central silicon carbide region 27 at the 31 measurement positions is 10.0 μm, the maximum value is 10.2 μm, and the minimum value is 9.8 μm, the circumferential uniformity of the thickness is , (10.2 μm-9.8 μm)/10 μm=4%.

(Film forming device)
Next, the configuration of the manufacturing apparatus 200 used in the method for manufacturing the silicon carbide epitaxial substrate 100 according to the present embodiment will be described.

As shown in FIG. 5, the manufacturing apparatus 200 is, for example, a hot wall type CVD (Chemical Vapor Deposition) apparatus. The manufacturing apparatus 200 mainly has a heating element 203, a quartz tube 204, a heat insulating material 205, an induction heating coil 206, and a preheating mechanism 211. The cavity surrounded by the heating element 203 is the reaction chamber 201. Reaction chamber 201 is provided with susceptor plate 210 that holds silicon carbide single crystal substrate 10. The susceptor plate 210 can rotate. Silicon carbide single crystal substrate 10 is placed on susceptor plate 210 with first main surface 11 facing upward.

The heating element 203 is made of graphite, for example. The induction heating coil 206 is wound around the outer circumference of the quartz tube 204. The heating element 203 is induction-heated by supplying a predetermined alternating current to the induction heating coil 206. As a result, the reaction chamber 201 is heated.

The manufacturing apparatus 200 further has a gas inlet 207 and a gas outlet 208. The gas exhaust port 208 is connected to an exhaust pump (not shown). The arrow in FIG. 5 has shown the flow of gas. The carrier gas, the source gas and the doping gas are introduced into the reaction chamber 201 through the gas introduction 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 exhaust amount.

(Feedback control unit)
As shown in FIG. 6, the manufacturing apparatus 200 may further include a tachometer 51, a controller 52, an MFC (Mass Flow Controller) 53, and a gas supply source 54. The tachometer 51 may be a laser tachometer configured to be able to monitor the number of revolutions of the silicon carbide single crystal substrate 10 (in other words, the number of revolutions of the susceptor plate 210) using, for example, laser light. .. Revolution counter 51 may monitor the rotation speed of silicon carbide single crystal substrate 10 with reference to first flat 5 of silicon carbide single crystal substrate 10. The tachometer 51 is arranged at a position facing the first main surface 11.

The heating element 203 has a recess 68. The recess 68 is composed of a bottom surface 62 and a side surface 67. A gas ejection hole 63 is provided on the bottom surface 62. The gas ejection hole 63 communicates with the flow path 64 provided in the heating element 203. The gas supply source 54 is configured to be able to supply a gas such as hydrogen to the flow path 64. The MFC 53 is provided between the gas supply source 54 and the flow path 64. The MFC 53 is configured to control the flow rate of gas supplied from the gas supply source 54 to the flow path 64. The gas supply source is a gas cylinder capable of supplying an inert gas such as hydrogen or argon.

As shown in FIG. 7, the bottom surface 62 is provided with a plurality of gas ejection holes 63. The gas ejection holes 63 may be provided at, for example, 0°, 90°, 180°, and 270° positions when viewed from the direction perpendicular to the bottom surface 62. Each of the plurality of gas ejection holes 63 is configured to eject gas along the circumferential direction of the bottom surface 61 of the susceptor plate 210. When viewed from a direction parallel to the bottom surface 62 (in the field of view of FIG. 6), the direction of the gas ejected from the gas ejection holes 63 may be inclined with respect to the bottom surface 61. 6 and 7, the direction of the arrow indicates the direction of gas flow. The gas is sprayed onto bottom surface 61, so that susceptor plate 210 floats and rotates in the circumferential direction 103 of silicon carbide single crystal substrate 10. The susceptor plate 210 rotates in the circumferential direction 103 with the bottom surface 61 of the susceptor plate 210 separated from the bottom surface 62 of the recess 68 and the side surface 65 of the susceptor plate 210 separated from the side surface 67 of the recess 68.

Control unit 52 is configured to be able to acquire information on the number of revolutions of silicon carbide single crystal substrate 10 measured by revolution counter 51. Control unit 52 is configured to be able to transmit a signal to MFC 53 based on the information on the number of rotations of silicon carbide single crystal substrate 10. For example, when the rotation speed of the susceptor plate 210 is lower than the desired rotation speed, the control unit 52 sends a signal to the MFC 53 to increase the flow rate of the gas supplied to the flow path 64. As a result, the flow rate of the gas supplied from the gas supply source 54 to the flow path 64 increases. As a result, the rotation speed of silicon carbide single crystal substrate 10 increases. On the contrary, when the rotation speed of the susceptor plate 210 is higher than the desired rotation speed, the control unit 52 sends a signal to the MFC 53 to decrease the flow rate of the gas supplied to the flow path 64. As a result, the flow rate of the gas supplied from the gas supply source 54 to the flow path 64 decreases. As a result, the rotation speed of silicon carbide single crystal substrate 10 is reduced.

That is, the flow rate of the gas introduced into flow path 64 is adjusted based on the number of revolutions of silicon carbide single crystal substrate 10 detected by revolution counter 51. In other words, the revolution counter 51, the controller 52, and the MFC 53 form a feedback circuit. Thereby, the change in the rotation speed of silicon carbide single crystal substrate 10 can be suppressed. As a result, it is possible to improve the uniformity of carrier concentration in the circumferential direction of the second main surface 30.

Usually, the susceptor plate 210 and the single crystal substrate 10 are arranged in the approximate center in the axial direction of the reaction chamber 201. As shown in FIG. 5, in the present disclosure, the susceptor plate 210 and the single crystal substrate 10 may be arranged on the downstream side of the center of the reaction chamber 201, that is, on the gas exhaust port 208 side. This is because the decomposition reaction of the raw material gas is sufficiently advanced before the raw material gas reaches the single crystal substrate 10. This is expected to make the distribution of the C/Si ratio uniform in the plane of the single crystal substrate 10.

(Preheating mechanism)
It is desirable that the dopant gas, ammonia gas, be sufficiently heated and thermally decomposed in advance before being supplied to the reaction chamber 201. Thereby, it can be expected that in-plane uniformity of nitrogen concentration (carrier concentration) in silicon carbide layer 20 is improved. As shown in FIG. 5, a preheating mechanism 211 is provided on the upstream side of the reaction chamber 201. The preheating mechanism 211 can preheat the ammonia gas. The preheating mechanism 211 includes a room heated to, for example, 1300° C. or higher. The ammonia gas is sufficiently thermally decomposed when passing through the inside of the preheating mechanism 211, and then supplied to the reaction chamber 201. With this configuration, the ammonia gas can be pyrolyzed without causing a large turbulence in the gas flow.

The temperature of the inner wall surface of the preheating mechanism 211 is more preferably 1350° C. or higher. This is to accelerate the thermal decomposition of ammonia gas. In consideration of thermal efficiency, the temperature of the inner wall surface of the preheating mechanism 211 is preferably 1600°C or lower. The preheating mechanism 211 may be integrated with the reaction chamber 201 or may be a separate body. The gas that passes through the inside of the preheating mechanism 211 may be only ammonia gas or may contain other gas. For example, the entire source gas may be passed through the inside of the preheating mechanism 211.

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

First, a silicon carbide single crystal of polytype 6H is manufactured by, for example, a sublimation method. Then, silicon carbide single crystal substrate 10 is prepared by slicing the silicon carbide single crystal with a wire saw, for example. Silicon carbide single crystal substrate 10 has a first main surface 11 and a third main surface 13 opposite to first main surface 11. The first main surface 11 is, for example, a surface inclined by 8° or less from the {0001} surface. As shown in FIGS. 5 and 6, silicon carbide single crystal substrate 10 is arranged in recess 66 of susceptor plate 210 such that first main surface 11 is exposed from susceptor plate 210. Next, using manufacturing apparatus 200 described above, silicon carbide layer 20 is formed on silicon carbide single crystal substrate 10 by epitaxial growth.

For example, after the pressure in reaction chamber 201 is reduced from atmospheric pressure to about 1×10 ⁻⁶ Pa, the temperature rise of silicon carbide single crystal substrate 10 is started. Hydrogen (H ₂ ) gas, which is a carrier gas, is introduced into the reaction chamber 201 during the temperature rise.

After the temperature in the reaction chamber 201 reaches, for example, about 1600° C., the source gas and the doping gas are introduced into the reaction chamber 201. The source gas contains a Si source gas and a C source gas. As the Si source gas, for example, silane (SiH ₄ ) gas can be used. As the C source gas, for example, propane (C ₃ H ₈ ) gas can be used. The flow rates of the silane gas and the propane gas are, for example, 46 sccm and 14 sccm. The volume ratio of silane gas to hydrogen is, for example, 0.04%. The C/Si ratio of the source gas is 0.9, for example.

As the doping gas, for example, ammonia (NH ₃ ) gas is used. Ammonia gas is more likely to be thermally decomposed than nitrogen gas having a triple bond. The use of ammonia gas can be expected to improve the in-plane uniformity of carrier concentration. The concentration of ammonia gas with respect to hydrogen gas is, for example, 1 ppm. It is desirable that the ammonia gas be thermally decomposed in advance by the preheating mechanism 211 before being introduced into the reaction chamber 201. Ammonia gas is heated to, for example, 1300° C. or higher by the preheating mechanism 211.

The silicon carbide layer 20 is epitaxially grown on the silicon carbide single crystal substrate 10 by introducing the carrier gas, the source gas and the doping gas into the reaction chamber 201 while the silicon carbide single crystal substrate 10 is heated to about 1600° C. Is formed by. While the silicon carbide layer 20 is epitaxially grown, the susceptor plate 210 is rotating around the rotating shaft 212 (see FIG. 5). The average rotation speed of the susceptor plate 210 is, for example, 20 rpm.

As shown in FIG. 6, while silicon carbide layer 20 is formed on silicon carbide single crystal substrate 10 by epitaxial growth, revolution counter 51 monitors the number of revolutions of silicon carbide single crystal substrate 10. Control unit 52 acquires information on the number of revolutions of silicon carbide single crystal substrate 10 measured by revolution counter 51. Control unit 52 transmits a signal to MFC 53 based on the information on the rotation speed of silicon carbide single crystal substrate 10. That is, the flow rate of the gas introduced into flow path 64 is adjusted based on the number of revolutions of silicon carbide single crystal substrate 10 detected by revolution counter 51.

For example, assume that the target rotation speed of the susceptor plate 210 is 20 rpm. For example, when the rotation speed of the susceptor plate 210 becomes lower than 20 rpm by a predetermined value, the control unit 52 sends a signal to the MFC 53 to increase the flow rate of the gas supplied to the flow path 64. As a result, the flow rate of the gas supplied from the gas supply source 54 to the flow path 64 increases. As a result, the rotation speed increases and approaches 20 rpm. On the contrary, when the rotation speed becomes higher than 20 rpm by a predetermined value, the control unit 52 sends a signal to the MFC 53 to decrease the flow rate of the gas supplied to the flow path 64. As a result, the flow rate of the gas supplied from the gas supply source 54 to the flow path 64 decreases. As a result, the rotation speed decreases and approaches 20 rpm.

As shown in FIG. 8, the rotation speed of susceptor plate 210 slightly changes from the time when the growth of silicon carbide layer 20 starts to the time when the growth ends. During the step of forming silicon carbide layer 20, the number of revolutions may be alternately increased and decreased repeatedly. The amplitude of the rotation speed may decrease with the passage of time. The rotation speed may converge to a constant value over time. Preferably, the rotation speed of the susceptor plate 210 is controlled to an average rotation speed ±10%. For example, when the average rotation speed is 20 rpm, it is desirable that the rotation speed is controlled to 18 rpm or more and 22 rpm or less during the process of forming silicon carbide layer 20. That is, it is desirable that the maximum rotation speed R2 be 22 rpm or less and the minimum rotation speed R1 be 18 rpm or more. More preferably, the rotation speed of the susceptor plate 210 is controlled to an average rotation speed of ±8%, and even more preferably to an average rotation speed of ±5%. As described above, silicon carbide layer 20 is formed on silicon carbide single crystal substrate 10 by epitaxial growth. Thereby, in the circumferential direction of silicon carbide single crystal substrate 10, the uniformity of carrier concentration in silicon carbide layer 20 and the uniformity of the thickness of silicon carbide layer 20 can be improved. As a result, in-plane uniformity of carrier concentration in silicon carbide layer 20 and in-plane uniformity of thickness of silicon carbide layer 20 can be improved.

(Method for manufacturing silicon carbide semiconductor device)
Next, a method for manufacturing 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. 9) and a substrate processing step (S20: FIG. 9).

First, the epitaxial substrate preparation step (S10: FIG. 9) is performed. Specifically, silicon carbide epitaxial substrate 100 is prepared by the method for manufacturing a silicon carbide epitaxial substrate described above (see FIG. 1 ).

Next, the substrate processing step (S20: FIG. 9) is performed. Specifically, a silicon carbide semiconductor device is manufactured by processing a silicon carbide epitaxial substrate. "Processing" includes various processes such as ion implantation, heat treatment, etching, oxide film formation, electrode formation, and dicing. 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(Metal Oxide Semiconductor Field Effect Transistor) as an example of a silicon carbide semiconductor device is demonstrated. The substrate processing step (S20: FIG. 9) includes an ion implantation step (S21: FIG. 9), an oxide film forming step (S22: FIG. 9), an electrode forming step (S23: FIG. 9) and a dicing step (S24: FIG. 9). including.

First, the ion implantation step (S21: FIG. 9) is performed. A p-type impurity such as aluminum (Al) is implanted into second main surface 30 on which a mask (not shown) having an opening is formed. Thus, body region 132 having p-type conductivity is formed. Then, an n-type impurity such as phosphorus (P) is implanted at a predetermined position in body region 132. As a result, the source region 133 having the n-type conductivity is formed. Next, a p-type impurity such as aluminum is implanted into the source region 133 at a predetermined position. As a result, the contact region 134 having p-type conductivity is formed (see FIG. 10).

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

Next, an oxide film forming step (S22: FIG. 9) is performed. For example, silicon carbide epitaxial substrate 100 is heated in an atmosphere containing oxygen to form oxide film 136 on second main surface 30 (see FIG. 11 ). Oxide film 136 is made of, for example, silicon dioxide (SiO ₂ ). The oxide film 136 functions as a gate insulating film. The temperature of the thermal oxidation treatment may be, for example, about 1300°C. The time for the thermal oxidation treatment may be, for example, about 30 minutes.

After the oxide film 136 is formed, heat treatment may be further performed in a nitrogen atmosphere. For example, the heat treatment may be performed in an atmosphere of nitric oxide (NO), nitrous oxide (N ₂ O), or the like at about 1100° C. for about 1 hour. Further thereafter, heat treatment may be performed in an argon atmosphere. For example, the heat treatment may be performed at 1100 to 1500° C. for about 1 hour in an argon atmosphere.

Next, an electrode forming step (S23: FIG. 9) is performed. The first electrode 141 is formed on the oxide film 136. The first electrode 141 functions as a gate electrode. The first electrode 141 is formed by, for example, the CVD method. The first electrode 141 is made of, for example, polysilicon containing impurities and having conductivity. The first electrode 141 is formed at a position facing the source region 133 and the body region 132.

Next, an interlayer insulating film 137 that covers the first electrode 141 is formed. The interlayer insulating film 137 is formed by, for example, the CVD method. The interlayer insulating film 137 is made of, for example, silicon dioxide or the like. The interlayer insulating film 137 is formed so as to contact the first electrode 141 and the oxide film 136. Next, the oxide film 136 and the interlayer insulating film 137 at predetermined positions are removed by etching. As a result, the source region 133 and the contact region 134 are exposed from the oxide film 136.

For example, the second electrode 142 is formed on the exposed portion by a sputtering method. The second electrode 142 functions as a source electrode. The second electrode 142 is made of, for example, titanium, aluminum, silicon or the like. After second electrode 142 is formed, second electrode 142 and silicon carbide epitaxial substrate 100 are heated at a temperature of, for example, about 900 to 1100°C. Thereby, second electrode 142 and silicon carbide epitaxial substrate 100 come into ohmic contact with each other. Next, the wiring layer 138 is formed so as to be in contact with the second electrode 142. Wiring layer 138 is made of a material containing aluminum, for example.

Next, the third electrode 143 is formed on the third major surface 13. The third electrode 143 functions as a drain electrode. The third electrode 143 is made of, for example, an alloy containing nickel and silicon (for example, NiSi).

Next, a dicing step (S24: FIG. 9) is performed. For example, silicon carbide epitaxial substrate 100 is diced along a dicing line to divide silicon carbide epitaxial substrate 100 into a plurality of semiconductor chips. From the above, silicon carbide semiconductor device 300 is manufactured (see FIG. 12 ).

In the above, the method for manufacturing the silicon carbide semiconductor device according to the present disclosure has been described by taking the MOSFET as an example, but the manufacturing method according to the present disclosure is not limited thereto. The manufacturing method according to the present disclosure is applicable to various silicon carbide semiconductor devices such as an IGBT (Insulated Gate Bipolar Transistor), an SBD (Schottky Barrier Diode), a thyristor, a GTO (Gate Turn Off thyristor), and a PiN diode.

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

3, 4, 6 Straight line 5 First flat 7 Arc part 10 Silicon carbide single crystal substrate 11 First main surface 13 Third main surface 14 Fourth main surface (plane)
15 outer peripheral buffer area 16 central buffer area 17 outer peripheral deep area 18 central deep area 19 outer peripheral surface area 20 silicon carbide layer 21 buffer layer 22 deep area 23 surface area 24 drift layer 25 central surface layer 26 outer peripheral silicon carbide area 27 central silicon carbide area (part)
30 2nd main surface 31 Outer edge 32 Outer peripheral area 33 Central area 34 Concentric circle 35 Center 51 Rotation speed meter 52 Control part 54 Gas supply sources 61, 62 Bottom surface 63 Gas ejection hole 64 Flow path 65, 67 Side surface 68 Recess 100 Silicon carbide epitaxial substrate 101 First Direction 102 Second Direction 103 Circumferential 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 First Electrode 142 Second Electrode 143 Third Electrode 200 Manufacturing Apparatus 201 Reaction chamber 202 Preheating mechanism 203 Heating element 204 Quartz tube 205 Insulating material 206 Induction heating coil 207 Gas inlet port 208 Gas exhaust port 210 Susceptor plate 211 Preheating mechanism 212 Rotating shaft 300 Silicon carbide semiconductor device

Claims (6)

A silicon carbide single crystal substrate including a first main surface,
A silicon carbide epitaxial layer on the first main surface,
The silicon carbide single crystal substrate is composed of a silicon carbide single crystal having a polytype of 4H—SiC,
The silicon carbide epitaxial layer includes a second main surface opposite to a surface in contact with the silicon carbide single crystal substrate,
The dopant of the silicon carbide epitaxial layer is nitrogen,
The maximum diameter of the second main surface is 100 mm or more,
The second main surface has an outer peripheral region within 5 mm from an outer edge of the second main surface, and a central region surrounded by the outer peripheral region,
The silicon carbide epitaxial layer has a central surface layer including the central region,
The central surface layer is a region within 5 μm from the central region toward the first main surface,
The average value of the carrier concentration in the central surface layer is 1×10 ¹⁴ cm ⁻³ or more and 5×10 ¹⁶ cm ⁻³ or less,
The uniformity of the carrier concentration in the circumferential direction is obtained by passing through a position where a line segment that connects the boundary line between the outer peripheral region and the central region and the center of the second main surface is equally divided, and is centered on the center. 2% or less and the in-plane uniformity of the carrier concentration is 10% or less in each of the five concentric circles
The average value of the thickness of the portion of the silicon carbide epitaxial layer sandwiched between the central region and the silicon carbide single crystal substrate is 5 μm or more,
The circumferential uniformity of the thickness is 1% or less in each of the five concentric circles, and the in-plane uniformity of the thickness is 4% or less,
The circumferential uniformity of the carrier concentration is the ratio of the absolute value of the difference between the maximum value and the minimum value of the carrier concentration of the central surface layer in the circumferential direction to the average value of the carrier concentration of the central surface layer in the circumferential direction. Yes,
The in-plane uniformity of the carrier concentration is the difference between the maximum value and the minimum value of the carrier concentration of the central surface layer in the entire central region with respect to the average value of the carrier concentration of the central surface layer in the entire central region. Is the ratio of the absolute value of
The circumferential uniformity of the thickness is the ratio of the absolute value of the difference between the maximum value and the minimum value of the thickness of the portion in the circumferential direction to the average value of the thickness of the portion in the circumferential direction,
The in-plane uniformity of the thickness is a ratio of an absolute value of a difference between the maximum value and the minimum value of the thickness of the portion in the entire central region to the average value of the thickness of the portion in the entire central region. , Silicon carbide epitaxial substrate. The silicon carbide epitaxial substrate according to claim 1, wherein the maximum diameter is 150 mm or more. The silicon carbide epitaxial substrate according to claim 1, wherein the average value of the carrier concentration is 1×10 ¹⁵ cm ⁻³ or more and 1×10 ¹⁶ cm ⁻³ or less. The silicon carbide epitaxial substrate according to claim 1, wherein the carrier concentration has a circumferential uniformity of 1% or less. The silicon carbide epitaxial substrate according to claim 1, wherein the in-plane uniformity of the carrier concentration is 5% or less. A step of preparing the silicon carbide epitaxial substrate according to any one of claims 1 to 5,
A method of manufacturing a silicon carbide semiconductor device, comprising the step of processing the silicon carbide epitaxial substrate.

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