Selection method of silicon carbide substrate, silicon carbide substrate, and silicon carbide epitaxial substrate

Abstract

To provide a SiC substrate and a SiC epitaxial substrate capable of suppressing process errors in transport and suction, and a selection method thereof.SOLUTION: When viewed from above, and the predetermined support region R1 with its center C as the center is supported, a SiC substrate 2 is selected according to the difference in the amount of warping in the two states; i.e., a vertical placement with a three-point reference plane PS aligned along the vertical direction, a horizontal placement with the three-point reference plane PS aligned along a horizontal plane PH. The horizontal plane PH is a plane perpendicular to the vertical direction. The larger absolute values of the change in BOW or WARP between horizontal and vertical placements are used as the warpage evaluation value. In the SiC substrate 2, the warpage evaluation value is equal to or less than a predetermined threshold value set according to the diameter of the substrate.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present disclosure relates to a method for selecting substrates made of silicon carbide (hereinafter referred to as "SiC"), a SiC substrate, and a SiC epitaxial substrate. [Background technology]

[0002] Conventionally, it has been important for SiC substrates and SiC epitaxial substrates having an epitaxial layer laminated on their surfaces to have reduced amounts of warping and bending in order to prevent errors in transportation and adsorption during the manufacturing process of SiC devices. For example, Patent Document 1 proposes a method for reducing the amount of warping in SiC substrates and SiC epitaxial substrates, and a SiC substrate with reduced amount of warping.

[0003] The SiC substrate described in Patent Document 1 has a BOW of less than 40 μm, with the plane connecting the first point that overlaps with the inner support surface in a top view as a reference plane when the substrate is supported on the inner support surface located at a position overlapping with the circumference of a circle with a radius of 17.5 mm from the center. The BOW is the height of the center of the SiC substrate, and is the distance from a three-point reference plane to the center, and is a positive value if the center is above the three-point reference plane and a negative value if the center is below the three-point reference plane. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 7258277 Summary of the Invention [Problem to be solved by the invention]

[0005] However, as a result of intensive research by the present inventors, it has been found that the SiC substrate described in Patent Document 1 may not be sufficient in suppressing process errors in transportation and suction during the manufacturing process of SiC devices.

[0006] In view of the above, an object of the present disclosure is to provide a method for selecting SiC substrates that can suppress process errors in transportation and adsorption during the manufacturing process of SiC devices, and a SiC substrate and a SiC epitaxial substrate in which such process errors are suppressed. [Means for solving the problem]

[0007] According to one aspect of the present disclosure, a method for selecting substrates made of SiC is a method for selecting substrates made of silicon carbide, comprising the steps of: preparing a plurality of substrates (2, 3) made of silicon carbide; defining a region within a predetermined range from a center (C) of the substrate as a support region (R1); suctioning and holding the support region by a suction jig (J); and determining whether or not the support region is a three-point reference plane (P S ) is vertically aligned, and the surface perpendicular to the vertical direction is the horizontal plane (P H ), a state in which the three-point reference plane is aligned with a horizontal plane is regarded as horizontal placement, the BOW and WARP of the horizontally placed substrate are BOW1 and WARP1, respectively, and the BOW and WARP of the vertically placed substrate are BOW2 and WARP2, respectively, calculating the value of |BOW1-BOW2| and the value of |WARP1-WARP2| as evaluation values ​​of the amount of warping of the substrate, and selecting substrates whose diameter is the substrate diameter and whose larger of the evaluation values ​​is equal to or less than a predetermined threshold value set according to the substrate diameter and whose WARP1 is equal to or less than a predetermined upper limit value set according to the substrate diameter, wherein the substrate is a silicon carbide substrate (2) or a silicon carbide epitaxial substrate (3) having an epitaxial layer (21) laminated on a silicon carbide substrate, and a suction jig having a suction port with a diameter of 5% to 15% of the substrate diameter is used to suction the substrate.

[0008] This makes it possible to select SiC substrates and SiC epitaxial substrates with a small amount of warping and with reduced process errors in transportation and suction during the manufacturing process of SiC devices.

[0009] According to another aspect of the present disclosure, the SiC substrate is a silicon carbide substrate (2) having a diameter within a range of 145 mm to 155 mm, a predetermined region from a center (C) of the silicon carbide substrate that is 5% to 15% of the diameter is defined as a support region (R1), and a three-point reference plane (P S ) is vertically aligned, and the surface perpendicular to the vertical direction is the horizontal plane (P H ), a state in which the three-point reference plane is aligned along a horizontal plane is considered to be horizontal, the BOW and WARP of the horizontally oriented silicon carbide substrate are BOW1 and WARP1, respectively, and the BOW and WARP of the vertically oriented silicon carbide substrate are BOW2 and WARP2, respectively, and the larger of the value of |BOW1-BOW2| and the value of |WARP1-WARP2| is 60 μm or less.

[0010] This results in a SiC substrate with less warping and reduced process errors in transportation and adsorption during the manufacturing process of SiC devices. Furthermore, SiC substrates with a WARP1 of 80 μm or less further reduce process errors in transportation and adsorption.

[0011] According to another aspect of the present disclosure, the SiC substrate is a silicon carbide substrate (2) having a diameter within a range of 195 mm to 205 mm, a predetermined region from a center (C) of the silicon carbide substrate that is 5% to 15% of the diameter is defined as a support region (R1), and a three-point reference plane (P S ) is vertically aligned, and the surface perpendicular to the vertical direction is the horizontal plane (P H ), a state in which the three-point reference plane is aligned along a horizontal plane is considered to be horizontal, the BOW and WARP of the horizontally oriented silicon carbide substrate are BOW1 and WARP1, respectively, and the BOW and WARP of the vertically oriented silicon carbide substrate are BOW2 and WARP2, respectively, and the larger of the value of |BOW1-BOW2| and the value of |WARP1-WARP2| is 80 μm or less.

[0012] This results in a SiC substrate with less warping and reduced process errors in transportation and adsorption during the manufacturing process of SiC devices. Furthermore, SiC substrates with a WARP of 100 μm or less further reduce process errors in transportation and adsorption.

[0013] The reference symbols in parentheses attached to each component indicate an example of the correspondence between the component and specific components described in the embodiments described below. [Brief description of the drawings]

[0014] [Figure 1] 4A to 4C are explanatory diagrams of the SiC substrate according to the first embodiment and the adsorption region in the evaluation of the amount of warpage. [Diagram 2] 1A and 1B are cross-sectional views of a SiC substrate and a SiC epitaxial substrate, where (a) is a cross-sectional view of the SiC substrate, and (b) is a cross-sectional view of the SiC epitaxial substrate. [Diagram 3] FIG. 1 is a cross-sectional view showing an example of a SiC single crystal manufacturing apparatus. [Figure 4] FIG. 13 is an explanatory diagram for measuring the amount of warpage of a SiC substrate of a comparative example. [Diagram 5] FIG. 1 is an explanatory diagram of BOW and WARP of a SiC substrate in a horizontally placed state. [Figure 6] FIG. 1 is an explanatory diagram of BOW and WARP of a SiC substrate in a vertically placed state. [Figure 7] FIG. 13 is a diagram showing the relationship between the warp evaluation value and the WARP in a horizontally placed state, and the allowable range of warp. [Figure 8] 1A and 1B are explanatory diagrams illustrating changes in the amount of warpage in the case of a SiC substrate having a first warpage shape in which one surface side is convex in the horizontal and vertical placement states. [Figure 9] 10A and 10B are explanatory diagrams illustrating changes in the amount of warpage in the case of a SiC substrate having a second warpage shape in which one surface side is concave in the horizontal and vertical placement states. [Figure 10] 10 is an explanatory diagram illustrating the change in the amount of warpage in the case of a SiC substrate having a third warpage shape in which one surface is concave when placed vertically and one surface is convex when placed horizontally. FIG. [Figure 11] 10 is an explanatory diagram illustrating a change in the amount of warpage in the case of a SiC substrate having a fourth warpage shape in which one surface side is shaped like a horse's saddle when placed vertically. FIG. [Figure 12] FIG. 13 is a diagram showing the results of investigating the relationship between the evaluation value of the amount of warpage and WARP in a horizontally placed state, and the occurrence or absence of a process error, in a 6-inch diameter SiC substrate. [Figure 13] 13 is a table showing details of the results shown in FIG. 12. [Figure 14] FIG. 13 is a diagram showing the results of investigating the relationship between the evaluation value of the amount of warpage and WARP in a horizontally placed state, and the occurrence or absence of a process error, in an 8-inch diameter SiC substrate. [Figure 15] 15 is a table showing details of the results shown in FIG. 14. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In the following embodiments, parts that are the same or equivalent to each other will be denoted by the same reference numerals.

[0016] (First embodiment) The first embodiment will be described with reference to the drawings.

[0017] [SiC substrate] The SiC substrate 2 of this embodiment is, for example, as shown in FIG. 1, approximately circular when viewed from above, that is, when viewed from the normal direction to the one surface 2a, and is also called a SiC wafer. The SiC substrate 2 is selected as a result of satisfying a predetermined standard by performing an evaluation of the amount of warping described later in a state where a predetermined support region R1 is supported from the center C in the top view. This results in a SiC substrate 2 that suppresses errors in suction / transport when manufacturing a SiC device. The SiC substrate 2 is, for example, as shown in FIG. 2(a), a plate-like shape having one surface 2a and another surface 2b that are in a front-back relationship, with the one surface 2a being a silicon surface and the other surface 2b being a carbon surface. The SiC substrate 2 can be made into a SiC epitaxial substrate 3 by stacking an epitaxial layer 21 on the one surface 2a, for example, as shown in FIG. 2(b). The SiC epitaxial substrate 3 can be called, for example, a SiC epitaxial wafer or a SiC epiwafer. For the SiC epitaxial substrate 3 as well, the amount of warping is evaluated and selected as described below, so that errors in chucking / transporting are suppressed in the same manner as for the SiC substrate 2.

[0018] Note that suction errors include, for example, a situation in which the substrate cannot be sucked and held, or a situation in which the substrate can be sucked and held but the suction force is so weak that the suction position is shifted during transport, etc. Transport errors include, for example, a situation in which the substrate is difficult to transport because it falls off the suction jig, the substrate comes into contact with other members during transport, or a detection error occurs in a sensor used in the device process, etc.

[0019] The SiC substrate 2 and the SiC epitaxial substrate 3 have a diameter of, for example, 6 inches or 8 inches, and in the former case, the diameter is 145 mm or more and 155 mm or less, and in the latter case, the diameter is 195 mm or more and 205 mm or less. The SiC substrate 2 and the SiC epitaxial substrate 3 have a larger diameter, and therefore, in the selection method described below, the SiC substrate 2 and the SiC epitaxial substrate 3 satisfy a standard value according to the diameter size. The SiC substrate 2 and the SiC epitaxial substrate 3 have a thickness of, for example, about 350 μm to 500 μm, but are not limited thereto. When viewed from above, the SiC substrate 2 is supported by the support region R1, which is a region of a predetermined diameter centered on the center C on the other surface 2b. The same applies to the SiC epitaxial substrate 3.

[0020] The support region R1 is, for example, circular with a diameter of 5% to 15% of the diameter of the substrates 2 and 3. The support region R1 has a diameter of 5% or more of the substrate diameter to enable adsorption of the substrates 2 and 3. The support region R1 has a diameter of 15% or less of the substrate diameter to prevent the amount of warping in the supported state from becoming excessively small and the evaluation standard for the amount of warping from becoming too lenient.

[0021] Next, a description will be given of an example of a method for manufacturing the SiC substrate 2. The SiC substrate 2 is obtained, for example, by slicing a SiC ingot manufactured using a SiC single crystal manufacturing apparatus shown in FIG.

[0022] The SiC single crystal manufacturing apparatus includes, for example, a bottomed cylindrical container body 10 having an inner wall surface 10a and an inner bottom surface 10b, and a lid body 20 that closes the opening of the container body 10, and includes a hollow, approximately cylindrical crucible 1. The SiC single crystal manufacturing apparatus includes, for example, a crucible 1 made of graphite, a seed crystal 30 made of a SiC crystal substrate attached to the inner surface side of the lid body 20, and a powder raw material 40 of SiC crystal is placed on the inner bottom surface 10b. The SiC single crystal manufacturing apparatus further includes, for example, a heating means such as a heater (not shown) on the outer periphery of the crucible 1, and heats the crucible 1 with the heating means in a reduced pressure atmosphere of an inert gas such as argon, thereby sublimating the powder raw material 40 to generate a sublimation gas. The SiC single crystal manufacturing apparatus supplies sublimation gas of the powder raw material 40 to surface 30a of seed crystal 30, which is set at a slightly lower temperature than the powder raw material 40, and recrystallizes and grows on surface 30a, thereby producing a SiC single crystal 50, i.e., a SiC ingot.

[0023] The SiC single crystal manufacturing apparatus is not limited to the above-mentioned configuration, but may have other known configurations, and the configuration etc. may be modified as appropriate.

[0024] In this way, relatively large internal stress remains in SiC ingots, which are grown using temperature differences. In addition, the impurity concentration incorporated into the SiC ingot is non-uniform, and the SiC ingot has complex internal stress. This non-uniform internal stress is thought to be the cause of various warping of the substrate and errors in the process.

[0025] For example, the SiC wafer is prepared by slicing / shaping an SiC ingot, grinding the cut surface, and polishing the surface with CMP (short for Chemical Mechanical Polishing) to reduce / remove the damaged surface layer. The SiC substrate 2 and the SiC epitaxial substrate 3 are, for example, SiC wafers selected from the multiple SiC wafers prepared by the above process using the following method, and are capable of suppressing suction / transport errors.

[0026] [Evaluation of board warpage] First, we will explain WARP, which is one of the evaluation indices for the warp and deflection of a substrate. In this substrate selection method, BOW and WARP are measured. WARP is a three-point reference plane P shown in Figure 5. S The distance from the highest point on the three-point reference plane P S The sum of the distance from the top to the lowest point below is always a positive value.

[0027] For ease of explanation, the direction along the thickness direction of the SiC substrate 2 from the other surface 2b to the one surface 2a will be referred to as "upper", and the direction from the one surface 2a to the other surface 2b will be referred to as "lower". This also applies to the SiC epitaxial substrate 3.

[0028] 3-point reference plane P S 1, for example, it is a plane that passes through points P1, P2, and P3 that are located 3% of the substrate diameter inward from the outer periphery in top view and are equidistant from the center C. For example, when viewed from top, the direction from the center C toward point P1 is defined as 0°, and point P2 is located in a direction rotated 120° clockwise from the 0° direction around the center C as an axis, and point P3 is located in a direction rotated another 120° clockwise from the direction of point P2 around the center C as an axis.

[0029] The BOW is a three-point reference plane P with center C. S The height from the center C is the three-point reference plane P S If the center C is above the three-point reference plane P, the value is positive. S If it is below, the value is negative.

[0030] BOW and WARP are one of the evaluation criteria for substrate warpage. For example, BOW and WARP are used as evaluation criteria when selecting substrates that suppress pickup / transport errors in the device manufacturing process from multiple substrates cut from a SiC ingot.

[0031] For example, in the method of selecting substrates in the comparative example, as shown in FIG. HAs the horizontal plane P H A pedestal having a horizontal plane P H In this selection method, the SiC substrate 100 is placed on the horizontal plane P H The WARP immediately before being placed on the horizontal plane P is designated as WARP-A. H If the WARP after placement is designated as WARP-B, then WARP-B is used in the evaluation of warpage. Note that the standard value of WARP-B in this selection method is appropriately set according to the substrate diameter of the SiC substrate 100, for example, 60 μm or less when the substrate diameter is 6 inches, and 85 μm or less when the substrate diameter is 8 inches.

[0032] However, in this case, when the SiC substrate 100 is placed on the pedestal, it bends toward the pedestal due to the influence of gravity, and WARP-B becomes smaller than WARP-A. In other words, this selection method uses a WARP-B value in which the warp of the SiC substrate 100 is reduced more than the actual warp, and thus includes SiC substrates 100 in which the suppression of adsorption / transportation errors is insufficient. In this selection method, the same thing occurs when the BOW value is used as the evaluation criterion.

[0033] In Figure 4, the outline of SiC substrate 100 immediately before it is placed on the pedestal is shown by a dashed line, SiC substrate 100 after it has been placed on the pedestal is shown by a solid line, and the direction of change in shape of SiC substrate 100 due to being placed on the pedestal is shown by a hollow arrow.

[0034] Also, as in the method described in Patent Document 1, a portion of the SiC substrate 100 that is a predetermined distance from the center is supported by a circular jig in a top view, and the SiC substrate 100 is not directly placed on a pedestal, and WARP and BOW are evaluated using the values. However, even with such a support method, it is not possible to prevent the SiC substrate 100 from warping smaller than the actual warp due to gravity, and SiC substrates 100 that cause suction / transport errors may be selected.

[0035] There are various methods for measuring warpage, such as optical interference and capacitance methods, but the method is not particularly limited.

[0036] [Substrate selection method] Next, the method for selecting substrates according to this embodiment will be described using the selection of SiC substrates 2 as a representative example, but the same applies to the selection of SiC epitaxial substrates 3.

[0037] The selection method for SiC substrates 2 according to this embodiment uses, as one of the evaluation criteria, the difference between BOW and WARP in a supported state in which the amount of warping changes significantly due to the influence of gravity, and BOW and WARP in a supported state in which the amount of warping changes very little due to the influence of gravity.

[0038] Specifically, in this selection method, as shown in FIG. 5, while supporting the support region R1 of the SiC substrate 2 with a jig J, a three-point reference plane P S But in the vertical direction D V A horizontal plane P perpendicular to H The bow and warp are measured as the support state along the three-point reference plane P. For example, a suction jig connected to a vacuum source (not shown) that suctions and holds the SiC substrate 2 by vacuuming can be used as the jig J. Hereinafter, the above support state is referred to as "horizontal placement" for convenience, but it can also be referred to as "horizontal placement." The bow and warp of the SiC substrate 2 in the horizontal placement are referred to as BOW1 and WARP1, respectively. The horizontal placement is, for example, S and horizontal plane P H The angle between the two points is the inclination angle, and the inclination angle is 10° or less. In other words, the three-point reference plane P S and horizontal plane P H The horizontal placement corresponds to the above-mentioned "support state in which the change in the amount of warping due to the influence of gravity is large."

[0039] In addition, in the present selection method, as shown in FIG. 6, while supporting the support region R1 of the SiC substrate 2 with a jig J, a three-point reference plane P S But in the vertical direction D VThe bow and warp are measured in a supported state along the three-point reference plane P. Hereinafter, this supported state is referred to as "vertical placement" for convenience, but may also be referred to as "vertical placement." The bow and warp of the SiC substrate 2 in the vertical placement are referred to as BOW2 and WARP2, respectively. The vertical placement is, for example, S and horizontal plane P H The inclination angle between the three-point reference plane P and the S and horizontal plane P H The vertical orientation corresponds to the above-mentioned "support state in which there is almost no change in the amount of warping due to the influence of gravity."

[0040] 5 and 6 show horizontal and vertical orientations of the SiC substrate 2 and BOW1, WARP1, BOW2, and WARP2 as representative examples, but the same applies to the selection of the SiC epitaxial substrate 3.

[0041] Here, the causes of substrate warpage are mainly three: internal strain of the substrate, processing effects, and gravity. Internal strain is caused by internal stress due to the distribution of various dislocation defects and impurity concentration that occurs during the manufacture of SiC ingots. Processing effects are caused by mechanical processing such as cutting SiC ingots and polishing the cut surfaces, and are caused by damage to the surface of the substrate due to processing. Gravity effects are deformation due to the weight of the substrate itself.

[0042] The inventors have noticed that the warpage due to the internal distortion and processing influence of the substrate is hardly affected whether the SiC substrate 2 is placed horizontally or vertically, while the warpage due to gravity is negligibly small in the vertical position, but large in the horizontal position. Specifically, the warpage of the substrate is caused by two factors, internal distortion and processing influence, in the vertical position, and by three factors, internal distortion, processing influence, and gravity, in the horizontal position. Therefore, by checking the difference in the amount of warpage between the horizontal position and the vertical position, the change in the warpage due to the gravity factor of the substrate can be estimated. In addition, by estimating the change in the warpage due to the gravity factor, it is possible to more accurately predict the amount of warpage due to other processes such as ion implantation in the manufacturing process of SiC devices. As a result, it is possible to select SiC substrates 2 whose warpage is expected to be equal to or less than a predetermined amount, and to prevent the occurrence of suction / transport errors during the manufacturing process of SiC devices.

[0043] In the method for selecting SiC substrates 2 according to this embodiment, first, BOW1 and WARP1 of horizontally placed SiC substrates 2 and BOW2 and WARP2 of vertically placed SiC substrates 2 are measured. Then, the absolute value of the amount of change in BOW between horizontal and vertical placement is taken as ΔBOW, and the absolute value of the amount of change in WARP between horizontal and vertical placement is taken as ΔWARP, and ΔBOW and ΔWARP expressed by the following formulas (1) and (2) are calculated as evaluation values ​​of warpage.

[0044] ΔBOW = |BOW1-BOW2| (1) ΔWARP = |WARP1 - WARP2| (2) Next, for example, the larger of ΔBOW and ΔWARP is taken as the warpage evaluation value, and a first determination is made as to whether the warpage evaluation value is equal to or less than a predetermined threshold value α according to the substrate diameter of the SiC substrate 2. For example, this predetermined threshold value α is preset to a value at which no suction / transport error occurs according to the substrate diameter, such as 60 μm or less when the substrate diameter of the SiC substrate 2 is 6 inches, and 80 μm or less when the substrate diameter of the SiC substrate 2 is 8 inches.

[0045] In addition, in this selection method, a second determination is made as to whether or not WARP1 of the SiC substrate 2 is equal to or less than a predetermined upper limit value β set according to the substrate diameter. For example, this predetermined upper limit value β is set in advance to a value at which no suction / transport error occurs according to the substrate diameter, such as 80 μm or less when the substrate diameter of the SiC substrate 2 is 6 inches, and 100 μm or less when the substrate diameter of the SiC substrate 2 is 8 inches.

[0046] In this selection method, for example, as shown in Fig. 7, SiC substrates 2 that satisfy the conditions that the warpage evaluation value is equal to or less than the threshold value α and WARP1 is equal to or less than the upper limit value β are selected. In other words, the region where the warpage evaluation value is equal to or less than the threshold value α and WARP1 is equal to or less than the upper limit value β is the allowable range where the suction / transport error can be suppressed. This makes it possible to select SiC substrates 2 that can suppress the suction / transport error with high accuracy.

[0047] The threshold value α and upper limit value β can be determined, for example, by performing suction evaluation on a plurality of substrates for each substrate diameter and checking whether or not suction failure occurs.

[0048] Next, the warpage evaluation values ​​for each warpage shape of the SiC substrate 2 will be described with reference to FIGS.

[0049] 8 to 11, for ease of viewing, the outline of the vertically placed SiC substrate 2 is indicated by a solid line, and the outline of the horizontally placed SiC substrate 2 is indicated by a two-dot chain line. S is the lowest position on the surface 2a as a representative example, and only WARP1, WARP2, and ΔWARP, which are substantially the same as BOW1, BOW2, and ΔBOW, are shown. S1 and the second reference plane P S2They are each indicated by a thick solid line. In FIG. 11, the direction D1 of the arrow on the right side in the figure indicates the direction with the largest upward displacement, and the direction D2 of the arrow on the left side in the figure indicates the direction with the largest downward displacement. The two left and right directions D1 and D2 shown in FIG. 11 are radial directions with a virtual straight line passing through the center C along the thickness direction of the SiC substrate 2 as the axis. When viewed from the top as in FIG. 1, the angle formed by the directions D1 and D2 is actually 90°. For example, if the azimuth of the direction D1 is 0°, the azimuth of the direction D2 is 90°.

[0050] First, for example, as shown in FIG. 8, when the SiC substrate 2 has a warped shape (hereinafter referred to as "convex warp") that is uniformly warped with one surface 2a being convex about the center C in the vertical position, when the SiC substrate 2 is placed horizontally, the ends are deformed so as to drop downward due to gravity. In the case of convex warp, since ΔWARP is such that WARP1 > WARP2, it is the value obtained by subtracting WARP2 from WARP1. Also, since ΔBOW is such that both BOW1 and BOW2 are positive values and BOW1 > BOW2, it is the value obtained by subtracting BOW2 from BOW1. Therefore, in the case of convex warp, the warp evaluation value is the larger value of the formulas (1) and (2).

[0051] Next, for example, as shown in FIG. 9, consider the case where the SiC substrate 2 has a warped shape (hereinafter referred to as "concave warp") that is uniformly warped with one surface 2a being concave about the center C in the vertical position. In this case, assume that the SiC substrate 2 remains in the concave warp even when placed horizontally. At this time, when the SiC substrate 2 is placed horizontally, the ends drop downward due to gravity and the warp becomes smaller, and BOW and WARP become smaller than when in the vertical position. In such a case of concave warp, ΔWARP is the absolute value of the value obtained by subtracting WARP2 from WARP1. Also, since BOW1 and BOW2 are both negative values and BOW2 < BOW1, ΔBOW is the absolute value of the value obtained by subtracting BOW2 from BOW1. Therefore, in the case of concave warp in both the vertical and horizontal positions, the warp evaluation value is the larger value of the formulas (1) and (2).

[0052] 10, for example, consider a case where the SiC substrate 2 exhibits concave warpage when placed vertically, but exhibits convex warpage when placed horizontally. In this case, ΔWARP=|WARP1-WARP2| is evaluated to be smaller than the amount of change in the original warpage of the SiC substrate 2. Specifically, the amount of change in the original warpage is the absolute value of the sum of WARP1 and WARP2, as shown in equation (3).

[0053] Change in warp = |WARP1 + WARP2| (3) On the other hand, ΔBOW is the same as formula (1) because BOW1 is a positive value and BOW2 is a negative value. In this case, ΔBOW is larger than ΔWARP, and ΔBOW is adopted as the warpage evaluation value. Therefore, in the case of concave warpage in vertical placement and convex warpage in horizontal placement, the warpage evaluation value is the value expressed by formula (1).

[0054] Also, as shown in FIG. 11, for example, a case will be considered where the SiC substrate 2 has a warped shape in which, when placed vertically, one end of one surface 2a in direction D1 is located above the center C, and the other end in direction D2 rotated 90° from the one end is located below the center C. Hereinafter, for ease of explanation, the warped shape shown in FIG. 11 will be referred to as a "horse saddle shape." For example, when placed horizontally, the horse saddle shaped SiC substrate 2 has an end that deforms downward due to gravity, resulting in a shape close to a convex warp with one end located below the center C and the other end located even further below the one end. In FIG. 11, the three-point reference plane in the horizontal position is a first reference plane P S1 The BOW is BOW1. Similarly, the three-point reference plane in the vertical position is the second reference plane P S2 and the BOW is BOW2. At this time, ΔBOW is the value calculated by equation (1).

[0055] On the other hand, ΔWARP=|WARP1-WARP2| is the difference between "Δhorizontal" and "Δvertical" shown in Fig. 11. The difference between "Δhorizontal" and "Δvertical" cannot be determined in general because it depends on the size and the degree of deformation of the convex warped part and concave warped part of the horse saddle-shaped SiC substrate 2. Therefore, the larger of ΔBOW and ΔWARP should be used as the warpage change amount for the warpage evaluation value.

[0056] Therefore, in the case of any of the above-mentioned warpage shapes, the SiC substrate 2 is selected such that the larger of the warpage evaluation values ​​calculated by formula (1) or (2) is equal to or smaller than the predetermined threshold value α. Even if the warpage evaluation value, i.e., the amount of warpage due to gravity, is small, when the warpage due to the internal distortion or processing effect of the substrate is equal to or larger than a predetermined value, a suction / transport error may occur. Therefore, the SiC substrate 2 is selected such that the WARP1 is equal to or smaller than the predetermined upper limit value β.

[0057] [Example] Next, an example of evaluation of warpage of the SiC substrate 2 will be described.

[0058] Twenty SiC substrates with a diameter of 6 inches were prepared, and the BOW, WARP and warpage evaluation values ​​in both vertical and horizontal positions were measured by laser light interference to evaluate whether or not a process error occurred. The results are shown in Figures 12 and 13.

[0059] In Fig. 12, the vertical axis is the warpage evaluation value, and the horizontal axis is WARP1 in horizontal placement. The substrates that did not experience any process errors in any of the steps for device fabrication are plotted with black circles, and the substrates that experienced process errors are plotted with white triangles. The evaluation shown in Fig. 12 was performed with an inclination angle of 90° in vertical placement and 0° in horizontal placement, and the support region R1 was suction-held using a jig J with a suction port that is 10% of the substrate diameter, and the process errors were determined based on whether or not suction failure occurred. The same applies to Fig. 14 described below.

[0060] When the substrate diameter was 6 inches, as shown in FIG. 13, no process errors occurred in Samples No. 1 to No. 11 among the SiC substrates, whereas process errors occurred in Samples No. 12 to No. 20.

[0061] In samples No. 1 to 11, the warpage evaluation value, which is the larger value of ΔBOW and ΔWARP, was in the range of 11 μm to 60 μm, and WARP1 was in the range of 11 μm to 80 μm. On the other hand, in samples No. 12, 14, 15, and 17 to 20, the warpage evaluation value was in the range of 62 μm to 90 μm, and WARP1 was in the range of 9 μm to 90 μm. This result shows that in a SiC substrate with a substrate diameter of 6 inches, a process error is unlikely to occur when the warpage evaluation value is 60 μm or less, and a process error occurs when the warpage evaluation value is at least 62 μm or more. In addition, samples No. 13 and 16 in which a process error occurred had warpage evaluation values ​​of 25 μm and 24 μm, respectively, and WARP1 was 89 μm and 88 μm, respectively. This result shows that even if the warpage evaluation value is a small value below a certain value, a process error cannot be suppressed in a SiC substrate with WARP1 of at least 88 μm or more. From the above results, when the substrate diameter is 6 inches, it is expected that the condition that the warpage evaluation value is 60 μm or less and WARP1 is 80 μm or less is the allowable range in which process errors can be suppressed, so products that satisfy this condition should be selected. In other words, when the substrate diameter is 6 inches, the threshold value α of the warpage evaluation value is 60 μm, and the upper limit value β of WARP1 is 80 μm.

[0062] When the substrate diameter was 8 inches, as shown in FIG. 15, no process errors occurred in Samples Nos. 1 to 12 among the SiC substrates, whereas process errors occurred in Samples Nos. 13 to 20.

[0063] Samples No. 1 to 12 had a warpage evaluation value in the range of 9 μm to 80 μm, and WARP1 in the range of 22 μm to 100 μm. On the other hand, samples No. 14 to 20 had a warpage evaluation value in the range of 83 μm to 103 μm, and WARP1 in the range of 9 μm to 112 μm. This result shows that in a SiC substrate with a substrate diameter of 8 inches, a process error is unlikely to occur when the warpage evaluation value is 80 μm or less, and a process error occurs when the warpage evaluation value is at least 83 μm or more. Sample No. 13, in which a process error occurred, had a warpage evaluation value of 22 μm, and WARP1 was 103 μm. This result shows that even if the warpage evaluation value is a small value below a certain value, a process error cannot be suppressed in a SiC substrate with a WARP1 of at least 103 μm or more.

[0064] From the above results, when the substrate diameter is 8 inches, it is expected that the condition that the warpage evaluation value is 80 μm or less and WARP1 is 100 μm or less is the allowable range in which process errors can be suppressed, so products that satisfy this condition should be selected. In other words, when the substrate diameter is 8 inches, the threshold value α of the warpage evaluation value is 80 μm, and the upper limit value β of WARP1 is 100 μm.

[0065] The evaluation results for a vertical tilt angle of 90° and a horizontal tilt angle of 0° have been described as representative examples, but the results were roughly the same for vertical tilt angles of 70° to 110° and horizontal tilt angles of 10° or less. The above describes the warpage evaluation and selection of SiC substrates 2, but the results were roughly the same for SiC epitaxial substrates 3. For this reason, even if the horizontal tilt angle is not 0° and the vertical tilt angle is not 90°, it is expected that SiC substrates 2 and SiC epitaxial substrates 3 with reduced process errors can be selected as long as the tilt angle is within the above range.

[0066] According to this embodiment, the SiC substrate 2 or the SiC epitaxial substrate 3 is placed horizontally or vertically, the BOW and WARP are measured, and the substrate selection method uses the value with the largest change in the BOW and WARP in each support state as one of the evaluation criteria. This makes it possible to accurately predict the change in the warp caused by gravity. In addition to the warp evaluation value, which is the value with the largest change in the BOW and WARP, this selection method uses WARP1 in the horizontal position as an evaluation criterion to select substrates that satisfy the conditions that the warp evaluation value is equal to or less than the threshold value α and WARP1 is equal to or less than the upper limit value β. This makes it possible to select SiC substrates 2 and SiC epitaxial substrates 3 that can suppress the occurrence of suction / transport errors with higher accuracy than in the past.

[0067] Note that, as the substrate diameter increases, the amount of warpage of the substrate increases, but the allowable range of the amount of warpage that does not cause a process error also changes depending on the size, so the threshold value α of the warpage evaluation value and the upper limit value β of WARP1 are set depending on the substrate diameter. Therefore, even if the substrate diameter is a size other than 6 inches or 8 inches, by setting the threshold value α and the upper limit value β according to the size, it is possible to accurately select SiC substrates 2 and SiC epitaxial substrates 3 that suppress the occurrence of process errors.

[0068] In addition, this selection method measures the inherent warpage of substrates during the SiC device manufacturing process and the amount of warpage deformation due to gravity, and performs selection based on the results, so it can be performed regardless of the thickness of the substrate.

[0069] (Other embodiments) Although the present disclosure has been described based on the embodiment, it is understood that the present disclosure is not limited to the embodiment or structure. The present disclosure also includes various modifications and modifications within the equivalent range. In addition, various combinations and forms, and other combinations and forms including only one element, more than one, or less than one, are also within the scope and concept of the present disclosure.

[0070] In each of the above embodiments, it goes without saying that the elements constituting the embodiment are not necessarily essential, except when it is specifically stated that they are essential or when it is clearly considered essential in principle. In addition, in each of the above embodiments, when the numbers, values, amounts, ranges, etc. of the components of the embodiment are mentioned, they are not limited to the specific numbers, except when it is specifically stated that they are essential or when it is clearly limited to a specific number in principle. In addition, in each of the above embodiments, when the shapes, positional relationships, etc. of the components are mentioned, they are not limited to the shapes, positional relationships, etc., except when it is specifically stated that they are essential or when it is clearly limited to a specific shape, positional relationship, etc. in principle. [Explanation of symbols]

[0071] 2. SiC substrate 2a one side 21 Epitaxial layer 3. SiC epitaxial substrate C Center of the board J Jig P H horizontal plane P S 3-point reference plane R1: A specified area from the center of the SiC substrate

Claims

1. A method for selecting substrates made of silicon carbide, comprising the steps of: preparing a plurality of substrates (2, 3) made of silicon carbide, defining regions within a predetermined range from a center (C) of the substrates as support regions (R1), and holding the support regions by suction with a suction jig (J); The three-point reference plane (P Ｓ The state in which the plane is perpendicular to the vertical direction is called the horizontal plane (P Ｈ ) and the state in which the three-point reference plane is aligned with the horizontal plane is defined as horizontal placement, and the BOW and WARP of the horizontally placed board are defined as BOW1 and WARP1, respectively, and the BOW and WARP of the vertically placed board are defined as BOW2 and WARP2, respectively. calculating the value of |BOW1-BOW2| and the value of |WARP1-WARP2| as evaluation values ​​of the amount of warpage of the substrate; and sorting out the substrates whose diameter is a substrate diameter and whose larger one of the evaluation values ​​is equal to or smaller than a predetermined threshold value set in accordance with the substrate diameter and whose WARP1 is equal to or smaller than a predetermined upper limit value set in accordance with the substrate diameter, The substrate is a silicon carbide substrate (2) or a silicon carbide epitaxial substrate (3) in which an epitaxial layer (21) is stacked on the silicon carbide substrate, In the method for selecting substrates made of silicon carbide, the suction tool having a suction opening with a diameter of 5% to 15% of the diameter of the substrate is used to suction the substrate.

2. 2. The method for selecting silicon carbide substrates according to claim 1, wherein in selecting the substrates, the substrate diameter is 145 mm or more and 155 mm or less, the threshold value is 60 μm or less, and the upper limit value is 80 μm or less.

3. 2. The method for selecting silicon carbide substrates according to claim 1, wherein in selecting the substrates, the substrates having a diameter of 195 mm or more and 205 mm or less, the threshold value being 80 μm or less, and the upper limit value being 100 μm or less are selected.

4. A silicon carbide substrate (2), The diameter is within the range of 145 mm to 155 mm, A predetermined region from the center (C) of the silicon carbide substrate to 5% or more and 15% or less of the diameter is defined as a support region (R1), and a three-point reference plane (P Ｓ The state in which the plane is aligned vertically is called a vertical installation, and the plane perpendicular to the vertical direction is called a horizontal plane (P Ｈ ) and a state in which the three-point reference plane is aligned with the horizontal plane is defined as a horizontal placement, and the bow and warp of the horizontally placed silicon carbide substrate are defined as BOW1 and WARP1, respectively, and the bow and warp of the vertically placed silicon carbide substrate are defined as BOW2 and WARP2, respectively; A silicon carbide substrate in which the larger of the value of |BOW1-BOW2| and the value of |WARP1-WARP2| is 60 μm or less.

5. The silicon carbide substrate according to claim 4 , wherein WARP1 is equal to or less than 80 μm.

6. A silicon carbide substrate (2), The diameter is within the range of 195 mm to 205 mm, A predetermined region from the center (C) of the silicon carbide substrate to 5% or more and 15% or less of the diameter is defined as a support region (R1), and a three-point reference plane (P Ｓ The state in which the plane is perpendicular to the vertical direction is called the horizontal plane (P Ｈ ) and a state in which the three-point reference plane is aligned with the horizontal plane is defined as a horizontal placement, and the bow and warp of the horizontally placed silicon carbide substrate are defined as BOW1 and WARP1, respectively, and the bow and warp of the vertically placed silicon carbide substrate are defined as BOW2 and WARP2, respectively; A silicon carbide substrate in which the larger of the value of |BOW1-BOW2| and the value of |WARP1-WARP2| is 80 μm or less.

7. The silicon carbide substrate according to claim 6 , wherein WARP1 is equal to or less than 100 μm.

8. The silicon carbide substrate according to any one of claims 4 to 7; and an epitaxial layer (21) stacked on one surface (2a) of the silicon carbide substrate.

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