N-type 4h sic single crystal ingots, n-type 4h sic single crystal wafers, methods for manufacturing n-type 4h sic single crystal ingots, and methods for manufacturing n-type 4h sic single crystal wafers

Abstract

To develop a technique related to an n-type 4H-SiC single crystal.SOLUTION: The ratio [N] / [Al] of [N], which is the concentration of N, to [Al], which is the concentration of Al, is 1.5 or more and 3.0 or less, the total of [N] and [Al] is 1.0 * 4H / 1020atoms or less, and the cm3 is 4 inches or more.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an n-type 4H—SiC single crystal ingot, an n-type 4H—SiC single crystal wafer, a method for manufacturing an n-type 4H—SiC single crystal ingot, and a method for manufacturing an n-type 4H—SiC single crystal wafer. [Background technology]

[0002] Related technology is disclosed in Patent Document 1. Patent Document 1 discloses a method for producing n-type SiC single crystals by a solution process. Specifically, Patent Document 1 discloses growing SiC single crystals under production conditions in which both N and Al are doped and the ratio ([N] / [Al]) of the N concentration [N] to the Al concentration [Al] in the SiC single crystal is 1 or more and 50 or less. Note that Patent Document 1 actually discloses only two examples in which the ratio [N] / [Al] is 50. In one of the two examples, [Al] is 4×10 17 cm -3 and [N] is 2×10 19 cm -3 In another embodiment, [Al] is 8×10 17 cm -3 and [N] is 4×10 19 cm -3 is. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-31316 Summary of the Invention [Problem to be solved by the invention]

[0004] An example of the objective of the present disclosure is to develop technology related to n-type 4H—SiC single crystals. [Means for solving the problem]

[0005] According to the present disclosure, Contains N and Al, The ratio of [N] / [Al], which is the ratio of [N], the concentration of N, to [Al], the concentration of Al, is 1.5 or more and 3.0 or less; The sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 is as follows: An n-type 4H-SiC single crystal ingot with a diameter of 4 inches or more is provided.

[0006] Further, according to the present disclosure, Contains N and Al, The ratio of [N] / [Al], which is the ratio of [N], the concentration of N, to [Al], the concentration of Al, is 1.5 or more and 3.0 or less; The sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 is as follows: An n-type 4H—SiC single crystal wafer having a diameter of 4 inches or greater is provided.

[0007] Further, according to the present disclosure, a growth step of contacting a seed crystal with a raw material solution containing Si and C to form a growth layer of n-type 4H—SiC single crystal on the surface of the seed crystal; In the growth step, N and Al are doped into the growth layer, and the ratio of [N], which is the concentration of N in the growth layer, to [Al], which is the concentration of Al, in the growth layer, [N] / [Al], is 1.5 or more and 3.0 or less, and the sum of [N] and [Al] is 1.0×10 20 atoms / cm 3 A method for producing an n-type 4H—SiC single crystal ingot that produces the growth layer is provided under the following conditions:

[0008] Further, according to the present disclosure, There is provided a method for producing an n-type 4H—SiC single crystal ingot by the method for producing an n-type 4H—SiC single crystal ingot, and a method for producing an n-type 4H—SiC single crystal wafer by slicing wafers from the n-type 4H—SiC single crystal ingot. [Effects of the Invention]

[0009] According to one aspect of the present disclosure, technology relating to n-type 4H—SiC single crystal wafers can be advanced. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a diagram for explaining the characteristics of an n-type 4H—SiC single crystal ingot. [Figure 2] FIG. 2 is another diagram for explaining the characteristics of the n-type 4H—SiC single crystal ingot. [Figure 3] FIG. 3 is another diagram for explaining the characteristics of the n-type 4H—SiC single crystal ingot. [Figure 4] FIG. 4 is a diagram showing an outline of an example of a crystal growth apparatus. [Figure 5] FIG. 5 is a diagram showing the evaluation results of Example 1. [Figure 6] FIG. 6 is another diagram showing the evaluation results of Example 1. [Figure 7] FIG. 7 is another diagram showing the evaluation results of Example 1. [Figure 8] FIG. 8 is a diagram showing the evaluation results of Comparative Example 1. [Figure 9] FIG. 9 is another diagram showing the evaluation results of Comparative Example 1. [Figure 10] FIG. 10 is another diagram showing the evaluation results of Comparative Example 1. [Figure 11] FIG. 11 is a diagram for explaining measurement points. [Figure 12] FIG. 12 is a diagram showing the evaluation results of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. In this disclosure, the drawings relate to one or more embodiments. In all drawings, similar components are designated by similar reference numerals, and descriptions thereof will be omitted as appropriate.

[0012] <<First embodiment>> <Problems with the First Embodiment> The solution method has been proposed as a SiC single crystal growth method. Due to its characteristics, the solution method is said to be easier to produce high-quality crystals than the sublimation method, but it also has its challenges. One of these is the issue of resistivity control. It has been reported that adding Al to SiC single crystal growth reduces the terrace width of the growth surface, suppressing heterogeneous polymorphism due to two-dimensional nucleation and maintaining the polymorphism (polymorphism maintenance effect). However, because Al is an acceptor element, it causes an increase in resistivity in n-type SiC single crystal growth. In other words, while the addition of Al achieves the polymorphism maintenance effect, it also creates the problem of increased resistivity. The increase in resistivity can be suppressed by reducing the addition of Al. However, in this case, it becomes difficult to achieve the polymorphism maintenance effect.

[0013] There is a need for a technology that can suppress resistivity increases while realizing the polymorphism-maintaining effect of adding Al element, even for "large-diameter" n-type 4H—SiC single crystals produced by the solution method. Patent Document 1 does not disclose the diameter of the n-type SiC single crystal obtained in the "Examples that satisfy the above-mentioned manufacturing conditions." However, according to the inventors' investigations, the manufacturing conditions disclosed in Patent Document 1 include conditions that make it impossible to achieve both the polymorphism-maintaining effect and the effect of suppressing resistivity increases (resistivity increase suppression effect) when "large-diameter" n-type 4H—SiC single crystals are produced.

[0014] An example of a problem to be solved by the first embodiment is to achieve both the effect of maintaining the polymorphism and the effect of suppressing an increase in resistivity in a technology for growing large-diameter n-type 4H—SiC single crystal by a solution method.

[0015] <N-type 4H—SiC single crystal wafer of the first embodiment> The n-type 4H—SiC single crystal wafer of this embodiment has the following wafer features 1-1 to 1-3. The n-type 4H—SiC single crystal wafer of this embodiment may further have at least one of the following wafer features 1-4 to 1-7.

[0016] "Wafer characteristic 1-1": Contains N and Al, and the ratio [N] / [Al], which is the ratio of the N concentration [N] to the Al concentration [Al], is 1.5 or more and 3.0 or less, 1.7 or more and 2.7 or less, 1.5 or more and 2.0 or less, or 1.7 or more and 2.0 or less "Wafer feature 1-2" The sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 Below, 8.0 x 10 19 atoms / cm 3 Below, 7.0 x 10 19 atoms / cm 3 Below, 6.0 x 10 19 atoms / cm 3 or less, or 5.5 x 10 19 atoms / cm 3 below "Wafer Feature 1-3" Diameter is 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more. There is no particular upper limit to the diameter, but in reality, it is thought that it will be 18 inches or less, or 12 inches or less. "Wafer feature 1-4" Resistivity at the center is 1mΩ·cm or more, 2mΩ·cm or more, 5mΩ·cm or more, 10mΩ·cm or more, 15mΩ·cm or more, 20mΩ·cm or more, or 25mΩ·cm or more "Wafer Characteristics 1-5" Resistivity at the center is 50 mΩ·cm or less, preferably 25 mΩ·cm or less "Wafer Feature 1-6" 4H polymorphism retention rate is 99% or more. By definition, it is 100% or less. "Wafer Characteristics 1-7" Manufactured by solution method

[0017] In addition, [N] is 5.0 × 10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 That is 6.0 x 10 19 atoms / cm 3 Less than or equal to 5.0 × 10 19 atoms / cm 3or less, more preferably 4.5 × 10 19 atoms / cm 3 It is preferable that [Al] is 5.0 × 10 or less. 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 1.5 × 10 19 atoms / cm 3 That is 6.0 x 10 19 atoms / cm 3 Less than 4.0 × 10 19 atoms / cm 3 or less, more preferably 3.0 × 10 19 atoms / cm 3 It is preferable that:

[0018] In addition, in wafer feature 1-2, the sum of [N] and [Al] is 1.0 × 10 19 atoms / cm 3 That's it, 2.0 x 10 19 atoms / cm 3 That's it, 3.0 x 10 19 atoms / cm 3 That's it, 4.0 x 10 19 atoms / cm 3 That's it, 5.0 x 10 19 atoms / cm 3 or more than 6.0 x 10 19 atoms / cm 3 That is, the sum of [N] and [Al] may be 1.0 × 10 19 atoms / cm 3 Over 1.0 x 10 20 atoms / cm 3 may be less than 4.0 x 10 19 atoms / cm 3 Over 6.0 x 10 19 atoms / cm 3 It may be the following:

[0019] [N] and [Al] were measured by secondary ion mass spectrometry in a 6 mm square area centered at the midpoint between the periphery and center of the n-type 4H—SiC single crystal wafer.

[0020] "Resistivity" is a value measured using a non-destructive (eddy current) resistance measuring instrument. Specifically, it is a value measured using a Napson EC-80P. The "resistivity at the center" is measured by contacting the tip of the probe of the resistance measuring instrument with approximately the center of the n-type 4H—SiC single crystal wafer. The resistivity at each location on the n-type 4H—SiC single crystal wafer is also measured by contacting the tip of the probe of the resistance measuring instrument with each location on the n-type 4H—SiC single crystal wafer.

[0021] The "4H polymorphism retention rate" is a value calculated using a digital microscope. First, a transmission image of the n-type 4H-SiC single crystal wafer is taken. The 4H polymorph exhibits a green transmission hue, while heterogeneous polymorphic regions exhibit transmission hues such as blue and yellow. The heterogeneous polymorphic regions are identified based on this difference in transmission hue, and their areas are measured. The "4H polymorphism retention rate" is then calculated using the formula: (total wafer area - total area of ​​heterogeneous polymorphic regions) / (total wafer area) x 100.

[0022] The n-type 4H—SiC single crystal wafer of this embodiment is produced by a solution method, as shown in wafer feature 1-7, yet achieves a large diameter, polymorphism retention effect, and resistivity increase suppression effect, as shown in wafer features 1-3 to 1-6.

[0023] In the n-type 4H—SiC single crystal wafer of this embodiment, the [N] / [Al] and the sum of [N] and [Al] fall within the characteristic numerical ranges described above, as shown in wafer features 1-1 and 1-2. By controlling the [N] / [Al] and the sum of [N] and [Al] to fall within the characteristic numerical ranges described above, the n-type 4H—SiC single crystal wafer of this embodiment, which has wafer features 1-3 to 1-7, can be realized. In other words, by producing an n-type 4H—SiC single crystal wafer by solution processing (wafer feature 1-7) so as to have both wafer features 1-1 and 1-2, it is possible to obtain an n-type 4H—SiC single crystal wafer of this embodiment that has a large diameter, as shown in wafer feature 1-3, yet simultaneously achieves both the polymorphic form retention effect and the resistivity increase suppression effect, as shown in wafer features 1-4 to 1-6.

[0024] Meanwhile, n-type 4H—SiC single crystal wafers produced by the “solution method,” i.e., n-type 4H—SiC single crystal wafers having wafer feature 1-7, tend to have the following wafer features 1-8 and 1-9.

[0025] "Wafer Feature 1-8" The resistivity of the center of the wafer is higher than that of the outer periphery "Wafer Feature 1-9" Resistivity increases monotonically from the periphery to the center within the wafer surface

[0026] As described above, the "resistivity at the center" is measured by contacting the tip of the probe of the resistance measuring instrument with the approximate center of the n-type 4H—SiC single crystal wafer. The "resistivity at the outer periphery" is measured by contacting the tip of the probe of the resistance measuring instrument with the vicinity of the outer periphery of the n-type 4H—SiC single crystal wafer (a position closer to the periphery than the approximate center). Furthermore, the resistivity at multiple points between the center and the outer periphery is measured by contacting the tip of the probe of the resistance measuring instrument with multiple points that are gradually separated from the approximate center of the n-type 4H—SiC single crystal wafer.

[0027] The ratio of the resistivity of the central portion to the resistivity of the peripheral portion may exceed 1 as in wafer feature 1-8, but even in this case it is preferably 3 or less, and more preferably 2 or less.

[0028] It should be noted that while n-type 4H—SiC single crystal wafers manufactured by the “solution method” have the above wafer characteristics 1-8 and 1-9, n-type 4H—SiC single crystal wafers manufactured by the “sublimation method” tend to have the opposite characteristics, such as “the resistivity at the center of the wafer is lower than that at the periphery” and “the resistivity decreases monotonically from the periphery to the center of the wafer.”

[0029] For this reason, n-type 4H—SiC single crystal wafers having wafer characteristics 1-8 and / or 1-9 can be presumed to be wafers manufactured by a solution method rather than a sublimation method. In other words, by checking whether a target n-type 4H—SiC single crystal wafer has wafer characteristics 1-8 and / or 1-9, it can be confirmed whether the n-type 4H—SiC single crystal wafer has wafer characteristic 1-7.

[0030] The n-type 4H—SiC single crystal wafer of this embodiment may be an on-substrate whose surface is the (0001) or (000-1) plane, or an off-substrate whose surface is cut at an angle of 0.5 to 5 degrees relative to the (0001) or (000-1) plane.

[0031] <N-type 4H—SiC single crystal ingot according to the first embodiment> The n-type 4H—SiC single crystal ingot of this embodiment has the following ingot features 1-1 to 1-3. The n-type 4H—SiC single crystal ingot of this embodiment may further have at least one of the following ingot features 1-4 to 1-7.

[0032] "Ingot characteristic 1-1": Contains N and Al, and the ratio of [N] (the concentration of N) to [Al] (the concentration of Al) is 1.5 or more and 3.0 or less, 1.7 or more and 2.7 or less, 1.5 or more and 2.0 or less, or 1.7 or more and 2.0 or less "Ingot Characteristics 1-2" The sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 Below, 8.0 x 10 19 atoms / cm3 Below, 7.0 x 10 19 atoms / cm 3 Below, 6.0 x 10 19 atoms / cm 3 or less, or 5.5 x 10 19 atoms / cm 3 below "Ingot Characteristics 1-3" Diameter is 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more. There is no upper limit to the diameter, but in reality, it is thought that it will be 18 inches or less, or 12 inches or less. "Ingot characteristics 1-4" Resistivity at the center is 1mΩ·cm or more, 2mΩ·cm or more, 5mΩ·cm or more, 10mΩ·cm or more, 15mΩ·cm or more, 20mΩ·cm or more, or 25mΩ·cm or more "Ingot Characteristics 1-5" Resistivity of the center is 50 mΩ·cm or less, preferably 25 mΩ·cm or less "Ingot Characteristics 1-6" 4H polymorphism retention rate is 99% or more. By definition, it is less than 100%. "Ingot Characteristics 1-7" Produced by the solution method

[0033] In addition, [N] is 5.0 × 10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 That is 6.0 x 10 19 atoms / cm 3 Less than or equal to 5.0 × 10 19 atoms / cm 3 or less, more preferably 4.5 × 10 19 atoms / cm 3 It is preferable that [Al] is 5.0 × 10 or less. 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 1.5 × 10 19 atoms / cm 3 That is 6.0 x 1019 atoms / cm 3 Less than 4.0 × 10 19 atoms / cm 3 or less, more preferably 3.0 × 10 19 atoms / cm 3 It is preferable that:

[0034] In ingot feature 1-2, the sum of [N] and [Al] is 1.0 × 10 19 atoms / cm 3 That's it, 2.0 x 10 19 atoms / cm 3 That's it, 3.0 x 10 19 atoms / cm 3 That's it, 4.0 x 10 19 atoms / cm 3 or more than 5.0 x 10 19 atoms / cm 3 That is, the sum of [N] and [Al] may be 1.0 × 10 19 atoms / cm 3 Over 1.0 x 10 20 atoms / cm 3 may be less than 4.0 x 10 19 atoms / cm 3 Over 6.0 x 10 19 atoms / cm 3 It may be the following:

[0035] [N] and [Al] were measured by secondary ion mass spectrometry in a 6 mm square area centered at the midpoint between the periphery and the center of the crystal growth surface (the surface that comes into contact with the raw material solution in the crucible during crystal growth) of an n-type 4H-SiC single crystal ingot.

[0036] The "resistivity" is a value measured using a non-destructive (eddy current) resistance measuring instrument. Specifically, it is a value measured using a Napson EC-80P. The "resistivity at the center" is measured by contacting the tip of the probe of the resistance measuring instrument with approximately the center of the crystal growth surface of an n-type 4H—SiC single crystal ingot.

[0037] The "4H polymorphism retention rate" is the average value of the 4H polymorphism retention rates of two wafers cut from regions within 2 mm from both ends of an n-type 4H-SiC single crystal ingot. If the n-type 4H-SiC single crystal ingot is too thin to cut two wafers using the method described above, the 4H polymorphism retention rate of one of the cut wafers is used as the 4H polymorphism retention rate of the n-type 4H-SiC single crystal ingot. The 4H polymorphism retention rate of each wafer was calculated using a digital microscope, and the details of the calculation method are as described above.

[0038] The "diameter" of an n-type 4H—SiC single crystal ingot is the diameter of a cross section perpendicular to the pulling direction (long axis direction) during crystal growth. In the n-type 4H—SiC single crystal ingot of this embodiment, any cross section perpendicular to the pulling direction (long axis direction) satisfies the requirement that "the diameter is 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more."

[0039] The n-type 4H—SiC single crystal ingot of this embodiment is produced by the solution method as shown in Ingot Feature 1-7, but achieves a large diameter, a polymorphism retention effect, and a resistivity increase suppression effect as shown in Ingot Feature 1-3 to 1-6. Note that, since the solution method enables continuous crystal growth and allows the ingot to be thick, the thickness of the n-type 4H—SiC single crystal ingot is preferably 1 mm or more, 10 mm or more, 5 cm or more, 10 cm or more, or 20 cm or more.

[0040] In the n-type 4H—SiC single crystal ingot of this embodiment, the [N] / [Al] and the sum of [N] and [Al] fall within the characteristic numerical ranges described above, as shown in ingot features 1-1 and 1-2. By controlling the [N] / [Al] and the sum of [N] and [Al] to fall within the characteristic numerical ranges described above, the n-type 4H—SiC single crystal ingot of this embodiment, which has ingot features 1-3 to 1-7, can be realized. In other words, by producing an n-type 4H—SiC single crystal ingot by the solution method (ingot feature 1-7) so as to have both ingot features 1-1 and 1-2, it is possible to obtain an n-type 4H—SiC single crystal ingot of this embodiment that has a large diameter, as shown in ingot feature 1-3, while simultaneously achieving both the polymorphism retention effect and the resistivity increase suppression effect, as shown in ingot features 1-4 to 1-6.

[0041] Incidentally, n-type 4H—SiC single crystal ingots produced by the “solution method,” i.e., n-type 4H—SiC single crystal ingots having ingot feature 1-7, tend to have the following ingot features 1-8 and 1-9.

[0042] "Ingot characteristic 1-8" The resistivity of the center is higher than that of the outer periphery within the cross section at any position perpendicular to the crystal growth surface or the pulling direction (long axis direction). "Ingot characteristic 1-9" Resistivity increases monotonically from the periphery to the center in a cross section at any position perpendicular to the crystal growth surface or the pulling direction (long axis direction).

[0043] As described above, the "center resistivity" is measured by contacting the tip of the probe of the resistance measuring instrument with the approximate center of the cross section of the n-type 4H-SiC single crystal ingot at any position perpendicular to the crystal growth surface or the pulling direction (long axis). The "periphery resistivity" is measured by contacting the tip of the probe of the resistance measuring instrument with the approximate center (a position closer to the periphery than the approximate center) of the cross section of the n-type 4H-SiC single crystal ingot at any position perpendicular to the crystal growth surface or the pulling direction (long axis). The resistivity of multiple points between the center and the periphery is measured by contacting the tip of the probe of the resistance measuring instrument with the approximate center (a position closer to the periphery than the approximate center) of the cross section of the n-type 4H-SiC single crystal ingot at any position perpendicular to the crystal growth surface or the pulling direction (long axis).

[0044] While n-type 4H—SiC single crystal ingots produced by the “solution method” have the above ingot characteristics 1-8 and 1-9, n-type 4H—SiC single crystal ingots produced by the “sublimation method” tend to have the opposite characteristics, such as “the resistivity is lower in the center than in the outer periphery within a cross section at any position perpendicular to the crystal growth surface or the pulling direction (long axis)” and “the resistivity monotonically decreases from the outer periphery to the center within a cross section at any position perpendicular to the crystal growth surface or the pulling direction (long axis).”

[0045] Therefore, an n-type 4H—SiC single crystal ingot having ingot characteristics 1-8 and / or 1-9 can be presumed to have been produced by a solution method rather than a sublimation method. In other words, by checking whether a target n-type 4H—SiC single crystal ingot has ingot characteristics 1-8 and / or 1-9, it can be determined whether the n-type 4H—SiC single crystal ingot has ingot characteristic 1-7.

[0046] Furthermore, the n-type 4H—SiC single crystal ingot of this embodiment can further have the following ingot feature 1-10 in the as-grown state: The as-grown state is the state obtained by crystal growth, without any processing such as polishing of the crystal growth surface.

[0047] "Ingot characteristic 1-10" A step-terrace structure is present on the crystal growth surface, and the ratio of the average central terrace width to the average peripheral terrace width, (average central terrace width) / (average peripheral terrace width), is 1.3 or less.

[0048] The "average central terrace width" is the average terrace width of four terraces, including one terrace located at the center of the crystal growth surface of an n-type 4H—SiC single crystal ingot, and three consecutive terraces connected to that terrace and located closer to the periphery of the crystal growth surface than that terrace.

[0049] The "average peripheral terrace width" is the average terrace width of four terraces, including one terrace located 5 mm away from the periphery of the crystal growth surface toward the center of the crystal growth surface, and three consecutive terraces connected to that terrace and located closer to the center of the crystal growth surface than that terrace.

[0050] Ingot features 1-10 will be described in detail below with reference to the drawings.

[0051] 1 is a schematic diagram of an as-grown n-type 4H—SiC single crystal ingot 10 observed from the side. As shown in FIG. 1, n-type 4H—SiC single crystal ingot 10 of this embodiment has a step-terrace structure in which steps and terraces appear alternately from the periphery toward the center on crystal growth surface 10a in the “as-grown state.”

[0052] In the n-type 4H—SiC single crystal ingot 10 of this embodiment, which is produced by the solution method, the starting points of step-flow growth occur on the periphery of the crystal growth surface 10a, and crystal growth proceeds from the periphery toward the center as indicated by the arrows in the figure.

[0053] The terrace width is the width of each terrace in the direction from the periphery to the center of the crystal growth surface 10a. W in FIG. 1 is the terrace width.

[0054] Next, the average central terrace width will be described with reference to Figure 2. As shown in Figure 2, the average central terrace width is the average value of the terrace widths of four terraces (1) to (4), including one terrace (1) located at the center of the crystal growth surface 10a of the n-type 4H-SiC single crystal ingot 10 and three consecutive terraces (2) to (4) connected to the single terrace (1) and located closer to the periphery of the crystal growth surface 10a than the single terrace (1). There are no other terraces between the central terrace (1) and the three consecutive terraces (2) to (4). In other words, the central terrace (1) and the three consecutive terraces (2) to (4) form four consecutive terraces.

[0055] Next, the average peripheral terrace width will be described with reference to FIG. 3. As shown in FIG. 3, the average peripheral terrace width is the average terrace width of four terraces (1)' to (4)', including one terrace (1)' located 5 mm away from the periphery of the crystal growth surface 10a of the n-type 4H—SiC single crystal ingot 10 toward the center of the crystal growth surface 10a, and three consecutive terraces (2)' to (4)' connected to the single terrace (1)' and located closer to the center of the crystal growth surface 10a than the single terrace (1)'. There are no other terraces between the one terrace (1)' located 5 mm away from the periphery and the three consecutive terraces (2)' to (4)'. In other words, the one terrace (1)' located 5 mm away from the periphery and the three consecutive terraces (2)' to (4)' are four consecutive terraces.

[0056] As described above, in the as-grown n-type 4H—SiC single crystal ingot 10 of this embodiment, the ratio of the average central terrace width to the average peripheral terrace width, (average central terrace width) / (average peripheral terrace width), is 1.3 or less.

[0057] In the case of the solution method, where the starting point of step-flow growth occurs on the periphery of the crystal growth surface and the crystal grows from the periphery toward the center, the (average peripheral terrace width)<(average central terrace width), and therefore the (average central terrace width) / (average peripheral terrace width) is greater than 1.0.

[0058] That is, the as-grown n-type 4H—SiC single crystal ingot 10 of this embodiment has a characteristic configuration in which the ratio (average central terrace width) / (average peripheral terrace width) is greater than 1.0 and not more than 1.3, close to 1.0. That is, the n-type 4H—SiC single crystal ingot 10 of this embodiment has the same average central terrace width and average peripheral terrace width.

[0059] It is known that step meandering and bunching can occur during step flow growth. When step meandering and bunching occur, the difference between the average central terrace width and the average peripheral terrace width increases. Increasing the diameter of an n-type 4H—SiC single crystal ingot increases the distance in the growth direction from the periphery of the crystal growth surface toward the center, making step meandering and bunching more likely to occur. Despite the large diameter of the n-type 4H—SiC single crystal ingot 10 of this embodiment, which is 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more, the average central terrace width and the average peripheral terrace width are equivalent as described above, thereby suppressing step meandering and bunching during step flow growth.

[0060] However, when step meandering or bunching occurs, crystal growth at each step becomes unstable, and the impurity incorporation behavior may also become unstable. As a result, problems such as a large resistivity distribution within the crystal growth surface may occur. The 4H—SiC single crystal ingot 10 of this embodiment, in which step meandering and bunching during step flow growth are suppressed, suppresses problems such as a large resistivity distribution within the crystal growth surface.

[0061] In the n-type 4H—SiC single crystal ingot of this embodiment, the [N] / [Al] and the sum of [N] and [Al] fall within the characteristic numerical ranges described above, as shown in ingot features 1-1 and 1-2. By controlling the [N] / [Al] and the sum of [N] and [Al] to fall within the characteristic numerical ranges described above, the n-type 4H—SiC single crystal ingot of this embodiment having ingot feature 1-10 is realized. In other words, by producing an n-type 4H—SiC single crystal ingot by the solution method (ingot feature 1-7) so as to have both ingot features 1-1 and 1-2, the n-type 4H—SiC single crystal ingot of this embodiment can be obtained in which the average central terrace width and the average peripheral terrace width are equivalent, as shown in ingot feature 1-10.

[0062] In addition, as-grown n-type 4H—SiC single crystal ingots produced by the “solution method,” i.e., as-grown n-type 4H—SiC single crystal ingots having ingot characteristic 1-7, tend to further have the following ingot characteristics 1-11 and 1-12.

[0063] "Ingot Feature 1-11" The average width of the outer terrace is 5.0 μm or more and 20 μm or less, preferably 5.0 μm or more and 15 μm or less, "Ingot Characteristics 1-12" The outer periphery of the crystal growth surface is thicker than the center

[0064] The average width of the peripheral terraces of n-type 4H-SiC single crystal ingots produced by the "sublimation method" is smaller than the average width of the peripheral terraces of n-type 4H-SiC single crystal ingots produced by the "solution method," at about 3 μm.

[0065] Therefore, an n-type 4H—SiC single crystal ingot having ingot characteristic 1-11 can be presumed to have been produced by the solution method rather than the sublimation method. In other words, by checking whether a target n-type 4H—SiC single crystal ingot has ingot characteristic 1-11, it can be determined whether the n-type 4H—SiC single crystal ingot has ingot characteristic 1-7.

[0066] Furthermore, as mentioned above, in n-type 4H—SiC single crystal ingots produced by solution deposition, the starting points of step-flow growth occur on the periphery of the crystal growth surface, and crystal growth proceeds from the periphery toward the center. As a result, as-grown n-type 4H—SiC single crystal ingots produced by solution deposition tend to have the above-mentioned ingot characteristics 1-12.

[0067] In contrast, in n-type 4H-SiC single crystal ingots produced by sublimation, the starting point of step-flow growth occurs at the center of the crystal growth surface, and crystal growth proceeds from the center toward the periphery. As a result, as-grown n-type 4H-SiC single crystal ingots produced by sublimation tend to have the opposite characteristic to ingot characteristic 1-12 above, in that the periphery of the crystal growth surface is thinner than the center.

[0068] Therefore, an n-type 4H—SiC single crystal ingot having ingot characteristic 1-12 can be presumed to have been produced by the solution method rather than the sublimation method. In other words, by checking whether a target n-type 4H—SiC single crystal ingot has ingot characteristic 1-12, it can be determined whether the n-type 4H—SiC single crystal ingot has ingot characteristic 1-7.

[0069] The n-type 4H—SiC single crystal ingot of this embodiment may have a surface that is either the (0001) plane or the (000-1) plane, or may have a surface that is cut at an angle of 0.5 to 5 degrees relative to the (0001) plane or the (000-1) plane.

[0070] <Method for manufacturing n-type 4H—SiC single crystal ingot according to the first embodiment> Next, an example of a method for producing the above-mentioned n-type 4H—SiC single crystal ingot will be described.

[0071] The method for producing an n-type 4H—SiC single crystal ingot of this embodiment includes a growth step in which a seed crystal is brought into contact with a raw material solution containing Si and C to produce a growth layer of n-type 4H—SiC single crystal on the surface of the seed crystal. The raw material solution may further contain Cr in addition to Si and C. The surface of the seed crystal that comes into contact with the raw material solution is the carbon surface ((000-1) plane), and the deviation from the (000-1) plane is preferably ±0.1° or less. An off-substrate may also be used, as described below. The TTV (Total Thickness Variation) of the seed crystal is preferably 10 μm or less. The micropipe density is 0.1 / cm. 2 The TTV is the thickness variation based on the back surface of the wafer, which is the seed crystal, and is calculated by subtracting the highest point from the lowest point on the back surface of the wafer when the back surface of the wafer is adsorbed onto a flat chuck surface.

[0072] In the growth process, N and Al are doped into the growth layer, and the ratio of [N], the concentration of N in the growth layer, to [Al], the concentration of Al, [N] / [Al], is 1.5 to 3.0, and the sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 The growth layer is generated under the following conditions:

[0073] There are various ways to achieve these conditions. One example is by adjusting the amount of Al placed in the crucible and the amount of N2 circulating in the furnace. For example, this can be achieved by setting the amount of Al placed in the crucible to about 0.3 to 0.5 mol% relative to the Si and Cr in the crucible, and setting the amount of N2 circulating in the furnace to about 0.10 to 0.20 vol% or 0.10 to 0.40 vol%. Note that the example here is merely an example and is not limiting.

[0074] In the growth step, a growth layer having a diameter of 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more can be produced. The method of diameter expansion is not limited, and widely known techniques can be used. An example will be described below. By producing a growth layer under the above conditions, it is possible to achieve both the effect of maintaining polymorphism and the effect of suppressing an increase in resistivity, even when a large-diameter growth layer having a diameter of 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more is produced.

[0075] The method for producing an n-type 4H—SiC single crystal ingot of this embodiment can employ widely known techniques, except that it produces a grown layer of an n-type 4H—SiC single crystal under the conditions described above. This method for producing an n-type 4H—SiC single crystal ingot of this embodiment can produce an n-type 4H—SiC single crystal ingot having the ingot characteristics 1-1 to 1-3 described above, and an n-type 4H—SiC single crystal ingot further having at least one of the ingot characteristics 1-4 to 1-7 described above. Furthermore, the method for producing an n-type 4H—SiC single crystal ingot of this embodiment can produce an n-type 4H—SiC single crystal ingot in an as-grown state that further has the ingot characteristics 1-10 to 1-12 described above.

[0076] 4 is a schematic diagram showing an example of a crystal growth apparatus 1 that can be used in the method for producing an n-type 4H—SiC single crystal ingot according to this embodiment. The crystal growth apparatus 1 includes a crucible 3, a pulling shaft 7, and heaters 4a and 4b (hereinafter, sometimes collectively referred to as heater 4).

[0077] The crystal growth apparatus 1 shown in Fig. 4 contains a raw material solution 5 inside a crucible 3. A pulling shaft 7 is capable of rotating a seed crystal 9 attached to the tip thereof, with its long axis serving as the rotation axis. The centers of the crucible 3 and the pulling shaft 7 do not necessarily have to coincide, but it is preferable that they do, and it is more preferable that the center of the crucible 3, the rotation axis of the crucible 3 (described below), the center of the pulling shaft 7, and the rotation axis of the pulling shaft 7 all coincide.

[0078] The crucible 3 is preferably a graphite crucible made of graphite, which can supply carbon to the raw material solution 5. However, crucibles other than graphite crucibles can be used as long as they can add hydrocarbon gas or a solid carbon source. To ensure a uniform composition of the raw material solution 5, it is preferable to rotate the crucible 3, and more preferably to use the center of the crucible 3 as the rotation axis. The rotation speed of the crucible 3 is preferably 5 to 50 rpm, more preferably 20 to 40 rpm. Setting the rotation speed within the above range enables efficient crystal growth without placing excessive strain on the device. Alternatively, the crucible 3 may be rotated while periodically reversing its rotation direction between forward and reverse directions.

[0079] The raw material solution 5 is heated by heaters 4a, 4b, etc., provided around the crucible 3, and is kept in a molten state. The heaters 4a, 4b may be of an induction heating type or a resistance heating type. The temperature inside the crucible 3 is preferably 1700 to 2100°C. The temperature inside the crucible can be measured by using a non-contact thermometer (manufactured by Chino, IR-CZH7 type) to measure the temperature at or near the surface of the raw material solution 5 or inside the crucible 3.

[0080] It is preferable to circulate an inert gas such as a rare gas inside the crystal growth apparatus 1 to create an inert atmosphere. There are no particular restrictions on the pressure, but it may be around atmospheric pressure (approximately 100 kPa). When supplying conductive impurities into the grown 4H—SiC single crystal, a mixed gas atmosphere can be created by adding a gas that serves as a source of the conductive impurities.

[0081] The pulling shaft 7 adjusts the position of the seed crystal 9, and an n-type 4H—SiC single crystal 11 grows on the surface of the seed crystal 9. By forming a meniscus on the side of the seed crystal 9, the diameter of the grown crystal can be made larger than the diameter of the seed crystal 9, as shown in Figure 4. Specifically, by lowering the temperature of the solution around the seed crystal and increasing the carbon supersaturation, the growth rate toward the side of the seed crystal increases, and the crystal diameter can be enlarged.

[0082] In the method for producing a SiC single crystal ingot of this embodiment, when the seed crystal 9 is brought into contact with the raw material solution 5, a melt-back process may be performed in which the silicon carbide seed crystal 9 is brought into contact with the raw material solution 5 whose concentration is not saturated, and a portion of the seed crystal 9 is dissolved, and then a SiC single crystal may be grown on the seed crystal 9.

[0083] In the melt-back process, the seed crystal 9 dissolves because the carbon concentration of the raw material solution 5 is not saturated. In the melt-back process, the irregularities on the surface of the seed crystal 9 disappear, and the lower surface of the seed crystal 9 becomes smooth. Note that, to prevent the entire seed crystal 9 from dissolving in the melt-back process, the immersion time of the seed crystal 9 is adjusted to a time during which only a portion of the seed crystal 9 dissolves, taking into account the dissolution rate. Thereafter, the raw material solution 5 is made supersaturated near the seed crystal 9, thereby growing a silicon carbide single crystal on the seed crystal 9.

[0084] The method for performing the melt-back process is not particularly limited. However, when the crucible 3 is made of graphite and carbon is supplied from the crucible 3 to the raw material solution 5, a method of contacting a seed crystal with the raw material solution 5 at temperature T1 during the temperature rise is considered. Carbon dissolution from the crucible 3 is slow, and the carbon concentration of the raw material solution is always unsaturated during the temperature rise. Therefore, when the seed crystal is contacted, carbon dissolves from the crucible 3 and SiC dissolves from the seed crystal at the same time. The temperature is then raised from temperature T1 to temperature T2 and maintained for a certain period of time to stabilize. This allows carbon to dissolve sufficiently from the crucible 3, saturating the carbon concentration in the raw material solution, and growing a silicon carbide single crystal on the seed crystal at temperature T2. The temperature T1 during the melt-back process of the raw material solution 5 is preferably 1420°C or higher and 2100°C or lower, and more preferably 1500°C or higher and 2000°C or lower. Furthermore, the temperature T2 in the crystal growth step is preferably 5° C. or more higher than T1, more preferably 50° C. or more higher, and even more preferably 100° C. or more higher.

[0085] Alternatively, when the crucible 3 is made of a material other than graphite, the amount of carbon source at the time of charging can be reduced, and the melt-back process can be performed in a state where the raw material solution 5 is undersaturated, and then the carbon source can be supplied to the raw material solution 5 to increase the carbon concentration and perform the crystal growth process.

[0086] In the melt-back step, the lower surface of the seed crystal 9 is smoothed, resulting in good morphology in the subsequent crystal growth step.

[0087] The seed crystal 9 can be a crystal polymorph such as 4H—SiC. The seed crystal 9 may be an on-substrate whose surface is a (000-1) plane, or an off-substrate whose surface is cut at an angle of 0.5 to 5 degrees relative to the (000-1) plane. For example, the seed crystal 9 may have an off-angle of 0.5 to 5 degrees from the

[0001] direction to the [11-20] direction. The seed crystal 9 is attached to the pulling shaft 7 so that the off-angled plane serves as the crystal growth surface and is in contact with the raw material solution 5. The thickness of the seed crystal 9 is not particularly limited, but is typically 0.1 mm or more. Note that an excessively thick seed crystal 9 would be too expensive, so the thickness of the seed crystal 9 is typically 10 mm or less.

[0088] At least the raw material solution 5 in contact with the crystal growth surface of the seed crystal 9 must be in a supersaturated state. Methods for achieving a supersaturated state of carbon as a solute include a cooling method in which a seed crystal substrate is immersed in a silicon carbide solution of saturated concentration and then supercooled to achieve a supersaturated state, and a temperature difference method in which a seed crystal substrate is immersed in a silicon carbide solution having a temperature gradient and silicon carbide crystals are crystallized in the low-temperature portion.

[0089] When the temperature difference method is used, only the vicinity of the seed crystal 9 becomes supersaturated by controlling the heating of the heater 4 or by cooling using the seed crystal 9, and the pulling shaft 7 brings the seed crystal 9 into contact with the raw material solution 5, and by adjusting the position of the seed crystal 9, SiC crystals are precipitated on the crystal growth surface of the seed crystal 9.

[0090] When the cooling method is used, the entire raw material solution 5 becomes supersaturated, so that crystal growth can also be achieved by rotating the pulling shaft 7 while the seed crystal 9 is immersed in the raw material solution 5.

[0091] The seed crystal 9 may be fixed, but is preferably rotated in a plane parallel to the surface of the raw material solution 5. When the seed crystal 9 is rotated, the rotation speed is preferably 20 to 300 rpm, and more preferably 20 to 150 rpm. By setting the rotation speed within the above range, efficient crystal growth is possible without placing an excessive burden on the apparatus.

[0092] Furthermore, the seed crystal 9 is preferably rotated in a cycle of periodically repeating forward and reverse rotation, with the cycle being approximately 30 seconds to 5 minutes. By periodically switching the rotation direction, the flow of the raw material solution on the growth surface of the seed crystal during crystal growth can be controlled.

[0093] The n-type 4H—SiC single crystal 11 is separated from the pulling shaft 7, and its periphery is processed as needed by polishing or the like to form an n-type 4H—SiC single crystal ingot. The crystal growth direction of the n-type 4H—SiC single crystal ingot coincides with the long axis direction of the n-type 4H—SiC single crystal.

[0094] <Method for manufacturing n-type 4H—SiC single crystal wafer according to the first embodiment> The method for producing n-type 4H—SiC single crystal wafers of this embodiment involves producing an n-type 4H—SiC single crystal ingot by the method for producing an n-type 4H—SiC single crystal ingot described above, and then slicing wafers from the n-type 4H—SiC single crystal ingot. There are no particular restrictions on the method for slicing n-type 4H—SiC single crystal wafers from the n-type 4H—SiC single crystal ingot, and widely known techniques such as wire saw cutting and laser cutting can be used.

[0095] According to the method for manufacturing n-type 4H—SiC single crystal wafers of this embodiment, it is possible to manufacture n-type 4H—SiC single crystal wafers having the above-mentioned wafer features 1-1 to 1-3, and also n-type 4H—SiC single crystal wafers further having at least one of the above-mentioned wafer features 1-4 to 1-7.

[0096] "Example of the first embodiment" Example 1 The lower end surface is a (000-1) plane, the deviation from the (000-1) plane is ±0.1° or less, the thickness is about 500 μm, the TTV is 7 μm or less, and the micropipe density is 0.07 pieces / cm 2 The following 6-inch disk-shaped 4H-SiC single crystal (seed crystal) was attached to a graphite pulling shaft.

[0097] In Example 1, n-type 4H-SiC single crystals were grown by the solution method. First, a graphite crucible was charged with 59.6 mol% Si, 40 mol% Cr, and 0.4 mol% Al. The crucible and raw materials were then heated to 1800°C to 2100°C in a crystal growth apparatus to melt the raw materials. After melting, He gas containing 0.15 vol% N2 was circulated through the crystal growth apparatus at 1 atmosphere. A seed crystal attached to a pulling shaft was brought into contact with the solution, and crystal growth occurred on the seed crystal. During crystal growth, the weight of the growing crystal was monitored using a load cell connected to the pulling shaft holding the seed crystal, and the pulling shaft was raised and lowered as necessary. After a certain period of time, the crystal was pulled and cooled, yielding a crystal with an average thickness of 2 mm on the seed crystal. This n-type 4H-SiC single crystal ingot was sliced ​​using a free-abrasive wire saw. After slicing, the front and back surfaces were lapped to obtain 0.5 mm-thick n-type 4H-SiC single crystal wafers.

[0098] The [N] and [Al] were measured by secondary ion mass spectrometry in a 6 mm square area centered at the midpoint between the periphery and the center of the obtained n-type 4H—SiC single crystal wafer. The measurement results are shown in Table 1.

[0099] [Table 1]

[0100] The crystal growth surface of the obtained as-grown n-type 4H-SiC single crystal ingot was also observed using a laser microscope, and the average central terrace width and average peripheral terrace width were measured. Figure 5 shows the peripheral portion of the as-grown n-type 4H-SiC single crystal ingot observed using a laser microscope. Figure 6 shows the central portion of the as-grown n-type 4H-SiC single crystal ingot observed using a laser microscope. Table 2 shows the measurement results for the average central terrace width and the average peripheral terrace width. The average value for the peripheral portion in Table 2 is the average peripheral terrace width. The average value for the central portion in Table 2 is the average central terrace width. Table 2 also shows the terrace widths of each of the four terraces used to calculate the average central terrace width and the average peripheral terrace width.

[0101] [Table 2]

[0102] The resistivity of the resulting n-type 4H-SiC single crystal wafer was also measured using a Napson EC-80P. Measurements were taken at multiple measurement points separated by a specified distance from the periphery. Table 3 shows the measured values ​​at each measurement point. Figure 7 shows the measurement results in graph form. Figure 7 shows that the resistivity increases monotonically from the periphery to the center. The resistivity ranged from 15 to 25 mΩ·cm. The resistivity at the center of the wafer was 50 mΩ·cm or less.

[0103] [Table 3]

[0104] The diameter of the resulting n-type 4H—SiC single crystal wafer and the resulting n-type 4H—SiC single crystal ingot was 6 inches.

[0105] The 4H polymorphism retention rate of the resulting n-type 4H-SiC single crystal wafer and the resulting n-type 4H-SiC single crystal ingot was 99% or higher. The 4H polymorphism retention rate of the n-type 4H-SiC single crystal wafer was calculated using a digital microscope (Keyence Corporation, VHX-8000) and its accompanying software with an area measurement function. First, transmission images of the entire crystal of the resulting n-type 4H-SiC single crystal wafer were taken using coaxial illumination and 20x magnification, with multiple images overlapping. The 4H polymorph exhibited a green transmission hue, while heterogeneous polymorphic regions exhibited transmission hues such as blue and yellow. The areas of these heterogeneous polymorphic regions were measured, and the "4H polymorphism retention rate" was calculated by (total wafer area - total area of ​​heterogeneous polymorphic regions) / (total wafer area) × 100. In Example 1, since only one wafer was cut from the ingot, the 4H polymorphism retention rate of the wafer was determined as the 4H polymorphism retention rate of the n-type 4H—SiC single crystal ingot.

[0106] <Example 2> In Example 2, n-type 4H—SiC single crystals were grown by the solution method. First, a graphite crucible was charged with 59.6 mol% Si, 40 mol% Cr, and 0.4 mol% Al, and the crucible and raw materials were heated to 1800°C or higher and 2100°C or lower in a crystal growth apparatus to melt the raw materials. After melting, crystal growth was carried out while circulating N2 at 0.3 vol% through the crystal growth apparatus. The remaining manufacturing methods were the same as in Example 1.

[0107] The [N] and [Al] were measured by secondary ion mass spectrometry in a 6 mm square area centered at the midpoint between the periphery and the center of the obtained n-type 4H—SiC single crystal wafer. The measurement results are shown in Table 4.

[0108] [Table 4]

[0109] The resistivity of the resulting n-type 4H-SiC single crystal wafer was also measured using a Napson EC-80P. Measurements were taken at multiple measurement points separated by a specified distance from the periphery. Table 5 shows the measured values ​​at each measurement point. Figure 12 shows the measurement results in graph form. Figure 12 shows that the resistivity increases monotonically from the periphery to the center. The resistivity at the center of the wafer was also 50 mΩ·cm or less.

[0110] [Table 5]

[0111] The diameter of the resulting n-type 4H—SiC single crystal wafer and the resulting n-type 4H—SiC single crystal ingot was 6 inches.

[0112] Furthermore, the 4H polymorphism retention rate of the obtained n-type 4H—SiC single crystal wafer and the obtained n-type 4H—SiC single crystal ingot was 99% or more.

[0113] <Comparative Example 1> In Comparative Example 1, n-type 4H—SiC single crystal was grown by the solution method. First, a graphite crucible was charged with 59.25 mol% Si, 40 mol% Cr, and 0.75 mol% Al, and the crucible and raw materials were heated to 1800°C or higher and 2100°C or lower in a crystal growth apparatus to melt the raw materials. After melting, crystal growth was carried out while circulating N2 at 0.23 vol% through the crystal growth apparatus. The remaining manufacturing methods were the same as in Example 1.

[0114] The [N] and [Al] were measured by secondary ion mass spectrometry in a 6 mm square area centered at the midpoint between the periphery and the center of the obtained n-type 4H—SiC single crystal wafer. The measurement results are shown in Table 6.

[0115] [Table 6]

[0116] The crystal growth surface of the obtained as-grown n-type 4H—SiC single crystal ingot was also observed using a laser microscope, and the average central terrace width and average peripheral terrace width were measured. Figure 8 shows the peripheral portion of the as-grown n-type 4H—SiC single crystal ingot observed with a laser microscope. Figure 9 shows the central portion of the as-grown n-type 4H—SiC single crystal ingot observed with a laser microscope. Figure 9 shows that in Comparative Example 1, meandering and bunching frequently occurred in the central portion.

[0117] Table 7 shows the measurement results of the average central terrace width and the average peripheral terrace width. The average value in the peripheral region in Table 7 is the average peripheral terrace width. The average value in the central region in Table 7 is the average central terrace width. Table 7 also shows the terrace width of each of the four terraces used to calculate the average central terrace width and the average peripheral terrace width.

[0118] [Table 7]

[0119] The resistivity of the resulting n-type 4H—SiC single crystal wafers was also measured using a Napson EC-80P. Measurements were performed with a first measurement point 5 mm from the periphery, with measurements taken at 10 mm intervals from the first measurement point toward the center. Table 8 shows the measured values ​​at each measurement point. Figure 10 graphically illustrates the measurement results. Figure 10 shows that the resistivity increases from the periphery toward the center. However, due to meandering and bunching, the impurity incorporation behavior becomes unstable, and it is clear that the resistivity does not increase monotonically. Furthermore, the resistivity ranged from 116 to 239 mΩ·cm, significantly different from Example 1.

[0120] [Table 8]

[0121] The diameter of the resulting n-type 4H—SiC single crystal wafer and the resulting n-type 4H—SiC single crystal ingot was 6 inches.

[0122] Furthermore, the 4H polymorphism retention rate of the obtained n-type 4H—SiC single crystal wafer and the obtained n-type 4H—SiC single crystal ingot was 90%.

[0123] <Comparative Examples 2 to 4> Crystal growth was carried out in the same manner as in Example 1, except that a 4-inch 4H—SiC single crystal (seed crystal) was used as the seed crystal and the Al concentration in the raw material solution and the N gas concentration in the atmosphere were changed. The resistivity of the resulting n-type 4H—SiC single crystal wafer was then measured using an EC-80P manufactured by Napson Corporation. The measurement point was the midpoint between the crystal edge and the crystal center.

[0124] <Comparative Example 2> Table 9 shows the measurement results of the dopant concentration and resistivity of Comparative Example 2. When the sum of [N] and [Al] was 1.0×10 20 atoms / cm 3 However, when the [N] / [Al] ratio is less than 1.5 (i.e., when the amount of N is extremely small compared to Al), the proportion of Al, which is an acceptor element, increases relatively, causing an increase in the resistivity of the SiC single crystal. As a result, the crystal has a high resistance of over 25 mΩ cm.

[0125] [Table 9]

[0126] <Comparative Example 3> Table 10 shows the measurement results of the dopant concentration and resistivity of Comparative Example 3. When the sum of [N] and [Al] was 1.0×10 20 atoms / cm 3As shown below, when [N] / [Al] is greater than 3.0 (i.e., when N is extremely high compared to Al), the Al proportion becomes small, making it difficult to maintain the crystal polymorphism, resulting in a crystal with a 4H polymorphism retention rate reduced to 10-20%. On the other hand, since the N proportion is sufficient, it is expected that a SiC single crystal with sufficiently reduced resistivity can be obtained, but due to the influence of grain boundaries caused by the occurrence of heterogeneous polymorphism, it is not a crystal in which the in-plane distribution of resistivity can be generally evaluated.

[0127] [Table 10]

[0128] <Comparative Example 4> Table 11 shows the measurement results of the dopant concentration and resistivity of Comparative Example 4. [N] / [Al] is 1.5 or more and 3.0 or less, but the sum of [N] and [Al] is 1.0×10 20 atoms / cm 3 When the total amount of N and Al is higher (i.e., when SiC single crystals are co-doped with extremely high amounts of N and Al), the total amount of N and Al impurities is high, making step meandering and bunching more likely to occur during step-flow growth. Therefore, it is expected that the impurity incorporation behavior will differ between the crystal periphery and the center. The resistivity results (30 mΩ·cm) shown in Table 11 were measured at the midpoint between the crystal edge and the crystal center. Although not shown in the table, the resistivity near the crystal center increases, exceeding 50 mΩ·cm. Furthermore, the increased total amount of impurities is likely to induce deterioration in crystallinity and morphology, adversely affecting crystal quality. The 4H polymorph retention rate was low at 40%.

[0129] [Table 11]

[0130] <<Second embodiment>> <Problems with the second embodiment> There is a demand for technology that suppresses in-plane characteristic variations in n-type 4H—SiC single crystal wafers. One example of the objective of the second embodiment is to provide technology that suppresses in-plane characteristic variations in n-type 4H—SiC single crystal wafers.

[0131] <N-type 4H—SiC single crystal wafer of the second embodiment> The n-type 4H—SiC single crystal wafer of this embodiment comprises the following wafer features 2-1 and 2-2. As another example, the n-type 4H—SiC single crystal wafer of this embodiment can comprise the following wafer features 2-1 to 2-3. As another example, the n-type 4H—SiC single crystal wafer of this embodiment can comprise the following wafer features 2-2 to 2-4. As another example, the n-type 4H—SiC single crystal wafer of this embodiment may comprise the following wafer features 2-1 to 2-4. As another example, the n-type 4H—SiC single crystal wafer of this embodiment may comprise the following wafer features 2-1 to 2-5.

[0132] "Wafer characteristics 2-1" Absorption coefficient α at the first point on the substrate surface at a wavelength of 1064 nm 1064-1 and an absorption coefficient α of a wavelength of 1064 nm at a second point on the substrate surface located closer to the outer periphery of the substrate surface than the first point. 1064―2 The ratio of α 1064-1 / α 1064-2 is 0.80 or more and 1.3 or less, preferably 1.0 or more and 1.2 or less. "Wafer characteristic 2-2" Diameter is 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more. There is no particular upper limit to the diameter, but in reality it is 18 inches or less, or 12 inches or less. "Wafer Feature 2-3" 4H polymorphism retention rate is 99% or more. By definition, the 4H polymorphism retention rate is 100% or less. "Wafer feature 2-4" Absorption coefficient α at the first point at a wavelength of 532 nm 532-1 and the absorption coefficient α at the second point at a wavelength of 532 nm 532-2 The ratio of α 532-1 / α 532-2 is 0.80 or more and 1.3 or less, preferably 1.0 or more and 1.2 or less. "Wafer feature 2-5" α measured at the same point (e.g., first point or second point) 1064-1 and α 532-1 The ratio of α 1064-1 / α 532-1 is 1.1 or more and 1.6 or less, preferably 1.45 or more and 1.6 or less.

[0133] The "first point" and "second point" are arbitrarily determined on the substrate surface. The first point and the second point can be separated from each other by 10 mm or more, preferably 40 mm or more, and more preferably 50 mm or more. One of the first point and the second point may be, for example, the center of the wafer.

[0134] Furthermore, the n-type 4H—SiC single crystal wafer of this embodiment can have at least one of wafer feature 2-1 and wafer feature 2-4, and preferably both, in multiple pairs of first and second points. The number of pairs is 3 or more, preferably 5 or more, more preferably 10 or more, even more preferably 20 or more, and even more preferably 30 or more. The in-plane positions of the paired first and second points can vary, but it is preferable that they are not concentrated locally within the wafer plane but are dispersed. When the positions of the first and second points are determined in this manner, it can be said that the n-type 4H—SiC single crystal wafer of this embodiment, which has at least one of wafer feature 2-1 and wafer feature 2-4 in multiple pairs of first and second points, has reduced in-plane characteristic variation.

[0135] In this embodiment, multiple measurement points 1 to 37 were defined as shown in FIG. 11 . Specifically, measurement point 7, measuring 10 mm × 10 mm, was defined in the center of the wafer. Multiple measurement points of the same size were linearly arranged adjacent to each other above, below, left, and right of measurement point 7 (measurement points 1 to 6, 8 to 25). The vertical direction is the <1-100> direction. The horizontal direction is the <11-20> direction. Multiple measurement points of the same size were further arranged in the remaining empty areas (measurement points 26 to 37). Specifically, measurement points 27 and 32 were arranged at the intersections of a line extending vertically from measurement point 14 and a line extending horizontally from measurement points 5 and 9, respectively. Measurement points 26, 28, 33, and 34 were arranged at the intersections of a line extending vertically from measurement point 18 and a line extending horizontally from measurement points 1, 5, 9, and 13, respectively. Measurement points 29, 30, 35, and 37 were placed at the intersections of a line extending vertically from measurement point 21 and lines extending horizontally from measurement points 1, 5, 9, and 13. Measurement points 31 and 36 were placed at the intersections of a line extending vertically from measurement point 25 and lines extending horizontally from measurement points 5 and 9. The number of measurement points can be increased or decreased depending on the wafer size.

[0136] The n-type 4H—SiC single crystal wafer of this embodiment can have at least one, and preferably both, of wafer feature 2-1 and wafer feature 2-4 in 36 pairs of the central measurement point 7 (second point) and each of the other multiple measurement points 1 to 6 and 8 to 37 (first points).

[0137] Furthermore, the n-type 4H—SiC single crystal wafer of this embodiment can have wafer feature 2-5 at multiple points within its surface. The number of points is 3 or more, preferably 5 or more, more preferably 10 or more, even more preferably 20 or more, and even more preferably 30 or more. The multiple points can be located at various positions within the surface, but it is preferable to distribute the positions so that they are not concentrated locally within the wafer surface. When the positions of the multiple points are determined in this manner, it can be said that the n-type 4H—SiC single crystal wafer of this embodiment, which has wafer feature 2-5 at multiple points, has reduced variation in its surface characteristics. In this embodiment, multiple measurement points 1 to 37 are defined as shown in FIG. 11. The n-type 4H—SiC single crystal wafer of this embodiment can have wafer feature 2-5 at each of the multiple measurement points 1 to 37.

[0138] Here, the definition of the absorption coefficient and a specific calculation method will be explained.

[0139] When the transmittance is T, the intensity of the incident light is I0, and the intensity of the transmitted light is I1, the transmittance T is defined as in Equation 1.

[0140]

number

[0141] The absorption coefficient is a constant that indicates how much light a medium absorbs when it is incident on that medium, and is expressed by the Beer-Lambert law as shown in Equation 2. Here, A is the absorbance, α is the absorption coefficient, and L is the distance that light travels within the medium.

[0142]

number

[0143] Equation 3 is derived from equations 1 and 2. The absorption coefficient α is calculated using equation 3.

[0144]

number

[0145] After slicing, the crystal was polished by chemical mechanical polishing (CMP) and placed in a spectrophotometer (Shimadzu UV-3600). The transmittance at each of the first and second points was measured at predetermined wavelengths (532 nm and 1064 nm). The first and second points can be determined arbitrarily as long as they satisfy the condition that "the first point is located closer to the center of the substrate than the second point." The first and second points may also be determined so as to further satisfy the condition that "the first and second points are at least 40 mm apart" or "the first and second points are at least 50 mm apart."

[0146] Then, using the transmittance T of the wavelength 1064 nm at the first point, the absorption coefficient α of the wavelength 1064 nm at the first point is calculated from Equation 3. 1064-1 Furthermore, the absorption coefficient α of the wavelength 1064 nm at the second point is calculated from Equation 3 using the transmittance T of the wavelength 1064 nm at the second point. 1064-2 Similarly, the absorption coefficient α of the wavelength 532 nm at the first point is calculated. 532-1 , and the absorption coefficient α at the second point at a wavelength of 532 nm 532-2 where L is the thickness of the n-type 4H—SiC single crystal wafer at the transmittance measurement positions (first point and second point). The thickness of the n-type 4H—SiC single crystal wafer is measured using a micrometer.

[0147] The method for calculating the "4H polymorphism retention rate" is as explained in the first embodiment.

[0148] An n-type 4H—SiC single crystal wafer having wafer feature 2-1 has a ratio of absorption coefficients at a wavelength of 1064 nm at two in-plane points of 0.80 or more and 1.3 or less, preferably 1.0 or more and 1.2 or less, a value close to 1. In other words, the absorption coefficients at a wavelength of 1064 nm at the two points have equivalent values. An n-type 4H—SiC single crystal wafer having such wafer feature 2-1 has reduced in-plane variation in the absorption coefficient at a wavelength of 1064 nm.

[0149] An n-type 4H—SiC single crystal wafer having wafer feature 2-4 has a ratio of the absorption coefficient at a wavelength of 532 nm at two in-plane points of 0.80 or more and 1.3 or less, preferably 1.0 or more and 1.2 or less, a value close to 1. In other words, the absorption coefficients at a wavelength of 532 nm at the two points have equivalent values. An n-type 4H—SiC single crystal wafer having such wafer feature 2-4 has reduced in-plane variation in the absorption coefficient at a wavelength of 532 nm.

[0150] n-type 4H—SiC single crystal wafers having wafer feature 2-3 have a 4H polymorphism retention rate of 99% or more and extremely small heterogeneous polymorphic regions. Such n-type 4H—SiC single crystal wafers having wafer feature 2-3 have reduced in-plane characteristic variations due to the presence of heterogeneous polymorphic regions.

[0151] An n-type 4H—SiC single crystal wafer having wafer feature 2-2 has a large diameter of 4 inches or more, preferably 6 inches or more, and more preferably 8 inches or more. Despite its large diameter, the n-type 4H—SiC single crystal wafer of this embodiment can have wafer features 2-1, 2-3, 2-4, and 2-5, etc., as described above.

[0152] In addition to the features described above, the n-type 4H—SiC single crystal wafer of this embodiment can further have at least one of the following wafer features 2-6 to 2-11.

[0153] "Wafer feature 2-6" contains N and Al, and the sum of the N concentration [N] and the Al concentration [Al], [N] + [Al], is 1.0 × 10 20 atoms / cm 3 Below, 8.0 x 10 19 atoms / cm 3 Below, 7.0 x 10 19 atoms / cm 3 Below, 6.0 x 10 19 atoms / cm 3 or less, or 5.5 x 10 19 atoms / cm 3 below "Wafer Feature 2-7" The difference between [N] and [Al], [N]-[Al], is 5.0×10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 or more, or 1.4 x 10 19 atoms / cm 3 That's all. "Wafer characteristic 2-8" The ratio of [N] to [Al], [N] / [Al], is 1.5 or more and 3.0 or less, 1.7 or more and 2.7 or less, 1.5 or more and 2.0 or less, or 1.7 or more and 2.0 or less. "Wafer feature 2-9" [N] is 5.0 × 10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 2.0 × 10 19 atoms / cm 3 That is 6.0 x 10 19 atoms / cm 3 Less than or equal to 5.0 × 10 19 atoms / cm 3 or less, more preferably 4.5 × 10 19 atoms / cm 3 In addition, [Al] is 5.0 × 10 18 atoms / cm 3 or more, preferably 1.0 × 10 19 atoms / cm 3 More preferably, 1.5 × 10 19 atoms / cm 3 That is 6.0 x 10 19 atoms / cm 3 Less than 4.0 × 10 19 atoms / cm 3 or less, more preferably 3.0 × 10 19 atoms / cm 3 The following is the result. "Wafer Feature 2-10" Resistivity of the center is 1mΩ·cm or more, 2mΩ·cm or more, 5mΩ·cm or more, 10mΩ·cm or more, 15mΩ·cm or more, 20mΩ·cm or more, or 25mΩ·cm or more. "Wafer Feature 2-11" Resistivity of the center portion is 50 mΩ·cm or less, preferably 25 mΩ·cm or less.

[0154] In addition, in wafer feature 2-6, the sum of [N] and [Al] is 1.0 × 10 19 atoms / cm 3 That's it, 2.0 x 10 19 atoms / cm 3 That's it, 3.0 x 10 19 atoms / cm 3 That's it, 4.0 x 10 19 atoms / cm 3 That's it, 5.0 x 10 19 atoms / cm 3 or more than 6.0 x 10 19 atoms / cm 3 That is, the sum of [N] and [Al] may be 1.0 × 10 19 atoms / cm 3 Over 1.0 x 10 20 atoms / cm 3 may be less than 4.0 x 10 19 atoms / cm 3 Over 6.0 x 10 19 atoms / cm 3 It may be the following:

[0155] The method for measuring [N] and [Al] is the same as that described in the first embodiment, and the method for measuring the resistivity is the same as that described in the first embodiment.

[0156] The n-type 4H—SiC single crystal wafers having wafer characteristics 2-10 and 2-11 have resistivity suppressed to 50 mΩ·cm or less, preferably 25 mΩ·cm or less.

[0157] In one example, by realizing wafer features 2-6 and 2-7, and preferably also 2-9, an n-type 4H—SiC single crystal wafer of this embodiment comprising wafer features 2-1 through 2-5, etc. can be realized. In another example, by further realizing wafer feature 2-8, an n-type 4H—SiC single crystal wafer of this embodiment comprising wafer features 2-10 and 2-11, etc. can be realized. Note that n-type 4H—SiC single crystal wafers of this embodiment comprising wafer features 2-1 through 2-5, etc. may also be realized by other means. Note that n-type 4H—SiC single crystal wafers of this embodiment comprising wafer features 2-10 and 2-11, etc. may also be realized by other means.

[0158] Also, in one example, the n-type 4H—SiC single crystal wafer of this embodiment is produced by a solution process. When produced by a solution process, the n-type 4H—SiC single crystal wafer of this embodiment can further have the following wafer features 2-12 and 2-13. The resistivity measurement method is as described in the first embodiment.

[0159] "Wafer characteristic 2-12" The resistivity at the first point located on the central side is higher than the resistivity at the second point located on the outer periphery. "Wafer feature 2-13" The resistivity increases monotonically from the outer periphery to the center within the wafer surface.

[0160] The ratio of the resistivity of the central portion to the resistivity of the peripheral portion may exceed 1, but even in this case, it is preferably 3 or less, and more preferably 2 or less.

[0161] While n-type 4H—SiC single crystal wafers manufactured by the “solution method” have the above wafer characteristics 2-12 and 2-13, n-type 4H—SiC single crystal wafers manufactured by the “sublimation method” tend to have the opposite characteristics, such as “the resistivity at the center of the wafer is lower than that at the periphery” and “the resistivity decreases monotonically from the periphery to the center of the wafer.”

[0162] For this reason, it can be assumed that n-type 4H—SiC single crystal wafers having wafer features 2-12 and / or 2-13 are wafers produced by a solution method, not a sublimation method.

[0163] The n-type 4H—SiC single crystal wafer of this embodiment may be an on-substrate with a (0001) or (000-1) plane surface, or an off-substrate with a surface cut at an inclination of 0.5 to 5 degrees relative to the (0001) or (000-1) plane. The n-type 4H—SiC single crystal wafer of this embodiment also has a boron concentration of 1.0×10 18 cm -3 The boron concentration may be a value measured by secondary ion mass spectrometry.

[0164] The n-type 4H—SiC single crystal wafer of this embodiment may further include the features of the n-type 4H—SiC single crystal wafer of the first embodiment.

[0165] <N-type 4H—SiC single crystal ingot according to the second embodiment> The n-type 4H—SiC single crystal ingot of this embodiment can have the following ingot feature 2-1:

[0166] "Ingot Characteristics 2-1" The sliced ​​n-type 4H—SiC single crystal wafer has the characteristics of the n-type 4H—SiC single crystal wafer of this embodiment described above.

[0167] Furthermore, the n-type 4H—SiC single crystal ingot of this embodiment can further have the following ingot feature 2-2 in the as-grown state: The as-grown state is the state obtained by crystal growth, without any processing such as polishing of the crystal growth surface.

[0168] "Ingot characteristic 2-2" A step-terrace structure exists on the crystal growth surface, and the ratio of the average central terrace width to the average peripheral terrace width, (average central terrace width) / (average peripheral terrace width), is 1.3 or less.

[0169] The "average central terrace width" and the "average peripheral terrace width" are as described in the first embodiment. Ingot feature 2-2 is the same feature as ingot feature 1-10 described in the first embodiment. Since ingot feature 1-10 was described in detail in the first embodiment, a description of ingot feature 2-2 will be omitted here.

[0170] In the n-type 4H—SiC single crystal ingot of this embodiment, [N], [Al], and their sum, difference, and ratio are controlled to fall within characteristic numerical ranges. This control realizes an n-type 4H—SiC single crystal ingot of this embodiment that has ingot characteristics 2-1 and 2-2.

[0171] An as-grown n-type 4H—SiC single crystal ingot produced by the “solution method” can further have at least one of the following ingot characteristics 2-3 to 2-5.

[0172] "Ingot feature 2-3" The average width of the outer terrace is 5.0 μm or more and 20 μm or less, preferably 5.0 μm or more and 15 μm or less, "Ingot characteristic 2-4" The outer periphery of the crystal growth surface is thicker than the center "Ingot Characteristics 2-5" Thickness: 1mm or more, 10mm or more, 5cm or more, 10cm or more, 20cm or more

[0173] The average width of the peripheral terraces of n-type 4H-SiC single crystal ingots produced by the "sublimation method" is smaller than the average width of the peripheral terraces of n-type 4H-SiC single crystal ingots produced by the "solution method," at about 3 μm.

[0174] Therefore, it can be assumed that the n-type 4H—SiC single crystal ingot having ingot feature 2-3 was produced by the solution method, not the sublimation method.

[0175] Furthermore, as mentioned above, in n-type 4H—SiC single crystal ingots produced by solution annealing, the starting point of step-flow growth occurs on the periphery of the crystal growth surface, and crystal growth proceeds from the periphery toward the center. As a result, as-grown n-type 4H—SiC single crystal ingots produced by solution annealing tend to have the above-mentioned ingot characteristics 2-4.

[0176] In contrast, in n-type 4H-SiC single crystal ingots produced by sublimation, the starting point of step-flow growth occurs at the center of the crystal growth surface, and crystal growth proceeds from the center toward the periphery. As a result, as-grown n-type 4H-SiC single crystal ingots produced by sublimation tend to have the opposite characteristic to ingot characteristic 2-4 above, in that the periphery of the crystal growth surface is thinner than the center.

[0177] Therefore, it can be assumed that the n-type 4H—SiC single crystal ingot having ingot feature 2-4 was produced by the solution method, not the sublimation method.

[0178] Furthermore, the solution method allows for continuous crystal growth, making it possible to produce n-type 4H—SiC single crystal ingots with thicknesses as shown in ingot feature 2-5.

[0179] The n-type 4H—SiC single crystal ingot of this embodiment may have a surface that is the (0001) plane or the (000-1) plane, or may have a surface that is cut at an angle of 0.5 to 5 degrees relative to the (0001) plane or the (000-1) plane. The n-type 4H—SiC single crystal ingot of this embodiment also has a boron concentration of 1.0×10 18 cm -3 The boron concentration may be a value measured by secondary ion mass spectrometry.

[0180] The n-type 4H—SiC single crystal ingot of this embodiment may further include the features of the n-type 4H—SiC single crystal ingot of the first embodiment.

[0181] <Method for manufacturing n-type 4H—SiC single crystal ingot according to the second embodiment> Next, an example of a method for manufacturing the above-mentioned n-type 4H—SiC single crystal ingot will be described. The method for manufacturing the n-type 4H—SiC single crystal ingot of the second embodiment is realized by the same method as the method for manufacturing the n-type 4H—SiC single crystal ingot of the first embodiment.

[0182] As is clear from the above description, the method for producing an n-type 4H—SiC single crystal ingot according to the first embodiment and the method for producing an n-type 4H—SiC single crystal ingot according to the second embodiment can be configured similarly. Furthermore, there are common growth conditions (conditions for [N] and [Al]) in the growth step of the method for producing an n-type 4H—SiC single crystal ingot according to the first embodiment and the growth conditions (conditions for [N] and [Al]) in the growth step of the method for producing an n-type 4H—SiC single crystal ingot according to the second embodiment. When these common growth conditions are adopted, an n-type 4H—SiC single crystal ingot having both the features described in the first embodiment and the features described in the second embodiment can be produced.

[0183] <Method for manufacturing n-type 4H—SiC single crystal wafer according to the second embodiment> The method for manufacturing n-type 4H—SiC single crystal wafers of the second embodiment is similar to the method for manufacturing n-type 4H—SiC single crystal wafers of the first embodiment.

[0184] As is clear from the above description, the method for producing an n-type 4H—SiC single crystal ingot according to the first embodiment and the method for producing an n-type 4H—SiC single crystal ingot according to the second embodiment can be configured similarly. The growth conditions (conditions for [N] and [Al]) in the growth step of the method for producing an n-type 4H—SiC single crystal ingot according to the first embodiment and the growth conditions (conditions for [N] and [Al]) in the growth step of the method for producing an n-type 4H—SiC single crystal ingot according to the second embodiment share some commonality. By adopting these common growth conditions, an n-type 4H—SiC single crystal ingot having both the features described in the first embodiment and the features described in the second embodiment can be produced. Furthermore, by slicing wafers from an n-type 4H—SiC single crystal ingot having both the features described in the first embodiment and the features described in the second embodiment, n-type 4H—SiC single crystal wafers having both the features described in the first embodiment and the features described in the second embodiment can be produced.

[0185] <Laser Processing Method for n-Type 4H—SiC Single Crystal Ingot or Wafer According to Second Embodiment> The n-type 4H—SiC single crystal ingot or wafer of this embodiment can be processed using a laser. For example, laser irradiation can be used for processing when slicing SiC single crystal wafers from a SiC single crystal ingot, when slicing thinner wafers from a SiC single crystal wafer, when dividing a SiC single crystal wafer into chips, and when forming predetermined shapes such as holes or notches in a SiC single crystal wafer.

[0186] The fundamental wavelength of the YAG (yttrium, aluminum, garnet) laser, which is often used in laser processing, is 1064 nm, and the second harmonic is 532 nm, so the absorption coefficient at these wavelengths is important in processing using a YAG laser. If the absorption coefficient changes locally, the laser output must be changed suddenly, but the n-type 4H—SiC single crystal wafer of this embodiment has little change in absorption coefficient, so there is no sudden change in laser output and laser processing can be stabilized.

[0187] "Example of the second embodiment" Theme 1 In Theme 1, [N] + [Al] is 7.0 × 10 19 atoms / cm 3 Adjust the [N]-[Al] to 5.0×10 18 atoms / cm 3 By making the above adjustments, it will be confirmed that n-type 4H-SiC single crystal wafers can be produced with reduced in-plane variation in the absorption coefficient at wavelengths of 532 nm and 1064 nm.

[0188] Example 1 The configuration of Example 1 is as described in the first embodiment. As shown in Table 1 above, Example 1 has a [N]+[Al] of 7.0×10 19 atoms / cm 3 or less, and [N]-[Al] is 5.0 × 10 18 atoms / cm 3 Meet the above.

[0189] The sliced ​​n-type 4H—SiC single crystal wafers were polished by CMP and placed in a spectrophotometer (Shimadzu UV-3600), and the transmittance was measured at predetermined wavelengths (532 nm, 1064 nm) at points 1 and 2. The first point (measurement point on the central side) was located 2.0 cm from the center of the wafer, and the second point (measurement point on the outer periphery) was located 6.0 cm from the center of the wafer.

[0190] Then, using the transmittance T at the wavelength of 1064 nm at the first point (measurement point on the center side), the absorption coefficient α at the wavelength of 1064 nm at the first point (measurement point on the center side) is calculated from Equation 3. 1064-1 In addition, the absorption coefficient α at the wavelength of 1064 nm at the second point (measurement point on the outer periphery side) was calculated from Equation 3 using the transmittance T at the wavelength of 1064 nm at the second point (measurement point on the outer periphery side). 1064-2 Similarly, the absorption coefficient α at the wavelength of 532 nm at the first point (measurement point on the center side) was calculated. 532-1 , and the absorption coefficient α at a wavelength of 532 nm at the second point (the outer peripheral measurement point) 532-2was calculated. L was defined as the thickness of the n-type 4H—SiC single crystal wafer at the transmittance measurement positions (first point and second point). The thickness of the n-type 4H—SiC single crystal wafer was measured using a micrometer. Various ratios were then calculated using the above calculation results.

[0191] The results are shown in Table 12. As shown in Table 12, Example 1 showed a 1064-1 / α 1064-2 satisfies 0.80 or more and 1.3 or less, and further 1.0 or more and 1.2 or less. 532-1 / α 532-2 satisfies 0.80 or more and 1.3 or less, and further 1.0 or more and 1.2 or less. That is, in Example 1, the in-plane variation of the absorption coefficient at wavelengths of 532 nm and 1064 nm is suppressed.

[0192] [Table 12]

[0193] Furthermore, as shown in Table 2 above, in Example 1, (average central terrace width) / (average peripheral terrace width) is 1.198, a value close to 1, and the in-plane variation in terrace width is suppressed.

[0194] <Example 2> The configuration of Example 2 is as described in the first embodiment. As shown in Table 4 above, in Example 2, [N]+[Al] is 7.0×10 19 atoms / cm 3 or less, and [N]-[Al] is 5.0 × 10 18 atoms / cm 3 All of the above are met.

[0195] The wafer was placed in a spectrophotometer (Shimadzu Solidspec-3700i) and the transmittance was measured in the wavelength range of 400 to 1800 nm. The transmittance T at a wavelength of 1064 nm was used to calculate the absorption coefficient α at a wavelength of 1064 nm (similarly for a wavelength of 532 nm). The thickness L at the transmittance measurement position was measured using a non-contact thickness gauge.

[0196] The measurement points are as shown in Figure 11. The measurement results are shown in Table 13. 1064 is the absorption coefficient α at the wavelength of 1064 nm at each measurement point. 532 is the absorption coefficient α at the wavelength of 532 nm at each measurement point. 1064-1 / α 1064-2 is the α of the center point, measurement point 07 (second point) 1064 to "α 1064-2 " and α for each of the other measurement points 1064 to "α 1064-1 The value calculated by defining α in the table 532-1 / α 532-2 is the α of the center point, measurement point 07 (second point) 532 to "α 532-2 " and α for each of the other measurement points 532 to "α 532-1 " is the value calculated by defining α as ". In all 36 pairs of measurement point 07 (second point) and each of the other measurement points 01 to 06 and 08 to 37 (first points), 1064-1 / α 1064-2 and α 532-1 / α 532-2 was between 0.80 and 1.3. 1064 / α 532 was between 1.1 and 1.6.

[0197] [Table 13]

[0198] <Comparative Example 1> The configuration of Comparative Example 1 is as described in the first embodiment. As shown in Table 6 above, Comparative Example 1 has a [N]+[Al] of 7.0×10 19 atoms / cm 3 or less, and [N]-[Al] is 5.0 × 10 18 atoms / cm 3 None of the above is met.

[0199] The n-type 4H—SiC single crystal wafer, which had been sliced ​​and then polished by CMP, was placed in a spectrophotometer (Shimadzu UV-3600), and the transmittance at each of the first and second points was measured at predetermined wavelengths (532 nm, 1064 nm). The first point (center-side measurement point) was located 2.0 cm away from the wafer center, and the second point (outer-side measurement point) was located 6.0 cm away from the wafer center. The remaining procedures were the same as in Example 1, and various absorption coefficients and ratios were calculated.

[0200] The results are shown in Table 14. As shown in Table 14, in Comparative Example 1, α 1064-1 / α 1064-2 does not satisfy the range of 0.80 or more and 1.3 or less, or 1.0 or more and 1.2 or less.

[0201] [Table 14]

[0202] <Considerations on Theme 1> From the above, [N] + [Al] is 7.0 × 10 19 atoms / cm 3 Adjust the [N]-[Al] to 5.0×10 18 atoms / cm 3 It can be seen that by making the above adjustments, it is possible to realize n-type 4H—SiC single crystal wafers with reduced in-plane variation in the absorption coefficients at wavelengths of 532 nm and 1064 nm. It can also be seen that n-type 4H—SiC single crystal wafers that have undergone this adjustment have reduced variation in the absorption coefficients at wavelengths of 532 nm and 1064 nm at the same point (first point or second point). It can also be seen that n-type 4H—SiC single crystal wafers that have undergone this adjustment have reduced in-plane variation in terrace width. Furthermore, it can be seen that n-type 4H—SiC single crystal wafers that have undergone this adjustment have a high 4H polymorphism retention rate.

[0203] Theme 2 In Theme 2, [N] + [Al] is 7.0 × 10 19 atoms / cm 3 Adjust the [N]-[Al] to 5.0×1018 atoms / cm 3 By adjusting the above and further adjusting the [N] / [Al] ratio to between 1.5 and 3.0, it is confirmed that the in-plane variation in the absorption coefficient at wavelengths of 532 nm and 1064 nm can be suppressed, and n-type 4H-SiC single crystal wafers with reduced resistivity can be produced.

[0204] Example 1 The configuration of Example 1 is as described in the first embodiment. As shown in Table 1 above, Example 1 has a [N]+[Al] of 7.0×10 19 atoms / cm 3 Below, [N]-[Al] is 5.0 × 10 18 atoms / cm 3 or more, and [N] / [Al] satisfies 1.5 or more and 3.0 or less.

[0205] The resistivity of the resulting n-type 4H-SiC single crystal wafer was measured using a Napson EC-80P. Measurements were taken at multiple measurement points separated by a specified distance from the periphery. Table 3 above shows the measured values ​​at each measurement point. Figure 7 shows a graph of the measurement results. Figure 7 shows that the resistivity increases monotonically from the periphery to the center. The resistivity ranged from 15 to 25 mΩ·cm, with little variation (the difference between the upper and lower limits). Furthermore, the resistivity at the center of the wafer was kept below 50 mΩ·cm.

[0206] <Comparative Examples 1 to 4> The configurations of Comparative Examples 1 to 4 are as described in the first embodiment.

[0207] As shown in Table 6 above, in Comparative Example 1, [N] + [Al] was 7.0 × 10 19 atoms / cm 3 Below, [N]-[Al] is 5.0 × 10 18 atoms / cm 3 or more, and [N] / [Al] does not satisfy either of the conditions of 1.5 or more and 3.0 or less. As shown in Table 9, in Comparative Example 2, [N]-[Al] was 5.0 × 10 18 atoms / cm 3or more, and [N] / [Al] does not satisfy the condition of 1.5 or more and 3.0 or less. Furthermore, as shown in Table 10 above, in Comparative Example 3, the [N] / [Al] ratio does not satisfy the range of 1.5 or more and 3.0 or less. As shown in Table 11, in Comparative Example 4, [N] + [Al] was 7.0 × 10 19 atoms / cm 3 Does not meet the following:

[0208] The measurement results of the resistivity of Comparative Examples 1 to 4 are shown in Tables 8 to 11. As shown in Tables 8 to 11, the resistivity of Comparative Examples 1 to 4 was higher than that of Example 1, which had a resistivity range of 15 to 25 mΩ cm. Furthermore, as shown in Table 8, the resistivity of Comparative Example 1 measured at multiple locations within the surface varied greatly.

[0209] <Considerations on Theme 2> From the above, [N] + [Al] is 7.0 × 10 19 atoms / cm 3 Adjust the [N]-[Al] to 5.0×10 18 atoms / cm 3 By adjusting the above and further adjusting the [N] / [Al] ratio to between 1.5 and 3.0, it is clear that it is possible to suppress the in-plane variation in the absorption coefficient at wavelengths of 532 nm and 1064 nm, and to realize n-type 4H—SiC single crystal wafers with reduced resistivity.

[0210] As described above, in this embodiment, in n-type 4H—SiC single crystal wafers manufactured under N and Al co-doping conditions, optimal adjustment of [N] + [Al] and [N] - [Al] can suppress in-plane variations in the absorption coefficient at wavelengths of 1064 nm and 532 nm. Absorption coefficients are known to be related to dopant concentration. It can be said that n-type 4H—SiC single crystal wafers with suppressed in-plane variations in absorption coefficients have suppressed in-plane variations in dopant concentration.

[0211] Although the present disclosure has been described above with reference to the embodiments, the present disclosure is not limited to the above-described embodiments. Various modifications that can be understood by those skilled in the art can be made to the configuration and details of the present disclosure within the scope of the present disclosure. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0212] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. 1. Contains N and Al, The ratio of [N] / [Al], which is the ratio of [N], the concentration of N, to [Al], the concentration of Al, is 1.5 or more and 3.0 or less; The sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 is as follows: An n-type 4H-SiC single crystal ingot with a diameter of at least 4 inches. 2. An n-type 4H—SiC single crystal ingot according to 1, wherein the resistivity of the center portion is 50 mΩ·cm or less. 3. An n-type 4H—SiC single crystal ingot according to 2, having a resistivity of the center portion of 10 mΩ·cm or more. 4. An n-type 4H—SiC single crystal ingot according to any one of 1 to 3, having a 4H polymorphism retention rate of 99% or more. 5. An n-type 4H—SiC single crystal ingot according to any one of 1 to 4, in which the resistivity of the central portion is higher than that of the peripheral portion. 6. An n-type 4H—SiC single crystal ingot according to 5, wherein the resistivity increases monotonically from the outer periphery toward the center. 7. There is a step-terrace structure on the crystal growth surface, an average central terrace width, which is the average value of terrace widths of four terraces including one terrace present at the center of the crystal growth surface and three consecutive terraces connected to the one terrace and located closer to the periphery of the crystal growth surface than the one terrace; an average peripheral terrace width, which is the average of the terrace widths of four terraces, including one terrace located 5 mm away from the periphery of the crystal growth surface toward the center of the crystal growth surface, and three consecutive terraces connected to the one terrace and located closer to the center of the crystal growth surface than the one terrace; 7. An n-type 4H—SiC single crystal ingot according to any one of 1 to 6, wherein the ratio of (average central terrace width) / (average peripheral terrace width) is 1.3 or less. 8. An n-type 4H—SiC single crystal ingot according to 7, wherein the average width of the peripheral terrace is 5.0 μm or more. 9. An n-type 4H—SiC single crystal ingot according to 7 or 8, wherein the periphery of the crystal growth surface is thicker than the center of the crystal growth surface. 10. Contains N and Al, The ratio of [N] / [Al], which is the ratio of [N], the concentration of N, to [Al], the concentration of Al, is 1.5 or more and 3.0 or less; The sum of [N] and [Al] is 1.0 × 10 20 atoms / cm 3 is as follows: n-type 4H-SiC single crystal wafer with a diameter of 4 inches or more. 11. An n-type 4H—SiC single crystal wafer according to 10, wherein the resistivity of the center portion is 50 mΩ·cm or less. 12. An n-type 4H—SiC single crystal wafer according to 11, wherein the resistivity of the center portion is 10 mΩ·cm or more. 13. An n-type 4H—SiC single crystal wafer according to any one of 10 to 12, having a 4H polymorphism retention rate of 99% or more. 14. An n-type 4H—SiC single crystal wafer according to any one of 10 to 13, in which the resistivity of the central portion is higher than that of the peripheral portion within the wafer surface. 15. An n-type 4H—SiC single crystal wafer according to 14, wherein the resistivity within the plane of the wafer increases monotonically from the periphery toward the center. 16. Absorption coefficient α at a wavelength of 1064 nm at a first point on the substrate surface 1064-1 and an absorption coefficient α of a wavelength of 1064 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. 1064―2 The ratio of α 1064-1 / α 1064-2 16. The n-type 4H—SiC single crystal wafer according to any one of 10 to 15, wherein 17. An n-type 4H—SiC single crystal wafer according to 16, wherein the first point and the second point are separated by a distance of 40 mm or more. 18. Absorption coefficient α at the wavelength of 532 nm at the first point 532-1 and the absorption coefficient α at the second point at a wavelength of 532 nm. 532-2 The ratio of α 532-1 / α 532-2 18. An n-type 4H—SiC single crystal wafer according to 16 or 17, wherein 19. Alpha 1064-1 and the absorption coefficient α at the first point at a wavelength of 532 nm. 532-1 The ratio of α 1064-1 / α 532-1 19. An n-type 4H—SiC single crystal wafer according to any one of 16 to 18, wherein 20. Absorption coefficient α at a wavelength of 532 nm at a first point on the substrate surface 532-1 and an absorption coefficient α of a wavelength of 532 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. 532-2 The ratio of α 532-1 / α 532-2 20. The n-type 4H—SiC single crystal wafer according to any one of 10 to 19, wherein 21. An n-type 4H—SiC single crystal wafer according to 20, wherein the first point and the second point are separated by a distance of 40 mm or more. 22. Absorption coefficient α at the first point at a wavelength of 1064 nm 1064-1 and α 532-1 The ratio of α 1064-1 / α 532-1 22. The n-type 4H—SiC single crystal wafer according to 20 or 21, wherein 23. Contains N and Al, If the concentration of N is [N] and the concentration of Al is [Al], then [N] + [Al] is 7.0 × 10 19 atoms / cm 3 or less, and [N]-[Al] is 5.0×10 18atoms / cm 3 23. An n-type 4H—SiC single crystal wafer as set forth in any one of 10 to 22 above. 24. A growth step of contacting a seed crystal with a raw material solution containing Si and C to form a growth layer of n-type 4H—SiC single crystal on the surface of the seed crystal, In the growth step, N and Al are doped into the growth layer, and the ratio of [N], which is the concentration of N in the growth layer, to [Al], which is the concentration of Al, in the growth layer, [N] / [Al], is 1.5 or more and 3.0 or less, and the sum of [N] and [Al] is 1.0×10 20 atoms / cm 3 A method for producing an n-type 4H—SiC single crystal ingot in which the growth layer is produced under the following conditions: 25. A method for producing an n-type 4H—SiC single crystal ingot according to 24, wherein the raw material solution further contains Cr. 26. A method for producing an n-type 4H—SiC single crystal ingot according to 25, wherein the total content of Si, C, and Cr in the raw material solution is 99 mol % or more. 27. In the growing step: 27. A method for producing an n-type 4H—SiC single crystal ingot according to any one of 24 to 26, wherein the growth layer has a diameter of 4 inches or more. 28. In the growing step: 28. A method for producing an n-type 4H—SiC single crystal ingot according to any one of 24 to 27, wherein the growth layer has a resistivity of 50 mΩ·cm or less in the center. 29. In the growing step: 29. A method for producing an n-type 4H—SiC single crystal ingot according to 28, which produces a growth layer having a resistivity of 10 mΩ·cm or more at its center. 30. In the growing step, 30. A method for producing an n-type 4H—SiC single crystal ingot according to any one of 24 to 29, which produces a growth layer having a 4H polymorphism retention rate of 99% or more. 31. A method for producing an n-type 4H—SiC single crystal ingot according to any one of 24 to 30, in which the resistivity of the central portion is higher than that of the peripheral portion. 32. In the growing step: 31. A method for producing an n-type 4H—SiC single crystal ingot according to 31, which produces a growth layer whose resistivity monotonically increases from the outer periphery toward the center. 33. In the growing step: There is a step-terrace structure on the crystal growth surface, an average central terrace width, which is the average value of terrace widths of four terraces including one terrace present at the center of the crystal growth surface and three consecutive terraces connected to the one terrace and located closer to the periphery of the crystal growth surface than the one terrace; an average peripheral terrace width, which is the average of the terrace widths of four terraces, including one terrace located 5 mm away from the periphery of the crystal growth surface toward the center of the crystal growth surface, and three consecutive terraces connected to the one terrace and located closer to the center of the crystal growth surface than the one terrace; 33. A method for producing an n-type 4H—SiC single crystal ingot according to any one of 24 to 32, which produces a growth layer in which the ratio (average central terrace width) / (average peripheral terrace width) is 1.3 or less. 34. In the growth step, when the concentration of N in the growth layer is [N] and the concentration of Al is [Al], [N] + [Al] is 7.0 × 10 19 atoms / cm 3 and [N]-[Al] is 5.0×10 18 atoms / cm 3 34. A method for producing an n-type 4H—SiC single crystal wafer according to any one of 24 to 33, wherein the growth layer is formed under the above conditions. 35. A method for producing n-type 4H—SiC single crystal wafers, comprising producing an n-type 4H—SiC single crystal ingot by the method for producing an n-type 4H—SiC single crystal ingot according to any one of 24 to 34, and slicing wafers from the n-type 4H—SiC single crystal ingot.

[0213] Furthermore, some or all of the above-described embodiments can be described as, but are not limited to, the following supplementary notes. 1´. Absorption coefficient α at a wavelength of 1064 nm at the first point on the substrate surface 1064-1and an absorption coefficient α of a wavelength of 1064 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. 1064―2 The ratio of α 1064-1 / α 1064-2 is between 0.80 and 1.3, n-type 4H-SiC single crystal wafer with a diameter of 4 inches or more. 2'. An n-type 4H—SiC single crystal wafer as recited in 1', wherein the first point and the second point are separated by a distance of 40 mm or more. 3´. Absorption coefficient α at the wavelength of 532 nm at the first point 532-1 and the absorption coefficient α at the second point at a wavelength of 532 nm. 532-2 The ratio of α 532-1 / α 532-2 1'. The n-type 4H—SiC single crystal wafer according to 1' or 2', wherein 4´. α 1064-1 and the absorption coefficient α at the first point at a wavelength of 532 nm. 532-1 The ratio of α 1064-1 / α 532-1 4. The n-type 4H—SiC single crystal wafer according to any one of 1′ to 3′, wherein 5´. Absorption coefficient α at a wavelength of 532 nm at the first point on the substrate surface 532-1 and an absorption coefficient α of a wavelength of 532 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. 532-2 The ratio of α 532-1 / α 532-2 is between 0.80 and 1.3, n-type 4H-SiC single crystal wafer with a diameter of 4 inches or more. 6'. An n-type 4H—SiC single crystal wafer as set forth in 5', wherein the first point and the second point are separated by a distance of 40 mm or more. 7´. Absorption coefficient α at the wavelength of 1064 nm at the first point 1064-1 and α 532-1 The ratio of α 1064-1 / α 532-1 5' or 6', wherein the n-type 4H—SiC single crystal wafer has a ρ of 1.1 or more and 1.6 or less. 8´. Contains N and Al, If the concentration of N is [N] and the concentration of Al is [Al], then [N] + [Al] is 7.0 × 10 19 atoms / cm 3 or less, and [N]-[Al] is 5.0×10 18 atoms / cm 3 8. An n-type 4H—SiC single crystal wafer as set forth in any one of 1′ to 7′ above. 9´. An n-type 4H—SiC single crystal wafer as recited in 8´, wherein [N] / [Al] is 1.5 or more and 3.0 or less. 10´. An n-type 4H—SiC single crystal wafer according to any one of 1´ to 9´, having a resistivity of the center portion of 50 mΩ·cm or less. 11´. An n-type 4H—SiC single crystal wafer according to any one of 1´ to 10´, having a resistivity of the center portion of 10 mΩ·cm or more. 12'. An n-type 4H—SiC single crystal wafer according to any one of 1' to 11', wherein the resistivity at the first point is higher than the resistivity at the second point. 13´. An n-type 4H—SiC single crystal wafer as set forth in any one of 1´ to 12´, wherein the resistivity within the plane of the wafer increases monotonically from the outer periphery toward the center. 14'. An n-type 4H—SiC single crystal wafer according to any one of 1' to 13', having a 4H polymorphism retention rate of 99% or more. 15'. A growth step of contacting a seed crystal with a raw material solution containing Si and C to form a growth layer of n-type 4H—SiC single crystal having a diameter of 4 inches or more on the surface of the seed crystal; a slicing step of cutting wafers from the growth layer; and In the growth step, N and Al are doped into the growth layer. When the concentration of N in the growth layer is [N] and the concentration of Al is [Al], [N] + [Al] is 7.0 × 10 19 atoms / cm 3 and [N]-[Al] is 5.0×10 18 atoms / cm 3 A method for producing an n-type 4H—SiC single crystal wafer in which the growth layer is formed under the above conditions. 16'. A method for producing an n-type 4H—SiC single crystal wafer as set forth in 15', wherein in the growth step, the growth layer is formed under conditions in which the [N] / [Al] ratio is 1.5 or more and 3.0 or less. 17'. The method for producing an n-type 4H—SiC single crystal wafer according to 15' or 16', wherein the raw material solution further contains Cr. 18'. In the growing step, The wafer obtained by cutting out the growth layer is Absorption coefficient α at a wavelength of 1064 nm at a first point on the substrate surface 1064-1 and an absorption coefficient α of a wavelength of 1064 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. 1064―2 The ratio of α 1064-1 / α 1064-2 is between 0.80 and 1.3, It is 4 inches or larger in diameter, 18. A method for producing an n-type 4H—SiC single crystal wafer as set forth in any one of 15′ to 17′, wherein the growth layer has a 4H polymorphism retention rate of 99% or higher. 19'. A method for producing an n-type 4H—SiC single crystal wafer as set forth in 18', wherein the first point and the second point are separated by a distance of 40 mm or more. 20'. In the growing step, The wafer obtained by cutting out the growth layer is Absorption coefficient α at a wavelength of 532 nm at a first point on the substrate surface 532-1 and an absorption coefficient α of a wavelength of 532 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. 532―2 The ratio of α 532-1 / α 532-2 is between 0.80 and 1.3, It is 4 inches or larger in diameter, 19'. The method for producing an n-type 4H—SiC single crystal wafer according to any one of 15' to 19', wherein the growth layer has a 4H polymorphism retention rate of 99% or more. 21'. A method for cutting an n-type 4H—SiC single crystal wafer, comprising irradiating a laser onto an n-type 4H—SiC single crystal wafer as set forth in any one of 1' to 14' to divide the wafer.

[0214] This application claims priority based on Japanese Patent Application No. 2024-116771, filed July 22, 2024, the disclosure of which is incorporated herein by reference in its entirety. [Explanation of symbols]

[0215] 1 Crystal growth equipment 3 Crucible 4a, 4b heater 5 Raw material solution 7. Lifting shaft 9 seed crystals 10 n-type 4H-SiC single crystal ingots 11 n-type 4H-SiC single crystal 10a Crystal growth surface

Claims

1. Contains N and Al, [N] / [Al], which is the ratio of [N], which is the concentration of N, to [Al], which is the concentration of Al, is 1.5 or more and 3.0 or less; The sum of [N] and [Al] is 1.0 × 10 ２０ atoms / cm 3 is as follows: An n-type 4H-SiC single crystal ingot having a diameter of 4 inches or more.

2. 2. The n-type 4H—SiC single crystal ingot according to claim 1, wherein the resistivity of the center portion is 50 mΩ·cm or less.

3. 3. The n-type 4H—SiC single crystal ingot according to claim 2, wherein the resistivity of the center portion is 10 mΩ·cm or more.

4. 2. The n-type 4H—SiC single crystal ingot according to claim 1, wherein the 4H polymorphism retention rate is 99% or more.

5. 2. An n-type 4H—SiC single crystal ingot according to claim 1, wherein the resistivity of the central portion is higher than that of the peripheral portion.

6. 6. An n-type 4H—SiC single crystal ingot according to claim 5, wherein the resistivity increases monotonically from the outer periphery toward the center.

7. A step-terrace structure exists on the crystal growth surface, an average central terrace width, which is the average value of terrace widths of four terraces including one terrace present at the center of the crystal growth surface and three consecutive terraces connected to the one terrace and located closer to the outer periphery of the crystal growth surface than the one terrace; an average peripheral terrace width, which is the average of the terrace widths of four terraces, including one terrace located 5 mm away from the outer periphery of the crystal growth surface toward the center of the crystal growth surface, and three consecutive terraces connected to the one terrace and located closer to the center of the crystal growth surface than the one terrace; 2. An n-type 4H—SiC single crystal ingot according to claim 1, wherein the ratio of (average central terrace width) / (average peripheral terrace width) is 1.3 or less.

8. 8. The n-type 4H—SiC single crystal ingot according to claim 7, wherein the average width of the peripheral terrace is 5.0 μm or more.

9. 8. An n-type 4H—SiC single crystal ingot according to claim 7, wherein the periphery of the crystal growth surface is thicker than the center of the crystal growth surface.

10. Contains N and Al, [N] / [Al], which is the ratio of [N], which is the concentration of N, to [Al], which is the concentration of Al, is 1.5 or more and 3.0 or less; The sum of [N] and [Al] is 1.0 × 10 ２０ atoms / cm 3 is as follows: An n-type 4H—SiC single crystal wafer having a diameter of 4 inches or more.

11. The n-type 4H—SiC single crystal wafer according to claim 10, wherein the resistivity of the center portion is 50 mΩ·cm or less.

12. The n-type 4H—SiC single crystal wafer according to claim 11, wherein the resistivity of the center portion is 10 mΩ·cm or greater.

13. The n-type 4H—SiC single crystal wafer according to claim 10, wherein the 4H polymorphism retention rate is 99% or more.

14. 11. The n-type 4H—SiC single crystal wafer according to claim 10, wherein the resistivity of the central portion is higher than the resistivity of the peripheral portion within the plane of the wafer.

15. The n-type 4H—SiC single crystal wafer according to claim 14, wherein the resistivity increases monotonically from the outer periphery toward the center within the plane of the wafer.

16. Absorption coefficient α at a wavelength of 1064 nm at a first point on the substrate surface １０６４－１ and an absorption coefficient α of a wavelength of 1064 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. １０６４―２ The ratio of α １０６４－１ / α １０６４－２ The n-type 4H—SiC single crystal wafer according to claim 10, wherein the σ is not less than 0.80 and not more than 1.

3.

17. 17. The n-type 4H—SiC single crystal wafer according to claim 16, wherein the first point and the second point are separated by 40 mm or more.

18. The absorption coefficient α at the first point at a wavelength of 532 nm ５３２－１ and the absorption coefficient α at the second point at a wavelength of 532 nm. ５３２－２ The ratio of α ５３２－１ / α ５３２－２ The n-type 4H—SiC single crystal wafer according to claim 16, wherein the n-type 4H—SiC single crystal wafer has a ρ of 0.80 or more and 1.3 or less.

19. α １０６４－１ and the absorption coefficient α at the first point at a wavelength of 532 nm. ５３２－１ The ratio of α １０６４－１ / α ５３２－１ The n-type 4H—SiC single crystal wafer according to claim 16, wherein the n-type 4H—SiC single crystal wafer has a ρ of 1.1 or more and 1.6 or less.

20. Absorption coefficient α at a wavelength of 532 nm at a first point on the substrate surface ５３２－１ and an absorption coefficient α of a wavelength of 532 nm at a second point on the substrate surface that is located closer to the outer periphery of the substrate surface than the first point. ５３２－２ The ratio of α ５３２－１ / α ５３２－２ The n-type 4H—SiC single crystal wafer according to claim 10, wherein the σ is not less than 0.80 and not more than 1.

3.

21. 21. The n-type 4H—SiC single crystal wafer according to claim 20, wherein the first point and the second point are separated by 40 mm or more.

22. The absorption coefficient α at the first point at a wavelength of 1064 nm １０６４－１ and α ５３２－１ The ratio of α １０６４－１ / α ５３２－１ The n-type 4H—SiC single crystal wafer according to claim 20, wherein the n-type 4H—SiC single crystal wafer has a ρ of 1.1 or more and 1.6 or less.

23. Contains N and Al, If the concentration of N is [N] and the concentration of Al is [Al], then [N] + [Al] is 7.0 × 10 １９ atoms / cm 3 or less, and [N]-[Al] is 5.0 × 10 １８ atoms / cm 3 The n-type 4H—SiC single crystal wafer according to claim 10.

24. a growth step of contacting a seed crystal with a raw material solution containing Si and C to form a growth layer of an n-type 4H—SiC single crystal on the surface of the seed crystal; In the growth step, the growth layer is doped with N and Al, and the ratio of [N], which is the concentration of N in the growth layer, to [Al], which is the concentration of Al, is [N] / [Al], is 1.5 to 3.0, and the sum of [N] and [Al] is 1.0×10 ２０ atoms / cm 3 A method for producing an n-type 4H—SiC single crystal ingot in which the growth layer is produced under the following conditions:

25. The method for producing an n-type 4H—SiC single crystal ingot according to claim 24, wherein the raw material solution further contains Cr.

26. 26. The method for producing an n-type 4H—SiC single crystal ingot according to claim 25, wherein the total content of Si, C, and Cr in the raw material solution is 99 mol % or more.

27. In the growing step, 25. The method for producing an n-type 4H—SiC single crystal ingot according to claim 24, which produces the growth layer having a diameter of 4 inches or more.

28. In the growing step, 25. The method for producing an n-type 4H—SiC single crystal ingot according to claim 24, wherein the growth layer has a resistivity of 50 mΩ·cm or less in the center portion.

29. In the growing step, 29. The method for producing an n-type 4H—SiC single crystal ingot according to claim 28, wherein the growth layer has a resistivity of 10 mΩ·cm or more in the center portion.

30. In the growing step, 25. The method for producing an n-type 4H—SiC single crystal ingot according to claim 24, wherein the growth layer has a 4H polymorphism retention rate of 99% or more.

31. The method for producing an n-type 4H—SiC single crystal ingot according to claim 24, wherein the resistivity of the central portion is higher than the resistivity of the peripheral portion.

32. In the growing step, 32. The method for producing an n-type 4H—SiC single crystal ingot according to claim 31, wherein the growth layer has a resistivity that monotonically increases from the outer periphery toward the center.

33. In the growing step, A step-terrace structure exists on the crystal growth surface, an average central terrace width, which is the average value of terrace widths of four terraces including one terrace present at the center of the crystal growth surface and three consecutive terraces connected to the one terrace and located closer to the outer periphery of the crystal growth surface than the one terrace; an average peripheral terrace width, which is the average of the terrace widths of four terraces, including one terrace located 5 mm away from the outer periphery of the crystal growth surface toward the center of the crystal growth surface, and three consecutive terraces connected to the one terrace and located closer to the center of the crystal growth surface than the one terrace; 25. The method for producing an n-type 4H—SiC single crystal ingot according to claim 24, wherein the growth layer has a ratio of (average central terrace width) / (average peripheral terrace width) of 1.3 or less.

34. In the growth step, when the concentration of N in the growth layer is [N] and the concentration of Al is [Al], [N] + [Al] is 7.0 × 10 １９ atoms / cm 3 or less, and [N]-[Al] is 5.0 × 10 １８ atoms / cm 3 The method for producing an n-type 4H—SiC single crystal wafer according to claim 24, wherein the growth layer is formed under the above conditions.

35. A method for producing an n-type 4H—SiC single crystal wafer, comprising producing an n-type 4H—SiC single crystal ingot by the method for producing an n-type 4H—SiC single crystal ingot according to any one of claims 24 to 34, and slicing wafers from the n-type 4H—SiC single crystal ingot.

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