Method for manufacturing a homogeneous SiC bulk single crystal with shear dislocation distribution and a SiC substrate

Abstract

This invention provides a method for manufacturing SiC bulk single crystals and an improved single-crystal SiC substrate. [Solution] A SiC seed crystal 8 having a growth surface 18 is placed in the crystal growth region of a growth crucible, raw material is introduced into the growth crucible, and a SiC growth gas phase is generated at a growth temperature of up to 2400°C and a growth pressure of 0.1 mbar to 100 mbar, and a SiC bulk single crystal 2 grows on the SiC seed crystal by deposition from the gas phase. Before starting growth, the presence of seed helical dislocations is checked on the growth surface, the growth surface is divided into seed segments, the local helical dislocation seed segment density associated with each seed segment is identified and processed, and nucleation centers are generated in each seed segment where the local helical dislocation seed segment density exceeds the total helical dislocation seed density identified for the entire growth surface by at least 1.5 to 4 times, and each nucleation center is the starting point for at least one compensating helical dislocation during the subsequent growth.

Description

[Technical Field]

[0001] The contents of European patent application EP21163803.6 are incorporated herein by reference.

[0002] The present invention relates to a method for producing at least one SiC bulk single crystal by sublimation growth and to a single-crystal SiC substrate. [Background technology]

[0003] Silicon carbide (SiC), a semiconductor material, is used as a starting material for power electronics semiconductor components, high-frequency components, and special light-emitting semiconductor components due to its excellent physical, chemical, electrical, and optical properties. These components require SiC substrates (=SiC wafers) with the largest possible substrate diameter and the highest possible quality.

[0004] The base of a SiC substrate is a high-quality SiC bulk single crystal, which is typically manufactured by physical vapor deposition (PVT), particularly by the (sublimation) method—an example of which is described in Patent Document 1. In this growth method, a single-crystal SiC disk, as a SiC seed crystal, is introduced into a growth crucible along with suitable raw material. Under controlled temperature and pressure conditions, the raw material is sublimated, and gaseous seeds are deposited onto the SiC seed crystal, thereby allowing the SiC bulk single crystal to grow there.

[0005] Next, a disc-shaped single-crystal SiC substrate is cut from a SiC bulk single crystal, for example using a jigsaw. After the surface is purified through a multi-stage process, particularly several polishing steps, at least one thin single-crystal epitaxial layer made of SiC or GaN (gallium nitride) is added to these single-crystal SiC substrates as part of the component production process. The properties of this epitaxial layer, and ultimately the properties of the component manufactured from it, depend heavily on the quality of the SiC substrate or the underlying SiC bulk single crystal.

[0006] In the fabrication of epitaxial layers, helical dislocations (TSDs), which may be present in the SiC substrate, are particularly important. This is because helical dislocations can propagate into the epitaxial layer, potentially resulting in reduced quality and / or yield of the resulting electronic components. To achieve high yield, crystal defects such as helical dislocations, which can occur due to deviations from the ideal crystal shape during crystal growth (Kristallwachstum), should be avoided as much as possible. Furthermore, the fabrication of SiC bulk single crystals using the PVT process is very costly and time-consuming. Materials that cannot be further used for component manufacturing due to imperfect crystal structures caused by dislocations result in a significant decrease in yield and an increase in cost.

[0007] Patent Document 2 describes a method based on a two-stage growth process, in which, in the first growth stage, with a low growth rate and high pressure, helical dislocations in the edge region of the growing SiC bulk single crystal are converted into stacking faults, which then grow outward perpendicular to the growth direction (wachsen). In the subsequent second growth stage, the growth rate is increased (under reduced pressure), and the SiC bulk single crystal that grows thereafter has a crystal bulk with a reduced number of helical dislocations in the edge region. However, even if the helical dislocation density is low only in the edge region, it is not sufficient to make it economically possible to manufacture electronic components on a SiC substrate. Therefore, a further reduction in the helical dislocation density is desirable. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] U.S. Patent No. 8,865,324 [Patent Document 2] U.S. Patent No. 9,234,297 [Patent Document 3] U.S. Patent Application Publication No. 2006 / 0073707 Specification [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] The object of the present invention is to provide a method for manufacturing SiC bulk single crystals and an improved single-crystal SiC substrate, which are improved compared to known solutions. [Means for solving the problem]

[0010] To solve the problems of this method, a method corresponding to the features of claim 1 is described. The method according to the present invention is a method for producing at least one SiC bulk single crystal by sublimation growth, wherein, prior to the start of growth, a SiC seed crystal having a growth surface is placed in the crystal growth region of a growth crucible, and in the SiC storage region of the growth crucible, a SiC raw material, in the form of a single crystal or polycrystalline solid block, preferably 3.0 g / cm³ 2 ~3.21 g / cm³ 2This method involves introducing SiC raw material materials having a certain density, or in particular, combinations of these different SiC raw material materials. During growth (Zuechtung), particularly at the growth interface of the growing SiC bulk single crystal, at growth temperatures of up to 2400°C and growth pressures of 0.1 mbar to 100 mbar, a SiC growth gas phase is generated there by the sublimation of the SiC raw material materials and the transport of the sublimated gaseous components into the crystal growth region. Within this phase, a SiC bulk single crystal grows on the SiC seed crystal by deposition from the SiC growth gas phase. In this process, before growth begins, the SiC seed crystal is inspected for the presence of seed helical dislocations on the growth surface. In this inspection, the growth surface is divided into seed segments, and the density of the relevant local helical dislocation seed segment is identified for each seed segment. Furthermore, before growth begins, the growth surface of the SiC seed crystal is treated to generate nucleation centers within each seed segment, thereby creating a local helical dislocation seed segment density at least 1.5 to 4 times, and particularly at least 2 times, higher than the total helical dislocation seed density identified for the entire growth surface. These nucleation centers are (particularly possible) starting points for at least one compensating helical dislocation each during subsequent growth.

[0011] Each seed segment may be circular, square, or rectangular, and each is preferably 1 mm in diameter. 2 ~100mm 2 Preferably 5 mm 2 or 10mm 2 , may have a seed segment area. Other seed segment geometries are also possible. Preferably, the seed segment geometry and / or seed segment area of ​​all seed segments are the same. An exception to this may be, for example, a seed segment at the edge of a SiC seed crystal. However, in principle, seed segments may also have seed segment geometry and / or seed segment area that deviate from each other in other respects, particularly to an arbitrary degree.

[0012] In this case, the total helical dislocation species density can be determined, in particular, by relating the number of all species helical dislocations identified on the entire growth surface of the SiC seed crystal to the total area of ​​this growth surface. Alternatively, the total helical dislocation species density can also be determined as the arithmetic mean of the local helical dislocation species segment densities of all species segments on the growth surface. In this respect, the total helical dislocation species density is also called the overall and / or average helical dislocation species density.

[0013] Here, a helical dislocation is understood to be both a pure helical dislocation and a mixed form that also has at least one component in the m-crystal direction or the a-crystal direction.

[0014] Each nucleation center can, though not necessarily, be an actual starting point for compensating helical dislocations formed during crystal growth. In particular, this type of compensating helical dislocation forms at exactly one nucleation center. However, a nucleation center can also be a starting point for two or more compensating helical dislocations. In particular, a nucleation center is generated for all types of helical dislocations detected.

[0015] Conveniently, nucleation centers are generated in locations where an increase in local helical dislocation seed segment density was detected in previous, particularly segment-by-segment, examinations.

[0016] It is recognized that the main cause of the local increase in screw dislocation density in a growing SiC bulk single crystal (and thus also in the subsequently produced disk-shaped SiC substrate) is the SiC seed crystal used for growth. Therefore, the seed screw dislocations present in the SiC seed crystal can propagate in the growth direction into the growing SiC bulk single crystal during the growth process. To avoid this, the growth surface of the SiC seed crystal is treated, thereby providing specifically inserted or applied nucleation centers. At the start of the growth process, these nucleation centers serve as the starting points for additional screw dislocations, i.e., compensating screw dislocations. Then, such compensating screw dislocations arising from specifically placed nucleation centers can preferably recombine with the screw dislocations continuing from the SiC seed crystal at the position of the nucleation center.

[0017] By the interaction between the screw dislocations originating from the SiC seed crystal and the screw dislocations (= compensating screw dislocations) nucleated at the nucleation centers, for example in its artificial surface structure, these screw dislocations recombine and cancel each other out. This favorable recombination occurs particularly when screw dislocations with different rotation directions, i.e., different signs of their Burgers vectors, are involved. In the SiC seed crystal, the ratio of the number of screw dislocations with a positive Burgers vector to the number of screw dislocations with a negative Burgers vector is usually approximately 1. Therefore, due to the deliberately induced compensating screw dislocations, the proportions of both in the growing SiC bulk single crystal can be reduced. This is particularly true at the positions where an increase in the local screw dislocation species segment density is detected within the SiC seed crystal during inspection and the nucleation centers are formed in the targeted manner accordingly.

[0018] In addition to the above mechanisms for generating compensating screw dislocations, it is also possible to additionally generate microscopic internal surfaces by treating, in particular structuring, the growth surface of the SiC seed crystal in relation to the initial crystal growth process. This microscopic inner surface can, inter alia, be the starting point for additional screw dislocations having positive or negative Burgers vectors, which can advantageously also contribute, as compensating screw dislocations, to reducing the (increased local) screw dislocation density.

[0019] That is, screw dislocations that recombine with each other preferably cancel each other out and no longer exist in the crystal structure of the growing SiC bulk single crystal after the recombination site. Thereby, the screw dislocation density in the growing SiC bulk single crystal decreases both locally and globally. Furthermore, in the growing SiC bulk single crystal, the distribution of screw dislocations becomes uniform. Then, the remaining screw dislocations are preferably distributed and arranged very homogeneously in the radial or transverse direction (i.e., inside the cross-sectional area of the growing SiC bulk single crystal in a direction perpendicular to the growth direction; in contrast, the growth direction of the growing SiC bulk single crystal is also understood as the axial direction).

[0020] By the method according to the invention, it is possible to preferably reduce and in particular homogenize the screw dislocation density in the growing SiC bulk single crystal (and thus also in the disk-shaped SiC substrate subsequently manufactured therefrom), everywhere and not only, for example, in the edge region. This has advantages compared to the methods known hitherto.

[0021] Inspection and processing of SiC seed crystals before growth commencement are performed, particularly before placing the SiC seed crystals in the growth crucible. During inspection, the SiC seed crystals are characterized with respect to their seed helical dislocations before being used in the growth process. In particular, seed segments with increased local helical dislocation seed segment density are defined (=identified) and marked in order to carry out processing to generate nucleation centers in the correct locations. Marking is performed, in particular, by using an xy stage, which allows for precise positioning of the SiC seed crystal being inspected in two mutually orthogonal lateral directions (= x and y directions). The x and y coordinates of seed segments with increased local helical dislocation seed segment density are determined and stored.

[0022] Overall, the growth method according to the present invention can be used to produce bulk SiC single crystals that can be obtained from high-quality SiC substrates. Such SiC substrates, having high precision in their SiC crystal structure, provide nearly ideal conditions for subsequent process steps to be carried out in connection with component manufacturing. That is, the SiC bulk single crystals produced by the present invention can be further used very efficiently, particularly in the manufacture of semiconductor components and / or high-frequency components.

[0023] The method according to the present invention can produce not only a single SiC bulk single crystal, but also a larger number, for example, 2, 3, 4, 5, or preferably up to 10 SiC bulk single crystals. A method of growing two SiC bulk single crystals, particularly those positioned vertically or horizontally in the direction of the central longitudinal axis, is advantageous, as they grow (aufwachsen) on both sides of the SiC storage region when viewed in the direction of the central longitudinal axis.

[0024] Advantageous embodiments of the method according to the present invention will become apparent from the features of the claims dependent on claim 1.

[0025] In each seed segment where an increase in local helical dislocation seed segment density is detected, it is preferable to have an embodiment in which a number of nucleation centers is generated that is at least half the number of dislocations of the seed helical dislocations identified within that seed segment. In particular, the ratio of nucleation number to dislocation number is in the range of 0.5 to 1. This achieves that for as many, preferably all, of the identified seed helical dislocations as possible, there is a starting point for compensating helical dislocations to be formed later in the SiC bulk single crystal grown on the seed crystal.

[0026] In a further favorable embodiment, nucleation centers are generated by locally limited, and particularly additionally implemented, structuring of the growth surface. In this case, structuring can be carried out, in particular, by material removal and / or material application. By targeted structuring of the growth surface, for example, by locally generating one or more scratches and / or locally etching, nucleation centers, and thus possible starting points for compensating helical dislocations, can be formed very easily and very efficiently. On such specifically generated structures on the growth surface of the SiC seed crystal, compensating helical dislocations nucleate particularly well, especially simultaneously with the start of the growth process. The structuring roughens the growth surface, particularly in the areas of structuring. In such structured regions, the growth surface preferably has 2 to 3 times higher roughness compared to unstructured regions on the SiC seed crystal growth surface where no seed helical dislocations are detected and where a roughness of Ra ≤ 0.4 nm is particularly given. In other words, the surface roughness in the region of the SiC seed crystal growth surface that is specifically structured to form a nucleation center is set to be at least 2 to 3 times greater than that in the unstructured region of the SiC seed crystal growth surface.

[0027] In a more favorable embodiment, nucleation centers are generated by localized treatment or processing of the growth surface by laser irradiation. Laser radiation is typically used to structure the growth surface, particularly by removing material, but sometimes it is used in a way that applies material as needed. Laser radiation can very simply structure the growth surface so that nucleation centers can be formed.

[0028] In a more favorable embodiment, nucleation centers are generated by a locally limited coating of the growth surface with an additive, particularly by lithography. The coating with the additive carries out structuring of the growth surface by material application. As the additive for the locally limited coating of the growth surface, at least one material selected from the group consisting of carbon (C), silicon dioxide (SiO2), graphite, and graphene is used.

[0029] In another favorable embodiment, nucleation centers are generated by locally limited polishing of the growth surface. Polishing, in particular, carries out structuring by material removal of the growth surface. Preferably, the locally limited polishing is carried out by a diamond suspension and / or a suitable chemical mechanical polishing method—which is preferred—where the chemical mechanical polishing method is preferably carried out defect-selectively or TSD-selectively, i.e., in particular, only at locations where seed helical dislocations are present on the growth surface of the SiC seed crystal. With respect to the polishing process, it is possible to achieve particularly higher surface roughness locally, for example, by subsequently treating the corresponding area with a coarser-grained polishing paste (and thus roughening it again) or by omitting the finer-grained polishing paste from the final treatment.

[0030] In a further favorable embodiment, nucleation centers are generated by locally limited etching of the growth surface. In particular, etching results in a material removal structure on the growth surface. The etching is preferably carried out selectively from defects or TSDs, i.e., only at locations where seed helical dislocations are present on the growth surface of the SiC seed crystal.

[0031] In another further advantageous embodiment, nanostructures are generated on the growth surface of a SiC seed crystal to generate nucleation centers. The generated nanostructures have geometric dimensions in the thickness or height direction, particularly in the range of 1 nanometer (1 nm) to several nanometers, preferably up to 10 nm, although in principle, even thicker nanostructures are possible. The actual thickness of the nanostructure depends in particular on the method applied to manufacture it.

[0032] The above embodiments for generating nucleation centers on the growth surface of SiC seed crystals can preferably be combined with each other.

[0033] In a more convenient embodiment, the inspection for seed helical dislocations is performed by X-ray topography. X-ray topography is a commercially available, advantageously non-destructive measurement method that allows for the examination of the growth surface of a SiC seed crystal for the presence and distribution of seed helical dislocations across the entire surface.

[0034] In another convenient embodiment, the inspection for seed helical dislocations and the treatment of the growth surface of the SiC seed crystal for generating nucleation centers are carried out in a combined manner. In this combined method, the inspection for seed helical dislocations and the treatment of the growth surface are carried out simultaneously (in parallel). This saves time and cost. However, in principle, these two method steps can be carried out sequentially.

[0035] To solve the problems related to the SiC substrate, a SiC substrate corresponding to the features of claim 11 is disclosed. The single-crystal SiC substrate according to the present invention is a single-crystal SiC substrate manufactured from a sublimation-grown SiC bulk single crystal, having all major surfaces, where each major surface is virtually divided into substrate segments each having a related substrate segment surface, and each substrate segment has a local screw dislocation substrate segment density. This density is a numerical value indicating the number of substrate screw dislocations present in this substrate segment, particularly detectable on all major surfaces, with respect to the substrate segment area of this substrate segment. Further, the SiC substrate has a total screw dislocation substrate density applied to all major surfaces. The SiC substrate also has a partial surface formed by at least 85% of all major surfaces, where the local screw dislocation substrate segment density of all substrate segments located inside the partial surface deviates from the total screw dislocation substrate density by a maximum of 25%.

[0036] The virtual substrate segments can each be, in particular, circular, square or rectangular, and each preferably has a substrate segment area of 1 mm 2 ~100 mm 2 Preferably 5 mm 2 or 10 mm 2 and may have a substrate segment area of. Other substrate segment geometries are also possible. Preferably, the substrate segment geometries and / or substrate segment areas of all substrate segments are each the same. The exception may apply, for example, to substrate segments located at the edges of the SiC substrate. However, in principle, the substrate segments can have substrate segment geometries and / or substrate segment areas that deviate from each other at other points, particularly deviating from each other to any extent.

[0037] In this case, the total helical dislocation substrate density can be determined in particular by relating the number of all substrate helical dislocations present and / or detectable on the entire main surface of the SiC substrate to the area value of this entire main surface. Alternatively, the total helical dislocation substrate density can also be determined in particular as the arithmetic mean of the local helical dislocation substrate segment densities of all substrate segments on the entire main surface. In this respect, the total helical dislocation substrate density can also be referred to as the overall and / or average helical dislocation substrate density.

[0038] The partial surface, formed by at least 85% of the total main surface, may be continuous and may include, for example, a central or edge region. However, the partial surface may be formed discontinuously. This partial surface advantageously has a very homogeneous distribution of substrate helical dislocations and is therefore particularly suitable for the manufacture of electronic components.

[0039] In the field of epitaxial coating of SiC substrates for manufacturing high-quality components with high yield, it is crucial that the SiC substrate has not only a low number of substrate helical dislocations, but also that the substrate helical dislocations are distributed as uniformly as possible in the lateral direction. This is because substrate helical dislocations can propagate into the epitaxial layer. For example, a large number of helical dislocations in a small space (i.e., a high local helical dislocation density) can lead to a decrease in the lifetime of local charge carriers and a decrease in the breakdown voltage of electronic components manufactured from them. Using a SiC substrate with a heterogeneous and locally increased helical dislocation density can result in a decrease in the quality or yield of electronic components produced from it. Despite these adverse effects, known solutions, as can be seen from, for example, Patent Document 3, have a heterogeneous distribution of substrate helical dislocations in the lateral direction in the SiC substrate.

[0040] In contrast, this problem does not occur with the SiC substrate according to the present invention. In particular, the SiC substrate according to the present invention has a low helical dislocation density and, preferably, a substantially homogeneous lateral distribution of the remaining substrate helical dislocations, that is, a substantially homogeneous helical dislocation distribution over a very large portion of the surface and preferably over the entire main surface of the SiC substrate.

[0041] The SiC substrate according to the present invention satisfies the industrial requirements for use in manufacturing semiconductor components. The substrate thickness of such a SiC substrate, measured perpendicular to the entire main surface, is particularly in the range of about 100 μm to about 1000 μm, preferably in the range of about 200 μm to about 500 μm, where the substrate thickness has an overall thickness variation of preferably a maximum of 20 μm across the entire main surface. The SiC substrate has a certain mechanical stability, particularly self-supporting. The SiC substrate preferably has a substantially circular disk shape, i.e., the entire main surface is substantially circular. In some cases, there may be a slight deviation from the exact circular geometry, such that at least one identification marking is provided on the periphery. This identification marking may be a plane or a notch. In particular, the SiC substrate is manufactured from a sublimation-grown SiC bulk single crystal, for example, from a SiC bulk single crystal grown by the manufacturing method according to the present invention described above, by cutting it as a disk perpendicular to the central longitudinal axis of the SiC bulk single crystal.

[0042] In all other respects, the SiC substrate and its advantageous modified form according to the present invention substantially provide the same advantages as those already described in relation to the manufacturing method and its advantageous modified form according to the present invention.

[0043] Further advantageous embodiments of the SiC substrate according to the present invention will become apparent from the features of the claims dependent on claim 11.

[0044] Embodiments in which the local helical dislocation substrate segment density of all substrate segments located within a partial surface deviates from the total helical dislocation substrate density by up to 20%, and especially up to 15%, are advantageous. This results in even greater and more advantageous homogeneity of the helical dislocation distribution.

[0045] According to a further advantageous embodiment, the partial surface has a size of at least 90% of the total main surface. Thereafter, a larger proportion of the total main surface has favorable lateral high homogeneity of the helical dislocation distribution. This allows a larger portion of the SiC substrate to be used in the manufacture of high-quality components.

[0046] According to another favorable embodiment, the total helical dislocation substrate density of the SiC substrate is up to 1000 cm². -2 , especially up to 500cm -2 These materials have very low helical dislocation densities, and therefore, SiC substrates are very well suited for use in the manufacture of high-quality components in this respect as well.

[0047] In yet another favorable embodiment, the local helical dislocation substrate segment densities of any two substrate segments located within a partial surface and adjacent to each other differ from one another by up to 25%, particularly up to 20%, and preferably up to 15%. Thus, adjacent substrate segments have very similar values ​​for their respective local helical dislocation substrate segment densities. Consequently, the substrate helical dislocations are distributed very homogeneously within the SiC substrate.

[0048] In a more favorable embodiment, the entire main surface (and thus, in particular, the entire SiC substrate) has a substrate diameter of at least 150 mm, and more particularly, at least 200 mm. Preferably, the substrate diameter is about 200 mm. The current upper limit for production-related substrate diameters is particularly 250 mm, but in principle, even larger substrate diameters are conceivable. The larger the substrate diameter, the more efficiently the single-crystal SiC substrate can be used in the manufacture of semiconductor components and / or high-frequency components, thereby reducing component manufacturing costs. Furthermore, a SiC substrate having such a large diameter can also be about 1 cm 2 It can also be advantageously used to manufacture relatively large semiconductor components and / or high-frequency components with a base area (Grundflaeche), etc.

[0049] According to another favorable embodiment, the SiC substrate has a SiC crystal structure having only a single SiC polytype, particularly one of SiC polytypes 4H, 6H, 15R, and 3C. Preferably, it is characterized by high modification stability, and in particular, little polytype change. When the SiC substrate has only a single SiC polytype, the SiC substrate also advantageously has a very low defect density. Thereafter, a very high-quality SiC substrate is obtained. Polytype 4H is particularly preferred.

[0050] In another convenient embodiment, the SiC substrate has a crystalline structure having an orientation that is slightly tilted (=off-orientation) with respect to the plane normal of the entire main surface, with a tilt angle in the range of 0° to 8°, preferably about 4°. In particular, the plane normal of the entire main surface corresponds at least substantially to the growth direction of the SiC bulk single crystal from which the SiC substrate is manufactured. Specifically, in the off-orientation, the entire main surface of the SiC substrate is tilted at an angle in the range of 0° to 8° in the direction of the [-1-120] crystal direction with respect to the (0001) plane of the crystalline structure.

[0051] According to a further favorable embodiment, the SiC substrate has an electrical resistivity of 8 mΩcm to 26 mΩcm, particularly 10 mΩcm to 24 mΩcm.

[0052] According to another convenient embodiment, the SiC substrate has a bow of less than 25 μm, and more particularly less than 15 μm.

[0053] According to another favorable embodiment, the SiC substrate has a strain (warp) of less than 40 μm, particularly less than 30 μm.

[0054] Further features, advantages, and details of the present invention will become apparent from the following description of embodiments based on the drawings. [Brief explanation of the drawing]

[0055] [Figure 1]This document shows an example of an embodiment of a growth apparatus for sublimation growth of SiC bulk single crystals. [Figure 2] An example of an embodiment of a SiC seed crystal having a seed helical dislocation, which is typically used in sublimation growth, is shown in a longitudinal cross-section of the SiC seed crystal along the growth direction. [Figure 3] Figure 2 shows a longitudinal cross-sectional view of an example of an embodiment of a SiC bulk single crystal having a high helical dislocation density and heterogeneous helical dislocation distribution, grown on a conventional SiC seed crystal. [Figure 4] Figure 1 shows a longitudinal cross-sectional view of an embodiment of a SiC bulk single crystal grown on a SiC seed crystal equipped with nucleation centers, using the growth apparatus shown in Figure 1, with a targeted and locally limited growth method. The single crystal has a reduced sheen dislocation density and a homogeneous sheen dislocation distribution. [Figure 5] Figure 4 shows the cross-section V, along with an enlarged schematic diagram of the recombination of helical dislocations in a growing SiC bulk single crystal. [Figure 6] Figure 2 shows an example of an embodiment of a method that combines the location of seed helical dislocations in a SiC seed crystal by X-ray topography with laser structuring of the SiC seed crystal in the region where an increased local helical dislocation density was detected. [Figure 7] This example shows an embodiment of a SiC seed crystal structured by local coating in a region where an increased local helical dislocation density was detected. [Figure 8] The top view shows an example of a SiC substrate obtained from a SiC bulk single crystal having a reduced shear dislocation density and a homogeneous shear dislocation distribution, grown using a targeted and locally limited method with a SiC seed crystal containing nucleating centers. [Figure 9] The top view shows an example of a SiC substrate obtained from a SiC bulk single crystal, as shown in Figure 3, grown using a conventional SiC seed crystal having a high helical dislocation density and a heterogeneous helical dislocation distribution.

[0056] In Figures 1-12, corresponding parts are given the same reference numerals. The details of the embodiments described below may constitute the invention itself or form part of the subject matter of the invention.

[0057] Figure 1 illustrates an example of an embodiment of a growth apparatus 1 for producing a SiC bulk single crystal 2 by sublimation growth. The growth apparatus 1 comprises a growth crucible 3 including a SiC storage region 4 and a crystal growth region 5. The SiC storage region 4 contains, for example, a powdered SiC raw material 6, which is pre-produced as a starting material and is filled into the SiC storage region 4 of the growth crucible 3 before the start of the growth process.

[0058] A SiC seed crystal 8 is attached to the crucible end wall 7 of the growth crucible 3, opposite the SiC storage region 4, extending axially to the crystal growth region 5. The SiC seed crystal 8 is specifically a single crystal. In the shown embodiment, the crucible end wall 7 is formed as the crucible lid of the growth crucible 3. However, this is not essential. On the SiC seed crystal 8, the SiC bulk single crystal 2 to be grown grows by deposition from the SiC growth gas phase 9 formed within the crystal growth region 5. The growing SiC bulk single crystal 2 and the SiC seed crystal 8 have approximately the same diameter. Even if there is a difference, the error in which the seed diameter of the SiC seed crystal 8 is smaller than the single crystal diameter of the SiC bulk single crystal 2 is less than 10%. However, there may be gaps between the inside of the crucible side wall 13 and the growing SiC bulk single crystal 2, on the one hand, and between the SiC seed crystal 8 and the SiC seed crystal 8, which are not shown in Figure 1.

[0059] In the embodiment shown in Figure 1, the growing crucible 3, including the crucible lid 7, contains, for example, at least 1.75 g / cm³ of material. 3 It consists of a conductive and heat-conductive graphite crucible material having a density of . A thermal insulating layer 10 is arranged around it. The latter is made of, for example, a foamed graphite insulating material, and its porosity is particularly significantly higher than that of the graphite crucible material.

[0060] A heat-insulated growth crucible 3 is placed inside a tubular container 11, which in this embodiment is designed as a quartz glass tube and forms an autoclave or reactor. To heat the growth crucible 3, an induction heating device in the form of a heating coil 12 is positioned around the container 11. The growth crucible 3 is heated by the heating coil 12 to the temperature required for growth. In the embodiment shown, these growth temperatures are at least 2250°C. The heating coil 12 inductively couples an electric current to the conductive crucible sidewall 13 of the growth crucible 3. This current flows substantially as a circular current circumferentially inside the circular, hollow cylindrical crucible sidewall 13, thereby heating the growth crucible 3. If necessary, and in particular to adjust and, if applicable, change the temperature or temperature profile inside the growth crucible 3, the relative position between the heating coil 12 and the growth crucible 3 can be changed axially, i.e., in the direction of the central longitudinal axis 14 of the growing SiC bulk single crystal 2. The axially variable position of the heating coil 12 during the growth process is indicated by the double arrow 15 in Figure 1. In particular, the heating coil 12 changes position in accordance with the growth progress of the growing SiC bulk single crystal 2. This displacement preferably occurs downward, i.e., in the direction of the SiC raw material 6, preferably by the same length as the SiC bulk single crystal 2 grows, for example, about 20 mm in total. For this purpose, the growth apparatus 1 includes, but correspondingly configured, monitoring means, control means and adjustment means.

[0061] The SiC growth gas phase 9 within the crystal growth region 5 is supplied by the SiC raw material 6. The SiC growth gas phase 9 contains gaseous components (=SiC gas species) in the form of at least Si, Si2C, and SiC2. Material transport from the SiC raw material 6 to the growth interface 16 of the growing SiC bulk single crystal 2 occurs, on the one hand, along an axial temperature gradient. In the sublimation method (=PVT method) used for SiC crystal growth, growth conditions, including material transport, are adjusted and controlled via the temperature generated in the growth crucible 3. At the growth interface 16, a relatively high growth temperature of at least 2250°C, and particularly at least 2350°C or even 2400°C, is generated. Furthermore, at the growth interface 16, an axial temperature gradient of at least 5 K / cm, preferably at least 15 K / cm, is set, measured in the direction of the central longitudinal axis 14. The temperature inside the growth crucible 3 decreases towards the growing SiC bulk single crystal 2. The maximum temperature in the SiC storage region 4 is approximately 2450°C to 2550°C. This temperature profile, which has a temperature difference of particularly large 100°C to 150°C between the SiC storage region 4 and the growth interface 16, can be achieved by various means. For example, axially variable heating can be provided by dividing the heating coil 12 into two or more axial sections (not shown in detail). Furthermore, a stronger heating effect can be set in the lower part of the growth crucible 3 than in the upper part of the growth crucible 3, for example, by appropriate axial positioning of the heating coil 12. Furthermore, the insulation sections of the two axial crucible end walls can be designed differently. As schematically shown in Figure 1, the insulation layer 10 can be thicker at the lower end wall than at the upper end wall of the crucible. Furthermore, the insulation layer 10 adjacent to the upper crucible end wall 7 can have a central cooling opening 17 positioned around the central longitudinal axis 14 through which heat is dissipated. This central cooling opening 17 is shown by a dashed line in Figure 1.

[0062] Furthermore, during actual crystal growth, growth pressures of particularly high levels, ranging from 0.1 hPa (= mbar) to 10 hPa (= mbar), are generated within the growth crucible 3.

[0063] The SiC bulk single crystal 2 grows in a growth direction 19, which in the embodiment shown in Figure 1 is from top to bottom, i.e., from the crucible lid 7 to the SiC storage region 4. The growth direction 19 extends parallel to the central longitudinal axis 14. In the embodiment shown, the growing SiC bulk single crystal 2 is arranged concentrically inside the growth apparatus 1, so the central longitudinal axis 14 can also be allocated to the growth apparatus 1 as a whole.

[0064] The growing SiC bulk single crystal 2 has a 4H polytype SiC crystal structure. However, in principle, other polytypes (=other crystal transformations) such as 6H-SiC, 3C-SiC, or 15R-SiC are also possible. Advantageously, SiC bulk single crystal 2 has only a single SiC polytype, which in this embodiment is the aforementioned 4H-SiC. SiC bulk single crystal 2 grows with high transformation stability, and in this respect, it essentially has only a single polytype. The latter is advantageous in that it has high crystal quality with very few defects.

[0065] The growth method carried out by the growth apparatus 1 for producing SiC bulk single crystals 2 is also characterized in other respects by the high crystal quality achieved. Specifically, the growing SiC bulk single crystal 2 has a very low helical dislocation density and a nearly homogeneous distribution of residual helical dislocations (TSDs). In this respect, the properties of the SiC seed crystal 8 are an important factor for the quality of the growing SiC bulk single crystal 2.

[0066] In particular, seed helical dislocations 20 (see Figure 2) present in a commonly used SiC seed crystal 8a can continue into the SiC bulk single crystal 2a growing in the growth direction 19, as illustrated in Figure 3. Seed helical dislocations 20 in the SiC seed crystal 8a, when processed as usual, i.e., polished to a perfectly smooth state, result in the formation of bulk single crystal helical dislocations 21 in the growing SiC bulk single crystal 2a. In this respect, bulk single crystal helical dislocations 21 represent the (undesirable) continuation of seed helical dislocations 20.

[0067] To prevent the latter as much as possible, the SiC seed crystal 8 is subjected to a special two-step treatment before being used to grow the SiC bulk single crystal 2.

[0068] Meanwhile, as the first processing step, seed helical dislocations are inspected, in which the growth surface 18 of the SiC seed crystal 8 is inspected for the presence of seed helical dislocations 20 segment by segment (particularly for segmentation comparable to or similar to the segmentation schematically shown in Figure 8 in relation to the SiC substrate). At this time, the distribution of these seed helical dislocations 20 and the total helical dislocation seed density and / or the density of several local helical dislocation seed segments identified across the entire growth surface 18 are also determined. These are approximately 10 mm² each. 2 This relates only to specific species segments of the growth surface 18 of a certain size. In particular, species segments in which an increase in local helical dislocation species segment density is detected can be marked. Local helical dislocation species segment density is increased when their values ​​are at least twice as large as the total helical dislocation species density, i.e., at least 2 times larger.

[0069] On the other hand, as a second processing step, surface treatment is performed, and in the process, nucleation centers 22 are provided on the growth surface 18 in the regions of the species segment in which an increase in local helical dislocation density is detected.

[0070] Each of these nucleation centers 22 can function as a starting point for compensating helical dislocations 23 during the actual sublimation growth of the SiC bulk single crystal 2. During the actual sublimation growth, such compensating helical dislocations 23 arising from the specifically placed nucleation centers 22 can recombine with bulk single crystal helical dislocations 21 continuing from the SiC seed crystal 8 at the location of the nucleation centers 22 (see enlarged detail in Figures 4 and 5). The bulk single crystal helical dislocations 21 and compensating helical dislocations 23 originating from the SiC seed crystal 8 and actually continuing in the SiC bulk single crystal 2 advantageously cancel each other out. This results in a decrease in helical dislocation density in the growing SiC bulk single crystal 2 and also in the disk-shaped single-crystal SiC substrate 31 manufactured therefrom for component manufacturing (see Figure 8), as well as homogenization of the distribution of the remaining bulk single crystal helical dislocations 21.

[0071] The formation of favorable nucleation centers 22 is achieved by locally limited structuring of the growth surface 18, particularly in seed segments where an increase in local helical dislocation seed segment density is detected. The growth surface 18 is specifically provided with locally limited nucleation structures 24, which are designed as roughened surface regions according to the embodiments shown in Figures 4 and 5. However, other forms of nucleation structures 24, such as locally limited polished, etched, and / or coated surface regions, are also possible. The nucleation structures 24 in the form of roughened surface regions on the growth surface 18 of the SiC seed crystal 8, as shown in Figures 4 and 5, can be generated, for example, by laser radiation.

[0072] It was shown that locally limited structuring of the growth surface 18 yields significantly better results than continuous structuring of the growth surface 18 in terms of the desired reduction in helical dislocation density and homogenization of the helical dislocation distribution in the growing SiC bulk single crystal 2.

[0073] The first processing step, seed helical dislocation inspection, and the second processing step, surface treatment, can usually be performed sequentially in time and, if necessary, using separate systems. However, the embodiment shown in Figure 6, in which these two processing steps are combined and performed simultaneously, is particularly efficient. In this case, seed helical dislocation inspection is performed by X-ray topography. The X-ray source 25 emits X-rays 26 in the direction of the growth surface 18, and continuously, and especially completely, scans the growth surface 18 with these X-rays 26. The X-ray detector 27 receives the X-rays 26 reflected from the growth surface 18, converts them into a received signal, and this received signal is then transmitted to an evaluation unit (not shown) for further evaluation of whether a seed helical dislocation 20 is present at the current reflection position of the X-rays 26 on the growth surface 18. If this evaluation indicates the presence of an increased density of relevant local helical dislocation species segments in the species segment that has just been examined, the laser writer 28 is activated and the species segment of the growth surface 18 is treated with laser irradiation 29 to generate a nucleating structure 24 therein that has a nucleating center 22.

[0074] Figure 7 shows an example of an embodiment of a SiC seed crystal 8b having other nucleation structures 24b on its growth surface 18b. The latter is similarly localized and located within the seed segment of the growth surface 18b where an increase in local helical dislocation seed segment density is detected. To generate these nucleation structures 24b, the growth surface 18b is nanostructured by lithography in the relevant seed segment, and in the embodiment shown in Figure 7, a carbon coating 30 is provided.

[0075] When using one of the SiC seed crystals 8, 8b having appropriate locally limited surface structuring, the growth apparatus 1 enables the growth of high-quality SiC bulk single crystals 2 that have only a few bulk single crystal helical dislocations 21 and have a very homogeneous lateral distribution.

[0076] Next, equivalently high-quality SiC substrates 31 can be manufactured from these high-quality SiC bulk single crystals 2 (see schematic top view in Figure 8). These disk-shaped SiC substrates 31 are obtained from the relevant SiC bulk single crystals 2 by cutting or sawing them axially as continuous disks perpendicular to the growth direction 19 or the central longitudinal axis 14. Such SiC substrates 31 are large and thin. In possible embodiments, their entire main surface 32 has a substrate diameter of at least 150 mm, e.g., 200 mm, while the substrate thickness is about 500 μm. The SiC substrates 31, like the SiC bulk single crystals 2 from which it is manufactured, are preferably up to 1000 cm². -2 It has a low total helical dislocation density and a very homogeneous distribution of remaining bulk single-crystal helical dislocations 21. Both improve the suitability of the SiC substrate 31 for use in manufacturing parts. Total helical dislocation density, in the case of SiC bulk single crystal 2, relates to the complete cross-section of the SiC bulk single crystal 2 perpendicular to the central longitudinal axis 14 or growth direction 19, and in the case of SiC substrate 31, relates to the complete entire main surface 32. Here, in the case of SiC substrate 31, this is also called the total helical dislocation substrate density. The very homogeneous helical dislocation distribution can be seen from the illustration in Figure 8, which shows the Si side of the SiC substrate 31.

[0077] In Figure 8, the (virtual) separation or division of the entire main surface 32 into substrate segments 33 is also illustrated with dashed lines, and each substrate segment 33 is square, at least as far as it is concerned with the substrate edge, and in particular 10 mm 2The substrate segment area is as follows: Each substrate segment 33 has a local helical dislocation substrate segment density, which is the number of bulk single-crystal helical dislocations 21 present within its substrate segment area. With respect to the SiC substrate 31, bulk single-crystal helical dislocations 21 are understood and can be referred to as substrate helical dislocations 21. Within 85% of the subsurface of the entire main surface 32, the substrate segments 33 have a local helical dislocation substrate segment density that deviates by up to 25% each from the total helical dislocation substrate density. That is, even the few substrate helical dislocations 21 are distributed very homogeneously. Furthermore, the latter is also achieved by any adjacent substrate segments 34 and 35 within this subsurface differing from each other by up to 25% in their respective local helical dislocation substrate segment densities.

[0078] For comparison, Figure 9 similarly illustrates the Si side of a commonly used SiC substrate 31a fabricated from a SiC bulk single crystal 2a (see Figure 3) grown from a commonly used SiC seed crystal 8a without locally limited surface structures. The higher total helical dislocation density and the more heterogeneous helical dislocation distribution across the entire main surface 32a can be seen in the schematic representation in Figure 9.

Claims

1. a) Before training begins, a1) The growth surface (18, 18b) is located within the crystal growth region (5) of the growth crucible (3). A SiC seed crystal (8,8b) is arranged, a2) In the SiC storage area (4) of the growth crucible (3), the SiC raw material (6) To introduce, b) At a maximum growth temperature of 2400°C and a growth pressure of 0.1 mbar to 100 mbar During the growth process, the SiC raw material (6) sublimes, and the crystal growth region (5) The transport of the sublimated gaseous component generates a SiC growth gas phase (9) therein, Then, S is deposited on the SiC seed crystals (8, 8b) by deposition from the SiC growth gas phase (9). iC bulk single crystal (2) grows, A method for producing at least one SiC bulk single crystal (2) by sublimation growth. That is, c) Before starting growth, the SiC seed crystal (8, 8b) c1) The presence of seed spiral dislocations (20) is examined, and here the growth surface (18, 18b) is divided into species segments, and for each species segment, the related local spiral dislocation species segment Identify the ment density, c2) Process the local helical dislocation species segment density on the growth surface (18 ,18b) The total spiral dislocation species density identified for the whole is multiplied by at least 1.5 to 4. Within each of the species segments, a nucleation center (22) is generated, and here the nucleation The center (22) will provide at least one compensation during the subsequent development period. The starting point of the helical transposition (23) A method characterized by the following features.

2. Within the species segment in which an increase in local helical dislocation species segment density was detected, this species segment Nucleation centers that are at least half the number of dislocations of the species helical dislocation (20) identified within the nucleation center The method according to claim 1, characterized by generating the nucleation number of 22).

3. The nucleation center (22) is a locally limited structure of the growth surface (18, 18b). The method according to claim 1 or 2, characterized by generating by chemical reaction.

4. The nucleation center (22) is subjected to laser irradiation (29) to the growth surface (18, 18b One of claims 1 to 3, characterized in that it is generated by a locally limited processing of ) The method described in item 1.

5. The nucleation center (22) is locally limited on the growth surface (18b) by the additive. Any one of claims 1 to 4, characterized in that it is produced by a coating (30). The method described in paragraph 1.

6. The nucleation center (22) is locally and limitedly polished on the growth surface (18, 18b) The method according to any one of claims 1 to 5, characterized by generating by

7. The nucleation center (22) is locally limited on the growth surface (18, 18b) The method according to any one of claims 1 to 6, characterized by being produced by ching. 。

8. The growth surface (18, 18b) of the SiC seed crystal (8, 8b) contains the nucleation center (2 Claims characterized by generating at least one nanostructure in order to generate (2) P.2 The method described in any one of items 1 to 7.

9. The examination of the type of spiral dislocation (20) is performed by X-ray topography. The method according to any one of claims 1 to 8, characterized by...

10. Examination of seed spiral dislocations (20) and pre-existing conditions for generating the nucleation center (22) The treatment of the growth surface (18, 18b) of the SiC seed crystal (8, 8b) is combined with the treatment of the growth surface (18, 18b) The method according to any one of claims 1 to 9, characterized in that it is carried out by the method described above.

11. A single SiC bulk single crystal (2) produced from a sublimation-grown SiC bulk single crystal (2) having the entire main surface (32) A crystalline SiC substrate (31), a) The entire main surface (32) has a substrate segment area to which each belongs It is virtually divided into segments (33), and each substrate segment (33) is this substrate The base present in this substrate segment (33) relative to the substrate segment area of ​​the plate segment The local helical dislocation substrate segment density is the number of plate helical dislocations (21), b) A total helical dislocation substrate in which the SiC substrate (31) is applied to the entire main surface (32) Having density, c) The SiC substrate (31) is formed by at least 85% of the total main surface (32) Having a partial surface, all substrate segments (33, 34, 3) located inside the partial surface 5) The local helical dislocation substrate segment density is up to 2% of the total helical dislocation substrate density. It deviates by 5%. SiC substrate (31).

12. The local helix of all substrate segments (33, 34, 35) located inside the partial surface The dislocation substrate segment density is up to 20%, particularly up to 15%, of the total helical dislocation substrate density. The SiC substrate according to claim 11, characterized by deviating from the description.

13. The aforementioned partial surface is characterized in that it has a size of at least 90% of the entire main surface (32). The SiC substrate according to claim 11 or 12.

14. The total helical dislocation substrate density of the SiC substrate (31) is a maximum of 1000 cm⁻², particularly The present invention is characterized by having a maximum of 500 cm⁻², as described in any one of claims 11 to 13. SiC substrate.

15. Two arbitrary substrate segments (34, 35) adjacent to each other located within the aforementioned partial surface The helical dislocation substrate segment density is up to 25%, particularly up to 20%, preferably up to 15%. SiC groups according to any one of claims 11 to 14, characterized by being different in %, from each other. Board.

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