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

Abstract

The method aims to produce at least one SiC bulk single crystal (2) by sublimation growth, and before the start of growth, a SiC seed crystal (8) having a growth surface is placed in a crystal growth region of a growth crucible and a source material is introduced into a SiC storage region of the growth crucible. During growth, at a growth temperature of up to 2400°C and a growth pressure of 0.1 mbar to 100 mbar, a SiC growth gas phase is generated there by sublimation of the SiC source material and by transport of the sublimated gaseous components to the crystal growth region, in which a SiC bulk single crystal (2) is grown on the SiC seed crystal by deposition from the SiC growth gas phase. Before the start of growth, a mechanical stress is introduced into the SiC seed crystal (8) at room temperature, so that seed screw dislocations (24) present in the SiC seed crystal (8) undergo dislocation movement under the effect of the mechanical stress, whereby seed screw dislocations (24) approaching each other due to their respective dislocation movements recombine with each other and cancel each other out.

Description

Technical Field

[0001] The content of European Patent Application EP21163801.0 is incorporated herein by reference.

[0002] The present invention relates to a method for manufacturing at least one SiC bulk single crystal by sublimation growth (Sublimationszuechtung) and to a single crystal SiC substrate.

Background Art

[0003] Silicon carbide (SiC), a semiconductor material, is used, among other things, 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) having the largest possible substrate diameter and the highest possible quality.

[0004] The base of an SiC substrate is a high-quality SiC bulk single crystal, which is usually produced by physical vapor deposition (PVT), particularly the (sublimation) method - an example of which is described in Patent Document 1. In this growth method (Zuechtungsverfahren), a single crystal SiC disk as an SiC seed crystal is introduced into a crucible in which it grows together with a suitable raw material substance. Under controlled temperature and pressure conditions, the raw material substance is sublimated, and the gaseous species are deposited on the SiC seed crystal, whereby the SiC bulk single crystal grows there.

[0005] Subsequently, a disk-shaped single crystal SiC substrate is cut out from the SiC bulk single crystal, for example using a wire saw, and its surface is purified in multiple steps, particularly by several polishing steps, after which at least one thin single crystal epitaxial layer made of SiC or GaN (gallium nitride), etc., is applied to these single crystal SiC substrates as part of the component production process. The properties of this epitaxial layer, and ultimately also the properties of the components manufactured therefrom, depend greatly on the quality of the SiC substrate or the SiC bulk single crystal beneath it.

[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, the reduction in helical dislocation density achieved is not sufficient to make it economically possible to manufacture electronic components on SiC substrates. Therefore, a further reduction 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 [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 2 This method involves introducing SiC raw material materials having a density of, or in particular, combinations of these different SiC raw material materials. During growth, 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. Prior to the start of growth, mechanical stress is introduced into the SiC seed crystal at room temperature, causing seed helical dislocations present in the SiC seed crystal to move under the influence of mechanical stress. As a result, seed helical dislocations that approach each other in relation to the movement of each dislocation recombine with each other and cancel each other out.

[0011] Dislocation migration and recombination of seed helical dislocations preferably occur within the SiC seed crystal. Furthermore, dislocation migration of seed helical dislocations occurs, in particular, substantially radially or laterally (= transversely), that is, in a direction substantially perpendicular to the growth direction of the growing SiC bulk single crystal. In contrast, the growth direction of the growing SiC bulk single crystal can also be understood as axial.

[0012] 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.

[0013] It is recognized that the main cause of the increase in helical dislocation density in growing SiC bulk single crystals (and therefore, disk-shaped SiC substrates subsequently manufactured therefrom) is the SiC seed crystal used for growth. Thus, seed helical dislocations present in the SiC seed crystal can propagate in the direction of growth into the growing SiC bulk single crystal during the growth process. To avoid this as much as possible, the SiC seed crystal is subjected to mechanical stress, preferably at room temperature, before growth begins, to reduce the number of seed helical dislocations originally present in the SiC seed crystal before growth commences.

[0014] In other words, through the interaction of seed helical dislocations, the relevant helical dislocations can recombine with each other and, as a result, cancel each other out. This favorable recombination occurs particularly when seed helical dislocations are close to each other and have different rotation directions, i.e., they are helical dislocations with different signs of Burgers vectors (+1c and 1c). In SiC seed crystals, the ratio of helical dislocations with positive Burgers vectors to those with negative Burgers vectors is usually approximately 1, and therefore, in principle, there are many possibilities for favorable recombination of seed helical dislocations. Mechanical tension or stress is applied to the SiC seed crystal to initiate favorable recombination. The latter creates a driving force that causes existing seed helical dislocations to start moving and change their positions by a certain distance within the SiC seed crystal. In the process of these dislocation movements, locally adjacent seed helical dislocations with different rotation directions can approach each other to the extent that recombination occurs. This effect becomes more pronounced as the mechanical stress in each region increases. As the mechanical stress increases, the mobility of the seed helical dislocations also increases. Furthermore, in their dislocation movement, the seed helical dislocations move particularly in accordance with the gradient of the mechanical stress, preferably in the direction of this gradient.

[0015] In other words, helical dislocations that recombine with each other preferably cancel each other out within the SiC seed crystal, and as a result cannot survive in the crystal structure of the growing SiC bulk single crystal. This reduces the helical dislocation density in the growing SiC bulk single crystal. The remaining helical dislocations are particularly heterogeneously distributed. In particular, there are regions with higher local helical dislocation densities than other regions, especially in the transverse or radial direction. Preferably, based on a cross section perpendicular to the growth direction of the growing SiC bulk single crystal, multiple broad regions (or just one broad region) with relatively low local helical dislocation densities can be targeted and generated, while there are relatively few multiple regions (or just one relatively small region) with higher local helical dislocation densities. For further processing, preferably, multiple broad regions (or simply broad regions) with relatively low local helical dislocation densities are determined. If necessary, mechanical stress can also be applied only to the recombining region of the SiC seed crystal (e.g., only the central region or only the edge region) to particularly promote the favorable recombination of seed helical dislocations there.

[0016] The method according to the present invention can reduce the helical dislocation density in a growing SiC bulk single crystal (and subsequently in a disk-shaped SiC substrate manufactured therefrom), preferably in specific regions, such as the edge region or the central region. The SiC bulk single crystal preferably contains almost, ideally completely, helical dislocations. Compared to previously known methods, the regions with relatively low local helical dislocation density are larger, and more preferably, have even lower local helical dislocation densities. It is advantageous to concentrate the majority of helical dislocations in a significantly smaller region. Thanks to this favorable heterogeneous distribution of helical dislocation density, where the local helical dislocation density is increased only in small excluded regions, SiC substrates obtained from such SiC bulk single crystals are very well suited for the economical manufacture of high-quality electronic components. The achievable yield is high.

[0017] 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, which have high precision over a wide area 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.

[0018] 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. [Modes for carrying out the invention]

[0019] An advantageous embodiment of the method according to the present invention can be obtained from the features of the claims dependent on claim 1.

[0020] In a preferred embodiment, dislocation migration of seed helical dislocations is thermally activated by heating the SiC seed crystal. In particular, the SiC seed crystal is heated to a temperature slightly, preferably up to about 200°C, below the growth temperature during an activation period of 20 to 2000 minutes, preferably about 200 minutes. Dislocation migration is preferably initiated to a significant degree from a temperature about 200°C below the growth temperature that occurs on the growth surface of the SiC seed crystal during actual growth, i.e., from a temperature of about 2000°C to 2200°C. Thus, dislocation migration is particularly mechanically induced and thermally activated. Heating of the SiC seed crystal to thermally activate dislocation migration can preferably be carried out in conjunction with a heating step before the start of growth. Alternatively, this can be carried out separately from the actual growth, i.e., as part of a heat treatment of the SiC seed crystal that is not particularly closely time-related to the growth.

[0021] According to a more preferred embodiment, mechanical stress is introduced into the SiC seed crystal in a rotationally symmetric manner. Applying stress rotationally symmetrically can be carried out particularly easily and is at the same time very effective.

[0022] According to another advantageous embodiment, the SiC seed crystal is deflected with a maximum deflection distance, particularly between 0.1 mm and 5 mm, preferably 1 mm, to introduce mechanical stress. At that time, the maximum deflection with the maximum deflection distance is carried out particularly at the axis center of the SiC seed crystal, preferably in the direction of the central longitudinal axis of the SiC bulk single crystal that will grow on the SiC seed crystal later. The mechanical stress generated in the SiC seed crystal is a particularly effective driving force for dislocation movement. The mechanical stress is particularly in a correlation with the deflection.

[0023] According to another advantageous embodiment, the SiC seed crystal is deflected by at least one punch (Stempel) particularly within the growth crucible to introduce mechanical stress. At that time, it is possible to particularly directly or indirectly affect the deflection of the SiC seed crystal. For example, it can be deflected by directly applying the force of at least one punch to the SiC seed crystal itself. Similarly, this can also be done by, for example, applying an indirect force on a seed holder system having a seed holder and the SiC seed crystal placed thereon. The punch preferably has a cylindrical shape particularly with a punch diameter between 2 mm and 10 mm. Further, the punch contact surface of the punch that pushes the SiC seed crystal (directly or indirectly) can be designed in various ways, such as flat, round or pointed. The punch is particularly made of a punch material in the form of graphite, other carbon materials, or a heat-resistant metal such as tantalum. By such a punch, the SiC seed crystal can be very easily placed in a state of being stressed or tensioned to an almost arbitrary degree, causing the recombination of the target screw dislocations.

[0024] In a further favorable embodiment, at least one punch is centrally positioned and acts on the center of the SiC seed crystal. Furthermore, there are other favorable embodiments in which several punches act on the SiC seed crystal, in particular at least some of the punches are positioned preferably equidistant along a virtual circular line around the center of the SiC seed crystal. Each of these embodiments is very well suited for introducing mechanical stress into the SiC seed crystal.

[0025] In another convenient embodiment, a SiC seed crystal is firmly connected to a non-planar contact surface of a shaped seed holder to introduce mechanical stress. The SiC seed crystal is itself particularly disc-shaped and preferably has at least one flat main surface. The non-planar contact surface of the shaped seed holder functions to abut the SiC seed crystal in particular, and in the abutted and / or interconnected state, brings about warping of the SiC seed crystal, and thus the desired mechanical stress of the SiC seed crystal. For connection, the SiC seed crystal is preferably bonded to the contact surface. The contact surface is curved, for example, convex or concave. However, the contact surface may also have substantially any non-planar shape. In particular, the contact surface may also be non-planar only in a first partial region and planar in a second partial region. In this way, mechanical stress can be introduced to the SiC seed crystal in a very targeted manner, particularly limited to specific partial regions. Recombination of seed helical dislocations preferably occurs only in a partial region of the SiC seed crystal that is subjected to mechanical stress (for example, only the central region or only the edge region).

[0026] In another advantageous embodiment, the SiC seed crystal is inspected for the presence of seed helical dislocations on its growth surface, for example, by X-ray topography, before mechanical stress is introduced. This makes it possible to apply mechanical stress specifically to SiC seed crystals in which a particularly large number of seed helical dislocations were detected in the previous inspection. In this way, an exceptionally large number of seed helical dislocations (or above-average numbers) in a subregion with a particularly large number of seed helical dislocations can be targeted and significantly reduced.

[0027] To address the challenges related to SiC substrates, a SiC substrate is disclosed according to the features of claim 9. The SiC single crystal substrate according to the present invention has a full main surface, where the full main surface has an accumulation subsurface formed by up to 20% of the full main surface, and this accumulation subsurface has at least 80% of the total substrate helical dislocations present on the full main surface.

[0028] The accumulation subsurface, formed by up to 20% of the total main surface, may be particularly continuous and may include, for example, a central region or an edge region. However, the accumulation subsurface may be discontinuous. Most of the substrate helical dislocations are concentrated within this accumulation subsurface. This has the advantage of allowing us to know where specific accumulations of substrate helical dislocations occur, and conversely, where, advantageously, only a small number of substrate helical dislocations exist. This can be taken into consideration when using SiC substrates for further applications such as the manufacture of electronic components, for example, by treating the subsurface region of the SiC substrate as defective and not using it for the manufacture of electronic components.

[0029] In epitaxial coating of SiC substrates, a low number of substrate helical dislocations in the epitaxially coated portion of the SiC substrate is crucial for manufacturing high-yield, high-quality components. This is because substrate helical dislocations can propagate into the epitaxial layer. For example, too many substrate helical dislocations can lead to a decrease in local charge carrier lifetime and a decrease in the breakdown voltage of the resulting electronic components. Compared to known solutions, the SiC substrate according to the present invention has a significantly higher concentration of substrate helical dislocations on a smaller subsurface, resulting in a substantially and ideally complete absence of substrate helical dislocations and thus ideally suitable for further use in all conceivable cases. The assumed disadvantage of heterogeneous distribution of substrate helical dislocations has proven to be an advantage in the case of the SiC substrate according to the present invention. The SiC substrate is particularly well suited for manufacturing high-quality electronic components with high yield.

[0030] In particular, the SiC substrate according to the present invention, manufactured from sublimation-grown SiC bulk single crystals, 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, as 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 vertical axis of the SiC bulk single crystal.

[0031] In all other respects, the SiC substrate and its advantageous modified form according to the present invention offer substantially the same advantages as those already described in relation to the manufacturing method and its advantageous modified form according to the present invention.

[0032] Further advantageous embodiments of the SiC substrate according to the present invention can be obtained from the features of the claims dependent on claim 9.

[0033] A preferred embodiment is one in which the accumulation subsurface has at least 85%, and particularly at least 90%, of all substrate helical dislocations present on the entire main surface. This results in a better concentration of helical dislocations on the substrate, and consequently, a better suitability for further use of the remaining subsurface area of ​​the SiC substrate, particularly for the manufacture of high-quality components.

[0034] In a further favorable embodiment, the accumulation area has a size of up to 15% of the total main surface. This results in an even smaller accumulation area where most of the substrate helical dislocations reside. This also results in even better suitability of the remaining surface of the SiC substrate for further use, particularly for the manufacture of high-quality components.

[0035] According to another convenient embodiment, the SiC substrate can withstand up to 1000 / cm². 2 , especially up to 500 / cm 2 The total helical dislocation density is such that the total helical dislocation density can be determined 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 density can also be determined as the arithmetic mean of the local helical dislocation segment densities, where the local helical dislocation segment densities are applied to one of several segments into which the entire main surface is virtually divided. In this respect, the total helical dislocation density can also be referred to as the overall and / or average helical dislocation substrate density. The above-mentioned value for the total helical dislocation density is very low, and therefore, SiC substrates are very well suited for use in the manufacture of high-quality components.

[0036] 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] According to another convenient embodiment, the SiC substrate has a bow of less than 25 μm, and more particularly less than 15 μm.

[0041] According to another favorable embodiment, the SiC substrate has a strain (warp) of less than 40 μm, particularly less than 30 μm.

[0042] 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]

[0043] [Figure 1]This document shows an example of an embodiment of a growth apparatus for sublimation growth of SiC bulk single crystals. [Figure 2] Figure 1 shows an example of an embodiment of a SiC bulk single crystal having heterogeneously distributed shear dislocations, grown on a SiC seed crystal using the growth apparatus shown in Figure 1, in a longitudinal cross-sectional view in the growth direction. [Figure 3] Figure 1 shows an example of a seed holder that can be bent by a push-out tool, used in the cultivation apparatus shown in Figure 1. [Figure 4] Figure 3 shows an example of an embodiment of a push-out tool used in a seed holder that can be bent. [Figure 5] Figure 3 shows an example of an embodiment of a push-out tool used in a seed holder that can be bent. [Figure 6] Figure 3 shows an example of an embodiment of a push-out tool used in a seed holder that can be bent. [Figure 7] A schematic top view of the seed holder shown in Figure 3, which can be bent by a single push-out tool, is provided. [Figure 8] A schematic top view shows a further embodiment of a seed holder that can be bent by several push-out tools, used in the cultivation apparatus shown in Figure 1. [Figure 9] Figure 1 shows an example of an embodiment of a shaped seed holder, each having a non-flat contact surface for contacting a SiC seed crystal, used in the growth apparatus shown in Figure 1. [Figure 10] Figure 1 shows an example of an embodiment of a shaped seed holder, each having a non-flat contact surface for contacting a SiC seed crystal, used in the growth apparatus shown in Figure 1. [Figure 11] A top view shows an example of an embodiment of a SiC substrate obtained from a SiC bulk single crystal similar to that shown in Figure 2. [Figure 12] The top view shows an example of an embodiment of a SiC substrate obtained from a SiC bulk single crystal having heterogeneously distributed shear dislocations concentrated in the central region.

[0044] 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. [Examples]

[0045] 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.

[0046] On the region of the crucible end wall 7 of the growth crucible 3, opposite the SiC storage region 4, a SiC seed crystal 8 is attached, extending axially to the crystal growth region 5. The method of attaching the seed crystal is described in more detail below. 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, gaps not shown in Figure 1 may exist between the inside of the crucible sidewall 13 and the growing SiC bulk single crystal 2, on the one hand, and between it and the SiC seed crystal 8, on the other hand.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] Furthermore, during actual crystal growth, growth pressures of 0.1 hPa (= mbar) to 10 hPa (= mbar) are generated within the growth crucible 3.

[0051] The SiC bulk single crystal 2 grows on the growth surface 18 of the SiC seed crystal 8. This growth occurs in the 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 centrally located 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 centrally located central longitudinal axis 14 can also be allocated to the growth apparatus 1 as a whole.

[0052] 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. Because SiC bulk single crystal 2 grows with high transformation stability, it essentially has only a single polytype. The latter is advantageous in terms of high crystal quality with very few defects.

[0053] 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. For example, the growing SiC bulk single crystal 2 has a heterogeneous distribution of bulk single crystal helical dislocations 20 within any cross section perpendicular to the growth direction 19 (see Figure 2). This heterogeneous distribution can preferably be divided into an accumulation region 21 (consisting of one or more parts) in which most of the bulk single crystal helical dislocations 20 are concentrated, and a utilization region 22 (consisting of one or more parts) that contains significantly fewer bulk single crystal helical dislocations 20 compared to the accumulation region 21, but at the same time has a larger area. In the example shown in Figure 2, the accumulation region 21 is a single part and is formed by the radial edge region of the SiC bulk single crystal 2. Similarly, the utilization region 22 also consists of a single part and is formed by the central region of the SiC bulk single crystal 2 arranged around a centrally located central longitudinal axis 14. The boundary between the accumulation region 21 and the utilization region 22 is shown in Figure 2 by a (virtual) boundary line 23. The larger utilization region 22 contains very few bulk single-crystal helical dislocations 20 and is therefore of very high quality.

[0054] The high quality of the SiC bulk single crystal 2 is also due to the original SiC seed crystal 8, which has a favorable heterogeneous distribution of seed helical dislocations 24, similar to the SiC bulk single crystal 2 that grows on it during subsequent growth. In particular, the seed helical dislocations 24 present in the SiC seed crystal 8 continue in the growth direction 19 in the growing SiC bulk single crystal 2, as illustrated in Figure 2. The seed helical dislocations 24 lead to the formation of bulk single crystal helical dislocations 20 on the growth surface 18 of the SiC seed crystal 8 within the growing SiC bulk single crystal 2. 。 This application discloses the following configuration. [Configuration 1] a) Before training begins, a1) A SiC seed crystal (8) having a growth surface (18) is placed within the crystal growth region (5) of the growth crucible (3), a2) Introducing SiC raw material (6) into the SiC storage area (4) of the growth crucible (3), b) A method for producing at least one SiC bulk single crystal (2) by sublimation growth, wherein, during growth at a growth temperature of up to 2400°C and a growth pressure of 0.1 mbar to 100 mbar, a SiC growth gas phase (9) is generated therein by sublimation of the SiC raw material (6) and by transport of the sublimated gaseous components to the crystal growth region (5), and within this phase, a SiC bulk single crystal (2) is grown on the SiC seed crystal (8) by deposition from the SiC growth gas phase (9), c) A method characterized in that, before starting growth, mechanical stress is introduced into the SiC seed crystal (8) at room temperature, causing seed helical dislocations (24) present in the SiC seed crystal (8) to move under the influence of the mechanical stress, thereby causing the seed helical dislocations (24) that approach each other in relation to their respective dislocation movements to recombine and cancel each other out. [Configuration 2] The method according to configuration 1, characterized in that the dislocation movement of the seed helical dislocation (24) is thermally activated by heating the SiC seed crystal (8). [Configuration 3] The method according to configuration 1 or 2, characterized in that the mechanical stress is introduced to the SiC seed crystal (8) in a rotationally symmetric manner. [Structure 4] A method according to any one of the above configurations 1 to 3, characterized in that the SiC seed crystal (8) is bent to a maximum bend distance of 0.1 mm to 5 mm to introduce the mechanical stress. [Composition 5] The method according to any one of the above configurations 1 to 4, characterized in that the SiC seed crystal (8) is bent by at least one punching tool (28; 28a; 28b; 28c; 32) to introduce the mechanical stress. [Composition 6] The method according to configuration 5, characterized in that at least one of the punching tools (28) is placed in the center and acts on the center of the SiC seed crystal (8). [Composition 7] The method according to configuration 5 or 6, characterized in that several punching tools (28, 32) act on the SiC seed crystal (8), and at least a portion of these punching tools (32) are placed along a virtual circular line (33) around the center of the SiC seed crystal (8). [Structure 8] The method according to any one of the above configurations 1 to 7, characterized in that the SiC seed crystal (8) is firmly connected to the non-flat contact surfaces (36;37) of the shaped seed holder (34;35) to introduce the mechanical stress. [Composition 9] A single-crystal SiC substrate (38;39) having an entire main surface (41;42), wherein the entire main surface (41;42) has an accumulation subsurface (48;49) formed by up to 20% of the entire main surface (41;42), and the accumulation subsurface (48;49) contains at least 80% of all substrate helical dislocations (43) present on the entire main surface (41;42). [Configuration 10] The SiC substrate according to configuration 9, characterized in that the accumulation portion surface (48;49) contains at least 85% of all substrate helical dislocations (43) present on the entire main surface (41;42). [Composition 11] The SiC substrate according to configuration 9 or 10, characterized in that the accumulation portion surface (48;49) has a size of up to 15% of the total main surface (41;42). [Composition 12] The aforementioned SiC substrate (38;39) has a maximum temperature of 1000 / cm². 2 A SiC substrate according to any one of the above configurations 9 to 11, characterized by having a total helical dislocation density. [Composition 13] The SiC substrate according to any one of the above configurations 9 to 12, characterized in that the entire main surface (41;42) has a substrate diameter of at least 150 mm. [Composition 14] The SiC substrate according to any one of the above configurations 9 to 13, characterized in that the SiC substrate (38;39) has a SiC crystal structure having only a single SiC polytype. [Composition 15] The SiC substrate (38;39) is characterized in that it has an electrical resistivity of 8 mΩcm to 26 mΩcm, as described in any one of the above configurations 9 to 14. .

[0055] In this regard, it is particularly advantageous that, at the latest when the actual growth of the SiC bulk single crystal 2 begins, the SiC seed crystal 8 has a distribution of its seed helical dislocations 24 and / or a total seed helical dislocation density related to its growth surface 18 that should and can be inherited by the SiC bulk single crystal 2 in at least approximately this form.

[0056] To achieve this, the SiC seed crystal 8 is subjected to a treatment that at least partially recombines and cancels out the seed helical dislocations 24 that are still present in considerable numbers in the SiC seed crystal 8 at this initial stage, before being used to grow the SiC bulk single crystal 2. For this purpose, the SiC seed crystal 8 is preferably exposed to mechanical stress at room temperature and then heated in particular. This brings about dislocation migration of the seed helical dislocations 24 that were initially present. In the process of this dislocation migration, seed helical dislocations 24 with opposite Burgers vectors can approach each other to such an extent that recombination and mutual cancellation of each pair of seed helical dislocations 24 occurs. Thus, this favorable selective reduction of seed helical dislocations 24 is mechanically induced (by the mechanical stress introduced into the SiC seed crystal 8) and thermally activated (by the subsequent heat treatment). During the heat treatment to initiate favorable dislocation migration, the mechanically strained SiC seed crystal 8 is brought to a temperature up to 200°C lower than the growth temperature at which dislocations will later spread throughout the SiC seed crystal 8 during actual growth. For example, the treatment temperature is approximately 2100°C. This heat treatment preferably lasts for approximately 200 minutes. After the completion of this pretreatment, the SiC seed crystal 8 has a favorable heterogeneous distribution of seed helical dislocations 24, with only a very small number of seed helical dislocations in the central region, as illustrated in the representation in Figure 2.

[0057] The following describes an example of introducing a mechanical stress favorable to seed crystal 8.

[0058] Figure 3 shows an example of a seed holder 25 used as part of the growth apparatus 1. This seed holder 25 has a holding plate 27 placed on a wall projection 26 of the crucible side wall 13 and an extruder 28 that is adjustable in the direction of the central longitudinal axis 14. The SiC seed crystal 8 is fixed, and in particular bonded, to the front surface of the holding plate 27 facing the crystal growth region 5. The extruder 28 is in contact with the opposite side, the back surface of the holding plate 27. By moving the extruder 28 toward the crystal growth region 5, the unit consisting of the holding plate 27 and the bonded SiC seed crystal 8 is bent. The bend is greatest in the center. Here, the SiC seed crystal 8 is bent by a bend distance 29 of approximately 1 mm. The bend of the SiC seed crystal 8 correlates with the mechanical stress σ introduced into it. Figure 3 schematically illustrates the profile of this mechanical stress σ introduced into the SiC seed crystal 8. The maximum value of these stresses is also located at the center of the SiC seed crystal 8. There, the mobility of seed helical dislocations 24 is highest. This is because this mobility depends on the strength of the mechanical stress at each location. During heating, which is performed as part of the annealing process, seed helical dislocations 24, especially those located in the central region of the SiC seed crystal 8, begin to move and recombine with a particularly high probability.

[0059] The adjustable pry tool 28 has a cylindrical shape. Its tip, which presses against the back of the retaining plate 27, can have various shapes. Three embodiments are shown in Figures 4-6. The pry tool 28a shown in Figure 4 has a flat pry tool tip 30a, the pry tool 28b shown in Figure 5 has a tapered conical pry tool tip 30b, and the pry tool 28c shown in Figure 6 has a hemispherical round pry tool tip 30c.

[0060] Figure 7 shows a schematic top view of the back side of the holding plate 27, where the seed holder 25 shown in Figure 3, which can be bent by a single punching tool 28, is located in the growth direction 19 of the SiC bulk single crystal 2 to be grown.

[0061] Figure 8 shows a further embodiment of the seed holder 31 used in the growth apparatus 1, illustrated in the same diagram as the seed holder 25 in Figure 7. The seed holder 31 is constructed essentially the same as the seed holder 25. The seed holder 31 is also bendable, thus allowing mechanical stress to be applied to the SiC seed crystal 8. However, unlike the seed holder 25, the seed holder 31 has, in addition to the centrally located extruder 28, several further extruders 32 placed concentrically and equidistantly around the extruder 28 along a circular line 33. The extruders 32 are also cylindrical and adjustable in the direction of the central longitudinal axis 14. The diameters of these extruders are somewhat smaller than the diameter of the central extruder 28. In other words, the seed holder 31 has several push-out tools 28 and 32 to compensate for its warping, thereby allowing for very precise adjustment of the warping of the SiC seed crystal 8, and consequently, the mechanical stress to be introduced into the SiC seed crystal 8.

[0062] The curvature of the SiC seed crystal 8 can be adjusted only during pretreatment to reduce the seed helical dislocations 24 present in the SiC seed crystal, using the seed holders 25 and 31. After the pretreatment is complete, the extruders 28 and 32 can be retracted, returning the seed holder 25 or 31 containing the SiC seed crystal 8 fixed thereto to an uncurved state, and then the actual growth of the SiC bulk single crystal 2 is carried out in this state.

[0063] In contrast, Figures 9 and 10 show further embodiments of shaped seed holders 34 and 35 used in the growth apparatus 1. These have non-flat contact surfaces 36 and 37 for contacting the SiC seed crystal 8, respectively, and are similarly resting on wall projections 26 of the crucible sidewall 13. Unlike seed holders 25 and 31, seed holders 34 and 35 cannot be adjusted or bent. In these cases, the SiC seed crystal 8 bonded to the respective contact surface 36 or 37 undergoes permanent bending, but even in these embodiments, the mechanical stress crucial for reducing seed helical dislocations 24 is introduced to the SiC seed crystal 8 corresponding to the non-flat shape of the respective contact surface 36 or 37. In the case of seed holder 34, the contact surface 36 is concavely curved. Therefore, the SiC seed crystal 8 bonded to it is bent backward, i.e., away from the crystal growth region 5. In the case of the seed holder 35, the contact surface 37 is curved in a convex shape, and therefore, the SiC seed crystal 8 bonded to it is bent forward toward the direction of the crystal growth region 5, similar to the seed holders 34 and 35. In principle, any other shape for non-flat contact surfaces can be realized, and its exact shape can be adapted to the mechanical stress profile to be introduced into the SiC seed crystal 8 in each individual case.

[0064] If necessary, the presence of seed helical dislocations 24 can be first examined for in the SiC seed crystal 8. This examination is performed, for example, by X-ray topography. Subsequently, any region found to have a particularly high concentration of seed helical dislocations 24 in this examination can be selectively subjected to mechanical stress in order to reduce the unusually high (or above-average) number of seed helical dislocations 24 therein.

[0065] Overall, the growth apparatus 1, combined with the various deformation forms described above to reduce the seed helical dislocations 24 present in the SiC seed crystal 8, enables the growth of high-quality SiC bulk single crystals 2 having only a small number of bulk single crystal helical dislocations 20, where the bulk single crystal helical dislocations 20 are heterogeneously distributed and preferably concentrated within accumulation regions 21, which can be advantageously removed when the SiC bulk single crystals 2 are further used in the manufacture of high-quality electronic components.

[0066] Next, equivalently high-quality SiC substrates 38,39 can be manufactured from these high-quality SiC bulk single crystals 2 (see schematic top view depictions in Figures 11 and 12). These disk-shaped SiC substrates 38,39 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. The location of such disks 40 forming the SiC substrate within the SiC bulk single crystal 2 is illustrated by dashed rectangles in the depiction in Figure 2. Such SiC substrates 38 or 39 are large and thin. In possible embodiments, their entire main surface 41 or 42 has a substrate diameter of at least 150 mm, e.g., 200 mm, while the substrate thickness is about 500 μm. The SiC substrates 38 or 39, like the SiC bulk single crystals 2 from which they are manufactured, are preferably up to 1000 cm². -2 It has a low total helical dislocation density and a heterogeneous distribution of residual bulk single-crystal helical dislocations 20, which can also be understood and referred to as substrate helical dislocations 43 in relation to the substrates 38 and 39. Both improve the suitability of the SiC substrates 38 or 39 for use in manufacturing parts. The total helical dislocation density, in the case of the SiC bulk single crystal 2, is related to the complete cross-section of the SiC bulk single crystal 2 perpendicular to the central longitudinal axis 14 or the growth direction 19, and in the case of the SiC substrates 38 or 39, is related to the complete entire main surface 41 or 42. The heterogeneous helical dislocation distribution can be seen from the illustrations in Figures 11 and 12, which show the Si side of the relevant SiC substrates 38 and 39, respectively.

[0067] In the case of the SiC substrate 38 shown in Figure 11, the substrate helical dislocations 43 are concentrated in the accumulation region 44 formed by the axial edge region, while the utilization region 45 formed by the central region has significantly fewer substrate helical dislocations 43. Therefore, the latter is particularly suitable for use in the manufacture of high-quality components. In this respect, a helical dislocation distribution exists similar to that of the bulk single crystal 2 schematically shown in Figure 2, and similar to that which can be achieved by using a SiC seed crystal 8 that has been pretreated by warping and heat pretreatment corresponding to the indications shown in Figures 3, 9, or 10 before actual growth.

[0068] In the case of the SiC substrate 39 shown in Figure 12, the conditions are exactly the opposite. In this case, the substrate helical dislocations 43 are concentrated in the accumulation region 46 formed by the central region, while significantly fewer substrate helical dislocations 43 are present in the utilization region 47 formed by the axial edge region. Therefore, the latter is also particularly well suited for use in the manufacture of high-quality components.

[0069] In the case of SiC substrates 38 and 39, each usable portion 45 or 47 is significantly larger than each accumulation portion 44 or 46. Each accumulation portion 44 or 46 has an associated accumulation portion 48 or 49, which is part of each total main surface 41 or 42, accounting for at most only 20% of it. Nevertheless, at least 80% of all substrate helical dislocations 43 present on the associated total main surface 41 or 42 are located within this accumulation portion 48 or 49. The boundary between the smaller accumulation portion 44 or 46 and the larger usable portion 45 or 47, which is intended for further use, is indicated in Figures 11 and 12 by a dashed (virtual) boundary line 50, respectively.

Claims

1. a) Before training begins, a1) A SiC seed crystal (8) having a growth surface (18) is placed within the crystal growth region (5) of the growth crucible (3), a2) Introducing SiC raw material (6) into the SiC storage area (4) of the growth crucible (3), b) A method for producing at least one SiC bulk single crystal (2) by sublimation growth, wherein, during growth at a growth temperature of up to 2400°C and a growth pressure of 0.1 mbar to 100 mbar, a SiC growth gas phase (9) is generated therein by sublimation of the SiC raw material (6) and by transport of the sublimated gaseous components to the crystal growth region (5), and within that, a SiC bulk single crystal (2) is grown on the SiC seed crystal (8) by deposition from the SiC growth gas phase (9), c) Before starting the growth, mechanical stress is introduced into the SiC seed crystal (8) at room temperature to cause the seed helical dislocations (24) present in the SiC seed crystal (8) to move under the influence of the mechanical stress, thereby causing the seed helical dislocations (24) that approach each other in relation to their respective dislocation movements to recombine and cancel each other out. d) A method for bending the SiC seed crystal (8) in order to introduce the mechanical stress, by using at least one extruder (28; 28a; 28b; 28c; 32) adjustable in the direction of the central longitudinal axis (14) of the growing SiC volume single crystal (2), and by feeding the at least one extruder (28; 28a; 28b; 28c; 32) in the direction of the crystal growth region (5).

2. The method according to claim 1, characterized in that the dislocation movement of the seed helical dislocation (24) is thermally activated by heating the SiC seed crystal (8).

3. The method according to claim 1 or 2, characterized in that the mechanical stress is introduced to the SiC seed crystal (8) in a rotationally symmetric manner.

4. The method according to any one of claims 1 to 3, characterized in that the SiC seed crystal (8) is bent by a maximum bend distance of 0.1 mm to 5 mm to introduce the mechanical stress.

5. The method according to any one of claims 1 to 4, characterized in that at least one of the punching tools (28) is placed in the center and acts on the center of the SiC seed crystal (8).

6. The method according to any one of claims 1 to 5, wherein several punching tools (28, 32) act on the SiC seed crystal (8).

7. The method according to claim 6, wherein at least some of the several punching tools (32) are placed along a virtual circular line (33) around the center of the SiC seed crystal (8).

8. The method according to claim 7, wherein at least some of the several punching tools (32) are arranged at equal intervals on a virtual circle (33) surrounding the center of the SiC seed crystal (8).

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