A system for manufacturing high-quality semiconductor single crystals, and a method for manufacturing high-quality semiconductor single crystals.

Abstract

To provide systems and methods for growing bulk semiconductor single crystals, more specifically, for growing bulk semiconductor single crystals, such as silicon carbide, based on physical vapor transport.SOLUTION: A sublimation system for growing at least one single crystal of a semiconductor material by a sublimation growing process comprises a crucible (102) having a longitudinal axis (120) and comprising fixing means for at least one seed crystal (110) and at least one source material compartment (104) for storing a source material (108); a heating system formed to generate an irregular temperature field around the circumference of the crucible at one or more defined heights along the longitudinal axis of the crucible; and a rotary drive that is operable to cause a rotational movement of the fixing means around the longitudinal axis relative to the heating system.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a system and method for growing bulk semiconductor single crystals, and more specifically, for growing single crystals of bulk semiconductors such as silicon carbide based on physical vapor transport.

Background Art

[0002] Silicon carbide (SiC) is widely used as a semiconductor substrate material for electronic components in a wide range of applications such as power electronics, radio frequency, and light-emitting semiconductor components.

[0003] Physical vapor transport (PVT) is generally used, particularly for commercial purposes, to grow bulk SiC single crystals. SiC substrates are manufactured by cutting slices from bulk SiC crystals (e.g., using a wire saw) and finishing the slice surfaces in a series of polishing steps. The finished SiC substrates are used in the manufacture of semiconductor components in an epitaxial process, etc., where thin single crystal layers of a suitable semiconductor material (e.g., SiC, GaN) are deposited on the SiC substrate. The properties of the deposited monolayers and the components manufactured therefrom are critically determined by the quality and homogeneity of the underlying substrate. For this reason, the excellent physical, chemical, electrical, and optical properties of SiC make it a preferred semiconductor substrate material for power device applications. [[ID=

[17] ]]

[0004] PVT is basically a crystal growth method involving the sublimation of a suitable material followed by re-solidification onto a seed crystal, where the formation of a single crystal occurs on the seed crystal. The raw material and the seed crystal are placed inside the growth structure, and the raw material is sublimated by heating. The sublimated vapor then diffuses in a controlled manner due to a temperature field having a gradient set between the raw material and the seed crystal, and deposits on the seed and grows as a single crystal.

[0005] Conventional PVT-based growth systems generally utilize either an induction heating system or a resistance heating system to sublimate the raw materials. In both cases, the core of the PVT-based growth system is a so-called reactor. Essentially, it comprises a crucible and means for fixing seed crystals, and the growth structure, conventionally made from graphite and carbon materials for insulation, is placed inside the reactor and heated by either an induction coil located outside the reactor or a resistance heater located outside or inside the reactor. The temperature inside the growth structure is measured by one or more pyrometers or one or more thermocouples placed near the overture of the growth structure. The vacuum-sealed reactor is evacuated by one or more vacuum pumps and supplied with inert gas or doped gas via one or more gas supplies to create a controlled gas (gas mixture atmosphere). All process parameters (pressure, temperature, gas flow rate, etc.) can be adjusted, controlled, and stored by a computer-operated system controller, which communicates with all relevant components (e.g., inverter, pyrometer, vacuum control valve, mass flow control (MFC), and pressure gauge).

[0006] In induction-heated PVT systems, the reactor typically includes one or more glass tubes, which are sometimes cooled with water and have flanges at both ends to seal the inside of the reactor to the atmosphere. An example of such an induction-heated PVT system is described in U.S. Patent No. 8,865,324. Figure 8 shows such a conventional induction-heated PVT system 800.

[0007] The growth mechanism 800 comprises a growth crucible 802, which includes a SiC supply region 804 and a crystal growth region 806. Powdered SiC raw material 808 is injected into the SiC supply region 804 of the growth crucible 802 as a pre-processed starting material before the start of the growth process, and is placed, for example, in the SiC supply region 804. A seed crystal 810 is provided in the crystal growth region 806, on the inner wall of the growth crucible 802 facing the SiC supply region 804, for example, on the lid 812 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 810 by deposition from the SiC growth gas phase formed in the crystal growth region 806. The bulk SiC single crystal to be grown and the seed crystal 810 may have approximately the same diameter.

[0008] The growing crucible 802, including the crucible lid 812, may be manufactured from a conductive and thermally conductive graphite crucible material. A thermal insulator (not shown in the figure) is placed around it, which may include, for example, a cellular graphite insulating material, the porosity of which is particularly higher than that of the graphite crucible material.

[0009] A heat-insulated growth crucible 802 is placed inside a tubular container 814, which may be constructed as a quartz glass tube and form an autoclave or reactor. An induction heating device in the form of a heating coil 816 is placed around the container 814 to heat the growth crucible 802. The growth crucible 802 is heated by the heating coil 816 to a growth temperature exceeding 2000°C, particularly up to about 2200°C. The heating coil 816 inductively couples an electric current to the conductive crucible wall (so-called susceptor) of the growth crucible 802. This current flows substantially as a circulating current in the circular, hollow, cylindrical crucible wall, heating the growth crucible 802 in the process. The susceptor may be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals. The primary purpose of the susceptor is to provide a heat source inside the crucible 802. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 802 through conduction and / or radiation.

[0010] As described above, the induction coil 816 is mounted on the outside of the glass tube 814 and is usually surrounded by a Faraday cage (not visible in the drawing) that forms an electromagnetic shield to block electromagnetic radiation. The induction coil 816 has equidistant windings, with each winding at a distance d_1 from the adjacent winding.

[0011] Furthermore, in conventional resistance-heated PVT systems, the heating resistance element is mounted inside the reactor. If the reactor is made of metal, it can be cooled by water or air. Examples of resistance-heated PVT systems are described in the published patent applications, U.S. Patent Application Publication No. 2016 / 0138185 and U.S. Patent Application Publication No. 2017 / 0321345.

[0012] Currently, other conventional PVT growth systems with these and similar components are based on the idea of ​​heating the inside of the crucible in a temperature field as homogeneous as possible in the radial direction and providing a predetermined temperature gradient in the axial direction in order to set the driving force for the sublimated gas species to move toward the seed and growing single crystal.

[0013] For the growth of high-quality crystals, homogeneous heat bonding to the growth crucible in the radial direction is considered extremely important. By bonding heat as homogeneously as possible, the crystal should grow as homogeneously and symmetrically as possible. In particular, this should prevent the formation of threading screw dislocations (TSDs) and threading edge dislocations (TEDs), also known as step dislocations. Heterogeneous and asymmetrical heat distribution, and the resulting heterogeneous and asymmetrical growth, are advantageous for the formation of these dislocations.

[0014] Therefore, every effort is usually made to design a thermal coupling growth system that is homogeneous and radially symmetrical in an ideal form, and according to current technology, structural elements that may affect the induced magnetic field are made of materials such as plastic or rigid paper or similar composite and structural materials in order to avoid such effects.

[0015] However, the inventors of this disclosure have found that even with the most homogeneous and ideal growth system that bonds heat to the crucible radially symmetrically, it is not possible to grow the highest quality crystals, i.e., crystals with as few spiral and step dislocations as possible.

[0016] The published European Patent Application Publication No. 3699328 describes a method for improving the quality of SiC single crystals, particularly by using homogeneous insulation.

[0017] However, while the use of homogeneous isolation already works favorably for the growth of homogeneous and therefore low-defect crystals, the use of optimized isolation is not always sufficient to produce dislocation-free crystals.

[0018] Furthermore, the published European Patent Application Publication No. 4060098 discloses a method for reducing helical dislocations, in which helical dislocations present in a seed crystal are made movable by mechanically tensioning the seed crystal used, thereby allowing the dislocations to annihilate each other when they meet, if necessary. However, this method cannot move newly formed dislocations during crystal growth, particularly helical and step dislocations, to annihilate each other. As a result, it is not possible to grow crystals that are as free of helical and step dislocations as possible. [Prior art documents] [Patent Documents]

[0019] [Patent Document 1] U.S. Patent No. 8,865,324 [Patent Document 2] U.S. Patent Application Publication No. 2016 / 0138185 [Patent Document 3] U.S. Patent Application Publication No. 2017 / 0321345 [Patent Document 4] European Patent Application Publication No. 3699328 [Patent Document 5] European Patent Application Publication No. 4060098 [Patent Document 6] European Patent No. 2664695 [Summary of the Invention]

[0020] The present invention has been made in view of the drawbacks and inconveniences of the prior art, and an object thereof is to provide a system for growing a single crystal of a semiconductor material by physical vapor transport (PVT), and a method for manufacturing a single crystal of a semiconductor material with improved single crystal quality and high cost effectiveness.

[0021] This object is solved by the subject matter of the independent claims. Advantageous embodiments of the present invention are the subject matter of the dependent claims.

[0022] Based on the idea that, instead of attempting to achieve a temperature field that is as uniform and rotationally symmetric as possible during crystal growth, it is also possible to allow the growing crystal to experience a time-varying temperature field. The inventors of the present disclosure have discovered that such temporal variations can move the possible screw dislocations and / or step dislocations that are being formed, such that the dislocations can encounter each other and annihilate each other. Specifically, since an ideally homogeneous field is clearly not sufficient to obtain the desired crystal quality, the approach presented here induces the movement of dislocations during growth by a periodically varying temperature field such that the dislocations cancel each other out.

[0023] Specifically, a sublimation system is provided for growing at least one single crystal of a semiconductor material by a sublimation growth method. The sublimation system includes a crucible having a longitudinal axis, fixing means for at least one seed crystal, and at least one raw material section for containing a raw material, a heating system formed to generate an irregular temperature field at one or more defined heights along the longitudinal axis of the crucible around the circumference of the crucible, and a rotational drive device operable to cause a rotational movement of the fixing means about the longitudinal axis with respect to the heating system.

[0024] Note that the radial temperature field and the axial temperature field must be distinguished.

[0025] In particular, the radial field within the region of the crystal to be grown must have inhomogeneities through which the crystal constantly passes by means of the rotating device. This can also occur at different angular ranges and at several heights due to various irregularities of the system.

[0026] The axial temperature gradient is mainly the driving force for growth, i.e., since the seed is colder than the (powder-like) raw material, sublimated Si and C species can be transported. However, the axial gradient in the peripheral part is disturbed by the irregularities of the growth system in the same way as the radial gradient.

[0027] Therefore, these two gradients are coupled in the radial and axial directions.

[0028] Advantageously, the sublimation system has a heating system comprising an induction coil and / or a resistive heating coil operable to generate a magnetic field, in each case the coil at least partially surrounding the crucible. Whether inductive or resistive, such a coil-type heating system can be easily deformed to provide an asymmetric temperature field through which the growing single crystal moves.

[0029] If the heating system is based on an induction coil, the heating system may include an electromagnetic field control element for manipulating the magnetic field. Such an electromagnetic field control element may include, for example, a metal support member and / or pole piece. This allows for the creation of irregularities in a particularly easy manner without the need to interfere with the coil itself.

[0030] On the other hand, the heating system may include a coil having a deformed cross-section in at least one of its windings, and / or a coil having at least one winding positioned at a different distance from adjacent windings. In other words, a portion of the coil is either deformed in cross-section or axially shifted relative to the remaining equidistant windings. This allows for a particularly well-defined scheme that creates an irregular temperature field.

[0031] A particularly simple way to introduce irregularity into the temperature field can be achieved if the coil has at least one electrical contact located in an axial position close to the crucible, rather than at the circumferential end of the sublimation system.

[0032] Various possibilities exist for providing the rotation necessary to cause the seed crystal and growing crystal to periodically pass through an asymmetric temperature field, and these may be used according to the respective structural conditions of the sublimation system. The rotation drive may be coupled to a stationary means so that the seed crystal and growing single crystal are rotatable relative to the crucible, and / or the rotation drive may be coupled to the crucible so that the crucible, together with the seed crystal and growing single crystal, is rotatable relative to the heating system.

[0033] If the sublimation system includes a thermal insulating element, the rotary drive may be coupled to the thermal insulating element and the crucible, thereby allowing the thermal insulating element and the crucible to rotate relative to the heating system. Any other combination of movable and fixed components is also possible, as long as the seed crystal moves relative to a radially asymmetric temperature field.

[0034] Advantageously, the rotary drive unit can be operated to produce rotational speeds in the range of 1 rpm to 60 rpm, preferably 10 rpm. These speeds may be shown to produce the best results.

[0035] This disclosure further provides a method for growing at least one single crystal of a semiconductor material by sublimation growth, the method being A crucible having a longitudinal axis is prepared, at least one seed crystal is fixed to the fixing means of the crucible, and raw materials are filled into at least one raw material compartment. Using a heating system, an irregular temperature field is generated around the circumference of the crucible along the longitudinal axis of the crucible, This includes generating rotational motion of a fixing means about its longitudinal axis relative to the heating system, such that the growing single crystal is exposed to a time-varying temperature field.

[0036] As mentioned above, the term “asymmetric” or “irregular” temperature field means that different axial temperature gradients around the circumference correlate with different radial temperature gradients.

[0037] In a favorable example, a thermal insulator unit is provided between the crucible and the heating system, and the fixing means is rotated in relation to the thermal insulator unit.

[0038] The crucible may be rotated in relation to the heating system and / or in relation to a thermal insulator unit provided between the crucible and the heating system.

[0039] In a favorable example, a thermal insulator unit is placed between the crucible and the heating system, and the crucible and the thermal insulator unit are rotated in relation to the heating system.

[0040] As described above, the rotational motion may be performed at a rotational speed in the range of 1 rpm to 60 rpm, preferably 10 rpm.

[0041] Advantageously, the generated temperature fields have regions that differ from each other by at least 2K to 15K, preferably 5K.

[0042] In particular, the combination of a 5K temperature difference and a speed of 10 rpm results in ideal conditions for activating helical and step dislocations.

[0043] By introducing intentional asymmetry into the growth system in combination with a rotating device, dislocations, namely TSDs and TEDs, are made mobile and, under appropriate conditions, can cancel each other out when they encounter one another. This reduces the overall dislocation budget and improves the quality of the grown single crystals.

[0044] The accompanying drawings are incorporated herein by reference and form part of this specification to illustrate several embodiments of the present invention. These drawings, together with the description, serve to illustrate the principles of the present invention. The drawings are intended solely to illustrate preferred and alternative examples of how the present invention may be made and used, and should not be construed as limiting the present invention to the embodiments shown and described. Furthermore, several aspects of the embodiments may, individually or in different combinations, form solutions according to the present invention. Thus, the embodiments described below may be considered individually or in any combination thereof. Further features and advantages will become apparent from a more detailed description of the various embodiments of the present invention shown below in the accompanying drawings. In the accompanying drawings, similar reference numerals refer to similar elements. [Brief explanation of the drawing]

[0045] [Figure 1] This is a schematic cross-sectional side view of a sublimation system according to the first example. [Figure 2] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 3] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 4] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 5] A schematic top view of a sublimation system with further examples. [Figure 6] A schematic top view of a sublimation system with further examples. [Figure 7] This is a schematic cross-sectional side view of a sublimation system, illustrating a further example. [Figure 8] This is a schematic cross-sectional side view of a known sublimation system. [Modes for carrying out the invention]

[0046] The present invention will now be described in detail with reference to the figures, starting with Figure 1.

[0047] Figure 1 shows a sublimation system 100 according to a first example of the present disclosure. Note that the term sublimation system is intended to encompass any system for growing at least one single crystal of a semiconductor material using sublimation growth. Preferably, the term refers to a physical vapor transport (PVT) system for growing a silicon carbide (SiC) volume single crystal, as described with reference to Figure 8.

[0048] The sublimation system 100 includes a growth crucible 102, which includes raw material compartments, in particular a SiC supply area 104 and a crystal growth area 106. Powdered SiC raw material 108 is injected into the SiC supply area 104 of the growth crucible 102 as a pre-processed starting material before the start of the growth process, and is placed, for example, in the SiC supply area 104. The raw material 108 may be densified or composed of at least partially solid material in order to increase the density of the raw material 108.

[0049] The seed crystal 110 is provided in the crystal growth region 106, on the inner wall of the growth crucible 102 facing the SiC supply region 104, for example, on the lid 112 of the crucible. The bulk SiC single crystal to be grown grows on the seed crystal 110 by deposition from the SiC growth gas phase formed in the crystal growth region 106. The growing bulk SiC single crystal and the seed crystal 110 may have approximately the same diameter. If the diameter of the crystal channels is larger than the diameter of the seed crystal 110, the bulk SiC single crystal may have a larger diameter than the seed crystal 110. However, the usable low-defect diameter of the grown bulk SiC single crystal is usually the same as the diameter of the seed crystal.

[0050] The growing crucible 102, including the crucible lid 112, may be manufactured from a conductive and heat-conductive graphite crucible material. A thermal insulator (not shown in the figure) is placed around it, which may include, for example, a cellular graphite insulating material, the porosity of which is particularly higher than that of the graphite crucible material.

[0051] In induction heating, the thermally insulated growth crucible 102 is placed inside a tubular container (not shown in Figure 1), which may be a quartz glass tube forming an autoclave or reactor. An induction heating device in the form of a heating coil 116 is positioned around the container to heat the growth crucible 102. The heating coil 116 generates the required temperature field by inductively coupling an electric current within the conductive crucible wall (susceptor) of the growth crucible 102. This current flows substantially as a circulating current within the circular, hollow, cylindrical crucible wall, heating the growth crucible 102 in the process. The susceptor can be made from graphite, TaC, WC, Ta, W, or other heat-resistant metals, and may be an integral part of the crucible 102 or a separate part close to the crucible wall. The primary purpose of the susceptor is to provide a heat source inside the crucible 102. When the susceptor is heated by induction, its surface reaches a high temperature, and that temperature is then transferred to the inside of the crucible 102 through conduction and / or radiation.

[0052] As described above, in the case of induction heating, the coil 116 is mounted on the outside of the glass tube and is usually surrounded by a Faraday cage (not visible in Figure 1) to block electromagnetic radiation. In the case of resistance heating, the coil 116 is also mounted inside the reactor and in thermal insulation, thereby making close contact with the crucible 102. The principle of this disclosure is applicable to both heating techniques. Thus, the coil 116 is more broadly referred to as the heating means below and encompasses both induction heating and resistance heating (or a combination thereof). Furthermore, it should be noted that in this disclosure, the coil windings are illustrated as having a round, specifically circular or elliptical cross-section. However, the coil windings may have other preferred cross-sections such as square or rectangular.

[0053] As shown in Figure 1, the coil 116 has at least one deformation region 115, in which the cross-section of the coil 116 deviates from the circular cross-section of the remaining windings. In Figure 1, this deviation is depicted as a compression leading to an elliptical cross-section within the deformation region 115. Of course, other cross-sectional irregularities may be applied to the coil 116. In the deformation region 115, the distance between a deformed winding and an adjacent winding is increased to a distance d_2 compared to the normal distance d_1 between the remaining undeformed windings.

[0054] During operation, structural asymmetry resulting from this deformation region 115, which can cover, for example, 10° to 90°, preferably 10° to 45°, of the circumference, introduces irregularities in the temperature field. These irregularities extend both radially (around the circumference of the crucible) and axially (along the central axis 120).

[0055] According to this disclosure, the sublimation system further comprises a rotary drive (not shown in the figure) which causes the seed crystal 110, represented by arrow 118, to rotate around a central axis 120 while the heating means 116 generates a spatially varying temperature field. The direction of rotation is, needless to say, arbitrary.

[0056] The rotational motion of a seed crystal, along with the growing single crystal in a spatially heterogeneous temperature field, results in the seed crystal experiencing a time-varying, or in other words, fluctuating, temperature field together with the growing single crystal. This dynamic fluctuation of the temperature field acting on the growing crystal moves helical and step dislocations within the growing single crystal, giving them opportunities to encounter and annihilate each other.

[0057] In other words, the growing crystal undergoes a periodic temperature cycle resulting from the combination of a structurally asymmetric growth system and the rotational motion of the growing crystal in relation to the temperature field.

[0058] To enable spiral and step dislocations, it can be shown that the temperatures measured at two points at a specific height of the growing crystal, at the same radial distance from the rotation axis of the seed crystal 110, must differ by at least 2K and up to 15K. Preferably, the temperatures should differ by 5K.

[0059] The axial location of the temperature disorder may correspond to the current growth / gas phase boundary, or it may be located anywhere between the seed crystal 110 and the current growth / gas phase boundary. This means that periodic temperature circulation acts on the very surface of the growing crystal, or on deeper regions, to activate newly formed or previously formed helical and / or edge dislocations.

[0060] The radial distance may, but is not limited to, the final diameter of the substrate machined from the grown crystal. Furthermore, the diameter can be larger or smaller than the corresponding radius of the resulting SiC substrate.

[0061] The growing crystal can also be exposed to a variety of local maximum and minimum temperatures, because a structurally asymmetric growth system can have multiple asymmetries and irregularities along its longitudinal axis in the resulting temperature field, each having a radial spread of 10° to 90°, preferably 10° to 45°, of the circumference.

[0062] For example, in the case of a substrate diameter of 150 mm (i.e., a radius of 75 mm), the magnitude of the temperature irregularity may correspond to a radial spread of 10° to 90°, and thus can range from 1.3 cm to a maximum of 11.8 cm, preferably from 10° to 45°, and thus a maximum of 5.9 cm. These values ​​are calculated using the following formula for the arc L, with a radius of r = 7.5 cm: L = [α·π·r] / 180 In the formula, α is the angle value in degrees.

[0063] Therefore, for a diameter of 200 mm, each value should be fitted using a radius r = 10.0 cm.

[0064] Furthermore, optimal mobility of helical and step dislocations can be achieved when the seed crystal, along with the growing single crystal, is rotated in relation to the heating means at a rotational speed ranging from 1 rpm (revolutions per minute) to 60 rpm, preferably 10 rpm.

[0065] The rotation according to the present invention can be mechanically provided by attaching a rotation drive to various components of the sublimation system 100, insofar as a heterogeneous temperature field moves relative to the growing single crystal. For example, the fixed portion of the seed crystal 110 can be rotated relative to the heating coil 116, with a stationary insulator. Furthermore, the crucible 102 can be rotated while the heating coil and insulator are stationary. Furthermore, the crucible and insulator can be rotated relative to the heating coil 116 while the heating coil is stationary. Any suitable combination for rotating multiple elements may be applied.

[0066] Figure 2 shows another example of how the rotational symmetry of the heating means 116 can be disrupted to create a non-uniform temperature field. Note that the remaining features of the sublimation system 100 correspond to the features of the sublimation system 100 shown in Figure 1.

[0067] As shown in Figure 2, the heating means comprises a heating coil 116, which has a substantially uniform cross-section throughout all its windings, but has at least one winding that is in a portion of the circumference that is displaced axially (i.e., along the central axis 120). Thus, while all the remaining windings are at a uniform distance d_1 from each other, the displaced region 122 of the coil 116 has a reduced distance d_3 (less than d_1) from the closer adjacent windings and an increased distance d_2 (greater than d_1) from the farther adjacent windings. This intentional asymmetry generates a non-uniform temperature field, which, along with the rotational motion described above with reference to Figure 1, leads to a dynamic temperature field being experienced by the crystal growing within the crystal growth region 106.

[0068] It should be noted that the transition from the normal distance d_1 to the maximum displacements (maximum) values ​​d_2 and d_3 along the circumference of coil 116 may be a gradual transition. However, of course, a stepped displacement may be provided by applying sharp bends. Here again, the irregularity of the coil may be provided along 10° to 90°, preferably 10° to 45°, of the entire 360° circumference of coil 116.

[0069] The rotation is then performed as described above with respect to Figure 1.

[0070] Figure 3 shows another example of how the rotational symmetry of the heating means 116 can be disrupted to create a non-uniform temperature field. Note that the remaining features of the sublimation system 100 correspond to the features of the sublimation system 100 shown in Figure 1.

[0071] In the example shown in Figure 3, all windings of the coil 116 are shifted along the central axis 120 to have an increased inclination. Thus, two opposing regions of each winding are offset axially by, for example, a distance d_1. This results in a rotationally asymmetric temperature field through which the growing single crystal periodically passes by rotation according to one of the configurations described for the example in Figure 1.

[0072] Furthermore, intentional structural asymmetry can also be introduced into the sublimation system 100 by positioning the electrical contacts 124 of the heating coil 116 in an area surrounding the crucible 102. An example of this is shown in Figure 4. At least one of the electrical contacts 124 supplying current is moved axially to an area that constitutes structural asymmetry, rather than being located at the circumferential end of the heating coil 116, and particularly near the crucible 102, especially near the crystal growth region 106. Thus, during operation, the heating coil 116 generates a non-uniform temperature field, through which the growing single crystal rotates. This rotation leads to a pulsed temperature field in the growing single crystal, mobilizing step and helical dislocations. The moving step and helical dislocations encounter and annihilate each other, thereby potentially greatly improving the overall quality of the grown single crystal boule.

[0073] Figure 5 shows a top view of a sublimation system 100 according to a further example of the present disclosure. In this figure, the heating coil 116 is located inside a shield 126 that shields the external environment from electromagnetic radiation. The coil 116 surrounds a reactor 114 in which a seed crystal 110 is located.

[0074] In this favorable example, one or more first pole pieces 128 (also called pole pieces) are arranged along the coil winding at one or more different positions (and axial heights). These pole pieces 128 act as inductors of the electromagnetic field generated by the coil 116. Thus, intentional asymmetry is introduced into the resulting temperature field. As mentioned with reference to the previous example, the sublimation system 100 further comprises a rotational drive (not shown in the figure) which causes the seed crystal 110, represented by arrow 118, to rotate around the central axis 120 while the heating means 116 generates a spatially varying temperature field. The direction of rotation is, needless to say, arbitrary.

[0075] The rotational motion 118 of the seed crystal 110, along with the single crystal growing in a spatially heterogeneous temperature field, creates the effect that the seed crystal 110, together with the growing single crystal, experiences a time-varying, or in other words, fluctuating, temperature field. This dynamic fluctuation moves the helical and step dislocations within the growing single crystal, giving them opportunities to encounter and annihilate each other.

[0076] In other words, the growing crystal undergoes a periodic temperature cycle resulting from the combination of a structurally asymmetric growth system and the rotational motion of the growing crystal in relation to the temperature field.

[0077] The rotation according to this disclosure can be provided mechanically by attaching a rotation drive to various components, insofar as a heterogeneous temperature field moves relative to the growing single crystal. For example, the fixed portion of the seed crystal 110 can be rotated relative to the heating coil 116, with a stationary insulator. Furthermore, the crucible 102 can be rotated while the heating coil and insulator are stationary. Furthermore, the crucible and insulator can be rotated relative to the heating coil 116 while the heating coil is stationary. Any preferred combination for rotating multiple elements may be applied.

[0078] As an addition or alternative, a second pole piece 130 may be provided in the electromagnetic shield 126 and extend into the gap between the shield 126 and the coil 116. Here again, this pole piece 130 constitutes a structural asymmetry near the crucible 102, particularly near the crystal growth region 106. Thus, during operation, the heating coil 116 generates a non-uniform temperature field, through which the growing single crystal rotates. This rotation leads to a pulsed temperature field in the growing single crystal, mobilizing step and helical dislocations. The moving step and helical dislocations encounter and annihilate each other, thereby potentially greatly improving the overall quality of the grown single crystal boule.

[0079] Figure 6 shows a top view of a sublimation system 100 according to a further advantageous example. As shown in this figure, the asymmetry of the temperature field may be created by an asymmetric shielding 126 and a metal holder 132 of the shielding 126. The holder 132 may advantageously extend into the gap between the coil 116 and the shielding 126.

[0080] Therefore, during operation, the heating coil 116 generates a non-uniform temperature field, through which the growing single crystal rotates, as indicated by arrow 118. Thus, spiral dislocations and step dislocations in the growing single crystal are made mobile, and therefore they can encounter each other and annihilate one another.

[0081] Moving on to Figure 7, the principle of the present disclosure may further be applied to a sublimation system 200 capable of operating to grow two single-crystal Boules simultaneously. For this purpose, the crucible 202 comprises a first seed crystal 210A and a second seed crystal 210B. Figure 7 shows an example similar to the configuration shown in Figure 4. However, it is clear that any other possibility of generating an asymmetric temperature field, such as described in European Patent No. 2664695, may be applied to the sublimation system 200 for growing two or more single-crystal Boules simultaneously.

[0082] More specifically, Figure 7 shows a schematic cross-sectional view of a physical vapor transport (PVT) growth system 200 for simultaneously growing two SiC bulk crystals. The system 200 comprises a crucible 202, which includes a central raw material compartment 234 containing SiC powder 208, which is the raw material for SiC.

[0083] Two seed crystals 210A and 210B are placed in growth regions 206A and 206B. Each of the growth regions 206A and 206B is separated from the powdered, compressed, or solid SiC raw material 208 by gas-permeable porous barriers 236A and 236B. Thus, it is ensured that only gaseous Si and C-containing components enter the growth regions 206A and 206B. A heating coil 216 provides the required temperature field. Temperature field asymmetry is achieved by providing electrical contacts 224 near the crystal growth regions 206A and 206B.

[0084] Both seed crystals 210A and 210B are rotated in an asymmetric temperature field generated by coil 216 to activate step dislocations and / or helical dislocations in the growing single crystal, as described above with reference to Figures 1 to 6.

[0085] In summary, this disclosure is based on the idea that, instead of attempting to achieve the most uniform and rotationally symmetric temperature field possible during crystal growth, it is also possible to allow the growing crystal to experience a time-variable temperature field. The inventors of this disclosure have found that such time variations can move any forming helical dislocations and / or step dislocations, thereby causing the dislocations to encounter and annihilate each other. In detail, since an ideally homogeneous field is clearly insufficient to obtain the desired crystal quality, the method presented herein induces dislocation movement by a periodically changing temperature field during growth, such that the dislocations cancel each other out.

[0086] For this purpose, several conditions must be met. The technical problem of growing crystals with virtually no helical and step dislocations lies, on the one hand, in designing a growth system that intentionally creates heterogeneous and radially asymmetric thermal bonding in the growth crucible.

[0087] Such heterogeneous and asymmetric thermal bonding may be achieved, for example, by the following characteristics of the crystal growth system: - Uneven alignment results in uneven spacing of coil windings. • Unequal spacing of coil windings due to uneven winding configuration • Inlet and outlet for coil / resistance heater within the susceptor and growth crucible area. • The winding ends of the coil (within the area of ​​the susceptor and growth crucible) - Insertion of one or more induction magnetic field guides, such as at least one metal support, magnetic pole piece, etc.; conductive components may be attached directly to the induction coil or between the induction coil and the electromagnetic shielding. • Use of asymmetric shielding of electromagnetic fields

[0088] On the other hand, the technical problem of growing crystals with virtually no spiral dislocations and / or step dislocations can be solved by installing a rotating device within a heterogeneously thermally bonded growth system.

[0089] Rotation can induce dislocation dynamics in the following configurations: • Rotation of the seed in conjunction with stationary insulator / coil / resistance heating. • Rotation of the crucible combined with stationary insulator / coil / resistance heating. • Rotation of the crucible and insulator in conjunction with stationary coil / resistance heating. • Combinations for rotating multiple elements

[0090] A dynamic method for mobilizing helical and step dislocations is implemented through a combination of a rotating device and an asymmetric growth system according to the present invention. This mobilization allows dislocations to meet and cancel each other out.

[0091] The growing crystal rotates, repeatedly passing through low-temperature and high-temperature areas (sinusoidally), which is a result of the special design of this crystal growth system and the resulting asymmetrical thermal coupling.

[0092] To activate dislocations, the temperatures measured at two points on the diameter of the substrate fabricated from the crystal must differ by at least 2K, up to 15K, and preferably 5K. The rotation frequency should be 1 to 60 revolutions per minute (rpm), preferably 10 rpm, for optimal dislocation activation. This combination of a 5K temperature difference and 10 rpm results in ideal conditions for activating helical and step dislocations.

[0093] By introducing intentional asymmetry into the growth system in combination with a rotating device, dislocations, namely TSDs and TEDs, are made mobile and, under appropriate conditions, can cancel each other out when they encounter one another. This reduces the overall dislocation budget and improves the quality of the grown single crystals. [Explanation of Symbols]

[0094] 100, 200 sublimation system, PVT system 102, 202 Crucible 104 SiC supply area, raw material section 106, 206A, 206B Crystal growth region 108, 208 Ingredients 110, 210A, 210B seed crystals 112 Crucible Lid 114 Vessels, reactors 115 Deformation Region 116, 216 Induction or resistance heating coil, heating means 118, 218 rotational motion 120, 220 center axis 122 Displacement Region 124, 224 electrical contacts 126 Shielding 128 First pole piece 130 Second pole piece 132 Holder 234 Raw materials section 236A, 236B barrier 800 PVT system 802 Crucible 804 SiC supply area 806 Crystal growth region 808 Ingredients 810 seed crystals 812 Crucible Lid 814 Containers, reactors 816 Induction heating coil

Claims

1. A sublimation system for growing at least one single crystal of a semiconductor material by sublimation growth, wherein the sublimation system (100) is A crucible (102) having a longitudinal axis (120) and comprising fixing means for at least one seed crystal (110) and at least one raw material compartment (104) for containing raw material (108), A heating system formed to generate an irregular temperature field around the circumference of the crucible at one or more predetermined heights along the longitudinal axis of the crucible, The heating system comprises a rotary drive device capable of operating to generate rotational motion of the fixing means about the longitudinal axis, A sublimation system configured such that the generated irregular temperature fields have different regions from each other, ranging from at least 2K to 15K, and the temperatures measured at two points at a specific height of the growing single crystal, which are at the same radial distance from the respective rotation axes of the seed crystals (110, 210A, 210B), differ by at least 2K to a maximum of 15K.

2. The sublimation system according to claim 1, wherein the heating system comprises an induction coil as a heating coil, which is operable to generate an electromagnetic field, and the induction coil at least partially surrounds the crucible (102).

3. The sublimation system according to claim 2, wherein the heating system comprises an electromagnetic field control element for manipulating the electromagnetic field.

4. The sublimation system according to claim 3, wherein the electromagnetic field control element comprises a metal support member and / or pole piece.

5. The sublimation system according to any one of claims 2 to 4, wherein the induction coil as a heating coil has a cross-section that is deformed in the form of at least one of its windings, and / or the induction coil as a heating coil has at least one winding that is arranged to be at different distances from adjacent windings.

6. The sublimation system according to any one of claims 2 to 5, wherein the induction coil, which serves as the heating coil, comprises at least one electrical contact (124) positioned in an axial location close to the crucible (102).

7. The sublimation system according to any one of claims 1 to 6, wherein the rotation drive is coupled to the fixing means so that the seed crystal (110) is rotatable relative to the crucible (102), and / or the rotation drive is coupled to the crucible (102) so that the crucible (102) is rotatable relative to the heating system.

8. The sublimation system according to any one of claims 1 to 7, wherein the sublimation system (100) comprises a thermal insulating element, and the rotary drive device is coupled to the thermal insulating element and the crucible (102), thereby allowing the thermal insulating element and the crucible (102) to rotate relative to the heating system.

9. The sublimation system according to any one of claims 1 to 8, wherein the rotary drive device is operable to produce a rotational speed in the range of 1 rpm to 60 rpm, or a rotational speed of 10 rpm.

10. The sublimation system according to claim 1 or 2, wherein the heating system comprises a resistance heating coil as a heating coil that at least partially surrounds the crucible (102) and generates a non-uniform temperature field.

11. A method for growing at least one single crystal of a semiconductor material by sublimation growth, A crucible (102) having a longitudinal axis is prepared, at least one seed crystal (110) is fixed to the fixing means of the crucible, and at least one raw material compartment (104) is filled with raw material (108), Using a heating system, an irregular temperature field is generated around the circumference of the crucible (102) along the longitudinal axis of the crucible (102), This includes causing rotational motion of the fixing means about its longitudinal axis relative to the heating system so that the growing single crystal is exposed to a time-varying temperature field, A method in which the generated irregular temperature fields have different regions from each other, ranging from at least 2K to 15K, and the temperatures measured at two points at a specific height of the growing single crystal, which are at the same radial distance from the respective rotation axes of the seed crystals (110, 210A, 210B), differ by at least 2K and up to 15K.

12. The method according to claim 11, wherein a thermal insulator unit is provided between the crucible (102) and the heating system, and the fixing means is rotated in relation to the thermal insulator unit.

13. The method according to claim 11 or 12, wherein the crucible is rotated in relation to the heating system and / or in relation to a thermal insulator unit provided between the crucible and the heating system.

14. The method according to one of claims 11 to 13, wherein a thermal insulator unit is provided between the crucible and the heating system, and the crucible and the thermal insulator unit are rotated in relation to the heating system.

15. The method according to one of claims 11 to 14, wherein the rotational motion is performed at a rotational speed in the range of 1 rpm to 60 rpm, or at a rotational speed of 10 rpm.

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