Method and device for measuring single crystals

Abstract

The invention relates to a measuring device (1) and a method for determining quality parameters of a growth crystal, comprising an electrode arrangement (4), which has a plurality of electrodes (5) for contacting the growth crystal (2) to be received, and a signal source (6) connected to the electrodes (5) of the electrode arrangement (4). Furthermore, a measuring unit (7) is provided, which is connected to the electrode arrangement (4) and is designed to measure electrical signals with respect to the growth crystal (2) to be received, by means of the individual electrodes (5). The measuring device (1) is designed to couple a signal into the growth crystal (2) to be received by means of at least two electrodes (5) of the electrode arrangement (4) and to measure the electrical signal by means of at least one further electrode (5) of the electrode arrangement (4), wherein changes in the electrical properties of the growth crystal (2) can be detected on the basis of the variation of the electrical signal, and the signal can be coupled in and the signals can be measured by means of the electrodes at a plurality of different positions with respect to a crystal surface of the growth crystal (2), such that the respective measured changes in the electrical properties can be spatially resolved.

Description

[0001] METHOD AND DEVICE FOR MEASURING SINGLE CRYSTALS

[0002] The invention relates to a measuring device and a method for testing the quality parameters of a growth crystal, in particular a SiC single-crystal ingot.

[0003] Artificially produced crystals are widely used in the state of the art and are used in a variety of technological fields. One of the most prominent areas is the semiconductor industry, where individual electronic components are manufactured from crystals grown using this process. For this purpose, artificial SiC single crystals ("ingots") are cut into thin wafers for semiconductor production, for example, by sawing with diamond-tipped sawing wire or by laser cutting.

[0004] In order to obtain high-quality wafers, it is necessary that the SiC single crystal or ingot already has the necessary properties and therefore must meet high quality requirements.

[0005] A disadvantage of the state of the art is that these quality characteristics are usually only checked during the production of the wafers, or that it is only at this stage that it is discovered that a wafer that has already been produced has defects.

[0006] The object of the present invention was to overcome the disadvantages of the prior art and to provide a measuring device and a method by means of which a user is able to check the quality of the growth crystals.

[0007] This object is achieved by a measuring device and a method according to the claims.

[0008] The measuring device according to the invention comprises a crystal holder for at least one growth crystal and an electrode arrangement, wherein the electrode arrangement has a plurality of electrodes for contact with the growth crystal to be held. Furthermore, the measuring device has an alternating current or direct current signal source connected to the electrodes of the electrode arrangement, and a measuring unit, wherein the measuring unit is connected to the electrode arrangement and is configured to measure electrical signals using the individual electrodes relating to the growth crystal to be held.

[0009] The measuring device is configured to couple an electrical signal into the growth crystal to be recorded by means of at least two electrodes of the electrode arrangement and to measure electrical signals by means of at least one further electrode of the electrode arrangement, wherein a variation of the electrical signal at this electrode - caused by changes in the electrical properties within the growth crystal - can be detected; and wherein the coupling of the signal and the measurement of the signal can be carried out by means of the plurality of electrodes at several different positions on a crystal surface of the growth crystal, so that the respective electrical properties of the growth crystal can be spatially resolved by a mathematical evaluation of the variations in the measured signals.

[0010] Each electrode of the electrode arrangement can be used both as a signal source and as a signal probe (measurement using the measuring unit).

[0011] The invention offers the advantage of non-destructively examining a grown single crystal for various defects and locally resolving existing defects. This allows single-crystal ingots to be evaluated for potential defects or generally assessed for their overall quality before they are separated into wafers. Furthermore, they can be classified into quality classes or similar, or even declared as rejects, even before they are separated.

[0012] The method according to the invention focuses on macrodefects and material properties that deviate from the desired crystal structure. Furthermore, it is also conceivable to detect microdefects.

[0013] For the sake of completeness, it should be mentioned that measuring the electrical signals preferably includes storing or archiving the measured values ​​for further evaluation, e.g., in a storage unit or in a central control or processing unit. Furthermore, a position of the respective electrode can also be assigned to a respective measured value and stored.

[0014] Furthermore, it should be noted that a respective electrical line with a corresponding device for signal conditioning or data connection is provided between the measuring unit and the individual electrodes, as well as between the signal source and the electrodes, so that an electrical signal flow can be generated in the crystal by selecting any pair of electrodes. The electrodes can, for example, be arranged in a network, with each electrode being separately connected to the signal source or the measuring unit and being uniquely assigned via a control or processing unit.

[0015] Preferably, the surface of the growth crystal or ingot is processed before the measurement, e.g. ground, so that it has a round outer contour, as is usual when processing ingots.

[0016] An advantageous embodiment provides that the measuring device is configured to redistribute the individual functions of the electrodes with respect to generating the electrical signal and measuring the electrical signals in the electrode arrangement during a measurement process with respect to the growth crystal to be recorded. This can preferably be provided in a system or pattern, so that a numbering / sequence (with respect to the electrodes) or the like is provided, which is switched through sequentially.

[0017] Preferably, a type of reference system can be provided for the electrodes, with respect to which a calibration of the position of the electrodes (relative to the growth crystal) is performed, or, when using adjustable electrodes, after each adjustment. For completeness, it should be mentioned that the position of the respective electrode can be included in the evaluation or stored in a computing unit and updated with respect to each calibration.

[0018] Particularly preferably, an evaluation unit can be provided that is configured to convert the electrical signals (as well as the variations in the signals) acquired by the measuring unit into an imaging process and to display them graphically. The resolution of the imaging process increases with the number of electrodes or the number of different positions of the measurement processes.

[0019] Furthermore, it can be provided, for example with regard to the number of electrodes or measuring processes, that the measuring device is further set up to terminate area measurements in which no relevant changes in the electrical properties can be detected early on. This is done by gradually generating an electrical signal flow in these areas using a targeted selection of electrodes (e.g. in the circumferential direction every quarter or the like) and then measuring the changes. An imaging process essentially measures the physical parameters of an object. Depending on the process and type of signal, the measured values ​​are further processed or evaluated until the information is available in the required form. It is displayed as a spatially resolved image of the object. The information is displayed as brightness values ​​or encoded using false colors or.also represented in a coordinate system, so that a virtual image of the crystal is available.

[0020] With regard to the electrical properties of the growth crystal, these can preferably include the electrical resistance and / or electrical wave impedance. In principle, the electrical properties within the crystal correlate with the defect density, meaning that multiple neighboring defects or property changes in the crystal structure have a stronger influence on the electrical signals to be measured. These signals cannot be localized with only a single current path (relative to the signal) or a single measurement, or would only be identified as a single disturbance. By means of the design according to the invention, however, it is possible to determine different properties at higher defect densities due to multiple electrode positions and to separate them from one another.

[0021] Preferably, the quality parameters to be determined comprise at least one of the following features;

[0022] - Doping of the crystal; preferably by determining the electrical wave impedance

[0023] - Polytype of the crystal; preferred by electrical resistance or band gaps.

[0024] - Defects in the crystal; particularly in the form of cracks, cavities or defects

[0025] - polycrystalline inclusions;

[0026] - Dislocation densities, also via the electrical resistance.

[0027] The mathematical evaluation of the recorded measurement results for the spatial resolution of the material properties is performed by solving the inversion problem, which forms the basis of all known tomography methods. The inverse problem is the "reverse" of the forward problem: instead of determining the data generated by specific material properties, the material properties that generate the data representing the recorded measurements are determined. To solve this mathematical problem numerically, a large number of measurement results from locally known probes are processed. The numerical methods used are based on standard methods of linear algebra and adjustment calculus.

[0028] Crystal defects – microscopic or macroscopic – have a direct impact on the electrical material properties in the affected crystal regions and can therefore be determined both quantitatively and qualitatively using an electrical tomography method. Furthermore, for the classification of crystal defects, a pre-prepared table (or database) of the specific material property characteristics is preferably created, which correlates with the corresponding crystal defect classes.

[0029] With regard to the aforementioned signal source, it can be provided that an alternating voltage can be applied to the growth crystal via the at least two electrodes, or alternatively a direct voltage. Alternating current is preferably high frequency, e.g., at least 50 GHz. Regarding the signal sources to be used, reference is generally made to the extensive state of the art.

[0030] The electrode arrangement itself can comprise a plurality of electrodes, e.g., at least 6 electrodes, but preferably significantly more, e.g., at least 12, 16, or at least 20 electrodes. As already mentioned, the number of electrodes contributes to improving the measurement quality with regard to the possible selection of electrode pairs. However, the number also increases the quality of an individual measurement process, since each additional electrode is used to measure the electrical signals, thus improving the spatial resolution.

[0031] In one possible embodiment, it can be provided that at least one electrode of the electrode arrangement is adjustable in terms of its position, so that the at least one electrode of the electrode arrangement can be guided to a selectable position along a crystal surface of the growth crystal to be recorded. In this way, a signal for measurement can be induced at different, further positions, or measurements can be taken at an additional position. With regard to a possible adjustment of electrodes, it can further be provided that they are adjustable in the circumferential direction (radial to the longitudinal central axis) and in the height direction (parallel to the longitudinal central axis) relative to the crystal. Furthermore, they can preferably be pressed against the crystal surface or slightly pre-tensioned. If an adjustment is possible, a relative reference system can also preferably be provided for the electrode, so that its position relative to the crystal orThe position of the measuring device is known at all times. Adjustment of the electrodes can be automated or performed manually.

[0032] Furthermore, it can be provided that at least one electrode of the electrode arrangement is positioned stationary (relative to the crystal) in the crystal holder. Furthermore, the entire electrode arrangement, with its multitude of electrodes, can also be positioned stationary relative to the crystal.

[0033] In one possible embodiment, the electrode arrangement can be arranged in a ring-shaped manner, so that the electrodes are arranged in a circumferential direction (in a plane) around the longitudinal central axis of the growth crystal to be recorded. Furthermore, it can be provided that, using such a ring-shaped arrangement, the crystal to be measured is measured layer by layer (transverse to the longitudinal central axis / z-axis) by moving the ring-shaped arrangement step by step over the crystal surface for individual measurement periods.

[0034] Furthermore, the invention relates to a method for testing the quality of a growth crystal, comprising the steps;

[0035] - Providing at least one growth crystal

[0036] - Attaching several electrodes of an electrode arrangement to the growth crystal;

[0037] - Providing an AC or DC signal source, wherein the signal source is connected to the electrodes of the electrode arrangement;

[0038] - Providing a measuring unit, wherein the measuring unit is connected to the electrode arrangement and is configured to measure electrical signals by means of the individual electrodes with respect to the growth crystal to be recorded;

[0039] - coupling an electrical signal into the growth crystal by means of the signal source, using at least two electrodes;

[0040] - measuring electrical signals by means of at least one further electrode of the electrode arrangement with respect to the coupled signal;

[0041] - continuously repeating the steps, comprising coupling and measuring the electrical signals, at several different positions of the growth crystal by means of the electrodes (on the crystal surface), wherein a variation of the electrical signal caused by a change in electrical properties of the growth crystal is detected, and during each repetition of these steps: i) a new electrode pair is selected for coupling in the electrical signal and the further electrodes of the electrode arrangement are determined for measuring the electrical signals; and / or ii) at least one of the electrodes is moved to a new position with respect to a crystal surface of the growth crystal.

[0042] By comparing the electrical signals measured during repetition of the steps, the changes in the electrical properties can be spatially resolved by combining the respective measured values ​​with respect to the respective electrode position of the individual signal sources and signal probes and mathematically evaluating them.

[0043] As already mentioned, it can be particularly preferably provided that the measured electrical signals are combined by means of an evaluation unit (or a computing unit) and graphically displayed or evaluated in an imaging process. This can preferably be done without changing the positions of the electrodes.

[0044] Preferably, an alternating current can be coupled into the growth crystal with regard to the electrical signal; in particular, a frequency of the alternating current can be at least 50 GHz.

[0045] Regarding the generation of the signal, it should be mentioned for the sake of completeness that the same signal level or the same frequency (for alternating current) is used for each electrode.

[0046] As already mentioned, the aforementioned computing or evaluation unit is preferably used to evaluate the electrical properties, so that the method according to the invention is carried out in a computer-implemented manner.

[0047] For a better understanding of the invention, it is explained in more detail using the following figures.

[0048] They show in a highly simplified, schematic representation:

[0049] Fig. 1 shows a measuring device for determining quality parameters of a growing crystal; Fig. 2 shows a schematic illustration of an imaging method;

[0050] Fig. 3 an electrode arrangement with a growth crystal to be measured in cross section.

[0051] By way of introduction, it should be noted that in the variously described embodiments, identical parts are provided with identical reference symbols or component designations. The disclosures contained throughout the description can be applied analogously to identical parts with identical reference symbols or component designations. Furthermore, the positional information chosen in the description, such as top, bottom, side, etc., refers to the directly described and illustrated figure, and these positional information must be applied analogously to the new position in the event of a change in position.

[0052] Fig. 1 schematically shows a measuring device 1 for determining quality parameters of a growth crystal 2, e.g., a SiC crystal.

[0053] The measuring device 1 comprises a crystal holder 3 for at least one growth crystal 2, which can be designed, for example, in the form of adjustable grippers or the like, so that a crystal can be mounted therein and is preferably aligned to a referenced coordinate system. Optionally, an optical measurement device or the like can also be integrated, which additionally records the contours of the crystal.

[0054] Furthermore, an electrode arrangement 4 is provided, wherein the electrode arrangement 4 has a plurality of electrodes 5 for contact with the growth crystal 2 to be accommodated. The electrodes 5 can also (independently of the illustrated embodiment) be attached (e.g., fixed) to the crystal or its surfaces, or, as mentioned above, prestressed against its surface, so that their contact with the surface is ensured.

[0055] Particularly in the case of a fixed arrangement (or position) of the electrodes 5, these are preferably accommodated in a common cage, belt or the like, which is electrically insulated from the electrodes.

[0056] The electrodes can, as further shown, be arranged at different height positions with respect to the longitudinal central axis 13. The electrodes 5 of the electrode arrangement 4 are connected to a voltage source 6 (e.g. alternating current generator), so that an electrical signal can be coupled into the growth crystal 2 by means of at least two electrodes 5.

[0057] A measuring unit 7, which is also connected to the electrodes 5, serves to measure electrical signals 8 (by means of the individual electrodes 5) in the growth crystal, so that changes in the electrical properties within the growth crystal 2 with respect to the coupled-in signal can be detected by means of at least one further electrode 5 of the electrode arrangement 4.

[0058] The generation and measurement of electrical signal 8 is carried out at several different positions on the crystal surface (e.g. in the height direction and circumferential direction) with respect to a longitudinal central axis 13 (or Z-axis) of the growth crystal 2, so that the respective detected changes can be localized or spatially resolved.

[0059] With regard to the plurality of different positions, these can, for example, be redetermined in the circumferential direction around the longitudinal center axis 13 and / or reselected in the vertical direction along the longitudinal center axis 13. Thus, the different positions can be arranged in the circumferential direction, optionally in a common plane and / or perpendicular to this plane at different vertical positions.

[0060] The positions can be determined or varied by selecting a new electrode pair 5 for coupling the signal 8, and by determining the other electrodes 5 of the electrode arrangement 4 for measuring the electrical signals 8 (in the circumferential direction and / or height direction). However, instead of this or in addition, it can also be provided that at least one of the electrodes 5 is moved to a new position in the circumferential direction and / or height direction relative to the crystal surface 12 of the growth crystal 2.

[0061] The measuring device preferably comprises a central controller or a computing unit configured to redistribute the individual functions of the electrodes 5 with regard to coupling in the electrical signal 8 and measuring the electrical signals 8 in the electrode arrangement 4 during a measuring process with respect to the growth crystal 2 to be recorded and / or to cause the electrodes 5 to be adjusted to a new position, or at least in the case of an adjustment, to record the amount and direction of the adjustment movement. Such a computing unit preferably comprises the evaluation unit or forms a component of the measuring device 1 or is connected thereto. The computing unit is preferably also configured to determine or mathematically evaluate the electrical properties associated with the variation of the signal.

[0062] In this regard, Fig. 1 shows a plurality of electrodes 5 of an electrode arrangement 4, which are arranged distributed over a crystal surface 12 of the growth crystal 2 in the form of a single crystal or ingot. As shown, the electrodes 5 can thus be arranged distributed over the entire surface, comprising a lateral surface, base surface and top surface. Furthermore, the electrodes 5 can also be arranged only circumferentially in a ring shape, e.g. essentially in one plane (e.g. perpendicular to the longitudinal central axis 13) and, e.g., step by step along the longitudinal central axis 13, check the respective sections / regions with regard to the planes by displacing them to a new height position. Thus, an electrode 5 of the electrode arrangement 4 can be designed to be movable / adjustable by means of an actuator, so that it can be guided along a crystal surface 12 of the growth crystal 2 to be recorded, or else, for example, an entire ring-shaped arrangement.

[0063] Furthermore, the electrodes 5 can be prestressed or pressed against the crystal surface 12 so that contact is ensured, in particular to compensate for possible unevenness or the like of a surface of an ingot.

[0064] It should also be noted that the respective position of each electrode in the electrode array (at the time of measurement) relative to the crystal can be determined or continuously updated, thus ensuring spatial resolution, especially with movable / adjustable electrodes.

[0065] With regard to the spatial resolution, it is preferably provided that the measuring device 1 comprises an evaluation unit 9 which is designed to convert the electrical quantities 8 detected by means of the measuring unit 7 in an imaging process and to display them graphically, as already mentioned at the beginning.

[0066] In this regard, Fig. 2 shows a possible scheme for an imaging procedure in which the measured changes are graphically displayed. The various recorded changes in the electrical properties are combined and evaluated both with respect to a respective cross-section along the longitudinal central axis 13 and along this axis in the height direction, allowing the localized properties of the growth crystal obtained through a large number of measurements to be visualized. In principle, increasing the number of "measuring electrodes" (or associated measurement processes) leads to higher resolution of the results.

[0067] By detecting the electrical resistance and the electrical characteristic impedance and the associated electrical properties, depending on the induced electrical signals8, a conclusion can be drawn about the material of the crystal or ingot located between the electrodes (or current path).

[0068] The quality parameters to be determined can include, for example, doping of the crystal, which can be localized using the individual measured conductivities. Defects 11 in the form of cracks / defects or macrodefects can also be resolved locally. For example, by combining several measurements, a particular "band gap" can be located. In this regard, polytypes 10 of the crystal can be located. SiC crystals are known to be polytypes such as 6H, 4H, and 3C, which exhibit different band gaps.

[0069] Furthermore, polycrystalline inclusions, cavities, etc. can be detected, as well as dislocations and dislocation densities.

[0070] The crystal parameters attributable to the changes in the electrical properties can be processed and displayed in the imaging process, if necessary in several planes, two-dimensionally or even three-dimensionally, in the form of a virtual image of the measured crystal.

[0071] The signal source 6 is configured to apply a direct voltage or an alternating voltage to the growth crystal 2 by means of the at least two electrodes 5.

[0072] In general, it can be said that a signal conditioning device, such as a signal amplifier or a matching network, is preferably used. A signal conditioning device significantly improves the quality of the measurement by increasing sensitivity and / or improving the signal-to-noise ratio. Such a matching network is connected between a source and a load, establishing a relationship between the output impedance of the source and the input impedance of the load, and allowing power matching. A change in impedance that would cause a reflection at the interfaces is detected, which is then attenuated or matched.

[0073] In principle, different methods for generating the electrical signal can be used with regard to the voltage source: direct current, alternating current, or high-frequency signals.

[0074] In Fig. 3, an aforementioned annular arrangement of the electrodes 5 in the circumferential direction 15 is shown as an example; in addition, the general functional principle of the invention is also illustrated below.

[0075] A plurality of electrodes 5 are positioned on the crystal surface 12; for example, they can be evenly distributed (as in Fig. 3); with the electrical signal 8 being coupled in by means of a selected electrode pair 14. The electrical signals 8 are measured by means of the further electrodes 5, and the electrical properties are thereby determined based on the variation in the electrical signal 8 (conductance; resistance, or also electrical potential, or even eddy currents). This form of the measuring principle is continuously repeated by determining a new electrode pair 14a (or a possible displacement of the electrodes), so that several measurement results are obtained for the same region of the crystal (or a cross-section), which can be combined to form an overall measurement result.

[0076] Taking into account the position of the respective electrodes, each measured value obtained contributes to the localization of the respective causes of the changes in electrical properties. The more measured values ​​that can be obtained, the more precise the localization.

[0077] The aforementioned different electrode pairs 14 can be formed using any desired selection of electrodes. Preferably, the redistribution of the electrode tasks is carried out (repeatedly) such that all possible combinations of electrode pairs have been formed or a sufficient number of measurements have been taken, as mentioned above. As shown, a voltage can first be applied using a first electrode pair 14a and measured using the other electrodes 5, then a voltage can be applied using another, newly selected electrode pair 14b, and so on.

[0078] In principle, an algorithm or a fixed sequence can be provided for determining the electrodes 5.

[0079] The results of the individual measurements carried out are then combined to form an overall result and evaluated by a computing unit, as already mentioned, preferably using an imaging procedure.

[0080] Regarding the arrangement of the electrodes, a referenced reference system can be stored for the computing unit, which is used to assign the measured changes with respect to their location. As already mentioned, calibration of the electrodes can also be provided, which is performed, for example, before each measurement process after the electrodes have been applied to the growth crystal, or after each adjustment when using adjustable electrodes.

[0081] Fig. 3 shows a further and possibly independent embodiment of the measuring device, wherein the same reference numerals or component designations are used for the same parts as in the previous Fig. 1. To avoid unnecessary repetition, reference is made to the detailed description in the previous Fig. 1.

[0082] All information on value ranges in this description is to be understood as including any and all sub-ranges thereof, e.g. the information 1 to 10 is to be understood as including all sub-ranges starting from the lower limit of 1 and the upper limit of 10, ie all sub-ranges begin with a lower limit of 1 or greater and end with an upper limit of 10 or less, e.g. 1 to 1.7, or 3.2 to 8.1, or 5.5 to 10.

[0083] For the sake of clarity, it should be noted that some elements have been shown not to scale and / or enlarged and / or reduced in size to improve understanding of the structure.

[0084] Measuring device Growing crystal Crystal holder Electrode arrangement Electrode Signal source Measuring unit Electrical signal Evaluation unit

[0085] Polytype Defective Crystal Surface

[0086] Longitudinal central axis of electrode pair circumferential direction

Claims

Patent claims 1. Measuring device (1) for determining quality parameters of a growth crystal (2); comprising; - a crystal holder (3) for at least one growth crystal (2); - an electrode arrangement (4), wherein the electrode arrangement (4) has a plurality of electrodes (5) for contact with the growth crystal (2) to be accommodated; - an AC or DC signal source (6), wherein the signal source (6) is connected to the electrodes (5) of the electrode arrangement (4); - a measuring unit (7), wherein the measuring unit (7) is connected to the electrode arrangement (4) and is configured to measure electrical signals (8) by means of the individual electrodes (5) with respect to the growth crystal (2) to be recorded; wherein the measuring device (1) is configured to couple an electrical signal (8) into the growth crystal (2) to be recorded by means of at least two electrodes (5) of the electrode arrangement (4) and to measure electrical signals (8) by means of at least one further electrode (5) of the electrode arrangement (4), wherein a variation in the electrical signal (8) at this further electrode, caused by changes in the electrical properties within the growth crystal (2), can be detected;and wherein the coupling and measuring of the signal by means of the electrodes can be carried out at several different positions on a crystal surface (12) of the growth crystal (2), so that the respective electrical properties of the growth crystal can be spatially resolved by means of a mathematical evaluation of the variations of the measured signals.; 2. Measuring device (1) according to claim 1, characterized in that the measuring device (1) is designed to redistribute the individual functions of the electrodes (5) with regard to the coupling of the signal and the measuring of the signals in the electrode arrangement (4) during a measuring process with regard to the growth crystal (2) to be recorded.

3. Measuring device (1) according to claim 1 or 2, further comprising an evaluation unit (9) which is designed to convert the electrical signals (8) detected by means of the measuring unit (7) in an imaging process and to display them graphically.

4. Measuring device (1) according to one of claims 1 to 3, characterized in that the electrode arrangement (4) comprises at least 6 electrodes (5).

5. Measuring device (1) according to one of claims 1 to 4, characterized in that at least one electrode (5) of the electrode arrangement (4) is adjustable with respect to its position, so that the at least one electrode (5) of the electrode arrangement (4) can be guided to a selectable position along a crystal surface (12) of the growth crystal (2) to be recorded.

6. Measuring device (1) according to one of claims 1 to 5, characterized in that at least one electrode (5) of the electrode arrangement (4) is fixedly positioned in the crystal holder (3).

7. Measuring device according to one of claims 1 to 6, characterized in that the electrode arrangement (4) is arranged in a ring shape, so that the electrodes (5) are arranged in a circumferential direction around a longitudinal central axis (13) of the growth crystal to be recorded.

8. A method for testing the quality of a growth crystal (2), comprising the steps; - Providing at least one growth crystal (2) - attaching a plurality of electrodes (5) of an electrode arrangement (4) to the growth crystal (2); - Providing an AC or DC signal source (6), wherein the signal source (6) is connected to the electrodes (5) of the electrode arrangement (4); - Providing a measuring unit (7), wherein the measuring unit (7) is connected to the electrode arrangement (4) and is used to measure electrical signals by means of the individual electrodes (5) is arranged with respect to the growth crystal (2) to be accommodated; - coupling an electrical signal (8) into the growth crystal (2) by means of the signal source (6), using at least two electrodes (5); - measuring electrical signals (8) by means of at least one further electrode (5) of the electrode arrangement (4); - continuously repeating the steps, comprising coupling in the electrical signal (8) and measuring the electrical signals (8), at a plurality of different positions of the growth crystal by means of the electrodes (5), wherein a variation of the electrical signal caused by a change in the electrical properties of the growth crystal is detected; and during each repetition of these steps: i) a new electrode pair is selected for coupling in the signal and the further electrodes (5) of the electrode arrangement (4) are determined for measuring the electrical signals (8); and / or ii) at least one of the electrodes (5) is moved to a new position with respect to a crystal surface (12) of the growth crystal (2).

9. Method according to claim 8, characterized in that the measured electrical signals (8) are combined by means of an evaluation unit (9) and are graphically reproduced in an imaging process.

10. Method according to claim 8 or 9, characterized in that an alternating current is coupled into the growth crystal (2) with respect to the electrical signal (8).

11. Method according to claim 10, characterized in that a frequency of the alternating current is at least 50 GHz.

12. Method according to one of claims 8 to 11, characterized in that the electrical properties of the growth crystal comprise at least one of the following parameters; - the electrical resistance - the electrical wave impedance.

13. Method according to one of claims 8 to 12, characterized in that the quality parameters to be determined comprise at least one of the following features; - doping of the crystal; - Polytype (10) of the crystal; - Defects (11) in the crystal, particularly in the form of cracks or imperfections.

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