AT527995A1 - Method and device for measuring single crystals - Google Patents

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) having a plurality of electrodes (5) for contact with the growth crystal (2) to be recorded, 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 configured to measure electrical signals by means of the individual electrodes (5) relating to the growth crystal (2) to be recorded. The measuring device (1) is designed to couple a signal into the growth crystal (2) to be recorded 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 due to the variation in the electrical signal and the coupling of the signal and the measurement of the signals can be carried out by means of the electrodes at several different positions with respect to a crystal surface of the growth crystal (2), so that the respective measured changes in the electrical properties can be resolved spatially.

Description

Ingots.

Artificially produced crystals are widely used in the state of the art and are used in various technological fields. One of the most important areas is the semiconductor industry, where individual electronic components are manufactured from crystals grown using growth processes. For example, artificial SiC single crystals ("ingots") are cut into thin wafers for semiconductor production, sawed with diamond-coated blades, and then

pieced saw wire or cutting by laser.

In order to obtain high-quality wafers, it is necessary that the SiC single crystal or ingot already has the necessary properties, and thus high-

must meet high quality requirements.

A disadvantage of the state of the art is that these quality features are usually only checked during the production of the wafers, or only in this state

it is discovered that a wafer that has already been manufactured has defects.

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 determine the quality of the growth crystals.

talle to check.

This task is achieved by a measuring device and a method according to the

Claims resolved.

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The measuring device is designed 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 measuring of the signal by means of the plurality of electrodes can be carried out at several different positions on a crystal surface of the growth crystal, so that the respective electrical properties of the growth crystal can be determined by a mathematical evaluation of the variations

the measured signals are spatially resolvable.

Each electrode of the electrode array can be used as a signal source as well as

can also be used as a signal probe (measurement using the measuring unit).

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 the like before they are separated.

can also be declared as waste.

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Furthermore, it is also conceivable to detect micro-defects.

For completeness, it should be mentioned that the measurement of the electrical signals preferably includes the storage or archiving of the measured values for their evaluation, e.g., in a storage unit or in a central control or processing unit. Furthermore, the position of the respective electrode can also be

assigned to a respective measured value and saved.

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 can be clearly assigned via a control or processing unit.

Preferably, the surface of the growing 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.

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, as well as 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, such that a numbering/sequence (with respect to the electrodes) or the like is provided, which is switched through sequentially.

is tested.

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updated with each calibration.

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 measuring device.

gears.

Furthermore, it can be provided, for example, with regard to the number of electrodes or measuring processes, that the measuring device is further designed to terminate area measurements in which no relevant changes in the electrical properties can be detected at an early stage by gradually measuring larger sections in these areas with a targeted selection of electrodes (e.g. in the circumferential direction quarterly or the like) to create an electrical signal flow.

and the changes are measured.

Basically, an imaging process measures the physical dimensions of an object. Depending on the process and signal type, the measured values are further processed or evaluated until the information is available in the desired form. They are displayed as a spatially resolved image of the object. The information is displayed as brightness values or coded using false colors, or even in a coordinate system, so that a virtual image

of the crystal is available.

Regarding the electrical properties of the growth crystal, these can be

preferably the electrical resistance and/or electrical wave impedance

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to separate from each other.

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

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

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

- Defects in the crystal; particularly in the form of cracks, cavities or defects - polycrystalline inclusions;

- Dislocation densities, also via the electrical resistance.

The mathematical evaluation of recorded measurement results for the spatial resolution of material properties is performed by solving the inversion problem, which forms the basis of all known tomography techniques. 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

Standard methods of linear algebra and adjustment calculus.

Crystal defects — microscopic or macroscopic — have a direct impact

on the electrical material properties in the affected crystal regions, and

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sen correlates.

With regard to the aforementioned signal source, it can be provided that an alternating voltage can be applied to the growth crystal by means of the at least two electrodes, or else a direct voltage. Alternating current is preferably high frequency, e.g., at least 50 GHz. For the signal source to be used,

sources, reference should generally be made to the broad state of the art.

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, but the number also increases the quality of an individual measurement process, since each additional electrode is used to measure the electrical signals and thus improves the spatial resolution.

can be.

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, additional 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 (radially 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 prestressed. With a possible adjustment, a relative reference system for the electrode can also preferably be provided, so that

their position relative to the crystal or the measuring device is known at any time

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be feasible.

Furthermore, it can be provided that at least one electrode of the electrode arrangement is positioned in a fixed position (relative to the crystal) in the crystal holder. Furthermore, the entire electrode arrangement can also be positioned with respect to the crystal.

their multitude of electrodes must be positioned in a fixed location.

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

periods.

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

- Providing at least one growth crystal

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

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

- 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; - Coupling an electrical signal into the growth crystal by means of the signal source, using at least two electrodes;

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

- continuous repetition of the steps, including coupling and measuring

sen of the electrical signals at several different positions of the breeding

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i) a new pair of electrodes is selected for coupling the electrical signal and the further electrodes of the electrode arrangement are determined for measuring the electrical signals; and/or

il) at least one of the electrodes with respect to a crystal surface of the

growing crystal is moved to a new position.

By comparing the electrical signals measured during the repetition of the steps, the changes in the electrical properties can be resolved locally by combining the respective measured values with respect to the respective electrode position of the individual signal sources and signal probes.

and evaluated mathematically.

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 changes.

The positions of the electrodes

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 min 50 GHz.

Regarding the generation of the signal, it should be mentioned for the sake of completeness that the same signal level or the same frequency (in case of alternating

selstrom) is used.

As already mentioned, the aforementioned computing or evaluation unit is preferably used to evaluate the electrical properties, so that the

the method according to the invention is carried out in a computer-implemented manner.

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The figures explain this in more detail. They show, in a highly simplified, schematic representation:

Fig. 1 a measuring device for determining quality parameters of a

growth crystal; Fig. 2 shows a schematic illustration of an imaging process;

Fig. 3 an electrode arrangement with a growth crystal to be measured

in cross section.

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, whereby the disclosures contained in the entire 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 transferred to the new location in the event of a change in location.

Fig. 1 shows schematically a measuring device 1 for determining quality parameters.

parameters of a growth crystal 2; e.g., a SiC crystal.

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

Contours of the crystal are also recorded.

Furthermore, an electrode arrangement 4 is provided, wherein the electrode arrangement 4 comprises a plurality of electrodes 5 for contact with the

growth crystal 2. The electrodes 5 can also (independently of the

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shown embodiment) to the crystal or its surfaces (e.g. fixed), or, as mentioned above, against its surface

pre-stressed so that their support on the surface is guaranteed.

Particularly in the case of a fixed arrangement (or position) of the electrodes 5, these are preferably arranged in a common cage, belt or the like.

which is electrically insulated from the electrodes.

The electrodes can, as further shown, be arranged with respect to the longitudinal central axis 13

be arranged at different heights

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

can.

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 can be detected by means of at least one further electrode 5 of the electrode arrangement 4.

regarding the coupled signal can be detected.

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 lo-

calisated or locally dissolved.

With regard to the several different positions, these can, for example, be newly determined in the circumferential direction around the longitudinal center axis 13 and/or newly selected in the height direction along the longitudinal center axis 13. Thus, the different positions can be arranged in the circumferential direction, if necessary in a common plane and/or perpendicular to this at different heights.

hen positions.

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The determination or variation of the positions can be carried out in such a way that a new electrode pair 5 is selected for coupling the signal 8 and the further electrodes 5 of the electrode arrangement 4 are determined for measuring the electrical signals 8 (in the circumferential direction and/or height direction). However, it can also be provided instead or additionally that at least one of the electrodes 5 is positioned with respect to the crystal surface 12 of the growth crystal 2

is moved to a new position in the circumferential and/or height direction.

The measuring device preferably comprises a central controller or a computing unit that is configured to redistribute the individual functions of the electrodes 5 with respect to the coupling of the electrical signal 8 and the measuring of 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 the electrical properties associated with the variation of the signal.

to determine or mathematically evaluate.

In this regard, Fig. 1 shows several electrodes 5 of an electrode arrangement 4, which are 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 distributed over the entire surface, comprising a lateral surface, base surface, and top surface. Furthermore, the electrodes 5 can also be arranged only circumferentially, e.g., essentially in a 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 respect to the planes by shifting them to a new height position.

Thus, an electrode 5 of the electrode arrangement 4 can be adjusted by means of an adjusting

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drive can be designed to be movable/adjustable, so that it can be guided along a crystal surface 12 of the growth crystal 2 to be accommodated or

also, for example, an entire ring-shaped arrangement.

Furthermore, the electrodes 5 can be pre-tensioned or pressed against the crystal surface 12 so that contact is ensured, in particular to avoid possible

to compensate for any unevenness or the like on the surface of an ingot.

It should be noted that the respective position of each electrode in the electrode arrangement (at the time of measurement) relative to the crystal can be determined or continuously updated, so that a local

solution is guaranteed, especially with movable/adjustable electrodes.

With regard to the spatial resolution, it is preferably provided that the measuring device 1 comprises an evaluation unit 9 which is designed to process the electrical quantities 8 detected by the measuring unit 7 in an imaging process

to convert and display graphically, as already mentioned at the beginning.

In this regard, Fig. 2 shows a possible scheme for an imaging method 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 to the longitudinal central axis 13 and along this in the height direction, so that the localized properties of the growth crystal obtained by means of a large number of measurements can be visualized. In principle, an increase in the number of "measuring electrodes" (or the associated

measurement processes) leads to a higher resolution of the results.

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).

be affected.

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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 respective "band gap" can be localized. In this regard, polytypes 10 of the crystal can be localized. SiC crystals are known to be polytypes such as 6H, 4H, 3C, which have different band-

have gaps.

Furthermore, polycrystalline inclusions, cavities, etc. can also be detected,

including dislocations and dislocation densities.

The crystal parameters that are associated with 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.

dimensional, in the form of a virtual image of the measured crystal.

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

to create.

In general, it can be said that a signal conditioning device, such as a signal amplifier or a matching network, is preferred. A signal conditioning device significantly improves the quality of the measurement by increasing the sensitivity and/or by

improved 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, allowing power matching. A change in impedance is detected that would cause a reflection at the interfaces, which is damped or attenuated.

is adjusted.

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In principle, different methods for generating the electrical signal can be provided with regard to the voltage source; direct current, alternating current

current or high-frequency signals.

In Fig. 3, an example of a previously mentioned annular arrangement of the electrodes 5 in the circumferential direction 15 is shown, in addition, the gene-

The real functional principle of the invention is illustrated.

In this case, a plurality of electrodes 5 are positioned on the crystal surface 12, e.g., they can be arranged evenly distributed (as in Fig. 3); wherein the electrical signal 8 is 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 of the electrical signal 8 (conductance; resistance, or also electrical potential, or also 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 lead to a

entire measurement result can be combined.

Taking into account the position of the respective electrodes, each measured value obtained contributes to locating the respective causes of the changes in electrical properties. The more measured values that can be obtained, the more

ziser is the localization.

The mentioned different electrode pairs 14 can be formed using any desired selection of electrodes. Preferably, the redistribution of the electrode tasks is carried out (repeatedly) in such a way that all possible combinations of electrode pairs have been formed or a sufficient number of measurements have been carried out, as mentioned above. As shown, a voltage can first be applied successively using a first electrode pair 14a and measured with the other electrodes 5, then

another, newly selected electrode pair 14b a voltage is applied, etc.

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In principle, an algorithm can be provided to determine the electrodes 5

or a fixed order.

The results of the individual measurements carried out are then combined to form an overall result and processed by a computing unit.

evaluated, as already mentioned, preferably in an imaging procedure.

Regarding the arrangement of the electrodes, a referenced reference system can be stored for the computing unit, by means of which the measured changes are assigned with respect to their location. As already mentioned, calibration of the electrodes can also be provided, which is carried out, for example, before each measurement process after the electrodes have been applied to the growth crystal, or when using adjustable electrodes.

after each adjustment.

In Fig. 3, a further and possibly independent embodiment of the measuring device is shown, wherein again 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 or

taken.

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, i.e. 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.

For the sake of clarity, it should be noted that for a better understanding of the structure, some elements are not to scale and/or enlarged.

and/or reduced in size.

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16

List of reference symbols

Measuring device Growing crystal Crystal holder Electrode arrangement Electrode Signal source Measuring unit Electrical signal Evaluation unit Polytype

Defective crystal surface Longitudinal central axis Electrode pair

circumferential direction

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Claims (13)

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 designed 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 designed 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 of the electrical signal (8) at this further electrode, caused by changes in the electrical properties within the growth crystal (2), is detectable; 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 determined by means of a mathematical evaluation of the variation- the measured signals are spatially resolvable. 2. Measuring device (1) according to claim 1, characterized in that the measuring device (1) is designed to carry out 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 taking growth crystal (2). A2024/87403-AT 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 the measuring unit (7) into an imaging method and represent 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) summarizes. 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) along a crystal surface (12) of the increasing growth crystal (2) can be guided to a selectable position. 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) in the crystal holder (3) is positioned in a fixed position. 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 taking growth crystal. 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) connected to the electrodes (5) of the electrode arrangement (4) A2024/87403-AT is; - Providing a measuring unit (7), wherein the measuring unit (7) is connected to the electrode arrangement (4) and is configured to measure electrical signals by means of the individual electrodes (5) with respect to the growth crystal (2) to be recorded; - 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 the electrical signal (8) and measuring the electrical signals (8), at several 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 a respective repetition of these steps: i) a new pair of electrodes is selected for coupling the signal and the further electrodes (5) of the electrode arrangement (4) are determined for measuring the electrical signals (8); and/or il) at least one of the electrodes (5) with respect to a crystal surface (12) of the growth crystal (2) is moved to a new position. 9. Method according to claim 8, characterized in that the measured electrical signals (8) are combined by means of an evaluation unit (9) and graphically reproduced using an imaging process. 10. Method according to claim 8 or 9, characterized in that with respect to the electrical signal (8) an alternating current is introduced into the growth crystal (2) is coupled in. 11. Method according to claim 10, characterized in that a frequency frequency of the alternating current is min 50 GHz. A2024/87403-AT 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. A2024/87403-AT