Power supply and plasma system

Abstract

A power supply (1) for generating an electrical high frequency power signal for a plasma, comprising a generator (2) and an impedance matching device (6) connected to the generator (2), the power supply (1) being configured in particular to determine an impedance quantity at an input (5) of the impedance matching device (6) or at an output (3) of the generator (2) and to calculate and output an impedance-based quality score (17) for a predefined time period.

Description

[Technical field]

[0001] The present invention relates to a power supply for generating an electrical high frequency power signal for a plasma, and to a plasma system including such a power supply.

[0002] The present invention relates to a power supply for generating an electrical HF power signal for a plasma and a method of operating the power supply.

[0003] An impedance matching network is used to match the impedance of the load to the impedance of the generator.

[0004] Impedance matching networks are often used in HF excited plasma processes. The frequency is typically 1 MHz or higher. HF excited plasma processes are used, for example, for coating (sputtering) and / or etching substrates in the manufacture of architectural glass, semiconductors, solar cell elements, flat screens, displays, etc. The impedance in such processes often changes very rapidly, so that impedance matching must often be performed very quickly (within a few milliseconds). The power typically supplied to such processes is several hundred watts, e.g., 300 W or more, but not infrequently 1 kilowatt or more, and often 10 kW or more. At such powers, the voltage in the impedance matching device is often several hundred volts, e.g., 300 V or more, and not infrequently 1000 V or more. The current in such circuits can be several amperes, often 10 A or more, and sometimes even 100 A or more. It has always been a great challenge to realize an impedance matching network at such voltages and currents. To be able to change the reactance in such an impedance matching network quickly is an additional very great challenge. Examples of such impedance matching networks are disclosed, for example, in DE 10 2015 220 847 A1 or DE Utility Model No. 20 2020103 539 A1.

[0005] Typically, an impedance matching network is used to transform the impedance of the load to 50 Ohms. To obtain information about the quality of the impedance matching, the value of the average reflected power is often calculated and used as an indicator of the quality of the matching process. At the same time, the value of the average reflected power is used as a stability criterion for the plasma. In pulsed applications, transient and decay processes occur at the beginning and end of each pulse, which lead to reflected power despite stable plasma processing and the best matching.

[0006] It is therefore an object of the invention as a whole to provide a power supply device which is able to give a more reliable indication of the quality of the matching process.

[0007] This problem is solved according to the invention by a power supply device for generating an electric HF power signal for a plasma, comprising a generator and an impedance matching device connected to the generator, the power supply device being configured to determine an impedance quantity, in particular at the input of the impedance matching device or at the output of the generator, calculate an impedance-based quality score for a pre-defined time period and output it, in particular for further processing and / or use.

[0008] The impedance quantity can be a complex impedance, a complex reflection coefficient, the magnitude and phase of the impedance, or values ​​derived therefrom, such as admittance or nominal impedance. In principle, it is also conceivable to detect complex or two-dimensional real quantities as impedance quantity. It is advantageous, particularly if this is an integrated system in which the impedance matching device and the generator are integrated, if the impedance quantity is detected at the output of the generator.

[0009] Unlike the average reflected power, the impedance-based quality score is calculated over a preset period of time. The preset period can be selected such that transient and decay processes are not included in the impedance-based quality score calculation. This allows a convincing quality score for the matching process to be calculated. The impedance-based quality score can be a dimensionless quantity.

[0010] The power supply device can be configured to calculate an impedance mean value, in particular a geometric mean value, a geometric centroid, an arithmetic mean value or a median value of the measured impedance quantities as the impedance-based quality score. In particular, the geometric mean value can be calculated in a particularly easy manner.

[0011] The power supply device can be configured to generate a manipulated variable of the impedance matching device such that the quality score takes a pre-set value, whereby the impedance matching device can perform impedance matching based on the quality score, for example via the manipulated variable a variable reactance of the impedance matching device can be set such that impedance matching is performed.

[0012] If the impedance matching device is not adjustable, then it is conceivable to vary the power output by the generator based on the calculated quality score, which would result in a better quality score and thus a better impedance match. For example, the frequency of the HF power signal could be varied.

[0013] The power supply can be configured to calculate an assessed reflected power based on the quality score. The assessed reflected power is a quantity that the user is familiar with and therefore can determine and classify. The calculated assessed reflected power is also referred to below as (virtual) reflected power and does not correspond to a real (measurable) reflected power. The calculated assessed reflected power can also be understood as a quality score.

[0014] The impedance matching device may comprise a measuring device arranged to calculate the quality score, whereby the quality score can be calculated directly.

[0015] Alternatively, it is conceivable that the impedance matching device has a controller configured to calculate a quality score, in particular an integral part of the controller can implicitly average the detected impedance quantity over a period of time, the controller being used in this case to match or control the quality score as close as possible to a target value.

[0016] The quality score can be output to the generator. This allows the generator to calculate an estimated (virtual) reflected power from the detected forward power. In particular, if the control algorithm for matching is not changed, this results in a large reflected power. Therefore, the reflected power is generally used as a measure for whether the control or matching is successful or not. However, this is not the case with transient impedances, especially with high pulse frequencies. Reflected power occurs even when the control algorithm achieves the best possible matching. The quality score, in particular the geometric mean value of the impedance quantity, is used in the present invention to calculate the estimated (virtual) reflected power. This can be shown instead of or in addition to the actual reflected power, thus providing a quantity that is familiar and known to the user.

[0017] The quality score can be output, for example, as an analog signal, but it is particularly advantageous if a display device is provided for outputting the calculated evaluated reflected power.

[0018] The generator can be configured to measure the generated (forward) power. This measured generated power can be used to calculate an estimated (virtual) reflected power.

[0019] The preset period can be determined such that maximum energy transfer to the plasma occurs without affecting the calculated estimated (virtual) reflected power. In particular, the period can be shorter than the pulse duration. Furthermore, the period can be selected such that the pulse start is outside the period.

[0020] The present invention further includes a method for operating a power supply for generating an electrical high frequency (HF) power signal for a plasma, determining an impedance quantity, in particular at the input of an impedance matching device or at the output of a generator, calculating an impedance-based quality score for a predefined period of time, and outputting the impedance-based quality score. In particular, the impedance-based quality score can be output for further use or processing. The impedance-based quality score can be output as a digital or analog signal.

[0021] As an impedance-based quality score, an impedance mean value, in particular a geometric mean, geometric centroid, arithmetic mean or median value of the measured impedance quantities can be calculated.

[0022] An operating variable for the impedance matching device can be generated such that the quality score takes a pre-set value.

[0023] Based on the quality score, an estimated (virtual) reflected power can be calculated. The estimated (virtual) reflected power is a calculated output based on the quality score that differs from the actual reflected power measured.

[0024] The quality score can be calculated directly in the measurement device or indirectly by a controller of the impedance matching device.

[0025] The quality score can be output to the generator. Based on the quality score, a (virtual) reflected power can be calculated in the generator. The estimated reflected power can be output in a display device.

[0026] The preset period can be determined to provide maximum energy transfer to the plasma without affecting the calculated estimated (virtual) reflected power.

[0027] The invention also includes a plasma system comprising a power supply as previously described and a plasma treatment device, in particular an HF-excited plasma treatment device, i.e. a device for carrying out plasma treatment. The plasma device is preferably used, for example, for coating (sputtering) and / or etching substrates. The plasma device is preferably suitable for use in the manufacture of architectural glass, semiconductors, solar cell elements, flat screens or displays.

[0028] The high frequency of the high frequency power signal may be 1 MHz or higher.

[0029] The power required for powering the plasma treatment, and for which the power supply is designed to supply, may be 300 W or more, in particular 1 kilowatt or more. The plasma processing device may be designed to connect different power supplies, of which one or more of the following can be used, for example: HF power supplies with the same or different high frequencies; -DC power supplies, especially pulsed DC power supplies MF power supplies with frequencies below -1 MHz are available.

[0030] Further advantages of the invention are obtained from the description and the drawings. Likewise, the characteristic features mentioned above and further described subsequently can be used according to the invention, each individually on its own or in any combination of several. The embodiments shown and described should not be understood as a complete enumeration, but rather have exemplary features for describing the invention. [Brief description of the drawings]

[0031] [Figure 1]FIG. [Figure 2a] FIG. 13 illustrates how to calculate a quality score based on an admittance plane. [Figure 2b] FIG. 13 is another diagram showing how to calculate a quality score based on an admittance plane. [Figure 2c] FIG. 11 is yet another diagram illustrating how a quality score is calculated based on an admittance plane. [Figure 2d] FIG. 11 is yet another diagram illustrating how a quality score is calculated based on an admittance plane. [Diagram 3] 1 is a flow diagram of a method for calculating a quality score.

[0032] In Fig. 1 a power supply device 1 is shown with a generator 2 for generating a (pulsed) electric HF power signal, for example at 60 MHz. The generator 2 has an output 3 which is connected via an HF cable 4 to an input 5 of an impedance matching device 6. The impedance matching device 6 is connected to a load 7. The generator 2 and the impedance matching device 6 are further connected to each other via a signal connection 8. The load 7 may be a plasma of a plasma process, in particular of an HF excited plasma process, e.g. for coating (sputtering) and / or etching of substrates in the manufacture of architectural glass, semiconductors, photovoltaic elements, flat screens, displays.

[0033] The impedance matching device 6 is used to match the impedance of the load 7 with the impedance of the generator 2 at the input 3. The generator 2 may be configured to supply pulsed HF power to the load 7. Since the impedance of the load 7, especially if it is a plasma, can change often and rapidly, the impedance matching device 6 has special requirements to match the impedance of the load 7 with the impedance of the generator 2.

[0034] In the region of the input 5 of the impedance matching device 6 a measuring device 10 can be provided for detecting an impedance quantity. Alternatively or additionally a measuring device 11 can be provided in the region of the output 3 of the generator 2 for detecting an impedance quantity, which can be a complex impedance, a complex reflection coefficient, the magnitude and phase of the impedance, etc. Based on this detected impedance quantity an impedance-based quality score can be calculated, which gives information about how good the impedance match is for a predefined period of time.

[0035] This is explained on the basis of figure 2. Figure 2a shows the locus 15 (over time) of the impedance of the load 7 during a high frequency pulse of the generator 2. It can be seen that the impedance of the load 7 changes significantly during the pulse.

[0036] 2b, it can be seen that the first portion 15a, which corresponds to the pulse onset, is not taken into account in the calculation of the quality score, i.e. is essentially ignored. Only the second portion 15b of the trajectory 15 is taken into account.

[0037] In Fig. 2c it can be seen that discrete impedance points 16, i.e. impedance quantities at different times on portion 15b of locus 15, are measured by one of measuring devices 10, 11. In Fig. 2d it can be seen that the geometric centroid is calculated as an impedance-based quality score 17.

[0038] The controller 13 of the impedance matching device 6 is fed with manipulated variables such that the quality score 17 is minimized and thus a better match is achieved.

[0039] Furthermore, the quality score 17 can be used to calculate the estimated (virtual) reflected power. For this purpose, the quality score can be output, for example, via the signal connection 8 to the generator 2, whereby the estimated (virtual) reflected power can be calculated by the calculation device 14.

[0040] A flow diagram of the method according to the invention is shown in Figure 3. In step 100, impedance quantities are measured. In step 101, an impedance-based quality score is calculated from the impedance quantities measured over a pre-defined period of time. In step 102, the impedance-based quality score is output so that it can be further processed.

Claims

1. A power supply (1) for generating an electric high frequency power signal for a plasma, comprising a generator (2) and an impedance matching device (6) connected to the generator (2), the power supply device (1) is configured to determine an impedance quantity at the input (5) of the impedance matching device (6) or at the output (3) of the generator (2) and to calculate and output a geometric centroid of a plurality of discrete impedance points (16) for a preset time period as an impedance-based quality score (17) for the preset time period, the impedance quality score being shorter than a pulse duration and outside the pulse start, the magnitude of the impedance varies along a trajectory within the preset time period, and the power supply device (1) determines the magnitude of the impedance that varies during the preset time period as a plurality of discrete impedance points (16) at different times within the preset time period for determining a quality score; The power supply device (1) is configured to generate an operation amount of the impedance matching device (6) so that the quality score (17) takes a preset value.

2. 2. The power supply device (1) according to claim 1, characterized in that the power supply device (1) is configured to calculate an estimated reflected power based on the quality score (17).

3. 3. The power supply device according to claim 1, wherein the impedance matching device or the generator comprises a measuring device configured to calculate the quality score.

4. 4. The power supply arrangement according to claim 1, wherein the impedance matching device (6) comprises a controller (13) configured to calculate the quality score (17).

5. 5. The power supply arrangement according to claim 1, wherein the quality score (17) is output to the generator (2).

6. 3. The power supply device according to claim 2, further comprising a display device for outputting the calculated evaluated reflected power.

7. 7. The power supply arrangement according to any one of the preceding claims, characterized in that the generator (2) is configured to measure the generated power.

8. 8. The power supply device according to claim 1, wherein the voltage in the impedance matching device (6) is greater than or equal to 300 V during operation.

9. 9. The power supply device according to any one of the preceding claims, characterized in that the current in the impedance matching device (6) is greater than or equal to 10 A in operation.

10. 10. A plasma system comprising a power supply device according to any one of claims 1 to 9 and an HF excited plasma device for coating (sputtering) and / or etching substrates, suitable for use in a plasma processing device.

11. A method of operating a power supply (1) for generating an electrical high frequency power signal for a plasma, comprising the steps of: determining an impedance quantity at the input of the impedance matching device (6) or at the output of the generator (2), calculating a geometric centroid of a plurality of discrete impedance points (16) in a predetermined time period as an impedance-based quality score (17) in the predetermined time period, the impedance-based quality score (17) being shorter than the pulse duration and outside the time period; and outputting the impedance-based quality score (17); the impedance quantity varies along a trajectory within the preset time period, and the power supply device (1) determines the impedance quantity varying during the preset time period as a plurality of discrete impedance points (16) at different times within the preset time period for determining a quality score; The power supply device (1) is configured to generate an operating variable of the impedance matching device (6) such that a quality score (17) assumes a pre-set value.

12. The method of claim 11, further comprising calculating an estimated reflected power based on the quality score (17).

13. 13. The method according to claim 11, further comprising calculating the quality score (17) directly in a measuring device (10, 11) or indirectly by a controller of the impedance matching device (6).

14. The method according to any one of claims 11 to 13, further comprising outputting the quality score (17) to the generator (2).

15. The method of claim 12 , further comprising determining the predetermined time period to provide maximum energy transfer to the plasma without affecting the calculated estimated reflected power.

16. 16. The method according to any one of claims 11 to 15, characterized in that the impedance matching device (6) is operated at a voltage of 300V or more.

17. 17. The method according to any one of claims 11 to 16, wherein the impedance matching device (6) is operated with a current of 10 A or more.

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