Method for igniting and / or maintaining plasma by a pulsed high-frequency signal, power generator, and plasma device

Abstract

A method for igniting and / or maintaining a plasma using a pulsed high-frequency signal includes: a) generating a pulsed high-frequency signal; b) changing the frequency of the high-frequency signal according to a frequency sweep and / or changing the amplitude of the high-frequency signal according to a power sweep during a predetermined first time interval (I) within one pulse (10); and / or c) monitoring at least one process parameter of the plasma process; d) determining the relationship of the process parameter to the performed sweep; and e) detecting whether one or more monitored process parameters associated with one or more sweeps each take a predetermined value or are within a predetermined value range.

Description

Technical Field

[0001] The present invention relates to a method for igniting and / or maintaining a plasma by a pulsed high-frequency signal. Further, the present invention relates to a power generator and a plasma device.

Background Art

[0002] In a plasma process using a pulse source, an impedance trajectory that depends on process parameters is executed during one pulse. The purpose is to reliably ignite the plasma and bring it into a matching state without the need to readjust the impedance matching network.

[0003] How quickly the plasma is ignited and how stable the plasma process is depend on the shape of the pulsed high-frequency signal. FIG. 1a shows a typical transition of the power of the pulsed high-frequency signal. FIG. 1b shows a typical transition of the frequency of the pulsed high-frequency signal, and FIG. 1c shows a typical transition of the magnitude of the reflectivity. In the prior art, multi-stage pulses are often used to ignite and operate the plasma, and an attempt is made to ignite the plasma in the first time interval indicated by I in FIGS. 1a, b, and c. For this purpose, energy is supplied to the plasma chamber between the first time interval I and the second time interval II. The time intervals can also be used to achieve different plasma operating states. In the prior art, the power and frequency of the time intervals are at most optimized manually. During the time intervals I and II, the frequency and amplitude of the high-frequency signal are not changed. The durations of the time intervals I and II are also at most optimized to the extent that is manually possible.

[0004] During the second time interval II, power can be supplied to the plasma process. The frequency and amplitude of the high-frequency signal are determined such that it can be assumed that the plasma is stable during the second time interval II and there is impedance matching.

[0005] The plasma parameters change during a first time interval I. At the start of the first time interval I, the plasma is not ignited. Therefore, the impedance is high. At the end of the first time interval I, the impedance approaches the system impedance after the plasma is ignited. This can be recognized by the decrease in the value of the reflection coefficient, as shown in Figure 1c. The change in the plasma impedance leads to the above impedance trajectory.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] The problem of the present invention is to provide a method and a power generator that can improve plasma ignition and energy supply.

Means for Solving the Problems

[0008] According to the present invention, this problem is solved by a method for plasma ignition and / or maintenance using a pulsed high-frequency signal, the method including the following method steps. a) Generating a pulsed high-frequency signal, b) During a predetermined first time interval within one pulse, changing the frequency of the high-frequency signal according to a frequency sweep and / or changing the amplitude of the high-frequency signal according to a power sweep, c) Monitoring at least one process parameter of the plasma process, d) Determining the relationship of the process parameter with respect to the executed sweep, e) Detecting whether one or more monitored process parameters associated with one or more sweeps take a predetermined value or are within a predetermined value range.

[0009] The high-frequency signal in the gist of the present invention is a signal having a frequency of 1 MHz or higher. Preferably, the high-frequency signal has a frequency in the range of 10 to 100 MHz.

[0010] The pulsed high-frequency signal in the gist of the present invention is a high-frequency signal with a modulated pulse shape. A possible generation method for such a pulsed high-frequency signal is described, for example, in Patent Document 1. The pulsed high-frequency signal can be pulsed at a frequency of up to 500 kHz. The pulsed high-frequency signal can be pulsed at multiple power levels.

[0011] In the first time interval, the frequency can change by ±30%, particularly ±20%, preferably ±10%. The amplitude of the high-frequency signal can also change by ±30%, particularly ±20%, preferably ±10% in the first time interval.

[0012] In the gist of the present invention, "sweeping" is understood as a predetermined change in one quantity over a predetermined period, or a temporal change in one quantity that conforms to a measured value. "Temporal change" is understood as a change in that quantity over time. Therefore, frequency sweeping is a predetermined change in frequency, or a change in frequency that conforms to a measured value, over a predetermined period, for example, during the first and / or second time intervals. Power sweeping is a predetermined change in the amplitude of the high-frequency signal, or a change in the amplitude of the high-frequency signal that conforms to a measured value, over a predetermined period, for example, during the first and / or second time intervals.

[0013] Determining the relationship between process parameters and the executed sweep can include that the detection of plasma parameters and the execution of the sweep are in one temporal relationship, for example, are carried out simultaneously or overlap temporally. The relationship between the process parameters and the sweep can lie in that the process parameters change depending on the temporal change of the frequency or amplitude of the high-frequency signal during the sweep. For example, the process parameters can change during the ignition of the plasma, where a predetermined frequency value and / or amplitude value of the high-frequency signal can be associated with the ignition of the plasma. The relationship between the process parameters and the sweep can also be determined by a correlation algorithm determining such a relationship.

[0014] Detecting whether the monitored process parameters are each at a predetermined value or within a predetermined value range can give an indication of whether it is necessary to change the sweep, for example, for the ignition of the plasma, for the improvement of the process.

[0015] An evaluation of one or more sweeps can be carried out based on that detection, in particular based on that detection in step e). In particular, it is possible to evaluate whether a sweep leads to a good or bad, better or worse process behavior compared to a previous sweep. Furthermore, it is also possible to examine at which point in time during the sweep the ignition took place. The influence of the sweep on one or more process parameters can be determined. These influences can occur only after a certain time, for example, only after the end of the sweep. The relationship between the process parameters and the sweep can also consist in that the sweep has no influence on the process parameters.

[0016] The sweep can be selected based on the evaluation of one or more preceding sweeps for subsequent pulses and / or for a second time interval of the pulse, particularly for the first pulse or a further pulse. Thus, based on the analysis of previous sweeps, a modified sweep for subsequent pulses and / or for the time interval can be set. The second time interval may be suitable for the normal operation of the plasma, i.e., for the maintenance of the plasma. For this, impedance matching may exist.

[0017] The evaluation can include an inspection of the sweep based on detection, particularly the detection according to step e). In particular, thereby, it can be determined at which point in the sweep the process parameters exhibit a predetermined behavior.

[0018] The duration of the time interval can be adapted based on the evaluation for subsequent pulses. For example, if it is recognized that plasma ignition occurs at a very early stage during the frequency sweep or power sweep of the pulse, the first time interval can be shortened for subsequent pulses. Thereby, for example, the second time interval can be extended accordingly, so that more energy can be supplied to the plasma.

[0019] During a predetermined second time interval within the pulse, the frequency of the high-frequency signal can be changed according to a frequency sweep and / or the amplitude of the high-frequency signal can be changed according to a power sweep. Thereby, an optimal supply of energy to the plasma can be achieved. Preferably, two different sweeps can be performed alternately.

[0020] Steps c) to e) can also be performed in the second time interval. Thereby, more analysis data is available, and for achieving a predetermined target process parameter value, the second time interval for subsequent pulses or the frequency sweep and / or power sweep for the second time interval of subsequent pulses can be set.

[0021] For at least one additional pulse, a different frequency sweep and / or a different power sweep can be used compared to the previous pulse, particularly the first pulse. By comparing the situation with the previous pulse, it is possible to determine whether the plasma process has changed, particularly whether it has improved or deteriorated. Depending on the result of this analysis, the frequency sweep and / or the power sweep can be adapted for subsequent pulses.

[0022] Different frequency sweeps and / or power sweeps can be set until one or more monitored process parameters reach a predetermined value or a predetermined value range. This can be done until the optimal process parameters are reached. It is also conceivable to change the target value of the process parameter. Thereby, optimization can be performed during the plasma process.

[0023] In a calibration process, a frequency sweep and / or a power sweep suitable for igniting the plasma can be determined. Thereby, a suitable frequency sweep and / or power sweep can also be determined outside the plasma process.

[0024] In particular, one or more of the following process parameters can be monitored. The ignition behavior of the plasma, the power loss of the generator generating the pulsed high-frequency signal, the reflection coefficient, the amplitude of the high-frequency signal, the relative phase between the traveling wave and the backward wave of the pulsed high-frequency signal.

[0025] The analysis is facilitated when the frequency and / or the amplitude are continuously changed during the frequency sweep and / or the power sweep.

[0026] Frequency sweeping and / or power sweeping can have multiple intervals, where the frequency and / or amplitude are constant in each interval. At that time, one interval can include multiple periods of the high-frequency signal. Basically, it is possible to view the high-frequency signal on a per-period basis. However, when the signal is generated and measured / detected on a per-interval basis, the detection and control of process parameters are greatly simplified. At that time, the interval is composed of multiple periods of the high-frequency signal, and those multiple periods are not distinguishable within that interval at the set power and / or frequency.

[0027] At least some of the intervals can have different lengths, especially the time length increases as the pulse progresses. For example, the interval at the beginning of the first time interval of the pulse can be shorter than the interval at the end of the first time interval and, in some cases, the interval in the second time interval. Thereby, the length of the interval can be adapted to the dynamics of the plasma.

[0028] Within the scope of the present invention, furthermore, a power generator for a plasma device is included, and the power generator a. generates a pulsed high-frequency signal, b. changes the frequency of the high-frequency signal according to a frequency sweep and / or changes the amplitude of the high-frequency signal according to a power sweep during a predetermined first time interval within one pulse, c. is configured to generate a frequency sweep and / or a power sweep depending on at least one detected process parameter.

[0029] Using such a power generator, the method according to the present invention can be carried out particularly well.

[0030] The power generator can include a digital / analog converter for generating a pulsed high-frequency signal. The signal generated in this way can be amplified. Thereby, the amplitude of the high-frequency signal and the frequency of the high-frequency signal can be controlled. In particular, the frequency sweep and the power sweep can be set very easily by such a power generator.

[0031] Alternatively, the power generator can include a direct digital synthesizer (DDS) having a subsequent amplitude modulation device for generating a pulsed high-frequency signal.

[0032] Within the scope of the present invention, further, a plasma device is included, and the plasma device includes a power generator according to the present invention, a plasma chamber, and an impedance matching unit disposed between the power generator and the plasma chamber. A detection device for detecting at least one process parameter can be provided. Further, the power generator can be configured to generate a frequency sweep and / or a power sweep depending on at least one detected process parameter.

[0033] Further features and advantages of the present invention will become apparent from the following detailed description of embodiments of the present invention with reference to the figures showing details essential to the present invention, and from the claims. The features shown therein are illustrated so that special features according to the present invention can be clearly visualized. The various features can be realized individually or in any combination in variations of the present invention.

[0034] Embodiments of the present invention are shown in schematic diagrams and will be described in more detail in the following description.

Brief Description of the Drawings

[0035]

Figure 1a

Figure 1b

Figure 1c

Figure 2a

Figure 2b

Figure 2c

Figure 3a

Figure 3b

Figure 4

Mode for Carrying Out the Invention

[0036] FIG. 2a shows that in the first time interval I, the amplitude of the pulsed high-frequency signal and then the power between one pulse 10 changed. In the first time interval I, the amplitude of the high-frequency signal thus changes according to the power sweep. On the other hand, during the second time interval II of the pulse, the amplitude of the pulsed high-frequency signal does not change. The third time interval III can represent the pulse pause of the pulsed high-frequency signal. In this case, no power is supplied to the plasma process during the pulse pause. Alternatively, in this third time interval III, it is also possible to supply additional power different from the power in the second time interval II to the plasma process.

[0037] Basically, it is possible to switch between a plurality of power levels within one pulse signal. In a plasma process, it is known that switching is performed between two, preferably three, especially four or more power levels. For this purpose, individual time intervals (not shown in the figure) can also be defined. In each of these time intervals, the frequency can be changed according to a frequency sweep, especially according to the frequency sweep generated as described above.

[0038] At each of these time intervals, additionally or alternatively, the amplitude can be changed according to a power sweep, in particular according to the power sweep generated as described above.

[0039] FIG. 2b shows that the frequency of the pulsed high-frequency signal has been changed during a first time interval I between one pulse 10. Thus, the frequency has been changed according to a frequency sweep. Also in a second time interval II, the frequency has changed according to a frequency sweep. In this case, it is also possible to carry out a first sweep, for example a frequency sweep, in the first time interval I and a second sweep different from the first sweep, for example a power sweep, in the second time interval II, and vice versa. Alternatively, it is also possible to carry out both sweeps in at least one time interval.

[0040] FIG. 2c shows that the magnitude of the reflection coefficient is very large at the start of the first time interval I and then drops sharply. The drop in the magnitude of the reflection coefficient is related to the fact that the plasma has been ignited. By appropriate analysis, the frequency and amplitude of the pulsed high-frequency signal at which ignition occurred can be determined. Different frequency sweeps and / or power sweeps can be used for subsequent pulses 12 in order to improve the ignition behavior. Furthermore, the duration of the first and / or second time intervals I, II can be changed in order to improve the plasma process.

[0041] FIG. 3a shows a power sweep in the time interval I, where the power of the high-frequency signal and the corresponding amplitude have a plurality of sections 14, 16. The power or amplitude is constant in each section 14, 16. The sections 14, 16 at the start of the pulse 10 are shorter in time than the sections 18, 20 at the end of the pulse 10. In this case, the section 22 at the end of the first time interval I can be made longer in time than the first section 14 at the start of the first time interval I. The section 22 can be made the same length as or shorter than the time section 24 at the start of the second time interval II.

[0042] Figure 3b shows the variation of the frequency of the pulsed high-frequency signal. The frequency also changes for each interval in the range 14 - 24. The frequency is constant within one interval in the range 14 - 24. In Figures 3a and 3b, for power and frequency, the intervals 14 - 24 are of the same length. However, it is also conceivable to select intervals 14 - 24 of different lengths for power than for frequency.

[0043] Figure 4 shows a plasma device 100 equipped with a power generator 102. The power generator 102 is configured to generate a pulsed high-frequency signal, and in so doing, different frequency sweeps and / or power sweeps can be set for the individual pulses of the high-frequency signal. The pulsed high-frequency signal can be amplified by an amplifier 104 and supplied to a plasma chamber 108 via an impedance matching unit 106. The processing parameters are detected directly in the plasma chamber 108 by a detection device 109 and supplied to an evaluation device 110. This is indicated by arrow 112. Further process parameters, especially electrical parameters, can be detected by a detection device 114 formed as a measuring device and supplied to the evaluation device 110. This is represented by arrow 116.

[0044] The detected processing parameters and the pulsed high-frequency signal, especially the individual pulses of the pulsed high-frequency signal, can be related to each other in the evaluation device 110. By this analysis, it can be determined whether it is necessary to change the generation of the pulses of the pulsed high-frequency signal and in what way it is necessary to change it in order to improve the plasma process.

Explanation of Reference Numerals

[0045] 10 Pulse 12 Subsequent Pulse 100 Plasma Device 102 Power Generator 106 Impedance Matching Unit 108 Plasma Chamber I First Time Interval II The second time interval

Claims

1. A method for igniting and / or maintaining a plasma using a pulsed high-frequency signal, comprising: a) generating a pulsed high-frequency signal; b) changing the frequency of the high-frequency signal according to a frequency sweep and / or changing the amplitude of the high-frequency signal according to a power sweep during a predetermined first time interval (I) within one pulse (10); and / or c) monitoring at least one process parameter of the plasma process; d) determining the relationship of the process parameter with respect to the performed sweep; e) detecting whether one or more monitored process parameters associated with one or more sweeps each take a predetermined value or are within a predetermined value range.

2. The method according to claim 1, wherein an evaluation of one or more sweeps is performed based on the detection.

3. The method according to claim 1 or 2, wherein a sweep is selected for a subsequent pulse (12) and / or for a second time interval (II) of a pulse based on an evaluation of one or more preceding sweeps.

4. The method according to any one of claims 1 to 3, wherein the evaluation includes an examination of the sweep based on the detection.

5. The method according to any one of claims 1 to 4, wherein the duration of the time intervals (I, II) is adapted based on the evaluation for the subsequent pulse (12).

6. The method according to any one of claims 1 to 5, wherein different frequency sweeps and / or power sweeps are set until one or more monitored process parameters reach a predetermined value or a predetermined value range.

7. The method according to any one of claims 1 to 6, wherein in a calibration process, a frequency sweep and / or a power sweep suitable for igniting the plasma is determined.

8. A power generator (102) for a plasma device (100), wherein the power generator (102) is configured to a. generate a pulsed high-frequency signal, b. change the frequency of the high-frequency signal according to a frequency sweep and / or change the amplitude of the high-frequency signal according to a power sweep during a predetermined first time interval (I) within one pulse (10), c. A power generator (102) configured to generate a frequency sweep and / or a power sweep depending on at least one detected process parameter. **Claim 9** The power generator (102) according to claim 8, characterized in that it comprises a DDS with a subsequent amplitude modulator for generating a pulsed high-frequency signal. **Claim 10** a. A power generator (102) according to claim 8 or 9; b. A plasma chamber (108); and c. An impedance matching unit (106) disposed between the power generator (102) and the plasma chamber (108), a plasma device (100).

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