High power generator and method for supplying high power pulses

Abstract

A high power (HP) generator (10) and a method for delivering pulsed high power at high voltage and / or current values ​​to a capacitive load, in particular a plasma process, comprising: - several low power (LP) generators (14, 16, 18), each including an energy storage component (C1, L1), wherein, during use, the energy storage component (C1, L1) is charged to a predetermined value associated with the energy storage component; Each provides, when in use, at its output an LP generator value that corresponds to the value of the energy storage components (C1, C2, Cn, L1, L2, Ln) incorporated in the respective LP generator (14, 16, 18) Several LP generators (14, 16, 18) and - a coupling (20), the LP generators (14, 16, 18) being electrically connected such that a coupling value at an output of the coupling (20) can be obtained which corresponds to an output value of the HP generator (10) and which is higher than the LP generator value at the output of one of the LP generators (14, 16, 18) during use, at least in some states of the HP generator (10); - a control unit (22) configured to select the contribution of the LP generators (14, 16, 18) to the output value of the HP generator (10) during the power delivery of the HP generator (10) in order to produce a rise and / or a decay of a pulse at the output of the coupling (20); Including, The control unit (22) may further be configured to sequentially select the contributions of the LP generators (14, 16, 18) through the LP generators (14, 16, 18), in particular each pulse sequence may start with a different LP generator (14, 16, 18).

Description

[Technical field]

[0001] The present invention relates to a high power (HP) generator configured to deliver pulsed high power of high voltage value and / or high current to a capacitive load, in particular to a plasma process. The present invention also relates to a method for supplying high power pulses to a plasma process. [Background technology]

[0002] By capacitive load is meant a load having a capacitive portion, meaning that the voltage rise across this load indicates high current characteristics. The capacitive portion in such a case may be at least 100 pF, preferably 200 pF or more, for example about 500 pF. This may be a load in a plasma process, for example for plasma processing applications.

[0003] Some plasma processing applications, such as etching and deposition, require the supply of high voltage (HV), high frequency (HF) rectangular asymmetric pulse voltages, the voltage values ​​of which often exceed the voltage handling capabilities of individual semiconductor switches, especially when high frequency operation is required. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] U.S. Patent No. 10,474,184B2 [Patent Document 2] U.S. Patent No. 10,607,813B2 [Patent Document 3] US Patent Application Publication No. 20200118794A1 [Patent Document 4] U.S. Patent No. 9,287,086B2

[0005] Summary of the Invention The object of the present invention is to provide a high power generator and a method for supplying high power pulses to a plasma, which allows for the supply of rapidly varying power (pulses) to a plasma process.

[0006] According to a first aspect, the present invention relates to a high power (HP) generator configured to deliver high power of high voltage and / or current values ​​to a load, in particular a plasma process, comprising: Some low power (LP) generators, each including an energy storage component, wherein during use, the energy storage component is charged to a predetermined value associated with the energy storage component; Each provides an LP generator value, when in use, at its output that corresponds to the value of the energy storage component built into the respective LP generator Several low power generators, a coupling, the LP generators being electrically connected in such a way that a coupling value at the output of the coupling can be obtained which corresponds to an output value of the HP generators and which is higher than the LP generator value at the output of one of the LP generators in at least some states of the HP generators during use; a control unit configured to select the contribution of the LP generator to the output value of the HP generator during the power delivery of the HP generator in order to produce a rise and / or a decay of a pulse at the output of the coupling; Includes.

[0007] In one embodiment, the control unit may be configured to select the contribution of the LP generators sequentially throughout the LP generators.

[0008] In one embodiment, at least one pulse sequence may use a different contribution of the LP generator than the previous one.

[0009] In one embodiment, at least one pulse sequence may begin with a different LP generator than the previous one.

[0010] In one embodiment, each pulse sequence may start with a different LP generator, so that after n pulses, all n LP generators are equally loaded, which improves load sharing among the stack of LP generators and therefore better balances power losses among the switching elements.

[0011] According to one embodiment, the output of the coupling and / or the output of the HP generator (10), in use, is a stepped waveform, in particular a true stepped waveform having no continuous slope.

[0012] According to one embodiment, the LP generators are activated sequentially during a pulse. This means that not all LP generators are activated at once at the beginning of the pulse. So, for example, for a pulse length of 0.5 μs to 2 μs, a first LP generator or a stack of several of the LP generators is activated at the beginning of the pulse. After a few tens or hundreds of nm, one or several additional LP generators are activated, which causes the pulse at the output of the HP generator to rise. Then, after another few tens or hundreds of nm, the next LP generator or a stack of LP generators is additionally activated, which causes the pulse to rise further. For the decay of the pulse, one or several of the LP generators are deactivated in a similar manner. By "activating one or several LP generators" it is meant that the control unit selects these LP generators to contribute to the output value of the HP generator during the power delivery of the HP generator. In other words, the control unit may be configured to select the contribution of each LP generator to the output value of the HP generator multiple times during a pulse at the output of the HP generator.

[0013] According to one embodiment, the coupling comprises 5 or more electrically connected LP generators, in particular 6 or more LP generators, preferably 10 or more, most preferably 15 or more LP generators. Such a large number of LP generators makes it possible to provide a true stepped waveform without a continuous gradient.

[0014] In one embodiment, the control unit is configured to select the contribution of the LP generator such that at least one amplitude step is less than 500V and / or such that a generator with a continuous gradient output is not required.

[0015] Such a solution would eliminate the need for a generator that produces a continuous gradient, making the HP generator more efficient.

[0016] In one embodiment, the coupling and control unit is configured to connect the LP generator by switching only.

[0017] In one embodiment, the control unit may be configured to select the contribution of the LP generator to the output value of the HP generator to form a step line pulse waveform at the rising and / or falling edge of the pulse.

[0018] In one embodiment, the number of LP generators is sufficiently large to produce at the output of the coupling a pulse having a voltage rise and / or fall equal to or greater than the sum of the values ​​of the LP generators and a step line pulse waveform in which the value of one step corresponds to a value equal to or greater than the value of one or more of the LP generators.

[0019] According to one embodiment, charging energy for the LP generators is provided through a transformer having a primary winding and a secondary winding for each LP generator, the secondary windings being connected to a rectifier, and each rectifier being connected to an energy storage component of a corresponding LP generator. The rectifier may include at least one semiconductor device, such as a diode. The rectifier may include four diodes connected as a bridge rectifier. The rectifier and / or the transformer may be part of the generator.

[0020] Some, and in particular each LP generator may have a transformer associated with it.

[0021] Each of the transformers corresponding to several, particularly one, LP generators may have its own magnetic core.

[0022] Each transformer corresponding to several, in particular one, LP generators may include a balance winding, preferably two balance windings.

[0023] This allows the AC supply current to flow freely around the transformer to provide charge to the loaded stages, i.e., LP generators connected to a load, and prevent overcharging the unloaded stages, i.e., LP generators that are not connected to a load and therefore do not contribute to the output of the HP generator. The same concept can be used to power driver circuits.

[0024] One balance winding of one transformer may be connected to the balance winding of another transformer.

[0025] Thus, the transformers corresponding to several, in particular one, LP generators may be connected in an open chain configuration.

[0026] Some of the primary windings, in particular the primary windings of the transformers corresponding to one LP generator, may be connected in series, which may mean that one wire is guided through all the transformers in series that are arranged to be supplied with an AC supply current.

[0027] High voltages and currents can be efficiently and effectively separated if each transformer has its own magnetic core and the only shared element is the primary winding which can be made from a single common wire.

[0028] Each transformer corresponding to several, particularly one, LP generators, also called "stages", may be implemented as a ring core transformer.

[0029] In one embodiment, a balancing circuit is connected between the two LP generators, including components that allow current to flow only in one direction, in particular diodes or components that behave like diodes. For example, the negative output of the energy storage components, in particular capacitors, of some, in particular each LP generator are connected to the same potential of the preceding LP generator with such a balancing circuit. This may allow a switch in parallel with the load to be operated so that when the value of the energy storage component of the lower LP generator exceeds that of the higher LP generator, a charge from the energy storage component of the lower LP generator is transferred to the energy storage component of the higher LP generator. "Activated" means "switched to the on state" or "switched to a low impedance at its output". "Switch in parallel with the load" means a switching element that, when activated, is responsible for disconnecting the corresponding LP generator from the connected LP generators in its vicinity. In Figs. 2a, 2b, 4, 5, these are switching elements S1. In Fig. 3, these are switching elements S2. By connecting switch, we mean a switching element that, when activated, is responsible for connecting the corresponding LP generator. In Figures 2a, 2b, 4, 5 these are switching elements S2. In Figure 3 these are switching elements S1. The energy storage components of the highest LP generators accumulate excess charge from the entire stack. These highest LP generators can therefore advantageously be controlled in such a way that they provide more power to the load than the other LP generators to remove the excess charge.

[0030] In one embodiment, a damping circuit may be positioned between some, especially all, of the LP generators in an open chain topology. Open chain topology is intended to mean that such a damping circuit is positioned between each LP generator and its neighboring, higher LP generator, rather than between the highest and the lowest. The damping circuit may include resistors and / or inductors if the energy storage component is a capacitor. The damping circuit may include resistors and / or capacitors if the energy storage component is an inductor. The damping circuit between the LP generators may be preferably positioned in series with the balance circuit. The damping circuit may be used to eliminate oscillations on parasitic components of the charge handling path.

[0031] The entire HP generator can be directly liquid cooled. This can be done by immersion dielectric cooling liquid, especially the LP generator is immersed in the dielectric cooling liquid. All components of the HP generator, including the transformer, can be immersed in the dielectric cooling liquid providing high cooling capacity while reducing clearance and creepage requirements. This allows better utilization of the safe operating area of ​​all components, resulting in further miniaturization and lower parasitic inductance and capacitance. This leads to a smaller overall HP generator and improved efficiency.

[0032] Some, in particular all, of the LP generator and the control unit may be at least partially arranged in one housing, together with at least the switching unit. The couplings may be arranged in the same housing. The transformer and the rectifier may be arranged in the housing. The housing may be waterproof. A dielectric cooling liquid may flow in the housing, thereby improving cooling and isolation. Distances may be reduced. This allows shorter wire lengths to be used, which reduces the inherent inductance, which allows faster switching functions. Temperature differences between different switches and other components and / or couplings of the LP generator may be reduced by this kind of series liquid arrangement. Thus, improved balance is possible.

[0033] In one embodiment, the control unit may include a switching unit having a current boosting capability of at least 10 A / μs. Such a high current boosting capability allows a capacitive load to be charged at a sufficiently high rate.

[0034] In one embodiment, the control unit may include a switching unit having a voltage withstand capability of about 0.5 kV or more with a voltage change rate of 15 kV / μs or more, whereby extreme pulses with very well defined voltage transitions may be achievable, which is a highly desirable feature for many applications such as plasma processing, particularly semiconductor plasma processing.

[0035] In one embodiment, the control unit may be configured to select the contribution of the LP generators (14, 16, 18) in such a way as to reduce the voltage overshoot at the output of the HP generators and / or at a particular location of the load, in particular at the substrate of the plasma process. This may be done, for example, by having a first step at the output of the HP generators being only a fraction, in particular half, of the value of a second step which may be the full amount.

[0036] In one embodiment, at least one, preferably some, and most preferably all, of the LP generators includes a LP generator value limiting circuit, such as a voltage limiting circuit or a current limiting circuit. This can be an additional switching element with an additional resistor, or an electrically controllable variable impedance with a power dissipation. By using such a circuit, the HP generator becomes much more reliable.

[0037] In one embodiment, the control unit is configured to select the contribution of the LP generators via a galvanically isolated, in particular optical fiber connection or magnetic coupling. Several, preferably each of the LP generators, can be selected by the control unit through the control of the switching unit. The connection between the output of the data processor and the switching unit can be realized by optical fiber or by magnetic coupling. This serves to switch all LP generators effectively, quickly and without delay, for example to form pulses with sharp edges of the voltage. Several switching elements of one switching unit can be connected by one galvanically isolated connection. Several LP generators with corresponding switching units can be grouped in one group, which can be configured in such a way that this group can always be activated or deactivated only together. It is then possible to use only one galvanically isolated connection for such a group. Reducing the number of galvanically isolated connections reduces costs and makes the HP generator more reliable, since there are fewer parts with a risk of failure. Advantageously, each switch has its own galvanically isolated connection. However, several transmitters can be controlled by one control signal if they are grouped together. This reduces the number of I / O ports required.

[0038] In one embodiment, the voltages on all LP generators, also called "stages", are equal even if their loads are unbalanced. Also, primary-secondary winding isolation (ground-HV) is easily obtained by locating the primary path near the center of the ring-core transformer and keeping the secondary windings near the core and away from the primary windings. The balance windings can be placed near the secondary windings since now only inter-stage voltage isolation has to be provided.

[0039] "The control unit is configured to select the contribution of the LP generator to the output value of the HP generator" is to be understood as the capability and configuration of the circuitry of the HP generator, in combination with the programming of the control unit, to enable the HP generator to select a choice of LP generators having respective LP generator values ​​for providing a contribution to the output value of the HP generator.

[0040] The control unit may include, for example, a data processor implemented as an embedded microprocessor having a program memory implemented, for example, as a non-volatile data memory, and a data memory implemented, for example, as a volatile data memory. Such a control unit typically includes data interfaces for incoming data, e.g., measurement data, control input data, and the like, as well as outgoing data, e.g., control signals, information signals, warning signals, and the like. Such a control unit typically includes data calculations, data comparison functions, and similar circuits that enable it to calculate new data from incoming data, to make decisions regarding the entered and / or calculated data, to output relevant data signals for controlling other electrical circuits of the HP generator, etc.

[0041] The output of the coupling can be the output of the HP generator. However, it is also possible that some small additional voltage or current shaping components are connected between the output of the coupling and the output of the HP generator. This small additional voltage or current shaping component can be a filter or a small voltage, current or power source with an amount much smaller than the output value of the coupling.

[0042] "HP generator state" means the different states that the HP generator can be in during use depending on the operation of different LP generators and / or switching units and / or switching elements within the HP generator.

[0043] High power means 10 kW or more during pulsed operation. High voltage value means 4 kV or more. High current means 10 A or more. The HP generator may be configured to affect the voltage and / or charge carrier movement within the plasma and / or between the plasma potential and the substrate during the plasma process. The energy storage component may be a capacitor or an inductor and / or other energy storage component. This should be understood as an energy storage component configured to store an amount of energy that may be a reasonable portion of the output energy of one pulse of the HP generator, i.e. at least 1 / 200, preferably at least 1 / 100, even more preferably at least 1 / 50 of the energy of one pulse of the HP generator. Continuously charging the energy storage component includes charging to a predetermined voltage value of the capacitor or a predetermined current value of the inductor. The electrical connection of the LP generators in the coupling may be in series, parallel or a combination of both. The coupling value may be voltage, current or power. The control unit may identify which of the LP generators contributes to the output power of the HP generator. The control unit may be configured to control the at least two LP generators such that they contribute to an output of the HP generator, i.e. such that output values ​​of the at least two LP generators are added together to form the HP output value.

[0044] The main advantage is that the energy storage component is charged independently of the state of the control unit. This means that there are no limitations on the duty cycle of the generated output values, especially the output pulses, their width and, as a result, the average output power. The second advantage is that each LP generator has its own energy storage component, which protects the switches in the control unit against overvoltages or overcurrents, respectively. The third advantage is that all components are relatively cheap, being low power components.

[0045] The control unit may include switching units, one switching unit associated with each LP generator. Each switching unit may include one or two transistors, in particular MOSFETs. MOSFETs provide high switching capabilities and can be used with currents of 50 A or more, allowing switching to voltages of 500 V or more. If MOSFETs are used, anti-parallel diodes may be provided for each MOSFET, in particular in parallel with each MOSFET. The MOSFETs may be silicon carbide (SIC) type or gallium nitride (GaN) based MOSFETs suitable for fast switching voltages of 500 V or more with fast voltage rise and fall times (15 kV / μs or more) as well as high currents (50 A or more) with fast current rise and fall times (10 A / μs or more).

[0046] Each switching unit may include a half-bridge circuit including two switching elements connected in series. One transistor may be configured to connect two of the LP generators in such a way that when closed, both values ​​of both LP generators affect the value at the output of the coupling. In particular, the output values ​​of both LP generators may be added. The other transistor may be configured to short-circuit the load when it is activated, i.e. when the transistor is in the closed, i.e. conductive, state.

[0047] The half-bridge circuit can be clamped by its storage component, e.g. a capacitor. This means that the storage component is directly parallel connected to the half-bridge. This configuration protects both switches from overvoltage up to the voltage of the capacitor. The storage component can also be an inductor. This configuration then protects both switches from overcurrent up to the current in the inductor. To prevent faults related to overvoltage or overcurrent respectively, one only needs to keep separate safe voltages / currents on all LP generators. Therefore, each LP generator keeps its operating level within its own level. This results in a self-maintaining safe state.

[0048] The control unit may include a driver. The driver may be configured to drive a switching unit, in particular a transistor, in particular a MOSFET. The control unit, in particular the switching unit, may be part of the respective LP generator.

[0049] At least six, preferably ten or more, preferably fifteen or more LP generators may be coupled in one coupling. At least two LP generators may provide equal LP generator values. Preferably, most of the LP generators, or even all of the LP generators, provide equal values. It is also possible that at least two LP generators provide different LP generator values, in particular all of the LP generators may provide different values. One LP generator may provide an LP generator value that is half the LP generator value of another LP generator.

[0050] A capacitor may be provided as an energy storage component in parallel with the switching units, especially the half bridges. This allows the output value of the coupling to be stabilized. Each LP generator may have its own capacitor, which is charged to an appropriate voltage level. Activating one switch of the associated switching unit connects a load, e.g. a plasma process, to the capacitor. Activating the other switch of the switching unit shorts the load. The output of the entire HP generator may become a true dynamic voltage source during each pulse, allowing very large output currents and the required fast voltage transitions.

[0051] An inverter including a full bridge circuit, and preferably a buck converter, may be connected to the primary winding, allowing efficient power delivery to the LP generator.

[0052] In yet another aspect, the present invention relates to a method of supplying high power pulses of different amplitudes provided by a high power (HP) generator to a plasma process, comprising: a. continuously charging an energy storage component of each of a plurality of low power (LP) generators to a predetermined value; b. selectively combining output values ​​of at least some of the LP generators by controlling the contribution of the LP generator to the output of the HP generator to obtain a desired output value of the HP generator corresponding to a pulse having a desired amplitude; Includes.

[0053] By using many LP generators, each containing an energy storage component, together with the coupling, it is possible to select how many LP generators contribute to the generation of the output pulse. This solution is relatively safe, universal and cheap. It is safe because each LP generator can be configured to protect its own associated switch from powers higher than the power value of its energy storage component. It is universal because it is possible to rapidly change the amplitude of the output pulse with a resolution equal to the number of low power generators. It is cheap because many low power generators and low voltage switches can be used, which is usually cheaper than one HP generator and high power pulse unit.

[0054] In one embodiment, the LP generators, also referred to as "stages", can be controlled individually or in groups. Control signals can be provided to the drivers of the switching units, preferably by optical fiber, although other means can be used. Not only can all switches of the switching units be controlled separately from one main control board, but one signal can control an entire stage (e.g., control signals for the connecting switches of the switching units can be provided from the main control board, signals for the load parallel switches of the switching units can be generated on the connecting switch driver board), one signal can control multiple switches / stages in a collective control, etc. The total output value is the sum of the output values ​​of only the activated / selected LP generators. The total output value can be varied from pulse to pulse by activating or selecting a different number of LP generators for each pulse.

[0055] In one embodiment, the output value of the LP generators, i.e., the LP generator value, can be dynamically stabilized. Each LP generator can have its own capacitor, charged to the appropriate voltage level. Activating one switch connects the load to the capacitor. Activating the other switch shorts the load. The output of the entire HP generator becomes a true dynamic generator during each pulse, allowing very large output currents and the required fast voltage transitions.

[0056] A two-step transition can be realized instead of a one-step output value transition. By connecting a low impedance voltage source to a capacitive load through any connector impedance, current and voltage oscillations inevitably occur. The load peak voltage reaches twice the applied voltage level. The resistive damping circuit consumes a large amount of power. By applying a two-step transition, the power loss can be significantly reduced. This is possible with the presented topology. The two-step transition allows to obtain a nearly rectangular voltage waveform, lower overshoot, and significantly reduced power loss.

[0057] Several stages, also called "LP generators", can be activated sequentially during a continuous output pulse. Activating an LP generator means activating the corresponding connected switching element. To compensate for the decaying wafer voltage, the output voltage can be increased in several steps. At each step, its voltage is added to the total output voltage value. If the voltages of all stages are equal, the resolution of each step is 1 / n times the voltage of the entire stack of LP generators. Another stack can be built to handle the compensation function. It can be controlled separately, resulting in a much finer step resolution, which results in a more stable wafer voltage and a better ion energy distribution.

[0058] Other features and advantages of the invention can be obtained from the following detailed description of an embodiment of the invention based on the drawings of figures showing details essential to the invention, and from the patent claims. The features shown therein should not necessarily be understood to be to scale, but are shown in such a way that the special features according to the invention are clearly visible. The various features can be implemented individually or in any combination in the various embodiments of the invention.

[0059] Examples of the invention in various stages of use are shown in the diagrams and are explained in more detail in the following description. [Brief description of the drawings]

[0060] [Figure 1] Pulse sequences of different amplitudes are shown. [Figure 2a] 1 shows a first embodiment of an HP generator. [Figure 2b] 2 shows a second embodiment of the HP generator. [Diagram 3] 1 shows a first embodiment of a part of an HP generator for generating a positive voltage pulse. [Figure 4] 1 shows a second embodiment of a part of an HP generator for generating a positive voltage pulse. [Diagram 5] 1 illustrates an embodiment of an HP generator having a power supply for powering an LP generator. [Figure 6] 1 shows an embodiment of an HP generator having a balance and damping circuit. [Figure 7] Wave shaping and power loss in one-step and two-step transitions are shown. [Figure 8] 1 shows the waveforms resulting from sequential actuation of the LP generator. [Figure 9] 1 shows the result of passing a periodic control signal sequence through an LP generator. [Figure 10] 1 illustrates a plasma processing system having a plasma chamber. [Figure 11] 1 shows an alternative embodiment of an HP generator. [Figure 12] 1 shows an alternative embodiment of an HP generator. [Figure 13] 1 shows an alternative embodiment of an HP generator. [Figure 14] 1 shows an alternative embodiment of an HP generator. [Figure 15] 1 shows an example of an LP generator value limiting circuit. [Figure 16] 1 shows an embodiment of an HP generator having a balancing circuit. [Figure 17] 1 shows an embodiment of an HP generator with liquid cooling. [Figure 18a] 1 illustrates an embodiment of an HP generator with a galvanically isolated driver. [Figure 18b] 1 illustrates an embodiment of an HP generator with a galvanically isolated driver. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0061] Figure 1 shows a sequence of pulses 1 required by the plasma application. It can be seen that the amplitude of pulse 1 must be constant for several pulses, but may have an amplitude variation from pulse 1 to pulse 1a.

[0062] Fig. 2a shows a first embodiment of a high power (HP) generator 10 suitable for generating high power pulses. The HP generator has a positive output 32 and a negative output 12. The HP generator 10 comprises a number of low power (LP) generators 14, 16, 18, each of which comprises an energy storage component C1, C2, Cn, in this case implemented as a capacitor. In use, the energy storage component C1 is continuously charged to a predetermined value related to the energy storage component C1 to keep the energy stored therein constant. In use, each LP generator 14, 16, 18 provides at its output an LP generator value corresponding to the value of the energy storage component C1 incorporated in the respective LP generator 14, 16, 18. The LP generators 14, 16, 18 are electrically connected in a coupling 20, so that at the output of the coupling 20 a coupling value corresponding to the output value of the HP generator 10 can be obtained, which is higher than the LP generator value at the output of one of the LP generators 14, 16, 18. The control unit 22 is configured to select the contributions of the LP generators 14, 16, 18 to the output value of the HP generator 10 during power delivery of the HP generator 10. For clarity, only three LP generators are shown. In practice, many more LP generators would be used, typically six or more, even ten or more, especially fifteen or more, to produce a step-type transition in the output that may be as smooth as required for the load.

[0063] The control unit 22 comprises switching units 24, 26, 28 associated with each LP generator 14, 16, 18. Each of the switching units 24, 26, 28 comprises a switching element S1, S2. In the embodiment shown in the figures, the switching elements S1, S2 are connected in series, thus realizing a half-bridge. The switching units 24, 26, 28, and therefore the switching elements S1, S2, are driven by a driver 30 of the control unit 22.

[0064] The positive output 32 of the HP generator is connected to earth, also referred to as ground potential PE. All LP generators are connected to a power supply 34, which includes a transformer, a rectifier and an inverter connected to the power grid, which itself includes a full bridge and a buck converter, as will be explained in more detail later.

[0065] FIG. 2b corresponds approximately to FIG. 2a. Thus, similar elements are numbered similarly. The difference between FIG. 2a and FIG. 2b is that in FIG. 2b the energy storage components are implemented as inductances L1, L2, Ln. Thus, the electrical connections / wirings in the coupling 20 are slightly different. In general, the energy stored in the inductor becomes a current source. Therefore, the energy storage components are connected in parallel with other current sources, leading to current amplification.

[0066] In both figures 2a and 2b, a ground potential, also called earth potential PE, can be connected to one of the outputs of one of the LP generators 14, 16, 18. This makes it possible to form voltage signals with positive and negative voltages with respect to ground, as shown for example in figure 10 of (US Pat. No. 5,393,631) or in figure 21 of (US Pat. No. 5,393,631). The ground potential can also be connected to the positive output 32 or to the negative output 12. In figures 2a and 2b, it is connected to the positive output 32 by way of example.

[0067] FIG. 3 shows a simplified embodiment of a part of the HP generator 10 with several LP generators 14, 16, 18. To generate high voltage pulses, it is advantageous to build a push-pull switch, which means that the switching unit should have at least two switching elements S1, S2, namely a "push" (switching element S1) used to perform the charging of the capacitance of the plasma reactor and a "pull" (S2) used to perform the discharging of the capacitance of the plasma reactor. In order to generate pulses with different amplitudes, while being able to change the amplitude rapidly between the pulses (as shown in FIGS. 1, 7, 8), it is necessary to combine the outputs of two or more LP generators 14, 16, 18. The LP generator values ​​of the LP generators 14, 16, 18, in this case the voltage amplitudes, may be the same or different. In FIG. 3, the ground potential, also called earth potential PE, is connected to the negative output of the LP generator 18.

[0068] In some circumstances, if none of the switching elements S1, S2 are switched on (during the transition between the two operating states) and the LP generators 14, 16, 18 are connected in series and in series with the load (e.g., a plasma reactor), the switching elements S1, S2 may be destroyed by overvoltage. For this reason, it is advantageous to add diodes D1, D2 in parallel with all switching elements S1, S2 to protect them from voltages higher than the voltage stored in the respective energy storage components. This is especially true if the switching elements S1, S2 are implemented as MOSFETs. If the switching elements are implemented as unipolar transistors, as MOSFETs typically are, the diodes are already included as part of the transistor or are an integral part of the transistor die. A die, in terms of integrated circuits, is a small block of semiconductor material on which some functional circuitry is built. These diodes can then be used and there is no need to add them separately.

[0069] A ground potential can be generated at the output of the HP generator (the load is short-circuited to the ground potential PE). This state is realized by switching-on switching element S2 when the ground potential is connected to the negative output 12 or to the positive output 32 of the HP generator. In this state, switching element S1 is opened (switched off). To generate a (voltage) pulse to the load, an appropriate number of switching elements S1 must be switched on. The LP generators 14, 16, 18 can provide the same or different LP generator values, in this case voltage amplitudes. By switching on several switching elements S1, the associated LP generators, e.g. LP generators 14, 16, are connected in series and the amplitude of the voltage pulse to the load is equal to the sum of the LP generator values, e.g. their output voltages.

[0070] The complementary switching element S2 associated with the LP generators 14,16 should be switched off to avoid a short circuit within the LP generators 14,16.

[0071] The switching element S1 associated with the LP generator 18 (or another LP generator) should be switched off, and the switching element S2 can be switched either on or off (current flows through the diode D2 in any case).

[0072] The configuration of switching elements that are switched on and off can be changed quickly, which leads to a fast change in the amplitude of the pulses generated at the output of the HP generator 10. The number of LP generators 14, 16, 18 supplying the load can be quickly changed to any feasible number (0 to n).

[0073] Figure 4 differs from Figure 3 only in the wiring, i.e. the interconnection of the LP generators 14, 16, 18 and the connection point of the load with PE. However, the same result as in Figure 3 can be obtained, i.e. voltage pulses of different amplitudes can be realized by selecting the LP generators 14, 16, 18 that contribute to the output voltage pulse by appropriately driving the switching elements S1, S2. In Figure 4, the earth potential, also called earth potential PE, is connected to the negative output of the HP generator 10.

[0074] FIG. 5 shows the power supply of the LP generators 14, 16, 18 in more detail. The energy storage components C1, C2, Cn of the LP generators 14, 16, 18 are continuously charged by the transformers T1, T2, Tn and the associated rectifiers X1, X2, Xn, respectively. It is much easier and cheaper if every transformer T1, T2, Tn has its own magnetic core and the only common element is the primary winding P1, P2 which can be made from one common wire. To have the same voltage regardless of the load, a balance winding BW is added. The balance winding BW makes the magnetic flux in the individual transformers T1, T2, Tn equal. If the number of wires in the secondary windings SW1, SW2, SWn is the same, the voltage on the energy storage component C1 is equal. By changing the number of turns in the secondary windings SW1, SW2, SWn, the charging voltage of the energy storage component C1 can be changed. In that way it can be ensured that the individual energy storage components C1 are charged to different voltages.

[0075] The balance winding BW in the transformers T1, T2, Tn works like that, if the magnetic flux in both adjacent transformers T1, T2, Tn is the same, then both windings BW have the same voltage and hence no current flows between the windings BW. If for some reason the magnetic flux in one core is different (e.g. higher) than the next core, then the induced voltages in the different transformers T1, T2, Tn will be different and hence some current will start flowing between this winding BW. Due to this current, the transformer T1, T2, Tn having higher magnetic flux will be more loaded and the magnetic flux of the next transformer will increase due to this current. By making the magnetic flux in the magnetic cores equal, the induced voltages will be equal. The balance winding BW should have the same number of turns in both connected transformers using the flux equalization method.

[0076] The primary windings P1, P2, Pn are connected to an inverter 40, which is connected to a power grid 42. The inverter 40 is part of the power source 34 and includes a full bridge 44 and a buck converter 46 upstream of the full bridge 44, which is connected to a rectifier 48.

[0077] FIG. 6 shows an HP generator 10, for example similar to that of FIG. 2a, in which a balancing circuit is connected between two LP generators 14, 16, 18 with components that allow current flow in only one direction, in particular diodes D or components acting like diodes. The switching units 24, 26, 28 include switching elements of a half bridge. These switching elements are shown as transistors, more precisely as bipolar transistors. For faster switching times, a more preferred type of transistor would be MOSFETs, in particular MOSFETs based on SiC or GaN. In this embodiment, the negative terminal of each LP generator 14, 16, 18, also called a stage, is connected to the same potential as the preceding LP generator 14, 16, 18, which has a circuit including diodes D or diodes. This allows that, when the switching elements are activated, the energy stored in the energy storage components of the lower stage is transferred to the energy storage components of the higher stage if the voltage of the energy storage components of the lower stage exceeds that of the higher stage. The charge of the highest stage 14 accumulates the excess charge from the whole stack. The highest stage 14 is therefore controlled to provide the most power to the load in order to eliminate excess charge. Using a diode D or a circuit including a diode results in a better voltage distribution along the LP generator stack. A damping circuit 50, particularly in series with the balancing circuit, here the diode D, may be used to eliminate oscillations on parasitic components in the charge handling path. The damping circuit may particularly include an inductor L and / or a resistor R connected in parallel as shown in FIG. 6.

[0078] Connecting a low impedance voltage source, such as a capacitive voltage source with a capacitive load due to any connector inductance, inevitably generates current and voltage oscillations. The load peak voltage can then reach twice the applied voltage level. This can damage the load and is highly undesirable. To dampen the peak voltage, resistive snubber circuits are often used. These loss circuits consume a lot of power and therefore generate a lot of heat, which is also highly undesirable. By applying a two-step transition, this overshoot can be controlled, reduced, or even avoided. The energy dissipation in the loss circuits can be dramatically reduced or even avoided. The components that have to consume energy can then be much smaller or completely avoided. The power losses can be significantly reduced. This is possible in the presented topology and is shown in FIG. 7. Waveform 70 shows a one-step transition from 0 kV to 10 kV at the output of coupling 20 by activating all 15 stages for example in an instant. This causes a voltage overshoot as can be seen in waveform 74. As shown by waveform 71, a stepwise transition, for example from 0V to 5.5kV in a first step by activating only 8 of the 15 stages, and then from 5.5kV to 10kV in a second step by activating the remaining 15 stages after a few tens or hundreds of nms, gives much better results. The resulting waveform 73 has a much lower overshoot peak voltage and the voltage rises slower, but is still fast enough for the process. As can be seen from waveform 73, the two-step transition gives a nearly rectangular output waveform and a lower overshoot, and therefore little power dissipation, whereas the one-step transition leads to waveform 74 showing a voltage overshoot and thus a large power loss 75. The same overshoot peak and its fall can be seen in the downward slope after, for example, 1 μs and 3.5 μs.

[0079] 8 shows the stepwise increase in amplitude of a pulse 80 by sequentially activating the LP generators 14, 16, 18 to contribute to the HP output signal. Waveform 81 shows the voltage at the output of the HP generators, and waveform 82 shows the voltage on the wafer in the plasma chamber.

[0080] FIG. 9 shows the result of cycling a control signal sequence through an LP generator stack containing 15 LP generators #01-#015. The figure shows a timeline t on the horizontal axis, as in FIG. 8. On the vertical axis, the actuation of 15 switching elements corresponding to 15 LP generators #01...#15 is shown. The shaded areas 92 are where the connected switching elements are actuated. The white squared areas 91 are where the switching elements in parallel with the load are actuated. Thus, there are no pulses at the output in time frames where there are no shaded areas. In the first column, LP generators #01-#06 are switched with their corresponding connected switching elements. In the second column, LP generators #01-#10 are switched with their corresponding connected switching elements. In the third column, LP generators #01-#11 are switched with their corresponding connected switching elements. In the fourth column, LP generators #01-#12 are switched with their corresponding connected switching elements, and so on. Thus, the pulse has the shape of a stepped waveform. In the ninth column, the pulse ends and all connected switching elements are deactivated. Then, in the tenth column, the next pulse begins, this time using LP generators #02 to #07 instead of LP generators #01 to #06. In this example, all LP generators have the same output value, but the output value at the output of coupling 20 is the same as it was for the first pulse. The advantage is that each pulse sequence starts with a different LP generator stack, so that all 15 LP generators and their corresponding switching elements are equally loaded after 15 pulses. This allows a better load distribution between the LP generator stacks and therefore also a better power loss balance between the switching elements.

[0081] FIG. 10 shows a plasma processing system having a plasma chamber 100 in which a plasma space is generated with a plasma 101. Such or similar systems are shown and described, for example, in US Pat. No. 5,399,633, US Pat. No. 5,499,667, or US Pat. No. 5,499,677. In the plasma chamber, an upper electrode 103 may be positioned. Gas inlets and outlets, in particular gas supply tubes 104, may be installed from the outside to the inside of the plasma chamber 100 and may be connected, in particular, to the electrode 103. Inside the plasma chamber 100, a substrate 102, in particular a semiconductor wafer, may be placed on a support 105 including a substrate holder. In use, the substrate 102 may be treated by the plasma 101, for example in the process of etching, ashing, or deposition, in particular by atomic layer deposition. The etching process may be very difficult, for example, when the ratio of the diameter of the etching hole to the length of the hole is very low, for example <1 / 100, as is often necessary for deep etching. A conductive electrode 106 may be installed in the plasma chamber 100, in particular near the substrate 102, for example around the substrate 102. The conductive electrode 106 may be an edge ring, which may also be called a focus ring. The conductive electrode 106 may be connected to a first power supply 114 via a first connection line 115. The first power supply 114 may be a DC pulsed power supply, in particular where the pulses may have different lengths, different amplitudes and waveforms, as shown for example in Figs. 11 and 14 of (Patent Document 4) or Fig. 2 of (Patent Document 1). By controlling the first power supply 114, the conductive electrode 106 may additionally or alternatively be used as an ion energy and / or ion acceleration direction control means, which is also described in (Patent Document 4) or (Patent Document 1). A first radio frequency (RF) power supply 118 may be electrically connected to the support 105 via a first power supply rod 119 and a first matching unit 116 and a first connection unit 117. A second radio frequency (RF) power source 108 may be electrically connected to the upper electrode 103 via a second power supply rod 109 as well as a second matching unit 110 and a second connecting unit 111. The electrode 107 may be positioned in or near the support 105 and is electrically connected to a second power source 112 via a second connecting line 113.The second power supply 112 may be a DC pulsed power supply, where in particular the pulses may have different lengths, different amplitudes and waveforms, as shown for example in Figures 11 and 14 of (US Pat. No. 6,399,411) or Figure 2 of (US Pat. No. 6,399,411). The substrate 102 may be secured to the support 105 via an electrode 107, which may function as an electrostatic chuck. Through control of the second power supply 112, the electrode 107 may additionally or alternatively be used as an ion energy and / or ion acceleration direction control means, also as described in (US Pat. No. 6,399,411) or (US Pat. No. 6,399,411).

[0082] Some plasma processing applications, such as etching and deposition, require high voltage (HV), high frequency (HF) rectangular asymmetric pulse voltage supplies. In many cases, the voltage values ​​greatly exceed the voltage handling capabilities of individual semiconductor switches, especially when high frequency operation is required.

[0083] Some plasma applications require not only pulsed operation, but also pulse-to-pulse amplitude variation. Some plasma applications require the power supply to deliver high peak currents to obtain short voltage transition times. Most plasma applications present a load, which includes capacitive components. Large power losses are associated with the charging and discharging of the capacitance of this load with each pulse. Some plasma applications require pulse shaping, as shown for example in Figs. 11 and 14 of (US Pat. No. 5,399,433) or Fig. 2 of (US Pat. No. 5,499,433).

[0084] Therefore, a series connection of such switches is one possible solution. Series connections require voltage balancing means. These voltage balancing means are not easily realizable in HF operation.

[0085] Figure 11 shows an alternative embodiment of the HP generator stack shown in Figure 5. The difference between the HP generators shown in Figures 5 and 11 is that in Figure 11 the primary windings P1, P2, ... Pn are connected in parallel to the transformers T1, T2, ... Tn and no balance winding BW is provided.

[0086] Figure 12 shows another alternative embodiment of the HP generator shown in Figure 5. The difference between the HP generators shown in Figures 5 and 12 is that in Figure 12, all the transformers T1, T2, Tn of Figure 5 are integrated into one main transformer T1 with only one core. Only one primary winding P is required and no balance winding Bw is provided.

[0087] Figure 13 shows another alternative embodiment of the HP generator shown in Figure 5. The difference between the HP generators shown in Figures 5 and 13 is that in Figure 13 the primary windings P1, P2, ... Pn are connected in parallel to the transformers T1, T2, ... Tn. A balance winding is shown but is not absolutely necessary in such a configuration.

[0088] Figure 14 shows an alternative embodiment of the HP generator shown in Figure 5. The difference between the HP generators shown in Figures 5 and 14 is that in Figure 14, the primary winding P1 is connected only to the transformer T1. The balance winding BW is used to transport energy from transformer T1 to T2 and from transformer T2 to the subsequent transformer.

[0089] FIG. 15 shows an example of an LP generator value limiting circuit 151. This LP generator value limiting circuit 151 is a voltage limiting circuit. It can be connected in parallel at its terminals 152a, 152b to one, some or all of the LP generators 14, 16, 18. It can also be connected in parallel at its terminals 152a, 152b to one, some or all of the switching units 24, 26, 28. This LP generator value limiting circuit 151 includes a series circuit of a diode D15 and a capacitor C15 and clamps the overvoltage present at its terminals 152, 153 to the voltage to which the capacitor C15 is charged. The voltage of the capacitor C15 is controlled by a discharge circuit 153. The discharge circuit 153 includes a transistor T15, in this case a MOSFET, and a resistor R15, in this case a power resistor, arranged to be cooled very effectively. The transistor T15 is therefore controlled in a pulsed mode so that it can be switched on or off. Therefore, the transistor T15 does not dissipate much energy into heat and remains very cool. When the transistor T15 is switched on, the capacitor is discharged and a discharge current flows through the resistor R15, dissipating the energy into heat. Most of the heat is generated in the resistor R15, which is easier and cheaper to keep cool enough than the transistor T15. The transistor T15 is controlled by a voltage control circuit 154 at its control input G15. The voltage control circuit 154 includes a series connection of a first high-voltage Zener diode 155, a current-limiting resistor 156, and a second low-voltage Zener diode 158. The junction of the current-limiting resistor 156 and the second low-voltage Zener diode 158 is connected to the control input G15 of the transistor T15. The voltage control circuit 154 may further include a driver 157. The driver 157 may be connected at its input to the junction between the current-limiting resistor 156 and the second low-voltage Zener diode 158. The driver 157 may be connected at its output to the control input G15 of the transistor T15. A voltage divider 159 may be connected between the output of the driver 157 and the control input G15 of the transistor T15.

[0090] The driver has hysteresis at its input and can therefore be implemented as a Schmitt trigger. It thus generates a pulse signal to drive the discharge transistor T15 at a frequency of about 2-20 kHz. In such a configuration, more than 90% of the power is dissipated in resistor R15. This keeps the transistor cool enough to operate reliably for long periods of time.

[0091] FIG. 16 shows an embodiment of the HP generator 10 in which a balancing circuit is connected between the two LP generators 14, 16, and 18, including components that allow current to flow in only one direction, specifically diodes or components that act like diodes. The balancing circuit, specifically diode D, is connected between the two negative outputs of the LP generators 14, 16, and 18. This allows the switching element S1 to be activated and energy from the lower stage energy storage component to be transferred to the higher stage energy storage component when the voltage of the lower stage energy storage component exceeds that of the higher stage. The charge of the highest stage 14 accumulates excess charge from the entire stack. Therefore, the highest stage 14 should be controlled to provide the most power to the load to eliminate the excess charge. The use of diode D or a circuit including diodes improves the voltage distribution along the LP generator stack.

[0092] 17 shows an embodiment of the HP generator 10 with liquid cooling. All electronic components of the HP generator 10, such as the LP generators 14, 16, 18, the switching units 24, 26, 28, the transformers T1, T2, Tn, and the inverter 40, are arranged in a waterproof housing 171. A liquid reservoir 174 is arranged near the housing. Between the housing and the reservoir 174, a liquid pump 173 is arranged for circulating the liquid 171 between the housing and the reservoir 174 as a closed liquid loop. The reservoir is in thermal contact with a heat exchanger 175 to transfer heat from the closed cooling liquid loop to the environment.

[0093] 18a and 18b show an embodiment of the HP generator 10 having a galvanically isolated connection 181 between the driver 30 and the switching elements S1, S2.

[0094] Therefore, here the control unit 22 is configured to select the contribution of the LP generators 14, 16, 18 in such a way that they are galvanically isolated, in particular by optical fiber connection or magnetic coupling. The connection between the output of the data processor and the switching units 24, 26, 28 can be realized by optical fiber or by magnetic coupling. This serves to switch all LP generators 14, 16, 18 effectively, quickly and without delay, forming pulses with sharp edges in the voltage, for example. Several switching elements S1, S2 of one switching unit 24, 26, 28 can be connected by one galvanically isolated connection. Several LP generators 14, 16, 18 together with the corresponding switching units 24, 26, 28 can be grouped in one group, which can be configured in such a way that this group is always activated or deactivated together. Then for such a group only one galvanically isolated connection 181 can be used. Galvanic isolation (transmitter and receiver) can be used for each switch. Groups of transmitters can be controlled simultaneously, reducing the number of control signals required. Reducing the number of galvanically isolated connections 181 reduces costs and makes the HP generator 10 more reliable since there are fewer parts at risk of failure. [Explanation of symbols]

[0095] 1 Pulse 10 High Power (HP) Generator 12 HP Generator Negative Output 14, 16, 18 Low Power (LP) Generators 20 Coupling 22 Control Unit 24, 26, 28 Switching Unit 30 Drivers 32 HP Generator Positive Output 34 Power supply 40 Inverter 42 Power grid 44 Full Bridge 46 Buck Converter 48 Rectifier 50 Damping circuit 70 waveforms 71 Waveform 73 Waveform 74 Waveform 75 Power loss 80 Pulse 81 Waveform 82 Waveform 91 areas 92 areas 100 Plasma Chamber 101 Plasma 102 Substrate 103 Electrode 104 Gas supply pipe 105 Support 106 Conductive electrode 107 Electrode 108 Power supply 109 Second Power Supply Rod 110 Second Matching Unit 111 Second connection unit 112 Second Power Source 113 Second connecting line 114 First Power Source 115 First connecting line 116 First Matching Unit 117 First Connection Unit 118 Power supply 119 First Power Supply Rod 151 LP Generator Value Limiting Circuit 152 edge 152a end 152b end 153 Discharge circuit 154 Voltage control circuit 155 First High Voltage Zener Diode 156 Current limiting resistor 157 Drivers 158 Second Low Voltage Zener Diode 159 Voltage Divider 171 Waterproof housing 173 Liquid Pump 174 Reservoir 175 Heat exchanger 181 Connections BW Balance winding C1, C2, Cn capacitors D1, D2 Diodes L1, L2, Ln Inductors P1, P2, Pn Primary winding PE Earth potential R resistor S1, S2 switching elements SW1, SW2, SWn Secondary winding T1, T2, Tn transformers X1, X2, Xn rectifier

Claims

1. A high power (HP) generator (10) configured to deliver pulsed high power of high voltage and / or current values ​​to a capacitive load, in particular a plasma process, comprising: several low power (LP) generators (14, 16, 18), each LP generator (14, 16, 18) includes an energy storage component (C1, L1), said energy storage component (C1, L1) being charged, during use, to a predetermined value for said energy storage component; Each LP generator (14, 16, 18), when in use, provides at its output an LP generator value that corresponds to the value of the energy storage components (C1, C2, Cn, L1, L2, Ln) incorporated in the respective LP generator (14, 16, 18). Several LP generators (14, 16, 18); a coupling (20) to which the LP generators (14, 16, 18) are electrically connected in such a way that a coupling value at the output of the coupling (20) can be obtained which corresponds to an output value of the HP generator (10) and which, in use, is higher than the LP generator value at the output of one of the LP generators (14, 16, 18) in at least some states of the HP generator (10); a control unit (22) configured to select the contribution of the LP generators (14, 16, 18) to the output value of the HP generator (10) during the power delivery of the HP generator (10) in order to produce a rise and / or a decay of a pulse at the output of the coupling (20); Including, - a high power (HP) generator (10), wherein the control unit (22) is further configured to sequentially select the contributions of the LP generators (14, 16, 18) through the LP generators (14, 16, 18), and at least one pulse sequence may use a contribution of a LP generator (14, 16, 18) different from its previous one or may start with a LP generator (14, 16, 18) different from its previous one.

2. The control unit (22) further determines the contribution of the LP generators (14, 16, 18) according to the following characteristics: the output of the coupling (20) and / or the output of the HP generator (10) is a stepped waveform, in particular at the rising and / or falling edges of the pulses and / or during the pulses, the LP generators (14, 16, 18) are operated sequentially during one pulse; At least one amplitude step is less than 1 kV, in particular less than 500 V; The LP generators (14, 16, 18) are connected by switching only 2. The HP generator of claim 1, configured to select in such a way that one or a combination of:

3. said coupling (20) comprises five or more electrically connected LP generators (14, 16, 18), in particular at least six, in particular ten or more, preferably fifteen or more LP generators (14, 16, 18) are combined in one coupling (20); and / or the number of LP generators (14, 16, 18) at the output of the coupling (20), - a pulse with a voltage rise and / or fall equal to or higher than the sum of the values ​​of several of the LP generators (14, 16, 18), and A step line pulse waveform in which the step value corresponds to a value equal to or higher than the value of one or more of the LP generators (14, 16, 18). There are enough of them to form 3. A HP generator according to claim 1 or 2.

4. The charging energy of the LP generators (14, 16, 18) is provided on transformers (T1, T2, ... Tn) having a primary winding (P1, P2, ... Pn) and a secondary winding (SW1, SW2, ... SWn) for each LP generator (14, 16, 18), a. the secondary windings (SW1, SW2, ... SWn) are connected to rectifiers (X1, X2, ... Xn), each rectifier (X1, X2, ... Xn) being connected to the energy storage components (C1, C2, Cn, L1, L2, Ln) of a corresponding one of the LP generators (14, 16, 18); and / or b. some of said primary windings (P1, P2, ... Pn), in particular each primary winding corresponding to an LP generator of a transformer, are connected in series; An HP generator according to any one of claims 1 to 3.

5. 5. HP generator according to any one of claims 1 to 4, wherein the charging energy of the LP generators (14, 16, 18) is supplied over transformers (T1, T2, ... Tn), each transformer corresponding to several, in particular one, LP generators, may include a balance winding (BW), preferably two balance windings, preferably one balance winding (BW) of one transformer (T1) may be connected to a balance winding of a different transformer (T2).

6. 6. An HP generator according to claim 1, wherein a balancing circuit including a component that allows current to flow in only one direction, in particular a diode D or a component acting like a diode, is connected between the two LP generators.

7. 7. The HP generator according to claim 1, wherein a damping circuit (50) is positioned in an open chain configuration between some, in particular all, of said LP generators (14, 16, 18), in particular said damping circuit (50) comprising a resistor (R) and / or an inductor (L).

8. HP generator according to any one of claims 1 to 7, at least partially directly liquid cooled, in particular by an immersion dielectric cooling liquid, in particular the LP generator (14, 16, 18) being immersed in the dielectric cooling liquid.

9. 9. The HP generator according to any one of claims 1 to 8, wherein the control unit (22) comprises a switching unit (24, 26, 28) having a current ramp-up capability of at least 10 A / μs and / or capable of withstanding a voltage of about 0.5 kV or more with a voltage change rate of 15 kV / μs or more.

10. 10. The HP generator according to any one of claims 1 to 9, wherein the control unit (22) is configured to select the contribution of the LP generators (14, 16, 18) in such a way as to reduce voltage overshoots at the output of the HP generator (10) and / or at specific locations on the load, in particular at a substrate of a plasma process.

11. 11. The HP generator according to any one of claims 1 to 10, wherein at least one, preferably several, most preferably all, of the LP generators (14, 16, 18) comprises a LP generator value limiting circuit (151), e.g. a voltage limiting circuit or a current limiting circuit.

12. The HP generator according to any one of claims 1 to 11, wherein the control unit (22) is configured to select the contribution of the LP generators (14, 16, 18) to be galvanically isolated, in particular via an optical fibre connection or a magnetic coupling.

13. HP generator according to any one of the preceding claims, wherein a capacitance is provided in parallel with the switching units (24, 26, 28), in particular with the half-bridges.

14. HP generator according to any one of the preceding claims, wherein an inverter (40) including a full bridge circuit (44) and a buck converter (46) is connected to the primary windings (PW1, PW2, PWn).

15. A method for providing high power pulses of different amplitudes provided by a high power (HP) generator (10) to a plasma process, comprising: a. continuously charging energy storage components (C1, L1) of a plurality of low power generators (14, 16, 18) to a respective predetermined value; b. selectively combining output values ​​of at least some of the LP generators (14, 16, 18) to obtain a desired output value of the HP generator (10) corresponding to a pulse having a desired amplitude by controlling the LP generators (14, 16, 18); c. selecting the contributions of the LP generators (14, 16, 18) sequentially through the LP generators (14, 16, 18); The method includes:

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