Dual plasma applicator for a plasma generator, plasma generator, plasma processing system, and method for igniting a plasma

Abstract

The invention relates to a dual plasma applicator (10) for a plasma generator (30) for igniting a plasma (22) in an ignition time period (61) and for maintaining the plasma (22) in a subsequent holding time period (62), the applicator (10) comprising: a) an electrode arrangement comprising at least one first electrode (12) and at least one second electrode (16), wherein b) a first electrical potential (14) can be applied to the first electrode (12) and a second electrical potential (18) can be applied to the second electrode (16) by a potential generating unit (32, 36) of the plasma generator (30), c) the first electrical potential (14) has a phase shift and / or an amplitude difference relative to the second electrical potential (18) at least during one of the time periods, and d) an absolute value of the phase shift during the ignition time period (61) is greater by a phase difference >0 than an absolute value of the phase shift during the holding time period (62), e) as a result of which an electric field generated by the electrodes (12, 16) in an inter-electrode space (20) is stronger during the ignition time period (61) than during the holding time period (62).

Description

[0001] Dual plasma applicator for a plasma generator, plasma generator, plasma processing system and method for igniting a plasma

[0002] The invention relates to a dual plasma applicator for a plasma generator, wherein the plasma applicator is particularly designed for igniting a plasma during an ignition time period and maintaining the plasma during a subsequent holding time period. Furthermore, the invention relates to a plasma generator for generating a plasma, which preferably comprises at least one dual plasma applicator, and to a plasma processing system, which preferably comprises at least one plasma generator. The invention further relates to a method for igniting a plasma.

[0003] Microwave-induced or capacitive plasma systems are frequently used in industrial applications such as materials processing or coating. A key challenge is the reliable and efficient ignition and maintenance of the plasma. Existing systems require high power levels to generate the plasma, which necessitates significant technological effort. Given that the power required to maintain the plasma is significantly lower, harmonizing the technological requirements in both phases would be desirable.

[0004] However, the challenge of meeting different power requirements for generating and maintaining the plasma remains.

[0005] Object of the invention

[0006] The invention is based on the object of improving the efficiency and / or reliability of plasma generation and maintenance in applications for machining workpieces using plasma.

[0007] The object is achieved by a dual plasma applicator according to claim 1, a plasma generator according to claim 6, a plasma processing system according to claim 12, and a method for igniting a plasma according to claim 15.

[0008] Some terms used in this application are explained below. An electrical potential, for example, a potential applied to an electrode, refers to a voltage difference relative to a ground potential, for example, relative to a wall of a plasma process chamber. This can be, in particular, an alternating voltage, in particular an alternating voltage at high frequencies, preferably at microwave frequencies above 300 MHz, particularly preferably above 2 GHz.

[0009] The term "approximately" means that some deviation, e.g., up to 1%, up to 3%, or up to 10%, from the characteristic designated "approximately" may exist. The term "predominantly," similar to "predominantly," means a frequency of occurrence of a characteristic that is close to 100%, e.g., 99.9% or 90% to 99%.

[0010] The punctuation mark (slash) is understood as "or".

[0011] The term "proximal" refers to the side facing a plasma applicator's plasma outlet; the term "distal" refers to the side facing a plasma applicator's gas inlet. The terms "proximal" and "distal" thus refer to the proximity and distance, respectively, of a plasma processing chamber.

[0012] One aspect of the invention relates to a dual, preferably two-phase plasma applicator for a plasma generator for igniting a plasma in an ignition time period and maintaining the plasma in a subsequent hold time period. Preferably, the ignition and hold period refers to a time period or a time interval that may or may not be periodic.

[0013] Preferably, the word "for" implies suitability of the applicator for a plasma generator or that the applicator is adapted for use in the plasma generator based on the functionality for igniting and maintaining a plasma in the respective phases.

[0014] The dual plasma applicator is a unit for a) introducing a gas to be ionized, b) ionizing the gas or generating a plasma in an ignition zone of the plasma applicator, c) coupling the plasma from the ignition zone into a plasma effective zone, where the plasma exerts its intended effect on a workpiece to be processed, and d) maintaining the plasma in the plasma effective zone. Preferably, the plasma applicator serves as an interface between a potential generation unit and the plasma effective zone, where a plasma processing process is carried out.

[0015] The ignition time period is the time during which the plasma is ignited in the ignition zone of the plasma applicator. A high electric field strength is generated in the ignition zone, which at least partially ionizes a gas introduced into the ignition zone and generates a plasma there.

[0016] The hold time is a time period during which the plasma or ionized gas generated during the ignition period is conveyed from the ignition zone into the plasma effective zone for processing a workpiece, such as surface treatment or material processing, and is maintained there in an ionized state. Maintaining the plasma generally requires a lower electric field strength than for ignition. Preferably, the ignition and hold time periods follow one another cyclically.

[0017] The dual plasma applicator can be considered as a plasma applicator configured to be operated differently in at least two time periods, with the ignition time period as the first time period and the hold time period as the second time period, wherein the term "dual" refers to the two time periods.

[0018] The plasma effective zone refers to an area around the plasma applicator in the interior of a plasma processing chamber, between the plasma applicator and a wall of the plasma processing chamber from which the plasma applicator protrudes, preferably vertically. In the plasma effective zone, the plasma exerts its intended effect on the workpiece to be processed, which is arranged within the plasma effective zone.

[0019] The ignition zone refers to an electrode gap in the plasma applicator in which the gas contained therein is ionized and converted into the plasma state.

[0020] The dual plasma applicator comprises an electrode arrangement comprising at least one first electrode and at least one second electrode. A first electrical potential can be applied to the first electrode and a second electrical potential can be applied to the second electrode by a potential generation unit.

[0021] The dual plasma applicator can also comprise a third electrode, to which a third electrical potential can be applied by a potential generation unit of the plasma generator. Analogously, further electrodes are conceivable.

[0022] Preferably, the potential generation unit refers to a technical device designed to generate a potential at the relevant electrode, such as a microwave generator or a voltage source.

[0023] The first electrical potential exhibits a phase shift and / or an amplitude difference relative to the second electrical potential at least in one of the time periods, preferably in the ignition time period. Accordingly, the first electrical potential preferably exhibits i) a phase shift or ii) an amplitude difference or iii) a phase shift and an amplitude difference relative to the second electrical potential.

[0024] An amount of the phase shift during the ignition time period is greater by a phase difference >0 than an amount of the phase shift during the holding time period, which means in particular that the two potentials do not reach their maximum or minimum value at the same time, so that in an electrode gap, which preferably forms an ignition region for the gas to be ionized, an E-field generated by the electrodes is stronger during the ignition time period than during the holding time period.

[0025] The phase shift is defined as follows: In a scenario with two time-varying, periodic or non-periodic potentials of the same or different waveforms, it is the temporal offset between i) the maxima, minima, or other characteristic points of the electrical potentials or ii) the times at which the correlation function of their temporal profiles reaches a maximum or minimum. In a scenario with one time-varying and one time-constant potential, the phase shift corresponds to the phase of the time-varying potential.

[0026] The amplitude difference is defined as the amplitude of the time-dependent difference between the two potentials.

[0027] The amplitude difference may i) be predominantly non-zero, possibly with the exception of zero transitions of the amplitude difference, and / or ii) be greater during the ignition period than during the hold period. Consequently, an electric field generated by the electrodes in the interelectrode space may be stronger during the ignition period than during the hold period.

[0028] Another aspect of the invention relates to a plasma generator for generating a

[0029] Plasmas. The plasma generator comprises: a) at least one dual plasma applicator, and b) a potential generation unit.

[0030] A plasma generator is a unit that creates the conditions required for generating and maintaining a plasma in the plasma applicator, e.g., by using microwaves or other methods for ionizing a gas.

[0031] Preferably, the potential generation unit refers to a technical device designed to generate the electrical potential at the relevant electrode, such as a microwave generator or a voltage source.

[0032] A further aspect of the invention relates to a plasma processing system comprising a) a plasma process chamber, preferably with a substrate carrier arranged therein for receiving a substrate for treatment with a plasma, and b) at least one plasma generator for generating the plasma.

[0033] A plasma processing system is a unit or system with one or more plasma generators for performing plasma processing processes such as coating, etching, or cleaning. The plasma effective area, in which the processing of a workpiece, for example, surface treatment or material processing, can be carried out, is preferably located within the plasma processing chamber.

[0034] Another aspect of the invention relates to a method for igniting a plasma during an ignition period and maintaining the plasma during a holding period. The ignition and maintenance of the plasma is carried out by means of a dual plasma applicator comprising a first electrode and a second electrode.

[0035] The method comprises: a) generating a first electrical potential and a second electrical potential, and b) applying the first electrical potential to the first electrode of the applicator and the second electrical potential to the second electrode of the applicator.

[0036] The first electrical potential exhibits a phase shift and / or an amplitude difference relative to the second electrical potential at least in one of the time periods. The magnitude of the phase shift during the ignition time period is greater than the magnitude of the phase shift during the holding time period by a phase difference > 0.

[0037] The features, mechanisms and effects associated with the described aspects of the invention are explained in more detail below.

[0038] Preferably, the decisive variable for the electric field generated in the ignition region during the ignition time period is the electric potential between the respective electrodes. This means that the electrodes carry electric charges represented by corresponding potentials. The potentials can be generated by the potential generation unit, which, for example, generates microwave signals directed at the electrodes. Different potentials or potential pairs can be applied to the electrodes at specified times or periods, e.g., +230 / -230V or +100 V / +20 V or -30 V / -180 V, which generate a corresponding voltage difference. As a result of this voltage difference, an electric field forms between the electrodes, creating the conditions for plasma formation.In particular, there is a functional relationship between the magnitude of the phase shift / amplitude difference and the strength of the electric field in the interelectrode space, with a larger phase shift / amplitude difference resulting in a stronger electric field (E-field). Thus, the larger phase shift / amplitude difference in the ignition period results in the electric field in the interelectrode space / ignition area being stronger during the ignition period than during the holding period, which promotes the ionization of the gas and thus the formation of plasma, without requiring a higher power requirement in one period than in the other.

[0039] Preferably, the E-field formed in the plasma effective region outside the ignition region during the holding period is based on a potential difference between the electrodes and the wall of a plasma processing chamber, which is normally conductive and grounded. This potential difference is sufficient to maintain the plasma ignited in the ignition region within the plasma effective region. In particular, the smaller phase shift in the plasma effective region during the holding period favors the formation of an E-field that is stronger than the E-field during the ignition period. Preferably, the applicator, in interaction with the wall of the plasma processing chamber, behaves like a monopole on a conductive plane during the holding period and like a dipole on a conductive plane during the ignition period.

[0040] Advantageously, the phase shift / amplitude difference between the electrical potentials at the plasma applicator electrodes causes the electric field to be stronger during the ignition period than during the hold period. This results in gas ionization and plasma generation occurring more efficiently during the ignition period. This requires less energy to generate and maintain the plasma, resulting in higher overall process efficiency.

[0041] Another advantage is that the ability to adjust the phase shift as needed allows the process to be flexibly adapted to different materials and requirements. This creates a high degree of flexibility and opens up possibilities for a wide range of applications. For example, this flexibility can be used to tailor the plasma for various surface treatments or material processing.

[0042] The phase shift / amplitude difference has the advantage of ionizing the plasma more intensively and evenly during the ignition period. This reduces unwanted fluctuations in plasma quality. This results in a more stable and higher-quality plasma, which improves the quality of the machining results.

[0043] The present concept solves a long-standing problem with conventional applicators, in which a voltage applied between the applicator and the plasma chamber to maintain the plasma is insufficient to ignite it, requiring a significantly higher voltage for ignition. The present concept solves this problem by making the phase difference / amplitude difference of the applied potentials between the electrodes larger in magnitude during the ignition period than during the hold period, while maintaining a constant power supply. In this document, the terms "phase difference" and "phase shift" are used interchangeably.

[0044] The efficient generation and maintenance of plasma based on the concepts of phase shift, amplitude difference, and potential difference enables a reduction in energy consumption. This contributes to lower operating costs and resource conservation and preferably allows for the use of simpler technical means, for example, by using microwave generators or lower-power voltage sources.

[0045] In the following, the invention is explained in more detail using exemplary embodiments and with reference to the drawings, in which:

[0046] Fig. 1a shows a schematic representation of a dual plasma applicator;

[0047] Fig. 1b a dual plasma applicator in a 3D view;

[0048] Fig. Ic-le embodiments of the dual plasma applicator in sectional view;

[0049] Fig. 2a- 2c embodiments of the plasma generator in schematic representation;

[0050] Fig. 2d shows a plasma generator in a sectional view;

[0051] Fig. 3a shows a plasma processing system in schematic representation;

[0052] Fig. 3b shows the ceiling area of ​​the plasma processing system in a 3D view; Fig. 3c shows the ceiling area of ​​the plasma processing system in a bottom view;

[0053] Fig. 4a-4d temporal courses of the potentials at the electrodes of the dual plasma applicator and the difference potential;

[0054] Fig. 5 shows a method for igniting a plasma in a block diagram.

[0055] The various embodiments, one or more examples of which are shown in each figure, are explained in more detail below. Each embodiment can be combined with any other embodiment, as far as this is technically reasonable and / or permissible. Features shown or described as part of one embodiment can be used in or together with another embodiment to obtain a further embodiment. In the following description of the drawings, like reference numerals refer to like or similar elements.

[0056] Fig. 1a shows a dual plasma applicator 10 for a plasma generator 30 for igniting a plasma 22 in an ignition time period 61 and for maintaining the plasma 22 in a subsequent holding time period 62. The applicator 10 comprises: a) an electrode arrangement comprising at least one first electrode 12 and at least one second electrode 16, wherein b) a first electrical potential 14 can be applied to the first electrode 12 and a second electrical potential 18 to the second electrode 16 by a potential generation unit 32, 36 of the plasma generator 30, wherein the dual plasma applicator 10 is particularly designed such that it can ignite the plasma 22 in the ignition time period 61 and maintain it in the holding time period 62 when c) the first electrical potential 14 is phase-shifted relative to the second electrical potential 18 by a phase shift,and d) an amount of the phase shift during the ignition time period 61 is greater by a phase difference >0 than an amount of the phase shift during the holding time period 62, e) whereby in an electrode gap 20 an E-field generated by the electrodes 12, 16 is stronger during the ignition time period 61 than during the holding time period 62.,

[0057] Fig. 1b shows an embodiment of the proximal half of the dual plasma applicator 10 according to the invention in a 3D view, and Figs. 1c-1e show sections through the plasma applicator 10. The electrodes 12, 16 can be designed as half-cylinders that lie opposite one another in a flat surface area. Advantageously, in this embodiment, a space is available within the half-cylinders that can be used for various purposes, e.g., to guide a portion of the microwaves generated by a microwave generator in the proximal direction into the plasma effective area and couple them there in order to increase the degree of ionization of the plasma present in the plasma effective area through direct action of the microwaves.

[0058] The plasma applicator 10 according to Fig. 1a-1e enables the transmission of microwaves from a waveguide / coaxial cable arranged outside the plasma processing system into the plasma effective area 50. According to one embodiment, the plasma applicator 10 may comprise:

[0059] - the electrodes 12, 16, which form a conductive, axially split, central core, wherein the core extends along a longitudinal axis of the plasma applicator 10 and the core halves lie opposite each other in a flat surface area

[0060] - a conductive outer shield 15 surrounding the central core

[0061] - a first / second coupling connection 19 / 21 for coupling the first / second electrode 12 / 16 to a waveguide, a hollow guide or a coaxial cable which carries the microwaves generated by a microwave generator 32

[0062] - a propagation medium 17, for example air, arranged between the central core and the outer shield 15 for propagating the microwaves from the coupling connection 19, 21 to the plasma effective area 52,

[0063] - an insulator 13 made of dielectric material permeable to microwave energy.

[0064] According to one embodiment, the shield 15 may surround the central core and / or the propagation medium 17 and preferably has the shape of a hollow sleeve closed at a distal end by a bottom wall and open at the opposite proximal end to discharge into the plasma processing chamber 50 (not shown). The open proximal end may be closed by the insulator 13 and have an outer surface designed to come into contact with a gas present in the plasma processing chamber 50 and to be excited. The gas supply 23 may be provided laterally or from the distal end.

[0065] Particularly preferably, the electrical potentials 14, 18, in particular the microwave signals, are guided to the applicator electrodes 12, 16 with a field-limiting power, in particular with a shielded line, preferably with a coaxial line 11.

[0066] According to one embodiment, the shield 15 may provide a structural boundary for the plasma applicator 10, which contributes to effective microwave propagation / transmission within the plasma applicator 10 and / or prevents energy losses to the outside.

[0067] According to one embodiment, Fig. 1e, the insulator can be arranged at the proximal end of the plasma applicator, comprise a dielectric material transparent to microwaves, and have an outer side that forms a boundary to the plasma active region 50 and to the gas to be excited in the plasma active region 50. The insulator can project beyond the shield by a length that is less than or equal to the inner diameter of the shield at its proximal end. The diameter of the outer side can decrease continuously along the main axis of the plasma applicator toward the proximal end of the plasma applicator and can be truncated conically, for example.

[0068] According to one embodiment (Fig. 1c, 1d), the insulator may have an inner surface in contact with the propagation medium, which is completely surrounded by the shield and penetrated by the central core and / or serves to seal the proximal end of the plasma applicator and / or ensure the separation of the propagation medium from the plasma effective region 52 and / or maintain the integrity of the plasma applicator and ensure that the microwaves are efficiently transmitted into the plasma effective region 52.

[0069] According to one embodiment (Fig. 1b, 1e), the outer shield may have a proximal end defined by the insulator made of a microwave-transparent dielectric material and having an outer surface intended to come into contact with a plasma located in the plasma action region 52. The outer surface has a rotational symmetry about the longitudinal axis of the plasma applicator, with the insulator protruding from the shield along the major axis in the proximal direction and / or having an outer diameter that decreases along the major axis from the shield to its tip.Preferably, the insulator penetrates into the interior of the plasma effective area 52, and its non-planar outer surface makes it possible to generate a plasma volume controlled by the shape of this outer surface itself, thus ensuring a smooth transition between the impedance of the insulator and the impedance of the plasma, which allows a reduction of the reflected power.

[0070] In particular, the insulator tapers in the proximal direction and in a region at the proximal end of the plasma applicator, i.e. where it enters the interior of the gas to be ionized, in order to improve the transition between the impedance of the insulator and the impedance of the plasma.

[0071] According to one embodiment, the outer diameter of the outer side of the insulator may decrease continuously along the main axis in the proximal direction.

[0072] Preferably, the outer surface does not have a discontinuous change in diameter, i.e. it does not have a step, staircase or notch, but the insulator has a continuous outer surface up to its tip in order to improve wave transmission.

[0073] According to one embodiment, the outer surface of the insulator may be approximately frustoconical in two alternatives: the outer surface of the insulator has a generally frustoconical shape that is truncated at its end and has a flat or rounded tip (Fig. 1b, le); or the outer surface of the insulator has a generally frustoconical shape that is not truncated at its end and has a sharp tip.

[0074] According to one embodiment, the outer side of the insulator may have an approximately hemispherical shape or may not have any right-angled edges.

[0075] According to one embodiment (Fig. 1d, le), the proximal end of the central core may be embedded in the insulator without completely penetrating the insulator.

[0076] According to one embodiment (Figs. 1b, 1c), the proximal end of the central core can protrude from the shield in the direction of the main axis. This allows the central core to be longer than the shield. According to one embodiment (Figs. 1b, 1e), the insulator and the shield can be rotationally symmetrical about a common main axis, and the maximum outer diameter of the insulating body can be approximately equal to or larger than the outer diameter of the shield.

[0077] According to one embodiment, the insulator may have an inner surface in contact with the propagation medium and penetrated by the central core, wherein the inner surface is not planar and not orthogonal to the main axis.

[0078] According to one embodiment, the inner surface of the insulator may be approximately frustoconical.

[0079] According to one embodiment (Fig. 1b, 1e), the insulator may protrude outward along the longitudinal axis by a distance less than or equal to the inner diameter of the shield at its proximal end. Thus, the insulator protrudes beyond a limited distance, less than or equal to its own outer diameter at the proximal end of the shield, to facilitate the penetration of microwave energy, i.e., to reduce losses and reflections during transmission.

[0080] According to one embodiment, the electrodes 12, 16 can be designed as opposing, particularly flat, plates. This can, in particular, enable the generation of a high electric field and / or plasma with uniform distribution.

[0081] According to the following three embodiments, the insulator can be constructed in the axial direction a) as a single-layer insulator 13 (Fig. 1e), b) as a two-layer insulator 13, 13a (Fig. 1c), or c) as a three-layer insulator 13, 13b, 13a (Fig. 1d). The dielectric constant of each layer can differ from the dielectric constants of the other layers. An insulator with different dielectric constants, whether two- or three-layer, is preferably capable of influencing the propagation of microwaves in such a way that reflections at interfaces between different media are reduced and impedance matching is enabled. According to one embodiment, the insulator 13 can comprise quartz, aluminum oxide, and / or boron nitride and can enable a connection between the propagation medium 17 and the interior of the plasma processing chamber 50.The insulator 13 can, on the one hand, enable the transport of the microwaves in the direction of the plasma process chamber 50 and, on the other hand, ensure the sealing between the propagation medium 17 and the interior of the plasma process chamber 50, in which a pressure reduced compared to the atmospheric ambient pressure usually prevails.

[0082] According to one embodiment, an outer surface of the insulator 13 may be flat, regardless of whether the plasma applicator 10 with the central core completely penetrates the insulator 13 and protrudes from it (Fig. 1c) or whether the central core penetrates the insulator 13 and ends flush with the outer surface (Fig. 1d, 1e).

[0083] According to one embodiment, the coupling port may be connected to a microwave generator via a coaxial cable or a waveguide and / or may have a coaxial structure comprising an outer conductor connected to the shield of the plasma applicator and surrounding an inner conductor connected to the central core.

[0084] According to one embodiment (Fig. 1c-1e), the coupling port can enable transmission of microwave energy from the microwave generator, thereby enabling generation and maintenance of the plasma in the plasma effective region 50. The coaxial structure of the coupling port contributes to reducing energy losses.

[0085] According to one embodiment (Fig. 1c-1e), the coupling port can be connected to a microwave generator via a coaxial cable or a waveguide and / or have a coaxial structure with an outer conductor connected to the shielding of the plasma applicator and surrounding an inner conductor connected to the central core. Preferably, the inner conductor, without an outer conductor, extends perpendicular to the longitudinal axis of the plasma applicator through the propagation medium running along the longitudinal axis and terminates approximately perpendicularly in the central core.

[0086] Preferably, according to this embodiment, the inner conductor can a) open directly into the central core, whereby the inner conductor can transmit microwave energy into the central core, i.e. to the electrodes 12, 16, which enables a focused transmission of the microwaves and is essential for the generation of the potentials 14, 18 at the electrodes 12, 16, and thus for the generation / maintenance of the plasma, and / or b) axially in the proximal direction guide the microwaves through the propagation medium into the plasma effective region and couple them in there in order to increase the degree of ionization of the plasma present in the plasma effective region through the direct action of the microwaves.

[0087] According to one embodiment, the phase difference may be greater than 45°, greater than 90°, greater than 135°, or equal to 180°. This may, in particular, result in the E-field generated in the interelectrode space / ignition region 20 during the ignition time period 61 increasing in strength with increasing phase difference compared to the holding time period 62, thereby achieving increasingly more efficient plasma generation and maintenance.

[0088] According to one embodiment, the phase shift can have a value of 1° to 180° or from -1° to -180°. This can particularly improve the adaptability of the dual plasma applicator, allowing the plasma generation process to be precisely adapted to different requirements and materials.

[0089] According to one embodiment, the phase shift may be i) + / - 180° during the ignition time period 61 of the plasma 22 and / or ii) 220° during the holding time period 62 of the plasma.

[0090] This can in particular help to achieve maximum energy efficiency for the ignition and maintenance of the plasma within the framework of available resources.

[0091] According to one embodiment, the electrodes 12, 16 can each comprise an electrically conductive material, preferably a metal, or can be at least partially formed from a metal. This can, in particular, enable good conduction of electrical potentials and efficient / reliable generation of the electric field required for plasma generation. According to one embodiment, the electrodes 12, 16 can each comprise: a thin metal layer, whereby a strong electric field or a plasma with good conductivity can be generated, or a metal foil, whereby a less strong electric field or a broader and less concentrated plasma can be generated, or a metal grid, whereby a uniform electric field or a flat and evenly distributed plasma can be generated, or a conductive polymer layer, whereby a plasma with lower conductivity can be generated.

[0092] According to one embodiment, the electrodes 12, 16 can be designed as mutually parallel plates, whereby preferably an elongated plasma can be generated, since the plasma spreads along the plates, or can be designed as curved plates, whereby preferably a concentrated plasma with a pronounced energy density (in the case of concave plates) or an extended plasma with a lower energy density (in the case of convex plates) can be generated.

[0093] According to one embodiment, the first electrode 12 can be designed as a hollow cylinder, and the second electrode 16 as a pin arranged within the hollow cylinder, preferably along the cylinder's axis of symmetry. This can, in particular, enable a concentration of the electrical discharge along the cylinder's axis of symmetry and thus precise and controlled plasma generation in this region.

[0094] According to one embodiment, the electrodes 12, 16 can each be surrounded by an insulator. Advantageously, the insulator can stabilize the plasma, particularly during the hold time period 62, by preventing unwanted electrical discharges to other components.

[0095] According to one embodiment, the electrode arrangement 12, 16 can have a T-shaped cross-section and preferably end faces facing the microwave generators 32 and receiving microwave signals 34. Advantageously, the end face 24 of the T-structure can be used to couple microwave signals 34. Such an arrangement is shown, for example, in Fig. 2c. According to one embodiment, the electrode gap 20 can form an electrode channel through which a gas can be supplied from outside the applicator 10. This can, in particular, enable a demand-based gas supply to the plasma.

[0096] According to one embodiment, the gas in the electrode channel can be or is converted into a plasma 22 during the ignition time period 61. This can, in particular, enable efficient operation of the applicator.

[0097] According to one embodiment, the plasma 22 can be conveyed through the electrode channel into an interior region of a plasma processing chamber 52 during the holding time period 62. This can, in particular, enable a targeted introduction of the plasma into the plasma effective area in which the processing or treatment of the workpiece by the plasma takes place.

[0098] According to one embodiment, the plasma 22 can be conveyed or can be conveyed during the holding period 62 by a magnetic field generated by electrodes 12, 16 or by the supplied gas through the electrode channel into an interior region of a plasma processing chamber 52. This can, in particular, enable a targeted supply of the plasma into the desired area of ​​the plasma effective zone and thus a precise placement and alignment of the plasma, which can be advantageous for applications in which the plasma must be applied in specific areas of a workpiece to achieve the desired processing effects.

[0099] According to one embodiment, a minimum distance between the first and second electrodes 12, 16 may be smaller than a predetermined threshold to enable a concentrated E-field between the electrodes 12, 16. Advantageously, this allows the E-field strength to be concentrated in a spatial area between the electrodes 12, 16, rather than being distributed over a larger area.

[0100] According to one embodiment, with periodically oscillating potentials 14, 18, the minimum distance between the first and second electrodes 12, 16 can be approximately an integer multiple of half the wavelength. This can, in particular, enable adaptation of the electrical potentials 14, 18 to the resonance conditions of the interelectrode gap 20, thereby improving energy transfer to the gas, which can lead to more efficient and stable plasma generation.

[0101] According to one embodiment, a temporal profile Q1(t) of the first electrical potential 14 can be temporally variable, preferably with temporal periodicity. The following can apply to the temporal profile Q2(t) of the second electrical potential 18: i) during the ignition time period 61, Q2(t)=constant, preferably Q2(t)=0, and ii) during the holding time period 62, Q2(t)=Q1(t).

[0102] As a result, preferably i) during the ignition time period 61, a potential difference between the potentials 14, 18 corresponding to the curve Ql (t) can generate an E-field strength in the electrode gap 20 that changes over time according to the curve Ql (t), and ii) during the holding time period 62, a potential corresponding to the curve Q2(t) = Ql (t) at both electrodes 12, 16 can generate an E-field that is different from zero only outside the electrode gap 20, i.e. in the plasma effective range.

[0103] According to one embodiment, the curve Q1(t) of the first electrical potential 14 can be rectangular, for example, where Q1(omega*t)=(sign(sin(omega*t))+1) / 2 or Q1(t)=sign(sin(omega*t)), with a frequency = omega. Preferably, the curve Q2(t) of the second electrical potential 18 can be rectangular, for example, Q2(t)=Q1(omega*t+phi), with a phase shift = phi. Here, the signum function sign(x) is defined as follows: sign(x) = 1 if x > 0, = 0 if x = 0, = -1 if x < 0.

[0104] Preferably, this can increase the time of maximum phase shift between Ql and Q2 and thus also the energy density in the ignition region.

[0105] Fig. 2a shows a plasma generator 30 for generating a plasma 22, comprising: a) at least one dual plasma applicator 10, and b) a potential generation unit 32, 36.

[0106] The potential generation unit 32, 36 can be configured to enable the generation of the electrical potentials 14, 18, wherein the prior art provides several possibilities for implementing this functionality, which are known to those skilled in the art. According to an embodiment shown in Fig. 2b, the potential generation unit can comprise at least one microwave generator 32 for generating microwave signals 34. The microwave signals 34 can be directed to the first and second electrodes 12, 16, respectively, in order to apply a first electrical potential 14 to the first electrode 12 and a second electrical potential 18 to the second electrode 16.

[0107] When the microwave signals strike the electrodes 12, 16, the electromagnetic fields of the microwaves can preferably induce currents in the electrodes 12, 16, which in turn generate the electrical potentials 14, 18. These can generate an electric field between the electrodes, leading to the ionization of the gas between them and thus to the formation of plasma.

[0108] According to one embodiment, the microwave generator 32 may include: a solid state power amplifier (SSPA) and / or a solid state power generator (SSPG) that has a high efficiency and a compact design, and / or a circulator that directs the microwave energy in a specific direction and thus protects the SSPA or SSPG from reflected radiation that could damage the device, and / or an isolator that separates the SSPA or SSPG from the load and thus prevents the load from affecting the performance of the SSPA or SSPG, and / or a filter that removes unwanted frequencies from the microwave signal in order to adapt the signal to the requirements of the plasma generation.

[0109] According to one embodiment, the plasma generator 30 may include a splitter. Advantageously, the splitter may be connectable to an output of the microwave generator 32 to split the microwave signal generated by the microwave generator 32 into two microwave signals 34.

[0110] According to one embodiment, the plasma generator 30 can comprise a phase shifter for generating the phase shift, wherein one of the microwave signals 34 can be fed to the phase shifter 38. Advantageously, two microwave signals 34 that are phase-shifted from one another by the phase shift can thereby be generated by the microwave generator 32.

[0111] According to one embodiment, the plasma generator 30 can comprise two microwave generators 32, which are configured to generate two microwave signals 34 that are phase-shifted relative to one another by the phase offset. Advantageously, an implementation with two microwave generators 32 with a specific total power P is more cost-effective than with one microwave generator with the power P.

[0112] According to one embodiment, a first of the two microwave signals 34 can be directed to the first electrode 12, and a second of the two microwave signals 34 can be directed to the second electrode 16. Advantageously, the first and second electrical potentials 14, 18 can thereby be applied to the first and second electrodes 12, 14.

[0113] According to one embodiment, the plasma generator 30 may include at least one antenna for directing the microwave signals 34 generated by the microwave generators 32 toward the first and second electrodes 12, 16 to enable effective transmission of the microwave signals 34 to the electrodes 12, 16. This advantageously enables bundling / focusing of the microwave signals 34 onto the electrodes 12, 14.

[0114] According to one embodiment, the frequency of the microwave signals 34 can be approximately 2450 MHz. This frequency is advantageous for plasma generation because, on the one hand, it lies in the ISM band for industry, science, and medicine, and, on the other hand, it can generate a plasma with high density and high homogeneity.

[0115] According to an embodiment of the plasma generator 30 shown in Fig. 2c, the potential generation unit may comprise a voltage source 36 electrically coupled to the first and second electrodes 12, 16 for applying a first electrical potential 14 to the first electrode 12 and a second electrical potential 18 to the second electrode 16.

[0116] Preferably, the voltage source 36 can apply the electrical potentials 14, 18 to the first and second electrodes 12, 16. The potentials 14, 18 can generate an electric field between the electrodes 12, 16. This field enables the ionization of the gas in the interelectrode space 20 of the plasma applicator 10 and thus the generation of the plasma 22.

[0117] According to one embodiment, the voltage source 36 may comprise i) a conventional AC voltage source for generating a conventionally generated electrical potential pair having a first and a second electrical primary potential, wherein the primary potentials are 180° out of phase, and ii) a phase shifter 38, such as an RC phase shifter network, wherein the phase shifter 38 is connected to one of the two primary potentials.

[0118] This allows the phase shift determined by the phase shifter 38 to be generated between a potential provided by the phase shifter 38 and the other of the two primary potentials. Advantageously, the use of the conventional voltage source allows for the use of proven and cost-effective products.

[0119] According to one embodiment, the plasma generator 30 may include a controller for controlling or regulating the microwave generators 32 with respect to the power, frequency, phase, and / or timing of the microwave signals 34. Advantageously, this allows the operating conditions for the plasma generator 30 to be adjusted.

[0120] According to one embodiment, the controller of the plasma generator 30 can be configured to synchronize the microwave generators 32 in phase and / or frequency. This advantageously allows the operating conditions, particularly with regard to the phase shift of the microwave signals 34, for the plasma generator 30, preferably including the dual plasma applicator 20, to be adjusted.

[0121] According to one embodiment, the controller of the plasma generator 30 can be configured to control or regulate the voltage source with respect to the amplitude, frequency, phase, and / or timing of the provided potentials 14, 18. Advantageously, this allows the operating conditions, in particular with respect to the phase shift of the potentials 14, 18, for the plasma generator 30 to be adjusted, preferably including the dual plasma applicator 20. According to an embodiment of the plasma generator 30 shown in Fig. 2d, the microwaves generated by the microwave generator 32 can be coupled to the electrodes 12, 16 of the plasma applicator 10 via supply connections 58 arranged on a base plate 54 of the plasma process chamber 52.

[0122] Fig. 3a shows a plasma processing system 50 comprising a) a plasma process chamber 52, preferably with a substrate carrier arranged therein for receiving a substrate for treatment with a plasma 22, and b) at least one plasma generator 30 for generating the plasma 22.

[0123] According to one embodiment, the electrodes 12, 16 of the plasma applicator 10 are spaced apart by a distance A, which is preferably adjusted to enable reliable ignition in the interelectrode space, here: ignition region 20. According to one embodiment, a non-insulated free end of an electrode 12, 16 and a reference ground of the plasma process chamber 52 are spaced apart by a minimum distance B, which is preferably not exceeded to enable reliable maintenance of the plasma in the plasma effective region 52.

[0124] Furthermore, a ceiling area of ​​the plasma processing system 50 is shown in a 3D view, Fig. 3b, and in a bottom view, Fig. 3c.

[0125] According to the embodiment shown in Fig. 3c, the plasma processing system 50 may include a base plate 54 for receiving the at least one plasma generator 30. The base plate 54 may be arranged on an upper side of the plasma processing chamber 52 and may enable a separation of the exterior space from the plasma processing chamber.

[0126] A microwave generator 32 can be arranged on the base plate 54. This can be designed as a semiconductor power amplifier (SSPA) or a semiconductor power generator (SSPG). Compared to a magnetron array / tube amplifier, the semiconductor-based power amplifier has the advantage of high efficiency and a small and compact design, making it particularly suitable for the present application. Preferably, the plasma generator can generate the plasma 22, which is guided into the process chamber 52. There, the plasma 22 can interact with the substrate on the substrate carrier for various treatments such as etching or coating.

[0127] Advantageously, by the targeted phase shift between the potentials 14, 18 at the electrodes 12, 16 of the applicator 10 of the plasma generator 30, the plasma 22 can be ignited with a weaker E-field compared to conventional solutions, whereby the power requirements on the components of the plasma processing system 50 and / or the resource consumption can be reduced.

[0128] According to one embodiment, the plasma processing chamber 52 may comprise a wall having a constant potential, in particular ground potential. Preferably, the components of the plasma processing system 50, for example, the dual plasma applicator 10, may be electrically insulated from the wall.

[0129] According to one embodiment, the at least one plasma generator 30 may comprise several, preferably 5 to 10, particularly preferably up to 20, in particular up to 40 microwave generators 32.

[0130] According to one embodiment, the controller of the plasma generator 30 can be designed to carry out the transition from the ignition time period 61 to the holding time period 62 i) immediately after the plasma ignition, preferably in response to a sensor message, or ii) with a time delay, optionally iii) in one step, or iv) in several steps.

[0131] Advantageously, the transition can be

[0132] Option i) contribute to rapid stabilization of the plasma, in accordance with

[0133] Option ii) give the plasma more time to stabilize in the ignition time period 61 before entering the holding time period 62, according to

[0134] Option iii) be easier to implement and control, and option iv) allow better control of the plasma properties through stepwise adjustment of the electrical potentials and phase shifts, which may lead to a higher quality plasma.

[0135] According to one embodiment, the controller of the plasma generator 30 can be configured to vary the frequency of the potentials 14, 18 or the electromagnetic field in the inter-electrode space 20 of the dual plasma applicator 10 to compensate for fluctuations in the dimensions of the plasma processing chamber 52 in order to maintain the resonator properties of the plasma processing chamber 52. Advantageously, this can help maintain optimal resonance conditions for plasma generation and maintenance, thus ensuring consistent plasma quality, even if the chamber dimensions deviate from the specified values ​​due to factors such as thermal expansion, wear, or manufacturing tolerances.

[0136] Figures 4a to 4d show the temporal profiles of the electrical potentials 14, 18 at the electrodes 12, 16 of the dual plasma applicator 10 and of the differential potential 18d, which is formed from the difference between the first electrical potential 14 and the second electrical potential 18. This shows how the temporal profiles of the first and second electrical potentials 14, 18 in the ignition phase 61 and the holding phase 62 and the phase shift / amplitude difference between the first and second electrical potentials 14, 18 in the ignition phase 61 and the holding phase 62 affect the temporal profile of the differential potential 18d.

[0137] Fig. 5 shows a block diagram of the method 100 for igniting a plasma 22 during an ignition time period 61 and maintaining the plasma 22 during a holding time period 62 by means of a dual plasma applicator 10 comprising a first electrode 12 and a second electrode 16. The method comprises: a) generating 102 a first electrical potential 14 and a second electrical potential 18, and b) applying 104 the first electrical potential 14 to the first electrode 12 of the applicator 10 and the second electrical potential 18 to the second electrode 16 of the applicator 10. The first electrical potential 14 has a phase shift and / or an amplitude difference with respect to the second electrical potential 18 at least in one of the time periods, wherein an amount of the phase shift during the ignition time period 61 is greater by a phase difference >0 than an amount of the phase shift during the holding time period 62. is.

[0138] According to one embodiment, the phase difference may be greater than 45°, greater than 90°, greater than 135°, or equal to 180°. According to another embodiment, the phase shift may have a value from 1° to 180° or from -1° to -180°. According to one embodiment, the phase shift may be i) + / - 180° during the ignition time period 61 of the plasma 22 and / or ii) 220° during the holding time period 62 of the plasma.

[0139] The advantageous effects of these embodiments are described in the sections of this document relating to the dual plasma applicator 10.

[0140] According to one embodiment, the method may comprise igniting a plasma 22 in an electrode gap 20 between the first and second electrodes 12, 16 of the applicator 10. Advantageously, due to the greater phase difference between the potentials 14, 18 applied to the electrodes 12, 16 in the ignition time period 61 compared to the holding time period 62, a lower microwave power or voltage may be required to ignite the plasma 22 compared to conventional solutions.

[0141] According to one embodiment, the method may include supplying gas to be converted into plasma 22 into the electrode gap 20, particularly during the holding time period 62. This may enable plasma resupply and preferably contribute to a distribution of the plasma 22 in a space of a plasma processing chamber 52 outside the applicator 10.

[0142] According to one embodiment, the ignition time period 61 and the holding time period 62 can alternate periodically. This cyclical nature can ensure that the plasma in the plasma effective region remains stable over time, since fresh plasma is introduced into the plasma effective region with each ignition time period 61, compensating for possible recombination effects.

Claims

Claims 1. Dual plasma applicator (10) for a plasma generator (30) for igniting a plasma (22) in an ignition time period (61) and for maintaining the plasma (22) in a subsequent holding time period (62), the applicator (10) comprising: a) an electrode arrangement comprising at least one first electrode (12) and at least one second electrode (16), wherein b) a first electrical potential (14) can be applied to the first electrode (12) and a second electrical potential (18) can be applied to the second electrode (16) by a potential generation unit (32, 36) of the plasma generator (30), c) the first electrical potential (14) has a phase shift and / or an amplitude difference with respect to the second electrical potential (18) at least in one of the time periods, and d) an amount of the phase shift during the ignition time period (61) is greater by a phase difference >0 than an amount of the phase shift during the Holding period (62),e) whereby in an electrode gap (20) an E-field generated by the electrodes (12, 16) is stronger during the ignition time period (61) than during the holding time period (62)., 2. The dual plasma applicator (10) of claim 1, wherein the phase difference is greater than 45°, or greater than 90°, or greater than 135°, or equal to 180°; and / or the phase difference has a value from 1° to 180° or from -1° to -180°, or i) is + / - 180° during the ignition time period (61) of the plasma (22) and / or ii) is 0° during the hold time period (62) of the plasma (22); and / or the amplitude difference is i) predominantly non-zero and / or ii) greater during the ignition time period (61) than during the hold time period (62).

3. Dual plasma applicator (10) according to claim 1 or 2, wherein the electrodes (12, 16) each comprise an electrically conductive material, preferably a metal, for example a thin metal layer, a metal foil, a Metal grid and / or a conductive polymer layer, and / or the electrodes (12, 16) are formed at least partially from a metal; the electrodes (12, 16) are designed as opposing, preferably flat, in particular parallel to one another, optionally curved plates, and / or the electrodes (12, 16) are designed as half-cylinders that lie opposite one another in a flat surface area; and / or the first electrode (12) is designed as a hollow cylinder and the second electrode (16) is designed as a pin that is arranged within the hollow cylinder, preferably along the axis of symmetry of the cylinder; and / or the electrodes (12, 16) are each surrounded by an insulator (13).

4. Dual plasma applicator (10) according to one of the preceding claims, wherein the electrode gap (20) forms an electrode channel through which a gas can be supplied from an outer region of the applicator (10), wherein the gas can preferably be converted into a plasma (22) in the electrode channel during the ignition time period (61), in particular wherein the plasma (22) can be conveyed through the electrode channel into an inner region of a plasma process chamber (52) during the holding time period (62), in particular by a magnetic field generated by electrodes (12, 16) or by the supplied gas;and / or a minimum distance (A) between the first and second electrodes (12,16) i) is smaller than a predetermined threshold value to enable a concentrated E-field between the electrodes (12,16), whereby preferably the E-field strength is concentrated in a spatial area between the electrodes (12,16) instead of being distributed over a larger area, and / or ii), in the case of periodically oscillating potentials (14,18), is approximately an integer multiple of half the wavelength.; 5. Dual plasma applicator (10) according to one of the preceding claims, wherein the course of the potentials (14, 18) is periodic, and / or the course of the potentials (14, 18) has the same or possibly different waveform, and / or the waveform of the potentials (14, 18) varies periodically; and / or the course Ql(t) of the first electrical potential (14) varies over time, preferably with temporal periodicity, and for the course Q2(t) of the second electrical potential (18) over time i) during the ignition time period (61) Q2(t)=constant, preferably Q2(t)=0, and ii) during the holding time period (62) the second potential (18) has the same waveform as the first potential (14) and in particular Q2(t)=Ql(t); and / or the curve Ql(t) of the first electrical potential (14) is rectangular, for example Ql(omega*t)=(sign(sin(omega*t))+l) / 2 or Ql(t)=sign(sin(omega*t)), with a frequency = omega, wherein preferably the curve Q2(t) of the second electrical potential (18) is rectangular, for example Q2(t)=Ql(omega*t+phi), with a phase shift = phi.

6. Plasma generator (30) for generating a plasma (22), comprising: a) at least one dual plasma applicator (10) according to one of the preceding claims, and b) a potential generation unit (32, 36).

7. The plasma generator (30) according to claim 6, wherein the potential generation unit (32, 36) is configured to apply a first electrical potential (14) to the first electrode (12) and a second electrical potential (18) to the second electrode (16); and / or the potential generation unit comprises at least one microwave generator (32) for generating microwave signals (34), each directed toward the first and second electrodes (12, 16), for applying a first electrical potential (14) to the first electrode (12) and a second electrical potential (18) to the second electrode (16); and / or the potential generation unit comprises a voltage source (36) electrically coupled to the first and second electrodes (12, 16) for applying a first electrical potential (14) to the first electrode (12) and a second electrical potential (18) to the second electrode (16).

8. Plasma generator (30) according to claim 7, wherein the at least one microwave generator comprises two microwave generators (32) configured to generate two microwave signals (34) that are phase-shifted from one another by the phase shift; and / or the plasma generator (30) comprises a splitter, and in particular a phase shifter, wherein the splitter is preferably connectable to an output of the microwave generator (32) in order to split the microwave signal generated by the microwave generator (32) into two microwave signals (34), wherein, for example, one of the microwave signals can be fed to the phase shifter, whereby two microwave signals (34) that are phase-shifted from one another by the phase shift can be generated by the microwave generator (32); and / or a first of the two microwave signals (34) is directed toward the first electrode (12), and a second of the two microwave signals (34) is directed toward the second electrode (16).

9. Plasma generator (30) according to one of the preceding claims 7 to 8, wherein the plasma generator (30) comprises at least one antenna for directing the microwave signals (34) generated by the microwave generators (32) toward the first and second electrodes (12, 16) to enable effective transmission of the microwave signals (34) to the electrodes (12, 16); and / or the plasma generator (30) comprises a controller for controlling or regulating the microwave generators (32) with regard to power, frequency, phase, and / or timing of the microwave signals (34), preferably for synchronizing the microwave generators (32) with regard to phase and / or frequency.

10. Plasma generator (30) according to one of the preceding claims 7 to 9, wherein the voltage source (36) comprises i) a conventional AC voltage source for generating a conventionally generated electrical potential pair having a first and a second electrical primary potential, wherein the primary potentials are in antiphase, and ii) a phase shifter (38), such as an LC or RC phase shifter network, wherein the phase shifter (38) is connected to one of the two primary potentials, so that between a potential provided by the phase shifter (38) and the other of the two Primary potentials which can be generated with a phase shift determined by the phase shifter (38); and / or the controller is designed to control or regulate the voltage source with regard to amplitude, frequency, phase and / or time behavior of the potentials provided (14, 18).

11. Plasma generator (30) according to one of the preceding claims 6 to 10, wherein the control is designed to control the transition from the ignition time period (61) to the Holding time period (62) i) immediately after the plasma ignition, preferably in response to a sensor message, or ii) with a time delay, optionally iii) in one step, or iv) in stages.

12. Plasma processing system (50) comprising a) a plasma process chamber (52), preferably with a substrate carrier arranged therein for receiving a substrate for treatment with a plasma (22), and b) at least one plasma generator (30) according to one of the preceding claims 6 to 11 for generating the plasma (22).

13. Plasma processing system (50) according to claim 12, further comprising: a base plate (54) for receiving the at least one plasma generator (30), wherein the base plate (54) can be arranged on an upper side of the plasma processing chamber (52); 14. Plasma processing system (50) according to one of the preceding claims 12 to 13, wherein the control of the plasma generator (30) is designed to change the frequency of the electromagnetic field in the electrode gap (20) of the dual plasma applicator (10) in order to compensate for deviations in the dimensions of the plasma processing chamber (52) in order to maintain the resonator property of the plasma processing chamber (52).

15. A method (100) for igniting a plasma (22) during an ignition time period (61) and maintaining the plasma (22) during a holding time period (62) by means of a dual plasma applicator (10), in particular according to one of the preceding claims 1 to 5, comprising a first electrode (12) and a second electrode (16), the method comprising: a) generating (102) a first electrical potential (14) and a second electrical potential (18), b) applying (104) the first electrical potential (14) to the first electrode (12) of the applicator (10) and the second electrical potential (18) to the second electrode (16) of the applicator (10), wherein - the first electrical potential (14) has a phase shift and / or an amplitude difference with respect to the second electrical potential (18) at least in one of the time periods, and - an amount of the phase shift during the ignition time period (61) is greater than an amount of the phase shift during the holding time period (62) by a phase difference >0.

16. The method according to claim 15, wherein the phase difference is greater than 45°, or greater than 90°, or greater than 135°, or equal to 180°; and / or the phase shift has a value from 1° to 180° or from -1° to -180 and preferably i) is + / - 180° during the ignition time period (61) of the plasma (22) and / or ii) is 0° during the hold time period (62) of the plasma (22); and / or the amplitude difference is i) predominantly not equal to zero and / or ii) greater during the ignition time period (61) than during the hold time period (62).

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