WO2021245289A1

WO2021245289A1 - Measuring probe for measuring variables characteristic for a plasma

Info

Publication number: WO2021245289A1
Application number: PCT/EP2021/065154
Authority: WO
Inventors: Thorben BRENNER; Klaus Vissing
Original assignee: Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung eingetragener Verein
Priority date: 2020-06-05
Filing date: 2021-06-07
Publication date: 2021-12-09
Also published as: EP4162517A1; DE102020115056A1

Abstract

According to the invention, a measuring probe (100) for measuring variables characteristic for a plasma is provided, the measuring probe having a probe body (110) with a probe head (120), the probe body extending along a longitudinal axis of the measuring probe and being adapted to be inserted, with the probe head, in the plasma in order to measure variables that are characteristic for a plasma. The measuring probe further has a measuring electrode (101) which is arranged on the probe head, the probe body providing an electrical connection (102) between the measuring electrode and the probe head along a part of the measuring probe lying opposite the probe head along the longitudinal axis. The measuring probe also has a dielectric cap (103) which extends over the measuring electrode and is designed to isolate the measuring electrode from the plasma. The measuring probe is configured to generate an electric opposing field which repels negative charge carriers from the probe head.

Description

Measuring probe for measuring parameters characteristic of a plasma

The invention relates to a measuring probe and a measuring method for measuring quantities characteristic of a plasma, such as charge carrier densities, time-varying potentials and charge carrier energy probability functions. The invention also relates to a measuring system that includes the measuring probe, to a plasma coating device that includes the measuring system, and to a corresponding plasma coating method. In addition, the invention relates to a cap for use with the measuring probe according to the invention and to using the cap with the measuring probe.

Plasma sensor technology is an area in which very different approaches are pursued in order to determine the properties of a plasma. Known measuring methods can be broken down into direct and indirect methods, for example, with "direct" being understood in the sense of a material interaction of the measuring means with the plasma, while "indirect" is understood in the sense of an immaterial interaction of the measuring means with the plasma. The electrical processes in which the material interaction consists of a current flow between the plasma and the measuring equipment can be counted among the direct processes. Processes in which the immaterial interaction is of an electromagnetic nature can be counted among the indirect processes.

The quantities characteristic of a plasma include, for example, the electron density (also known as plasma density), the electron temperature, the electron energy Distribution, the ion density, the ion temperature and the ion energy distribution. In the context of plasma processes, such as plasma-assisted chemical vapor deposition (PECVD), the variables mentioned can be understood as internal parameters, while variables such as a gas flow, a prevailing pressure or an applied high-frequency power and its frequency represent external parameters.

Other very important quantities are characteristic electrical potentials. Depending on the process, both the so-called floating potential and the plasma potential can be of relevance. In process technology, the value of the plasma potential or floating potential is mostly neglected, especially when it comes to plasma processes with a high (self) bias, i.e. with a high DC voltage component or a constant electrical field component. However, depending on the electrode structure, for example, the plasma potential can definitely assume a relevant order of magnitude with regard to the bias and should therefore be determined, if possible, to control plasma processes. According to a classic, widespread electrical measurement method for characterizing low-pressure plasmas in particular, a so-called Langmuir probe is inserted into a plasma in order to extract plasma parameters from the course of a current-voltage characteristic. To increase the measurement accuracy, the current-voltage characteristic can be recorded while a compensation electrode of the Langmuir probe is used to generate an electric field that compensates for the influence of an external high-frequency field that generates or maintains the plasma on the current to be measured. The electron density, the electron temperature, the electron energy distribution, the floating potential, the plasma potential, the ion density and the ion flux can be extracted from the current-voltage characteristic, for which various analysis methods are known. The recording of a current-voltage characteristic, however, requires that Langmuir probes have an electrically conductive surface. In coating plasmas, such as those used in PECVD processes, the conductivity of the surface of a Langmuir probe would change over time, and for insulating coating materials, in particular, would decrease rapidly to zero. This excludes the sensible use of Langmuir probes for measuring plasma parameters in coating plasmas.

A known electrical method for measuring the ion energy distribution uses a retarding field analyzer. Simple retarding field analyzers have three grids and a plate, with various positive voltages being applied to one of the grids, which generate a voltage-dependent current that is measured on the plate called the collector. The remaining two grids can have negative voltages applied to them in order to exclude electrons from the measurement, so that the measured current can be referred to as the ion current. The ion energy distribution is deduced from the dependence of the ion current on the voltage. The measuring principle of a retarding field analyzer is thus similar to that of the Langmuir probe, with an ion current and not an electron current being measured. In particular, the measuring principle of a retarding field analyzer is also not based on plasma absorption spectroscopy. Similar to Langmuir probes, retarding field analyzers are therefore not suitable for use under coating plasma conditions. In addition, the ion flow to the collector can be measured in an energy-selective manner by means of a retarding field analyzer. The ion density itself cannot, however, be measured using a retarding field analyzer.

Information about the ions of a plasma can be obtained, for example, by means of energy-selective mass spectrometry, which, in addition to measurements using a Langmuir probe and a retarding field analyzer, could also be counted among the direct measurement methods. With energy-selective mass spectrometry, the mass spectrometer must be placed as close as possible to the plasma. For this purpose, a hole in an electrode is typically used, which serves directly as the entrance pupil into the mass spectrometer. By means of energy-selective mass spectrometry, the ion energy distribution can be determined for individual ion types that can be identified on the basis of their mass. However, it requires a considerable outlay in terms of equipment and a correspondingly designed electrode and is therefore difficult to integrate into existing systems. In addition, in a manner similar to that using the retarding field analyzer, only an ion flow through the entrance pupil can be measured, but no ion density.

Optical measuring methods, such as optical emission spectroscopy (OES) or optical absorption spectroscopy (OAS), which could be counted among the indirect measuring methods, can in principle also be used for layer-forming plasmas. You do not need a probe to come into contact with the plasma. Instead, the plasma is typically optically measured through a window in a container containing the plasma. The problem with the use of optical measuring methods for coating plasmas is that a corresponding coating can develop over time on such a window. The coating can falsify the optical measurement results, such as a recorded emission spectrum or absorption spectrum. Optical measurement methods are therefore sufficiently sensitive usually only achieved with considerable technical effort. In the case of optical absorption spectroscopy, for example, suitable measures must be taken to enable the longest possible interaction path between the plasma phase and the radiated light. Optical measurement methods are therefore particularly less suitable for complex, that is to say dusty, plasmas, such as those that arise, for example, when using molecular precursors, ie coating materials. One reason for this is that many precursors, such as hexamethyldisiloxane (HMDSO), only supply a few and only very weak signals for the Si-containing species, which, however, primarily contribute to the formation of the layer. In this respect, the informative value of optical measurement methods for layer-forming processes is clearly limited. But even for non-coated plasmas, the plasma density can usually only be determined with difficulty by means of optical measuring methods, since the optical measured variables, such as a recorded emission spectrum, can only rarely be assigned directly to the plasma density. The non-coating gases argon and oxygen are among the rare cases in which a connection between emission lines and plasma density is known.

Plasma absorption probes (PAP), also known as surface wave probes (SWP), can be used to measure the density of electrons in a plasma. They use the property of the plasma that there are free charge carriers and a plasma frequency. This enables sharp absorption of an electromagnetic wave. For this purpose, plasma absorption probes have a cavity on the probe head, for example, in which an electromagnetic wave is excited by an antenna. The electron density can be determined from the measured absorption frequency of the system consisting of probe and plasma. The patent specifications DE 10 2006 014 106 B3 and DE 10 2010 055 799 B3 describe a multipole resonance probe without a cavity on the probe head, which is constructed in an electrically symmetrical manner. The described multipole resonance probe can in particular be a dipole radiator. The multipole resonance probe can be used to record an absorption spectrum that can be determined analytically via a multipole expansion as a function of the shape and material of the probe. The described multipole resonance probe is used to determine the electron density, a collision frequency and an electron temperature derived therefrom. It can be understood as a further development of the measuring probes disclosed in US Pat. No. 6,339,297 B1 and US Pat. No. 6,744,211 B2, in which a fundamentally similar measuring principle is otherwise described. It is true that the electron density is measured according to the patent specifications mentioned is a fundamental parameter for a plasma and of correspondingly great relevance for a large number of plasma processes, but in practice it would be desirable to determine further parameters that characterize the plasma, such as the electron energy distribution. In addition, some capacitive measuring probes based on the principle of capacitive voltage division are described in the scientific literature. Measurements using capacitive measuring probes can be counted among the indirect measuring methods. By means of capacitive measuring probes, a potential curve is measured capacitively and time-resolved over a conductor housed in a dielectric. The plasma is not excited beforehand, so that the measurement can be described as "passive". The geometry of the conductors used can vary widely. Large-area, planar probes as well as conductor loops and simple cylindrical wires can be found in the literature. If all the impedances of the measuring probe, which is understood as a capacitive voltage divider in its three-dimensional structure, are known, the time-resolved measured potential can be used to calculate the potential profile in the plasma over time. With the capacitive probes described in the literature, however, typically, depending on the design, only either the plasma potential or the floating potential, but not both, is accessible.

So far, no measuring probe has been known with which several parameters characteristic of a plasma could be measured during a plasma coating process. It is therefore an object of the invention to provide a measuring probe which allows several quantities characteristic of a plasma to be measured during a plasma coating process. It is also an object of the invention to provide a corresponding measuring system and method and a cap for use with the measuring probe. In addition, it is an object of the present invention to provide a plasma coating system, which comprises the measuring system, and a corresponding plasma coating method.

These objects are achieved by a measuring probe, a measuring system and method, a dielectric cap for use with the measuring probe, and a plasma coating system and method in accordance with the aspects described below. According to the invention, a measuring probe is provided for measuring quantities characteristic of a plasma, the measuring probe having a probe body with a probe head, the probe body extending along a longitudinal axis of the measuring probe and is adapted to be introduced into the plasma with the probe head for measuring the quantities characteristic of a plasma. The measuring probe furthermore has a measuring electrode which is arranged on the probe head, the probe body providing an electrical connection between the measuring electrode and a part of the measuring probe opposite the probe head along the longitudinal axis. In addition, the measuring probe has a dielectric cap which extends over the measuring electrode and is designed to isolate the measuring electrode from the plasma. The measuring probe is set up to generate an opposing electrical field, in particular by applying a voltage, which displaces negative charge carriers from the probe head. The measuring probe is set up in such a way that it can generate an opposing electrical field that displaces negative charge carriers from the probe head.

Because the measuring probe is set up to generate an opposing electrical field that displaces negative charge carriers from the probe head, the plasma in the vicinity of the measuring probe can be influenced in a controlled manner, which enables further information to be obtained about the plasma. In particular, when using the opposing field, quantities based on positive ions, such as the ion density, can be determined. If, on the other hand, the opposing field is not used, the electron density, for example, can be determined with the same measuring probe. For this reason alone, the measuring probe according to the invention therefore permits a measurement of several parameters characteristic of the plasma, in particular under layer-forming plasma conditions.

The measuring probe can also be used to take passive measurements by means of the measuring electrode, the word “passive” here referring to the fact that no voltage is applied to the measuring electrode. However, it is also possible to carry out active measurements with the same measuring probe, in which case a voltage is applied to the measuring electrode. Since the passive and the active measuring principle make different measured variables accessible, the measuring probe according to the invention enables several variables characteristic of the plasma to be measured, in particular under layer-forming plasma conditions, for this reason as well. The passive measurement could also be referred to as a capacitive measurement and the active measurement as an absorption spectroscopic measurement, the measuring probe enabling both capacitive and absorption spectroscopic measurements and in this way being able to make various quantities characteristic of the plasma accessible. Since the inventive Measuring probe can enable capacitive as well as absorption spectroscopic measurements, it could also be referred to as PACP, where PACP stands for “plasma absorption and capacitive probe”.

Because several quantities characteristic of the plasma can be measured with one and the same measuring probe, it is possible, for example, to avoid having to exchange the measuring probe for a different measuring probe in order to measure a further quantity. Such a replacement would be costly and would involve the risk that the other measuring probe would not assume the same measuring position as the original measuring probe, which would negatively affect the comparability of the measurements. While the measuring probe according to the invention enables a measurement of several quantities characteristic of a plasma under layer-forming plasma conditions, it enables the measurement of quantities characteristic of a plasma, of course, also under non-film-forming plasma conditions. In particular, it makes use of the same measuring principles for measuring under non-layer-forming plasma conditions as under layer-forming plasma conditions.

The suitability of the measuring probe for measuring under film-forming plasma conditions is preferably to be understood as long-term suitability, which can mean, for example, that the measurement accuracy can remain essentially constant even over long measurement periods under film-forming plasma conditions. In particular, the measuring probe can be set up and therefore also suitable for use in low-pressure plasmas. Low pressure plasmas are used for a variety of coating tasks.

The opposing electric field that can be generated by the measuring probe can be understood as a type of influencing a plasma edge layer surrounding the probe head, the influencing including the displacement of negative charge carriers from the probe head. The fact that the generated opposing electric field displaces negative charge carriers from the probe head can mean that an electron density in the vicinity of the probe head is reduced by generating the opposing field. It can also mean that the plasma edge layer is enlarged. The opposing field can thus increase the interaction between the measuring probe and the ions in the plasma. It is particularly advantageous to generate the opposing field in high-density plasmas. The measuring probe can in particular be set up to generate the opposing electric field by generating an electric potential at the probe head. The opposing field then corresponds to the generated potential. For example, the opposing field results from a gradient of the generated potential. The potential corresponding to the opposing field preferably has a value in the area of the probe head which is lower than a value of an electrical potential which is assigned to the plasma. It is particularly preferred that the value of the potential corresponding to the opposing field is lower everywhere, in particular in the area of the probe head, than the corresponding value of the electrical potential that is assigned to the plasma. The potential assigned to the plasma can in particular be a plasma potential. At the same time, the value of the potential corresponding to the opposing field is preferably greater everywhere, in particular in the area of the probe head, than a potential value of a plasma container in which the plasma is enclosed. In particular, the potential corresponding to the opposing electric field can have a negative value. The plasma potential can be understood as an electrical potential that prevails in the plasma, in particular in the interior of the plasma. The interior of the plasma can be, for example, a spatial area which is occupied by the plasma and which is located so far away from surfaces that the plasma in the area is not influenced by the surfaces or is only influenced to a negligible extent. The interior of the plasma could also be referred to as a plasma bulk. In the plasma bulk, the principle of quasi-neutrality that applies to the plasma comes into play, so that the electron density there is equal to the ion density and indicates the degree of ionization of the plasma.

Since the dielectric cap extends over the measuring electrode and is designed to isolate the measuring electrode from the plasma, the probe head forms a cavity in which electromagnetic waves emanating from the measuring electrode can propagate and form cavity modes. The dielectric cap can in particular be displaceable along the probe body. In this way, a size of the cavity can be changed. The properties of the cavity can also be specifically influenced by different shapes and materials of the dielectric cap. The freedom in the selection and positioning of the dielectric cap makes it possible to design the measurement of the parameters characteristic of the plasma in a technically simpler manner, since in particular the level of the measurement frequencies, i.e., for example, the frequency of the wave emanating from the measurement electrode, depends on the parameters to be measured can be largely decoupled. The measuring electrode consists of an electrically conductive material. For example, the measuring electrode can be formed from a metal wire. The measuring electrode can also be designed differently, in particular with regard to its shape. In a particularly simple embodiment, the measuring electrode is cylindrical and arranged along the longitudinal axis of the measuring probe. One end of the measuring electrode, which could also be referred to as the head end of the measuring electrode and which is arranged in the probe head, is particularly preferred, curved, in particular hemispherical, ie implemented as a hemisphere, for example. However, it is also conceivable that the head end of the measuring electrode is flat, ie is described by a plane, in particular perpendicular to the longitudinal axis of the measuring probe. However, the measuring electrode can also form a conductor loop, for example. Since the measuring electrode defines nodes for the cavity modes in the cavity, the required measuring frequencies can also be influenced in this way, i.e. by selecting different shapes of the measuring electrode. In particular, by selecting certain shapes of the measuring electrode, the number of cavity modes that form in the probe head can be kept small and the formation of multiple absorption signals can be suppressed. The measuring electrode can be shaped, for example, in such a way that the measuring probe essentially represents a monopole radiator.

It can be advantageous that the measuring probe is designed in such a way that the dielectric cap is located completely in the interior of the container, in particular completely in the plasma, when the measuring probe is inserted into a container that generates or maintains the plasma. The dielectric cap can also be designed to be completely inserted into a plasma.

In a preferred embodiment, the measuring probe also has a counter electrode which is arranged on the dielectric cap, the probe body providing an electrical connection between the counter electrode and the part of the measuring probe lying opposite along the longitudinal axis, the measuring probe being set up by means of the Counter electrode to generate the opposing electric field.

The use of a counter electrode to generate the opposing electrical field has the advantage that the opposing electrical field can be generated in the immediate vicinity of the plasma, so that only relatively low field strengths have to be generated to displace negative charge carriers from the probe head. The field strength to be generated at the electrode required for a given degree of displacement depends relatively strongly on the proximity of the electrode to the plasma due to the decrease in field strength with the square of the distance from the electrode. The use of a counter-electrode to generate the counter-electric field also has the advantage that special properties of different geometries and textures of the counter-electrode can be used to generate special counter-fields. The special opposing fields generated in this way can further increase the measuring accuracy of the measuring probe.

In one embodiment, the counter electrode has a covering structure with a distribution of openings which covers a surface of the dielectric cap at least in the region of the probe head. The covering structure therefore comprises a plurality of openings at least in the area of the probe head. The distribution of openings is preferably designed to be spatially homogeneous, at least in the area of the probe head. Spatially homogeneous here means in particular that the cover structure has the same density and size of openings in each of its regions, which could also be understood as partial areas of the cover structure, with this definition the respective region comprising several openings, otherwise the density of the openings would not be determinable. The counter electrode therefore does not include a distribution of openings that is spatially homogeneous when the counter electrode is formed by a metal film that completely covers the dielectric cap at least in the area of the probe head, except for an area of the probe head in which the dielectric cap is not covered with the metal film to form a kind of window. In this case, there would be an opening in one region of the covering structure, that is to say the window, and there would be no opening in any other region of the covering structure, at least in the region of the probe head. So there would not be the same density and size of openings in every region of the cover structure.

The degree of coverage of the coverage structure on the dielectric cap in the area of the probe head is preferably designed so that the transmission capability of the electromagnetic wave to be detected is hindered as little as possible and, on the other hand, negative charge carriers can be kept away from the probe head with the counter electrode. In particular, the covering structure can cover the dielectric cap at least in the area of the probe head with a degree of coverage in a range from 10% to 70%, in particular with a degree of coverage of 50%. Here, the degree of coverage is preferably defined as the ratio of a) the area of the non-openings of the cover structure to b) the total area of the cover structure, which includes both the openings and the non-openings of the cover structure. A value of 100% would therefore correspond to a completely closed structure and a value of 1% would correspond to a hardly existing structure. When the distribution of the openings is spatially homogeneous, the degree of coverage is preferably the same for each region of the coverage structure.

In one embodiment, the area of the probe head begins at the level at which the measuring electrode emerges from an insulator. This area of the probe head is preferably covered, as stated above, by the structure of the counter electrode with the distribution of openings. The area of the probe head could also be understood as a sensitive area of the probe body, it being possible in this area, that is to say the sensitive area, to measure a variable that is characteristic of a plasma.

In particular, the counter electrode or the covering structure of the counter electrode can be formed from a wire mesh, wherein the wire mesh can have different degrees of fineness. For example, the counter electrode can be designed as a grid electrode with grid openings of a predetermined size, or the counter electrode can be designed as a multi-wire, that is to say as a wire braided to form a wire bundle. The covering structure of the counter electrode with the distribution of openings can also be produced by vapor deposition of electrically conductive materials, the free areas being covered during the vapor deposition. Aluminum or copper, for example, can be used as the electrically conductive material.

The covering by the covering structure of the counterelectrode on the surface of the dielectric cap could, at least in the area of the probe head, also be designed to be rotationally symmetrical about the longitudinal axis of the measuring probe.

If the counter electrode is designed as a grid electrode, it can for example lie uniformly, ie homogeneously, as a layer on the outside of the dielectric cap, in particular in the area of the probe head. If the counter electrode is designed as a multi-wire, it can for example run in several turns or loops on the outside of the dielectric cap around the latter. The counter electrode, whether as a grid electrode, multi-wire or in another form, can also form several longitudinal strips along the longitudinal axis of the measuring probe, or it can form one or more rings around the longitudinal axis of the measuring probe. Here, the longitudinal strips or the rings are preferably arranged in a rotationally symmetrical manner around the longitudinal axis of the measuring probe. A particularly uniform covering of the dielectric cap, in particular in the area of the probe head, can, as already indicated above, by a partially, ie partially wise, counter-electrode vapor-deposited on the dielectric cap or sputtered on the dielectric cap can be achieved. Such types of counter-electrodes could be understood as layered, with a layer thickness of the counter-electrode of at least 50 μm being preferred. When using layered counterelectrodes, the electrical connection between the counterelectrode and the part of the measuring probe opposite the probe head along the longitudinal axis can preferably be closed by a sliding contact which is arranged on the probe head side directly in front of the fastening element on the probe body.

The counter electrode is not necessarily arranged on the outside of the dielectric cap, but can also be arranged on the inside or even inside the dielectric cap. For example, the counter electrode can preferably be arranged as a ring, i.e. as an annular counter electrode, on the inside of the dielectric cap. In particular, the counter electrode can be arranged on the inside of the dielectric cap in the vicinity of the probe head, that is to say for example in the longitudinal direction of the measuring probe directly behind the measuring electrode.

The type of counterelectrode used can be selected, for example, depending on the desired properties of the plasma, such as depending on an electron density desired at the start of a coating process. Likewise, the type of counter-electrode used can be selected, for example, depending on a priority with which a certain quantity characteristic of the plasma is to be measured. The background to this is that different types of counter-electrodes can be suitable for the measurement of a given quantity characteristic of the plasma in different ways. For example, the use of counter electrodes with a relatively low degree of coverage, for example 10%, of the dielectric cap, in the case of grid electrodes, for example with a relatively low degree of fineness, is preferred for carrying out electron-related measurements such as measurements of electron density. This is based on the knowledge that the presence of a counter electrode generally inhibits the influence that the application of a voltage to the measuring electrode has on the plasma, according to the principle of a Faraday cage. Conversely, for example, the use of counter electrodes with a relatively high degree of coverage, for example 70%, of the dielectric cap, in the case of grid electrodes, for example with a relatively high degree of fineness, can be preferred for performing ion-related measurements such as measurements of the ion density, because such counter electrodes create suitable counter fields with a corresponding influence on the plasma in the near range the measuring probe. In the case of using partially vapor-deposited or sputtered, ie layer-like, counter-electrodes, layer thicknesses that are small enough to carry out both electron-related and ion-related measurements with sufficient accuracy are to be preferred. In general, the nature of the counter electrode can be taken into account when calibrating the measuring probe.

In one embodiment, the electrical connection between the measuring electrode and the part of the measuring probe opposite along the longitudinal axis can be flexible or semi-rigid, for example as a coaxial cable. This can enable the measuring probe, in particular the probe head, to be positioned by bending. The electrical connection between the counter electrode and the part of the measuring probe opposite along the longitudinal axis can also be flexible or semi-rigid, for example as a coaxial cable.

In one embodiment, the measuring probe can be set up to be attached to a plasma container with the probe body or the part of the measuring probe opposite the probe head along the longitudinal axis by means of a flange, the flange being set up an opening of the plasma container through which the measuring probe is inserted into the plasma container for measuring, to close when the measuring probe is inserted.

In a preferred embodiment, the measuring probe also has a fastening element which is arranged on the probe body, the fastening element being adapted to detachably fasten the dielectric cap to the probe body.

Such a fastening element enables the dielectric cap to be exchanged without the probe body or other parts of the measuring probe having to be manipulated. The replacement of the dielectric cap can be advantageous, for example, under layer-forming plasma conditions, for example if a layer with a high thickness has formed on the dielectric cap, which would falsify the measurement of the parameters characteristic of the plasma too much.

The fastening element is preferably designed as a screw or clamping element. The attachment and detachment of the dielectric cap is then particularly simple. However, other types of fasteners can also be used. If the measuring probe has a counter electrode arranged on the dielectric cap, which is connected to the part of the measuring probe opposite the head end along the longitudinal axis of the measuring probe via an electrical connection provided by the probe body, the fastening element is preferably adapted to provide part of the electrical connection. For example, the fastening element can be adapted to provide electrical contact between the electrical connection and the counter-electrode. The contact can be a screw or clamp contact, for example.

In a preferred embodiment, the fastening element is adapted to create a space for the measuring electrode that is free of a plasma discharge by fastening the dielectric cap. The created space can be understood as a dark room.

The fastening element thus preferably serves at the same time as a means for producing a dark space seal for an area below the dielectric cap in which the measuring electrode is located. A dark room is an area in which, in particular, the electrons of the plasma do not have the necessary kinetic energy to ignite a plasma and cause shock-induced radiation emissions. A dark room appears accordingly dark and does not have any plasma-typical glow. The dark room seal is not necessarily a vacuum seal. On the contrary, it is preferred that the same pressure prevails inside and outside the dielectric cap during a measurement. The fastening element has the advantage that it can enable the measuring electrode to be sealed off from the plasma in the dark without further sealing elements, in particular without vacuum sealing elements.

In a preferred embodiment, the counter electrode can be detached from the dielectric cap.

This has the advantage that different counter-electrodes can be used in an otherwise unchanged measuring arrangement, for example to generate different counter-fields due to different geometries and properties of the counter-electrodes. If the dielectric cap itself is detachably attached to the probe body, a counter-electrode which can be detached from the dielectric cap also enables the dielectric cap to be replaced without replacing the counter-electrode. The counter electrode and the dielectric cap can then be replaced independently of one another. In a preferred embodiment, the probe body has a collar element which faces the dielectric cap, the collar element having a thickness which matches an outer cross section of the probe body to an inner cross section of the dielectric cap. The collar element is arranged in particular on the outside of the probe body and so close to the probe head that the dielectric cap can extend over the collar element.

Such a collar element can have the advantage of a form fit between the dielectric cap and the probe body with simultaneous flexibility with regard to the selection of the remaining components of the measuring probe, in particular the dielectric cap and the remaining elements of the probe body, since these do not have to be selected based on their cross-sections . The form fit can in particular produce a dark space seal for the area below the dielectric cap in which the measuring electrode is located. If the form fit is achieved by an outer cross-section of the probe body that is matched to the inner cross-section of the dielectric cap, the fastening element can also be designed more simply, since there is no need for an additional dark space seal by the fastening element. The provision of the collar element can also mean the advantage of centering the dielectric cap about the longitudinal axis of the measuring probe.

The collar element is preferably designed as a collar layer, that is to say in the form of a layer. A collar element does not necessarily have to be provided for a form fit of the type described. Then, for example, a form fit can also be provided between the dielectric cap and the electrical connection between the measuring electrode and the part of the measuring probe opposite the probe head along the longitudinal axis. If the electrical connection is a coaxial cable, for example, the form fit can be established between an outer shield of the coaxial cable and the inside of the dielectric cap.

The collar element, that is to say in particular the collar layer, can consist of an electrically conductive material as well as an electrically non-conductive material such as a dielectric. If the collar element, that is to say in particular the collar layer, consists of an electrically conductive material, it is preferred that it does not extend beyond an edge of the dielectric cap. In this way, an electrical coupling of the plasma to the area within the dielectric Cap over the collar element can be avoided. The choice of material for the collar element must be taken into account when calibrating the measuring probe. For example, the collar element can be designed not to change a cavity mode assigned to the probe head, in particular within a range of measurement parameters provided for measurement. The measurement parameters can in particular include the frequencies of an input signal that is generated at the measurement electrode. This can be achieved in particular in that the collar element consists of an electrically conductive material, since a frequency-independent boundary condition can be achieved at the front end of the collar element for cavity modes that are formed in the probe head. If the collar element consists of an electrically non-conductive material with a frequency-dependent permittivity within the range of measurement parameters provided for measurement, this can result in different effective geometries of the probe head for different frequencies of the input signal, since waves forming in the probe head penetrate the collar element partially and to different extents be able. The cavity modes assigned to the probe head can shift in this way and also change their relative intensity. If the collar element changes the cavity modes assigned to the probe head within the range of measurement parameters provided for measurement, that is to say in particular if it consists of a non-conductive material, a frequency-dependent calibration of the measurement probe is preferably provided.

In a preferred embodiment, the probe body has an insulating jacket layer in a region which adjoins the dielectric cap in the longitudinal direction.

The insulating cladding layer preferably has a thickness which, in its outer cross section, aligns the region which adjoins the dielectric cap in the longitudinal direction to an outer cross section of the dielectric cap. In this way, the measuring probe can form a stepless exterior, which can reduce gas turbulence on the surface of the measuring probe. This is particularly advantageous in plasma coating processes, that is to say under layer-forming plasma conditions, since gas turbulence can negatively affect the actual layer-forming process. For example, a stepless exterior can prevent local dust formation. A stepless exterior of the measuring probe is also generally advantageous, since this can promote the formation of a uniform plasma edge layer around the measuring probe during a measurement, with a uniform plasma edge layer, in particular in the area of the probe head, being able to increase the measurement accuracy. In principle, the cladding layer can alternatively also be designed to be non-insulating, that is to say to be electrically conductive. In this case, however, it must be ensured that the cladding layer is sufficiently earthed in order to avoid lightning-like discharges during a measurement. Even with adequate grounding, local discharges can still arise when the measuring probe is inserted into the plasma, and these can be tolerated under certain circumstances. Such discharge processes can only be avoided entirely or at least to the greatest possible extent by means of a dielectric cladding layer. This is due to the fact that a dielectric jacket layer is only charged once to the floating potential when the measuring probe is introduced into the plasma and is consequently in equilibrium with the plasma.

In a preferred embodiment, the measuring probe is designed to be cylindrically symmetrical with respect to the longitudinal axis, the dielectric cap having a dome-shaped head end with a U-shaped longitudinal section.

The dielectric cap thus also has cylindrical symmetry up to its head end. The cylinder symmetry offers the advantage of high mechanical stability. Cylindrical symmetrical caps with a dome-shaped head end can also typically be manufactured with a highly uniform material thickness. In principle, however, a dielectric cap with a flat head end can also be used, in which case an increased thickness of the cap in the area of the head end can be tolerated. Regardless of its specific shape, the dielectric cap is preferably closed at its head end. At its end opposite the head end, the dielectric cap is preferably open. It is therefore preferably made hollow, that is to say, apart from its outer wall, which itself can be made hollow or solid, not solid. The dielectric cap, ie the wall of the dielectric cap, can, for example, be made essentially or entirely of glass, preferably heat-resistant glass. However, the dielectric cap can also have or consist of other dielectric materials. The relative permittivity e _{r of} the material of the dielectric cap can preferably be between 4.50 and 5.50, for example assume the value 4.84. In principle, however, dielectric caps with any desired values of the relative permittivity can be used. The value of 4.84 is a glass. However, higher values, such as values between 6 and 8, are certainly conceivable. As a result of this, the measured absorption frequency is shifted to lower frequencies, which can definitely be advantageous for certain measuring arrangements. According to the invention, a measuring structure for measuring quantities characteristic of a plasma is also provided, which has a probe body with a probe head, the probe body extending along a longitudinal axis of the measuring structure and being adapted for measuring the quantities characteristic of a plasma with the probe head in the Plasma to be introduced. The measuring structure has a measuring electrode which is arranged on the probe head, the probe body providing an electrical connection between the measuring electrode and a part of the measuring structure opposite the probe head along the longitudinal axis. The measuring structure is set up to generate an opposing electrical field that displaces negative charge carriers from the probe head, and the probe body is designed to accommodate a dielectric cap in such a way that it extends over the measuring electrode after recording and isolates the measuring electrode from the plasma .

The dielectric cap can for example be provided as a consumable part.

The dielectric cap can be exchanged, for example, simply by pulling the dielectric cap off the probe body in the direction of the probe head and then attaching a new dielectric cap in a correspondingly reversed direction. The plugged-on new dielectric cap can then already be fixed to the probe body by a form fit with a collar layer of the probe body and / or be fastened to the probe body by means of the fastening element.

The dielectric cap is preferably only replaced when the coating on the outside of the dielectric cap is so thick that measurements are impaired, in particular measurement accuracy is reduced. Such an impairment can be present, for example, with a thickness of the wall of the dielectric cap of 1 mm already with coating thicknesses of a few 10 μm, in particular at the latest with coating thicknesses of more than 100 μm. However, such coating thicknesses are typically only achieved after a relatively long period of use, for example only after a few days in the case of measurements carried out several times a day. Accordingly, the replacement of the dielectric cap is typically only required at relatively long time intervals.

According to the invention, a dielectric cap is also provided for use with the measuring structure as a measuring probe, the dielectric cap being designed in such a way from the Probe body to be received that the dielectric cap extends over the measuring electrode and seals the measuring electrode from the plasma.

The dielectric cap preferably comprises a counter electrode with a covering structure with a distribution of openings that covers a surface of the dielectric cap. In particular, the dielectric cap is designed in such a way that the covering structure with the distribution of openings is present at least in the area of the probe head when the dielectric cap has been placed on the measuring structure. The covering structure therefore comprises a plurality of openings at least in the area of the probe head. The distribution of openings within the covering structure is preferably designed to be spatially homogeneous, at least in the area of the probe head.

According to the invention, a measuring system for measuring parameters characteristic of a plasma is also provided, the measuring system having the measuring probe and a voltage device for generating an input signal and for generating the opposing electrical field, the voltage device, via an electrical connection to the measuring probe, for generating the Input signal can be connected to the measuring electrode. The measuring system also has a signal receiving unit for receiving an output signal, the signal receiving unit being connectable via the electrical connection to the measuring probe for receiving the output signal with the measuring electrode, and an evaluation unit for determining the parameters characteristic of the plasma based on the output signal.

The output signal can, for example, be indicative of a degree of absorption of the input signal by the plasma, the evaluation unit then being able to use the input signal and the output signal to determine, for example, the electron density or the ion density. If the output signal is used as an indicator of the degree of absorption of the input signal by the plasma, it could also be understood as an impulse response, in which case the input signal could be understood as the corresponding stimulating impulse. The degree of absorption could, for example, be specifiable on the basis of an insertion loss. The output signal can also, in the context of a passive, capacitive measurement, simply be the electrical measurement signal measured by means of the measuring electrode, which can then be used, for example, to measure the time profile of the plasma potential or the time profile of the floating potential. The capacitive measurement can, for example, be based on the principle of capacitive voltage division. In a preferred embodiment, the voltage device is adapted to provide the input signal at a high frequency and to provide the opposing electrical field at a low frequency or constant.

In a preferred embodiment, the voltage device has a first voltage source and a second voltage source, wherein the first voltage source is adapted to generate the input signal, and wherein the second voltage source is adapted to generate the opposing electrical field.

The first voltage source and the signal receiving unit can be integrated in a common unit, for example in the form of a network analyzer. The signal receiving unit can, however, also be designed as a unit separate from the first and the second voltage source, for example as an oscilloscope.

The first voltage source can be connected to the measuring probe via a first electrical connection and the second voltage source can be connected to the measuring probe via a second electrical connection, wherein the first voltage source can be adapted to provide the input signal via the first electrical connection, and the second voltage source can be adapted to provide the opposing electrical field via the second electrical connection.

In a preferred embodiment, the measuring system has a high-pass filter for filtering the output signal. This enables the output signal to be cleared of any reaction of the opposing electric field. If the voltage device has a first voltage source for generating the input signal and a second voltage source for generating the opposing electrical field and if the first voltage source is integrated with the signal receiving unit in a common unit, the high-pass filter can in particular between the two voltage sources, i.e. between the first voltage source be arranged with the signal receiving unit and the second voltage source. It can thus be made possible that a low-frequency voltage or direct voltage, which the second voltage source provides for generating the opposing field, does not react directly on the signal receiving unit. In a preferred embodiment, the voltage device is adapted to generate the opposing electrical field via the electrical connection with the measuring probe on the measuring electrode.

In this way, the measuring probe of the measuring system does not necessarily have to have a counter electrode on which the counter electric field is generated.

The generation of the opposing electrical field by means of the measuring electrode can considerably reduce maintenance costs for the measuring probe. In this case, in particular, dispensing with a counterelectrode can simplify the separate replacement of the dielectric cap, since there is no need to detach the counterelectrode from the dielectric cap. If the measuring probe has a fastening element that provides part of the electrical connection to the counterelectrode, in particular the loosening of the counterelectrode from the fastening element and the subsequent reconnection, for example the loosening and subsequent re-establishment of corresponding electrical contacts, can be dispensed with. Since reconnecting is prone to errors, dispensing with a counter electrode can also reduce the measuring probe's susceptibility to errors. Since not only the dielectric cap, but also the counter-electrode is currently being replaced, the additional material and time expenditure that this causes is also dispensed with.

The generation of the opposing electric field by means of the measuring electrode also enables the parameters characteristic of the plasma to be measured with high measuring accuracy due to a high signal quality, in particular in the case of active measurements, such as absorption measurements. The signal quality is increased compared to embodiments with a counter electrode, for example, in that there is no attenuation of signals by the counter electrode.

In a preferred embodiment, the measuring probe, as described above, has a counter-electrode arranged on the dielectric cap, the voltage device being adapted to generate the counter-electric field via the electrical connection with the measuring probe on the counter-electrode.

A measuring system designed in this way adopts the advantages of the measuring probe having the counter electrode, which have already been described. The measuring system preferably has a low-pass filter for filtering signals along the second electrical connection. The low-pass filter is preferably close to or at one arranged electrical contact of the measuring probe and the voltage device. In particular, the low-pass filter can be arranged at or near an electrical contact which closes the electrical connection between the counter electrode and that part of the measuring probe opposite the probe head along the longitudinal axis of the measuring probe. In the simplest case, a coil, for example, can be provided as the low-pass filter. The low-pass filter can prevent high-frequency input signals, which are provided by the first voltage source, from also being transmitted to the counter electrode. The low-pass filter can also prevent a high-frequency current possibly picked up via the counter electrode from reaching the voltage device. The reason for this is that the second voltage source can form a sink in terms of high frequency technology. However, it must be avoided that a net current flows in the case of capacitive high-frequency discharges. Disturbance of the discharges by the counter electrode can be avoided by using a low-pass filter.

In a preferred embodiment, the measuring system is adapted for high-resistance measurement and for low-resistance measurement.

This enables the measurement of different parameters characterizing the plasma. For example, the high-resistance measurement can be used to determine the time profile of the plasma potential, and the low-resistance measurement can be used to determine the time profile of the floating potential. A switch between high-resistance measurement and low-resistance measurement can be made, for example, by a switching element, wherein the switching element can be set up to change an impedance that is assigned to a part of the measuring system that lies between the measuring probe and the evaluation unit.

As already explained, the plasma potential can be understood as an electrical potential that prevails in the plasma, in particular in the interior of the plasma, the interior of the plasma, for example, being a spatial area that is occupied by the plasma and that is so far away of surfaces is that the plasma in the area is not or only negligibly influenced by the surfaces. The floating potential, on the other hand, can be understood as an electrical potential to which a surface in a plasma, i.e. for example by generating a plasma in its environment or by introducing the surface into a plasma, charges when the surface is not grounded or connected to a voltage source, i.e. when it is electrically isolated.

The difference between the plasma potential and the floating potential is determined by the plasma edge layer, in particular the thickness of which in turn depends on variables that are characteristic of the plasma, such as the electron density and electron temperature, for example.

In a preferred embodiment, the measuring system is adapted to determine at least one variable selected from the group consisting of electron density, ion density, temporal progression of the plasma potential, temporal progression of the floating potential and electron energy probability function, as the quantities characteristic of the plasma.

In a preferred embodiment, the voltage device is adapted to generate the input signal with varying frequency during a measurement period for measuring the electron density and not to generate an opposing electrical field, the signal receiving unit being adapted to receive the output signal during the measurement period, the evaluation unit being adapted to the Determine electron density based on the input signal and the output signal.

The evaluation unit can in particular be designed to use the input signal and the output signal in order to determine a frequency-dependent reflection coefficient and the electron density as a function of the frequency at which the reflection coefficient has a minimum.

In a preferred embodiment, the voltage device is adapted to generate the input signal with varying frequency during a measurement period for measuring the ion density and to generate the opposing electrical field, the signal reception unit being adapted to receive the output signal during the measurement period, the evaluation unit being adapted to determine the ion density based on the input signal and the output signal.

The evaluation unit is designed in particular to use the input signal and the output signal in order to determine a frequency-dependent reflection coefficient and the ion density as a function of the frequency at which the reflection coefficient has a minimum. In a preferred embodiment, the signal receiving unit is adapted to record the output signal with high resistance during a measurement period for measuring the time profile of the plasma potential, the evaluation unit being adapted to determine the time profile of the plasma potential on the basis of the output signal recorded with high resistance.

During the measurement period for measuring the time profile of the plasma potential, the voltage device preferably delivers no voltage and thus no input signal and also no opposing field.

In a preferred embodiment, the signal receiving unit is adapted to record the output signal with low resistance during a measurement period for measuring the time profile of the floating potential, the evaluation unit being adapted to determine the time profile of the floating potential on the basis of the output signal recorded with low resistance.

Even during the measurement period for measuring the time profile of the floating potential, the voltage device preferably does not supply any voltage and thus no input signal and also no opposing field.

In a preferred embodiment, the voltage device and the signal receiving unit are adapted to measure the electron energy probability function, to generate the input signal with varying frequency for different opposing fields and to record the output signal, the evaluation unit being adapted to generate the electron energy probability function on the basis of the for to determine the input signals generated by the different opposing fields and the output signals recorded for the different opposing fields.

The evaluation unit is designed in particular to use the input signal and the output signal to determine a frequency-dependent reflection coefficient and a frequency at which the reflection coefficient has a minimum for each opposing field, the evaluation unit being further designed to perform the electron energy probability function To determine the basis of the frequencies determined for the various opposing fields. According to the invention, a plasma coating system is also provided which has a plasma generating device for generating a plasma with a coating material, the measuring system for measuring parameters characteristic of the plasma and a control unit for controlling the plasma generating device, the control unit being adapted to the plasma generating device depending on the measured values to control quantities characteristic of the plasma.

This enables the plasma to be generated and maintained in a controlled manner. In particular, the generation and maintenance of the plasma can be adapted to a coating process, for example to the material to be coated, the coating material and / or a degree of progress in the coating process. Controlling the plasma generating device as a function of the measured values characteristic of the plasma therefore allows plasma coatings to be generated with high quality. In particular, use is made of the fact that the parameters characteristic of the plasma can be measured in a time-resolved manner by means of the measuring probe according to the invention.

For example, the control unit can be adapted to cause the plasma generating device to adapt a power generating or maintaining the plasma or a composition or total amount of the gas located in the plasma container to the measured values characteristic of the plasma. According to the invention, a measuring method for measuring a variable characteristic of a plasma is also provided, the method having the following steps: a) introducing a probe head of a measuring probe into the plasma, b) generating an opposing electric field that displaces negative charge carriers from the probe head, c) Generating an input signal at a measuring electrode of the measuring probe, which is arranged on the probe head, d) receiving an output signal from the measuring electrode which is indicative of a degree of absorption of the input signal by the plasma, and e) determining the variable characteristic of the plasma based on on the output signal.

In particular, the measuring system can be designed to carry out this method. The measuring probe can thus be designed according to the invention, for example, whereby the generation of the opposing electrical field and the input signal, the reception of the output signal and the determination of the parameters characteristic of the plasma can take place by means of the measuring system according to the invention. According to the invention, a plasma coating method is also provided which has the following steps: a) generating a plasma with a coating material and b) measuring a variable that is characteristic of the plasma.

In particular, the plasma coating process can be carried out by means of the plasma coating system.

The plasma coating method also has a control of the generation of the plasma as a function of the measured variable characteristic of the plasma. For example, by controlling, in particular increasing, the electron density and thus the degree of ionization of the plasma, a deposition rate can be influenced, in particular increased. For example, a power generating or maintaining the plasma or a composition or total amount of the gas located in the plasma container can be adapted to the measured values characteristic of the plasma.

According to the invention, use of the dielectric cap with the measuring structure for carrying out the measuring method is also provided. It should be understood that the measuring probe according to claim 1, the measuring structure according to claim 6, the dielectric cap according to claim 7, the measuring system according to claim 8, the plasma coating system according to claim 13, the measuring method according to claim 14, the plasma coating method according to claim 15 and the use of the dielectric cap according to claim 16 have similar or identical embodiments as are defined in particular in the dependent claims.

In the following, embodiments of the invention are described with reference to the figures mentioned below.

1 to 6 are exemplary and schematic illustrations of embodiments of the measuring probe, FIG. 7 is an exemplary and schematic illustration of an embodiment of a measuring electrode,

8 is an exemplary and schematic representation of the mobility of an embodiment of the measuring probe, 9 is an exemplary and schematic representation of an embodiment of the measuring system,

FIG. 10 is an exemplary and schematic illustration of an embodiment of the plasma coating system, FIG. 11 is an exemplary and schematic illustration of an embodiment of the measuring method,

FIG. 12 is an exemplary and schematic illustration of a model of a

Embodiment of the measuring probe,

13 is an exemplary and schematic illustration of a model of an embodiment of the measurement system and

14 is an exemplary and schematic illustration of an embodiment of the plasma coating process.

1 shows a measuring probe 100 for measuring quantities characteristic of a plasma. The measuring probe has a probe body 110 with a probe head 120, the probe body 110 extending along a longitudinal axis of the measuring probe 100. The probe body 110 is adapted to be introduced into the plasma with the probe head 120 in order to measure the quantities characteristic of a plasma. The measuring probe 100 shown in FIG. 1 also has a measuring electrode 101 which is arranged on the probe head 120. The probe body 110 provides an electrical connection 102 between the measuring electrode 101 and one of the probe bodies 120 along the

Longitudinal opposite part of the measuring probe 100 ready. 1 likewise shows a dielectric cap 103 of the measuring probe 100, the dielectric cap extending over the measuring electrode 101 and being designed to isolate the measuring electrode 101 from the plasma. The measuring probe 100 is set up to generate an opposing electric field which displaces negative charge carriers from the probe head 120.

The measuring probe 100 shown in FIG. 1 has a counter electrode 104 which is arranged on the dielectric cap 103, the probe body 110 providing an electrical connection 105 between the counter electrode 104 and the part of the measuring probe 100 opposite along the longitudinal axis. The measuring probe 100 is set up to generate the opposing electrical field by means of the opposing electrode 104. Furthermore, the measuring probe 100 shown in FIG. 1 has a fastening element 106 which is arranged on the probe body 110, the fastening element 106 being adapted to detachably fasten the dielectric cap 103 to the probe body 110.

As shown in FIG. 1, the electrical connection 102 between the measuring electrode 101 and the part of the measuring probe 100 opposite the probe head 120 and also the electrical connection 105 between the counter electrode 104 and the opposite part of the measuring probe 100 can each be designed as a coaxial cable being. As coaxial cables, the connections 102, 105 each have an inner conductor 111, 114, an insulating or dielectric layer 112, 115 and a shield 113, 116. The shielding of a coaxial cable is also referred to as an outer conductor and is preferably electrically grounded. The measuring electrode 101, which could also be referred to as an antenna, is in FIG. 1 a part of the inner conductor 111 of the coaxial cable protruding from the rest of the coaxial cable, which serves as an electrical connection 102 between the measuring electrode 101 and the opposite part of the measuring probe 100. In FIG. 1 and also in the other figures, the measuring electrode 101 is shown spaced apart from the dielectric cap 103. However, it is also conceivable that the measuring electrode 101 touches the dielectric cap 103. A corresponding part of the inner conductor 114 of the coaxial cable, which serves as an electrical connection 105 between the counter electrode 104 and the opposite part of the measuring probe 100, also protrudes from the coaxial cable and, according to FIG. 1, establishes an electrical contact 117 with the counter electrode 104.

The part of the measuring probe 100 opposite the probe head 120 along the longitudinal axis of the measuring probe 100 cannot be seen in FIG 202 for connection to one of the coaxial cables.

The counter electrode 104 shown in FIG. 1 is formed from a wire mesh in the form of a grid electrode, the wire mesh having a relatively low degree of fineness and the grid openings being only slightly smaller than the wire itself. For example, the grid electrode shown could lie uniformly as a layer on the outside of the dielectric cap 103. Since FIG. 1 shows a longitudinal section of the measuring probe 100, the impression arises that the counter electrode 104 consists of unconnected pieces, which of course is not the case in reality. The Wire mesh or the grid electrode 104 can be understood as a covering structure with a distribution of openings, the covering structure 104 covering the surface of the dielectric cap 103. The distribution of the openings, that is to say in this embodiment the distribution of the grid openings, is preferably designed to be spatially homogeneous.

In one embodiment according to FIG. 1, the fastening element 106 is preferably adapted to create a dark space for the measuring electrode 101 by fastening the dielectric cap 103. According to FIG. 1, a dark space can thus be generated inside the dielectric cap 103, that is to say in a spatial region which is delimited by the coaxial cable, the fastening element 106 and the inside of the dielectric cap 103. In particular, the dark room is not closed in a vacuum-tight manner, so that in principle plasma can penetrate into the dark room. However, the plasma that penetrates the dark room does not have the kinetic energy required to ignite. In the dark room, for example, a vacuum of the same quality, that is to say for example with the same pressure, as outside the dielectric cap 103, in particular in the plasma, can prevail.

The counter electrode 104 according to FIG. 1 can be detached from the dielectric cap 103. It therefore only rests on the outside of the dielectric cap 103 and is not firmly connected to it, for example by vapor deposition or sputtering, which is entirely possible in other embodiments.

FIG. 2 shows an embodiment of the measuring probe which differs from that shown in FIG. 1. A measuring probe 100 'with a probe body 110' and a probe head 120 'can be seen, the probe body 110' extending along a longitudinal axis of the measuring probe 100 'and being adapted for measuring the variables characteristic of a plasma with the probe head 120' in FIG the plasma to be introduced. The measuring probe 100 'also has a measuring electrode 101', which is arranged on the probe head 120 ', the probe body 110' providing an electrical connection 102 'between the measuring electrode 10 and a part of the measuring probe 100' opposite the probe head 120 'along the longitudinal axis . The measuring probe 100 'also has a dielectric cap 103' which extends over the measuring electrode 101 'and is designed to isolate the measuring electrode 101' from the plasma. The measuring probe 100 'is also set up to generate an opposing electrical field which displaces negative charge carriers from the probe head 120'. With regard to the probe head 120, 120 ', the measuring electrode 101, 10T and the dielectric cap 103, 103', the measuring probes 100, 100 'are according to FIGS Fig. 1 and 2 formed similarly or identically. For example, the connection 102 'is also designed as a coaxial cable with an inner conductor 11G, an insulating or dielectric layer 112' and a shield 113 '. The measuring probe 100 'differs from the measuring probe 100 shown in FIG. 1, for example, in that the counter-electrode 104' is arranged in the interior of the dielectric cap 103 '. In addition, the counter electrode 104 'of the measuring probe 100' shown in FIG. 2 is designed as a ring arranged centered around the longitudinal axis of the measuring probe 100 '. In contrast to the one in Fig.

1, the probe body 110 'of the measuring probe 100' furthermore has a collar layer 107 'which faces the dielectric cap 103', the collar layer 107 'having a thickness that corresponds to an outer cross section of the probe body 110' to an inner one Aligns cross-section of the dielectric cap 103 '. The collar layer 107 ‘in FIG. 2 is an outer layer of the probe body 110‘, which surrounds the coaxial cable to the measuring electrode 101 ‘to below the probe head 120‘. The counter electrode 104 ‘does not necessarily have to be attached to the inside of the dielectric cap 103‘, but can also be embedded in the collar layer 107 ‘. Not in Fig.

2 shows the electrical connection 105 to the counter electrode 104 ‘. In the case shown, this can be embedded in the collar layer 107 '. For example, the electrical connection 105 can be designed as a coaxial cable which extends along a bore in the collar layer, wherein the bore can run parallel to the longitudinal axis of the probe body. If the collar layer 107 ‘consists of an electrically conductive material, the collar layer 107‘ can then preferably serve as a shield for the coaxial cable which forms the electrical connection 105 to the counter electrode 104 ‘.

3 shows a measuring probe 100 ″ with a probe body 110 ″, a probe head 120 ″ of the probe body 110 ″, a measuring electrode 101 ″ and a dielectric cap 103 ″, with respect to which the measuring probe 100 ″ differs from the measuring probe 100 shown in FIG 'Little or no difference. However, the measuring probe 100 ″ shown in FIG. 3 does not have a counter electrode, as is shown, for example, in FIG. 2 as an annular counter electrode 104 ′. Nevertheless, the measuring probe 100 ′ shown in FIG. 3 is set up to generate an opposing electrical field which displaces negative charge carriers from the probe head 120 ″. In particular, the opposing field can be generated at the measuring electrode 101 ″ itself, for example by applying a voltage to the measuring electrode 101 ″ via the electrical connection 102 ″, for example via the coaxial cable with the inner conductor 111 ″, the insulating or dielectric layer 112 ″ and the Shield 113 ". A suitable voltage can be applied, for example, by a voltage device 201, 202 to which the measuring probe 100 ″ is connected at its part opposite the probe head 120 ″. The measuring probes 100 ', 100 “der 2 and 3 have in common that a dark space is only in the area of the probe head 120 ', 120 ", that is to say the measuring electrode 10G, 101", through a form fit of the dielectric cap 103', 103 "and the collar layer 107 ', 107 “Can form. A fastening element 106, as shown in FIG. 1, can accordingly be dispensed with in the presence of a collar layer 107, 107 '. In particular, the form fit achieved by the collar layer 107 ', 107 "with the dielectric cap 103', 103" can already ensure sufficient attachment of the dielectric cap 103 ', 103 "to the probe body 120', 120". However, this is not mandatory. In particular, a collar layer 107, 107 ′ can also be provided together with a fastening element 106. 4 shows a measuring probe 100 '"according to the invention, the probe body 110'", the probe head 120 '", the probe body 110'", the measuring electrode 101 '", the electrical connection 102'" between the measuring electrode 101 and the probe head 120 '"along the longitudinal axis of the measuring probe 100'" opposite part of the measuring probe 100 '"and the dielectric cap 103'" corresponds to the measuring probes 100, 100 ', 100 "described with reference to FIGS. 1 to 3. The measuring probe 100 '"is also set up to generate an opposing electrical field that displaces negative charge carriers from the probe head 120'".

4 serves in particular to illustrate embodiments according to the invention, in which the probe body 110, 110 ', 110 ", 110'" is located in an area which extends in the longitudinal direction to the dielectric cap 103, 103 ', 103 ", 103'" adjoins, has an insulating cladding layer 108 '". The insulating cladding layer 108 '"shown in FIG. 4 has a thickness which, in its outer cross-section, has the area that adjoins the dielectric cap 103, 103', 103", 103 '"in its outer cross section to the outer cross section of the dielectric cap 103, 103 ', 103 ", 103'". The stepless exterior of the measuring probe 100 ″ that can be achieved in this way can in principle also be achieved in the presence of a fastening element 106 if the fastening element 106 is appropriately adapted in terms of its arrangement and geometry.

5 shows, by way of example and schematically, a further measuring probe 800 with a probe body 810, a probe head 820 of the probe body 810, a measuring electrode 801 and a dielectric cap 803 is arranged, wherein the probe body 810 provides an electrical connection 805 between the counter electrode 804 and the opposite part of the measuring probe 800 along the longitudinal axis. The measuring probe 800 is set up to generate the opposing electrical field by means of the opposing electrode 804. In particular, the counter electrode 804 has a structure that partially covers a surface of the dielectric cap 803 in the region of the probe head 820, the degree of coverage of the structure of the counter electrode 804 being spatially homogeneous. That is, the ratio a) of the area of the non-openings of the cover structure Regarding b) the total area of the covering structure, which comprises both the openings and the non-openings of the covering structure, is preferably constant for different regions of the dielectric cap 803 in which the covering structure is located.

In this embodiment, the measuring probe 800 is also designed such that the dielectric cap, when the measuring probe is inserted into a plasma-generating container 830, which is partially shown in FIG Plasma, is located.

In the embodiment shown in FIG. 5, an electrical connection 802 between the measuring electrode 801 and the part of the measuring probe 800 opposite the probe head 820 is also shown, which in this case has an inner conductor 811, a dielectric layer 812 and a shield 813, such as for Example in the case of a coaxial cable. The embodiment shown in FIG. 5 also shows an electrical connection 805 between the counter electrode 804 and the opposite part of the measuring probe 800, which has an inner conductor 814, a dielectric layer 815 and a shield 816.

6 shows, by way of example and schematically, a further measuring probe 900 according to the invention with a probe body 910, a probe head 920 of the probe body 910, a measuring electrode 901 and a dielectric cap 903 - urges. In particular, the opposing field can be generated by the measuring electrode 901 itself, for example by applying a voltage to the measuring electrode 901 via the electrical connection 902, for example via an inner conductor 911, which is comprised of an insulating or dielectric layer 912 and a shield 913, which is also called Part of a plasma container can be understood is surrounded. In Figures 1 to 6, the measuring electrode 101, 10T, 101 ", 101 801, 901 is cylindrical, with a head end of the measuring electrode 101, 10T, 101", 10T ", 801, 901 is flat, ie is described by a plane, which runs in particular perpendicular to the longitudinal axis of the measuring probe. The head end of the measuring electrode can, however, also be designed differently. 7 is an exemplary and schematic representation of an embodiment of a further measuring electrode which can be used in the measuring probe 100, 100 ', 100 ", 100'", 800, 900 according to the invention. For reasons of space, only the reference symbol 101 is used in FIG. 7, although the measuring electrodes 10, 101 ″, 101 ′ ″, 801, 901 can also have corresponding head ends. The measuring electrode 101 shown in FIG. 7 is curved, in particular hemispherical, at its head end, which is arranged in the probe head 120, 120 ', 120 ", 120'", 820, 920, other curved shapes such as an elliptical shape also being conceivable .

All of the measuring probes 100, 100 ′, 100 ″, 100 ′ ″, 800, 900 described with reference to FIGS. 1 to 6 have in common that they are designed to be cylindrically symmetrical with respect to their longitudinal axis, the dielectric cap 103, 103 ′, 103 “, 103 '“, 803, 903 has a dome-shaped head end with a U-shaped longitudinal section. The dielectric cap 103, 103, 103 ″, 103 ‘″, 803, 903 is also preferably designed to be cylinder-symmetrical and, for example, arranged centered on the longitudinal axis of the measuring probe 100, 100‘, 100 ″, 100 ‘“, 800, 900.

It goes without saying that the measuring probes 100, 100 ', 100 ", 100'", 800, 900 shown in FIGS. 1 to 6 can also be used as a combination of the respective measuring probe 100, 100 ', 100 ", 100'", 800 , 900 without dielectric cap 103, 103 ', 103 ", 103'", 803, 903 and the corresponding dielectric cap 103, 103 ', 103 ", 103"' 803, 903 could be considered. According to this approach, the measuring probes shown are preferably measuring structures 110, 110 ', 110 ", 110'", 810, 910, 101, 101 ', 101 ", 101 801, 901, that is to say measuring structures which, with regard to the probe body 110, 110', 110 ", 110 '", 810, 910, of the probe head 120, 120', 120 ", 120 '", 820, 920, of the probe body 110, 110', 110 ", 110 '", 810, 910, of the measuring electrode 101 , 101 ', 101 ", 101 801, 901 and the electrical connection 102, 102',

102 ", 102 '", 802, 902 between the measuring electrode 101, 101', 101 ", 101 '" 801, 901 and the one opposite the probe head 120, 120', 120 ", 120 '", 820, 920 along the longitudinal axis Part of the measuring probe 100, 100 ', 100 ", 100'", 800, 900 correspond to the measuring probe 100, 100 ', 100 ", 100"', 800, 900, whereby the measuring structure 110, 110 ", 110", 110 '", 810, 910, 101, 10T, 101", 10T ", 801, 901 are each set up to generate an opposing electrical field that displaces negative charge carriers from the probe head, and the probe body 110, 110", 110 ", 110 '", 810, 910 is designed to receive a dielectric cap 103, 103", 103 ", 103 '", 803, 903 in such a way that it is positioned over the measuring electrode 101, 101', 101 ", 10T", 801 , 901 extends and the measuring electrode 101, 10T, 101 ″, 10T ″, 801 901 seals off the plasma. According to the same approach, FIGS. 1 to 6 also show a dielectric cap 103, 103 ", 103", 103 '", 803, 903 for use with a measuring structure 110, 110 ', 110 ", 110'", 810, 910, 101, 10, 101 ", 101 801, 901, whereby the dielectric cap 103, 103 ', 103", 103'" , 803, 903 is designed to be received by the probe body 110, 110 ', 110 ", 110'", 810, 910 in such a way that the dielectric cap 103, 103 ', 103 ", 103'", 803, 903 extends over the measuring electrode 101, 101 ', 101 ", 101'", 801, 901 and separates the measuring electrode 101, 10, 101 ", 101 '", 801, 901 from the plasma. 1 to 6 could also show the use of such a dielectric cap 103, 103 ', 103 ", 103'", 803, 903 with a corresponding measuring structure 110, 110 ', 110 ", 110'", 810, 910, 101, 101 ', 101 ", 101 801, 901 are understood. 8 illustrates that the electrical connection 102 ', 102 "between the measuring electrode 101', 101" and the part of the measuring probe 100 ', 100 "opposite along the longitudinal axis can be designed to be flexible or semi-rigid. In the embodiment shown in FIG. 8, the electrical connection 102 ', 102 "is a flexible or semi-rigid coaxial cable that is bent out of its orientation along the longitudinal axis in two different ways. The probe body 110 ', 110 ", over the collar layer 107, 107" of which the dielectric cap 103', 103 "extends, has corresponding orientations. The probe head 120 ', 120 ″ and thus the measuring electrode 101, 101 ″ can therefore be brought into different measuring positions in a simple manner by means of a flexible or semi-rigid design of the electrical connection 102 ′, 102 ″. Also shown in FIG. 8 is the electrical connection 210 of the measuring probe 110 ′, 110 ″ for connecting a voltage device 201, 202, a signal receiving unit 203 and an evaluation unit 204. FIG. 8 only mentions the embodiments of the measuring probes 100 ′, 100 as examples ". The electrical connections 102, 102 ′ ″, 802, 902 between the measuring electrode 101, 101, 801, 901 and the part of the measuring probe 100, 100 ′ ″, 800, 900 opposite along the longitudinal axis can also be flexible or semi-rigid.

9 shows a measuring system 300 for measuring quantities characteristic of a plasma. In the case shown in FIG. 9, the measuring system 300 has, for example, a measuring probe 100 ′ ″, as shown in FIG. 4. However, it is also conceivable that the measuring system 300, instead of the measuring probe 100 ′ ″, has one of the measuring probes 100, 100 ′, 100 ″, 800, 900. The measuring system 300 also has a voltage device 201, 202, a signal receiving unit 203 and an evaluation unit 204. The voltage device 201, 202 is set up to generate an input signal and an electrical opposing field, the voltage device 201, 202 being connected to the measuring electrode 101 via an electrical connection 210 to the measuring probe 100 '"to generate the input signal. is bound. The signal receiving unit 203 is set up to receive an output signal, the signal receiving unit 203 being connected via the electrical connection 210 to the measuring probe for receiving the output signal to the measuring electrode 101. The evaluation unit 204 is set up to determine the variables characteristic of the plasma based on the output signal.

The voltage device 201, 202 of the measuring system 300 is preferably adapted to provide the input signal at a high frequency and to provide the opposing electrical field at a low frequency or constant. In FIG. 9 it is shown that the voltage device can for this purpose, for example, have a first voltage source 201 and a second voltage source 202, the first voltage source 201 being adapted to generate the input signal, and the second voltage source 202 being adapted to the electrical Generate opposing field. In the measuring system 300 shown in FIG. 9, the first voltage source 201, the signal receiving unit 203 and the evaluation unit 204 are designed in the form of a network analyzer, specifically a vector network analyzer (VNA), the second voltage source 202 according to Fig. 9 is not part of the network analyzer.

As is also shown in FIG. 9, the measurement system 300 can have a high-pass filter 205 for filtering the output signal. Such a device can be arranged, for example, between the first signal source 201 and the second signal source 202. In the measuring system 300 shown in FIG. 9, the second voltage source 202 of the voltage device 201, 202 is adapted to generate the opposing electric field via the electrical connection 210 with the measuring probe 100 ′ ″ on the measuring electrode 10T ″, as is also the case with the measuring probe 100 "with the measuring electrode 101" or the measuring probe 900 with the measuring electrode 901. If the measuring probe were designed according to FIG. 1, FIG. 2 or FIG. 5, that is, if it had, in particular, a counter-electrode 104, 104 ', 804 different from the measuring electrode 101, 10T, 801, the counter-electrical field could also be via the electrical counter-field Connection 210 to the measuring probe can be generated, the opposing field then being able to be generated at the opposing electrode 104, 104 ', 804.

A measuring system 300, as shown in FIG. 9, can be adapted for high-resistance measurement and for low-resistance measurement. For example, it is conceivable that the measuring system 300 for this purpose has a resistance control unit for regulating a resistance, in particular an impedance, of the measuring system 300. The measuring system 300 can in particular be adapted to determine at least one variable selected from the group consisting of electron density, ion density, temporal progression of the plasma potential, temporal progression of the floating potential and electron energy probability function as the quantities characteristic of the plasma. For measuring the electron density, the voltage device 201, 202 can be adapted to generate the input signal with varying frequency during a measuring period for measuring the electron density and not to generate an opposing electric field, wherein the signal receiving unit 203 can be adapted to receive the output signal during the measuring period, wherein the evaluation unit 204 can be adapted to determine the electron density on the basis of the input signal and the output signal. In particular, the measuring probe can be used as a plasma absorption probe.

To measure the temporal course of the plasma potential, the signal receiving unit 203 of the measuring system 300 can be adapted to receive the output signal with high resistance during a measuring period for measuring the temporal course of the plasma potential to determine high resistance recorded output signal. To measure the temporal course of the floating potential, on the other hand, the signal receiving unit 203 can be adapted to record the output signal with low resistance during a measuring period for measuring the temporal course of the floating potential, wherein the evaluation unit 204 can be adapted to the temporal course of the floating potential To determine the basis of the low-resistance recorded output signal.

The measuring probe can therefore be used as a capacitive measuring probe in different ways.

To measure the electron energy probability function, the voltage device 201, 202 and the signal receiving unit 203 of the measuring system 300 can be adapted to generate the input signal with varying frequency for different opposing fields and to record the output signal, wherein the evaluation unit 204 can be adapted to the electron energy To determine the probability function on the basis of the input signals generated for the different opposing fields and the output signals recorded for the different opposing fields. 10 shows a plasma coating system 500 with a plasma generating device

400 for generating a plasma with a coating material and a measuring system 300 for measuring quantities characteristic of the plasma, as is shown, for example, in FIG. 9. The plasma generating device 400 has an excitation electrode 401 which is electrically connected to a capacitive high-frequency energy source 403 via an adapter circuit 402. In the sectional illustration of FIG. 10, the excitation electrode 401 has the shape of an angular Us, with the excitation electrode

401 also extends in the direction orthogonal to the cutting plane. If the excitation electrode 401 is subjected to an excitation voltage of, for example, 13.56 MHz at a power of, for example, 2300 W, a plasma can form inside the plasma container 410. The door 411, the rear wall of the plasma container 410 opposite the door 411 and not shown in FIG. 10, and a grid 407 in the upper part of the container interior serve as a counter electrode for the excitation electrode 401 for the excitation electrode 401, when the door 411 of the plasma container 410 is closed, also has the shape of an angular U with a corresponding depth, the counter-electrode being rotated by 45 ° with respect to the excitation electrode 401 with respect to a vertical axis of the plasma container 410. In this way, a symmetrical electrode arrangement for generating the plasma is achieved. The door 411 and the rear wall of the plasma container 410 and the grid 407 are preferably grounded. The adaptation circuit 402 serves to compensate for the uneven resistance of the plasma and at the same time to protect the high-frequency energy source 403 from backscattered power. The plasma container 410, specifically the excitation electrode 401, is connected to the matching circuit 402 and thus indirectly to the high-frequency energy source 403 via a vacuum current feedthrough 404. The excitation electrode 401 is insulated from the outer wall of the plasma container 410 by an insulation 405. The pressure in the interior of the plasma container 410 is controlled via a valve 406, via which gas can escape from the interior of the plasma container 410. The valve 406 can have a butterfly valve, for example. The grille 407 prevents burning plasma from escaping through the valve 406. Gas enters the interior of the plasma container 410 via a feed line 408.

In order to generate a coating plasma by means of the plasma generating device 400, the interior of the plasma container 410 can, for example, first be evacuated to a pressure of 1.0 Pa (Pascal) and then hexamethyldisiloxane (HMDSO) and oxygen (O2) in a ratio of HMDSO to O2 of 1.73, the pressure inside the plasma container being reduced to 1.2 Pa during the coating process can be held. The use of HMDSO can serve to form plasma polymer layers. Instead of HMDSO, however, argon (Ar) could also be used. The material to be coated can be introduced into the interior of the plasma container 410 via an opening 412 in the door 411 of the plasma container 410, for example. A further opening 413 in the door 411 of the plasma container 410 can be provided in order to introduce a measuring probe into the interior of the plasma container 410. The measuring probe inserted through the opening 413 can in particular be a known measuring probe such as a Langmuir probe. The measuring probe 100, 100 ′, 100 ″, 100 ′ ″, 800, 900 can then, for example, be introduced into the interior of the plasma container 410 via an opening in the rear wall of the plasma container 410.

10 also shows that the plasma coating system 500 has a control unit 501 for controlling the plasma generating device 400, which is adapted to control the plasma generating device 400 as a function of the measured values characteristic of the plasma. Such a control unit 501 could, for example, be connected to the measurement system 200 in order to receive measurement data from the measurement probe

100 to receive. The control unit 501 could also be connected, for example, to the plasma generating device 400, in particular to the high-frequency energy source 403, the supply line 408 and the valve 406, in order to control them. However, the control unit 501 could also be provided integrated in the measuring system 200 or in the plasma layering device 400.

11 shows a measuring method 600 for measuring a variable that is characteristic of a plasma, the method introducing 601 a probe head 120, 120 ', 120 ", 120'", 820, 920 of a measuring probe 100, 100 ', 100 ", 100 '", 800, 900 into the plasma as well as generating 602 an opposing electric field which displaces negative charge carriers from the probe head 120, 120', 120", 120 '", 820, 920. Furthermore, the procedure

600 a generation 603 of an input signal at a measuring electrode 101, 10T, 101 ",

101 801, 901 of the measuring probe 100, 100 ‘, 100“, 100 ‘“, 800, 900, which are attached to the probe head

120, 120 ', 120 ", 120'", 820, 920 is arranged, and receiving or recording 604 of an output signal from the measuring electrode 101, 10T, 101 ", 101 801, 901, which is indicative of a degree of Absorption of the input signal by the plasma is on. In addition, the method 600 includes determining 605 the variable characteristic of the plasma based on the output signal. In particular, the input signal can be generated with a varying frequency and the variable characteristic of the plasma can be determined based on the input signal and the output signal.

The input signal can be understood physically as an electromagnetic wave or an electromagnetic pulse, which is initially located within the area defined by the dielectric cap 103, 103 ', 103 ", 103'", 803, 903 on the probe head 120, 120 ' , 120 ", 120 '", 820, 920 expands and stimulates one or more cavity modes there. With regard to their intensity, part of the cavity mode or cavity modes is coupled out of the cavity into the surrounding plasma. The decoupled part excites a surface wave which propagates between the dielectric cap and the plasma according to a certain dispersion relation w = w (l), where w is the (circular) frequency and l is the wavelength of the surface wave.

The characteristic variable which is measured according to the method 600 can in particular be an ion density of the plasma. Likewise, the characteristic variable measured according to method 600 could be an electron density of the plasma, in which case the step of generating 602 the opposing electrical field can be omitted or the opposing electrical field can only be generated with a low intensity. Furthermore, the characteristic variable measured according to method 600 can also be an electron energy probability function of the plasma, in which case the step of generating 602 the opposing electrical field could be repeated, with a different opposing electrical field being generated with each repetition could, and wherein the steps of generating 603 the input signal, receiving 604 the output signal and determining 605 the variable characteristic of the plasma, that is in this case the electron energy probability function, would be repeated for the different generated opposing electric fields. In this sense, FIG. 11 illustrates, in very general terms, plasma absorption spectroscopic measurements by means of the measuring probe 100, 100, 100 ″, 100 ″, 800, 900.

The degree of absorption of the input signal by the plasma, for which the received or recorded output signal is indicative, is preferably indicated by a reflection coefficient, but can also be indicated, for example, by an absorption coefficient. Derived variables such as a standing wave ratio or additional variables such as the phase can also be used to represent the output signal. The degree of absorption can be determined, for example, by means of the evaluation unit 204. An evaluation unit 204 suitable for this can be, for example, a network analyzer, which can also serve as a voltage device 201 and a signal receiving unit 203 at the same time. Commercially available network ca na lysers are able to display reflection coefficients directly. A determination of the degree of absorption is particularly easy with network catalysts. The network analyzer can be calibrated in a conventional manner, for example using the open, short and load standards. In order to keep the signal-to-noise ratio low and to avoid setting a delay time, the network analyzer can be calibrated while it is connected to the measuring probe. For this purpose, for example, the short and load standards can be connected to the probe head without the dielectric cap attached, in particular to the measuring electrode itself. It is important to ensure that the connection is adequately grounded, especially for long probe heads. The open calibration can then be carried out with the dielectric cap attached. The open calibration can preferably be carried out when the measuring probe is already in its later measuring position, for example in the plasma container. In this way, parasitic influences of the grounding environment can be reduced.

Alternatively, the voltage device 201, 202 can have a function generator to determine the degree of absorption, the function generator generating the input signal as a signal which has a relatively high spread in the frequency domain. For example, it can be provided that the spread exceeds a predetermined spread value. The input signal can then have a sawtooth shape, for example. Furthermore, a directional coupler can be provided as part of the measuring system 300, which is adapted to separate the input signal generated by the function generator from the corresponding output signal, wherein the signal receiving unit 203 can be set up to receive the input signal and the output signal separately. The evaluation unit 204 can be set up to determine the degree of absorption, in particular a reflection coefficient, from the frequency spectra of the input signal and the output signal obtained via a Fourier transformation. Compared to the use of a network analyzer, the use of a function generator is inexpensive and also has the advantage that relatively high signal levels can be achieved.

The degree of absorption of the input signal by the plasma is dependent on the frequency of the input signal in accordance with the spectral properties of the plasma. The spectral properties of the plasma are such that, for example, in a Representation of the degree of absorption of the input signal by the plasma, the reflection coefficient has a minimum, in particular a local minimum, at a frequency W. The frequency W could be understood as a resonance frequency at which the plasma absorbs the input signal particularly strongly, in particular most strongly. In physical terms, the resonance frequency W is that frequency which, according to the dispersion relation w = w (l) of the excited surface wave, corresponds to a wavelength l of the surface wave that is in an integer ratio to an expansion of the probe head serving as a cavity. In particular, the resonance frequency W can be l = 2d _l , where

can denote the length of the probe head in the longitudinal direction. To determine the electron density of the plasma, it is assumed that the frequency W is related to the plasma frequency w _b . The latter is given by

wherein n _{e is} the electron density, e is the elementary charge, e is _0, the dielectric constant Fe Id and m _e is the (rest) electron mass. It is preferably assumed that the frequency W is proportional to the plasma frequency w _b , that is to say W = aw _b , the proportionality factor a depending on the measuring probe used. To determine the proportionality factor a, the measuring probe is preferably calibrated, it being possible in particular to use a known probe model for the calibration. For example, such a probe model can parameterize a dependency of the proportionality factor a on a geometry of the probe head on the basis of selected geometric variables. These variables can specify, for example, the volume of an area within the dielectric cap, in particular the volume of the dark space around the measuring electrode formed by the dielectric cap. If this volume is changed by moving the dielectric cap, the proportionality factor a can be determined from the dependence of the frequency W, at which the reflection coefficient becomes minimal, on the changed volume based on the probe model. For example, the proportionality factor a can be determined by fitting the measured dependence of the frequency W, at which the reflection coefficient becomes minimal, on the changed volume of the area within the dielectric cap to a dependency predetermined by the probe model. The proportionality factor a preferably corresponds to a value of the quotient calculated based on the probe model from the frequency w one of the Input signal excited surface wave and the plasma frequency a> _e for a first order resonance.

Selected geometric variables on which a probe model can be based are, for example, the following: a length d _{t of} the measuring electrode 101, 101 ', 101 ″, 101 801, 901, that is, for example, the length by which the inner conductor of the coaxial cable is used

Probe head 120, 120 ', 120 ", 120'", 820, 920 protrudes, the length d _{t being} measured in the longitudinal direction of the measuring probe 100, 100 ', 100 ", 100'", 800, 900 (here the index " f for "tip"); an extension l _{p of} the measuring electrode 101, 101 ', 101 ", 101 801, 901 in a direction transverse to the longitudinal direction of the measuring probe 100, 100', 100", 100 '", 800, 900, that is, for example, a radius l _p des Inner conductor of the coaxial cable (here “p” stands for “probe”); a length of the probe head 120, 120 ', 120 ", 120'", 820, 920, that is, for example, the distance between the end of the coaxial cable from which the inner conductor protrudes as measuring electrode 101, 101 ', 101 ", 101 801, 901 , and the foremost piece of the head end of the dielectric cap 103, 103 ', 103 ", 103'", 803, 903, where also the length

is measured in the longitudinal direction of the measuring probe 100, 100 ', 100 ", 100'" (here the index stands for "length"); an internal extension of the dielectric cap in a direction transverse to the longitudinal axis of the measuring probe 100, 100 ', 100 ", 100'", 800, 900, that is to say, for example, the inner radius of a U-shaped dielectric cap 103, 103 ', 103 ", 103'", 803, 903; and / or an outer extension r _{a of} the dielectric cap 103, 103 ', 103 ", 103'", 803, 903 in a direction transverse to the longitudinal axis of the measuring probe 100, 100 ', 100 ", 100'", 800, 900, the is, for example, the outer radius of the U-shaped dielectric cap 103, 103 ', 103 ", 103'", 803, 903. In one embodiment, these variables can for example be the values d _t = 15 mm, l _p = 0.45 mm,

= 15 mm, = 4 mm and r _a = 5 mm, although other values can also be advantageous. In particular, it is not decisive which specific value l _p the radius of the inner conductor of the coaxial cable assumes. An exemplary probe model is described in the article “Plasma Absorption Probe for Measuring Electron Density in an Environment Soiled with Processing Plasmas” by H. Kokura et al. , Japanese Journal of Applied Physics, Vol. 38, pp. 5262 to 5266 (1999). As an alternative or in addition to the calibration using a probe model, the measuring probe 100, 100 ', 100 ", 100'", 800, 900 can be calibrated using a comparative measurement using a second measuring probe. For the second measuring probe, there is preferably the relationship between the frequency u 'measurable with it, at which the degree of absorption of the input signal by the plasma becomes particularly strong or strongest, and the plasma frequency w _b , that is, for example, a corresponding proportionality factor a ', is known. For example, the proportionality factor a can then be determined by comparing the frequencies W and u 'determined with the two measuring probes, with a = - a'. In general terms, for the purpose of calibration, a value of the electron density determined with the measuring probe to be calibrated could be corrected in accordance with a value of the electron density determined with the second measuring probe. The second measuring probe can be, for example, a calibrated measuring probe 100, 100 ', 100 ", 100'", 800, 900, a Langmuir probe or another measuring probe.

If the relationship between the frequency W, at which the absorption of the input signal by the plasma becomes particularly strong or preferably maximal, and the plasma frequency w ", that is, for example, the proportionality factor, is known, the frequency W can start directly the electron density n _{e can be} closed, since the right-hand side of Eq. (1) otherwise only contains natural constants.

The Gl. (1) also applies in a corresponding manner to the ions in the plasma. A frequency w * characteristic of the ions in the plasma is thus given by

where the ion density, e the elementary charge, e ₀ the dielectric field constant and

denotes the ion mass. However, the frequency w _{έ is} not easily accessible, since the electrons, which are much lighter and therefore more mobile than the ions, shield the heavier and therefore more inert ions instantaneously or quasi-instantaneously (m * »m _e ), which is also reflected in the In comparison to the plasma frequency w _b , the frequency w * which is characteristic of the ions and which is typically at values below 10 MHz is significantly lower. A measurement of the frequency w * and thus the ion density rii of the plasma is therefore impaired by the electrons, since the electrons can easily follow an input signal that actually excites the ions and thus reduce the excitation of the ions by shielding. The impairment occurs although the plasma edge layer surrounding the probe head 120, 120 ', 120 ", 120'", 820, 920 is dominated by ions according to the plasma theory. In order to still be able to perceive an absorption of the input signal by the ions, an electrical opposing field is generated by means of the measuring probe 100, 100 ', 100 ", 100'", 800, 900, which the electrons displaced by the probe head 120, 120 ', 120 ", 120'", 820, 920 and thus the width of the plasma edge layer, that is to say, for example, its extension in an area to the outer surface of the dielectric cap 103, 103 ', 103 ", 103'", 803 , 903 local vertical direction, enlarged. The widened plasma edge layer leads to an increased interaction of the measuring probe 100, 100 ', 100 ", 100'", 800, 900, in particular that on the measuring electrode 101, 101 ', 101 ", 101 801, 901 of the measuring probe 100, 100 ', 100 ", 100'", 800, 900 generated input signals with the plasma. An interaction surface between the measuring probe 100, 100 ', 100 ", 100'", 800, 900 and the plasma can also be designed to be as large as possible, for example through corresponding geometries of the dielectric cap 103, 103 ', 103 ", 103'", 803, 903. The intensification of the interaction between ions and measuring probe achieved by an enlarged interaction surface is mainly considerable in very thin plasmas, in particular with plasma densities below 10 ¹⁵ mr ³ . For higher plasma densities, the increase in the interaction with the ions that can be generated by an opposing field becomes more important. In the presence of the opposing electric field, the ion density can be calculated based on Eq. (2) can be determined analogously to the electron density, whereby the ions contained and thus the ion mass mi can be assumed to be known for a given plasma.

The opposing electric field is preferably generated by generating an electric potential on the probe head, the value of which in the area of the probe head is lower than the floating potential. In this way, an increase in the quality, in particular the intensity, of the recorded output signal can be achieved without the resonance frequency and thus the value of the ion density to be determined shifting due to the increased interaction of the input signal with the ions in the plasma due to the opposing field. An additional calibration of the measuring probe can be carried out to measure the ion density. As above with regard to the measurement of the electron density, this can be done using a measurement using a second measuring probe. For example, a reference value for the ion density can be determined by measuring the electron density in the interior of the plasma by means of a Langmuir probe. According to the principle of quasi-neutrality, which can be assumed for the interior of the plasma, this value can serve as a reference value for the ion density. Instead of the Langmuir probe, the measuring probe calibrated for measuring the electron density itself can also be used. In particular, however, a direct comparison of the absorption frequency determined by means of the measuring probe for the measurement of the ion density and an ion density determined by means of a Langmuir probe should be avoided, since that determined by the Langmuir probe ion density can be falsified by influences of the probe geometry, in particular on the ion current measured by the Langmuir probe.

The network analyzer can also have an additional calibration for measuring the ion density, which is adapted to the lower range of measurement frequencies compared to the measurement of the electron density, in particular the lower absorption frequency, which is typically in the megahertz or kilohertz range. Common network analyzers are able to save various calibrations and load them on demand. For a particularly rapid switchover between the measurement of the electron density and the measurement of the ion density, a fine calibration of the network analyzer over all required measurement frequencies can also be provided.

The opposing electric field also offers the possibility of energizing the electrons in the plasma in an energy-selective manner. In particular, the electron density can be measured with a varying strength of the opposing field, i.e., for example, with a varying size of a DC voltage applied to the opposing electrode 104, 104 ', 804, the dependence of the measured electron density on the strength of the opposing field as a measure of the electron energy probability function (EEPF) can be used. This makes use of the fact that, with increasing strength of the opposing field, fewer electrons can penetrate into the plasma edge layer surrounding the probe head 120, 120 ', 120 ", 120'", 820, 920 and thus fewer electrons from the plasma from the one at the measuring electrode 101, 101 ', 101 ", 101 801, 901 of the measuring probe 100, 100', 100", 100 '", 800, 900 generated input signal can be excited. The electron energy probability function indicates the number of electrons with a certain energy present in a volume element of the plasma and is essentially equivalent to the electron energy distribution function, the difference being only one normalization. This becomes clear from the following equation, in which f _p e) denotes the electron energy probability function of the plasma for an electron energy e and F (e) denotes the electron energy distribution function for the same electron energy.

The electron energy distribution function indicates the number of electrons in the plasma per volume element that have an energy between e and e + Ae. Usually the electron energy distribution function is given in units of (eV · m ³ ) ^-1 . Both the electron energy probability function and the electron energy distribution function therefore generally contain more information about the electrons in the plasma than would be given by an electron temperature. Only in the special and only theoretically achievable case of a perfect Maxwell-Boltzmann distribution would the electron temperature give an electron energy probability function. However, a Maxwell-Boltzmann distribution is only achieved under a few plasma conditions, and even then only approximately in general practice. In particular, no Maxwell-Boltzmann distribution can be assumed under layer-forming plasma conditions. Deviations from a perfect Maxwell-Boltzmann distribution are particularly clear in a semi-logarithmic representation of the electron energy probability function, since in the case of a perfect Maxwell-Boltzmann distribution this takes the form of a straight line. The following explanations therefore relate only to the electron energy probability function, with the same applies to the electron energy distribution function. The electron energy distribution function can thus be measured according to the same principle as is explained below with reference to the electron energy probability function.

The measurement of the electron energy probability function can be understood as a measurement of the electron density for different electron energies, i.e. as a measurement of a function N = n _e (e). This makes use of the fact that a measurement volume can be defined by the penetration depth of the input signals in the plasma. In particular, the skin depth d can be used as a measure for the measurement volume. The following applies to the skin depth

where c is the speed of propagation of electromagnetic waves and thus also of the input signals in the plasma and w _{r is} the plasma frequency. Together with the expression for the plasma frequency from Eq. (1) it follows that the skin depth only depends on the electron density, whereby the skin depth decreases with increasing electron densities,

The measurement volume will also only depend on the electron density, whereby it will decrease with increasing electron densities.

To measure the electron energy probability function, the opposing electric field is _{generated by means of the measuring probe in accordance with an electric potential V g} , the value of which is varied over a predetermined range. The range over which the potential V is varied is selected such that the potential V _g is smaller than the plasma potential V _p over the entire range. The potential V _g corresponds, for example, to a voltage which is applied to the counter electrode 104, 104 ', 804 of the measuring probe 100, the voltage in relation to the ground, i.e. for example to the shielding 116 of the coaxial cable 105, 805 to the counter electrode 104, 804, can be measured. The plasma potential V _p can also be understood as a voltage in relation to ground, that is to say for example likewise to the shield 116, 816 or also to the shield 113, 813 of the coaxial cable 110, 810. The electron energy e corresponding to a certain potential V _g and thus also a certain opposing field results in e = e (V _p - V _g ). (6)

The electron energy is therefore proportional to a value of the potential V _g renormalized by the plasma potential. If the potential V _g _{and thus the opposing field is now varied, the electron density n t being} determined for different opposing fields as described above, pairs of values can be formed from electron energy e and electron density n _t , each corresponding to a potential V _g and thus to an opposing field and from which the electron energy probability function results as a function of the form N = h _b (e). In particular, the electron energy probability function can be determined in this way up to a proportionality factor.

The measured electron energy probability function can be made more precise with regard to the proportionality factor by taking into account the drop in the opposing field with the distance to the probe tip. For example, the electron energies of the pairs of values, from which the function N = h _b (e) results, can be renormalized, taking into account the potential corresponding to the opposing field, which decreases with the reciprocal of the distance, that is, Eq. (6) should be corrected accordingly. This correction takes into account the fact that by means of the measuring probe 100, 100 ', 100 ", 100 '“, 800, 900 is not measured, as with a Langmuir probe by measuring an electron current on the probe surface, only along an interaction surface, but within a measurement volume, and that increasingly stronger opposing fields are generated to displace the electrons from outer areas of the measurement volume - have to.

Analogously to the measurement of the electron energy probability function, the measuring probe can also be used for a measurement of the ion energy probability function. Alternatively, the ion energy probability function can also be determined via an increase in the output signal corresponding to a width, such as a half-width, of a resonance frequency W, it being possible to make use of the fact that the width can correlate with an average energy of the ions.

As mentioned above, FIG. 11 illustrates primarily plasma absorption spectroscopic measurements, that is to say, for example, the methods described above for measuring the electron density, the ion density and the electron energy probability function. However, the steps of inserting 601 the probe head, receiving or recording 604 an output signal from the measuring electrode and determining 605 the variable characteristic of the plasma are also carried out in passive measurements using the measuring probe 100, 100 ', 100 ", 100'", 800, 900, in which case the received or recorded output signal is not indicative of a degree of absorption by the plasma, since no input signal is generated. The capacitive measuring principle is explained in more detail below with reference to FIGS. 12 and 13, the capacitive measuring principle being described using the example of the measuring probe 100 "and equivalent to the measuring probes 100, 100, 100‘ ", 800, 900.

12 shows a measuring probe 100 ″ inserted into a plasma P, only electrical parameters of the system comprising plasma P and measuring probe 100 ″ being specified. The electrical connection 102 ″ and the measuring electrode 101 ″, which in the example shown are formed by an extended inner conductor 111 ″ of a coaxial cable 111 ″, 112 ″, 113 ″, can be assigned a first inductance L _x . The probe tip, more precisely the inner conductor 111 ″ and the head end of the dielectric cap 103 ″, can also be assigned a first capacitance C _x . Together with the shielding 113 ″ of the coaxial cable 111 ″, 112 ″, 113 ″, the inner conductor 111 ″ meanwhile forms a capacitance C ₂ . In addition, the coupling between the probe head 120 ″ and the plasma can be described by a capacitance C _s which is formed by the head end of the dielectric cap 103 ′ and the plasma. The capacitance C _s can also be understood as the capacitance of the plasma edge layer, which forms around the probe head 120 "when the measuring probe 100" is inserted into the plasma (the index "s" stands for "sheath"). The plasma edge layer can be assumed to be purely capacitive for most high-frequency plasmas.

13 shows an equivalent circuit diagram corresponding in parts to FIG. 12, from which it can be seen that the capacitance C ₂ , the inductance L _lt, the first capacitance C _x and the capacitance C _s can be understood as being connected in series. The inductance L _lt, the first capacitance C and the capacitance C _s can be combined to form a first impedance Z ₁ , whereby the second capacitance C ₂ would form a second impedance Z _2. The voltage drop across the entire series circuit, which corresponds to the floating potential V _f , is divided into a portion _{that drops across the second impedance Z 2} , that is to say _{across the second capacitance C 2} , and a remaining portion. The portion that drops across the second impedance, ie across the second capacitance C ₂ , corresponds to a potential V _pp (here the index “pp” stands for “peak-to-peak”). Thus z 2 applies

^Vpp z ₁ + z ₂ V ^f _f (7) with

1 1

Zi + jio L ₁ (8) jo C _s juiCi and

where j denotes the imaginary unit.

The equivalent circuit diagram shown in Fig. 13 contains about derivable from Fig. 12, to the measuring probe 100 "associated elements, the impedances Z _a and Z _b, which a part of the measuring system outside the probe 100" are assigned. The choice of the impedances Z _a and Z _b determines whether high-resistance and thus the plasma potential is measured or whether low-resistance and thus the floating potential is measured. Preferably, Z _{b is} fixed and only Z _{a is} varied. Z _b can be used in particular for both Both moderate and high-resistance measurement can be selected in order _{to influence a voltage drop across Z a} as little as possible. Particularly in the event that an oscilloscope is provided as the evaluation unit 204 of the measuring system 200, an appropriate choice of the impedance Z _{b is} decisive, since the input resistance of the oscilloscope is usually of the order of 1 MW and is therefore not sufficient. The choice of impedances Z _a and Z _b is ensured by using appropriate components, particularly in the megahertz range.

_{If Z a is} measured with low resistance by choosing an impedance that is low in relation to Z _b _{, the capacitance C s of} the plasma edge layer can dominate, so that

In other words, the impedance Z _a should be selected so low for the low-resistance measurement that the voltage drop across the plasma edge layer dominates compared to the voltage drop across the impedance Z _a . Are C _lt C ₂ and

known, for example from previous electrical measurement of the measuring probe 100 ″, it is therefore possible to deduce the floating potential V _f _{for a given frequency w from the potential V pp} measured at the measuring electrode 101 ″. The frequency w can be, for example, the frequency with which the floating potential V _f oscillates. In particular, in the case of capacitive high-frequency excitations, the frequency w can be the excitation frequency with which the floating potential V _f oscillates. This frequency w is also determined during the measurement.

Although the capacitance C _{s of} the plasma edge layer dominates in a low-resistance measurement, Eq. (10) only approximate. For a more precise determination of the floating potential V _f , in particular with a less dominant capacitance C _s , C _{s can} also be estimated mathematically in order to obtain the floating potential V _f from Eq. (7) using the full Eq. (8) to be determined. For example, it can be assumed that

where A is an outer surface area of the dielectric cap 103, 103 ', 103 ", 103'", in particular an interaction surface of the measuring probe 100, 100 ', 100 "100'" with the plasma, ie for example part of an outer surface of the dielectric cap 103 , 103 ', 103 ", 103'" in the area of the probe head 120, 120 ', 120 ", 120'", and d _s denotes a thickness of the plasma edge layer. In the case of a U-shaped dielectric cap 103, 103 ', 103 ", 103'" it can be assumed, for example, that A = 2nr _a d where r _{a is} the outer radius of the cap and d _{l is} the length of the probe head 120, 120 ', 120 ", 120 '". The plasma edge layer thickness d _s is given by

where V _{f is} a DC voltage value of the floating potential, which can be determined, for example, via a comparison measurement with a Langmuir probe. _{The plasma edge layer thickness} is therefore a multiple of the Debye length l Ό, which is given by

In Eq. (12) and Eq. (13) k _{B is} the Boltzmann constant and T _{e is} the electron temperature of the plasma. By measuring the electron density n _e and the electric temperature T _e at a second measurement probe, for example with a Langmuir probe, and under the assumption of a ratio between the plasma edge layer thickness d _s and the Debye length Ä _D, so the capacity of the plasma boundary layer C _s can consist of Gl. (11) and Eq. (12) can be estimated. It is usually assumed that the ratio between the plasma _{edge layer thickness} _{d s} and the Debye length l Ό is approximately between 3 and 5, that is to say 3 <d _s / Ä _D <5.

_{If Z a is} measured with high resistance by choosing an impedance that is high in relation to Z _b _{, the capacitance C s of} the plasma edge layer can be negligible. In this case, the voltage drop across Z _{2 can be} large and the plasma potential can be determined. In particular, for a high-resistance measurement, the impedance Z _a should be selected so high that the voltage drop across the impedance Z _{a dominates} compared to the voltage drop across the plasma edge layer.

The construction of the measuring probe 100, 100 ', 100 ", 100'", 800, 900, which is described here using the example of the measuring probe 100 ", as a capacitive voltage divider enables only a small part of the plasma potential or the floating voltage. Potential speaking voltage can be decoupled. The plasma conditions can therefore be changed very little by the measurement, which makes the measurement particularly "passive".

The plasma potential and the floating potential define the energy that is applied, for example, to a substrate to be coated. With regard to the ions, the DC voltage component is ultimately of interest here. Often, however, this can be estimated from the part of the potential that varies over time. In addition, a potential measurement makes it possible to compare different systems or electrode structures, which under certain circumstances lead to the same electron density. In addition, by measuring the potential that varies over time, the ion energy can be set and checked with particularly high accuracy and thus the coating quality can be set and checked particularly precisely.

When measuring both the plasma potential and the floating potential and estimating the DC voltage components, the electron temperature T _e can also be calculated from the difference between the potentials, analogously to the Langmuir probe. From the explanations given above in relation to FIGS. 11 to 13 it follows that with a single measuring probe 100, 100 ', 100 ", 100'", 800, 900 several important quantities characteristic of a plasma locally, that is to say at the location of the probe head 120, 120 ', 120 ", 120'", 820, 920 in the plasma, in particular the electron density, the ion density, the temporal course of the plasma potential, the temporal course of the floating potential and the electron energy probability function. The various measurement modes for measuring the various variables are implemented by changing the control of the measuring probe 100, 100 ', 100 ", 100'", 800, 900, with control being carried out, for example, by means of the measuring probe 100 arranged outside a container for the plasma , 100 ', 100 ", 100'", 800, 900 connected part of a measuring system 300 can be made.

The measurement quality in the various measurement modes can differ in different embodiments of the measuring probe 100, 100, 100 ″, 100 ‘″, 800, 900. For example, through different arrangements of the dielectric cap 103, 103 ', 103 ", 103'", 803, 903 relative to the probe body 110, 110 ', 110 ", 110'", 810, 910, the probe head 120, 120 ', 120 " , 120 '“, 820, 920 in its size and thus in particular the value of the

Capacity C can be changed. For example, the capacitance C can be selected in this way as a compromise between the measurement quality in the active measurement mode and the measurement quality in the passive measurement mode. FIG. 14 shows a plasma coating method 700, which comprises generating 701 a plasma with a coating material and measuring 702 a quantity characteristic of the plasma in accordance with method 600 shown in FIG. 11. In this embodiment, steps 701 and 702 are carried out cyclically, the generation of the plasma in step 701 taking place as a function of the variable characteristic of the plasma, which was measured in a preceding step 702.

In the claims, the words “comprising” and “comprising” do not exclude other elements or steps, and the indefinite article “including” does not exclude a plurality. A single unit or device can perform the functions of several elements set out in the claims. The fact that individual functions and elements are listed in different dependent claims does not mean that a combination of these functions or elements cannot also be used to advantage.

The reference symbols in the claims are not to be understood in such a way that the subject matter and the scope of protection of the claims are restricted by these reference symbols.

Claims

Expectations

1 . Measuring probe (100, 100 ', 100 ", 100'", 800, 900) for measuring parameters characteristic of a plasma, whereby the measuring probe (100, 100 ', 100 ", 100'", 800, 900) has: one Probe body (110, 110 ', 110 ", 110'", 810, 910) with a probe head (120, 120 ', 120 ", 120'", 820, 920), whereby the probe body (110, 110 ', 110 ", 110 '",

810, 910) extends along a longitudinal axis of the measuring probe (100, 100 ', 100 ", 100'", 800, 900) and is adapted to measure the parameters characteristic of a plasma with the probe head (120, 120 ', 120 " , 120 '", 820, 920) to be inserted into the plasma, a measuring electrode (101, 10, 101", 101' ", 801, 901) attached to the probe head (120, 120 ', 120", 120' " , 820, 920), the probe body (110, 110 ', 110 ",

110 '", 810, 910) an electrical connection (102, 102', 102", 102 ", 802, 902) between the measuring electrode (101, 101 ', 101", 101' ", 801, 901) and one of the Probe head (120, 120 ', 120 ", 120'", 820, 920) along the longitudinal axis of the opposite part of the measuring probe (100, 100 ', 100 ", 100'", 800, 900) provides, - a dielectric cap (103 , 103 ', 103 “, 103'“, 803, 903), which are about the

Measuring electrode (101, 10T, 101 ", 10T", 801, 901) extends and is designed to isolate the measuring electrode (101, 10T, 101 ", 101 801, 901) from the plasma, the measuring probe (100, 100 ', 100 ", 100 '", 800, 900) is set up to generate an electrical opposing field that displaces negative charge carriers from the probe head (120, 120', 120 ", 120 '", 820, 920).

2. Measuring probe (100, 100 ', 800) according to claim 1, characterized in that the measuring probe (100, 100', 800) furthermore has a counter-electrode (104, 104 ', 804) which is placed on the dielectric cap (103, 103 ', 103 ", 103'", 804, 904), the probe body (110, 110 ', 110 ", 110'", 810, 910) having an electrical connection (105, 805) between the counter electrode (104, 104 ', 804) and the part of the measuring probe (100, 100', 800) opposite along the longitudinal axis, the measuring probe (100, 100 ', 800) being set up by means of the counter electrode (104, 104', 804) to generate the opposing electric field.

3. Measuring probe (100, 100 ', 800) according to claim 2, characterized in that the counter-electrode (104, 104', 804) has a covering structure with a distribution of openings which encompasses a surface of the dielectric cap (103, 103 ', 103 ", 103 '", 803, 903) at least in the area of the probe head (120, 120', 120 ", 120 '", 820, 920).

4. Measuring probe (100, 100 ', 800) according to claim 3, characterized in that the distribution of openings at least in the area of the dielectric cap (103, 103', 103 ", 103 '", 803, 903) is spatially homogeneous .

5. Measuring probe (100, 100 ', 100 ", 100'", 800, 900) according to one of the preceding claims, characterized in that the measuring probe (100, 100 ', 100 ", 100'", 800, 900) furthermore Having fastening element (106) which is arranged on the probe body (110, 110 ', 110 ", 110'", 810, 910), wherein the fastening element (106) is adapted to the dielectric cap (103, 103 ', 103 " , 103 '", 803, 903) to be detachably attached to the probe body (110, 110', 110", 110 '", 810, 910), a counter-electrode (104, 104', 804) being removed from the dielectric cap (103 , 103 ', 103 ", 103'", 803, 903) is removable.

6. Measuring structure (110, 110 ', 110 ", 110'", 810, 910; 101, 101 ', 101 ", 101'", 801, 901) for measuring parameters characteristic of a plasma, the measuring structure (110 , 110 ', 110 ", 110'", 810, 910; 101, 101 ', 101 ", 101'", 801, 901) has: a probe body (110, 110 ', 110 ", 110'", 810, 910) with a probe head (120, 120 ', 120 ", 120'", 820, 920), whereby the probe body (110, 110 ', 110 ", 110'", 810, 910) is located along a longitudinal axis of the measuring structure ( 110, 110 ', 110 ", 110'", 810, 910; 101, 10, 101 ", 101 '", 801, 901) is extended and adapted to measure the parameters characteristic of a plasma with the probe head (120, 120 ', 120 ", 120'", 820, 920) to be inserted into the plasma, and a measuring electrode (101, 10, 101 ", 101 '", 801, 901) attached to the probe head (120, 120', 120 ", 120 '", 820, 920), the probe body (110, 110', 110 ", 110 '", 810, 910) having an electrical connection (102, 102', 102 ", 102 '", 802, 902) between the measuring electrode (101, 101 ', 101 ", 101'", 801, 901) and a part of the measurement structure (110, 110 ', 110 ") opposite the probe head (120, 120', 120", 120 '", 820, 920) along the longitudinal axis , 110 '", 810, 910; 101, 101 ', 101 ", 101'", 801 901) provides wherein the measuring structure (110, 110 ', 110 ", 110'", 810, 910; 101, 101 ', 101 ", 101'", 801, 901) is set up to generate an opposing electrical field that removes negative charge carriers from the probe head (120, 120 ', 120 ", 120'", 820, 920), and the probe body (110, 110 ', 110 ", 110'", 810, 910) is formed, a dielectric cap (103, 103 ', 103 ", 103'", 803, 903) in such a way that after the recording it extends over the measuring electrode (101, 101 ', 101 ", 101'", 801, 901) and the measuring electrode (101, 10 , 101 ", 101 '", 801, 901) from the plasma.

7. Dielectric cap (103, 103 ', 103 ", 103'", 803, 903) for use with a measuring structure (110, 110 ', 110 ", 110'", 810, 910; 101, 101 ', 101 " , 101 '", 801, 901) according to claim 6 as a measuring probe (100, 100', 100", 100 '", 800, 900) according to one of claims 1 to 5, wherein the dielectric cap (103, 103' , 103 ", 103 '", 803, 903) is designed to be received by the probe body (110, 110', 110 ", 110 '", 810, 910) in such a way that the dielectric cap (103, 103' , 103 ", 103 '", 803, 903) extends over the measuring electrode (101, 101', 101 ", 101 801, 901) and separates the measuring electrode (101, 101 ', 101", 101 801, 901) from the plasma .

8. Measuring system (300) for measuring parameters characteristic of a plasma, the measuring system having: a measuring probe (100, 100 ‘, 100 ″, 100‘ ″, 800, 900) according to one of the claims

1 to 5, a voltage device (201, 202) for generating an input signal and for generating the opposing electrical field, wherein the voltage device (201, 202), via an electrical connection (210) with the measuring probe (100, 100 ', 100 ", 100 '", 800, 900), for generating the input signal with the measuring electrode (101, 10, 101", 101'", 801, 901) can be connected, and - a signal receiving unit (203) for receiving an output signal, the signal receiving unit (203) via the electrical connection (210) with the measuring probe (100, 100 ', 100 ", 100'", 800, 900) for receiving the output signal with the measuring electrode (101, 10, 101 ", 101 '", 801 , 901) can be connected, an evaluation unit (204) for determining the parameters characteristic of the plasma, based on the output signal.

9. Measuring system (300) according to claim 8, characterized in that the voltage device (201, 202) is adapted to provide the input signal at high frequency and to provide the opposing electric field at low frequency or constant, the measuring system (300) having a high-pass filter (205) for Having filtering the output signal.

10. Measuring system (300) according to one of claims 8 and 9, characterized in that a) the voltage device (201, 202) is adapted to the opposing electrical field via the electrical connection (210, 910) with the measuring probe (100 ″, 100 '", 900) on the measuring electrode (101", 101 901), and / or by b) the measuring probe

(100, 100 ', 800) according to claim 2, wherein the voltage device (201, 202) is adapted to the electrical opposing field via the electrical connection (210, 810) with the measuring probe (100, 100', 800) at the To generate counter electrode (104, 104 ', 804).

11th Measuring system (300) according to one of Claims 8 to 10, characterized in that the measuring system (300) is adapted for high-resistance measurement and for low-resistance measurement, the measurement system (300) being adapted as at least the values characteristic of the plasma to determine a variable selected from the group consisting of electron density, ion density, temporal progression of the plasma potential, temporal progression of the floating potential and electron energy probability function.

12. Measuring system (300) according to claim 11, characterized in that i) the voltage device (201, 202) is adapted to generate the input signal with varying frequency during a measurement period for measuring the electron density and not to generate an opposing electrical field, and the signal receiving unit (203) is adapted to record the output signal during the measurement period, the evaluation unit (204) being adapted to determine the electron density on the basis of the input signal and the output signal, and / or by ii) adapting the voltage device (201, 202) is to generate the input signal with varying frequency during a measuring period for measuring the ion density and to generate the opposing electric field, and the signal receiving unit (203) is adapted to receive the output signal during the measuring period, the evaluation unit (204) being adapted to the ion density to be determined on the basis of the input signal and the output signal men, and / or in that iii) the signal receiving unit (203) is adapted to record the output signal with high resistance during a measurement period for measuring the time profile of the plasma potential, the evaluation unit (204) being adapted to record the time profile of the plasma potential To determine the basis of the output signal recorded with high resistance, and / or in that iv) the signal receiving unit (203) is adapted, record the output signal with low resistance during a measurement period for measuring the time profile of the floating potential, the evaluation unit (204) being adapted to determine the time profile of the floating potential on the basis of the output signal recorded with low resistance, and / or by v) the voltage device (201, 202) and the signal receiving unit (203) are adapted to measure the electron energy probability function, to generate the input signal with varying frequency for different opposing fields and to record the output signal, and the evaluation unit (204) is adapted to the To determine the electron energy probability function on the basis of the input signals generated for the different opposing fields and the output signals recorded for the different opposing fields.

13. Plasma coating system (500) with a plasma generating device (400) for generating a plasma with a coating material, - a measuring system (300) for measuring parameters characteristic of the plasma according to one of claims 8 to 12 and a control unit (501) for controlling the Plasma generating device (400), the control unit being adapted to control the plasma generating device (400) as a function of the measured values characteristic of the plasma.

14. Measuring method (600) for measuring a variable that is characteristic of a plasma, the method (600) comprising the following steps:

Introducing (601) a probe head (120, 120 ', 120 ", 120'", 820, 920) of a measuring probe (100, 100 ', 100 ", 100'", 800, 900) into the plasma, - generating (602 ) an opposing electric field that displaces negative charge carriers from the probe head (120, 120 ', 120 ", 120'", 820, 920),

Generating (603) an input signal at a measuring electrode (101, 10, 101 ", 101 801, 901) of the measuring probe (100, 100 ', 100", 100'", 800, 900), which is attached to the probe head (120, 120 ', 120 ", 120'", 820, 920) is arranged, Receiving (604) an output signal from the measuring electrode (101, 10, 101 ", 101 '", 801, 901) which is indicative of a degree of absorption of the input signal by the plasma, and

Determining (605) the variable characteristic of the plasma based on the output signal.

15. Plasma coating process (700) with the steps:

Generating (701) a plasma with a coating material,

Measuring (702) a variable characteristic of the plasma according to claim 14 and - controlling the generation (701) of the plasma as a function of the measured variable characteristic of the plasma.

16. Using a dielectric cap (103, 103 ', 103 ", 103'", 803, 903) according to claim 7 with a measuring structure (110, 110 ', 110 ", 110'", 810, 910; 101, 101 ' , 101 ", 101 801, 901) according to claim 6 for carrying out the measuring method (600) according to claim 14.