DE102019133608A1 - Contactless determination of a plasma parameter characterizing a plasma - Google Patents

Abstract

The invention relates to the contactless determination of a plasma parameter characterizing a plasma. To this end, the method according to the invention has the following method steps: generating a plasma, applying radar radiation to the plasma, acquiring a reflected and / or transmitted portion of the radar radiation and determining the phase difference between the radar radiation with which the plasma was applied and the recorded reflected and / or transmitted portion of the radar radiation. This provides a simple and reliable possibility for a contactless determination of a plasma parameter characterizing a plasma, which has a high measurement sensitivity, creates a direct connection between measurement and internal plasma parameters and can be used universally even at high temperatures.

Description

The invention relates to a method for the contactless determination of at least one plasma parameter characterizing a plasma in real time and to a device suitable for this.

In the current research, development and manufacture of new and innovative products, plasma-assisted processes represent a key technology. Here, technical plasmas at low pressure are generally used. The spectrum of areas of application extends from optics, aerospace, automotive and materials science to medical technology. For the production of high-quality thin layers, plasmas are an indispensable tool that enables the deposition of new types of surfaces and multifunctional layer systems, especially on glass and plastics. In addition, there is an increasing use of plasma-assisted sterilization processes for the effective inactivation of multi-resistant germs.

Due to its high market potential, plasma diagnostics has received special attention in international research areas in recent years. Due to the great importance of plasma technology in research and development, the investigation of innovative probe concepts for the precise determination of internal plasma parameters is an important pillar for the entire industry. The high demands on the corresponding measuring system place the focus on the development of suitable minimally invasive measuring concepts and systems current research projects.

Due to their mode of operation and design, existing probe systems can often only determine indirect dimensions of the plasma and can only be used to a limited extent in dielectric coating processes, since they are also coated during the measurement in the plasma. The result is a sometimes dramatic deterioration in the measurement, which can lead to a complete failure of the measuring system. However, the effective, fast and reliable regulation of a plasma process can only be guaranteed with precise knowledge of the internal plasma parameters.

• - Eingeschränkte Messempfindlichkeit bei Beschichtungsprozessen
• - Teils kein direkter Zusammenhang zwischen Messung und inneren Plasmaparametern
• - Kompliziertes Auswerteverfahren (komplexe math. Modelle)
• - Eingeschränkte Nutzbarkeit bei hohen Temperaturen (Temperatur kann einige 100 °C erreichen)
• - Nicht universell, also nur für ausgewählte Anregeverfahren und Gastypen verwendbar
• - Komplexer oder teurer Aufbau
• - Zu träge, um plasmadynamische Effekte zu detektieren

Conventional methods for plasma diagnostics sometimes have the following disadvantages:

• - Limited measurement sensitivity in coating processes
• - Partly no direct connection between measurement and internal plasma parameters
• - Complicated evaluation procedure (complex math. Models)
• - Limited usability at high temperatures (temperature can reach several 100 ° C)
• - Not universal, so can only be used for selected excitation methods and gas types
• - Complex or expensive structure
• - Too slow to detect plasma dynamic effects

Contactless or minimally invasive measurement methods are preferred in industrial use. While probes such as the Langmuir probe or the multipole resonance probe have to be introduced into the plasma, methods such as optical emission spectroscopy (OES) can monitor the plasma from the outside without contact. In both cases, however, sometimes complex mathematical models are necessary in order to correlate the measurement effect with the plasma state. Probes are suitable for measuring locally, whereby the mere presence of the probe in the plasma already has an effect on this. The OES, for its part, is an integral measurement method, since measurements are made over a certain volume of plasma. However, this method requires optical access to the process and uses a very complex model to interpret the results. Both methods have certain advantages and disadvantages, so that combinations of both measurement methods are sometimes used. In order to be able to record plasma dynamic processes, a fast measurement is advantageous, which can resolve the smallest inhomogeneities and fluctuations in the plasma, regardless of the gas or the composition as well as the excitation method.

According to the article "Accurate Double Transmission Measurement Concepts for the Permittivity Determination in Pneumatic Conveying Tubes with Microwaves" in the Asia-Pacific Microwave Conference 2011, pneumatically conveyed bulk materials were recorded based on the measured transit times of a radar and their volume density and conveying speed were examined. The desired reflection can be separated more effectively from undesired reflections by means of modulating targets or by means of a transpolarizing reflector. In this approach, the medium to be examined is also passed through twice, which increases the measuring effect. Various versions of this measuring principle are shown in the US 8 958 068 B2 and in the US 9 778 082 B2 to find.

According to the WO 2019/170648 A1 the reflection on a reference object is evaluated in order to be able to determine a physical variable of a system. Especially distances and Material properties should be determined depending on a priori knowledge. In addition, the US 2019/0187071 A1 a system for determining the dielectric properties of filling media in a tank / silo is shown. The phase differences are determined and evaluated on the basis of two high-frequency signals.

Based on this, the object of the invention is to provide a simple and reliable possibility for a contactless determination of a plasma parameter characterizing a plasma, which has a high measurement sensitivity, creates a direct relationship between measurement and internal plasma parameters and can be used universally even at high temperatures.

This object is achieved by the subjects of the independent claims. Preferred developments can be found in the subclaims.

• - Erzeugen eines Plasmas,
• - Beaufschlagen des Plasmas mit einer Radarstrahlung,
• - Erfassen eines reflektierten und/oder transmittierten Anteils der Radarstrahlung und
• - Ermitteln der Phasendifferenz zwischen der Radarstrahlung, mit der das Plasma beaufschlagt worden ist, und dem erfassten reflektierten und/oder transmitierten Anteil der Radarstrahlung.

The invention thus relates to a method for the contactless determination of at least one plasma parameter characterizing a plasma in real time, with the following method steps:

• - generation of a plasma,
• - Exposure of the plasma to radar radiation,
• - Detecting a reflected and / or transmitted portion of the radar radiation and
• - Determination of the phase difference between the radar radiation with which the plasma has been applied, and the detected reflected and / or transmitted portion of the radar radiation.

According to the invention, a radar-based approach is used for contactless monitoring and / or characterization of the plasma state in real time. This makes it possible to monitor the power coupled in and thus used for excitation and thus to determine the change in the so-called plasma density. The plasma density, for its part, is directly related to the so-called plasma electron frequency, which is typically less than 10 GHz and can be used to describe the dielectric properties. In addition to monitoring the density, further information about the plasma can also be obtained: Preferably, it is also monitored whether the plasma has settled and / or whether the plasma is contaminated and / or whether the power adjustment is working. Here, an approach comes into play, according to which the phase change is evaluated at a reference target.

The present invention thus takes advantage of the fact that there is a direct relationship between input power and electron density in plasmas. The electron density is linked to the plasma electron frequency, which in turn has a dominant influence on the frequency-dependent permittivity of the plasma. With radar measurements, both the time of flight (TOF) and the phase depend on the permittivity. The phase is more sensitive and is therefore preferably evaluated for rapid changes. As a result, the phase change can be evaluated as a measure for the power or the density of the plasma and used, for example, to regulate the plasma generation.

In principle, the type of radar radiation can be selected differently. According to a preferred embodiment of the invention, however, the radar radiation is FMCW radar radiation.

For the use of the invention it can be sufficient to determine the phase difference between the radar radiation with which the plasma has been applied and the recorded reflected portion of the radar radiation. According to a preferred embodiment of the invention, however, the dispersion is determined in addition to the phase difference. The observation of dispersion can in principle allow a direct determination of the plasma electron frequency. The phase change is not only evaluated at a fixed frequency but at several frequency points so that the frequency-dependent course of the permittivity can be derived. The plasma electron frequency can be determined by extrapolating the course.

In principle it is possible to implement the invention without a special reflector. Preferably, however, the reflected portion of the radar radiation originates from the reflection at a target introduced into the beam path of the radar radiation for the purpose of reflecting the radar radiation. According to preferred embodiments, the target for reflecting the radar radiation is transpolarizing and / or switchable, e.g. to suppress further reflections.

A preferred development of the invention provides that the plasma is generated in a plasma reactor chamber, hereinafter also referred to as a plasma reactor, and the target for reflecting the radar radiation is formed by a wall of the plasma reactor chamber. In this way, a separate reflector to be introduced into the plasma reactor chamber can be avoided. Furthermore, it is preferred that the radar radiation is applied to the plasma from outside the plasma reactor chamber. This means that the radar radiation is generated outside the plasma reactor chamber. In this respect, it preferably also applies that the Radar radiation is coupled through a window in the plasma reactor chamber or by means of a waveguide using a pressure stage in the plasma reactor chamber. In particular, waveguides or dielectric waveguides come into consideration as waveguides. In addition, according to a preferred embodiment of the invention, it can be provided that the radar radiation is coupled in with the aid of a pressure-tight coupling structure, in particular by means of at least one dielectric lens. Such a lens is preferably made of PTFE, PP, or PEEK, a glass or a ceramic. In addition, according to a preferred development of the invention, the radar radiation is coupled in using at least one deflecting mirror and / or a beam-pivoting system.

In principle, a single measurement section can be sufficient for the invention. According to a preferred development of the invention, however, the plasma is exposed to the radar radiation along a plurality of different measuring sections, e.g. to compensate for thermal drift and / or for a reference measuring section measurement. It also preferably applies here that the signals of the plurality of different measurement sections are evaluated in parallel, on the one hand with regard to the phase difference between the radar radiation with which the plasma has been applied and the recorded reflected portion of the radar radiation and optionally also with regard to other parameters, such as the Dispersion.

The invention also relates to a device for contactless determination of at least one plasma parameter characterizing a plasma in real time, with a plasma reactor chamber for generating a plasma, an antenna for applying radar radiation to the plasma, an antenna for detecting a reflected portion of the radar radiation and an evaluation device for determining the phase difference between the radar radiation with which the plasma has been exposed and the recorded reflected portion of the radar radiation.

In principle, the mode of operation and the possible configurations of this device for contactless determination of at least one plasma parameter characterizing a plasma correspond to the previously described modes of operation and possible configurations of the method according to the invention.

In this respect, it preferably also applies that a target for reflecting the radar radiation is arranged in the plasma reactor chamber in the beam path of the radar radiation. The target for reflecting the radar radiation is preferably transpolarizing and / or switchable. According to a preferred embodiment, the target for reflecting the radar radiation is formed by a wall of the plasma reactor chamber. Furthermore, the antenna for subjecting the plasma to the radar radiation is preferably arranged outside the plasma reactor chamber.

According to a preferred development of the invention, the radar radiation is coupled into the plasma reactor chamber through a window in the plasma reactor chamber or by means of a waveguide using a pressure stage. A pressure-tight coupling structure for coupling in the radar radiation can preferably be provided, in particular in the form of a dielectric lens, which consists, for example, of PTFE, PP or PEEK, a glass or a ceramic. According to a preferred development of the invention, a deflection mirror and / or a beam-pivoting system for coupling in the radar radiation can also be provided.

A plurality of different measurement sections are preferably provided for the radar radiation. The evaluation device is particularly preferably set up for the parallel evaluation of the signals of the plurality of different measuring sections.

The invention is explained in more detail below using a preferred exemplary embodiment with reference to the drawings.

• 1 schematisch eine Vorrichtung zur berührungslosen Ermittlung eines Plasmaparameters in Echtzeit gemäß einem Ausführungsbeispiel der Erfindung,
• 2 die Phase am beobachteten Ziel über der Messhistorie im Ruhezustand,
• 3 die Phase am beobachteten Ziel über der Messhistorie, wobei der Einfluss von Vibrationen aufgrund der Vakuumpumpen zu erkennen ist,
• 4 die Phase am beobachteten Ziel über der Messhistorie, wobei die Phasenänderung beim Öffnen der Ventile und beim Einlass von Argon zu sehen ist,
• 5 die Phase am beobachteten Ziel über der Messhistorie, wobei die Situation vor dem Matching zu sehen ist,
• 6 die Phase am beobachteten Ziel über der Messhistorie, wobei der Einschwingvorgang und die Änderungen im Matching erkannt werden können,
• 7 die Phase am beobachteten Ziel über der Messhistorie, wobei Leistungsvariationen in einem Argonplasma zu erkennen sind,
• 8 die Phase am beobachteten Ziel über der Messhistorie, wobei Leistungsvariationen in einem Stickstoffplasma zu erkennen sind,
• 9 schematisch eine Anordnung zur Bestimmung der Homogenität des Plasmas gemäß einem Ausführungsbeispiel der Erfindung und
• 10 schematisch eine Anordnung zur Erfassung des Dichteverlaufs des Plasmas gemäß einem Ausführungsbeispiel der Erfindung.

Show in the drawings

• 1 schematically a device for the contactless determination of a plasma parameter in real time according to an embodiment of the invention,
• 2 the phase at the observed target over the measurement history in the idle state,
• 3rd the phase at the observed target over the measurement history, whereby the influence of vibrations due to the vacuum pumps can be recognized,
• 4th the phase at the observed target over the measurement history, whereby the phase change can be seen when the valves are opened and when argon is introduced,
• 5 the phase at the observed target over the measurement history, whereby the situation can be seen before the matching,
• 6th the phase at the observed target over the measurement history, whereby the transient process and the changes in the matching can be recognized,
• 7th the phase at the observed target over the measurement history, whereby power variations can be seen in an argon plasma,
• 8th the phase at the observed target over the measurement history, whereby performance variations can be seen in a nitrogen plasma,
• 9 schematically an arrangement for determining the homogeneity of the plasma according to an embodiment of the invention and
• 10 schematically an arrangement for detecting the density profile of the plasma according to an embodiment of the invention.

mit der Zentralfrequenz f_c, der Lichtgeschwindigkeit co, der relativen effektiven Dielektrizitätskonstante ε_r,eff, der Länge der Messtrecke l und der zusätzliche Phase ϕ₀. Letztere kann durch eine Referenzmessung eliminiert werden. Im einfachsten Falle handelt es sich hierbei um eine Messung vor der Zündung im Plasmas bei ansonsten identischem Aufbau. Hierbei können absolute Messwerte der Plasmaparameter bestimmt werden. Bei Verwendung einer Referenzmessung im genzündeten Zustand, als aktuellen Ist-Zustand, lässt sich eine Regelung auf diesen Zustand durchführen, bei der abweichende Phasen identifiziert werden.As already explained above, the present invention uses a radar-based approach for contactless monitoring and / or characterization of the plasma state in real time. A plasma can be assumed to be a frequency-dependent dielectric material ε _{r, p} (ω). The following applies to the influence on the time of flight measurement (TOF) or the influence of the transmitted electromagnetic signals on phase ϕ: $$\varphi =360°\cdot \frac{{\mathrm{<figure-callout\; id="0"\; label="f\; c\; c"\; filenames="DE102019133608A1\_0003.png,DE102019133608A1\_0004.png"\; state="\{\{state\}\}">f</figure-callout>}}_c}{c_{}}\sqrt{{\mathrm{\epsilon }}_{\text{r}\text{, eff}}}\cdot 2l+{\mathrm{<figure-callout\; id="0"\; label="\phi "\; filenames="DE102019133608A1\_0003.png,DE102019133608A1\_0004.png"\; state="\{\{state\}\}">\varphi </figure-callout>}}_0$$

with the central frequency f _c , the speed of light co, the relative effective dielectric constant ε _{r, eff} , the length of the measuring section l and the additional phase ϕ ₀ . The latter can be eliminated by a reference measurement. In the simplest case, this is a measurement before ignition in the plasma with an otherwise identical structure. Absolute measured values of the plasma parameters can be determined here. When using a reference measurement in the ignited state, as the current actual state, a control can be carried out on this state, in which the deviating phases are identified.

1 shows an apparatus 1 for the contactless determination of a plasma parameter in real time according to an embodiment of the invention with a so-called double-inductively coupled plasma reactor 2 (DICP). In general, other excitation methods can also be used (capacitively coupled - CCP, inductively coupled - ICP, high-frequency excitations - RF, ...). The plasma reactor 2 includes a cylindrical tube 15th with a dielectric window 5 on a flange 6th and two planar coils 7th on the outside to stimulate and maintain the plasma. The spools 7th are to excite the plasma with control devices 12th connected by a power source 13th are supplied. An excitation frequency of 13.56 MHz with input powers in the range of a few 100 W is used here. The signal goes through the coils 7th fed into the plasma, comparable to a transformer. This is in one via a gas inlet 10 into the plasma reactor 2 Inlet gas induces an electric field, which finally excites the plasma state.

With two pumps arranged behind a valve 11 can the plasma reactor 2 for operation in a high vacuum with a pressure between 0.01 and 100 Pa. Via the gas inlet 10 various gases can enter the plasma reactor 2 be introduced to achieve different plasma behavior. Finally, the device comprises 1 another evaluation and control device 14th which is used to evaluate the recorded measured values and to regulate the power of the plasma excitation. As mentioned above, the invention makes it possible to use the determined phase to determine the plasma density in the plasma reactor 2 and thus to carry out a density control over the power used for the excitation.

According to the present embodiment of the invention, the radar 3rd on the outside of the plasma reactor 2 arranged to pass through the dielectric window 5 throughout the running time relative to a target 9 to measure, which is arranged at a distance / in the plasma reactor. This non-contact measurement can be used to detect changes in the plasma that arise directly from internal parameters of the plasma. The plasma reactor 2 in the present case has a diameter of 400 mm, a height of 200 mm and a volume of 24 liters.

The excitation power is between 500 W and 700 W. As a radar 3rd an 80 GHz FMCW radar system is used in a frequency range of 68-92 GHz. The radar 3rd has an antenna 4th on that in the distance in front of the dielectric window 5 mounted to the phase of reflection on the target 9 inside the plasma reactor 2 to determine.

The distance / the measuring distance 8th between the antenna 4th and the goal 9 measures approx. 20 cm.

In principle, for example, an aluminum target could enter the plasma reactor 2 be introduced. However, the rear wall of the reactor will be the target 9 and thus used as a reflector. Alternatively, it is possible to decouple the signal at the rear and to modulate it before it is reflected or wired to the radar 3rd is fed back (multi-channel radar). The enlargement of the measuring section is advantageous here, since the losses in the plasma are negligible and the measuring effect increases as the distance increases. It can also be advantageous to split the signal over several measurement paths, as shown in detail below.

As described above, the antenna is 4th for coupling in front of the dielectric window 5 placed, which serves to separate the process. As long as the goal 9 can be detected and separated, a Phase change can be detected. This arises due to a change in the material (or the goal 9 , e.g. due to thermal expansion) between radar 3rd and goal 9 and is therefore directly related to properties of the plasma.

In addition, pressure-tight coupling structures can of course also be used, for example dielectric lenses (for example made of PTFE, PP or PEEK), which are known from antenna technology. However, a glass lens or a ceramic lens can also be used. The target that acts as a reflector 9 can be transpolarizing to suppress further reflections. In addition, depending on the placement of the radar 3rd directly the target or the substrate in the plasma can be used as the target.

In the present case, the plasma is understood as a frequency-dependent material, the permittivity of which changes with a change in the power and thus the plasma electron frequency. To describe the plasma, the so-called Drude model for cold plasmas can be applied, which is generally used to describe plasmas below the plasma electron frequency. This model describes the plasma as a frequency-dependent dielectric material, its change with the help of radar 3rd can be captured. It is assumed here that the electrons can resonate in the vicinity of their plasma electron frequency, while the plasma approaches the vacuum permittivity of 1 at high frequencies. At the same time, the losses in the plasma decrease.

In the context of the invention, it has now been established that the change in the plasma electron frequency at high frequencies represents a change in the permittivity that is sufficiently large for reliable detection, so that, due to the low losses, large measurement paths can be observed, which in turn increase the measurement effect. Thus, the invention enables the detection of plasma devices with the help of relatively large and therefore easy to detect phase differences, which can be used, for example, to control the process and / or to improve the excitation.

Compared to conventional measuring systems, the radar system provided according to the invention is very sensitive and even the smallest changes in the plasma can be detected. For example, fluctuations in the matching network of the power source of the plasma can be recorded. Depending on the design, focusing lens systems or several measuring sections can also be used in the plasma reactor 2 be used. Thermal effects can be compensated with the help of a reference measuring section.

In the figures described below, the phase is on the observed target 9 shown above the measurement history. 2 first shows the phase change in the idle state. The standard deviation σ is in the range of 0.055 °. In 3rd is the small influence of vibrations due to the vacuum pumps 11 shown. The standard deviation σ increases to 0.157 °. The valves of the vacuum pumps 11 are closed so that measurements can still be made under normal pressure. In 4th you can see the phase change when the valves are opened and when argon is introduced. In addition, the expected effect can also be recognized: As the pressure decreases, the phase decreases. The phase undergoes a large change due to the change in material between radars 3rd and goal 9 .

The figures described below show the ignition of the plasma with and without matching. It can be seen how the plasma is initially contaminated with oxygen residues and how the plasma approaches a constant state, pure argon plasma, through the measurements and thus over time. 5 shows the situation before the matching and in 6th the transient process and the changes in the matching can be recognized.

In 7th are power variations in an argon plasma and in 8th shown in a nitrogen plasma. The changes in performance can be clearly measured. In addition, a thermal effect of the target used can be observed, namely the thermal expansion at 1000 W.

Out 9 an arrangement for determining the homogeneity of the plasma according to an exemplary embodiment of the invention can be seen schematically. The plasma reactor 2 has four flanges for this purpose 6a , 6b , 6c , 6d on, with the longitudinal axes of adjacent flanges 6a , 6b , 6c , 6d each enclose an angle of 45 °. These flanges 6a , 6b , 6c , 6d are each provided with a dielectric window, not shown in detail, for process separation. In this way there are four measuring sections 8a , 8b , 8c , 8d formed, with as goals of these measuring sections 8a , 8b , 8c , 8d the respective flange 6a , 6b , 6c , 6d opposite wall of the plasma reactor 2 be used. All measuring sections 8a , 8b , 8c , 8d are present from the same radar 3rd supplied (but individual radar systems can also be used), whereby the coupling of the radar radiation does not take place directly, but via a splitter 16 with switch and delay function. In this way, the phase differences Δϕ ₁ , Δϕ ₂ , Δϕ ₃ , Δϕ ₄ are obtained for different regions of the plasma, which allow information about the homogeneity of the plasma density.

An arrangement for detecting the density profile of the plasma according to an exemplary embodiment of the invention is shown schematically in FIG 10 evident. Similar to the in 9 The arrangement shown is a plurality of flanges 6a , 6b , 6c and thus a plurality of measuring sections 8a , 8b , 8c provided, namely three. Here, too, the coupling of the radar radiation takes place via a common radar 3rd over a splinter 16 with switch and delay function. However, the measuring sections run 8a , 8b , 8c in the present case parallel to one another, so that the determination of the density profile of the plasma in a direction perpendicular to the longitudinal axes of the measuring sections 8a , 8b , 8c is made possible by means of the detected phase differences Δϕ ₁ , Δϕ ₂ , Δϕ ₃ .

List of reference symbols

1

Device for the contactless determination of a plasma parameter in real time

2

Plasma reactor

3

radar

4th

antenna

5

dielectric window

6th

flange

6a

flange

6b

flange

6c

flange

6d

flange

7th

planar coils

8th

Measuring section

8a

Measuring section

8b

Measuring section

8c

Measuring section

8d

Measuring section

9

aim

10

Gas inlet

11

pump

12th

Control devices

13th

Power source

14th

Evaluation and control device

15th

cylindrical tube

16

Splinter

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 8958068 B2 [0007]
• US 9778082 B2 [0007]
• WO 2019/170648 A1 [0008]
• US 2019/0187071 A1 [0008]

Claims (10)

Method for the contactless determination of at least one plasma parameter characterizing a plasma in real time, with the following method steps: - generation of a plasma, - Exposure of the plasma to radar radiation, - Detecting a reflected and / or transmitted portion of the radar radiation and Determination of the phase difference between the radar radiation with which the plasma has been applied and the recorded reflected and / or transmitted portion of the radar radiation. Procedure according to Claim 1 , the dispersion behavior being determined in addition to the phase difference. Procedure according to Claim 1 or 2 , wherein at least a transmitted portion of the radar radiation is detected and the detected reflected portion of the radar radiation originates from the reflection at a target (9) introduced into the beam path of the radar radiation. Procedure according to Claim 3 , the target (9) being transpolarizing and / or switchable for reflecting the radar radiation. Method according to one of the preceding claims, wherein the plasma is generated in a plasma reactor chamber (2), at least a transmitted portion of the radar radiation is detected and the target (9) for reflecting the radar radiation is formed by a wall of the plasma reactor chamber (2). Method according to one of the preceding claims, wherein the application of the radar radiation to the plasma takes place along a plurality of different measuring sections (8a, 8b, 8c, 8d). Procedure according to Claim 6 , the signals of the plurality of different measuring sections (8a, 8b, 8c, 8d) being evaluated in parallel. Device for contactless determination of at least one plasma parameter characterizing a plasma in real time, with a plasma reactor chamber (2) for generating a plasma, an antenna (4) for applying radar radiation to the plasma, an antenna (4) for detecting a reflected and / or transmitted portion of the radar radiation and an evaluation device (14) for determining the phase difference between the radar radiation with which the plasma has been applied and the detected reflected and / or transmitted portion of the radar radiation. Device according to Claim 8 wherein a target (9) for reflecting the radar radiation is arranged in the plasma reactor chamber (2) in the beam path of the radar radiation. Device according to Claim 8 or 9 , with a plurality of different measuring sections (8a, 8b, 8c, 8d) being provided for the radar radiation.

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