Device and method for detecting the intensity of a plasma emission

Abstract

The invention relates to a method for detecting the intensity of an emission (12) of a plasma (14) which can be generated in a plasma-generating device (16). According to the method, received voltage signals (46) of a photomultiplier (18) are assigned to a respective duration (52) within a period (50) of a periodic signal (48) of the plasma-generating device (16) using at least one received synchronization signal. The invention additionally relates to an analysis unit (22) for carrying out the aforementioned method and to a device (10) for detecting the intensity of an emission (12) of a plasma (14) which can be generated in a plasma-generating device (16), comprising the plasma-generating device (16), a photomultiplier (18), a synchronization signal generator (20), and the aforementioned analysis unit (22).

Description

[0001] Apparatus and method for detecting an intensity of an emission of a plasma

[0002] The invention relates to a method for detecting an intensity of an emission of a plasma generated in a plasma generation device.

[0003] The invention further relates to an evaluation unit which is designed to carry out the above method.

[0004] The invention further relates to a device for detecting an intensity of an emission of a plasma that can be generated in a plasma generation device, comprising the above evaluation unit.

[0005] Plasmas are used, for example, in the semiconductor industry to deposit layers a few nanometers thick on silicon wafers or to etch other structures of the same size into the wafer. Plasma monitoring techniques are required to monitor and control plasma processes, as well as to develop improved plasma processes. For example, process drifts induced by changes in the wall conditions in the plasma chamber are a problem in wafer processing. One possible form of such process drift is known as the "first wafer effect."

[0006] One way to monitor plasma processes is phase-resolved optical emission spectroscopy, or PROES for short, which allows a spatially and temporally resolved measurement of the electron dynamics in the plasma. PROES is based on the measurement of the plasma emission with an ICCD camera (intensified-charge coupled device camera), i.e. a camera that uses a CCD sensor (charge-coupled device) as an image sensor, to which a microchannel plate is coupled, for example, via a fiber optic cable to increase sensitivity. This type of camera allows exposure times of less than 1 ns. Accordingly, the plasma can be optically detected in a spatially and temporally resolved manner within one period of the alternating voltage used to generate the plasma, which is typically around 74 ns (corresponding to a frequency of 13.56 MHz), and the plasma emission can thus be measured.

[0007] A disadvantage of PROES, however, is that ICCD cameras are very expensive, which means the technology is associated with high acquisition costs. Furthermore, PROES requires a clear field of view of the plasma for the camera. Accordingly, the chamber of the plasma generation device must have a sufficiently large viewing window. These viewing windows are generally not available in industrial plasma generation devices. For several reasons, installing a viewing window in industrial plasma generation devices for the purpose of conducting PROES with an ICCD camera is out of the question: Firstly, it would entail expensive retrofitting of the chambers, if not even new purchases. Secondly, the input parameters such as gas mixture, gas pressure, the power output of the generators, etc., which are required to structure the wafer in a specific way (also known as "recipes"), would have to be redetermined.These recipes are determined with great effort by the manufacturers of plasma generation equipment and purchased at great expense by the industry. The use of ICCD cameras for PROES would therefore involve massive investments and structural changes. For these reasons, it is advantageous if new process monitoring systems can be integrated into the existing infrastructure and are minimally invasive.

[0008] Alternative techniques for performing phase-resolved optical emission spectroscopy are described in the articles "Evidence for a time dependent excitation process in silane radio frequency glow discharges" by G. de Rosny et al. (Journal of Applied Physics 54, 2272 (1983); DOI: 10.1063 / 1.332381) and "Time- and space-resolved spectroscopy of electron transport in low-frequency discharge plasma in argon" by T. Makabe and M. Nakaya (Journal of Physics D: Applied Physics 20, 1243 (1987); DOI: 10.1088 / 0022-3727 / 20 / 10 / 006). In each case, a photomultiplier tube (PMT) is used to measure the emissions emanating from the plasma.

[0009] Regarding the measurement of the PMT signal, de Rosney et al. teach measuring the time difference between the rising edge of the voltage pulse generated by the PMT and the next zero crossing of the measured AC voltage used to generate the plasma. This time difference is plotted in a histogram, from which the time-resolved emission of the plasma is derived. Makabe and Nakaya, on the other hand, describe tapping the PMT signal in short time windows with a sampling gate, thus achieving temporal resolution. To achieve spatial resolution, both techniques described in the scientific articles require shifting the PMT relative to the plasma. In both techniques, the PMT has since been replaced by an ICCD camera, as the use of an ICCD camera allows for higher spatial resolution.

[0010] Based on this, it is the object of the invention to provide means that simplify and / or improve the monitoring of plasma processes.

[0011] According to the invention, the object is achieved by the features of the independent claims. Preferred embodiments of the invention are specified in the subclaims, each of which may represent an aspect of the invention individually or in combination.

[0012] According to the invention, a method is provided for detecting an intensity of an emission of a plasma generated in a plasma generation device, comprising the steps

[0013] - Receiving temporally successive voltage signals from a photomultiplier used to detect optical signals from the plasma,

[0014] - receiving at least one synchronization signal correlating with a periodic signal of the plasma generation device, - assigning the received voltage signals to a respective time segment within a period of the periodic signal with the aid of the received synchronization signal, and

[0015] Determining the intensity by summing a number of voltage signals assigned to the respective time period.

[0016] The object is also achieved by an evaluation unit of a device for detecting an intensity of an emission of a plasma that can be generated in a plasma generation device, wherein the evaluation unit is configured to carry out the above method.

[0017] Furthermore, the invention relates to a device for detecting an intensity of an emission of a plasma that can be generated in a plasma generation device, comprising the plasma generation device, a photomultiplier, a synchronization signal generator, and the above evaluation unit, wherein the plasma generation device comprises a chamber for providing the plasma and a generator for generating a periodic signal and is designed to generate a plasma in the chamber, wherein the chamber is connected to the photomultiplier via an optical passage such that an optical signal generated by the plasma can be transmitted to the photomultiplier, wherein the photomultiplier is designed to generate a voltage signal based on the optical signal, wherein the synchronization signal generator is designed to generate at least one synchronization signal correlating with the periodic signal,and wherein the evaluation unit is connected to the photomultiplier for receiving the voltage signal and to the synchronization signal generator for receiving the synchronization signal. One aspect of the invention is that the voltage signals generated by the photomultiplier are assigned to the respective time segment within the period of the periodic signal in the evaluation unit with the aid of the synchronization signal. This creates a histogram of the emission intensity over a period of the periodic signal. The periodic signal is preferably a periodic high-frequency signal, particularly preferably a signal with a frequency between 1 MHz and 100 MHz. In other words,that each photon detected as a voltage signal is assigned to a time segment—also called a bin—within the period of the periodic signal using the synchronization signal. Particularly preferably, the voltage signals in the evaluation unit are assigned to the phase of the periodic signal using the synchronization signal in order to generate the histogram in this way, wherein it is further preferably provided that the length of the time segment—also called binwidth—is predefined. The length of the time segment is selected such thatthat sufficient resolution is achieved and is preferably between 1 ns and 5 ns. In other words, the electrode dynamics of the plasma are measured in a time-resolved manner using a method similar to time-correlated single-photon counting. Time-correlated single-photon counting is also used, among other things, to measure the fluorescence lifetime of various light sources. Following a "start" signal, the time difference until a "stop" signal, triggered, for example, by a voltage signal from a photomultiplier, is counted. By frequently repeating this process, a histogram is created, e.g., of the time-resolved fluorescence of the light source. The present method differs from previous methods of time-correlated single-photon counting in that the data acquisition is not stopped after the measurement of a voltage signal generated by a photon,Rather, over a specific number of periods of the synchronization signal and / or over a specific time, all signals emitted by the photomultiplier are assigned to the respective period. The present method has the advantage that it is possible to detect the intensity of the plasma emission even when only a very low intensity is present. For example, only a single photon can be received by the photomultiplier over several hundred periods of the periodic signal. This simply results in longer data acquisition times. Furthermore, it is not necessary to use a photomultiplier with a particularly short response time.Because the synchronization signal is used to assign the voltage signal to the corresponding time segment of the periodic signal. When using a photomultiplier with a short response time, the method allows a significant reduction in measurement time compared to conventional methods, since it also allows multiple photons to be measured per period of the periodic signal.

[0018] In contrast to the method described in the article by Makabe and Nakaya, the period of an applied trigger signal is not scanned with a sampling gate. Instead, all incoming photons—or all resulting voltage signals at the photomultiplier—are assigned to the respective time segment of the periodic signal.

[0019] Likewise, in the present method, unlike in the paper by G. de Rosny et al., the voltage signal generated by the photon arriving at the photomultiplier is not used as a "start" signal to initiate a measurement, which is then terminated by a "stop" signal temporally correlated with the periodic signal.

[0020] Compared to the methods described in the articles by Makabe and Nakaya or by G. de Rosny, the present method has the advantage that it allows a significantly shorter measurement time and has a high signal-to-noise ratio.

[0021] A further aspect of the invention is that the chamber of the plasma generation device is connected to the photomultiplier via the optical passage. Preferably, the chamber is therefore free of a viewing window, as is necessary for PROES with ICCD cameras. Since industrially used plasma generation devices are generally equipped with devices for temporally and spatially averaged optical emission spectroscopy, which also includes an optical passage, it is particularly easy to apply the method to existing industrially available plasma generation devices, as both technologies use the same connection. In contrast to temporally and spatially averaged optical emission spectroscopy, in which only individual emission lines of the plasma are observable, the present method enables an analysis of the so-called electron heating mode of the plasma.

[0022] In the context of the present application, a synchronization signal is understood to mean a signal that can be used for synchronization and that correlates in time with the periodic signal. The synchronization signal can itself be a periodic signal, for example a sinusoidal signal or a square-wave signal. In this case, it is preferably provided that the period of the periodic signal corresponds to the period of the synchronization signal. The periodic synchronization signal can also be understood as a sequence of multiple pulses, wherein the sequence correlates in time with the periodic signal. Alternatively, it is possible for the synchronization signal not to be a sequence of multiple pulses, but rather to be designed as a single pulse, by means of which the starting time of the measurement can be synchronized.

[0023] The photomultiplier is preferably operated in photon counting mode for detecting optical signals. Photon counting mode is also called digital operating mode or pulse mode. Depending on requirements, a photomultiplier can be operated either in current mode (DC mode) or in photon counting mode (pulse mode). In current mode, the charge of the electrons at the anode is measured and integrated over time to produce an averaged current value. In photon counting mode, the signal is measured as a voltage across a resistor. Accordingly, the photomultiplier is configured to generate the voltage signal based on the optical signal.

[0024] An optical signal is understood here as a signal with a wavelength between 100 nm and 1000 nm. Preferably, the optical signal is an emission from the plasma in the wavelength range from 350 nm to 900 nm.With regard to the method, according to a preferred development of the invention, it is provided that in a first alternative the step of receiving at least one synchronization signal correlating with the periodic signal of the plasma generation device comprises receiving a plurality of pulses temporally correlating with the periodic signal of the plasma generation device or receiving a periodic synchronization signal over a plurality of periods and the step of assigning the received voltage signals to the respective time period within the period of the periodic signal with the aid of the received synchronization signal comprises assigning the received voltage signals to the respective time period within the period of the periodic signal with the aid of the plurality of pulses or with the aid of the periodic synchronization signal.In other words, this embodiment provides for the synchronization signal itself to be configured as a periodic synchronization signal that is received over multiple periods and / or for the synchronization signal to comprise multiple temporally consecutive pulses that correlate with the periodic signal. This makes the method particularly precise, since such possible irregularities in the periodic signal are taken into account during the assignment.

[0025] Alternatively, it is preferably provided that the step of receiving at least one synchronization signal correlating with the periodic signal of the plasma generation device comprises receiving an initial phase signal of the plasma generation device, and the step of assigning the received voltage signals to the respective time segment within the period of the periodic signal using the received synchronization signal comprises assigning the received voltage signals to the respective time segment within the period of the periodic signal using the received initial phase signal, a time of the received voltage signal, and a period duration of the periodic signal. In other words, in this embodiment, it is therefore provided that the initial phase signal of the periodic signal is received only at the beginning of the measurement.The assignment of the received voltage signals to the respective time period within the period is then carried out by means of knowledge of the period duration of the periodic signal and the time of the received voltage signal.

[0026] It is also preferably provided that the step of receiving the temporally successive voltage signals of the photomultiplier used to detect the optical signals of the plasma comprises receiving the temporally successive voltage signals of the photomultiplier used to detect the optical signals of the plasma over a predefined integration time. Particularly in connection with the first alternative mentioned above, it is further preferably provided that the step of receiving the plurality of synchronization signals correlating with the periodic signal of the plasma generation device takes place over the same predefined integration time.

[0027] Furthermore, it is preferably provided that the steps of the method for improving signal strength are repeatable. Performing the measurement multiple times is preferably used if, after the maximum integration time of the evaluation unit, insufficient voltage signals have been received. The method can then be repeated, with the voltage signals being added to the originally generated histogram until a satisfactory signal strength is achieved.

[0028] With regard to the device for detecting the intensity of an emission of a plasma that can be generated in a plasma generation device, according to a preferred development of the invention, the synchronization signal generator is formed by the generator. In this embodiment, the synchronization signal preferably corresponds to the signal output by the generator of the plasma generation device via a synchronization output. This has the advantage that no additional device needs to be used to generate the synchronization signal, since this task is performed by the generator itself. Alternatively, according to a further preferred development, the synchronization signal generator is formed by a voltage measuring device connected to the chamber.In this preferred alternative, the synchronization signal is generated by a time-resolved measurement of the voltage applied to the chamber using the voltage measuring device. This has the advantage that a synchronization signal can be generated even with generators without a synchronization output.

[0029] In relation to the method, this means in other words that the received synchronization signals are preferably generated a) by tapping a periodic signal at the synchronization output of the generator of the plasma generation device, or b) by measuring the periodic voltage signal at the chamber of the plasma generation device by means of the voltage measuring device.

[0030] According to a further preferred development of the invention, it is preferably provided that the device for detecting the optical signal and for transmitting the detected optical signal to the photomultiplier comprises a light guide. This makes transmitting the optical signal to the photomultiplier particularly simple. In particular, it is provided that the light guide leads from an interior of the chamber via the optical passage to the area outside the chamber, so that the chamber is connected to the photomultiplier via the optical passage.

[0031] In this context, according to a further preferred development of the invention, an end of the light guide arranged in the chamber comprises an optic for detecting the incident optical signal. Accordingly, even weak emissions from the plasma can be transmitted particularly easily as optical signals to the photomultiplier. Likewise, according to a further preferred development of the invention, the end of the light guide arranged in the chamber is displaceable within the chamber relative to the chamber. This enables a spatially resolved measurement of the plasma emission in a simple manner. In addition, the point of maximum emission can be determined, thereby improving the signal-to-noise ratio and thus reducing the integration time.

[0032] According to a further preferred development of the invention, the device also comprises an optical filter arranged upstream of the photomultiplier in the signal direction for selecting a wavelength of the optical signal. "In the signal direction" in this case preferably refers to the direction of the optical signal guided through the device—i.e., from the plasma to the photomultiplier. Accordingly, this preferably also means that an optical filter for a specific wavelength is interposed between the end of the light guide arranged outside the chamber and an input for the optical signal of the photomultiplier. This enables wavelength-specific emissions of the plasma to be examined.

[0033] In this context, according to a further preferred development of the invention, the device comprises a monochromator and / or interferometer arranged upstream of the photomultiplier in the signal direction for selecting a wavelength of the optical signal. Preferably, the end of the light guide arranged outside the chamber has a focusable collimator for this purpose in order to guide the optical signal emerging from the light guide into an entrance slit of the monochromator. The monochromator preferably has a dispersing element or an optical grating for spreading the optical signal according to the wavelength. Alternatively, the interferometer can be used for wavelength selection. The monochromator and / or the interferometer has the advantage over the variant with a filter described above that the wavelength to be selected can be easily changed.Further preferably, the device for simultaneously measuring multiple wavelengths can also comprise more than one photomultiplier. In this regard, it is further preferably provided that a multi-arm optical fiber is used to split the optical signal, so that the one optical signal detected in the chamber is transmitted to multiple photomultipliers.

[0034] It is further preferred that the end of the optical fiber in the plasma generation device be protected from coating by a protective device. This increases the service life of the device.

[0035] According to a further preferred embodiment of the invention, the device is free of an ICCD camera. Accordingly, the chamber of the plasma generation device is also free of a viewing window for the ICCD camera.

[0036] With regard to the evaluation unit, according to a further preferred development of the invention, it is provided that the evaluation unit comprises an oscilloscope or FPGA (Field Programmable Gate Array). It can further preferably be provided that the evaluation unit also comprises a measuring computer connected to the oscilloscope or FPGA. Oscilloscopes or FPGAs are particularly suitable for receiving the chronologically successive voltage signals and the synchronization signal. In addition, oscilloscopes and / or FPGAs also make it particularly easy to assign the received voltage signals to the respective time segment within the period of the periodic signal with the aid of the received synchronization signal. It is also possible for the oscilloscope or the FPGA to be used to digitize the received signals, and for the assignment steps to be carried out by the measuring computer.

[0037] In this context, a further preferred embodiment of the invention provides that the evaluation unit, and particularly preferably the oscilloscope or the FPGA, has a time resolution of less than or equal to 10 ns. This makes the evaluation unit particularly suitable for processing high-frequency signals.

[0038] According to a further preferred development of the invention, the pulse width of the photomultiplier is smaller than the period of the periodic signal. While a pulse width smaller than the period of the periodic signal is not necessary for implementing the method, it has the advantage that multiple photons can be counted per period. By evaluating multiple photons per unit of time, the system's integration time until a usable result is achieved can be significantly reduced.

[0039] With regard to the photomultiplier, according to a further preferred embodiment, it is also provided that the photomultiplier exhibits a temporal fluctuation in the time response – also called time jitter – of less than or equal to 500 ps. This enables the evaluation unit to perform a particularly precise assignment of the received voltage signals to the respective time segment within the period of the periodic signal using the received synchronization signal, and accordingly, a particularly precise measurement of the plasma emission.

[0040] The invention will now be explained by way of example with reference to the accompanying drawings using preferred embodiments, wherein the features presented below may represent an aspect of the invention both individually and in combination. They show:

[0041] Fig. 1 is a schematic representation of a device for detecting an intensity of an emission of a plasma, according to a preferred embodiment of the invention, Fig. 2 is a schematic representation of the device for detecting the intensity of an emission of the plasma, according to a further preferred embodiment of the invention, and

[0042] Fig. 3 is a schematic representation of process steps of a measuring method that can be carried out with the device from Figure 1 or 2.

[0043] Figure 1 shows a schematic representation of a device 10 for detecting the intensity of an emission 12 of a plasma 14, according to a preferred embodiment of the invention. The device 10 comprises a plasma generation device 16, a photomultiplier 18, a synchronization signal generator 20, and an evaluation unit 22. The plasma generation device 16 comprises a chamber 24 for providing the plasma 14 and a generator 26 for generating a periodic signal—in this case, an alternating voltage as a periodic high-frequency signal.

[0044] The synchronization signal generator 20 is configured to generate at least one synchronization signal that correlates with the periodic signal. In the embodiment shown in Figure 1, the generator 26 also serves directly as the synchronization signal generator 20, with the synchronization signal being tapped via the synchronization output of the generator 20.

[0045] Furthermore, the chamber 24 is connected to the photomultiplier 18 via an optical passage 28 such that an optical signal generated by the plasma 14 can be transmitted to the photomultiplier 18. As shown in Figure 1, the device 10 has a light guide 30 that leads from an interior of the chamber 24 via the optical passage 28 into the area outside the chamber 24. An end of the light guide 30 arranged in the chamber 24 also has an optic 32 for detecting the incident optical signal. It can also be seen that an optical filter 34 for a specific wavelength is interposed between the end of the light guide 30 arranged outside the chamber 24 and an input for the optical signal of the photomultiplier 18.

[0046] The photomultiplier 18 is configured to generate a voltage signal based on the optical signal. For this purpose, the photomultiplier 18 can be operated in photon counting mode.

[0047] As can be seen in Figure 1, the evaluation unit 22 is connected to the photomultiplier for receiving the voltage signal and to the synchronization signal generator 20 for receiving the synchronization signal. Figure 1 also shows that the evaluation unit 22 is designed as a combination of an oscilloscope 23 for receiving the voltage signals and the synchronization signal and a measurement computer 36 for evaluating the recorded data.

[0048] Figure 2 shows a schematic representation of the device 10 for detecting the intensity of an emission 12 of the plasma 14, according to another preferred embodiment of the invention. The embodiment shown in Figure 2 is constructed similarly to the embodiment shown in Figure 1, so only the differences from the embodiment shown in Figure 1 will be discussed below:

[0049] In the embodiment shown in Figure 2, the synchronization signal generator 20 is not formed by the generator 26 of the plasma generation device 16, but by a voltage measuring device 38 connected to the chamber 24. Furthermore, the device 10 for wavelength selection does not have an optical filter 34, but rather a monochromator 40. In order to guide the optical signal coming from the light guide 30 into an entrance slit 42 of the monochromator 40, the end of the light guide 30 arranged outside the chamber 24 has a focusable collimator 44. Also schematically indicated in Figure 2 is a displacement device 45, with which the optics 32 can be displaced in the chamber 24 to detect the incident optical signal.The evaluation unit 22 shown in Figures 1 and 2 is also configured to carry out the method described below with reference to Figure 3 for detecting an intensity of an emission 12 of the plasma 14.

[0050] In a first step of the method, the evaluation unit 22 receives temporally successive voltage signals 46 from the photomultiplier 18 used to detect the optical signals of the plasma. A schematic representation of the temporally successive voltage signals 46 received by the evaluation unit 22 is shown in the lower half of Figure 3a), wherein each spike corresponds to a voltage signal 46 generated by a photon incident on the photomultiplier 18.

[0051] In a further step of the method, the evaluation unit 22 receives at least one synchronization signal correlating with the periodic signal 48 of the plasma generation device 16. The periodic signal 48 of the plasma generation device 16 is shown in the upper half of Figure 3a), with the arrow 50 indicating a period 50 of the periodic signal 48. N indicates the number of periods 50 and can assume values ​​of several million.

[0052] In a further step of the method, the evaluation unit 22 assigns the received voltage signals 46 to a corresponding time segment 52 within a period 50 of the periodic signal 48 using the received synchronization signal. This is done in the present case—as schematically shown in Figure 3—by assigning the voltage signals 46 to the phase of the periodic signal 48 in the evaluation unit 22 using the synchronization signal and then sorting them into the predefined time segments 52 according to their assignment. In the present case, the predefined time segment 52 has a length of 2 ns. In this step, noise is also filtered out, since only signals whose amplitude reaches a certain limit are evaluated.By summing a number of voltage signals 48 assigned to the respective time period 52, the histogram shown as an example in Figure 3c) is created, which corresponds to the determined intensity of the emission.

[0053] List of reference symbols

[0054] 10 Device

[0055] 12 Emissions

[0056] 14 Plasma

[0057] 16 Plasma generation device

[0058] 18 photomultipliers

[0059] 20 synchronization signal generators

[0060] 22 Evaluation unit

[0061] 23 Oscilloscope

[0062] 24 chambers

[0063] 26 Generator

[0064] 28 optical passage

[0065] 30 light guides

[0066] 32 Optics

[0067] 34 optical filters

[0068] 36 measuring computers

[0069] 38 Voltage measuring device

[0070] 40 Monochromator

[0071] 42 Entrance slit

[0072] 44 focusable collimator

[0073] 45 Shifting device

[0074] 46 voltage signals

[0075] 48 periodic signal of the plasma generation device

[0076] 50 Arrow, Period

[0077] 52 Time period

Claims

A method for detecting an intensity of an emission (12) of a plasma (14) that can be generated in a plasma generation device (16), comprising the steps - receiving temporally successive voltage signals (46) of a photomultiplier (18) used to detect optical signals of the plasma (14), - receiving at least one synchronization signal correlating with a periodic signal (48) of the plasma generating device (16), - Assigning the received voltage signals (46) to a respective time segment (52) within a period (50) of the periodic signal (48) with the aid of the received synchronization signal, and - Determining the intensity by summing a number of voltage signals (46) assigned to the respective time period (52). The method according to claim 1, wherein a) the step of receiving at least one synchronization signal correlating with the periodic signal (48) of the plasma generation device (16) comprises receiving a plurality of pulses temporally correlating with the periodic signal (48) of the plasma generation device (16) or receiving a periodic synchronization signal over a plurality of periods, and the step of assigning the received voltage signals (46) to the respective time period (52) within the period (50) of the periodic signal (48) with the aid of the received synchronization signal comprises assigning the received voltage signals (46) to the respective time period (52) within the period (50) of the periodic signal (48) with the aid of the plurality of received pulses or with the aid of the periodic synchronization signal,or b) the step of receiving at least one synchronization signal correlating with the periodic signal (48) of the plasma generating device (16), Receiving an initial phase signal from the plasma generation device (16), and the step of assigning the received voltage signals (46) to the respective time segment (52) within the period (50) of the periodic signal (48) with the aid of the received synchronization signal comprises assigning the received voltage signals (46) to the respective time segment (52) within the period (50) of the periodic signal (48) with the aid of the received initial phase signal, a time of the received voltage signal, and a period duration of the periodic signal. An evaluation unit (22) of a device (10) for detecting an intensity of an emission (12) of a plasma (14) that can be generated in a plasma generation device (16), wherein the evaluation unit (22) is configured to carry out the method according to the preceding claim.

4. A device (10) for detecting an intensity of an emission (12) of a plasma (14) that can be generated in a plasma generation device (16), comprising the plasma generation device (16), a photomultiplier (18), a synchronization signal generator (20), and an evaluation unit (22) configured according to the preceding claim, wherein the plasma generation device (16) comprises a chamber (24) for providing the plasma (14) and a generator (26) for generating a periodic signal (48) and is configured to generate a plasma (14) in the chamber (24), wherein the chamber (24) is connected to the photomultiplier (18) via an optical passage (28) such that an optical signal generated by the plasma (14) can be transmitted to the photomultiplier (18), wherein the photomultiplier (18) is configured to generate a voltage signal (46) based on the optical signal, wherein the synchronization signal generator (20) is configured to generate at least one synchronization signal correlating with the periodic signal (48), and wherein the evaluation unit (22) is connected to the photomultiplier (18) for receiving the voltage signal (46) and to the synchronization signal generator (20) for receiving the synchronization signal. Device (10) according to the preceding device claim, wherein the synchronization signal generator (20) is formed by the generator (26), or wherein the synchronization signal generator (20) is formed by a voltage measuring device (38) connected to the chamber (24). Device (10) according to one of the preceding device claims, wherein the device (10) comprises an optical fiber (30) for detecting the optical signal and for transmitting the detected optical signal to the photomultiplier (18).Device (10) according to the preceding device claim, wherein an end of the light guide (30) arranged in the chamber (24) comprises an optic (32) for detecting the incident optical signal, and / or is displaceable within the chamber (24) with respect to the chamber (24). Device (10) according to one of the preceding device claims, wherein the device (10) comprises an optical filter (34) arranged upstream of the photomultiplier (18) in the signal direction for selecting a wavelength of the optical signal, and / or wherein the device (10) comprises a monochromator (40) and / or interferometer arranged upstream of the photomultiplier (18) in the signal direction for selecting a wavelength of the optical signal. Device (10) according to one of the preceding device claims, wherein the device (10) is free of an ICCD camera. Device (10) according to one of the preceding device claims, wherein the evaluation unit (22) comprises an oscilloscope or FPGA and / or wherein the The evaluation unit (22) has a time resolution of less than or equal to 10 ns. The device (10) according to any one of the preceding device claims, wherein a pulse width of the photomultiplier (18) is smaller than the period (50) of the periodic signal (48), and / or wherein the photomultiplier (18) has a temporal fluctuation in the time response of less than or equal to 500 ps.

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