DE102024203350B4 - Energy detection assembly for a lighting system of a mask inspection system for use with EUV lighting light - Google Patents

Abstract

An energy detection assembly (26) for a lighting system of a mask inspection system for use with EUV illumination light (3) has a beam homogenizing element (11) for guiding the illumination light (3). The beam homogenizing element (11) has an inlet opening (12) and an outlet opening (14) for the illumination light (3). The assembly (26) has at least one EUV energy sensor device (24) that detects illumination light (3) that is guided along an illumination light beam path outside the inlet opening (12) of the beam homogenizing element (11). In further embodiments of corresponding assemblies, the EUV energy sensor device detects illumination light that is guided within the outlet opening or also illumination light that is guided beyond a detection range of a spatially resolved detection device. In another embodiment of the assembly, an EUV energy sensor detects light that is blocked by a useful light filter and does not pass into a subsequent illumination light beam path. Another embodiment of the assembly has an EUV energy sensor that measures a photocurrent. Another embodiment of the assembly has an energy sensor arranged in the beam path of fluorescence detection light generated in a fluorescent layer of an EUV mirror. Another embodiment of the assembly has an EUV energy sensor that detects illumination light guided in a central region of an illumination pupil or illumination light beam path of the illumination optics. Another embodiment of the assembly has an ion detector or an electron detector.
This results in an energy detection assembly that can improve the inspection accuracy of a mask inspection system.

Description

The invention relates to an energy detection assembly for a lighting system of a mass inspection system for use with EUV illumination. The invention further relates to a mask inspection system with such an energy detection assembly.

Such a mask inspection system is known from the US 10,042,248 B2 , the DE 102 20 815 A1 and from the WO 2012/101269 A1 . The DE 10 2021 213 327 B3 reveals a metrology system for examining objects using EUV measuring light. DE 10 2020 207 566 A1 discloses a device and a method for characterizing a mask for microlithography. DE 10 2012 219 169 A1 Disclosing a beam control device for an illumination beam and a metrology system with an optical system containing such a beam control device. DE 10 2016 225 563 A1 reveals a hollow waveguide for guiding EUV light with a usable wavelength. US 6,456,362 B1 discloses an integrating waveguide for use in a lithographic projection exposure system.

It is an object of the present invention to help improve the inspection accuracy of a mask inspection system.

This problem is solved according to the invention by an energy detection assembly for a lighting system of a mask inspection system for use with EUV lighting light with the features mentioned in claims 1 and 7.

According to the invention, it has been recognized that such an energy detection assembly makes it possible to achieve high-precision mask inspection even when using a light source in the mask inspection system whose energy or intensity fluctuates over time. This can be the case, in particular, with pulsed EUV light sources. The EUV energy sensor device can detect energy fluctuations of the light source, allowing these fluctuations to be subtracted during post-processing using sensor data from the EUV energy sensor device, especially during image post-processing of image data from a detection device of the mask inspection system. For each part of the image data, the energy of the light pulses that contributed to the measurement of that part of the image data can be summed or averaged. This is particularly useful when a scanning measurement is performed using the EUV energy sensor device, which can then be implemented as a TDI camera. The corresponding summation or averaging results can then, in turn, serve as input parameters for controlling the intensity of the light source. An energy value measured by the EUV energy sensor can be used to correct measured image or camera data, particularly computationally. Alternatively or additionally, the sensor data from the EUV energy sensor can be used as a control signal to regulate the intensity of the light source. The coupling point and/or coupling direction of the illumination light into the beam homogenizing element can also be controlled parameters. The energy detection assembly can include multiple EUV energy sensors, which can detect or monitor different partial beams of the illumination light. An energy sensor in at least one EUV energy sensor can be implemented as an EUV photodiode. Such EUV photodiodes are commercially available.

The measurement accuracy of an energy measurement by the EUV energy sensor device can be better than 3%, better than 1%, better than 0.5%, and especially better than 0.2%. A correspondingly precise measurement of certain energy-dependent inspection parameters is then possible via a mask inspection system equipped with the energy detection module.

The EUV energy sensor device according to claim 1 detects the illumination light that is guided along the illumination light beam path outside the entrance aperture of the beam homogenizing element. Thus, the EUV energy sensor device detects the illumination light that does not pass through the entrance aperture of the beam homogenizing element. The distance between the illumination light detection areas of the EUV energy sensor device and an edge boundary of the entrance aperture of the beam homogenizing element is typically less than 50% of the mean diameter of the entrance aperture. This distance can also be smaller, for example, less than 40%, less than 30%, less than 25%, less than 20%, less than 15%, less than 10%, or even less than 5% of this mean diameter of the entrance aperture. Typically, the distance is greater than 0.01% of the mean diameter.

The illuminance detected by the EUV energy sensor device is guided along an illumination beam path if this illuminance detected by the EUV energy sensor device is between a source The EUV light source generating the EUV illumination light and the beam homogenizing element are guided within predetermined edge aperture limits of the optical components that guide the illumination light.

Because the EUV energy sensor device according to claim 1 detects illumination light that is guided outside the entrance aperture of the beam homogenizing element along the illumination light beam path, it is possible to measure energy without disruptive light loss. The energy detection assembly avoids light loss because it uses illumination light for energy detection, which, since it is not guided by the beam homogenizing element, would not be available for illuminating an object to be inspected anyway.

The beam homogenizing element generates a desired intensity distribution and/or illumination angle distribution of the illuminating light via its exit aperture. This effect of the beam homogenizing element is then used to illuminate an object field of the mask inspection system according to a predefined field intensity distribution and/or field illumination angle distribution.

The beam homogenizing element can comprise at least one micromirror array, which is used to divide the illumination light into a plurality of illumination channels superimposed on one another in the exit aperture. The beam homogenizing element can comprise several such micromirror arrays arranged one behind the other in the beam path of the illumination light. The beam homogenizing element can comprise exactly two such micromirror arrays. Micromirrors of the at least one micromirror array can be designed as concave micromirrors. If at least two such micromirror arrays are used, the radii of curvature of the micromirrors can be dimensioned such that the illumination light is guided parallel along the illumination channels between at least two successive micromirror arrays of the beam homogenizing element.

The beam homogenizing element can alternatively be designed as a hollow waveguide.

An EUV energy sensor device according to claim 2 does not lead to any disturbing loss of illumination, wherein, in particular by a correspondingly small design of the EUV deflecting mirror, the assembly can be designed compactly adjacent to the beam homogenizing element, which enables energy detection even in confined spaces in the vicinity of the beam homogenizing element.

A corresponding advantage is offered by an energy sensor device according to claim 3, which can also be used to measure the directional stability of the illumination light, similar to a quadrant detector. The four EUV energy sensor devices can be arranged evenly distributed around the entrance aperture of the beam homogenizing element. The entrance aperture of the beam homogenizing element can be rectangular. The EUV energy sensor devices can then be arranged near the four sides of the rectangle, outside the entrance aperture. The distances of the areas distributed around the entrance aperture to the entrance aperture can be the same as those already described above in connection with the detection of the illumination light outside the entrance aperture. In the circumferential direction, the areas distributed around the entrance aperture in which the EUV energy sensor devices detect the illumination light can cover, for example, between 5% and 50% of a total circumference around a center of the entrance aperture, for example, in the range between 10% and 40%, and particularly in the range of 25%. Such a covered partial area around the entrance opening represents a good compromise between the complexity of the sensor technology on the one hand and the gain in information through the detection of the illumination light in the detection areas distributed around the entrance opening on the other.

A coupling sensor device according to claim 4 enables energy-efficient coupling of the illumination light into the entrance opening. If the coupling location and the coupling direction are monitored simultaneously, adjustment optimization with respect to both dimensions is made possible.

Monitoring of the coupling point can be performed along the two spatial coordinates that define an entry plane in which the entrance aperture of the beam homogenizing element lies, as well as along a plane perpendicular to this plane. This allows for position monitoring, particularly of the coupling focus of the illumination light relative to the position of the entrance aperture, in all three spatial directions. In particular, a defocus during the coupling of the illumination light into the entrance aperture can then be detected.

The coupling sensor device can be combined with a control/regulation device of the energy detection assembly to enable control or regulation of the coupling point and/or which are in signal connection in the coupling direction.

The coupling sensor device can simultaneously function as the EUV energy sensor device, thus also assuming its function. One version of the coupling sensor device can correspond to the versions of the EUV energy sensor device already described above.

A coupling sensor device according to claim 5 has proven effective in practice. The coupling location on the one hand and the coupling direction on the other hand are monitored separately via the respective sensor units, whereby the corresponding monitoring results can be supplied to a common control device to enable coupling location and/or coupling direction control.

With the aid of such a control system, a control loop can be implemented for a coupling point and/or for a coupling direction of a bundle of illumination light into the entrance opening of the beam homogenizing element.

Such a control loop can have a control bandwidth that leads to a shorter control response time than temporal changes of an actual coupling location and/or an actual coupling direction to be controlled.

The coupling direction sensor unit can include several EUV energy sensors. These sensors can, in turn, detect light that is extracted from an incident beam of illumination via deflecting mirrors in the coupling direction sensor unit. The design of such a coupling direction sensor unit can correspond to those already described above in connection with the coupling location sensor unit or the EUV energy sensor device.

An embodiment of the coupling direction sensor unit according to claim 6 is practical.

An energy detection assembly according to claim 7 actually detects illumination light that is guided within the exit aperture of the beam homogenizing element along the illumination light beam path, i.e., within a beam path of the beam homogenizing element, and could therefore, in principle, be used for object field illumination. This detection of the illumination light that is guided within the exit aperture thus leads to a high level of monitoring reliability.

In an embodiment of the EUV energy sensor device according to claim 8, the EUV deflecting mirror arranged within the exit aperture of the beam homogenizing element can be very small, which can lead to a minimization of illumination light loss.

An embodiment according to claim 9 avoids a loss of illumination, i.e., a loss of illumination that can be effectively used for object field illumination. The useful exit aperture area is that area of the exit aperture of the beam homogenizing element within which illumination is guided, which is used to illuminate an object to be inspected.

• - mit einer ortsauflösenden Detektionseinrichtung zur Erfassung des Beleuchtungslichts, in einem Bildfeld, wobei das Beleuchtungslicht über ein Objektfeld in das Bildfeld geführt ist, wobei im Bildfeld eine zu inspizierende Maske angeordnet ist,
• - mit mindestens einer EUV-Energiesensor- Einrichtung, die so ausgeführt ist, dass sie Beleuchtungslicht erfasst, das jenseits eines Detektionsbereichs der Detektionseinrichtung längs eines Beleuchtungslicht-Strahlengangs geführt ist.

In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV lighting in a mask inspection system:

• - with a spatially resolving detection device for capturing the illumination light in an image field, wherein the illumination light is guided into the image field via an object field, wherein a mask to be inspected is arranged in the image field,
• - with at least one EUV energy sensor device designed to detect illumination light that is guided beyond a detection range of the detection device along an illumination light beam path.

Such an energy detection assembly avoids unwanted loss of illumination or imaging light. The detection area of the detection device can be defined by detection surfaces of CCD and/or TDI sensors of the detection device, which define the respective detection sections of the detection area. With regard to known designs of TDI sensors, only examples are mentioned. DE 197 14 221 A1 referred.

The EUV energy sensor device in this energy detection assembly can be configured to detect illumination light guided along the light beam path between two detection sections of the detection unit's detection area. Such a design of the EUV energy sensor device is easily implemented. Multiple such EUV energy sensor devices can be positioned between the detection sections of the detection unit's detection area, particularly between... adjacent CCD and/or TDI sensors.

• - mit einem Nutzlicht-Filter, anordenbar in einem Strahlengang des Beleuchtungslichts zwischen einer Lichtquelle und einem Objektfeld (4), in dem eine zu inspizierende Maske anordenbar ist, und
• - mit mindestens einer EUV-Energiesensor-Einrichtung, die so ausgeführt ist, dass sie Detektionslicht erfasst, das vom Nutzlicht-Filter nicht in den nachfolgenden Beleuchtungslicht-Strahlengangs durchgelassen wird.

In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV lighting in a mask inspection system:

• - with a useful light filter, arrangable in a beam path of the illumination light between a light source and an object field (4) in which a mask to be inspected can be arranged, and
• - with at least one EUV energy sensor device designed to detect light that is not passed through the subsequent illumination light beam path by the useful light filter.

Such an energy detection assembly avoids the loss of illumination light. It does not detect the illumination light itself, but rather the energetically correlated detection light, from which the energy of the illumination light can be deduced. The EUV energy sensor device can, in particular, detect light reflected from the useful light filter.

Such an energy detection assembly can include a bandpass filter that can be arranged in a beam path between the useful light filter and an energy sensor of the EUV energy sensor device. Such a bandpass filter enables a reduction of out-of-band (OOB) light that could distort the detection.

• - mit einem Nutzlicht-Filter, anordenbar in einem Strahlengang des Beleuchtungslichts zwischen einer Lichtquelle und einem Objektfeld, in dem eine zu inspizierende Maske anordenbar ist, und
• - mit mindestens einer EUV-Energiesensor-Einrichtung, die so ausgeführt ist, dass sie einen Fotostrom misst, der im Nutzlicht-Filter oder in einer Tragstruktur des Nutzlicht-Filters durch das Beleuchtungslicht erzeugt wird.

In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV lighting in a mask inspection system:

• - with a useful light filter, arrangable in a beam path of the illumination light between a light source and an object field in which a mask to be inspected can be arranged, and
• - with at least one EUV energy sensor device designed to measure a photocurrent generated in the useful light filter or in a supporting structure of the useful light filter by the illumination light.

Such an energy detection assembly enables elegant energy measurement that is not carried out optically, but is based on charge or photocurrent measurement.

• - mit einer Beleuchtungsoptik zur Führung des Beleuchtungslichts hin zu einem Objektfeld, in dem eine zu inspizierende Maske anordenbar ist,
• - wobei die Beleuchtungsoptik mindestens einen EUV-Spiegel aufweist, der eine Fluoreszenzschicht zur Überführung eines Bruchteils des auftreffenden Beleuchtungslichts in Fluoreszenz-Detektionslicht mit von einer Nutzlichtwellenlänge verschiedener Wellenlänge aufweist, und
• - mit einer im Strahlengang des Fluoreszenz-Detektionslichts angeordneten Energiesensor-Einrichtung mit mindestens einem Energiesensor zur Erfassung einer Energie des Fluoreszenz-Detektionslichts.

In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV lighting in a mask inspection system:

• - with a lighting optic for guiding the lighting light towards an object field in which a mask to be inspected can be arranged,
• - wherein the illumination optics comprise at least one EUV mirror having a fluorescent layer for converting a fraction of the incident illumination light into fluorescent detection light with a wavelength different from that of the useful light wavelength, and
• - with an energy sensor device arranged in the beam path of the fluorescence detection light, with at least one energy sensor for detecting the energy of the fluorescence detection light.

Such an energy detection assembly enables the use of sensitive energy sensors that are sensitive to fluorescence detection light with a longer wavelength than the illumination light wavelength. These longer wavelengths, within which such sensitive energy sensors can be sensitive, include wavelengths in the DUV, UV, VIS, NIR, and IR ranges. The mirror with the fluorescent layer can be the final mirror in the illumination optics, positioned in the illumination beam path before the object field.

• - mit einer Beleuchtungsoptik zur Führung des Beleuchtungslichts hin zu einem Objektfeld, in dem eine zu inspizierende Maske anordenbar ist, und
• - mit mindestens einer EUV-Energiesensor-Einrichtung, die so ausgeführt ist, dass sie Beleuchtungslicht erfasst, das in einem Zentralbereich einer Beleuchtungspupille und/oder im Zentralbereich eines Beleuchtungslicht-Strahlengangs der Beleuchtungsoptik geführt ist.

In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV lighting in a mask inspection system:

• - with a lighting optic for guiding the lighting light towards an object field in which a mask to be inspected can be arranged, and
• - with at least one EUV energy sensor device designed to detect illuminating light that is guided in a central area of an illumination pupil and/or in the central area of an illuminating light beam path of the illumination optics.

Such an energy detection assembly can exploit the fact that a mask inspection system often simulates an optical production system with central obscuration. In this case, a central area of the illumination pupil of the lighting optics and/or a central area of the illumination beam path is effectively not used for object illumination or object imaging. Therefore, illumination light that passes through such a central area can also be used for energy monitoring. The EUV energy sensor device can include an EUV deflecting mirror located in the central area of the illumination pupil or the illumination beam path and an energy sensor. The energy sensor is positioned such that EUV light, which is guided along the illumination beam path and strikes the EUV deflecting mirror, is directed towards the energy sensor. Such an EUV deflecting mirror can be small, which particularly reduces obscuration light loss.

• - mit einer Gasquelle zum Führen von Ionisationsgas in einem Ionisationsraum, durch den ein Beleuchtungslicht-Strahlengang des Beleuchtungssystems geführt ist, und
• - mit einem Ionen-Detektor und/oder mit einem Elektronen-Detektor zum Detektieren einer Anzahl von Ionen und/oder Elektronen, die durch Ionisation des Ionisationsgases im Ionisationsraum durch das Beleuchtungslicht erzeugt werden.

In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV lighting in a mask inspection system:

• - with a gas source for guiding ionization gas into an ionization chamber through which an illumination light beam path of the illumination system is guided, and
• - with an ion detector and/or with an electron detector for detecting a number of ions and/or electrons generated by ionization of the ionization gas in the ionization chamber by the illumination light.

Such an energy detection assembly, in turn, uses a different measurement principle for energy measurement, namely the ionization of an ionization gas by the illumination light. This enables low-loss energy monitoring.

The energy detection assemblies claimed or described above, or individual components or functions thereof, can also be used in combination with each other within a mask inspection system.

The advantages of a mask inspection system according to claim 10 correspond to those already explained above with reference to the respective energy detection assembly.

A wafer inspection system can be structured accordingly.

The inspection system can have an object holder for holding the object to be inspected, which is mechanically coupled to an object displacement drive, so that scanning displacement of the object is possible during illumination.

The inspection system can be a system for actinic mask or wafer inspection.

• 1 schematisch in einem Meridionalschnitt ein Maskeninspektionssystem für Lithographiemasken zum Einsatz mit EUV-Beleuchtungslicht mit einem Beleuchtungssystem, aufweisend eine Energie-Detektions-Baugruppe mit einem strahlhomogenisierenden Element und mit mindestens einer EUV-Energiesensor-Einrichtung;
• 1A im Vergleich zur 1 vergrößert und interne Details zeigend das strahlhomogenisierende Element des Maskeninspektionssystems;
• 2 schematisch eine perspektivische, eintrittsseiteige Ansicht einer Ausführung des strahlhomogenisierenden Elements;
• 3 im Vergleich zur 2 vergrößert einen Bereich um eine Eintrittsöffnung des strahlhomogenisierenden Elements für das Beleuchtungslicht, wobei zusätzlich vier Umlenkspiegel im Umfeld der Eintrittsöffnung dargestellt sind, die jeweils zu einer EUV-Energiesensor-Einrichtung der Energie-Detektions-Baugruppe gehören, wobei zusätzlich eine Einkoppel-Intensitätsverteilung des Beleuchtungslichts in einer Eintrittsebene des strahlhomogenisierenden Elements veranschaulicht ist;
• 4 schematisch einen Schnitt gemäß Linie IV-IV in 3 mit einer Veranschaulichung eines Beleuchtungs- und Detektions-Lichtweges zwischen zwei Umlenkspiegeln der Energie-Detektions-Baugruppe und zugeordneten Energiesensoren;
• 5 in einer zu 4 ähnlichen Darstellung eine weitere Ausführung einer Energie-Detektions-Baugruppe mit einer EUV-Energiesensor-Einrichtung zur Erfassung von Beleuchtungslicht, das innerhalb einer Austrittsöffnung des strahlhomogenisierenden Elements längs eines Beleuchtungs-Strahlengangs geführt ist, wobei wiederum ein Detektionslicht-Strahlengang zwischen einem Umlenkspiegel und einem Energiesensor der EUV-Energiesensor-Einrichtung der Energie-Detektions-Baugruppe veranschaulicht ist;
• 6 in einer zu 3 ähnlichen Darstellung eine Aufsicht auf die Eintrittsöffnung des strahlhomogenisierenden Elements, geeignet zum Einsatz mit einer Energie-Detektions-Baugruppe nach 5;
• 7 in einer zu 6 ähnlichen Darstellung eine Aufsicht auf eine Austrittsöffnung des strahlhomogenisierenden Elements nach 6;
• 8 eine Aufsicht auf eine weitere Ausführung einer Energie-Detektions-Baugruppe für das Maskeninspektionssystem nach 1 mit einer ortsauflösenden Detektionseinrichtung und einer EUV-Energiesensor-Einrichtung, die zur Erfassung von Beleuchtungslicht ausgeführt ist, das jenseits eines Detektionsbereichs der Detektionseinrichtung, nämlich zwischen zwei Detektionsabschnitten des Detektionsbereichs, längs eines Beleuchtungslicht-Strahlengangs geführt ist;
• 9 in einer zu 1 ähnlichen Darstellung einen Beleuchtungslicht-Strahlengang nach der Austrittsöffnung des strahlhomogenisierenden Elements, wobei zudem eine weitere Ausführung einer Energie-Detektions-Baugruppe mit einem EUV-Spiegel mit einer Fluoreszenzschicht und einer im Strahlengang von Fluoreszenz-Detektionslicht angeordneten Energiesensor-Einrichtung dargestellt ist;
• 10 eine Aufsicht auf eine Beleuchtungspupille der Beleuchtungsoptik einer Ausführung des Maskeninspektionssystems mit einer Ausführung einer Energie-Detektions-Baugruppe mit einer EUV-Energiesensor-Einrichtung zur Erfassung von Beleuchtungslicht, das unter anderem in einem Zentralbereich der Beleuchtungspupille der Beleuchtungsoptik geführt ist;
• 11 in einem Meridionalschnitt einen Abschnitt eines Beleuchtungslicht-Strahlengangs nach einem Austritt aus einer Ausführung des strahlhomogenisierenden Elements mit einer zentral in einem Austritts-Beleuchtungslichtbündel angeordneten Energiesensor einer weiteren Ausführung einer Energie-Detektions-Baugruppe;
• 12 in einer zu 11 ähnlichen Darstellung eine weitere Ausführung einer Energie-Detektions-Baugruppe, bei der mittig im Austritts-Beleuchtungslicht-Bündel ein Auskoppelspiegel einer weiteren Ausführung einer Energie-Detektions-Baugruppe angeordnet ist und ein Detektionslicht-Strahlengang hin zu einem Energiesensor der Energie-Detektions-Baugruppe veranschaulicht ist;
• 13 in einer zu den 11 und 12 ähnlichen Darstellung eine weitere Ausführung einer Energie-Detektions-Baugruppe mit einem Auskoppelspiegel und einem nachgeordneten Umlenkspiegel für Detektionslicht hin zu einem Energiesensor der Energie-Detektions-Baugruppe;
• 14 einen Querschnitt durch einen Ionisationsraum einer weiteren Ausführung einer Energie-Detektions-Baugruppe mit einer Ionen/Elektronen-Detektion zur Erfassung geladener Teilchen, die durch Ionisation eines Ionisationsgases im Ionisationsraum durch das Beleuchtungslicht erzeugt werden;
• 15 schematisch eine Funktion eines Time-Delay-Integration (TDI)-Sensors, der für die ortsauflösende Detektionseinrichtung des Maskeninspektionssystems zur Erfassung eines Bildes der zu inspizierenden Maske zum Einsatz kommen kann;
• 16 in einer 15 entsprechenden Darstellung einen zeitlichen Ablauf einer Beleuchtung der zu inspizierenden Lithographiemaske mit Beleuchtungslicht einer gepulsten Lichtquelle des Maskeninspektionssystems;
• 17 eine Ausführung einer Lichtquelle des Maskeninspektionssystems mit einem Energieänderungs-Sensor einer Ausführung der ansonsten in der 17 nicht dargestellten Energie-Detektions-Baugruppe zur Erfassung einer zeitlichen Entwicklung einer Beleuchtungsenergie des Beleuchtungslichts über einen Belichtungszeitraum;
• 18 in einer zu 17 ähnlichen Darstellung die Lichtquelle des Maskeninspektionssystems mit einer weiteren Ausführung einer Energie-Detektions-Baugruppe mit einem in einer Quellkammer der Lichtquelle angeordneten Energieänderungs-Sensor;
• 19 im Vergleich zur 1 nicht maßstabsgetreu einen Ausschnitt des Beleuchtungssystems im Bereich einer Aperturblende und eines eintrittsseitigen Abschnitts des strahlhomogenisierenden Elements in einem Meridionalschnitt, wobei Komponenten einer Einkopplungs-Sensoreinrichtung des Beleuchtungssystems dargestellt sind;
• 20 perspektivisch eine Einkoppelort-Sensoreinheit der Einkopplungs-Sensoreinrichtung, aufweisend vier um eine Eintrittsöffnung des strahlhomogenisierenden Elements herum angeordnete Umlenkspiegel und vier diesen zugeordnete Energiesensoren;
• 21 ebenfalls in perspektivischer Darstellung eine Ausführung einer Einkoppelrichtungs-Sensoreinheit der Einkopplungs-Sensoreinrichtung, angeordnet im Bereich der Aperturblende.

An embodiment of the invention is explained in more detail below with reference to the drawing. This drawing shows:

• 1 schematically in a meridional section a mask inspection system for lithography masks for use with EUV illumination light with an illumination system, comprising an energy detection assembly with a beam homogenizing element and with at least one EUV energy sensor device;
• 1A compared to 1 enlarged and showing internal details of the beam homogenizing element of the mask inspection system;
• 2 schematically a perspective, entry-side view of a version of the beam homogenizing element;
• 3 compared to 2 Enlarges an area around an inlet opening of the beam homogenizing element for the illumination light, wherein four deflecting mirrors in the vicinity of the inlet opening are additionally shown, each belonging to an EUV energy sensor device of the energy detection assembly, wherein an inlet intensity distribution of the illumination light in an inlet plane of the beam homogenizing element is additionally illustrated;
• 4 schematically a section according to line IV-IV in 3 with an illustration of an illumination and detection light path between two deflection mirrors of the energy detection assembly and associated energy sensors;
• 5 in a to 4 Similar to a representation, another embodiment of an energy detection assembly with an EUV energy sensor device for detecting illumination light, which is guided along an illumination beam path within an exit aperture of the beam homogenizing element, wherein again a detection light beam path is located between a deflecting mirror and an energy sensor of the EUV energy sensor. The setup of the energy detection assembly is illustrated;
• 6 in a to 3 A similar representation shows a top view of the inlet opening of the beam homogenizing element, suitable for use with an energy detection assembly according to 5 ;
• 7 in a to 6 similar representation shows a top view of an outlet opening of the beam homogenizing element according to 6 ;
• 8 a supervision of a further execution of an energy detection assembly for the mask inspection system according to 1 with a spatially resolving detection device and an EUV energy sensor device designed to detect illumination light that is guided along an illumination light beam path beyond a detection range of the detection device, namely between two detection sections of the detection range;
• 9 in a to 1 In a similar representation, an illumination light beam path is shown after the exit aperture of the beam homogenizing element, and a further embodiment of an energy detection assembly with an EUV mirror with a fluorescence layer and an energy sensor device arranged in the beam path of fluorescence detection light is also shown;
• 10 a view of an illumination pupil of the illumination optics of an embodiment of the mask inspection system with an embodiment of an energy detection assembly with an EUV energy sensor device for detecting illumination light, which is guided, among other things, in a central area of the illumination pupil of the illumination optics;
• 11 in a meridional section a section of an illumination light beam path after an exit from a version of the beam homogenizing element with an energy sensor of another version of an energy detection assembly arranged centrally in an exit illumination light beam;
• 12 in a to 11 A similar representation shows another embodiment of an energy detection assembly in which an output coupling mirror of another embodiment of an energy detection assembly is arranged centrally in the exit illumination light bundle and a detection light beam path towards an energy sensor of the energy detection assembly is illustrated;
• 13 in one of the 11 and 12 A similar representation shows another embodiment of an energy detection assembly with an output coupling mirror and a downstream deflection mirror for detection light towards an energy sensor of the energy detection assembly;
• 14 a cross-section through an ionization chamber of another embodiment of an energy detection assembly with ion/electron detection for detecting charged particles that are generated by ionization of an ionization gas in the ionization chamber by the illumination light;
• 15 schematically a function of a Time-Delay-Integration (TDI) sensor, which can be used for the spatially resolved detection device of the mask inspection system to capture an image of the mask to be inspected;
• 16 in one 15 The corresponding representation shows a temporal sequence of illumination of the lithography mask to be inspected with illumination light from a pulsed light source of the mask inspection system;
• 17 a version of a light source for the mask inspection system with an energy change sensor of a version otherwise found in the 17 Energy detection assembly not shown for recording the temporal development of the illumination energy of the illumination light over an exposure period;
• 18 in a to 17 In a similar representation, the light source of the mask inspection system is shown with a further embodiment of an energy detection assembly with an energy change sensor arranged in a source chamber of the light source;
• 19 compared to 1 not to scale, a section of the lighting system in the area of an aperture diaphragm and an entry-side section of the beam homogenizing element in a meridional section, showing components of a coupling sensor device of the lighting system;
• 20 In perspective, a coupling point sensor unit of the coupling sensor device, comprising four deflecting mirrors arranged around an entrance opening of the beam homogenizing element and four energy sensors associated with them;
• 21 also shown in perspective is a design of a coupling direction sensor. Sense purity of the coupling sensor device, arranged in the area of the aperture diaphragm.

An illumination optic 1 is part of an optical system 2 of a mask inspection system 2a for use with EUV illumination light 3. A beam path of the illumination light 3 is in the 1 The illumination optics 1 are illustrated using marginal rays and a main ray. The illumination light 3 illuminates an illumination field 4 of the mask inspection system.

The illumination 3 is generated by an EUV light source 5 in a source area 6. The light source 5 can generate EUV useful radiation in a wavelength range between 2 nm and 30 nm, for example in the range between 2.3 nm and 4.4 nm or in the range between 5 nm and 30 nm, for example at 13.5 nm.

Light source 5 is designed as a plasma light source. This could be, for example, a laser-produced plasma (LPP) source or a discharge-produced plasma (DPP) source. Such plasma sources are generally known as light sources for EUV projection systems. Alternatively, light source 5 could also be a high-harmonic EUV source. The pulse frequency of light source 5 can be in the kHz range.

To facilitate spatial relationships, a Cartesian xyz coordinate system is used below. The x-axis is perpendicular to the drawing plane. 1 and runs into it. The y-axis runs in the 1 horizontally to the left and the z-axis runs in the 1 vertically upwards.

After emission by the light source 5, the illumination light 3 first passes through a useful light filter 8, which is positioned in an operating position in the beam path of the illumination light 3 between the source volume 6 and a first ellipsoidal mirror IL1 of the illumination optics 1. The useful light filter 8 can be one of a plurality of filters, which, for example, in metrology system 2a, are stored in a filter magazine. Another useful light filter can be positioned in a standby position outside the illumination light beam path of the illumination optics 1. The useful light filters 8 can have the same transmission characteristics, allowing for a change between them if a degradation of the filtering effect of the operating useful light filter 8 is observed. Alternatively, the useful light filters can also have different filter characteristics and, for example, transmit different wavelength ranges of useful light into the subsequent illumination light beam path or be optimized to filter out different components of stray light.

The useful light filters can be designed in such a way that they filter out, in particular, pump light carried along in the illumination light beam path, which was used in the source volume 6 for useful light generation.

After passing through filter 8 and mirror IL1, the illumination light 3 first passes through an aperture diaphragm 9, which limits a beam of the illumination light 3 at its edges. Subsequently, the illumination light beam 3 is directed towards a beam homogenizing element 11 of the illumination optics 1. Mirror IL1 serves as a coupling optic 10 for coupling the illumination light 3 into the beam homogenizing element 11.

Between the source volume 6 and the beam homogenizing element 11, typically after the first mirror IL1 of the illumination optics 1, the illumination light 3 passes through an opening in a wall of a vacuum chamber VK, which is located in the 1 is indicated in the illumination light beam path between the mirror IL1 and the illumination light aperture diaphragm 9.

The aperture diaphragm 9 limits a numerical aperture of the illumination beam 3 emitted from the source area 6, also to a value of the numerical aperture in the range between 0.02 and 0.2, for example in the range between 0.07 and 0.15 or also in the range between 0.05 and 0.08. Alternatively or additionally to the aperture diaphragm 9, an aperture-limiting diaphragm can be arranged between the beam homogenizing element 11 and a subsequent optical component of the illumination optics 1, as shown in the 1 at 9a indicated. It is also possible to arrange such a further aperture stop in the beam path of the illumination light 3 after the beam homogenizing element 11 between two downstream optical components of the illumination optics 1.

The ellipsoidal mirror IL1 serves to image the source region 6 of the EUV light source 5 into an entrance aperture 12 in an entrance plane 13 of the beam homogenizing element 11. A first focal point of the ellipsoidal mirror IL1 is thus located in the source region 6 and a second focal point of the ellipsoidal mirror IL1 in the entrance aperture 12. The ellipsoidal mirror IL1 focuses the illumination beam 3 into the entrance aperture 12 in the entrance plane 13 of the beam homogenizing element 11. An entrance-side numerical aperture The diameter of the illumination bundle 3 at the entrance to the opening 12 can be in the range of 0.02 to 0.2, for example in the range of 0.05.

The angle of incidence of a central main ray of the illumination beam 3 on the coupling mirror IL1 can be in the range between 10° and 20°. The ellipsoidal mirror IL1 can be a normal incidence (NI) mirror, but can also be configured as a grazing incidence (GI) mirror.

The inlet opening 12 and an outlet opening 14 of the beam homogenizing element 11 are each square or rectangular with typical dimensions in the range between 0.5 mm and 5 mm and, for example, between 0.5 mm and 2 mm or between 0.5 mm and 1 mm.

The aspect ratio of the inlet aperture 12 and an equally sized outlet aperture 14 of the beam homogenizing element 11 for the illumination light 3 in an exit plane 15 lies between 0.5 and 2. A typical size of the inlet aperture 12 and the outlet aperture 14 of the beam homogenizing element 11 is, for example, 0.5 mm × 1.0 mm, 0.75 mm × 0.75 mm, 1.0 mm × 2.0 mm or 1.5 mm × 2.0 mm.

1A Illustrates details of the beam homogenizing element 11.

In the beam path of the beam homogenizing element 11, a pair of micromirror arrays 15a, 15b are arranged one behind the other between the inlet aperture 12 and the outlet aperture 14. These are shown in the 1A Exemplary partial beam paths of illumination channels _3i (i = 1 to 4), each guided by a micromirror 15c of the first micromirror array 15a in the beam path and by a micromirror 15d of the second micromirror array 15b downstream in the beam path. The actual number of illumination channels _3i is larger in practice and can, for example, be several hundred, guided by corresponding pairs of micromirrors 15c, 15d of the two micromirror arrays 15a, 15b. The micromirrors 15c and 15d are each designed as concave mirrors and have a radius of curvature such that the illumination light 3 is parallelized along the illumination channels _3i in the beam path between the micromirrors 15c and 15d. The micromirror arrays 15a and 15b are arranged and dimensioned such that the partial beams of the illumination light 3 along the illumination channels 3 overlap _each other in the exit aperture 14, so that beam homogenization of the illumination light 3 takes place between the inlet aperture 12 and the exit aperture 14 in the beam homogenizing element 11.

The two micromirror arrays 15a and 15b are housed in a casing 15e of the beam homogenizing element 11. The inlet opening 12 and the outlet opening 14 are located in this casing 15e.

The beam homogenizing element 11 can alternatively be designed as a hollow waveguide.

The beam homogenizing element 11 has a typical length perpendicular to the planes 13 and 15, i.e. along a principal beam direction of the illumination light 3, in the range between 50 mm and 500 mm, e.g. in the range between 50 mm and 150 mm, in particular in the range between 50 mm and 100 mm.

An angle between a normal to the entrance plane 13 of the beam homogenizing element 11 and the main beam CR of the illumination beam 3 incident into the entrance aperture 12 can be 0° or alternatively can be different from 0° and, for example, be in the range between 0° and 1.5°, for example between 0.25° and 0.75° and especially in the range of 0.5°.

A ratio of the distance between the inlet plane 13 and the outlet plane 15, and a size or typical diameter of the inlet opening or outlet opening 12, 14, lies in the range between 50 and 1000 and can, for example, lie in the range between 50 and 200.

A downstream imaging output coupler optic 16 with two mirrors IL2, IL3, located after the beam homogenizing element 11, images the exit aperture 14 of the beam homogenizing element 11, which lies in an exit plane 15, into the illumination field 4 in an object plane 17. The image-side numerical aperture of this imaging can be in the range of 0.05 to 0.2.

In the illustrated embodiment, the output coupling mirror optic 16 has exactly two mirrors, namely mirrors IL2 and IL3. The aperture diaphragm described above, which may be used after the beam homogenizing element 11, can be arranged between the beam homogenizing element 11 and mirror IL2 or between mirrors IL2 and IL3.

The output coupler optics 16 can be designed in the manner of a Wolter telescope, specifically in the manner of a Wolter optics type I. Such Wolter optics are described in JD Mangus, JH Underwood “Optical Design of a Glancing Incidence X-ray Telescope”, Applied Optics, Vol. 8, 1969, page 95 , and the references given therein. Instead of a paraboloid, a hyperboloid can also be used in such Wolter optics. Such a combination of an ellipsoidal mirror with a hyperboloid mirror also constitutes a Wolter optic of type I.

An embodiment of the output coupling mirror optics 16 is described in the US 10,042,248 B2 .

The imaging factor _β1 of the input-coupling mirror optics 10 can range from 0.1 to 50, thus reducing the image by a factor of 10 to magnifying it by a factor of 50. The imaging factor _β2 of the output-coupling mirror optics 16 can range from 0.02 to 10, thus again reducing the image by a factor of 50 to magnifying it by a factor of 1. The product _β1 , _β2 of the two imaging factors in the illumination optics 1 can range from 0.25 to 10.

In object plane 17, a reticle 18 to be inspected is arranged as the object or mask to be inspected, held by a reticle holder 19. The reticle holder 19 is mechanically connected to a reticle displacement drive 20, via which the reticle 18 is displaced along an object displacement direction y during a mask inspection. This enables a scanning displacement of the reticle 18 in object plane 17.

The illumination field 4 has a typical dimension in the object plane 17 that is less than 0.5 mm. In the illustrated embodiment, the extent of the illumination field 4 is 0.5 mm in the x-direction and 0.5 mm in the y-direction.

The x/y aspect ratio of the illumination field 4 matches the x/y aspect ratio of the exit aperture 14.

The illumination field 4, or a part of the illumination field 4 which then represents an object field, is projected by a projection optic PO onto an image field 21 in an image plane 22. The size of the image field 21 can be in the range of 150 mm × 250 mm. The shorter image field extent runs along the scan direction y.

The projection optics PO have numbered mirrors M1 and M2 in the imaging beam path, thus comprising a total of two mirrors. Depending on the design of the projection optics PO, the number of mirrors can also be greater than two. An aperture diaphragm 9b is arranged in an entrance pupil plane EP of the projection optics PO, which lies in the imaging beam path of the illumination/imaging light between the reflecting reticle 18 and the first mirror M1. This aperture diaphragm 9b can also serve to define any internal obscuration of the projection optics PO.

The mirrors M1 and M2 of the projection optics PO are designed as NI mirrors with an angle of incidence of the illumination and imaging light 3 of less than 45°.

An illumination light beam path of illumination light 3 for illuminating reticulum 18 and an imaging light beam path of projection optics PO for imaging the object field 4 into the image field 21 intersect in a crossing area K. This crossing area K lies in the region of the entrance pupil plane EP of projection optics PO. The imaging light beam path intersects here with the illumination light beam path between the exit aperture 14 and the mirror IL2 of illumination optics 1, as well as between the mirrors IL2 and IL3 of illumination optics 1.

The image field 21 is captured by a detection device 23, e.g., by a CCD camera or several CCD cameras. For details of the image being rendered in the image field, refer to the US 10,042,248 B2 as well as those in the US 10,042,248 B2 References are made to the references provided. The detection device 23 can also be implemented as a TDI (time delay integration) detection device with a plurality of TDI detectors. Such an implementation is explained in more detail below.

The mask inspection system 2a makes it possible to inspect, for example, a structure on reticulum 18.

2 shows a perspective and schematic view of a version of the beam homogenizing element 11 with a view towards the entrance opening 12.

3 shows in comparison to 2 Enlarges a section of an entrance end face of the beam homogenizing element 11, which is arranged in the entrance plane 13, with the entrance aperture 12. EUV energy sensor devices 24 _i (i = 1 to 4), of which in the 3 The four EUV deflection mirrors 25 _i (i = 1 to 4) shown are part of an embodiment of an energy detection assembly 26 for a lighting system of the mask inspection system 2a, which includes the lighting optics 1 and the light source 5. The energy detection assembly 26 also includes the beam homogenizing element 11.

The four EUV deflection mirrors 25 ₁ to 25 ₄ are arranged around the outside of the inlet opening 12. Each of the EUV deflection mirrors 25 _i is located close to one of the four sides of the inlet opening 12 and is centered with respect to that side.

The 3 The diagram further shows isolines of an energy distribution of the illumination light 3 in the entrance plane 13. The vast majority of the illumination light energy is coupled into the entrance opening 12.

A measure of the respective illuminance energy present at the entry level is in the 3 illustrated by different hatching types, for which in the 3 A table of dimensions is shown on the right as a legend. The coupled illumination energy is greatest at the center of the entrance aperture 12 in the region of the main beam CR and decreases radially with approximately rotational symmetry with the distance from the main beam CR. Since the entrance aperture 12 is rectangular, slightly more illumination energy is cut off in the region of the long sides of the entrance aperture 12 than in the region of the short sides of the entrance aperture 12. The two deflecting mirrors ₂₅₁ and ₂₅₃ arranged on the long sides therefore capture more illumination 3, which is not coupled into the entrance aperture 12, than the two deflecting mirrors ₂₅₂ and ₂₅₄ arranged on the short sides of the entrance aperture 12.

The uncoupled energy component of the illuminating light 3 is less than 30% and regularly less than 5%. The component of the illuminating light 3 captured by the four deflecting mirrors 25 ₁ is regularly in the range of less than 1 × ^10⁻⁴ of the total energy of the illuminating light 3.

4 illustrated in a longitudinal section representation in particular a further detection beam path of the two energy sensor devices 24 ₄ with the deflecting mirror 25 ₄ and the energy sensor device 24 ₂ with the deflecting mirror 25 ₂ .

The illumination light 3 incident on the deflecting mirror 25 ₂ is directed towards an energy sensor 27 _2. This can be a photodiode sensitive to EUV light. EUV sensitivity can be achieved via appropriate fluorescent or scintillation layers.

The energy sensor 27 represents an energy value sensor for detecting the illumination energy of the illumination light 3 over an exposure period of the reticulum 18.

An energy value measurement via the energy value sensor 27 can be more accurate than 3%, can be more accurate than 1%, can be more accurate than 0.5%, and can be more accurate than 0.2%.

Energy value measurement via the energy value sensor 27 can be pulse-resolved, i.e., separately for each light pulse of the light source 5.

Accordingly, the further one in the 4 visible deflecting mirrors 25 ₄ the portion of the illumination light 3 incident on it towards an associated energy sensor 27 ₄ of the energy sensor device 24 ₄ .

Others, in which 4 The non-visible energy sensors 27 ₁ and 27 ₃ are assigned to the deflecting mirrors 25 ₁ and 25 ₃ .

In total, the energy detection assembly 26 has four deflecting mirrors 25 ₁ to 25 ₄ and four associated energy sensors 27 ₁ to 27 ₄ , i.e. a total of four EUV energy sensor devices 24 ₁ to 24 ₄ .

The energy sensors 27 are connected to a central control/regulating device 27a (see 1 ) of the mask inspection system 2a in signal connection.

The illumination light beam path visible in the meridional section of the 4 It can also be seen that the deflecting mirrors 25 ₂ and 25 ₄ deflect only illumination light 3, which does not enter the inlet opening 12 of the beam homogenizing element 11.

Based on the 5 to 7 A further embodiment of an energy detection assembly 28 is described below, which can be used as an alternative or in addition to the energy detection assembly 26 according to the 3 and 4 components and functions that correspond to those mentioned above with reference to the 1 to 4 and in particular with reference to the 3 and 4 Those already explained bear the same reference numbers and will not be discussed again in detail.

The energy detection assembly 28 has an EUV energy sensor device 29, which is designed to detect illumination 3 that is within the exit aperture 14 of the beam homogenizing element 11 along a path in the 5 The illustrated illumination light beam path is shown.

A corresponding, exit-side sensor component 3 _S of the illumination light 3 is generated without significant light loss by this, that instead of a beam homogenizing element with a rectangular inlet opening 12 as in the energy detection assembly 26 according to the 3 and 4 a beam homogenizing element 11 with a square entrance opening 12 _Q is used.

6 This difference is clearly illustrated. It is consistently shown in the 6 the rectangular inlet opening of the variant of the energy detection assembly 26 according to the 3 and 4 , this time shown in "standing" form. The dashed line indicates the 6 the square enlarged entrance opening 12 _Q of the energy detection assembly 28 according to 5 As shown above, a deflection mirror arrangement with deflection mirrors 25 ₁ to 25 ₄ outside the square entrance opening 12 _Q can also be present in the case of the squarely enlarged entrance opening 12 _Q , as shown above with reference to the energy detection assembly 26, in particular according to 4 explained.

As a result of the quadratic expansion, in the energy detection assembly 28, the sensor component 3 _S is located on the outlet side after the then also square outlet opening 14 _Q in an outlet opening area 14 _S (cf. 7 left) of the entire outlet opening 14 _Q is available. The remaining outlet opening, i.e., the cross-section of the square outlet opening 14 _Q reduced by the sensor portion 14 _S , can then be used to illuminate the illumination field 4. Alternatively, the opposite side, in the 7 On the right side, a further sensor component 14 _S2 of the outlet opening 14 _Q can be used for energy-sensing or other purposes, so that on the side of the outlet opening 14 _Q there is effectively a rectangular outlet opening 14 corresponding to that of the beam homogenizing element of the energy detection assembly 26. 3 remains.

The exit aperture 14 _Q of the beam homogenizing element 11 is therefore larger than the usable exit aperture area in the form of the effectively rectangular exit aperture 14, which is required for the subsequent illumination of the object field in which the mask or reticle 18 to be inspected is located. As a result, some of the illumination light 3 coupled out of the beam homogenizing element 11 is no longer available to illuminate the object field 4. This effective reduction of the usable illumination light for illuminating the object field 4 is, at least partially, compensated for by the fact that the inlet aperture 12 _Q of the beam homogenizing element 11 is also larger, allowing more illumination light 3 to be coupled into the beam homogenizing element 11.

The EUV energy sensor device 29 is designed to detect the sensor portion _3S of the illumination light 3, which is guided within the exit aperture _14Q of the beam homogenizing element 11 beyond this useful exit aperture area, namely in the exit aperture sensor portion _14S along the illumination light beam path.

The sensor component _3S of the illumination light 3 is guided in the EUV energy sensor device 29 via a first deflecting mirror _29a , which is arranged in the exit-side region of the sensor component _14S of the exit aperture _14Q . Subsequently, the sensor component _3S is guided via a further, imaging deflecting mirror _29b to an energy sensor 27.

The EUV detection assembly 28 can connect several EUV energy sensor devices 29 _i according to the type in the 5 The EUV energy sensor device 29 shown, wherein, for example, a deflecting mirror of the type of deflecting mirror 29 _a can be arranged on both sides of the rectangular useful exit opening 14, to which components of the type of deflecting mirror 29 _b and energy sensor 27 can then be arranged in the beam path of the further sensor component of the illumination light.

Based on the 8 A further embodiment of an energy detection assembly 30 is described below, which can be used as an alternative or in addition to the energy detection assemblies explained above.

Part of the energy detection assembly 30 is an EUV energy sensor device 31, which detects the illumination light 3 that is guided along the beam path of the illumination light 3 beyond a detection range of the detection device 23. This detection range of the detection device 23 is defined by detection areas of TDI or CCD sensors 32 ₁ to 32 ₁₂ , which are arranged in the image plane 22 of the detection device 23 in the form of a 4 × 3 array. A y-spacing exists between the rows of this sensor array of sensors 32 _i , which is sufficiently large to allow a component of the EUV energy sensor device 31 to be arranged within this row spacing. This component can be a deflecting mirror of the type of deflecting mirrors 25 _i or an energy sensor of the type of energy sensors 27 _i .

The energy detection assembly 30 may also contain several such EUV energy sensor devices 31.

The energy sensor device 31 is therefore designed in such a way that it detects a portion of the illumination light 3 which is guided between two detection sections of the detection area of the detection device 23 along the illumination light beam path, namely between the detection sections of the sensors 32 ₄ and 32 ₇ .

In a further embodiment of an energy detection assembly 33 (see 1 ), which can be used instead of the energy detection assemblies discussed above, the respective useful light filter 8 simultaneously serves as a deflecting mirror for detection light 34, which is reflected from the beam path of the illumination light 3 by the respective useful light filter 8. This is in the 1 The useful light filter 8 is shown, which reflects the detection light 34 towards an energy sensor 35. The useful light filter 8, used to reflect the detection light 34, and the energy sensor 35 each constitute an EUV sensor device 36 of the energy detection assembly 33.

The detection light 34 is light with a wavelength reflected by the useful light filter 8, which may differ from the wavelength of the illumination light 3. The wavelength of the detection light 34 can be in the UV or visible range, but also in the NIR range. Accordingly, the energy sensor 35 is sensitive to the respective reflected wavelength of the detection light 34. The energy sensor 35 can therefore be a photodiode sensitive to UV light, visible light, or NIR light.

The detection light 34 is light that is not transmitted along the subsequent illumination light beam path by the useful light filter 8.

The energy detection assembly 33 can additionally include a bandpass filter 37, which is arranged in the beam path of the detection light 34 between the useful light filter 8 and the energy sensor 35 of the EUV energy sensor device 36. The bandpass filter 37 can have filter properties that filter out wavelength ranges that would distort a conclusion between the measurement result of the energy sensor 35 and the energy content of the illumination light 3. The bandpass filter 37 thus ensures a reduction of so-called out-of-band light.

At least one of the useful light filters 8, which are housed in the filter wheel 7, may have a metallic support structure.

An alternative and additional variant of an energy detection assembly 39 can be used in the 1 The schematic representation of an EUV energy sensor device 40 is designed to measure a photocurrent generated in the metallic support structure of the useful light filter 8 or in the useful light filter 8 itself by the illumination light 3. The magnitude of the measured photocurrent is then a measure of the energy content of the illumination light 3.

Based on the 9 A further embodiment of an energy detection assembly 41 is described below. Components and functions mentioned above with reference to the 1 to 8 Those already explained bear the same reference numbers and will not be discussed again in detail.

In the case of the energy detection assembly 41 according to 9 One of the mirrors of the illumination optics 1, namely mirror IL2, is designed as a fluorescent mirror. For this purpose, mirror IL2 has a fluorescent layer 42 to convert a fraction of the incident illumination light 3 into fluorescent detection light 43 with a wavelength different from the useful wavelength of the illumination light 3.

The wavelength of the detection light 43 is greater than that of the EUV illumination light 3. The wavelength of the fluorescence detection light 43 can be in the UV range, in the visible range (VIS), or in the near-infrared range (NIR).

In the 9 The beam path of the illumination light 3 between the exit plane 15 of the beam homogenizing element 11 and the mirror IL2 is shown, as is the beam path of the fluorescence detection light 43. The latter extends from the fluorescence layer 42 through a lens 44, which focuses the detection light 43 towards an energy sensor 45. The lens 44 and the energy sensor 45 are components of an energy sensor device 46 of the energy detection assembly 41, which is arranged in the beam path of the fluorescence detection light 43.

In the detection light beam path between the lens 44 and the energy sensor 45, the detection light 43 passes through a window 47 in the wall of the vacuum chamber VK.

Based on the 10 A further embodiment of an energy detection assembly 48 is described below, which can be used as an alternative or in addition to the embodiments of the energy detection assembly described above.

The image is shown in the 10 In top view, an embodiment of the aperture diaphragm 9 of the illumination optics 1. This has an outer aperture diaphragm section 49, which limits the numerical aperture of the illumination light 1 in the beam path in front of the entrance aperture 12 of the beam homogenizing element 11 and extends outwards in the 10 The aperture diaphragm 9 is shown in a fractured representation. Furthermore, the aperture diaphragm 9 has an inner obscuration diaphragm section 50 for specifying a central obscuration of the illumination light 3 in the pupil center. The two diaphragm sections 49, 50 are separated by three in the 10 Indicated bridges 51, which can be very thin, are connected to each other.

The energy detection assembly 48 has an EUV energy sensor device 52, which is designed to detect that part of the illumination light 3 that strikes the aperture diaphragm 9 and is guided in the central area of an illumination pupil of the illumination optics 1, which is covered by the inner obscuration diaphragm section 50. Part of the EUV energy sensor device 52 is, in turn, an EUV deflecting mirror 53 and a component arranged in the beam path of the deflected illumination light 3. 10 Energy sensor not shown, type of energy sensor 27. The structure of the EUV energy sensor device 52 can be as described above, for example, in connection with one of the EUV energy sensor devices 24 _i according to 3 and 4 described.

The EUV energy sensor device 52 can, as described in the 10 illustrated, further EUV deflection mirrors 54 ₁ , 54 ₂ , 54 ₃ and 54 ₄ , which in turn can be part of further EUV energy sensor devices of the type of EUV energy sensor device 52.

Based on the 11 A further embodiment of an energy detection assembly 55 is described below, which can be used as an alternative or in addition to the variants of the energy detection assemblies described above. Components and functions that were described above with reference to the 1 to 10 Those already explained bear the same reference numbers and will not be discussed again in detail.

An EUV sensor device 56 of the energy detection assembly 55 is designed as an energy sensor similar to, for example, the energy sensors 27. In the energy detection assembly 55, the energy sensor 27 is arranged centrally in the beam path of the illumination light 3 after the exit plane 15 of the beam homogenizing element 11, so that the energy sensor 27 of the energy detection assembly 55 detects a portion of the illumination light 3 that is guided in a central region of an illumination pupil of the illumination optics 1.

Based on the 12 A further embodiment of an energy detection assembly 57 is described below, which can be used as an alternative or in addition to the energy detection assembly variants described above. Components and functions described above with reference to the 1 to 11 Those already explained bear the same reference numbers and will not be discussed again in detail.

A diagram of the energy detection assembly 57 according to 12 basically corresponds to that of the energy detection assembly 55 according to 11 An EUV energy sensor device 58 of the energy detection assembly 57 is comparable to that described, for example, in [reference to relevant document]. 4 constructed and has a focusing deflecting mirror 59, which, comparable to the energy sensor 27 of the energy detection assembly 55, 11 in turn is arranged in a central area of the illumination light beam path after the exit plane 15 and focuses the portion of the illumination light 3 running there onto an energy sensor 27 of the EUV energy sensor device 58.

Based on the 13 A further embodiment of an energy detection assembly 60 is described below, which can be used as an alternative or in addition to the variants of the energy detection assemblies described above. Components and functions that were described above with reference to the 1 to 12 Those already explained bear the same reference numbers and will not be discussed again in detail.

In contrast to the energy detection assembly 57, a deflecting mirror 61 of an EUV energy sensor device 62 of the energy detection assembly 60 is according to 13 The deflecting mirror 61 of the energy detection assembly 60 is located at the same position as the deflecting mirror 59 of the energy detection assembly 57, i.e., again centrally in an illumination light beam path after the exit plane 15. The flat and compact deflecting mirror 61 directs the portion of the illumination light 3 incident on it towards a further deflecting mirror 63, which in turn focuses this portion of the illumination light 3 towards an energy sensor 27.

Based on the 14 The following is a further example of an energy detection system. Group 64 describes components that can be used as an alternative or in addition to the energy detection module variants described above. Components and functions described above with reference to the 1 to 13 Those already explained bear the same reference numbers and will not be discussed again in detail.

Part of the energy detection assembly 64 is an ionization chamber 65, which can be arranged in the beam path of the illumination light 3, for example, in front of the vacuum chamber VK (see also 1 The ionization chamber 65 defines an ionization space 66. A gas source 67 serves to introduce ionization gas 68 via a control valve 69 into the ionization chamber 65, i.e., into the ionization space 66.

The beam path of the illumination light 3 is guided through the ionization chamber 66.

An EUV energy sensor device 70 of the energy detection assembly 64 has an ion detector 71 for detecting a number of ions 71a generated by the ionization of the ionization gas 68 in the ionization chamber 66 by the illumination light 3. Furthermore, the EUV energy sensor device 70 has an electron detector 72 for detecting a number of electrons 72a generated by the ionization of the ionization gas 68 in the ionization chamber 66 by the illumination light 3.

The detectors 71, 72 each have an accelerating electrode 71b, 72b, which in the case of the ion detector 71 can be at a potential of -50 V, for example, and in the case of the electron detector 72 at a potential of 20 kV.

Electrodes 71b and 72b are designed as grid electrodes.

To detect the accelerated ions 71a on the one hand and the accelerated electrons 72a on the other, a metallic ion trap 71c of the ion detector 71 and a metallic electron trap 72c of the electron detector 72 are used. These traps 71c, 72c are at ground potential and can have a comb-like structure, as shown in the 14 hinted at.

The two detectors 71, 72 each have a charge signal receiver 71d, 72d, which receives a charge signal detected by the captures 71c, 72c and generates an energy signal from it. The charge receivers 71d, 72d thus represent energy sensors of the EUV energy sensor unit 70 of the energy detector assembly 64.

15 The diagram illustrates an operating scheme of one of the TDI sensors 32 _{i of} the detection device 23 of the mask inspection system 2a.

The example of 15 The circularly bordered reticule 18 is moved along the object displacement direction y relative to the object field 4 during a mask inspection step, as shown in the 15 Indicated on the left in a side view. In this schematic view according to 15 Reticulum 18 is shown as a transmissive object for simplified representation. The light source 5 and the illumination optics 1 are in the 15 The left side is also shown schematically.

In the 15 The center is shown at the top, showing how an image of reticulum 18 is generated due to object displacement during the mask inspection step across a column-wise view. 15 The detection surface of the TDI sensor 32 _i , with sensor columns I to IV, moves as shown. This is illustrated by Figure 75 of the circular boundary of reticle 18 on the detection surface, which is shown in the 15 The instantaneous recording situations A to D shown in the middle above move from left to right across the detection surface.

Synchronized with the displacement of the object from reticulum 18 to the TDI sensor 32 _i , sensor columns I to IV are read out, again along the object displacement direction y. A charge accumulation q that builds up along the position coordinate y on the detection surface of the TDI sensor 32 _i is in the 15 Below, again shown for the current situations A to D.

When the image of reticulum 18 is shifted by one column width of sensor columns I to IV in the object displacement direction y, a charge displacement occurs simultaneously on the TDI sensor 32 _i from one column to the column nearest in the y-direction. This causes a charge q to increase on the columns that detect image structures, such as a boundary section of image 75, with each displacement/charge displacement step, as shown by the charge distribution curves in the 15 The lower center illustrates the instantaneous situations A to D. Situation D shows the moment when a leading section of image 75 has completely migrated across all columns I to IV of the TDI sensor 32 _i and the image charge corresponding to this image section has accumulated to its maximum on the rightmost sensor column IV due to the synchronized charge displacement.

15 The resulting overall image 75 of the depicted structure on reticulum 18 is shown on the right, after this entire structure was shifted along the y-direction by object field 4. Due to the synchronized shifts The shift in charge/rotation results in a more contrast-rich image than would be the case with a non-time-shift-integrated recording using a conventional CCD sensor.

Additionally, when imaging reticulum 18 with the mask inspection system 2a, a pulsed version of the light source 5 must be taken into account. During the object displacement of reticulum 18 through the object field 4, different sections of reticulum 18 see different numbers of light pulses from the light source 5.

This is in the 16 This illustrates the temporal sequence of a pulsed exposure of reticulum 18, which is displaced along the object displacement direction y. The illumination field 4 _i (i = 1 to 5) currently illuminated on reticulum 18 during a light pulse from the light source 5 is shown. Due to the displacement of reticulum 18, this field also moves along the object displacement direction y. Certain illumination field overlap areas 76 _i are highlighted with arrows.

In the overlap area 76 ₁ , which is in the 16 The section of the reticulum that is also highlighted with a dashed line is exposed to a total of three light pulses, as it lies in the three illumination fields 4 ₁ , 4 ₂ and 4 ₃ , each of which is assigned to a light pulse.

The overlap area 76 ₂ is illuminated by exactly one light pulse, as it lies exclusively in the illumination field 4 ₃ .

Overlap areas 76 ₃ and 76 ₄ are each illuminated by exactly two light pulses from the light source 5, since they lie on the one hand (overlap area 76 ₃ ) in the illumination fields 4 ₃ and 4 ₄ and on the other hand (overlap area 76 ₄ ) in the illumination fields 4 ₄ and 4 ₅ .

Not every section of the object in reticulum 18 is illuminated by the same number of light pulses from the light source 5. In this sense, reticulum 18 is therefore unevenly exposed to the illumination light 3.

To compensate for this exposure unevenness, an EUV energy sensor device 77 has an energy detector assembly 78, which is located in the 17 In addition to an energy value sensor of the type of energy sensors, for example the energy sensors 27 of the embodiments described above, at least one energy change sensor 79 is shown for detecting a temporal development of an illumination energy of the illumination light 3 over an exposure period of the reticle 18, in particular for detecting a pulsed temporal energy profile of the light source 5.

Functions and components mentioned above in connection with the 1 to 16 Those already explained bear the same reference numbers and will not be discussed again in detail.

The 17 Figure 1 schematically shows components of the light source 5, namely the source volume 6, which is housed in a source chamber 80, and an exit aperture 81 in the source chamber 80, which defines an exit aperture of a bundle of the illumination light 3.

Due to the plasma generation process of the light source 5, scattered light 82 emanates from the source volume 6, some of which is used as detection light and travels along a path in the 17 The detection beam path is illustrated as an example. Along this detection beam path, the detection light 82 is reflected at an inner wall 83 of the source chamber 80 and passes through the exit opening 81 of the source chamber 80 at an angle to a main beam of the illumination light 3, thus crossing the beam of the illumination light 3 in the exit opening 81.

The detection light 82 has a significantly longer wavelength than the illumination light 3, for example, in the visible wavelength range. The detection light 82 is false light that is generated simultaneously with the illumination light 3. The detection light 82 is emitted by the plasma in the source volume 6 in a time-correlated manner with the emission of the illumination light 3.

After passing through the exit aperture 81, the detection light 82 passes through a window 84, for example made of glass, and a lens 85, which focuses the detection light 82 onto the energy change sensor 79 of the EUV energy sensor device 77. The energy change sensor 79 is a fast photodiode with a bandwidth of several MHz, which, depending on the wavelength of the detection light 82, can be sensitive to UV light, visible light (VIS), or near-infrared light (NIR).

18 shows another variant of an energy detection assembly 86, which can be used as an alternative or in addition to the energy detection assembly 78 according to 17 The energy detection assembly 86 has an EUV energy sensor device 87, which includes an energy change sensor 88 that is housed in the source chamber 80 and directly detects scattered light 82 emitted from the source volume 6 as detection light.

A temporal evolution of the energy of the detection light 82 correlates directly with the temporal evolution of the energy of the illumination light 3, so that a temporal evolution of the illumination energy of the illumination light 3 can be detected via the energy change sensors 79 and 88 respectively.

The energy change sensors 79 and 88 have a temporal resolution better than 10 µs. The temporal resolution can be better than 1 µs and can even be better.

19 shows in a meridional section a section of the illumination system of the mask inspection system 2a in the area between the aperture diaphragm 9 and an entry-side section of the beam homogenizing element 11 in the area of the entry opening 12.

The image is shown in the 19 A coupling sensor device 91 for monitoring a coupling location and a coupling direction of a beam of illumination light 3 into the inlet opening 12 of the beam homogenizing element 11. The coupling sensor device 91 has a coupling location sensor unit 92 and a coupling direction sensor unit 93.

The coupling point sensor unit 92 is arranged in the area of the inlet opening 12 of the beam homogenizing element 11.

20 Figure 1 shows a perspective view of the coupling point sensor unit 92. For illustration, individual rays 3 _i of the entire beam of illumination 3 are shown in the area of the beam path in front of the inlet opening 12 of the beam homogenizing element 11. The beam homogenizing element 11 is, apart from the inlet opening 12, in the 20 omitted.

The coupling point sensor unit 92 has a total of four deflecting mirrors 94 ₁ , 94 ₂ , 94 ₃ and 94 ₄ , which are arranged around the inlet opening 12 such that the inlet opening 12 is completely bounded by the deflecting mirrors 94 _i . During coupling, any illumination 3 that does not pass through the inlet opening 12 is thus reflected by one of the deflecting mirrors 94 ₁ to 94 ₄ .

20 Figure 1 also shows exemplary single-beam beam paths of light components not coupled into the entrance aperture 12, i.e., sensor components _3S of the illumination light 3, which is reflected by one of the respective deflecting mirrors _94i . Energy sensors ₂₇₁ , ₂₇₂ , 273 and ₂₇₄ of the coupling point sensor unit 92 are arranged in the beam direction of these sensor components _3S of the illumination light ₃ after reflection by one of the deflecting mirrors ₉₄₁ to ₉₄₄ .

The deflecting mirrors 94 _i are each oriented such that the respective sensor component 3 _S reflects the beam of illumination 3 incident towards the entrance opening 12, crossing it and towards the associated energy sensor 27 _i . This also illustrates the 19 , which on average represents the deflecting mirrors 94 ₁ and 94 ₃ and the associated energy sensors 27 ₁ and 27 _3. The deflecting mirror 94 ₁ is in the 19 above the inlet opening 12, i.e. above the incident beam of the illumination light 3, and the associated energy sensor 27 ₁ in the 19 below the incident beam of the illumination light 3. Accordingly, the deflecting mirror 94 ₃ is below and the associated energy sensor 27 ₃ is above this incident beam of the illumination light 3 in the 19 depicted.

The deflecting mirrors 94 _i can be configured as a coating on an entrance-side end wall of the housing 15e of the beam homogenizing element 11. This entrance-side end wall can be configured according to the deflecting mirror arrangement. 19 It can be designed to be concave or, alternatively, convex.

As an alternative to a coating, the deflecting mirrors 94 _i can be applied to this entrance-side end wall, for example, by being glued on. Alternatively again, the deflecting mirrors 94 _i can be components separate from the beam homogenizing element 11 and, in particular, adjustable separately from it.

The energy sensors 27 _i can be selected to control the coupling point of the illumination beam 3 into the entrance aperture 12 in the manner of a quadrant detector. Adjustment control pulses can be processed using energy or intensity values generated by the energy sensors 27 _i as follows:

A control signal Δx in one of the dimensions of the inlet opening 12 can be generated according to the following relationship: $$\Delta x={\eta }_x\cdot \frac{I_1-I_3}{I_1+I_3}$$ Δx is a control signal for an adjustment component to shift the beam of the illumination light 3 in the x-direction. For simplicity, it is assumed that the entrance opening 12 lies in the xy-plane.

_I1 and _I3 are the sensor signals of the energy sensors ₂₇₁ and _{273. ηx} is a scaling parameter. ter, which can be obtained as part of a calibration.

Accordingly, a control signal Δy for the y-coordinates can be obtained via the following relationship: $$\Delta y={\eta }_y\cdot \frac{I_2-I_4}{I_2+I_4}$$ _I2 and _I4 are the sensor signals of the energy sensors ₂₇₂ and _{274. ηy} is in turn a scaling factor that can be obtained by means of a preceding calibration step.

The control signals Δx, Δy generated in this way can be used as input signals for position control of the beam of illumination 3 relative to the inlet opening 12. This allows for position control of the coupling point of the beam of illumination 3 into the inlet opening 12 of the beam homogenizing element 11.

The coupling point sensor unit 92 can basically be constructed like the energy detection assembly 26, which was described above based on the 4 As explained above, the coupling point sensor unit 92 can also take over the function of the energy detection assembly 26, which was explained above.

21 Figure 1 shows an embodiment of the coupling direction sensor unit 93. The beam of the illumination light 3 is in turn illustrated by a multitude of individual beams 3 _i .

Ideally, the beam of illumination 3 passes through the aperture diaphragm 9 without any significant portion of the illumination 3 being cut off by the aperture diaphragm 9.

In the beam path of the illumination light 3 directly before or directly after the aperture diaphragm 9, four energy sensors ₂₇₁ , ₂₇₂ , ₂₇₃ and ₂₇₄ are arranged. These energy sensors 27i _of the coupling direction sensor unit 93 are held by a sensor frame 95 which also surrounds the beam of the illumination light 3.

The energy sensors _27i are located so close to the beam of illumination 3 that if a sensor component _3S of the illumination 3 were to strike one of the energy sensors 27i _of the coupling direction sensor unit 93, this sensor component _3S would also be cut off by the aperture diaphragm 9. Insofar as the energy sensors _27i are arranged in the beam path downstream of the aperture diaphragm 9, these energy sensors 27i, arranged in this way, constitute _sections of the aperture diaphragm 9.

The coupling direction of the beam of illumination 3 into the inlet opening 12 of the beam homogenizing element 11 is monitored by means of the energy sensors 27 ₁ to 27 ₄ of the coupling direction sensor unit 93. In addition, control signals Δx, Δy can be generated by appropriate evaluation of the energy sensors 27 ₁ , again in the manner of a quadrant sensor, as explained above in connection with the coupling location sensor unit 92, and the direction of the beam of illumination 3 can be controlled via these signals.

Alternatively to the execution according 21 The coupling direction sensor unit 93 can also be used, as in the 19 illustrated, deflecting mirror 96 _i , of which in the 19 The mirrors 96 ₁ and 96 ₃ are shown, as well as associated energy sensors 27 ₁ and 27 _3. The deflecting mirrors 96 _i are then arranged according to the arrangement of the energy sensors 27 _i in the arrangement according to 21 The deflecting mirrors _96i are arranged around the aperture opening of the aperture diaphragm 9. As explained above in connection with the deflecting mirrors _94i , they can be designed as coatings of the aperture diaphragm 9, as deflecting mirrors applied to the aperture diaphragm 9, or as deflecting mirrors separate from the aperture diaphragm 9 and, in particular, separately adjustable. The deflecting mirrors _96i are designed such that they reflect sensor components _3S of the illumination light that does not pass through the aperture opening of the aperture diaphragm 9 outwards to the respective associated energy sensor _27i .

Alternatively or in addition to the coupling sensor device 91 described above, in particular the coupling point sensor unit 92, variants already described above in connection with the various versions of the energy detection assembly can also be used. In particular, part of a variant of the coupling point sensor unit can be a deflecting mirror that reflects at least, and preferably in the circumferential direction, several sensor components _3S of the beam of illumination 3 directed towards the inlet opening 12 at the edge towards at least one corresponding energy sensor.

Alternatively or additionally, a coupling sensor device with a corresponding control function can be implemented by scanning corresponding relative motion components to shift the position and direction of the incident beam of illumination 3 towards the beam homogenizing element 11 and, in particular, towards the inlet of the beam homogenizing element 11. Depending on the respective scan position, it can then be measured how much of the The illumination light 3 is coupled into the entrance opening 12 and can then be regulated to a coupling maximum.

Alternatively or additionally, the coupling of the illumination light 3 into the entrance opening 12 can be monitored by means of a suitable coupling point sensor unit via an EUV fluorescent screen in the entrance plane 13, wherein the screen is arranged around the entrance opening 12, in particular, similar to the deflecting mirrors 94 _i . Fluorescence light generated by extensions of the illumination light 3 beam onto this fluorescent screen when coupled into the entrance opening 12 can then be monitored by a suitable camera, and the coupling of the illumination light 3 beam into the entrance opening 12 can be adjusted to minimize or symmetrize this detected fluorescent light.

In principle, the sensor units of the coupling sensor device 91 described above can be arranged in the beam path in front of an opening of the respective sensor unit, i.e. in front of the aperture diaphragm 9 and/or in front of the entrance opening 12, or alternatively arranged behind a corresponding opening.

Positioning the sensors in front of the aperture allows for a usable sensor signal even in a centered, optimally coupled state, provided the energy sensors are still within the beam path of the illumination light 3 and thus receive a corresponding sensor component _3S . Positioning the sensors downstream of the aperture enables measurements with high signal dynamics because the energy sensors used in this configuration can detect a significant drop in intensity at the coupling edge.

Adjusting the coupling point and direction can be achieved using identical control steps. This adjustment can be accomplished by moving optically active components of the lighting system in one or more degrees of freedom of translation and/or rotation. Such optically active components for adjusting the coupling direction and location can be components of the light source and/or other beam guidance components.

The coupling point on the one hand and the coupling direction on the other hand can be alternately iteratively adjusted and thus optimized.

Alternating control of the coupling point and coupling direction, or a combined control, is possible.

The coupling sensor device 91 can, in addition to monitoring the coupling point in the two spatial dimensions x and y in the entry plane 13 of the entry aperture 12, also monitor along the component z perpendicular to it. This can be achieved in this z-direction by linking this monitoring with a focus adjustment capability of an coupling focus of the illumination light 3 relative to the position of the entry aperture 12. For example, the beam homogenizing element 11 can be moved along the beam direction, i.e., along the z-direction perpendicular to the entry plane 13, to enable this degree of adjustment freedom.

The energy value sensors and energy change sensors described above can each include a conversion medium for converting light incident on the respective sensor into a detection light of a longer wavelength, for example a fluorescent medium and/or a scintillation medium.

The respective energy value sensors or energy change sensors are in signal communication with the control unit 27a, which in turn is in signal communication with the light source 5 and the detection unit 23. This makes it possible to correlate a detection result with the performance of the light source 5, in particular with the respective energy of a light pulse from the light source 5 and the respective temporal development of this energy, which can be recorded via the at least one energy value sensor or the at least one energy change sensor of the energy detection assemblies described above. A correspondingly high-precision image generation of the structures of the reticulum 18 is the result.

The control/regulating device 27a is in signal communication with the coupling mirror optics 10 for the execution of the control/regulation processes described above.

Claims (10)

Energy detection assembly (26) for a lighting system of a mask inspection system (2a) for use with EUV lighting light (3), - with a beam homogenizing element (11) for guiding the lighting light (3), which has an inlet opening (12) for the lighting light (3) and an outlet opening (14) for the lighting light (3) - with at least one EUV energy sensor device (24 _i ) designed to detect illumination light (3) that is guided outside the inlet opening (12) of the beam homogenizing element (11) along an illumination light beam path. Energy detection assembly according to Claim 1 , characterized in that the EUV energy sensor device (24) has an EUV deflecting mirror (25 _i ) arranged outside the inlet opening (12) of the beam homogenizing element (11) and an energy sensor (27 _i ) which is arranged such that illumination light (3), which is guided along the illumination light beam path and hits the EUV deflecting mirror (25 _i ), is guided towards the energy sensor (27 _i ). Energy detection assembly according to Claim 1 or 2 , characterized by several EUV energy sensor devices (24 ₁ to 24 ₄ ) designed to detect illumination light (3) directed towards several areas distributed around the inlet opening (12) outside the inlet opening (12) of the beam homogenizing element (11) along the illumination light beam path. Energy detection assembly according to one of the Claims 1 until 3 , characterized by a coupling sensor device (91) for monitoring a coupling point and/or a coupling direction of a bundle of the illumination light (3) into the inlet opening (12) of the beam homogenizing element (11). Energy detection assembly according to Claim 4 , characterized in that the coupling sensor device (91) comprises: - a coupling location sensor unit (92) for monitoring a coupling location of the beam of illumination light (3) into the inlet opening (12) of the beam homogenizing element (11) and - a coupling direction sensor unit (93) separate from this for monitoring a coupling direction of the beam of illumination light (3) into the inlet opening (12) of the beam homogenizing element (11). Energy detection assembly according to Claim 4 or 5 , characterized in that the coupling sensor device (91) has at least one EUV energy sensor (27 _i ) which detects illumination light (3) which is guided outside an aperture opening of an aperture diaphragm (9) of the illumination system. Energy detection assembly (28) for a lighting system of a mask inspection system (2a) for use with EUV lighting light (3), - with a beam homogenizing element (11) for guiding the lighting light (3) with an inlet opening (12) for the lighting light (3) and with an outlet opening (14) for the lighting light (3), and - with at least one EUV energy sensor device (29) designed to detect lighting light (3) that is guided within the outlet opening (14) of the beam homogenizing element (11) along a lighting light beam path. Energy detection assembly according to Claim 7 , characterized in that the EUV energy sensor device (29) has an EUV deflecting mirror (29a) arranged within the exit opening (14) of the beam homogenizing element (11) and an energy sensor (27) which is arranged such that illumination light (3), which is guided along the illumination light beam path and hits the EUV deflecting mirror (29a), is guided towards the energy sensor (27). Energy detection assembly according to Claim 7 or 8 , characterized in that the exit aperture (14 _Q ) of the beam homogenizing element (11) is designed to be larger than a useful exit aperture area (14) which is required for the subsequent illumination of an object field (4) in which a mask (18) to be inspected can be arranged, wherein the EUV energy sensor device (29) is designed to detect illumination light (3) which is guided within the exit aperture (14 _Q ) of the beam homogenizing element (11) beyond the useful exit aperture area (14) along an illumination light beam path. Mask inspection system (2a) for use with EUV illumination light (3), - with an illumination system with a light source (5) for generating illumination light (3) and with an illumination optic (1) for guiding the illumination light (3) towards an object field (4) in which a mask (18) to be inspected can be arranged, - with an imaging optic (PO) for imaging the object field (4) into an image field (21), - with a spatially resolved detection device (23) for detecting the illumination light (3) guided into the image field (21), and - with at least one energy detection device group (26; 28; 30; 33; 39; 41; 48; 55; 57; 60; 64; 78; 86) according to one of the Claims 1 until 9 .