Energy detection assembly for a lighting system of a mask inspection system for use with EUV lighting light

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

[0001] 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.

[0002] Such a mask inspection system is known from US 10,042,248 B2, DE 102 20 815 A1, and WO 2012 / 101269 A1. DE 10 2021 213 327 B3 discloses a metrology system for examining objects with 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 discloses 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 discloses a hollow waveguide for guiding EUV light with a useful wavelength. US patent 6,456,362 B1 discloses an integrating waveguide for use in a lithographic projection exposure system.

[0003] It is an object of the present invention to help improve the inspection accuracy of a mask inspection system.

[0004] 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.

[0005] 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 from image data of the mask inspection system during post-processing using sensor data from the EUV energy sensor device, especially during image post-processing. 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 can be achieved primarily by performing a scanning measurement using the EUV energy sensor device, which can then be implemented as a TDI camera. The resulting summation or averaging data can then serve as input for controlling the light source intensity. An energy value measured by the EUV energy sensor device can be used to correct measured image or camera data, particularly computationally. Alternatively or additionally, the sensor data from the EUV energy sensor device can be used as a control signal to regulate the light source intensity. The coupling point and / or direction of the illumination light coupling into the beam homogenizing element can also be controlled variables. The energy detection assembly can include multiple EUV energy sensor devices, which can detect different partial beams of the illumination light.They can be monitored. An energy sensor of at least one EUV energy sensor device can be implemented as an EUV photodiode. Such EUV photodiodes are known on the market.

[0006] 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.

[0007] 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.

[0008] Along an illumination light beam path, the illumination light detected by the EUV energy sensor device is guided if this illumination light detected by the EUV energy sensor device is guided between a source area of ​​an EUV light source generating the EUV illumination light and the beam homogenizing element within specified edge aperture limits of the optical components guiding the illumination light.

[0009] 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.

[0010] 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.

[0011] 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.

[0012] The beam homogenizing element can alternatively be designed as a hollow waveguide.

[0013] 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.

[0014] 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 determined as described above in connection with the detection of the illumination light outside the entrance aperture.In the circumferential direction, the areas distributed around the inlet opening, in which the EUV energy sensor devices detect the ambient light, can cover, for example, between 5% and 50% of the total circumference around the center of the inlet opening, for example, in the range between 10% and 40%, and particularly in the range of 25%. Such a covered partial circumference around the inlet opening represents a good compromise between the complexity of the sensor technology on the one hand and the information gained from detecting the ambient light in the detection areas distributed around the inlet opening on the other.

[0015] 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.

[0016] 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.

[0017] The coupling sensor device can be connected to a control / regulation device of the energy detection assembly to enable control or regulation of the coupling location and / or the coupling direction.

[0018] 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.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] 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.

[0023] An embodiment of the coupling direction sensor unit according to claim 6 is practical.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV illumination light in a lighting system of 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.

[0028] 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, reference is made only by way of example to DE 197 14 221 A1.

[0029] 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 arranged between the detection sections of the detection unit's detection area, particularly between adjacent CCD and / or TDI sensors.

[0030] In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV illumination light in a lighting system of 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.

[0031] 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.

[0032] 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.

[0033] In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV illumination light in a lighting system of 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.

[0034] Such an energy detection assembly enables elegant energy measurement that is not carried out optically, but is based on charge or photocurrent measurement.

[0035] In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV illumination light in a lighting system of 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.

[0036] 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.

[0037] In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV illumination light in a lighting system of 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.

[0038] 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 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.

[0039] In one variant of the energy detection assembly, which also solves the aforementioned task, the energy detection assembly is designed for use with EUV illumination light in a lighting system of 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.

[0040] 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.

[0041] 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.

[0042] 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.

[0043] A wafer inspection system can be structured accordingly.

[0044] 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.

[0045] The inspection system can be a system for actinic mask or wafer inspection.

[0046] An embodiment of the invention is explained in more detail below with reference to the drawing. This drawing shows: Fig. 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; Fig. 1A compared to the Fig. 1 Enlarged and showing internal details of the beam homogenizing element of the mask inspection system; Fig. 2 schematically a perspective, entry-side view of a version of the beam homogenizing element; Fig. 3 compared to the Fig. 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; Fig. 4 schematically a section according to line IV-IV in Fig. 3 with an illustration of an illumination and detection light path between two deflection mirrors of the energy detection assembly and associated energy sensors; Fig. 5 in one to Fig. 4. Similar illustration shows 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 between a deflecting mirror and an energy sensor of the EUV energy sensor device of the energy detection assembly is illustrated; Fig. 6 in one to Fig. Figure 3 shows a top view of the inlet opening of the beam homogenizing element, suitable for use with an energy detection assembly according to Fig. 5; Fig. 7 in one to Fig. 6 similar representation a top view of an outlet opening of the beam homogenizing element according to Fig. 6; Fig. 8 a supervision of a further embodiment of an energy detection assembly for the mask inspection system according to Fig. 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; Fig. 9 in a to Fig. 1 similar representation shows an illumination light beam path after the exit aperture of the beam homogenizing element, in addition to which 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 shown; Fig. 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; Fig. 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 a further version of an energy detection assembly arranged centrally in an exit illumination light beam; Fig. 12 in one to Fig. 11. Similar illustration 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 to an energy sensor of the energy detection assembly is illustrated; Fig. 13 in one of the Fig. 11 and Fig. 12. Similar illustration shows another embodiment of an energy detection assembly with an output coupling mirror and a downstream deflecting mirror for detection light towards an energy sensor of the energy detection assembly; Fig. 14 a cross-section through an ionization chamber of a further embodiment of an energy detection assembly with an ion / electron detection for detecting charged particles that are generated by ionization of an ionization gas in the ionization chamber by the illumination light; Fig. 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; Fig. 16 in one Fig. 15 corresponding representation a temporal sequence of illumination of the lithography mask to be inspected with illumination light of a pulsed light source of the mask inspection system; Fig. 17. An embodiment of a light source of the mask inspection system with an energy change sensor of an embodiment otherwise in the Fig. 17 energy detection assembly not shown for recording a temporal development of the illumination energy of the illumination light over an exposure period; Fig. 18 in a to Fig. 17 similar representation the light source of the mask inspection system with a further embodiment of an energy detection assembly with an energy change sensor arranged in a source chamber of the light source; Fig. 19 compared to Fig. 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, wherein components of a coupling sensor device of the lighting system are shown; Fig. 20 perspectively 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; Fig. 21 also in perspective representation an embodiment of a coupling direction sensor unit of the coupling sensor device, arranged in the area of ​​the aperture diaphragm.

[0047] 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 Fig. Figure 1 illustrates the illumination optics via marginal rays and a main ray. The illumination light 3 illuminates an illumination field 4 of the mask inspection system.

[0048] 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.

[0049] 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.

[0050] To facilitate spatial relationships, a Cartesian xyz coordinate system is used below. The x-axis is perpendicular to the drawing plane. Fig. 1 and runs into it. The y-axis runs in the Fig. 1 horizontally to the left and the z-axis runs in the Fig. 1 vertically upwards.

[0051] 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 the 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, and a change between the useful light filters can then be made if a degradation of the filtering effect of the operating useful light filter 8 is detected.Alternatively, the useful light filters can also have different filter characteristics and, for example, allow different useful light wavelength ranges to pass through into the subsequent illumination light beam path or be optimized to filter out different proportions of false light.

[0052] 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.

[0053] 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.

[0054] 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 Fig. 1 is indicated in the illumination light beam path between the mirror IL1 and the illumination light aperture diaphragm 9.

[0055] 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 Fig. 1 is indicated in 9a. 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.

[0056] 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 is located 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. The entrance-side numerical aperture of the illumination beam 3 at the entrance aperture 12 can be in the range of 0.02 to 0.2, for example, in the range of 0.05.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] Fig. Figure 1A illustrates details of the beam homogenizing element 11.

[0061] 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 Fig. 1A Exemplary partial beam paths of lighting channels 3 i(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. An actual number of illumination channels 3 i In practice, this is larger and can, for example, involve several hundred illumination channels guided over 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 directed along the illumination channels 3 i The beam path between micromirrors 15c and 15d is parallelized. The micromirror arrays 15a and 15b are arranged and dimensioned such that the partial beams of the illumination light 3 are aligned along the illumination channels 3. ioverlap in the exit opening 14, so that a beam homogenization of the illumination light 3 takes place between the inlet opening 12 and the exit opening 14 in the beam homogenizing element 11.

[0062] 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.

[0063] The beam homogenizing element 11 can alternatively be designed as a hollow waveguide.

[0064] 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.

[0065] 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°.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] The output coupler 16 can be designed in the manner of a Wolter telescope, specifically as a Wolter optic of type I. Such Wolter optics are described in J.D. Mangus, J.H. Underwood, "Optical Design of a Glancing Incidence X-ray Telescope," Applied Optics, Vol. 8, 1969, page 95, and the references cited 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.

[0070] An embodiment of the output coupling mirror optics 16 is described in US 10,042,248 B2.

[0071] The imaging factor β1 of the input-coupling mirror optics 10 can range from 0.1 to 50, meaning it can reduce the image by a factor of 10 to magnify it by a factor of 50. The imaging factor β2 of the output-coupling mirror optics 16 can range from 0.02 to 10, meaning it can itself reduce the image by a factor of 50 to magnify 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.

[0072] 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.

[0073] 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.

[0074] The x / y aspect ratio of the illumination field 4 matches the x / y aspect ratio of the exit aperture 14.

[0075] 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.

[0076] 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.

[0077] 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°.

[0078] 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.

[0079] The image field 21 is captured by a detection device 23, e.g., by one or more CCD cameras. For details of the imaging into the image field, reference is made to US 10,042,248 B2 and the references given in US 10,042,248 B2. 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.

[0080] The mask inspection system 2a makes it possible to inspect, for example, a structure on reticulum 18.

[0081] Fig. Figure 2 shows a perspective and schematic view of an embodiment of the beam homogenizing element 11 with a view towards the inlet opening 12.

[0082] Fig. 3 shows in comparison to the Fig. Figure 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 Fig. 3 four EUV deflection mirrors 25 i The components shown (i = 1 to 4) 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.

[0083] The four EUV deflection mirrors 251 to 254 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 entrance opening 12 and is centered in relation to the respective side.

[0084] The Fig. Figure 3 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.

[0085] A measure of the respective illuminance energy present at the entry level is in the Fig. 3 illustrated by different hatching types, for which in the Fig. Figure 3 shows a table of dimensions 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. The two deflecting mirrors 251 and 253 arranged on the long sides therefore capture more illumination 3 that 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.

[0086] 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 251 is regularly in the range of less than 1 × 10 -4 the total energy of the lighting light 3.

[0087] Fig. Figure 4 illustrates in a longitudinal section view in particular a further detection beam path of the two energy sensor devices 244 with the deflecting mirror 254 and the energy sensor device 242 with the deflecting mirror 252.

[0088] The illumination light 3 incident on the deflecting mirror 252 is directed towards an energy sensor 272. This can be a photodiode sensitive to EUV light. EUV sensitivity can be achieved via appropriate fluorescent or scintillation layers.

[0089] 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.

[0090] 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%.

[0091] 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.

[0092] Accordingly, the further one in the Fig. 4 visible deflecting mirrors 254 direct the portion of the illumination light 3 hitting it towards an associated energy sensor 274 of the energy sensor device 244.

[0093] Others, in which Fig. Four non-visible energy sensors 271 and 273 are assigned to the deflecting mirrors 251 and 253.

[0094] In total, the energy detection assembly 26 has four deflecting mirrors 251 to 254 and four associated energy sensors 271 to 274, i.e. a total of four EUV energy sensor devices 241 to 244.

[0095] The energy sensors 27 are connected to a central control / regulating device 27a (see Fig. 1) of the mask inspection system 2a in signal connection.

[0096] The illumination light beam path visible in the meridional section of the Fig. It can also be seen from Figure 4 that the deflecting mirrors 252 and 254 deflect only illumination light 3, which does not enter the inlet opening 12 of the beam homogenizing element 11.

[0097] Based on the Fig. Sections 5 to 7 below describe a further embodiment of an energy detection assembly 28, which can be used as an alternative or in addition to the energy detection assembly 26 according to the Fig. 3 and Fig. 4 can be used. Components and functions that correspond to those mentioned above with reference to the Fig. 1 to 4 and in particular with reference to the Fig. 3 and Fig. Items 4, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0098] 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 Fig. The 5 illustrated illumination light beam path is shown.

[0099] A corresponding, outlet-side sensor component 3 S The illumination 3 is generated without significant light loss by using, instead of a beam homogenizing element with a rectangular inlet opening 12 as in the energy detection assembly 26, according to the Fig. 3 and Fig. 4 a beam homogenizing element 11 with a square entrance opening 12 Q is used.

[0100] Fig. 6 illustrates this difference. It is consistently shown in the Fig. 6 the rectangular inlet opening of the variant of the energy detection assembly 26 according to the Fig. 3 and Fig. 4, this time shown in "standing" form. The dashed line indicates... Fig. 6 the square enlarged entrance opening 12 Q the energy detection assembly 28 after Fig. 5 shown. In principle, even with the square-enlarged entrance opening 12 Q a deflection mirror arrangement with deflection mirrors 251 to 254 outside this square entrance opening 12 Q as shown above with reference to the energy detection assembly 26, in particular according to Fig. 4 explained.

[0101] As a result of the square expansion, the energy detection assembly 28 has a square outlet opening 14 on the outlet side. Q the sensor component 3 S in an exit opening area 14 S (cf.) Fig. 7 left) of the entire exit opening 14 Q available. The remaining outlet opening, i.e., the one around the sensor portion 14 S reduced cross-section of the square outlet opening 14 Q can then be used to illuminate lighting field 4. Alternatively, it can also be used on the opposite side, in the Fig. 7 on the right side another sensor component 14 S2 the exit opening 14 Q for energy-sensor or other purposes, so that on the side of the outlet opening 14 Q effectively a rectangular outlet opening 14 corresponding to that of the beam homogenizing element of the energy detection assembly 26 according to Fig. 3 remains.

[0102] The exit opening 14 Q The beam homogenizing element 11 is therefore larger than the useful 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, a portion of the illumination light 3 coupled out of the beam homogenizing element 11 is no longer available for illuminating the object field 4. This effective reduction of the useful illumination light for illuminating the object field 4 is, at least partially, compensated for by the fact that the inlet aperture 12 Q the beam homogenizing element 11 is also larger, and therefore more illumination light 3 can be coupled into the beam homogenizing element 11.

[0103] The EUV energy sensor device 29 is designed such that it includes the sensor component 3 S of the illumination light 3, which is within the exit opening 14 Q of the beam homogenizing element 11 beyond this useful outlet aperture area, namely in the outlet aperture sensor portion 14 S is guided along the path of the lighting light beam.

[0104] The sensor component 3 S The illumination light 3 is guided in the EUV energy sensor device 29 via a first deflecting mirror 29 a , which is located in the outlet-side area of ​​the sensor component 14 S the exit opening 14 Q is arranged. The sensor component 3 is described below. S via a further, imaging deflecting mirror 29 b led to an energy sensor 27.

[0105] The EUV detection assembly 28 can accommodate several EUV energy sensor devices 29 iaccording to the type of in the Fig. 5 depicted EUV energy sensor device 29, wherein, for example, a deflecting mirror of the type of deflecting mirror 29 is located on both sides of the rectangular utility outlet opening 14. a can be arranged, which in turn in the beam path of the further sensor component of the illumination light components such as the deflecting mirror 29 b and may be subordinate to the energy sensor 27.

[0106] Based on the Fig. Section 8 below describes a further embodiment of an energy detection assembly 30, which can be used as an alternative or in addition to the energy detection assemblies described above.

[0107] 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 321 to 32. 12 , which are arranged in the image plane 22 of the detection device 23 in the manner of a 4 × 3 array. Between the rows of this sensor array of sensors 32 i A y-distance exists that is sufficiently large to allow a component of the EUV energy sensor device 31 to be arranged within this line spacing. This component could be a deflecting mirror of the type of deflecting mirror 25. i trade or an energy sensor of the type of energy sensors 27 i .

[0108] The energy detection assembly 30 may also contain several such EUV energy sensor devices 31.

[0109] 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 324 and 327.

[0110] In a further embodiment of an energy detection assembly 33 (see Fig. 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 Fig. Figure 1 shows the useful light filter 8, 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.

[0111] 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.

[0112] The detection light 34 is light that is not transmitted along the subsequent illumination light beam path by the useful light filter 8.

[0113] 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.

[0114] At least one of the useful light filters 8, which are housed in the filter wheel 7, may have a metallic support structure.

[0115] An alternative and additional variant of an energy detection assembly 39 can be used in the Fig. 1. A schematically represented EUV energy sensor device 40 is configured 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.

[0116] Based on the Fig. Section 9 below describes a further embodiment of an energy detection assembly 41. Components and functions described above with reference to the Fig. Items 1 to 8, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0117] In the case of the energy detection assembly 41 according to Fig. 9 is one of the mirrors of the illumination optics 1, namely mirror IL2, 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 light wavelength of the illumination light 3.

[0118] 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).

[0119] In the Fig. Figure 9 shows the beam path of the illumination light 3 from the exit plane 15 of the beam homogenizing element 11 to the mirror IL2, as well as a beam path of the fluorescence detection light 43. The latter runs 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.

[0120] 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.

[0121] Based on the Fig. Section 10 below describes a further embodiment of an energy detection assembly 48, which can be used as an alternative or in addition to the embodiments of the energy detection assembly described above.

[0122] The image is shown in the Fig. 10 in plan 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 which extends outwards in the Fig. 10 is shown in a broken representation. Furthermore, the aperture diaphragm 9 has an inner obscuration aperture section 50 to provide central obscuration of the illumination light 3 in the pupil center. The two aperture sections 49, 50 are separated by three in the Fig. 10 indicated bridges 51, which can be very thin, connected to each other.

[0123] 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. Fig. 10 Energy sensor not shown, similar to 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 after Fig. 3 and Fig. 4 described.

[0124] The EUV energy sensor device 52 can, as described in the Fig. Figure 10 illustrates further EUV deflection mirrors 541, 542, 543 and 544, which in turn can be part of further EUV energy sensor devices of the type of EUV energy sensor device 52.

[0125] Based on the Fig. Section 11 below describes a further embodiment of an energy detection assembly 55, 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 Fig. Items 1 to 10, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0126] 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.

[0127] Based on the Fig. Section 12 below describes a further embodiment of an energy detection assembly 57, which can be used as an alternative or in addition to the variants of the energy detection assemblies described above. Components and functions described above with reference to the Fig. Items 1 to 11, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0128] A diagram of the energy detection assembly 57 according to Fig. 12 basically corresponds to that of the energy detection assembly 55 according to Fig. 11. An EUV energy sensor device 58 of the energy detection assembly 57 is comparable to that described, for example, in Fig. 4 is constructed and has a focusing deflecting mirror 59, which, comparable to the energy sensor 27 of the energy detection assembly 55, Fig. 11 is in turn 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.

[0129] Based on the Fig. Section 13 below describes a further embodiment of an energy detection assembly 60, which can be used as an alternative or in addition to the variants of the energy detection assemblies described above. Components and functions described above with reference to the Fig. Items 1 to 12, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0130] 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 Fig. 13 is designed as a planar deflecting mirror. The deflecting mirror 61 of the energy detection assembly 60 is arranged at the location of 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 planar 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.

[0131] Based on the Fig. Section 14 below describes a further embodiment of an energy detection assembly 64, 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 Fig. Items 1 to 13, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0132] 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 Fig. 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.

[0133] The beam path of the illumination light 3 is guided through the ionization chamber 66.

[0134] 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.

[0135] 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.

[0136] Electrodes 71b and 72b are designed as grid electrodes.

[0137] 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 Fig. 14 indicated.

[0138] 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.

[0139] Fig. Figure 15 illustrates an operating diagram of one of the TDI sensors. Figure 32 i the detection device 23 of the mask inspection system 2a.

[0140] The example of Fig. 15 circularly bordered reticles 18 are displaced along the object displacement direction y relative to the object field 4 during a mask inspection step, as shown in the Fig. 15 is indicated on the left in a side view. In this schematic view according to Fig. Reticule 18 is shown in Figure 15 as a transmissive object for simplified representation. The light source 5 and the illumination optics 1 are shown in the Fig. 15 on the left is also shown schematically.

[0141] In the Fig. 15 Middle is shown above, showing how an image of reticle 18 is generated due to object displacement during the mask inspection step across a column-wise view in the Fig. 15 Detect area of ​​the TDI sensor shown 32 i with sensor columns I to IV. This is illustrated by image 75 of the circular boundary of reticle 18 on the detection surface, which is shown in the Fig. 15 instantaneous recording situations A to D shown in the middle above move from left to right across the detection surface.

[0142] Synchronized with the object relocation of reticle 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 builds up along the position coordinate y on the detection surface of the TDI sensor 32. i is in the Fig. 15 below, again shown for the current situations A to D.

[0143] If 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. ifrom one column to the column nearest in the y-direction. This causes the charge q on the columns capturing image structures, such as a boundary section of image 75, to increase with each displacement / charge shift step, as shown by the charge distribution curves in the Fig. Figure 15, bottom center, illustrates the instantaneous situations A to D. Situation D shows the moment when a leading section of Figure 75 completely covers all columns I to IV of the TDI sensor 32. i has migrated and the image charge corresponding to this image section has accumulated maximally on the rightmost sensor column IV through the synchronized charge displacement.

[0144] Fig. Figure 15 shows on the right the resulting overall image 75 of the depicted structure on reticulum 18, after this entire structure was shifted along the y-direction by object field 4. Due to the synchronized shift / charge displacement, a higher-contrast image is obtained than would be the case with a non-time-shift-integrated image using a conventional CCD sensor.

[0145] 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.

[0146] This is in the Fig. Figure 16 illustrates the temporal sequence of a pulsed exposure of reticulum 18 displaced along the object displacement direction y. The illumination field 4 currently exposed on reticulum 18 during a light pulse from the light source 5 is shown. i (i = 1 to 5), which, due to the displacement of reticle 18, also migrates along the object displacement direction y. Certain illumination field overlap areas 76 are highlighted with arrows. i .

[0147] In the overlap area 761, which is in the Fig. 16, which is also highlighted with a dashed line, represents a section of the reticulum that is illuminated by a total of three light pulses, as it lies within the three illumination fields 41, 42 and 43, each of which is assigned to a light pulse.

[0148] The overlap area 762 is illuminated by exactly one light pulse, as it lies exclusively in the illumination field 43.

[0149] Overlap areas 763 and 764 are each illuminated by exactly two light pulses from the light source 5, since they lie on the one hand (overlap area 763) in the illumination fields 43 and 44 and on the other hand (overlap area 764) in the illumination fields 44 and 45.

[0150] 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.

[0151] To compensate for this exposure unevenness, an EUV energy sensor device 77 has an energy detector assembly 78, which is located in the Fig. Figure 17 shows that, 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 also provided 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.

[0152] Functions and components mentioned above in connection with the Fig. Items 1 to 16, which have already been explained, bear the same reference numbers and will not be discussed again in detail.

[0153] The Fig. Figure 17 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.

[0154] 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 Fig. The detection beam path is illustrated in Figure 17 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.

[0155] 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.

[0156] 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).

[0157] Fig. Figure 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. Fig. 17 can be used. 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.

[0158] 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.

[0159] 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.

[0160] Fig. Figure 19 shows a section of the illumination system of the mask inspection system 2a in a meridional section 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.

[0161] The image is shown in the Fig. 19 a coupling sensor device 91 for monitoring a coupling location and a coupling direction of a bundle of the 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.

[0162] The coupling point sensor unit 92 is arranged in the area of ​​the inlet opening 12 of the beam homogenizing element 11.

[0163] Fig. Figure 20 shows a perspective view of the coupling point sensor unit 92. Individual beams 3 are shown for illustration. i The entire beam of illumination 3 in the area of ​​the beam path in front of the entrance aperture 12 of the beam homogenizing element 11 is shown. The beam homogenizing element 11 is, apart from the entrance aperture 12, in the Fig. 20 omitted.

[0164] The coupling point sensor unit 92 has a total of four deflecting mirrors 941, 942, 943 and 944, which are arranged around the inlet opening 12 such that the inlet opening 12 is deflected by the deflecting mirrors 94 i is completely limited. Any illumination light 3 that does not pass through the inlet opening 12 during coupling is thus reflected by one of the deflecting mirrors 941 to 944.

[0165] Fig. Figure 20 also shows exemplary single-beam beam paths of light components not coupled into the entrance aperture 12, i.e. sensor components 3 S of the illumination light 3, which is emitted from one of the respective deflecting mirrors 94 i is reflected. In the direction of the beam of these sensor components 3 S Energy sensors 271, 272, 273 and 274 of the coupling point sensor unit 92 are arranged after reflection of the illumination light 3 at each of the deflecting mirrors 941 to 944.

[0166] The deflecting mirrors 94 i are each oriented so that the respective sensor component 3 S the beam of illumination incident towards the entrance opening 12, crossing towards the associated energy sensor 27 i This is reflected. This is also illustrated by the Fig. 19, which on average represents the deflecting mirrors 941 and 943 and the associated energy sensors 271 and 273. The deflecting mirror 941 is in the Fig. 19 is arranged above the inlet opening 12, i.e., above the incident beam of the illumination light 3, and the associated energy sensor 271 is located in the Fig. 19 below the incident beam of the illumination light 3. Accordingly, the deflecting mirror 943 is below and the associated energy sensor 273 is above this incident beam of the illumination light 3 in the Fig. 19 shown.

[0167] The deflecting mirrors 94 i can be implemented 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. Fig. 19. They may be designed to be concave or alternatively convex.

[0168] As an alternative to a coating, the deflecting mirrors 94 i applied to this entrance-side end wall, for example, it may be glued on. Alternatively, the deflecting mirrors 94 may bei to be components separate from the beam homogenizing element 11 and, in particular, adjustable separately from it.

[0169] The energy sensors 27 i The coupling point of the beam of illumination 3 into the entrance aperture 12 can be selected in the manner of a quadrant detector to control this coupling point. Adjustment control pulses can be generated using energy or intensity values ​​provided by the energy sensors 27. i generated, processed as follows:

[0170] A control signal Δx in one of the dimensions of the inlet opening 12 can be generated according to the following relationship: Δx=ηx⋅I1−I3I1+I3 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.

[0171] I1 and I3 are the sensor signals of energy sensors 271 and 273. x is a scaling parameter that can be obtained during calibration.

[0172] Accordingly, a control signal Δy for the y-coordinates can be obtained via the following relationship: Δy=ηy⋅I2−I4I2+I4 I2 and I4 are the sensor signals of energy sensors 272 and 274. y This in turn is a scaling factor that can be obtained by means of a preceding calibration step.

[0173] 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.

[0174] The coupling point sensor unit 92 can basically be constructed like the energy detection assembly 26, which was described above based on the Fig. 4 explained. Accordingly, the coupling point sensor unit 92 can also take over the function of the energy detection assembly 26, which was explained above.

[0175] Fig. Figure 21 shows an embodiment of the coupling direction sensor unit 93. The beam of the illumination light 3 is in turn divided by a multitude of individual beams 3. i illustrated.

[0176] 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.

[0177] 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 27 iThe coupling direction sensor unit 93 are held by a sensor frame 95 which also surrounds the bundle of illumination light 3.

[0178] The energy sensors 27 i are so close to the beam of illumination 3 that when a sensor component 3 S of the illumination light 3 onto one of the energy sensors 27 i the coupling direction sensor unit 93 would encounter, this sensor component 3 S would also be cut off by aperture 9. As far as the energy sensors 27 are concerned. i These energy sensors 27, arranged in the beam path after the aperture diaphragm 9, represent i Sections of aperture diaphragm 9 are shown.

[0179] 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 271 to 274 of the coupling direction sensor unit 93. In addition, control signals Δx, Δy can be generated by appropriate evaluation of the energy sensors 271, again in the manner of a quadrant sensor, as explained above in connection with the coupling location sensor unit 92, and thereby the direction of the beam of illumination 3 can be controlled.

[0180] Alternatively to the execution according Fig. 21 can also be the coupling direction sensor unit 93, as in the Fig. 19 illustrated, deflecting mirror 96 i , of which in the Fig. Figure 19 shows mirrors 961 and 963, as well as associated energy sensors 271 and 273. The deflecting mirrors 96 i are then, according to the arrangement of the energy sensors, 27 iin the arrangement according Fig. 21 arranged around the aperture opening of the aperture diaphragm 9. The deflecting mirrors 96 i can, in accordance with what was stated above in connection with the deflection mirrors 94 i As explained, the deflecting mirrors 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 96 i are designed in such a way that they have sensor components 3 S of the illumination light not passing through the aperture opening of the aperture diaphragm 9 outwards to the respective associated energy sensor 27 i reflect.

[0181] Alternatively or additionally 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 which has at least, and preferably, several sensor elements 3 in the circumferential direction. S the bundle of illumination light 3 directed towards the entrance opening 12 is reflected at the edge towards at least one corresponding energy sensor.

[0182] Alternatively or additionally, a coupling sensor device with a corresponding control function can be implemented by scanning appropriate 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 illumination 3 is coupled into the inlet 12 and then controlled to a coupling maximum.

[0183] Alternatively or additionally, the coupling of the illumination light 3 into the inlet opening 12 via the arrangement of an EUV fluorescent screen in the inlet plane 13 can be monitored by means of a corresponding coupling point sensor unit, wherein the screen, in particular, is comparable to the deflecting mirrors 94 iaround the entrance aperture 12. Fluorescence light, which is generated by extensions of the beam of the illumination light 3 when coupled into the entrance aperture 12 onto this fluorescent screen, can then be monitored via a suitable camera and the coupling of the beam of the illumination light 3 into the entrance aperture 12 can be adjusted to minimize or symmetrize this detected fluorescence light.

[0184] 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.

[0185] By arranging the sensors in front of the opening, it is possible to obtain a usable sensor signal even in a centered, optimally coupled state, provided that the energy sensors are still in the beam path of the illumination light 3 and thus have a corresponding sensor component 3. S The arrangement after the respective opening enables a measurement with high signal dynamics, because the energy sensors used can detect a strong drop in intensity in the respective coupling edge region.

[0186] 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.

[0187] The coupling point on the one hand and the coupling direction on the other hand can be alternately iteratively adjusted and thus optimized.

[0188] Alternating control of the coupling point and coupling direction, or a combined control, is possible.

[0189] 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.

[0190] 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.

[0191] 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.

[0192] 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

[1] 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 illumination light (3), which has an inlet opening (12) for the illumination light (3) and an outlet opening (14) for the illumination light (3), - with at least one EUV energy sensor device (24 i ), which is designed to capture illumination light (3) that is guided along an illumination light beam path outside the entrance opening (12) of the beam homogenizing element (11). [2] Energy detection assembly according to claim 1, characterized by , that the EUV energy sensor device (24) has an EUV deflecting mirror (25) arranged outside the inlet opening (12) of the beam homogenizing element (11). i ) and an energy sensor (27 i) which is arranged such that illumination light (3), which is guided along the illumination light beam path and onto the EUV deflecting mirror (25) i ) meets, towards the energy sensor (27 i ) is conducted. [3] Energy detection assembly according to claim 1 or 2, characterized by several EUV energy sensor devices (241 to 244) 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. [4] Energy detection assembly according to one of claims 1 to 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). [5] Energy detection assembly according to claim 4, characterized by , that the coupling sensor device (91) has: - a coupling point sensor unit (92) for monitoring a coupling point of the beam of illumination light (3) into the inlet opening (12) of the beam homogenizing element (11) and - a separate coupling direction sensor unit (93) for monitoring a coupling direction of the bundle of illumination light (3) into the inlet opening (12) of the beam homogenizing element (11). [6] Energy detection assembly according to claim 4 or 5, characterized by , that the coupling sensor device (91) includes at least one EUV energy sensor (27) i ) exhibits the illumination light (3) that is directed outside an aperture opening of an aperture diaphragm (9) of the illumination system. [7] 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 illumination light (3) with an inlet opening (12) for the illumination light (3) and with an outlet opening (14) for the illumination light (3), and - with at least one EUV energy sensor device (29) designed to detect illumination light (3) that is guided along an illumination light beam path within the exit aperture (14) of the beam homogenizing element (11). [8] Energy detection assembly according to claim 7, characterized by, 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 directed towards the energy sensor (27). [9] Energy detection assembly according to claim 7 or 8, characterized by , that the outlet opening (14 Q ) of the beam homogenizing element (11) is designed to be larger than a useful exit aperture area (14) 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) that is 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. [10] Mask inspection system (2a) for use with EUV illumination light (3), - with a lighting system with a light source (5) for generating illumination light (3) and with a lighting 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 resolving detection device (23) for detecting the illumination light (3) directed into the image field (21), and - with at least one energy detection assembly (26; 28; 30; 33; 39; 41; 48; 55; 57; 60; 64; 78; 86) according to one of claims 1 to 9.

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