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

Abstract

An energy detection assembly (78) is suitable for an illumination system of a mask inspection system for use with EUV illumination light (3). The assembly (78) has at least one EUV energy sensor device (77) designed to detect energy of the illumination light (3) guided along an illumination light beam path. The EUV energy sensor device (77) has at least one energy value sensor and at least one energy change sensor (79). The energy value sensor serves to detect an illumination energy of the illumination light (3) over an exposure period. The energy change sensor (79) serves to detect a temporal development of the illumination energy of the illumination light (3) over the exposure period. This results in an energy detection assembly by means of which the inspection accuracy of the mask inspection system can be improved.

Description

[0001] The invention relates to an energy detection assembly for an illumination system of a mass inspection system for use with EUV illumination light. Furthermore, the invention 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.

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

[0004] This object is achieved according to the invention by an energy detection assembly for an illumination system of a mask inspection system for use with EUV illumination light having the features mentioned in claim 1.

[0005] According to the invention, it was recognized that, particularly depending on the detection, it can be important, in addition to knowing the illumination energy over an exposure period of a mask to be inspected, to have knowledge of the temporal development of the illumination energy over the exposure period. The EUV energy sensor device according to the invention enables the detection of both parameters, "illumination energy" on the one hand and "temporal development of the illumination energy" on the other, via the energy value sensor on the one hand and the energy change sensor on the other, with high precision. This allows, in particular, detection distortion effects that can arise due to pulsed illumination light impinging on the mask to be inspected during the exposure period to be compensated or corrected.The energy detection assembly can comprise multiple EUV energy sensor devices, each with at least one energy value sensor and at least one energy change sensor, which increases the measurement accuracy of the energy detection assembly. An energy sensor of the EUV energy sensor device can be embodied as an EUV photodiode.

[0006] A signal from the energy change sensor can be used to computationally correct the fact that different sections of an object to be inspected have been exposed to different numbers and / or different intensities of light pulses from a pulsed light source used in the mask inspection system.

[0007] The EUV energy sensor device according to claim 1 can detect the illumination light that is guided outside the entrance opening of the beam-homogenizing element along the illumination light beam path. In this case, the EUV energy sensor device detects the illumination light that does not pass through the entrance opening of the beam-homogenizing element. A distance between the illumination light detection areas of the EUV energy sensor device and an edge boundary of the entrance opening of the beam-homogenizing element can generally be less than 50% of an average diameter of the entrance opening. This distance can also be even 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 average diameter of the entrance opening. The distance is generally greater than 0.01% of the average diameter.

[0008] The illumination light detected by the EUV energy sensor device is guided along an illumination light beam path when this illumination light detected by the EUV energy sensor device is guided between a source region of an EUV light source generating the EUV illumination light and the beam homogenizing element within predetermined edge-side aperture limitations of optical components guiding the illumination light.

[0009] The temporal resolution of the energy change sensor according to claim 2 is well adapted to typical pulse frequencies of a light source, which can be in the kHz range, for example, in the range between 2 and 50 kHz, in particular between 2.5 and 25 kHz. The temporal resolution of the energy change sensor can be better than 1 µs, and in particular can be better than 0.2 µs.

[0010] An energy change sensor according to claim 3 can be designed with high precision and, in particular, with a very high temporal bandwidth, i.e., very high temporal resolution. The detection light can be false light, which is generated simultaneously with the generation of the illumination light. The wavelength of the detection light can be in the UV range, the VIS range, and / or the NIR range.

[0011] A conversion medium according to claim 4 has proven itself in practice, particularly in connection with the detection of EUV light. The conversion medium can be a fluorescence medium and / or a scintillation medium.

[0012] The advantages of a mask inspection system according to claim 5 correspond to those already explained above with reference to the energy detection assembly.

[0013] A wafer inspection system can also be constructed accordingly.

[0014] The inspection system may comprise an object holder for holding the object to be inspected, which is mechanically coupled to an object displacement drive so that a scanning displacement of the object is possible during illumination.

[0015] The inspection system can be a system for actinic mask inspection.

[0016] When using at least one TDI detector according to claim 6, a temporal resolution of the energy change sensor allows a conclusion to be drawn about how much illumination light energy reaches a particular section of a mask to be inspected during an object displacement of the mask to be inspected through the object field of the mask inspection system. Detection errors that may be caused by this can then be corrected or avoided. Such detection errors can be corrected, e.g., by computationally correcting the intensity data measured by an image capture device, in particular the TDI detector, in a data processing device.

[0017] The advantages of the energy detection assembly are particularly evident when using a pulsed light source according to claim 7. The energy change sensor can detect the temporal position of an illumination pulse with high accuracy, which in particular allows synchronization of the detection with a readout rate or a charge shift of at least one TDI detector of the detection device. During operation of the mask inspection system, it is possible to determine which part of the mask or object to be inspected was imaged onto the detection device, which can be embodied as a camera, by how many and by which light pulses from the light source. The intensity data measured by the detection device can then be corrected using an algorithm.A corresponding correction can be carried out in particular by combining intensity information obtained from the spatially resolving detection device with time information obtained via the energy change sensor of the EUV energy sensor device.

[0018] The energy change sensor can be used to determine, in particular, the exact time at which a light pulse from the light source reaches the object or mask to be inspected. This is particularly important for pulsed light sources, where the light pulse duration is much shorter than the time interval between two light pulses. A light pulse duration can be in the range of 1 µs or even shorter. Depending on the light pulse frequency of the pulsed light source, which can be in the range between 2 kHz and 50 kHz, for example, the time interval between two adjacent light pulses from the pulsed light source can be in the range between 100 µs and 500 µs.

[0019] The energy value sensor can measure the energy of the respective light pulse. The energy change sensor can measure the absolute temporal development of the light pulse, in particular the exact point in time at which the light pulse hits the object or mask being inspected.

[0020] The energy change sensor can then also be understood as a sensor for detecting an absolute temporal development of a light pulse of the then pulsed light source, i.e. as a pulse-time sensor.

[0021] An embodiment of the invention is explained in more detail below with reference to the drawing, in which: Fig. 1 schematically shows, 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 Fig. 1 enlarged and showing internal details of the beam homogenizing element of the mask inspection system; Fig. 2 schematically shows a perspective, inlet-side view of an embodiment of the beam homogenizing element; Fig. 3 compared to Fig. 2 is an enlarged view of an area around an entrance opening of the beam-homogenizing element for the illumination light, wherein four deflection mirrors are additionally shown in the vicinity of the entrance opening, each of which belongs to an EUV energy sensor device of the energy detection assembly, wherein a coupling intensity distribution of the illumination light in an entrance plane of the beam-homogenizing element is additionally illustrated; Fig. 4 schematically shows a section along 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 shows a further 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 opening of the beam homogenizing element, wherein a detection light beam path between a deflection mirror and an energy sensor of the EUV energy sensor device of the energy detection assembly is again illustrated; Fig. 6 in one to Fig. 3 similar representation a plan 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 plan view of an outlet opening of the jet homogenizing element according to Fig. 6; Fig. 8 is a plan view of another 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 region of the detection device, namely between two detection sections of the detection region; Fig. 9 in one to Fig. 1 shows an illumination light beam path after the exit opening of the beam homogenizing element, wherein a further embodiment of an energy detection assembly with an EUV mirror with a fluorescent layer and an energy sensor device arranged in the beam path of fluorescence detection light is also shown; Fig. 10 is a plan 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, inter alia, in a central region of the illumination pupil of the illumination optics; Fig. 11 shows, in a meridional section, a section of an illuminating light beam path after exiting an embodiment of the beam homogenizing element with an energy sensor of a further embodiment of an energy detection assembly arranged centrally in an exit illuminating light beam; Fig. 12 in one to Fig. 11 shows a further embodiment of an energy detection assembly, in which an output mirror of a further embodiment of an energy detection assembly is arranged centrally in the exit illumination light beam 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 representation of a further embodiment of an energy detection assembly with an output mirror and a downstream deflection mirror for detection light towards an energy sensor of the energy detection assembly; Fig. 14 shows a cross section through an ionization chamber of a further embodiment of an energy detection assembly with an ion / electron detector for detecting charged particles generated by ionization of an ionization gas in the ionization chamber by the illumination light; Fig. 15 schematically shows a function of a time-delay integration (TDI) sensor, which can be used for the spatially resolving detection device of the mask inspection system for capturing an image of the mask to be inspected; Fig. 16 in one Fig. 15 corresponding representation a temporal sequence of an illumination of the lithography mask to be inspected with illumination light from a pulsed light source of the mask inspection system; Fig. 17 shows an embodiment of a light source of the mask inspection system with an energy change sensor of an embodiment of the invention otherwise described in the Fig. 17 not shown energy detection assembly for detecting a temporal development of an illumination energy of the illumination light over an exposure period; Fig. 18 in one to Fig. 17 shows a representation similar to 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 shows, not to scale, a section of the illumination system in the region of an aperture stop and an entrance-side section of the beam-homogenizing element in a meridional section, wherein components of a coupling sensor device of the illumination system are shown; Fig. 20 shows a perspective view of a coupling location sensor unit of the coupling sensor device, comprising four deflection mirrors arranged around an inlet opening of the beam homogenizing element and four energy sensors associated with them; Fig. 21 also shows in perspective an embodiment of a coupling direction sensor unit of the coupling sensor device, arranged in the region of the aperture stop.

[0022] An illumination optics 1 is a component 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. 1 illustrates the illumination optics 1 via marginal rays and a main beam. The illumination light 3 illuminates an illumination field 4 of the mask inspection system.

[0023] The illumination light 3 is generated by an EUV light source 5 into a source region 6. The light source 5 can generate useful EUV 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.

[0024] The light source 5 is designed as a plasma light source. This can be, for example, a laser plasma source (LPP; laser produced plasma) or a discharge source (DPP; discharge produced plasma). Such plasma sources are known in principle as light sources for EUV projection exposure systems. Alternatively, the light source 5 can also be designed as a high-harmonic EUV source. The pulse frequency of the light source 5 can be in the kHz range.

[0025] To facilitate positional relationships, a Cartesian xyz coordinate system is used below. The x-axis is perpendicular to the drawing plane of the 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.

[0026] After emission by the light source 5, the illumination light 3 first passes through a useful light filter 8, which is arranged 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 that are stored in the metrology system 2a, for example, in a filter magazine. A further useful light filter can be arranged in a waiting position outside the illumination light beam path of the illumination optics 1. The useful light filters 8 can have the same transmission characteristics, whereby a change between the useful light filters can then be made if a degradation of the filter 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 amounts of false light.

[0027] The useful light filters can be designed in such a way that they filter out pump light carried in the illumination light beam path, in particular, which was used in the generation of useful light in the source volume 6.

[0028] After the filter 8 and the mirror IL1, the illumination light 3 first passes through an aperture diaphragm 9 that limits the beam of the illumination light 3 at the edges. Subsequently, the illumination light beam 3 is transferred to a beam-homogenizing element 11 of the illumination optics 1. The mirror IL1 serves as the coupling optics 10 for coupling the illumination light 3 into the beam-homogenizing element 11.

[0029] Between the source volume 6 and the beam homogenizing element 11, usually 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 in the Fig. 1 in the illumination light beam path between the mirror IL1 and the illumination light aperture diaphragm 9.

[0030] The aperture stop 9 limits a numerical aperture of the illumination light beam 3 emitted by the source region 6, also 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 in addition to the aperture stop 9, an aperture-limiting stop 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 at 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.

[0031] The ellipsoidal mirror IL1 serves to image the source region 6 of the EUV light source 5 into an entrance opening 12 in an entrance plane 13 of the beam-homogenizing element 11. A first focal point of the ellipsoidal mirror IL1 is therefore located in the source region 6, and a second focal point of the ellipsoidal mirror IL1 is located in the entrance opening 12. The ellipsoidal mirror IL1 focuses the illumination light beam 3 into the entrance opening 12 in the entrance plane 13 of the beam-homogenizing element 11. An entrance-side numerical aperture of the illumination light beam 3 upon entering the entrance opening 12 can be in the range from 0.02 to 0.2, for example in the range of 0.05.

[0032] The angle of incidence of a central principal ray of the illumination light 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 designed as a grazing incidence (GI) mirror.

[0033] 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 even between 0.5 mm and 1 mm. An aspect ratio of the inlet opening 12 and an equally sized outlet opening 14 of the beam homogenizing element 11 for the illumination light 3 in an exit plane 15 is between 0.5 and 2. A typical size of the inlet opening 12 and the outlet opening 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.

[0034] Fig. Figure 1A illustrates details of the beam homogenizing element 11.

[0035] 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 opening 12 and the outlet opening 14. Shown in the Fig. 1A exemplary partial beam paths of illumination 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 arranged downstream in the beam path. The actual number of illumination channels 3 i is larger in practice and can, for example, be several hundred illumination channels, which are guided via 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 iin 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 are directed along the illumination channels 3 i superimpose each other in the exit opening 14, so that a beam homogenization of the illuminating light 3 takes place between the inlet opening 12 and the exit opening 14 in the beam homogenizing element 11.

[0036] The two micromirror arrays 15a and 15b are housed in a housing 15e of the beam homogenizing element 11. This housing 15e contains the inlet opening 12 on the one hand and the outlet opening 14 on the other.

[0037] The beam homogenizing element 11 can alternatively be designed as a hollow waveguide.

[0038] The beam homogenizing element 11 has a typical length perpendicular to the planes 13 and 15, i.e. along a main 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.

[0039] An angle between a normal to the entrance plane 13 of the beam homogenizing element 11 and the main beam CR of the illuminating light beam 3 incident into the entrance opening 12 can be 0° or can alternatively 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 in particular in the range of 0.5°.

[0040] A ratio of the distance between the inlet plane 13 and the outlet plane 15, and a size or the typical diameter of the inlet opening or the outlet opening 12, 14, is in the range between 50 and 1000 and can, for example, be in the range between 50 and 200.

[0041] An imaging output mirror optic 16 arranged downstream of the beam homogenizing element 11, comprising two mirrors IL2, IL3, images the exit aperture 14 of the beam homogenizing element 11, located in an exit plane 15, into the illumination field 4 in an object plane 17. The image-side numerical aperture of this image can be in the range from 0.05 to 0.2.

[0042] In the illustrated embodiment, the output mirror optics 16 has exactly two mirrors, namely mirrors IL2 and IL3. The aperture stop described above, which may be used after the beam homogenizing element 11, can be arranged between the beam homogenizing element 11 and the mirror IL2 or between the mirrors IL2 and IL3.

[0043] The output mirror optics 16 can be designed in the manner of a Wolter telescope, namely a Type I Wolter optic. 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 hyperboloidal mirror also represents a Type I Wolter optic.

[0044] An embodiment of the output coupling mirror optics 16 is described in US 10,042,248 B2.

[0045] An imaging factor β1 of the input-coupling mirror optics 10 can range between 0.1 and 50, thus reducing by a factor of 10 up to magnifying by a factor of 50. An imaging factor β2 of the output-coupling mirror optics 16 can range between 0.02 and 10, thus in turn reducing by a factor of 50 up to magnifying by a factor of 10. A product β1, β2 of the two imaging factors can range between 0.25 and 10 for the illumination optics 1.

[0046] A reticle 18 to be inspected is arranged in the object plane 17 as the object to be inspected or the mask to be inspected. The reticle 18 is 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 the object plane 17.

[0047] 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 extension of the illumination field 4 is 0.5 mm in the x-direction and 0.5 mm in the y-direction.

[0048] The x / y aspect ratio of the illumination field 4 corresponds to the x / y aspect ratio of the exit opening 14.

[0049] The illumination field 4, or a portion of the illumination field 4, which then represents an object field, is imaged into an image field 21 in an image plane 22 using projection optics PO. The size of the image field 21 can be in the range of 150 mm × 250 mm. The shorter image field extension runs along the scanning direction y.

[0050] The projection optics PO has numbered mirrors M1 in the imaging beam path of the projection optics PO, and M2 has 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 stop 9b is arranged in an entrance pupil plane EP of the projection optics PO, which lies in the imaging beam path of the illumination or imaging light between the reflecting reticle 18 and the first mirror M1. This aperture stop 9b can also be used to specify any internal obscuration of the projection optics PO.

[0051] 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°.

[0052] An illumination light beam path of the illumination light 3 for illuminating the reticle 18 and an imaging light beam path of the projection optics PO for imaging the object field 4 into the image field 21 intersect in an intersection region K. This intersection region K lies in the area of ​​the entrance pupil plane EP of the projection optics PO. Here, the imaging light beam path intersects with the illumination light beam path between the exit aperture 14 and the mirror IL2 of the illumination optics 1, as well as between the mirrors IL2 and IL3 of the illumination optics 1.

[0053] The image field 21 is captured by a detection device 23, e.g., by a CCD camera or multiple CCD cameras. For details of the imaging in the image field, reference is made to US Pat. No. 10,042,248 B2 and the references cited in US Pat. No. 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. A corresponding embodiment is explained in more detail below.

[0054] With the mask inspection system 2a, an inspection of, for example, a structure on the reticle 18 is possible.

[0055] Fig. 2 shows a perspective and schematic view of an embodiment of the jet homogenizing element 11 looking towards the inlet opening 12.

[0056] Fig. 3 shows in comparison to Fig. 2 shows an enlarged section of an entrance face of the beam homogenizing element 11, which is arranged in the entrance plane 13, with the entrance opening 12. EUV energy sensor devices 24 i (i = 1 to 4), of which in the Fig. 3 four EUV deflection mirrors 25 i (i = 1 to 4) are part of an embodiment of an energy detection assembly 26 for an illumination system of the mask inspection system 2a, which includes the light source 5 in addition to the illumination optics 1. The energy detection assembly 26 also includes the beam homogenizing element 11.

[0057] The four EUV deflection mirrors 251 to 254 are arranged outside the entrance opening 12 around it. Each of the EUV deflection mirrors 25 i is closely adjacent to one of the four sides of the inlet opening 12 and is arranged centrally with respect to the respective side.

[0058] The Fig. 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.

[0059] A measure for the respective illumination light energy present in the entrance plane is given in the Fig. 3 by different hatching types, for which the Fig. 3, a dimension table is shown as a legend on the right. The coupled-in illumination light energy is greatest in the center of the entrance opening 12 in the region of the main beam CR and decreases approximately rotationally symmetrically radially with the distance from the main beam CR. Since the entrance opening 12 is rectangular, slightly more illumination light energy is cut off in the region of the long sides of the entrance opening 12 than in the region of the short sides of the entrance opening 12. The two deflection mirrors 251 and 253 arranged on the long sides therefore capture more illumination light 3 that is not coupled into the entrance opening 12 than the two deflection mirrors 252 and 254 arranged on the short sides of the entrance opening 12.

[0060] The uncoupled energy portion of the illumination light 3 is less than 30% and regularly less than 5%. The portion of the illumination light 3 that is captured by the four deflection mirrors 251 is regularly in the range of less than 1 × 10 -4 the total energy of the illuminating light 3.

[0061] Fig. 4 illustrates in a longitudinal section in particular a further detection beam path of the two energy sensor devices 244 with the deflection mirror 254 and the energy sensor device 242 with the deflection mirror 252.

[0062] The illumination light 3 incident on the deflection mirror 252 is directed toward an energy sensor 272. This can be a photodiode sensitive to EUV light. EUV sensitivity can be achieved using appropriate fluorescence or scintillation layers.

[0063] The energy sensor 27 represents an energy value sensor for detecting an illumination energy of the illumination light 3 over an exposure period of the reticle 18.

[0064] An energy value detection 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%.

[0065] An energy value detection via the energy value sensor 27 can be carried out pulse-resolved, i.e. separately for each light pulse of the light source 5.

[0066] Accordingly, the further in the Fig. 4 visible deflecting mirrors 254 direct the portion of the illumination light 3 incident on it to an associated energy sensor 274 of the energy sensor device 244.

[0067] Further, in the Fig. 4 invisible energy sensors 271 and 273 are assigned to the deflection mirrors 251 and 253, respectively.

[0068] In total, the energy detection assembly 26 has four deflection mirrors 251 to 254 and four associated energy sensors 271 to 274, thus a total of four EUV energy sensor devices 241 to 244.

[0069] The energy sensors 27 are connected to a central control / regulating device 27a (cf. Fig. 1) of the mask inspection system 2a in signal connection.

[0070] The illumination light beam path of the Fig. 4 also shows that the deflecting mirrors 252 and 254 only deflect illumination light 3 which does not enter the entrance opening 12 of the beam homogenizing element 11.

[0071] Based on the Fig. 5 to 7, a further embodiment of an energy detection assembly 28 is described below, which alternatively or in addition to the energy detection assembly 26 according to the Fig. 3 and Fig. 4. Components and functions corresponding to those described above with reference to the Fig. 1 to 4 and in particular with reference to the Fig. 3 and Fig. 4 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0072] The energy detection assembly 28 has an EUV energy sensor device 29 which is designed to detect illumination light 3 which is emitted within the exit opening 14 of the beam homogenizing element 11 along a Fig. 5 illustrated illumination light beam path.

[0073] A corresponding outlet-side sensor component 3 s of the illumination light 3 is generated without any significant loss of light by using, instead of a beam homogenizing element with a rectangular entrance 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 inlet opening 12 Q is used.

[0074] Fig. 6 illustrates this difference. 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 a “standing” form. The dashed line in the Fig. 6 the square extended inlet opening 12 Q the energy detection assembly 28 according to Fig. 5. In principle, even with the square-enlarged inlet opening 12 Q a deflection mirror arrangement with deflection mirrors 251 to 254 outside this square entrance opening 12 Q present, as described above with reference to the energy detection assembly 26, in particular Fig. 4 explained.

[0075] As a result of the square extension, the energy detection assembly 28 has on the exit side the then also square exit opening 14 Q the sensor part 3 S in an outlet opening area 14 S (cf. Fig. 7 left) of the entire outlet opening 14 Q The remaining outlet opening, i.e. the area around the sensor portion 14 S reduced cross-section of the square outlet opening 14 Q can then be used to illuminate the illumination field 4. Alternatively, on the opposite side, in the Fig. 7 right side another sensor part 14 S2 the outlet opening 14 Q be used for energy sensing or other purposes, so that on the side of the outlet opening 14 Q effectively a rectangular exit opening 14 corresponding to that of the beam homogenizing element of the energy detection assembly 26 according to Fig. 3 remains.

[0076] The outlet opening 14 Q The beam homogenizing element 11 is thus designed larger than a useful exit opening area in the form of the effectively rectangular exit opening 14, which is required for the subsequent illumination of the object field in which the mask or reticle 18 to be inspected is arranged. 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 in the useful illumination light for illuminating the object field 4 is, at least in part, compensated by the entrance opening 12 Q of the beam homogenizing element 11 is also larger and thus more illumination light 3 can be coupled into the beam homogenizing element 11.

[0077] The EUV energy sensor device 29 is designed accordingly so that it detects 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 opening area, namely in the outlet opening sensor portion 14 S is guided along the illumination light beam path.

[0078] The sensor part 3 S of the illumination light 3 is guided in the EUV energy sensor device 29 via a first deflection mirror 29 a , which is located in the outlet area of ​​the sensor part 14 S the outlet opening 14 Q The sensor part 3 is shown below S via another, imaging deflecting mirror 29 b to an energy sensor 27.

[0079] The EUV detection assembly 28 can comprise several EUV energy sensor devices 29 iaccording to the type of Fig. 5, wherein, for example, on both sides of the rectangular useful exit opening 14 there is a deflection mirror of the type of deflection mirror 29 a can be arranged, which in turn in the beam path of the then further sensor part of the illumination light components like the deflection mirror 29 b and the energy sensor 27 can be arranged downstream.

[0080] Based on the Fig. 8, a further embodiment of an energy detection assembly 30 is described below, which can be used alternatively or in addition to the energy detection assemblies explained above.

[0081] Part of the energy detection assembly 30 is an EUV energy sensor device 31, which detects the illumination light 3, which is guided beyond a detection range of the detection device 23 along the beam path of the illumination light 3. This detection range of the detection device 23 is defined by detection surfaces of TDI or CCD sensors 321 to 32 12 , which are arranged in the manner of a 4 x 3 array in the image plane 22 of the detection device 23. Between the rows of this sensor array of sensors 32 i there is a y-distance that is sufficiently large that a component of the EUV energy sensor device 31 can be arranged in the area of ​​this line spacing. This can be a deflection mirror of the type of deflection mirror 25 i or an energy sensor of the type Energy Sensors 27 i .

[0082] The energy detection assembly 30 may also include several such EUV energy sensor devices 31.

[0083] The energy sensor device 31 is thus designed such that it detects a portion of the illumination light 3 that 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.

[0084] In a further embodiment of an energy detection assembly 33 (cf. Fig. 1), which can be used instead of the energy detection assemblies discussed above, the respectively used useful light filter 8 simultaneously serves as a deflection mirror for detection light 34, which is reflected by the respective useful light filter 8 out of the beam path of the illumination light 3. This is shown in the Fig. 1 shows the useful light filter 8, which reflects the detection light 34 toward an energy sensor 35. The useful light filter 8, which is used to reflect the detection light 34, and the energy sensor 35 each represent an EUV sensor device 36 of the energy detection assembly 33.

[0085] The detection light 34 is light with a wavelength reflected by the useful light filter 8, which can 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, VIS light, or NIR light.

[0086] The detection light 34 is light that is not transmitted by the useful light filter 8 along the subsequent illumination light beam path.

[0087] The energy detection assembly 33 can also 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 connection 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.

[0088] At least one of the useful light filters 8 accommodated in the filter wheel 7 may have a metallic support structure.

[0089] An alternative and additionally usable further variant of an energy detection assembly 39 can be one in the Fig. 1, which 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 illuminating light 3. The strength of the measured photocurrent is then a measure of the energy content of the illuminating light 3.

[0090] Based on the Fig. 9, a further embodiment of an energy detection assembly 41 is described below. Components and functions described above with reference to the Fig. 1 to 8 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0091] In the energy detection assembly 41 according to Fig. 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 for converting a fraction of the incident illumination light 3 into fluorescence detection light 43 with a wavelength different from a useful light wavelength of the illumination light 3.

[0092] A wavelength of the detection light 43 is longer 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).

[0093] In the Fig. Figure 9 shows the beam path of the illumination light 3 between the exit plane 15 of the beam-homogenizing element 11 and beyond the mirror IL2, as well as a beam path of the fluorescence detection light 43. The latter extends from the fluorescent layer 42 through a lens 44, which focuses the detection light 43 toward 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, arranged in the beam path of the fluorescence detection light 43.

[0094] 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.

[0095] Based on the Fig. 10, a further embodiment of an energy detection assembly 48 is described below, which can be used alternatively or in addition to the embodiments of the energy detection assembly described above.

[0096] 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 opening 12 of the beam homogenizing element 11 and which extends outwards in the Fig. 10 is shown broken away. Furthermore, the aperture diaphragm 9 has an inner obscuration diaphragm section 50 for specifying a central obscuration of the illumination light 3 in a pupil center. The two diaphragm sections 49, 50 are connected by three Fig. 10 indicated webs 51, which can be very thin, are connected to each other.

[0097] The energy detection assembly 48 has an EUV energy sensor device 52, which is designed to detect that part of the illumination light 3 which strikes the aperture stop 9 and is guided in the central region of an illumination pupil of the illumination optics 1, which is covered by the inner obscuration stop section 50. Part of the EUV energy sensor device 52 is in turn an EUV deflection mirror 53 and a Fig. 10 not shown energy sensor of the 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 after Fig. 3 and Fig. 4 described.

[0098] The EUV energy sensor device 52 can, as in the Fig. 10, 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.

[0099] Based on the Fig. 11, a further embodiment of an energy detection assembly 55 is described below, which can be used alternatively or in addition to the variants of the energy detection assemblies described above. Components and functions described above with reference to the Fig. 1 to 10 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0100] 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 in the beam path of the illumination light 3, downstream of the exit plane 15 of the beam-homogenizing element 11, centrally in the illumination light beam, so that a portion of the illumination light 3 guided in a central region of an illumination pupil of the illumination optics 1 is detected via the energy sensor 27 of the energy detection assembly 55.

[0101] Based on the Fig. 12, a further embodiment of an energy detection assembly 57 is described below, which can be used alternatively or in addition to the variants of the energy detection assemblies described above. Components and functions described above with reference to the Fig. 1 to 11 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0102] A structure 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 according to, for example, Fig. 4 and has a focusing deflection mirror 59, which, comparable to the energy sensor 27 of the energy detection assembly 55 according to Fig. 11 is in turn arranged in a central region of the illumination light beam path after the exit plane 15 and focuses the portion of the illumination light 3 passing there onto an energy sensor 27 of the EUV energy sensor device 58.

[0103] Based on the Fig. 13, a further embodiment of an energy detection assembly 60 is described below, which can be used alternatively or in addition to the variants of the energy detection assemblies described above. Components and functions described above with reference to the Fig. 1 to 12 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0104] In contrast to the energy detection assembly 57, a deflection mirror 61 of an EUV energy sensor device 62 of the energy detection assembly 60 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 illuminating light beam path after the exit plane 15. The planar and compact deflecting mirror 61 directs the portion of the illuminating light 3 incident on it toward another deflecting mirror 63, which in turn focuses this portion of the illuminating light 3 onto an energy sensor 27.

[0105] Based on the Fig. 14, a further embodiment of an energy detection assembly 64 is described below, which can be used alternatively or in addition to the variants of the energy detection assemblies described above. Components and functions described above with reference to the Fig. 1 to 13 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0106] 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 guide ionization gas 68 via a control valve 69 into the ionization chamber 65, i.e., into the ionization space 66.

[0107] The beam path of the illumination light 3 is guided through the ionization chamber 66.

[0108] 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.

[0109] The detectors 71, 72 each have an accelerating electrode 71b, 72b, which in the case of the ion detector 71 can, for example, be at a potential of -50 V and in the case of the electron detector 72 at a potential of 20 kV.

[0110] The electrodes 71b, 72b are designed as grid electrodes.

[0111] A metallic ion trap 71c of the ion detector 71 and a metallic electron trap 72c of the electron detector 72 are used to detect the accelerated ions 71a on the one hand and the accelerated electrons 72a on the other hand. These traps 71c, 72c are at ground potential and can have a comb-like structure, as shown in the Fig. 14 indicated.

[0112] The two detectors 71, 72 each have a charge signal receiver 71d, 72d, which receives a charge signal detected by the collectors 71c, 72c and generates an energy signal from it. The charge receivers 71d, 72d thus represent energy sensors of the EUV energy sensor device 70 of the energy detector assembly 64.

[0113] Fig. 15 illustrates an operating diagram of one of the TDI sensors 32 i the detection device 23 of the mask inspection system 2a.

[0114] The example of the Fig. 15 circularly edged reticle 18 is displaced along the object displacement direction y relative to the object field 4 during a mask inspection step, as shown in the Fig. 15 on the left in a side view. In this schematic view according to Fig. 15, the reticle 18 is shown as a transmissive object for simplified representation. The light source 5 and the illumination optics 1 are shown in the Fig. 15 left also shown schematically.

[0115] In the Fig. 15 Middle is shown above, how an image of the reticle 18 is scanned over a column-wise image in the Fig. 15 shown detection area of ​​the TDI sensor 32 i with sensor columns I to IV. This is illustrated by an image 75 of the circular edge of the reticle 18 on the detection surface, which is shown in the Fig. 15 The instantaneous recording situations A to D shown in the middle above move from left to right across the detection area.

[0116] Synchronized with the object displacement of the reticle 18 to the TDI sensor 32 i The sensor columns I to IV are read out, again along the object displacement direction y. A charge accumulation q that builds up over the spatial coordinate y on the detection surface of the TDI sensor 32 i is in the Fig. 15 below, again shown for the instantaneous situations A to D.

[0117] When the image of the reticle 18 is shifted by one column width of the sensor columns I to IV in the object displacement direction y, a charge shift occurs simultaneously on the TDI sensor 32 ifrom one column to the nearest column in the y-direction. As a result, a charge q on the columns that capture image structures, such as a boundary section of the image 75, increases with each displacement / charge transfer step, as the charge distribution curves in the Fig. 15 middle bottom for the momentary situations A to D. Situation D shows the moment at which a leading section of image 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 to its maximum through the synchronized charge shift on the rightmost sensor column IV.

[0118] Fig. Figure 15 shows the resulting overall image 75 of the imaged structure on the reticle 18 after this entire structure has been displaced along the y-direction through the object field 4. Due to the synchronized displacement / charge shift, a higher-contrast image is obtained than would be the case with a non-time-shift-integrated image taken using a conventional CCD sensor.

[0119] Additionally, a pulsed version of the light source 5 must be taken into account when imaging the reticle 18 with the mask inspection system 2a. During the object displacement of the reticle 18 through the object field 4, different sections of the reticle 18 receive different numbers of light pulses from the light source 5.

[0120] This is in the Fig. 16, which represents a temporal sequence of a pulsed exposure of the reticle 18 displaced along the object displacement direction y. Shown is the illumination field 4 currently exposed on the reticle 18 during a light pulse from the light source 5. i (i = 1 to 5), which, due to the displacement of the reticle 18, also moves along the object displacement direction y. Arrows highlight certain illumination field overlap areas 76 i .

[0121] In the overlap area 761, which is in the Fig. 16 is also highlighted in dashed lines, there is a section of the reticle which is illuminated by a total of three light pulses, since it lies in the three illumination fields 41, 42 and 43, each of which is assigned to a light pulse.

[0122] The overlap area 762 is illuminated by exactly one light pulse, since it lies exclusively in the illumination field 43.

[0123] Overlap areas 763 and 764 are each illuminated by exactly two light pulses of 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.

[0124] Not every object section of the reticle 18 is therefore illuminated by the same number of light pulses from the light source 5. In this sense, the reticle 18 is exposed to the illumination light 3 unevenly.

[0125] To compensate for this exposure non-uniformity, an EUV energy sensor device 77 has an energy detector assembly 78 which is located in the Fig. 17, in addition to an energy value sensor of the type of energy sensors, for example the energy sensors 27, of the above-described embodiments, at least one energy change sensor 79 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.

[0126] Functions and components described above in connection with the Fig. 1 to 16 have already been explained, have the same reference numbers and will not be discussed in detail again.

[0127] The Fig. 17 again schematically shows components of the light source 5, namely the source volume 6, which is accommodated in a source chamber 80, and an exit opening 81 in the source chamber 80, which defines an exit aperture of a bundle of the illumination light 3.

[0128] Due to the plasma generation process of the light source 5, scattered light 82 emanates from the source volume 6, which is partly used as detection light and is directed along a Fig. 17. Along this detection beam path, the detection light 82 is reflected by 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 intersecting the beam of the illumination light 3 in the exit opening 81.

[0129] 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 generation of the illumination light 3. The detection light 82 is also emitted by the plasma in the source volume 6 in a temporally correlated manner with the emission of the illumination light 3.

[0130] After passing through the exit opening 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).

[0131] Fig. 18 shows a further variant of an energy detection assembly 86, which alternatively or additionally to the energy detection assembly 78 according to Fig. 17 can be used. The energy detection assembly 86 has an EUV energy sensor device 87, which has an energy change sensor 88, which is housed in the source chamber 80 and directly detects scattered light 82 emitted by the source volume 6 as detection light.

[0132] A temporal development of an energy of the detection light 82 correlates directly with the temporal development of an energy of the illumination light 3, so that a temporal development of the illumination energy of the illumination light 3 can be detected via the energy change sensors 79 and 88, respectively.

[0133] 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.

[0134] Fig. 19 shows, in a meridional section, a section of the illumination system of the mask inspection system 2a in the area between the aperture stop 9 and an entrance-side section of the beam homogenizing element 11 in the area of ​​the entrance opening 12.

[0135] Shown in the Fig. 19 a coupling sensor device 91 for monitoring a coupling location and a coupling direction of a beam 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.

[0136] The coupling location sensor unit 92 is arranged in the region of the inlet opening 12 of the beam homogenizing element 11.

[0137] Fig. Figure 20 shows a perspective view of an embodiment of the coupling-point sensor unit 92. For illustration, individual beams 3 i of the entire beam of the illuminating light 3 in the area of ​​the beam path in front of the entrance opening 12 of the beam homogenizing element 11. The beam homogenizing element 11 is, apart from the entrance opening 12, in the Fig. 20 omitted.

[0138] The coupling location sensor unit 92 has a total of four deflection mirrors 941, 942, 943 and 944, which are arranged around the entrance opening 12 in such a way that the entrance opening 12 is deflected by the deflection mirrors 94 i is completely limited. Illumination light 3 that does not pass through the entrance opening 12 during coupling is thus reflected by one of the deflection mirrors 941 to 944.

[0139] Fig. 20 also shows exemplary single beam paths of light components not coupled into the entrance opening 12, i.e. sensor components 3 S of the illumination light 3, which is emitted by a respective deflection mirror 94 i is reflected. In the beam direction of these sensor components 3 S of the illumination light 3 after reflection at one of the deflection mirrors 941 to 944, energy sensors 271, 272, 273 and 274 of the coupling location sensor unit 92 are arranged.

[0140] The deflecting mirrors 94 i are each oriented so that the respective sensor part 3 S the beam of illumination light 3 incident in the direction of the entrance opening 12 crosses towards the associated energy sensor 27 i This also illustrates the Fig. 19, which shows in section the deflection mirrors 941 and 943 and the energy sensors 271 and 273 associated with them. The deflection mirror 941 is in the Fig. 19 above the entrance opening 12, i.e. above the incident beam of the illumination light 3 and the associated energy sensor 271 in the Fig. 19 below the incident beam of the illumination light 3. Accordingly, the deflection mirror 943 is below and the associated energy sensor 273 above this incident beam of the illumination light 3 in the Fig. 19 shown.

[0141] The deflecting mirrors 94 i can be designed as a coating on an inlet-side end wall of the housing 15e of the beam homogenizing element 11. This inlet-side end wall can be in the deflection mirror arrangement according to Fig. 19 can be concave or alternatively convex.

[0142] As an alternative to a coating, the deflection mirrors 94 i be applied to this entrance-side end wall, for example glued. Alternatively, the deflection mirrors 94i These are components that are separate from the beam homogenizing element 11 and, in particular, can be adjusted separately therefrom.

[0143] The energy sensors 27 i can be selected to control the coupling point of the beam of illumination light 3 into the entrance opening 12 in the manner of a quadrant detector. Adjustment control pulses can be generated using energy or intensity values ​​received from the energy sensors 27. i generated, are processed as follows:

[0144] 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 for shifting the beam of illumination light 3 in the x-direction. For simplicity, it is assumed that the entrance aperture 12 lies in the xy-plane.

[0145] I1 and I3 are the sensor signals of the energy sensors 271 and 273. η x is a scaling parameter that can be obtained during calibration.

[0146] Accordingly, a control signal Δy for the y-coordinates can be obtained using the following relationship: Δy=ηy⋅I2−I4I2+I4 I2 and I4 are the sensor signals of the energy sensors 272 and 274. η y is in turn a scaling factor that can be obtained by means of a preceding calibration step.

[0147] The control signals Δx, Δy generated in this way can be used as input signals for spatial control of the beam of illumination light 3 relative to the entrance opening 12. This allows spatial control of the coupling point of the beam of illumination light 3 into the entrance opening 12 of the beam-homogenizing element 11.

[0148] The coupling location sensor unit 92 can basically be constructed like the energy detection assembly 26, which was described above with reference to the Fig. 4. Accordingly, the coupling location sensor unit 92 can also take over the function of the energy detection assembly 26, which was explained above.

[0149] Fig. 21 shows an embodiment of the coupling direction sensor unit 93. The bundle of the illumination light 3 is in turn divided into a plurality of individual beams 3 i illustrated.

[0150] Ideally, the beam of the illuminating light 3 passes through the aperture stop 9 without any significant portions of the illuminating light 3 being cut off by the aperture stop 9.

[0151] In the beam path of the illumination light 3, directly before or after the aperture stop 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 beam of the illumination light 3.

[0152] The energy sensors 27 i are so close to the beam of the illumination light 3 that when a sensor component 3 S of the illumination light 3 to one of the energy sensors 27 i the coupling direction sensor unit 93, this sensor part 3 S would also be cut off by the aperture stop 9. As far as the energy sensors 27 i in the beam path after the aperture stop 9, these energy sensors arranged in this way represent 27 i Sections of the aperture stop 9.

[0153] With the aid of the energy sensors 271 to 274 of the coupling direction sensor unit 93, the coupling direction of the beam of the illuminating light 3 into the inlet opening 12 of the beam homogenizing element 11 is monitored. In addition, 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, control signals Δx, Δy can be generated and, via these, the direction of the beam of the illuminating light 3 can be controlled.

[0154] Alternatively to execution according to 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. 19, the mirrors 961 and 963 are shown, as well as associated energy sensors 271 and 273. The deflection mirrors 96 i are then according to the arrangement of the energy sensors 27 iin the arrangement according to Fig. 21 arranged around the aperture opening of the aperture diaphragm 9. The deflection mirrors 96 i can, according to what was mentioned above in connection with the deflection mirrors 94 i explained, 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 to have sensor components 3 S of the illumination light not passing through the aperture opening of the aperture diaphragm 9 outwards to the respectively assigned energy sensor 27 i reflect.

[0155] Alternatively or in addition to the above-explained embodiments of the coupling sensor device 91, in particular the coupling-location sensor unit 92, variants can also be used that have already been explained above in connection with the various embodiments of the energy detection assembly. In particular, part of a variant of the coupling-location sensor unit can be a deflection mirror, which has at least, and preferably in the circumferential direction, several sensor components 3 S the beam of illumination light 3 guided towards the inlet opening 12 is reflected at the edge towards at least one corresponding energy sensor.

[0156] Alternatively or additionally, a coupling sensor device with a corresponding control function can be implemented by scanning corresponding relative movement components to shift the location and direction of the incident beam of the illuminating light 3 toward the beam-homogenizing element 11 and, in particular, toward the entrance opening of the beam-homogenizing element 11. Depending on the respective scanning position, it is then possible to measure how much of the illuminating light 3 is coupled into the entrance opening 12 and can then be controlled to a maximum coupling level.

[0157] Alternatively or additionally, the coupling of the illumination light 3 into the entrance opening 12 can be monitored by sensors via the arrangement of an EUV fluorescent screen in the entrance plane 13 by means of a corresponding coupling location sensor unit, wherein the screen in particular, comparable to the deflection mirrors 94 iis mounted around the entrance opening 12. Fluorescent light generated by the extensions of the beam of illumination light 3 upon coupling into the entrance opening 12 onto this fluorescent screen can then be monitored via a corresponding camera, and the coupling of the beam of illumination light 3 into the entrance opening 12 can be adjusted to minimize or symmetrize this detected fluorescent light.

[0158] 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 can be arranged behind a corresponding opening.

[0159] The arrangement in front of the aperture creates the possibility of obtaining a usable sensor signal even in a centered, optimally coupled state, provided the energy sensors are still in the beam path of the illumination light 3 and accordingly receive a sensor component of 3s. The arrangement after the respective aperture enables measurement with high signal dynamics because the energy sensors used in this way can detect a strong drop in intensity in the respective coupling edge area.

[0160] Adjustment of the coupling location and coupling direction can be performed using identical control steps. The coupling direction and coupling location can be adjusted by moving optically active components of the illumination system in one or more degrees of freedom of translation and / or rotation. Such optically active components for adjusting the coupling direction and coupling location can be components of the light source and / or other beam guidance components.

[0161] The coupling location on the one hand and the coupling direction on the other hand can be alternately adjusted iteratively and thus optimized.

[0162] Alternating control of the coupling location and coupling direction or combined control are possible.

[0163] When monitoring the coupling location, the coupling sensor device 91 can, in addition to monitoring in the two spatial dimensions x and y in the entrance plane 13 of the entrance opening 12, also monitor along the component z perpendicular thereto. This can also be achieved in this z-direction by linking this monitoring with a focus adjustment option for a coupling focus of the illumination light 3 relative to the position of the entrance opening 12. For example, the beam homogenizing element 11 can be displaced along the beam direction, i.e., along the z-direction perpendicular to the entrance plane 13, to enable this degree of adjustment freedom.

[0164] The above-described embodiments of the energy value sensors or the energy change sensors can each have a conversion medium for converting light incident on the respective sensor into a detection light of a longer wavelength, for example a fluorescence medium and / or a scintillation medium.

[0165] The respective energy value sensors or energy change sensors are in signal communication with the control / regulating device 27a, which in turn is in signal communication with the light source 5 and with the detection device 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 of the light source 5 and a respective temporal development of this energy, which can be detected via the at least one energy value sensor or the at least one energy change sensor of the above-described embodiments of the energy detection assemblies. This results in correspondingly high-precision imaging of the structures of the reticle 18.

[0166] The control / regulating device 27a is in signal connection, in particular, with the coupling mirror optics 10 in order to carry out the control / regulating processes explained above. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] US 10,042,248 B2 [0002, 0044, 0053] DE 102 20 815 A1

[0002] WO 2012 / 101269 A1

[0002] Cited non-patent literature

[0000] JD Mangus, JH Underwood “Optical Design of a Glancing Incidence X-ray Telescope”, Applied Optics, Vol. 8, 1969, page 95

[0043]

Claims

[1] Energy detection assembly (78; 86) for a lighting system of a mask inspection system (2a) for use with EUV lighting light (3) - with at least one EUV energy sensor device (77; 87) designed to detect energy of the illumination light (3) guided along an illumination light beam path, - wherein the EUV energy sensor device (77; 87) features: -- at least one energy value sensor (27; 35; 45; 71, 72) for detecting an illuminance energy of the illuminance light (3) over an exposure period; -- at least one energy change sensor (79; 88) for detecting a temporal development of the illumination energy of the illumination light (3) over the exposure period. [2] Energy detection assembly according to claim 1, characterized by , that the energy change sensor (79; 88) has a temporal resolution better than 10 µs. [3] Energy detection assembly according to claim 1 or 2, characterized by , that the energy change sensor (79; 88) has a photodiode for time-resolved detection of detection light (82) with a longer wavelength than the EUV illumination light (3). [4] Energy detection assembly according to one of claims 1 to 3, characterized by , that the energy value sensor (27) and / or the energy change sensor has a conversion medium for converting the EUV illumination light (3) into detection light of a longer wavelength. [5] 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), - with at least one energy detection assembly (78; 86) according to one of claims 1 to 4. [6] Mask inspection system according to claim 5, characterized by that the detection device has at least one TDI detector. [7] Mask inspection system according to claim 5 or 6, characterized by , that the light source (5) is designed as a pulsed light source.

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