Mask inspection device for photomasks of EUV lithography and carrier element for use in a mask inspection device

Abstract

The invention relates to a mask inspection device (1) for photomasks (2) used in EUV lithography. The mask inspection device comprises a receiving device (3) for a photomask (2), a light source (4) for illuminating the photomask with an illumination beam (5), and a detection unit (6) for at least partially receiving the photomask (2). Furthermore, the mask inspection device includes at least one beam shaping element (7) for adjusting the illumination beam (5) and at least one aperture (8) in the light path between the photomask (2) and the detection unit (6). According to the invention, the at least one beam shaping element (7) and the at least one aperture (8) are arranged in a fixed spatial relationship to each other on a common support element (9, 9'). The invention also relates to a corresponding support element (9, 9').

Description

The invention relates to a mask inspection device for photomasks of EUV lithography and to a carrier element for use in a mask inspection device.Mask inspection devices are described, for example, in Patrick P. Naulleau, et al. (2014), "Electro-optical system for scanning microscopy of EUV masks with a high harmonic generation source" (Optics Express) or in U.S. Patent Application US2012008123 A1.Such a system essentially comprises a zone plate as a beam shaping element, which focuses coherent EUV radiation from a light source onto a photomask arranged on a movable recording apparatus, and a detection unit for recording an image of the photomask. By means of a diaphragm in front of the detection unit, the illumination setting of the image can be adjusted, in particular with regard to the situation when using the photomask in a specific projection exposure apparatus, in order to obtain an assessment of the effect of the photomask in the production operation of semiconductor components that is as realistic as possible.In this context, the spatial relationship of the beam shaping element, photomask, aperture and detector is important.However, a first problem here is that, due to the non-telecentric design of the associated projection exposure apparatus, the azimuth of the main beam of the illumination beam varies over the lateral extent of the photomask. In particular, since shading effects on the photomask depend on the illumination direction, a significant effect is given on the imaging in the projection exposure apparatus, and it is desirable to emulate this effect also in the inspection of the photomask in the mask inspection apparatus. In mask inspection devices according to the prior art, this is achieved, for example, by a displacement of sigma and NA diaphragms.However, a single zone plate is always only designed for a specific illumination direction. Oblique illumination, as would be required for changing the main beam direction at the photomask, would lead to unacceptable imaging errors.Furthermore, the illumination setting in the projection exposure apparatus can be emulated via a segmented detector, which can also be designed as a camera; however, this solution is technically demanding and comparatively expensive. Alternatively, the illumination setting can also be realized by a diaphragm in front of a detection unit designed as a photodiode or a photodiode array. This is simpler from a detector point of view, but requires a complex mechanism for changing and positioning the diaphragm.Moreover, for realistic replication of the conditions in a projection exposure apparatus, the illumination setting must be centered with respect to the numerical aperture of the corresponding imaging optical unit, i.e. the main beam of the illumination must be identical to the main beam of the imaging optical unit. Decentration leads to imaging errors such as a displacement of the aerial image through the focus. Thus, for the mask inspection apparatus described, it is necessary to position the detection unit with high accuracy.It is an object of the present invention to specify a mask inspection apparatus for EUV photomasks and an element which produces as good an emulation of the conditions as possible in a projection exposure apparatus with reasonable technical complexity.This object is achieved by the devices having the features of the independent claims. The dependent claims relate to advantageous refinements and variants of the invention.A mask inspection apparatus for photomasks of EUV lithography according to the invention comprises:a photomask pick-up devicea light source for illuminating the photomask with an illumination beama detection unit for at least regionally receiving the photomaskat least one beam shaping element for adapting the illumination beamat least one aperture in the light path between the photomask and the detection unit.According to the invention, the at least one beam shaping element and the at least one aperture are arranged in a fixed spatial relationship to one another on a common carrier element. As a result, an optimum configuration of the beam shaping element and aperture can be defined in advance for a specific measurement situation, and complex alignment of the two elements with respect to one another in the mask inspection device is superfluous.Simple production of the common carrier element can be achieved by being designed as a lithographically processed plate.In particular, the at least one beam shaping element can be designed as a diffraction structure, which is written into the carrier element, for example, by a lithographic process.In an advantageous variant, the at least one beam shaping element is designed as a Fresnel zone plate; furthermore, the at least one aperture can be designed as a sigma aperture.An adaptation to the respective measurement positions and illumination settings can be achieved in that a plurality of diaphragms and beam shaping elements are arranged on the carrier element in pairs in a fixedly assigned manner to one another.In particular, pairs of beam shaping elements and apertures can be arranged in rows and columns on the carrier element.Thus, for example, a specific aperture shape can be selected for individual lines, which corresponds to a specific illumination setting. Furthermore, a specific shape of a beam shaping element and a specific spatial arrangement of beam shaping element and aperture can be selected for individual columns. In this case, in particular five or more such gaps can be present on the carrier element.When the respective photomask is recorded, therefore, firstly that row which corresponds to the respectively selected illumination setting is moved into the beam path. Depending on the position of the region under consideration on the photomask, in particular the position of the region under consideration in the direction of the course of the scanner slot of the respective associated projection exposure apparatus, the respectively corresponding combinations of beam shaping element and spatial assignment of beam shaping element and aperture, which most closely correspond to the respective main beam direction, are then selected within this row.In this case, in particular, the shape of the beam shaping element can also change from column to column.This takes account of the fact that in a projection exposure apparatus the scanner slot naturally has a considerable lateral extent, as a result of which the main beam direction changes.In order to realize the movement of the carrier element required for this purpose, the mask inspection device can comprise a device for positioning the carrier element in two mutually perpendicular directions.The detector unit can be designed comparatively easily, for example as a large-area photodiode. It is advantageous if the area of the photodiode is at least as large as the sigma diaphragm. With a distance between photomask and diaphragm of 10 mm and a numerical aperture of 0.1, a diameter of the detection surface of the photodiode of 2 mm would be useful, for example.Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawings. They show FIG. 1 shows a basic representation of the idea underlying the invention FIG. 2 shows a schematic illustration of an exemplary carrier elementFIG. 1 shows a schematic illustration of a mask inspection device 1 according to the invention. The mask inspection device 1 shown here comprises a light source 4 which illuminates a specific region on a photomask 2 by means of an illumination beam 5.The light emanating from the illuminated photomask 2 is detected by a detection unit 6 and fed to a further evaluation unit, not shown in the figure, for generating an image of the photomask 2.The surface of the photomask 2 is detected in regions, i.e. the photomask 2 can be moved on a recording device 3 in two mutually perpendicular directions in order to record individual regions of its surface within its own mask plane, with the result that regions of interest on the photomask 2 are illuminated and recorded. The movement of the photomask 2 for positioning is illustrated in FIG. 1 by the two double arrows, which are not designated.Arranged between the photomask 2 and the light source 4 or the detector unit 6 is a carrier element 9, on which a plurality of pairs of beam shaping units, which are embodied both as a Fresnel zone plate 7 in the example shown, and apertures realized as sigma diaphragms 8, are arranged in a fixed spatial relationship to one another. For reasons of clarity, only a single pair is shown in FIG. 1.The illumination beam 5 passes through the zone plate 7 and is focused by the latter onto the desired region of the photomask 2. Starting from the photomask 2, the radiation reflected on it passes through the sigma diaphragm 8 and then falls onto the detector unit 6, which can be designed, for example, as a large-area photodiode.It can be seen clearly in the figure that, by using the carrier element 9 with the beam deformation element 7 arranged thereon and the aperture 8, a fixed spatial relationship can be established in a comparatively simple manner between the two last-mentioned elements 7, 8. In particular, the solution shown enables a corresponding carrier element with the elements arranged thereon to be prepared outside the mask inspection device 1 and subsequently inserted therein, wherein the spatial relationship of the beam forming unit 7 and the aperture 8 is maintained on account of the monolithic solution shown.In general, it is desirable to be able to emulate different illumination settings and main beam directions in a simple manner in a mask inspection device. For this reason, the carrier unit 9 is arranged on a device 10 for positioning, by means of which the pair matching the respective setting / the respective main beam direction can be introduced into the beam path. The corresponding directions of movement are represented in FIG. 2 by arrows which are not separately designated.FIG. 2 shows a schematic representation of an exemplary carrier element 9'. On the carrier element 9' shown in FIG. 2, a total of nine pairs of Fresnel zone plates 70, 71, 72 and sigma diaphragms 80, 81, 82 are arranged in three rows and three columns. The same sigma diaphragms 80, 81, 82 are used within a row and the same Fresnel zone plates 70, 71, 72 are used within a column. Similarly, the relative arrangements of zone plate and sigma diaphragm within the respective pairs within a column correspond to one another.During operation of the associated mask inspection device 1, the illumination setting for which the photomask 2 currently under examination is to be measured is first selected by the selection of the respective row. In other words, the shape of the sigma diaphragm 80, 81 or 82 is first selected. During the measuring process, depending on the position of the currently examined area on the photomask 2, that pair of zone plate and sigma diaphragm is then selected which best images the conditions in a projection exposure apparatus for the respectively examined area.In other words, by selecting the column corresponding to the area under consideration, the associated main beam direction (presented in the figure by arrows not designated) is simulated. It goes without saying that a subdivision into three columns and thus into three different main beam directions as shown in the figure will not meet the requirements in all cases. It is to be understood that five or more columns or main beam directions are required.In practice, it is necessary to find a compromise between the fineness of division into different principal beam directions and the total time required for displacing the supporting element 9' for changing the gaps.List of reference characters1 Mask inspection device 2 Photomask 3 Recording device 4 Light source 5 Illumination beam 6 Detection unit 7 Beam shaping unit 8 Aperture 9, 9' Carrier element 10 Device for positioning 70, 71, 72 Fresnel zone plates 80, 81, 82 Sigma aperturesReferences included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedUS2012008123A1

[0002] Cited Non-Patent LiteraturePatrick P. Naulleau, et al. (2014), "Electro-optical system for scanning microscopy of EUV masks with a high harmonic generation source" (Optics Express

[0002]

Claims

Mask inspection device (1) for photomasks (2) of EUV lithography, comprising - a recording device (3) for a photomask (2) - a light source (4) for illuminating the photomask with an illumination beam (5) - a detection unit (6) for at least regionally recording the photomask (2) - at least one beam shaping element (7) for adapting the illumination beam (5) - at least one aperture (8) in the light path between the photomask (2) and the detection unit (6) characterized in that the at least one beam shaping element (7) and the at least one aperture (8) are arranged in a fixed spatial relationship to one another on a common carrier element (9, 9').Mask inspection device (1) according to claim 1, characterised in that the common carrier element (9, 9') is formed as a lithographically processed plate.Mask inspection device (1) according to Claim 1 or 2, characterized in that at least one beam shaping element (7) is designed as a diffraction structure.Mask inspection device (1) according to Claim 3, characterized in that the at least one beam shaping element (7) is designed as a Fresnel zone plate.Mask inspection device (1) according to one of the preceding claims, characterized in that the at least one aperture (8) is designed as a sigma aperture.Mask inspection device (1) according to one of the preceding claims, characterized in that a plurality of apertures (8) and beam shaping elements (7) are arranged on the carrier element (9, 9') in a manner fixedly associated with one another in pairs.Mask inspection device (1) according to one of the preceding claims, characterized in that pairs of beam shaping elements (7) and apertures (8) are arranged in rows and columns on the carrier element (9, 9').Mask inspection device (1) according to Claim 7, characterized in that a specific aperture shape is selected in each case for individual lines.Mask inspection device (1) according to Claim 7 or 8, characterized in that a specific shape of a beam shaping element (7) and a specific spatial arrangement of beam shaping element (7) and aperture (8) are selected in each case for individual columns.Mask inspection device (1) according to one of Claims 7 to 9, characterized in that the carrier element (9, 9') has at least five columns.Mask inspection device (1) according to one of the preceding claims, characterized in that the mask inspection device (1) comprises a device (10) for positioning the carrier element (9, 9') in two mutually perpendicular directions.Mask inspection device (1) according to one of the preceding claims, characterized in that the detector unit (6) is designed as a large-area photodiode.Carrier element (9, 9') with at least one beam shaping element (7) and at least one aperture (8) for a mask inspection device (1) for photomasks (2) of EUV lithography, wherein the at least one beam shaping element (7) and the at least one aperture (8) are arranged on the carrier element (9, 9') in a fixed spatial relationship to one another.Carrier element (9, 9') according to claim 13, characterised in that the carrier element (9, 9') is formed as a lithographically processed plate.Carrier element (9, 9') according to claim 13 or 14, characterised in that at least one beam shaping element (7) is designed as a diffraction structure.Carrier element (9, 9') according to claim 15, characterised in that the at least one beam shaping element (7) is formed as a Fresnel zone plate.Carrier element (9, 9') according to one of the preceding claims 13 to 16, characterized in that the at least one diaphragm (8) is designed as a sigma diaphragm.Carrier element (9, 9') according to one of the preceding claims 13 to 17, characterized in that a plurality of apertures (8) and beam shaping elements (7) are arranged on the carrier element (9, 9') in pairs fixedly assigned to one another.Carrier element (9, 9') according to one of the preceding claims 13 to 18, characterized in that pairs of beam shaping elements (7) and apertures (8) are arranged in rows and columns on the carrier element (9, 9').Carrier element (9, 9') according to claim 19, characterised in that a specific aperture shape is selected for individual lines.Carrier element (9, 9') according to claim 19 or 20, characterised in that a specific shape of a beam shaping element (7) and a specific spatial arrangement of beam shaping element (7) and aperture (8) is selected for individual columns.Carrier element (9, 9') according to one of claims 19 to 21, characterized in that the carrier element (9, 9') has at least five gaps.

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