DE102007055096A1 - Optical characteristic determining method for illustrating optical system, involves determining image produced on image recording device in each relative position by device, where device is provided opposite to image plane - Google Patents

Abstract

The method involves arranging a test-structure (24) in an object level (26) of an illustrating optical system (14). An image recording device (28) is provided opposite to an image plane (30) in each of two relative positions such that an image of a pupil (18) of the optical system is produced on the image recording device by the optical system by the test-structure . The image produced on the image recording device is determined in each relative position by the image recording device. Independent claims are also included for the following: (1) a device for determining an optical characteristic of an illustrating optical system (2) a microlithography exposure system.

Description

Background of the invention

The The invention relates to a method for determining at least one optical property of an imaging optical system which for imaging one located in an object plane of the optical system Object is designed in an associated image plane. Furthermore The invention relates to a device for determining at least an optical property of an imaging optical system which for imaging one located in an object plane of the optical system Object is designed in an associated image plane. Furthermore The invention relates to a microlithography exposure system with a lighting system and / or a projection lens and such a device.

An optical property of an imaging optical system that can be determined by means of such a method or such a device can be, for example, the numerical aperture or the telecentricity of the optical system. The numerical aperture of an optical system is a dimensionless number which describes an angular range for the entry or exit of electromagnetic radiation into the optical system. The numerical aperture of an optical system, such as a projection objective of a microlithography exposure apparatus, is defined as follows: NA = n × sinθ (1) where n is the refractive index of the medium surrounding the optical system, and θ is the half angle of aperture of the maximum entrance cone for electromagnetic radiation entering the optical system and the maximum exit cone for the optical system, respectively.

Previously known Method for determining the numerical aperture of an imaging The optical system measures the electromagnetic energy emitted by the system Radiation by means of an interferometer. The accuracy of the determination the numerical aperture of the optical system by means of interferometric methods is limited. Also is a measurement of the variation the numerical aperture over the Image field of the optical system very expensive.

The Determination of the telecentricity of an optical system is known to be, Deviations of the telecentricity behavior of optical imaging systems from their ideal telecentricity behavior of optical imaging systems, d. H. Detect telecentric errors. In an imaging optical System that is subject to a telecentric error, runs the Main beam for a respective field point not, as in the error-free case, in parallel to the optical axis of the imaging system, but with respect to this tilted, wherein the tilt angle is a quantitative measure of the telecentric error represents. It is close by, the telecentric error thereby determine by the energetic center of gravity of the figure a respective field point in the image plane of the optical system measured in different focus settings and from this the Tilt angle is calculated trigonometrically. But that is the Difficulty that the energetic center of gravity of the Image of a respective field point in the image plane depending on the focus adjustment also vary due to other aberrations can typically be associated with imaging systems such as coma and bowl defects. From such a measurement the energetic center of gravity in the image plane as a function The focus adjustment alone can therefore only with great inaccuracy be closed the telecentric error.

Underlying task

It is an object of the invention, a method of the aforementioned Art and a microlithography exposure system with a device of the type mentioned above, by means of or by means of an optical property of the imaging optical system, in particular the numerical aperture and / or the telecentricity of the optical system, with improved accuracy can.

Inventive solution

This object is achieved according to the invention with a generic method, which comprises the following steps: arranging at least one test structure, for example in the form of a pinhole of a shadow mask, in the object plane of the optical system, arranging an image capture device in at least two different relative positions relative to the image plane of the optical system wherein each of the at least two relative positions ver the image capture device so far from the image plane ver is set by the optical system by means of the test structure in each case an image of the pupil of the optical system on the image capture device is generated, and detecting an image generated by the optical system by means of the test structure on the image capture device in each of the at least two relative positions by means of the image capture device. Furthermore, the object is achieved according to the invention with a generic method comprising the following steps: arranging at least one test structure in the object plane of the optical system, arranging an image capture device in at least two different relative positions relative to the image plane of the optical system, wherein in each of the at least two relative positions the image capture device is displaced so far in relation to the image plane that an image on the image capture device is generated by the optical system by means of the test structure whose maximum extent exceeds a maximum extent of the image structure of the test structure by at least one order of magnitude, and detecting one of the optical system by means of the test structure on the image capture device generated image in each of the at least two relative positions by means of the image capture device.

Further is the task according to the invention with a generic device solved, which at least one test structure and an image capture device wherein the device is adapted to at least a test structure in the object plane of the optical system and the image capture device in at least two different relative positions relative to the image plane of the optical system, wherein in each of the at least two relative positions the image capture device so far across from the image plane is offset from that of the optical system by means of The test structure in each case an image of the pupil of the optical system is generated on the image capture device, and the image capture device designed to be one of the optical system by means of the test structure on the image capture device generated image in each of the at least to capture two relative positions. Furthermore, the object according to the invention with a generic device solved, which is adapted to the at least one test structure in the object plane of the optical system and the image capture device in at least two different relative positions relative to the image plane of the optical system, wherein in each of the at least two relative positions the image capture device so far across from the image plane is offset from that of the optical system by means of the test structure in each case an image on the image capture device is generated whose maximum extent a maximum extent the mapping of the test structure in the image plane by at least one Order of magnitude exceeds, and the image capture device is adapted to receive one of the optical system by means of the test structure on the image capture device generated image in each of the at least two relative positions to capture. About that addition, the object according to the invention with a microlithography exposure system, such as a stepper or scanner, with a lighting system and / or a projection lens with such a device for determining a mapping characteristic of the illumination system and / or the projection lens.

With In other words, according to the invention, a method and a device providing at least one optical property an imaging optical system, in particular the determining the numerical aperture and / or the telecentricity of the optical system enable. The optical system is designed to be one in an object plane to image arranged object in an associated image plane. there is every possible Object level in which the object can be arranged, a corresponding Assigned image level.

According to the invention, at least arranged a test structure in an object plane of the optical system. Furthermore, an image capture device in at least two different relative positions relative to the image plane of the optical Systems, i. at least two along the optical axis of the optical system against each other shifted positions, arranged. For switching between the relative positions, the image capture device and / or the image plane of the optical system are shifted. The image plane of the optical system can be changed, for example the location of the test structure relative to the optical system along its optical axis and thus offset by moving the object plane become.

According to one first embodiment the solution according to the invention in a first and a second relative position, the image capture device so far opposite the image plane offset that by means of the test structure in each of the Relative positions a respective image of the pupil of the optical Systems, such as a light spot, on the image capture device is produced. The image of the pupil is thereby directly on the image capture device optically generated, i. The image of the pupil does not have to go through arithmetic evaluation of a detected structure, such as a Interference pattern can be determined. In this case, the image capture device across from the image plane extra or intrafokal be moved.

Under the pupil of the optical system becomes particular in this context understood the exit pupil of the optical system. Every optical System has an image aperture regulating the brightness of the image on. This can be formed in the case of a lens from the edge of the lens or even behind the optical elements of a multi-lens System arranged louver aperture etc. The exit pupil of an optical system is the image of the aperture diaphragm, as it is from an axial point of the image plane through between the aperture stop and the point in the image plane lying lenses of the optical system is seen.

According to the invention, the image capture device is arranged in the relative positions in each case in a plane in which an image of the pupil is produced by means of the test structure. This image of the pupil is in particular an image of the illumination of the pupil by an illumination radiation used to generate the image on the image capture device. Such an image of pupil illumination is also called a pupillogram. Regarding the definition of a pupillogram is expressly based on the article of Joe Kirk and Christopher Progler, "Pinholes and pupil fills", Microlithography World, Autumn 1997, pp. 25-34 directed. In other words, according to the invention, the image capture device is arranged in the relative positions at positions at which the pupillogram can be measured directly.

According to one second embodiment the solution according to the invention is the image capture device is offset so far from the image plane, that of the optical system by means of the test structure an image is generated on the image capture device whose maximum Extension a maximum extent of the image of the test structure in the picture plane by at least one order of magnitude. This should be the maximum Extension of the image structure generated by means of the test structure at least be ten times as big like the maximum extent of the test structure when mapped in the picture plane.

According to the invention is then in each of the at least two relative positions by means of the test structure recorded on the image capture device generated image. through These images can then at least one optical property of the optical system can be determined with high accuracy. In particular, can so that the numerical aperture and / or the telecentricity of the optical Systems can be determined with high accuracy.

By the arrangement according to the invention the image capture device in the two relative positions according to the first embodiment or the second embodiment the solution according to the invention is the image generated by the test structure at focus errors, the for example, by deviations of the image capture device in the direction the optical axis of the optical system can hardly be caused by aberrations due to wavefront aberrations of the optical system.

such Image aberrations, such as coma or other aberrations are in higher order depends on the z-position along the optical axis. by virtue of of the big one Distance of the image capture device of the image plane and thus from the nominal focus position is the sensitivity to the image aberrations caused by wavefront aberrations in small changes low along the optical axis. This reduced influence the aberration caused by wavefront aberrations in the measurement of the optical property contributes to improved accuracy of the method. This applies in particular to the determination of telecentricity of the optical system. The aforementioned aberrations are particular negligible, when in the at least two relative positions by means of the test structure Images generated on the image capture device each one Expansion of at least 100 μm having. The inventive method is a differential process. A calibration step becomes so not required, in contrast to interferometric measuring methods, in which a so-called defocus mapping necessary is.

In an advantageous embodiment The invention relates to the image capture device in a first relative position at least 50 μm, advantageously 200-500 microns, compared to the Image plane offset. Advantageously, the optical system with one wavelength in the UV wavelength range or operated at shorter wavelengths. At such illumination wavelengths, a focus offset of at least 50 μm in addition, that you no longer have a picture of the test structure on the Image capture device can speak, but that the pupillogram of the optical system is visualized by means of the test structure. Image aberrations due to wavefront aberrations have hardly any influence on the Determination of the optical property.

In a further advantageous embodiment, a plurality of test structures are arranged at different positions of an object field in the object plane. Furthermore, the object field in each of the at least two relative positions is converted by the optical system into an image field on the image capture device, as well as the respective image field captured by the image capture device and determines therefrom the distribution of the optical property of the optical system as a function of the position in the image field. In other words, the method according to the invention is carried out in parallel for a multiplicity of test structures arranged in the object field. The test structures thus form parallel measuring channels. By this parallelized measurement of the optical property over the entire field of view of the optical system, the optical system can be measured with high time efficiency. Thus, the optical system with respect to the distribution of the optical property over the image field after its production or in the context of a maintenance can be checked without much time.

Advantageously, the at least one optical property of the optical system is determined by evaluating the images acquired in the various relative positions. Furthermore, it is advantageous if the at least one specific optical property comprises the numerical aperture of the optical system. In particular, both the input-side and the output-side numerical aperture are determined. In this case, the output-side numerical aperture (NA _{output side} ) is linked to the input-side numerical aperture (NA _{input side} ) via the imaging scale of the optical system as follows: N / A the input side = Magnification × NA output side (2)

wobei die G₀ die maximale Ausdehnung der Teststruktur in seiner Abbildung in der Bildebene und NA die ausgangsseitige numerische Apertur des optischen Systems ist. Der Abstand d₀ soll also erheblich größer, insbesondere um mindestens eine Größenordnung größer sein als der in Gleichung (3) angegebene Ausdruck. Mittels des erfindungsgemäßen Verfahrens ist die numerische Apertur mit einer Auflösung von kleiner als 0,0001, also 0,1 mNA, absolut bestimmbar.It is furthermore advantageous for determining the numerical aperture of the optical system if the distance d ₀ between the image capture device and the image plane in the first relative position satisfies the following relation:

where G _{0 is} the maximum extent of the test structure in its image plane image and NA is the output numerical aperture of the optical system. The distance d ₀ should therefore be considerably larger, in particular at least an order of magnitude greater than the expression given in equation (3). By means of the method according to the invention, the numerical aperture with a resolution of less than 0.0001, ie 0.1 mNA, is absolutely determinable.

Advantageously, an extent, in particular a radius, of the image or light spot generated by means of the test structure is determined for each relative position, and the output-side numerical aperture of the optical system is calculated therefrom. In particular, a radius change rate dR / dz at an operating point z _o , which advantageously corresponds to the position of the image capture device along the optical axis in the first relative position, is determined from the radii R of the images of the test structures determined for the different relative positions and from this the numerical aperture NA calculated as follows:

To obtain the change in radius dR / dz, the pupil radii R are advantageously made of a focal length measurement z _i , which is carried out to set the different relative positions; i = 1, .... I extracted and plotted against the heights z _i . By linear regression, the increases dR / dz can then be evaluated. Furthermore, it is possible to characterize the lens aperture of the optical system from the images captured in the various relative positions, in particular to determine deviations of the shape of the image from a desired shape and to draw conclusions therefrom about vignetting and diaphragm lamellation.

Farther it is advantageous if the at least one specific optical Property that includes telecentricity of the optical system. The inventive method allows a telecentric measurement with high dynamics. In this case it is advantageous if the distance between the image capture device and the image plane in the first relative position at least one order of magnitude is larger as the maximum extent of the test structure when mapped in the Image plane.

wobei z_o ein Arbeitspunkt für den Abstand zwischen der Bildebene und der Bilderfassungseinrichtung ist, an dem die die Positionsänderungsrate dX/dz bzw. dY/dz bestimmt wird.In order to determine the telecentricity of the optical system, the center of gravity or the center of the image or light spot generated by the test structure is advantageously determined for each relative position and the output-side or image-side telecentricity of the optical system is calculated therefrom. Advantageously, the image generated by means of the test structure has a circular edge. In this case, in the evaluation of the images, the coordinates X and Y of the center points of the images in the various relative positions, advantageously determined by a circle adjustment. The telecentricity F can then be determined as follows become:

where z _{o is} an operating point for the distance between the image plane and the image capture device at which the position change rate dX / dz or dY / dz is determined.

Furthermore it is advantageous if the image capture device for rasterized Image capture is set up and the size difference between the along the images captured in the various relative positions a detection direction at least one distance between two Raster points or pixels of the image capture device is. The Image capture device is advantageously as a digital camera with a CCD or CMOS detector designed. In a favorable Distance between the halftone dots of the image capture device of a maximum of 5 μm should the size difference between the images captured in the various relative positions also at least 5 microns be so that it can be measured by the method according to the invention.

Farther it is advantageous if the test structure has a rounded shape, in particular circular is designed. In this case too, this is indicated by the test structure Image created on the image capture device as possible round shape, what the further evaluation for the determination of the numerical aperture or telecentricity. In an alternative embodiment the test structure has a shape deviating from the circular shape. When evaluating the images, therefore, the influence of the shape of the test structure taken into account by means of a correction algorithm.

Furthermore it is useful if the test structure punctiform is, in particular as a punctiform opening in a shadow mask or as punctiform strahlungsabschwächendes Element in a basically radiolucent Mask is formed. The test structure can be designed as a "positive" or as a "negative" pinhole. With such a Pinholemaske the pupil illumination of the optical system can be detected very accurately. advantageously, is the test structure with electromagnetic radiation with a predetermined illumination wavelength illuminated and is dimensioned such that a maximum extent the image generated by the optical system in the image plane the test structure in the order of magnitude the illumination wavelength lies. This means the maximum extent of the mapping of the test structure is maximum ten times the illumination wavelength.

Furthermore it is advantageous if the test structure with highly incoherent electromagnetic Radiation, i. with radiation as possible greater partial coherence σ, illuminated becomes. The partial coherence σ of the illumination radiation is defined by the quotient of the numerical aperture of a the electromagnetic radiation generating illumination system and the numerical aperture of the optical system. The lighting the test structure with highly incoherent electromagnetic Radiation allows to "illuminate" the entire numerical aperture of the optical system, and thus the numerical one Aperture or the telecentricity of the optical system with high accuracy to determine. The illumination of the test structure with highly incoherent electromagnetic Radiation can advantageously by over-illuminating the Test structure can be achieved. For this purpose, one in the illumination beam path the optical system arranged lens are used, the one with as possible great partial coherence (e.g., σ of about 0.8) is irradiated. In an alternative embodiment a focusing the illumination radiation on the test structure Microlens be provided. In this case, the microlens should with as possible small partial coherence (eg σ of approximately 0.3) are illuminated. The overshadowing Illumination of the test structure leads to ensure that the illumination radiation from a test structure huge Illuminated angle range. In such a radiating illumination can the maximum extent of the test structure is also considerably larger than the illumination wavelength be. The overarching illumination leads to, that the effect of the test structure itself compared to one to the illumination wavelength considerably larger extent the one of a punctiform. Pinholes stays. A possible by means of overshadowing greater extent of the test structures has in the case of designed as pinholes test structures the advantage that a comparatively greater radiation intensity passes through the test structures, whereby the measurement accuracy and Speed of the method is increased.

In a further advantageous embodiment, in at least one second relative position between the image capturing device and the image plane, the distance between the image capturing device of the image plane relative to the first relative position by a relation to the distance between the Bildfas sungseinrichtung and the image plane in the first relative position small distance, for example, a few microns changed. In particular, the distance is changed by a distance which is smaller by at least an order of magnitude than the distance between the image capture device and the image plane in the first relative position. In other words, a relative position which essentially corresponds to the first relative position is defined as the operating point. The distance between the image plane and the image capture device varies between the different relative positions only by a relatively small amount around this operating point. Advantageously, a Fokusstaffel is set with a pitch of about 2.5 microns around this operating point. Thus, the image generated by the test structure on the image capture device in each of the relative positions is an image of the pupil of the optical system or has a maximum extent that exceeds the maximum formation of the image of the test structure in the image plane by at least one order of magnitude. In this case, edge blurring in the image captured by the image capture device does not substantially change between the relative positions, so that its influence can be disregarded. In an alternative embodiment, in a second relative position, the image capture device is comparatively closer to the image plane, in extreme cases even in the image plane itself. In this case, the nature of the edge smearing of the image on the image capture device varies considerably between the different relative positions. However, this change of edge blurring is predictable by means of a mathematical model. Therefore, their influence in the evaluation of the captured images can be considered.

It is also advantageous if to switch between the different Relativstellungen the image capture device relative to the optical System is moved and / or tilted. The image capture device should be moved parallel to the optical axis of the optical system or tilted relative to it.

Farther it is useful if the at least one test structure on a slide, in particular on a mask for a microlithography exposure system, is arranged, and to switch between the different relative positions the slide shifted and / or tilted relative to the optical system. Both the offset of the image capture device and the slide relative to the optical system to that the distance between the image plane and the image capture device changed or that the focus setting for that by means of the test structure generated image is changed.

In In another advantageous embodiment, several are each parallel to the optical axis of the optical system staggered Test structures on a slide, in particular a mask for one Microlithography exposure system arranged. The pictures will be in different relative positions generated by means of staggered test structures. With others Words, the slide points defined levels on. The arranged at the different stages Test structures are thus assigned to different image levels. By exposing the slide once so pictures are in various relative positions on the image capture device generated. these can then evaluated to determine the optical property.

It is furthermore advantageous if the determination of the optical property on one or more optical systems of a microlithography exposure apparatus, in particular on a projection lens and / or a lighting system the microlithography exposure system is performed.

Furthermore, it is advantageous if the at least one test structure is illuminated by means of an illumination system with an electromagnetic illumination radiation having a specific angular distribution with respect to the optical axis of the optical system and the method further comprises the following step: determining an angle-resolved intensity distribution of the illumination radiation from that of the image acquisition device captured image in the first relative position. The angular distribution of the electromagnetic radiation illuminating the test structure is determined by the so-called illumination setting of the illumination system. Such a lighting setting may include, for example, annular illumination, dipole illumination, or quadrupole illumination. In this embodiment of the method according to the invention thus the angular distribution of the illumination is determined in relation to the numerical aperture of the optical system. By setting different relative positions, as already mentioned, the numerical aperture can be determined with a particularly high accuracy. By setting the numerical aperture to the angle-resolved intensity distribution of the illumination radiation determined from the image acquired in the first relative position, the angular distribution can be determined with particularly high absolute accuracy. In the case of deviations of the specific angle-resolved intensity distribution from a desired intensity distribution, corrective measures can then be taken on the illumination system. Advantageously, to determine the angle-resolved intensity distribution, an edge profile of the acquired image and a position of an area of increased radiation intensity, in particular a light spot, arranged within the edge profile are determined in the image, and the angle-resolved intensity distribution or the illumination setting with respect to an aperture stop of the optical system is determined therefrom becomes.

The in terms of those listed above advantageous embodiments the method according to the invention specified characteristics can be transferred accordingly to the device according to the invention. The resulting advantageous embodiments of the inventive devices are intended be expressly encompassed by the disclosure of the invention. Farther refer the respect the advantageous embodiments the inventive method mentioned above Advantages thus also on the corresponding advantageous embodiments the device according to the invention.

Brief description of the drawings

following Be exemplary embodiments a method according to the invention and a device according to the invention for determining at least one optical property of an imaging optical system with reference to the attached schematic drawings explained in more detail. It shows:

1 a schematic view of a microlithography Projektionsbelichtanlage with a projection optics and a device for determining an optical property of the projection optics,

2 an edge course of a means of the device according to 1 detected light spot,

3 a first embodiment of the device according to 1 used mask,

4 a second embodiment of the device according to 1 used mask,

5 an experimentally by means of the device according to 1 detected light spot,

6 a circle fit of the light spot according to 5 .

7 a histogram of the intensity distribution of the light spot according to 5 .

8th a means of the device according to 1 determined NA distribution over the image field of the projection optics of the associated microlithography projection exposure apparatus according to 1 .

9 an illustration of the generation of a pupil illumination of the projection optics according to 1 having a light spot in so-called dipole illumination,

10 a plan view of the light spot according to 9 ,

In 1 is a microlithography exposure system 10 shown. The microlithography exposure system 10 has a lighting system 12 as well as an imaging optical system 14 in the form of a projection lens. The imaging optical system 14 has an optical axis 16 on, parallel to the z-axis of the in 1 indicated catholic xyz coordinate system runs. The optical system 14 is designed to be one of the lighting system 12 illuminated object from an object plane 26 into an assigned image plane 30 map. The optical system 14 has an aperture stop which is the optical system 14 continuous beam 40 limited. The image of the aperture diaphragm, as seen from an axial point of the image plane 30 from any intervening lenses of the optical system 14 is seen as the exit pupil of the optical system 14 subsequently defined merely as a pupil 18 referred to as. In the in 1 In the case shown schematically, for simplicity, the aperture and the pupil fall 18 together.

The microlithography exposure system 10 further comprises a device 20 for determining an optical property of the imaging optical system 14 , The device 20 in turn comprises a reticle or a mask 22 with test structures arranged thereon 24 in the form of so-called pinholes. This is the mask shown 22 with it a shadow mask. Alternatively, however, it is also possible to use a basically radiation-permeable mask with radiopaque point-shaped test structures 24 be used. The test structures 24 are evenly over one of the optical system 14 detectable Distributed object field. The mask 22 becomes in the object plane 26 of the optical system 14 arranged.

In a first embodiment 22 the mask are the test structures 24 with a maximum extension on the order of the illumination wavelength. 3 and 4 each show a section of further embodiments 22a and 22b the mask of the device 20 , Compared to the first embodiment 22 the mask can be the test structures 24 according to 3 and 4 be made comparatively larger. This has the advantage that a comparatively greater radiation intensity is achieved by the test structures designed as pinholes 24 passes through, whereby the measurement accuracy and speed of the method is increased.

Nevertheless, a broad radiation cone for those of the test structures 24 outgoing radiation 38 to generate the test structure 24 according to 3 and 4 illuminated overshadowed. In the embodiment according to 3 assigns the mask 22a one at the top of a radiolucent main body 50 the mask 22a arranged lens 48 on. The diffuser 48 comes with illumination radiation 36 comparatively incoherent form (eg σ of about 0.8) irradiated. Through the lens 48 becomes the illumination radiation 36 in overblazing lighting 54 regarding the test structure 24 transformed. The pinhole is a hole in a radiation-attenuating or blocking layer 52 which is a bottom of the radiation-transmissive main body 50 covers. In the embodiment according to 4 is instead of the lens 48 a microlens 56 at the radiation-attenuating layer 52 opposite side of the main body 50 arranged. The microlens 56 is irradiated with illumination radiation having a comparatively high degree of conicity (eg σ of 0.3).

In addition, the device includes 20 an image capture device 28 which may be implemented as a CCD camera, for example. The image capture device 28 becomes either in an intrafocal position 32 or an extrafocal position 34 arranged. Here are the two positions 32 and 34 so far from the picture plane 30 remove that on a detection surface 28a the image capture device 28 by means of a test structure 24 generated light spot 42 a picture of the pupil 18 of the optical system 14 is. The image of the pupil 18 is a picture of the illumination of the pupil 18 and is also referred to below as Pupillogram. The image of the pupil 18 will be in the two positions 32 and 34 directly on the image capture device 28 optically generated, ie the image does not have to be determined by computational evaluation of a detected structure, such as an interference pattern.

The course of the electromagnetic radiation through the microlithography exposure system 10 is as follows: the on the mask 22 arranged test structures 24 be from the lighting system 12 with illumination radiation 36 irradiated with a narrow wavelength spectrum. The wavelength of the illumination radiation 36 is usually in the UV range, but can also be in the range of shorter or longer wavelengths. The test structures punctiform with respect to the illumination wavelength 24 radiated radiation 38 has a large angular distribution with respect to the optical axis 16 on. That through the pupil 18 of the optical system 14 transmitted beams 40 only represents part of the radiation 38 represents.

In 2 is the edge course 44 respectively. 46 of the image capture device 28 in the intrafocal position 32 detected light spot 42 shown in plan view. In this case, the reference numeral 46 one of the circular shape slightly different real edge course and the reference numeral 46 the ideal edge of the light spot 42 , The diameter of the light spot 42 exceeds the diameter of the image of a test structure 24 into the picture plane 30 by at least one order of magnitude, that is by at least a factor of ten.

According to one embodiment of the method according to the invention, the corresponding light spots 42 by means of the image capture device 28 at different slightly opposite to the position 32 respectively. 34 recorded shifted positions. It can be z. B. the position 32 serve as the operating point of a focus scale. In the mentioned embodiment, the pitch of the focus scale is small compared to the distance of the working point to the image plane 30 , The step size can be for example 2.5 microns. The resulting for a given test structure 24 recorded light spots 42 These are all pupillograms of the optical system 14 with different diameter and possibly different position of its center.

The radius R of the pupillograms 42 changes depending on the z position of the image capture device 28 at an operating point z _o at each field location (k, l) of the image field of the optical system 14 at which a light spot 42 is generated as a function of the numerical aperture NA of the optical system 14 as follows:

The Reversal of this equation leads to

To obtain the radius change dR (k, l; z) / dz, the radii of the light spots or the pupil radii R (k, l; i) = R (k, l; z _i ), i = 1, a Fokusstaffel z _i , i = 1, ... I extracted and plotted against the heights z _i . By linear regression, the slopes dR (k, l; z) / dz are then evaluated for all field locations.

That is, to determine the numerical aperture of the optical system 14 only needs the radius change dR (k, l; z) / dz for each light spot 42 in the image field 62 be determined. For this purpose, first the respective edge course of the image acquisition device 28 detected light spots 42 determined. An example of such an experimentally detecting light spot 42 is in 5 shown. First, the captured images of the light spot 42 removed by background correction at selected edge regions of the background signal. From the corrected intensity images, respective histograms of the intensity modulation are then determined.

Such a histogram is exemplary in 7 shown. Using the histograms, you can use pixels that are the edge of the light spot 42 mark, make out as minima. Around the minima are intensity thresholds 60 placed so that a predetermined number of pixels comes to the evaluation. In the actual evaluation, from the coordinates x _n (k, l; i), y _n (k, l; i) of the selected pixels (n = 1), ..... N (k, l; i) a circle fit the centers X (k, l; i), Y (k, l; i) and radii R (k, l; i) of the light spots 42 won. Due to a special outlier filtering based on the residuals, only the pixels whose residuals can be found within the statically determinant 3 sigma band are evaluated. By such filtering, the loop matching becomes very robust against fuzziness, local intensity dips or other defects in the light spot 42 , An ascertained by this method Kreisfit 58 is exemplary in 6 shown.

die ermittelnden Radien gegen die z-Stellungen der Bilderfassungseinrichtung 28 aufgetragen und die Steigungen dR(k, l; z)/dz durch lineare Regression gewonnen. 8 zeigt beispielhaft eine mittels der Vorrichtung gemäß 1 ermittelte NA-Verteilung über das Bildfeld 64 des optischen Systems 14.Last will be based on the relationship

the determining radii against the z-positions of the image capture device 28 plotted and the slopes dR (k, l; z) / dz obtained by linear regression. 8th shows an example by means of the device according to 1 determined NA distribution over the image field 64 of the optical system 14 ,

In addition to the radii, the coordinates are given by the coordinates X (k, l, i) and Y (k, l; i) of the centers of the light spots 42 for the different z positions of the image capture device 28 , By means of a method analogous to the NA evaluation method, the change dX (k, l; z) / dz or dy (k, l; z) / dz of the center points is determined at an operating point z ₀ . From this, the output side telecentric of the optical system can be located 14 over the entire image field as follows:

Furthermore, by means of the device 20 according to 1 in the arrangement of the image capture device 28 in eg one of the positions 32 and 34 the lighting setting of the lighting system 12 be measured. The lighting setting defines a specific angular distribution of the test structure 24 radiating illumination radiation 36 opposite the optical axis 16 , The illumination radiation 36 generated in the plane of the pupil 18 a corresponding intensity distribution, which by means of the image capture device 28 can be made visible in the same position in the above-mentioned position. 9 shows this with the example of a dipole setting of the lighting. The in such a Dipolsetting from the optical system 14 emerging radiation is has two radiation cone 64 on. These meet in the picture plane 30 that is, at the focus position of the optical system 14 together. When arranging image acquisition Facility 28 in the position 32 or 34 form the two radiation cone 64 two disc-shaped pictures 66 a subaperture of the lighting system 12 on the image capture device 28 from. The pictures 66 are inside a light spot 42 which, as already mentioned, an image of the aperture or the pupil 18 of the optical system 14 is. 10 shows the light spot 42 according to 9 in plan view. Due to the high accuracy of the numerical aperture of the optical system 14 By means of the method according to the invention, the illumination setting can also be determined with a high absolute accuracy.

The device 20 is according to 1 into the microlithography exposure system 10 integrated, alternatively, it can be constructed as an independent measuring station, in the z. B. a projection lens before installation in the exposure system 10 is introduced for surveying. In the beam path between the optical system 14 and the image capture device 28 For example, transparent plane plates can be located. These do not produce any diffraction, so the detected light spots 42 not additionally smeared. However, alternatively, continuous image gratings can also be introduced into the beam path between the optical system 14 and the image capture device 28 be introduced. In this case, however, the image capture device must 28 so far opposite the picture plane 30 be shifted that the spatial modulation in the interferogram generated by the image grid due to their high spatial frequencies are no longer resolved.

In order that the pupil margin softening due to the diffraction (effective enlargement of the pupil) on the image grid remains manageable, the modulation range of the focus graduation should be selected such that the induced pupil radius change remains small compared to the pupil radius at the operating point z _o . In the event that grating in the beam path between the optical system 14 and the image capture device 28 are provided, the use of parceled or patched grids is advantageous.

10

Microlithography exposure system

12

lighting system

14

imaging optical system

16

optical axis

18

pupil

20

contraption for determining an optical property

22

mask

22a

mask

22b

mask

24

test structure

26

object level

28

Image capture device

28a

detection area

30

image plane

32

intrafokale position

34

extrafocal position

36

illumination radiation

38

outbound radiation

40

by running radiation beam

42

light spot

44

ideal edge profile

46

real edge profile

48

diffuser

50

Radiolucent main body

52

radiation-reducing or blocking layer

54

about radiant lighting

56

microlens

58

circle fit

60

intensity threshold

62

field

64

radiation cone

66

image the illumination sub-aperture

Claims (29)

Method for determining at least one optical property of an imaging optical system ( 14 ), which is used to map one in an object plane ( 26 ) of the optical system ( 14 ) arranged object in an associated image plane ( 30 ), comprising the following steps: arranging at least one test structure ( 24 ) in the object plane ( 26 ) of the optical system ( 14 ), - arranging an image capture device ( 28 ) in at least two different relative positions relative to the image plane ( 30 ) of the optical system ( 14 ), wherein in each of the at least two relative positions the image capture device ( 28 ) so far opposite the image plane ( 30 ) is offset from the optical system ( 14 ) by means of the test structure ( 24 ) one picture each ( 42 ) of the pupil ( 18 ) of the optical system ( 14 ) on the image capture device ( 28 ), and - detecting one of the optical system ( 14 ) by means of the test structure ( 24 ) on the image capture device ( 28 ) generated image ( 42 ) in each of the at least two relative positions by means of the image capture device ( 28 ). A method according to claim 1, characterized in that on the image capture device ( 28 ) generated image ( 42 ) of the pupil ( 18 ) has a maximum extent, the maximum extent of the image of the test structure in the image plane ( 30 ) exceeds by at least one order of magnitude. Method for determining at least one optical property of an imaging optical system ( 14 ), which is used to map one in an object plane ( 26 ) of the optical system ( 14 ) arranged object in an associated image plane ( 30 ), comprising the following steps: arranging at least one test structure ( 24 ) in the object plane ( 26 ) of the optical system ( 14 ), - arranging an image capture device ( 28 ) in at least two different relative positions relative to the image plane ( 30 ) of the optical system ( 14 ), wherein in each of the at least two relative positions the image capture device ( 28 ) so far opposite the image plane ( 30 ) is offset from the optical system ( 14 ) by means of the test structure ( 24 ) one picture each ( 42 ) on the image capture device ( 28 ) whose maximum extent is a maximum extent of the mapping of the test structure ( 24 ) in the image plane ( 30 ) exceeds by at least one order of magnitude, and - detecting one of the optical system ( 14 ) by means of the test structure ( 24 ) on the image capture device ( 28 ) generated image ( 42 ) in each of the at least two relative positions by means of the image capture device ( 28 ). Method according to one of the preceding claims, characterized in that in a first relative position ( 32 . 34 ) by means of the test structure ( 24 ) on the image capture device ( 28 ) generated image ( 42 ) has a maximum extension of at least 100 microns. Method according to one of the preceding claims, characterized in that the image capture device ( 28 ) in a first relative position ( 32 . 34 ) at least 50 μm with respect to the image plane ( 30 ) is offset. Method according to one of the preceding claims, characterized in that a plurality of test structures ( 24 ) at different positions of an object field in the object plane ( 26 ), the object field in each of the at least two relative positions of the optical system ( 14 ) in an image field ( 62 ) on the image capture device ( 28 ), as well as the respective image field ( 62 ) from the image capture device ( 28 ) and from this the distribution of the optical property of the optical system ( 14 ) depending on the position in the image field ( 62 ) is determined. Method according to one of the preceding claims, characterized by the step of determining the at least one optical property of the optical system ( 14 ) by evaluating the images captured in the various relative positions ( 42 ). Method according to one of the preceding claims, characterized in that the at least one optical property is the numerical aperture of the optical system ( 14 ). Method according to claim 8, characterized in that the numerical aperture of the optical system ( 14 ) with a resolution of less than 0.0001 is determined absolutely. Method according to one of the preceding claims, characterized in that an expansion, in particular a radius, of the means of the test structure ( 24 ) generated image ( 42 ) for each relative position is determined and from this the output-side numerical aperture of the optical system ( 14 ) is calculated. Method according to one of the preceding claims, characterized in that the at least one optical property is the telecentricity of the optical system ( 14 ). Method according to one of the preceding claims, characterized in that the center of gravity of the test device ( 24 ) generated image ( 42 ), in particular the center of gravity of the boundary ( 46 ) of the picture ( 42 ), is determined for each relative position and from this the output-side telecentricity of the optical system ( 14 ) is calculated. Method according to one of the preceding claims, characterized in that the image capture device ( 28 ) is arranged for rastered image acquisition and the size difference between images captured in the different relative positions ( 42 ) along a detection direction at least one distance between two grid points of the image capture device ( 28 ) is. Method according to one of the preceding claims, characterized in that the test structure ( 24 ) has a rounded shape, in particular is designed circular. Method according to one of the preceding claims, characterized in that the test structure ( 24 ) is punctiform, in particular as a punctiform opening in a shadow mask ( 20 ) or is formed as a point-shaped radiation-attenuating element in a basically radiation-permeable mask. Method according to one of the preceding claims, characterized in that the test structure ( 24 ) is illuminated with electromagnetic radiation of a predetermined illumination wavelength and the test structure ( 42 ) is dimensioned such that a maximum extent of the by means of the optical system ( 14 ) in the image plane ( 30 ) of the test structure is on the order of the illumination wavelength. Method according to one of the preceding claims, characterized in that the test structure ( 24 ) with highly incoherent electromagnetic radiation ( 36 . 54 ) is illuminated. Method according to one of the preceding claims, characterized by a in the illumination beam path ( 36 ) of the optical system ( 14 ) arranged spreading disc ( 48 ) and / or one on the test structure ( 24 ) focused microlens ( 56 ) in each case with respect to illuminating the test structure with respect to the input aperture ( 24 ). Method according to one of the preceding claims, characterized in that in at least one second relative position between the image capture device ( 28 ) and the image plane ( 30 ) the distance between the image capture device ( 28 ) and the image plane ( 30 ) relative to a first relative position ( 32 . 34 ) to one compared to the distance between the image capture device ( 28 ) and the image plane ( 30 ) is changed in the first relative position small distance, in particular by a distance is changed, which is smaller by at least an order of magnitude than the distance between the image capture device ( 28 ) and the image plane ( 30 ) in the first relative position ( 32 . 34 ). Method according to one of the preceding claims, characterized in that for switching between the different relative positions the image capture device ( 28 ) relative to the optical system ( 14 ) is shifted and / or tilted. Method according to one of the preceding claims, characterized in that the at least one test structure ( 24 ) on a microscope slide ( 22 ), in particular on a mask for a microlithography exposure apparatus ( 10 ) and for switching between the different relative positions of the slides ( 22 ) relative to the optical system ( 14 ) is shifted and / or tilted. Method according to one of the preceding claims, characterized in that a plurality of each parallel to the optical axis ( 16 ) of the optical system ( 14 ) staggered test structures ( 24 ) on a microscope slide ( 22 ), in particular a mask for a microlithography exposure apparatus ( 10 ) and the images in the various relative positions by means of a respective one of the staggered test structures ( 24 ) be generated. Method according to one of the preceding claims, characterized in that the Bestim optical property of one or more optical systems of a microlithography exposure apparatus ( 10 ), in particular on a projection objective ( 14 ) and / or a lighting system ( 12 ) of the microlithography exposure apparatus ( 10 ) is carried out. Method according to one of the preceding claims, characterized in that the at least one test structure ( 24 ) by means of a lighting system ( 12 ) with a certain angular distribution with respect to the optical axis of the optical system ( 14 ) having electromagnetic illumination radiation ( 36 ) and the method further comprises the following step: determining an angle-resolved intensity distribution of the illumination radiation ( 36 ) from the image capture device ( 28 ) captured image ( 42 ) in a first relative position. A method according to claim 24, characterized in that for determining the angle-resolved intensity distribution an edge course ( 46 ) of the captured image ( 42 ) as well as a location within the boundary ( 46 ) ( 66 ) increased radiation intensity in the image ( 42 ) and from this the angle-resolved intensity distribution with respect to an aperture diaphragm ( 18 ) of the optical system ( 14 ) is determined. Contraption ( 20 ) for determining at least one optical property of an imaging optical system ( 14 ), which is particularly adapted to carry out the method according to any one of the preceding claims, wherein the optical system ( 14 ) for mapping one in an object plane ( 26 ) of the optical system ( 14 ) arranged object in an associated image plane ( 30 ) and the device has at least one test structure ( 24 ) and an image capture device ( 28 ) and designed to provide the at least one test structure ( 24 ) in the object plane ( 26 ) of the optical system ( 14 ) and the image capture device ( 26 ) in at least two different relative positions relative to the image plane of the optical system ( 14 ) and thereby in each of the at least two relative positions, the image capture device ( 28 ) so far opposite the image plane ( 30 ) to arrange that of the optical system ( 14 ) by means of the test structure ( 24 ) one picture each ( 42 ) of the pupil ( 18 ) of the optical system ( 14 ) on the image capture device ( 28 ), and the image capture device ( 28 ), one of the optical system ( 14 ) by means of the test structure ( 24 ) on the image capture device ( 28 ) generated image ( 42 ) in each of the at least two relative positions. Contraption ( 20 ) for determining at least one optical property of an imaging optical system ( 14 ), which is particularly adapted to carry out the method according to one of claims 1 to 24, wherein the optical system ( 14 ) for mapping one in an object plane ( 26 ) of the optical system ( 14 ) arranged object in an associated image plane ( 30 ) and the device has at least one test structure ( 24 ) and an image capture device ( 28 ) and designed to provide the at least one test structure ( 24 ) in the object plane ( 26 ) of the optical system ( 14 ) and the image capture device ( 28 ) in at least two different relative positions relative to the image plane ( 30 ) of the optical system ( 14 ) and thereby in each of the at least two relative positions, the image capture device ( 28 ) so far opposite the image plane ( 30 ) to arrange that of the optical system ( 14 ) by means of the test structure ( 24 ) one picture each ( 42 ) on the image capture device ( 28 ) whose maximum extent is a maximum extent of the mapping of the test structure ( 24 ) in the image plane ( 30 ) exceeds by at least one order of magnitude, and the image capture device ( 28 ), one of the optical system ( 14 ) by means of the test structure ( 24 ) on the image capture device ( 28 ) in each of the at least two relative positions. Apparatus according to claim 26 or 27, characterized by an evaluation device, which is designed, the at least one optical property of the optical system ( 14 ) by evaluating the images captured in the various relative positions ( 42 ). Microlithography exposure system ( 10 ) with a lighting system ( 12 ) and / or a projection lens ( 14 ) as well as a device ( 20 ) according to one of claims 26 to 28 for determining an imaging property of the illumination system ( 12 ) and / or the projection lens ( 14 ).