DE102022203999A1 - Method for calibrating a diffractive measurement structure, device for calibrating a diffractive measurement structure and lithography system - Google Patents

Abstract

The invention relates to a method for calibrating a diffractive measurement structure (2) to form a measurement wave front of a measurement radiation (3) incident on the measurement structure (2), in particular a computer-generated hologram, the measurement structure (2) being illuminated with a calibration radiation (5). and the calibration radiation (5) is diffracted by the measurement structure (2), and- a plurality of images of the calibration radiation (5) are recorded, which differ at least in part with regard to a region (7) of the measurement structure (2) that contributes to a respective image. distinguish, and- at least one property of the measurement structure (2) is determined from the images.According to the invention, it is provided that- a main beam angle and an angular distribution of the calibration radiation (5) are set according to the measurement radiation (3) expected to be incident on the measurement structure (2). are, and- a wavelength of the calibration radiation (5) according to the expected wavelength of the measuring line measurement (3) is selected, and- a phase and/or amplitude of the calibration radiation (5) directly at the measurement structure (2) is reconstructed, and- the at least one property of the measurement structure (2 ) is closed.

Description

The invention relates to a method for calibrating a diffractive measurement structure for forming a measurement wave front of a measurement radiation incident on the measurement structure, in particular a computer-generated hologram, the measurement structure being illuminated with calibration radiation and the calibration radiation being diffracted by the measurement structure, and a plurality of images of the calibration radiation is recorded, which differ at least in part with regard to a region of the measurement structure contributing to a respective image, and at least one property of the measurement structure is determined from the images.

The invention also relates to a device for calibrating a diffractive measurement structure for forming a measurement wavefront of a measurement radiation incident on the measurement structure, having a calibration radiation source for forming a calibration radiation, which can be diffracted by the measurement structure, and a positioning device for illuminating the measurement structure with the calibration radiation on several different Areas, and a detection device for recording a plurality of images of the calibration radiation, and a computing device for determining at least one property of the measurement structure from the images.

The invention also relates to a lithography system, in particular a projection exposure system for semiconductor lithography, having an illumination system with a radiation source and an optical system which has at least one optical element.

Optical elements for guiding and shaping radiation in projection exposure systems are known from the prior art. In the known optical elements, a surface of the optical element often guides and shapes the light waves incident on the optical element. Precise control of the shape of the surface is therefore of particular advantage in order to form an exact wavefront with the desired properties.

Lithography systems are known from the prior art which use ultraviolet radiation, in particular DUV (deep ultraviolet) and/or EUV (extreme ultraviolet) light, in order to produce microlithographic structures with the greatest precision. In this case, the light from a radiation source is directed via a number of mirrors to a wafer to be exposed. An exact formation of the surface shape of the mirror makes a decisive contribution to the quality of the exposure.

Since the accuracy requirements on the optical elements of a lithography system, in particular on mirror surfaces, amount to fractions of nanometers, for example, it is known from the prior art to use interferometric measuring methods and devices to check the quality of the optical elements of the lithography system.

It is known from the prior art to use diffractive measuring structures, in particular computer-generated holograms, to check the optical surface of mirrors, with the measuring structure forming a wavefront which corresponds to the desired shape of the optical element to be checked. Deviations of the actual shape of the mirror from a target shape of the mirror are determined according to the prior art using interferometric methods.

The accuracy with which the wavefront can be formed and thus also the accuracy with which the optical surface can be checked depends on the manufacturing quality of the diffractive measurement structure.

It is known from the prior art to calibrate the diffractive measurement structure.

The generic DE 10 2017 221 005 A1 discloses a method and a device for calibrating a diffractive measurement structure.

According to the general state of the art, diffractive optical masks and/or diffractive gratings or more generally diffractive measuring structures are often used in beam paths of optical measuring systems in order to enable a measuring technique. Test towers for mirror pass measurement technology using computer-generated holograms (CGH) as measurement structures are known from the prior art. Furthermore, absorbing measuring gratings for system qualifications and/or masks for measuring imaging qualities are known.

What the aforementioned measurement techniques known from the prior art have in common is that optical properties of the measurement techniques or precise knowledge of the optical properties of the components of the measurement structures have a major influence on the measurement accuracy that can be achieved. Properties of the diffractive measurement structures that are not precisely known can lead to relevant error contributions, in particular for a required measurement accuracy in the nanometer range or below.

The approaches described below are known from the prior art for avoiding relevant error contributions.

Undesirable error contributions can be minimized by optimizing the design of the diffractive measurement structure, in particular optical masks. For example, it is known to optimize the geometries of diaphragms in such a way that a description using simple mask models, in particular Kirchhoff's mask models, represents the actual optical properties of the diaphragm with sufficient accuracy, so that the computing effort can be reduced.

If, for example, the geometry and the material properties, in particular the refractive index of a diffractive measurement structure, are known with sufficient accuracy, the optical properties of the diffractive measurement structure can be calculated using Maxwell solvers, for example the finite element method or RCWA methods, in order to thereby determine the contributions of the measurement structure to eliminate a measurement signal algorithmically.

The above-described approaches known from the prior art have fundamental limitations. In the case of the design optimization of an optical measurement structure, the available materials with finite refractive indices and tolerances in possible manufacturing processes restrict a solution form.

In the case of the above-described computational prediction of the optical properties, the accuracy with which the geometry of the measurement structure, including manufacturing errors, is known and the accuracy of the computational models limit the accuracy of the prediction.

A complexity of the solution approaches in both cases stems from the necessary precise knowledge and control of the mask material and its distribution in the three-dimensional volume of the measurement structure.

The object of the invention is therefore to create a further method in which the light is measured directly at a passage through the measurement structure. Information about the measurement structure itself, in particular information about a geometry and/or a material, is neither required nor obtained.

The disadvantage of the methods known from the prior art is that a great deal of time is required in order to be able to determine the shape of the optical surface with the desired reliability and precision.

The object of the present invention is to create a method for calibrating a diffractive measurement structure which avoids the disadvantages of the prior art, in particular enabling a time-efficient and precise determination of the shape of the surface.

According to the invention, this object is achieved by a method having the features specified in claim 1.

The present invention is also based on the object of creating a device for calibrating a diffractive measurement structure which avoids the disadvantages of the prior art, in particular enabling a time-efficient and precise determination of the shape of the surface.

According to the invention, this object is achieved by a device having the features specified in claim 8 .

The present invention is also based on the object of creating a lithography system which avoids the disadvantages of the prior art, in particular having optical elements with precisely shaped optical surfaces.

According to the invention, this object is achieved by a lithography system having the features specified in claim 15.

• - die Messstruktur mit einer Kalibrierstrahlung beleuchtet wird und die Kalibrierstrahlung durch die Messstruktur gebeugt, und
• - eine Mehrzahl von Bildern der Kalibrierstrahlung aufgenommen, welche sich wenigstens zum Teil hinsichtlich eines zu einem jeweiligen Bild beitragenden Bereichs der Messstruktur unterscheiden, und
• - wenigstens eine Eigenschaft der Messstruktur aus den Bildern ermittelt.

In the method according to the invention for calibrating a diffractive measurement structure for forming a measurement wave front of a measurement radiation incident on the measurement structure, in particular a computer-generated hologram

• - the measurement structure is illuminated with a calibration radiation and the calibration radiation is diffracted by the measurement structure, and
• - a plurality of images of the calibration radiation recorded, which differ at least in part with regard to a region of the measurement structure that contributes to a respective image, and
• - determines at least one property of the measurement structure from the images.

• - ein Hauptstrahlwinkel und eine Winkelverteilung der Kalibrierstrahlung gemäß der zu erwartenden auf die Messstruktur einfallenden Messstrahlung eingestellt werden, und
• - eine Wellenlänge der Kalibrierstrahlung gemäß der zu erwartenden Wellenlänge der Messstrahlung gewählt wird, und
• - eine unmittelbar an der Messstruktur herrschende Phase und/oder eine Amplitude der Kalibrierstrahlung rekonstruiert wird, und
• - aus der Phase und/oder der Amplitude auf die wenigstens eine Eigenschaft der Messstruktur geschlossen wird.

According to the invention it is further provided that

• - a main ray angle and an angular distribution of the calibration radiation are set according to the measurement radiation to be expected incident on the measurement structure, and
• - a wavelength of the calibration radiation is selected according to the expected wavelength of the measurement radiation, and
• - a phase prevailing directly at the measurement structure and/or an amplitude of the calibration radiation is reconstructed, and
• - the at least one property of the measurement structure is inferred from the phase and/or the amplitude.

The method according to the invention has the advantage that, during the calibration, the incidence of light is experimentally simulated to a certain extent in the subsequent measurement application of the measurement structure. As a result, optical properties of the diffractive measurement structure can be measured directly without having to know details about an exact geometry or material properties of the diffractive measurement structure. As a result, this method relies neither on high-precision Maxwell solvers for calculating light propagation through the diffractive measurement structure and/or on the diffractive measurement structure, nor on high-precision measurement techniques for determining a geometry and/or refractive indices of the diffractive measurement structure. Both of the aforementioned aspects can cause a limitation in the qualification of computer-generated holograms, such as are used to check optical surfaces for EUV projection exposure systems.

Since no detailed knowledge of a geometry and/or a material of the measurement structure is required, the method described above can be applied to practically any other optical grating with small, diffractive structures. Exemplary applications can represent phase gratings, such as computer-generated holograms in particular, amplitude gratings, such as measuring gratings in particular, and optical gratings, in particular EUV masks.

In the method according to the invention, an interaction of the calibration radiation with the measurement structure, which is to be used for a measurement application, is measured directly. In this case, the phase and/or the amplitude of the calibration radiation is reconstructed after it has passed through or after it has been reflected at the mask.

If the incident calibration radiation in such a calibration measurement has the same wavelengths and the same angles of incidence or incidence angle distributions as in the measurement application and the measurement structure, all relevant optical properties of the measurement structure for the measurement application can be determined in this way. The method according to the invention therefore aims to measure an optical effect specifically for wavelength distributions and angle of incidence distributions defined by the measurement application. To determine this effect, images of the measurement structure are recorded and evaluated using a suitable method.

The method according to the invention is described in connection with diffractive measurement structures. In particular, these can be computer-generated holograms, optical measurement masks or measurement grids. Alternatively, the disclosure of the method can also be understood to apply to other diffractive structures, such as optical gratings that are operated in reflection, in particular EUV masks of EUV projection exposure systems.

If properties of the diffractive measurement structure are unknown, this can often lead to measurement errors. If, however, precise knowledge about the properties of the measurement structure is obtained, this generally makes it possible, at least in principle, to compensate for any deviations from an ideal mask by means of computational methods.

An interaction of the diffractive measurement structure with the calibration radiation can be described via a transfer function J(x,k) according to the formula (1) explained later. Here x is the coordinate in spatial space and k is the wave vector of the incident calibration radiation, i.e. the angle of incidence. For a choice of (x,k), J(x,k) has the form of a complex-valued 2x2 Jones matrix relating an amplitude of the incident electromagnetic field Ein to an amplitude of the output field _Eout and defined for a particular wavelength λ.

• - eine Polarisationsrichtung der Kalibrierstrahlung vor einem Einfall auf die Messstruktur eingestellt wird, und
• - die Kalibrierstrahlung vor der Aufnahme der Bilder polarisationsgefiltert wird.

In an advantageous development of the method according to the invention, it can be provided that

• - a polarization direction of the calibration radiation is set before it is incident on the measurement structure, and
• - the calibration radiation is polarization-filtered before the images are recorded.

Including the direction of polarization of the calibration radiation in the method has the advantage that the precision of the calibration can be increased as a result.

In general, diffractive measurement structures can have polarization-dependent and/or polarization-changing properties. Consequently, even with precise knowledge of an input polarization state Ein, the output polarization state of E _out can remain unknown after a passage through the measurement structure and/or a reflection at the measurement structure. Formula (1) describes the relationship between the input field Ein and the output field E _out . where J represents the Jones matrix. $$\left(\begin{array}{c}{E}_{O\mathrm{and}t,x}\left(x,k\right)\\ E_{O\mathrm{and}t,y}\left(x,k\right)\end{array}\right)=\left(\begin{array}{c}{J}_{11}\left(x,k\right)\\ J_{21}\left(x,k\right)\end{array}\begin{array}{c}{J}_{12}\left(x,k\right)\\ J_{22}\left(x,k\right)\end{array}\right)\left(\begin{array}{c}{E}_{in,x}\left(x,k\right)\\ E_{in,y}\left(x,k\right)\end{array}\right)$$

In order to fully determine an optical effect J of the measurement structure, the field amplitudes E _in,x , E _in,y , E _out,x and E _out,y can first be determined. E _in,x and E in, _y can be set in a defined manner, for example, by a polarizer device in an illumination unit for the calibration radiation. E _out,x and E _out,y can advantageously be reconstructed from measurement data, in particular from the images.

In the calibration method, it can be provided that the images are recorded as intensity images.

If, for example, E _out,x( x, k) is an electromagnetic field distribution immediately behind or on the measurement structure and is defined by T _n,x (x,k) and x _sensor and T _n,y (x,k, x _sensor ). Given the transfer function of the measurement setup for x-polarized and/or y-polarized components of the calibration radiation, formula (2) can be formulated. In this case, Eout(x,k) can be converted into an electromagnetic field distribution E _sensor,n (x _sensor ) in the nth measurement position on the sensor by a convolution. $$E_{sensO\mathrm{right},n}\left(x_{sensO\mathrm{right}}\right)=\left(\begin{array}{c}{E}_{sensO\mathrm{right},n,x}\left(x,k\right)\\ E_{sensO\mathrm{right},n,y}\left(x,k\right)\end{array}\right)=\left(\begin{array}{c}{T}_{n,x}\left(x,k,x_{sensO\mathrm{right}}\right)\cdot \\ T_{n,y}\left(x,k,x_{sensO\mathrm{right}}\right)\end{array}\begin{array}{c}{E}_{O\mathrm{and}t,x}\left(x,k\right)\\ E_{O\mathrm{and}t,y}\left(x,k\right)\end{array}\right)$$

When the calibration radiation is recorded on a measurement sensor in the form of an intensity image, a measurement signal of the intensity image is proportional to the intensity of the calibration radiation.

Formula (3) describes the intensity distribution S at the sensor location where the intensity image is recorded. The intensity S represents a superimposition of the contributions from E _out,x and E _out,y . $$\begin{array}{l}{S}_{sensO\mathrm{right},n}\left(x_{sensO\mathrm{right}}\right)={\left|E_{sensO\mathrm{right},n,x}\left(x,k\right)\right|}^2+{\left|E_{sensO\mathrm{right},n,y}\left(x,k\right)\right|}^2\\ ={\left|T_{n,x}\left(x,k,x_{sensO\mathrm{right}}\right)\cdot E_{O\mathrm{and}t,x}\left(x,k\right)\right|}^2\\ +{\left|T_{n,y}\left(x,k,x_{sensO\mathrm{right}}\right)\cdot E_{O\mathrm{and}t,y}\left(x,k\right)\right|}^2\end{array}$$

In order to determine Eout,x and Eout,y individually, it is advantageous if variations in the transfer functions T _n,x and T _n,y differ sufficiently clearly from one another over individual measuring points n.

This can be achieved by introducing a polarization filter device, in particular a polarizing element, into a beam path of the calibration radiation downstream of the measurement structure to be tested, with n-fold modulation taking place between the recording of the individual images. With sufficiently precise knowledge of a polarization effect of the polarizing element, the contributions from E _out,x and E _out,y can then be mathematically separated.

It is of particular advantage if, for this purpose, the polarization filter device is designed and set up as a linear polarization analyzer to strongly suppress a polarization orientation.

Provision can be made for the polarization direction, with respect to which the calibration radiation is polarization-filtered, to be varied.

In particular, it can be provided that the direction of polarization, according to which the calibration radiation is filtered, is rotated.

By rotating the polarization direction, in particular by rotating the polarization analyzer, contributions from individual polarization components to the measurement signal S can then be determined individually and sequentially.

• - die Bereiche der Messstruktur durch die Kalibrierstrahlung kohärent und kollimiert beleuchtet werden, und
• - die Bereiche mittels einer Abbildungsoptik in eine Bildebene abgebildet werden, und
• - die Bilder in der Bildebene als Luftbilder aufgenommenen werden.

In an advantageous development of the method according to the invention, it can be provided that

• - the areas of the measurement structure are illuminated coherently and collimated by the calibration radiation, and
• - the areas are imaged in an image plane by means of imaging optics, and
• - the images in the image plane are recorded as aerial photographs.

When using aerial measurement technology, a square of the amplitude distribution at the point of passage or reflection at the measurement structure can be recorded as an image. This gives a direct impression of the amplitude distribution at the point of passage.

It can be provided that the diameter of the areas of the measurement structure to be measured is 10 μm to 10000 μm, preferably 50 μm to 1000 μm. An optical effect of the measurement structure can be assumed to be constant over such a diameter. Accordingly, in such selected areas, an incidence direction of the measurement radiation and/or the calibration radiation and a direction of the diffraction order emanating from the measurement structure change only to a small extent.

• - eine Position der Messstruktur gegenüber der Kalibrierstrahlung lateral und axial variiert wird
• - für jede Variation der Position der Messstruktur wenigstens ein Bild aufgenommen wird.

In an advantageous development of the method according to the invention, it can be provided that

• - a position of the measurement structure relative to the calibration radiation is varied laterally and axially
• - At least one image is recorded for each variation in the position of the measurement structure.

Due to a lateral variation of the measurement structure compared to the calibration radiation, the entire measurement structure can be scanned by a relatively small beam of the calibration radiation. As a result, the areas can advantageously be kept small.

By varying the position of the measurement structure axially, aerial images of the measurement structure can be recorded in different defocus positions. As a result, an angle of incidence of the calibration radiation on the measurement structure remains constant, while a part of the calibration radiation emanating from the respective region that contributes to the formation of the aerial image is varied.

Accordingly, aerial photos can be taken in different defocus positions of the area to be measured. With a suitable evaluation method, an amplitude and/or a phase of the electromagnetic field distribution of the calibration radiation can be reconstructed from the image stack of aerial images directly after passing through the measurement structure in an object plane.

If, in particular, an amplitude and a phase in the object plane are known, a field distribution and thus also a phase distribution in individual diffraction orders of the calibration radiation or the measurement radiation can be determined by a Fourier transformation.

• - die Kalibrierstrahlung mittels einer Blendeneinrichtung beschnitten wird, und
• - die Kalibrierstrahlung mittels einer Fokussieroptik auf die Bereiche der Messstruktur fokussiert wird, und
• - die Bereiche der Messstruktur durch die Kalibrierstrahlung kohärent und fokussiert beleuchtet werden, und
• - die Bilder in einem Fernfeld der Kalibrierstrahlung als Beugungsbilder aufgenommenen werden.

In an advantageous development of the method according to the invention, it can be provided that

• - the calibration radiation is cut off by means of an aperture device, and
• - the calibration radiation is focused onto the areas of the measurement structure by means of focusing optics, and
• - the areas of the measurement structure are illuminated coherently and in a focused manner by the calibration radiation, and
• - the images are recorded as diffraction images in a far field of the calibration radiation.

In contrast to the aerial photo measurement technology described above, in the embodiment described above, which is also referred to as coherent diffraction imaging (CDI), the calibration radiation is recorded in a far field behind the measurement structure. A defined, coherently illuminated small illumination spot is generated on the area of the measurement structure to be measured.

Provision can be made for an illumination spot to be formed with a diameter of 1 μm to 1000 μm, preferably 5 μm to 200 μm. In particular, it can be provided that the illumination spot corresponds to the area to be examined.

Provision can be made for an illumination cone of the calibration radiation to have a finite aperture angle due to the spatially limited illumination spot. As a result, the illumination of the area to be measured is composed of more than one angle. In order to achieve a sufficiently precise statement for the respective angle of incidence of the expected measurement radiation, it is advantageous if either a numerical aperture of the illumination is chosen small enough or a suitable calibration method is used to extract optical properties in the expected measurement application.

• - eine Position der Messstruktur gegenüber der Kalibrierstrahlung lateral derart variiert wird, dass jeder Bereich der Messstruktur von der Kalibrierstrahlung wenigstens zweimal bestrichen wird, und
• - für jede Variation der Position der Messstruktur wenigstens ein Bild aufgenommen wird.

In an advantageous development of the method according to the invention, it can be provided that

• - a position of the measurement structure relative to the calibration radiation is varied laterally in such a way that each area of the measurement structure is covered at least twice by the calibration radiation, and
• - At least one image is recorded for each variation in the position of the measurement structure.

Provision can be made for a large number of diffraction images to be recorded for a measurement in a region of the measurement structure. Between the measurements of the individual diffraction images, the measurement structure is laterally shifted relative to the illumination spot formed by the calibration radiation.

Provision can be made for the displacement position of the measurement structure to be selected in such a way that the illumination spot covers every location on the measurement structure within the area to be measured at least twice. Provision can in particular be made for the illumination spot to overlap in different measurements.

Proceeding from this, it can be provided that the phase and the amplitude of the electromagnetic field distribution is determined directly behind and/or on the measurement structure and in the diffraction image in the far field behind the measurement structure using a suitable method.

Such a measurement method is also known as ptychography.

In an advantageous development of the method according to the invention, it can be provided that the images are recorded after the calibration radiation has passed through the measurement structure and/or after the calibration radiation has been reflected at the measurement structure.

If the diffractive measurement structure is operated in a measurement application in a passage and/or a reflection, it is also advantageous if the calibration method is carried out accordingly.

The invention also relates to a device having the features specified in claim 8 .

• - eine Kalibrierstrahlungsquelle zur Ausbildung einer Kalibrierstrahlung, welche durch die Messstruktur beugbar ist, und
• - eine Positioniereinrichtung zur Beleuchtung der Messstruktur mit der Kalibrierstrahlung auf mehreren unterschiedlichen Bereichen, und
• - eine Erfassungseinrichtung zur Aufnahme einer Mehrzahl von Bildern der Kalibrierstrahlung, und
• - eine Recheneinrichtung zur Ermittlung wenigstens einer Eigenschaft der Messstruktur aus den Bildern.

The device according to the invention for calibrating a diffractive measurement structure for forming a measurement wave front of a measurement radiation incident on the measurement structure has at least the following components:

• - a calibration radiation source for forming a calibration radiation, which can be diffracted by the measurement structure, and
• - a positioning device for illuminating the measurement structure with the calibration radiation in a number of different areas, and
• - a detection device for recording a plurality of images of the calibration radiation, and
• - A computing device for determining at least one property of the measurement structure from the images.

• - eine Steuereinrichtung vorgesehen und eingerichtet ist, einen Hauptstrahlwinkel und eine Winkelverteilung der Kalibrierstrahlung gemäß der zu erwartenden auf die Messstruktur einfallenden Messstrahlung einzustellen, und
• - eine Wellenlänge der Kalibrierstrahlung wenigstens annähernd der zu erwartenden Wellenlänge der Messstrahlung entspricht, und
• - die Recheneinrichtung eingerichtet ist, eine unmittelbar nach einem Durchtritt durch und/oder einer Reflexion an der Messstruktur herrschende Phase und/oder Amplitude der Kalibrierstrahlung zu rekonstruieren

According to the invention it is provided that

• - a control device is provided and set up to set a main beam angle and an angular distribution of the calibration radiation according to the measurement radiation to be expected incident on the measurement structure, and
• - a wavelength of the calibration radiation corresponds at least approximately to the expected wavelength of the measurement radiation, and
• the computing device is set up to reconstruct a phase and/or amplitude of the calibration radiation that prevails immediately after it has passed through and/or been reflected at the measurement structure

The fits of mirrors, in particular of EUV mirrors, can be measured by means of measuring structures. The measurement application for which the measurement structure is intended takes place in a measurement setup designed as an interferometer, and a desired interferometer signal is created here from a transit time difference in two interferometer arms each. If a different phase offset in the useful diffraction orders is imposed on the measurement radiation due to passage through the measurement structure, in particular the computer-generated hologram, this generates an interference signal in an interferogram.

In order to achieve the necessary measurement accuracy, it is advantageous if the optical properties, i. H. the phases in the individual diffraction orders are known with sufficient accuracy. If the phases are known with sufficient accuracy, an algorithmic correction of the measurement signal can be implemented in the measurement application to eliminate this interference signal.

The phases in the diffraction orders can be measured directly by means of the device according to the invention, without previously requiring precise information about a geometry and/or materials of the measurement structure, in particular of the computer-generated hologram.

It can be provided that the wavelength or a wavelength spectrum of the measurement radiation or the calibration radiation is 100 nm to 1000 nm, preferably 400 nm to 600 nm, particularly preferably 532 nm.

• - eine Polarisatoreinrichtung vorgesehen und eingerichtet ist, eine Polarisationsrichtung der Kalibrierstrahlung vor einem Einfall auf die Messstruktur einzustellen, und
• - eine Polarisationsfiltereinrichtung vorgesehen und eingerichtet ist, die Kalibrierstrahlung vor der Aufnahme der Bilder hinsichtlich ihrer Polarisationsrichtung zu filtern.

In an advantageous development of the device according to the invention, it can be provided that

• - a polarizer device is provided and set up to set a polarization direction of the calibration radiation before it is incident on the measurement structure, and
• - A polarization filter device is provided and configured to filter the calibration radiation with regard to its polarization direction before the images are recorded.

The use of a polarization filter device, in particular a polarization analyzer, in a beam path of the calibration radiation behind the measurement structure has the advantage that polarization orientations of the calibration radiation that impinge on the detection device can be selected. This can simplify an evaluation of the images. It is of particular advantage if the measurement radiation incident on the measurement structure is already linearly polarized by means of the polarization device.

• - die Positioniereinrichtung eingerichtet ist, eine Position der Messstruktur gegenüber der Kalibrierstrahlung lateral und/oder axial zu variieren.

In an advantageous development of the device according to the invention, it can be provided that

• - The positioning device is set up to vary a position of the measurement structure relative to the calibration radiation laterally and/or axially.

The positioning device is preferably set up to support and position the measurement structure. A lateral movability of the positioning device enables a movement of the area to be measured on the measurement structure to the calibration radiation. An axial displacement of the positioning device or the measurement structure enables imaging of the measurement structure during a measurement sequence in different defocus positions.

• - eine Blendeneinrichtung vorgesehen und eingerichtet ist, die Kalibrierstrahlung zu beschneiden, und
• - eine Fokussieroptik vorgesehen und eingerichtet ist, die Kalibrierstrahlung auf die Bereiche der Messstruktur zu fokussieren, und
• - die Bereiche der Messstruktur durch die Kalibrierstrahlung kohärent und fokussiert beleuchtbar sind, und
• - die Erfassungseinrichtung in einem Fernfeld der Kalibrierstrahlung angeordnet ist.

In an advantageous development of the device according to the invention, it can be provided that

• - an aperture device is provided and set up to cut the calibration radiation, and
• - focusing optics are provided and set up to focus the calibration radiation onto the areas of the measurement structure, and
• - the areas of the measurement structure can be illuminated by the calibration radiation in a coherent and focused manner, and
• - the detection device is arranged in a far field of the calibration radiation.

It can be provided that the diaphragm device and the calibration radiation source as well as the polarizer device are part of an illumination unit.

Provision can be made for the focusing optics to focus the calibration radiation onto a stationary illumination spot and for the measurement structure to be positioned relative to the illumination spot. As a result, the focusing optics can focus the calibration radiation onto different areas by displacing the measurement structure.

It can be provided that the focusing optics, the polarizer device, the aperture device and the calibration radiation source generate a defined, coherently illuminated, small illumination spot on the CGH, which is preferably identical to the area to be measured.

It can be advantageous if the diameter of the illumination spot is between 1 μm and 1000 μm, preferably between 5 μm and 200 μm.

In particular, it can be provided that the calibration radiation source is designed as a coherent and collimated illumination source, which illuminates the diaphragm device, as a result of which the illumination spot is defined. The aperture of the aperture device can be imaged onto the measurement structure by means of the focusing optics.

Provision can be made for the illumination unit to be set in such a way that a wavelength, a main beam angle on the measurement structure and polarization orientations of the calibration radiation are adapted to use in the measurement application.

In this case, it is advantageous if the positioning device is set up to laterally displace the measurement structure. In this case, the positioning device serves to position the measurement structure and to record a plurality of diffraction images when the measurement structure positions are slightly shifted relative to the calibration radiation or to the illumination spot.

Because the detector is positioned in the far field behind the measurement structure, a diffraction image can be recorded.

Provision can be made for the detector to be positioned in such a way that the diffraction image can be recorded in a Fraunhofer regime, in particular positioned at a very large distance from the measurement structure. However, this is not a fundamental requirement, but rather facilitates an evaluation. The Fraunhofer regime will be discussed again later.

In an advantageous development of the device according to the invention, it can be provided that a Fourier optics device is arranged between the measurement structure and the detection device and set up to image the calibration radiation to infinity in such a way that the detection device is arranged in a Fraunhofer far field of the calibration radiation.

To facilitate the evaluation, a Fraunhofer regime can be formed by the Fourier optics device. In this way, space can be saved, for example, since the registering device device can be arranged close to the measurement structure and only space for the Fourier optics device must be available between the measurement structure and the detection device.

• - die Bereiche der Messstruktur durch die Kalibrierstrahlung kohärent und kollimiert beleuchtbar sind, und
• - eine Abbildungsoptik vorgesehen und eingerichtet ist, die Bereiche in eine Bildebene abzubilden, und
• - die Erfassungseinrichtung in der Bildebene angeordnet ist.

In an advantageous development of the device according to the invention, it can be provided that

• - the areas of the measurement structure can be illuminated in a coherent and collimated manner by the calibration radiation, and
• - imaging optics are provided and set up to image the areas in an image plane, and
• - The detection device is arranged in the image plane.

The embodiment of the device according to the invention described above has the advantage that the amplitude distribution at the location of the measurement structure is thereby mapped onto the detection device, as a result of which a tangible, direct impression of the amplitude distribution can arise.

Provision can be made for the calibration radiation source and/or the control device to be set up to generate a coherent incident illumination source of the calibration radiation with a defined wavelength at a defined angle and in a defined polarization state. Provision can in particular be made to set an illumination of the measurement structure with the calibration radiation using the calibration radiation source and/or the control device in such a way that a corresponding illumination setting is adjusted in the measurement application of the measurement structure for each measured area of the measurement structure.

It can be provided that a numerical aperture of the imaging optics is selected in such a way that at least those useful orders of diffraction are detected which are also detected in an expected measurement application of the measurement structure.

It can be provided that a numerical aperture when entering the imaging optics is between 0.1 and 1.5, preferably between 0.3 and 0.9.

It can be provided that the imaging optics are designed to have a magnifying effect and preferably have a scale of 10x to 10,000x, preferably 100x to 1,000x, preferably 500x. As a result, a signal from structures of the diffractive measurement structure, which are usually small, can also be detected.

In an advantageous development of the device according to the invention, it can be provided that a beam splitter device is provided and set up to direct the radiation reflected from the measurement structure to the detection device and/or to direct the calibration radiation to the measurement structure.

By using the beam splitter device, the device can also be operated in reflection. As a result, measurement structures that work in reflection or also EUV masks can also be measured in a simple manner using the device.

The invention also relates to a lithography system having the features specified in claim 15.

The lithography system according to the invention, in particular a projection exposure system for semiconductor lithography, comprises an illumination system with a radiation source and an optical system which has at least one optical element. According to the invention, it is provided that at least one of the optical elements has an optical surface, which is at least partially measured with a measuring structure, which is at least partially measured using the above-described method according to the invention or one of its embodiments and/or at least partially using the above-described device according to the invention or one of its embodiments is calibrated.

The lithography system according to the invention has the advantage that it has optical elements that are produced with high precision and at the same time cost-effectively, since the measurement structures used for checking and qualifying the optical elements can be calibrated quickly and precisely.

The method described above and the device described above for qualifying diffractive measurement structures for mirrors, in particular EUV mirrors, are of particular advantage. The invention is therefore particularly suitable for EUV projection exposure systems.

However, diffractive measurement structures for qualifying lenses can also be calibrated using the method according to the invention and/or the device according to the invention. The invention thus also offers great advantages for use in DUV projection exposure systems.

Features that have been described in connection with one of the objects of the invention, specifically given by the method according to the invention, the device according to the invention and the lithography system according to the invention, can also be advantageously implemented for the other objects of the invention. Likewise, advantages that were mentioned in connection with one of the objects of the invention can also be understood in relation to the other objects of the invention.

In addition, it should be noted that terms such as "comprising", "having" or "with" do not exclude any other features or steps. Furthermore, terms such as "a" or "that" which indicate a singular number of steps or features do not exclude a plurality of features or steps - and vice versa.

In a puristic embodiment of the invention, however, it can also be provided that the features introduced in the invention with the terms “comprising”, “having” or “with” are listed exhaustively. Accordingly, one or more listings of features may be considered complete within the scope of the invention, e.g. considered for each claim. The invention can consist exclusively of the features mentioned in claim 1, for example.

It should be mentioned that designations such as “first” or “second” etc. are primarily used for reasons of distinguishing the respective device or method features and are not necessarily intended to indicate that features are mutually dependent or related to one another.

Exemplary embodiments of the invention are described in more detail below with reference to the drawing.

The figures each show preferred exemplary embodiments in which individual features of the present invention are shown in combination with one another. Features of an exemplary embodiment can also be implemented separately from the other features of the same exemplary embodiment and can accordingly easily be combined with features of other exemplary embodiments by a person skilled in the art to form further meaningful combinations and sub-combinations.

Elements with the same function are provided with the same reference symbols in the figures.

• 1 eine EUV-Projektionsbelichtungsanlage im Meridionalschnitt;
• 2 eine DUV-Projektionsbelichtungsanlage;
• 3 eine schematische Darstellung einer möglichen Ausführungsform der erfindungsgemäßen Vorrichtung;
• 4 eine schematische Darstellung einer weiteren möglichen Ausführungsform der erfindungsgemäßen Vorrichtung;
• 5 eine schematische Darstellung einer Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 4;
• 6 eine schematische Darstellung einer weiteren möglichen Ausführungsform der erfindungsgemäßen Vorrichtung;
• 7 eine schematische Darstellung einer möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 6;
• 8 eine schematische Darstellung einer weiteren möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 6;
• 9 eine schematische Darstellung einer weiteren möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 6;
• 10 eine schematische Darstellung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 9 unter schrägem Einfall;
• 11 eine schematische Darstellung einer weiteren möglichen Ausführungsform der erfindungsgemäßen Vorrichtung;
• 12 eine schematische Darstellung einer möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 11;
• 13 eine schematische Darstellung einer möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 5;
• 14 eine schematische Darstellung einer möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 13;
• 15 eine schematische Darstellung einer möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 5;
• 16 eine schematische Darstellung einer möglichen Abwandlung der Ausführungsform der erfindungsgemäßen Vorrichtung nach 15;
• 17 eine schematische Darstellung eines möglichen Messaufbaus zur Verwendung einer Messstruktur; und
• 18 eine blockdiagrammartige Darstellung eines möglichen Ausführungsform des erfindungsgemäßen Verfahrens.

Show it:

• 1 an EUV projection exposure system in the meridional section;
• 2 a DUV projection exposure system;
• 3 a schematic representation of a possible embodiment of the device according to the invention;
• 4 a schematic representation of a further possible embodiment of the device according to the invention;
• 5 a schematic representation of a modification of the embodiment of the device according to the invention 4 ;
• 6 a schematic representation of a further possible embodiment of the device according to the invention;
• 7 a schematic representation of a possible modification of the embodiment of the device according to the invention 6 ;
• 8th a schematic representation of a further possible modification of the embodiment of the device according to the invention 6 ;
• 9 a schematic representation of a further possible modification of the embodiment of the device according to the invention 6 ;
• 10 a schematic representation of the embodiment of the device according to the invention 9 under oblique incidence;
• 11 a schematic representation of a further possible embodiment of the device according to the invention;
• 12 a schematic representation of a possible modification of the embodiment of the device according to the invention 11 ;
• 13 a schematic representation of a possible modification of the embodiment of the device according to the invention 5 ;
• 14 a schematic representation of a possible modification of the embodiment of the device according to the invention 13 ;
• 15 a schematic representation of a possible modification of the embodiment of the device according to the invention 5 ;
• 16 a schematic representation of a possible modification of the embodiment of the device according to the invention 15 ;
• 17 a schematic representation of a possible measurement setup for using a measurement structure; and
• 18 a block diagram representation of a possible embodiment of the method according to the invention.

The following are first with reference to 1 the essential components of an EUV projection exposure system 100 for microlithography are described as an example of a lithography system. The description of the basic structure of the EUV projection exposure system 100 and its components should not be understood as limiting here.

In addition to a radiation source 102 , an illumination system 101 of the EUV projection exposure system 100 has illumination optics 103 for illuminating an object field 104 in an object plane 105 . In this case, a reticle 106 arranged in the object field 104 is exposed. The reticle 106 is held by a reticle holder 107 . The reticle holder 107 can be displaced via a reticle displacement drive 108, in particular in a scanning direction.

In 1 a Cartesian xyz coordinate system is drawn in for explanation. The x-direction runs perpendicularly into the plane of the drawing. The y-direction is horizontal and the z-direction is vertical. The scan direction is in 1 along the y-direction. The z-direction runs perpendicular to the object plane 105.

The EUV projection exposure system 100 includes projection optics 109. The projection optics 109 are used to image the object field 104 in an image field 110 in an image plane 111. The image plane 111 runs parallel to the object plane 105. Alternatively, there is also an angle other than 0° between the object plane 105 and the image plane 111 is possible.

A structure on the reticle 106 is imaged onto a light-sensitive layer of a wafer 112 arranged in the region of the image field 110 in the image plane 111. The wafer 112 is held by a wafer holder 113. The wafer holder 113 can be displaced via a wafer displacement drive 114, in particular along the y-direction. The displacement of the reticle 106 via the reticle displacement drive 108 on the one hand and the wafer 112 on the other hand via the wafer displacement drive 114 can be synchronized with one another.

The radiation source 102 is an EUV radiation source. The radiation source 102 emits in particular EUV radiation 115, which is also referred to below as useful radiation, illumination radiation or projection radiation. The useful radiation 115 has in particular a wavelength in the range between 5 nm and 30 nm. The radiation source 102 can be a plasma source, for example an LPP source (“laser produced plasma”, plasma generated using a laser radiation source) or a DPP (Gas Discharged Produced Plasma) source. It can also be a synchrotron-based radiation source. The radiation source 102 can be a free-electron laser (FEL).

The illumination radiation 115 emanating from the radiation source 102 is bundled by a collector 116 . The collector 116 can be a collector with one or more ellipsoids act len and / or hyperboloidal reflection surfaces. The at least one reflection surface of the collector 116 can be used in grazing incidence ("Grazing Incidence", Gl), i.e. with angles of incidence greater than 45°, or in normal incidence ("Normal Incidence", NI), i.e. with angles of incidence smaller than 45° of the illumination radiation 115 are applied. The collector 116 can be structured and/or coated on the one hand to optimize its reflectivity for the useful radiation 115 and on the other hand to suppress stray light.

After the collector 116, the illumination radiation 115 propagates through an intermediate focus in an intermediate focal plane 117. The intermediate focal plane 117 can represent a separation between a radiation source module, comprising the radiation source 102 and the collector 116, and the illumination optics 103.

The illumination optics 103 includes a deflection mirror 118 and a first facet mirror 119 downstream of this in the beam path. The deflection mirror 118 can be a plane deflection mirror or alternatively a mirror with an effect that influences the bundle beyond the pure deflection effect. Alternatively or additionally, the deflection mirror 118 can be designed as a spectral filter, which separates a useful light wavelength of the illumination radiation 115 from stray light of a different wavelength. If the first facet mirror 119 is arranged in a plane of the illumination optics 103 which is optically conjugate to the object plane 105 as a field plane, it is also referred to as a field facet mirror. The first facet mirror 119 includes a multiplicity of individual first facets 120, which are also referred to below as field facets. Of these facets 120 are in the 1 only a few shown as examples.

The first facets 120 can be embodied as macroscopic facets, in particular as rectangular facets or as facets with an arcuate or part-circular edge contour. The first facets 120 can be embodied as planar facets or alternatively as convexly or concavely curved facets.

Like for example from the DE 10 2008 009 600 A1 is known, the first facets 120 themselves can each also be composed of a multiplicity of individual mirrors, in particular a multiplicity of micromirrors. The first facet mirror 119 can be embodied in particular as a microelectromechanical system (MEMS system). For details refer to the DE 10 2008 009 600 A1 referred.

The illumination radiation 115 runs horizontally between the collector 116 and the deflection mirror 118, ie along the y-direction.

A second facet mirror 121 is arranged downstream of the first facet mirror 119 in the beam path of the illumination optics 103. If the second facet mirror 121 is arranged in a pupil plane of the illumination optics 103, it is also referred to as a pupil facet mirror. The second facet mirror 121 can also be arranged at a distance from a pupil plane of the illumination optics 103 . In this case, the combination of the first facet mirror 119 and the second facet mirror 121 is also referred to as a specular reflector. Specular reflectors are known from US 2006/0132747 A1 , the EP 1 614 008 B1 and the U.S. 6,573,978 .

The second facet mirror 121 includes a plurality of second facets 122. In the case of a pupil facet mirror, the second facets 122 are also referred to as pupil facets.

The second facets 122 can also be macroscopic facets, which can have round, rectangular or hexagonal borders, for example, or alternatively facets composed of micromirrors. In this regard, also on the DE 10 2008 009 600 A1 referred.

The second facets 122 can have plane or alternatively convexly or concavely curved reflection surfaces.

The illumination optics 103 thus forms a double-faceted system. This basic principle is also known as the "Fly's Eye Integrator".

It can be advantageous not to arrange the second facet mirror 121 exactly in a plane which is optically conjugate to a pupil plane of the projection optics 109 .

The individual first facets 120 are imaged in the object field 104 with the aid of the second facet mirror 121 . The second facet mirror 121 is the last beam-forming mirror or actually the last mirror for the illumination radiation 115 in the beam path in front of the object field 104.

In a further embodiment of the illumination optics 103 that is not shown, transmission optics can be arranged in the beam path between the second facet mirror 121 and the object field 104 , which particularly contribute to the imaging of the first facets 120 in the object field 104 . The transmission optics can have exactly one mirror, but alternatively also have two or more mirrors, which are arranged one behind the other in the beam path of the illumination optics 103 . The transmission optics can in particular comprise one or two mirrors for normal incidence (NI mirror, "normal incidence" mirror) and/or one or two mirrors for grazing incidence (GI mirror, "gracing incidence" mirror).

The illumination optics 103 has the version in which 1 shown, exactly three mirrors after the collector 116, namely the deflection mirror 118, the field facet mirror 119 and the pupil facet mirror 121.

In a further embodiment of the illumination optics 103, the deflection mirror 118 can also be omitted, so that the illumination optics 103 can then have exactly two mirrors downstream of the collector 116, namely the first facet mirror 119 and the second facet mirror 121.

The imaging of the first facets 120 by means of the second facets 122 or with the second facets 122 and transmission optics in the object plane 105 is generally only an approximate imaging.

The projection optics 109 includes a plurality of mirrors Mi, which are numbered consecutively according to their arrangement in the beam path of the EUV projection exposure system 100 .

At the in the 1 example shown, the projection optics 109 includes six mirrors M1 to M6. Alternatives with four, eight, ten, twelve or another number of mirrors Mi are also possible. The penultimate mirror M5 and the last mirror M6 each have a passage opening for the illumination radiation 115. The projection optics 109 are doubly obscured optics. The projection optics 109 has an image-side numerical aperture which is greater than 0.5 and which can also be greater than 0.6 and which can be 0.7 or 0.75, for example.

Reflection surfaces of the mirrors Mi can be designed as free-form surfaces without an axis of rotational symmetry. Alternatively, the reflection surfaces of the mirrors Mi can be designed as aspherical surfaces with exactly one axis of rotational symmetry of the reflection surface shape. Just like the mirrors of the illumination optics 103, the mirrors Mi can have highly reflective coatings for the illumination radiation 115. These coatings can be designed as multilayer coatings, in particular with alternating layers of molybdenum and silicon.

The projection optics 109 has a large object-image offset in the y-direction between a y-coordinate of a center of the object field 104 and a y-coordinate of the center of the image field 110. This object-image offset in the y-direction can be something like this be as large as a z-distance between the object plane 105 and the image plane 111.

The projection optics 109 can in particular be anamorphic. In particular, it has different image scales βx, βy in the x and y directions. The two image scales βx, βy of the projection optics 109 are preferably at (βx, βy)=(+/−0.25, +/-0.125). A positive image scale β means an image without image reversal. A negative sign for the imaging scale β means imaging with image inversion.

The projection optics 109 thus leads to a reduction in the ratio 4:1 in the x-direction, ie in the direction perpendicular to the scanning direction.

The projection optics 109 lead to a reduction of 8:1 in the y-direction, ie in the scanning direction.

Other imaging scales are also possible. Image scales with the same sign and absolutely the same in the x and y directions, for example with absolute values of 0.125 or 0.25, are also possible.

The number of intermediate image planes in the x-direction and in the y-direction in the beam path between the object field 104 and the image field 110 can be the same or, depending on the design of the projection optics 109, can be different. Examples of projection optics with different numbers of such intermediate images in the x and y directions are known from U.S. 2018/0074303 A1 .

In each case one of the pupil facets 122 is assigned to precisely one of the field facets 120 in order to form a respective illumination channel for illuminating the object field 104 . In this way, in particular, lighting can result according to Köhler's principle. The far field is broken down into a large number of object fields 104 with the aid of the field facets 120 . The field facets 120 generate a plurality of images of the intermediate focus on the pupil facets 122 respectively assigned to them.

The field facets 120 are each imaged onto the reticle 106 by an associated pupil facet 122 in a superimposed manner in order to illuminate the object field 104 . In particular, the illumination of the object field 104 is as homogeneous as possible. It preferably has a uniformity error of less than 2%. Field uniformity can be achieved by superimposing different illumination channels.

The illumination of the entrance pupil of the projection optics 109 can be geometrically defined by an arrangement of the pupil facets. The intensity distribution in the entrance pupil of the projection optics 109 can be set by selecting the illumination channels, in particular the subset of the pupil facets that guide light. This intensity distribution is also referred to as an illumination setting.

A likewise preferred pupil uniformity in the area of defined illuminated sections of an illumination pupil of the illumination optics 103 can be achieved by redistributing the illumination channels.

Further aspects and details of the illumination of the object field 104 and in particular the entrance pupil of the projection optics 109 are described below.

The projection optics 109 can in particular have a homocentric entrance pupil. This can be accessible. It can also be inaccessible.

The entrance pupil of the projection optics 109 cannot regularly be illuminated exactly with the pupil facet mirror 121 . When imaging the projection optics 109, which telecentrically images the center of the pupil facet mirror 121 onto the wafer 112, the aperture rays often do not intersect at a single point. However, a surface can be found in which the distance between the aperture rays, which is determined in pairs, is minimal. This surface represents the entrance pupil or a surface conjugate to it in position space. In particular, this surface shows a finite curvature.

The projection optics 109 may have different positions of the entrance pupil for the tangential and for the sagittal beam path. In this case, an imaging element, in particular an optical component of the transmission optics, should be provided between the second facet mirror 121 and the reticle 106 . With the help of this optical component, the different positions of the tangential entrance pupil and the sagittal entrance pupil can be taken into account.

At the in the 1 In the arrangement of the components of the illumination optics 103 shown, the pupil facet mirror 121 is arranged in a surface conjugate to the entrance pupil of the projection optics 109 . The first field facet mirror 119 is arranged tilted to the object plane 105 . The first facet mirror 119 is tilted relative to an arrangement plane that is defined by the deflection mirror 118 .

The first facet mirror 119 is tilted relative to an arrangement plane that is defined by the second facet mirror 121 .

In 2 an exemplary DUV projection exposure system 200 is shown, in which the principle of the present invention for cleaning foreign particles from the lenses can basically also be used. The EUV-specific components, such as a collector mirror 116, are then not required for this or can be substituted accordingly. The DUV projection exposure system 200 has an illumination system 201, a device known as a reticle stage 202 for receiving and precisely positioning a reticle 203, by means of which the later structures on a wafer 204 are determined, a wafer holder 205 for holding, moving and precisely positioning the wafer 204 and an imaging device, namely projection optics 206, with a plurality of optical elements, in particular lenses 207, which are held in an objective housing 209 of the projection optics 206 via mounts 208.

As an alternative or in addition to the lenses 207 shown, various refractive, diffractive and/or reflective optical elements, including mirrors, prisms, end plates and the like, can be provided.

The basic functional principle of the DUV projection exposure system 200 provides that the structures introduced into the reticle 203 are imaged onto the wafer 204 .

The illumination system 201 provides a projection beam 210 required for imaging the reticle 203 onto the wafer 204 or a projection radiation in the form of electromagnetic radiation. A laser, a plasma source or the like can be used as the source for this radiation. The radiation is shaped in the illumination system 201 via optical elements in such a way that the projection beam 210 has the desired properties in terms of diameter, polarization, shape of the wave front and the like when it strikes the reticle 203 .

An image of the reticle 203 is generated by means of the projection beam 210 and transmitted to the wafer 204 in a correspondingly reduced size by the projection optics 206 . The reticle 203 and the wafer 204 can be moved synchronously, so that areas of the reticle 203 are imaged onto corresponding areas of the wafer 204 practically continuously during a so-called scanning process.

Optionally, an air gap between the last lens 207 and the wafer 204 can be replaced by a liquid medium that has a refractive index greater than 1.0. The liquid medium can be, for example, ultrapure water. Such a structure is also referred to as immersion lithography and has an increased photolithographic resolution.

The use of the invention is not limited to use in projection exposure systems 100, 200, in particular not with the structure described. The invention is suitable for any lithography system, but in particular for projection exposure systems with the structure described. The invention is also suitable for EUV projection exposure systems, which have a lower image-side numerical aperture than those associated with 1 is described. In particular, the invention is also suitable for EUV projection exposure systems which have an image-side numerical aperture of 0.25 to 0.5, preferably 0.3 to 0.4, particularly preferably 0.33. Furthermore, the invention and the following exemplary embodiments are not to be understood as being restricted to a specific design. The following figures represent the invention only by way of example and in a highly schematic manner.

It should be pointed out that the device according to the invention described below and the method according to the invention for calibration can be used in particular in lithography systems and here in particular in projection exposure systems for semiconductor lithography, but can also be used in other areas in which precise measurement is important or in which a test object, in particular an optical element, is to be measured or processed with high precision can be used.

The exemplary embodiments presented below, in particular the exemplary embodiments that are based on the 3 until 18 are explained are to be understood accordingly.

3 shows a schematic representation of a possible embodiment of the device 1 according to the invention.

The device 1 for calibrating a diffractive measurement structure 2 for forming a measurement wave front of a measurement radiation 3 incident on the measurement structure 2 (see 17 ) has a calibration radiation source 4 for forming a calibration radiation 5, which can be diffracted by the measurement structure 2. Furthermore, the device 1 has a positioning device 6 for illuminating the measurement structure 2 with the calibration radiation 5 in a number of different areas 7 and a detection device 8 for recording a plurality of images of the calibration radiation 5 and a computing device 9 for determining at least one property of the measurement structure 2 from the images.

A control device 10 is provided in the device 1 and set up to set a main beam angle and an angular distribution of the calibration radiation 5 according to the measurement radiation 3 to be expected to be incident on the measurement structure 2 . In this case, a wavelength of the calibration radiation 5 corresponds at least approximately to the expected wavelength of the measurement radiation 3. Furthermore, the computing device 9 is set up to reconstruct a phase or amplitude of the calibration radiation 5 immediately after it has passed through and/or been reflected at the measurement structure 2.

in the in 3 In the exemplary embodiment illustrated, a polarizer device 11 is also provided and set up to set a polarization direction of the calibration radiation 5 before it is incident on the measurement structure 2 .

Furthermore, in the in 3 illustrated embodiment preferably a polarization filter device 12 is provided and set up to filter the calibration radiation 5 before recording the images with respect to their polarization direction.

in the in 3 illustrated embodiment, the positioning device 6 is preferably set up to vary a position of the measurement structure 2 relative to the calibration radiation 5 laterally and/or axially. The positioning device 6 is therefore preferably set up to displace the measurement structure 2 in all three spatial directions along a Cartesian coordinate system, with a z-direction of the coordinate system preferably being arranged along a surface normal of the measurement structure 2 .

4 shows a schematic representation of a further possible embodiment of the device 1 according to the invention.

in the in 4 In the exemplary embodiment shown, an aperture device 13 is provided and set up to cut the calibration radiation 5 . Furthermore, focusing optics 14 are provided and set up to focus the calibration radiation 5 onto the areas 7 of the measurement structure 2 .

Furthermore, the areas 7 of the measurement structure 2 can be illuminated by the calibration radiation 5 in a coherent and focused manner. In the exemplary embodiment shown, the detection device 8 is arranged in a far field, preferably in a Fraunhofer far field, of the calibration radiation 5 .

Regarding other reference symbols is on the 1 referred.

5 FIG. 12 shows a schematic representation of a modification of the embodiment of the device 1 according to FIG 4 .

in the in 5 illustrated embodiment is in addition to the 4 illustrated embodiment, the polarization filter device 12 is arranged in front of the detection device 8 .

Regarding the reference numerals is on the 3 and 4 referred.

6 shows a schematic representation of a further possible embodiment of the device 1.

in the in 6 illustrated embodiment, the areas 7 of the measurement structure 2 can be illuminated by the calibration radiation 5 in a coherent and collimated manner. Furthermore, imaging optics 15 are provided and set up to image the areas 7 in an image plane 16 . In addition, in the in 6 illustrated embodiment of the device 1, the detection device 8 is arranged in the image plane 16. In this way, so-called aerial images of the areas 7 can be recorded.

in the in 6 illustrated embodiment, the positioning device 6 is set up to move the measurement structure 2 axially to the calibration radiation 5, which in 6 is indicated by a vertical double arrow.

7 FIG. 12 shows a schematic representation of a modification of the embodiment of the device 1 according to FIG 6 .

In addition to the in 6 illustrated embodiment is in the in 7 illustrated embodiment, the polarization filter device 12 is present and arranged within the imaging device 15 . In particular, the polarization filter device 12 is arranged between two lenses of the imaging optics 15 and thus in a collimated area of the calibration radiation 5 .

Regarding the further assignment of reference numbers is on the 4 until 6 referred.

8th FIG. 12 shows a schematic representation of a further possible modification of the embodiment of the device 1 according to FIG 6 .

in the in 8th illustrated embodiment, the calibration radiation source 4 is formed at least approximately as a point light source. For the collimation of the calibration radiation 5, in 8th illustrated embodiment, a collimator device 17 is provided.

The collimator device 17 has a housing in which the calibration radiation source 4 and a lens are arranged, with the calibration radiation source 4 preferably being located at a focal point of the lens.

in the in 8th In the exemplary embodiment illustrated, the polarizer device 12 is also arranged between the calibration radiation source 4 and the measurement structure 2 , in particular between the collimator device 17 and the measurement structure 2 . As a result, the not yet polarized calibration radiation 5 emanating from the calibration radiation source 4 is aligned with respect to its polarization direction.

Regarding the further assignment of reference numbers is on the 4 until 7 referred.

9 FIG. 1 shows another possible modification of the embodiment of the device 1. FIG 6 and 8th .

In addition to the in 8th illustrated embodiment is in FIG 9 illustrated embodiment, the polarization filter device 12 is also arranged within the imaging optics 15 .

Regarding the further assignment of reference numbers is on the 4 until 8th referred.

10 FIG. 1 shows a schematic representation of the embodiment of the device 1 according to FIG 9 under an oblique incidence of the calibration radiation 5.

By means of the control device 10 (in 10 not shown), the main beam angle and the angular distribution of the calibration radiation 5 are aligned according to the measurement radiation 3 (not shown) to be expected incident on the measurement structure 2 .

11 shows a schematic representation of a further possible embodiment of the device 1.

At the in 11 In the embodiment of the device 1 shown in the embodiment shown, a beam splitter device 18 is present and set up to guide the calibration radiation 5 reflected by the measurement structure 2 onto the detection device 8 .

Alternatively or additionally, it can be provided that a beam splitter device 18 is provided and set up to guide the calibration radiation 5 propagating to the measurement structure 2 onto the measurement structure 2 .

In this way, the measurement structure 2 operating in reflection can be measured by the calibration radiation 5 being coupled into a beam path of the calibration radiation 5 and/or coupled out of it.

Furthermore, the in 11 illustrated embodiment of the device 1 is preferably set up to record an aerial image of the calibration radiation 5 . Therefore, the allocation of reference numbers to the 6 until 10 referred.

12 shows a possible modification of the embodiment of the device 1 after 11 . Here, in addition to the in 11 illustrated embodiment, the polarization filter device 12 is present and arranged between the lenses of the imaging optics 15 .

With regard to the assignment of reference numbers is on the 4 until 11 referred.

13 shows a schematic representation of a possible modification of the embodiment of the device 1 according to the invention 5 .

in the in 13 illustrated embodiment, the images are recorded as diffraction images and the detection device 8 is arranged in a far field. The diaphragm device 13, in particular a field aperture diaphragm, is in 13 illustrated embodiment is arranged between the polarizer device 11 and the focusing optics 14 and thereby cuts the calibration radiation 5.

Regarding the further assignment of reference numbers is on the 4 until 12 referred.

14 shows a schematic representation of a possible modification of the embodiment shown in 13 is shown.

In addition to the in 13 illustrated embodiment is in the in 14 illustrated embodiment of the device 1, the polarization filter device 12 is present and arranged between the measurement structure 2 and the detection device 8.

With regard to the further allocation of reference numbers is on the 4 until 13 referred.

15 shows a schematic representation of a possible imaging of the embodiment of the device according to the invention 5 .

in the in 15 In the exemplary embodiment shown, a Fourier optics device 19 is arranged between the measurement structure 2 and the detection device 8 and is preferably set up to image the calibration radiation 5 into infinity in such a way that the detection device 8 is arranged in a Fraunhofer far field of the calibration radiation 5 .

in the in 15 illustrated embodiment, the Fourier optical device 19 is designed as a lens. Alternatively or additionally, the Fourier optics device 19 can also be designed as a lens system.

With regard to the assignment of reference numbers is on the 4 until 14 referred.

16 shows a schematic representation of a possible modification of the embodiment of the device 1 according to the invention 15 .

In addition to the in 15 illustrated embodiment is in FIG 16 illustrated embodiment, the polarization filter device 12 is present and arranged between the Fourier optics device 19 and the detection device 8 .

With regard to the further allocation of reference numbers is on the 4 until 15 referred.

In the 4 until 16 the imaging optics 15, the focusing optics 14 and the Fourier optics device 19 have lenses. Alternatively or additionally, it can be provided that the imaging optics 15, the focusing optics 14 and the Fourier optics device 19 have lenses and/or mirrors and/or other optical elements.

17 shows a possible embodiment of a measurement setup 30, in which the measurement structure 2 is calibrated by means of the device 1 described above, can be used. The measurement radiation 3 is directed onto the measurement structure 2 . The measurement structure 2 forms a wave front of the measurement radiation 3 which is incident on a test object 31 . 17 shows a beam path in an interferometric tower for the application of measurement structure 2.

in the in 17 example shown, the measurement structure 2 is designed as a computer-generated hologram (CGH) and is used in the 17 shown interferometric measurement setup 30 as a beam splitter. An illumination wave of the measurement radiation 3 impinges at each point of the measurement structure 2 at a defined angle of incidence. For each of the up to five interferometer arms of the measurement setup 30, the incident illumination wave of the measurement radiation 3 is diffracted in such a way that a direction of diffraction coincides exactly with the direction of the respective interferometer arm. The measurement radiation diffracted in this way then strikes the test specimen 31, in particular a mirror to be tested, perpendicularly. At the test object 31, the measurement radiation 3 is thrown back into itself and hits the same spot on the measurement structure 2 again. After passing through the measurement structure 2 again, part of the reflected measurement radiation 3 is again thrown back by diffraction in an opposite direction of illumination and with measurement radiation 3 out recombined in another interferometer arm.

The in the 3 until 16 The illustrated embodiments of the device 1 are particularly suitable for carrying out a method for calibrating the diffractive measurement structure 2.

18 shows a block diagram representation of a possible embodiment of the method for calibrating the diffractive measurement structure 2 for forming the measurement wavefront of the measurement radiation 3 incident on the measurement structure 2, in particular a method for calibrating a computer-generated hologram.

The measurement structure 2 is illuminated with the calibration radiation 5 in an illumination block 40 and the calibration radiation 5 is diffracted by the measurement structure 2 . A plurality of images of the calibration radiation 5 are recorded in a recording block 41, which differ at least in part with regard to the region 7 of the measurement structure 2 contributing to the respective image.

At least one property of the measurement structure 2 is determined from the images in a determination block 42 . In an imitation block 43, the main beam angle and the angular distribution of the calibration radiation 5 are set in accordance with the measurement radiation 3 to be expected incident on the measurement structure 2.

Furthermore, within the framework of the imitation block 43, a wavelength of the calibration radiation 5 is selected according to the wavelength of the measurement radiation 3 to be expected. As part of the determination block 42, a phase and/or an amplitude of the calibration radiation 5 directly prevailing at the measurement structure 2 is reconstructed and the at least one property of the measurement structure 2 is inferred from the phase and/or the amplitude.

in the in 18 In the illustrated embodiment, blocks 40 through 43 are arranged in a preferred chronology. In particular, begins in the in 18 illustrated embodiment, the method with the imitation block 43 and ends with the determination block 42.

However, other chronological embodiments are also conceivable. In particular, sequential execution and/or parallel execution of the blocks and/or multiple iteration of one or more or all blocks can also be advantageous. For example, a measurement accuracy can be increased by a multiple iteration.

It can be advantageous to partially or completely omit one or more of the blocks 40 to 43 when carrying out the method.

Within the framework of the illumination block 40, provision can preferably be made for the polarization direction of the calibration radiation 5 to be set before it is incident on the measurement structure 2 and/or for the calibration radiation 5 to be polarization-filtered before the images are recorded.

As part of the illumination block 40, it can preferably be provided that the areas 7 of the measurement structure 2 are illuminated by the calibration radiation 5 in a coherent and collimated manner.

Furthermore, an imaging block 44 can preferably be provided, in which the regions 7 are imaged in the image plane 16 by means of the imaging optics 15 .

If the imaging block 44 is provided, the images within the frame of the recording block 43 in the image plane are preferably recorded as aerial images.

Provision can preferably be made in the illumination block 40 for a position of the measurement structure 2 to be varied laterally and axially relative to the calibration radiation 5 and for each variation in the position of the measurement structure 2 to be recorded in the recording block 43 at least one image.

Provision can also preferably be made within the framework of the illumination block 40 for the calibration radiation 5 to be clipped by means of the aperture device 13 and for the calibration radiation 5 to be focused on the regions 7 of the measurement structure 2 by means of the focusing optics, in particular to form an illumination spot on the measurement structure 2. In the illumination block 40, the areas 7 of the measurement structure 2 are preferably illuminated by the calibration radiation 5 in a coherent and focused manner.

Images are preferably recorded in a far field of the calibration radiation 5 as diffraction images in the frame of the recording block 41 .

As part of the illumination block 40, it can alternatively or additionally be provided that the position of the measurement structure 2 relative to the calibration radiation 5 is moved laterally in such a way that the areas 7 of the measurement structure 2 are covered by the calibration radiation 5 at least twice. Provision can then preferably be made within the framework of the recording block 41 for at least one image to be recorded for each variation in the position of the measurement structure 2 .

In blocks 40 to 44 it can be provided that the images are recorded after the calibration radiation 5 has passed through the measurement structure 2 and/or after the calibration radiation 5 has been reflected on the measurement structure 2 .

the 1 and 2 each show a lithography system, in particular a projection exposure system 100, 200 for semiconductor lithography, with an illumination system 101, 201 with a radiation source 102 and optics 103, 109, 206, which have at least one optical element 116, 118, 119, 120, 121, 122 , Mi, 207 exhibits. At the in the 1 and 2 In the projection exposure systems 100, 200 shown, at least one of the optical elements 116, 118, 119, 120, 121, 122, Mi, 207 has an optical surface which is at least partially measured with the measurement structure 2, which is at least partially measured using the method described above and/or at least is partially calibrated by means of the device 1 described above.

Reference List

1

contraption

2

diffractive measurement structure

3

measuring radiation

4

calibration radiation source

5

calibration radiation

6

positioning device

7

area

8th

detection device

9

computing device

10

control device

11

polarizer device

12

polarizing filter device

13

aperture device

14

focusing optics

15

imaging optics

16

picture plane

17

collimator device

18

beam splitter device

19

Fourier optics device

30

measurement setup

31

examinee

40

lighting block

41

recording block

42

investigation block

43

imitation block

44

figure block

100

EUV projection exposure system

101

lighting system

102

radiation source

103

lighting optics

104

object field

105

object level

106

reticle

107

reticle holder

108

reticle displacement drive

109

projection optics

110

image field

111

picture plane

112

wafers

113

wafer holder

114

Wafer displacement drive

115

EUV / useful / illumination radiation

116

collector

117

intermediate focal plane

118

deflection mirror

119

first facet mirror / field facet mirror

120

first facets / field facets

121

second facet mirror / pupil facet mirror

122

second facets / pupil facets

200

DUV projection exposure system

201

lighting system

202

reticle stage

203

reticle

204

wafers

205

wafer holder

206

projection optics

207

lens

208

version

209

lens body

210

projection beam

wed

mirror

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent Literature Cited

• DE 102017221005 A1 [0010]
• DE 102008009600 A1 [0123, 0127]
• US 2006/0132747 A1 [0125]
• EP 1614008 B1 [0125]
• US6573978 [0125]
• US 2018/0074303 A1 [0144]

Claims (15)

Method for calibrating a diffractive measurement structure (2) for forming a measurement wave front of a measurement radiation (3) incident on the measurement structure (2), in particular a computer-generated hologram, wherein - the measurement structure (2) is illuminated with a calibration radiation (5) and the calibration radiation ( 5) is diffracted by the measurement structure (2), and - a plurality of images of the calibration radiation (5) is recorded, which differ at least in part with regard to a region (7) of the measurement structure (2) that contributes to a respective image, and - at least one property of the measurement structure (2) is determined from the images, characterized in that - a main beam angle and an angular distribution of the calibration radiation (5) are set according to the measurement radiation (3) expected to be incident on the measurement structure (2), and - a Wavelength of the calibration radiation (5) is selected according to the wavelength of the measurement radiation (3) to be expected, and - a phase and/or amplitude of the calibration radiation (5) directly at the measurement structure (2) is reconstructed, and - the at least one property of the measurement structure (2) is deduced from the phase and/or the amplitude. procedure after claim 1 , characterized in that - a polarization direction of the calibration radiation (5) is set before it is incident on the measurement structure (2), and - the calibration radiation (5) is polarization-filtered before the images are recorded. procedure after claim 1 or 2 , characterized in that - the areas (7) of the measurement structure (2) are illuminated by the calibration radiation (5) in a coherent and collimated manner, and - the areas (7) are imaged in an image plane (16) by means of imaging optics (15), and - the images in the image plane (16) are recorded as aerial images. Procedure according to one of Claims 1 until 3 , characterized in that - a position of the measurement structure (2) relative to the calibration radiation (3) is varied laterally and axially, and - at least one image is recorded for each variation in the position of the measurement structure (2). Procedure according to one of Claims 1 until 4 , characterized in that - the calibration radiation (5) is cut off by means of an aperture device (13), and - the calibration radiation (5) is focused onto the areas (7) of the measurement structure (2) by means of focusing optics (14), and - the Areas (7) of the measurement structure (2) are illuminated coherently and in a focused manner by the calibration radiation (5), and the images (5) are recorded as diffraction images in a far field of the calibration radiation (5). Procedure according to one of Claims 1 until 5 , characterized in that - a position of the measurement structure (2) relative to the calibration radiation (5) is varied laterally in such a way that each region (7) of the measurement structure (2) is swept by the calibration radiation (5) at least twice, and - for each Variation of the position of the measurement structure (2) at least one image is recorded. Method according to claim one of Claims 1 until 6 , characterized in that the images are recorded after the calibration radiation (5) has passed through the measurement structure (2) and/or the calibration radiation (5) has been reflected on the measurement structure (2). Device (1) for calibrating a diffractive measurement structure (2) for forming a measurement wave front of a measurement radiation (3) incident on the measurement structure (2), comprising: - a calibration radiation source (4) for forming a calibration radiation (5) which passes through the measurement structure ( 2) is bendable, and - a positioning device (6) for illuminating the measurement structure (2) with the calibration radiation (5) in a number of different areas (7), and - a detection device (8) for recording a plurality of images of the calibration radiation (5), and - a computing device (9) for determining at least one property of the measurement structure (2) from the images, characterized in that - a control device (10) is provided and is set up to set a main beam angle and an angular distribution of the calibration radiation (5) according to the measurement radiation (3) to be expected incident on the measurement structure (2), and - a wavelength of the calibration radiation (5) at least approximately the expected wavelength of the measurement radiation (3 ) corresponds, and - the computing device (9) is set up to reconstruct a phase and/or amplitude of the calibration radiation (5) that prevails immediately after it has passed through and/or been reflected at the measurement structure (2). Device (1) after claim 8 , characterized in that - a polarization device (11) is provided and set up to set a polarization direction of the calibration radiation (5) before it is incident on the measurement structure (2), and - a polarization filter device (12) is provided and set up to set the calibration radiation (5 ) before recording the images with regard to their polarization direction. Device (1) after claim 8 or 9 , characterized in that - the positioning device (6) is set up to vary a position of the measurement structure (2) relative to the calibration radiation (5) laterally and/or axially. Device (1) according to one of Claims 8 until 10 , characterized in that - an aperture device (12) is provided and set up to cut the calibration radiation (5), and - focusing optics (14) are provided and set up, the calibration radiation (5) onto the regions (7) of the measurement structure ( 2) to focus, and - the areas (7) of the measurement structure (2) can be illuminated coherently and in a focused manner by the calibration radiation (5), and - the detection device (8) is arranged in a far field of the calibration radiation (5). Device (1) according to one of Claims 8 until 11 , characterized in that a Fourier optics device (19) is arranged between the measuring structure (2) and the detection device (8) and set up to image the calibration radiation (5) into infinity in such a way that the detection device (8) in a Fraunhofer far field of the Calibration radiation (5) is arranged. Device (1) according to one of Claims 8 until 11 , characterized in that - the areas (7) of the measurement structure (2) can be illuminated by the calibration radiation (5) in a coherent and collimated manner, and - imaging optics (15) are provided and set up, the areas (7) in an image plane (16 ) to image, and - the detection device (8) is arranged in the image plane (16). Device (1) according to one of Claims 8 until 13 , characterized in that - a beam splitter device (18) is provided and set up to direct the calibration radiation (5) reflected by the measurement structure (2) to the detection device (8) and/or the calibration radiation (5) to the measurement structure (2) to direct. Lithography system, in particular projection exposure system (100, 200) for semiconductor lithography, with an illumination system (101, 201) with a radiation source (102) and an optical system (103, 109, 206) which has at least one optical element (116, 118, 119, 120, 121, 122, Mi, 207), characterized in that at least one of the optical elements (116, 118, 119, 120, 121, 122, Mi, 207) has an optical surface which is at least partially covered with a measuring structure ( 2) is measured, which at least partially by means of a method according to one of Claims 1 until 7 and/or at least partially by means of a device (1) according to one of Claims 8 until 14 is calibrated.

Images