DE102008002247A1 - Method and device for determining an optical property of an optical system - Google Patents

Abstract

A method for determining an optical property of an optical system (12) comprises the steps of: irradiating electromagnetic radiation (17) on the optical system (12), detecting the electromagnetic radiation (17) by means of a detector (36) after interaction thereof with the optical System (12), periodically interrupting the electromagnetic radiation (17), so that the electromagnetic radiation (17) impinges on the detector (36) in time-limited radiation packets, as well as evaluation of at least two detected by the detector (36) radiation packets for determining the optical Property of the optical system (12).

Description

Background of the invention

The The invention relates to a method and a device for determining an optical property of an optical system. An important application The invention is the wavefront measurement of high resolution Projection objectives in microlithography for semiconductor wafer structuring, aberrations of the projection lens with high precision to be able to determine. For this purpose, as is known in the art, for. B. on lateral shear interferometry based technique as well as other interferometric techniques, like point diffraction interferometry (PDI - "Point Diffraction interferometer "), line diffraction interferometry (LDI - "Line Diffraction Interferometer") used become. Furthermore, the use of a Shack-Hartmann sensor or a sensor based on moiré techniques.

In one embodiment of the shear interferometry, a so-called coherence mask is arranged in the object plane of the optical system to be tested. On this an object pattern is arranged. In the image plane of the imaging system is a trained as a diffraction grating reference pattern. The superposition of the waves generated by diffraction at the diffraction grating results in an overlay pattern in the form of an interferogram, which is detected by means of a suitable detector. Possible embodiments of a coherence mask and of a diffraction grating of a shear interferometer are, for example, in DE 10 2005 041 373 A1 listed.

Indeed are the reproducibility and the absolute accuracy of the means the conventional shear interferometric method Wavefront measurements are often inadequate, especially for EUV radiation designed optical systems.

Underlying task

It It is an object of the invention to overcome the aforementioned problems and in particular to provide a method and a device, with which an optical property of an optical system, in particular one designed for the EUV wavelength range optical system, can be determined with improved accuracy.

invention solution

The The aforementioned object can according to the invention by means of a method for determining an optical property of a optical system, in particular an imaging optical system for microlithography, which comprises: Irradiation of electromagnetic radiation onto the optical system, Detecting the electromagnetic radiation by means of a detector after interaction of the electromagnetic radiation with the optical System, periodic interruption of electromagnetic radiation, so that the electromagnetic radiation in time-limited radiation packets impinges on the detector, as well as evaluating at least two Radiation packets detected by the detector for determining the optical Property of the optical system. In an advantageous embodiment the process of the invention further comprises the step of determining the optical characteristic from the evaluated one Radiation packages, such. B. from interferograms derived from the radiation packets be generated on the detector.

The The aforementioned object can continue according to the invention by means of a device for determining an optical property an optical system, in particular an imaging optical system for microlithography, to be solved. These Apparatus comprises: a radiation source configured to is to generate electromagnetic radiation and a detector for detecting the electromagnetic radiation after interaction the same with the optical system, the device configured to is to periodically interrupt the electromagnetic radiation, so that the electromagnetic radiation is limited in time Radiation packets impinges on the detector, and the device further comprises: an evaluation device which is configured to at least two radiation packets detected by the detector for determining evaluate the optical property of the optical system. In An advantageous embodiment is the evaluation device set up the optical property of the evaluated Determine radiation packets.

In an embodiment according to the invention is the periodic Interruption of electromagnetic radiation by in and out Moving out of a Verschusselements in the beam path or off the beam path of the electromagnetic radiation. In another Embodiment according to the invention, the periodic takes place Interrupting the electromagnetic radiation by triggering a the electromagnetic radiation generating radiation source.

The above object can be achieved according to the invention further by means of a further method for determining an optical property of an optical system, which comprises: irradiation of electromagnetic radiation to the opti cal system, detecting the electromagnetic radiation by means of a detector after interaction of the electromagnetic radiation with the optical system, and evaluating at least two temporally limited radiation packets detected by the detector electromagnetic radiation for determining the optical property of the optical system, wherein the radiation packets each have a minimum time length of 50 milliseconds, especially 100 milliseconds. In an advantageous embodiment, the inventive method further comprises the step of determining the optical property of the evaluated radiation packets, such as. B. from interferograms generated by the radiation packets on the detector.

The The aforementioned object can continue according to the invention by means of a further device for determining an optical Property of an optical system to be solved. These Apparatus comprises: a radiation source configured to is to generate electromagnetic radiation and a detector for detecting the electromagnetic radiation after interaction same with the optical system, as well as an evaluation device, which is configured to have at least two time-limited Radiation packets of the electromagnetic radiation detected by the detector to evaluate the optical property of the optical system, wherein the radiation packets each have a minimum time length of 50 milliseconds, in particular 100 milliseconds have.

The by means of the device according to the invention or the inventive method certain optical Property of the optical system can, for. B. the aberration behavior of the optical system. The optical property can but also other properties such. B. the polarization behavior of optical system.

The Detecting the at least two radiation packets by means of the detector For example, in the case of a shear interferometric Measurement include the detection of two generated interferograms. By evaluating at least two radiation packets leave the measured data determined for the respective radiation packet charge each other. The periodic interruption of the electromagnetic Radiation can be achieved, for example, by triggering the radiation source, for example by switching the radiation source itself on or off, or by a mechanical interruption of the beam path of the electromagnetic Radiation done. By providing defined radiation packets can be a measurement of the detected interferograms with a high Accuracy done.

The Generation of the radiation packets allows in particular the measurement results from the detector in the intervals between irradiation read the individual radiation packets. This can be an improved Readout accuracy versus readout during continuous irradiation of the detector can be achieved.

In an embodiment according to the invention each of the radiation packets has a maximum time length of 4 seconds. By providing the electromagnetic Radiation in radiation packets with a maximum time length 4 seconds can be several consecutive radiation packets to measure the optical system. This makes possible, As already stated above, a determination of the optical Property with improved accuracy.

The The aforementioned object can further according to the invention with another method for determining an optical property an optical system can be solved. This method includes an irradiation of electromagnetic radiation to the optical System, detecting the electromagnetic radiation by means of a Detector for determining the optical property of the optical system, wherein the electromagnetic radiation in time-limited radiation packets occurs on the detector, as well as determining the respective radiation energy the individual radiation packets by means of an additional to the detector provided energy sensor. advantageously, the process of the invention further comprises an evaluation of the electromagnetic radiation detected by the detector, for example in the form of interferograms, for the determination of optical property of the optical system.

The The aforementioned object can further according to the invention with another device for determining an optical property an optical system can be solved. This device comprising: a radiation source configured to be electromagnetic Generate radiation and a detector for detecting the electromagnetic radiation, wherein the device is configured such that the electromagnetic Radiation in time-limited radiation packets to the detector occurs, and the apparatus further comprises: a power sensor, which is arranged in the beam path of the electromagnetic radiation and configured to the respective radiant energy of the individual To determine radiation packets. Advantageously, the inventive Device further comprises an evaluation device for determining the optical property by evaluating the detected by the detector electromagnetic radiation, for example in the form of interferograms.

Under the respective radiant energy determined by the energy sensor The individual radiation packets do not become the energy of individual radiation quanta the radiation packets, which is a function of wavelength the radiation is understood, but the entire energy of a Radiation packets or the total energy per unit time of Radiation package is transported. It is about the Energy generated by a variety of radiation quanta of each Radiation packets is transported. In particular, by means of the energy sensor the respective radiation dose or radiation power of the individual Radiation packages determined.

By determining the respective radiation energy of the individual radiation packets leave by means of the energy sensor according to the invention Fluctuations in the radiation intensity at the Take into account the determination of the optical property. As already mentioned above, the determination of the radiation energy the individual radiation packets z. B. a temporally resolved Determine the radiation energy during the temporal Duration of the respective radiation packet and / or determining the Total energy of the respective radiation package include. The means of the energy sensor for a respective radiation packet determined Radiation energy can then z. B. used to capture the detected To correct the interferogram mathematically. Leave it the optical property with improved accuracy and determine reproducibility.

Especially is prior to splitting the detected electromagnetic radiation in temporally limited successive radiation packets first the radiant energy electromagnetic radiation time resolved detected by the evaluation. Thereupon by means of the evaluation device defines the radiation packets such that each of the radiation packets has a total radiation energy, which lies within a given energy range.

In an embodiment of the invention, the electromagnetic Radiation by means of a beam interruption device, in particular periodically, interrupted, so that the electromagnetic radiation impinges on the detector in the time-limited radiation packets. The beam interruption device can, for example, the beam path mechanically interrupt the electromagnetic radiation and about executed as a so-called "shutter" be. In such an interruption of the electromagnetic Radiation can be caused by resulting intensity fluctuations limit a minimum.

In a further embodiment according to the invention the beam interrupting device comprises a shutter member which when interrupting the electromagnetic radiation in the beam path the electromagnetic radiation is moved in. The beam interrupting device can be executed in the form of an optical shutter or the so-called "shutter" be, which the closure element in the form of a radiation-tight mechanically movable element for interrupting the beam path having the electromagnetic radiation.

The The aforementioned object can further according to the invention by a method for determining an optical property an optical system which comprises: Irradiation of electromagnetic radiation onto the optical system, Detecting the electromagnetic radiation by means of a detector after interaction of the electromagnetic radiation with the optical System, evaluating the detected electromagnetic radiation by Defining time-limited consecutive radiation packets, by splitting the detected electromagnetic radiation is that the respective total radiant energy of the individual Radiation packages in a given energy range is, as well Determining the optical property of the optical system from the defined radiation packages. This will generate the radiation packets shifted to the evaluation page, d. H. the radiation packages must not physically present. The detected electromagnetic radiation can therefore be continuous. The radiation packets are then only defined during the evaluation.

The The aforementioned object can continue by means of a further device for determining an optical property of an optical system become. This device comprises: a radiation source, which configured to generate electromagnetic radiation, and a detector for detecting the electromagnetic radiation after interaction of the same with the optical system, as well as a Evaluation device, which is configured to, from the detected electromagnetic radiation temporally limited successive Defining radiation packets by the detected electromagnetic Radiation is divided so that the respective total radiant energy the individual radiation packets in a given energy range lies. Furthermore, the evaluation device is configured to the defined radiation packets for determining the optical property of the optical system.

In a further embodiment according to the invention, the electromagnetic radiation is optically changed by their interaction with the optical system by means of an analysis element dert, the optically altered electromagnetic radiation is detected by means of the detector for determining the optical property of the optical system and the radiation energy of the individual radiation packets is determined prior to their impact on the analysis element by means of the energy sensor. In the case in which the aberration behavior of the optical system is determined by means of shear interferometry as an optical property, the analysis element may be, for example, the diffraction grating used therein. In this case, the electromagnetic radiation is changed to produce an interferogram. In alternative measuring methods z. B. also conceivable to design the analysis element as a polarizer.

In an embodiment of the invention is the wavelength the electromagnetic radiation in the EUV and / or higher frequency Wavelength range. Advantageously, the radiation source as EUV radiation source, z. B. in the form of a plasma source, for Generating extreme ultraviolet radiation with z. As a wavelength configured by 13.4 nm.

In a further embodiment according to the invention the optical property of the optical system by evaluating the determined by the detector radiation, the optical property the aberration behavior of the optical system is by which Determine the wavefront of the electromagnetic radiation Interaction with the optical system is determined.

In a further embodiment according to the invention the wavefront of electromagnetic radiation after interaction with the optical system by means of a detector comprising Wavefront measuring device determined. The wavefront measuring device includes in particular the aforementioned analysis structure. In one embodiment According to the invention, the wavefront measuring device is an interferometer executed. Alternatively, this can also be used as a Shack-Hartmann sensor be designed.

In a further embodiment according to the invention, the wavefront measuring device is configured as a shear interferometer or so-called "shearing interferometer". In this case, the analysis element is designed as a diffraction grating. Alternatively, as a wavefront measuring device, for example, a point diffraction interferometer or so-called "point diffraction interferometer" in question. Such a point diffraction interferometer is for example the expert US Pat. No. 6,307,635 B1 known.

In a further embodiment according to the invention by means of each of the radiation packets an interferogram on the detector generated. Furthermore, the respective radiation energy of the individual radiation packets, in particular time-resolved, by means of an energy sensor measured, the respective measured radiation energy is through assigned the corresponding radiation packet generated interferogram, the interferograms are assigned using the individual interferograms Radiation energies manipulated, and from the manipulated interferograms becomes the wavefront of the electromagnetic radiation after their Interaction with the optical system determined. By the appropriate Manipulation of the interferograms can be the Keep measurement results free from the influence of during generation the electromagnetic radiation occurring intensity fluctuations. The manipulation of the interferograms can be done in different ways done as described below.

In An embodiment according to the invention comprises the manipulation the interferograms the measure, the respective intensity of the individual interferograms detected by the detector to the radiation energy assigned to the respective interferogram adapt. For example, it is possible to calibrate the interferograms ensure that the interferograms recorded are the respective interferograms divided radiation energies become.

In a further embodiment according to the invention, the interferograms are respectively generated by superposition of a reference wave with a test wave generated by the respective radiation packet after their interaction with the optical system. In successive phase steps different phase differences are generated between the test wave and the reference wave, and the interferograms generated at the individual phase steps are recorded by means of the detector. The manipulation of the interferograms comprises the measure of adapting the respective duration of the interferogram recording taking place during the individual phase steps using the radiation energy assigned to the respective interferogram. The different phase differences of the individual phase steps can be generated, for example, by shifting the diffraction grating or shifting the radiation source transversely to the propagation direction of the electromagnetic radiation, in each case by fractions of the grating period. Thus, in the method according to the invention, n phase steps, for example 16 phase steps, can be carried out with a respective increment of one nth of the period of the diffraction grating. The inventive manipulation of the interferograms by adaptation of the respective duration of taking place during the individual phase steps interferogram Recording using the radiant energy associated with the respective interferogram can be effected, for example, by stopping the recording of the interferograms by the detector as soon as the intensity temporally integrated by the energy sensor has exceeded a nominal value. Thus, intensity fluctuation in the radiation intensity can be corrected. In particular, a synchronization of the interferogram recording with the beam interruption device is advantageous, so that, depending on the radiation energy recorded by the detector, the next radiation packet is released sooner or later.

In a further embodiment according to the invention the manipulation of interferograms the measure, a dependent on the interferogram recorded interferogram from the radiant energy determined for this radiation packet or to exploit fluctuations. So can be a recorded Interferogram are deleted when the associated radiant energy exceeds a certain upper limit or one certain lower limit. Also may be due an inadmissibly high fluctuation of the incoming electromagnetic Radiation that measured for a particular radiation packet Interferogram are deleted from the evaluation and the measurement of the deleted interferogram. Alternatively, you can also a derivative of the wavefront calculated from interferograms or the wavefront calculated from the derivatives is deleted.

In a further embodiment of the invention the interferograms each by superposition of a reference wave with a test wave generated by the respective radiation packet produced according to their interaction with the optical system. In successive Phase steps are different phase differences between the Test wave and the reference wave generated, and the individual Phase steps generated interferograms by means of the detector recorded. The respective test wave is by means of a diffraction grating generated with a grating period, and during recording of an interferogram associated with a single phase step becomes the phase difference between the test wave and the reference wave changed by an integer multiple of the grating period. The manipulation of the interferograms includes the measure, the change of the phase difference during the single phase steps (slow phase shift) using the radiation energy assigned to the respective interferogram to control. This change in the phase difference by one integral multiple of the grating period during the individual Phase steps and thus during the integration time of Detector is also referred to as so-called "fast phase shifting". In contrast, the change is the phase difference by fractions of the diffraction grating between the individual phase steps referred to as "slow phase shifting". The "fast Phase shifting "is advantageous when both the coherence mask as well as the diffraction grating in each case as two-dimensional structures are formed. By the "fast phase shifting" become unused orthogonal interference orders in the respective Interferogram suppressed. The "fast phase shifting" can like the "slow phase shifting" described above a lateral movement of the diffraction grating or the coherence mask be effected.

In a further embodiment according to the invention by means of several in the beam path of the electromagnetic radiation arranged energy sensors, the radiation energy of the radiation packets pupil-resolved with respect to the optical system. The energy sensors are advantageously over distributes the beam cross section of the electromagnetic radiation. This can be a calibration of the measurement result of the optical property also be carried out spatially resolved, which the measuring accuracy can be further increased.

In a further embodiment according to the invention Manipulation of interferograms measure, intensity the interferograms by means of pupil-resolved radiation energy as a function of the pupil location, of the complete interruption the electromagnetic radiation by means of the beam interrupting device required period (or closing time) as well as the temporal length of the radiation packet (or the exposure time of the detector).

In a further embodiment according to the invention, the shear interferometer comprises a coherence mask with a two-dimensional measurement pattern and a two-dimensional diffraction grating. The measurement pattern can be designed, for example, in the form of a checkerboard pattern. The same applies analogously to the two-dimensional diffraction grating. Examples of such coherence masks and diffraction gratings are e.g. In DE 10 2005 041 373 A1 illustrated.

In an alternative embodiment according to the invention, the shear interferometer comprises a coherence mask with a measurement pattern and a diffraction grating, wherein the measurement pattern and / or the diffraction grating is configured in a one-dimensional manner. Such shear interferometers are referred to herein as Ronchi shear interferometers. This is understood to mean a shear interferometer with one of the following mask-grid combinations: two-dimensional nale coherence mask combined with one-dimensional diffraction grating, one-dimensional coherence mask combined with two-dimensional diffraction grating, and one-dimensional coherence mask combined with one-dimensional diffraction grating. The Ronchi shear interferometer does not require a "fast phase shift" because orthogonal interference orders do not exist.

In a further embodiment according to the invention by means of each of the radiation packets an interferogram on the detector generated by superimposing a reference wave with a test wave generated by the respective radiation packet after their interaction with the optical system is formed, in successive phase steps are different Generates phase differences between the test wave and the reference wave, the interferograms generated during the individual phase steps be recorded by means of the detector recorded by means of an evaluation, where in the evaluation for each recorded interferogram is decided on the basis of a mathematical criterion, whether the respective interferogram for determining the optical property is used or discarded instead. As a result, you can as well as several interferograms, especially a whole collective Interferograms are discarded. Advantageously, then the measurement of the discarded interferogram or discarded one Interferograms repeated. In one embodiment of the Evaluation of the interferograms is made in the individual steps recorded by the "slow phase shifting" Interferograms calculated the derivative of the wavefront. there At each point of the interferograms, their course becomes the course compared to a sine function and exceeding a certain value Deviation, z. Eg with a deviation of more than 5% or 10%, at one point discarded the corresponding interferogram. In this Case, strong phase fluctuations during the integration time were at least an interferogram occurred by the described mathematical Criterion can be detected.

According to the invention, the aforementioned object can also be achieved by means of a further method for determining an optical property of an optical system which comprises: irradiating electromagnetic radiation onto the optical system, detecting the electromagnetic radiation by means of a detector after interacting with the optical system in temporally limited successive ones Radiation packets, checking the individual radiation packets based on at least one predetermined criterion, and determining the optical property of the optical system ( 12 ) by evaluating only those radiation packets that meet the predetermined criterion.

The The aforementioned object can further according to the invention by means of a further device for determining an optical Property of an optical system to be solved. These Apparatus comprises: a radiation source configured to is to generate electromagnetic radiation, a detector for Detecting the electromagnetic radiation after interaction of the same with the optical system in temporally limited successive Radiation packages, as well as an evaluation, which is configured is, the individual radiation packets based on at least one predetermined Criteria, as well as the optical property the optical system by evaluating only those radiation packets, that meet the given criterion.

With In other words, the evaluation of the radiation packets is checked decided on the basis of the at least one predetermined criterion, whether a single radiation packet is discarded or further evaluation should be used. For example, an interferogram recorded by the detector can be used depending on the intended for this radiation package Radiation energy or fluctuations discarded. A recorded Interferogram can z. B. be deleted if the associated Radiation energy exceeds a certain upper limit or below a certain lower limit. Also can due to an inadmissibly high fluctuation of the incoming electromagnetic radiation that for a given radiation packet measured interferograms are deleted from the evaluation and the Measurement of the deleted interferogram can be repeated. alternative can also be calculated from interferograms derivative of the wavefront or the wavefront calculated from the derivatives is deleted.

In one embodiment of the device according to the invention, the radiation source is configured as an EUV radiation source. In a further embodiment according to the invention, the apparatus further comprises a beam interruption device which is configured to interrupt the electromagnetic radiation, so that the electromagnetic radiation impinges on the detector in the time-limited radiation packets. In a further embodiment according to the invention, the beam interruption device comprises a closure element and a displacement device, wherein the displacement device is configured to move the closure element into the beam path of the electromagnetic radiation and / or move out therefrom. In a According to a further embodiment of the invention, the device comprises a wavefront measuring device comprising the detector for measuring the wavefront of the electromagnetic radiation after interaction thereof with the optical system, and the optical property of the optical system which can be determined by the device is the aberration behavior of the optical system. In a further embodiment according to the invention, the wavefront measuring device comprises a shear interferometer.

According to the Invention will continue an exposure system for the Lithography provided, which is an optical system z. In Shape of a projection optics for imaging mask structures includes a wafer. Furthermore, the exposure system includes the Inventive device for determining a optical property of the optical system. In one embodiment According to the invention, the exposure system is an EUV exposure system configured.

The with respect to the embodiments listed above of the inventive method specified features can according to the inventive Device are transmitted, and vice versa. Which resulting embodiments of the invention Apparatus is expressly intended from the disclosure of the invention includes his.

Brief description of the drawings

following Be exemplary embodiments of an inventive Device and a method according to the invention for determining an optical property of an optical system the attached schematic drawings explained. It shows:

1 1 is a schematic side view of a first embodiment of a device according to the invention for determining an optical property of an optical system,

2 1 is a schematic side view of an exemplary embodiment of a projection exposure apparatus according to the invention for microlithography with a projection optical system and an embodiment of an apparatus according to the invention for determining an optical property of the projection optical system integrated therein;

3 a diagram which illustrates intensity fluctuations of an emitted from a plasma source EUV radiation,

4 a power of a plasma source integrated over the beam cross section of the EUV radiation as a function of time when closing an optical shutter,

5 an illustration of a movement of a closure element of the optical shutter when interrupting an electromagnetic illumination beam,

6 for different shear interferometric measurements at individual phase steps certain interferogram intensities in conventional evaluation of the interferograms, compared with an evaluation according to the invention, as well as

7 Diagrams for illustrating the reproducibility of aberrations determined by conventional shear interferometric measurement compared with the reproducibility of aberrations, which were determined by means of the measuring method according to the invention.

Detailed description inventive embodiments

In the embodiments described below are functionally or structurally similar elements as far as possible with the same or similar Provided with reference numerals. Therefore, to understand the Features of the individual elements of a particular embodiment to the description of other embodiments or the general description of the invention will be referred to.

1 shows a first embodiment of a device according to the invention 10 for determining an optical property of an optical system 12 in the form of a projection optical system of a projection exposure apparatus for microlithography. In the present embodiment, the optical system to be measured for EUV radiation, ie extreme ultraviolet radiation having a wavelength of z. B. 13.4 nm, designed. The optical system 12 includes only reflective optical elements in the form of mirrors. 1 illustrated next to the optical axis 13 of the optical system 12 an aperture stop 14 which is a pupil 15 of the optical system 12 Are defined.

The device 10 includes a radiation source 16 , which as a plasma source for generating electromagnetic radiation 17 is designed in the form of EUV radiation. The EUV radiation 17 is from the radiation source 16 in pulsed form at a repetition rate of about one pulse per millisecond. The respective pulse duration amounts to a few nanoseconds. 3 shows a measurement of the intensity fluctuations of such produced by a plasma source EUV radiation 17 in pulse-resolved form.

The device 10 further comprises a beam interrupting device 20 in the form of an optical shutter or a so-called "shutter". In the in 1 the embodiment shown is the beam interrupting device 20 between the radiation source 16 and a lighting mirror 18 arranged. Alternatively, the beam interruption device 20 but also at other points of the beam path of the electromagnetic radiation 17 be arranged. The beam interrupting device 20 includes a closure element 22 and a displacement device 24 , by means of the closure element 22 along a displacement direction 26 can be moved back and forth. In this case, the closure element 22 in the beam path of the electromagnetic radiation 17 moved in or moved out of it. As a result, so can the electromagnetic radiation 17 be interrupted so that the electromagnetic radiation 17 in time-limited radiation packets to a detector 36 the device 10 incident.

In operation of the device 10 becomes the beam interrupting device 20 actuated such that the resulting radiation packets have a maximum time length of 4 seconds, in particular a time length of 100 to 500 milliseconds. The electromagnetic radiation 17 is by means of the illumination mirror 18 on a coherence mask 30 a shear interferometer steered. The shear interferometer includes the coherence mask 30 , an analysis element in the form of a diffraction grating 32 as well as the detector 36 ,

The coherence mask 30 has measuring structures, for example in the form of two-dimensional checkerboard patterns. In the in 1 The embodiment shown is the coherence mask 30 designed as a transmission mask. Furthermore, the electromagnetic radiation is located in the beam path 17 an energy sensor 28 which is configured to determine the radiant energy of the individual radiation packets. The energy sensor 28 is advantageously in the beam path of the electromagnetic radiation 17 in front of the diffraction grating 32 arranged. In the example shown, the energy sensor is between the illumination mirror 18 and the coherence mask 30 positioned.

In one embodiment, multiple energy sensors may also be used 28 in the beam path of the electromagnetic radiation 17 be arranged such that the radiation energy of the radiation packets pupillreleased with respect to the pupil 15 of the optical system 12 can be determined. The diffraction grating 32 is at a displacement device 34 attached, with which the diffraction grating 32 in the xy plane according to the coordinate system of 1 , and thus across the optical axis 13 , is displaceable.

By superposition of by diffraction at the diffraction grating 32 generated waves, especially by superposition of a reference wave with a test wave, a changed electromagnetic radiation 17b generates an overlay pattern in the form of an interferogram 39 on a detector surface 38 of the detector 36 forms.

The device 10 further comprises a control device 40 with which the displacement device 24 the beam interrupting device 20 , the displacement device 34 of the diffraction grating 32 as well as the detector 36 , as described below, are operated synchronized with each other. On a control signal of the control device 40 interrupts the beam interrupting device 20 the electromagnetic radiation 17 in periodic order so that the electromagnetic radiation 17 in time-limited radiation packets, the optical system 12 passes.

The maximum length of the radiation packets is 4 seconds. In one embodiment, the time length is 100 to 1000 milliseconds. Between the individual radiation packets is the diffraction grating 32 by means of the displacement device 34 by a fraction of the period of the diffraction grating 32 , for example, one-sixteenth of the grating period, shifted. In this case, sixteen so-called phase steps are performed, between which the diffraction grating 32 each offset by a fraction of the grating period. The phase steps are respectively synchronized with the successive radiation packets in the form that in each case a phase step takes place when the electromagnetic radiation 17 is interrupted, ie the shutter 20 to is. The detector 36 is from the controller 40 controlled such that the interferogram generated during a single phase step 39 over the entire exposure time of a radiation packet from the detector 36 recorded or integrated.

In one embodiment of the elements 30 . 32 . 34 such as 36 comprehensive shear interferometer has the coherence mask 30 a two-dimensional measurement pattern, and the diffraction grating 32 is also structured in two dimensions. In this case, the diffraction grating becomes 32 phase-shifted in both the x and y directions in n steps in each case. From the interferograms generated by phase shifting in the x and y directions 39 be by means of an evaluation 42 calculates the derivatives of the wavefront in the x and y directions. By integrating the two derivatives, the wavefront of the electromagnetic radiation then becomes 17 after passing through the optical system 12 calculated.

From the wavefront thus determined, the aberration behavior of the optical system can be determined 12 determine. Before the evaluation of the interferograms 39 to calculate the wavefront, the interferograms become 39 first by means of the individual radiation packets from the energy sensor 28 manipulated measured radiation energies. As already mentioned, the energy sensor measures 28 for each of the individual phase steps, the respective radiation energy of the associated radiation packet. The respective measured radiation energy is assigned to the respective interferogram generated by the corresponding radiation packet.

In a first embodiment of the manipulation of the interferograms 39 is the respective intensity of the individual from the detector 36 recorded interferograms 39 arithmetically to the respective interferogram 39 adapted radiation energy adjusted. This is done, for example, by dividing the individual interferograms before their further processing by the respectively associated radiation energy.

In a further embodiment of the manipulation of the interferograms, that of the energy sensor 28 radiant energy measured for the respective radiation packet is used to adjust the respective duration of the interferogram recording taking place during the corresponding phase step. So z. B. the integration of the respective interferogram by the detector 36 be canceled as soon as the energy sensor 28 it is reported that the energy of the radiation packet integrated since the start of the radiation packet has exceeded a certain value.

In a further embodiment of the manipulation of the interferograms, a by means of the detector 36 recorded interferogram 39 discarded if the means of the energy sensor 28 certain associated radiant energy exceeds a certain maximum value or falls below a certain minimum value. Then the measurement of the discarded interferogram is made 39 repeated. In a further embodiment, in the evaluation of the recorded interferograms 39 based on a mathematical criterion decided whether the respective interferogram 39 for determining the optical property of the optical system 12 is used or discarded instead. This can also apply to an entire single measurement. In particular, a derivative of the wavefront calculated from interferograms or the wavefront calculated from the derivatives can also be deleted.

In one embodiment, the manipulation includes the interferograms 39 measure, intensity of interferograms 39 by means of the aforementioned pupil-resolved radiation energy as a function of the pupil location, which is determined on the basis of 4 and 5 illustrated closing time of the beam interrupting device 20 and the exposure time of the detector 36 for recording an interferogram 39 to correct. This correction is particularly advantageous when the closing time accounts for a significant proportion of the exposure time.

The above-described shifting of the diffraction grating 32 By fractions of the grating period in n different phase steps is also referred to as so-called "slow phase shifting". In addition, in the embodiment of the shear interferometer, in which both the coherence mask 30 as well as the diffraction grating 32 two-dimensionally designed, in addition a so-called "fast phase shifting" carried out.

When "fast phase shifting" is the diffraction grating 32 while recording an interferogram 39 through the detector 36 shifted in the course of a single phase step of the "slow phase shift" by an integer multiple of the grating period orthogonal to the direction of the "slow phase shift". Thus, unnecessary orthogonal interference orders in the associated interferogram can be suppressed. The shift of the phase grating 32 "Fast Phase Shifting" is controlled using the radiant energy measured during each "slow phase shift" phase step. This makes it possible to improve the reproducibility of the wavefront measurements.

In another embodiment of the shear interferometer, the measurement pattern is the coherence mask 30 and / or the diffraction grating 32 designed one-dimensionally. In this case we speak of a Ronchi shear interferometer. In the Ronchi shear interferometer, the "fast phase shift" is not performed because orthogonal interference orders do not exist.

The device 10 according to 1 may be configured to be independent of a projection exposure equipment in the laboratory for measuring a single optical system 12 , such as a microlithographic projection optics, can be used. In an alternative embodiment, the device is 10 integrated into a microlithographic projection exposure machine.

2 shows an embodiment of an EUV projection exposure system 50 for microlithography, in which the device 10 in a opposite to the in 1 illustrated device 10 slightly modified embodiment is integrated. The projection exposure machine 50 can be used as a stepper or be executed as a scanner. The device 10 according to 2 is different from the device 10 according to 1 in that the coherence mask 30 is not formed as a transmission mask but as a reflection mask, and that the beam interruption device 20 not in front of the illumination mirror 18 but between the illumination mirror 18 and the coherence mask 30 is arranged.

The radiation source 16 and the illumination mirror 18 are part of a lighting system 52 the projection exposure system 50 for exposing a product mask during the exposure operation of the projection exposure apparatus 50 , The projection exposure machine 50 includes a mask table 58 , which is also called a "reticle stage" and a reference frame 54 and a relative to this slidably mounted mask holding device 56 having. The coherence mask 30 is held in the execution of the measuring method according to the invention of the mask holder. 2 shows an exemplary projection optics 12 which has several reflective optical elements 60 includes.

Furthermore, the projection exposure system includes 50 a substrate table 66 which can also be referred to as a "wafer stage" and a reference frame 64 and a substrate holding device 62 includes. On the substrate holding device 62 is in the exposure mode of the projection exposure apparatus 50 arranged to be exposed wafer. In the embodiment shown, the detector is 36 in an edge region of the substrate holding device 37 integrated.

4 shows in the upper section over the beam cross section of the electromagnetic radiation 17 integrated power P as a function of time when breaking the electromagnetic radiation 17 by means of the beam interrupting device 20 in the form of a so-called "shutter" in response to a in the lower section of the 4 The triggering signal S is shown. The time between the triggering of the trigger signal and the closing of the "shutter" is approximately 15 milliseconds. The closing time and, analogously, the opening time of the "shutter" are thus an order of magnitude smaller than the integration time in the phase shift of preferably 100 to 500 milliseconds.

5 illustrates the interruption of electromagnetic radiation 17 by moving the closure element 22 in the direction of displacement 26 so that the closure element 22 successively in the illumination beam 17a the electromagnetic radiation 17 penetrates.

6 illustrates the manipulation of the interferograms according to the invention 39 achieved improvement of the reproducibility of the intensity of the interferograms 39 , That under (a) in 6 The graph shown shows the intensity of interferograms taken for the individual phase steps of "slow phase shifting" using a conventional Ronchi interferometer for ten consecutive measurements. The diagram labeled (b) shows the intensities of these interferograms when measured by the device 10 in an embodiment of the invention.

7 shows a comparison of the reproducibility of measured wavefront deviations, broken down by Zernike coefficients. This in 7 The graph labeled (a) shows the 3-sigma value of the reproducibility of a wavefront deviation measured by a conventional Ronchi interferometer. The diagram labeled (b) in 7 shows for comparison the reproducibility of the wavefront deviation in the determination of the same by means of the device 10 in an embodiment of the invention.

In another not graphically illustrated embodiment of the device 10 According to the invention, the radiation packets are only after the impact of electromagnetic radiation 17 on the detector 36 Are defined. For this purpose, the detected electromagnetic radiation is subdivided into temporally limited successive radiation packets such that the respective total radiant energy of the individual radiation packets lies within a predetermined energy range.

10

contraption for determining an optical property

12

optical system

13

optical axis

14

aperture

15

pupil

16

radiation source

17

electromagnetic radiation

17a

illumination beam

17b

changed electromagnetic radiation

18

lighting levels

20

Beam interruption device

22

closure element

24

shifter

26

shift direction

28

energy sensor

30

coherence mask

32

diffraction grating

34

shifter

36

detector

38

detector surface

39

interferogram

40

control device

42

evaluation

50

EUV projection exposure system

52

lighting system

54

frame of reference

56

Mask holding device

58

mask table

60

reflective optical element

62

Substrate holder

64

frame of reference

66

substrate table

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 102005041373 A1 [0002, 0035]
• - US 6307635 B1 [0027]

Claims (36)

Method for determining an optical property of an optical system ( 12 ) comprising the steps of: - irradiating electromagnetic radiation ( 17 ) on the optical system ( 12 ), - detecting the electromagnetic radiation ( 17 ) by means of a detector ( 36 ) after interaction thereof with the optical system ( 12 ), - Periodic interruption of the electromagnetic radiation ( 17 ), so that the electromagnetic radiation ( 17 ) in time-limited radiation packets to the detector ( 36 ), and - evaluating at least two of the detector ( 36 ) detected radiation packets for determining the optical property of the optical system ( 12 ). Method for determining an optical property of an optical system ( 12 ) comprising the steps of: - irradiating electromagnetic radiation ( 17 ) on the optical system ( 12 ), - detecting the electromagnetic radiation ( 17 ) by means of a detector ( 36 ) after interaction thereof with the optical system ( 12 ), and - evaluating the detected electromagnetic radiation by defining temporally limited successive radiation packets by detecting the detected electromagnetic radiation ( 17 ) is divided such that the respective total radiant energy of the individual radiation packets is in a predetermined energy range, and determining the optical property of the optical system ( 12 ) from the defined radiation packets. Method for determining an optical property of an optical system ( 12 ) comprising the steps of: - irradiating electromagnetic radiation ( 17 ) on the optical system ( 12 ), - detecting the electromagnetic radiation ( 17 ) by means of a detector ( 36 ) after interaction thereof with the optical system ( 12 ) in temporally limited successive radiation packets, - checking the individual radiation packets on the basis of at least one predetermined criterion, and - determining the optical property of the optical system ( 12 ) by evaluating only those radiation packets that meet the predetermined criterion. Method for determining an optical property of an optical system ( 12 ) comprising the steps of: - irradiating electromagnetic radiation ( 17 ) on the optical system ( 12 ), - detecting the electromagnetic radiation ( 17 ) by means of a detector ( 36 ) after interaction thereof with the optical system ( 12 ), and - evaluating at least two temporally limited radiation packets from the detector ( 36 ) detected electromagnetic radiation ( 17 ) for determining the optical property of the optical system ( 12 ), wherein the radiation packets each have a minimum time length of 50 milliseconds. Method for determining an optical property of an optical system ( 12 ) comprising the steps of: - irradiating electromagnetic radiation ( 17 ) on the optical system ( 12 ), - detecting the electromagnetic radiation ( 17b ) by means of a detector ( 36 ) for determining the optical property of the optical system ( 12 ), the electromagnetic radiation ( 17 ) in time-limited radiation packets to the detector ( 36 ), and determining the respective radiation energy of the individual radiation packets by means of an energy sensor ( 28 ). Method according to one of the preceding claims, which the features of the method according to at least another of the preceding claims. Method according to Claim 1 or 6, in which the periodic interruption of the electromagnetic radiation ( 17 ) by moving in and out a Verschusselements ( 22 ) in the beam path or from the beam path of the electromagnetic radiation ( 17 ) he follows. Method according to Claim 1 or 6, in which the periodic interruption of the electromagnetic radiation ( 17 ) by triggering the electromagnetic radiation ( 17 ) generating radiation source ( 16 ) he follows. Method according to one of Claims 5 to 8, in which the electromagnetic radiation ( 17 ) after their interaction with the optical system ( 12 ) by means of an analysis element ( 32 ) is optically altered, the optically altered electromagnetic radiation ( 17b ) by means of the detector ( 36 ) for determining the optical property of the optical system ( 12 ) and the radiation energy of the individual radiation packets before their impact on the analysis element ( 32 ) by means of the energy sensor ( 28 ) is determined. Method according to one of the preceding claims, in which the radiation packets each have a maximum time length of 4 seconds. Method according to one of the preceding claims, in which the wavelength of the electromagnetic radiation ( 17 ) is in the EUV wavelength range. Method according to one of the preceding claims, in which the optical property of the optical system ( 12 ) by evaluating the from the detector ( 36 ) is determined, wherein the optical property of the aberration behavior of the optical system ( 12 ) which is determined by determining the wavefront of the electromagnetic radiation ( 17 ) after interaction with the optical system ( 12 ) is determined. Method according to one of the preceding claims, in which the wavefront of the electromagnetic radiation ( 17 ) after interaction with the optical system ( 12 ) by means of a detector ( 36 ) wavefront measuring device ( 30 . 32 . 38 ) is determined. Method according to Claim 13, in which the wavefront measuring device ( 30 . 32 . 38 ) is configured as a shear interferometer. Method according to one of the preceding claims, in which by means of each of the radiation packets an interferogram ( 39 ) on the detector ( 36 ) is generated, the respective radiation energy of the individual radiation packets by means of an energy sensor ( 28 ), the respective measured radiation energy is the interferogram generated by the corresponding radiation packet ( 39 ), the interferograms ( 39 ) using the individual interferograms ( 39 ) are manipulated and from the manipulated interferograms ( 39 ) the wavefront of the electromagnetic radiation ( 17 ) after their interaction with the optical system ( 12 ) is determined. Method according to Claim 15, in which the manipulation of the interferograms ( 39 ) comprises the measure, the respective intensity of the individual from the detector ( 36 ) recorded interferograms ( 39 ) to the respective interferogram ( 39 ) to adjust associated radiation energy. Method according to Claim 15 or 16, in which the interferograms ( 39 ) in each case by superposition of a reference wave with a test wave generated by the respective radiation packet after its interaction with the optical system ( 12 ), different phase differences between the test wave and the reference wave are generated in successive phase steps, the interferograms generated at the individual phase steps ( 39 ) by means of the detector ( 36 ) and the manipulation of the interferograms ( 39 ) comprises the measure of the duration of each interferogram recording during the individual phase steps using the respective interferogram ( 39 ) to adjust the associated radiation energy. Method according to one of Claims 15 to 17, in which the manipulation of the interferograms ( 39 ) comprises the measure, one by means of the detector ( 36 ) recorded interferogram ( 39 ) depending on the radiation energy or fluctuations determined for this radiation packet. Method according to one of Claims 15 to 18, in which the interferograms ( 39 ) in each case by superposition of a reference wave with a test wave generated by the respective radiation packet after its interaction with the optical system ( 12 ), different phase differences between the test wave and the reference wave are generated in successive phase steps, the interferograms generated at the individual phase steps ( 39 ) by means of the detector ( 36 ), the respective test wave by means of a diffraction grating ( 32 ) with a grating period during the recording of an interferogram associated with a single phase step ( 39 ) the phase difference between the test wave and the reference wave is changed by an integer multiple of the grating period, and the manipulation of the interferograms ( 39 ) comprises the measure to control the change in the phase difference during the individual phase steps using the radiant energy associated with the respective interferogram. Method according to one of the preceding claims, in which by means of several in the beam path of the electromagnetic radiation ( 17 ) arranged energy sensors ( 28 ) the radiation energy of the radiation packets is pupil-resolved with respect to the optical system ( 12 ) is determined. Method according to Claim 20, in which the manipulation of the interferograms ( 39 ) comprises the measure, the intensity of the interferograms ( 39 ) by means of the pupil-resolved radiation energy as a function of the pupil location, of the complete interruption of the electromagnetic radiation by means of the beam interruption device ( 20 ) and the time length of the radiation packet. Method according to one of Claims 14 to 21, in which the shear interferometer ( 30 . 32 . 38 ) a coherence mask ( 30 ) with a two-dimensional measurement pattern and a two-dimensional diffraction grating ( 32 ). Method according to one of Claims 14 to 21, in which the shear interferometer ( 30 . 32 . 38 ) a coherence mask ( 30 ) with a measuring pattern and a diffraction grating ( 32 ), wherein the measuring pattern and / or the diffraction grating ( 32 ) is designed one-dimensionally. Method according to one of the preceding claims, in which by means of each of the radiation packets an interferogram ( 39 ) on the detector ( 36 ), which is formed by superposition of a reference wave with a test wave generated by the respective radiation packet after their interaction with the optical system, different phase differences between the test wave and the reference wave are generated in successive phase steps, the interferograms generated at the individual phase steps ( 39 ) by means of the detector ( 36 ) and by means of an evaluation device ( 42 ), whereby in the evaluation for each recorded interferogram ( 39 ) is decided on the basis of a mathematical criterion, whether the respective interferogram ( 39 ) is used to determine the optical property or is discarded instead. Contraption ( 10 ) for determining an optical property of an optical system ( 12 ) with: a radiation source ( 16 ) which is configured to emit electromagnetic radiation ( 17 ) and a detector ( 36 ) for detecting the electromagnetic radiation ( 17 ) after interaction thereof with the optical system ( 12 ), the device ( 10 ) is configured to periodically interrupt the electromagnetic radiation so that the electromagnetic radiation ( 17 ) in time-limited radiation packets to the detector ( 36 ), and the device ( 10 ) further comprises: an evaluation device ( 42 ) which is configured to receive at least two from the detector ( 36 ) detected radiation packets for determining the optical property of the optical system ( 12 ). Contraption ( 10 ) for determining an optical property of an optical system ( 12 ) with: a radiation source ( 16 ) which is configured to emit electromagnetic radiation ( 17 ) and a detector ( 36 ) for detecting the electromagnetic radiation ( 17 ) after interaction thereof with the optical system ( 12 ), as well as an evaluation device ( 42 ), which is configured from the detected electromagnetic radiation ( 17 ) define temporally limited successive radiation packets by detecting the detected electromagnetic radiation ( 17 ) is divided such that the respective total radiant energy of the individual radiation packets is within a predetermined energy range, and the defined radiation packets for determining the optical property of the optical system ( 12 ). Contraption ( 10 ) for determining an optical property of an optical system ( 12 ) with: a radiation source ( 16 ) which is configured to emit electromagnetic radiation ( 17 ), a detector ( 36 ) for detecting the electromagnetic radiation ( 17 ) after interaction thereof with the optical system ( 12 ) in temporally limited successive radiation packets, as well as an evaluation device ( 42 ), which is configured to check the individual radiation packets based on at least one predetermined criterion, as well as the optical property of the optical system ( 12 ) by evaluating only those radiation packets that meet the predetermined criterion. Contraption ( 10 ) for determining an optical property of an optical system ( 12 ) with: a radiation source ( 16 ) which is configured to emit electromagnetic radiation ( 17 ) and a detector ( 36 ) for detecting the electromagnetic radiation ( 17 ) after interaction thereof with the optical system ( 12 ), as well as an evaluation device ( 42 ) which is configured to receive at least two time-limited radiation packets from the detector ( 36 ) detected electromagnetic radiation ( 17 ) for determining the optical property of the optical system ( 12 ), wherein the radiation packets each have a minimum time length of 50 milliseconds. Contraption ( 10 ) for determining an optical property of an optical system ( 12 ) with: a radiation source ( 16 ) which is configured to emit electromagnetic radiation ( 17 ) and a detector ( 36 ) for detecting the electromagnetic radiation ( 17 ), the device ( 10 ) is configured such that the electromagnetic radiation ( 17 ) in time-limited radiation packets to the detector ( 36 ), and the device ( 10 ) further comprises: an energy sensor ( 28 ), which in the beam path of the electromagnetic radiation ( 17 ) is arranged and configured to determine the respective radiation energy of the individual radiation packets. Device according to one of claims 25 to 29, which the features of the device according to at least another of claims 25 to 29. Device according to one of Claims 25 to 30, in which the radiation source ( 16 ) is configured as EUV radiation source. Device according to one of claims 25 to 31, which comprises a detector ( 36 ) comprehensive wavefront measuring device ( 30 . 32 . 38 ) for measuring the wavefront of the electromagnetic radiation ( 17 ) after interaction thereof with the optical system ( 12 ) and in which by means of the device ( 10 ) determinable optical property of the optical system ( 12 ) the aberration behavior of the optical system ( 12 ). Device according to Claim 32, in which the wavefront measuring device ( 30 . 32 . 38 ) comprises a shear interferometer. Device according to one of claims 25 to 33, which is configured to perform the method according to any one of Perform claims 1 to 24. Exposure system ( 50 ) for lithography with an optical system ( 12 ) as well as the device ( 10 ) according to one of claims 25 to 34 for determining the optical property of the optical system ( 12 ). Exposure plant according to Claim 35, which is used as an EUV exposure system ( 50 ) is configured.