DE102006059823A1 - Method for loading case aberration measurement of optical system, involves providing multi-channel measuring device for parallel production of aberration indicative measuring values for multiple field points - Google Patents

Abstract

The method involves providing a multi-channel measuring device for parallel production of aberration indicative measuring values for multiple field points. The measuring device has a measuring sensor element (7) and a device (8) for controlled masking of the measuring sensor elements before emitting a radiation (5). Positioning of pre selected loading case reproduces a case of operation of the optical system with corresponding radiation heating loading of the optical system by masking measuring sensor element for case of operation. The aberrations of the optical system are determined for the preset loading case by recorded evaluated measuring value. Independent claims are also included for the following: (1) a measuring device for loading case aberration measurement of an optical system (2) a method for adjustment of an optical system.

Description

The The invention relates to a method and a device for Load case aberration measurement of an optical system and on a related one Method for adjusting an optical system, wherein the optical system in particular to act a microlithography projection lens can.

In microlithography for semiconductor wafer patterning by projection exposure as an important field of application of the invention is the generation ever finer structures to further increase the density of integration demanded by thus generated integrated circuits. This brings the Use of ever shorter Exposure wavelengths and higher Radiation powers of the laser light sources used with it. This also increases the requirement for imaging quality of the associated exposure system, d. H. the illumination system and in particular the projection objective, resulting in decreasing aberration specifications, d. H. Requirements maximum allowable aberrations, especially the projection lens manifests.

traditionally, the adjustment and removal of microlithography exposure systems takes place and in particular the projection lens based on measurements, the relevant optical system using a measuring device and a measuring radiation are made, which has no relation to the planned, later Use of the optical system. In particular, the radiation load of the optical system, d. H. the radiation intensity with which the optical. System is applied during the measuring operations to Obtaining measured values that make up the aberration behavior of the optical system, traditionally much lower as in later operational use. Due to the required high imaging quality correspondingly high-precision wavefront measurement techniques come used, in particular high-precision moire measuring techniques and interferometric Measurement techniques such as lateral shear interferometry and point diffraction interferometry, what for more Details on this earlier Patent applications of the applicant can be referenced.

The Most components of an optical system, such. As lenses show a known one strahlungsaufheizabhängiges Aberration behavior, d. H. their aberrations can be increased by heating up change due to the applied radiation load. In modern microlithography projection lenses meanwhile, a point has been reached where it is no longer always guaranteed is that the exposure system and in particular the projection lens under the radiation load in the case of application, the aberration specification comply, to which it has been adjusted at the end of the manufacturing process, if this adjustment was made on the basis of the aforementioned conventional "cold case", in which the radiation exposure while the Aberrationsmessungen is much lower than in the later application.

The publication DE 103 43 313 A1 deals with the problem of radiation heating induced deformations of a z. B. masking unit used in a wavefront measuring device, as a remedy a compensating temperature of the mask unit is proposed.

In the published patent application WO 2004/099877 A1 is a measuring device for optically measuring an imaging system, such as a microlithography projection objective, disclosed that comprises mask structures in the form of a measurement pattern, which serves for aberration determination, and a Aufheizbestrahlungsmusters, which is chosen so that the heating effect of the transmitted radiation for the zu surveying optical imaging system within a predetermined tolerance range of the heating effect of the radiation corresponds, which is transmitted in the application of the optical imaging system of an associated, pictured Nutzmuster. Thus, the radiation heating effect, also referred to as "lens heating", as it occurs during later use of the optical imaging system, is taken into account in the Aberrationsvermessung, ie with this measuring device can be found in the practical later operational use aberrations including the radiation heating related contributions determine In this case, the utility model can also be provided by the optical imaging system with aberration-corrective control or regulation as a function of the previously ascertained, The aberration-corrective control or regulation can, for example, be set to a corresponding setting from FIG include manipulators provided. For this purpose, the aberration information obtained from the measurement is stored and the error correction information is derived at the time when it is needed for the corrective control of the imaging system. Alternatively, the error correction information may also be immediately derived from the acquired aberration information and stored until needed for aberration correction in the imaging mode. In the not pre-published, correspon Applicants' expanding US Patent Application No. 11 / 271,806 specifies specific supplementary measures with regard to a temporal switchover between a heating and a measuring radiation, simulating the application case radiation heating effect in the measuring stage and the type and direction of the heating radiation on the one hand and the measuring radiation on the other hand. The disclosure of these two applications of the applicant is hereby incorporated by reference in the present application to avoid repetition, in particular with regard to corresponding details of the measuring device and the measuring method, taking into account the lens heating effect.

The Adjustment of an optical system, d. H. the mutual setup or adjusting its optical components to fulfill a specified specification, in particular with regard to the aberration behavior, took place earlier often on the basis of subjective observations of the measuring staff. These Method encounters the demanded high imaging quality in microlithography to their limits and makes objectified and therefore more reproducible Approaches desirable. There are therefore already various automated adjustment processes have been proposed on a set of preferably orthogonal Basic functions, such as Zernike polynomials, for describing measured ones Aberrations are based and appropriate adjustment calculations to minimize of aberrations. This is not the previously published Applicant's US Patent Application No. 11 / 238,841, the contents of which are hereby incorporated by reference to avoid repetition by reference completely in the present application specifically incorporated with respect to such adjustment operations , and the prior art cited therein.

Of the Invention is the technical problem of providing a Method and apparatus for load case aberration measurement and a corresponding adjustment procedure with which optical systems and in particular microlithography projection objectives in front of the mentioned above Improved measurement and adjustment of the state of the art especially considering of the lens heating effect.

The Invention solves this problem by providing a load-case aberration survey method with the features of claim 1, 2 or 5, a load case aberration measuring device with the features of claim 11, 12 or 13 and an adjustment method with the features of claim 15. Advantageous developments The invention are specified in the subclaims.

The The method of claim 1 allows in efficiently a multi-channel load case aberration measurement of an optical system while achieving correspondingly short measuring times and consideration of the lens heating effect. For this purpose, a suitable multi-channel measuring device is provided, and before the beginning of the survey is a predeterminable load case of optical system, which is in the radiation heating load of the optical system a typical predetermined, planned application equivalent. The set by this load case caused Strahlungsaufheizbelastung the The optical system is thus within a predefinable tolerance range equal to the radiation heating load, as the optical system in a typical operational mission, in the case of a microlithography exposure system z. B. in use for semiconductor wafer structuring.

During the Setting the load case remains a radiation-sensitive measuring sensor element the measuring device hidden, d. H. the replica of the If necessary, the optical system impinging radiation does not apply on the measuring sensor element. After reaching the application modeled If necessary, the multichannel measuring process takes place in parallel for several up to all considered field points, including the measuring sensor element associated Measuring radiation receives. The measuring process can in particular be a wavefront measurement z. B. using a for this comprise per se known interferometric measurement technique, z. B. a lateral shear interferometry technique with multiple measurement cycles at different phase shifts between reference and Image wavefront. The load case is maintained during the measuring process. Subsequently the measuring sensor element is again shielded from incident radiation, and it closes an evaluation of the recorded, read from the measuring sensor element Measurements to based on aberrations of the optical system for the determined load case.

The method of claim 2 also efficiently enables multichannel load-case aberration measurement of an optical system while achieving short measurement times and taking into account the lens-heating effect. In this method, no means is required for controllably blanking the measuring sensor element from incident radiation. Instead, the measured value is recorded using a highly dynamic imaging camera, as it is, for example, under the trade name HDRC ^® CCTV camera on the market. Such a camera has, for example, a dy namic in the order of 120 dB, an electrical clock of 8 MHz and a pixel access time of 125 ns. So that needs integrated in such a camera Measuring sensor element between each two measuring operations can not be hidden by an additional device controllable from incident radiation. Incidentally, this method has the same properties and advantages as explained above for the method according to claim 1.

The Method according to claim 5 allows specifically the determination of a decay behavior of load case aberrations and / or a back-extrapolated determination the full load case aberrations itself, by first a Load case is set, which in its radiation heating load for the optical system is modeled on a typical application, and subsequently to a measuring state with a lower measuring radiation load of the converted optical system and a plurality of sequential measuring operations is performed. The measured values thus obtained are calculated using a sentence of suitable aberration functions, e.g. From Zernike polynomials, evaluated to the sought decay behavior of the load case aberrations and / or to determine the load-case aberrations themselves, the latter by back extrapolation the decay behavior to the beginning time, d. H. the time the end of the set load case when switching to the measuring state. Preferably, the load case aberration measurement also takes place at this process variant multi-channel, d. H. parallel or simultaneously for many to all considered field points.

In Embodiment of the invention is corresponding to a measuring reticle with an array of measurement units an image grid mask with a appropriate array of Bildgitterstruktureinheiten used. this makes possible multi-channel wavefront measurements of the optical system with simultaneous Obtaining Aberration-Indicative Measurements for Several or all the field points considered, for example by means of lateral Shearing interferometry. Preferably, the image grid mask is in the range outside the Bildgitterstruktureinheiten non-transparent executed. Advantageous can individually assign a corresponding one to the measurement structure units Diffuser area be upstream.

In a development of the invention includes adjusting the If necessary, setting a corresponding load case lighting setting, which switched to a lighting setting for the measurement process when the measuring process is started after the load has been reached becomes. When the relaxation of the radiation heating effect is sufficient is slow, changes the aberration behavior of the measured optical system in the period between the end of the activated load case lighting setting and the beginning of the measurement process is not significant. Alternatively, you can the lighting setting unchanged to be left.

Preferably becomes the method according to the invention performed using a wavefront measurement technique and / or for load case aberration measurement of a microlithography projection objective used.

The Measuring devices according to the invention are suitable especially for implementation the load case aberration surveying method according to the invention.

at The measuring device according to claim 11 is specifically a measuring reticle for this purpose provided an array of measuring units each with one upstream lens area and a load case structure to simulate an application case radiation heating load of optical system, wherein the load case structure in areas is provided between the measuring structural units.

at The measuring device according to claim 12 is specifically a measuring sensor element upstream, controllable shutter provided by a suitably established control unit is activated, so that the measuring sensor element through the shutter during the Setting the load case shielded from incident radiation stays while it can receive the measurement radiation to be evaluated during the measurement process.

at The measuring device according to claim 13 is especially for the detection part provided a high dynamic range imaging camera, so that with this Measuring device, in particular the multi-channel load case aberration measurement carried out according to claim 2 can be.

At the Inventive adjustment method is the optical system in a load case with respect to aberrations measure, the re Radiation heating load a predetermined typical application the optical system is modeled. The at this survey determined aberrations thus already include the radiation heating caused Contribution, allowing the optical system taking into account this aberration contribution is adjusted to an appropriately specified aberration specification to fulfill. This avoids that the optical system in the later operational use that for the production including Adjustment given aberration specification due to radiation heating induced changes which no longer complies with aberrations.

In Further development of this adjustment method can involve several typical applications different radiation exposure and associated aberration specifications be specified to the optical system in the adjustment to this several Einsätzfälle out to optimize.

In Design of the adjustment method includes setting the optical system in the adjustment process, providing an interchangeable insertable into the optical system Correction element for the respective predetermined application case, with regard to minimization a deviation of the for the associated Load case measured aberrations of the given aberration specification is produced.

In In a development, the adjustment process of the adjustment method according to the invention comprises a Cold Calibration Running Before Load Case Adjustment d. H. before the final adjustment, in which the radiation heating caused, considered in the set load case measured aberrations or best possible be compensated. The cold adjustment includes an adjustment process in itself more conventional Kind, in which the optical system under much lower radiation heating load as in the typical later Use case measured and adjusted to the aberrations without the radiation heating-related contribution, which is only in the case of application yields as much as possible to correct or minimize. This can be a reduction as needed the aberrations to fulfillment the given aberration specification in this cold case or at least the largest possible aberration reduction in the direction of the given aberration specification.

The Invention is particularly for the adjustment of microlithography projection lenses can be used, wherein the measurement in particular by a wavefront measurement, like a lateral shear interferometry technique, a point diffraction interferometry technique or a moiré measuring technique, can be done.

advantageous embodiments The invention is illustrated in the drawings and will be described below described. Hereby show:

1 a schematic side view of a microlithography projection exposure apparatus with associated measuring / adjusting device,

2 a schematic cross-sectional view of a for the measurement / adjustment system part of 1 usable measuring tablet,

3 a schematic plan view of a corresponding to the measuring reticle of 2 in the measuring / adjustment system part of 1 usable image grid,

4 a schematic side view of a picture side in the measurement / adjustment system part of 1 usable measuring head,

5 a flowchart of a method for load case aberration measurement of an optical system such as a projection lens of the exposure of 1 .

6 a flowchart of a method for adjusting an optical system such as the projection lens of 1 and

7 a flowchart of a variant of the adjustment of 6 ,

The components of interest in a typical microlithography projection exposure apparatus are shown schematically in FIG 1 shown. As can be seen, such a system includes a lighting system 1 with a light source 2 , typically a UV laser, and illumination system optics 3 for illuminating a reticle 4 with from the light source 2 emitted radiation 5 , A projection lens 6 forms on the reticle 4 existing structures, including the reticle 4 typically in or near an associated object plane of the objective 6 is positioned. In the measurement / adjustment case shown, the reticle is 4 designed as a measuring reticle and carries corresponding measurement structures, eg. For example, such as those for wavefront measurement by lateral Scherinterfe rometrie or Punktbeugungsinterferometrie are suitable. An only schematically shown detection part 7 receives the from the projection lens 6 emerging measuring radiation 5a and outputs corresponding measurement signals to an evaluation unit 8th , typically a calculator, off. The evaluation unit 8th evaluates the received measurement signals and determines from them aberrations, ie aberrations, of the considered optical system, here the projection objective 6 ,

In the adjustment process are those of the evaluation 8th obtained aberration information used to adjust the optical system. The evaluation unit controls this in an automated process 8th for example, manipulators 9 of the projection lens 6 to which one or more moving components of the lens are attached 6 can be adjusted. The adjustment is made in the sense of minimizing the aberrations determined by the measurement process until they comply with a predetermined aberration specification. In addition or as an alternative to such adjustment measures, one or more correction elements can be produced on the basis of the determined aberrations, which then at a suitable point in the projection objective 6 for aberration reduction, as known to those skilled in the art. For further details of a typical automated adjustment process, which preferably makes use of a set of orthogonal basis functions to describe the aberrations, such as Zernike polynomials, reference may be made to the above-mentioned prior US application Ser. 11 / 238,841 to the applicant. Of course, it is alternatively also possible to make the adjustment entirely or partially manually based on the determined aberrations.

It is understood that in 1 during its Aberrationsvermessung or adjustment shown projection exposure system in the actual utility z. B. can be used for semiconductor wafer structuring, what then on the image side, a wafer stage is provided and in the object plane of the projection lens 6 a reticle is positioned with corresponding useful structures. It comes in modern microlithography projection exposure systems z. B. from the scanner or stepper type very short-wavelength exposure radiation in the wavelength range below 100 nm, z. B. with a wavelength of 13 nm, used to produce very fine structures with high resolution on semiconductor wafers can.

According to the invention, it is provided aberration contributions, caused by radiation heating of the optical system components are, d. H. the lens heating effect, already while adjusting the Projection lens to be considered and thereby to avoid that the projection lens a predetermined Aberration specification still at the end of its production during the Adjustment and acceptance fulfilled, but not in the subsequent actual Operational use. For this purpose, the measurement is already carried out in the adjustment stage under the typical load conditions of the later operational use. For fast and economic Surveying / adjustment processes is to use a parallel Measuring method of advantage, in which for several and preferably All considered field points simultaneously display the aberration-indicative measured values be recorded.

2 shows a detail and schematically a suitable measuring reticle for this purpose 4a , How out 2 As can be seen, this measuring reticle 4a an array 10 of measurement structure units or measurement structure areas, ie one measurement structure unit per observed field point, on each of which an upstream lens area 11 assigned. The measurement units are each surrounded by a nontransparent area, and between these nontransparent areas is a load case structure 12 educated. The latter is modeled on a typical actual useful structure which is to be imaged by the projection objective to be adjusted in its later operational use.

In other words, the load case structure 12 realized in such a way that the exposure radiation emitted by it corresponds in its heating effect for the projection lens to the useful radiation present in later operation. This means that through the load case structure 12 on the measuring reticle 4a the optical system is subject to radiation heating during the measuring process, which corresponds to the order of magnitude in later operation. In extreme cases, this load case structure 12 to simulate real load cases also be an empty, that is to say completely transparent "structure".

Accordingly, during the measurement, the aberration contribution that results from the radiation heating of the optical system components is also detected. The diffuser areas 11 make it possible to fill the objective pupil of the projected projection objective with a wealth of settings for the measurement structures. In this case, the same or an equivalent illumination setting can be selected for the measurement process, as planned in the later operational use. Alternatively, the illumination setting can first be set specifically to achieve the radiation-heated load case and then switched over to a different illumination setting for the measurement process. This is possible in particular when the relaxation times of the radiation-heating-related aberration contributions for the measured objective are small compared to the time scale of the setting change of the illumination system.

3 schematically shows a z. For example, for multichannel lateral shear interferometry measurements in conjunction with the measuring reticle 4a from 2 usable image grid 13 , As shown, this includes image grid mask 13 an array of here only symbolically reproduced as bright circles, known per se Bildgitterstruktureinheiten 14 corresponding to the array of measurement structures 10 of the measuring tablet 4a , Otherwise, the image grid mask 13 nontransparent. The Bildgitterstrukturein units for the corresponding measurement channels have z. B. on a diameter of the order of 100 microns. The nontransparent areas which are on the measuring reticle 4a from 2 the measuring units 10 are in their extent corresponding to the diameter of the corresponding Bildgitterstruktureinheiten 14 selected.

4 shows a presently usable detector-side measuring head, which the image grid mask 13 is connected to the directly shown in the example, a fluorescence converter 14 is coupled. The measuring head contains, as shown only schematically, a relay lens 15 with a controllable shutter 16 , The relay lens 15 forms the aberration-indicative wavefront overlay pattern from the image grating plane onto a radiation-sensitive measurement sensor element 17 which may in particular be a CCD array of an image recording camera. In not shown, usual way then the evaluation unit 8th from 1 to the measuring sensor element 17 coupled to read its measurement information.

The evaluation calculator 8th from 1 can simultaneously act as a plant control unit, including the shutter 16 in a conventional manner z. B. analogous to the shutter in cameras controls. In the present case, the shutter control is synchronized with the other conventional control measures of the wavefront measurement, such as the lateral motion control of the image grid mask and the CCD sensor element 17 in the case of a lateral shear interferometry technique. The provision of the closure 16 allows a simple comparison with the readout duration of the CCD element 17 , which is typically of the order of 1 s, short exposure time of the order of z. B. 50 ms. With the help of the lock 16 can therefore the measured projection lens 6 continuously even during the reading of the CCD element 17 continue to be acted upon by the load radiation, so that the radar heating-related Aberrationsbeiträge do not change between successive measurement cycles.

With the above-mentioned measuring device components, a load case aberration measurement of the projection lens can be performed 6 or another optical system with the following procedure as described in 5 outlined. First, the measuring device is provided, including the act of aligning the measuring reticle and the measuring head. Then the illumination radiation is activated in accordance with the load case specifications, so that the objective heats up according to the specifications of adjustment and acceptance until the steady-state load case (lens heating state) is reached. Subsequently, the measuring operation is carried out, for which purpose, for example, in the case of the use of lateral shear interferometry, several measuring cycles with lateral phase shifting are carried out. At the beginning of each measuring cycle, the laser light source is synchronized by the evaluation / control computer which simultaneously functions as the measuring machine, and a first phase step is set. Then, the shutter of the relay lens in the probe is opened, so that the CCD element records a multi-channel full field of the wavefront overlay pattern. The shutter is then closed again, and the synchronization of the laser light source can be deactivated. The evaluation part reads out the measurement information from the CCD sensor element, and then a next measurement cycle can be carried out starting from resynchronization of the laser light source. When all the required measuring cycles have been carried out, the evaluation of the recorded measured values in the evaluation part is carried out for the purpose of determining the lens aberrations including the radiation-heating-related contributions according to an algorithm known per se, which consequently requires no further explanation here.

A similar multi-channel load case aberration measurement can also be performed with a modified multi-channel measuring device, which differs from that of 1 to 4 in the measuring head part differs by the detection part 7 in this case is formed by a picture taking camera with very high dynamics of preferably in the order of 120 dB, as marketed, for example, under the trade name HDRC ^® CCTV camera. When using such an image recording camera, the measuring sensor element integrated into it does not need to be shaded or moved out of the beam path between the individual measuring cycles since the dynamics of the camera are sufficiently high to prevent measured value falsifications by the heating radiation between the measuring cycles. Moreover, for such a modified measuring device, the same properties and advantages as described above for the measuring device of 1 to 4 are explained, which can be referred to.

above Surveying implementations were described in which the Measuring process during continuously sustained load radiation exposure carried out becomes. Alternatively, the invention comprises a timely aberration measurement directly after the previously set load case or lens-heating state.

A related load case aberration measurement can be z. B. with a turn through the flowchart of 5 Represent the course as follows. First, the measuring device is provided, for which purpose in particular the reticle and measuring head components are brought into lens heating position. For this purpose, during the heating period z. B. the reticle holder are kept out with the Messretikel from the beam path, or it is a Streuscheibenfreier Retikelmaskenbereich driven with a transparent area in field size in the beam path. Detector side of the measuring sensor element is hidden from the load case simulating Aufheizstrahlung, z. B. by closing an existing measuring head or a measuring head upstream shutter or alternatively by retracting the measuring head from the beam path, or it is as mentioned a highly dynamic imaging camera used.

As soon as the stationary, radiation-heated load case has been reached, it is possible to switch over to the measuring process. For this purpose, in particular the reticle and detector components are brought into their corresponding measuring position, for which a certain Duration of z. B. 1 min is required. In order to carry out timely measurements and thus still be able to record the heating-related aberration contributions, the measurement time per complete measurement is kept sufficiently short, for which particular preference is given to using a multi-channel, parallel measurement method and to separate the measurement data acquisition including measurement data storage from the measurement data evaluation.

To When the measuring position is reached, complete measurements, ie. H. in the case of lateral shear interferometry, one set of measurement cycles each in phase-shifted positions, performed at predetermined intervals, z. B. at intervals from about 1 min. Subsequently the measurement results of the complete measurements are evaluated. To are the aberrations determined in their time by a described a suitable set of preferably orthogonal basis functions, z. B. by means of this customary Zernike polynomials. For a pure study of lens heating effects can do so gained Zernike field distributions with regard to lens heating and, for example, associated cooldowns the corresponding aberrations are determined. For acceptance and adjustment measurements can be taken from the information obtained over the Time course of the aberrations after deactivation of the load-case radiation heating in the case of load actually existing aberrations are closed by at this initial time back extrapolated becomes. So z. B. a Zernike field distribution, based on the results of after deactivating the load-case radiation heating executed at a time t = 0 sequential measurements for the Period of z. B. t> 2 based on min is determined on the Zernike field distribution at time t = 0 back-extrapolated become.

With the above explained Methods and devices are advantageously an aberration measurement optical systems in the simulated load state possible, which make use of this leaves, the optical system already in the adjustment and acceptance stage at the end of the manufacturing process to those aberration contributions towards Optimize, which usually only in the planned later operation due to the then prevailing radiation exposure result. On some advantageous acceptance and adjustment variants will be below exemplary closer received. This is exemplified by a microlithography projection lens is referred to as an optical system, however, is a corresponding Decrease and adjustment also for any other optical system possible.

In A pure acceptance measurement variant is first for the lens to be produced a lens heating load case by specifying appropriate parameters what, in particular, the nature of the structures on the reticle, the illuminance and the lighting setting (angle distribution) belong. In addition, to be respected Specification values for given the aberrations. Typical specification values are in the order of magnitude from mm for the individual, described by corresponding Zernike polynomials Aberrations. Due to the lens heating effect z. B. in projection lenses for scanners Aberrationswerte reached between about 50 nm and about 100 nm, wherein in particular the Zernike aberrations Z5, focus and scale and in something weaker Dimensions Z9 and Z12 on Lens-Heating are sensitive. The Zernike aberration is the dominant one Effect often one Constant over the field away. The one constant across the field. The aberrations change by Lens-Heating typically only in one sign direction.

The produced lens is then first by means of a conventional Adjustment process optimized until the required aberration specification is reached. The lens only becomes during the associated measuring operations burdened with relatively low radiation energy, the much lower than in the typical case and not to significant aberration changes leads.

Subsequently, will the lens using one of the above Methods and devices with regard to aberrations in the case of load, d. H. under typical application radiation exposure, measured, why one of the above explained Measuring reticle used and set an associated lighting setting become. From the measurement data thus obtained, the associated load case aberrations determined, which contain the radiation heating caused Aberrationsbeiträge. With the help of this aberration data, the lens is then taken off in terms of lens heating behavior. An additional Adjustment for the optimization of the load case does not take place here. The obtained aberration data are used as later operating parameters, with those, for example, in a scanner-type exposure system during the Nutzbelichtungsbetriebs a feed-forward correction is performed.

6 roughly illustrates the sequence of a first adjustment variant, with which the lens is adjusted taking into account the load case. For this purpose, first, as described for the above pure acceptance measurement variant, a lens heating load case is defined and an aberration specification is specified. Then, as the next step, the load case aberration determination using one of the methods and devices explained above, as also explained above for the pure acceptance measurement variant. On the basis of such Measured in the load state of the lens aberration measurement data then an adjustment process is performed with conventional adjustment steps for aberration optimization of the lens. Such adjustment steps include z. B. Steps relating to tuning, centering, compensation and ICA. If necessary, the load case aberration determination and the adjustment process are repeated once or several times until the required specification state of the objective has been reached, ie its measured aberrations in the load state fulfill the specified aberration specification.

Depending on your needs, the in 6 illustrated Justageablauf also with specification of not just one, but several typical load cases are performed. In this case, an associated aberration specification is defined for each of the different load cases, ie predetermined, and the objective is then optimized by the described adjustment process to these several typical load cases.

7 illustrates a further adjustment variant, in addition to the load case adjustment upstream cold adjustment is provided. First, as above, to the adjustment variant of 6 which defines the load case (s) to which the lens is to be optimized and specifies the respective aberration specification. Subsequently, the lens is "cold-adjusted" in a conventional manner, ie measured with respect to its aberrations using a measuring radiation such that the radiation exposure remains well below the typical application radiation exposure, so that the aberrations measured thereby practically the aberrations of the "cold" lens without radiation heating caused Aberrationsbeiträge correspond. This "cold measurement" is followed by an associated cold adjustment in which the objective is optimized or pre-optimized on the basis of the measured cold-fall aberrations with customary adjustment steps, as mentioned above for the previous adjustment variant, wherein the surveying and adjustment steps in turn once or as required Depending on the application, this includes a conventional optimization until the predetermined aberration specification is met, or merely a pre-optimization to aberration values that are at most still a predetermined difference from the acceptance specification, this difference For example, in a specific example, the pre-optimization may be carried out until the respectively measured aberration value amounts to at most approximately five times the specified value.

Subsequently, will on the cold-adjusted lens, the load case aberration determination according to the invention executed as explained in the above adjustment variants, the aberration behavior of the lens in the loading situation. Based The aberration information thus obtained is then the associated load case adjustment as a final adjustment. This includes, as also above the previous adjustment variant explains a load case aberration determination according to the invention using one of the measuring methods according to the invention explained above and measuring devices and performing appropriate adjustment measures based on the acquired load case aberration measurement data. Depending on Use case can these adjustment measures the implementation typical adjustment steps, such as tuning, centering, compensation and / or ICA, and / or producing one or more suitable ones Correction elements for insertion in the lens. So z. B. with the help of Load case aberration measurement data a replaceable pupil element, abbreviated EPLE refers to being manufactured when used in the lens at the appropriate place in the beam path through the lens heating conditional aberrations corrected as much as possible.

It It is understood that even with this adjustment variant, the lens if required, to several different predefined load cases can be optimized by the load case aberration determination and the final adjustment possibly repeated taking into account the several predefined load cases carried out become. In doing so, if desired, Also, several EPLEs are produced which are specific to each are assigned to a predefined load case, or it can be a middle one EPLE produced the load-case aberrations for the different ones predefined load cases corrected in an averaged way.

As the exemplary embodiments explained above by way of example make it clear that allows Invention a multi-channel load case aberration measurement of optical Systems and an adjustment of the optical system under consideration of aberrations measured under load. The invention is especially for the measurement and adjustment of microlithography projection lenses z. B. suitable for use in wafer scanners, but also for all others Applications where there is a need, an optical system, this is a radiation heating dependent Aberration behavior shows, with high precision with regard to aberrations, as they occur in practical use, to measure and aberration-optimizing to adjust.

Claims (21)

Method for load-case aberration measurement of an optical system ( 6 ) with radiation heating dependent aberration behavior, comprising the following steps: provision of a multichannel measuring device for the parallel acquisition of aberration-indicative measured values for a plurality of field points, wherein the measuring device is a measuring sensor element ( 7 . 17 ) and a facility ( 8th . 16 ) for controllably blanking the measuring sensor element from incident radiation, - setting a predefinable, a use case of the optical system simulated load case with the corresponding application Strahlungsaufheizbelastung the optical system with hidden measuring sensor element, - performing a measuring operation with one or more measuring cycles when the load case is reached wherein the load case is maintained and for each measurement cycle the measurement sensor element receives measurement radiation in parallel for the plurality of field points and is then masked again by incident radiation, and - determining aberrations of the optical system for the adjusted load case by evaluating the acquired measurements , Method for load-case aberration measurement of an optical system ( 6 ) with radiation-heating-dependent aberration behavior, comprising the following steps: providing a multichannel measuring device for obtaining aberration-indicative measured values for a plurality of field points in parallel, the measuring device having a high-dynamic-range image recording camera of at least approximately 100 dB with associated measuring sensor element ( 7 . 17 ), - Setting a predefinable, an application case of the optical system simulated load case with the application corresponding Strahlungsaufheizbelastung the optical system, - Performing a measurement with one or more measurement cycles when the load case is reached, the load case is maintained and for the respective measurement cycle the measurement sensor element receives measurement radiation parallel to the plurality of field points for recording measured values, and - determining aberrations of the optical system for the set load case by evaluating the recorded measurement values. A method according to claim 1 or 2, further characterized in that for performing the measuring operations, a measuring reticle ( 4a ) with an array of measurement units ( 10 ), wherein the measuring reticle is also used to set the load case, for which purpose it has a load-case structure ( 12 ) in areas between the measurement structure units used to emulate the incident radiation heating load of the optical system. Method according to one of claims 2, 4 and 5, further characterized in that only the Meßstruktureinheiten corresponding lens areas ( 11 ) are connected upstream. Method for load-case aberration measurement of an optical system ( 6 with radiation-radiation-dependent aberration behavior, with the following steps: provision of a measuring apparatus for obtaining aberration-indicative measured values, setting of a predeterminable load case simulating a use case of the optical system with radiation heating load corresponding to the application of the optical system, setting a measuring condition of the measuring apparatus after reaching the load case with less load radiation load on the optical system and performing a plurality of measurements at predetermined time intervals during a decay time period of the optical load radiation heating load of the optical system; and determining load case aberration decay behavior and / or load case aberrations of the optical system by evaluating the successive measurements using a set of aberration functions. Method according to claim 5, further characterized that Zernike polynomials are used as the aberration function set Method according to one of claims 1 to 6, further characterized in that a measuring reticle ( 4a ) with an array of measurement units and an image grid mask ( 13 ) with a corresponding array of image grid structure units ( 14 ), wherein the structures of the measurement reticle and the image grid mask are designed for measurement by means of an associated wavefront measurement technique. Method according to one of claims 1 to 7, further characterized characterized in that the setting of the load case is a setting a corresponding load case lighting setting includes switched to a different measurement illumination setting when the measuring process is started after the load has been reached becomes. Method according to one of claims 1 to 8, further characterized characterized in that it is for load case aberration measurement of a Microlithography projection lens is used. Method according to one of claims 1 to 9, further characterized in that the measuring process (s) are measured using a Wavefront measurement technique to be performed. Measuring device for load case aberration measurement of an optical system designed as a multichannel measuring device and a measuring reticle ( 4a ) comprising an array of measurement units ( 10 ), each with an individually upstream lens area ( 11 ) and a load case structure ( 12 ) for simulating an incident radiation heating load of the optical system in areas between the measurement structure units. Measuring device for load-case aberration measurement of an optical system, comprising - a radiation-sensitive measuring sensor element ( 17 ), - one of the measuring sensor element upstream, controllable shutter ( 16 ) and - a control unit ( 8th ), which is adapted to keep the shutter closed during the setting of a predeterminable, a use case of the optical system simulating load case and to keep open during a measurement operation after reaching the load case. Measuring device for load-case aberration measurement of an optical system, comprising a detector section comprising a high dynamic range image pick-up camera of at least about 100 dB with a radiation-sensitive measuring sensor element ( 7 . 17 ) and is configured to evaluate only measured values for aberration determination supplied by the measuring sensor element during a respective measuring operation. Measuring device according to one of Claims 11 to 13, further characterized by an image grid mask ( 13 ) with an array of image grid structure units corresponding to an array of measurement structure units of a measurement reticle ( 14 ), wherein the image grid mask in the area outside the Bildgitterstruktureinheiten is made non-transparent. Measuring device according to one of claims 11 to 14, further characterized in that they are used to carry out the Last fall Aberrationsvermessungsverfahrens according to one of the claims 1 to 10 is set up. Method for adjusting an optical system with strahlungsaufheizabhängigem Aberration behavior, with the following steps: - Specify at least one for a predetermined application of the optical system with appropriate Radiation load representative If necessary, and specifying an aberration specification for the optical System and - Perform a Adjustment process, which involves a surveying of the optical system Aberrations and adjustment of the optical system to minimize the measured aberrations with respect to the given aberration specification includes, - in which the adjustment process involves a load case adjustment in which the Measuring the implementation a load case measurement includes what set the case of use simulating load case and so the optical system of a representative for the application Radiation exposure is exposed, and - wherein the setting of the optical system based on the criterion that in the Load case measurement measured aberrations the given aberration specification comply. A method according to claim 16, further characterized that multiple use cases with different radiation exposure of the optical system and related Aberration specifications are given to which the optical System is optimized in the adjustment process. The method of claim 16 or 17, further characterized characterized in that the setting of the optical system is the provision a replaceable insertable in the optical system correction element for each predetermined application case, wherein the correction element in terms Minimization of a deviation of the aberrations measured for the associated load case is generated by the given aberration specification. The method of any one of claims 16 to 18, further characterized characterized in that the adjustment process includes a cold adjustment, which is performed before the load case adjustment and measuring the optical system with respect to aberrations over predeterminable use case lower radiation load and a Adjusting the optical system to reduce the thus measured Aberrations with respect to the given aberration specification includes. The method of any one of claims 16 to 19, further characterized characterized in that for measuring a measuring device according to a the claims 11-15 and / or a load-case aberration survey method according to one of the claims 1 to 10 is used. The method of any of claims 16 to 20, further characterized characterized in that it is used for adjusting a microlithography projection objective becomes.