EP1704445A2

EP1704445A2 - Device and method for the optical measurement of an optical system, measurement structure support, and microlithographic projection exposure apparatus

Info

Publication number: EP1704445A2
Application number: EP05700815A
Authority: EP
Inventors: Ulrich Wegmann
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2004-01-16
Filing date: 2005-01-12
Publication date: 2006-09-27
Also published as: WO2005069080A3; US20090116036A1; JP4782019B2; WO2005069080A2; JP2007518257A; US8004690B2

Abstract

The invention relates to a device for optically measuring an optical system that receives effective radiation on an incident side and emits effective radiation on an emission side in a working mode of operation. Said device comprises a measurement radiation source by which at least one element that is located on the emission side and emits measurement radiation to the optical system can be placed on the emission side of the optical system, and a detector by which at least one element that is located on the incident side and receives measurement radiation emanating from the optical system can be positioned on the incident side of the optical system. The invention further relates to a measurement structure support that can be used for such a device, a microlithographic projection exposure apparatus which is equipped with such a device, and an associated method. According to the invention, the measurement radiation source encompasses a measurement structure mask that is located on the source side and is positioned on the emission side, and/or the detector is provided with a measurement structure mask which is located on the detector side and is placed on the incident side. The invention is used for wavefront measurement of projection lenses in microlithographic projection exposure apparatuses, for example.

Description

description

Device and method for the optical measurement of an optical system. Measurement structure support and microlithography therapy exposure system

The invention relates to a device for the optical measurement of an optical system that receives useful radiation in a useful operating mode on a useful radiation entry side and emits it on a useful radiation exit side, with a measuring radiation source, of which at least one exit-side element that emits measuring radiation to the optical system on the useful radiation exit side of the optical system, and a detector, of which at least one entry-side element that receives measurement radiation coming from the optical system can be positioned on the useful radiation entry side of the optical system, on a measurement structure support that can be used for such a device, on a device equipped with such a device Microlithography projection exposure system and an associated method.

Various devices are known for measuring optical systems, such as optical imaging systems. In the useful operating mode of the optical system, useful radiation arrives in a useful radiation direction e.g. from an illuminated object on the useful radiation entry side, i.e. on the object side, to the optical system, this passes through and emerges from it on the useful radiation exit side, i.e. image side, from.

To measure the optical system, for example with regard to imaging errors in the case of an imaging system, such as a projection objective for microlithography, the latter is operated in a measuring mode. In this operating mode, a measurement radiation source for emitting measurement radiation and an image detection side are usually used on the object side. positioned to receive the measuring radiation. In this case, a single radiation generation unit can be provided for the measuring radiation source in the measuring mode on the one hand and for a useful radiation source in the useful mode on the other.

The published patent application DE 101 09 929 A1 describes a device for measuring the wavefront of an optical system which, as the measurement radiation source, has a wavefront source to be positioned on the object side with a two-dimensional measurement structure mask on the source side for generating a wavefront passing through the optical system, while a detector is provided on the image side a diffraction grating is provided behind the optical system and a spatially resolving detector element arranged downstream of the diffraction grating. A shear interferometry technique is used for the wavefront measurement, in which the diffraction grating is shifted laterally. Alternatively, wavefront measuring devices are used that use other measuring techniques, such as point diffraction interferometry, Moire method and Shack-Hartmann method. The radiation used for the measurement can be identical to the useful radiation used in normal operation of the optical system.

An important area of application is the measurement of projection lenses in lithography exposure systems, such as corresponding steppers or scanners, at their place of use. For this purpose, it has already been proposed to at least partially integrate the measurement radiation source, in particular an associated measurement structure mask, into a reticle or to introduce it into the system with a conventional reticle day in exchange for a reticle, and / or to at least partially integrate the detector into a wafer stage or in exchange for a wafer with the wafer stage in the system. When integrating the detector into a wafer stage, there is the difficulty that only relatively little installation space is available and from the detector, in particular electronic components of the same, emitted heat can influence the projection lens above.

In a Shack-Hartmann measuring method, as described in US Pat. No. 5,978,085, a complex measuring reticle is used, the structures of which are exposed on a detector wafer coated with photoresist. The evaluation is carried out by measuring the structures produced on the detector wafer outside the exposure system using suitable measuring devices. This procedure is comparatively time-consuming.

US Pat. No. 6,278,514 B1 describes a projection exposure system in which a device for determining wavefront aberrations is integrated, which works in the double-pass method. For this purpose, it comprises a beam deflection device, e.g. a mirror, which is integrated into a wafer stage next to a wafer holding area and reflects light coming from the projection lens back to it, so that it passes through the projection lens in the same light path, but in the opposite direction a second time. The light is then laterally coupled out in the direction of a detector element by means of a semitransparent mirror which is arranged between a reticle plane and the projection objective.

The published patent application WO 2004/057295 A2 and a corresponding US patent application by the applicant describe devices and methods for optically measuring an optical system, such as a microlithography projection objective, which work with an immersion fluid which is adjacent to at least one of one or more object-side and / or one or more image-side components of the measuring device can be introduced, for example, by designing corresponding gaps between optical components that follow one another in the beam path as an expansion fluid chamber. The content of these two documents is fully incorporated in this immersion fluid issue by reference herein to avoid unnecessary repetition of text.

The invention is based on the technical problem of providing a device of the type mentioned at the outset for measuring an optical system which offers functional and handling advantages, in particular when measuring projection lenses in lithography exposure systems, and for this purpose can also be retrofitted in such exposure systems. Furthermore, a measurement structure carrier suitable for this purpose and a microlithography projection exposure system equipped with such a device are to be provided.

The invention solves this problem by providing a device with the features of claim 1, a measurement structure support with the features of claim 12, a microlithography projection exposure system with the features of claim 21 and a method with the features of claim 24.

In the device according to the invention according to claim 1, the measurement radiation source comprises a measurement structure mask on the source side for positioning on the useful radiation exit side and / or the detector a measurement structure mask on the detector side for positioning on the useful radiation entry side. Accordingly, the measuring radiation in the measuring mode passes through the optical system in a direction opposite to the direction in which the useful radiation passes through the optical system in the useful mode. This reversal of the direction of the measuring radiation in comparison to the useful mode, in particular when measuring projection lenses in lithography exposure systems, allows the above-mentioned difficulties of conventional devices in which the measuring radiation in the measuring mode in the same direction as the useful radiation in the useful mode due to the Avoid projection lens completely or partially. Thus, no detector component needs to be arranged in the possibly narrowed image area, and existing systems, such as wafer stepper and wafer scanner systems, can be retrofitted with this device relatively easily, largely regardless of type. For this purpose, the components of the measurement radiation source can be arranged entirely or partially on the image side, in particular the measurement structure mask on the source side can be introduced, for example, over a wafer stage. The components of the detector can be arranged entirely or partially on the object side, in particular the detector-side measurement structure mask can be placed on the object side, for example in a reticle plane of the objective.

In a development of the invention according to claim 2, the measurement radiation source is designed for back-lighting the source-side measurement structure mask, the source-side measurement structure mask being designed for operation in transmission and the measurement radiation source having a measurement radiation conversion device in the beam path of the measurement radiation in front of the source-side measurement structure mask. The measuring radiation conversion device is expediently designed in such a way that the measuring radiation illuminates the source-side measurement structure mask largely homogeneously, incoherently and completely with regard to intensity and direction. A homogeneous distribution of the measurement beam directions results in uniform or at least only slowly varying illumination of the pupil, and a homogeneous distribution of the intensity on the source-side measurement structure mask results in a homogeneous intensity distribution on the detector-side measurement structure mask.

In the device according to claim 3, the measuring radiation shaping device has one or more light-deflecting elements and / or one or more light-scattering elements. Rough surfaces, microprisms or diffraction gratings can be used as light-scattering elements. NEN. The reflecting elements can be implemented, for example, as light guides, prisms or mirrors and increase the efficiency of the beam shaping both with regard to the amount of light and mixing by low-loss multiple reflections. Such reflective and light-scattering structures are easy and inexpensive to manufacture.

In a further development of the device according to claim 4, the measurement radiation source contains a beam-generating unit for positioning on the useful radiation entry side and the detector-side measurement structure mask has a pass-through area for the measurement radiation outside a measurement structure area. The measuring radiation can cross the detector through the passband and reach the source-side measurement structure mask from the beam-generating unit. In this case, the beam-generating unit can in particular be the one which supplies the useful radiation when the optical system is in use.

In the device according to claim 5, the source-side measurement structure mask has a pass-through area outside a measurement structure area in order to let through measurement radiation emitted by a beam-generating unit for illuminating the back of the measurement structure area. This can be supported by a beam deflection device which deflects the transmitted measurement radiation to the measurement structure area.

In the device according to claim 6, the measurement radiation source is designed to illuminate the front of the source-side measurement structure mask, the source-side measurement structure mask being designed for operation in reflection. This can be particularly useful when measuring radiation with wavelengths in the EUV range, ie less than 100 nm, is used. In a further embodiment according to claim 7, a measurement structure area of the source-side measurement structure mask has scattering areas on the one hand and reflective areas on the other. ting and / or absorbent areas. The scattering areas of the measurement structure mask working in reflection correspond to transparent areas of a measurement structure mask working in transmission and the areas reflecting and / or absorbing outside the aperture angle correspond to opaque areas thereof.

The device according to claim 8 has a measurement radiation guiding device for the lateral supply of the measurement radiation emitted by a beam-generating unit into an area in front of or behind the measurement structure mask on the source side. As measuring radiation guiding device e.g. Serve mirror segments that are designed so that they have both focusing and scattering effect. In the case of short-wave radiation in the EUV range, flat angles of incidence using the total reflection are advantageous. Refractive focusing optics or light guides can also be used for lateral feeding. A beam generating unit that is simple and inexpensive to produce can be sufficient to provide the laterally supplied measuring radiation.

In a development of the device according to claim 9, the detector has a detector carrier which is to be arranged on the useful radiation entry side of the optical system and which carries the detector-side measurement structure mask and a downstream detector element. The detector carrier can be arranged laterally displaceable if necessary, e.g. to carry out a wave front measurement using shear interferometry. The detector element can be an optoelectronic unit suitable for rapid registration, e.g. a CCD, CMOS or CID unit, or a unit that measures the light intensity photochemically depending on the location. The required electronic components can be implemented in a very flat design.

In a development of the device according to claim 10, the detector carrier carries a detector power supply unit. This allows the Detector can be designed as a self-sufficient, mobile unit that can be positioned on the useful radiation entry side of the optical system. The detector carrier can optionally also have imaging optics, a camera, control electronics, an image memory and / or a wireless communication unit.

In a development of the device according to claim 11, an immersion fluid can be introduced into or adjacent to the measuring radiation source and / or in or adjacent to the detector, so that the associated advantages can be used.

The measuring structure carrier according to the invention according to claim 12 has a transparent carrier body, on the front of which a measuring structure mask operable in transmission is provided with a measuring structure area and in which a measuring radiation shaping device for the back illumination of the measuring structure area is integrated, the measuring structure carrier being on the front, outside of the Measuring structure area of the measuring structure mask and / or on the back has a pass-through area for coupling measuring radiation into the carrier body. The measurement structure carrier can be designed, for example, as a plate which consists of transparent material and carries the measurement structure mask on one side. The measurement structure carrier with the measurement structure mask can be arranged laterally displaceable if necessary, for example if a wavefront measurement is to be carried out using a shear interferometry technique.

In a further development of the measurement structure support according to claim 13, the measurement radiation conversion device comprises reflecting and / or light-scattering areas on the front and / or the back of the support body or in the interior of the support body. The reflecting areas can be used to direct light and, through multiple reflection, to homogenize the measuring radiation. Light-scattering areas can easily be found in sufficient numbers and close to the measurement Attach a structural mask to allow the most homogeneous illumination possible, if desired.

In a further development of the measurement structure carrier according to claim 14, the measurement radiation conversion device has a first beam-deflecting surface below the measurement structure area for deflecting the measurement radiation onto the back of the measurement structure area. When the measurement radiation is coupled in laterally through the end face of the measurement structure carrier, the beam-deflecting surface can be used to specifically deflect the measurement structure area.

In a further development of the measuring structure carrier according to claim 15, the measuring radiation shaping device comprises a second beam deflecting surface for deflecting measuring radiation incident on the front and / or rear side at a pass area into the measuring structure carrier onto the first beam deflecting surface. The targeted deflection with two beam-deflecting surfaces enables a high light efficiency to be achieved.

In a further development of the measurement structure support according to claim 16, the measurement radiation shaping device comprises a beam shaping lens. With this, the light efficiency can also be increased. In addition, the measuring radiation can be focused with the beam shaping optics on a passband in such a way that it can be dimensioned small.

In a further development of the invention according to claim 17, the measuring structure carrier is realized in such a way that an immersion fluid with the known advantages resulting therefrom can be introduced into it.

In a further development of the device according to claim 18, the measurement radiation source thereof has a measurement structure carrier according to the invention.

The device according to claim 19 is designed for the wavefront measurement of a lithography projection objective, the source side , -

Measurement structure mask are arranged on an image side of the projection objective and / or the detector-side measurement structure mask is arranged on an object side of the projection objective and the detector detects an image of the source-side measurement structure mask or an overlay pattern from the image of the source-side measurement structure mask with the detector-side measurement structure mask. On the object side, especially in the vicinity of the reticle plane, there is sufficient installation space for the detector components compared to the conventional image-side positioning, with a reduced thermal load for the lens. The measurement radiation source with the measurement structure mask on the source side can be wafer-like, i.e. with a thickness of e.g. less than 1 mm, can be designed and handled like a wafer in a wafer stage. It does not need to be integrated into the wafer days. The detector component with the detector-side measurement structure mask can be integrated in the reticle days or be designed as a mobile reticle-like unit that can be inserted into the reticle days. If the detector has a camera as a detector element, the waste heat generated by the camera electronics rises, so that the projection lens arranged under the detector is not influenced by this waste heat, but at most by a certain amount of heat radiation. Since reticles that can be positioned on the object side typically have a thickness of approximately 6 mm to 11 mm and thus have a significantly greater stability than wafers on the image side, a registering detector element can be attached relatively easily here.

The device according to claim 20 is designed for a wavefront measurement using a shear interferometry technique or a point diffraction interferometry technique or a moiré superposition technique. All three techniques can be used alone or in combination. In the case of point diffraction interferometry, the measurement structure mask on the source side consists of a pinhole. In the case of shear interferometry technology, the source-side measurement structure mask is usually a coherence mask, the detector-side measurement structure mask, on the other hand, a diffraction grating.

The measuring device according to the invention is advantageously integrated in the exposure system according to claim 21. The demands on the flatness of the diffraction grating tend to be lower on the object side than on the image side, since the imaging scale of a projection lens for microlithography is usually less than one, e.g. 0.25. The diffractive structures of the diffraction grating can also be positioned around the reciprocal of the imaging scale, i.e. for example, by a factor of four, larger than in the case of positioning on the image side. The structures can therefore be written with simpler devices or can be reproduced inexpensively in good quality as simple contact copies of a master template. This is particularly advantageous in cases in which the source-side measurement structure mask does not have such fine structures and is therefore relatively easy to manufacture even with structures reduced by the imaging scale. The source-side and / or the detector-side measurement structure mask can be designed to be laterally displaceable in order to carry out the above-mentioned measurement techniques.

According to claim 22, the exposure system can be e.g. act of the scanner type, wherein according to claim 23 the measuring radiation serving for measurement and the useful radiation serving for exposure can be supplied by a common or each own radiation generating unit.

To measure an optical system, the method according to claim 24 can be used, in particular the device according to the invention can be used. Advantageous embodiments of the invention are shown in the drawings and are described below. Show it:

1 shows a schematic side view of a device for wavefront measurement of an optical imaging system with an object-side detector and a measurement radiation source with object-side radiation generation and an image-side measurement structure mask,

FIG. 2 shows a schematic top view of a measurement structure mask for the detector from FIG. 1, FIG.

3 shows a schematic side view of a variant of the device from FIG. 1 for wavefront measurement with a measurement radiation source with lateral measurement beam coupling on a front side of an image-side measurement structure mask,

FIG. 4 shows a schematic detailed side view of a variant of the measurement radiation source from FIG. 3 with lateral measurement beam coupling on the end face into a measurement structure carrier, FIG.

5 shows a view of a variant of the measuring radiation source from FIG. 4 with a deflecting mirror,

6 shows a view of a further variant of the measuring radiation source from FIG. 4 with two deflecting mirrors and front measuring beam coupling,

7 shows a schematic detailed side view of a variant of the measuring radiation source from FIG. 6 with two deflecting mirrors with a scattering function, 8 shows a view corresponding to FIG. 7 for a variant of a measuring radiation source with a scattering structure between the two deflecting mirrors,

9 is a view corresponding to FIG. 7 for a further variant of a measuring radiation source with two deflecting mirrors and a beam shaping lens,

10 is a schematic side view of a variant of the device of FIG. 3 for wavefront measurement with a source-side measurement structure mask operated in reflection,

1 1 is a schematic side view of a variant of the detector of FIG. 1 with an integrated power supply,

12 is a schematic side view of a variant of the detector of FIG. 11 with a quartz carrier,

13 shows a schematic side view of a device for the wavefront measurement of an optical imaging system by means of point diffraction interferometry,

14 is a schematic side view corresponding to FIG. 1 for a measuring device variant with immersion fluid,

FIG. 15 shows a schematic side view corresponding to FIG. 4 for a measurement radiation source variant with immersion fluid and

FIG. 16 shows a schematic side view corresponding to FIG. 13 for a measuring device variant with immersion fluid.

1 shows a schematic side view of a device for the wavefront measurement of a projection objective 1 of a microlitho- graphical projection exposure system, which can be, for example, of the scanner type. Here and in the remaining figures, only the components of the measuring device that are of interest here are shown, which can furthermore have further components of conventional type as required. For the sake of simplicity, only one entry-side lens 9 with an associated lens plane 2, an aperture diaphragm 8 and an exit-side lens 10 with an associated lens plane 3 are shown by the projection objective 1 as representative of other common components. In a commercial operation of the exposure system, wafers are exposed in the usual way with useful radiation, by means of which the projection objective 1 images a reticle structure on the wafer. For this purpose, a reticle is introduced into an object plane of the objective 1 and the wafer is positioned in an image plane thereof. The radiation, for example UV radiation, is supplied by an illumination system, of which only one lens 11 on the exit side is shown. The area in front of the entry-side lens 9 of the objective 1, usually referred to as the object side, thus represents a useful radiation entry side thereof, the area behind the exit-side lens 10, usually referred to as the image side, correspondingly a useful radiation exit side of the objective 1.

1 shows the projection objective 1 in a measuring operation, for which the components of the measuring device are introduced into the exposure system and / or are integrated into the exposure system. Alternatively, the measuring device can be designed as an independent measuring station into which the objective 1 is inserted. The measuring device contains a measurement radiation source with an associated source-side measurement structure mask 62 and a detector 12 with an associated detector-side measurement structure mask 19 and is designed to transmit measurement radiation 80 from the source-side measurement structure mask 62 in the direction opposite to the direction of useful radiation of the above-mentioned utility operation through the objective 1 to pass through, ie from the image side or useful radiation exit side to the object side or useful radiation entry side.

For this purpose, the measurement radiation source has a measurement structure carrier 5, which is positioned on the image side of the objective 1 and carries the source-side measurement structure mask 62 on a front side 60 facing the objective 1. The measurement structure carrier 5 is positioned such that the measurement structure mask 62 on the source side lies in the image plane of the objective 1, the measurement structure mask 62 being operated in transmission and for this purpose having a measurement structure with transparent and opaque structure elements in a measurement structure area 4.

The detector 12 is arranged on the object side or useful radiation entry side of the lens 1 and comprises a detector carrier 83, which carries a detector-side measurement structure mask 19 as an entry-side detector element on a front side facing the lens 1 and is positioned such that the detector-side measurement structure mask 19 is in the object plane of the lens 1 lies. The detector carrier 83 is formed in the form of a plate from a transparent material and has a detector element 16 on a rear side. The detector-side measurement structure mask 19 includes a detector-side measurement structure area 13, onto which the objective 1 images the measurement structure area 4 of the source-side measurement structure mask 62, in order to generate an interference or overlay pattern that is detected by the detector element 16. This means that the measuring radiation 80 emanating from the source-side measuring structure region 4 passes through the objective 1 in the measuring radiation direction reversed to the useful radiation direction and falls on the detector-side measuring structure region 13 in order to then be detected by the detector element 16.

To provide the measuring radiation, the measuring device uses the existing lighting system 11 of the exposure system, which is consequently part of the measuring radiation source. For this purpose, the _

detector-side measurement structure mask 19 has a strip-shaped passage region 14 lying outside the detector-side measurement structure region 13, which alternatively can also have a different shape. Outside of its measurement structure area 13 and its transmission area 14, the detector-side measurement structure mask 19 has an opaque layer 17. In this way, radiation 80a generated by the illumination system 11 in the strip-shaped region outside the detector-side measurement structure region 13 can pass through the detector carrier 83 and in particular through the measurement structure mask 19 via the objective 1 to the measurement structure carrier 5 of the measurement radiation source. The source-side measurement structure mask 62 is provided with a corresponding, in the example shown, strip-shaped passage area 7, which corresponds in shape and position to the image of the detector carrier passage area 14 generated by the objective 1 and lies outside the source-side measurement structure area 4.

The measuring structure carrier 5 is plate-shaped or disk-shaped in accordance with the shape of a wafer, for example with a thickness of approximately 1 mm, so that it can be introduced over a wafer stage of the exposure system. Furthermore, the measurement structure carrier 5 is designed to illuminate the measurement structure area 4 of its measurement structure mask 62 with the radiation 80a coupled in on the front via the transmission area 7 of its measurement structure mask 62 as homogeneously and incoherently as possible. For this purpose, the measurement structure carrier 5 is provided over its entire area on its rear side 61 and on the front outside the measurement structure area 4 and the passage area 7 on the inside of the measurement structure mask 62 with light-scattering and thus also beam-deflecting layer areas 6, which can be formed, for example, by roughening the surface of a support core. on which the measurement structure mask 62 is then generated on the front side. On the outside, the measurement structure carrier 5 is provided on its rear side 61 and on the front outside the measurement structure area 4 and the passage area 7 of the measurement structure mask 62 with a suitable light-absorbing shielding layer. In domestic Neren, the measuring structure carrier 5 consists of a transparent material. As indicated in FIG. 1, this structure of the measurement structure carrier 5 causes multiple reflections of the coupled radiation 80a, as a result of which the measurement structure area 4 of the measurement structure mask 62 on the source side is illuminated in transmission in a sufficiently homogeneous and incoherent manner. It goes without saying that, in alternative embodiments, the measurement structure carrier 5 can also be constructed differently for this purpose, wherein anti-reflective, mirrored, absorbing and / or scattering areas can be provided. Micro-prism structures and light-diffractive structures can also be used for this.

In the present example, the detector element 16 is designed as a CCD array and enables a relatively fast detection. Alternatively, other optoelectronic detector elements, for example CID units or CMOS units, are possible. A photochemically detecting element can also be used. A cover 15 protects the detector unit 16 on the back from direct irradiation with the radiation coming from the illumination system 11.

The device of FIG. 1 is preferably designed for wavefront measurement using a shear interferometry technique, for which purpose the measurement structure area 4 of the source-side measurement structure mask 62 is then designed as a so-called coherence mask, which has one of the structures customary for wavefront sources, while the measurement structure area 13 of the detector-side measurement structure mask 19 is designed as a diffraction grating structure. With a typical reduction scale of the projection objective 1 of, for example, 1: 4, the requirements for the flatness of the diffraction grating are correspondingly lower, for example, by a factor of sixteen than in the case of conventional measuring devices with the image-side positioning thereof. Likewise, the structures of the diffraction grating can be kept larger by a factor of four so that they can be written with simpler devices or _ _

can be reproduced inexpensively as simple contact copies of a master template in good quality. This is particularly advantageous if the structures of the measurement structure mask 62 on the source side can also be generated relatively easily in a reduction corresponding to the imaging scale. The detector-side and / or the source-side measurement structure mask 19, 62 can be shifted laterally to carry out the measurement by moving the detector 12 or the structure support 5, as indicated in the figure by double arrows 81, 82.

FIG. 2 shows in more detail an advantageous implementation for the detector-side measurement structure mask 19 serving as the entry-side optical element. In this example, the detector-side measurement structure mask 19 has strip-shaped passage regions 14 at a distance to the right and left of the measurement structure region 13. The measuring structure area 13 is designed as a chessboard diffraction grating. The remaining mask area is covered by the opaque layer 17. The shown pattern of passage strip 14 and diffraction grating strip 13 can be repeated many times in an alternative advantageous embodiment (not shown) on the detector-side measurement structure mask 19.

FIG. 3 shows a schematic side view of a further device for the wavefront measurement of an optical system, for which here and in the following examples the projection objective 1 from FIG. 1 is again considered representative of any other optical systems that can be measured with the device according to the invention. For the sake of simplicity, the same reference numerals have been chosen in all the figures for functionally corresponding, not necessarily identical elements, an unnecessarily repeated description of such elements being omitted. The device of FIG. 3 has a detector 12a, the mode of operation of which largely corresponds to that of the detector 12 of FIG. 2. As the only difference from the detector of FIG. 2, the detector 12a of FIG. 3 has no passband. The measuring In the device of FIG. 3, radiation is irradiated laterally, that is to say transversely to an optical axis 28 of the projection objective 1, in front of a measurement structure mask 62a on the source side of a measurement structure carrier 5a of a measurement radiation source. With one or more measuring radiation conversion devices 21, 22, which can be used individually or in combination as required, the laterally supplied measuring radiation is deflected from the front into a respective pass region 7a, 7b of the source-side measuring structure mask 62a.

3 corresponds to the measurement structure support 5 of FIG. 1. In FIG. 3, two variants of the measurement radiation conversion devices are shown in order to appropriately deflect laterally supplied measurement radiation 80b, 80c, namely a plane mirror 22 and an alternative or additionally usable right-angled prism 21, which rests with a catheter surface on the front side of the measurement structure support 5a and whose hypotenuse surface is mirrored for beam deflection. A positive lens 20 is attached to the second catheter surface of the prism and is used to focus the light for targeted coupling into the measurement structure support 5a, in that the focal length of the lens 20 matches the beam path of the light up to the transmission area 7b, which is relatively small in this way can be held.

As in the example of FIG. 1, a conventional illumination system of an exposure system can serve as the radiation-generating unit of the measurement radiation source, in which case the radiation supplied by the illumination system is coupled out in front of the objective 1 in a manner not shown and then laterally supplied in front of the measurement structure mask 62a. Alternatively, an independent measuring radiation generating unit can be used, whereby a relatively simple, inexpensive radiation generating unit, such as is used, for example, in measuring apparatuses for lens adjustment, can be sufficient for objective measurement. The measuring structure carrier 5a is on a wafer stage or shifting device 23 for lateral displacement in the shear interferometry measurement applied, as symbolized in FIG. 3 by crossed double arrows 84.

FIG. 4 shows a schematic side view of a measuring radiation source that can be used alternatively in FIG. 3 with light coupling at the end. The measuring radiation source of FIG. 4 contains a measuring structure carrier 5b, which essentially differs from that in FIG. 3 in that it is transparent on an end coupling surface and the measuring radiation 80b, 80c supplied from the side is directly coupled there. For better coupling, two measurement radiation guiding devices 20a, 24 at the end are shown, of which in turn only one or both can be provided. A first such device is designed as a light guide 24 brought up to the coupling surface, a second one is formed by a positive lens 20a attached to the coupling surface as focusing optics. Both devices 20a, 24 couple the measurement radiation laterally into the interior of the measurement structure carrier 5b, where it is reflected, diffracted and / or scattered several times on the scattering or deflecting surfaces 6 in order to homogeneously illuminate the measurement structure region 4 from behind. In this example, the measurement structure area 4 is formed on an otherwise opaque source-side measurement structure mask 62b.

5 shows a schematic side view of a variant of a measuring radiation source with light coupling at the end. In this example, the measuring radiation is coupled in through the positive lens 20a into a measuring structure carrier 5c, which, in contrast to that of FIG. 4, has a right-angled prism 25, which is installed on the inside and serves as a beam deflecting device, and the measuring structure region 4 is located on the front catheter surface. The hypothesis surface of the prism 25 is designed as a deflection surface 63, which, if necessary after multiple reflection, diffraction and / or scattering to the measurement structure area, the measurement radiation irradiated on the face side 4 redirects. The deflection surface 63 can be realized in a scattering and / or reflecting manner.

It should be mentioned at this point that the lateral radiation supply shown in FIGS. 3 to 5 and the measurement structure supports suitable for this purpose can in principle also be used for measurement structure masks positioned in the conventional way on the object side.

FIG. 6 shows a schematic side view of a further variant of a measurement structure carrier 5d for the measurement radiation source, into which the measurement radiation 80a is coupled on the front side and which has a measurement radiation conversion device 26 with two beam deflection elements 27, 28. The measuring radiation can e.g. as in the case of Fig. 1 can be supplied by an illumination system of the exposure system. The measurement structure carrier 5d has on the front a measurement structure mask 30 with a pass-through area 7c for coupling in the measurement radiation and at a distance therefrom with the measurement structure area 4. A first beam deflecting element 27 with a beam deflecting surface 27, which is inclined by 45 ° with respect to the optical axis 28 of the objective, is attached to the inside of the measurement structure carrier 5d below the passage region 7c. 5 as a prism with a mirrored hypotenuse surface or as a simple mirror and reflects the measurement radiation to an adjacent area of the measurement structure support 5d with the front and rear, scattering and / or reflecting layer areas 6 before it is applied a subsequent second beam deflecting element 18 hits. This can be designed like the first beam deflecting element 27. The mirror surface of the second beam deflection element 18 is also inclined at 45 ° to the optical lens axis 28 and deflects the measurement radiation to the measurement structure area 4.

FIGS. 7 to 9 show possible variants of the measuring radiation conversion device 26 from FIG. 6 with the basic structure described above. They differ only in the way in which scattering and / or focusing elements are introduced into the beam path. 7, a first and a second beam deflecting element in the form of a deflecting mirror 27a, 18a each with an additional light-scattering surface are realized. 8 shows a measuring radiation shaping device 26b with a scattering transverse wall structure 39, which is provided between the first and the second beam deflecting element 27, 18 in the form of a deflecting mirror. 9 shows a measuring radiation conversion device 26c, in which only the second beam deflection element 18a additionally has a scattering surface, and a first lens 37 is located in the light path in front of the first beam deflection element 27 and a second lens 38 in the light path behind the second beam deflection element 18a. Both lenses lie in a plane parallel to the plane of the measurement structure mask 30 and serve as beam shaping optics. With this embodiment, a very high light efficiency can be achieved.

The measuring radiation shaping devices 26, 26a, 26b, 26c shown in FIGS. 6 to 9 can be manufactured as quasi-monolithic functional units with high precision and used individually or in groups in the measuring structure carrier 5d. The beam deflection surfaces and further beam-shaping elements can be coated and / or structured in a suitable manner in order to optimally utilize the injected radiation. The redirection with two beam deflection surfaces is particularly efficient because the light is redirected in the preferred directions.

10 shows a schematic side view of a further, modified device for the wavefront measurement of an optical imaging system, such as the objective 1, with a measurement radiation source, which comprises a measurement structure mask 41 and measurement radiation guiding devices 42 operated in reflection at the source. On the object side, the device has the detector 12a from FIG. 3. The reflection-driven The source-side measurement structure mask 41 is positioned in an image plane of the objective 1 and attached to a measurement structure carrier 40, which can be moved laterally with the displacement unit 23 for measurement purposes. The measuring radiation guiding devices 42 are in the form of mirror surfaces and deflect the radiation laterally supplied by a beam-generating unit, not shown, onto the source-side measurement structure mask 41. The measuring radiation guiding devices 42 can additionally have a focusing and / or scattering effect. In addition, zone plates operated in reflection or transmission can be used to focus the illuminating radiation, which is particularly advantageous in the case of short-wave radiation, such as EUV radiation. It is also advantageous if the radiation strikes the measuring radiation guiding devices 42 at flat angles of incidence, so that it is deflected using the total reflection. A measurement structure area 43 of the source-side measurement structure mask 41 has first structure areas 44 that scatter the illuminating light and second structure areas 43 that reflect or absorb the illuminating light. Measuring radiation 80 only reaches the lens 1 to be measured from the first, scattering structural regions 44. The second structural regions 43 either absorb the illuminating radiation or are hit by the latter at an angle of incidence such that the radiation is reflected at an angle that is greater than the opening angle of the lens Lens 1 is.

11 shows a schematic side view of a reticle-like detector 12b with electronic components 50. The detector 12b is positioned between the illumination system 11 and the lens 9 on the entry side of the objective to be measured. The detector 12b has a detector carrier 51, on the side facing the objective of which a detector-side measurement structure mask 19a with the measurement structure area 13 and the passage area 14 is provided. For the functioning of the detector 12b, reference is made to the description of FIG. 1 referenced. On the side facing the lighting system 11, the detector 12b has a detector element 16a, for example a CCD array or a flat image recording camera unit, with a shield 15a against direct radiation from the lighting system 11 and electronic components 50, which, as indicated in FIG. 11, in FIG flat design are realized in addition to the radiation-sensitive detector element 16a. The electronic components can include, for example, an internal energy supply, a data line for remote data transmission and an evaluation unit for evaluating the measurement signals of the detector element. The internal energy supply can be, for example, a battery, a rechargeable battery or an electricity-generating unit, for example a solar cell unit.

12 shows a schematic side view of a further example of a detector 12c that can be used in the measuring device according to the invention on a quartz carrier 51a. For the functioning of the detector 12c, reference is made to the description of the detectors in FIGS. 1 and 11. In contrast to the detector 12b shown in FIG. 11, the detector 12c on the side facing the objective has a measurement structure mask 19b with the measurement structure area 13, but without a pass-through area. The detector 12c is therefore suitable e.g. for use in the device of FIG. 3. Inside the quartz carrier 51a, the electronic components 50 as well as the detector element 16a and the shield 15a are attached. An electronics board 52 in the quartz carrier 51 a serves as a carrier for the electronic components.

13 shows a schematic side view of a further device for the wavefront measurement of an optical imaging system, such as the objective 1, by means of point diffraction interferometry (PDI). The device of FIG. 13 has a detector 12d on the object side, the construction of which largely corresponds to that of FIG. 11, a modified detector-side measurement structure mask 19c having a PDI detection structure 13a being provided. On the image side, a source-side measurement - -

Structure support 5e in the manner of FIG. 6, but with a modified measurement structure mask 62c and with a measuring radiation conversion device 26d in the manner of FIG. 9, and a beam-splitting diffraction grating 84 are positioned. 1, 6 and 9 above apply to the functioning of the device, with the difference that a pinhole is used as the measurement structure area 4a of the source-side measurement structure mask 62c of the measurement structure support 5e and, as shown in FIG. 13, the wave front emanating from the pinhole structure 4a is diffracted by the diffraction grating 84 into a test specimen wave 80d (solid line) which meets a first, larger opening of the PDI detection structure 13a for the test specimen wave 80d to pass through, and a reference wave 80e (dashed line) , which meets a second, smaller pinhole opening of the PDI detection structure 13a in order to be bent thereon. As in the case of shear interferometry, conclusions can be drawn about the aberration properties of the measured objective 1 from the interference pattern of the transmitted test specimen wave and the diffracted reference wave at the detector element 16a.

As the exemplary embodiments above make clear, the device according to the invention can be used in particular for measuring projection objectives of microlithography projection exposure systems, the shear interferometry technique shown in FIG. 1, the point diffraction interferometry technique shown in FIG. 13, a moiré Technology or other conventional wavefront measurement techniques, such as a wavefront measurement technique of the Hartmann or Shack-Hartmann type, can be used. It is particularly advantageous in the use according to the invention of a measuring radiation direction that is inverse to the useful radiation direction that there is sufficient space on the object side, in the vicinity of the reticle plane, for the relatively space-intensive detector, while only limited space is available in the vicinity of the wafer plane, but this is good is sufficient to be able to position a wafer-like, thin source-side measurement structure carrier in a space-saving manner.

The problem of the heat development of electronic components of the detector is also reduced, since the waste heat of the detector rises and therefore the heat development of the detector does not have a negative effect on the imaging properties of the projection lens below, apart from any thermal radiation effects. Both the detector and the measurement radiation source with their measurement structure support can be integrated in the microlithography projection exposure system or can be designed as independent units. It is essential that they are introduced into the beam path of the projection objective in order to carry out the wavefront measurement and can be removed from the latter after the measurement has been completed. Alternatively, it is also possible to set up the measuring device as a separate measuring station, into which the projection objective or any other optical system to be measured can be placed.

The invention further includes the possibility of carrying out the optical measurement using an immersion fluid, for which purpose this can be introduced in particular in the measurement radiation source and / or adjacent to it and / or in the detector and / or adjacent to it. This is explained below using three examples as an example and representative of further possible realizations.

14 shows a device variant which corresponds to the device of FIG. 1 except for the immersion fluid application, to which reference can be made for the rest and where the same reference numerals are used for identical or functionally equivalent elements. 14 shows the measuring operation for a projection objective 1 ′, which ends on the exit side with a flat end plate 10 ′, wherein the final lens element can alternatively also be another optical component, such as a lens element. A gap 90 between this closing element 10 'of the objective 1' and a subsequent measurement structure carrier 5 'is formed as an immersion fluid chamber using a circumferential seal 91, for example a bellows seal. As indicated by arrows, an immersion fluid can be fed into this via an inlet 92. The immersion fluid is discharged from the immersion fluid chamber 90 via an outlet 93 on a side opposite the inlet 92. In the example shown, the inlet and outlet lines 92, 93 each lead through an end face of the measurement structure carrier 5 '. Depending on requirements, provision can be made to fill the immersion fluid chamber 90 with the immersion fluid and then to hold it therein, or alternatively to maintain a continuous immersion fluid flow through the immersion fluid chamber 90. Means for tempering the immersion fluid outside or inside the immersion fluid chamber 90 are optionally provided. For this purpose, means for measuring the temperature and, if necessary, for regulating the temperature of the immersion fluid can also be present, for example integrated into the measuring structure support 5 '.

As in the example in FIG. 1, the measurement structure carrier 5 'can consist of a transparent material or alternatively can be formed with the formation of a cavity 94 between its front side 60 and its rear side 61, into which immersion fluid can then also be introduced. For this purpose, this cavity 94 of the measurement structure carrier 5 ¹ can be in fluid communication with the immersion fluid chamber 90 between the objective 1 ¹ and the measurement structure carrier 5 ', forming a common immersion fluid chamber, or else form a second immersion fluid chamber separately therefrom. The use of immersion fluid has the known advantages, in particular a very high aperture illumination of the lens 1 'to be tested can be used with the Measurement structure area 4 are provided from the image side of the lens 1 '.

15 correspondingly shows an implementation variant for the arrangement of the measurement structure support 5b from FIG. 4, in which an intermediate space 96 between the exit-side element 10 of the optical system to be tested and the measurement structure support 5b is formed as an immersion fluid chamber by a circumferential seal 95, such as a bellows seal is. A suitable immersion fluid can be introduced into this using conventional means which are not shown in detail. For other measures relating to the immersion fluid and the advantages or properties achieved thereby, what has been said above in relation to FIG. 14 applies in the same way, which is not explicitly shown in FIG. 15, to which reference can be made.

FIG. 16 shows an immersion fluid variant of the device of FIG. 13 in an analogous manner, with only the modifications relating to the immersion fluid needing to be discussed at this point, while the rest of what has been said about FIG. 13 can be referred to and so far the same reference numerals are used. In the example of FIG. 16, a space 97 is again formed between the exit-side component 10 of the lens 1 to be tested and the measurement structure support 5e using a circumferential seal 98, such as a bellows seal, as an immersion fluid chamber. This includes means for supplying and removing the immersion fluid, for example as a continuous fluid flow, and means for measuring and controlling the fluid temperature if required. In this regard and with regard to the other possible modifications, advantages and properties of the use of an immersion fluid, reference can be made to what has been said above with regard to FIGS. 14 and 15 and to the prior art mentioned at the beginning. It goes without saying that means for introducing an immersion fluid can also be provided in the same way in the other exemplary embodiments shown and described above. In addition, such means can be provided in the same way on the detector side, in addition or as an alternative to the presence on the side of the measurement radiation source described above with reference to FIGS. 14 to 16, ie an immersion fluid can be introduced into a detector component or adjacent to it in an analogous manner, For example, in a detector carrier or a space between it and the optical system to be tested, which does not require any further explanation. , - _ -. , _ - _.

Claims

claims

1. Device for the optical measurement of an optical system (1) which receives useful radiation in a useful operating mode on a useful radiation entry side and emits it on a useful radiation exit side, with - a measuring radiation source (5, 5a - 5e, 40, 1 1), of which at least one exit side Element (62, 62a - 62c, 41) which emits measurement radiation to the optical system, can be positioned on the usage radiation exit side of the optical system, and - a detector (12, 12a - 12d), of which at least one entry-side element ( 19, 19a - 19c), which receives measuring radiation coming from the optical system, can be positioned on the useful radiation entry side of the optical system, - the measuring radiation source having a source-side measurement structure mask (62, 62a - 62c, 41) for positioning on the useful radiation exit side and / or the detector a detector-side measurement structure mask (19, 19a - 19c) for positioning on the useful radiation entry side u mfasst.

2. Device according to claim 1, characterized in that the measurement radiation source is designed for back-lighting the source-side measurement structure mask, wherein the source-side measurement structure mask is designed for operation in transmission and the measurement radiation source is a measurement radiation conversion device (6, 26, 26a-26c) in Has beam path of the measuring radiation in front of the source-side measurement structure mask.

3. Apparatus according to claim 2, characterized in that the measuring radiation conversion device one or more light-deflecting - ol - oling elements (63, 27, 27a, 18, 18a) and / or one or more light scattering elements (6, 39).

4. Device according to one of the preceding claims, characterized in that the measurement radiation source includes a beam-generating unit (11) for positioning on the useful radiation entry side and the detector-side measurement structure mask outside a measurement structure area has a pass-through area (14, 14a) for the measurement radiation.

5. Device according to one of the preceding claims, characterized in that the source-side measurement structure mask has a pass-through area (7, 7a, 7b) outside a measurement structure area in order to let through measurement radiation emitted by a beam-generating unit for illuminating the back of the measurement structure area.

6. The device according to claim 1 or 4, characterized in that the measuring radiation source is designed for illuminating the front of the source-side measurement structure mask (41), the source-side measurement structure mask being designed for operation in reflection.

7. The device according to claim 6, characterized in that a measurement structure area of the source-side measurement structure mask has scattering areas (44) on the one hand and reflecting and / or absorbing areas (43) on the other hand.

8. Device according to one of the preceding claims, characterized in that the measuring radiation source comprises a measuring radiation guiding device (20, 20a, 24) for the lateral supply of the measuring radiation emitted by a beam-generating unit in an area in front of or behind the source-side measurement structure mask.

9. Device according to one of the preceding claims, characterized in that the detector has a detector carrier (51, 51a) to be arranged on the useful radiation entry side of the optical system, which has the detector-side measurement structure mask (19, 19a, 19b) and a downstream detector element (16, 16a) ) wearing.

10. The device according to claim 9, characterized in that the detector carrier carries a detector power supply unit (50).

11. Device according to one of the preceding claims, characterized in that an immersion fluid can be introduced into or adjacent to the measuring radiation source and / or in or adjacent to the detector.

12. Measurement structure support, in particular for use in the device according to one of claims 2 to 5 or 8 to 11, characterized by a transparent support body, on the front side of which a measurement structure mask (62, 62a-62c) that can be operated in transmission with a measurement structure area (4, 4a ) is provided and in which a measuring radiation conversion device (6, 26, 26a-26c) is integrated for back-lighting of the measuring structure area, the measuring structure carrier on the front, outside the measuring structure area of the measuring structure mask and / or on the back a pass-through area for coupling measuring radiation into the Has carrier body.

13. Measuring structure carrier according to claim 12, characterized in that the measuring radiation conversion device reflecting and / or light-scattering areas (6, 39) on the front and / or Back of the carrier body or inside the carrier body includes.

14. The measuring structure support according to claim 12 or 13, characterized in that the measuring radiation shaping device has a first beam-deflecting surface (18, 18a) below the measuring structure area for deflecting the measuring radiation onto the rear of the measuring structure area.

15. The measuring structure carrier according to claim 14, characterized in that the measuring radiation shaping device comprises a second beam-deflecting surface (27, 27a) for deflecting measuring radiation incident on the front and / or rear side at a pass region into the measuring structure carrier onto the first beam-deflecting surface.

16. Measuring structure support according to one of claims 12 to 15, characterized in that the measuring radiation shaping device comprises beam shaping optics (37, 38).

17. Measuring structure support according to one of claims 12 to 16, characterized in that an immersion fluid can be introduced into it.

18. Device according to one of claims 2 to 5 and 8 to 11, characterized in that the measuring radiation source comprises a measuring structure carrier according to one of claims 12 to 17.

19. Device according to one of claims 1 to 1 1 and 17, characterized in that it is designed for the wavefront measurement of a lithography projection objective, the source-side measurement structure mask being arranged on an image side of the projection objective and / or the detector-side measurement structure mask being arranged on an object side of the projection objective and the detector Image of the source-side measurement structure mask or an overlay pattern from the image of the source-side measurement structure mask with the detector-side measurement structure mask.

20. The device according to claim 19, characterized in that the device is designed for a wavefront measurement using a shear interferometry technique or a point diffraction interferometry technique or a moiré superposition technique.

21. Microlithography projection exposure system, characterized in that it comprises a device according to claim 19 or 20.

22. Microlithography projection exposure system according to claim 21, characterized in that it is one of the scanner type.

23. The microlithography projection exposure system as claimed in claim 21 or 22, characterized in that it has a common radiation generation unit or a separate radiation generation unit for the useful radiation on the one hand and the measurement radiation on the other hand for providing the useful radiation and the measuring radiation.

24.Method for the optical measurement of an optical system (1) which receives useful radiation in a useful operating mode on a useful radiation entry side and emits it on a useful radiation exit side, with the following steps for carrying out the measurement with measuring radiation in a measuring mode: positioning a source-side measurement structure mask of a measurement radiation source on the Effective radiation exit side and / or positioning of a detector-side measurement structure mask a detector on the useful radiation entry side and performing a measurement process by emitting measuring radiation provided by the measuring radiation source to the optical system on the useful radiation exit side and receiving measuring radiation coming from the optical system on the

Useful radiation entry side for the detection of the same.