WO2010149436A1

WO2010149436A1 - Illumination optical unit with a reflective optical element comprising a measuring device

Info

Publication number: WO2010149436A1
Application number: PCT/EP2010/056966
Authority: WO
Inventors: Frank Melzer; Adrian Staicu; Jürgen Baier; Berndt Warm; Markus Knüfermann; Michael Layh
Original assignee: Carl Zeiss SMT GmbH
Current assignee: Carl Zeiss SMT GmbH
Priority date: 2009-06-23
Filing date: 2010-05-20
Publication date: 2010-12-29
Anticipated expiration: 2011-12-23
Also published as: DE102009030230A1

Abstract

The invention relates to a reflective optical element comprising a substrate (1), a reflective coating (3) and a measuring device (5). In this case, the measuring device (5) is contigured such that it is arranged at leapt partly between the coating (3) and the substrate (1). What is thereby achieved is that ail regions of the optical element on which relevant radiation impinges act in reflective fashion and, in addition, it is possible to measure the radiation at different locations. This has the further advantage that no additional loss occurs as a result of a portion of the radiation having to be screened out for measuring and monitoring purposes. Instead, that portion of the radiation which is not reflected anyway is used for these purposes.

Description

Illumination optical unit with a reflective optical element comprising a measuring device

Description:

The present invention relates to a reflective optical element comprising a measuring device, an illumination optical unit for illuminating an object field comprising such a reflective optical element, and a projection optical unit for imaging an object field comprising a reflective optical element according to the invention.

Microlithography projection exposure apparatuses serve for producing microstructured components by means of a photolithographic method. In this case, a structure-bearing mask, the so-called reticle, is illuminated with the aid of an illumination system and imaged onto a photosensitive layer with the aid of a projection optical unit. The illumination system comprises a light source, which provides a radiation having a suitable wavelength, and an illumination optical unit, which comprises various components and which serves to provide a uniform illumination with s predetermined angle distribution at the location of the structure-bearing mask. The structure- bearing mask illuminated in this way is imaged onto a photosensitive layer with the aid of the projection optical unit. Xn this case, the minimum feature size which can be imaged with the aid of such a projection optical unit is determined by the wavelength of. the imaging light used. The smaller the wavelength of the imaging light, the smaller the structures that can be imaged with the aid of the projection optical unit. Imaging light ha\^ring the wavelength of 193 nm or imaging light having a wavelength in the range of extreme ultraviolet (EUV) , that is to say in the range of 5 nm to 15 nm, is principally used nowadays. When imaging light having a wavelength of 193 nm is used, both refractive optical elements and reflective optical elements are employed within the microiithography projection exposure apparatus. By contrast, when imaging light having a wavelength in the range of 5 nm to 15 run is used, exclusively reflective optical elements (mirrors) are used. In the case of a microlithography projection exposure apparatus it is necessary for irradiation conditions that remain constant to foe present at the photosensitive layer throughout operation. It is only in this way that it is possible to produce microstructured components with uniform quality. Therefore, the irradiation conditions at the structure-bearing mask also have to be as constant as possible. However, various influences can alter the irradiation condition at the structure-bearing mask and/or the photosensitive layer during operation. This can be e.g. heating of the reflective optical elements, which thereupon change their position or form slightly. Furthermore, it is possible for the radiation source to change during continuous operation, i.e. for the position of the light source to shift slightly, by way of example. Furthermore, by way of example, contamination can also have the effect that the reflectivity of individual or all mirrors changes, All these influences lead to an alteration of the irradiation conditions at. the structure-bearing mask and at the photosensitive layer. For this reason, it is necessary to continuously monitor the irradiation conditions during operation. In this case, the measuring device provided for monitoring should be configured in such a way that monitoring is made possible without the microlithography projection exposure apparatus having to be deactivated for this purpose.

The patent application US 2008/0151221A1 proposes for this purpose a reflective optical element wherein the reflective coating is partly interrupted in order to direct the radiation impinging at these locations onto a measuring device. This has the disadvantage that the reflective optical element then has regions which are no longer reflective. Furthermore, only that portion of radiation is monitored which is not reflected and thus does not contribute to the irradiation conditions at the structure-bearing mask and the photosensitive layer. Accordingly, the object of the present invention is to provide a reflective optical element which enables the impinging radiation to be monitored without hav.-i.ng non-reflective regions.

This object is achieved by means of a reflective optical element comprising a substrate, a reflective coating and a measuring device, wherein the measuring device is arranged at least partly between the coating and the substrate. What is thereby achieved is that all regions of the optical element on which relevant radiation impinges act in reflective fashion and, in addition, it is possible to measure the radiation at different locations. This has the further advantage that no additional loss occurs as a result of a portion of the radiation having to be screened out for measuring and monitoring purposes. Instead, that portion of the radiation which is not reflected anyway is used for these purposes .

In this case, it is advantageous, in particular, if the measuring device at. least partly adjoins the coating and the substrate, with the result that no further components that could influence the radiation to be measured are arranged between measuring device and coating.

In one development, the reflective optical element comprises a substrate and a reflective coating, wherein the substrate is embodied at least partly as a measuring device. This has the advantage that the substrate, and the measuring device can be produced together in a simple manner.

In one specific embodiment of the reflective optical element, wherein the substrate consists of a dopabie material or comprises a dopabie layer, the measuring device has been ac least, partly integrated into the dopabie material. In this case, this integration has been effected with the aid of at least one lithographic step. Such a method enables particularly cost- effective production since the production of microelectronic components by means of lithographic methods from dopafole material is a well-known technique.

In one form of the reflective optical element according to the invention, the element is configured in such a way that the measuring device detects radiation that has passed through the coating. This has the advantage that the measuring device reacts directly to the local irradiance and no further secondary influences have to be taken into account.

In one specific embodiment, the reflective optical element is designed for the reflection of radiation having a wavelength in the range of 5-15 run. What is thereby achieved is that such an optical element can also be used in microlithography projection exposure apparatuses which are operated with radiation having a wavelength of in the range of 5 nm to 15 nm.

Alternatively or supplementarily, the reflective optical element is provided with a coating comprising a plurality of layers with different materials. A particularly high reflectivity of the reflective optical element can be achieved by means of such a coating.

Additionally or supplementarilly , the reflective optical element can be developed in such a way that the measuring device comprises a plurality of sensors which enable a spatially resolved measurement of the impinging radiation. In this way it is possible to gather a larger amount of information about the incident radiation, which enables better monitoring of the beam path in which the element is employed.

Specifically, the plurality of sensors can be arranged in the form of a measuring grid in order in this way to be able to assign the measurement signals to the associated location on the ref.lecr.ive optical element in a simple manner. In one of the embodiments according to the invention, the measuring device comprises at least one semiconductor detector, which is embodied for example in the form of a MOS diode, a Schottky diode, a ρ-1-n photodiode or a phototransistor. Components which have well-know properties are involved here, such that the Irradiance can be deduced from the measurement signals in a simple manner.

in some cashes, the reflective optical element comprises a measuring device that measures a temperature change on account of radiation absorption within the coating or the substrate.

This has the advantage that such a measuring device can be employed even when the reflective coating does not transmit a sufficient quantity of light to achieve a good measurement accuracy, in such a case, the absorbed quantity of light, which leads to a temperature change, is also measured indirectly.

In an alternative embodiment of the optical element according to the invention, the measuring device comprises a component which emits a secondary radiation upon the passage or the absorption of the radiation. A conversion of the wavelength is thereby achieved, by way of example. While the primary radiation has a wavelength in the range of extreme ultraviolet, for example, the secondary radiation can have a different wavelength. A simpler measurement can thereby be achieved since radiation having specific wavelengths can be measured more simply and more cost- effectively.

Specific configurations thereof are scintillator materials or fluorescent coatings .

Alternatively or supplementarily, the reflective optical element can also have a measuring device, that comprises at least one optical waveguide. It is thereby possible for the detectors to be spatially separated from the measuring position, by way or example. This enables a simple replacement or simple repair auring maintenance work. If the measuring devic-2 of the reflective optical element is connected to evaluation electronics, then particularly fast and efficient evaluation of the measurement, signals generated is made possible.

In I one specific form of the component according to the invention, the substrate consists of a dopable material or comprises a dopable layer. Therefore, at least individual parts of the evaluation electronics can be integrated into the dopable material with the aid of at least one lithographic step. This has the advantage that, the reflective optical element can already contain a part of the evaluation electronics, as a result of which the entire optical unit is composed of only a small number of components. A fast and efficient assembly is thereby ensured.

Alternatively or supplementarily, the component according to the invention can be equipped with a measuring device comprising a plurality of sensors which enable a spatially resolved and directionally resolved iaeasureiftent of the impinging radiation. Xn this way, it is possible to gather a larger amount, of information about the incident radiation, which enables better monitoring of the beam path in which the element is employed. Such a directionally resolved measurement can be achieved for example by means of the plurality of sensors comprising a first set of sensors and a second set of sensors. In this case., the two sets are arranged one above another in such a way that at least parts of the impinging radiation are successively detected by two sensors. Simple determination of the direction of the measured radiation is thereby made possible by taking account of the relative position of the two sensors with respect to one- another.

An optical unit for use in a microiithography projection exposure apparatus comprising a reflective optical element according to the invention has the advantages which have already been described above with regard to the element. In one specific embodiment, measurement radiation registered by the measuring device and the useful radiation of che microlithography projection exposure apparatus differ in their wavelength. In such a case, by way of example, the reflective coating can be embodied in the font! of a wavelength-dependent filter. That is to say that the reflective coating substantially reflects the useful radiation of the microiithograph projection exposure apparatus, while a further radiation having a different wavelength at least partly passes through the reflective coating, such that it can be registered by the measuring device. What can thereby be achieved is that a smallest possible proportion of the useful radiation is lost during reflection. Furthermore, this can also be advantageous since, for different wavelengths, different sensors have to be used in the Pleasuring device. It. can thus happen that the useful radiation is relatively difficult to detect, whereas the measurement, radiation having a different wavelength can be detected simply and cost-effectively. In this case, by way of example, the measurement, radiation can be coupled into the optical system in a targeted manner. Alternatively, it is also possible to use a radiation source which produces radiation having a plurality of wavelengths, as is the case for example with a plasma source for •generating SUV radiation. Supplementarily , in the case of such a broadband source, a spectral filter can additionally be employed in the optical system, said filter transmitting only the useful radiation and the measurement radiation.

In one embodiment, the optical unit comprises a correction unit for influencing a useful radiation used in the microiithography projection exposure apparatus. This has the advantage that a correction of the radiation properties of the useful radiation used can be performed. Such a correction may be necessary, for example, if optical elements are heated during operation and thus change their optical properties. Furthermore, contamination of optical surfaces during the operation of the microlithograpny projection exposure apparatus likewise leads to a change in the optical properties such as the reflectivity, for example. Such alterations can be at least partly compensated for with the aid of a correction unit according to the invention.

Specifically, the correction unit can influence for example the energy distribution, angle distribution, polarization distribution, phase distribution or the wavefront aberration at specific positions. A correction of the energy distribution has the advantage that, different locations of the photosensitive layer are exposed with the same energy. By contrast, a correction of the angle distribution and of the polarization distribution in the object plane, for example, has the advantage that it is thereby possible to influence the resolution of the imaging of the object field into the image plane. The correction of phase distribution and wavefront aberrations leads to a correction of the image aberrations in the image plane and therefore likewise to an improvement in the resolution of the imaging of the object field. ft correction of the phase distribution and the wavefront aberrations can be performed for example with the aid of an actively deformable mirror within the microlithography projection exposure apparatus.

If the measuring device of the reflective optical element is additionally connected to evaluation electronics and the evaluation electronics provide a control signal for driving the correction unit, then one of the corrections described can be performed particu1ar Iy rapidly .

If the optical unit is an illumination optical unit for illuminating an object field, then the illumination optical unit has the advantages which have already been described above with regard to the optical unit.

In one specific embodiment, the reflective optical component is arranged near a pupil plane of the illumination optical unit and the measuring device measures an energy distribution of an illumination on the reflective optical component. Furthermore, an energy di3tri.bur.ion in the same or a different pupil plane can be altered by means of the correction unit. This embodiment, has the advantage that there is a simpIe relationship between the angle distribution of the irradiation at the object field and the illumination in a pupil plane. The angle distribution of the radiation at the object field can therefore be corrected witViout major prob1ems .

Alternatively, it is advantageous if, in one specific embodiment, the reflective optical component is arranged near a field plane of the illumination optical unit and the measuring device measures an energy distribution of an illumination on the reflective optical component and an energy distribution in the same or a different field plane can be altered by means of. the correction unit. This embodiment has the advantage that there is a simple relationship between the intensity distribution of the illumination of the object field and the illumination in a field plane. The intensity distribution of the illumination of the object field can therefore be corrected without major problems.

A projection optical unit for imaging an object field comprising a reflective optical element according to the invention has the advantages which have already been described above with regard to the element .

A micro!ithography projection exposure apparatus comprising a described illumination optical unit and/or a described projection optical, unit has the advantages which have already been described above with regard to the illumination optical unit and the projection optical unit, respectively.

The invention will be explained in greater detail, with reference to the drawings .

Figure 1 shows a first embodiment of a reflective optical element with a measuring device between the coating and the substrate. Figure 2 shows a further embodiment of a reflective optical element according to the invention with & component for generating a secondary radiation.

Figure 3 shows an embodiment of a re-f.lfect.ive optical element', wherein the substrate is embodied at least partly as a measuring device.

Figure 4 shows a plan view of a reflective optical element wherein a plurality of sensors are arranged in the form of a measuring grid .

Figure 5 shows a section through a reflective optical element wherein the measuring device comprises a plurality of optical waveguides.

Figure 6 .shows an embodiment of a reflective optical element which comprises two sets of sensors arranged one above another.

Figure 7 shows a micro-lithography projection exposure apparatus wherein the reflective optical element according to the invention can be employed.

Figure 8 shows a plan view of a first faceted optical element.

Figure 9 shows a plan view of a second faceted optical element.

Figure 10 shows a correction unit by means of which the illumination of a pupil plane of the illumination optical unit can be altered.

Figure 11 shows an embodiment of a correction unit by means of which the illumination in a field plane of the illumination optical unit can be altered. The reference signs have been chosen such that objects which are i.11 ustraced in figure 1 r.-ave b&en provided with single-digit or two-digit numbers. The objects illustrated in the further figures have reference signs having three or more digits , where 5 the last two digits indicate the object and the preceding digits indicate the number of the figure in which the object is illustrated. The reference numerals of identical objects illustrated in a plurality of figures thus correspond in respect of the last two digits. By way of example, the reference signs0 1, 201 arid 301 identify the object 1 in figures 1, 2 and 3. The mirror substrate is involved in this case.

Figure 1 shows a first embodiment of a reflective optical element according to the invention. In this case, the reflective5 optical element comprises a substrate 1, to which a reflective coating 3 has been applied. A measuring device 5 is situated at least in part between the substrate 1 and the reflective coating 3, said measuring device comprising the sensors 7 in the present case. The reflective coating 3 is in this case configured such 20 that only the part 11 of the incident radiation 9 is reflected. At least a certain proportion of another part 13 of the radiation is incident on the sensors 7. The sensors 7 can be e.g. different types of semiconductor detectors. By way of example, HOS diodes, Schottky diodes, photodiodes or25 phototransistors are possible. Alternatively, the sensors 7 can also be configured such that they do not directly detect the part 13 of the incident radiation, but rather a secondary effect caused by the incident radiation 9. Thus, the incident radiation 9 provides e.g. for the heating of at least parts of the 30 substrate 1 or of the reflective coating 3. This heating can be detected e.g. by the sensors 7 being configured in the form of thermistors, for example. The incident radiation 9 can be radiation having different wavelengths. Particularly if the reflective optical element is employed in a microlithography 35 projection exposure apparatus, radiation having a wavelength in the region of 193 nm or in the range of 5 - 15 nm, the so-called extreme ultraviolet, is involved. Depending on the wavelength of the incident radiation 9, the reflective coating 3 is embodied differently. Flexure 1 already indicates that the reflective coating 3 consists of two individual layers 15 and 17. This construction shown should be understood as purely schematic bot.h in this figure and in the following figures. If the reflective optical element is designed to reflect radiation having a wavelength of 193 nm, then the reflective coating usually consists of 6 - 12 individual layers. By contrast, if radiation in the range of 5 - 15 nm is intended to be reflected, then the reflective coating 3 iε constructed from a multiplicity of individual layers. By way of example, multilayers composed of 50 double layers composed alternately of silicon and molybdenum or lanthanum and B₄C are customary. Other constructions of the reflective coating 3 are likewise possible. In the illustrated configuration of the reflective optical element according to the invention, the measuring device 5 comprises a plurality of sensors 7. This division into a plurality of sensors 7 makes it possible to perform a spatially resolved measurement of the impinging radiation. Thus, the sensors 7 can be configured e.g. such that the sensor signal is dependent on the intensity of the incident radiation .9. By this means, it is then possible to measure an intensity profile of the incident radiation 9 at the location of the reflective optical element. Xn an alternative configuration, the sensor signal is dependent on the temperature. In that case, a temperature profile over the reflective optical element can be determined with the aid of the sensors 7. The intensity profile of the incident radiation 9 can be deduced from such a temperature profile.

Figure 2 illustrates an alternative oonfigurational form of there-fleetive optical element according to the invention. Alongside the sensors 207, in this case the measuring device 205 comprises a component 219 which emits a secondary radiation 221 upon passage of the radiation or absorption of the radiation 213. Said component 219 can be a coating, for example, which contains a phosphorescent material or else a scintillator material. Once again a certain portion 211 of the incident radiation 209 is reflected. Another portion 213 at least partly passes througn the reflective coating 203, which is once again indicated in the form of two individual layers 215 and 217. If said portion 213 enters into the component 215, then a secondary radiation 221 is initiated there. This takes place by virtue of the fact that the radiation 2.13 excites a material of the component 213 to phosphorescence, by way of example. The secondary radiation 221 is then detected with the aid of the sensors 207. In this case, too, on che basis of the measurement signal generated by the sensors 207, it is possible to deduce the intensity distribution of the radiation 209 at the location of the reflective optical component. In a variation of this embodiment, not illustrated in the figure, at least partly substrate is situated between the component 215 for generating the secondary radiation 221 and the sensors 207. Thus, by way of example, the sensors 207 can be applied on the rear side of the reflective optical component. In this case, however, the substrate material has to be transparent to the secondary radiation 221. In other words, the secondary radiation 221 at least partly passes through the substrate 20.1 and is only then detected by the sensors 207. Such an arrangement may have the advantage that the detectors 207 do not have to be applied between coating and substrate, but rather also on the rear side of the substrate. It is thus possible, by way of example, for sensors to be replaced more easily in the context of maintenance work.

Figure 3 shows a further embodiment of the reflective optical components according to the invention. In this case, the substrate 301 comprises a dopafole material, such as e.g. silicon. In this case, the substrate 301 can be constructed completely from the dopable material or alternatively have a dopable layer. The figure illustrates the case in which the substrate itself has a dopable material. The sensors 307 can then be integrated into saz.ά dopabie material with the aid of at least one .lithographic step. This exploits the fact that sensors 307 in the form of semiconductor detectors can be produced with the aid of lithographic methods just like other microelectronic components. Semiconductor detectors can thus be integrated directly into the dopable substrate material or the dopable layer. It is not necessary for the detectors to be manufactured separately and subsequently be connected to the mirror 5 substrate. Virtually the entire surface of the mirror subsrate 301 which faces the coating is constructed as a, if appropriate multipartite, semiconductor detector. Particularly efficient production of a reflective optical element according to the invention can thereby be achieved. After the integration of the 10 semiconductor detectors by lithographic methods, the reflective coating 303 is applied in order thus to obtain the reflective optica1 eiement .

figure 4 illustrates a plan view of a reflective optical element 15 according to the invention. In this case, the reflective optical element is subdivided into regions which are in each case assigned to a sensor 407, The sensors 407 in turn lie between the reflective coating and the substrate of the reflective optical element. In the present case, the entire reflective area 20 of the reflective optical element, is equipped with sensors 407 arranged in the form of a measuring grid. The exact position of the illumination 423 of the reflective optical element can thereby be ascertained. On the basis of the sensor signals, it is possible to ascertain which of the sensors within the 25 measuring grid is illuminated. Together with the known form of the measuring grid, the position and form of the illuminated region 423 follow therefrom. Supplemeπtarily, it is also possible to determine the intensity distribution of the incident radiation in the illuminated region 423 from the sensor signals.

30

Figure 5 illustrates a further embodiment of the reflective optical element according to the invention. In this case, optical waveguides 525 are arranged below the reflective coating 503 within the substrate 501, and forward a portion 513 of the 35 incident radiation 509, which portion is not reflected, to a measuring arrangement. By virtue of this construction, wherein although the optical waveguides 525 are arranged as part of the measuring device between the reflective coating and the substrate 501, the sensors for detecting the radiation are not in direct contact with the costing, what can be achieved is that the sensors can easily be replaced for maintenance purposes or repair purposes without having to dismantle the optical element.

Figure 6 shows a development of the reflective optical element wherein, in addition to the location, the direction of the incident radiation can also be measured. In this case, the reflective optical element comprises a substrate 601 and a first set of sensors 627, said first set in this case being applied directly on the substrate 601. The measuring device 60S furthermore comprises a second set of sensors 629, said second set being fitted above the first set 627. It is possible, by way of example, as in the present case, to apply a layer 631 between the two sets of sensors, said layer serving to produce a certain distance between the first set 627 snά the second set 629 of sensors. A reflective coating 603 is furthermore arranged above the sensors 629. If incident radiation 609 impinges on the reflective optical element, then once again a certain portion 613 of the incident radiation 609 is not reflected, but rather passes through the reflective coating 603. A photon of this radiation temporally successively passes through the second set 629 of sensors and then the first set 627 of sensors. In this case, the photon is detected by in each case at least one of the sensors- from each of the two sets of sensors. The sensors which detect the respective photon are identified by the reference- numeral 633 in the figure. The direction of the incident radiation can then be deduced from the spatial position of the sensors 633. In this way, it is possible not only to determine a spatially resolved intensity distribution at the location of the reflective optical element, but also to measure the direction of the incident radiation at the location of the reflective optical element .

Figures 7 to 10 show an exemplary construction of the components: of a ϊfticrolithography projection exposure apparatus. In this case, figure 7 shows an overview of the construction of the microiithography projection exposure apparatus, and figures 8 to .1.0 show detail illustrations of specific components. The components illustrated comprise a light source 735, an illumination optical unit 737 and a projection optical unit 739. In this case, the light source 735 generates radiation in the extreme ultraviolet, that is to say having a wavelength in the range of 5 - 15 nm. This radiation is then directed into the illumination optical unit 737, which conditions the radiation in a suitable manner in order thereby to illuminate a structure- bearing raaslc at the location of an object field 741. The object field 741 is then imaged with the aid of the projection optical unit 739 onto a photosensitive layer in an image plane 743 of the microlithography projection exposure apparatus. The components of the light source, of the illumination optical unit and of the projection optical unit will be described in detail below- The .light source 735 is a xenon light source in the present case. With the aid of the gas feed 745 and. the gas extractor 747, a gas target is produced at the location 743. At the same time, the radiation generated by the laser 751 is likewise concentrated at the location 745 with the aid of the focusing optical unit 753. Aε a result, of this meeting of xenon gas and concentrated laser radiation, the xenon gas is converted to a plasma state at the location 749. The plasma 749 then imitates radiation in the range of the extreme ultraviolet, that is to say in the wavelength range of 5 nm - 15 run. The resulting radiation is collected with the aid of the ellipsoid nrirrcr 755 and fed to the first mirror 757 of the illumination optical unit 737. As the next component in the light path, the illumination optical unit 737 contains a fly's eye condenser 759, which consists of a first faceted mirror 761 and a second faceted mirror 763.

Figures 8 and 9 respectively show a plan view of the first faceted mirror (figure 8) and of the second faceted mirror

(figure 9} . The first faceted mirror 861 comprises a plurality of first facet elements 3€5, which have an arcuate cross section and are densely packed, such that they cover the first facet element 761 or 361 as completely as possible. The arcuate cross section of the first facet elements 365 is necessary since the first facet elements 865 are imaged onto the object field in superimposing fashion with the aid of the downstream optical unit (763, 771, 773} . As will be explained below, it is advantageous if the object field 741 has an arcuate cross section. T.t is thus advantageous if the first facet, elements 365 likewise have an arcuate cross section in order to ensure that the arcuate object field 741 is illuminated as efficiently as possible. The second faceted optical element 763 or 963 comprises a plurality of second facet elements 967, which in the present, case are densely packed and have a rectangular cross section. In this case, the first faceted optical element 761 and the first mirror 757 of the illumination optical unit are configured such that each of the first facet elements 865 generates an image of the plasma 749 at the location of a second facet element 967. In this case, the first facet elements &65 can be oriented such that two adjacent first facet elements 865 generate two images o.f the plasma 749 at locations of two non- adjacent second facet elements 967. it is thereby possible to achieve more uniform illumination of the second faceted mirror 763. A condenser 769 is arranged in the light path downstream of the fly's eye condenser 753. Said condenser 769 comprises a first condenser mirror 771 and a second condenser mirror 773. The condenser 769 serves, together with the second facet elements 967, to image the first facet elements 865 in superimposing fashion into the object field 741 and, at the same time, to image the second faceted mirror 763 into an exit pupil of the illumination optical unit 737. The object field 741 is then imaged into the image plane 743, in which a photosensitive layer can be arranged, with the aid of the projection optical unit 739. For this purpose, the projection optical unit comprises the mirrors M1, M2, M3, M4, M5 and M6. In this case, ail these mirrors have a surface form which follows a segment from an area that is rotationally symmetrical about the optical axis 775. For this reason, the recjion in which the best imaging quality is achieved, the object field 741, is also rotationaliy symmetrical about the optical axis 775. Consequently, this inevitably results in the arcuate cross section of the object field 741 and therefore also the arcuate cross section of the first facet element's 865. During the operation of the micro!.xenography projection exposure apparatus, a structure- bearing mask is arranged at the location of the object field 741. Said mask is illuminated with the aid of the light source 735 and the illumination optical unit 737 and then imaged into the image plane 743 in demagnified fashion by the projection optical unit 739. In the image plane 743, a photosensitive layer is then arranged on a substrate. The photosensitive layer is chemically altered by the exposure, such that, a microelectronic component can be produced therefrom with the aid of a lithographic chemical process. The microlithography projection exposure apparatus is often operated as a so-called scanner. In this case, the structure-bearing mask that is intended to be imaged is larc/er than the object field suitable for imaging. For this reason, the mask is moved through the static object field 741 in the Y-direction. At the same time, in the image plane, the substrate with the photosensitive layer is likewise moved in the Y-direction, at a correspondingly lower speed. Every point of the structure-bearing mask therefore moves in the Y-direction through the illuminated object field 741 and in the process n'a:~: applied to it a quantity of light, the so-called dose, which corresponds to the integral over the irradiance along the trajectory of the point. For the lithographic process it is advantageous if as far as possible the same dose is applied to every point on the mask. For this purpose, a correction unit 777 is provided in the vicinity of the object field 741.

The construction and the functioning of said correction unit 777 are schematically illustrated in figure 10. In this case, the correction unit 777 comprises a plurality of finger-like diaphragms 10-'9, the front edges 1081 of which delimit the illumination of the object field 741. If a point on the structure-bearing mask passes through the illuminated object. field during the scanning process, then after a certain time it enters into the shadow caused by a finger-like diaphragm 1079. The integrated irradiance, that is to say the dose, is therefore dependent on that position in the y--direction in which the corresponding finger- like diaphragm 1079 is situated. By altering the Y-position of the finger-like diaphragms 1079, it is therefore possible to set the dose on the object field. Since the correction unit 777 comprises a plurality of diaphragms which are offset in the X-direction, the dose can be set. separately for different y-ρositions on object field. During the operation of the microlithogr&phy projection exposure apparatus, it is necessary to permanently ensure a constant uniform dose in the X-direction over the object field 741. However, since certain properties of the tnicrolithography projection exposure apparatus can change during operation, it is necessary to readjust the correction unit 777, It can thus happen, .for example, that the reflective coating of the optical elements of the illumination optical unit or of the light source may over^¬ time become contaminated or change in some other way on account of the radiation effect. These effects have the consequence that the reflectivity of the reflective coatings changes. This means, however, that the intensity distribution of the radiation in the object field 741 also changes, which has the consequence that the correction unit 777 has to be readjusted. In order that such changes can be monitored actually during the operation of the microlithography projection exposure apparatus, according to the invention at least one of the mirrors of the illumination optical unit 737 or of the projection optical unit 739 is provided with a measuring device described above. It is thereby possible to monitor at any time whether the irradiance or the position of the illumination on one of the optical elements changes during operation. It is particularly advantageous if. at least one of the mirrors which are arranged in the vicinity of a field plane of the illumination optical unit is embodied as such an optical element with a measuring device. In figure 7, this is the first mirror 771 of the condenser 769. The arrangement of a reflective optical element according to the invention in the vicinity of a field plane of the illumination optical unit 737 has the advantage that the intensity distribution of the illumination on the reflective optical element 777 is related to the intensity distribution of the illumination of the object field Ir. a simple manner. Consequently, the setting of the correction unit 777 can be adapted on the basis of the result of the measurement of the illumination on the reflective optical element 771. For this purpose, a control unit 783 is provided, which takes up the signals of the sensors of the reflective optical element 771 and generates a control signal therefrom, which control signal is used to drive actuators that alter the position of the finger-like diaphragms .1079 in the Y-direction. This ensures that, during operation, a uniform dose is provided in the X-direction over the object field 741 without having to deactivate the apparatus in the meantime for monitoring measurement.

Alternatively or supplementariiy, the illumination optical unit 737 can be equipped with a second correction unit 785 for correcting the angle distribution of the radiation in the object field 741. During the operation of the microlithography projection exposure apparatus, it is advantageous if the angle distribution of the incident radiation at the object field changes only slightly. In particular, it is advantageous if the centroid direction of the incident radiation at the object field remains unchanged as far as possible. The deviation of the centroid direction from the desired direction is referred to as the telecentricity error. Relatively large telecentricity errors have an adverse influence on the quality of the imaging by the projection optical unit 739. In order to correct the angle distribution of the radiation at the object field, in the case of the illumination optical unit 737 shown, a correction unit 785 is arranged at the second faceted optical mirror 763. As already explained, the second faceted mirror 763 is imaged into an exit pupil of the illumination optical unit. The spatial intensity distribution at the second faceted mirror 763 is therefore in a simple relationship with the intensity distribution in the angle space at the object Held 741. By introducing diaphragms at the second faceted mirror 763, it is thus possible to influence the angle distribution in the object field. Figure 11 shows a suitable correction unit 1185, having a plurality of diaphragms .1187. The diaphragms 1187 can be altered in their position by means of actuators (not illustrated), such that they cover different regions of the second faceted mirror 1163. The positions of the diaphragms 1187 thus directly influence the angle distribution of the radiation at the object field and, in particular, the telecentricity error thereof. According to the invention, then, one of the mirrors of the illamination optical unit 737 or of the projection optical unit 739 iε equipped with a measuring device, such that alterations in the angle distribution at the object field are ascertained near-instantaneously during the operation of the microlithography projection exposure apparatus. By way of example, this is the mirror 773 in figure 7. The measuring device according to the invention thus makes it possible to .measure the position and intensity distribution of the illumination on the mirror 773. In this case, the measuring device is connected to a control unit 799, which takes up the generated information about the intensity distribution and position of the illumination and generates a control signal therefrom, which control signal is used to drive actuators that alter the position of the diaphragms 1187 in figure 1.1. In this way, a correction can be effected directly in the event of. an alteration of the illumination on the reflective optical element 773, such that the angle distribution in the object plane changes only slightly.

Claims

Patent Claims :

1. Illumination optical unit for illuminating an object field of a micro!ithography projection exposure apparatus with a useful radiation comprising at least one reflective optical element that comprises a substrate (1, 201, 301, 501, 601), a reflective coating (3, 203, 303, 503, €03} and a measuring device (5, 205, 305, 505, 605), characterized in that the measuring device (5, 205, 305, 505, 605} is arranged at least partly between the coating (3, 203, 303, 503, 603) and the substrate (1, 201, 301, 501, 601).

2. Illumination optical unit according to claim 1, characterised in that the measuring device (5, 205, 305, 505, 605} at least partly adjoins the coating (3, 203, 303, 503, 603} and the substrate (1, 201, 301, 501, 601).

3. Illumination optical unit for illuminating an object field of a jnicrolithogrctphy projection exposure apparatus with a useful radiation comprising at least one reflective optical element that comprises a substrate U, 201, 301, 501, 601 } and a reflective coating (3, 203, 303, 503, 603), characterized in that the substrate (1, 201, 301, 501, 601} is embodied at least partly &z a measuring device {5, 205, 305, 505, 605) .

4. Illumination optical unit according to Claim 3, characterized in that the substrate (1, 201, 301, 501, 601} consists of a dopable material or comprises a dopabie layer and the measuring device (5, 205, 305, 505, 605) has been at least partly integrated into the dopabie material, the integration having been effected with the aid of at least one lithographic step.

Illumination optical unit according to any of Claims 1-4, characterised in that the measuring device (5, 205, 305, 505, 605) detects radiation (13, 213, 513, 613) that has passed through the coating (3, 203, 303, 503, 603).

Illumination optical unit according to Claim 5, characterized in that measurement radiation registered by the measuring device (5, 205, 305, 505, COS) and the useful radiation of. the microlithography projection exposure apparatus differ in wavelength,

Illumination optical unit according to either of Claims 1- 6, characterized in that the optical unit corαprises a correction unit (785, 777) fox- influencing the useful radiation used in the microlithography projection exposure apparatus.

Illumination optical unit according to Claim 7, characterized in that the correction unit (777, 735} influences at least one of the useful radiation properties from the following group: energy distribution, angle distribution, polarization distribution, phase distribution, wavefront aberration.

Illumination optical unit according to any of Claims 7-6, characterized in that the measuring device (5, 205, 305, 505, 605} is connected to evaluation electronics and the evaluation electronics provide a control signal for driving the correction unit.

Illumination optical unit accordinc. to Claim 9, characterized in that. the substrate (1, 201, 301, 501, 601) consists of a dopable materia! or comprises a dopable layer and at least parts of the evaluation electronics have been integrated into the dopable material with the aid of at least .one lithographic step.

IlluiTiination optical unit according to any of Claims 1-10, characterized in that the reflective optical element is designed for the reflection of radiation having a wavelength in the range of 5-15 run.

Illumination optical unit according to any of Claims 1-11, characterized in that the coating (3, 203, 303, 503, 603) comprises a plurality of layers with different materials.

Illumination optical unit according to any of Claims 1-12, characterized in that the measuring device {5, 205, 305, 505, 605} comprises at least one semiconductor detector.

Illumination optica! unit according to any of Claims 1-13, characterized in that the measuring device (5, 205, 305, 505, 605) measures a temperature change on account of radiation absorption within the coating (3, 203, 303, 503, 603} or the substrate (1, 201, 301, 501, 601) .

Illumination optical unit according to any of Claims 1-14, characterized in that the measuring device (5, 205, 305, 505, 605) comprises a component (219) which emits a secondary radiation (221) upon the passage or the absorption of the radiation.

Illumination optical unit according to any of Claims 1-1 S, characterized in that the measuring device (5, 205, 305/ 505, 605) comprises a plurality of sensors (7, 207, 307, 407, 607) which enable a spatially resolved and/or directionally resolved measurement of the impinging radiation.

17. Illumination optical unit according to Claim 16, characterized in that the plurality of sensors (7, 207, 307, «07, 607) comprises a first set (627) of sensors and a second set. {629} of sensors, which are arranged one above another in such a way that an at least parts of the impinging radiation are successively detected by two sensors.

18. Illumination optical unit according to any of Claims 1-17, characterized in that the reflective optical component is arranged near a pupil plane of the illumination optical unit (737) and the measuring device (5, 205, 305, 505, 605) measures an energy distribution of an illumination on the reflective optical component and an energy distribution in the same or a different pupil plane can be altered by means of the correction unit (7δ5) .

19. Illumination optical unit according to any of Claims 1-18, characterized in that the reflective optical component is arranged near a field plane of the illumination optical unit and the measuring device {5, 205, 305, 505, 605) measures an energy distribution of an illumination on the reflective optical component and an energy distribution in the same or a different field plane can be altered by means of the correction unit (777).

20. Micro-lithography projection exposure apparatus comprising an illumination optical unit according to any of Claims 1-