Projection exposure tool for microlithography and method for microlithographic imaging

Abstract

A projection exposure tool for microlithography for imaging mask structures of an image-providing substrate onto a substrate to be structured includes a measuring apparatus configured to determine a relative position of measurement structures disposed on a surface of one of the substrates in relation to one another in at least one lateral direction with respect to the substrate surface and to thereby simultaneously measure a number of measurement structures disposed laterally offset in relation to one another.

Claims

1. A tool, comprising: a measuring apparatus configured to determine a relative position of measurement structures relative to each other in a lateral direction, wherein: the tool is a microlithography projection exposure tool configured to image mask structures of a first substrate onto a second substrate which is different from the first substrate; the measurement structures are disposed on a surface of the first substrate, or the measurement structures are disposed on a surface of the second substrate; and the measuring apparatus is configured so that, during use of the measuring apparatus, the measuring apparatus simultaneously measures a number of measurement structures which are laterally offset relative to each other using measuring light comprising two measuring beams that are irradiated onto the measurement structures via beam paths having different angles relative to the surface of the substrate on which the measurement structures are disposed.

2. The tool of claim 1, wherein the measuring apparatus comprises a beam splitter configured to split an incoming beam of the measuring light into the two measuring beams.

3. The tool of claim 2, wherein the beam splitter comprises a diffraction grating.

4. The tool of claim 3, wherein the diffraction grating is tilted relative to a propagation direction of the incoming beam of the measuring light.

5. The tool of claim 2, wherein the measuring apparatus is configured to superimpose coherently images of the measurement structures generated via the two measuring beams.

6. The tool of claim 1, wherein the measuring apparatus is configured to simultaneously measure the lateral relative position of measurement structures distributed over the whole substrate surface.

7. The tool of claim 1, wherein the measuring structures are on the surface of the second substrate.

8. The tool of claim 1, wherein the measuring apparatus comprises an interferometric measuring apparatus.

9. The tool of claim 1, wherein the measuring apparatus comprises at least two reflective elements configured to reflect back onto the measurement structures measuring light divided into two measuring beams by diffraction on the measurement structures.

10. The tool of claim 1, wherein the measuring apparatus is configured to take topography measurements at a number of points of the substrate surface simultaneously.

11. The tool of claim 1, wherein the measuring apparatus is configured to take the lateral position measurements with measuring light of a first wavelength, and the topography measurements with measuring light of a second wavelength.

12. The tool of claim 11, wherein the measuring apparatus comprises a diffraction grating configured to split the measuring light of the first wavelength into two measuring beams, and the diffraction grating being configured so that at least 90% of the measuring light of the second wavelength passes through the diffraction grating without being diffracted.

13. The tool of claim 12, wherein the diffraction grating is tilted relative to the propagation direction of the measuring light of the second wavelength.

14. A method, comprising: determining a relative position of measurement structures in a lateral direction with a respect to a substrate on which the measurement structures are disposed by simultaneously measuring a number of measurement structures which are laterally offset relative to each other using measuring light comprising two measuring beams that are irradiated onto the measurement structures via beam paths having different angles relative to a surface of the substrate on which the measurement structures are disposed, the substrate being a first substrate or a second substrate; and using a microlithography projection exposure tool to image mask structures on the first substrate onto the second substrate while simultaneously locally varying an imaging parameter based on the lateral position measurements.

15. The method of claim 14, comprising: using a beam splitter to split an incoming beam of the measuring light into two measuring beams with different propagation directions before striking the substrate to be measured; and irradiating the incoming beam of the measuring light at an angle to the substrate surface to be measured onto the beam splitter.

16. The method of claim 14, comprising using a diffraction grating to split an incoming beam of the measuring light into two measuring beams with different propagation directions before striking the substrate to be measured, wherein the diffraction grating is tilted relative to a propagation direction of the incoming beam of measuring light.

17. A tool, comprising: a measuring apparatus configured to determine a relative position of measurement structures relative to each other in a lateral direction, wherein: the tool is a microlithography projection exposure tool configured to image mask structures of a first substrate onto a second substrate which is different from the first substrate; the measurement structures are disposed on a surface of the first substrate, or the measurement structures are disposed on a surface of the second substrate; the measuring apparatus is configured so that, during use of the measuring apparatus, the measuring apparatus simultaneously measures a number of measurement structures which are laterally offset relative to each other using measuring light comprising first and second measuring light beams; the first light beam impinges on the surface of the substrate on which the measurement structures are disposed at a first angle; the second light beam impinges on the surface of the substrate on which the measurement structures are disposed at a second angle; and the first angle is different from the second angle.

18. The tool of claim 17, wherein the measuring apparatus comprises a beam splitter configured to split an incoming beam of the measuring light into the two measuring beams.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above and further advantageous features of the disclosure are illustrated in the following detailed description of exemplary embodiments according to the disclosure with reference to the attached diagrammatic drawings, in which:

(2) FIG. 1 an illustration of a projection exposure tool for microlithography in a sectional view with an embodiment according to the disclosure of a measuring apparatus for determining a distortion of a surface of a wafer and of the topography of the same;

(3) FIG. 2 mirror elements of the measuring apparatus according to FIG. 1 and the wafer to be measured in a sectional view;

(4) FIG. 3 a top view of the arrangement according to FIG. 2;

(5) FIG. 4 a further embodiment of the measuring apparatus according to the disclosure for use in the projection exposure tool according to FIG. 1;

(6) FIG. 5 a sectional view of a further embodiment of the measuring apparatus according to the disclosure for use in the projection exposure tool according to FIG. 1;

(7) FIG. 6 an illustration of the functional principle of the measuring apparatus according to FIG. 5;

(8) FIG. 7 an illustration of light paths between a diffractive optical element of the measuring apparatus according to FIG. 5 and the wafer to be measured;

(9) FIG. 8 an illustration of a variant according to the disclosure of the measuring apparatus according to FIG. 5;

(10) FIG. 9 a top view onto two different embodiments according to the disclosure of a diffraction pattern arrangement on a diffractive element of the measuring apparatus according to FIG. 5;

(11) FIG. 10 a top view onto a measuring structure arrangement on a wafer surface to be measured by the measuring apparatus according to FIG. 5;

(12) FIG. 11 a sectional view of a further embodiment of the measuring apparatus according to the disclosure for use in the projection exposure tool according to FIG. 1;

(13) FIG. 12 an illustration of light paths between a diffractive optical element of the measuring apparatus according to FIG. 11 and the wafer to be measured;

(14) FIG. 13 an illustration of a variant according to the disclosure of the diffractive optical element for use in the measuring apparatus according to FIG. 11; and

(15) FIG. 14 an illustration of a further variant according to the disclosure of the diffractive optical element for use in the measuring apparatus according to FIG. 11.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS ACCORDING TO THE DISCLOSURE

(16) In the exemplary embodiments described below elements which are similar to one another functionally or structurally are provided as far as possible with the same or similar reference numbers. Therefore, in order to understand the features of the individual elements of a specific exemplary embodiment one should refer to the description of other exemplary embodiments or the general description of the disclosure.

(17) In order to facilitate the description of the projection exposure tool, in the drawings a Cartesian xyz coordinate system is specified from which the respective relative position of the components shown in the figures can be gathered. In FIG. 1 the x direction extends to the right, the y direction extends perpendicularly to the plane of the drawing into the latter, and the z direction upwards.

(18) In FIG. 1 a projection exposure tool for microlithography in an embodiment according to the disclosure is illustrated. The projection exposure tool 10 includes an illumination system 12 for illuminating an image-providing substrate in the form of a mask 20 with exposure radiation 15 and a projection objective 18. The projection objective 18 serves to image mask structures 22 from a mask plane onto a substrate to be structured in the form of a wafer 30. In addition to a silicon wafer, a substrate for an LCD display, a transparent so-called flat panel can also be used, for example, as the substrate to be structured.

(19) The illumination system 12 includes an exposure radiation source 14 for generating the exposure radiation 15. Depending on the embodiment of the projection exposure tool 10, the wavelength of the exposure radiation 15 can be in the UV wavelength range, e.g. 248 nm or 193 nm, or also in the extreme ultraviolet wavelength range (EUV), e.g. approximately 13.5 nm or approximately 6.8 nm. Depending on the exposure wavelength the optical elements of the illumination system 12 and of the projection objective 18 are designed as lenses and/or mirrors.

(20) The exposure radiation 15 generated by the exposure radiation source 14 passes through beam propagation optics 16 and is then irradiated by an illuminator 17 onto the mask 20.

(21) The mask 20 is held by a mask table 24 which is mounted shiftably in relation to a frame 19 of the projection exposure tool 10. The wafer 30 is disposed on an exposure table 33 which serves as a wafer shifting apparatus.

(22) The exposure table 33 includes a wafer holder 34 for fixing the wafer 30 from its lower side, for example via negative pressure, and a shifting stage 36 by which the wafer 30 can be shifted laterally to the optical axis of the projection objective 18, i.e. in the x and y directions according to the coordinate system from FIG. 1. Furthermore, the shifting stage 36 enables shifting of the wafer 30 in the direction of the optical axis, and so in the z direction according to the coordinate system from FIG. 1. This type of shift in the z direction is used in particular, when exposing the wafer 30, to hold the surface 31 of the latter in the focus of the exposure radiation 15.

(23) Generally the surface 31 of the wafer 30 is exposed section by section, i.e. field by field. Both the wafer 30 and the mask 20 are thereby moved in opposite directions along the x axis so that a slot-shaped exposure region over the wafer surface 31 is scanned. This takes place a number of times so that the mask 20 is imaged in the form of a plurality of fields, next to one another, on the wafer surface 31.

(24) There is integrated into the projection exposure tool 10 a measuring apparatus 40 which is configured on the one hand to measure the whole surface of the wafer 30 with respect to its distortion, and on the other hand with respect to topography variations. The distortion of the wafer 30 is understood to mean a deviation of relative positions of measurement structures arranged on the wafer surface 31 in relation to one another in the lateral direction with respect to the wafer surface 31, i.e. in the X-Y plane. In FIG. 1 the measurement structures are provided with reference number 32 and have been applied to the wafer 30 in a previous wafer processing step. The measurement structures 32 are in the form of grating structures, as will be described in more detail below.

(25) In an embodiment of the projection exposure tool 10 the wafer 30 is disposed on the exposure table 33 beneath the measuring apparatus 40 for measuring. For this purpose the exposure table 33 is shifted into the position shown in FIG. 1 lateral to the optical axis of the projection objective 18. In an alternative embodiment the projection exposure tool 10 includes a separate measuring table 38 on which the wafer 30 is arranged during the measurement by the measuring apparatus 40, while an already measured wafer 30 is simultaneously located on the exposure table 33 and is exposed in parallel.

(26) The measuring apparatus 40 is designed as a two-dimensionally measuring optical measuring apparatus, i.e. during the measurement both of the distortion and the surface topography of the wafer 30 corresponding measurements are simultaneously determined at a number of locations of the surface 31 in contrast to point by point sampling of the wafer surface 31.

(27) The measuring apparatus 40 includes two measuring light sources 41 and 43 for generating measuring light of different wavelengths. A first measuring light source 41 generates a first measuring light 42 with a wavelength .sub.1 which is used for the surface topography measurement, also referred to in the following as the form measurement. The second measuring light source 43 generates a second measuring light 44 with a wavelength .sub.2 which is used to measure the lateral positioning of the measurement structures and so for the distortion measurement. The positioning of the measurement structures may also be referred to as placement of the measurement structures. The measuring light of both measuring light sources 41 and 43 is irradiated via a respective optical fibre 45 onto a beam splitter 48. Wavelengths in the visible or near infrared range can be used for the measuring light 42, as is explained in more detail below. Thus, helium neon lasers, laser diodes, solid state lasers and LEDs, for example, can be used as measuring light sources.

(28) For the measuring light wavelengths should be chosen with respect to which the photoresist, provided for the exposure with the exposure radiation 15 on the wafer 30, is not sensitive. Preferably, the measuring wavelengths should be below the exposure threshold of the photoresist. According to one embodiment the measuring wavelength is chosen such that the energy of the photons thus generated is below the band gap of silicon. Thus, wafer heating during the measurement can be minimised. The measuring light 42 for the form measurement is deflected by the beam splitter 48 in the direction of the wafer surface 31. Before striking the wafer surface 31 the measuring light passes through a Fizeau collimator 50.

(29) The Fizeau collimator 50 includes a Fizeau surface 52 on which part of the measuring light 42 is reflected back as reference light, whereas the unreflected part of the measuring light 42 is reflected on the wafer surface 31 and then interferes with the reference light after passing through a collimator lens 58 in the form of an ocular on a detection surface 61 of a locally resolving detector 60 in the form of a CCD camera. According to one embodiment the Fizeau collimator 50 is designed as a collimator open high up with a focal width to diameter ratio f/d<1 by which installation space in the projection exposure tool 10 can be saved.

(30) The interferogram on the detector surface 61 is detected by the detector 60. From the interferogram detected, by an evaluating device 62 the surface profile of the section of the wafer surface 21 irradiated by the measuring light is determined. In other words, the surface topography of the wafer 30 is determined at least section by section. According to one embodiment the detection region of the measuring apparatus 40 is large enough in order to measure the whole wafer surface 31 simultaneously with respect to a surface topography.

(31) The measuring light 44 for the positioning measurement is also deflected by the beam splitter 48 in the direction of the wafer surface 31. The propagation direction of the measuring light 44 is thereby tilted slightly in relation to the propagation direction of the measuring light 42. In the present exemplary embodiment the measuring light 42 is propagated along the optical axis 51 of the Fizeau collimator, while the propagation direction of the measuring light 44 is tilted in relation to the optical axis 51 such that upon passing through the Fizeau collimator 50, back reflexes of the measuring light 44 generated on the Fizeau surface 52 are blocked out on an aperture 56 disposed in front of the collimator lens 58 so that the back reflexes can not interfere with the positioning measurement, and when the form measurement is taken simultaneously, can not interfere with the form measurement either.

(32) After passing through the Fizeau collimator 50 the measuring light 44 strikes the wafer surface 31 and is reflected by the measurement structures 32 disposed here in the form of grating structures in minus first or plus first diffraction order onto plane mirrors 54 disposed at an angle above the wafer 30. This beam profile is shown clearly in FIG. 2. Generally speaking, the measuring radiation 44 is reflected on the measurement structure 32 in two diffraction orders different from zero, in the present case the minus first diffraction order and the plus first diffraction order.

(33) The light of the minus first diffraction order forms a first measuring beam 44a, and the light of the plus first diffraction order forms a second measuring beam 44b. After reflection on the plane mirror 54, the light of the first measuring beam 44a runs back to the measuring structure 32. Here the light of the first measuring beam 44a reflected in minus first diffraction order on the measurement structure 32 passes back to the beam splitter 48 in the beam path of the incoming measuring light 44, and strikes the detection surface 61. After reflection on the second plane mirror 54, after diffraction on the measurement structure 32, the light of the second measuring beam 44b also runs in plus first diffraction order through the beam splitter 48 and interferes with the light of the first measuring beam 44a on the detection surface 31.

(34) The image on the detection surface 61 is a coherent superposition of the images over the two mirrors 54 and thus forms an interferogram. The interferogram contains information on the relative phase of the two paths of the measuring beams 44a and 44b, and so the position of the measurement structure 32. With reference to FIG. 2, the phase of the light of the first measuring beam 44a on the detection surface 61 is identified by .sub.1, and the phase of the light of the second measuring beam 44b on the detection surface 61 by .sub.2. With a shift of the measuring structure 32 by x, the following phase difference is produced:
=.sub.1.sub.2=4.Math.2.Math.x/p(1)
p being the grating period of the measurement structure 32. With a shift of the measurement structure 32 by a period p, there thus follows a peak phase deviation of four times the wavelength of the measuring light 44. The phase difference can be read out from the interferogram generated by the coherent superposition of the images over the two mirrors 54, and from this a deviation of the position of the respective measurement structure 32 in the direction of the x coordinate from its desired position can be determined.

(35) FIG. 3 shows the arrangement of the wafer 30 and of the plane mirrors 54 according to FIG. 1 in a top view. The mirrors identified in FIG. 1 by the reference number 54 correspond in the designation according to FIG. 3 to the mirrors 54a. These mirrors are used for the lateral position determination of measurement structures with respect to the x coordinate. For this purpose the line gratings 32a, the grating lines of which run in the y direction, are used as measurement structures. For the measurement of the whole surface of the wafer 30 the line gratings 32a are positioned in a web-type arrangement on the wafer surface 31. In order to measure the position of measurement structures in the y direction, corresponding grating structures 32b are arranged over the wafer surface 31, the grating lines of which extend in the x direction.

(36) The grating structures 32b diffract the incident measuring light 44 onto the mirrors 54b which are disposed at an angle above in the +/y direction in relation to the wafer 30. At the intersection points 33 of the diffraction structures 32a and 32b the position in both coordinate directions x and y can be determined. Overall, the line gratings 32a and 32b form a web structure on the wafer surface 31, the respective surface regions within the web meshes being provided as exposure fields 68 onto which the mask 20 is respectively imaged. The exposure fields 68 are often called dies. According to one embodiment the plane mirrors 54a and 54b have a lateral expansion of at least 300 mm and a vertical expansion of at least 50 mm.

(37) In the embodiment shown in FIG. 1, as already mentioned above, the measuring light 42, which is used for the form measurement, and the measuring light 44, which is used for the positioning measurement, have different wavelengths. Thus, for example, the wavelength 1 of the measuring light 44 can be between 532 nm and 633 nm, and the wavelength 2 of the measuring light 42 can be between 700 nm and 1064 nm. The Fizeau collimator 50 and the ocular in the form of the collimator lens 58 should be colour-corrected. Similar wavelengths for the two measurements facilitate the colour correction. For simultaneous execution of the form measurement and the positioning measurement the measurements are taken wavelength-selectively. This can take place e.g. by the locally resolving detector 40 measuring the intensity distributions generated on the detection surface 61 wavelength-selectively. Alternatively, a colour beam splitter can also be provided in the detection module of the measuring apparatus 40, as explained below with reference to FIG. 4.

(38) Instead of different wavelengths, different polarisation can also be used for the different measurements. In an alternative embodiment measuring light of the same wavelength is used for the form measurement and the positioning measurement, and the two measuring processes are carried out one after the other.

(39) After taking the form and positioning measurements the measurements determined are stored in a recording device 64 shown in FIG. 1. The wafer 30 is then shifted to under the projection objective 18. For this purpose, depending on the embodiment, reloading of the wafer 30 from the measuring table 38 onto the exposure table 32 is performed, or however the wafer 30 remains on the exposure table 32 which moves to under the projection objective 18. With the now following exposure of the wafer 30 both the form and the positioning measurements are communicated by the recording device 64 to a control device 66. The control device 66 controls on the one hand the focus position (z) of the exposure radiation 15 by the form measurements, and on the other hand the x,y position by the positioning measurements and optionally the imaging scale during the exposure of the wafer 30. In order to control the imaging scale during the exposure, the latter is adapted dynamically to the local measured distortion of the measurement structures 32.

(40) The measuring apparatus 40 makes available measured data by which a high-frequency distortion on the wafer surface can be corrected. High-frequency distortion is understood to mean distortion which has a higher frequency than conventional scale errors. Conventional scale errors are proportional to the first power of the coordinate along the scanner slot. Thus, via the measured data provided by the measuring apparatus 40, distortions which are proportional to the third or higher power of the coordinate along the scanner slot can be corrected.

(41) FIG. 4 shows a further embodiment of the measuring apparatus 40 according to the disclosure. The latter differs from the measuring apparatus 40 according to FIG. 1 in two respects. The first respect is that instead of plane mirrors, cats' eye mirror arrays 154 are used to reflect the diffracted measuring light 44. A cats' eye mirror reflects an incoming planar wave precisely back into itself. The adjustment of the cats' eye mirror is non-critical here. The use of a cats' eye mirror array 154 makes it possible to achieve reflection passing back into itself for any grating periods on the wafer 30 without having to readjust the reflectors.

(42) The second respect in the embodiment according to FIG. 4 differing from the embodiment according to FIG. 1 is the use of a colour beam splitter 170 in the beam path of the measuring radiation 42 and 44 after the collimator lens 58. The colour beam splitter 170 is configured so that the measuring light 44 with the wavelength 2 passes through the beam splitter, whereas the measuring light 42 with the wavelength 1 is reflected on the latter. It is thus possible to separate the measuring light portions of the form measurement and the positioning measurement. A particular detector 60 is provided for each of the measured light portions. According to this embodiment the form measurement and the positioning measurement can be taken simultaneously using wavelength non-selective detectors.

(43) FIG. 5 shows a further embodiment 40 of a measuring apparatus according to the disclosure for use in the projection exposure tool 10 according to FIG. 1. In the embodiment shown the latter is only configured for the positioning measurement and the distortion measurement. The measuring apparatus 40 according to FIG. 5 differs from the measuring apparatus 40 according to FIG. 1 not only in that it has no measuring beam path for the topography measurement, but also in that it has no plane mirror 54. In fact, in the measuring apparatus 40 according to FIG. 5 there is disposed between the Fizeau collimator 50 and the wafer 30 a diffractive optical element 70.

(44) The diffractive optical element 70 includes grating structures 72 for the respective splitting of the incoming measuring light 44 into two measuring beams 74a and 74b. FIG. 6 shows the beam path for a grating structure 72 in detail. FIG. 6 shows the arrangement of the diffractive optical element 70 and of the wafer 30 in detail. The grating structure 72 is identified here by the letter A. The splitting of the incoming measuring light 44 into the measuring beams 74a and 74b is executed by diffraction on the grating A in minus first and plus first diffraction order. The measuring beams 74a and 74b are then reflected back into themselves on the measurement structures 32 on the surface of the wafer 30 by diffraction in plus first and minus first diffraction order. The grating structure 72 is advantageously designed with a diameter of at least 300 mm in order to be able to measure the whole surface of the wafer 30.

(45) The measurement structures 32 are also designed as grating structures, and in FIG. 6 are identified as gratings B, the grating 32 reflecting the measuring beam 74a being located at a position 1, and the grating 32 reflecting the measuring beam 74b being located at a position 2, and this is why the corresponding gratings are identified as B_pos1 and B_pos2. The measuring beams 74a and 74b reflected back are diffracted on the grating structure 72 as they pass through in minus first and plus first diffraction order, and are thus guided back into the beam path of the incoming measuring light 44. The images generated by the two measuring beams 74a and 74b are superimposed coherently on the detection surface 61 in analogy to the situation in the measuring apparatus 40 according to FIG. 1. With a shift of the wafer 30 in the x direction by the amount x the following phase difference is produced:
=.sub.1.sub.2=4.Math.x/p(2)
p indicating the grating period of the measurement structures 32. In comparison to the phase difference generated with the arrangement according to FIG. 2, according to FIG. 6, with the same shift x, only half the phase difference is produced.

(46) The position calculated from the measured phase difference corresponds to the centre of gravity shift of the positions of the gratings B_pos1 and B_pos2. FIG. 7 shows the diffractive optical element 70 and the wafer 30 according to FIG. 5 for a number of measuring channels which are respectively formed by a grating structure 72 and the two associated measurement structures 32. With the arrangement of the grating structures 72 on the diffractive optical element it is important to ensure that no interfering light 44s which is produced, for example, by reflection of the measuring light 74a or 74b due to diffraction on the measurement structures 32, reaches the detector 60. The grating structures 72 are therefore disposed on the wafer 30 such that the interfering light 44s does not strike the grating structures 72 of the diffractive optical element 70, but in fact is reflected on the regions of the element 70 between the grating structures 72. Therefore, the interfering light can not be injected into another measuring channel which would falsify the measurement.

(47) Furthermore, it is possible to arrange different gratings on the diffractive optical element 70 acting as a beam splitter. Correspondingly adapted gratings should be assigned to the latter on the wafer 30. Furthermore, special gratings can be provided on the diffractive optical element 70 which detect the position of the measuring table 38. Such gratings are adapted to grating structures on the measuring table 38.

(48) FIG. 8 illustrates a further embodiment of a measuring apparatus 40 for use in the projection exposure tool 10 according to FIG. 1. This embodiment only differs from the embodiment according to FIG. 5 in that the measuring radiation 44 is not irradiated perpendicularly, but at an angle in relation to the normal onto the diffractive optical element 70. The measuring beams 74a and 74b generated in minus or plus first diffraction order then strike the wafer surface at different angles. In order to guarantee the corresponding back-reflection of the measuring beams, the measurement structures 32 on the wafer 30 have different periods, the B_pos1 grating the period and the grating at B_pos2 the period +, where:
==2.Math..sub.gratingA and ==2.Math.1/.Math.sin(a),(3)
.sub.gratingA designating the period of the grating structure 72. According to one embodiment the angle is at least 0.1.

(49) Via the asymmetrical beam path in the arrangement according to FIG. 8 interfering light 44s can be prevented from being injected into an adjacent measuring channel independently of the arrangement of the grating structures 72 on the diffractive optical element 70. The measurement structures 32 can thus be disposed at any locations on the wafer surface 31. The grating structure 72 can also be designed throughout. With the embodiment according to FIG. 8 the size and position of the exposure fields 68 and dies are chosen arbitrarily from the viewpoint of the positioning measurement.

(50) Under (a) and (b) FIG. 9 shows two different variants for a throughout arrangement, also referred to as full surface or all-over arrangement, of the grating structure 72 on the diffractive optical element 70. In the variant (a) the grating structure 72 consists of a chessboard-type arrangement with grating sections aligned alternately in the x and y directions. Centre of gravity coordinates of the respectively irradiated grating pairs B_pos1 and B_pos2 can thus be measured on the wafer 30 with respect to the x or the y coordinate. The grating alignment of the grating pairs B_pos1 and B_pos2 defines whether x or y components are measured. In the (b) variant the grating structure 72 is in the form of a two-dimensional rhomboid grating with which a position measurement with respect to the x or the y component can also be taken.

(51) FIG. 10 shows a possible arrangement of the measurement structures 32 on the wafer 30 for use in the embodiment according to FIG. 8. Here the measurement structures B_pos1 and B_pos2 for measuring the x coordinate of the respective centre of gravity are designated by 32a and 32b. The grating structures for measuring the respective centre of gravity coordinate in the y direction are designated by 132a and 132b. As can be taken from FIG. 10, the grating structures 32a and 32b are positioned in horizontal strips in an alternating arrangement, whereas the grating structures 132a and 132b are arranged in vertical strips so that overall a web structure is produced the meshes of which surround the exposure fields 68.

(52) FIG. 11 shows a further embodiment of the measuring apparatus 40 for use in the projection exposure tool 10 according to FIG. 1. Like the embodiment according to FIG. 5, this embodiment includes a diffractive optical element 70. The diffractive optical element 70 according to FIG. 11 is, however, tilted in relation to the wafer 30. This makes it possible to simultaneously perform a form measurement by using the measuring light 42 of a measuring light source 41 already known from FIG. 1. The tilting of the diffractive optical element 70 leads to the measuring light 42 not striking the diffractive optical element 70 perpendicularly, and so no interfering back reflexes reach the detector 60 through the aperture 56. The period of the grating structure 72 is chosen such that the wavelength 2 of the measuring light 42 passes through the grating structure 72 without being diffracted, while the wavelength 1 of the measuring light 44 is diffracted in minus and plus first diffraction order.

(53) FIG. 12 shows the light paths both for the measuring light 44 for the distortion and positioning measurement and the measuring light 42 for the form and topography measurement in the region of the diffractive optical element 70 and the wafer 30 according to FIG. 11. Here, in FIG. 12 beams for the positioning and the form measurement are drawn in next to one another. However, the measuring method enables all-over measurement of the form at all positions and simultaneously to this a measurement of the positioning for all of the positioning gratings provided. A spatial separation into regions for positioning or form is not necessary. The incoming measuring light is identified by 44e and 42e. Furthermore, in the figure thick lines show the used light paths which for the positioning measurement include the incoming measuring light 44e, the measuring beams 44a and 44b and the returning used light beam 44n. For the form measurement the used light path includes the incoming measuring light 42e which passes through the diffractive optical element 70 without directional diversion, and after reflection on the wafer surface 31 the beam 42n returning to the interferometer.

(54) Furthermore, in FIG. 12 interfering light paths are drawn in with thin lines. Interfering light paths are produced by diffraction of the used light on one of the gratings 72, 32a and 32b. In FIG. 12 a few interfering light paths are drawn in which are produced in zero, minus first and plus first diffraction order on one of the gratings 72, 32a and 32b. An interfering light path is thus produced, for example, when the incoming measuring light 44e in the zero diffraction order passes through the grating 72, reflects on the wafer surface 31 and subsequently passes through the grating structure 72 in zero, plus first or minus first diffraction order. The resulting interfering light beams are identified by b, c and d in FIG. 12.

(55) A further example of interfering light in the positioning channel relates to light of the measuring beam 44a which upon reflection on the grating 32a is not reflected back in minus first diffraction order, but passes in zero diffraction order to the diffractive optical element 70 and is then diffracted on the grating 72 in plus first diffraction order and passes back into the optics of the measuring apparatus 40. The resulting interfering light is identified by a. In a similar way interfering light paths can be produced in the form channel, for example when the incoming measuring light 42e is diffracted on the grating 72 in a diffraction order different from zero, and then falls on one of the diffraction gratings 32a and 32b.

(56) As already mentioned above, the diffractive optical element 70 is tilted in relation to the wafer 30 at the angle drawn in in FIG. 12. Furthermore, the angle of incidence of the incoming measuring light 44e for the positioning measurement in relation to the normal to the wafer surface 31 is tilted by the angle . The dimensioning of the tilt angles and is executed such that as little interfering light as possible passes to the detector 60. By choosing the angles and cleverly the interfering light can be blocked out at least to a predominant extent by the aperture 56.

(57) Tab. 1 below includes a list of all of the light beams which can be produced during the positioning measurement taking into account the minus first, zeroth and plus first diffraction order on the gratings 72, 32a and 32b. In order to indicate the direction of the individual light beams the respective x component of the corresponding direction vector is specified in Tab. 1. For the direction of incidence of the measuring light 44e an x component of 5 is applied. The individual columns identify first of all the diffraction order of the incoming measuring light 44e on the diffractive optical element 70, the second column the diffraction order on the grating structure 32a on the wafer 30, the third column the diffraction order on the grating structure 72 on the return path of the light into the optics of the measuring apparatus 40. In the fourth column the x component of the direction vector of the corresponding light beam after passing through the diffractive optical element 70 for the second time is specified.

(58) TABLE-US-00001 TABLE 1 Positioning direction of emergent emergent incidence direction direction component DOE DOE component direction DOE DOE component of the outward return of the of outward return of the k-vector path Wafer path k-vector incidence path Wafer path k-vector 5 500 1010 ### 5 500 990 500 DIFFRACTION ORDERS DIFFRACTION ORDERS 1 1 1 2005 1 1 1 1985 1 1 0 1505 1 1 0 1485 1 1 1 1005 1 1 1 985 1 0 1 995 1 0 1 995 1 0 0 495 1 0 0 495 1 0 1 5 1 0 1 5 a 1 1 1 15 1 1 1 5 y used reflex 1 1 0 515 1 1 0 495 1 1 1 1015 1 1 1 995 0 1 1 1505 0 1 1 1485 0 1 0 1005 0 1 0 985 0 1 1 505 0 1 1 485 0 0 1 495 b 0 0 1 495 b 0 0 0 5 c 0 0 0 5 c 0 0 1 505 d 0 0 1 505d 0 1 1 515 0 1 1 495 0 1 0 1015 0 1 0 995 0 1 1 1515 0 1 1 1495 1 1 1 1005 1 1 1 985 1 1 0 505 1 1 0 485 1 1 1 5 y used reflex 1 1 1 15 1 0 1 5 e 1 0 1 5 1 0 0 505 1 0 0 505 1 0 1 1005 1 0 1 1005 1 1 1 1015 1 1 1 995 1 1 0 1515 1 1 0 1495 1 1 1 2015 1 1 1 1995

(59) Columns five to eight positioned on the right-hand side of Tab. 1 give the analogue information for the case in which a corresponding light path leads over the grating structure 32b onto the wafer 30. According to Tab. 1, for the grating 72 the value 500, for the grating 32a the value 1010, and for the grating 32b the value 990 are applied as grating periods. The values indicate the stripe density of the gratings in any units and correspond to the change in the x component of the propagation direction of the light wave with diffraction in 1.sup.st order. Lines per millimeter, for example, can be chosen as the unit. The beams a, b, c, d, e and y drawn in in FIG. 12 are identified in Table 1. As can be seen from the table, none of the interfering light vectors has the direction of the used light 44n which is identified by y.

(60) Tab. 2 shows the information similar to Tab. 1 for the form measuring channel. Here the x component of the incoming measuring light 42e is zero. It can be gathered from the table that two reflexes of the interfering light 42s, namely the interfering reflexes f and h have the propagation direction of the used reflex z. All other interfering light beams 42s point in directions different from the used reflex z. In the following measures which are used to also suppress the remaining interfering reflexes h and f are described.

(61) TABLE-US-00002 TABLE 2 Form direction of emergent emergent incidence direction direction component DOE DOE component direction DOE DOE component of the outward return of the of outward return of the k-vector path Wafer path k-vector incidence path Wafer path k-vector 5 500 1010 ### 5 500 990 500 DIFFRACTION ORDERS DIFFRACTION ORDERS 1 1 1 2010 1 1 1 1990 1 1 0 1510 1 1 0 1490 1 1 1 1010 1 1 1 990 1 0 1 1000 1 0 1 1000 1 0 0 500 1 0 0 500 1 0 1 0 interfering reflex 1 0 1 0 f interfering reflex 1 1 1 10 1 1 1 10 1 1 0 510 1 1 0 490 1 1 1 1010 1 1 1 990 0 1 1 1510 0 1 1 1490 0 1 0 1010 0 1 0 990 0 1 1 510 0 1 1 490 0 0 1 500 0 0 1 500 0 0 0 0 z used reflex 0 0 0 0 z used reflex 0 0 1 500 0 0 1 500 0 1 1 510 0 1 1 490 0 1 0 1010 0 1 0 990 0 1 1 1510 0 1 1 1490 1 1 1 1010 1 1 1 990 1 1 0 510 1 1 0 490 1 1 1 10 1 1 1 10 1 0 1 0 interfering reflex 1 0 1 0 interfering reflex 1 0 0 500 1 0 0 500 1 0 1 1000 1 0 1 1000 1 1 1 1010 1 1 1 990 1 1 0 1510 1 1 0 1490 1 1 1 2010 1 1 1 1990

(62) The dimensioning of the angles and can be executed according to the following list of criteria. Since the interfering light beams a, c and e return to the optics of the measuring apparatus 40 at the angle , the angle is greater than the numerical aperture NA of the imaging of the wafer 30 onto the detector 60:
sin()>NA(4)

(63) For the lateral resolution of the imaging wafer 30 to detector 60 the following applies for the resolution R:
R=/NA(5)

(64) being the wavelength of the measuring light in question. A resolution of R=0.25 mm with =633 nm results in NA=0.0025. For the angle of incidence this then gives a value of >0.14.

(65) Since the interfering light j has to return at the angle 2 the following applies:
sin(2)>NA(6)

(66) For the tilt angle this therefore gives a value of >0.07. With a wafer with a diameter of 300 mm there is only 0.37 mm distance variation between the diffractive optical element 70 and the wafer 30. It can also be advantageous to design the angle of incidence and the tilt angle to be perpendicular to one another. A higher lateral resolution involves a greater angle of incidence and a greater tilt angle .

(67) FIGS. 13 and 14 show two different embodiments for the grating structure 72 of the diffractive optical element according to FIG. 11. In the embodiment according to FIG. 13 the grating structure 72 is called the zero order grating and is designed for the wavelength 2 of the measuring light 42 of the form measurement. With a zero order grating all of the diffraction orders apart from the zeroth order are suppressed. The wavelength 1 of the measuring light 44 for the positioning measurement is smaller than 2 so that a plus/minus first diffraction order can be generated. The period p of the grating 72 is between the values of the wavelength 2 and 1. As specified in FIG. 13, for 2 wavelengths of between 700 and 1064 nm, and for 1 wavelengths of 532 to 632 nm are advantageous. It can be advantageous to use e.g. 1064 nm for 2 with the frequency doubled wavelength of 532 nm for 1.

(68) The height h of the grating structure 72 has the following dimensions:
h=0.52/(n1)=2 for n=1.5.(7)

(69) Alternatively to the method with zero order grating one can proceed as follows.

(70) In the embodiment of the diffractive optical element according to FIG. 14 the grating structure 72 is configured with an optimised grating profile for reducing the efficiencies of the higher diffraction orders of the measuring light 42 with the wavelength 2 for the form measurement. However, the corresponding diffraction efficiency can not be totally reduced to zero upon the basis of the electromagnetic effects. With a grating period of less than 5 one can expect efficiencies in the percentage range. This results in disturbances of the wavefront of only approximately 10 nm. As specified in FIG. 14, in this embodiment one can choose for 1 for example 1266 nm and for 2 for example 693 nm.

(71) As a further alternative for suppressing the interferences during the form measurement using higher diffraction orders white light interferometry with an upstream cavity can be used.

(72) The measuring apparatus 40 according to the disclosure for the form and positioning measurement was described above for the example of measuring a wafer 30. According to a further embodiment according to the disclosure the measuring apparatus 40 according to the disclosure for the form and positioning measurement is used on a reticle or the mask 20.

LIST OF REFERENCE NUMBER

(73) 10 projection exposure tool 12 illumination system 14 exposure radiation source 15 exposure radiation 116 beam propagation optics 17 illuminator 18 projection objective 19 frame 20 mask 22 mask structures 24 mask table 30 wafer 31 wafer surface 32 measurement structure 32a line grating 32b line grating 33 exposure table 34 wafer holder 36 shifting stage 38 measuring table 40 measuring apparatus 41 first measuring light source 42 first measuring light 42n used light 42s interfering light 43 second measuring light source 44 second measuring light 44a first measuring beam 44b second measuring beam 44e incoming measuring light 44n used light 44s interfering light 46 interferometer 48 beam splitter 50 Fizeau collimator 51 optical axis 52 Fizeau surface 54 plane mirror 54a plane mirror 54b plane mirror 56 aperture 58 collimator lens 60 locally resolving detector 61 detection surface 62 evaluating device 64 recording device 66 control device 68 exposure field 70 diffractive optical element 72 grating structure 74a, 74b measuring beam 132a grating structure 132b grating structure 154 cats' eye arrangement 170 colour beam splitter