DE10220815A1 - Reflective X-ray microscope e.g. for microlithography, includes additional subsystem arranged after first subsystem along beam path and containing third mirror - Google Patents

Abstract

A reflective X-ray microscope for examining an object in a object plane, when the object is illuminated by radiation at a wavelength of less than 100 nm, especially less than 30 nm. The microscope comprises a second subsystem arranged after the first subsystem in the beam path, and which has at least one third mirror (S3). Independent claims are also included for: (1) an inspection system for examining objects, especially masks for microlithography; (2) a method for inspection of objects, especially masks for microlithography; and (3) application of an inspection system.

Description

The invention relates to a reflective X-ray microscope for examining a Object in an object plane, the object with an optical path Wavelength <100 nm, in particular <30 nm illuminated and in an image plane is shown enlarged. Such a reflective X-ray microscope comprises a first arranged in the beam path from the object plane to the image plane Subsystem with a first mirror and a second mirror.

X-ray microscopes have become known from the following applications:
US 5,222,113
US 5,311,565
US 5,177,774
US 5,144,497
US 5,291,339
US 5,131,023
EP 0 459 833

A Schwarzschild system with a subordinate diffraction grating is out of the
US 5,022,064
become known and an inspection system with reflective X-ray microscope from the
JP 2001116900.

The applications US 5,222,113, US 5,311,565, US 5,177,774, EP 0 459 833 show X-ray microscopes with zone plates in the projection optics are provided for the illustration. Fresnel zone plates are around a wave-optically imaging component, in which the light on one System is bent from concentrically arranged circular rings. The disadvantage the use of Fresnel zone plates in imaging systems there are several optical elements in the field of X-rays see that Fresnel zone plates are transmissive components that are due to the poor transmission in the X-ray range lead to large light losses.

From US Patents US 5,144,497, US 5,291,339, US 5,131,023 X-ray microscopes comprising Schwarzschild systems as imaging Systems become known.

All of U.S. Patents 5,144,497, 5,291,339 and The x-ray microscope described in US Pat. No. 5,131,023 is the beam path at object to be examined is designed to be telecentric, which is an image of Objects in reflection difficult.

Another disadvantage of such systems for use in the investigation of Objects, especially those in the field of X-ray lithography Finding uses is their great length to achieve one sufficient image scale. This makes it difficult to use for example in inspection systems for examining masks in EUV Projection exposure systems.

A Schwarzschild system has become known from US Pat. No. 5,022,064 according to the Schwarzschild system a diffraction grating is arranged to X-rays of different wavelengths in different orders to bend and thus split the light spectrally. This system is also telecentric on the object.

A reflective X-ray microscope for examining an object for the Microlithography in an object plane with radiation of a wavelength <100 nm, in particular <30 nm, has become known from JP 2001116900. This in X-ray microscope disclosed in this application is a Schwarzschild System with a concave first mirror and a convex second mirror. In contrast to the systems described above, the beam path is Examination of the object on the object is not telecentric, so that a Examination in reflection, for example of EUV reflection masks, is made possible.

A disadvantage of the system disclosed in JP 2001116900 is that it is a has a very large overall length if large image scales are required become.

The object of the invention is to overcome the disadvantages of the prior art avoid, especially that of JP 2001116900, and a reflective X-ray microscope specifying the examination of objects for the Microlithography enables and has a short length. Preferably the Overall length of the X-ray microscope less than 5 m, particularly preferred less than 3 m at a magnification of 10-10000 ×, preferably 300-1000 × be.

In a further aspect of the invention, an inspection system is to be specified in particular the investigation of masks for photolithographic Processes with wavelengths <100 nm, preferably in the wavelength range 10-30 nm.

Inspection systems, in particular for the examination of transmission masks for photolithographic processes with wavelengths in the UV range, are out
EP-A-0628806
JP-A-4-321047
known. The content of these writings is fully included in the disclosure content of this application. In these systems, however, only the examination of transmission masks is described; an examination of reflection masks as used in EUV lithography is not mentioned.

According to the invention, the object is achieved in a first aspect in that the first subsystem, comprising a first and a second mirror, the is preferably in the form of a Schwarzschild system, a second Subsystem in the light path is subordinate to the at least a third mirror includes. This third mirror enables the beam path from the object to Fold picture and so the overall length compared to that from JP 2001116900 known system significantly reduce.

Systems with more than two mirrors are in the field of EUV lithography Projection lenses become known.

Such systems are shown, for example, in US 5,063,586, US 5,153,898, US 4,798,450 or EP 0962830.

Since all of these systems are reduction lenses, none can of these writings give an indication of how a system must be designed, with which the object is magnified in an image plane.

In particular, the problem does not arise with these lenses, if possible one to achieve short overall lengths; rather, the imaging properties are in the Foreground.

The at least one third mirror of the second subsystem serves as before executed, for folding the beam path and for setting an almost telecentric beam path on the image.

It is particularly preferred if the second subsystem has a total of two mirrors includes that reduce the overall length. In particular, it is at Such an arrangement possible, which in the region of the second mirror of the first subsystem and the image space conflicts that arise because Object level and image level in a four-mirror system spatially very far are separated from each other and also outside and on opposite Sides of the lens.

The beam path on the image is advantageously almost telecentric.

The first and the second mirror of the first subsystem are preferred Aspherical shaped, the third and fourth mirrors can be both be aspherical as well as spherical. Spherical mirrors are used for this preferred because they are easier to manufacture in terms of production technology.

To obtain a sufficient magnification of the object to be examined in the To ensure the image plane, the overall system has an image scale of β ≥ 10 ×, preferably in the range 300 × ≤ β ≤ 1000 ×.

The reflective X-ray microscope can either in the beam path from the Object plane to the image plane without or with a real intermediate image become. Embodiments with an intermediate image have the advantage that the first and second subsystem can be moved against each other and so pictures above and below the intermediate image focus plane can the z. B. mask inspections information about mask defects deliver as described below.

The reflective X-ray microscope according to the invention preferably has a optical axis to which the mirrors of the microscope are arranged centered.

In contrast to the X-ray microscopes known from the US patents is the object or the observation area on the object in the object plane in the reflective X-ray microscope according to the invention preferably outside arranged along the optical axis. This enables objects to be examined in reflection, for example reflective EUV masks, without object and Image plane are arranged tilted to each other, d. that is, both the object plane and the image plane is perpendicular to the optical axis of the reflective X-ray lenses under the boundary condition of an image side almost telecentric beam path. This can minimize image errors, because through this measure a uniform image scale for all field points in all directions is reached.

It is particularly advantageous if that for setting the numerical aperture reflective X-ray microscope includes an aperture stop. To different To be able to set numerical apertures, it is advantageous if the Aperture diaphragm is accessible. An advantageous arrangement of the aperture diaphragm is hence an arrangement in the beam path from the object to the image plane in the first Subsystem behind the object level and in front of the mirror. The aperture stop is arranged decentrally to the optical axis. The aperture preferably enables Setting different aperture levels with which different numerical Apertures of the projection exposure system can be simulated.

In a second aspect of the invention, an inspection system for Examination of objects, especially masks for microlithography, with Wavelengths ≤ 100 nm provided. The inspection system includes a lighting system for illuminating an object field in a Object level. As a light source, the lighting system includes, for example, a laser Plasma source, a discharge source or synchrotron source. The desired Radiation of, for example, 13.5 nm can be filtered out with grating spectral filters become. In the object plane there is at least within the illuminated field arranged part of the mask to be examined. This also includes Inspection system an imaging system for wavelengths ≤ 100 nm Imaging at least a part of the mask to be examined into a Image plane. In the image plane there is an observation system for observing the in this level is provided enlarged object.

The imaging system is in the inspection system according to the invention preferably a reflective X-ray microscope according to the invention.

The inspection system according to the invention preferably comprises Positioning devices for positioning the object in the object plane. This makes it possible to target the object to be examined in the To move the object plane and thus images of different parts of the Object in the image plane.

In a preferred embodiment, the imaging system comprises one accessible, adjustable aperture diaphragm. The adjustable aperture diaphragm enables it to adjust the aperture so that the imaging conditions on the object are equivalent to the mapping relationships in a Projection exposure system. Projection exposure systems are for example known from WO 02/27401, WO 02/27402 or US 6,244,717 become.

The disclosure content of all of the aforementioned writings is fully described in included the present application. The possible obscurations in an EUV projection exposure system can through an obscuration, which are arranged, for example, in the lighting system of the inspection system is to be simulated.

If the projection exposure system has, for example, a projection lens an image-side NA of 0.3 and with a magnification of 4 ×, so the aperture 0.3: 4 to be preselected on the adjustable aperture diaphragm, d. H. 0,075, to an image corresponding to the image in the projection system Get inspection system.

The adjustable aperture diaphragm can be freely set in a range of 0.001 ≤ NA ≤ 0.25 can be set.

In addition to the adjustable aperture diaphragm in the imaging system, a preferred embodiment of the invention that the Lighting system includes an adjustable aperture aperture.

With the aid of the illumination aperture diaphragm in the illumination system, which is in a plane that is conjugate to the plane of the aperture diaphragm of the imaging optics, the size of the pupil filling σ can be specified. The pupil filling is defined as:
σ = sinα / sinβ,
where sinα corresponds to the numerical aperture NA _{illumination of} the illumination system on the object and sinβ corresponds to the numerical aperture NA _{image of} the imaging system on the object. The setting of σ allows different types of lighting systems for projection exposure systems to be simulated. While aperture diaphragm and illumination aperture diaphragm enable the setting of a circular illumination with a predetermined pupil filling degree σ when using circular diaphragms, as described above, by inserting an aperture changer, for example an aperture wheel, into the illumination aperture diaphragm plane, it is also possible to provide an annular, quadrupolar or dipolar illumination simulate. To limit the field, a field diaphragm can be provided in a plane conjugate to the object level.

The image recording system of the inspection system preferably has a Analysis unit with which the images of the object are evaluated in the image plane can be.

In addition to a simulation of the properties of the projection exposure system, which is also designed as a stepper in a special embodiment, a This includes enabling qualitative and quantitative inspection of the masks Inspection system prefers focus adjustment devices with which the object in can be moved perpendicular to the object plane. this makes possible taking pictures in the same place on the object predetermined focus positions. The focus from bottom to top is preferred Drive through symmetrically in predetermined steps. The different ones Images captured in focus positions can be analyzed using the analyzer evaluated and so at least one statement about the quality of the mask to be hit. If the mask has defects at the examined area, see above enables the analysis unit to analyze them precisely. Possibly the mask can be repaired and then re-analyzed.

The analysis unit preferably comprises a microcomputer device in which the recorded image data can be processed digitally. A special one preferred embodiment of the invention comprises a parallel to the first Imaging system arranged second imaging system for wavelengths> 100 nm. This second imaging system makes it possible, for example, with UV or VUV light, for example, initially roughly mask the mask as a whole inspect. Such an auxiliary observation system is preferably parfocal and / or arranged centered. The entire mask can be, for example Have dimensions of 6 "× 6" (152 × 152 mm) and the object field ≤ 2 × 2 mm, so that a rough inspection of the entire mask is possible. The mask can then with the help of the positioning device at places where Defects occur. With the help of imaging optics for wavelengths of 100 nm it is possible to examine these selected locations. The object field with which the Imaging system for wavelengths 100 nm can be investigated, lies in Area 100 × 100 µm, particularly preferably 30 µm × 30 µm.

At least the imaging part is preferred for wavelengths 100 100 nm of the Inspection system arranged in vacuum.

In addition to the inspection system according to the invention, a method for Inspection of objects, especially masks for microlithography with Wavelengths ≤ 100 nm, provided at which in the object plane with an object field is illuminated in a lighting system, which too examining object with positioning device in the illuminated object field is spent and in an image plane in which an image recording system is arranged is imaged by means of an imaging system for wavelengths ≤ 100 nm. In a preferred method, this is used to characterize the masks examining object with a focus adjustment device perpendicular to the Move object level and images at predetermined focus positions above and recorded and evaluated below the focus. For systems with Alternatively or additionally, the intermediate image can be relative to the second subsystem Focus the intermediate image to be moved to predetermined images Record focus positions. Alternatively, the entire Imaging device or only the first subsystem in the direction of the axis Standing vertically on the object level.

The use of the inspection system according to the invention is diverse. So is such an inspection system, as previously described in detail, for Defect analysis of mask blanks, coated mask blanks, masks in the Manufacturing process suitable for microlithography with wavelengths ≤ 100 nm, as well as for the inspection of repaired masks. Furthermore, with a such inspection system the exposure process in one Projection exposure system by setting the aperture and the Pupil fill levels simulated and thus the projection exposure system configured and optimized. The inspection system is also for inspection of wafers.

The invention will be described below with reference to the figures.

Show it:

Fig. 1 is a general view of a first X-ray microscope objective according to the invention with a first subsystem comprising a first and a second mirror and a second subsystem comprising a third mirror

Fig. 2 shows a second X-ray microscope comprising a first subsystem having first and second mirror and a second subsystem comprising a third and a fourth mirror.

Fig. 3 shows a third X-ray microscope comprising a first subsystem having a first and second mirror and a second subsystem comprising a third and fourth mirror, the third mirror is designed spherically and the aperture between the object plane and the first mirror is located.

Fig. 4, comprising a first subsystem having first and second mirror and a second subsystem, is a fourth X-ray microscope comprising a third and fourth mirror, the third and fourth mirrors are configured spherical and the object field size 30 microns x 30 microns.

Fig. 5 shows a fifth X-ray microscope comprising a first subsystem having first and second mirror and a second subsystem including third and fourth mirror, the third and fourth mirrors are designed spherically and the object field has an area of 200 microns x 30 microns.

Fig. 6 shows a sixth X-ray microscope comprising a first subsystem having first and second mirror and a second subsystem comprising a third and fourth mirror, the third and fourth mirror is spherical and all mirrors are concave.

Fig. 7 shows a seventh X-ray microscope comprising a first subsystem having first and second mirror and a second subsystem comprising a third and fourth mirror, the first mirror is a concave mirror, the second mirror is a concave mirror, the third mirror is a convex mirror and the fourth mirror is a concave mirror.

Fig. 8 is a two mirror system, wherein the first mirror is a concave mirror and the second mirror is a concave mirror.

Fig. 9 shows an inspection system for EUV masks with an X-ray microscope according to the invention in a schematic representation

Fig. 10, an inspection system, the individual components of the inspection system are shown in greater detail

Fig. 11 flow chart for performing a measurement

Fig. 12 possible processing of the captured images

Fig. 13a-c possible areas of application of the inspection system according to the invention

In Fig. 1 a first embodiment of the invention is shown with a first subsystem comprising a first mirror and a second mirror S1 S2. In the present exemplary embodiment, the first mirror S1 is a concave mirror and the second mirror S2 is a convex mirror. The mirrors S1 and S2 are arranged centered on the optical axis HA. The second subsystem comprises a third mirror S3. The third mirror is also centered on the optical axis. The object in the object plane 1 , which is arranged decentrally to the optical axis HA, is imaged into the image plane 3 by the magnifying imaging X-ray microscope according to the invention. The image plane 3 lies in the vicinity of the second mirror S2 and the aperture diaphragm B arranged decentrally to the optical axis between the object plane and the first mirror.

All mirror surfaces of mirrors S1, S2 and S3 are rotationally symmetrical, aspherical mirror segment surfaces.

The radius of curvature of the first mirror is | R ₁ | = 500 mm, the radius of the second mirror | R ₂ | 3.5 mm and that of the third mirror | R ₃ | = 4000 mm. The second mirror has a relatively small radius of curvature. This is necessary to generate the required large image scale. The aperture B lies between the object plane and the first mirror, at a distance of 466 mm from the object plane and has a maximum decentered opening of 60 mm. The overall length of the optical system, that is to say the distance from the diaphragm plane in which the aperture diaphragm B is arranged, to the third mirror S3 is 2007 mm and the distance from the object plane 1 to the aperture diaphragm B is 466 mm. The overall system has an imaging scale of β = -500 ×. The object and image in the object plane or in the image plane lie decentrally on opposite sides with respect to the optical axis HA.

The advantage of the three-mirror system presented here can be seen in that, with only three mirrors, a small overall length of less than 2500 mm could be realized, the overall length, i.e. the distance from the aperture diaphragm to the apex of the third mirror, being 2007 mm and the Distance of the object plane 1 from the aperture diaphragm B in the aperture plane is 466 mm. The general objective data of the exemplary embodiment according to FIG. 1 can be found in Table 1a, the summary of the area data in Table 1b and the details of the area data in Table 1c in the appendix. All the preceding and following tables of optical data are data in ZEMAX format. The ZEMAX format is well known to those skilled in the art.

FIG. 2 shows a four-mirror system with a first subsystem, comprising a first mirror S1 and a second mirror S2, and a second subsystem, comprising a third and a fourth mirror. The first mirror has the reference number S1, the second mirror has the reference number S2, the third mirror has the reference number S3 and the fourth mirror has the reference number S4. The first mirror S1 is a concave mirror, the second mirror S2 is a convex mirror, and the third and fourth mirrors S3, S4 are concave mirrors. In the exemplary embodiment, the aperture diaphragm B is arranged at a short distance in front of the first mirror S1. Such an arrangement inevitably leads to low vignetting. The imaging scale of the overall system is β = 354, that is to say the object in the object plane 1 and the image in the image plane 3 lie decentrally on the same side to the optical axis HA. The general objective data of this embodiment variant of the invention are given in Table 2a, the summarized area data in Table 2b and the special area data in Table 2c.

In Fig. 3 is a four-mirror system with a first mirror S1, a second mirror S2, a third mirror and a fourth mirror S3 S4 in turn is shown. The same components as in the previous figures are given the same reference numbers.

The basic structure of the system of FIG. 3 is coaxial with rotationally symmetrical spherical or aspherical mirror segment surfaces. The object field is arranged decentrally to the optical axis HA. All mirrors are rotationally symmetrical about the optical axis HA. The first mirror is a concave mirror with a radius of curvature | R ₁ | = 500 mm, the second mirror is a convex mirror with a radius of curvature | R ₂ | = 50 mm, the third mirror is a concave mirror with radius of curvature | R ₃ | = 166 mm and the fourth mirror S4 is a concave mirror with a radius of curvature | R ₄ | = 4000 mm. From the point of view of production technology, it is advantageous that, in the embodiment according to FIG. 3, the third mirror S3 is spherical. The mirror surfaces of mirrors S1, S2 and S4, however, are rotational aspheres. The aperture diaphragm B lies between the object plane 1 and the first mirror S1 at a distance of 840.5 mm from the object plane 1 and has a maximum decentered opening of 146 mm. The overall length of the optical system, which is the distance from the aperture plane B to the image plane 3, is 2116 mm in the present case. The overall imaging scale of the present system is β = 530, that is to say the object in the object plane and the image in the image plane are decentred from the optical axis HA on the same side.

The general optical data of the system according to FIG. 3 are given in Table 3a, the summary of the area data in Table 3b and the special area data in Table 3c in the appendix.

FIGS. 4 and 5 turn describe 4-mirror systems with a first subsystem comprising mirrors S1, S2 and a second subsystem comprising mirror S3 and S4. The same components as in the previous FIGS. 2 and 3 are again given the same reference numerals. The basic structure of the systems according to FIGS. 4 and 5 is coaxial. It is particularly advantageous that the third mirror S3 and the fourth mirror S4 are spherical and only the first mirror S1 and the second mirror S2 comprise rotationally symmetrical aspherical mirror segment surfaces. The first mirror S1 is a concave mirror with a radius of curvature | R ₁ | = 500 mm, the second mirror is a convex mirror with radius of curvature | R ₂ | = 100 mm, the third mirror is a concave mirror with radius of curvature | R ₃ | = 216 mm and the fourth mirror is a concave mirror with radius of curvature | R ₄ | = 4000 mm. The overall length of the optical system, that is the distance from the diaphragm plane in which the diaphragm B is arranged to the image plane 3 is 2183 mm, the distance between the object plane 1 and the diaphragm plane is 466 mm.

The imaging scale is β = 500, that is to say the object in the object field and the image in the image field are off-centered on the optical axis HA on the same side. The object field of the embodiment shown in FIG. 4 has an extension of 30 μm × 30 μm and is slightly decentered, that is to say arranged off-axis to the optical axis HA. The general optical data for the exemplary embodiment according to FIG. 4 are given in Table 4a, the summary of the data of the optical surface data in Table 4b and the special surface data of the optical surface in Table 4c in the appendix.

FIG. 5 shows a variant of the exemplary embodiment according to FIG. 4. Essentially all system data were retained, only the aspherical surfaces of mirrors S1 and S2 were changed. This change makes it possible to expand the object field to a size of 200 μm × 30 μm without the wavefront error and the distortion deteriorating compared to the exemplary embodiment in FIG. 4.

Since only the aspheres on the first and second mirrors were changed, the general optical data according to Table 4a and the general Area data according to Table 4b also adopted for embodiment 5 become. Only in the special aspherical data of mirrors S1 and S2 results yourself a deviation. The special optical surface data according to Embodiment 5 are shown in Table 5c in the Appendix.

In FIG. 6, a further variant of a 4-mirror arrangement with a first mirror S1, a second mirror S2, a third mirror and a fourth mirror S3 S4 is specified. The same components as in FIGS . 2 to 5 are given the same reference numerals. The essential difference between the exemplary embodiment according to FIG. 6 and the exemplary embodiments 3, 4 and 5 can be seen in the fact that the second mirror S2 is a concave mirror and is used above the optical axis HA. The bundles after this mirror therefore also run above the optical axis. The imaging scale is β = -500, that is, the object in the object plane and the image in the image plane are on opposite sides of the optical axis HA.

The general optical data can be found in Table 6a, the general area data in Table 6b and the special area data of the embodiment according to FIG. 6 Table 6c in the appendix.

Except for the second mirror S2, the exemplary embodiment shown in FIG. 7 corresponds to the exemplary embodiment according to FIG. 6. The essential difference from the exemplary embodiment according to FIG. 6 is that the third mirror S3 is a convex mirror. The magnification of the system of Fig. 7 is β = 500, that is in contrast to the embodiment according to FIG. 6, the object is in the object plane and the image in the image plane on the same side with respect to the optical axis HA.

The optical data of the exemplary embodiment according to FIG. 6 can be found in table 7a, the general area data table 7b and the special area data table 7c in the appendix.

The exemplary embodiment according to FIG. 8 shows that if a length of less than 3 m is maintained with 2-mirror arrangements, imaging scales can be realized for the overall system under reasonable boundary conditions of a maximum of β = 100. The system shown in FIG. 8 is a 2-mirror system with a first mirror S1 and a second mirror S2, the first and second mirrors S1, S2 each being concave mirrors. The general optical data of the exemplary embodiment according to FIG. 8 are shown in Table 8a, the general area data in Table 8b and the special area data in Table 8c in the appendix.

The aperture on the object side of the systems according to FIGS. 1 to 8 can be set via the aperture diaphragm B and is 0.0625, for example, for the simulation of conventional projection exposure systems. The aperture diaphragm can be set in a range of 0.001 ≤ NA ≤ 0.25. The object field size, which is illuminated in level 1 by an illumination system, not shown, is, for example, 30 μm × 30 μm or 100 × 100 μm. If, for example, a mask, a so-called reticle, is examined for microlithography, such masks typically have dimensions of 152 × 152 mm. With the reflective X-ray microscope according to the invention, only an image of a section of the mask is possible. The object in the object plane 1 is imaged with systems according to FIGS. 1 to 7 300-10000 times enlarged in the image plane 3 . Since the aperture diaphragm plane B is accessible, the aperture in the diaphragm plane can be set in a range 0.001 NA NA 0,2 0.25 by means of the aperture diaphragm B. NA here denotes the image-side aperture, hereinafter also referred to as aperture NA _image , on the object. The angle α of the main beam 5 in the object plane 1 is generally 6 ° to the optical axis of the system. With the help of the X-ray microscopy according to FIGS. 1 to 7, which comprise more than two mirrors, it is possible to obtain a sufficiently magnifying X-ray microscope objective whose overall length is less than 3000 mm.

In Fig. 9 is an inventive inspection system, EUV masks coated in particular for the investigation shown with a small object field. An illumination system 100 illuminates a field 102 in an object plane 101 in a predetermined manner. The illumination system 100 can comprise an illumination aperture diaphragm , not shown, for setting the pupil filling degree σ. The pupil filling degree σ is defined as


where NA _{illumination represents} the numerical aperture in the illumination system, which is specified by the illumination aperture diaphragm, and NA _{image represents} the numerical aperture of the imaging system, which is specified by aperture diaphragm B of the imaging system, here the reflective X-ray microscope.

To be able to set different lighting settings, for example circular, annular, quadrupolar or bipolar Illumination, an aperture wheel can be arranged in an aperture diaphragm plane.

With the aid of the variably adjustable illumination aperture diaphragm, the aperture diaphragm in the imaging system or the aperture wheel, it is possible to use the inspection system according to the invention to simulate the settings in an EUV projection exposure system in which the mask or the reticle is used, and by evaluating the mask images to determine optimal setting parameters of the projection exposure system in relation to aperture, type of illumination, etc. This makes the inspection system suitable for much more than just examining masks for defects. If a mask is examined for defects, the defective locations of the EUV mask 104 to be examined are arranged within the illuminated, observed field.

The beam path of a bundle of rays is shown in FIG. 9 for the field center of the field 102 . The main beam 106 of the beam bundle 108 emanating from the field plane is inclined by an angle α with respect to the optical axis HA. The angle α corresponds to the main beam incidence angle in projection exposure systems on the object, which is preferably 6 °.

With the aid of an X-ray microscope according to the invention as an imaging system 110 , which is not shown in FIG. 9 but can comprise an X-ray microscope objective according to FIGS. 1 to 7, the object 104 is imaged in the object plane 101 into an image in the image plane 112 . As can be seen from FIG. 9, the beam path of a bundle of rays emanating from the center of the field in the image plane 112 is almost telecentric, ie the main beam 106 of a bundle of beams 108 strikes the image plane 112 almost perpendicularly. It would also be possible to deliberately introduce a larger telecentricity error by moving the aperture diaphragm. The image 114 of the object 104 in the image plane 112 is enlarged. The magnification is preferably in the range 300 × to 1000 ×. An observation device is arranged in the image plane 112 for observation. The observation device can be a camera, in particular a CCD camera, a multi-channel plate or a fluorescent screen.

The observation device in turn can be designed with an analysis unit, also not shown in FIG. 9, to which the image recorded by the observation device is supplied, for example in digital form, for evaluation. The analysis unit can be a programmable, digital computer.

The programmable digital computer can in turn include control devices which control the aperture diaphragm in the imaging optics, the illumination aperture diaphragm or the diaphragm wheel and the field diaphragms in the inspection system in order to adjust the size and shape of the illuminated object field in the object plane, the pupil filling and the numerical aperture. Furthermore, the system can include devices for positioning the object to be examined in the object plane, which is also referred to as the xy plane. This makes it possible to have different sections of the mask with a small object field, for example of 30 μm × 30 μm or 100 μm × 100 μm, with a mask size of z. B. 152 × 152 mm ² to investigate. By systematically moving the mask in the xy plane, the entire mask can be examined with the projection exposure system simulated by the adjustable diaphragms. However, since this is very complex, a parallel auxiliary observation system that works with UV light or VUV light can be provided for the rough inspection of the mask. If the entire mask has been roughly examined, the areas critical on the mask can be approached with the aid of the xy positioning device and these areas can then be examined for defects using the EUV optics. In addition to the movability in the xy plane with the positioning device, focus adjustment devices are also provided in a preferred embodiment of the invention, with which the object can move perpendicular to the object plane and images can be recorded at predetermined focus positions above and below the focus. In this way it is possible to take pictures of the mask at different predetermined focal planes. The number of these focus levels depends on the desired accuracy of the examination.

In addition to the image data at different focus levels, you can also Illumination intensity data in the illumination plane for each single picture can be taken.

From the captured image data, depending on the x, y position as well as the z-position intensity data maps of the mask examined become. These intensity data cards can be used with intensity data cards obtained on the basis of simulation calculations or reference data cards, when examining masks or objects that are in a Projection exposure process have produced acceptable results, be compared. In this way, an examination of the mask is on Defects and their repair as well as a qualification of the mask possible.

The inspection system according to the invention is not only for defect analysis and control of mask repairs suitable for microlithography, but also for local cleaning of the masks by irradiation with light from the Wavelength of the inspection system or optimization of the design of the Mask structure and for process optimization for the exposure process and System configuration in projection exposure systems.

In Fig. 10 is a schematic diagram of the entire inspection system is shown. The light from an EUV light source 100 is collected by a collector 102 and directed via mirrors 104 , 106 of the lighting system onto the object plane 108 in which the object to be examined is located. The bundle of rays of the lighting system 110 does not fall on the object in the object plane 108 telecentrically, but at an angle. The main beam angle of the beam bundle is preferably identical to the main beam angle at which the projection exposure system is also operated. This angle α relative to the normal 112 is preferably 6 ° in a first exemplary embodiment.

In the lighting system 110 , an illumination aperture diaphragm 120 and a field diaphragm 122 are arranged in the beam path from the collector 102 to the object plane 108 . The object in the object plane 108 , which is illuminated under reflection, is imaged with an imaging system according to the invention in an image plane 130 in which the object can be observed. The imaging takes place with an X-ray microscope according to one of FIGS. 1 to 7. In the embodiment shown, the first subsystem comprises a mirror 152 and a second mirror 154 . The second subsystem 156 comprises the third and fourth mirrors 155 , 157 and folds the beam path, so that a relatively large magnification is achieved with a small overall length. The aperture diaphragm 154 in the imaging system is located in the beam path from the object plane to the intermediate image plane between the object plane 108 and the first mirror 152 of the first subsystem 150 .

In Fig. 11, an exemplary measurement sequence for examining an object using the inspection system according to the invention is shown. In a first step 200 , the system setting is entered, for example the NA _mapping , the NA _lighting and the obscuration or field diaphragm. The diaphragms are then set in a second step 202 . The system settings are then checked in a step 204 using a test structure, for example a linear structure in the x or y direction. The system is fine-tuned in a step 206 using the test structure. Then, in a step 210, the measuring point is positioned in the measuring field, that is the area of the object to be examined, in which, for example, the xy table is moved to the corresponding point. Optionally, documentation of the measurement settings can also be carried out in a step 208 before positioning in the measurement field.

After the measuring point to be examined has been positioned, the focus is set in a last step 212 . If the focus is found in step 212 , then either a measurement image is recorded in step 214 or the focus is moved through as described above, ie measurement images are recorded for different z positions. After each measurement image, the same is checked in step 216 or the measurement images associated with the different focus positions are assessed in terms of quality. If these meet the quality requirements, the object, if present, is moved to another measuring point and the measurement series is again recorded there as described above. If the quality control leads to a negative result, a new measurement image is recorded at the same location or a large number of measurement images which are assigned to different z positions.

If there is no further measurement position 220 , either the system settings can be changed in step 222 or the measurement can be ended in step 224 .

In Fig. 12 are possible evaluations of obtained with the aid of the inspection system measurement images or measurement information which can be carried out for example with the aid of a computer device, is shown. The selected measurement image 300 , which is a function of the location on the object to be examined in the object plane, ie in the xy plane, and in the z direction if different measurement images have been recorded above and below the focus plane, can be carried out in one step 302 both in terms of the location on the sample, ie the xy position, ie with respect to the region, and with regard to the z position, ie with respect to the section, are selected and subsequently analyzed. The selected data can be numerically edited and certain representations calculated, as indicated in step 304 . For example, the data can be fitted, interpolated, correlated, smoothed, filtered or mirrored. The processing of the data by calculation or processing in step 304 can also, for. B. can be characterized automatically using key figures in relation to the quality in step 306 .

As an alternative to outputting quality indicators or in addition to this, various representations can be made in step 310 . An image representation of the intensity in the x, y direction is possible or a contour plot. This is identified by reference numbers 312 and 314 . Alternatively, the profiles for the cuts can be shown or the line width over the defocusing, ie the movement in the z direction. This is marked with 316 and 318 . The line width can also be displayed above the threshold. This is identified by reference number 320 . Alternative types of representation are the process window, which is identified by reference number 322 , and a display of the simulation data for measurement data for resist development, which is identified by reference number 324 . It is also possible to compare several measurements or to display the contrast via the defocusing, ie the movement in the z direction. This is identified by the reference numbers 326 and 328 . Other representations based on the evaluation of the measurement images according to step 330 are also possible. The possible display types for inspection systems that operate in the wavelength range ≥ 193 nm are described in detail in the Operating Manuel AIMS Fab B 41003E and / or Software Manual AIMS Fab B40409E from, Carl Zeiss Microelectronic Systems GmbH. The content of the disclosure of these documents is fully incorporated into the present application.

In FIGS. 13a to 13c possible areas of application of the inspection system according to the invention are shown. 13a shows as Fig. The use of the EUV inspection system, for example in the production of mask blanks, that mask blanks. The substrate manufactured according to step 400 , which is generally a glass substrate, can be checked in step 402 with regard to its quality with the aid of the EUV inspection system according to the invention. If this quality is sufficient, the substrate is coated with EUV mirror layers in step 404 . These mirror layers are now inspected for defects in step 406 , namely the entire area. The defect inspection according to step 406 is carried out with an inspection module, for example an imaging system that is parallel to the EUV imaging system and operates with visible light. If there are defects on the mask, then these defects can be examined in more detail using the EUV inspection system in accordance with step 408 . For this purpose, the mask previously examined over the entire surface is moved to the defect locations with an xy positioning device and these areas of the mask are specifically examined with the EUV inspection system. If the quality of the mask according to step 410 is sufficient after an EUV inspection, the mask can be delivered according to step 412 or is discarded according to step 414 .

Fig. 13b shows a further field of use of the EUV inspection system according to the invention the use in the mask production. The incoming coated mask substrate can be examined in accordance with FIG. 13b in step 450 with the aid of the EUV inspection system in the incoming inspection. If the mask is of sufficient quality, it can be structured in a subsequent step 452 . The entire structured mask according to step 452 can in turn be qualitatively examined in step 454 with the aid of the EUV inspection system. For this purpose, as with the incoming goods inspection 450 , a defect inspection of the entire mask area is first carried out using an inspection system that works, for example, with visible light, and a CD measurement, likewise using a system that works in the visible or UV or VUV wavelength range. If defects result from defect inspection or CD measurement, which is not carried out with EUV radiation, the EUV inspection system according to the invention can be used to classify the defects found there in more detail. If, based on the EUV inspection of the defects, the quality of the masks after defect inspection is found to be sufficient, this can be delivered in accordance with step 456 . If the mask is not of sufficient quality, the mask can be moved to the corresponding defect location and an examination can be carried out in step 458 to determine whether a repair is possible or not. If repair is not possible, the mask is discarded in accordance with step 460 . If a repair is possible, this is carried out in accordance with step 462 and subjected to the EUV inspection again. If the quality data is now sufficient, the repaired mask can be delivered.

Fig. 13c shows the application area of the EUV inspection system according to the invention the use of such inspection system in the wafer factory. In accordance with step 500 , the mask can first be subjected to an incoming inspection in the wafer factory. During the production process 502 , the mask ages. The masks can be examined at regular intervals with the aid of the EUV inspection system according to the invention for their quality after aging or after storage in accordance with step 504 . For this purpose, the mask is first examined for defects over the entire area with radiation in the visible or UV or VUV wavelength range. An EUV inspection is carried out at the points where defects occur. If the mask quality is still sufficient, the mask can still be used in production. If the EUV inspection reveals that the mask no longer meets the qualitative requirements, it can be examined whether the defect can be repaired. This step is referred to as step 506 . If a repair is ruled out, the mask is removed from the production process in accordance with step 508 . If a repair is possible, the mask is repaired according to step 510 and inspected again after the repair using the EUV inspection system. The defect is classified after the repair has been carried out and, if the quality is sufficient, the mask is transferred to the production process and discarded if the quality is insufficient.

With the invention thus an X-ray microscope and a Inspection system for objects that are used in EUV lithography, specified, which is characterized by a very short length and a compact Construction is characterized by a sufficient image scale.

Claims (38)

1. Reflective X-ray microscope for examining an object in an object plane, the object being illuminated with radiation of a wavelength <100 nm, in particular <30 nm, and magnified in an image plane with 1. 1.1 a first subsystem arranged in the beam path from the object plane ( 1 ) to the image plane ( 3 ), comprising a first mirror (S1) and a second mirror (S2), characterized in that 1. 1.2 the reflective X-ray microscope comprises a second subsystem which is arranged downstream of the first subsystem in the beam path and which has at least one third mirror (S3). 2. Reflective X-ray microscope according to claim 1, characterized in that that the first mirror (S1) is a concave mirror and the second mirror (S2) is a convex mirror. 3. Reflective X-ray microscope according to claim 1, characterized in that the first mirror (S1) is a concave mirror and the second mirror (S2) is a concave mirror. 4. Reflective X-ray microscope according to one of claims 1 to 3, characterized characterized in that the second subsystem a third (S3) and a fourth mirror (S4). 5. A reflective X-ray microscope according to claim 4, characterized characterized in that the third (S3) and the fourth mirror (S4) each Are concave mirrors. 6. A reflective X-ray microscope according to claim 4, characterized characterized in that the third mirror (S3) is a convex mirror and the fourth mirror (S4) is a concave mirror. 7. Reflective X-ray microscope according to one of claims 1 to 6, characterized characterized that the X-ray microscope has a magnification of β ≥ 50 ×, preferably in the range 100 × β β 1000 1000 ×. 8. reflective x-ray microscope according to one of claims 1 to 7, characterized in that in the beam path from the object plane to A real intermediate image is formed. 9. reflective X-ray microscope according to one of claims 1 to 8, characterized in that the x-ray microscope has an optical axis has, the first, second and third mirrors (S1, S2, S3) of the Microscope are arranged centered on the optical axis (HA). 10. reflective x-ray microscope according to one of claims 1 to 8, characterized in that the x-ray microscope has an optical axis having first, second, third and fourth mirrors (S1, S2, S3, S4) of the microscope are arranged centered on the optical axis (HA). 11. A reflective X-ray microscope according to one of claims 1 to 10, characterized in that the object in the object plane ( 1 ) is arranged decentrally to and preferably close to the optical axis (HA). 12. reflective x-ray microscope according to one of claims 1 to 11, characterized in that an aperture stop (B) is decentered for optical axis (HA) is provided. 13. reflection x-ray microscope according to claim 12, characterized in that the aperture diaphragm (B) is arranged in the beam path from the object ( 1 ) to the image plane ( 3 ) after the object plane ( 1 ) and in front of the first mirror (S1). 14. Inspection system for the examination of objects, in particular masks for microlithography with wavelengths <100 nm, preferably <30 nm, with 1. 14.1 an illumination system for illuminating a field in an object plane ( 1 ), wherein 2. 14.2 the object to be examined is arranged in the object plane within the illuminated field; 3. 14.3 an imaging system for wavelengths ≤ 100 nm for magnifying imaging of at least a section of the object in an image plane ( 3 ); 4. 14.4 an image recording system arranged in the image plane ( 3 ). 15. Inspection system according to claim 14, characterized in that the Inspection system positioning devices for positioning the object in the object plane. 16. Inspection system according to one of claims 14 to 15, characterized characterized that the imaging system is an adjustable Includes aperture diaphragm (B). 17. Inspection system according to one of claims 14 to 16, characterized characterized that the lighting system is adjustable Illumination aperture diaphragm in a plane that is conjugate to the plane of the Aperture diaphragm (B) is included in the imaging system. 18. Inspection system according to one of claims 14 to 16, characterized characterized that the lighting system or the imaging system an obscuration aperture in or near the aperture plane (B) or one Plane that is conjugated to the aperture plane (B). 19. Inspection system according to one of claims 14 to 18, characterized characterized that the lighting system is adjustable Field aperture includes. 20. Inspection system according to one of claims 14 to 19, characterized in that the image recording system comprises an analysis unit for analyzing the images of the object in the image plane ( 3 ). 21. Inspection system according to one of claims 14 to 20, characterized characterized that the inspection system focus adjustment devices includes. 22. Inspection system according to claim 21, characterized in that the focus setting devices comprise displacement devices for moving the object in a direction perpendicular to the object plane ( 1 ). 23. Inspection system according to claim 21 or 22, characterized in that that the image recording system images at predetermined focus positions, in which the object is moved through the focus adjustment device. 24. Inspection system according to one of claims 20 to 23, characterized characterized in that the analysis unit is a microcomputer device includes. 25. Inspection system according to one of claims 14 to 24, characterized characterized that the imaging system for wavelengths 100 nm includes reflective X-ray microscope. 26. Inspection system according to claim 25, characterized in that the reflective x-ray microscope according to a reflective x-ray microscope one of claims 1 to 13. 27. Inspection system according to one of claims 14 to 26, characterized characterized in that at least part of the inspection system in the Vacuum or in a protective gas is arranged. 28. Inspection system according to one of claims 14 to 27, characterized characterized that the inspection system further one to Imaging system for wavelengths ≤ 100 nm parallel Auxiliary observation system for wavelengths ≥ 100 nm for imaging comprises at least a part of the object in a further image plane. 29. Inspection system according to claim 28, characterized in that the Auxiliary observation system is arranged parfocal and / or centered. 30. Method for inspecting objects, in particular masks for microlithography with wavelengths of 100 nm, with the following steps: 1. 30.1 in the object plane, a field is illuminated with an illumination system; 2. 30.2 the object to be examined is brought into the illuminated field with positioning devices; 3. 30.3 the object to be examined is imaged in an image plane ( 3 ) with a reflective X-ray microscope for wavelengths 100 nm; 4. 30.4 the images of the object in the image plane ( 3 ) are recorded by an image recording system. 31. The method according to claim 30, characterized in that the of the Image recording system recorded images with an analysis unit characteristic sizes of the object can be evaluated. 32. The method according to claim 30 or 31, characterized in that the object is moved with a focus adjustment device perpendicular to the object plane ( 1 ) and images are recorded at predetermined focus positions above and below the focus. 33. The method according to any one of claims 30 to 32, characterized in that that the numerical aperture with the aperture diaphragm (B) and with the Illumination aperture diaphragm is set so that one with the Projection exposure system optically equivalent aperture results. 34. The method according to any one of claims 30 to 33, characterized in that the procedure with an inspection system according to one of the Claims 13 to 24 is carried out. 35. Use of an inspection system according to one of claims 14 to 30 for defect analysis of masks for microlithography with Wavelengths ≤ 100 nm. 36. Use of an inspection system according to one of claims 14 to 30 to control repairs of masks for microlithography with Wavelengths ≤ 100 nm. 37. Use of an inspection system according to one of claims 14 to 30 for process optimization for the exposure process in Projection exposure systems. 38. Use of an inspection system according to one of claims 14 to 30 for the system configuration of a projection exposure system.