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WO2024068294A1 - Procédé de mesure pour réflectométrie euv, et réflectomètre euv - Google Patents

Procédé de mesure pour réflectométrie euv, et réflectomètre euv Download PDF

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Publication number
WO2024068294A1
WO2024068294A1 PCT/EP2023/075336 EP2023075336W WO2024068294A1 WO 2024068294 A1 WO2024068294 A1 WO 2024068294A1 EP 2023075336 W EP2023075336 W EP 2023075336W WO 2024068294 A1 WO2024068294 A1 WO 2024068294A1
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WIPO (PCT)
Prior art keywords
measuring
mirror
test object
euv radiation
euv
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
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PCT/EP2023/075336
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German (de)
English (en)
Inventor
Markus Schwab
Anton Haase
Iris Pilch
Rainer Lebert
Oleksiy Maryasov
Erik Loopstra
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Carl Zeiss SMT GmbH
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Carl Zeiss SMT GmbH
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Filing date
Publication date
Application filed by Carl Zeiss SMT GmbH filed Critical Carl Zeiss SMT GmbH
Priority to CN202380069895.1A priority Critical patent/CN119998652A/zh
Publication of WO2024068294A1 publication Critical patent/WO2024068294A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
    • G01M11/00—Testing of optical apparatus; Testing structures by optical methods not otherwise provided for
    • G01M11/005—Testing of reflective surfaces, e.g. mirrors
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/25—Colour; Spectral properties, i.e. comparison of effect of material on the light at two or more different wavelengths or wavelength bands
    • G01N21/31—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry
    • G01N21/33—Investigating relative effect of material at wavelengths characteristic of specific elements or molecules, e.g. atomic absorption spectrometry using ultraviolet light

Definitions

  • German patent application number 10 2022 210 354.8 filed on September 29, 2022.
  • the disclosure content of this patent application is incorporated by reference into the content of the present application.
  • the invention relates to a measuring method for measuring the reflectivity of a test object that is reflective for EUV radiation as a function of the wavelength of the EUV radiation and the angle of incidence of the EUV radiation on a reflecting surface of the test object, as well as an EUV reflectometer suitable for carrying out the method.
  • EUV reflectometer is a measuring device for measuring the reflection properties of a test object for electromagnetic radiation at wavelengths in the extreme ultraviolet (EUV) spectral range.
  • EUV extreme ultraviolet
  • An EUV reflectometer can be used to measure the reflectivity of a test object that is reflective of EUV radiation, depending on the wavelength of the EUV radiation (“wavelength spectrum”) and the angle of incidence of the EUV radiation (“angle spectrum”) on a reflecting surface of the test object become. Wavelength spectra and angle spectra can be used, among other things, to characterize the materials involved in reflection and their structure. EUV reflectometers are suitable, among other things, for examining reflective test objects, such as mirrors or masks that have a large number of material layers as a reflective coating (multilayer mirror) or only one or a few layers, such as mirrors that are designed for grazing incidence (grazing incidence).
  • An EUV reflectometer should be able to determine the degree of reflectance of a reflective surface or its reflectivity in the EUV range with high accuracy.
  • Document DE 10 2020216 337 A1 discloses an EUV reflectometer with a radiation source for EUV radiation, a monochromator for adjusting the wavelength of a measuring beam directed at the sample, wherein the monochromator has a first reflection element arranged in the beam path of the measuring beam, a second reflection element arranged in the beam path of the measuring beam, a first exit slit arranged in the beam path after the second reflection element and a third reflection element arranged in the beam path after the first exit slit.
  • the first reflection element is designed to focus the measuring beam in the region of the first exit slit or in the first exit slit in a first direction and the second reflection element is designed to focus the measuring beam in the region of the first exit slit or in the first exit slit in a second direction perpendicular to the first direction.
  • the second reflection element is a concave grating.
  • a detector is provided for detecting radiation reflected from the sample.
  • At least one of the reflection elements is designed to be controllable. By controlling a controllable reflection element, for example, a particularly precise and simple adjustment of the measuring beam can be carried out.
  • the measuring beam can be aligned or adjusted particularly precisely to one of the elements in the beam path, for example to one of the reflection elements or the first exit slit and/or to the sample.
  • the controllable third reflection element ensures that the measuring beam can be aligned particularly easily to the sample, for example by rotation and/or a change in position or translation.
  • the drive elements can be controlled by a control unit.
  • the invention is based on the object of providing a measuring method of the type mentioned in the introduction and an EUV reflectometer configured to carry it out, which, compared to the prior art, have the potential for high Offer measurement accuracy with a relatively short overall time requirement for the work to be carried out in connection with a measurement.
  • the EUV reflectometer should enable short measurement times even when the test objects are large and heavy.
  • the invention provides a measuring method with the features of claim 1 and an EUV reflectometer with the features of claim 6.
  • Preferred further developments are specified in the dependent claims. The wording of all claims is incorporated by reference into the content of the description.
  • the measurement method according to the claimed invention is carried out with an EUV reflectometer.
  • the measuring method and the EUV reflectometer are used to measure the reflectivity of a test object that reflects EUV radiation depending on the wavelength of the EUV radiation and the angle of incidence of the EUV radiation on a reflective surface of the test object.
  • a measuring beam is generated with EUV radiation directed at the surface.
  • the EUV reflectometer has an EUV radiation source with devices for generating a source spot for emitting EUV radiation and a beam shaping unit for receiving EUV radiation from the source spot and generating the measuring beam.
  • the beam shaping unit has a first subsystem and a downstream second subsystem.
  • the first subsystem includes a monochromator for adjusting the wavelength of the measuring beam.
  • the monochromator has a concavely curved reflection grating and a diaphragm arrangement with an exit slit downstream of the reflection grating.
  • the second subsystem is designed to generate an approximate image of the illuminated area of the exit gap in order to form the measuring spot on the surface of the test object.
  • the measuring spot on the surface of the test object should be homogeneously illuminated.
  • the test specimen is held and positioned by a positioning device in such a way that the measuring beam can hit the reflecting surface at a predeterminable measuring point in the area of a measuring spot at a predeterminable angle of incidence.
  • a detector of the EUV reflectometer (at least) one property of the beam reflected from the surface of the test object is detected.
  • the detector generates detector signals that represent the EUV radiation reflected by the test object.
  • An evaluation device of the EUV reflectometer evaluates the detector signals and uses them to determine reflectivity measurement values.
  • a special feature is that during the beam direction control operation, the position of the measuring spot on the surface of the test object is changed by coordinating a first mirror and a second mirror connected downstream in the beam direction of a reflective manipulator of the second subsystem in response to control signals from the control unit at least one rigid body degree of freedom.
  • the first mirror and the (at least one) second mirror thus together form a reflective manipulator of the beam direction control system of the EUV reflectometer.
  • the invention also relates to an EUV reflectometer which is configured to carry out the measuring method in that the second subsystem has a reflective manipulator which has a first mirror and at least one second mirror optically connected downstream of the first mirror, wherein the mirrors can be displaced in a coordinated manner in at least one rigid body degree of freedom.
  • the reflective manipulator of the beam direction control system thus comprises at least two mirrors connected in series.
  • the concept can be implemented in an EUV reflectometer in that the beam direction control system has a reflective manipulator arranged in the second subsystem, which has a first mirror and at least one second mirror connected downstream in the beam path, which respond to control signals from a control unit by means of an adjusting device for reversibly changing the position of the mirrors with respect to a reference position can be moved in a coordinated manner with one another in at least one rigid body degree of freedom.
  • manipulator refers to an optomechanical device that has at least one manipulable optical element and one or more actuators or control elements acting on it. Based on appropriate control signals, the actuators or control elements can be used to actively influence individual optical elements or groups of optical elements of a manipulator in order to change the optical effect of the manipulable optical element in the beam path.
  • the reflective manipulator here causes a change in the beam direction of the measuring beam without changing the shape of the reflective surfaces of the mirrors. The measuring beam is thus reflected between the exit slit and the surface of the test object by at least two mirrors connected in series in the beam path. By changing the reflection conditions on the first and second mirrors, the beam direction can be changed without having to accept any significant loss in terms of the quality of the measuring spot. Manipulation is also possible by moving just one mirror in the second subsystem, but this would result in significantly poorer properties of the measuring spot.
  • the desired measuring position on the test specimen should intersect as closely as possible with a rotation axis of the positioning device.
  • the surface normal of the test object at the location of the measuring spot should be as perpendicular as possible to this axis of rotation.
  • These conditions can be met using adjustment movements on the positioning device.
  • the measuring spot should, if possible, intersect the axis of rotation of the positioning device.
  • a placement of the measuring spot, if possible on the axis of rotation of the positioning device can be achieved by changing the beam direction of the measuring beam.
  • the measuring spot should have a defined dimension so that the measurement can take into account how large the area is that contributes to the intensity of the detector signal.
  • a measuring spot can, for example, have a rectangular, in particular essentially square, shape with edge lengths of the order of a few hundred micrometers, for example 500 pm x 500 pm or 600 pm x 600 pm or 700 pm x 700 pm, but also values lying outside of these ranges or intermediate values from these areas.
  • the horizontal determines the monochromacy and the vertical influences the overall intensity or the location that is measured. In order to ultimately obtain a good signal-to-noise ratio, as much power as possible should be concentrated in the measuring spot.
  • the requirements for the most defined extent of the measuring spot and the highest possible power within the illuminated area can be achieved by optimizing the imaging properties of the second subsystem.
  • the claimed invention offers a good compromise between these different requirements. For example, it would be conceivable to provide only a single mirror as a reflective manipulator in the second subsystem, for example an ellipsoid mirror. In comparison to a reflective manipulator with at least two mirrors connected in series, this would theoretically have the advantage of higher transmission because transmission losses due to reflection only occur once.
  • relatively unfavorable properties would emerge with regard to the measuring spot, which could lead to light losses in the double-digit percentage range.
  • the reflection losses are theoretically greater, but significantly better spot quality can be achieved.
  • the improved spot quality allows the system's light tube to be enlarged so that overall performance can be significantly better than using a single mirror as a reflective manipulator.
  • the reflective manipulator comprises a mirror arrangement in the manner of a Wolter collector, i.e. a mirror arrangement with nested mirrors with rotationally symmetrical surfaces that reflect EUV radiation, preferably one of the mirrors, in particular the second mirror, as a paraboloid of revolution or as an ellipsoid of revolution and the other mirror, in particular the first mirror, is designed as a hyperboloid of revolution or as an ellipsoid of revolution.
  • the Wolter collector may have a construction according to type I, type II or type III of a Wolter collector.
  • Such a mirror arrangement makes it possible to create sharply defined measuring spots and at the same time to achieve the possibility of shifting the measuring spot by changing the position and/or orientation of the Wolter collector.
  • the reflective manipulator comprises, in addition to at least one other mirror, a plane mirror used in grazing radiation incidence, which is arranged in the beam path of the second subsystem behind the other mirror and can be pivoted about an axis of rotation or tilt axis.
  • a plane mirror used in grazing radiation incidence which is arranged in the beam path of the second subsystem behind the other mirror and can be pivoted about an axis of rotation or tilt axis.
  • the use of at least one pivotable plane mirror increases the degrees of freedom of spatial manipulation.
  • the plane mirror only acts in the sense of folding without changing the beam angle distribution and accordingly also without having a substantial influence on the quality of the measurement spot.
  • Such a plane mirror can be provided in addition to a mirror arrangement in the manner of a Wolter collector, optically between the latter and the positioning device, so that the measuring beam emerging from the Wolter collector can be deflected. Due to additional transmission losses, however, the additional plane mirror is generally not used.
  • the second subsystem has a first mirror in the form of a rotational ellipsoid and the second mirror is formed by the plane mirror.
  • a reflection element with a concavely curved reflection surface in the beam path of the second subsystem, which has a first curvature in a first direction and a second curvature in a second direction perpendicular to the first direction, wherein this reflection element is designed as a component of the reflective manipulator and can be displaced in at least one rigid body degree of freedom by means of at least one actuator of the reflective manipulator in response to control signals from the control unit.
  • the displacement operation comprises a rotation of the complete second subsystem about a tilt axis located in the center of the exit slit.
  • the reflective components of the second subsystem are preferably mounted with a fixed reference to a common reference system so that they can be tilted together about this tilt axis.
  • Another possible displacement operation includes a rotation of a plane mirror of the manipulator about a tilt axis running on or in the plane mirror. This can also ensure that the measuring spot is relocated on the surface of the test object without significantly changing its shape, size and illumination.
  • FIG. 1 shows schematically components of an exemplary embodiment of an EUV reflectometer
  • Fig. 2 shows an exemplary embodiment with components of a beam direction
  • Control system comprising a Wolter collector
  • Fig. 3 shows an embodiment with components of a beam direction
  • Control system comprising a tiltable plane mirror
  • Figure 4 shows an example of a Wolter collector used as part of a reflective manipulator
  • Fig. 5 shows a beam direction control operation in which the complete second subsystem is tilted about a tilt axis located in the exit slit;
  • Figs. 6A, 6B show a beam direction control operation in which a plane mirror is tilted
  • Fig. 7 shows a reflective manipulator with a mirror arrangement in the manner of a Wolter collector, followed by a tiltable plane mirror.
  • Fig. 1 shows schematically components of an embodiment of an EUV reflectometer EUVR or a measuring device for measuring the reflectivity of a test object PR that reflects EUV radiation as a function of the wavelength of the EUV radiation and the angle of incidence of the EUV radiation on a reflective surface OB of the test object.
  • the test object can be, for example, a mirror for an EUV lithography lens that has a flat or a generally concave or convex curved reflective surface.
  • the positional relationships between the components shown result from the right-handed Cartesian xyz coordinate system KS.
  • the EUV reflectometer allows, among other things, to measure the degree of reflectance or reflectivity of the test object at different wavelengths in a specified wavelength range of extreme ultraviolet (EUV) radiation. This preferably means wavelengths in the range from 6 nm to 20 nm, in particular from 8 nm to 20 nm.
  • the ready-to-use EUV reflectometer includes an EUV radiation source SQ for emitting EUV radiation and a downstream beam shaping unit SFE, which is configured to receive EUV radiation from the EUV radiation source and use it to generate a measuring beam STR, which is used during operation of the Measuring device at the end on the test object side hits the reflective surface OB of the test object PR and forms a measuring spot MFL there at a measuring point.
  • EUV extreme ultraviolet
  • the EUV radiation source SQ comprises a pulsed laser, the laser beam LS of which is focused onto a gold target T or another suitable material using focusing optics (not shown).
  • the laser beam generates a plasma PL on the surface of the target, which emits a quasi-continuous spectrum of electromagnetic radiation in the EUV range.
  • the plasma forms a source spot QF or emission spot that emits the EUV radiation.
  • This source spot QF serves as an effective radiation source.
  • other EUV radiation sources can also be used that emit a discrete or a quasi-continuous spectrum of electromagnetic radiation in the EUV range, for example a DPP source (DPP: “discharge produced plasma.”).
  • DPP discharge produced plasma.
  • Other EUV sources are also possible, e.g. HHG (high harmonic generation) sources. These are also based on lasers that shoot at a target, where the target here is gaseous.
  • the beam forming unit SFE is shown in a highly schematic manner in Fig. 1.
  • Figs. 2 and 3 show embodiments with components of a beam direction control system SRSS.
  • the beam shaping unit SFE comprises a first subsystem TS1 and a downstream second subsystem TS2.
  • the first subsystem TS1 has a monochromator MC for adjusting the wavelength of the measuring beam, whereby the monochromator has a concavely curved reflection grating RG and a diaphragm arrangement BL downstream of the reflection grating with an exit slit SP.
  • the diaphragm arrangement can have a rectangular diaphragm opening, the width of which can be continuously adjusted in two mutually perpendicular directions.
  • a front reflection element VRE is arranged in the beam path in front of the reflection grating RG, i.e. between the source spot QF or the radiation source SQ and the reflection grating.
  • Examples of the design of the first subsystem are described, for example, in DE 10 2018 205 163 A1 or WO 2021/156411 A1. Their disclosure content is made part of the content of the description by reference.
  • the second subsystem TS2 is designed to generate an approximate image of the illuminated area of the exit slit SP on the surface OB of the test object PR and thereby form the measuring spot MFL.
  • the extent of the area exposed to EUV radiation in the area of the measuring spot MFL can be sharply limited and continuously adjusted in two mutually perpendicular directions using the aperture arrangement BL.
  • the second subsystem TS2 has a reflective manipulator MAN of a beam direction control system SRSS. This is in signal-transmitting connection with the control unit STE of the beam direction control system STSS and can be controlled by a control unit to change the beam direction of the measuring beam STR.
  • a positioning device POS of the EUV reflectometer is configured to hold the test object PR to be measured and to position it in relation to the measuring beam STR in several degrees of freedom such that, during operation of the EUV reflectometer, the measuring beam can impinge on the reflective surface at a predeterminable measuring point or a predeterminable measuring location in the area of a measuring spot MFL and a predeterminable angle of incidence or angle of incidence range.
  • the EUV reflectometer also includes a detector DET that is sensitive to EUV radiation and is configured to detect the EUV radiation of the reflected EUV beam reflected by the reflecting surface OB and to generate corresponding detector signals that detect the EUV radiation reflected by the test object. represent radiation.
  • the detector has a measuring diode.
  • An evaluation device AW is connected to the detector DET in a signal-transmitting manner and is configured to determine reflectivity measured values using the detector signals.
  • the EUV reflectometer EUVR includes a reference detector RDET arranged outside the measuring beam path and a beam splitter ST, which serves to divide a portion of the incident radiation EUV radiation from the measuring beam STR to the reference detector RDET and a different (larger) portion to the test specimen PR to let through.
  • the beam splitter ST is a geometric beam splitter in the form of a flat beam splitter comb; other configurations are possible.
  • the evaluation of the reference detector signals generated by the reference detector RDET and the detector signals generated by the detector DET takes place in the evaluation device AW, which receives and processes these signals, in particular in order to obtain precise measured values for the reflectivity of the test object surface at the location of the measuring spot.
  • the reflectance (R) results from the ratio between the intensity of the reflected radiation, which is measured using a detector DET, and the intensity of the incident radiation, the size of which can be determined using signals from the reference detector RDET.
  • the measurements can be carried out for angles of incidence in the range between 0° and 90° (without the limit values).
  • the angle of incidence is defined here in relation to the surface normal at the point of impact.
  • the angles of incidence can also be larger, such as with mirrors for grazing incidence, where the angles of incidence can be larger than 60°, for example, and in particular in the range from approx. 65° to approx. 89°.
  • the wavelengths should be determined with an accuracy of approx. 1 - 3 pm (picometer). Since the angle of incidence of the incident beam on the surface of the test object to be measured influences the wavelength position of the spectra, it follows that the angle of incidence should be set or at least known precisely down to approximately one hundredth of a degree. Another requirement concerns the measurement of reflectivity, i.e. the intensity ratio of the reflected to the incident measuring beam. This value, i.e. the degree of reflection, should be able to be determined as accurately as possible to a fraction of a percent.
  • the reflectivity should be able to be measured over the entire surface of the test object if possible.
  • the test object is typically moved as a whole with the help of the positioning device POS in relation to the measuring beam STR until the measuring spot MFL is at the intended measuring point.
  • it is a challenge to position the mirror with the help of the positioning device in all the required degrees of freedom with high spatial accuracy.
  • the requirements for positioning accuracy on the part of the test object can be relaxed if the optical system for generating the measuring beam STR is designed in such a way that the beam direction of the measuring beam can be changed in a controlled manner within certain limits.
  • a two-stage positioning operation can then be carried out to position the measuring spot at the measuring point intended for the measurement.
  • the test object is roughly positioned by moving the test object in at least one degree of freedom using the positioning device POS.
  • a fine positioning of a measuring spot MFL is then carried out on the then stationary test object by changing the beam direction of the measuring beam STR in a controlled manner while the test object is at rest.
  • the beam forming unit SFE comprises a beam direction control system SRSS.
  • This comprises two mirrors arranged in the beam path of the beam forming unit within the second subsystem TS2, which can be moved in a coordinated manner in one rigid body degree of freedom or several rigid body degrees of freedom in response to control signals from the control unit.
  • the at least two mirrors together form a reflective manipulator MAN of the beam direction control system SRSS.
  • the reflective manipulator is thus an opto-mechanical device that has at least two manipulable optical elements in the form of mirrors and one or more actuators or control elements acting on them (not shown in detail).
  • the reflective manipulator causes a change in the beam direction of the measuring beam without changing the shape of the reflective surfaces of the mirrors.
  • a mirror arrangement WK in the manner of a Wolter collector is arranged within the second subsystem TS2 behind the exit slit SP of the monochromator.
  • the mirror arrangement has nested mirrors with rotationally symmetrical surfaces that reflect EUV radiation.
  • An embodiment of a Wolter collector WK is shown schematically in Fig. 4.
  • the first mirror S1 that is hit first by the EUV radiation is designed as a hyperboloid of revolution in which the EUV radiation hits a hyperboloid-shaped reflective surface on the outside of a correspondingly designed mirror substrate.
  • the second mirror S2 which is arranged downstream in the beam direction, is designed as a rotational ellipsoid or rotational paraboloid and has a rotationally ellipsoidal or rotationally paraboloidal mirror surface covered with a coating that reflects EUV radiation.
  • the arrangement of the reflecting surfaces is such that the two mirrors S1, S2 of the Wolter collector WK form an imaging system which can image the illuminated area of the exit gap SP onto the surface of the test specimen PR and produce a relatively sharp-edged measuring spot MFL there .
  • the two mirrors are mounted on a common support with a fixed relative spatial relationship to one another.
  • the mirror arrangement as a whole can be displaced in different rigid body degrees of freedom using suitable actuators, for example parallel to a reference axis of the beam shaping unit running in the x direction between light entry and light exit or perpendicular to this axis.
  • a rotation of the entire mirror arrangement about a tilt axis located outside the mirror arrangement is also possible.
  • the actuators can be designed in such a way that the Wolter collector WK as a whole can be tilted about a tilting axis which runs perpendicular to the optical axis of the Wolter collector and which lies in the area of the exit gap SP of the monochromator (see FIG. 5).
  • the second imaging subsystem TS2 also comprises two mirrors S1 and S2 of a reflective manipulator MAN.
  • the first mirror S1 immediately following the exit slit SP is designed as a rotational ellipsoid mirror that has a first curvature in a first direction and a second curvature that is different from the first curvature in a direction perpendicular to it.
  • This ellipsoid mirror is the only reflective imaging element in the second subsystem.
  • a second mirror S2 is arranged at a distance behind the first mirror S1 and is designed as a plane mirror with a flat reflective surface that is used under a grazing incidence (angle of incidence with respect to the surface normal, e.g. greater than 60°, in particular from approx. 65° to approx. 89°).
  • the first mirror S1 remains stationary, i.e. is not manipulated in relation to the slit SP, while only the plane mirror S2 is tilted about a suitable tilt axis in order to move the measuring spot MFL to the desired location MFL'.
  • first mirror S1 and the second mirror S2 have a fixed spatial relationship to each other and the two mirrors as a whole are displaced with a rotational movement whose axis of rotation is in the near the gap SP. This can also shift the measuring spot MFL on the surface of the test object.
  • Fig. 5 with tilting of a Wolter collector WK about a tilting axis located within the exit gap SP combines the advantage of relatively low transmission losses (only two reflections) with the advantage of a high spot quality of the measuring spot MFL, which makes precise measurements possible.
  • Figures 6A and 6B each show in the left part of the figure a top view of a surface to be measured with the measuring spot formed there, which is square in the example.
  • the right partial figure shows an intensity profile through the center of the measuring spot MFL in the x direction.
  • the intensity of the EUV radiation occurs exclusively within a measuring spot MFL of a defined size.
  • the measuring spot size corresponds to the illuminated area, which in the example case may have an edge length of 600 pm.
  • the measuring spot MFL forms an optical image of the illuminated exit slit SP of the monochromator onto the test object surface OB.
  • the image quality of this image is of great importance for the quality of the measurement.
  • theoretical image spots BI-1 and BI-2, respectively are shown in FIGS. 6A and 6B within the measuring spot MFL, which are intended to illustrate the imaging quality.
  • an object point in the object plane of the imaging second subsystem which corresponds to the plane of the illuminated slit of the monochromator.
  • the sizes of the associated image spots illustrate how well the imaging system can generate an image point in the image plane (corresponding to the surface OB of the test object) from an object point.
  • the pixel With relatively good imaging quality (see Figure 6B), the pixel is relatively small. If, on the other hand, the image quality is poorer (FIG. 6A), a larger image spot BI-1 results.
  • the quality of the image (represented by the sizes of the image spots) causes a more or less severe smearing of the images of the edges of the object, i.e. the edges of the image of the exit slit of the monochromator.
  • the lateral extent of the smeared area with poor imaging ( Figure 6A) is larger than with good imaging ( Figure 6B).
  • the size of the measuring spot MFL is fixed for metrological reasons, if the image is poor (Fig. 6A), the size of the illuminated gap must be reduced so that the image of the exit gap (smeared at the edge) is within the permitted range of the measuring spot MFL remains. This results in the intensity profile shown on the right in Figure 6A with an intensity drop over a broader area at the edge of the measurement spot. If, on the other hand, the image quality is good (Fig. 6B), the smeared edge area becomes narrower. This can be used to work with a larger exit slit without intensity falling outside the desired measurement spot. This corresponds to better spot quality.
  • the better imaging quality therefore makes it possible to work with a larger exit slit SP, which means that more intensity can be accommodated within the specified limits of the measuring spot MFL. This can be seen on the right in Figure 6B from the steeper drop in intensity in edge areas. With better imaging quality, the permitted illuminated area of the exit slit is therefore larger. Since the exit slit is essentially homogeneously illuminated, a larger object field also delivers more power within the specified size of the measuring spot MFL in proportion to the area. This increased power in the area of the measuring spot contributes to greater measurement accuracy.
  • the reflective manipulator MAN within the second subsystem TS2 comprises a mirror arrangement in the manner of a Wolter collector WK, which is followed by a tiltable plane mirror PL.
  • a Wolter collector WK which is followed by a tiltable plane mirror PL.
  • Three reflections are therefore provided here in order to achieve the displacement of the measuring spot MFL. Since the Wolter collector offers high imaging quality and the plane mirror simply folds the beam path without changing the imaging properties, it can also be used to move a precisely defined measuring spot to the desired measuring point without changing the spot quality. However, losses in intensity are to be expected due to the additional reflection.
  • the mirrors of the second subsystem TS2 are then operated off-axis, which affects the spot quality.

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Abstract

Dans un procédé de mesure qui utilise un réflectomètre EUV pour mesurer la réflectivité d'un objet de test réfléchissant le rayonnement EUV (PR) en fonction de la longueur d'onde du rayonnement EUV et de l'angle d'incidence du rayonnement EUV sur une surface réfléchissante (OB) de l'objet de test, un faisceau de mesure (STR) dirigé sur la surface (OB) est généré à l'aide d'un rayonnement EUV grâce à un premier système partiel (TS1) qui comprend un monochromateur (MC) et fait partie d'une unité de mise en forme de faisceau (SFE) qui est utilisée pour effectuer l'imagerie un point de source d'émission de rayonnement EUV (QF) sur un espace de sortie (SP) du monochromateur et grâce à un second système partiel (TS2) de l'unité de mise en forme de faisceau qui est utilisée pour effectuer l'imagerie de l'espace de sortie sur la surface (OB) de l'objet de test (PR) afin de générer un point de mesure (MFL). Par rapport au faisceau de mesure (STR), l'objet de test (PR) est positionné dans de multiples degrés de liberté de telle sorte que, pendant le fonctionnement, le faisceau de mesure (STR) est incident sur la surface réfléchissante (OB) à un angle d'incidence pouvant être spécifié dans la région d'un point de mesure (MFL). Une propriété d'un faisceau réfléchi par la surface de l'objet de test est détectée au moyen d'un détecteur (DET), des signaux de détecteur représentant le rayonnement EUV réfléchi par l'objet d'essai étant générés. Ces signaux de détecteur sont évalués afin de déterminer des valeurs de mesure de réflectivité. Dans une opération de commande de direction de faisceau, la position du point de mesure sur la surface de l'objet de test est modifiée au moyen d'une modification contrôlée d'une direction de faisceau du faisceau de mesure (STR) grâce à un manipulateur réfléchissant (MAN) qui est formé par un premier miroir (S1) et, en aval de celui-ci dans la direction de faisceau, au moins un second miroir (S2) du second système partiel et grâce à ces miroirs qui sont déplacés de manière coordonnée les uns avec les autres dans au moins un degré de liberté de corps rigide en réponse à des signaux de commande provenant de l'unité de commande.
PCT/EP2023/075336 2022-09-29 2023-09-14 Procédé de mesure pour réflectométrie euv, et réflectomètre euv Ceased WO2024068294A1 (fr)

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