WO2021094048A1 - Method for aligning an interferometer, and projection exposure apparatus for semiconductor technology - Google Patents

Method for aligning an interferometer, and projection exposure apparatus for semiconductor technology Download PDF

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Publication number
WO2021094048A1
WO2021094048A1 PCT/EP2020/078713 EP2020078713W WO2021094048A1 WO 2021094048 A1 WO2021094048 A1 WO 2021094048A1 EP 2020078713 W EP2020078713 W EP 2020078713W WO 2021094048 A1 WO2021094048 A1 WO 2021094048A1
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WO
WIPO (PCT)
Prior art keywords
interferometer
measuring
location
measuring head
measuring beam
Prior art date
Application number
PCT/EP2020/078713
Other languages
German (de)
French (fr)
Inventor
Peter Nieland
Torsten STEINBRÜCK
Ulfert Wiesendahl
Robert Schomers
Christoph MANZ
Emanuel Grupp
Original Assignee
Carl Zeiss Smt Gmbh
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Application filed by Carl Zeiss Smt Gmbh filed Critical Carl Zeiss Smt Gmbh
Publication of WO2021094048A1 publication Critical patent/WO2021094048A1/en

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Classifications

    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/708—Construction of apparatus, e.g. environment aspects, hygiene aspects or materials
    • G03F7/7085—Detection arrangement, e.g. detectors of apparatus alignment possibly mounted on wafers, exposure dose, photo-cleaning flux, stray light, thermal load
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B9/00—Measuring instruments characterised by the use of optical techniques
    • G01B9/02—Interferometers
    • G01B9/02055—Reduction or prevention of errors; Testing; Calibration
    • G01B9/0207—Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer
    • G01B9/02072—Error reduction by correction of the measurement signal based on independently determined error sources, e.g. using a reference interferometer by calibration or testing of interferometer
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70216—Mask projection systems
    • G03F7/70258—Projection system adjustments, e.g. adjustments during exposure or alignment during assembly of projection system
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
    • G01B11/005—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates coordinate measuring machines
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B5/00—Measuring arrangements characterised by the use of mechanical techniques
    • G01B5/004—Measuring arrangements characterised by the use of mechanical techniques for measuring coordinates of points
    • G01B5/008—Measuring arrangements characterised by the use of mechanical techniques for measuring coordinates of points using coordinate measuring machines

Definitions

  • the invention relates to a method for aligning an interferometer and a projection exposure system for semiconductor technology.
  • Projection exposure systems for semiconductor technology have extremely high demands on the imaging accuracy in order to be able to produce the desired microscopic structures as error-free as possible.
  • the optical components used for imaging for the systems described above must be positioned with the greatest precision in order to be able to guarantee adequate imaging quality.
  • the functional principle of the above-mentioned systems is based on generating the finest structures down to the nanometer range by means of a scaled-down image of structures on a mask, with a so-called reticle, on an element to be structured provided with photosensitive material.
  • the minimum dimensions of the structures produced depend directly on the wavelength of the light used.
  • light sources with an emission wavelength in the range of a few nanometers for example between 5 nm and 120 nm, in particular in the range of 13.5 nm, have been used more and more.
  • the wavelength range described is also referred to as the EUV range.
  • the move into the EUV area means doing without refractive optics, which can no longer be used with this wavelength, and the transition to pure mirror systems.
  • the basic structure of the optical elements and their arrangement in the imaging optics have also changed, which has made the structure of a fixed reference, the so-called sensor frame, more difficult.
  • One solution to this problem is to use interferometers as sensors for positioning the optical elements.
  • Interferometers have the advantage that the distance between the measuring head and the reference element, usually a reference mirror, can be very large. This allows the sensor frame to be relatively compact, stiff and simple despite the new arrangement of the optical elements, since the sensor heads no longer have to be arranged in the immediate vicinity of the reference elements, as is the case with most other types of sensors, such as linear scales .
  • the measuring beam of the interferometer which is usually designed as a laser beam, must be aligned with the reference mirror so precisely that the reflected beam is reflected back into the measuring head. In systems such as projection exposure systems, for example, this can lead to a very complex assembly and adjustment process.
  • the optical elements and thus the reference mirrors are not yet mounted when the sensor frame is set up with the measuring heads of the interferometer, an initial adjustment of the measuring heads to the reference mirror is not possible.
  • the reason for this is that the assembly of the optical elements is very complex and the interferometers are not necessarily accessible when the optical elements are also mounted.
  • the object of the present invention is to provide a method and an apparatus which eliminates the disadvantages of the prior art described above.
  • a method for aligning at least one interferometer, wherein a measuring head of the interferometer is arranged on a reference component and wherein the reference component is a component of a projection exposure system for semiconductor lithography, comprises the following method steps:
  • the reference component can be designed as a sensor frame of a projection exposure system and serve as a central reference for the optical elements of a projection optics of the projection exposure system.
  • the interferometers can be arranged on the sensor frame and detect the location and position of the optical elements, which are designed as mirrors, for example.
  • the interferometers comprise a measuring head which is arranged on the reference component and a reference mirror which is arranged on the optical element. The measuring head and the reference mirror must be very precisely aligned with one another.
  • the reference coordinate system of the reference component can be determined with a coordinate measuring machine.
  • the reference component designed as a sensor frame can be fixed on the base body of the coordinate measuring device and the position of the reference point of the sensor frame can be recorded with the coordinate measuring device.
  • the reference point is the origin of a reference coordinate system to which all other positions determined with the coordinate measuring machine are related.
  • the location and the position of the mechanical interface for the measuring head on the reference component can be taken into account.
  • the location and the position of the mechanical interface can be determined with the coordinate measuring machine.
  • the mechanical interface can be touched with a tactile or optical button on the coordinate measuring machine and in this way their position in the reference coordinate system can be determined, with the data being able to be stored, in particular, in a controller or database.
  • the location and direction of the measuring beam emitted by the measuring head of the interferometer can be determined in relation to one or more reference surfaces, for example surfaces on the measuring head that are in mechanical contact with surfaces of the sensor frame after the measuring head is screwed on are to be taken into account.
  • This data can consist of the deviation of the location and the direction with which the measuring beam is emitted from the housing of the measuring head of the interferometer and the deviation of the housing from the target geometry of the housing due to manufacturing tolerances.
  • the location and direction of the measuring beam emitted by the measuring head of the interferometer in relation to the reference surface of the measuring head can also be determined with the coordinate measuring machine, whereby the light beam is detected with an optical sensor or a camera instead of a tactile probe.
  • These data can often be made available by the manufacturers of the interferometers in the form of a data sheet.
  • At least one spacer can be arranged between the reference component and the measuring head of the interferometer.
  • the geometry of the spacer can be determined on the basis of the location and the position of the mechanical interface on the reference component and the location and the direction of the measuring beam of the measuring head of the interferometer in relation to the reference area of the measuring head.
  • the location and the direction of the measuring beam emitted by the measuring head of the interferometer can be determined in the reference coordinate system with an optical sensor.
  • the optical sensor can be designed, for example, as a camera, a four-quadrant diode or as an optical position sensor.
  • the optical sensor can be calibrated in the reference coordinate system of the coordinate measuring device.
  • the tactile button of the coordinate measuring machine used to determine the reference point of the sensor frame and the mechanical interfaces can be replaced by the optical sensor or an additional optical button can be mounted on the coordinate measuring machine. This is calibrated after being connected to the coordinate measuring machine, so that the measuring range of the optical sensor, that is, the area on which the measuring beam is incident, is known in the reference coordinate system.
  • the angle between the optical sensor and the target measuring beam can be set. This has the advantage that, via the known tilting of the optical sensor relative to the measuring beam, this can be taken into account when determining the location and the direction of the measuring beam depending on the location on the optical sensor on which the measuring beam impinges.
  • a measuring surface of the sensor can be set almost perpendicular to the target measuring beam.
  • almost is to be understood as an angle of 90 ° ⁇ 1.25 °. This has the advantage that the tilt can be neglected when determining the location and the direction of the measuring beam.
  • the direction of the measuring beam can thus be determined by at least two measurements at different points along the measuring beam. Using the two points that are absolutely known in the reference coordinate system, the location and direction of the measuring beam can be determined.
  • the location and direction of the measuring beam can be determined by a measurement.
  • the location and direction of the measuring beam can be measured by evaluating the near field and far field of the imaging of the measuring beam.
  • the optical sensor comprises at least two lenses which can be displaced to one another perpendicular to the optical axis.
  • One of the lenses can be coated with a special coating that creates so-called ghost images leads.
  • a partial reflection on the inside of the lens allows the image to be displayed twice, with the near field (without reflection on the lens) and the far field (with reflection on the lens) being displayed in one point when the lenses are centered on one another.
  • a projection exposure system according to the invention for semiconductor lithography comprises an interferometer with an accuracy of the alignment of the beam position on the reference mirror of less than 100 pm, in particular less than 50 pm, in particular less than 20 pm.
  • the distance between the measuring head of the interferometer and the reference mirror can be up to 1000mm, in particular up to 1500mm.
  • a projection exposure system according to the invention for semiconductor lithography comprises an interferometer with an accuracy of the alignment of the beam angle at the reference mirror of the interferometer of less than 500prad, in particular less than 250prad, in particular less than 100prad. Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. Show it
  • Figure 1 shows the basic structure of a projection exposure system in which the invention can be implemented
  • Figure 2 shows the basic structure of a projection optics in which the invention can be realized ver
  • FIG. 3 shows a coordinate measuring machine with which the invention can be implemented
  • FIG. 4 shows a coordinate measuring machine with which the invention can be implemented
  • FIG. 5 shows a flow chart for a method according to the invention.
  • FIG. 1 shows an example of the basic structure of an EUV projection exposure system 1 for microlithography, in which the invention can be used.
  • an illumination system of the projection exposure system 1 has illumination optics 4 for illuminating an object field 5 in an object plane 6.
  • EUV radiation 14 generated by light source 3 as useful optical radiation is aligned by means of a collector integrated in light source 3 in such a way that it passes through an intermediate focus in the area of an intermediate focus plane 15 before it hits a field facet mirror 2.
  • the EUV radiation 14 is reflected by a pupil facet mirror 16.
  • the pupil facet mirror 16 and an optical assembly 17 with mirrors 18, 19 and 20 field facets of the field facet mirror 2 are imaged in the object field 5.
  • a structure is imaged on the reticle 7 on a light-sensitive layer of a wafer 12 which is arranged in the area of the image field 10 in the image plane 11 and which is held by a wafer holder 13, which is also shown in detail.
  • the light source 3 can emit useful radiation preferably in a wavelength range between 5 nm and 120 nm, particularly preferably 13.5 nm.
  • a DUV system is basically constructed like the EUV system 1 described above, whereby mirrors and lenses can be used as optical elements in a DUV system and the light source of a DUV system emits useful radiation in a wavelength range from 100 nm to 300 nm .
  • FIG. 2 shows a basic view of the projection optics 9 of the projection exposure system, in which a plurality of optical elements designed as mirrors 21 .x are arranged. The mirrors 21.x are arranged on a support frame (both not shown) via actuators, for example, and can be moved relative to this.
  • interferometers 22.x each of which includes a measuring head 23.x and a reference mirror 24.x.
  • the measuring heads 23.x are arranged on a sensor frame 26 which is decoupled from the environment via decoupling elements 25.
  • interferometer 22.x only one interferometer 22.x was shown per mirror 21.x, the location and position of the mirror 21 .x being recorded in up to 6 degrees of freedom by interferometer 22.x.
  • the distance between the measuring heads 23.x arranged on the sensor frame 26 and the respective reference mirror 24.x of the interferometer 22.x on the mirror 21.x varies greatly.
  • the measuring heads 23.x of the interferometer 22.x which are arranged on the sensor frame 26, together with the reference mirrors 24.x.
  • a special procedure must therefore be used for the assembly and adjustment of the measuring heads 23.x of the interferometer 22.x on the sensor frame 26.
  • FIG. 3 shows a coordinate measuring device 29 with a stand 31 which is connected to an arm 32 via a swivel joint 35.1.
  • the arm 32 comprises a vertical arm 33 and a pivot arm 34, which are also connected by a Drehschwenkge joint 35.2.
  • the coordinate measuring device 29 is arranged on a base frame 30 and can alternatively also be designed as a portal measuring machine.
  • the sensor frame 26 is also fixed on the base frame 30 and arranged in such a way that the button 37, which is arranged on the swivel arm 34 of the arm 32 via a connection 38 and a further swivel joint 35.3, each mechanical interface 28.x for fastening the measuring heads reach the interferometer can.
  • the mechanical reference point 36 of the sensor frame 26 is measured and a reference coordinate system 27 is determined.
  • the location and the position of the mechanical interfaces 28.x for fastening the measuring heads of the interferometers in the reference coordinate system 27 are determined using the button 37, as shown by dashed lines in the figure for the mechanical interface 28.1.
  • These data are stored together, in particular, in a controller or database (not shown).
  • the control or database is also supplied with the data provided by the manufacturer of the interferometer on the deviation of the geometry of the measuring head from the target geometry and the deviation of the location and direction with which the measuring beam leaves the housing of the measuring head.
  • the geometry of the spacers is then calculated in order to compensate for the deviations caused by manufacturing and assembly tolerances Correct target values.
  • FIG. 4 shows a coordinate measuring device 29 with a camera 39 instead of the tactile button 37 shown in FIG. 3, which in turn is connected to the pivot arm 34 of the arm 32 of the coordinate measuring device 29 via the connection 38 and the joint 35.3.
  • the arm 32 is otherwise identical to the arm 32 described in FIG. 3 and is not described further here.
  • only one measuring head 23.1 of one of the interferometers is shown, which is connected to the mechanical interface 28.1 of the sensor frame 26 with the initial spacer 40.1.
  • the camera 39 is arranged opposite the measuring beam 41.1 emitted by the measuring head 23.1 in such a way that the measuring beam 41.1 strikes a CCD chip arranged in the camera 39 almost perpendicularly, i.e. at an angle of 90 ° ⁇ 1.25 °.
  • the same measurement is then repeated, the distance between the camera 39 to the measuring head 23.1 differs from that of the first measurement.
  • the camera 39 is moved along the emitted measuring beam 41.1 and carries out no or almost no movement perpendicular to the emitted measuring beam 41.1, whereby the angle of the camera 39 is identical for both measurements and therefore when calculating the measuring point by the camera 39 can be neglected or has no influence on the position of the measuring point.
  • the camera 39 is calibrated in such a way that the measuring range of the camera 39 in the reference coordinate system 27 is absolutely known, which means that the measuring point, i.e. the pixel on the CCD chip of the camera 39, which is in the center of the image of the measuring beam on the CCD
  • the point of light shown on the chip is absolutely known.
  • two points of the measuring beam 41 in the reference coordinate system 27 are known, from which the location and direction of the measuring beam 41 in the reference coordinate system 27 can be determined and compared with the target value.
  • the spacers 40.1 are exchanged with adapted spacers 40.2 if necessary.
  • the determination of the location and the direction of the emitted measuring beams 41.x and an adjustment of the spacers 40.x are repeated until all the measuring beams 41.x correspond to the target values within the tolerance.
  • the deviation can also be determined by intersecting the determined measuring beams 41 .x with a target which is arranged at the desired location of the respective reference mirror used later in the system with a desired direction. In this case, the camera can also serve as the target. The deviations must be calculated back to the interferometer.
  • FIG. 5 shows a flow chart of a method for aligning an interferometer 22.x, the measuring head 23.x of the interferometer 22.x being arranged on a reference component 26.
  • a first method step 51 the reference coordinate system 27 of the reference component 26 is determined.
  • a second method step 52 the measuring head 23.x of the interferometer 22.x is mounted.
  • a third method step 53 the location and the direction of the measuring beam 41.x emitted by the measuring head 23.x of the interferometer 22.x are determined in the reference coordinate system 27.
  • a deviation between the specific location and the specific direction of the measuring beam 41.x compared to a target location and a target direction of the measuring beam 41.x is determined.
  • a fifth method step 55 the measuring head 23.x of the interferometer 22.x is aligned on the basis of the deviation determined in the previous step.
  • a sixth method step 56 method steps three to five are repeated until the location and the direction correspond to the target value within the limits of the tolerances.

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  • Engineering & Computer Science (AREA)
  • Environmental & Geological Engineering (AREA)
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  • Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)
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Abstract

The invention relates to a method for aligning at least one measuring head (23.x) of an interferometer (22.x), wherein the measuring head (23.x) of the interferometer (22.x) is arranged on a reference component (26), wherein the reference component (26) is a component of a projection exposure apparatus (1) for semiconductor lithography and wherein the method comprises the following method steps: - determining the reference coordinate system (27) of the reference component (26), - mounting the measuring head (23.x) of the interferometer (22.x), - determining, in the reference coordinate system (27), the location and the direction of the measurement beam (41.x) emitted by the measuring head (23.x) of the interferometer (22.x), - determining a deviation between the measured location and the direction of the measurement beam (41.x) vis-à-vis a target location and a target direction of the measurement beam (41.x), - aligning the measuring head (23.x) of the interferometer (22.x) on the basis of the deviation determined in the preceding step, and - repeating method steps three to five, until the location and the direction of the measurement beam (41.x) correspond to the target value within the scope of the tolerance. Furthermore, the invention relates to a projection exposure apparatus (1) for semiconductor lithography, comprising an interferometer (22.x) with an accuracy of the alignment of the beam position at the reference mirror (24.x) within 100 µm, in particular within 50 µm, in particular within 20 µm. Furthermore, the invention relates to a projection exposure apparatus (1) for semiconductor lithography, comprising an interferometer (22.x) with an accuracy of the alignment of the beam angle at the reference mirror (24.x) of the interferometer (22.x) within 500 µrad, in particular within 250 µrad, in particular within 100 µrad.

Description

Verfahren zur Ausrichtung eines Interferometers und Proiektionsbelichtungsanlage für die Halbleitertechnik Method for aligning an interferometer and projection exposure system for semiconductor technology
Diese Anmeldung nimmt die Priorität der deutschen Patentanmeldung 10 2019 217 629.1 vom 15.11.2019 in Anspruch, deren Inhalt hierin vollumfänglich durch Bezug nahme aufgenommen wird. This application claims the priority of German patent application 10 2019 217 629.1 dated November 15, 2019, the content of which is incorporated herein by reference.
Die Erfindung betrifft ein Verfahren zur Ausrichtung eines Interferometers und eine Projektionsbelichtungsanlage für die Halbleitertechnik. The invention relates to a method for aligning an interferometer and a projection exposure system for semiconductor technology.
Projektionsbelichtungsanlagen für die Halbleitertechnik haben extrem hohe Anforde rungen an die Abbildungsgenauigkeit, um die gewünschten mikroskopisch kleinen Strukturen möglichst fehlerfrei hersteilen zu können. Die zur Abbildung verwendeten optischen Komponenten für die oben beschriebenen Anlagen müssen mit höchster Präzision positioniert werden, um eine ausreichende Abbildungsqualität gewährleis ten zu können. Das Funktionsprinzip der genannten Anlagen beruht dabei darauf, mittels einer verkleinernden Abbildung von Strukturen auf einer Maske, mit einem so genannten Reticle, auf einem mit photosensitivem Material versehenen zu strukturie renden Element, feinste Strukturen bis in den Nanometerbereich zu erzeugen. Die minimalen Abmessungen der erzeugten Strukturen hängen dabei direkt von der Wel lenlänge des verwendeten Lichtes ab. In jüngerer Zeit werden vermehrt Lichtquellen mit einer Emissionswellenlänge im Bereich weniger Nanometer, beispielsweise zwi schen 5 nm und 120 nm, insbesondere im Bereich von 13,5 nm verwendet. Der be schriebene Wellenlängenbereich wird auch als EUV-Bereich bezeichnet. Der Schritt in den EUV-Bereich bedeutet den Verzicht auf refraktive Optiken, die bei dieser Wel lenlänge nicht mehr einsetzbar sind und den Übergang zu reinen Spiegelsystemen. Dadurch haben sich auch der prinzipielle Aufbau der optischen Elemente und deren Anordnung in der Abbildungsoptik geändert, wodurch sich der Aufbau einer festen Referenz, des sogenannten Sensorrahmens, erschwert hat. Eine Lösung dieses Problems ist die Verwendung von Interferometern als Sensoren für die Positionierung der optischen Elemente. Interferometer haben den Vorteil, dass die Entfernung zwischen dem Messkopf und dem Referenzelement, üblicherweise einem Referenzspiegel, sehr groß sein kann. Dadurch kann der Sensorrahmen trotz der neuen Anordnung der optischen Elemente relativ kompakt, steif und einfach ge staltet werden, da die Sensorköpfe nicht mehr, wie bei den meisten anderen Arten von Sensoren, wie beispielsweise Linearmaßstäben, unmittelbar in der Nähe der Re ferenzelemente angeordnet sein müssen. Der üblicherweise als Laserstrahl ausgebil dete Messstrahl des Interferometers muss dabei zum Referenzspiegel so genau ausgerichtet werden, dass der reflektierte Strahl in den Messkopf zurück reflektiert wird. Dies kann bei Systemen, wie beispielsweise bei Projektionsbelichtungsanlagen, zu einem sehr komplexen Montage- und Justageverfahren führen. Da beim Aufbau des Sensorrahmens mit den Messköpfen des Interferometers die optischen Elemente und damit die Referenzspiegel noch nicht montiert sind, ist eine initiale Justage der Messköpfe zum Referenzspiegel nicht möglich. Grund dafür ist, dass die Montage der optischen Elemente sehr aufwendig ist und die Interferometer nicht zwangsläufig zugänglich sind, wenn die optischen Elemente ebenfalls montiert sind. Projection exposure systems for semiconductor technology have extremely high demands on the imaging accuracy in order to be able to produce the desired microscopic structures as error-free as possible. The optical components used for imaging for the systems described above must be positioned with the greatest precision in order to be able to guarantee adequate imaging quality. The functional principle of the above-mentioned systems is based on generating the finest structures down to the nanometer range by means of a scaled-down image of structures on a mask, with a so-called reticle, on an element to be structured provided with photosensitive material. The minimum dimensions of the structures produced depend directly on the wavelength of the light used. More recently, light sources with an emission wavelength in the range of a few nanometers, for example between 5 nm and 120 nm, in particular in the range of 13.5 nm, have been used more and more. The wavelength range described is also referred to as the EUV range. The move into the EUV area means doing without refractive optics, which can no longer be used with this wavelength, and the transition to pure mirror systems. As a result, the basic structure of the optical elements and their arrangement in the imaging optics have also changed, which has made the structure of a fixed reference, the so-called sensor frame, more difficult. One solution to this problem is to use interferometers as sensors for positioning the optical elements. Interferometers have the advantage that the distance between the measuring head and the reference element, usually a reference mirror, can be very large. This allows the sensor frame to be relatively compact, stiff and simple despite the new arrangement of the optical elements, since the sensor heads no longer have to be arranged in the immediate vicinity of the reference elements, as is the case with most other types of sensors, such as linear scales . The measuring beam of the interferometer, which is usually designed as a laser beam, must be aligned with the reference mirror so precisely that the reflected beam is reflected back into the measuring head. In systems such as projection exposure systems, for example, this can lead to a very complex assembly and adjustment process. Since the optical elements and thus the reference mirrors are not yet mounted when the sensor frame is set up with the measuring heads of the interferometer, an initial adjustment of the measuring heads to the reference mirror is not possible. The reason for this is that the assembly of the optical elements is very complex and the interferometers are not necessarily accessible when the optical elements are also mounted.
Aufgabe der vorliegenden Erfindung ist es, ein Verfahren und eine Vorrichtung anzu geben, welche die oben beschriebenen Nachteile des Standes der Technik beseiti gen. The object of the present invention is to provide a method and an apparatus which eliminates the disadvantages of the prior art described above.
Diese Aufgabe wird gelöst durch ein Verfahren und eine Vorrichtung mit den Merk malen der unabhängigen Ansprüche. Die Unteransprüche betreffen vorteilhafte Wei terbildungen und Varianten der Erfindung. This object is achieved by a method and a device with the characteristics of the independent claims. The subclaims relate to advantageous developments and variants of the invention.
Ein erfindungsgemäßes Verfahren zur Ausrichtung mindestens eines Interferome ters, wobei ein Messkopf des Interferometers auf einem Referenzbauteilangeordnet ist und wobei es sich bei dem Referenzbauteil um ein Bauteil einer Projektionsbelich tungsanlage für die Halbleiterlithographie handelt, umfasst folgende Verfahrens schritte: A method according to the invention for aligning at least one interferometer, wherein a measuring head of the interferometer is arranged on a reference component and wherein the reference component is a component of a projection exposure system for semiconductor lithography, comprises the following method steps:
- Bestimmung des Referenzkoordinatensystems des Referenzbauteils - Determination of the reference coordinate system of the reference component
- Montage des Messkopfes des Interferometers - Bestimmung des Ortes und der Richtung des von dem Messkopf des Interferome ters emittierten Messstrahls im Referenzkoordinatensystem - Assembly of the measuring head of the interferometer - Determination of the location and the direction of the measuring beam emitted by the measuring head of the interferometer in the reference coordinate system
- Bestimmung einer Abweichung zwischen dem gemessenen Ort und der Richtung des Messstrahls gegenüber einem Soll-Ort und einer Soll-Richtung des Messstrahls - Determination of a deviation between the measured location and the direction of the measuring beam compared to a target location and a target direction of the measuring beam
- Ausrichtung des Messkopfes des Interferometers auf Basis der im vorherigen Schritt bestimmten Abweichung - Alignment of the measuring head of the interferometer based on the deviation determined in the previous step
- Wiederholung der Verfahrensschritte drei bis fünf, bis der Ort und die Richtung des Messstrahls im Rahmen der Toleranz dem Soll-Wert entsprechen. - Repetition of process steps three to five until the location and direction of the measuring beam correspond to the target value within the tolerance.
Das Referenzbauteil kann als Sensorrahmen einer Projektionsbelichtungsanlage ausgebildet sein und als zentrale Referenz für die optischen Elemente einer Projekti onsoptik der Projektionsbelichtungsanlage dienen. Die Interferometer können an dem Sensorrahmen angeordnet sein und der Ort und die Lage der optischen Ele mente, die beispielsweise als Spiegel ausgebildet sind, erfassen. Die Interferometer umfassen einen Messkopf, welcher am Referenzbauteil angeordnet ist und einen Re ferenzspiegel, welcher an dem optischen Element angeordnet sind. Der Messkopf und der Referenzspiegel müssen dabei sehr genau zueinander ausgerichtet sein. The reference component can be designed as a sensor frame of a projection exposure system and serve as a central reference for the optical elements of a projection optics of the projection exposure system. The interferometers can be arranged on the sensor frame and detect the location and position of the optical elements, which are designed as mirrors, for example. The interferometers comprise a measuring head which is arranged on the reference component and a reference mirror which is arranged on the optical element. The measuring head and the reference mirror must be very precisely aligned with one another.
Insbesondere kann das Referenzkoordinatensystem des Referenzbauteils mit einem Koordinatenmessgerät bestimmt werden. Dazu kann das als Sensorrahmen ausge bildete Referenzbauteil auf dem Grundkörper des Koordinatenmessgerätes fixiert werden und die Position des Referenzpunktes des Sensorrahmens mit dem Koordi natenmessgerät erfasst werden. Der Referenzpunkt ist der Ursprung eines Referenz koordinatensystems, auf welches alle weiteren mit dem Koordinatenmessgerät bestimmten Positionen bezogen werden. In particular, the reference coordinate system of the reference component can be determined with a coordinate measuring machine. For this purpose, the reference component designed as a sensor frame can be fixed on the base body of the coordinate measuring device and the position of the reference point of the sensor frame can be recorded with the coordinate measuring device. The reference point is the origin of a reference coordinate system to which all other positions determined with the coordinate measuring machine are related.
Weiterhin können bei der Montage des Messkopfes des Interferometers der Ort und die Lage der mechanischen Schnittstelle für den Messkopf am Referenzbauteil be rücksichtigt werden. Furthermore, when mounting the measuring head of the interferometer, the location and the position of the mechanical interface for the measuring head on the reference component can be taken into account.
Insbesondere können der Ort und die Lage der mechanischen Schnittstelle mit dem Koordinatenmessgerät bestimmt werden. Dazu kann die mechanische Schnittstelle mit einem taktilen oder optischen Taster des Koordinatenmessgerätes angetastet und so deren Position im Referenzkoordinatensystem bestimmt werden, wobei die Daten insbesondere in einer Steuerung oder Datenbank abgespeichert werden kön nen. In particular, the location and the position of the mechanical interface can be determined with the coordinate measuring machine. For this purpose, the mechanical interface can be touched with a tactile or optical button on the coordinate measuring machine and in this way their position in the reference coordinate system can be determined, with the data being able to be stored, in particular, in a controller or database.
Daneben können bei der Montage des Messkopfes des Interferometers der Ort und die Richtung des vom Messkopf des Interferometers emittierten Messstrahls in Be zug auf eine oder mehrere Referenzflächen, also beispielsweise Flächen am Mess kopf, die nach dem Anschrauben des Messkopfes mit Flächen des Sensorrahmens in mechanischem Kontakt stehen, berücksichtigt werden. Diese Daten können sich aus der Abweichung des Ortes und der Richtung, mit der der Messstrahl aus dem Gehäuse des Messkopfes des Interferometers emittiert wird und der Abweichung des Gehäuses gegenüber der Soll-Geometrie des Gehäuses auf Grund von Fertigungsto leranzen zusammen setzen. Der Ort und die Richtung des vom Messkopf des Interfe rometers emittierten Messstrahls in Bezug auf die Referenzfläche des Messkopfes können ebenfalls mit dem Koordinatenmessgerät bestimmt werden, wobei dabei der Lichtstrahl mit einem optischen Sensor oder einer Kamera anstelle eines taktilen Tasters erfasst wird. Diese Daten können häufig von den Herstellern der Interferome ter in Form eines Datenblatts zur Verfügung gestellt werden. In addition, when mounting the measuring head of the interferometer, the location and direction of the measuring beam emitted by the measuring head of the interferometer can be determined in relation to one or more reference surfaces, for example surfaces on the measuring head that are in mechanical contact with surfaces of the sensor frame after the measuring head is screwed on are to be taken into account. This data can consist of the deviation of the location and the direction with which the measuring beam is emitted from the housing of the measuring head of the interferometer and the deviation of the housing from the target geometry of the housing due to manufacturing tolerances. The location and direction of the measuring beam emitted by the measuring head of the interferometer in relation to the reference surface of the measuring head can also be determined with the coordinate measuring machine, whereby the light beam is detected with an optical sensor or a camera instead of a tactile probe. These data can often be made available by the manufacturers of the interferometers in the form of a data sheet.
Weiterhin kann bei der Montage des Messkopfes des Interferometers zwischen dem Referenzbauteil und dem Messkopf des Interferometers mindestens ein Spacer an geordnet sein. Furthermore, during the assembly of the measuring head of the interferometer, at least one spacer can be arranged between the reference component and the measuring head of the interferometer.
Insbesondere kann die Geometrie des Spacers auf Basis des Ortes und der Lage der mechanischen Schnittstelle am Referenzbauteil und dem Ort und der Richtung des Messstrahls des Messkopfes des Interferometers in Bezug auf die Referenzflä che des Messkopfes festgelegt werden. Durch die Verwendung eines solchen Spa cers, der auch als initialer Spacer bezeichnet werden kann, können bereits vor der ersten Messung Fertigungstoleranzen vorteilhaft kompensiert werden. In particular, the geometry of the spacer can be determined on the basis of the location and the position of the mechanical interface on the reference component and the location and the direction of the measuring beam of the measuring head of the interferometer in relation to the reference area of the measuring head. By using such a spacer, which can also be referred to as an initial spacer, manufacturing tolerances can be advantageously compensated for even before the first measurement.
Weiterhin können der Ort und die Richtung des vom Messkopf des Interferometers emittierten Messstrahls im Referenzkoordinatensystem mit einem optischen Sensor bestimmt werden. Dabei kann der optische Sensor beispielsweise als eine Kamera, eine Vier-Quadranten-Diode oder als ein optischer Positionssensor ausgebildet sein. Insbesondere kann der optische Sensor im Referenzkoordinatensystem des Koordi natenmessgerätes kalibriert sein. Dazu kann der für die Bestimmung des Referenz punktes des Sensorrahmens und der mechanischen Schnittstellen verwendete taktile Taster des Koordinatenmessgerätes durch den optischen Sensor ersetzt werden o- der ein zusätzlicher optischer Taster an dem Koordinatenmessgerät montiert werden. Dieser wird nach dem Verbinden mit dem Koordinatenmessgerät kalibriert, so dass der Messbereich des optischen Sensors, also derjenige Bereich, auf welchen der Messstrahl einfällt, in dem Referenzkoordinatensystem bekannt ist. Furthermore, the location and the direction of the measuring beam emitted by the measuring head of the interferometer can be determined in the reference coordinate system with an optical sensor. In this case, the optical sensor can be designed, for example, as a camera, a four-quadrant diode or as an optical position sensor. In particular, the optical sensor can be calibrated in the reference coordinate system of the coordinate measuring device. For this purpose, the tactile button of the coordinate measuring machine used to determine the reference point of the sensor frame and the mechanical interfaces can be replaced by the optical sensor or an additional optical button can be mounted on the coordinate measuring machine. This is calibrated after being connected to the coordinate measuring machine, so that the measuring range of the optical sensor, that is, the area on which the measuring beam is incident, is known in the reference coordinate system.
Für die Messung des Ortes und der Richtung des Messstrahls kann der Winkel zwi schen dem optischen Sensor und dem Soll-Messstrahl eingestellt werden. Dies hat den Vorteil, dass über die bekannte Verkippung des optischen Sensors zum Mess strahl, diese bei der Bestimmung des Ortes und der Richtung des Messstrahls in Ab hängigkeit des Ortes auf dem optischen Sensor, auf dem der Messstrahl auftrifft, berücksichtigt werden kann. To measure the location and direction of the measuring beam, the angle between the optical sensor and the target measuring beam can be set. This has the advantage that, via the known tilting of the optical sensor relative to the measuring beam, this can be taken into account when determining the location and the direction of the measuring beam depending on the location on the optical sensor on which the measuring beam impinges.
Insbesondere kann eine Messfläche des Sensors nahezu senkrecht zum Soll-Mess- strahl eingestellt werden. Unter nahezu ist in diesem Zusammenhang ein Winkel von 90°±1 ,25° zu verstehen. Dies hat den Vorteil, dass die Verkippung bei der Bestim mung des Ortes und der Richtung des Messstrahls vernachlässigt werden kann. In particular, a measuring surface of the sensor can be set almost perpendicular to the target measuring beam. In this context, almost is to be understood as an angle of 90 ° ± 1.25 °. This has the advantage that the tilt can be neglected when determining the location and the direction of the measuring beam.
Somit kann die Richtung des Messstrahls durch mindestens zwei Messungen an ver schiedenen Punkten entlang des Messstrahls bestimmt werden. Anhand der zwei Punkte, die im Referenzkoordinatensystem absolut bekannt sind, können der Ort und die Richtung des Messstrahls bestimmt werden. The direction of the measuring beam can thus be determined by at least two measurements at different points along the measuring beam. Using the two points that are absolutely known in the reference coordinate system, the location and direction of the measuring beam can be determined.
Daneben können der Ort und die Richtung des Messstrahls durch eine Messung be stimmt werden. In addition, the location and direction of the measuring beam can be determined by a measurement.
Insbesondere kann die Messung des Ortes und der Richtung des Messstrahls durch die Auswertung von Nahfeld und Fernfeld der Abbildung des Messstrahls vorgenom men werden. Dabei umfasst der optische Sensor mindestens zwei Linsen, die senk recht zur optischen Achse zueinander verschiebbar sind. Eine der Linsen kann mit einer speziellen Beschichtung beschichtet sein, die zu sogenannten Geisterbildern führt. Dabei kann durch eine Teilreflexion an der Innenseite der Linse das Bild zwei mal abgebildet werden, wobei das Nahfeld (ohne Reflexion an der Linse) und das Fernfeld (mit Reflexion an der Linse) bei zueinander zentrierten Linsen in einem Punkt abgebildet werden. Werden die Linsen nun senkrecht zur optischen Achse ver- schoben, so verschieben sich auch die Abbildungen des Nahfeldes und des Fernfel des, wodurch anhand des Abstandes der beiden Abbildungen der Winkel des Messstrahls zur optischen Achse bestimmt werden kann. Die Beschichtung der einen Linse kann dabei so angepasst werden, dass die Intensitäten der beiden Abbildun gen im Nahfeld und im Fernfeld nahezu gleich sind. Eine erfindungsgemäße Projektionsbelichtungsanlage für die Halbleiterlithographie umfasst ein Interferometer mit einer Genauigkeit der Ausrichtung der Strahlposition am Referenzspiegel von kleiner als 100pm, insbesondere kleiner 50pm, insbeson dere kleiner 20pm. Der Abstand zwischen dem Messkopf des Interferometers und dem Referenzspiegel kann dabei bis zu 1000mm, insbesondere bis zu 1500mm be- tragen. In particular, the location and direction of the measuring beam can be measured by evaluating the near field and far field of the imaging of the measuring beam. The optical sensor comprises at least two lenses which can be displaced to one another perpendicular to the optical axis. One of the lenses can be coated with a special coating that creates so-called ghost images leads. A partial reflection on the inside of the lens allows the image to be displayed twice, with the near field (without reflection on the lens) and the far field (with reflection on the lens) being displayed in one point when the lenses are centered on one another. If the lenses are now shifted perpendicular to the optical axis, the images of the near field and the far field are also shifted, whereby the angle of the measuring beam to the optical axis can be determined based on the distance between the two images. The coating of one lens can be adapted so that the intensities of the two images in the near field and in the far field are almost the same. A projection exposure system according to the invention for semiconductor lithography comprises an interferometer with an accuracy of the alignment of the beam position on the reference mirror of less than 100 pm, in particular less than 50 pm, in particular less than 20 pm. The distance between the measuring head of the interferometer and the reference mirror can be up to 1000mm, in particular up to 1500mm.
Eine erfindungsgemäße Projektionsbelichtungsanlage für die Halbleiterlithographie umfasst ein Interferometer mit einer Genauigkeit der Ausrichtung des Strahlwinkels am Referenzspiegel des Interferometers kleiner 500prad insbesondere kleiner 250prad, insbesondere kleiner 100prad sein. Nachfolgend werden Ausführungsbeispiele und Varianten der Erfindung anhand der Zeichnung näher erläutert. Es zeigen A projection exposure system according to the invention for semiconductor lithography comprises an interferometer with an accuracy of the alignment of the beam angle at the reference mirror of the interferometer of less than 500prad, in particular less than 250prad, in particular less than 100prad. Exemplary embodiments and variants of the invention are explained in more detail below with reference to the drawing. Show it
Figur 1 den prinzipieller Aufbau einer Projektionsbelichtungsanlage in der die Erfindung verwirklicht sein kann, Figure 1 shows the basic structure of a projection exposure system in which the invention can be implemented,
Figur 2 den prinzipiellen Aufbau einer Projektionsoptik, in der die Erfindung ver wirklicht sein kann, Figure 2 shows the basic structure of a projection optics in which the invention can be realized ver,
Figur 3 ein Koordinatenmessgerät, mit der die Erfindung verwirklicht sein kann,FIG. 3 shows a coordinate measuring machine with which the invention can be implemented,
Figur 4 ein Koordinatenmessgerät, mit der die Erfindung verwirklicht sein kann, und Figur 5 ein Flussdiagramm zu einem erfindungsgemäßem Verfahren. FIG. 4 shows a coordinate measuring machine with which the invention can be implemented, and FIG. 5 shows a flow chart for a method according to the invention.
Figur 1 zeigt exemplarisch den prinzipiellen Aufbau einer EUV- Projektionsbelichtungsanlage 1 für die Mikrolithographie, in welcher die Erfindung Anwendung finden kann. Ein Beleuchtungssystem der Projektionsbelichtungsanlage 1 weist neben einer Lichtquelle 3 eine Beleuchtungsoptik 4 zur Beleuchtung eines Objektfeldes 5 in einer Objektebene 6 auf. Eine durch die Lichtquelle 3 erzeugte EUV-Strahlung 14 als optische Nutzstrahlung wird mittels eines in der Lichtquelle 3 integrierten Kollektors derart ausgerichtet, dass sie im Bereich einer Zwischenfokus ebene 15 einen Zwischenfokus durchläuft, bevor sie auf einen Feldfacettenspiegel 2 trifft. Nach dem Feldfacettenspiegel 2 wird die EUV-Strahlung 14 von einem Pupillen facettenspiegel 16 reflektiert. Unter Zuhilfenahme des Pupillenfacettenspiegels 16 und einer optischen Baugruppe 17 mit Spiegeln 18, 19 und 20 werden Feldfacetten des Feldfacettenspiegels 2 in das Objektfeld 5 abgebildet. FIG. 1 shows an example of the basic structure of an EUV projection exposure system 1 for microlithography, in which the invention can be used. In addition to a light source 3, an illumination system of the projection exposure system 1 has illumination optics 4 for illuminating an object field 5 in an object plane 6. EUV radiation 14 generated by light source 3 as useful optical radiation is aligned by means of a collector integrated in light source 3 in such a way that it passes through an intermediate focus in the area of an intermediate focus plane 15 before it hits a field facet mirror 2. After the field facet mirror 2, the EUV radiation 14 is reflected by a pupil facet mirror 16. With the aid of the pupil facet mirror 16 and an optical assembly 17 with mirrors 18, 19 and 20, field facets of the field facet mirror 2 are imaged in the object field 5.
Beleuchtet wird ein im Objektfeld 5 angeordnetes Retikel 7, das von einem schema tisch dargestellten Retikelhalter 8 gehalten wird. Eine lediglich schematisch darge stellte Projektionsoptik 9 dient zur Abbildung des Objektfeldes 5 in ein Bildfeld 10 in eine Bildebene 11 . Abgebildet wird eine Struktur auf dem Retikel 7 auf eine licht empfindliche Schicht eines im Bereich des Bildfeldes 10 in der Bildebene 11 ange ordneten Wafers 12, der von einem ebenfalls ausschnittsweise dargestellten Waferhalter 13 gehalten wird. Die Lichtquelle 3 kann Nutzstrahlung bevorzugt in ei nem Wellenlängenbereich zwischen 5 nm und 120 nm, besonders bevorzugt von 13,5nm emittieren. A reticle 7, which is arranged in the object field 5 and is held by a reticle holder 8 shown schematically, is illuminated. A projection optics 9, which is only shown schematically, is used to image the object field 5 in an image field 10 in an image plane 11. A structure is imaged on the reticle 7 on a light-sensitive layer of a wafer 12 which is arranged in the area of the image field 10 in the image plane 11 and which is held by a wafer holder 13, which is also shown in detail. The light source 3 can emit useful radiation preferably in a wavelength range between 5 nm and 120 nm, particularly preferably 13.5 nm.
Die Erfindung kann ebenso in einer DUV-Anlage verwendet werden, die nicht darge stellt ist. Eine DUV-Anlage ist prinzipiell wie die oben beschriebene EUV-Anlage 1 aufgebaut, wobei in einer DUV-Anlage Spiegel und Linsen als optische Elemente verwendet werden können und die Lichtquelle einer DUV-Anlage eine Nutzstrahlung in einem Wellenlängenbereich von 100 nm bis 300 nm emittiert. Figur 2 zeigt eine prinzipielle Ansicht der Projektionsoptik 9 der Projektionsbelich tungsanlage, in der mehrere als Spiegel 21 .x ausgebildete optische Elemente ange ordnet sind. Die Spiegel 21.x sind beispielsweise über Aktuatoren an einem Tragrahmen (beide nicht dargestellt) angeordnet und können relativ zu diesem be wegt werden. Der Ort und die Lage der Spiegel 21.x werden über Interferometer 22.x erfasst, die je einen Messkopf 23.x und einen Referenzspiegel 24.x umfassen. Die Messköpfe 23.x sind an einem Sensorrahmen 26, der gegenüber der Umgebung über Entkopplungselemente 25 entkoppelt ist, angeordnet. Aus Gründen der Über sichtlichkeit wurde nur ein Interferometer 22.x je Spiegel 21 .x dargestellt, wobei der Ort und die Lage der Spiegel 21 .x in bis zu 6 Freiheitsgraden durch Interferometer 22.x erfasst wird. Durch die räumliche Anordnung der Spiegel 21 .x, die durch das op tische Design vorgegeben ist, und durch das Bestreben, den Sensorrahmen 26 als Referenz für den Ort und die Lage der Messköpfe 23.x der Interferometer 22.x so steif wie möglich und daher auch so kompakt wie möglich zu gestalten, variiert der Abstand zwischen den am Sensorrahmen 26 angeordneten Messköpfen 23.x und dem jeweiligen Referenzspiegel 24.x der Interferometer 22.x am Spiegel 21.x stark. Im Rahmen der Montage der Projektionsoptik 9 ist es aus Gründen der Zugänglich keit und der Komplexität teilweise nicht möglich, die Messköpfe 23.x des Interferome ters 22.x, die auf dem Sensorrahmen 26 angeordnet sind, zusammen mit den Referenzspiegeln 24.x auf den Spiegeln 21 .x zu justieren oder auszurichten. Daher muss für die Montage und Justage der Messköpfe 23.x des Interferometers 22.x am Sensorrahmen 26 ein spezielles Verfahren verwendet werden. The invention can also be used in a DUV system that is not illustrated. A DUV system is basically constructed like the EUV system 1 described above, whereby mirrors and lenses can be used as optical elements in a DUV system and the light source of a DUV system emits useful radiation in a wavelength range from 100 nm to 300 nm . FIG. 2 shows a basic view of the projection optics 9 of the projection exposure system, in which a plurality of optical elements designed as mirrors 21 .x are arranged. The mirrors 21.x are arranged on a support frame (both not shown) via actuators, for example, and can be moved relative to this. The location and position of the mirrors 21.x are recorded by interferometers 22.x, each of which includes a measuring head 23.x and a reference mirror 24.x. The measuring heads 23.x are arranged on a sensor frame 26 which is decoupled from the environment via decoupling elements 25. For the sake of clarity, only one interferometer 22.x was shown per mirror 21.x, the location and position of the mirror 21 .x being recorded in up to 6 degrees of freedom by interferometer 22.x. Due to the spatial arrangement of the mirrors 21 .x, which is predetermined by the optical design, and the endeavor to make the sensor frame 26 as a reference for the location and position of the measuring heads 23.x of the interferometer 22.x as rigid as possible and Therefore, to make it as compact as possible, the distance between the measuring heads 23.x arranged on the sensor frame 26 and the respective reference mirror 24.x of the interferometer 22.x on the mirror 21.x varies greatly. As part of the assembly of the projection optics 9, for reasons of accessibility and complexity, it is sometimes not possible to mount the measuring heads 23.x of the interferometer 22.x, which are arranged on the sensor frame 26, together with the reference mirrors 24.x. To adjust or align mirrors 21 .x. A special procedure must therefore be used for the assembly and adjustment of the measuring heads 23.x of the interferometer 22.x on the sensor frame 26.
Figur 3 zeigt ein Koordinatenmessgerät 29 mit einem Stativ 31 , welches über ein Drehschwenkgelenk 35.1 mit einem Arm 32 verbunden ist. Der Arm 32 umfasst einen Vertikalarm 33 und einem Schwenkarm 34, die ebenfalls durch ein Drehschwenkge lenk 35.2 verbunden sind. Das Koordinatenmessgerät 29 ist auf einem Grundrahmen 30 angeordnet und kann alternativ auch als eine Portalmessmaschine ausgebildet sein. Auf dem Grundrahmen 30 ist ebenfalls der Sensorrahmen 26 fixiert und derart angeordnet, dass der Taster 37, der über eine Anbindung 38 und ein weiteres Dreh schwenkgelenk 35.3 am Schwenkarm 34 des Armes 32 angeordnet ist, jede mecha nische Schnittstelle 28.x zur Befestigung der Messköpfe der Interferometer erreichen kann. Zunächst wird der mechanische Referenzpunkt 36 des Sensorrahmens 26 ein gemessen und ein Referenzkoordinatensystem 27 bestimmt. Darauf folgend werden mit dem Taster 37 der Ort und die Lage der mechanischen Schnittstellen 28.x zur Befestigung der Messköpfe der Interferometer im Referenzkoordinatensystem 27 be stimmt, wie beispielhaft in der Figur für die mechanische Schnittstelle 28.1 gestrichelt dargestellt. Diese Daten werden insbesondere in einer nicht dargestellten Steuerung oder Datenbank zusammen abgelegt. Der Steuerung oder Datenbank werden auch die vom Hersteller der Interferometer zur Verfügung gestellten Daten über die Abwei chung der Geometrie des Messkopfes gegenüber der Sollgeometrie und die Abwei chung des Ortes und der Richtung, mit der der Messstrahl das Gehäuse des Messkopfes verlässt, zugeführt. Auf Basis aller Daten wird daraufhin die Geometrie der Spacer, der sogenannten initialen Spacer, die zwischen den Messköpfen der In terferometer und den mechanischen Schnittstellen 28.x des Sensorrahmens 26 an geordnet sind, berechnet, um die durch Fertigungs- und Montagetoleranzen bewirkten Abweichungen von den Soll-Werten zu korrigieren. FIG. 3 shows a coordinate measuring device 29 with a stand 31 which is connected to an arm 32 via a swivel joint 35.1. The arm 32 comprises a vertical arm 33 and a pivot arm 34, which are also connected by a Drehschwenkge joint 35.2. The coordinate measuring device 29 is arranged on a base frame 30 and can alternatively also be designed as a portal measuring machine. The sensor frame 26 is also fixed on the base frame 30 and arranged in such a way that the button 37, which is arranged on the swivel arm 34 of the arm 32 via a connection 38 and a further swivel joint 35.3, each mechanical interface 28.x for fastening the measuring heads reach the interferometer can. First, the mechanical reference point 36 of the sensor frame 26 is measured and a reference coordinate system 27 is determined. Subsequently, the location and the position of the mechanical interfaces 28.x for fastening the measuring heads of the interferometers in the reference coordinate system 27 are determined using the button 37, as shown by dashed lines in the figure for the mechanical interface 28.1. These data are stored together, in particular, in a controller or database (not shown). The control or database is also supplied with the data provided by the manufacturer of the interferometer on the deviation of the geometry of the measuring head from the target geometry and the deviation of the location and direction with which the measuring beam leaves the housing of the measuring head. On the basis of all the data, the geometry of the spacers, the so-called initial spacers, which are arranged between the measuring heads of the interferometer and the mechanical interfaces 28.x of the sensor frame 26, is then calculated in order to compensate for the deviations caused by manufacturing and assembly tolerances Correct target values.
Figur 4 zeigt ein Koordinatenmessgerät 29 mit einer Kamera 39 anstelle des in Figur 3 dargestellten taktilen Tasters 37, die wiederum über die Anbindung 38 und das Ge lenk 35.3 am Schwenkarm 34 des Arms 32 des Koordinatenmessgerätes 29 ange bunden ist. Der Arm 32 ist ansonsten identisch zu dem in Figur 3 beschriebenen Arm 32 ausgebildet und wird hier nicht weiter beschrieben. Aus Gründen der Übersicht lichkeit ist nur ein Messkopf 23.1 eines der Interferometer dargestellt, der mit dem ini tialen Spacer 40.1 mit der mechanischen Schnittstelle 28.1 des Sensorrahmens 26 verbunden ist. Die Kamera 39 ist derart gegenüber dem vom Messkopf 23.1 emittier ten Messstrahl 41.1 angeordnet, dass der Messstrahl 41.1 nahezu senkrecht, also in einem Winkel von 90° ± 1 ,25°, auf einen in der Kamera 39 angeordneten CCD-Chip auftrifft. Dies hat den Vorteil, dass der Winkel zwischen der Kamera 39 und dem emittierten Messstrahl 41.1 bei der Berechnung der Position des Messpunktes der Kamera 39 vernachlässigt werden kann. Dies bedeutet, dass die Verkippung klein genug ist, dass die durch den Winkel bewirkte elliptische Abbildung des emittierten Lichtstrahls 41.1 keinen Einfluss auf die Bestimmung des Messpunktes hat. Die glei che Messung wird anschließend wiederholt, wobei sich der Abstand der Kamera 39 zum Messkopf 23.1 von dem der ersten Messung unterscheidet. Dabei wird die Ka mera 39 entlang des emittierten Messstrahls 41.1 bewegt und führt dabei keine oder nahezu keine Bewegung senkrecht zu dem emittierten Messstrahl 41.1 aus, wodurch der Winkel der Kamera 39 bei beiden Messungen identisch ist und daher bei der Be rechnung des Messpunktes durch die Kamera 39 vernachlässigt werden kann bezie hungsweise keinen Einfluss auf die Lage des Messpunktes hat. Die Kamera 39 ist so kalibriert, dass der Messbereich der Kamera 39 im Referenzkoordinatensystem 27 absolut bekannt ist, womit auch der Messpunkt, also das Pixel auf dem CCD-Chip der Kamera 39, welcher im Zentrum des durch die Abbildung des Messstrahles auf den CCD-Chip abgebildeten Lichtpunktes liegt, absolut bekannt ist. Somit sind zwei Punkte des Messstrahls 41 im Referenzkoordinatensystem 27 bekannt, woraus der Ort und die Richtung des Messstrahls 41 im Referenzkoordinatensystem 27 be stimmt und mit dem Soll-Wert verglichen werden können. Nachdem für alle Mess köpfe 23.x die mindestens zwei Punkte und damit der Ort und die Richtung der Messstrahlen 41 .x bestimmt und mit den Soll-Werten verglichen wurden, werden bei Bedarf die Spacer 40.1 durch angepasste Spacer 40.2 ausgetauscht. Die Bestim mung des Ortes und der Richtung der emittierten Messstrahlen 41.x und eine Anpas sung der Spacer 40.x wird so lange wiederholt, bis alle Messstrahlen 41.x im Rahmen der Toleranz den Soll-Werten entsprechen. Alternativ kann die Abweichung auch durch einen Schnitt der ermittelten Messstrahlen 41 .x mit einem Target, wel ches am Soll-Ort des später im System verwendeten jeweiligen Referenzspiegels mit einer Soll-Richtung angeordnet ist, bestimmt werden. Als Target kann in diesem Fall auch die Kamera dienen. Die Abweichungen müssen dabei auf das Interferometer zurückgerechnet werden. FIG. 4 shows a coordinate measuring device 29 with a camera 39 instead of the tactile button 37 shown in FIG. 3, which in turn is connected to the pivot arm 34 of the arm 32 of the coordinate measuring device 29 via the connection 38 and the joint 35.3. The arm 32 is otherwise identical to the arm 32 described in FIG. 3 and is not described further here. For reasons of clarity, only one measuring head 23.1 of one of the interferometers is shown, which is connected to the mechanical interface 28.1 of the sensor frame 26 with the initial spacer 40.1. The camera 39 is arranged opposite the measuring beam 41.1 emitted by the measuring head 23.1 in such a way that the measuring beam 41.1 strikes a CCD chip arranged in the camera 39 almost perpendicularly, i.e. at an angle of 90 ° ± 1.25 °. This has the advantage that the angle between the camera 39 and the emitted measuring beam 41.1 can be neglected when calculating the position of the measuring point of the camera 39. This means that the tilt is small enough that the elliptical imaging of the emitted light beam 41.1 caused by the angle has no influence on the determination of the measuring point. The same measurement is then repeated, the distance between the camera 39 to the measuring head 23.1 differs from that of the first measurement. The camera 39 is moved along the emitted measuring beam 41.1 and carries out no or almost no movement perpendicular to the emitted measuring beam 41.1, whereby the angle of the camera 39 is identical for both measurements and therefore when calculating the measuring point by the camera 39 can be neglected or has no influence on the position of the measuring point. The camera 39 is calibrated in such a way that the measuring range of the camera 39 in the reference coordinate system 27 is absolutely known, which means that the measuring point, i.e. the pixel on the CCD chip of the camera 39, which is in the center of the image of the measuring beam on the CCD The point of light shown on the chip is absolutely known. Thus, two points of the measuring beam 41 in the reference coordinate system 27 are known, from which the location and direction of the measuring beam 41 in the reference coordinate system 27 can be determined and compared with the target value. After the at least two points and thus the location and direction of the measuring beams 41 .x have been determined for all measuring heads 23.x and compared with the target values, the spacers 40.1 are exchanged with adapted spacers 40.2 if necessary. The determination of the location and the direction of the emitted measuring beams 41.x and an adjustment of the spacers 40.x are repeated until all the measuring beams 41.x correspond to the target values within the tolerance. Alternatively, the deviation can also be determined by intersecting the determined measuring beams 41 .x with a target which is arranged at the desired location of the respective reference mirror used later in the system with a desired direction. In this case, the camera can also serve as the target. The deviations must be calculated back to the interferometer.
Figur 5 zeigt ein Flussdiagramm eines Verfahrens zur Ausrichtung eines Interferome ters 22.x, wobei der Messkopf 23.x des Interferometers 22.x auf einem Referenzbau teil 26 angeordnet ist. FIG. 5 shows a flow chart of a method for aligning an interferometer 22.x, the measuring head 23.x of the interferometer 22.x being arranged on a reference component 26.
In einem ersten Verfahrensschritt 51 wird das Referenzkoordinatensystem 27 des Referenzbauteils 26 bestimmt. In a first method step 51, the reference coordinate system 27 of the reference component 26 is determined.
In einem zweiten Verfahrensschritt 52 wird der Messkopf 23.x des Interferometers 22.x montiert. In einem dritten Verfahrensschritt 53 werden der Ort und die Richtung des von dem Messkopf 23.x des Interferometers 22.x emittierten Messstrahls 41.x im Referenzko ordinatensystem 27 bestimmt. In a second method step 52, the measuring head 23.x of the interferometer 22.x is mounted. In a third method step 53, the location and the direction of the measuring beam 41.x emitted by the measuring head 23.x of the interferometer 22.x are determined in the reference coordinate system 27.
In einem vierten Verfahrensschritt 54 wird eine Abweichung zwischen dem bestimm- ten Ort und der bestimmten Richtung des Messstrahls 41.x gegenüber eines Soll-Or tes und einer Soll-Richtung des Messstrahls 41.x bestimmt. In a fourth method step 54, a deviation between the specific location and the specific direction of the measuring beam 41.x compared to a target location and a target direction of the measuring beam 41.x is determined.
In einem fünften Verfahrensschritt 55 wird der Messkopf 23.x des Interferometers 22.x auf Basis der im vorherigen Schritt bestimmten Abweichung ausgerichtet. In a fifth method step 55, the measuring head 23.x of the interferometer 22.x is aligned on the basis of the deviation determined in the previous step.
In einem sechsten Verfahrensschritt 56 werden die Verfahrensschritte drei bis fünf solange wiederholt, bis der Ort und die Richtung im Rahmen der Toleranzen dem Soll-Wert entsprechen. In a sixth method step 56, method steps three to five are repeated until the location and the direction correspond to the target value within the limits of the tolerances.
Bezugszeichenliste List of reference symbols
1 Projektionsbelichtungsanlage1 projection exposure system
2 Feldfacettenspiegel 2 field facet mirror
3 Lichtquelle 3 light source
4 Beleuchtungsoptik 4 lighting optics
5 Objektfeld 5 object field
6 Objektebene 6 object level
7 Retikel 7 reticles
8 Retikelhalter 8 reticle holders
9 Projektionsoptik 9 projection optics
10 Bildfeld 10 field of view
11 Bildebene 11 image plane
12 Wafer 12 wafers
13 Waferhalter 13 wafer holder
14 EUV-Strahlung 14 EUV radiation
15 Zwischenfeldfokusebene 15 Interfield focus plane
16 Pupillenfacettenspiegel 16 pupil facet mirror
17 Baugruppe 17 assembly
18 Spiegel 18 mirrors
19 Spiegel 19 mirrors
20 Spiegel 20 mirrors
21.x Spiegel 21.x mirror
22.x Interferometer 22.x interferometer
23.x Messkopf Interferometer23.x Interferometer measuring head
24.x Referenzspiegel Interferometer24.x reference mirror interferometer
25 Entkopplungselement 25 decoupling element
26 Sensorrahmen 26 sensor frames
27 Referenzkoordinatensystem27 Reference coordinate system
28.x mechanische Schnittstelle 28.x mechanical interface
29 Koordinatenmessgerät Grundrahmen Stativ Ausleger Vertikalarm Schwenkarm Gelenk Referenzpunkt Sensorrahmen Taster (taktil) Anbindung Kamera Spacer Messstrahl Verfahrensschritt 1 Verfahrensschritt 2 Verfahrensschritt 3 Verfahrensschritt 4 Verfahrensschritt 5 Verfahrensschritt 6 29 Coordinate measuring machine Base frame stand boom vertical arm swivel arm joint reference point sensor frame button (tactile) connection camera spacer measuring beam process step 1 process step 2 process step 3 process step 4 process step 5 process step 6

Claims

Patentansprüche Claims
1. Verfahren zur Ausrichtung mindestens eines Interferometers (22.x), wobei ein Messkopf (23.x) des Interferometers (22.x) auf einem Referenzbauteil (26) an geordnet ist, wobei es sich bei dem Referenzbauteil (26) um ein Bauteil einer Projektionsbelichtungsanlage (1) für die Halbleiterlithographie handelt, umfas send folgende Verfahrensschritte: 1. A method for aligning at least one interferometer (22.x), wherein a measuring head (23.x) of the interferometer (22.x) is arranged on a reference component (26), the reference component (26) being a Component of a projection exposure system (1) for semiconductor lithography, comprising the following process steps:
- Bestimmung des Referenzkoordinatensystems (27) des Referenzbauteils (26), - Determination of the reference coordinate system (27) of the reference component (26),
- Montage des Messkopfes (23.x) des Interferometers (22.x), - Assembly of the measuring head (23.x) of the interferometer (22.x),
- Bestimmung des Ortes und der Richtung des von dem Messkopf (23.x) emit tierten Messstrahls (41.x) im Referenzkoordinatensystem (27), - Determination of the location and direction of the measuring beam (41.x) emitted by the measuring head (23.x) in the reference coordinate system (27),
- Bestimmung einer Abweichung zwischen dem gemessenen Ort und der Richtung des Messstrahls (41.x) gegenüber einem Soll-Ort und einer Soll- Richtung des Messstrahls (41.x), - Determination of a deviation between the measured location and the direction of the measuring beam (41.x) compared to a target location and a target direction of the measuring beam (41.x),
- Ausrichtung des Messkopfes (23.x) des Interferometers (22.x) auf Basis der im vorherigen Schritt bestimmten Abweichung, - Alignment of the measuring head (23.x) of the interferometer (22.x) on the basis of the deviation determined in the previous step,
- Wiederholung der Verfahrensschritte drei bis fünf, bis der Ort und die Rich tung des Messstrahls (41.x) im Rahmen der Toleranz dem Soll-Wert entspre chen. - Repetition of process steps three to five until the location and the direction of the measuring beam (41.x) correspond to the target value within the tolerance.
2. Verfahren nach Anspruch 1 , dadurch gekennzeichnet, dass das Referenzkoordinatensystem (27) des Referenzbauteils (26) mit einem Ko ordinatenmessgerät (29) bestimmt wird. 2. The method according to claim 1, characterized in that the reference coordinate system (27) of the reference component (26) is determined with a coordinate measuring device (29).
3. Verfahren nach einem der Ansprüche 1 oder 2, dadurch gekennzeichnet, dass bei der Montage des Messkopfes (23.x) des Interferometers (22.x) der Ort und die Lage der mechanischen Schnittstelle (28.x) für den Messkopf (23.x) am Referenzbauteil (26) berücksichtigt werden. 3. The method according to any one of claims 1 or 2, characterized in that during the assembly of the measuring head (23.x) of the interferometer (22.x) the location and the position of the mechanical interface (28.x) for the measuring head (23 .x) on the reference component (26) must be taken into account.
4. Verfahren nach Anspruch 3, dadurch gekennzeichnet, dass der Ort und die Lage der mechanischen Schnittstelle (28.x) mit dem Koordina tenmessgerät (29) bestimmt werden. 4. The method according to claim 3, characterized in that the location and position of the mechanical interface (28.x) can be determined with the coordinate measuring device (29).
5. Verfahren nach einem der Ansprüche 3 oder 4, dadurch gekennzeichnet, dass bei der Montage des Messkopfes (23.x) des Interferometers (22.x) der Ort und die Richtung des vom Interferometer emittierten Messstrahls (41.x) in Bezug auf eine Referenzfläche des Messkopfes (23.x) des Interferometers (22.x) be rücksichtigt werden. 5. The method according to any one of claims 3 or 4, characterized in that during the assembly of the measuring head (23.x) of the interferometer (22.x) the location and the direction of the measuring beam (41.x) emitted by the interferometer with respect to a reference surface of the measuring head (23.x) of the interferometer (22.x) must be taken into account.
6. Verfahren nach einem der vorangehenden Ansprüche, dadurch gekennzeichnet, dass bei der Montage des Messkopfes (23.x) des Interferometers (22.x) zwischen dem Referenzbauteil (26) und dem Messkopf (23.x) mindestens ein Spacer (40.x) angeordnet ist. 6. The method according to any one of the preceding claims, characterized in that during the assembly of the measuring head (23.x) of the interferometer (22.x) between the reference component (26) and the measuring head (23.x) at least one spacer (40. x) is arranged.
7. Verfahren nach Anspruch 6, dadurch gekennzeichnet, dass die Geometrie des Spacers (40.x) auf Basis des Ortes und der Lage der me chanischen Schnittstelle am Referenzbauteil (26) und des Ortes und der Rich tung des Messstrahls (41.x) des Messkopfes (23.x) des Interferometers (22.x) in Bezug auf die Referenzfläche des Messkopfes (23.x) festgelegt wird. 7. The method according to claim 6, characterized in that the geometry of the spacer (40.x) on the basis of the location and the position of the mechanical interface on the reference component (26) and the location and the direction of the measuring beam (41.x) of the measuring head (23.x) of the interferometer (22.x) is set in relation to the reference surface of the measuring head (23.x).
8. Verfahren nach einem der vorangegangenen Ansprüche, dadurch gekennzeichnet, dass der Ort und die Richtung des vom Messkopf (23.x) des Interferometers (22.x) emittierten Messstrahls (41.x) im Referenzkoordinatensystem (27) mit einem optischen Sensor (39) bestimmt werden. 8. The method according to any one of the preceding claims, characterized in that the location and the direction of the measuring beam (41.x) emitted by the measuring head (23.x) of the interferometer (22.x) in the reference coordinate system (27) with an optical sensor ( 39) can be determined.
9. Verfahren nach Anspruch 8, dadurch gekennzeichnet, dass der optische Sensor (39) im Referenzkoordinatensystem (27) des Koordina tenmessgerätes (29) kalibriert ist. 9. The method according to claim 8, characterized in that the optical sensor (39) is calibrated in the reference coordinate system (27) of the Koordina tenmessgerätes (29).
10. Verfahren nach einem der Ansprüche 8 oder 9, dadurch gekennzeichnet, dass der Winkel zwischen dem optischen Sensor (39) und dem Soll-Messstrahl ein gestellt wird. 10. The method according to any one of claims 8 or 9, characterized in that the angle between the optical sensor (39) and the target measuring beam is set.
11. Verfahren nach einem der Ansprüche 8 bis 10, dadurch gekennzeichnet, dass eine Messfläche des Sensors (39) nahezu senkrecht zum Soll-Messstrahl ein gestellt wird. 11. The method according to any one of claims 8 to 10, characterized in that a measuring surface of the sensor (39) is set almost perpendicular to the target measuring beam.
12. Verfahren nach einem der Ansprüche 5 bis 11 , dadurch gekennzeichnet, dass die Richtung des Messstrahls (41.x) durch mindestens zwei Messungen an verschiedenen Punkten entlang des Messstrahls (41.x) bestimmt wird. 12. The method according to any one of claims 5 to 11, characterized in that the direction of the measuring beam (41.x) is determined by at least two measurements at different points along the measuring beam (41.x).
13. Verfahren nach einem der Ansprüche 5 bis 11 , dadurch gekennzeichnet, dass der Ort und die Richtung des Messstrahls (41 .x) durch eine Messung be stimmt werden. 13. The method according to any one of claims 5 to 11, characterized in that the location and the direction of the measuring beam (41 .x) are determined by a measurement.
14. Verfahren nach Anspruch 13, dadurch gekennzeichnet, dass die Messung des Ortes und der Richtung des Messstrahls (41.x) durch die Auswertung von Nahfeld und Fernfeld der Abbildung des Messstrahls (41.x) vorgenommen wird. 14. The method according to claim 13, characterized in that the measurement of the location and the direction of the measuring beam (41.x) is carried out by evaluating the near field and far field of the imaging of the measuring beam (41.x).
15. Projektionsbelichtungsanlage (1) für die Halbleiterlithographie mit einem Inter ferometer (22.x) mit einer Genauigkeit der Ausrichtung der Strahlposition am Referenzspiegel (24.x) von kleiner als 100pm, insbesondere kleiner 50pm, insbesondere kleiner 20pm. 15. Projection exposure system (1) for semiconductor lithography with an inter ferometer (22.x) with an accuracy of the alignment of the beam position on the reference mirror (24.x) of less than 100pm, in particular less than 50pm, in particular less than 20pm.
16. Projektionsbelichtungsanlage (1) für die Halbleiterlithographie mit einem Inter ferometer (22.x) mit einer Genauigkeit der Ausrichtung des Strahlwinkels am Referenzspiegel (24.x) des Interferometers (22.x) kleiner 500prad, insbeson dere kleiner 250prad, insbesondere kleiner 100prad. 16. Projection exposure system (1) for semiconductor lithography with an inter ferometer (22.x) with an accuracy of the alignment of the beam angle on the reference mirror (24.x) of the interferometer (22.x) less than 500prad, in particular less than 250prad, in particular less than 100prad .
PCT/EP2020/078713 2019-11-15 2020-10-13 Method for aligning an interferometer, and projection exposure apparatus for semiconductor technology WO2021094048A1 (en)

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