DE102015209492A1 - Arrangement and method for determining the position of two objects in six degrees of freedom to each other - Google Patents

Abstract

The invention relates to an arrangement and a method for determining the position of two objects in six degrees of freedom to each other. An arrangement according to the invention comprises a first object, a second object, at least six absolutely measuring interferometers (441-446, 541-548) and at least three retroreflectors (451-456, 551-554), these retroreflectors 451-456, 551- 554) are arranged on the first object or the second object such that a total of at least six different length measuring sections (431-436, 531-538) are formed between the retroreflectors and the absolute measuring interferometers.

Description

The invention relates to an arrangement and a method for determining the position of two objects in six degrees of freedom to each other.

Microlithography is used to fabricate microstructured devices such as integrated circuits or LCDs. The microlithography process is carried out in a so-called projection exposure apparatus which has an illumination device and a projection objective. The image of a mask (= reticle) illuminated by means of the illumination device is hereby projected onto a substrate (eg a silicon wafer) coated with a photosensitive layer (photoresist) and arranged in the image plane of the projection objective in order to apply the mask structure to the photosensitive coating of the Transfer substrate.

In projection lenses designed for the EUV range (ie at wavelengths of, for example, about 13 nm or about 7 nm), mirrors are used as optical components for the imaging process due to the lack of availability of suitable light-transmissive refractive materials. Typical projection lenses designed for EUV, such as US 7,538,856 B2 As is known, for example, they may have an image-side numerical aperture (NA) in the range of NA = 0.2 to 0.3 and form an (eg annular) object field in the image plane or wafer plane. An enlargement of the mirror surfaces typically accompanied by approaches to increase the image-side numerical aperture (NA) leads, among other things, to production-related challenges.

In particular, with increasing dimensions of the mirrors, larger processing machines are required for fabrication, and stricter requirements are placed on the processing tools used (e.g., grinding, lapping, and polishing machines). Furthermore, to produce larger mirrors, heavier mirror bases must be used, which can bow to a significant degree due to gravity.

During the production of a mirror (hereinafter also generally referred to as a "workpiece") as precise and possibly repeated position determination relative to the respective machining tool (hereinafter referred to as "tool") required so that the machining tool the correct actions relative to the contour of the workpiece performs. This positional determination relates both to the start position for the machining and the maintenance of the geometry over the duration of the machining and to the minimization of errors in the necessary during the machining traversing movements.

A common procedure, for example, temporarily replace the workpiece against a button and measure with this button the position of the workpiece in the machine, after which the workpiece is aligned with respect to the tool or within the respective processing machine accordingly.

In practice, the problem may arise in practice, in particular with comparatively large mirrors, that not all degrees of freedom for the travel movements of such a probe are accessible. Furthermore, in practice it is often necessary to position the workpiece or the mirror not only in relation to a single machining tool, but in each case relative to a plurality of different production devices or machining tools over a plurality of manufacturing steps.

Further problems result from geometry changes which occur during processing e.g. gravitationally arising from the different, occurring loads.

The prior art is merely an example DE 10 2009 054 860 A1 such as DE 10 2007 004 934 A1 directed.

It is an object of the present invention to provide an arrangement and a method for determining the position of two objects in six degrees of freedom with respect to one another, which enable as accurate a position determination as possible while avoiding the problems described above.

This object is achieved by the arrangement according to the features of the independent claim 1 and the method according to the features of the independent claim 11.

• – ein erstes Objekt;
• – ein zweites Objekt;
• – wenigstens sechs absolut messende Interferometer; und
• – wenigstens drei Retroreflektoren;
• – wobei diese Retroreflektoren derart an dem ersten Objekt oder dem zweiten Objekt angeordnet sind, dass zwischen den Retroreflektoren und den absolut messenden Interferometern insgesamt wenigstens sechs unterschiedliche Längenmessstrecken ausgebildet sind.

An arrangement for determining the position of two objects in six degrees of freedom to one another has:

• A first object;
• A second object;
• - at least six absolutely measuring interferometers; and
• - at least three retroreflectors;
• - These retroreflectors are arranged on the first object or the second object such that a total of at least six different length measuring distances are formed between the retroreflectors and the absolute measuring interferometers.

According to one embodiment, the length measuring sections are formed in the geometry of a Stewart-Gough platform.

The invention is based in particular on the concept of constructing length measuring distances in the geometry of a Stewart-Gough platform from absolutely measuring interferometers and associated retroreflectors and thus making use of the principle of trilateration to determine the position of two objects in six degrees of freedom relative to one another.

For the purposes of the present application, an "absolutely measuring interferometer" means an interferometer which is not only suitable for incremental measurement or only for measuring changes in length, but also permits absolute length measurement. Such absolutely measuring interferometers are commercially available from Etalon AG under the name "Absolute Multiline System".

The invention makes use of the fact that, due to the commercial availability of absolute measuring interferometers, e.g. the position of a workpiece such as an EUV mirror in the processing machine can be measured in the reference position independently of the machine structure (which is not possible when using the buttons described in the beginning instead of the tool). Any deviations of the position from the desired position can then be corrected during processing by correcting the web data or by moving the workpiece. According to one embodiment, in each case two of these length measuring sections are assigned a common retroreflector. In other words, in each case a retroreflector complete two length measuring distances.

According to a further embodiment, each of the length measuring sections is assigned a separate retroreflector (in other words, the arrangement has a separate retroreflector for each of the length measuring sections).

According to one embodiment, at least two of the length measuring paths intersect each other.

According to one embodiment, all length measuring sections are arranged so that two length measuring sections intersect each other in pairs.

According to one embodiment, at least two, in particular at least three, of the length measuring sections are parallel to one another.

According to one embodiment, the arrangement has more than six absolute measuring interferometers. In this way, an overdetermined arrangement (e.g., with eight or more length measuring distances) can be provided, which in addition to the actual position determination can be used to deform also e.g. of the tool (such as gravitational deflection). Alternatively or additionally, such an overdetermined arrangement can also be used to determine measurement errors.

In one embodiment, the first object is a tool (such as a grinder) and the second object is a workpiece (such as a mirror) to be machined by this tool. According to a further embodiment, the first object and the second object are each EUV mirrors of a projection objective of a microlithographic projection exposure apparatus designed for operation in the EUV.

• – wobei eine Bestimmung der relativen Lage des ersten Objekts und des zweiten Objekts über wenigstens sechs absolut messende Interferometer erfolgt;
• – wobei diese Interferometer jeweils Längenmessungen zu Retroreflektoren, welche an dem ersten Objekt oder dem zweiten Objekt angeordnet sind, durchführen; und
• – wobei zwischen den Retroreflektoren und den absolut messenden Interferometern insgesamt wenigstens sechs unterschiedliche Längenmessstrecken ausgebildet sind.

The invention further relates to a method for determining the position of two objects in six degrees of freedom,

• - Wherein a determination of the relative position of the first object and the second object via at least six absolute measuring interferometer takes place;
• - These interferometers each perform length measurements to retroreflectors, which are arranged on the first object or the second object; and
• - Wherein a total of at least six different length measuring distances are formed between the retroreflectors and the absolute measuring interferometers.

For preferred embodiments and advantages of the method, reference is made to the above statements in connection with the optical system according to the invention.

Further embodiments of the invention are described in the description and the dependent claims.

The invention will be explained in more detail with reference to embodiments shown in the accompanying drawings.

Show it:

1 - 3 schematic representations for explaining different possible geometries based on a Stewart-Gough platform for the realization of existing in an inventive arrangement length measuring distances;

4a -B are schematic representations for explaining an arrangement according to the invention for determining the position of a workpiece relative to a tool in one embodiment; and

5 a schematic representation for explaining an inventive "overdetermined" arrangement for determining the position of a workpiece relative to a tool in a further embodiment.

Furthermore, the position determination according to the invention of two objects in six degrees of freedom with respect to one another is based on the application to the position determination of a workpiece relative to a tool, more particularly an EUV mirror in a processing machine, such as e.g. a grinding machine described.

With regard to the description of the tool can be made of the usual concept of the so-called TCP (= "Tool Center Point"), in which an imaginary reference point, which is located at a suitable position on the tool and, for. form the origin of the tool coordinate system, defined by its position and orientation in space, the position of the tool. This may be, for example, the center of curvature of a grinding wheel or other tool.

According to the invention, the absolute measuring interferometers used for position determination are now arranged in a constant and known position relative to the TCP, which as a rule is not accessible, and preferably close to the tool, as shown schematically in FIG 4a -B is shown.

Each of the interferometers is used for absolute length measurement along a length measuring path, at the other end of which a retroreflector is arranged on each side of the workpiece.

The individual length measuring distances 431 - 436 In this case, instead of the TCP, a suitable structural element can be assumed which is in a fixed spatial relationship with the TCP. According to 4a -B are the absolute measuring interferometers 441 - 446 (of which the interferometer 441 - 443 in 4b are covered) on a plate 440 arranged, in turn, in a movable in the z-direction and on a portal 470 mounted lifting device 460 is appropriate. At the other end of each length measuring section 431 - 436 is a retro reflector 451 - 456 is arranged on the side of the workpiece or mirror.

The invention is not limited to a concrete mounting of the interferometer 441 - 446 limited. So can the interferometer 441 - 446 For example, in the construction of 4 also on the grinding wheel 480 carrying yoke 490 or at another suitable location, the position of which should be as stable as possible with respect to the TCP or the center of curvature of the tool. Furthermore, the position of the interferometer should be 441 - 446 be chosen so that the interferometer 441 - 446 if possible, are not exposed to any undesirable fluctuations in the ambient conditions (eg temperature fluctuations or refractive index fluctuations).

In the context of the present invention are basically the positions of the respective interferometer 441 - 446 and the respectively associated retroreflectors 451 - 456 (To tool or workpiece) interchangeable with each other, which can be selected depending on the specific circumstances, whether that of a length measuring section 431 - 436 associated or this final retroreflector 451 - 456 is placed on the tool or on the workpiece.

For holding or fixing the retroreflectors 451 - 456 and Interferometerkomponenten are preferably materials with the lowest possible coefficient of thermal expansion (such as the marketed under the name "Invar" iron-nickel alloy) used.

When fitting the receiving machine structure (eg a pivot bearing as in 4a -B with six retroreflectors 451 - 456 ), the position of the pivot bearing to TCP-bearing machine part can be checked and set the starting point. In particular, comparatively slow temporal changes, eg due to seasonal fluctuations or gravitational deformations, can be measured.

For typical dimensions of the measuring beam with eg 3mm diameter, the diameter of the retroreflectors 451 - 456 only 5mm by way of example, which usually allows easy mounting on the workpiece.

5 shows in a schematic representation of another embodiment of the example of the processing of a mirror 520 with a grinding tool 510 , wherein more than six interferometers - example eight interferometers - are provided for the realization of an "overdetermined arrangement".

According to 5 are on a turntable four retroreflectors 551 - 554 arranged, each of these retroreflectors 551 - 554 each two of a total of eight length measuring distances 531 - 538 , the each to an interferometer of a total of eight interferometers 541 - 548 run, concludes.

According to 5 are therefore not six, but eight length measuring distances 531 - 538 formed so that there is an overdetermined arrangement insofar as there are more length measuring distances than would be required for a position determination in six degrees of freedom. This overdetermined arrangement can be used in particular to detect deformations of the tool (eg a gravitational deflection). Alternatively or additionally, measurement errors can also be determined by utilizing the over-determination.

In addition, with reference to 1 - 3 different possible geometries based on a Stewart-Gough platform for the realization of existing in an inventive arrangement length measuring distances explained.

In 1 are with the reference numerals 110 and 120 Sections of the first and second object, respectively, these sections are for the sake of simplicity hereinafter equated directly with said objects. Furthermore, with the reference numerals 131 - 136 Measuring distances or light channels, within which the light between the (in 1 upper) first object and the (in 1 lower) second object 120 runs. This is the beginning of each measuring section 131 - 136 or each light channel on one of the objects 110 . 120 , and the respective end lies on the other of the objects 120 . 110 , For example only, it may be in the in 1 upper object 110 to act to take a tool spindle while in the 1 lower object 120 the workpiece (or a workpiece holder) may be.

The measuring sections or light channels 131 - 136 are according to 1 designed to make a determination of the relative position of the second object 120 to the first object 110 allow in (all) six degrees of freedom. These six degrees of freedom in this case include three space coordinates and three angle coordinates for defining the unique relative position in the usual way, but according to the invention, six length measurements along the measuring distances 131 - 136 determined. Essential for this is that these measuring sections 131 - 136 are sufficiently independent or different from each other, so that by said length measurements and in fact in mathematically uniquely solvable manner a conclusion on all of the above six degrees of freedom is possible.

The arrangement of the measuring sections or light channels 131 - 136 according to 1 corresponds to the geometry of a so-called Stewart-Gough platform (also called "Stewart platform" or hexapod, cf. D. Stewart: A Platform with Six Degrees of Freedom, UK Institution of Mechanical Engineers Proceedings 1965-66, Vol 180, Pt. 1, No 15 ), but the usually physically executed "legs" of the hexapod are designed as non-body measuring sections.

The equations describing the geometric relationship between the two objects are polynomials. Each degree of freedom x, y, z, Rx, Ry, Rz can be described by a polynomial. The mathematical properties of the resulting systems of equations, the question of solvability, and, where appropriate, the construction of solutions are described, for example, in Andrew J. Sommerse, Charles W. Wamper: "The Numerical Solution of Systems of Polynomials", Word Scientific Publishing, Singapore, 2005 , treated and are well known to the skilled person.

A significant advantage of the inventive arrangement of six different measuring sections between the first object 110 and the second object 120 is that, to a certain extent, a flexible adaptation of the sensitivities resulting in the respective degrees of freedom (ie in the respective spatial directions or angles) to the specific circumstances or requirements is possible. For example, by suitable arrangement of the measuring sections 131 - 136 a more sensitive measurement for such degrees of freedom or directions are achieved in which the relative position determination is critical or of greater importance than in other directions or degrees of freedom.

2 shows an alternative embodiment, wherein analogous or substantially functionally identical elements are designated by reference numerals increased by "100". In the embodiment of 2 in each case two measuring sections intersect or intersect in pairs. How out 2 can be seen by this overlap or crossover on the one hand achieve improved utilization of the available space.

On the other hand results - due to the associated with the overlap, more pronounced inclination of the measuring sections - a greater sensitivity of the measuring arrangement in certain spatial directions or relative to certain relative position changes of the objects, these spatial directions can again just be chosen so that they especially in the system correspond to critical spatial directions. The alignment and exact arrangement of the measuring sections is thus preferably carried out in such a way that the maximum sensitivity results for the degrees of freedom which are to be determined as precisely as possible. For example, to achieve a comparatively high sensitivity in the z-direction of the measuring sections 131 - 136 respectively. 231 - 236 are also preferably arranged in the z-direction, whereas the measuring sections 131 - 136 respectively. 231 - 236 can be arranged in an inclined position to achieve a relatively high sensitivity in the y-direction.

In 3 is an arrangement of measuring sections 331 - 336 shown, with three measuring sections, namely the measuring sections 332 . 334 and 336 , are parallel to each other. By means of this arrangement, particularly small measurement uncertainties in the z direction are achieved (since the arrangement in the z direction is particularly "stiff").

While the invention has been described in terms of specific embodiments, numerous variations and alternative embodiments, e.g. by combination and / or exchange of features of individual embodiments. Accordingly, it will be understood by those skilled in the art that such variations and alternative embodiments are intended to be embraced by the present invention, and the scope of the invention is limited only in terms of the appended claims and their equivalents.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 7538856 B2 [0003]
• DE 102009054860 A1 [0009]
• DE 102007004934 A1 [0009]

Cited non-patent literature

• "Stewart platform" or hexapod, cf. D. Stewart: "A Platform with Six Degrees of Freedom", UK Institution of Mechanical Engineers Proceedings 1965-66, Vol 180, Pt 1, No 15 [0047]
• Andrew J. Sommerse, Charles W. Wamper: "The Numerical Solution of Systems of Polynomials", Word Scientific Publishing, Singapore, 2005 [0048]

Claims (11)

Arrangement for determining the position of two objects in six degrees of freedom with each other, comprising: a first object; • a second object; At least six absolutely measuring interferometers ( 441 - 446 . 541 - 548 ); and at least three retroreflectors ( 451 - 456 . 551 - 554 ); • whereby these retroreflectors ( 451 - 456 . 551 - 554 ) are arranged on the first object or the second object such that between the retroreflectors ( 451 - 456 . 551 - 554 ) and the absolute measuring interferometers ( 441 - 446 . 541 - 548 ) at least six different length measuring sections ( 431 - 436 . 531 - 538 ) are formed. Arrangement according to claim 1, characterized in that the length measuring distances ( 431 - 436 . 531 - 538 ) are formed in the geometry of a Stewart-Gough platform. Arrangement according to claim 1 or 2, characterized in that in each case two of these length measuring sections ( 531 - 538 ) a common retroreflector ( 551 - 554 ) assigned. Arrangement according to claim 1 or 2, characterized in that each of these length measuring sections ( 431 - 436 ) each have a separate retroreflector ( 451 - 456 ) assigned. Arrangement according to one of the preceding claims, characterized in that at least two of the length measuring paths intersect each other. Arrangement according to one of the preceding claims, characterized in that all length measuring sections are arranged so that in each case two length measuring sections intersect in pairs. Arrangement according to one of claims 1 to 5, characterized in that at least two, in particular at least three of the length measuring sections are parallel to each other. Arrangement according to one of the preceding claims, characterized in that it comprises more than six absolutely measuring interferometers ( 541 - 548 ) having. Arrangement according to one of claims 1 to 8, characterized in that the first object is a tool and the second object is a workpiece to be machined by this tool. Arrangement according to one of Claims 1 to 8, characterized in that the first object and the second object are each EUV mirrors of a projection objective of a microlithographic projection exposure apparatus designed for operation in the EUV. Method for determining the position of two objects in six degrees of freedom with respect to one another, wherein a determination of the relative position of the first object and the second object via at least six absolutely measuring interferometers ( 441 - 446 . 541 - 548 ) he follows; • where these interferometers ( 441 - 446 . 541 - 548 ) each length measurements to retroreflectors ( 451 - 456 . 551 - 554 ) arranged on the first object or the second object; and wherein between the retroreflectors ( 451 - 456 . 551 - 554 ) and the absolute measuring interferometers ( 441 - 446 . 541 - 548 ) at least six different length measuring sections ( 431 - 436 . 531 - 538 ) are formed.

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