Device for the low-deformation mounting of a rotationally asymmetric optical element

A low-deformation mounting device of a rotationally asymmetric optical element, particularly an optical element in a projection lens used in semiconductor lithography. Said optical element is mounted in a frame and is provided with at least three connection surfaces that are positioned perpendicular to each other. Frame-connecting members are disposed in such a way that at least one but no more than two degrees of translational freedom and at least one but no more than two degrees of rotational freedom are obtained by means of said connecting members.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a device for the low-deformation mounting of a rotationally asymmetric optical element, in particular of an optical element in a projection lens system for semiconductor lithography, which is mounted in a frame.

2. Description of the Related Art

In particular in the case of projection lens systems in semiconductor lithography for producing semiconductor elements, it is necessary to know the precise installation position of an optical element or of an optical subassembly in relation to reference surfaces. Furthermore, it is often necessary for an optical element or a subassembly, following removal and reinstallation, to be positioned precisely in relation to the previous position, it also being intended, in particular, for the same, or at least very similar, deformation to occur as in the case of installation first time around, in order that reproducibility is achieved and there are no chances in respect of the imaging quality of the projection lens system.

A reproducible installation position and at least more or less identical deformation forces are particularly difficult to achieve in the case of rotationally asymmetric optical elements. This applies, in particular, to beam splitter cubes, prisms and double mirrors.

SUMMARY OF THE INVENTION

The object of the present invention is thus to provide a mounting which is intended for a rotationally asymmetric optical element and by means of which reproducibility is achieved, in particular following removal and reinstallation. The intention, in particular, is for external influences during installation and operation not to give rise to any chances in the original deformation of the optical element.

This object is achieved according to the invention by a device, the optical element being mounted in a frame such that at least three application surfaces are provided on the optical element, in an angle in relation to one another, preferably orthogonally, wherein attachment members for attachment to the frame being arranged such that in each case at least one but not more than two degree/s of translational freedom and degree/s of rotational freedom is/are provided by the attachment members.

The mounting according to the invention achieves reproducibility for reinstallation of the optical element, the original deformation forces also being reproduced or maintained. This is the case, in particular, when the attachment members are each provided with a connecting member via which the optical element is fixed to the frame.

One of the essential features of the invention is that two degrees of translational freedom are available at each attachment location during installation. Following installation, that is to say following connection of each attachment location to the optical element via a connecting member, one degree of translational freedom is eliminated. This renders the mounting stiffer overall, as a result of which vibrations can be better avoided.

The attachment members will be very advantageously designed as solid-state articulations, it being possible for these to have leaf-spring-like, elastic elements.

Such a mounting is free of play.

If mounting via at least two leaf-spring-like elastic elements which are arranged perpendicularly to one another is provided, then there are still two degrees of translational freedom following installation, redundancy of the mounting being avoided as a result.

A very advantageous configuration of the invention is achieved if it is provided that the lines of effect of the possible lateral translational movements intersect one another at a point.

This arrangement gives rise to temperature compensation since, in the case of different temperature expansions of the optical element and frame, the attachment locations and/or bearing points move such that the optical element does not have to change shape.

An advantageous configuration of straightforward design is achieved when the attachment members slant in relation to the edges of the optical element, the lines of effect of the possible lateral translational movements intersecting one another at a corner of the optical element. In the case of an optical element forming a cube, this makes it possible to expand or contract, true to form, from the corner of the cube as fixed point.

Advantageous further configurations and developments of the inventions can be seen from the exemplary embodiments which are described in principle hereinbelow with reference to the drawings.

DETAILED DESCRIPTION

FIG. 1illustrates., in principle, a projection exposure installation with a projection lens system1for microlithography for producing semiconductor elements.

It has an illuminating system2with a laser (not illustrated) as light source. Located in the object plane of the projection exposure installation is a reticle3, of which the structure is to be replicated, on a correspondingly reduced scale, on a wafer4which is arranged beneath the projection lens system1and is located in the image plane.

The projection lens system1is provided with a first vertical lens-system part1aand a second horizontal lens-system part1b. Located in the lens-system part1bare a plurality of lenses5and a concave mirror6, which are arranged in a lens-system housing7of the lens-system part1b. A beam splitter cube10is provided in order to deflect the projection beam (see arrow) from the vertical lens-system part1a, with a vertical optical axis8, into the horizontal lens-system part1b, with a horizontal optical axis9.

Following reflection of the beams on the concave mirror6and subsequent passage through the beam splitter cube10, these beams impinge on a deflecting mirror11. The horizontal beam path9is deflected at the deflecting mirror11, in turn, into a vertical optical axis12. A third vertical lens-system part1cwith a further lens group13is locates beneath the deflecting mirror11. In addition, three λ/4 plates14,15and16are also located in the beam path. The λ/4 plate14is located in the projection lens system1, between the reticle3and the beam splitter cube10, behind a lens or lens group17. The π/4 plate15is located in the beam path of the horizontal lens-system part1b, and the λ/4 plate16is located in the third lens-system part1c. The three λ/4 plates serve to provide one full rotation of the polarization, as a result of which, inter alia, beam losses are minimized.

FIGS. 2 to 8use an enlarged illustration to describe in more detail the beam splitter cube10wish its bearing devices which is illustrated inFIG. 1. The beam splitter cube10is mounted in a frame21which is fixed, in a manner which is not illustrated specifically, to the projection lens system1.

The beam splitter cube10is mounted in the frame21via three attachment members22, which act on three attachment surfaces23of the beam splitter cube10which are located perpendicularly to one another or orthogonally in relation to one another. As can be seen fromFIG. 2, the attachment members22are designed as solid-state articulations and are integral with the frame21. As can also be seen fromFIG. 2, the attachment surfaces23constitute three sides of the beam splitter cube10. According toFIG. 3, each attachment member22has a central part24with a threaded bore25and two laterally adjoining leaf-spring-like elastic elements26. While in each case one end of the elastic elements26is connected to the central part25, the other ends of the elements26are each connected to the frame21. The central parts24of the attachment members22butt, by way of bearing surfaces27, against the attachment surfaces23of the beam splitter cube10.

The bore25of the central part24contains a screw28, which is screwed into a threaded bore29of the beam splitter cube10in each case (see the partially broken-away illustration of the beam splitter cube inFIG. 2).

In the case of the bearing device according toFIGS. 2 and 3, there are two degrees of rotational freedom and two degrees of translational freedom per attachment member22during installation.

As can be seen fromFIG. 3in conjunction withFIG. 2, vertical rotation30about the longitudinal axis of the screw and axial rotation31about the longitudinal axes of the leaf-spring-like elastic elements26are possible in each case. In addition, on account of the elasticity of the elements26, a lateral translational movement32in the direction transverse to the longitudinal axis of the leaf-spring-like elements26is possible. Furthermore, prior to the beam splatter cube10being connected to the frame21via the three screws28, a lateral translational movement in the longitudinal direction of the elastic elements26is also possible in each case, as is indicated by the dashed arrow33inFIG. 3. The possibility of lateral translational movement in arrow direction33, however, is eliminated on account of the statics of the elastic elements26in this direction once the screws28have been screwed into the threaded bore29of the beam splitter element10. As a result, once the beam splitter cube10has been connected to the frame21via the three screws28, only a lateral translational movement32in the direction transverse to the longitudinal axes of the elements26and to the two rotational movements30and31is possible in each case.

Redundancy, which gives rise to deformation at the beam splitter cube10, is present in the case of this type of mounting.

FIGS. 4 and 5illustrate mounting devices for the beam splitter cube10which still have two degrees of translational freedom present following installation.

Since essentially the same parts are used, and the same construction is present, in the case of the mounting devices illustrated inFIGS. 4 and 5, the same parts have also been provided with the same designations.

According toFIG. 4, the frame21is provided with two cut-outs34in the form of longitudinal grooves in each case in the region of its mounting devices. The cut-outs34extend transversely to the longitudinal axes of the leaf-spring-like elastic elements26and are each spaced apart from the outside of the frame21, in the region of the connection between the elements26and the frame21, such that only a narrow crosspiece35is present, this crosspiece likewise running transversely to the longitudinal axis or the elements26. It is thus the case that the two elongate cut-outs34, once the beam splitter cube10has been fixed0to the frame21, still allow a lateral translational movement in arrow direction33, since the narrow crosspieces35can flex like the leaf-spring-like elastic elements26.

FIG. 5illustrates a further possibility, in the case of which two lateral translational movements32and33are likewise possible following installation. In this case, this is made possible by a frame widening36which constitutes, at least more or less, a U-profile shape, with two legs37which, in relation to their respective longitudinal axes or the stiff surfaces thereof, run perpendicularly to the leaf-spring-like elastic element26. As can be seen, this configuration provides just one leaf-spring-like elastic element26, which is connected, on one side, to the central part24as the actual attachment member and, on the other side, to the transverse part of the U-profile between the two legs37.

In addition to the two degrees of rotational freedom30and31, the elasticity of the element26allows a lateral translational movement32and the elasticity of the two leas37allows a translational movement33which is perpendicular thereto.

FIG. 6shows a configuration of a device which is intended for connecting the beam splitter cube10to the frame21and in which the attachment members22slant, or are located at an angle, in relation to the edges of the beam splitter cube10. If the angle at which the leaf-spring-like elements26are connected to the sides of the frame21is 45°, in which case the attachment members22run diagonally on the attachment surfaces23, then the lines of effect of the possible lateral translational movements intersect one another at a point P, as can be seen from the effect-indicating arrows38,39and40. Point P is located at a corner of the beam splitter cube10. Since the movement directions are directed toward the point P, temperature compensation is achieved; that is to say, on account of different temperature expansions of the beam splitter cube10and frame21, there is no change in the shape of the beam splitter cube10.

FIG. 7shows a variant in respect of the screw28as connecting member between the frame21and the beam splitter cube20. In the case of this exemplary embodiment, it is possible to adjust the contact-pressure force. This is achieved by a stressed spring41which prevents the attachment surface23of the beam splitter cube10from lifting off from the bearing surface27of the attachment member22, to be precise by producing a tensile force between a bolt42and a bolt43, over which the ends of the spring41are wound in each case. The bolt42is located on an insert sleeve44in the beam splitter cube10. The connection between the insert sleeve44and the beam splitter cube10or between the spring41and the bolt42will preferably be provided as a quick-acting closure, for example as a bayonet closure, in order thus to allow quick release and reconnection during installation and removal.

The bolt43is connected to a screw45which is screwed into the central part24of the attachment member22.

The screw45can be used to adjust the tensile force of the spring41such that, upon removal and reinstallation, the beam splitter cube10undergoes the same deformation as before.

FIG. 8shows another possible way of regulating the contact-pressure force between the beam splatter cube10and the attachment member22as part of the frame21. In the case ofFIG. 8, the contact-pressure force is produced by a magnet46with a north pole and a south pole, of which the magnetic flux runs via a sleeve47in the beam splitter cube10and a sleeve48in the attachment member22. Adjustment of an adjusting screw49, which is fixed to the magnet46, allows the contact-pressure force between the beam splitter cube10and the attachment member22to be adjusted, in turn, such that, upon reinstallation, the beam splitter cube10assumes the same deformation as during earlier installation.

The invention has been described, in the case of the exemplary embodiment; with reference to a beam splitter cube. However, it is, of course, also suitable for other types of rotationally asymmetric optical elements, for example a prism or a double mirror.

Instead of fixing via the three screws28or the connecting members illustrated inFIGS. 7 and 8, by means of which it is possible to regulate the contact-pressure force, it is, of course, also possible to have other connecting members within the context of the invention.