DRAWING
Exemplary embodiments are shown in the diagrammatic drawing and are explained in the following description. The following are shown:
FIG. 1
a, b a diagrammatic view of the housing of an embodiment of monocular field glasses according to the invention (FIG. 1a) as well as a beam path in said monocular field glasses, which beam path comprises two opposing pairs of mirrors (FIG. 1b),
FIG. 2
a, b a view of an embodiment of a shaped body according to the invention with two reflective coatings that form two mirrors of one of the pairs of mirrors of FIG. 1b, in a top view (FIG. 2a) and a lateral view (FIG. 2b),
FIG. 3
a-d a lateral section of two glass blanks and of a sagging mold to illustrate a variant of the method according to the invention in different method steps,
FIG. 4
a-c two glass blanks and a sagging mold (FIG. 4a) as well as two sagged glass blanks (FIGS. 4b, c) to illustrate further variants of the method,
FIG. 5 a diagrammatic section view of an X-ray telescope with X-ray mirror elements that are formed by shaped bodies according to the invention, and
FIG. 6 a diagrammatic lateral section view of an EUV collector for an illumination system of projection illumination apparatus for microlithography, comprising EUV mirror elements that are formed by shaped bodies according to the invention.
FIG. 1
a diagrammatically shows monocular field glasses 1, also referred to as a spotting scope. The field glasses 1 comprise a housing 2 with an eyepiece 4 and a lens 3. The optical design in the interior of the field glasses 1 is diagrammatically shown in FIG. 1b. In an entry aperture 5 the light enters the field glasses 1, impinges a first mirror 6a′ of a first pair of mirrors 6 and by it is reflected onto a first mirror 7a′ of a second pair of mirrors 7 that is arranged opposite the first pair of mirrors 6. From there the light continues to a second mirror 6b′ of the first pair of mirrors 6 from which it is reflected to a second mirror 7b′ of the second pair of mirrors 7. Thereafter the light passes through an adjustable internal focusing device 8 before entering an eyepiece adapter 9. For the purpose of simplification, in FIG. 1b the aperture stops that are provided in the beam path are not shown.
The relative position of the mirrors 6a′, 6b′ or 7a′, 7b′ of the pairs of mirrors 6, 7 needs to be precisely matched in the magnitude of micrometers. Up to now this has taken place by placing the mirrors 6a′, 6b′ or 7a′, 7b′ in an internal support, with subsequent adjustment relative to each other, which required considerable effort. Fixing the relative arrangement of the mirrors 6a′, 6b′ e.g. of the first pair of mirrors 6 is achieved as described below, in that reflective coatings are applied in partial regions 6a, 6b to a shared shaped body 10 as shown in FIGS. 2a and 2b, which coatings form the mirrors 6a′, 6b′. The relative position of the partial regions 6a, 6b can be very precisely set when the reflective coating is applied. Of course the second pair of mirrors 7 can also be produced in the same manner.
The shaped body 10 must be produced as a free-form surface with little tolerance for surface form deviation of less than 100 μm in order to keep the occurrence of aberrations as a result of deformation of the mirrors 6a′, 6b′ as low as possible. The greatly different position planes and position angles of the two mirrors 6a′, 6b′ pose problems in the production of the shaped body 10 with such a tolerance for surface form deviation, e.g. by means of a conventional sagging method. Between the first partial region 6a and the second partial region 6b the above results in a kink 12 in the shaped body 10. This kink 12 prevents the shaped body 10 from being able to be produced by sagging a single glass blank, because in this case the necessary tolerance for surface form deviation would be exceeded.
For this reason the shaped body 10 comprises two glass blanks 10a, 10b, which have been produced by sagging, which blanks 10a, 10b adjoin at a contact edge 11 and at the contact edge 11 are fixed in their position in relation to each other. As a result of this the application of the reflective coatings in the partial regions 6a, 6b can take place jointly, in contrast to the conventional production of pairs of mirrors, where first two individual mirror elements have to be produced and subsequently joined and adjusted.
In this arrangement the shaped body 10 is produced in a method whose individual method steps are shown in FIG. 3a-d. As shown in FIG. 3a, first two glass blanks 12a, 12b, which are formed as plane sheets, are placed side-by-side on a shaped surface 14 of a temperature-resistant sagging mold 13. In a subsequent method step the glass blanks 12a, 12b are sagged onto the formed surface 14 by heating the sagging mold 13 with the glass blanks 12a, 12b. As a result of this, the sagged and shaped glass blanks 10a, 10b as shown in FIG. 3b are created from the plane sheets. After sagging, the sagged glass blanks 10a, 10b rest against a shared contact edge 11. There, in a subsequent method step, they are fastened to each other by pasting, which is shown in FIG. 3c by an arrow. In a final method step, shown in FIG. 3d, the formed glass blanks 10a, 10b, which form the shaped body 10, are lifted from the sagging mold 13. In a subsequent method-related step the shaped body 10 formed in this way is provided with a reflective coating in the two partial regions 6a, 6b and is finally pasted onto an internal support (not shown in the illustration) in the housing 2 of the field glasses 1 of FIG. 1a. In this arrangement the shaped body 10 can comprise a position reference structure, e.g. cross hairs, in one or several partial regions, as a result of which structure the adjustment of the shaped body 10 on the support is facilitated.
Further variants for producing the shaped body 10 are also possible, as shown for example in FIG. 4a-c with reference to two plane-parallel glass blanks 12a, 12b, whose corners are designated A1, B1, . . . or A2, B2, . . . . The glass blanks 12a, 12b are placed on the sagging mold 13 shown in FIG. 4a, with the shaped surface 14 of said sagging mold differing from the surface shown in FIG. 3 in that the glass blanks 12a, 12b after sagging do not rest against a shared contact edge, as indicated by the non-overlapping regions on the shaped surface 14, which regions show the position of the sagged glass blanks. In this arrangement the sagged glass blanks 10a, 10b, as shown in FIG. 4b, can be fastened to each other by connection pieces 15a, 15b between the adjacent edges B1-D1 and A2-C2, and can be fixed in their positions relative to each other. In addition, an integral connection, e.g. by point pasting in the region of the edges B1-D1 or A2-C2, can take place, in which their distance from each other is small enough for such a connection. As an alternative or in addition, the sagged glass blanks 10a, 10b can be attached to each other on the rear, i.e. on the side opposite the sagging mold 13, over a large area by means of a fixing structure 16 comprising fibre-reinforced plastic, as shown in FIG. 4c. In this arrangement the temperature expansion coefficient of the fixing structure 16 matches the temperature expansion coefficient of the glass blanks 10a, 10b so that position fixing does not change during subsequent coating. Of course in all the variants shown, if required, in a subsequent method step, the shaped body 10 can also be transformed to glass-ceramics by heating.
Apart from the application, shown in FIG. 1, of the shaped body 10 in the field glasses 1, which field glasses are designed for light in the visible spectrum, by applying suitable coatings the shaped body can also be used as a reflective element for other spectral ranges, as shown in FIG. 5 in relation to the X-ray spectral range, and in FIG. 6 in relation to the EUV spectral range.
FIG. 5 shows a diagrammatic view of an imaging telescope 21 of Wolter type I, which focuses incident X-ray light to a focusing plane 25 that is arranged at a right angle in relation to an optical axis 24 of the telescope 21. To this effect the telescope 21 comprises a multitude of mirror shells of the Wolter type that are concentrically arranged, are rotationally symmetric, and are nestled into each other, which mirror shells are azimuthally segmented. A first and a second mirror element 22a, 23a of a first mirror shell, and a first and a second mirror element 22b, 23b of a second mirror shell, which is arranged further inward, are shown in FIG. 5. The mirror elements 22a to 23b essentially comprise the shaped body 10, which has been produced as described above, and to which on one side a coating that is reflective to X-ray light has been applied. The mirror elements 22a to 23b are operated at grazing incidence, wherein the physical effect of total reflection is used. In the arrangement of FIG. 5 each of the X-ray mirror elements 22a to 23b comprises a first hyperbolic partial region (away from the focusing plane 25) and a second parabolic partial region (towards the focusing plane 25), with said partial regions being separated by a pronounced kink in the mirror segments 22a to 23b, which kink extends in a plane 26 parallel in relation to the focusing plane 25. In the nested configuration of FIG. 5 the thickness of the mirror elements is less than 2 mm. The shaped glass blanks 10a, 10b that form the shaped body 10, from which the X-ray mirrors 22a to 23b are made, are connected to each other at the kink by means of pasting, as shown further above.
FIG. 6 shows a further application for the EUV spectrum, namely an EUV collector 27 which is used in an illumination system of projection illumination apparatus for microlithography so as to concentrate the light emanating from a plasma light source 28 in a focal point in the focal plane 25. The EUV collector 27 comprises a structure that is comparable to that of the telescope 21 of FIG. 5, since said EUV collector 27 comprises a plural number of mirror shells that are concentrically nested into each other, which mirror shells are operated at grazing incidence. Due to the fact that the EUV collector 27 is designed to concentrate EUV radiation instead of hard X-ray radiation, the angles at which the mirror shells are impinged can be selected to be slightly larger. FIG. 6 shows mirror elements 22a′ to 23b′ that correspond to the mirror elements 22a to 23b and that comprise a first hyperbolic partial region near the light source 28, and a second elliptic partial region near the focal plane 25, which partial regions are separated by a kink in the mirror elements 22a′ to 23b′. At the kink, corresponding to FIG. 5, two glass blanks that have been formed by sagging are interconnected by pasting, which glass blanks correspond to the hyperbolically formed or elliptically formed partial region.
The method presented above, or the associated shaped body, makes it possible to produce reflective optical elements with small tolerances for surface form deviation and small slope tolerances, even if said shaped bodies comprise discontinuous regions, e.g. kinks, in that the reflective optical elements are composed of several blanks, wherein already during the replication process the relative position of the formed blanks in relation to each other is fixed, so that a shaped body with a defined geometry is created, which geometry corresponds to the geometry used in the respective optical application.
Patent Application
20070258156
