Optical: systems and elements – Lens – With support
Reexamination Certificate
1999-06-09
2001-05-08
Epps, Georgia (Department: 2873)
Optical: systems and elements
Lens
With support
C359S823000, C359S819000
Reexamination Certificate
active
06229657
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable.
CROSS-REFERENCES TO RELATED APPLICATIONS
Not Applicable.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to an assembly of optical element and mount, the use of such an assembly, an objective therewith and a projection exposure device for microlithography therewith. Optical components, such as lenses, prisms, mirrors, gratings, consisting usually of glass, crystal or ceramic, are regularly assembled by means of mounts, as a rule of metal, to give optical assemblies, for example, objectives.
The optical elements are then to be positioned while maintaining close tolerances relative to one another, and the whole assembly is to have a certain robustness against external influences. Particular requirements are then set both for astronomical telescopes, such as those in satellite-borne systems (for example, the ROSAT X-ray telescope), and in projection exposure systems for microlithography.
European Patent EP 0 053 463 teaches the suspension of precision mirrors on leaf spring elements, which are cemented.
A highly developed mounting technology for lenses of microlithographic projection objectives is also described in U.S. Pat. No. 5,428,482.
Either the lens is directly cemented with three radial bending beams, or an intermediate ring is connected to the outer mount ring by means of three monolithic joints evenly distributed on the periphery. Full-surface cementing of the lens and intermediate ring is provided. An optical assembly, in particular an objective, is then built up by stacking the mount rings.
Arrangements with actuators for the displacement or deformation of optical elements relative to the basic mount part are known in many embodiments. An example is provided by European Patent EP 0 145 902 A, where a mirror is suspended on a mount by means of three tangential spokes whose length can be varied by means of Peltier elements.
SUMMARY OF THE INVENTION
The invention has as its object the provision of an assembly of optical element and mount, in which the accuracy of positioning of the optical element and its decoupling from external effects acting on the mount are increased. The joint place between the optical element and mount, that is, a glass-metal or crystal-metal connection as a rule, is at the same time to be relieved of requirements for geometrical precision, so as to make it accessible for other jointing processes such as adhesion, particularly for the increase of DUV resistance.
The inventive solution is to cover as a construction principle a great bandwidth of cases of application. The integration into an objective and the use in a microlithography projection exposure device is provided, with particular suitability for very sensitive adjustment of its imaging power.
This object is attained by means of an assembly of optical element, a mount, a plurality of lugs, a rigid intermediate ring, adjusting members or passive decouplers, and a housing. The optical element is coupled by the lugs to the rigid intermediate ring. The rigid intermediate ring is connected by the adjusting members or the passive decouplers to the mount for connection to the housing or further mounts. In which the optical element is coupled by numerous lugs to a rigid intermediate ring, which is further connected via active adjusting members or passive decouplers to a mount which is to be connected to a housing and/or to further mounts.
The lugs are embodied as spring links or leaf springs. The different thermal expansion of the optical element (e.g., glass) and the mount (metal) is thereby substantially taken up. Altogether, stresses are minimized.
The connection of the optical element with the lugs is concerned to insure stability to the radiation which acts on the optical element (which is a problem in the UV region), and likewise not to build up any stresses in the optical element, as is unavoidable with positive connections (clamping). Material connections, e.g. metallic welded or soldered connections are therefore preferred.
This similarly holds for the connection of the lugs to the intermediate ring; here also, the homogeneous integral one-piece embodiment of the lugs and the intermediate ring is possible and in many cases is meaningful. However, where position tolerances of the lugs in the connection to the optical element are to be equalized, jointing to the intermediate ring, e.g. by laser welding is advantageous.
Piezoelements, or else Peltier elements (as in European Patent EP 0 145 902 A), are suitable driving means for the active adjusting members, which can in addition include suitable mechanisms (monolithic levers and joints).
Monolithic joints and mechanisms are principally suitable for the passive decouplers, somewhat corresponding to U.S. Pat. No. 5,428,482.
An important class of optical elements are those provided, with a rotationally symmetrical edge with a symmetry axis. This particularly includes the classic lenses with a cylindrical edge, certainly also with non-spherical and non-centered optical surfaces.
Advantageous embodiments of the intermediate ring and the lugs are realized in which the intermediate ring is rotationally symmetrical with respect to the symmetry axis. The lugs are arranged symmetrically with respect to the planes (E) containing the symmetry axis, and uniformly distributed over the periphery of the optical axis.
Particularly advantageous embodiments are possible regarding the arrangement of lugs. The optical element has a main plane that intersects the edge of the optical element with a closed curve (closed contour or closed loop). The lugs can be arranged substantially perpendicularly to the main plane. Or the lugs can be arranged substantially in the main plane radially of the edge of the optical element. According to this, the lugs are arranged like spokes between the “hub” represented by the optical element and the “rim” of the intermediate ring.
The lugs can also be arranged tangentially, similarly to the beams of U.S. Pat. No. 5,428,482.
An important advantage of the arrangement according to the invention, which with its many free constructional parameters makes quite possible the setting of a lowest characteristic frequency of mechanical vibrations greater than 200-400 Hz, (preferably greater than 300 Hz up to 1 K Hz). The disturbing vibration excitations which are present substantially at lower frequencies are thereby effectively suppressed.
High qualities of the stress-free mounting are attainable with the invention. Astigmatic or three-waviness residual lens deformations under 30 nm, down to under 20 nm, are attained. The deformations of the seating surface of the outer ring are decoupled from the lens to the extent of over 95%, preferably over 98% and in optimum constructions to over 99%.
Passive adjusting members are provided are particularly suitable for the adjustment of the lens to a reference outside the objective and within the objective.
In their preferred use, the assemblies are in objectives and projection exposure devices for microlithography, wherein tieing into a control circuit that drives the actuators makes possible the correction of extremely fine disturbances.
REFERENCES:
patent: 5428482 (1995-06-01), Bruning et al.
patent: 5523893 (1996-06-01), Haas
patent: 5555480 (1996-09-01), Tanaka
patent: 5991101 (1999-11-01), Holderer et al.
patent: 31 16579 A1 (1981-04-01), None
patent: 37 14745 A1 (1987-05-01), None
patent: 197 48 211 (1999-05-01), None
patent: 0 053 463 A2 (1981-11-01), None
patent: 0 053 463 (1981-11-01), None
patent: 0 145 902 (1983-10-01), None
Patent Abstract of Japan; Publication No. 60230609; Application Date Jan. 5, 1984: Konishiroku Photo Ind Ltd.
Patent Abstract of Japan; Publication No. 10026736; Application Date Oct. 7, 1996; Kodaira Takashi.
European Search Report Dated Oct. 20, 1999 EP 99110271.
Neue Werkstoffverbunde durch Ultraschall-schweissen. technologie & management. pp. 31-39 Erwin Roeder, Guntram Wagner, & Jochen Wagner, 1995. English Translation in not readily available.
Holderer Hubert
Rummer Peter
Trunz Michael
Carl-Zeiss-Stiftung
Epps Georgia
Lucas Michael A
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