This application relates to and claims priority to corresponding German Patent Application No. 100 46 379.7 filed on Sep. 20, 2000.
The invention relates to an optical element deformation system in an imaging device for the purpose of eliminating image errors or for active adjustment.
Very high imaging accuracies are required in many optical fields, in particular in micro-lithography. The aim is to minimize image errors even more. One of the main causes of image errors in this case is deformations of the optical elements. Such deformations can be introduced via mounts or be produced by mounts. Weight forces on optical elements can also lead to deformations and thus to image errors.
Reference is made to WO 97/34171 in relation to the general prior art.
Moreover, the precise adjustment of an imaging device, for example a projection lens, also requires individual optical elements to be actively adjusted in order, for example, to compensate errors in the lens in this way, or else to correct mounting inaccuracies.
It is the object of the present invention to create a system of the type mentioned at the beginning with the aid of which specific deformations can be undertaken on an optical element in a very comprehensive way, and/or very specific and sensitive active adjustments are also possible.
According to the invention, this object is achieved by means of an optical element deformation system in an purpose of eliminating image errors wherein an optical element bears piezoelectric elements being applied as actuators in the form of thin plates, films or layers to surfaces of the optical element, whereby forces and/or moments are being exerted on the optical element for deformation in conjunction with a servo loop having at least one sensor, and by controlled activation of the piezoelectric elements as actuators.
According to the invention, piezoelectric elements are now used as actuators in the form of thin plates, films or layers which are fitted specifically to surfaces to be deformed, or integrated in them. A type of adaptronic servo loop is created in cooperation with sensors, as a result of which it is possible to examine detected deformations very precisely and to treat them appropriately. It is also possible in this way to introduce specific deformations very precisely into the optical element by means of forces and/or moments applied via the activation of the piezoelectric elements.
Although the use of piezoelectric elements is already fundamentally known in optics, for which purpose reference is made, for ;example, to WO 97/09642, U.S. Pat. No. 4,202,605 and U.S. Pat. No. 5,986,795, piezoelectric elements in the form of piezostacks respectively exerting deformation forces on optical elements, in the present case, by contrast, use is made specifically of thin plates, films or layers which are applied, for example in the form of coatings or via bonding methods, directly to the surfaces to be deformed and are arranged and aligned there for a specific purpose. At the same time, feedback via sensors and an adaptronic servo loop is provided in this case in such a way that it is possible in this way to act very precisely and within very small tolerances.
It is possible to use as sensors, for example, capacitive ranging sensors, interferometers and the like, or, in a very advantageous development of the intention, also piezoelectric elements in the form of thin plates, films or layers such as, for example, ceramic films, which act as sensors and cooperate with the piezoelectric elements as actuators. The sensors and actuators can be arranged in an alternating fashion for this, purpose.
In this solution according to the invention, piezoelectric elements are used in two regards, specifically firstly deformations or vibrations which occur lead to changes in length of the piezoelectric elements which are thereby correspondingly bent in the manner of a strain gauge. These changes in the piezoelectric elements generate voltages which are correspondingly detected and evaluated. The piezoelectric elements act in this way as sensors.
The reverse action is employed in the case of use as actuators: voltages are impressed via control lines on the piezoelectric elements and lead to corresponding changes in length and/or bending of the piezoelectric elements. These changes thereby initiate vibrations and/or deformations in the adjoining structure. In this case, the deformations are controlled or regulated via the adaptronic control circuit such that the desired effects are achieved in an extremely precise fashion such as, for example, the counteracting of detected deformations in order to comply with imaging accuracy, or compensating weight forces which lead to deformations or else to active adjustment, in order to counteract image errors detected or to correct them.
In an advantageous refinement of the invention, it can also be provided that, to damp vibrations, all the piezoelectric elements are configured as sensors in the quiescent state or in a phase of slight excitation of vibrations. Disturbances which occur are then packed up by all the piezoelectric elements, and all, or else only specific piezoelectric elements can then subsequently be activated as actuators by appropriate control action. This refinement has the advantage that it is not necessary to identify specific piezoelectric elements as sensors or as actuators. All that need be provided is an appropriate regulating or control device.
In a further advantageous refinement of the invention, it is possible, for example, for the deforming surface to be provided over its entire area, or virtually over its entire area with a piezoelectric layer or film. Structures are then shaped in this layer, for example using lasers. The most varied patterns can be created in this way. If the structures of the most varied type are respectively provided with terminals in this case, the most varied deformation zones or regions and intensities of deformation can be achieved at any desired sites by appropriate activation. It is then also possible in this case to control the individual structures completely separately, as a result of which completely diverse deformations and force effects can be achieved as a function of the desired corrections and/or results.
Further advantageous refinements and developments of the invention emerge from the subclaims and from the exemplary embodiments described below in principle with the aid of the drawing, in which:
In accordance with
Capacitive ranging sensors 4 at a short distance from the rear 2 are provided in order to detect the state of deformation. The piezoelectric elements 3 are piezoelectric ceramic films (PZT films) which are integrated in the mirror material or bonded onto the rear 2, and which can for example, have a thickness of a few μm. When the PZT films are being driven, they experience in accordance with the piezoelectric effect a strain which impresses forces on the mirror via the connection with the mirror substrate, and this leads to deformation of the mirror. Multifarious “patterns” are conceivable for generating any desired states of deformation in any desired angular orientation. As a rule, the piezoelectric elements will be provided for low corrugations, although these are not, of course, restrictive.
Provided in
It may be seen from the enlarged illustration in
If a lens is provided for a deformation as optical element instead of a mirror, the piezoelectric elements 3 must, of course, be arranged in regions which are not optically active. Furthermore, the peripheral surface of the lens is also available in this case for the purposes of deformation.
Two exemplary embodiments relating to specific deformation of a mirror 1 and by means of which the focus and/or the mirror focal length can be varied are provided in
Both in the case of the exemplary embodiment according to
Two examples are shown in
A force and/or a moment can be applied in each case to the appropriate optical element by activating the piezoelectric elements 3, which are applied in the form of PZT films. In this case, the magnitudes of the forces and moments to be applied are selected such that their action is directed opposite to the action of gravity, and the weight force effect is thereby eliminated or at least substantially reduced.
As may be seen from
The deformation of the lens 9, reducing on the weight force, is reduced in a similar way in accordance with
Number | Date | Country | Kind |
---|---|---|---|
100 46 379 | Sep 2000 | DE | national |
Number | Name | Date | Kind |
---|---|---|---|
4202605 | Heinz | May 1980 | A |
5026977 | Hubbard, Jr. | Jun 1991 | A |
5428482 | Bruning et al. | Jun 1995 | A |
5719846 | Matoba et al. | Feb 1998 | A |
5986795 | Chapman et al. | Nov 1999 | A |
6411426 | Meehan et al. | Jun 2002 | B1 |
6496466 | Lee et al. | Dec 2002 | B1 |
6566627 | Brandinger et al. | May 2003 | B2 |
6585379 | Yokoyama et al. | Jul 2003 | B2 |
Number | Date | Country |
---|---|---|
371906 | Oct 1963 | CH |
3406907 A 1 | Oct 1984 | DE |
198 25 716 A 1 | Dec 1999 | DE |
199 10 947 A 1 | Sep 2000 | DE |
0 053 463 | Jun 1982 | EP |
0 230 277 | Jul 1987 | EP |
0 964 281 | Dec 1999 | EP |
1 209 500 | May 2002 | EP |
WO 9709642 | Mar 1997 | RU |
WO 9734171 | Sep 1997 | WO |
Number | Date | Country | |
---|---|---|---|
20020048096 A1 | Apr 2002 | US |