Abstract:
The disclosure generally relates to methods, devices, systems and components configured to position an element in a lens assembly, such as a lens assembly for microlithography, in which the element to be positioned is moved from an actual position to a target position via at least one actuator, and in which at least the positioning movement of the actuator is superimposed with an oscillating movement.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority under 35 U.S.C. §119 to German patent application serial number 10 2006 046 200.9, filed Sep. 29, 2006, the contents of which are hereby incorporated by reference. 
     FIELD 
     The disclosure generally relates to methods, devices, systems and components configured to position an element in a lens assembly, such as a lens assembly for microlithography, in which the element to be positioned is moved from an actual position to a target position via at least one actuator, and in which at least the positioning movement of the actuator is superimposed with an oscillating movement. 
     BACKGROUND 
     In lens assemblies for microlithography applications, it can be desirable for the optical elements like filters, apertures, lenses, mirrors, prisms, to be positioned with high precision, such as, for example, in the nanometer range. In some instances, one or more optical elements can be replaceable elements (e.g., to adapt the imaging properties in different applications). 
     SUMMARY 
     In one aspect, the disclosure features a method that includes using an actuator to move an element from a first position to a target position by superpositioning movement of the actuator with an oscillating movement. The element configured to be used in an optical device. The oscillating movement is changed while moving the element, after moving the element, or both. 
     In another aspect, the disclosure features a method that includes moving an element from a first position to a target position using an actuator. The element is configured to be used in an optical device, and the target position is reached to within 5 nm and less. 
     In a further aspect, the disclosure features a device that includes an actuator configured to move an element, where the element is configured to be used in an optical device. The device also includes a unit configured to superimpose an oscillation onto the actuator, and a detection apparatus configured to detect the actual position of the element to be positioned. The device further includes a control unit configured so that the oscillation is changed as the element increasingly approaches a target position, after the element has reached the target position, or both. 
     In an additional aspect, the disclosure features a device that includes an actuator configured to move an element, where the element is configured to be used in an optical device. The device also includes a unit configured to superimpose an oscillation onto the actuator, and a detection apparatus configured to detect the actual position of the element. The device further includes a control unit. The device is configured so that the element can be positioned to within 5 nm of a target position. 
     In some embodiments, the disclosure provides systems, components and methods that can allow for relatively exact positioning/adjusting of an element in an optical system, like a lens assembly, such as a lens assembly for microlithography. In certain embodiments, positioning in the sub-μm-range can be achieved in a simple and efficient manner. This can, for example, improve service life of the actuators, while at the same time providing precision and exactness of positioning. 
     The oscillation, with which the actuator is provided, can be changed during and/or after the termination of a motion step. This can have the advantage that the oscillation that is provided to the actuator can be adapted, so that the oscillation is optimized, with reference to the service life of the actuator and the entire manipulation system. Additionally, also an optimization, with respect to the reduction of the interference influence of the oscillation signal upon the entire optical system and the element to be positioned, can be performed. Furthermore, the variation of the oscillation during and/or after ending a motion step has the advantage, that the oscillation can also be adjusted with respect to reaching the target position of the element to be positioned in an optimum manner. With an increasing approach of the element to be positioned to the target position, next to changing the parameters of the approach motion, also a change of the superimposed oscillation can be advantageous respectively. 
     The superimposed oscillation can lead to an oscillating movement of the actuator, or the respective moving part of the actuator, as e.g. of a moveable valve body, or pin, in a valve- or gas pressure controller, so that friction influences during the start motion, or slip effects can be avoided. 
     The present disclosure can be used for continuous approximation movements, e.g. through a PID controller (Proportional Integral Differential Controller), or for the stepwise approach method described in EP 1 209 502 B1. In a continuous approach movement, the entire approach movement from the actual position to the target position is considered a movement step, while the approximation movement can be formed by several, or through a plurality of different motion steps, during the stepwise approximation. 
     The change of the oscillation movement can relate to the change of the amplitude, the frequency, and/or the frequency form. Herein, all possible changes are viable, which serve to extend the service life of the actuator or parts thereof, and of the entire manipulator to position the optical element. Respective values can be determined through suitable test series in each particular case, since, depending on the application, various changes can be necessary. For example, it is conceivable, that low frequencies are desirable in certain systems, whereas very high frequencies can be advantageous in other systems. 
     As forms for possible oscillation movements sine oscillations, triangular oscillations, saw tooth oscillations, rectangular oscillations, or any kind of oscillation forms is conceivable. 
     The disclosure can be used, for example, with actuators, which only indirectly lead to the movement of the element to be positioned, like e.g. a moveable valve body of a gas pressure regulator for a pneumatic bearing- or positioning device. Thus, there is the possibility to filter out the oscillation, superimposed onto the actuator, when transposing the actuator movement into the element movement, so that the element to be positioned is not loaded by the imparted oscillation. 
     Accordingly a filter or damper element can be provided between the actuator and the element to be positioned, to filter out or damping interfering oscillations. However, such a component can also be left out, when the imparted oscillation is turned off after reaching the target position, or transposed into a non interfering form. 
     The actuator can be formed by respective valves, pressure controllers, electric motors, electric magnets, piezoelectric components, and/or combinations thereof, which provide the opportunity to superimpose the control system for the actuator with a respective oscillation, the so-called Ditter-signal. 
     The elements of an optical system, like of a lens array, that can be positioned, can include optical lenses, mirrors, prisms, filters, apertures, structured plates and the like. In some embodiments, an element can be a replaceable component. 
     The disclosure also provides a device (e.g., configured to perform a respective process) which has at least one actuator configured to move the element to be positioned, a detection apparatus configured to detect the actual position of the element to be positioned, a unit to impart or superimpose an oscillation onto the actuator and a control unit, which is provided, so that a respective change of the oscillation can be performed with an increasing and/or final approach of the actual position to the target position. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       Further characteristics and features will be apparent during the subsequent detailed description of an embodiment based on the appended figures, in which: 
         FIG. 1  a schematic drawing of a device configured to position an element in a lens assembly; and 
         FIG. 2  a time distance diagram of an element to be positioned. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows a device to position an element in a lens assembly (e.g., a lens assembly for microlithography) in a purely schematic illustration. An optical element  10  (e.g., a lens) is received in a frame  11 , and is moveably supported through pneumatic gaiters  12 . 
     The gaiters  12  (of which only one is designated in  FIG. 1 , and which is used for description in an exemplary manner) are connected respectively through a gas, or air conduit  16  and  19  with a gas or compressed air supply which is not described in more detail. 
     Between the gas-, or compressed air supply, or in the conduit  16 , a pressure controller is provided in the form of a valve  18 , through which the pressure in the gaiters, and thus its expansion can be regulated. Through the gas pressure controller, thus through the gaiters  12 , a positioning change of the optical element  10  can be realized. To determine the position of the optical element  10 , or the expansion of the gaiters  12 , a detector  13  is provided, which is connected with a control unit  14  through a signal conduit  15 . The control unit  14  controls based on the predetermined target value of the position of the element  10  with reference to the gaiters  12  and to the actual state determined by the detector, the position of the gas pressure controller or the valve  18 , functioning as an actuator through the control conduit  20 . 
     In addition, the control unit  14 , which can, for example, be a computer with respective software, generates an output signal to generate a superimposed oscillation, which is transmitted through the signal conduit  21  to the module  22  to generate the oscillation. 
     The module  22  to generate oscillations then generates a so-called Ditter signal according to the respective command of the control unit  14 , wherein the Ditter signal is modulated onto the control signal for the gas pressure controller  18  in the modulation unit  24 , in order to be finally handed over to the gas pressure controller  18  in the signal conduit  23 . Through the control signal, superimposed with the Ditter signal, electric motors, electric magnets, or piezoelectric elements can be controlled to change the valve position of the pressure controller. 
     Through the superimposed oscillations, the moveable valve body constantly stays in motion, so that so-called slip stick effects can be avoided, when the motion of the valve body begins after a resting position, which can lead to a degradation of the positioning process. 
     In order not to transfer the oscillating motion to the optical element  10 , a filter unit  17  is provided, which is used to filter out the oscillations, which the valve body or the gas pressure controller performs, in order to avoid slip stick effects. 
     Such a filter unit  17  can e.g. be provided through respectively selected openings, or through damper elements, like e.g. Helmholtz resonators. 
     The filter unit  17 , however, can be dispensed with, when it is assured that after the positioning process, the oscillation or the so-called Ditter signal are equal to zero, or are located in a range, or occur in a manner, which are not critical for the application. 
     Instead of a gaiter  12 , also, an air, or a gas bearing can be selected, which can be operated with a respective gas, as it already is present in the interior volume of the lens assembly, e.g. dried nitrogen. 
     In  FIG. 1 , the entire device is only illustrated with reference to one bearing element in the form of a gaiter  12 , while, however, more bearing or positioning elements (e.g., four bearing or positioning elements) can be used in the form of gaiters  12 . Respective components can be provided in these, wherein a single signal control unit can be provided for all these support- or positioning elements and the actuators connected therewith. 
     Instead of or in addition to the actuation of the optical element shown in the illustrated embodiments, also all other conceivable devices to operate or move an optical element in a lens assembly, like e.g. electric motors, piezoelectric elements, or similar can be used, as described e.g. also in EP 1 209 502 B1. 
     The device described in  FIG. 1  now functions, so that through the detectors  13 , the actual position of the optical element  10  is detected, which is transferred through the signal conduits  15  (only one is shown) to the control unit  14 . In the control unit  14 , the actual position is compared with the target position, and according to the control requirements suitable control signals for the gas pressure regulator  18  or the actuator are put out through the signal conduit  20 . The control parameters can thus provide either for a step approach of the actual position to the target position according to EP 1 209 502 B1, or for a continuous approach according to a conventional control method (PID controller). 
     In any case, the control unit  14  provides an output signal to control the module configured to generate oscillation  22  through the signal conduit  21  depending on the comparison between actual position and target position. The module  22  generates an oscillation signal, which is superimposed to the control signal of the signal conduit  20  for the gas pressure controller  18  in the modulation unit  24 , so that the moveable valve body determining the gas pressure in the gas pressure regulator performs an oscillating movement in addition to its movement to set the respective gas pressure, wherein the oscillating movement can avoid so-called slip stick effects while performing the movement, thus allowing an exact pressure setting and thus position adjustment of the optical element  10  through the gaiters  12 . 
     The control unit  14  is thus provided, so that with an increasing approach of the element  10  to be positioned to the target position, the superimposed oscillation is changed with reference to the frequency, the amplitude, and/or the frequency form. In addition, after reaching the target position, an oscillation is set which is optimized for the service life of the actuator or the gas pressure regulator and/or for the interference free support of the optical element. Depending on the application, this can mean that the oscillation is set with very high or very low frequencies, with amplitudes approaching zero, and/or with certain frequency forms. For example, a very high frequency can be more advantageous under certain conditions through the inertia of the system and through avoiding respective friction effects at a certain amplitude, than a turned off oscillation with an amplitude equaling zero, in which through re-started movement of the respective actuator under certain conditions higher friction forces occur. 
       FIG. 2  shows the approach of a respective optical element to the target position in a time distance diagram, the target position being described by the broken illustration of the straight line  3 . 
       FIG. 2  shows time on axis  1  and the location or the position on axis  2 , wherein the straight line  3  represents the target position. The curve  5  hereby represents the approach of the element to be positioned to the target position  3 , wherein the curve  4  represents the actual motion, which is generated through the overlap of the approach motion according to the curve  5  with the oscillation. 
     The information in  FIG. 2  is also only to be regarded purely schematic, so that the magnitude of the amplitudes of the oscillation frequency, and of the form can differ significantly from the information in  FIG. 2 . 
     Through the superposition of the motion of an actuator to position an element with an oscillation, which is changed with increasing approach to the target position, and/or after terminating the approach motion, a precise and exact positioning of the element in the sub-μm-range becomes possible, wherein the service life of the moveable elements involved, and in particular of the actuators, can be optimized. 
     While certain embodiments have been described, other embodiments are also possible. As an example, some embodiments may involve the combination of certain features or the omission of certain features. 
     Other embodiments are in the claims.