Abstract:
The invention relates to a device for manipulation of the angular position of an object relative to a fixed structure, into which the object, in particular an optical element of a lens group for microlithography, is introduced, about three rotational axes, intersecting at a point. The object can also be held in a support frame. The support frame, with the object is connected to the fixed structure by means of three connection limbs each with three rotational degrees of freedom and one translational degree of freedom. The angular position of the support frame is adjustable about each one of the three rotational axes by means of one of the connection limbs.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a device for manipulating the angular position of an object relative to a fixed structure, about three tilt axes intersecting at a point. More particularly, the object may be constituted by an optical element disposed in a microlithographic projection lens.  
         [0003]     2. Description of the Related Art  
         [0004]     To date, only gimbal bearings for the tilting of an object about three axes intersecting at a point are generally known, in which the tilt axes are divided into a plurality of dividing gears. This necessitates that a plurality of supporting frames, generally one per tilt axis, must be fitted one inside the other, which detrimentally takes up an extraordinary amount of space. For the general state of the art, reference should here be made to JP 000735963.  
         [0005]     The dividing gears are also frequently constructed as spring joints. This can lead to the object supported by means of the gimbal bearing being able to be bounced and vibrated relative to the outside world.  
         [0006]     In addition, when the dividing gears or springs are fitted one behind the other in the gimbal bearing, the natural frequency at which the object vibrates falls heavily. A minimum natural frequency which is frequently demanded, especially in the field of microlithography, is thus often unattainable.  
       SUMMARY OF THE INVENTION  
       [0007]     The object of the present invention is therefore to provide a device for tilting an object about three tilt axes intersecting at a point, which device has a very low spatial requirement and allows a very rigid construction and hence a very high natural frequency of the mounted object.  
         [0008]     This object is achieved according to claim  1  by the fact that the object is connected to the fixed structure by three tie members, having respectively at least two rotational mobilities and one translational mobility, the angular position of the object being adjustable by, respectively, one of the tie members about, respectively, one of the three tilt axes. According to claim  23 , the object is achieved by virtue of the optical element being connected to the fixed structure by three tie members, having respectively at least two rotational mobilities and one translational mobility, the angular position of the optical element being adjustable by, respectively, one of the tie members about, respectively, one of the three tilt axes.  
         [0009]     The measures according to the invention allow the object to be tilted in a simple and advantageous manner about three tilt axes intersecting at a point. The device according to the invention can be made in a highly space-saving design, since several supporting frames are able to be eliminated. Furthermore, the device according to the invention produces better rigidity. This prevents unwanted vibrations and, at the same time, gains the natural frequency of the object, which in microlithography is essential. An additional, very substantial advantage is constituted by the good accessibility of the object.  
         [0010]     Advantageous designs and refinements of the invention can be obtained from the subclaims and from the illustrative embodiments described in basic terms below with reference to the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  shows a perspective view of the device according to the invention;  
         [0012]      FIG. 2  shows a perspective view of an embodiment of a tie member having ball joints, rods and a sliding block;  
         [0013]      FIG. 3  shows a perspective view of a monolithic embodiment of a tie member having solid state joints or leaf springs;  
         [0014]      FIG. 4   a  shows a perspective view of a second embodiment of the device according to the invention, having a prism mounted in a supporting frame and a tie member represented in greater detail in  FIG. 5 ;  
         [0015]      FIG. 4   b  shows a further perspective view of the device represented in  FIG. 4   a;    
         [0016]      FIG. 5  shows a perspective view of a further alternative embodiment of a tie member having solid state joints or leaf springs;  
         [0017]      FIG. 6  shows a side view of a third embodiment of the device according to the invention, having a prism mounted in a supporting frame;  
         [0018]      FIG. 7  shows a perspective view of a fourth embodiment of the device according to the invention, having a prism mounted in a supporting frame and a tie member represented in greater detail in  FIG. 8 ;  
         [0019]      FIG. 8  shows a perspective view of a further alternative embodiment of a tie member having solid state joints or leaf springs; 
     
    
     DETAILED DESCRIPTION  
       [0020]     Illustrative embodiments, as can be used in a microlithographic projection lens for the manufacture of semiconductor elements, for example, are described below. A projection lighting system having a projection lens is described, for example, in EP 1022617 A2.  
         [0021]     As can be seen from  FIG. 1 , an object  1  is mounted in a supporting frame  2 , which is connected to a fixed structure  4  with three tie members  3   a ,  3   b ,  3   c  respectively, the tie members  3   a ,  3   b ,  3   c  having, as mobilities, three rotations and one translation respectively, and thus the angular position of the supporting frame  2  with the object  1  is adjustable by, respectively, one of the tie members  3   a ,  3   b ,  3   c  about, respectively, a tilt axis x, y or z. The fixed structure  4  is connected to a housing of a projection lens  4   a  (indicated only in dashed representation in  FIG. 1 ). The object  1  can be, for example, a beam-bending mirror or a prism, what matters being an appropriately precise adjustment.  
         [0022]     In  FIG. 1  it is indicated that the tilt axes x, y and z intersect at a point.  
         [0023]     The of the respective translational mobilities of the three tie members  3   a ,  3   b ,  3   c  are linearly independent from one another.  
         [0024]     The x-tilt angle is adjusted by displacement of the tie member  3   a , the y-tilt angle by displacement of the tie member  3   b  and the z-tilt angle by displacement of the tie member  3   c . A manipulation of the angular position of the object  1  mounted in the supporting frame  2  about three tilt axes x, y and z intersecting at a point is thus made easily possible.  
         [0025]     As can further be seen from  FIG. 1 , the tie members  3   a ,  3   b ,  3   c , for the adjustment, respectively, of one of the tilt axes x, y or z, have adjusting mechanisms  5  for the translatory adjustment of at least one part-element  6  of the respective tie members  3   a ,  3   b ,  3   c . The motional direction of the adjusting mechanisms  5  of the respective tie members  3   a ,  3   b ,  3   c  runs perpendicular to their translational mobility.  
         [0026]     Each of the tie members  3   a ,  3   b ,  3   c  has two part-elements  6   a ,  6   b . These are joined together by a hinge  7 . The part-element  6   b  is connected to the supporting frame  2  by a ball joint  8 . The part-element  6   a  facing away from the supporting frame  2  is connected to the fixed structure  4  and can be purposefully moved therein, in a translatory motion, by means of the adjusting mechanisms  5 .  
         [0027]     As can further be seen from  FIG. 1 , the adjusting mechanisms  5  have dovetailed sliding blocks  9 , which can be purposefully moved, in a translatory motion, by means of adjusting means. The adjusting means  10  can be moved, for example, by manual, motor-driven, hydraulic, electromagnetic, piezoelectric or magnetostrictive means. In the present illustrative embodiment, the adjusting means are configured as setting screws  10 . The translational mobility of the setting screws  10  is indicated in  FIG. 1  by means of arrows  11 .  
         [0028]     The center points of the ball joints  8  and the axes of the hinges  7  respectively unfold planes, the translational mobilities of the respective tie members  3   a ,  3   b ,  3   c  being directed perpendicular to the respective planes.  
         [0029]     The sliding blocks  9  are provided with contact faces  12  for transmitting the displacement of the setting screws  10  to the sliding blocks  9 . The fixed structure  4  has recesses  13 , matched in shape and dimensions to the sliding blocks  9 , for receiving the sliding blocks  9 . The sliding blocks  9  can now be introduced into the recesses  13  in the fixed structure  4  in such a way that they are translatorily adjustable by means of the setting screws  10 , which act upon the contact faces  12  of the sliding blocks  9 .  
         [0030]     It can further be seen from  FIG. 1  that the axes of the hinges  7  of each of the tie members  3   a ,  3   b ,  3   c  are respectively disposed at least approximately parallel to the respective translatory motional direction of the adjusting mechanisms  5 .  
         [0031]     The tie member  3   a  is disposed such that the point of contact between the tie member  3   a  and the supporting frame  2  lies in the plane which is unfolded by the y-tilt axis and the z-tilt axis. The translational mobility of the tie member  3   a  is in this case orientated perpendicular to the plane unfolded by the y and z-tilt axes. The adjustment of the x-tilt angle is effected by displacement of the point of contact between the tie member  3   a  and the fixed structure  4 , the direction of displacement having a component parallel to the plane unfolded by the y and z-tilt axes and not intersecting the x-tilt axis. The displacement is adjusted by the setting screws  10 .  
         [0032]     The tie member  3   b  is disposed such that the point of contact between the tie member  3   b  and the supporting frame  2  lies in the plane unfolded by the z-tilt axis and the x-tilt axis. The translational mobility of the tie member  3   b  is in this case orientated perpendicular to the plane unfolded by the z and x-tilt axes. The adjustment of the y-tilt angle is effected by displacement of the point of contact between the tie member  3   b  and the fixed structure  4 , the direction of displacement having a component parallel to the plane unfolded by the z and x-tilt axes and not intersecting the y-tilt axis. The displacement is, once again, adjusted by the setting screws  10 .  
         [0033]     The tie member  3   c  is disposed such that the point of contact between the tie member  3   c  and the supporting frame  2  lies in the plane unfolded by the x-tilt axis and the y-tilt axis. The translational mobility of the tie member  3   c  is in this case orientated perpendicular to the plane unfolded by the x and y-tilt axes. The adjustment of the z-tilt angle is effected by displacement of the point of contact between the tie member  3   c  and the fixed structure  4 , the direction of displacement having a component parallel to the plane unfolded by the x and y-tilt axes and not intersecting the z-tilt axis. The displacement is in this case likewise adjusted by the setting screws  10 .  
         [0034]     The tie members  3   a ,  3   b ,  3   c  can be very different in design, but always have three rotational mobilities and one translational mobility in common. The rotational mobilities do not, however, necessarily have to be related to the point of contact between tie member  3   a ,  3   b ,  3   c  and supporting frame  2 . In this type of rotational mobility, the point of contact between tie member  3   a ,  3   b ,  3   c  and supporting frame  2  would perform a swivel motion, since the fulcrum of this rotational mobility would no longer lie at the point of contact.  
         [0035]      FIG. 2  shows a tie member  3   d  of this kind having two part-elements  6   c  and  6   d , which are joined together by two ball joints  8 . The elongated part-element  6   c  is connected to the fixed structure  4  by a dovetailed sliding block  9 —as already represented in  FIG. 1 . The part-element  6   e  has two rods  14 , which are fastened by two ball joints  8 , via a contact plate  15 , to the supporting frame  2 . A direct connection to the supporting frame  2 , without contact plate  15 , is also, of course, conceivable. In this case, the contact region of the supporting frame  2  between the ball joint contact points may be regarded as part of the tie member  3   d.    
         [0036]     In the case of this tie member  3   d , the axes of the rotational mobilities  16   a ,  16   b  and  16   c  do not intersect at any point. The vertical rotation axis  16   a  passes through the center points  6   f  the two ball joints  8  on the contact plate  15 . The horizontal rotation axis  16   b  lies in the plane unfolded by the two rods  14 , on the angle bisector between the rods  14 . The horizontal rotation axis  16   c  passes through the point of intersection of the extensions (indicated in dashed representation) of the rods  14  perpendicular to the plane unfolded by the two rods  14 .  
         [0037]     The tie members  3   d  must in this case be fitted such that their points of contact with the supporting frame  2  (here the ball joints  8  on the contact plate  15 ) lie respectively in the plane respectively unfolded by the two tilt axes x, y, z (see  FIG. 1 ) which are not adjusted by the respective tie member  3   d.    
         [0038]      FIG. 3  shows a tie member  3   e , which is constructed with solid state joints or spring joints  17 . In a simple and advantageous manner, this tie member  3   e  can be made in monolithic construction. A leaf spring  17   a  connects a part-element  6   f  of the tie member  3   e  to the supporting frame  2  and permits on the supporting frame  2  a translation in the direction of an axis  18  and rotations about the axes  16   a ,  16   b  and  16   c  relative to the part-element  6   f . Whilst a leaf spring  17   b  connects the part-element  6   f  to the fixed structure  4 , a leaf spring  17   c  creates the connection of the part-element  6   f  to an actuator  19 , which is fixedly mounted in the fixed structure  4 .  
         [0039]     The actuator  19 , in rest position, secures the leaf spring  17   c  by its end and, for the adjustment of a tilt angle, imparts a displacement in the specified arrow direction  11  to a part-element  6   e  of the tie member  3   e , which part-element is connected to the leaf spring  17   c . The part-element  6   e  possesses, for this purpose, a contact face  20  for transmitting the displacement of the actuator  19  to the part-element  6   e.    
         [0040]     The rotation axis  16   c  passes through the instantaneous center of rotation obtained from the point of intersection of the center lines of the leaf springs  17   b  and  17   c.    
         [0041]     In  FIGS. 4   a  and  4   b , a further constructional embodiment of the invention is represented, in which an optical element—in this case a prism  1 —can be tilted about three tilt axes x, y, z intersecting at a point PO.  
         [0042]     The prism  1  is mounted in the supporting frame  2 , which is connected to the fixed structure  4  by three tie members  3   f ,  3   g  and  3   h . Here too, the fixed structure  4  can be connected to a housing of a projection lens  4   a  (indicated only in dashed representation, for example in  FIG. 1 ). Integrated in each tie member  3   f ,  3   g ,  3   h  there is an adjusting mechanism  5 , which allows tilting by a respective angle. The prism  1  can thus be tilted, by adjustment of the tie member  3   f , about the tilt axis x, with the tie member  3   g  about the tilt axis y and with the tie member  3   h  about the tilt axis z.  
         [0043]     Generally, each tie member  3   f ,  3   g ,  3   h , in the contact with the supporting frame  2 , must possess a translational mobility and three rotational mobilities, a rotational mobility being alternatively replaceable by a swivel mobility in the contact with the supporting frame  2 .  
         [0044]     The point of contact of the tie member  3   f  with the supporting frame  2  lies in the plane unfolded by the two tilt axes which are adjusted by means of the tie members  3   g  and  3   h . The translational mobility of the tie member  3   f  stands perpendicular to this plane.  
         [0045]     The point of contact of the tie member  3   g  with the supporting frame  2  lies in the plane unfolded by the two tilt axes which are adjusted by means of the tie members  3   h  and  3   f . The translational mobility of the tie member  3   g  stands perpendicular to this plane.  
         [0046]     The point of contact of the tie member  3   h  with the supporting frame  2  lies in the plane unfolded by the two tilt axes which are adjusted by means of the tie members  3   f  and  3   g . The translational mobility of the tie member  3   h  stands perpendicular to this plane.  
         [0047]      FIG. 5  shows the tie member  3   h  in enlarged representation. In the cited example, the translation along an axis  18   c  and the rotations about the rotation axis  16   a  and about the rotation axis  16   b  is enabled by a leaf spring  17   d , which is flexible in these directions. For the third rotation or swivel motion, leaf springs are arranged as a “leaf spring four-bar mechanism”  17   e , so that, at the instantaneous center of rotation of this “leaf spring four-bar mechanism”, a rotational mobility about the rotation axis  16   c  and thus a corresponding swivel mobility in the contact with the supporting frame  2  is obtained.  
         [0048]     If the adjusting mechanism  5  is just not tilted, the translational mobilities should be secured along the axes  18   a  and  18   b  by the tie member  3   h  in order, in combination with the other two tie members  3   f ,  3   g , to bear the supporting frame  2  together with the prism  1  in a statically determinate manner.  
         [0049]     Each of the connecting members  3   f ,  3   g ,  3   h  has two part-elements or tie blocks  6   g  and  6   h.    
         [0050]     With the adjusting mechanism  5 , the movable tie block  6   h  connected to the supporting frame  2  is moved relative to the fixed tie block  6   g  connected to the fixed structure  4 .  
         [0051]     The movable tie block  6   h  is here supported by leaf springs  17   g  in such a way relative to the fixed tie block  6   g  that it can travel along the axis  18   a  or rotate about an axis parallel to the rotation axis  16   c.    
         [0052]     Through movement of the movable tie block  6   h  relative to the fixed tie block  6   g , the tilting motion of the supporting frame  2 , together with the prism  1 , is triggered.  
         [0053]     An adjusting lever  21  is supported by leaf springs  17   h  in the fixed tie block  6   g  in such a way that it rotates about the point of intersection of the center lines of the leaf springs  17   h , in a manner similar to that with the instantaneous center of rotation of a four-bar mechanism.  
         [0054]     The adjusting lever  21  can be turned with the setting screws  10 , the motion being transmitted with leaf springs  17   f  to the movable tie block  6   h , which produces a tilting motion of the supporting frame  2  together with the prism  1 .  
         [0055]     If the movable tie block  6   h  is mounted relative to the fixed tie block  6   g  and the fixed structure  4  in such a way that it swivels about the respectively desired x, y or z-tilt axis x, y, z, the pivot joint, formed by the leaf spring four-bar mechanism  17   e , about the rotation axis  16   c  can be omitted ( FIG. 6 ). Tie members  3   i ,  3   j  and  3   k  have in this case, in the contact with the supporting frame  2 , one translational mobility and only two rotational mobilities or swivel mobilities.  
         [0056]     In the contact with the supporting frame  2 , the tie member  3   k  possesses for example, if its adjusting mechanism  5  is not actuated, one translational mobility along an axis  18   c  and, respectively, one rotational mobility about the rotation axis  16   a  and one about the rotation axis  16   b.    
         [0057]     The movable tie block  6   h  is in this case supported by the leaf springs  17   g  in the tie block  6   g  such that the instantaneous center of rotation of the movable tie block  6   h  lies on the desired tilt axis. For this, center lines  19  (indicated in dashed representation in  FIG. 6 ) of the leaf springs  17   g  must intersect, for example, at the point PO or on the desired rotation axis.  
         [0058]     In  FIG. 6 , this is represented, by way of example, for the tie member  3   k  and its desired tilt axis z.  
         [0059]     The saving on the pivot or swivel joint about the rotation axis  16   c , which saving produces an additional stiffening of the system, allows reduced susceptibility to unwanted vibrations of the prism  1 .  
         [0060]     A further constructional embodiment based on the tie member  3   e  already represented in  FIG. 3  is represented in  FIG. 7 , with tie members  31 ,  3   m  and  3   n.    
         [0061]     For example, in  FIG. 8 , in respect of the tie member  3   n , a translational mobility along the axis  18   c  and rotational mobilities about the rotation axes  16   a  and  16   b  is enabled in the contact with the supporting frame  2  by a leaf spring joint  17   i.    
         [0062]     A leaf spring joint  17   j , in combination with a leaf spring joint  17   k , connects a movable tie block  6   j  to a fixed tie block  6   i  such that the movable tie block  6   j , upon the actuation of the adjusting mechanism  5 , can travel in a translatory motion along the axis  18   a  and rotate about the rotation axis  16   c.    
         [0063]     A tilting of the prism  1  about the tilt axis z through the point PO is then made up of this combination of displacement and rotation.  
         [0064]     The displacement is transmitted by the setting screws  10  via an adjusting lever  22 , which is fastened rotatably to the fixed tie block  6   i  with a leaf spring joint  17   l , and with the leaf spring joint  17   k , to the movable tie block  6   j.