Abstract:
A structure for mounting an assembly of optical elements disposed within a housing, in particular of a projection lens assembly of a projection exposure system for manufacturing semiconductor elements includes a plurality of supporting elements, each respective one of which forms part of a respective one of a plurality of connections though which the housing of the assembly is connected to said supporting structure through which the weight of the assembly is transferred to the supporting structure in such a way that supporting forces generated by said supporting structure are taken up by pressure forces and shear forces which act on at least one of the supporting elements.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. National Phase Entry under 35 U.S.C. §371 of International Application No. PCT/EP2005/001826 filed Feb. 22, 2005 and claims priority to German Patent Application No. 10 2004 0009 203.6 filed Feb. 2, 2004. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a housing structure for mounting optical elements, in particular of a projection lens housing in a projection exposure system for manufacturing semiconductor elements, attachment locations, which have connecting parts, for connection to a supporting structure being provided on structural elements. 
     2. Description of the Related Art 
     A housing structure of the kind mentioned in the introduction is described in EP 1 278 089 A2. The housing structure constitutes, in a projection exposure system, the housing of a projection lens, in which a plurality of optical elements, such as, for example, lens elements and mirrors, are mounted. The housing structure or projection lens housing is provided with attachment locations on structural elements, at which, via connecting elements, the housing structure is supported with its weight on a supporting structure of the projection exposure system since the housing structure is suspended into the system. In this connection, the attachment locations are also to be provided in such a way that kinematically defined mounting is brought about, exchangeability also having to be ensured. 
     For various reasons, the housing structure is, in particular in projection exposure systems in the EUV range, made from a glass ceramic structure, On the other hand, the supporting structure of the projection exposure system is made from a different material, in general from a metal material. This means that the connection between the housing structure and the supporting structure is problematic owing to the different materials, in particular with regard to stability, thermal expansion coefficient and temperature differences. 
     For further prior art, reference is made to US 2003/0162484 A1 and EP 1 338 911 A2. 
     SUMMARY OF THE INVENTION 
     The object of the present invention is to produce a housing structure with attachment locations for connection to a supporting structure, the attachment eliminating the disadvantages or problems indicated above, in particular by means of which a stable, easily separable connection is brought about, it being possible for the great associated forces arising to be dissipated without major constructional outlay. 
     According to the invention, this object is achieved by virtue of the fact that supporting elements, which are provided with mounting flanges for connection to the supporting structure, act on the structural elements in such a way that supporting forces, in particular weight forces, are taken up essentially by pressure forces and shear forces. 
     Owing to the construction and the support of the housing structure or lens housing, torques also arise in addition to tensile stresses and compressive stresses, which torques are based inter alia on the fact that different points of action exist between the attachment locations or flange connections between the housing structure and the supporting structure and the weight force component. 
     By means of the supporting elements according to the invention, torques which lead to stresses and bending are to a great extent avoided, so that the imaging quality of the optical system is not impaired. 
     If according to the invention the supporting elements are designed in such a way that essentially only shear forces and pressure forces arise, connections can be made in a relatively simple way by means of adhesive surfaces. This constitutes both a simple and a secure type of connection for the intended application. This is true in particular if, in one configuration according to the invention, the housing structure consists at least in part of glass ceramic with structural elements made of glass ceramic and the supporting structure consists of metal. In this case, the supporting elements will also be made from a metal material and an adhesive connection will accordingly be made between the structural elements and the supporting elements. 
     A constructional design according to the invention of a supporting element can consist in that the supporting elements each have at least approximately an L-shape with a mounting flange. 
     Instead of an L-shape, it is also possible to configure a supporting element in such a way that the supporting elements each have a U-shape seen in cross section, from which the mounting flange branches off, the associated structural element being received between the two U-legs. 
     A further configuration according to the invention can consist in that the supporting element has two clamping plates arranged at a distance from one another, between which the associated structural element is received, a shear plate running parallel to the outer wall of the structural element, and a mounting flange connected to the two clamping plates and the shear plate. 
     Advantageous developments and configurations emerge from the other subclaims and from the illustrative embodiment described in principle below with reference to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a diagrammatic illustration of a projection exposure system with a projection lens; 
         FIG. 2  shows the projection lens as a housing structure according to  FIG. 1 ; 
         FIG. 3  shows a structural plate of the housing structure according to  FIG. 2 ; 
         FIG. 4  shows an enlarged illustration of an attachment location with a supporting element in a first configuration; 
         FIG. 5  shows an enlarged illustration of an attachment location with a supporting element in a second configuration; 
         FIG. 6  shows an enlarged illustration of an attachment location with a supporting element in a third configuration, and 
         FIG. 7  shows an enlarged illustration of an attachment location with a supporting element in a fourth configuration. 
     
    
    
     DETAILED DESCRIPTION 
     As can be seen from  FIG. 1 , an EUV projection exposure system  1  has a light source  2 , an EUV illumination system  3  for illuminating a field in a plane  4  in which a structure-bearing mask is arranged, and a projection lens  5  for imaging the structure-bearing mask in the plane  4  onto a light-sensitive substrate  6 . The projection lens  5  has a number of optical elements, in particular mirrors  7 , in a lens housing  8 . 
     In  FIGS. 2 and 3 , the lens housing  8  is in each case illustrated in a simple configuration in an enlarged perspective view. 
     The lens housing  8  designed as a housing structure has a plurality of structural elements  9  in the form of support struts and support plates. Arranged in the central region is a structure reinforcement plate  10  running transversely to the optical axis, which interconnects the individual structural elements to form a stable unit. For clearer illustration of the structure reinforcement plate  10  illustrated in  FIG. 3  and its connection to the structural elements  9 , the structural elements lying at the front in the drawing are omitted in  FIG. 2 . 
     The attachment or suspension of the lens housing  8  via attachment locations to or on a supporting structure  11  of the projection exposure system  1  is effected by means of the structure reinforcement plate  10 . The supporting structure  11  is indicated only in part in  FIGS. 4 to 7 . 
       FIGS. 4 to 7  illustrate various embodiments for the configuration of attachment locations with supporting elements  12  for connection to the supporting structure. As can be seen from  FIG. 3 , three supporting elements  12  arranged at a distance from one another are provided on the structure reinforcement plate  10 , as the structural element, by means of which supporting elements a kinematically defined connection to the supporting structure  11  can be made. The structural elements, namely the structural struts and side plates  9  and the transversely running structure reinforcement plate  10 , are in general made of glass, ceramic or glass ceramic material, for example Zerodur. Each supporting element  12  has a mounting flange  13 , which is made of a metal material and is connected, in a way not illustrated further, to the supporting structure, which in general is likewise made of a metal material. Screw connections, for example, can be provided for this purpose. 
     Owing to the different materials of mounting flange  13  and structural elements  9  and  10 , a connection of these two parts is to be ensured which is designed in such a way that problems do not arise owing to different thermal expansion coefficients when temperature differences occur. Moreover, attention is to be paid to the fact that with glass ceramic, for example, connection techniques likewise give rise to problems. This applies, for example, to the introduction of stresses, which can moreover have a negative effect on the imaging quality of the projection lens  5 . 
     The illustrative embodiment according to  FIG. 4  shows a supporting element  12  with a mounting flange  13  in an L-shape, to which a mounting plate  14  for connection to the supporting structure  11  is attached. 
     In the case of a vertical arrangement of the lens housing  8 , the horizontal part of the L-shape constitutes a support plate  15  for the structure reinforcement plate  10 . The vertical part of the L-shape constitutes a peripheral plate  16 , to the outer side of which the mounting plate  14  is attached. The mounting flange  13  can be of one-piece design. An adhesive layer  17   a  and  17   b  is in each case introduced over the entire area between the support plate  15  and the structure reinforcement plate  10  and between the peripheral plate  16  and the structure reinforcement plate  10 . The connection between the structure reinforcement plate  10  and the supporting structure  11  is effected by means of the two adhesive layers  17   a  and  17   b . Pressure forces due to the weight force of the lens housing  8  and at the same time shear forces as well act on the adhesive surface of the adhesive layer  17   a . Only shear forces act on the vertically arranged adhesive layer  17   b.    
     As the supporting forces illustrated by an arrow act outside the weight force G of the lens housing  8 , and owing to the type of mounting illustrated, torque forces would also arise in addition. In order that only pressure forces and shear forces arise, and in order that there are no inadmissible stress peaks in the adhesive layers  17   a  and  17   b , bolts or screws  18   a  and  18   b  are additionally provided, which are prestressed by spring elements  19 . The screw  18   a  extends in the vertical direction through a through-bore  20  in the structure reinforcement plate  10  and is screwed into the support plate  15 , while the head of the screw lies on the upper side of the structure reinforcement plate  10  under prestress. 
     The screw  18   b  is passed through a horizontal bore in the peripheral plate  16  and screwed into a horizontal metal threaded bush  21 , which is glued into the structure reinforcement plate  10 . The head of the screw  18   b  lies under the prestress of the spring element  19  on that side of the peripheral plate  16  facing away from the structure reinforcement plate  10 . 
       FIG. 5  illustrates a configuration of the supporting element  12  which has a U-profile shape  13   a , with a lower support plate  15  and an upper clamping plate  22 , the support plate  15  and the clamping plate  22  forming the two legs of the U-profile shape. The mounting plate  14   a , similarly to the mounting plate  14 , branches off from the connecting part of the U-profile shape which interconnects the two legs. The connection to the supporting structure  11  is again effected by means of the mounting plate  14   a . The adhesive layer  17   a  is again located between the support plate  15  and the structure reinforcement plate  10 . Instead of the vertical adhesive layer  17   b , an all-over adhesive layer  17   c  is located on the surface of the structure reinforcement plate  10  between this and the clamping plate  22 . The connection of the structure reinforcement plate  10  to the mounting flange  13   a  is again effected by means of the two adhesive layers  17   a  and  17   c . The two adhesive connections  17   a  and  17   c  are subject to essentially only a shear stress. This is the case in particular if a bolt or screw  18   c  is additionally provided, which in its effect corresponds to the screw  18   a  according to  FIG. 4 . For this purpose, the screw  18   c  is likewise preloaded with a spring element  19  and screwed into the support plate  15 . 
     In order to avoid torques arising, it should be ensured that the adhesive gaps are each completely filled by an adhesive layer  17   a ,  17   b  or  17   c.    
       FIG. 6  shows a configuration which essentially corresponds to the embodiment according to  FIG. 4 , although here the U-profile shape is “broken up”. In this connection, as can be seen, the support plate  15  and the clamping plate  22  are not connected via a connecting plate or connecting part connected to the structure reinforcement plate  10 , by means of the vertical adhesive layer  17   b , on the outer peripheral wall of the structure reinforcement plate  10 . Instead, a mounting flange  13  in a T-shape with a mounting plate  14  for connection to the supporting structure  11  is arranged on the side facing the supporting structure  11 . The support plate  15 , the clamping plate  22  and the peripheral plate  16  are each connected to the mounting flange  13  on the side facing the mounting flange  13  via an articulated arm  23 . By means of the articulated arms  23 , it is ensured that no torques are introduced into the adhesive surfaces  17   a ,  17   b  and  17   c  owing to the eccentric supporting forces, but only shear stresses, as the support plate  15 , the clamping plate  22  and the peripheral plate  16  can adjust themselves positionally in relation to the mounting flange  13  connected firmly to the supporting structure  11 . 
     The articulated arms  23  can be designed and connected to the support plate  15 , the clamping plate  22 , the peripheral plate  16  and the mounting flange  13  in any way. Advantageously, however, the parts mentioned above will all be made in one piece and from the same metal material. 
     In this case as well, screws  18   d  can be additionally provided, which have the same effect as the screw  18   a  in  FIG. 4  and the screw  18   c  in  FIG. 5 . For the same purpose, spring elements  19  are also provided. One of the two screws  18   d  is passed through the upper clamping plate  22 , while, on the opposite side, a screw  18   d  is passed through the support plate  15  from below. Both screws  18   d  are connected to the structure reinforcement plate  10  by means of threaded bores in it. 
       FIG. 7  illustrates a similar configuration to the embodiment described with reference to  FIG. 6 , for which reason the same references have been kept for the same parts. Instead of articulated arms  23 , however, screws  18   e , which connect the support plate  15  and the clamping plate  22  to the mounting flange  13 , are provided as connecting elements. In this case, there is no peripheral plate  16 . In this case, the function of the peripheral plate  16  is taken over by a vertical T-leg  24  of the mounting flange  13  of T-shaped design. The horizontal part of the mounting flange  13  serves as the mounting plate  14   a  for connection to the supporting structure  11 . 
     The two screws  18   e  are each prestressed in the same way by a spring element  19 , passed tlirough through-bores in the vertical T-leg  24  and screwed into threaded bores of the structure reinforcement plate  10 . By means of the type of connection illustrated, a secure connection is brought about between the structure reinforcement plate  10  and the mounting flange  13 , essentially only shear stresses arising in the adhesive surfaces  17   a ,  17   b  and  17   c , and the stresses arising owing to the bearing forces being taken up via the two bolts or screws  18   e.    
     The invention is generally suitable for connecting load-removing flanges to components made of brittle materials and with minimum introduction of stresses.