Abstract:
The invention relates to a device for adjusting the temperature of elements, especially adjusting the temperature of a projection lens ( 1 ) or of parts of a projection lens ( 1 ) for use in semiconductor lithography. Said device comprises a temperature-adjusting jacket ( 18 ) which is provided with at least one temperature-adjusting line ( 19 ). Said at least one temperature-adjusting line ( 19 ) is formed into the temperature-adjusting jacket ( 18 ).

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The invention relates to a device for controlling the temperature of elements, in particular for controlling the temperature of a projection objective or of parts of a projection objective in semiconductor lithography, having a temperature control jacket that is provided with at least one temperature control line. The invention further relates to a method for producing a device for controlling the temperature of elements of a projection objective or parts of a projection objective in semiconductor lithography, the temperature control jacket with at least one temperature control line being used for controlling the temperature. The invention also relates to the use of a device for controlling the temperature in a EUV projection exposure machine.  
         [0003]     2. Description of the Related Art  
         [0004]     Projection objectives or parts of projection objectives in semiconductor lithography are frequently surrounded by cooling jackets in order to maintain a constant temperature for a high positional accuracy. Devices for cooling a projection objective are known, for example, from U.S. Pat. No. 5,812,242, from U.S. Pat. No. 6,153,877 and from US 2002/0027645 A1.  
         [0005]     Disadvantages of the prior art set forth above reside in a poor heat transfer between the cooling jacket and the cooling lines or cooling tubes, since the heat transfer surface is very small where the cooling lines are applied to the cooling jacket for example by bonding. Furthermore, the bonding of the cooling lines to the cooling jacket is attended by the risk of the adhesive used causing contamination by degassing. Again, the strength of the adhesive used is frequently not sufficient, and thus there is a need for additional connecting elements for fastening the cooling lines on the cooling jackets. It is, furthermore, disadvantageous that a large design space is required when use is made of round line cross sections for the cooling lines, it being possible however, for angular or oval line cross sections to be deformed or bent only with great difficulty. It is also very complicated to adapt the cooling lines to cooling jackets that are not of flat design, for example of round design.  
       SUMMARY OF THE INVENTION  
       [0006]     It is therefore the object of the present invention to provide a device for controlling the temperature of elements, in particular for controlling the temperature of a projection objective or of parts of a projection objective, with high accuracy and effectiveness and without a high structure outlay.  
         [0007]     According to the invention, this object is achieved by virtue of the fact that the at least one temperature control line is integrally formed in the temperature control jacket.  
         [0008]     Owing to the inventive integral formation of the temperature control line in the temperature control jacket, a good heat transfer is ensured between the temperature control jacket and the temperature control lines, since a temperature control means that is being used is in direct and/or full contact with the temperature control jacket. The configuration of the temperature control line, as also the distribution of the latter on the temperature control jacket, is simpler according to the invention and owing to the integral formation, and is possible without a separate high design outlay for a separate temperature control line. The temperature gradient can be set more freely in this way, since there is no need to adapt temperature control lines to the temperature control jacket. A further advantage of the device according to the invention is that after the integral formation of the temperature control line the temperature control jacket can be deformed as a whole depending on the configuration of the projection objective or parts of the projection objective. This avoids a complicated and difficult deformation or bending of the temperature control jacket with separate temperature control lines in order to adapt to the projection objective, as is the case in the prior art.  
         [0009]     In an advantageous refinement of the invention, it can be provided that the temperature control jacket is of bipartite design, the temperature control line being integrally formed in at least one subelement, and the subelements being interconnected via an adhesive. Accordingly, the connection of two subelements that form the temperature control jacket enables the use of an adhesive for bonding over a large surface without loss of strength. Since only end faces of the temperature control jacket respectively come into contact with the surroundings and/or the ambient air, degassing of the adhesive surface between the two subelements of the temperature control jacket is only minimal, and so less contamination occurs for the projection exposure machine.  
         [0010]     The present object is achieved, furthermore, by virtue of the fact that the at least one temperature control line is integrally formed on the temperature control jacket via an electroplating process.  
         [0011]     Consequently, according to the invention there is a further possibility for producing the temperature control jacket. It is also possible to produce temperature control jackets with complex geometries by means of the inventive electroplating process, in particular an electroforming.  
         [0012]     Advantageous refinements and developments of the invention follow from the remaining subclaims. Exemplary embodiment of the invention are explained in more detail below with the aid of the drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]      FIG. 1  shows a schematic with the mode of operation of a projection objective for microlithography, the projection objective having temperature control jackets;  
         [0014]      FIG. 2  shows a schematic of a temperature control jacket with an inserted temperature control line;  
         [0015]      FIG. 3  shows an enlarged view according to the line III-III of the temperature control jacket illustrated in  FIG. 2 ;  
         [0016]      FIG. 4  shows an alternative design of temperature control jacket of the view, illustrated in  FIG. 3 , according to the line III-III in accordance with  FIG. 2 ;  
         [0017]      FIG. 5  shows a schematic of an alternative temperature control jacket with temperature control lines, connected to a projection objective;  
         [0018]      FIGS. 6   a  to  6   c  show schematics of inventive method steps for producing a temperature control jacket with temperature control lines in accordance with  FIG. 5  by means of an electroplating process; and  
         [0019]      FIG. 7  shows a schematic design of an EUV projection exposure machine with a light source, an illumination system and projection objective. 
     
    
     DETAILED DESCRIPTION  
       [0020]      FIG. 1  illustrates schematically a projection exposure machine with a projection objective  1  for microlithography for the purpose of producing semiconductor components.  
         [0021]     The projection exposure machine has an illumination system  2  with a laser (not illustrated) as light source. Located in an objective plane of the projection exposure machine is a reticle  3  whose structure is to be imaged on an appropriately reduced scale on a wafer  4  that is arranged beneath the projection objective  1  and is located in an image plane.  
         [0022]     The projection objective  1  has a first vertical objective part  1   a  and a second horizontal objective part  1   b.  Provided in the objective part  1   b  are a number of lenses  5  and a concave mirror  6 , which together form a subassembly  70  and are arranged in an objective housing  7  of the objective part  1   b.  Provided for the purpose of deflecting a projection beam, marked here only by an arrow, from the vertical objective part  1   a  with a vertical optical axis  8  into the horizontal objective part  1   b  with the horizontal optical axis  9  is a beam splitter element  10  that is designed here as a beam splitter cube. After being reflected at the concave mirror  6  and subsequently passing through the beam splitter element  10 , the projection beam strikes a deflection mirror  11 . The horizontal beam path is deflected at the deflecting mirror  11  along the optical axis  9  into a vertical optical axis  12 , in turn. Provided underneath the deflecting mirror  11  is a third vertical objective part  1   c  with a further lens group  13 . In addition, three λ/4 plates  14 ,  15  and  16  are also located in the beam path. The λ/4 plate  14  is located in the projection objective  1  between the reticle  3  and the beam splitter element  10  downstream of a lens or lens group  17 . The λ/4 plate  15  is located in the beam path of the horizontal objective part  1   b,  and the λ/4 plate  16 , which forms an optical subassembly  700  with the lens group  13 , is located in the third objective part  1   c.  The three λ/4 plates  14 ,  15 ,  16  server the purpose of completely rotating the polarization once, as a result of which, inter alia, beam losses are minimized.  
         [0023]     Temperature control jackets  18  are also illustrated in  FIG. 1 . These serve to cool the elements. In this exemplary embodiment, the projection objective  1  is provided with a number of temperature control jackets  18 , the intention being to control the temperature of the projection objective  1  (the entire surface as far as possible). In order to keep the optical subassemblies  10 ,  11 ,  70  and  700  thermally stable, the temperature control jackets  18  are used to keep stress from the surroundings away from the subassemblies. In order to avoid heating of the projection objective  1  from inside, for example through absorption of the optical elements  5 ,  6 ,  10 ,  13 ,  15  and  16 , it is possible in addition further to provide inner temperature control jackets ( 18 ′) for the individual elements. Regions particularly sensitive in thermal terms such as, for example the mirror  6  or the deflecting mirror  11 , of the projection objective  1  can also be provided in a mechanically and thermally separate fashion with temperature control jackets  18 ′ and with a dedicated temperature control circuit. The fastening of the temperature control jackets  18  on the projection objective  1 , as also on individual parts and elements of the projection objective  1 , can be performed in the customary way known.  
         [0024]     The design and the production of a temperature control jacket  18  is described in more detail in the following exemplary embodiments.  
         [0025]     A view of a temperature control jacket  18  is illustrated schematically in  FIG. 2 . Integrally formed in the temperature control jacket  18  is a temperature control line  19  that has a temperature control means (a gas or a liquid) for controlling the temperature of, in the present case for cooling, the projection objective  1 . The temperature control jacket  18  is of bipartite design, that is to say the temperature control jacket  18  has a first subelement  20  and a second subelement  21 . In at least one of the two subelements  20  and/or  21 , cutouts for forming the temperature control line  19  are introduced via a cutting off process, for example by means of a milling operation. The subelements  20 ,  21  shown in this exemplary embodiment are illustrated transparently for the purpose of more easily detecting the temperature control line  19 .  
         [0026]      FIG. 3  illustrates schematically a longitudinal section, according to the line III-III in accordance with  FIG. 2 , through the temperature control jacket  18 , the temperature control line  19  being inserted only into the subelement  20 . It goes without saying that it is also possible to insert the temperature control line  19  only into the subelement  21  or else into both subelements  20  and  21 . The two subelements  20  and  21  are interconnected in such a way that an at least approximately full surface contact is present between the subelements  20  and  21 . This can be performed, for example, by bonding the subelements  20 ,  21  by means of an adhesive  22 . A large area bonding of this kind ensures high strength between the subelements  20  and  21 . In this case, bonding surfaces of the two subelements  20  and  21  connect to the surroundings or to the ambient air only at end faces  23 , the advantage thereby resulting that less adhesive surface can degas and lead to contamination. One advantage of the at least approximately full surface contact between the subelements  20  and  21  is, however, the very good heat transfer.  
         [0027]     An alternative possibility for connecting subelements  20 ,  21  is illustrated in  FIG. 4 . In this exemplary embodiment, the temperature control line  19  is formed by cutouts in the two subelements  20 ,  21  of the temperature control jacket  18 . Instead of the two subelements  20 ,  21  being bonded to one another, the two subelements  20 ,  21  are connected here via an alternative connecting operation, for example soldering. In this case, solders  24  are rolled onto each of the subelements  20  and  21  without supplying heat, that is to say in cold state. Hereafter, the two subelements  20  and  21  are joined to one another and interconnected by heating, as a result of which the two solders  24  fuse with the subelements  20  and  21 . Aluminum is preferred as material for the two subelements  20 ,  21  for reasons of good thermal conductivity. Aluminum can also be suitably soldered in a vacuum without flux. There is likewise in this way an at least approximately full surface connection of high strength between the two subelements  20  and  21 . Of course, other materials can also be used in case of need for the subelements  20  and  21 .  
         [0028]     One advantage of the method according to  FIG. 3  and  FIG. 4  is that after introduction of the temperature control lines  19  the temperature control jacket  18  can be deformed as an overall element depending on the design of the object or element whose temperature is to be controlled. A further advantage of the temperature control jacket  18  thus produced resides in a very good heat transfer, since the temperature control means is in direct or full contact with the temperature control jacket  18 . The configuration of the temperature control line  19 , and also the distribution thereof on the temperature control jacket  18  can be multifarious or be multifariously fashioned, since the temperature control line  19  need neither be applied nor adapted to the temperature control jacket  18  in a separate production or operating cycle.  
         [0029]     However, there is advantage in round temperature control lines that have a uniform cross section and no narrow radii or kinks, the result being the occurrence of less noise from the flow of temperature control means, and thus no transfer of vibrations to the optics. Furthermore, the aim should be as uniform as possible a distribution of the temperature control line or the temperature control lines over the surface of the jacket, so that a uniform temperature distribution is present over the surface of the jacket. In the event of flat surfaces or two-dimensional optics, temperature control lines can be introduced in coiled fashion in the temperature control jacket. In the case of round optics such as for example, the projection objective  1 , it is most advantageous to have a spiral arrangement of one or more temperature control lines in order to achieve a uniform temperature distribution.  
         [0030]      FIG. 5  shows a projection objective  25  that is surrounded by a temperature control jacket  26 . The temperature control jacket  26  can in this case be fitted on the outside of the projection objective  25  in a known way. In this alternative exemplary embodiment, temperature control lines  27  are integrally formed on the temperature control jacket  26 . The integral formation of the temperature control lines  27  is performed via an electroplating process, in particular an electroforming. In  FIG. 5 , the temperature control lines have connections  30  that are coupled to lines  31  that are, in turn, connected to a unit  32  for supplying and controlling the temperature control means. Furthermore, the temperature control lines  27  lead to a distribution connection  33  that is connected to a line  34  for transporting the temperature control means away to a discharge and control unit  35 .  
         [0031]     The process of electroforming for forming or producing a temperature control line  27  on the temperature control jacket  26  is to be explained in more detail below with the aid of  FIGS. 6   a ,  6   b  and  6   c.    
         [0032]     In accordance with  FIG. 6   a , in order to produce the temperature control line  27  on the temperature control jacket  26  a molding compound  28  is applied to the temperature control jacket  26  in such a way that the molding compound  28  forms an inner cross section of the temperature control line  27 . By way of example, wax filled with graphite, metallically filled plastics or another electrically conducting material that can be processed very effectively can be used as molding compound  28 . By way of example, the molding compound  28  can be applied to the temperature control jacket  26  by means of thermally unstable adhesive  36 , and be modeled depending on the configuration of the cross section and the provided course of the temperature control line  27 . Self-adhesive molding compounds can also be used.  
         [0033]     In accordance with  FIG. 6   b , the temperature control jacket  26  is introduced with the molding compound  28 , which is electrically conducting, into a plating tank, illustrated by dashes with the designation  37 . In this case, the objects to be coated with a metal layer, here the temperature control jacket  26  and the molding compound  28 , are connected as cathode. The metal ions of a metal salt solution that is being used are then discharged at the temperature control jacket  26  and the molding compound  28  as cathode, and are deposited as layer. The deposition conditions such as the composition of the electrolyte, cathodic current density, electrolyte temperature and electrolytic circulation as well as electrodeposition periods are selected in such a way that the deposited metal coating has a property profile correct for the application. In this way, the molding compound  28  and also the temperature control jacket  26  are covered with an electrodeposited layer  29 . The electrodeposited layer  29  can be formed, for example, of nickel, it also being possible, of course, to use other metals such as, for example, copper, tin, aluminum or combinations of a number of metals for the purpose of forming the electrodeposited layer  29 .  
         [0034]     After the desired layer thickness of the electrodeposited layer  29  has been reached on the temperature control jacket  26  and/or on the molding compound  28 , the temperature control jacket  26  is withdrawn from the plating tank. The molding compound  28  is removed in order to form the temperature control line  27 , thus resulting in a cutout. The removal of the molding compound  28  can be performed, for example, by heating, when a wax, for example, is used as molding compound  28 , by washing out when the molding compound  28  is water-soluble, or else by etching.  
         [0035]      FIG. 6   c  shows the temperature control jacket  26  with a temperature control line  27  formed in this way, through which the temperature control means can flow for the purpose of cooling the projection objective  26  according to  FIG. 5  or for cooling parts of the projection objective  1  in semiconductor lithography.  
         [0036]     Temperature control jackets with complex geometries can also be produced by means of this electroplating process, since only the molding compound  28  to be processed need be processed in order to form a temperature control line  27  and the processing can be performed very simply.  
         [0037]     The temperature control jackets  18 ,  18 ′ and  26  can be used with increased heat generation in order to cool or else to heat a projection objective, individual optical elements or else mechanical elements.  
         [0038]      FIG. 7  illustrates an EUV projection exposure machine  40  with a light source  41 , an EUV illumination system  42  for illuminating a field in an object plane  43 , in which a structure bearing mask is arranged, as well as a projection objective  44  with a housing  44   a  and a beam path  45 , provided by a number of deflecting mirrors  48 , for imaging the structure bearing mask in the object plane  43  onto a photosensitive substrate  46  for producing semiconductor components. The EUV illumination system  42  advantageously has a collector unit  47  on the side directed toward the light source  41 , in order to focus the radiation generated by the light source  41 .  
         [0039]     In the case of the EUV projection exposure machine  40  as well, parts of the objective housing  44   a , or the entire housing can, just like the optical elements in the interior of the projection objective  44 , be provided with a temperature control jacket  18  or  18 ′. The same holds for the collector unit  47  that is provided for collecting the radiation output by the light source  41 .  
         [0040]     Such collector units are used for an illumination system at wavelengths of ≦193 nm, and are generally known in principle. Reference is made by way of example to this end to DE 102 14 259 A1 and the older U.S. provisional application Ser. No. 60/695,932, whose contents are to be reckoned in the disclosure content of the present application.  
         [0041]     In addition to cooling the optical elements such as, for example, lenses and mirrors, it is also possible for further mechanical parts that are temperature-sensitive to be provided with a temperature control jacket  18 ′.  
         [0042]     In addition to the deflecting mirrors  48  arranged in the projection objective  44 , it is, of course, also possible for optical elements arranged in the EUV illumination system  42 , such as mirrors and other mechanical parts, to be subjected to temperature control by means of a temperature control jacket  18 ′. This holds, for example, for aperture elements  49 , as has been indicated schematically in the illumination system  42  in  FIG. 7 .