Abstract:
A relay lens is provided in an illumination system for use in microlithography. The relay lens can be used to uniformly illuminate a field at a reticle by telecentric light beams with variable aperture size. The relay lens can include first, second, and third lens groups. At least one of the second and third lens groups can include a single lens. This can reduce costs and increase transmission by requiring less CaF 2  because fewer optical elements are used compared to prior systems.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   The application claims the benefit under 35 USC 119(e) to U.S. Prov. Appl. No. 60/394,244, filed Jul. 9, 2002, which is incorporated by reference herein in its entirety. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a system and method for sharply illuminating a predetermined region of a reticle during exposure. 
   2. Background Art 
   A relay objective (e.g., lens) or a reticle edge masking assembly (REMA) objective (e.g., lens) is an objective that images an intermediate plane onto a plane of a reticle. The reticle supports a mask for lithography. By using the relay lens, the region illuminated on the reticle is sharply defined. Usually, the reticle masking device is assembled with adjustable edges. Conventionally, the relay lens is utilized in microlithographic exposure systems, steppers, or scanners, although the relay lens can be used in other optical systems. Diaphragm edges, which lie in the object plane of the relay lens, must be imaged precisely onto the reticle plane. An exposed corrected pupillary intermediate image is often desired because then, at the location of the intermediate image, further diaphragms and the like can be mounted, for example, to mask parts of an alignment system. 
   Typically, relay lens systems have very complicated structures (e.g., from about 7 to 10 lens elements). These optical systems have high Numerical Aperture (NA) (e.g., about 0.6 to 0.7). Basically, these systems include of three parts: a front portion (this part decreases NA), an intermediate portion (for pupil aberration and pupil shape correction) and a field portion (to create essential field size on the reticle). Following the relay lens system in a lithography tool is a projection objective, which normally operates in reduction and can include an inner-lying pupillary plane for non-telecentric input. A wafer follows in an image plane. An additional task of the relay lens system is to correct telecentricity on the reticle. 
   Conventional systems have a plurality of the optical elements in each of the above-mentioned front, intermediate, and field parts. The front part has 3-4 lenses, the intermediate part has 2-4 lenses, and the field part has 2-4 lenses. Conventional relay lens systems have several disadvantages because of the plurality of the optical elements in each part, these are: (1) a large volume of CaF 2  is needed for 157 nm lithography systems, which is quite costly; (2) there is low transmission caused by not only glass absorption, but also reflectance on each lens surface; (3) there are alignment difficulties  because too many lenses are required to be aligned, and (4) there is high cost due partially to the large volume of Ca F 2  required. These high costs are then passed on to purchasers of the systems, which can make purchasing additional or newer systems prohibitive. 
   What is needed is a relay lens that is a simpler, a less complex design, and that reduces costs involved in manufacturing, and thus in customer costs, which can all be achieved by reducing optical elements in the relay lens. 
   BRIEF SUMMARY OF THE INVENTION 
   A relay lens is provided in an illumination system, possibly for use in lithography. The relay lens can be used to uniformly illuminate a field at a reticle by telecentric light beams with variable aperture size. The relay lens can include first, second, and third lens groups. At least one of the second and third lens groups can include a single lens. This can reduce costs and increase transmission by requiring less CaF 2  because fewer optical elements are used compared to prior systems. 
   Some advantages of embodiments of the present invention over conventional systems are simplicity of design and manufacture and reduced costs of manufacture based on reducing an amount of optical material (e.g., fewer optical elements, and thus fewer optical surfaces) to reduce the amount of CaF 2  required. This is done without effecting optical output of the illuminating system or the relay lens. A lower volume of the CaF 2  can be used (e.g., about 30-50% lower) than conventional systems. There is a higher transmission (e.g., about 30% higher) than conventional systems. Alignment difficulties are virtually eliminated because only one lens may be used in certain parts. The relay lens system is less expensive than conventional systems, while producing the same image quality. 
   Still other advantages of the embodiments of the present invention is that it has a simpler structure than conventional systems because intermediate and field groups can include of single lens elements, instead of plurality of the lens elements. 
   Further embodiments, features, and advantages of the present inventions, as well as the structure and operation of the various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES 
     The accompanying drawings, which are incorporated herein and form a part of the specification, illustrate the present invention and, together with the description, further serve to explain the principles of the invention and to enable a person skilled in the pertinent art to make and use the invention. 
       FIG. 1  shows an example lithography system according to embodiments of the present invention. 
       FIGS. 2 ,  3 , and  4  show example relay lens systems or REMA objective lens systems in the lithography system of  FIG. 1 . 
   

   The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers may indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number can identify the drawing in which the reference number first appears. 
   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a system  100  that interacts with light  102  during exposure of a substrate  116  (e.g., a wafer) according to embodiments of the present invention. A light source  104  (e.g., a laser) can be an excimer or deep UV excimer laser, for example. In some embodiments, a multiplexer  106  in beam conditioner  108  receives light  102 . The beam conditioner  108  outputs light to illumination optics  110 , which in turn transmits light through a mask or reticle  112  onto a substrate (e.g., wafer)  116  via projection optics  114 . One embodiment for this system can be a lithography system, or the like. Another embodiment can be a holography system. 
     FIG. 2  shows a relay lens  200  in illuminating optics  110 , according to embodiments of the present invention. Relay lens  200  includes a delimiter plane  202 , a first lens group  204  (e.g., a front portion), an aperture stop  206  (e.g., a variable aperture stop), a second lens group  208  (e.g., an intermediate portion), a fold mirror  210 , a third lens group  212  (e.g., a field portion), and a reticle  214  having a reticle plane  216 . First lens group  204  can include a meniscus lens and a lens with an aspherical surface. In the embodiments shown in  FIG. 2 , second and third lens groups  208  and  212  each have only a single lens element. Second lens group  208  can have a single lens with one aspherical surface, which can be a convex surface. Third lens group  212  can have a single lens that has a spherical surface. 
   With continuing reference to  FIG. 2 , first lens group  204  (e.g., a front portion of relay lens  200 ) includes three lenses: a front thick meniscus lens with a first surface concentric to an object axial point, which can be used for Petzval sum correction, and two other lenses, which can be used for NA decrease. Second lens group  208  (e.g., an intermediate portion of relay lens  200 ) includes one lens (or two to three lenses in the embodiments shown  FIGS. 3-4  discussed below) with an aspheric surface. This one lens in second lens group  208  is located after aperture stop  206  and it can perform one or more of the following functions: pupil aberration correction, pupil shape correction (ellipticity), and telecentricity correction in the reticle space. Third lens group  212  (e.g., a field portion of relay lens  200 ) can include one lens. This one lens in third lens group  212  can perform one or more of the following functions: creating essential field size at the reticle plane and if, this lens has an aspheric surface, correcting telecentricity. 
   Again, with reference to  FIG. 2 , in operation, a light bean is received at delimiter plane  202  and expanded and collimated with first lens group  204 . A size of the expanded and collimated beam can be controlled by aperture stop  206 . A focus position on reticle  214  of the expanded and collimated beam can be controlled by second lens group  208 , third lens group  212 , or both second and third lens groups  208  and  212 . 
   To manufacture relay lens  200  in a more compact and economical manner, a folding mirror  210  can be used. In some embodiments it can be optional. Relay lens  200  images delimiter plane  202  onto reticle plane  216  with a predetermined magnification. Telecentric beams from delimiter plane  202  can be converted to telecentric beams on reticle  214 . Relay lens  200  can provide uniformity of illumination of the reticle plane and non-ellipticity of pupil shape. 
   In one example, a relay lens  200  can be constructed according to the following data: 
   
     
       
             
             
             
             
             
             
             
           
             
             
             
             
             
             
             
           
         
             
                 
             
             
               Surface 
               Surface 
                 
                 
                 
               Refract 
               Y Semi- 
             
             
               # 
               Type 
               Y Radius 
               Thickness 
               Glass 
               Mode 
               Aperture 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               Object 
               Sphere 
               Infinity 
               40.5759 
                 
               Refract 
               0 
             
             
               1 
               Sphere 
               −38.8954 
               48.5861 
               CaF2 
               Refract 
               34.3792 
             
             
               2 
               Sphere 
               −70.4454 
               1.0000 
                 
               Refract 
               64.7896 
             
             
               3 
               Asphere 
               1056.8762 
               55.0000 
               CaF2 
               Refract 
               103.1220 
             
             
               4 
               Sphere 
               −175.1412 
               1.0000 
                 
               Refract 
               108.0828 
             
             
               5 
               Sphere 
               336.3331 
               37.7241 
               CaF2 
               Refract 
               120.1833 
             
             
               6 
               Asphere 
               −840.2127 
               13.6072 
                 
               Refract 
               119.9937 
             
             
               7 
               Sphere 
               Infinity 
               84.3426 
                 
               Refract 
               119.5076 
             
             
               8 
               Sphere 
               Infinity 
               133.4129 
                 
               Refract 
               117.1521 
             
             
               Stop 
               Sphere 
               Infinity 
               55.9768 
                 
               Refract 
               113.4723 
             
             
               10 
               Sphere 
               1784.7806 
               35.1455 
               CaF2 
               Refract 
               122.2680 
             
             
               11 
               Asphere 
               −339.0580 
               93.6409 
                 
               Refract 
               123.0736 
             
             
               12 
               Sphere 
               Infinity 
               310.7213 
                 
               Refract 
               119.7255 
             
             
               13 
               Sphere 
               Infinity 
               85.0612 
                 
               Refract 
               110.6886 
             
             
               14 
               Sphere 
               417.5797 
               31.2151 
               CaF2 
               Refract 
               107.8689 
             
             
               15 
               Sphere 
               −1616.3317 
               224.6563 
                 
               Refract 
               106.3382 
             
             
               16 
               Sphere 
               Infinity 
               28.3500 
               CaF2 
               Refract 
               56.8430 
             
             
               17 
               Sphere 
               Infinity 
               0.0000 
                 
               Refract 
               53.0694 
             
             
               Image 
               Sphere 
               Infinity 
               0.0000 
               Air 
               Refract 
               53.0694 
             
             
                 
             
           
        
       
     
   
   Depending on the specifications of system  100 , it is possible in alternative embodiments of the present invention that only one of second lens group  208 ′ or  208 ″ and the third lens group  212  may have only one lens. Although, preferably both the second and third lens groups  208  and  212 , respectively, have only one lens each. When specifications dictate either second or third lens group  208  or  212 , respectively, to have more the one lens, preferably, third lens group  212  will continue to have only one lens.  FIGS. 3 and 4  show two possible example alternative configurations. 
   In  FIG. 3 , he second lens group  208 ′ has two lenses, which can have at least one aspheric surface on each lens. 
   In  FIG. 4 , second lens group  208 ″ has three lenses. At least two of the three lenses in second lens group  208 ″ can have at least one aspheric surface. 
   Even in these alternative embodiments dictated by desired specifications of system  100 , relay lens  200  can continue to have fewer optical elements compared to conventional systems, which keeps the cost down. It is to be appreciated that still other configurations based on other desired specifications are possible, and all are contemplated within the scope of the present invention. 
   CONCLUSION 
   While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.