Abstract:
Element for homogenizing the illumination with simultaneous setting of the polarization degree, wherein the element consists of at least two components. The first component is a microlens array, and the second component is a filter for setting the desired polarization.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This patent application claims priority of German Patent Application No. 10 2007 028 195.3, filed on May 30, 2007, the application is incorporated herein by reference. 
       FIELD OF THE INVENTION 
       [0002]    The invention relates to an element for homogenizing the illumination with simultaneous setting of the polarization degree. The element consists of at least two components. 
       SUMMARY OF THE INVENTION 
       [0003]    It is the object of the present invention to provide an element for homogenizing the illumination with which a structured illumination of a pupil of an objective may be achieved in a simple way. 
         [0004]    This object is achieved by an element for homogenizing the illumination with simultaneous setting of the polarization degree. The element has at least two components, wherein the first component includes a microlens array, and the second component includes a filter for setting the desired polarization. 
         [0005]    It is particularly advantageous if the element for homogenizing the illumination with simultaneous setting of the polarization degree consists of at least two components. The first component includes a microlens array. The second component consists of a filter used for setting the desired polarization. 
         [0006]    The filter may have a linear polarization in the X-coordinate direction. It is also contemplated that the filter has a linear polarization in the Y-coordinate direction. 
         [0007]    The orientation of the linear polarization will generally depend on the orientation of the structures on the substrate. If the structures have a preferred direction in the X-coordinate direction or in the Y-coordinate direction, the polarization will be oriented accordingly. This will generally not be the case for diagonal structures. 
         [0008]    The filter may be designed such that the result is a circular polarization. 
         [0009]    The filter and the microlens array may be arranged in a common holder. At least the filter is designed to be replaceable. The filter may also be arranged fixedly in the optical path. 
         [0010]    In a further embodiment, a filter may be associated with each lens element of the microlens array. In that case, each filter is fixedly connected to the microlens array. 
         [0011]    The element is mainly used for illuminating a pupil of an object of an optical system, wherein light with defined polarization is radiated onto the pupil of the objective. At the same time, the object field of the objective may be homogenized. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the following, embodiments of the invention and their advantages will be explained based on the accompanying figures, in which: 
           [0013]      FIG. 1  shows a schematic representation of the element consisting of a microlens array and a filter; 
           [0014]      FIG. 2  shows a schematic representation of the use of the element for illuminating a pupil of an objective; 
           [0015]      FIG. 3   a  shows a schematic representation of an example of a linearly polarized illumination pupil, each segment being polarized in the X-direction; 
           [0016]      FIG. 3   b  shows a schematic representation of the filter linearly polarized in the X-coordinate direction; 
           [0017]      FIG. 4   a  shows a further embodiment of the illumination pupil illuminated by linearly polarized light, wherein each segment is polarized in the Y-direction; 
           [0018]      FIG. 4   b  shows a schematic representation of the filter linearly polarized in the Y-direction; 
           [0019]      FIG. 5   a  shows a further embodiment of the illumination pupil, wherein the filter is designed such that, all in all, there is a radial polarization of the illumination pupil; 
           [0020]      FIG. 5   b  shows a schematic representation of the filter for generating a radial polarization of the illumination pupil; 
           [0021]      FIG. 6   a  shows a further embodiment of the illumination pupil, wherein a tangential polarization of the whole illumination pupil is achieved with the help of the filter; 
           [0022]      FIG. 6   b  shows a schematic representation of the filter for generating a tangential polarization of the illumination pupil; 
           [0023]      FIG. 7   a  shows a circular polarization of the illumination pupil, wherein each segment has a circular polarization; 
           [0024]      FIG. 7   b  shows a schematic representation of the element according to a further embodiment of the invention; and, 
           [0025]      FIG. 8  shows a schematic representation of a circular polarization of the illumination pupil, wherein the segments have a shape differing from that shown in  FIG. 7 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0026]      FIG. 1  shows a schematic representation of an element  1  for a defined adjustment of the polarization of the illumination light. Element  1  consists of at least a first element  3  and a second element  5 . First element  3  is a microlens array, and second element  5  represents a filter with which a predetermined polarization may be achieved. First element  3  and second element  5  are aligned along an optical axis  9 . 
         [0027]      FIG. 2  shows a schematic arrangement of the use of element  1  in an optical system  100 . The elements of optical system  100  are aligned along optical axis  9 . From a light source  4 , a light beam reaches a condenser  6  directing the light to element  1 . Element  1  is positioned in front of an illumination pupil  10 . The light coming from element  1  is directed to an intermediate image plane  14  by imaging optics  8 . It is known how to design the microlens array of element  1  and imaging optics  8  to achieve a homogeneous illumination. Together with further optics  11 , imaging optics  8  images illumination pupil  10  into the pupil of an objective  12 . Furthermore, intermediate image plane  14  is imaged into an objective plane  13  of objective  12  by optics  11  and objective  12 . Since intermediate image plane  14  is illuminated homogeneously, objective plane  13  is also illuminated homogeneously if optics  11  and objective  12  are suitably designed. The degree of polarization in the pupil of objective  12  is then identical to that of illumination pupil  10 . 
         [0028]      FIG. 3   a  shows the resulting illumination of the pupil of objective  12  when using a polarization filter  30  having a linear polarization in the X-coordinate direction (see also  FIG. 3   b ). Microlens array  3  thus allows imaging individual segments  31  exhibiting a linear polarization in the image in illumination pupil  10 . Taking the aperture of the pupil of objective  12  as a whole, the result is thus a linear polarization. 
         [0029]      FIG. 4   a  schematically shows the imaging of microlens array  3  in the pupil of objective  12 . A filter according to  FIG. 4   b  is used, which has a linear polarization in the Y-direction. When imaging element  1  into the pupil of objective  12 , the result is the pattern shown in  FIG. 4   a , wherein each segment  31  has an individual polarization in the Y-direction. Averaging across the whole aperture of the pupil of objective  12 , the result is thus a linear polarization in the Y-direction. 
         [0030]      FIG. 5   a  shows a further embodiment, wherein the imaging of microlens array  1  into the pupil of objective  12  results in a radial polarization. The radial polarization is achieved by means of a filter  35  as shown in  FIG. 5   b . Filter  35  is divided into individual segments  35   1 ,  35   2  to  35   n . The polarization of the individual segments is directed radially outwards from a center  36  of the filter. If the microlens array is illuminated via filter  35 , the result is individual segments  31  having an individual polarization in the pupil of objective  12 , wherein the polarization averaged across all elements yields a radial polarization. 
         [0031]      FIG. 6   a  shows a further embodiment of setting the polarization of an objective pupil  10  of an objective  12 . The pupil of objective  12  is illuminated by means of a filter  37  as shown in  FIG. 6   b . The filter includes several concentrically arranged circles  40   1 ,  40   2  to  40   n . Circles  40   2  to  40   n  following circle  40   1  are again divided into segments. Each segment has a polarization direction running tangentially. The illumination of the objective pupil by means of filter  37  shown in  FIG. 6   b  results in a polarization of the individual segments, wherein the polarization is oriented tangentially with respect to a center  40  of the objective. Averaging across all segments  31  yields a tangential polarization in the pupil of objective  12 . 
         [0032]      FIG. 7   a  shows a further embodiment of the polarization of the individual segments in the objective pupil of objective  12 . In the embodiment shown in  FIG. 7   a , the illumination is performed by means of element  1  shown in  FIG. 7   b . As shown in  FIG. 1 , the element consists of microlens array  3  and filter  5 . In the embodiment shown in  FIG. 7   b , the filter consists of individual elements  5   1 ,  5   2  to  5   n . Individual segments  5   1 ,  5   2  to  5   n  of filter  5  are associated with corresponding lenses  3   1 ,  3   2 ,  3   3  to  3   n  of microlens array  3 . Each element  5   1 ,  5   2  to  5   n  of filter  5  may have its own polarization. In the embodiment shown here, the filter is fixedly connected to the microlens array. The individual segments of filter  5   1 ,  5   2  to  5   n  have a circular polarization. The illumination of pupil  10  of objective  12  thus results in individual segments having a circular polarization. The circular polarization may also be carried out by a circularly polarizing filter without segmentation. The segmentation is mainly interesting for radial and tangential polarization. 
         [0033]    The embodiment shown in  FIG. 8  also shows a circular polarization of the individual elements within the pupil of objective  12 . Individual segments  5   1 ,  5   2  to  5   n  of filter  5  have a rectangular or square or hexagonal shape. Generally, the shape depends on the arrangement of the lenses in the microlens array. If the microlens array has a hexagonal structure (see  FIG. 7   c ), the segments in the filter will also be arranged hexagonally. In  FIG. 8 , the elements of the microlens array are arranged orthogonally. Someone skilled in the art will understand that individual segments  5   1 ,  5   2  to  5   n  of the filter may have any shape. The only requirement to be met is that the shape of individual segments  5   1 ,  5   2  to  5   n  of the filter is designed such that filter  5  may be completely covered. 
         [0034]    The invention has been described with respect to a particular embodiment. However, someone skilled in the art will understand that modifications and changes may be made to the invention without departing from the scope of the following claims.