Abstract:
A test mask  1  for microscopy is disclosed, which is formed on a substrate of quartz. The test mask  1  comprises a multiplicity of sub-masks  4,  which are implemented such that each sub-mask  4  comprises structures which differ within a sub-mask  4  with regard to form and size. In addition, the structures of the individual sub-masks  4  are designed for optical or particle optical measurements according to size.

Description:
RELATED APPLICATIONS  
       [0001]     This application claims benefit to provisional application Ser. No. 60/704,865 filed on Aug. 2, 2005, which is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to a test mask for microscopy. In particular, the invention relates to a test mask for microscopy that is applied to a substrate.  
       BACKGROUND OF THE INVENTION  
       [0003]     Different test masks have hitherto been used with different measurement systems (optical, particle optical). Here, a mask with larger structures was used with optical measurement systems. A mask that applied smaller structures was used with electron optical or particle optical measuring systems.  
       SUMMARY OF THE INVENTION  
       [0004]     The task underlying the invention is to create a test mask that is suitable for optical as well as for electron optical and particle optical measurement systems.  
         [0005]     The objective task is solved by a test mask that exhibits the characteristics in patent claim  1 .  
         [0006]     The invention has the advantage that the test mask comprises a multiplicity of sub-masks. Each sub-mask is provided with structures, which differ with regard to their form and their size. The sub-masks are formed such that they are suitable for optical or particle optical measurements, depending on size.  
         [0007]     The substrate of the test mask consists of glass and is coated with a chromium film. The structures may be utilized in the same form with masks such as a resist mask (exposed and developed photoresist), a chromium-coated glass or quartz glass substrate [ADI=after development inspection]), an etched but not yet stripped mask [AEI=after etch inspection], a semi-transparent MoSi mask, a chromeless mask, an EUV mask, or a comparable mask. A mask with chromium on quartz glass was selected for the concrete embodiment of the present invention. The different structures are formed by etching. In some of the sub-masks, these are present in positive and in negative. The sub-masks are placed in a two-dimensional matrix arrangement.  
         [0008]     The sub-masks are comprised of a first set and a second set. The first set of sub-masks differs from the second set of sub-masks with regard to size. In the embodiment of the invention described here, the first set of sub-masks has a side length that is 10 times larger than that of the second set of sub-masks. A person skilled in the art understands that the side ratio between the first and the second set of sub-masks may be something other than 10. Each sub-mask is formed with a central cross, which is formed by etching the chromium layer, and which is to be allocated to the first set of sub-masks.  
         [0009]     This first set of sub-masks has a side length of approximately 500 μm, and the second set of sub-masks exhibits a side length of approximately 50 μm.  
         [0010]     The first set of sub-masks comprises several structures, which are formed by etching the chromium layer. One structure is a cross that is arranged centrally within a square having a side length of 500 μm. The inverse structure of the cross also exists, that is, the cross is formed from a chromium layer, and the rest of the chromium layer is removed. A further structure consists of squares, which are also arranged within a square having a side length of 500 μm. The squares decrease in size along a line. Likewise, the squares are rotated by 45°, such that they stand on their corners. The inverse of this image also exists. A further possible structure is a multiplicity of parallel lines, which are arranged centrally within a square having a side length of 500 μm. The distance between the lines decreases toward the center. A central line has a length twice that of the other lines, which are arranged in parallel. These centrally arranged lines are rotated by 90° within a suitable structure. In a further structure, several squares are arranged within a square having a side length of 500 μm. The squares are created by removing the chromium layer. The individual squares are separated from each other by grid lines in the chromium layer. The inverse of this structure also exists. The squares consist of a chromium layer and are separated from each other by lines without a chromium layer. In a further structure, a square is arranged centrally within a square, which also has a side length of 500 μm. The square is formed from chromium layer and is separated from the rest of the chromium layer of the square by a perimeter line that is free of chromium. The centrally arranged square has a side length of 4 μm, and the perimeter line that is free of chromium has a width of 2 μm. The inverse of this structure also exists.  
         [0011]     The second set of sub-masks also comprises several different structures. In one, several lines, which are formed by etching the chromium layer, are arranged radially. The radially arranged lines are arranged centrally within a square having a side length of 50 μm. The inverse of this structure also exists. A further structure is formed by two diagonally running lines, which intersect each other. The lines are formed by etching the chromium layer and are arranged centrally within a square having a side length of 50 μm. The inverse of this structure also exists. In a further structure, several small squares are arranged centrally in the form of a matrix. The squares are created by removing the chromium layer. The squares are arranged within a square having a side length of 50 μm. The inverse of this structure also exists.  
         [0012]     A further structure is a single, centrally arranged square, which is created by etching away the chromium layer. This centrally arranged square is also arranged within a square having a side length of 50 μm. The inverse of this structure also exists. A further structure is a centrally arranged cross within a square having a side length of 50 μm. The lines of the cross are created by etching away the chromium layer. The inverse of this structure also exists. Finally, several parallel lines are provided, which are also formed by etching away the chromium layer. The lines run from one side of the square having a side length of 50 μm to the opposite side. Here, too, a structure exists in which the lines are rotated by 90°.  
         [0013]     Further advantageous embodiments of the invention are described in the subclaims.  
         [0014]     The above and other features of the invention including various novel details of construction and combinations of parts, and other advantages, will now be more particularly described with reference to the accompanying drawings and pointed out in the claims. It will be understood that the particular method and device embodying the invention are shown by way of illustration and not as a limitation of the invention. The principles and features of this invention may be employed in various and numerous embodiments without departing from the scope of the invention. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]     The object of the invention is schematically represented in the diagram, and is described below on the basis of figures, wherein elements that have the same function are given the same reference numbers. They show:  
         [0016]      FIG. 1  shows a schematic view of a mask on which several sub-masks are arranged in a matrix arrangement;  
         [0017]      FIG. 2   a  shows an enlarged representation of a sub-mask arranged on the test mask;  
         [0018]      FIG. 2   b  shows a schematic view of a second set of sub-masks as they are present within each of the sub-masks;  
         [0019]      FIG. 3  shows a cross on a first set of sub-masks;  
         [0020]      FIG. 4  shows the inverse structure of the structure represented in  FIG. 3 ;  
         [0021]      FIG. 5  shows the arrangement of several squares of descending size within a square having a side length of 500 μm;  
         [0022]      FIG. 6  shows the inverse structure of  FIG. 5 ;  
         [0023]      FIG. 7  shows parallel lines, which are arranged within a square having a side length of 500 μm, whereby a central line is double the length of the lines that are arranged in parallel;  
         [0024]      FIG. 8  shows the lines arranged in  FIG. 7  rotated by 90°;  
         [0025]      FIG. 9  shows several small squares, which are arranged in a matrix arrangement within a square having a side length of 500 μm;  
         [0026]      FIG. 10  shows the inverse structure of the structure in  FIG. 9 ;  
         [0027]      FIG. 11  shows a centrally arranged square, which is separated from the rest of the chromium layer by a perimeter line that is free of chromium layer;  
         [0028]      FIG. 12  shows the inverse structure of the structure represented in  FIG. 1   1 ;  
         [0029]      FIG. 13  shows several radially arranged lines, which are arranged centrally within a square having a side length of 50 μm;  
         [0030]      FIG. 14  shows the inverse structure of the structure represented in  FIG. 13 ;  
         [0031]      FIG. 15  shows two diagonally running lines, which are arranged within a square having a side length of 50 μm;  
         [0032]      FIG. 16  shows the inverse structure of that in  FIG. 15 ;  
         [0033]      FIG. 17  shows several small squares, which are arranged centrally within a square having a side length of 50 μm;  
         [0034]      FIG. 18  shows the inverse structure of that in  FIG. 17 ;  
         [0035]      FIG. 19  shows a small central square, which is arranged within a square having a side length of 50 μm;  
         [0036]      FIG. 20  shows the inverse structure of that in  FIG. 19 ;  
         [0037]      FIG. 21  shows a cross, which is arranged centrally within a square having a side length of 50 μm;  
         [0038]      FIG. 22  shows the inverse structure of that in  FIG. 21 ;  
         [0039]      FIG. 23  shows several parallel lines that run from one side of a square having a side length of 50 μm to the opposite side of the square;  
         [0040]      FIG. 24  shows the lines depicted in  FIG. 23 , whereby these are rotated by 90°. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.  
         [0042]      FIG. 1  shows a schematic representation of a test mask  1 . The test mask  1  exhibits a parts number  2  and is also provided with a product name  3 . Several sub-masks  4  or dies are arranged in the form of a matrix on the test mask. The embodiment of the test mask  1  represented in  FIG. 1  exhibits a square form and has a side length of 150 mm. 29 sub-masks 4 are arranged in each column and on each line. The substrate of the test mask  1  is quartz. The dimensions and ratios of the individual dimensions to each other given in the description are simply to be understood as guide values. A person skilled in the art understands how to select dimensions such that the individual sub-masks are suitable for optical and/or electron-optical testing.  
         [0043]      FIG. 2   a  shows an enlarged representation of a sub-masks  4  applied to a test mask  1 . Each sub-mask exhibits a side length  5  of 5 mm. In the representation of the test mask shown in  FIG. 2 , and in all following representations, the chromium layer  6  that is applied to the test mask is shown in dark. These structures are labeled with reference number  7 . A cross, which belongs to a first set of sub-masks, is arranged centrally on the sub-mask  4 . The cross is applied as an inverse cross to the sub-mask  4  to the left and to the right of the cross of the first set of sub-masks. A further group  9  of a first set of sub-masks is applied to the sub-mask. In addition to the first set of sub-masks, several groups  10  of a second set of sub-masks is arranged on the sub-mask  4 .  
         [0044]      FIG. 2   b  shows a group  10  of the second set of sub-masks. It should be noted that each sub-mask of the second set exhibits a side length that is smaller by a factor of 10 than the side length of the second set of sub-masks.  
         [0045]      FIG. 3  shows a central cross  11 , which is provided in each first set of sub-masks. The central cross is formed within a square having a side length  12  of 500 μm. The cross  11  represented in  FIG. 3  is formed by etching away a chromium layer. The square  13  in which the cross  11  is formed has a perimeter border  14 , which is also free of the chromium layer. The perimeter border  14  exhibits a thickness of 50 μm. The running numeration  15 , which identifies the row and the column of the test mask  1  in which the sub-mask is located, is also structured on the sub-mask  13  with the cross  11 . In the present example, the sub-mask  13  is located in the 18th row and the 25th column of the test mask  1 . The central cross  11  exhibits a crossbar length  16  of approximately 200 μm. Each end region of a crossbar of the cross  11  is provided with a broad surface area  20 . The surface area  20  has a width  17  of approximately 4 μm. The crossbars of the cross  11  have a width  18  of 1 μm. The distance between the broad surface areas  20  on the crossbars of the cross  11  is 10 μm.  
         [0046]      FIG. 4  shows a structure  21 , which is the inverse structure of the cross  11  in  FIG. 3 . The dimensions of the cross  11  in  FIG. 4  correspond to the dimensions of the cross  11  in  FIG. 3 . The cross  11  in  FIG. 4  is created by etching away the chromium layer around the cross  11 . In the same way, a perimeter border  22  is formed around the square having a side length  12  of 500 μm by means of a chromium layer. The broad surface areas  20  shown in  FIG. 3  and  FIG. 4  at the ends of the crossbars of the cross  11  are used to test the measuring accuracy of optical systems. The crossbars of the cross  11  in  FIG. 3  and  4  are used to test the measuring accuracy of electron-optical or particle-optical systems. A particle-optical system or an electron-optical system is a CDSEM, i.e., a scanning electron microscope used to measure critical breadths of structures.  
         [0047]      FIG. 5  shows a further structure of the first set of sub-masks. Here, the first set of sub-masks is formed with numerous squares  30 . The squares  30  are created by etching away the chromium layer around the squares  30 . The squares  30  are arranged along a first line  31 . In addition, the squares  30  are rotated by a 45° and are arranged along a second line  32 . The squares  30 , which are arranged along the first line  31  and along the second line  32  increase in size and surface area (viewed from left to right). The gradation of resolution of an optical system or of an electron-optical or particle-optical system can be determined by decreasing the size of the squares  30 .  
         [0048]     The squares  30  are structured within a square having a side length of 500 μm.  FIG. 6  is the inverse representation of the structured squares  30  in  FIG. 5 . The squares  30  are thus surface areas of the chromium layer, and the chromium layer that surrounds the squares has been removed by etching away.  
         [0049]      FIG. 7  shows a further first set of sub-masks in which the structure is realized within a square having a side length  12  of 500 μm. The structure is comprised of a first set  40  of centrally arranged lines  41 . The lines  41  are parallel and decrease in distance from each other toward the center of the sub-mask. Furthermore, a central line  44  is formed, which exhibits a length that is double that of the other lines  41 . The lines  41  exhibit a length  42  of 10 μm. The central line  44  has a length  43  of 20 μm. The lines  41  and the central line  44  are created by etching away the chromium layer.  FIG. 8  shows a different arrangement of the lines  41  and the central lines  44  shown in  FIG. 7 . Here, the lines are rotated by 90° and structured in the same way in a chromium layer by etching. The long central line  44  is used to center an optical beam path. The structures represented in  FIG. 7  and  FIG. 8  are on the mask in order to detect spherical aberration in optical microscopes.  
         [0050]      FIG. 9  also shows a first set of sub-masks, which is formed by a set of grid lines  51 . The grid lines  51 , which consist of chromium layer, are separated from each other by a multiplicity of squares  52 . The squares  52  are created by etching away the chromium layer. The multiplicity of squares  52  is formed on a square having a side length of 500 μm.  FIG. 10  shows the sub-mask represented in  FIG. 9  in inverse form. Here, the grid lines  51  are free of chromium layer. Consequently, the squares  52  are comprised of chromium layer.  
         [0051]      FIG. 11  shows a further first set of sub-masks, which comprises a square  61 , which is formed in a chromium layer and comprises a chromium layer. The square  61  is surrounded by a perimeter line  62 , which is formed by etching away the chromium layer. The rest of the sub-mask, which comprises a square having a side length  12  of 500 μm, remains covered with chromium layer. The square  61  has a side length of 4 μm, and the perimeter border has a side length  64  of 8 μm.  FIG. 12  shows the square  61  represented in  FIG. 11  in inverse form. Consequently, the square  61  is formed by etching away the chromium layer. Consequently, the perimeter line  62  is chromium layer. The structures represented in  FIG. 11  and  FIG. 12  are used to determine overlay (optical). By the same token, the structures are used to test algorithms to determine the overlay.  
         [0052]      FIG. 13  shows a second set of sub-masks, in which the structures are formed in a chromium layer, which exhibits a side length  120  of 50 μm. As a first structure, several lines  70  are arranged radially in the chromium layer. In the structure represented in  FIG. 13 , the lines  70  are formed by etching away the chromium layer.  FIG. 14  shows the negative representation of the structure represented in  FIG. 13 . The lines  70  are now represented as chromium layer. The structures represented in  FIGS. 13 and 14  are used to determine the astigmatism of various focal positions. With structures or structure intervals, respectively, that are less than 0.2 μm, measurement is therefore done by CDSEM.  
         [0053]      FIG. 15  shows a further second set of sub-masks, in which two diagonally arranged lines  80  are provided. The lines  80  are formed within a square having a side length of 50 μm. The lines  80  are created by etching away the chromium layer.  FIG. 16  shows the inverse of the structure represented in  FIG. 15 .  
         [0054]      FIG. 17  shows a further set of sub-masks, in which several square points  90  are structured. The square points  90  are created by etching away the chromium layer. The square points  90  are arranged centrally within a square having a side length  120  of 50 μm.  FIG. 18  shows the inverse of the structure in  FIG. 17 . Consequently, the squares  90  are comprised of chromium layer. The arrangement of dots ( FIG. 18 ) and holes ( FIG. 17 ) thus yields a tool with which the proximity effect of electron-optical or particle-optical systems may be determined.  
         [0055]      FIG. 19  shows a further embodiment of a second set of sub-masks. Here, a single square  95  is free of chromium layer. This square  95  is arranged centrally within a square having a side length  120  of 50 μm.  FIG. 20  shows the inverse of the structure in  FIG. 19 . Consequently, the square  95  is formed of chromium layer, which is surrounded by a free area, which contains no chromium. The structures represented in  FIG. 19  and  FIG. 20  are also used to determine the proximity effect of electron-optical or particle-optical systems.  
         [0056]      FIG. 21  shows a further embodiment of a second set of sub-masks, which is comprised of a cross  100 , which is centrally arranged within a square having a side length  120  of 50 μm. The cross  100  is formed by etching away the chromium layer.  FIG. 22  shows the inverse of the structure represented in  FIG. 21 . Consequently, the cross  100  is comprised of two chromium lines that intersect.  
         [0057]      FIG. 23  shows a multiplicity of lines  110 , which are etched within a square having a side length  120  of 50 μm.  FIG. 24 , by contrast, shows this multiplicity of lines  110  rotated by 90°. Both of the structures represented in  FIG. 23  and  FIG. 24  are used to determine the field curvature of optical systems.