Patent Publication Number: US-9846128-B2

Title: Inspection system and a method for evaluating an exit pupil of an inspection system

Description:
BACKGROUND 
     A variety of systems are used for automated inspection of objects such as semiconductor wafers, in order to detect defects, particles and/or patterns on the wafer surface as part of a quality assurance process in semiconductor manufacturing processes. It is a goal of current inspection systems to have high resolution and high contrast imaging in order to provide the reliability and accuracy demanded in sub-micron semiconductor manufacturing processes. 
     Various inspection systems have a masking module that controls the collection of beams that are scattered or reflected from the object. A masking module includes a predefined and limited number of apertures and the inspection system may select which of the apertures to use. 
     There is a growing need to evaluate existing masking modules and to evaluate future masking modules. 
     SUMMARY 
     According to an embodiment of the invention there may be provided a system that may include a first detection module; an illumination and collection module; a processor; wherein the illumination and collection module and the first detection module may be configured to execute one or more illumination and collection iterations; wherein each inspection iteration may include: (i) illuminating, by the illumination and collection module and with illuminating radiation, multiple points of an object; (ii) directing, by the illumination and collection module, first collected radiation from the multiple points of the object through one or more first exit pupil regions towards the first detection module; wherein one or more first exit pupil regions belong to multiple first exit pupil regions; wherein the multiple first exit pupil region belong to a first exit pupil; and (iii) generating, by the first detection module, first detection signals that may be indicative of the first collected radiation. The processor may be configured to process the first detection signals to provide a first mapping between (i) a characteristic of radiation at the first exit pupil, (ii) the multiple points of the object, and (iii) the multiple first exit pupil regions. 
     The illumination and collection module and the first detection module may be configured to execute multiple illumination and collection iterations; wherein during each inspection iteration the first collected radiation passes only through a single first exit pupil region. 
     The different illumination and collection iterations of the multiple illumination and collection iterations may be associated with different first exit pupil regions of the multiple first exit pupil regions. 
     The first detection module may include multiple first detectors that may be spaced apart from the first exit pupil, and wherein the illumination and collection module may include a first masking module that may be configured to selectively unmask the single first exit pupil region per illumination and collection iteration. 
     The multiple illumination and collection iterations may include a plurality of inspection iteration sets; wherein each inspection iteration set may include: (a) a first inspection iteration during which a single beam of illumination radiation scans the multiple points of the object and the collected radiation passes through a predefined first exit pupil region; (b) a second inspection iteration during which a pair of beams of illumination radiation that impinge on the object to provide a pair of spots that (i) may be spaced apart from each other by a predefined difference and (ii) scan the multiple points of the object; and wherein the collected radiation passes through the predefined first exit pupil region; and (c) a third inspection iteration during which another pair of beams of illumination radiation that impinge on the object to provide another pair of spots that (i) may be phase shifted from each other by a predefined phase shift and (ii) scan the multiple points of the object; and wherein the collected radiation passes through the predefined first exit pupil region. 
     The processor may be configured to calculate an S-matrix in response to the first detection signals. 
     The first detection module may include multiple first detectors that may be spaced apart from the first exit pupil, wherein the illumination and collection module may include a first masking module that may be configured to selectively mask different first exit pupil regions of the multiple first exit pupils. 
     The illumination and collection module may be configured to execute a single inspection iteration during which the first collected radiation passes through the multiple first exit pupil regions. 
     The first detection module may include multiple first detectors that may be positioned at the first exit pupil, and wherein at least one first detector of the multiple first detectors may be allocated per each first exit pupil region. 
     The illumination and collection module may be configured to direct the first collected radiation through the multiple first exit pupil regions. 
     The processor may be configured to evaluate, in response to the first mapping, an outcome of a first masking operation that masks at least one masked first exit pupil region while unmasking at least one unmasked first exit pupil region; and wherein the at least one masked first exit pupil region and the at least one at least one unmasked first exit pupil region belong to the multiple first exit pupil regions. 
     The characteristic of radiation at the first exit pupil may be an intensity of the radiation at the first exit pupil, and wherein the processor may be configured to evaluate the first masking operation by summing, for each of the multiple points of the objects, detections signals associated only with the at least one unmasked first exit pupil region. 
     The system may include a second detection module; wherein each inspection iteration further may include directing second collected radiation from the multiple points of the object through one or more second exit pupil regions towards the second detection module and generating second detection signals indicative of the second collected radiation; wherein the one or more second exit pupil regions belong to multiple second exit pupil regions of a second exit pupil. 
     The system may be configured to pass the second collected radiation through a same one or more second exit pupil regions during different illumination and collection iterations. 
     The processor may be configured to compare second detection signals obtained during the different illumination and collection iterations to provide comparison results; and to align first detection signals obtained during the different illumination and collection iterations based on the comparison results. 
     The processor may be configured to process the second detection signals to provide a second mapping between (i) a characteristic of radiation at the second exit pupil, (ii) the multiple points of the object, and (iii) the multiple second exit pupil regions. 
     The second collected radiation may be scattered from the multiple points of the object and wherein the first collected radiation may be reflected from the multiple points of the object. 
     The characteristic of radiation at the first exit pupil may be an intensity of the radiation at the first exit pupil. 
     The multiple points of the object may form a continuous area of the object. 
     According to an embodiment of the invention there may be provided a method that may include executing one or more illumination and collection iterations; wherein each inspection iteration may include: (i) illuminating, with illuminating radiation, multiple points of the object, (ii) directing first collected radiation from the multiple points of the object through one or more first exit pupil regions towards a first detection module; wherein one or more first exit pupil regions belong to multiple first exit pupil regions of a first exit pupil; and (iii) generating, by the first detection module, first detection signals indicative of the first collected radiation; and processing, by a processor, the first detection signals to provide a first mapping between (i) a characteristic of radiation at the first exit pupil, (ii) the multiple points of the object, and (iii) the multiple first exit pupil regions. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings in which: 
         FIG. 1  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 2A  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 2B  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 3  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 4  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 5  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 6  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 7  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 8  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 9  illustrates a system and an object according to an embodiment of the invention; 
         FIG. 10  illustrates a system and an object according to an embodiment of the invention; and 
         FIG. 11  illustrates a method according to an embodiment of the invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be understood by those skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known methods, procedures, and components have not been described in detail so as not to obscure the present invention. 
     The subject matter regarded as the invention is particularly pointed out and distinctly claimed in the concluding portion of the specification. The invention, however, both as to organization and method of operation, together with objects, features, and advantages thereof, may best be understood by reference to the following detailed description when read with the accompanying drawings. 
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements. 
     Because the illustrated embodiments of the present invention may for the most part, be implemented using electronic components and circuits known to those skilled in the art, details will not be explained in any greater extent than that considered necessary as illustrated above, for the understanding and appreciation of the underlying concepts of the present invention and in order not to obfuscate or distract from the teachings of the present invention. 
     Any reference in the specification to a method should be applied mutatis mutandis to a system capable of executing the method and should be applied mutatis mutandis to a non-transitory computer readable medium that stores instructions that once executed by a computer result in the execution of the method. 
     Any reference in the specification to a system should be applied mutatis mutandis to a method that may be executed by the system and should be applied mutatis mutandis to a non-transitory computer readable medium that stores instructions that may be executed by the system. 
     Any reference in the specification to a non-transitory computer readable medium should be applied mutatis mutandis to a system capable of executing the instructions stored in the non-transitory computer readable medium and should be applied mutatis mutandis to method that may be executed by a computer that reads the instructions stored in the non-transitory computer readable medium. 
     The following detailed description is of exemplary embodiments of the invention but the invention is not limited thereto, as modifications and supplemental structures may be added, as would be apparent to those skilled in the art. In particular, but without limitation, while an exemplary embodiment may be disclosed with regard to the inspection of a subject surface by detecting reflected light using a light source and detecting unit that are disposed on a common side of an object (a “reflective system”), it would be readily apparent to one skilled in the art that the teachings are readily adaptable to the inspection of an object by detecting transmitted light with a detecting unit that is on a side of an object opposite to that of the light source (a “transmissive system”). 
     While the reflective system and the transmissive system differ, for one example by the absence of a beam splitter in the transmissive system, the principles of the present invention are applicable to both types of systems. As would be understood by one skilled in the art, both types of systems may be utilized separately or together in the inspection of an object, in accordance with the present invention. 
       FIG. 1  illustrates system  101  and object  10  according to an embodiment of the invention. 
     Without limitation and only by example, object  10  may be any semiconductor product having multiple semiconductor devices thereon, at any of several stages of manufacture, or may be a mask, reticule or the like used in a manufacturing process, where such object must be inspected for defects, foreign objects or pattern accuracy. 
     System  101  is illustrated as including illumination and collection module  20 , first detection module  80 , processor  90  and mechanical stage  85 . 
     Mechanical stage  85  is configured to support object  10  and introduce a mechanical movement between object  10  and the illumination and collection module  20 . 
     In  FIG. 1  the mechanical movement follows a raster scan pattern  130  that scans the entire object  10 . It is noted that scan patterns other than a raster scan pattern can be applied. It is further noted that the scan pattern may scan only one or more parts of object  10 . 
     According to an embodiment of the invention, instead of moving the object  10  (as shown in  FIG. 1 ) the illumination and collection module  20  can be mechanically moved. Alternatively—both object  10  and illumination and collection module  20  can be mechanically moved during the scan of object  10 . 
     Illumination and collection module  20  and first detection module  80  are configured to execute one or more illumination and collection iterations. 
     During each inspection iteration illumination and collection module  20  is configured to (i) illuminate, by illuminating radiation (such as illuminating beam  131 ), multiple points of the object; and (ii) direct first collected radiation (such as collected beam  141 ) from the multiple points of the object through one or more first exit pupil regions towards the first detection module. 
     The multiple points of the object may be scanned by a single illuminating beam in a serial manner. Alternatively, the multiple points of the object may be scanned with a plurality of illuminating beams. 
     The multiple points of object  10  may cover the entire object or only one or more parts of object  10 . It is assumed, for simplicity of explanation that the multiple points of the object form cover the entire object. 
     Illumination and collection module  20  may include first masking module  70  that is positioned at first exit pupil  60 . 
     First exit pupil  60  include multiple first exit pupil regions  60 ( 1 , 1 )- 60 (A,B). In  FIG. 1  first exit pupil region  60 ( a,b ) is represented by a black box. The first exit pupil regions may be of the same size and shape. Alternatively—at least two of the first exit pupil regions may differ from each other by size or shape. 
     First masking module  70  may selectively mask includes first masking elements  70 ( 1 , 1 )- 70 (C,D) for selectively masking any first exit pupil region out of multiple first exit pupil regions  60 ( 1 , 1 )- 60 (A,B). There may be one or more first masking elements per first exit pupil region. In  FIG. 1  first masking element  70 ( c,d ) is represented by a black box. First masking element  70 ( c,d ) unmasks the first exit pupil region  60 ( a,b ). 
     In  FIG. 1  first masking module  70  is illustrated as unmasking only a single first exit pupil region  60 ( a,b ). 
     According to an embodiment of the invention there are multiple (R) first exit pupil regions and the first masking module  70  is configured to unmask only one first exit pupil region per illumination and collection iteration. 
     Executing R illumination and collection iterations, each illumination and collection iterations involving unmasking a different first exit pupil region, may provide information about each one of the first exit pupil regions  60 ( 1 , 1 )- 60 (A,B). 
     It is noted that the masking module  70  may be configured to unmask any combination of first exit pupil regions at any illumination and collection iteration. 
     During each inspection iteration the first detection module  80  is configured to generate first detection signals indicative of the first collected radiation. 
     In  FIG. 1  first detection module  80  is spaced apart from first exit pupil  60 . 
     Processor  90  is configured to process first detection signals obtained during the one or more illumination and collection iterations and to provide a first mapping between (i) a characteristic of radiation at the first exit pupil, (ii) the multiple points of the object, and (iii) the multiple first exit pupil regions. 
     It is assumed, for simplicity of explanation, that the characteristic of the radiation is the intensity of the radiation. 
     Each inspection iteration may provide a two dimensional scan image Uab(x,y)—wherein “ab” represents the first exit pupil region ( 60 ( a,b )) that was unmasked during the illumination and collection iteration. 
     When performing multiple (R) illumination and collection iterations during which information about each first exit pupil was obtained, the first mapping may provide the intensity of the radiation for each combination of first exit pupil region  60 ( a,b ) and for each point  10 ( x,y ) of the multiple points of the object. The first mapping may be represented by a four dimensional function U(a,b,x,y). 
     By adding, per point of the object, the values obtained during each of the multiple (R) illumination and collection iterations, a pupil image may be obtained. Uxy(a,b) is calculated by a slicing the four dimensional function to a two dimensional function by fixing the x and y coordinates. 
     Processor  90  may use differences in the pupil image between defect locations and reference locations in order to determine which spatial filter (involving selectively masking one or more first exit pupil region) is optimal for improving the detection capability. 
     Processor  90  may be configured to evaluate an outcome of a first masking operation that masks at least one masked first exit pupil region while unmasking at least one unmasked first exit pupil region. The evaluating may include summing, for each of the multiple points of the objects, detections signals associated only with the at least one unmasked first exit pupil region. 
     For example, when evaluating a masking operation that will unmask only a set of first exit pupil regions then the processor may calculate a sample image using the selected mask associated with the set by applying the following function: Uset=Sum (for all values of a and b associated with the set of first exit pupil regions) over U(a,b,x,y). 
       FIG. 2A  illustrates system  101  and object  10  according to an embodiment of the invention. 
       FIG. 2A  illustrates system  101  that scans object  10  with two illuminating beams  131  and  132 . Once the two illuminating beams  131  and  132  impinge on object  10  spots are formed on the object  10  that differ from each other by a predefined distance  139 . 
     It is noted that predefined distance  139  may be large enough to prevent an interference of illuminating beams  131  and  132 . Alternatively—predefined distance  139  may be a predefined distance that is small enough to allow illuminating beams  131  and  132  to interfere with each other. 
     In  FIG. 2A  first detection module  80  receives two collected beams  141  and  142 . 
       FIG. 2B  illustrates system  101  and object  10  according to an embodiment of the invention. 
       FIG. 2B  illustrates system  101  that scans object  10  with two illuminating beams  131 ′ and  132 ′. Once the two illuminating beams  131 ′ and  132 ′ impinge on object  10  the illuminating beams  131 ′ and  132 ′ are phase shifted by a predefined phase shift  139 ′. A non-limiting example of a predefined phase shift  139 ′ is pi/2. 
     In  FIG. 2B  the first detection module  80  receives two collected beams  141 ′ and  142 ′. 
     It should be noted that system  101  may scan object  10  with more than two illuminating beams. 
     According to an embodiment of the invention, system  101  may be configured to perform multiple (for example—3*R) illumination and collection iterations. 
     The multiple illumination and collection iterations include R sets of illumination and collection iterations. Different sets of illumination and collection iterations are associated with different first exit pupil regions. The R sets illumination and collection iterations “cover” the R first exit pupil regions. 
     Each inspection iteration set is associated with a first exit pupil region  60 ( a,b ) and includes a first illumination and collection iteration, a second inspection iteration and a third illumination and collection iteration. 
     The first inspection iteration includes scanning with a single illuminating beam (such as illuminating beam  131  of  FIG. 1 ) the multiple points of the object and the collected radiation passes through first exit pupil region  60 ( a,b ). 
     The second inspection iteration includes scanning the multiple points of the object by a pair of beams of illumination radiation (such as illuminating beams  131  and  132  of  FIG. 2A ) that impinge on the object to provide a pair of spots that are spaced apart from each other by a predefined difference (denoted  139  in  FIG. 2A ). The collected radiation (such as collected beams  141  and  142  of  FIG. 2A ) passes through first exit pupil region  60 ( a,b ). 
     The third inspection iteration includes scanning the multiple points of the object by a pair of beams of illumination radiation (such as illuminating beams  131 ′ and  132 ′ of  FIG. 2B ) that impinge on the object to provide a pair of spots that are phase shifted from each other by a predefined phase shift (denoted  139 ′ in  FIG. 2B ). The collected radiation (such as collected beams  141 ′ and  142 ′ of  FIG. 2B ) passes through first exit pupil region  60 ( a,b ). 
     The detection signals obtained during the first inspection iteration may be processed to provide exit pupil image denoted I(x,y). 
     The detection signals obtained during the second inspection iteration may be processed to provide exit pupil image denoted I 1 (x,y). 
     The detection signals obtained during the third inspection iteration may be processed to provide exit pupil image denoted I 2 (x,y). 
     Processor  90  may process I(x,y), I 1 (x,y) and I 2 (x,y). 
     If the complex field distribution for a single spot u(x,y) it is argued that:
 
 I ( x,y )=| u ( x,y )| 2  
 
 I   1 ( x,y )=| u ( x,y )+ u ( x+d,y )| 2   =I ( x,y )+ I ( x+d,y )+2√{square root over ( I ( x,y ) I ( x+d,y ))}cos(Δφ)
 
 I   2 ( x,y )=| u ( x,y )+ iu ( x+d,y )| 2 =1( x,y )− I ( x+d,y )+2√{square root over ( I ( x,y ) I ( x+d,y )sin(Δφ))}
 
Therefore:
 
     
       
         
           
             
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     The same analysis can be done for the 
               ∂   φ       ∂   y           
producing the full gradient of the phase.
 
     Finally, for each (a,b) location at the exit pupil which attributed to a wave in the s-matrix we have full phased image, therefore using the reciprocity of the s-matrix between incident and scattered waves, a full s-matrix can be reconstructed according to the spatial resolution of the pupil imaging. 
       FIG. 3  illustrates system  103  according to an embodiment of the invention. 
     System  103  differs from system  101  by including second exit pupil  62 , second masking module  72  that is positioned at the second exit pupil  62 , and second detection module  82 . In  FIG. 3 , first detection module  80  receives first collected beam  141  and second detection module  82  receives second collected beam  142 . 
     Second exit pupil  62  include multiple second exit pupil regions  62 ( 1 , 1 )- 62 (A,B). In  FIG. 1  second exit pupil region  62 ( a,b ) is represented by a black box. The second exit pupil regions may be of the same size and shape. Alternatively—at least two of the second exit pupil regions may differ from each other by size or shape. 
     Second masking module  72  includes second masking elements  72 ( 1 , 1 )- 72 (C,D) for selectively masking any second exit pupil region out of multiple second exit pupil regions  62 ( 1 , 1 )- 62 (A,B). There may be one or more second masking elements per second exit pupil region. In  FIG. 1  second masking element  72 ( c,d ) is represented by a black box. First masking element  72 ( c,d ) unmasks second exit pupil region  62 ( a,b ). 
     In  FIG. 3  second masking module  72  is illustrated as unmasking only a single second exit pupil region  62 ( a,b ). 
     Multiple second exit pupil regions  62 ( 1 , 1 )- 62 (A,B) may have the same shape and size as the multiple first exit pupil regions  60 ( 1 , 1 )- 60 (A,B). Alternatively—at least one second exit pupil region may differ by shape, size or both shape and size from at least one first exit pupil region. 
     System  103  may be configured to execute one or more illumination and collection iterations. 
     During each inspection iteration illumination and collection module  20  is configured to (i) illuminate, by illuminating radiation (such as illuminating beam  131 ), multiple points of the object; (ii) direct first collected radiation (such as collected beam  141 ) from the multiple points of the object through one or more first exit pupil regions towards first detection module  80 ; and (iii) direct second collected radiation (such as collected beam  144 ) from the multiple points of the object through one or more second exit pupil regions towards second detection module  82 . 
     During each inspection iteration, first detection module  80  is configured to generate first detection signals indicative of the first collected radiation and second detection module  82  is configured to generate second detection signals indicative of the second collected radiation. 
     Processor  90  may be configured to process second detection signals obtained during the one or more illumination and collection iterations and to provide a second mapping between (i) a characteristic of radiation at the second exit pupil, (ii) the multiple points of the object, and (iii) the multiple second exit pupil regions. 
     According to an embodiment of the invention the second masking module  72  second detection module  82  may be used for aligning first scan images obtained by first detection module  80 . 
     In order to perform the alignment the configuration of the second masking module  72  is fixed during multiple illumination and collection iterations. The second detection module  82  obtains, during different illumination and collection iterations, different second scan images. 
     Processor  90  is configured to calculate misalignments between the second scan images to provide second misalignment results. 
     Processor  90  may also be configured to align the first scan images using the second misalignment results. The alignment of the first scan image may be based upon an assumption that a first scan image and a second scan image that were obtained during the same inspection iteration will suffer from the same misalignment. 
     According to an embodiment of the invention, first masking module  70  and first detection module  80  may be used for aligning second scan images obtained by second detection module  82 . The alignment may be executed by (i) using, during multiple illumination and collection iterations, a first masking module  70  of a fixed configuration, (ii) calculating misalignments between the first scan images to provide first misalignment results, and (iii) aligning the second scan images using the first misalignment results. 
       FIG. 4  illustrates system  104  and object  10  according to an embodiment of the invention. 
     System  104  is illustrated as including illumination and collection module  20 , first detection module  80 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as including a radiation source  21 , first beam splitter  26 , objective lens  27 , lens  29 , and first masking module  70  that is positioned at first exit pupil  60 . 
     Radiation source  21  directs first radiation beam  11  towards first beam splitter  26 . 
     First radiation beam  11  passes through first beam splitter  26  and impinges on objective lens  27 . 
     Objective lens  27  directs an illuminating beam  131  onto object  10 . 
     Objective lens  27  collects reflected beam  12  and directs the reflected beam  12  onto first beam splitter  26 . 
     First beam splitter directs the reflected beam  12  to pass through lens  29  and to impinge on first masking module  70 . 
     First masking module  70  may unmask one or more first exit pupil region to allow a passage of collected beam  141  through first masking module  70  and onto first detection module  80 . 
       FIG. 5  illustrates system  105  and object  10  according to an embodiment of the invention. 
     System  105  is illustrated as including illumination and collection module  20 , second detection module  82 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as including a radiation source  21 , donut mirror  26 ′, objective lens  27 , lens  28 , and second masking module  72  that is positioned at second exit pupil  62 . 
     Radiation source  21  directs first radiation beam  11  towards donut mirror  26 ′. 
     First radiation beam  11  passes through an aperture formed in donut mirror  26 ′ and impinges on objective lens  27 . 
     Objective lens  27  directs an illuminating beam  131  onto object  10 . 
     Objective lens  27  collects reflected beam (not shown) and scattered beam  133  (that surrounds the reflected beam) and directs the reflected beam and the scattered beam  133  onto donut mirror  26 ′. 
     Donut mirror  26 ′ directs the scattered beam  133  to pass through lens  28  and to impinge on second masking module  72 . 
     Second masking module  72  may unmask one or more second exit pupil region to allow a passage of collected beam  145  through second masking module  72  and onto second detection module  82 . 
       FIG. 6  illustrates system  106  and object  10  according to an embodiment of the invention. 
     System  106  is illustrated as including illumination and collection module  20 , first detection module  80 , second detection module  82 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as including a radiation source  21 , first beam splitter  26 , objective lens  27 , lens  29 , first masking module  70  that is positioned at first exit pupil  60 , donut mirror  26 ′, lens  28 , and second masking module  72  that is positioned at second exit pupil  62 . 
     Radiation source  21  directs first radiation beam  11  towards donut mirror  26 ′. 
     First radiation beam  11  passes through passes an aperture formed in donut mirror  26 ′ and impinges on objective lens  27 . 
     Objective lens  27  directs an illuminating beam  131  onto object  10 . 
     Objective lens  27  collects reflected beam  12  and directs the reflected beam  12  to pass through the aperture formed in donut mirror  26 ′ and to impinge on first beam splitter  26 . 
     First beam splitter  26  directs the reflected beam  12  to pass through lens  29  and to impinge on first masking module  70 . 
     First masking module  70  may unmask one or more first exit pupil region to allow a passage of collected beam  141  through first masking module  70  and onto first detection module  80 . 
     Objective lens  27  also collects scattered beam  133  and directs the scattered beam  133  towards donut mirror  26 ′. 
     Donut mirror  26 ′ directs scattered beam  133  to pass through the lens  28  and to impinge (as second collected beam  145 ) on second masking module  72 . 
     Second masking module  72  may unmask one or more second exit pupil region to allow a passage of collected beam  145  through second masking module  72  and onto second detection module  82 . 
       FIG. 7  illustrates system  107  and object  10  according to an embodiment of the invention. 
     System  107  is illustrated as including illumination and collection module  20 , first detection module  80 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as directing an illuminating beam  131  onto object  10 . 
     First detection module  80  is positioned at the first exit pupil and has multiple first detectors  80 ( 1 , 1 )- 80 (E,F). Each first exit pupil region is “covered” by a dedicated one or more first detector (for example—a single first exit pupil region may be covered by first detector  80 ( e,f )). 
     System  107  may perform a single inspection iteration and obtain all the information obtained by system  101  in multiple (R) illumination and collection iterations. 
     System  107  does not require first masking module  70  of system  101 . 
       FIG. 8  illustrates system  108  and object  10  according to an embodiment of the invention. 
     System  108  is illustrated as including illumination and collection module  20 , first detection module  80 , second detection module  82 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as directing an illuminating beam  131  onto object  10 . 
     First detection module  80  is positioned at the first exit pupil  60  and has multiple first detectors  80 ( 1 , 1 )- 80 (E,F). Each first exit pupil region is “covered” by a dedicated one or more first detector (for example—a single first exit pupil region may be covered by first detector  80 ( e,f )). 
     Second detection module  82  is positioned at the second exit pupil  62  and has multiple second detectors  82 ( 1 , 1 )- 82 (E,F). Each second exit pupil region is “covered” by a dedicated one or more second detector (for example—a single second exit pupil region may be covered by second detector  82 ( e,f )). 
     System  108  may perform a single inspection iteration and obtain all the information obtained by system  103  in multiple (R) illumination and collection iterations. 
     System  108  does not require first masking module  70  and second masking module  72  of system  106 . 
       FIG. 9  illustrates system  109  and object  10  according to an embodiment of the invention. 
     System  109  is illustrated as including illumination and collection module  20 , first detection module  80 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as including a radiation source  21 , first beam splitter  26 , objective lens  27  and lens  29 . 
     First detection module  80  is positioned at first exit pupil  60 . 
     Radiation source  21  directs first radiation beam  11  towards first beam splitter  26 . 
     First radiation beam  11  passes through first beam splitter  26  and impinges on objective lens  27 . 
     Objective lens  27  directs an illuminating beam  131  onto object  10 . 
     Objective lens  27  collects reflected beam  12  and directs the reflected beam  12  onto first beam splitter  26 . 
     First beam splitter directs the reflected beam  12  to pass through lens  29  and to impinge (as first collected beam  141 ) on first detection module  80 . 
       FIG. 10  illustrates system  110  and object  10  according to an embodiment of the invention. 
     System  110  is illustrated as including illumination and collection module  20 , first detection module  80 , second detection module  82 , processor  90  and mechanical stage  85 . 
     Illumination and collection module  20  is illustrated as including a radiation source  21 , first beam splitter  26 , objective lens  27 , lens  29 , donut mirror  26 ′ and lens  28 . First detection module  80  is positioned at first exit pupil  60 . Second detection module  72  is positioned at second exit pupil  62 . 
     Radiation source  21  directs first radiation beam  11  towards donut mirror  26 ′. 
     First radiation beam  11  passes through passes an aperture formed in donut mirror  26 ′ and impinges on objective lens  27 . 
     Objective lens  27  directs an illuminating beam  131  onto object  10 . 
     Objective lens  27  collects reflected beam  12  and directs the reflected beam  12  to pass through the aperture formed in donut mirror  26 ′ and to impinge on first beam splitter  26 . 
     First beam splitter  26  directs the reflected beam  12  to pass through lens  29  and to impinge (as first collected beam  141 ) on first detection module  80 . 
     Objective lens  27  also collects scattered beam  133  and directs the scattered beam  133  towards donut mirror  26 ′. 
     Donut mirror  26 ′ directs scattered beam  133  to pass through the lens  28  and to impinge (as third collected beam  145 ) on second detection module  82 . 
       FIG. 11  illustrates method  200  according to an embodiment of the invention. 
     Method  200  may start by step  210  of executing one or more illumination and collection iterations. Each inspection iteration may include (i) illuminating, with illuminating radiation, multiple points of the object, (ii) directing first collected radiation from the multiple points of the object through one or more first exit pupil regions towards the first detection module; wherein one or more first exit pupil regions belong to multiple first exit pupil regions of a first exit pupil; and (iii) generating, by a first detection module, first detection signals indicative of the first collected radiation. 
     Step  210  may be followed by step  220  of processing, by a processor, the first detection signals to provide a first mapping between (i) a characteristic of radiation at the first exit pupil, (ii) the multiple points of the object, and (iii) the multiple first exit pupil regions. 
     In the foregoing specification, the invention has been described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein without departing from the broader spirit and scope of the invention as set forth in the appended claims. 
     Moreover, the terms “front,” “back,” “top,” “bottom,” “over,” “under” and the like in the description and in the claims, if any, are used for descriptive purposes and not necessarily for describing permanent relative positions. It is understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in other orientations than those illustrated or otherwise described herein. 
     The connections as discussed herein may be any type of connection suitable to transfer signals from or to the respective nodes, units or devices, for example via intermediate devices. Accordingly, unless implied or stated otherwise, the connections may for example be direct connections or indirect connections. The connections may be illustrated or described in reference to being a single connection, a plurality of connections, unidirectional connections, or bidirectional connections. However, different embodiments may vary the implementation of the connections. For example, separate unidirectional connections may be used rather than bidirectional connections and vice versa. Also, plurality of connections may be replaced with a single connection that transfers multiple signals serially or in a time multiplexed manner. Likewise, single connections carrying multiple signals may be separated out into various different connections carrying subsets of these signals. Therefore, many options exist for transferring signals. 
     Although specific conductivity types or polarity of potentials have been described in the examples, it will be appreciated that conductivity types and polarities of potentials may be reversed. 
     Each signal described herein may be designed as positive or negative logic. In the case of a negative logic signal, the signal is active low where the logically true state corresponds to a logic level zero. In the case of a positive logic signal, the signal is active high where the logically true state corresponds to a logic level one. Note that any of the signals described herein may be designed as either negative or positive logic signals. Therefore, in alternate embodiments, those signals described as positive logic signals may be implemented as negative logic signals, and those signals described as negative logic signals may be implemented as positive logic signals. 
     Furthermore, the terms “assert” or “set” and “negate” (or “deassert” or “clear”) are used herein when referring to the rendering of a signal, status bit, or similar apparatus into its logically true or logically false state, respectively. If the logically true state is a logic level one, the logically false state is a logic level zero. And if the logically true state is a logic level zero, the logically false state is a logic level one. 
     Those skilled in the art will recognize that the boundaries between logic blocks are merely illustrative and that alternative embodiments may merge logic blocks or circuit elements or impose an alternate decomposition of functionality upon various logic blocks or circuit elements. Thus, it is to be understood that the architectures depicted herein are merely exemplary, and that in fact many other architectures may be implemented which achieve the same functionality. 
     Any arrangement of components to achieve the same functionality is effectively “associated” such that the desired functionality is achieved. Hence, any two components herein combined to achieve a particular functionality may be seen as “associated with” each other such that the desired functionality is achieved, irrespective of architectures or intermedial components. Likewise, any two components so associated can also be viewed as being “operably connected,” or “operably coupled,” to each other to achieve the desired functionality. 
     Furthermore, those skilled in the art will recognize that boundaries between the above described operations merely illustrative. The multiple operations may be combined into a single operation, a single operation may be distributed in additional operations and operations may be executed at least partially overlapping in time. Moreover, alternative embodiments may include multiple instances of a particular operation, and the order of operations may be altered in various other embodiments. 
     Also for example, in one embodiment, the illustrated examples may be implemented as circuitry located on a single integrated circuit or within a same device. Alternatively, the examples may be implemented as any number of separate integrated circuits or separate devices interconnected with each other in a suitable manner. 
     However, other modifications, variations and alternatives are also possible. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than in a restrictive sense. 
     In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other elements or steps then those listed in a claim. Furthermore, the terms “a” or “an,” as used herein, are defined as one or more than one. Also, the use of introductory phrases such as “at least one” and “one or more” in the claims should not be construed to imply that the introduction of another claim element by the indefinite articles “a” or “an” limits any particular claim containing such introduced claim element to inventions containing only one such element, even when the same claim includes the introductory phrases “one or more” or “at least one” and indefinite articles such as “a” or “an.” The same holds true for the use of definite articles. Unless stated otherwise, terms such as “first” and “second” are used to arbitrarily distinguish between the elements such terms describe. Thus, these terms are not necessarily intended to indicate temporal or other prioritization of such elements. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents will now occur to those of ordinary skill in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.