Patent Publication Number: US-11662323-B2

Title: Method and system for inspecting an EUV mask

Description:
CLAIM OF PRIORITY 
     This application is a continuation of U.S. application Ser. No. 16/147,277 filed Sep. 28, 2018 which is a continuation of U.S. application Ser. No. 15/339,421 filed Oct. 31, 2016 (now U.S. Pat. No. 10,088,438 issued Oct. 2, 2018), which is a continuation of U.S. application Ser. No. 14/575,102 filed Dec. 18, 2014 (now U.S. Pat. No. 9,485,846 issued Nov. 1, 2016), which is a continuation-in-part of U.S. application Ser. No. 14/039,939 filed Sep. 27, 2013 (now U.S. Pat. No. 9,113,538 issued Aug. 18, 2015), which is a continuation of U.S. application Ser. No. 13/112,536 filed May 20, 2011, now U.S. Pat. No. 8,575,573 issued Nov. 5, 2013, the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a method for inspecting an EUV mask by using a charged particle beam, and more especially, to a method for inspecting the EUV mask with grounding means such that the EUV mask can be continuous scanned by electron beams. 
     2. Background of the Related Art 
     Optical inspection of a mask is based on a comparison of the light signals in the patterned regions relative to the non-patterned regions. A high contrast is necessary in order to achieve sufficient sensitivity for defect detection. The transmissive masks used in DUV (deep Ultra Violet) lithography can be inspected without difficulty since the contrast between the opaque regions and the clear regions is high at UV/DUV wavelengths. However, it is difficult to inspect the reflective masks, the EUV mask for example, used in EUV lithography since not only the contrast between the absorber region and the mirror region is low at UV/DUV wavelengths, but also wavelength of the UV/DUV is too lengthy to inspect EUV mask. 
     Now, a charged particle beam inspection system, an electron beam (E-beam) inspection tool, accordingly, is developed to inspect the EUV mask. However, accumulated charging on EUV mask will induce inspection issue while the EUV mask is inspected by the E-beam inspection tool. This issue will not happen to silicon wafer because silicon wafer can be grounded. Substrate of the EUV mask is dielectric, and cannot be grounded. 
     Furthermore, if the EUV mask on a moving stage is scanned continuously by the electron beam and charges are accumulated on the surface of the EUV mask without grounding, the contrast and intensity of the scanned images at different areas would not be consistent or equal during the inspection process. In other words, the electron beam scanning over different regions of the EUV mask would cause dwell times in order to make the images have better quality and consistent contrast and intensity during the inspection operation. The inspection speed and the throughput would be influenced greatly. 
     SUMMARY OF THE INVENTION 
     In order to solve the foregoing problems, one object of this invention is to provide a structure to discharge the EUV mask during inspection by an E-beam inspection tool, so that non accumulated charging is on the EUV mask during E-beam inspecting to enhance the inspection quality. 
     Accordingly, one embodiment of the present invention provides a structure for discharging EUV mask including: means for conducting charge on an EUV mask in inspecting the EUV mask by using a charged particle beam inspection system; and a grounding pin to contact the means. 
     Another embodiment of the present invention provides a structure for discharging EUV mask including: at least a conductive layer on one side of an EUV mask; and a grounding pin to contact the conductive layer, so that charge on a reflective surface of the EUV mask is grounded through the conductive layer to the grounding pin. 
     Another embodiment of the present invention provides a structure for discharging EUV mask including: a first conductive layer on one side of an EUV mask; a second conductive layer on a surface opposite to a reflective surface of the EUV mask; and a grounding pin to contact the second conductive layer, so that charge on the reflective surface of the EUV mask is grounded through the second conductive layer to the grounding pin. 
     Another embodiment of the present invention provides an electron beam inspection system inspecting an EUV mask including: an electron gun for providing electron beam; a lens for focusing the electron beam on the EUV mask; a detector for receiving signal electron emanating from the EUV mask; and means for discharging the EUV mask during the EUV mask is inspected. 
     Another embodiment of the present invention provides a method for inspecting an EUV mask by using a charged particle beam including: grounding the EUV mask; moving a stage, for supporting the EUV mask, continuously and scanning a surface of the EUV mask by using the charged particle beam simultaneously; and receiving signal electrons emanated from the surface of the EUV mask. 
     Another embodiment of the present invention provides a system for inspecting an EUV mask including: a source for providing an electron beam; an objective lens for focusing the electron beam on a surface of the EUV mask; a detector for receiving signal electrons emanated from the surface of the EUV mask; a stage for supporting the EUV mask; and means for grounding the EUV mask, wherein the surface of the EUV mask is scanned by the electron beam when the stage moves continuously, 
     Another embodiment of the present invention provides a method for inspecting an EUV mask by using a charged particle beam, which comprises steps of grounding the EUV mask, moving a stage continuously and scanning a reflective surface of the EUV mask by using the charged particle beam simultaneously, and receiving signal electrons emanated from the surface of the EUV mask, wherein the stage supports the EUV mask. 
     The charged particle beam can be an electron beam. A stage&#39;s moving direction is perpendicular to a scanning direction of the electron beam. The EUV mask can be inspected by a low voltage scanning electron microscope. The step of grounding the EUV mask can be performed by slightly contacting a grounding pin to the reflective surface of the EUV mask. 
     The step of grounding the EUV mask can be performed by contacting a grounding pin to a back surface of the EUV mask and electrically connecting to the reflective surface of the EUV mask. The grounding pin can contact the back surface of the EUV mask slightly. 
     The step of grounding the EUV mask can be performed by slightly contacting a grounding pin to a conductive layer on one side wall of the EUV mask. A trench can be formed in the side wall of the EUV mask. The conductive layer can be coated within the trench. 
     Another embodiment of the present invention provides a system for inspecting an EUV mask, which comprises a source for providing an electron beam, an objective lens for focusing the electron beam on a reflective surface of the EUV mask, a detector for receiving signal electrons emanated from the surface of the EUV mask, a stage for supporting the EUV mask, and means for grounding the EUV mask, wherein the surface of the EUV mask is scanned by the electron beam when the stage moves continuously. 
     A stage&#39;s moving direction is perpendicular to a scanning direction of the electron beam. The system can be a low voltage scanning electron microscope. The means for grounding the EUV mask can include a grounding pin slightly contacting the reflective surface of the EUV mask. 
     The means for grounding the EUV mask can include a grounding pin contacting a back surface of the EUV mask, and a conductive layer can be on the back surface of the EUV mask and electrically connecting to the reflective surface of the EUV mask. The grounding pin can contact the back surface of the EUV mask slightly. 
     The means for grounding the EUV mask can include a grounding pin contacting a conductive layer on one side wall of the EUV mask. A trench can be formed in the side wall of the EUV mask. The conductive layer can be coated within the trench. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    illustrates a cross-sectional view of a configuration of an EUV mask; 
         FIG.  2    illustrates a vertical view of a configuration of an EUV mask; 
         FIG.  3   a    and  FIG.  3   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the first embodiment of the present invention; 
         FIG.  4    illustrates a diagram about a configuration of the EUV mask and the slider; 
         FIG.  5    illustrates a diagram about a configuration of the EUV mask and the electron gun; 
         FIG.  6   a    and  FIG.  6   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the second embodiment of the present invention; 
         FIG.  7   a    and  FIG.  7   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the third embodiment of the present invention; 
         FIG.  8    illustrates a first embodiment of the grounding pin controlling structure; 
         FIG.  9   a   ,  FIG.  9   b    and  FIG.  9   c    illustrates a second embodiment of the grounding pin controlling structure; 
         FIG.  10   a   ,  FIG.  10   b    and  FIG.  10   c    illustrates a third embodiment of the grounding pin controlling structure; 
         FIG.  11    illustrates a cross-sectional view of a configuration of another EUV mask; 
         FIG.  12   a    and  FIG.  12   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the fourth embodiment of the present invention; 
         FIG.  13   a    and  FIG.  13   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the fifth embodiment of the present invention; 
         FIG.  14    illustrates the diagrams about the working status of the EUV mask and the grounding pin in accordance with the sixth embodiment of the present invention; 
         FIG.  15   a    and  FIG.  15   b    respectively illustrates a cross-sectional view and a vertical view of a configuration of another EUV mask; 
         FIG.  16    illustrates a diagram of a conductive holder clamping the EUV mask in accordance with another embodiment of the present invention; 
         FIG.  17    illustrates a vertical view of a configuration of another EUV mask; and 
         FIG.  18    illustrates a vertical view of a configuration of another EUV mask. 
         FIG.  19    is a flow chart illustrating a method for inspecting an EUV mask by using a charged particle beam in accordance with one embodiment of the present invention. 
         FIG.  20    shows an embodiment of a low voltage scanning electron microscope; and 
         FIG.  21    shows a schematic diagram of a structure for an electron beam inspection system processing continuous scanning on an EUV mask in accordance with one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG.  1    illustrates a cross-sectional view of a configuration of an EUV mask. The EUV mask  10  includes a substrate  12 , an EUV absorption layer  14  on the substrate  12  and a patterned reflective surface  16  formed on the absorption layer  14 . Referring to  FIG.  2    simultaneously, the patterned reflective surface  16  has a peripheral area  161  without any pattern and a middle area  162  with a plurality of pattern openings  163  thereon. Here, the patterned reflective surface of the EUV mask may be holes, circuits, devices, or any combination thereof. In one embodiment, the reflective layer, made of the same or different metals, is formed on a substrate of the EUV mask, and portion of the plurality of patterns may distribute on the reflective layer. A structure for discharging EUV mask includes: means for conducting charge on the EUV mask  10  in inspecting the EUV mask  10  by using a charged particle beam inspection system; and a grounding pin (shown in following diagrams) to contact the means. In one embodiment, the grounding pin is used to contact a portion of the peripheral area  161  of the patterned reflective surface  16 , which is made of electrical conductive materials, or electrical semiconductive materials, and thereby grounds charges on the reflective surface  16  of the EUV mask  10 . 
       FIG.  3   a    and  FIG.  3   b    illustrate the diagrams about the working of the EUV mask and the grounding pin in accordance with the first embodiment of the present invention. In the first embodiment, the structure  20  for discharging EUV mask further includes a slider  22 , a spring  24  and an arm structure  26 . The slider  22  has a top surface  28  divided into a flat area  281  and a downward-tilted area  282 . One end of the spring  24  connects to a back side  221  of the slider  22  and the other end of the spring  24  is fixed. The arm structure  26  is above the slider  22  and the arm structure  26  includes a body  261 , the grounding pin  262  on a front end of the body  261  and a prop  263  connecting to the body  261 . As shown in  FIG.  3   a   , when the EUV mask  10  is under the ungrounded status, the prop  263  of the arm structure  26  contact the flat area  281  of the slider  22  and the grounding pin  262  is far away from the EUV mask  10 . When the EUV mask  10  moves toward a front side  222  of the slider  22  to contact and push the slider  22  back, as shown in  FIG.  3   b   , the prop  263  moves along the top surface  28  of the slider  22  and then contacts the downward-tilted area  282 , and therefore the body  261  of the arm structure  26  tilts and the grounding pin  262  contacts the reflective surface  16  of the EUV mask  10 . 
     As shown in  FIG.  4   , the slider  22  has a gap  30  on the front side  222  of the slider  22  for holding one corner of the EUV mask  10 , so that the slider  22  may fix the EUV mask  10 , as the EUV mask  10  contacts with the slider  22  during the EUV mask  10  is grounded by the grounding pin  262  (shown in  FIG.  3   a   ,  FIG.  3   b   ) and inspected by charged particle beam inspection system, in which the electron gun  32  for providing electron beam is above the EUV mask  10 , as shown in  FIG.  5   . 
       FIG.  6   a    and  FIG.  6   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the second embodiment of the present invention. In the second embodiment, as shown in  FIG.  6   a    and  FIG.  6   b   , the structure  40  for discharging EUV mask further includes a gripper unit  42 , an arm structure  44 , a reciprocating member  46  and two resilient members  48 ,  48 ′. 
     The gripper unit  42  includes a head portion  421 , a base portion  422  and a first rolling member  423  set at a bottom end of the base portion  421 . The gripper unit  42  is used for fixing the EUV mask  10  in place, for example but not limited to, being held tight or to be released, through rotation of the gripper unit  42  about a first pivot  424  substantially parallel with a first center axis of the first rolling member  423 . 
     The arm structure  44  is configured near or opposite the gripper unit  42 . The arm structure  44  includes a body  441 , the grounding pin  50  on a top end of the body  441  and a second rolling member  442  set at a bottom end of the body  441 . The grounding pin  50  may reciprocate in contact the EUV mask  10  and leave the EUV mask  10  through rotation of the body  441  about a second pivot  443  substantially parallel with a second center axis of the second rolling member  442 . 
     The two resilient members are one first resilient member  48  and one second resilient member  48 ′ each with one end being fixed, and respectively with the other ends being connected to head portion  422  of the gripper unit  42  and to the body  441  of the arm structure  44  for respectively providing a first force to the gripper unit  42  toward a first direction  52  and a second force to the body  441  of the arm structure  44  toward a second direction  54 . 
     The reciprocating member  46  is configured for causing the first rolling member  423  and the second rolling member  442  to rotate. The reciprocating member  46  includes a fix end  461  and a mobile end  462  pivoting the fixed end  461 . The first rolling member  423  and the second rolling member  442  may be in contact with reciprocating member  46  and roll freely on the surface of the reciprocating member  46 . Here, the reciprocating member  46  is tilted by pushing up and pulling down the mobile end  462  of the reciprocating member  46  pivoting the fixed end  461  of the reciprocating member  46 , which results in the first rolling member  423  and the second rolling member  442  rolling on the reciprocating member  46 . 
     As shown in  FIG.  6   a   , when the reciprocating member  46  works to make the first rolling member  423  to move substantially along the first direction  52  and the second rolling member  442  move substantially along the second direction  54 , the head portion  422  of the gripper unit  42  moves toward the opposite direction of the first direction  52  and the grounding pin  50  moves toward the opposite direction of the second direction  54  so that the head portion  422  and the grounding pin  50  are led away from the EUV mask  10 . As shown in  FIG.  6   b   , when the reciprocating member  46  works to leave the first rolling member  423  and the second rolling member  442 , the head portion  422  of the gripper unit  42  moves toward the first direction  52  by means of the first force of the first resilient member  48  and an upper portion of the arm structure  44  moves toward the second direction  54  by means of the second force of the second resilient member  48 ′, so that the head portion  422  is therefore led toward the edge of the EUV mask  10  and in the end to abut against the EUV mask  10 , and the grounding pin  50  contacts the reflective surface  16  of the EUV mask  10 . Here, the head portion  422  of the gripper unit  42  is used to push tighter against the EUV mask  10  to hold it fixed in position during the EUV mask  10  is grounded by the grounding pin  50  and inspected by the charged particle beam inspection system. 
       FIG.  7   a    and  FIG.  7   b    illustrate the diagrams about the working status of the EUV mask and the grounding pin in accordance with the third embodiment of the present invention. In the third embodiment, the structure for discharging EUV mask further includes the foregoing gripper unit  42 , the foregoing first resilient member  48 , the foregoing reciprocating member  46  and a grounding pin controlling structure  60 . Here, the structures, the connection relations and the operation of the gripper unit  42 , the first resilient member  48  and the reciprocating member  46  are described in the second embodiment as shown in  FIG.  6   a    and  FIG.  6   b   , wherein the head portion  422  of the gripper unit  42  is used to push tighter against the EUV mask  10  to hold it fixed in position during the EUV mask  10  is grounded by the grounding pin  50 . The grounding pin controlling structure  60  includes a hollow cylinder  62  and a column  64  passing through the hollow cylinder  62 . A grounding pin  50  is arranged on a top surface of the column  64  and the position of the grounding pin  50  is changed by moving the column  64 . As shown in  FIG.  7   a   , when the gripper unit  42  pushes tighter against the EUV mask  10 , the column  64  moves down and the grounding pin  50  contacts the reflective surface  16  of the EUV mask  10 . As shown in  FIG.  7   b   , when the gripper unit  42  releases the EUV mask  10 , the column  62  moves up and the grounding pin  50  is far away from the EUV mask  10 . 
     In first embodiment of the grounding pin controlling structure, the grounding pin controlling structure  60  includes a hollow cylinder  62  and a column  64  passing through the hollow cylinder  62 , wherein the column  64  has an interior room  641 , as shown in  FIG.  8   . A first rod  66  with the spiral shells  661  on the outer surface and a second rod  68  with the sawtooth  681  on the outer surface are configured in the interior room  641 , wherein the spiral shells  661  and the sawtooth  681  are engaged with each other. A first pushing shaft  70  is connected to the bottom of the column  64  and a second pushing shaft  72  is connected to the bottom of the second rod  68  and passes through the bottom of the column  64 . One end of a connection rod  74  is connected to the top of the first rod  66 , and another end of the connection rod  74  is connected with a grounding pin  50 . During the inspection of the EUV mask  10 , the column  64  moves down in relative to the hollow cylinder  62  (shown in  FIG.  7   a   ), so that the grounding pin  50  contacts the reflective surface  16  of the EUV mask  10  (shown in  FIG.  7   a   ). After the inspection of the EUV mask  10 , the column  64  moves up continuously in relative to the hollow cylinder  62  (shown in  FIG.  7   b   ) so that the grounding pin  50  rise, wherein the second rod  72  also moves up to drive the first rod  66  to rotate with the sawtooth  681  engaging with the spiral shells  661 , so that the grounding pin  50  may rise and deflect, simultaneously to be far away from the EUV mask. 
     In second embodiment of the grounding pin controlling structure, as shown in  FIG.  9   a   , the grounding pin controlling structure  60  includes a hollow cylinder  62  and a column  64  passing through the hollow cylinder  62 . As shown in  FIG.  9   b   , the hollow cylinder  62  has two opposite trenches  80  formed on an inner surface  621  of a side wall  622  of the hollow cylinder  62 , wherein each trench  80  has a lengthwise ditch  801  and an upward-tilted ditch  802  connecting to a top end of the lengthwise ditch  801 . Correspondingly, as shown in  FIG.  9   c   , the column  64  has two opposite protrusions  82  on an outer surface of the column  64  and the protrusions  82  are respectively arranged within the opposite trenches  80 , as shown in  FIG.  9   a    to move along the lengthwise ditch  801  and the upward-tilted ditch  802 . During the inspection of the EUV mask, the column  64  moves down in relative to the hollow cylinder  62  (shown in  FIG.  7   a   ), so that the grounding pin  50  contacts the reflective surface  16  of the EUV mask  10  (shown in  FIG.  7   a   ). After the inspection of the EUV mask  10 , the column  64  moves up continuously in relative to the hollow cylinder  62 , wherein the column  64  moves up straightly and then deflects as protrusions  82  moves along the lengthwise ditch  801  and then the upward-tilted ditch  802 , so that the grounding pin  50  is far away from the EUV mask  10 . 
     In third embodiment of the grounding pin controlling structure, as shown in  FIG.  10   a   , the grounding pin controlling structure  60  includes a hollow cylinder  62  and a column  64  passing through the hollow cylinder  62 . As shown in  FIG.  10   b   , the hollow cylinder  62  has two opposite trenches  84  passing through a side wall  622  of the hollow cylinder  62 , wherein each trench  84  has a lengthwise ditch  841  passing through the side wall  622  and a upward-tilted ditch  842  passing through the side wall  622  and connecting to a top end of the lengthwise ditch  841 . Correspondingly, as shown in  FIG.  10   c   , the column  64  has two opposite branch structures  86  including at least two horizontal rods  861  respectively, and the branch structures  86  are respectively arranged within the opposite trenches  84 , as shown in  FIG.  10   a   , to move along the lengthwise ditch  841  and the upward-tilted ditch  842 . During the inspection of the EUV mask, the column  64  moves down in relative to the hollow cylinder  62  (shown in  FIG.  7   a   ), so that the grounding pin  50  contacts the reflective surface  16  of the EUV mask  10  (shown in  FIG.  7   a   ). After the inspection of the EUV mask  10 , the column  64  moves up continuously in relative to the hollow cylinder  62 , wherein the column  64  moves up straightly and then deflects as the branch structures  86  moves along the lengthwise ditch  841  and the upward-tilted ditch  842 , so that the grounding pin  50  is far away the EUV mask  10 . 
     In the foregoing embodiments, the grounding pin  50  is used to contact the reflective surface  16  which is formed on the top surface of the EUV mask  10 . Nevertheless, the position that the grounding pin contacts with may be changed. As shown in  FIG.  11   , a first conductive layer  90  and a second conductive layer  92  may respectively be coated on the side of the EUV mask  10  and coated on the bottom surface, which is opposed to the reflective layer  16 , of the EUV mask  10 . The reflective surface  16 , the first conductive layer  90  and the second conductive layer  92  are electrically connected, so that the foregoing grounding pin  50  may be used to contact the second conductive layer  92 , so that charge on the reflective surface  16  of the EUV  10  mask is grounded through the first conductive layer  90  and the second conductive layer  92  to the grounding pin  50 . The coated first conductive layer  90  and the second conductive layer  92  may be Al, Cr, Ti, alloy thereof, or non-metal such as carbon. The thickness of the first conductive layer  90  and the second conductive layer  92  may be 0.001 um to 1 mm. 
     Continuing the above description, the drive mechanism of the gripper unit described in the second embodiment of the present invention may be applied to the EUV mask with the first conductive layer and the second conductive layer. As shown in  FIG.  12   a   , when the reciprocating member  46  works to make the third rolling member  94  to move substantially along the third direction  98  and the fourth rolling member  96  move substantially along the fourth direction  100 , the head portion  422  of the gripper unit  42  moves toward the opposite direction of the third direction  98  and the grounding pin  50  moves toward the opposite direction of the fourth direction  100  so that the head portion  422  and the grounding pin  50  are led away from the EUV mask  10 . As shown in  FIG.  12   b   , when the reciprocating member  46  works to leave from the third rolling member  94  and the fourth rolling member  96 , the head portion  422  of the gripper unit  42  moves toward the third direction  98  by means of the third force of the third resilient member  102  and an upper portion of the arm structure  44  moves toward the fourth direction  100  by means of the fourth force of the fourth resilient member  102 ′ so that the head portion  422  is therefore led toward the edge of the EUV mask  10  and in the end to abut against the EUV mask  10 , and the grounding pin  50  contacts the second conductive layer  92  of the EUV mask  10  to discharge the charge on the reflective surface  16  of the EUV mask  10 . 
     On the other hand, the grounding pin controlling structure  60  described in third embodiment of the present invention may also be applied to the EUV mask  10  with the first conductive layer  90  and the second conductive layer  92  thereon. As shown in  FIG.  13   a   , during the inspection of the EUV mask  10 , the column  64  moves up and the grounding pin  50  contacts the second conductive layer  92  of the EUV mask  10 . After the inspection of the EUV mask  10 , as shown in  FIG.  13   b   , the column  64  moves down and the grounding pin  50  is far away from the EUV mask  10 . The embodiments of the grounding pin controlling structure  60  are described above, and unnecessary details would not be given here. 
     Furthermore, as shown in  FIG.  14   , the grounding pin may be a spring  110  with a trigger  112  on the top end of the spring  110 , and the bottom end of the spring  110  is grounded. When the EUV mask  10  moves to be inspected, the second conductive layer  92  of the EUV mask  10  may contact with the trigger  112  by the weight of the EUV mask  10  to discharge the charge on the reflective surface  16  of the EUV mask  10 . 
     In another embodiment, the grounding pin is used to contact at least one conductive layer on one side of the EUV mask. As shown in  FIG.  15   a    and  FIG.  15   b   , a conductive layer  93  is formed on one corner of the EUV mask  10 , the two adjacent side walls  105 ,  105 ′, accordingly, and the conductive layer  93  is electrically connected to the reflective surface  16  of the EUV mask  10 . The structure for discharging EUV mask includes a conductive holder  130  with the grounding pin  50 , as shown in  FIG.  16   , to clamp the corner of the EUV mask  10 , so that the grounding pin  50  may contact with the conductive layer  93 . Refer to  FIG.  16   , two grounding pins  50  are respectively formed on a pair of opposite clamp sections  131  of the conductive holder  130 , so that the two grounding pins  50  may contact the conductive layer  13  at two adjacent side walls  105 ,  105 ′ of the EUV mask  10 . 
     Further, as shown in  FIG.  17   , two trenches  132  or notches are respectively formed on two adjacent side walls  105 ,  105 ′ of the EUV mask  10 , and a conductive layer  93  formed on the trenches  132  or the notches is electrically connected to the reflective surface  16  of the EUV mask  10 . Here, the profile of the trenches  132  or notches may correspond to the grounding pins  50  arranged on the conductive holder  130  as shown in  FIG.  16   , so that the grounding pin  50  may closely contact the conductive layer  93 . 
     Furthermore, as shown in  FIG.  18   , the foregoing conductive layer  93  may be 3 the whole side wall, including the trenches  132  or the notches walls, of the EUV mask  10 , so that the grounding pin  50  may contact with the conductive layer  93  conveniently. The coated conductive layer  93  may be Al, Cr, Ti, alloy thereof, or non-metal such as carbon. The thickness of the conductive layer  93  may be 0.001 um to 1 mm. 
       FIG.  19    is a flow chart illustrating a method for inspecting an EUV mask by using a charged particle beam according to an embodiment of the present invention. In step of S 110 , a grounding pin slightly contacts to the EUV mask while the EUV mask is positioned. Here, the grounding pin can contact the reflective surface, backside surface, or sidewall surface of the EUV mask to achieve a discharging effect. In step of S 120 , a stage, for supporting the EUV mask, is moved continuously, and the reflective surface of the EUV mask is scanned by using a charged particle beam simultaneously. Furthermore, the moving direction of the stage is perpendicular to the scanning direction of the charged particle beam. The charged particle beam, in one embodiment, is electron beam. In step of S 130 , signal electrons emanated from the reflective surface of the EUV mask can be received by a detector to form an imaging. Here, the signal electrons can be secondary electrons or backscattered electrons. 
       FIG.  20    shows a low voltage scanning electron microscope (LVSEM) used to inspect a EUV mask. In this figure, an objective lens can be a SORIL optical system. 
     In this embodiment of the scanning electron microscope  300 , the electron beam  304  emitted from a cathode  302  is accelerated by an anode  306  voltage, passes through a gun aperture  308 , a condenser lens  310 , a beam limit aperture  312  and a SORIL system  316 , and then impinges onto a specimen surface  326  supported by a stage  328 . 
     When a fixed negative potential Vc and a potential Va, which is enough higher than Vc, are respectively applied to the field emission cathode  302  and the anode  306 , the electron beam  304  is emanated from the cathode  302  along optical axis. The emanated electrons are firstly accelerated in the space between the cathode  302  and anode  306 , and then decelerated (accelerated or remain even speed in some cases) the space between the anode  306  and a terminal electrode at ground potential. 
     Because the gun aperture  308  is closer to the electron source, the electron beam  304  with larger polar angles can be cut off by the gun aperture  306 , and trimmed down to a specific current value. It can also be earlier to prevent from the Coulomb interaction of the electron beam. Then the electron beam  304  passes the condenser lens  310  and the beam limit aperture  312 . The condenser lens  310  can weakly condense the electron beam  304 . The beam limit aperture  312  can determine the amount of the electron beam  304  to a desired beam current on the specimen  326 , and allow entering the objective lens system  316  with a fixed energy, a fixed brightness and a fixed beam current. 
     The SORIL system  316  includes an objective lens  318 , deflectors  320  and  322  which are located inside the objective lens  318 , and a control electrode  324 . The objective lens  318  can be an immersion electrostatic objective lens, an immersion magnetic objective lens, or an electromagnetic compound objective lens. In the embodiment, the immersion magnetic objective lens  318  is more preferred. The immersion magnetic objective lens  318  can focus the electron beam  304  into a small spot which is used to scan the studied specimen  326 . Because focusing the electron beam  304  is mainly accomplished by the magnetic objective lens  318 , the aberrations of the beam spot mostly come from the spherical aberration and the chromatic aberration of the magnetic objective lens  318 . The purpose of the immersion magnetic objective lens  318  is to generate a magnetic field with a large component perpendicular to the Z-axis for converging lens action above the specimen  326  and to have the magnetic field substantially parallel to the Z-axis at the specimen  326 . Accordingly, the specimen  326  can be immersed in the magnetic field of the lens. 
     The deflection units  320  and  322  in the SORIL system  316  can be equipped with electrostatic multi-pole deflectors or magnetic multi-pole deflectors. The embodiment is more preferred the electrostatic multi-pole deflectors because the magnetic multi-pole deflectors would produce magnetic hysteresis phenomenon on deflecting the electron beam  304  during operation. Therefore, it would affect the scanning speed. The electron beam  304  can be deflected by the deflection units  320  and  322  which can generate a small deflection field, or can work together with the control electrode  324  to increase the size of the deflection field, so that the specimen  326  can be scanned by the focused beam. Furthermore, the deflection units are designed to minimize the introduction of aberrations into the beam when deflecting the electron beam. In accordance with the embodiment, the deflection units  320  and  322  are dedicated to produce a more rapid scanning movement of the electron beam  304  to cover a suspected region, and it can enhance the throughput of the imaging. 
     The control electrode  324  is made of electrical conduction material. The control electrode  324  is shaped and positioned to be an extension of outer polepiece of the magnetic objective lens  318  towards optical axis. The control electrode  324 , on one hand, is set to a voltage Vce to control the electrical field on the specimen surface  326  lower than the predetermined value, which ensures on micro-arcing on the specimen surface  326 . On the other hand, the voltage Vce of the control electrode  324  can be dynamically adjusted to compensate the image defocus due to electric drifting. 
     Since an imaging with better quality can be obtained through the electron beam  304  impinging on the specimen surface  326 , the system needs to make every component&#39;s applied voltage and excitation current synchronize. Any electric drifting on these components will cause the spot size of the electron beam  304  varied and defocus of the image. The control electrode  324  can be dynamically performing micro-focusing while the image is defocused. The control electrode  324  can increase the magnetic field strength of the SORIL system  316  under a same excitation. Placing the control electrode  324  in the retarding field gives the control electrode  324  a great deal of influence over the trajectory of the electron beam  304  because the electron beam  304  has been reduced to a lower landing energy than the deflection units  320  and  322 , and it is nearest the landing point of the electron beam on the specimen  326 . Furthermore, because of its proximity to the specimen  326 , it can help to accurately position the electron beam  304  over a selected area of the specimen  326  prior to the rapid scan of the area, and improve the size of the deflection field over the specimen  326 . 
     The SORIL system  316  adopted in the embodiment is preferred because it can reduce the off-axis chromatic and spherical aberrations greatly in scanning imaging, and is better at extending its magnetic field below the lens aperture and through the specimen  326  to increase the field of view. 
     To reveal a stereo imaging of the specimen surface  326  with better imagine quality, the embodiment of the present invention can adopt the multi-channel detector  314  to collect the signal electrons during the scanning operation. The signal electrons, including the secondary electrons or the backscattered electrons, emanated from the different sides or features of the specimen surface  326  can be collected by different channels. Therefore, the signal electrons from the different emanated directions can generate a stereo image in combination, and finally ensure a topography analysis of the defects of interest regions. 
     The specimen  326  on the specimen stage  328  is charged with a negative voltage to create a retarding field Er; that is, a field in the opposite direction to the accelerating field Ea to reduce the energy of the electron beam prior to impact with the specimen  326 , and avoid great damage of the specimen surface. Furthermore, the retarding field can make the electron beam  304  land on the specimen surface with a lower landing energy. 
       FIG.  21    shows a schematic diagram of a structure  500  for an electron beam inspection system processing continuous scanning on a EUV mask. The electron beam inspection system adopts the LVSEM disclosed in the  FIG.  20   , and is expressed in a simplified manner. 
     A stage  522  on the inspecting system is used for supporting the EUV mask  520 . The reflective surface of the EUV mask  520  is continuously scanned by using the electron beam  504  when the stage  522  moves continuously at the same time. The stage  522  can move along the direction  526  and the surface of EUV mask  520  can be scanned by the electron beam  504  under the control of the first deflector  514  and the second deflector  516 . The moving direction of the stage is perpendicular to the scanning direction of the electron beam. When the EUV mask  520  is inspected by using the electron beam  504 , it should be grounded simultaneously. 
     And the signal electrons emanated from the surface of the EUV mask  520  would be received by a detector  512 . 
     No matter the grounding pin is contacted with the reflective surface, the bottom conductive layer or the side conductive layer, the present invention provides a structure to discharge the EUV mask during inspection by an E-beam inspection tool, so that non accumulated charging is on the EUV mask during E-beam inspecting to enhance the inspection quality. 
     In the present invention, when applying the foregoing structure to discharge the EUV mask to an electron beam inspection system, the electron beam inspection system for inspecting an EUV mask includes: an electron gun for providing electron beam; a lens for focusing the electron beam on the EUV mask; a detector for receiving signal electrons emanating from the EUV mask; and means for discharging the EUV mask during the EUV mask is inspected; the reflective surface of the EUV mask on a continuous moving stage is scanned by using the electron beam simultaneously under the control of the first deflector and second deflector; the movement direction of the stage is perpendicular to the scanning direction of the electron beam. The inspection quality of the EUV mask is enhanced by using the electron beam inspection system because the accumulated charging on the EUV mask is grounded. 
     Although the present invention has been explained in relation to its preferred embodiment, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.