Charged particle beam device with dynamic focus and method of operating thereof

Abstract

A retarding field scanning electron microscope is described. The microscope includes a scanning deflection assembly configured for scanning an electron beam over a specimen, one or more controllers in communication with the scanning deflection assembly for controlling the electron beam scanning pattern, and a combined magnetic-electrostatic objective lens configured for focusing the electron beam including an electrostatic lens portion. The electrostatic lens portion includes a first electrode with a high potential bias, and a second electrode disposed between the first electrode and the specimen plane with a potential bias lower than the first electrode, wherein the second electrode is configured for providing a retarding field. The microscope further includes a voltage supply connected to the second electrode for biasing the second electrode and being in communication with the controllers, wherein the controllers synchronize a variation of the potential of the second electrode with the scanning pattern.

1 . A retarding field scanning electron microscope for imaging a specimen provided in a specimen plane, comprising:
 a scanning deflection assembly configured for scanning an electron beam over the specimen;   one or more controllers in communication with the scanning deflection assembly for controlling a scanning pattern of the electron beam;   a combined magnetic-electrostatic objective lens configured for focusing the electron beam, wherein the objective lens includes a magnetic lens portion and an electrostatic lens portion, the electrostatic lens portion comprises:
 a first electrode configured to be biased to a high potential; and 
 a second electrode disposed between the first electrode and the specimen plane, the second electrode being configured to be biased to a potential lower than the first electrode, wherein the second electrode is configured for providing a retarding field of the retarding field scanning electron microscope, wherein the second electrode comprises:
 a substrate; 
 a through hole extending through the substrate; and 
 an electrode surrounding the through hole, wherein the electrode is arranged on a surface of the substrate; 
 
   a voltage supply being connected to the second electrode for biasing the second electrode to a potential and being in communication with the one or more controllers, wherein the one or more controllers synchronize a variation of the potential of the second electrode with the scanning pattern of the electron beam.   
     
     
         2 . The microscope according to  claim 1 , wherein the scanning deflection assembly is configured for scanning with a pixel rate of 1 GHz or above. 
     
     
         3 . The microscope according to  claim 1 , wherein the scanning deflection assembly is configured for scanning with a pixel rate of 3 GHz to 50 GHz. 
     
     
         4 . The microscope according to  claim 1 , wherein the scanning deflection assembly is configured for a field of view of 50 μm or above. 
     
     
         5 . The microscope according to  claim 2 , wherein the scanning deflection assembly is configured for a field of view of 50 μm or above. 
     
     
         6 . The microscope according to  claim 1 , wherein the scanning deflection assembly is configured for a field of view of 50 μm to 500 μm. 
     
     
         7 . The microscope according to  claim 1 , wherein the first and the second electrode are configured to decelerate the electron beam in the retarding field to reduce the beam energy by a factor of 5 or more. 
     
     
         8 . The microscope according to  claim 1 , wherein the voltage supply for the second electrode is configured for varying the potential of the second electrode by at least ±0.1 V and/or by not more than ±50 V. 
     
     
         9 . The microscope according to  claim 8 , wherein the voltage supply for the second electrode is configured for varying with a variation frequency of 1 MHz or more. 
     
     
         10 . (canceled) 
     
     
         11 . The microscope according to  claim 1 , wherein the substrate is comprised of a material having a specific electrical resistivity in a range from about 10 6  Ωcm to about 10 12  Ωcm. 
     
     
         12 . The microscope according to  claim 1 , wherein the second electrode further comprises:
 an electrical connection for connecting the electrode with the voltage supply, the electrode comprising a lower specific electrical resistivity than the conductive substrate.   
     
     
         13 . The microscope according to  claim 1 , wherein the microscope is a multi-beam microscope for two or more electron beams, comprising:
 two or more emitter tips, each emitting one electron beam.   
     
     
         14 . The microscope according to  claim 13 , wherein the two or more beams are each scanned with a respective individual scanning assembly and the two or more beams are each decelerated with a respective individual second electrode being configured for providing a retarding field of the retarding field scanning electron microscope for the respective electron beam of the two or more beams, or
 wherein the two or more beams are scanned with the scanning assembly being a common scanning assembly for the two or more beams and the two or more beams are decelerated with the second electrode being a common second electrode for the two or more beams.   
     
     
         15 . A method of imaging a specimen, comprising:
 generating an electron beam in a retarding field scanning electron microscope;   scanning the electron beam over a specimen for image generation; and   focusing the electron beam on the specimen with a combined magnetic-electrostatic objective lens, wherein the objective lens includes a magnetic lens portion and an electrostatic lens portion, and wherein the electrostatic lens portion comprises:
 a first electrode; and 
 a second electrode disposed between the first electrode and the specimen, wherein the second electrode comprises:
 a substrate; 
 a through hole extending through the substrate; and 
 an electrode surrounding the through hole, wherein the electrode is arranged on a surface of the substrate; 
 
   biasing the second electrode to a varying potential; and   synchronizing the variation of the potential of the second electrode with the scanning of the electron beam.   
     
     
         16 . The method according to  claim 15 , wherein the scanning is conducted with a pixel rate of 1 GHz or above. 
     
     
         17 . The method according to  claim 15 , wherein the scanning is conducted over field of view of 50 μm or above. 
     
     
         18 . The method according to  claim 15 , wherein the electron beam is decelerated by the first and second electrode such that the beam energy is reduced by a factor of 5 or more. 
     
     
         19 . The method according to  claim 15 , wherein the potential of the second electrode is varied by at least ±0.1 V and/or by not more than ±50 V. 
     
     
         20 . The method according to  claim 19 , wherein the potential of the second electrode is varied with a variation frequency of 1 MHz or more.