In-column detector for particle-optical column

Abstract

The invention relates to an in-column back-scattered electron detector, the detector placed in a combined electrostatic/magnetic objective lens for a SEM. The detector is formed as a charged particle sensitive surface, preferably a scintillator disk that acts as one of the electrode faces forming the electrostatic focusing field. The photons generated in the scintillator are detected by a photon detector, such as a photo-diode or a multi-pixel photon detector. The objective lens may be equipped with another electron detector for detecting secondary electrons that are kept closer to the axis. A light guide may be used to offer electrical insulation between the photon detector and the scintillator.

1 . A charged particle column comprising:
 a charged particle source for producing a beam of charged particles,   a sample carrier for holding and positioning a sample,   an objective lens for focusing the beam of charged particles on the sample, the objective lens having
 a first and a second electrode for generating a focusing electrostatic field, the first electrode positioned between the second electrode and the sample carrier, and 
 a first and a second pole piece for generating a focusing magnetic field, the first pole piece positioned between the second pole piece and the sample carrier, 
 the electrostatic field and the magnetic field showing overlap, 
   a detector at the source side of the first electrode for detecting charged particles, the detector showing a surface sensitive to charged particles,   the second electrode shows an electrode surface facing to the sample carrier, and   the sensitive surface forms at least part of said electrode surface.   
     
     
         2 . The charged particle column of  claim 1  in which at least part of the second electrode is positioned between the first and the second magnetic pole piece, and the first magnetic-pole piece coincides with the first electrode. 
     
     
         3 . The charged particle column of  claim 1  in which the sensitive surface is a scintillator, and the detector further comprises a photon detector. 
     
     
         4 . The charged particle column of  claim 3  in which the photon detector comprises a photo-diode, an avalanche photo-diode (APD), a Geiger mode APD, a multi-pixel photon detector, a CMOS device, a CCD device, or a PMT. 
     
     
         5 . The charged particle column of  claim 3  in which the detector comprises a light guide for guiding the photons produced by the scintillator to the photon detector. 
     
     
         6 . The charged particle column of  claim 1  in which the charged particle source is an electron source and the beam of charged particles is a beam of electrons. 
     
     
         7 . The charged particle column of  claim 1  in which the detector is equipped to operate with the face of the second electrode at a high potential with respect to the sample to attract charged particles emanating from the sample, and the photon detector operates at ground potential. 
     
     
         8 . The charged particle column of  claim 1  in which the column further comprises a further charged particle detector in a field free region inside the second electrode. 
     
     
         9 . A charged particle apparatus comprising a charged particle column according to  claim 1 . 
     
     
         10 . The charged particle apparatus of  claim 8  in which the charged particles impinging on the scintillator are at least in part electrons emitted by a conversion electrode, said electrons caused by positive or negative ions and/or electrons impinging on the conversion electrode. 
     
     
         11 . Method of detecting secondary and/or backscattered electrons emerging from a sample, the method comprising:
 Providing a sample on a sample position,   Providing a charged particle column producing a beam of charged particles, the column equipped with an objective lens focusing the beam of charged particles on the sample, the objective lens having a first electrode near the sample and a second electrode more removed from the sample for generating a focusing electrostatic field, the objective lens having a first pole piece near the sample and a second pole piece more removed from the sample for generating a magnetic focusing field, the electrostatic focusing field and the magnetic focusing field showing overlap,   Providing a charged particle detector at the side of the first electrode opposite to the sample,   accelerating secondary charged particles emanating from the sample to the charged particle detector, the charged particle detector showing a charged particle sensitive surface,   the second electrode shows an electrode surface facing the sample, and   the sensitive surface forms at least part of said electrode surface.   
     
     
         12 . The method of  claim 11  in which the sensitive surface is a scintillator and the method further comprises detecting the photons emitted by the scintillator as a result of charged particles impinging on the scintillator using a photon detector. 
     
     
         13 . The method of  claim 11  in which the secondary charged particles are electrons. 
     
     
         14 . The method of  claim 11  in which the beam of charged particles is a beam of electrons. 
     
     
         15 . The method of  claim 11  in which the method comprises detecting back-scattered electrons using a sensitive surface on the face of the second electrode and detecting secondary electrons with a detector mounted in a field free region inside the second electrode. 
     
     
         16 . The method of  claim 11  in which the column is part of an apparatus equipped with a conversion electrode and the method further comprises guiding at least part of the charged particle emanating from the sample to the conversion electrode, the conversion electrode in response to the charged particles impinging thereupon emitting electrons, the electrons guided to the sensitive surface or another detector sensitive to electrons. 
     
     
         17 . The method according to  claim 1  in which the method further comprises energizing a magnetic coil for generating a magnetic immersion field at the sample position. 
     
     
         18 . The charged particle column of  claim 4  in which the detector comprises a light guide for guiding the photons produced by the scintillator to the photon detector. 
     
     
         19 . The charged particle apparatus of  claim 9  in which the charged particles impinging on the scintillator are at least in part electrons emitted by a conversion electrode, said electrons caused by positive or negative ions and/or electrons impinging on the conversion electrode. 
     
     
         20 . A charged particle column comprising:
 a charged particle source for producing a beam of charged particles;   an objective lens for focusing the beam of charged particles on a sample, the objective lens having a first and a second electrode for generating a focusing electrostatic field, the second electrode having an electrode surface facing toward the sample; and   a detector for detecting charged particles, the detector having a surface sensitive to charged particles, the sensitive surface forming at least part of the second electrode surface.