Scanning electron microscope

Abstract

To make it possible to observe the bottom of a contact hole and internal wires, in observation of the contact hole 102, by scanning it at a predetermined acceleration voltage, the positive charge 106 is formed on the surface of the insulator 101, and the secondary electrons 104 are attracted in the hole by this electric field, and the hole is continuously scanned at an acceleration voltage different from the acceleration voltage, and the sample is observed. When the wires embedded in the insulator are to be observed, by observing the insulator at a predetermined acceleration voltage, an electron beam is allowed to enter the sample, and the sample is continuously scanned at an acceleration voltage different from the acceleration voltage, and hence the existence of wires is reflected as a change in the charge of the surface, and it is observed. In either case, the acceleration voltage before observation is different from the one during observation, and the sample surface is temporarily radiated at an acceleration voltage positively generating a positive or negative charge, and thereafter, the acceleration voltage is returned to a one suited to observation, and the sample is observed.

What is claimed is:  
     
         1 . A method of scanning a sample with a scanning electron microscope having an object lens for focusing an electron beam, and an acceleration cylinder for accelerating said electron beam when said electron beam passes through said object lens, said method comprising: 
 forming an electric field on a sample between said acceleration cylinder and said sample so as to promote said sample to be charged,    irradiating said electron beam on a surface of said sample which is promoted to be charged under conditions such that secondary electron generation efficiency of secondary electron generated from said sample by irradiating said electron beam on said sample becomes close to zero in comparison with conditions used when promoting said sample to be charged.    
     
     
         2 . A method of scanning a sample with a scanning electron microscope as defined in  claim 1 , wherein 
 a positive or negative voltage is added to said acceleration cylinder so as to promote said sample to be charged.    
     
     
         3 . A scanning electron microscope comprising: 
 an electron source for generating an electron beam,    an acceleration voltage supply for accelerating said electron beam generated from said electron source,    a scanning deflector for scanning said electron beam on a sample,    an object lens for focusing said electron beam, and    an acceleration cylinder for accelerating said electron beam when said electron beam passes through said object lens, said scanning electron microscope further comprising: 
 a controller for controlling said electron beam by 
 (a) adding a voltage on said acceleration cylinder to form an electric field, which promotes charging of said sample, between said acceleration cylinder and said sample, and  
 (b) irradiating said electron beam on a surface of said sample which is promoted to be charged under the conditions that secondary electron generation efficiency of secondary electrons generated from said sample by irradiating said electron beam on said sample becomes close to zero in comparison with conditions used when promoting said sample to be charged.