Apparatus for improving the signal information in the electron beam examination of sample topography

Claim 2

In an apparatus for analyzing the topography of a sample by utilizing secondary electron emission by said sample, said apparatus being of the known type that has (a) means for generating a primary electron beam, (b) means directing said primary electron beam onto a surface of said sample to bombard the same with primary electrons causing the emission of secondary electrons in a number of characterizing the intensity of said primary electron beam and the topography of the location bombarded and (c) means for deflecting said primary electron beam to scan said sample surface, the improvement comprising, A. electric field generating means for generating at said sample surface an electric field oriented for drawing and leading away from said sample surface at least a substantial portion of said secondary electrons, B. electric circuit means connected to said sample, said electric circuit means constituting conductor means for said sample current generated by said primary electron beam, the momentary intensity of said sample current being a function of the momentary magnitude of said secondary electron emission by said sample, C. function generator means controlling said electric field generating means for periodically decreasing the magnitude of said secondary electron emission to give said sample current an A.C. component being alternatingly affected and unaffected by said secondary electron emission with a periodicity determined by the frequency of said function generator means, D. separating means receiving said A.C. component, said separating means generating a signal containing information only of those portions of said A.C. component that are affected by said secondary electron emission, said signal characterizing the sample topography scanned, E. evaluating means receiving said signal from said separating means and F. means for correlating said evaluating means to the scanning motion of said primary electron beam.

Claim 3

An improvement as defined in claim 1, including means for reversing the polarity of said signal prior to applying it to said evaluating means.

Claim 4

An improvement as defined in claim 1, wherein said apparatus includes electrically conductive apparatus components in the immediate vicinity of said sample, said electric field generating means including means for applying a potential to at least one of said electrically conductive apparatus components; said potential is positive with respect to said sample and is without appreciable effect on said primary electron beam.

Claim 5

An improvement as defined in claim 1, wherein said electric field generating means includes A. a voltage source, B. a first electrode connected to one pole of said voltage source and C. a second electrode connected to the other pole of said voltage source; the electric field generated between said electrodes has a force component urging any electron on the sample surface away from said sample.

Claim 6

An improvement as defined in claim 4, wherein said second electrode has the configuration of a knife edge and is movable in a plane normal to the direction of said primary electron beam.

Claim 7

An improvement as defined in claim 4, wherein said second electrode is formed of an electrically conductive plate disposed in a plane transverse to the direction of said primary electron beam, said plate is provided with an opening of a dimension as to allow passage of said primary electron beam without being affected by the potential applied to said plate.

Claim 8

An improvement as defined in claim 4, wherein said second electrode has a pointed configuration.

Claim 9

An improvement as defined in claim 4, including means to displace said second electrode.

Claim 10

An improvement as defined in claim 4, including A. an additional voltage source and B. a third electrode disposed in the space in front of said sample surface when viewed in the direction of said primary electron beam and connected to said additional voltage source; the potential on said third electrode being variable independently from the potential of said second electrode.

Claim 11

An improvement as defined in claim 9, including means to move said third electrode with respect to the location of impingement of said primary electron beam on said sample.

Claim 12

An improvement as defined in claim 1, said separating means including a phase-responsive rectifier with preamplifier receiving said A.C. component.

Claim 13

An improvement as defined in claim 1, including means to move said sample with respect to the direction of said primary electron beam.

Claim 14

In an apparatus for analyzing the topography of a sample by utilizing secondary electron emission by said sample, said apparatus being of the known type that has (a) means for generating a primary electron beam, (b) means directing said primary electron beam onto a surface of said sample to bombard the same with primary electrons causing the emission of secondary electrons in a number characterizing the intensity of said primary electron beam and the topography of the location bombarded and (c) means for deflecting said primary electron beam to scan said sample surface, the improvement comprising, A. electric field generating means for generating at said sample surface an electric field oriented for drawing and leading away from said sample surface at least a substantial portion of said secondary electrons, B. magnetic field generating means for generating at said sample surface a magnetic field oriented for aiding said electric field in drawing and leading away from said sample surface at least a substantial portion of said secondary electrons, C. electric circuit means connected to said sample, said electric circuit means constituting conductor means for said sample current generated by said primary electron beam, the momentary intensity of said sample current being a function of the momentary magnitude of said secondary electron emission by said sample, D. function generator means controlling one of said field generating means for periodically decreasing the magnitude of said secondary electron emission to give said samplE current an A.C. component being alternatingly affected and unaffected by said secondary electron emission with a periodicity determined by the frequency of said function generator means, E. separating means receiving said A.C. component, said separating means generating a signal containing information only of those portions of said A.C. component that are affected by said secondary electron emission, said signal characterizing the sample topography scanned, F. evaluating means receiving said signal from said separating means and G. means for correlating said evaluating means to the scanning motion of said primary electron beam.

Claim 15

In an apparatus for analyzing the topography of a sample by utilizing secondary electron emission by said sample, said apparatus being of the known type that has (a) means for generating a primary electron beam, (b) means directing said primary electron beam onto a surface of said sample to bombard the same with primary electrons causing the emission of secondary electrons in a number characterizing the intensity of said primary electron beam and the topography of the location bombarded and (c) means for deflecting said primary electron beam to scan said sample surface, the improvement comprising, A. electric field generating means for generating at said sample surface an electric field oriented for drawing and leading away from said sample surface at least a substantial portion of said secondary electrons, B. magnetic field generating means for generating at said sample surface a magnetic field oriented for aiding said electric field in drawing and leading away from said sample surface at least a substantial portion of said secondary electrons, C. electric circuit means connected to said sample, said electric circuit means constituting conductor means for said sample current generated by said primary electron beam, the momentary intensity of said sample current being a function of the momentary magnitude of said secondary electron emission by said sample, D. function generator means controlling one of said field generating means for periodically decreasing the magnitude of said secondary electron emission to give said samplE current an A.C. component being alternatingly affected and unaffected by said secondary electron emission with a periodicity determined by the frequency of said function generator means, E. separating means receiving said A.C. component, said separating means generating a signal containing information only of those portions of said A.C. component that are affected by said secondary electron emission, said signal characterizing the sample topography scanned, F. evaluating means receiving said signal from said separating means and G. means for correlating said evaluating means to the scanning motion of said primary electron beam.