Patent ID: 7394066

Claim:
An electron microscope, comprising: an illuminating lens system that illuminates an electron beam that is emitted from an electron source onto a specimen as a planar illuminating electron beam having a two-dimensional spread; an imaging lens system that projects and magnifies the reflecting electron beam emitted from the specimen to project and form a specimen image; a beam separator that separates the illuminating electron beam from reflecting electron beam; control means for controlling the reflecting electron beam so as to go straight through the beam separator, and the illuminating electron beam so as to keep a deflection angle of the illuminating electron beam which is made by the beam separator substantially constant; wherein the beam separator is formed of an E×B deflector that makes an electric field and a magnetic field orthogonal to each other and superimposed on one another, and the control means controls a voltage and a current which are supplied to the E×B deflector so that a Wien condition by which the deflections caused by the electric field and the magnetic field cancel each other is met with respect to the reflecting electron beam while keeping the deflection angle with respect to the illuminating electron beam substantially constant; a mirror electron microscope mode that magnifies and projects the mirror electron beam, and a low energy electron microscope mode that magnifies and projects the secondary electron beam or the backscattered electron beam; and means for changing over the mirror electron microscope mode and the low energy electron microscope mode; wherein the changeover from the mirror electron microscope mode to the low energy electron microscope mode is conducted by supplying a deflection voltage and a supply current which are obtained by multiplying a deflection voltage and a supply current of the E×B deflector by a value of γ that is represented by the following expression γ = V 0 V 1 ⁢ 2 1 + V 1 V 0 at the same time as the changeover of the specimen supply voltage when it is assumed that an energy of the electron beam that is supplied to the E×B deflector is eV 0 , and an energy of the outgoing electron beam that is supplied to the E×B deflector in the low energy electron microscope mode is eV 1 .