Magnetic fine deflection system comprising sheet conductors

Improved magnetic fine deflection apparatus for an electron optical system of the type having a matrix lens member positioned substantially transverse to a system axis and having an array of a plurality of apertures formed therethrough, means for emitting a beam of electrons toward said matrix lens member, coarse deflector means for deflecting the electron beam through a selected one of the plurality of apertures toward the surface of a target positioned transverse to said system axis and beyond said lens member with respect to said source means, and means for focusing the beam upon said target surface after passage of said beam through said selected aperture, said fine deflection apparatus comprising:

• first means comprising first and second orthogonally-disposed sheet conductors, each lying in a plane substantially transverse to said system axis, and positioned beyond said target, with respect to said lens member, for generating a first magnetic fine deflection field substantially in a direction transverse to said system axis;
• and
• second means comprising third and fourth sheet conductors orthogonally-disposed in a plane substantially transverse to said system axis;
• said first and third sheet conductors extending substantially parallel to one another;
• said second and fourth sheet conductors extending substantially parallel to one another;
• each of said third and fourth sheet conductors having an array of apertures formed therethrough with each aperture in registration with an associated aperture in the other of said third and fourth sheet conductors and with an associated aperture of said lens member;
• said second means being positioned beyond said lens member, with respect to said target, for generating a second magnetic fine deflection field substantially in said direction transverse to said system axis;
• said first and second fields adding in a first region between said lens member and said target for finely deflecting electrons of said beam to impinge upon a selected point upon said target surface;
• the magnitude of said second magnetic field in a second region beyond said lens member, with respect to said target, being reduced by the magnitude of said first field in said second region to reduce errors in the deflection of said beam to said selected aperture by said coarse deflector means.