公开(公告)号：FR2305019A1

公开(公告)日：1976-10-15

申请号：FR7602501

申请日：1976-01-27

Applicant: IBM

Inventor： LOEFFLER KARL H ,  PFEIFFE HANS C

IPC: H01J37/09 ,  H01J37/141 ,  H01J37/147 ,  H01J37/30 ,  H01L21/027 ,  H01L21/70

Abstract: A shielded magnetic lens and deflection yoke structure for an electron beam column which minimizes aberrations in the lens system caused by winding asymmetry in the field coil, as well as aberrations due to eddy currents created within the magnetic circuit of the lens by interaction with the field of the deflection yoke. The shield includes a polepiece structure for the magnetic electron lens generally comprising a hollow cylinder formed of a plurality of precisely machined magnetic discs stacked concentrically with precisely machined nonmagnetic discs in alternating sequence with the lens coil positioned adjacent the periphery of the cylinder and the deflection yoke positioned within the cylinder or proximate to either end thereof. In one preferred embodiment of the invention the magnetic discs are formed of a nonconductive material such as ferrite and the nonmagnetic discs are formed of alumina.