EXTRA-HIGH VACUUM ELEMENT FOR CHARGED PARTICLE BEAM DEVICE

摘要

PURPOSE:To prevent any scattering of contaminant by reducing the influence of a magnetic field on an extra-high vacuum element by installing in the exhaust hole a contaminant-shielding plate which is made of a material with high permeability and also serves as an external magnetism shield. CONSTITUTION:Magnetic fluxes leaking outside through the exhaust hole 17 of an ionic pump are reduced by absorbing them into shield cylinders 22 formed by thin plates of a material with high permeability. Each of the shield cylinders 22 consists of a pipe 23 and a twisted shield plate 24 made of the same material as the pipe 23 so that contaminants such as active metal molecules which have absorbed scattering gas molecules produced in the ionic pump are shielded by a shielding plate 24 and not discharged outside. As a result, the decrease in the exhaust rate of the ionic pump is minimized, thereby reducing the amount of magnetic fluxes leaking through the exhaust hole 17 and the amount of scattering contaminates.