shown the system 100 includes a lens column 31 containing the electron gun 1 and electron optical system illumination optical system and projection optical system and a substrate chamber 33 containing the substrate stage 24 and peripheral components the lens column 31 desirably is made of soft iron or invar and includes a passive shield made of e g permalloy bonded to it e g with a suitable adhesive the substrate chamber 33 desirably is made of aluminum or non magnetic stainless steel and includes a passive shield made of e g permalloy bonded to it e g with a suitable adhesive the lens column 31 and substrate chamber 33 are connected together such that their interior spaces are contiguous the lens column 31 and substrate chamber 33 collectively form an u201c internal shielding barrier u201d 35 the internal shielding barrier 35 defines a vacuum duct 37 that is connected to a vacuum pump not shown the internal shielding barrier 35 also defines multiple apertures 39 as required for e g insertion and removal of the reticle and substrate and for wiring feed throughs a gap 40 also may be present at the junction of the lens column 31 with the substrate chamber 33 the substrate.