Patent Number: 061040347
Section: summary

The invention relates to an objective lens for influencing a particle beam, provided particularly an electron beam, with a magnetic single-pole lens and an electrostatic lens having a first and a second electrode which can be supplied with different potentials. BACKGROUND OF THE INVENTION Objective lenses of the general class to which the invention relates are used for example in electron beam probing and in other spheres of application of electron beam devices, such as microscopy, inspection, lithography, etc. The high-resolution objective lenses should have low aberration coefficients particularly in the low-voltage range. Therefore combined electric-magnetic pole piece objective lenses are known in the art which have low aberration coefficients and accordingly good low-voltage properties. An improvement to these known objective lenses is disclosed in EP-A-0 790 634, in which the magnetic lens is formed by a single-pole lens, an electrostatic retarding lens being disposed within the magnetic lens. The object of the invention is to improve the known objective lenses in such a way that even lower aberration coefficients are achieved. SUMMARY OF THE INVENTION According to the invention this object is achieved by disposing the electrostatic lens downstream of the magnetic single-pole lens in the direction of the particle. In a preferred embodiment the two electrodes of the electrostatic lens are constructed as tube electrodes, the first electrode being passed through the single-pole lens and the second electrode being disposed coaxially with the first electrode. By a slotted construction of one of the two electrodes, electrical multi-pole elements can be formed in a simple manner which can be connected and used for example as electrostatic deflectors, stigmators or other correcting elements.