Multi-beam charged particle system and method of controlling the working distance in a multi-beam charged particle system

#The disclosure relates to particle beam systems and methods for operating a multi-beam charged particle system.

#Particle beam systems use particle optical units to influence beams of charged particles in a desired way, such that for example an imaging can be obtained with the beams of the charged particles. The charged particles can be electrons or ions, for example, and the particle beam systems can be used for example as microscopes or lithography apparatuses.

#A multi-beam charged particle system for wafer inspection usually has a plurality of particle-optical components, each of which can influence a particle beam passing through the respective particle-optical component. By way of example, the particle-optical component can be a particle-optical lens, which has a focusing effect on the particle beam, or the particle-optical component can be a beam deflector, which deflects the particle beam by an angle. For this purpose, the particle-optical components provide electric and/or magnetic fields which act on the charged particles of the particle beam, and values or strengths of these effects can be settable by the strengths of the electric and/or magnetic fields being changed, for example by changing electrical voltages which are applied to elements which provide electric fields, or changing electric currents which are fed to coils which generate magnetic fields.

#Embodiments of the disclosure are explained in greater detail below with reference to figures, in which:

#FIG. 1 shows a particle beam system illustrating some aspects of the disclosure;

#FIG. 2 shows a particle beam system illustrating further aspects of the disclosure;

#FIG. 1 is a schematic illustration of a multi-beam inspection system which uses a plurality of particle beams. The inspection system generates a plurality of primary particle beams which impinge on an object to be examined in order to generate secondary electrons which proceed from the object and are subsequently detected. The inspection system 1 is of the scanning electron microscope (SEM) type which uses a plurality of primary electron beams 3 which are focused at locations on a surface of an object 7 and generate a plurality of electron beam spots 5 there. The object 7 to be inspected can be a wafer or other components such as a semiconductor mask for semiconductor fabrication or an arrangement of miniaturized elements. The surface of the object 7 is arranged in an object plane 101 of an objective lens 102. The distance between the object plane and a reference surface of the objective lens 102 is called the working distance WD.

#The enlarged excerpt I1 in FIG. 1 shows a plan view of the object plane 101 with a regular rectangular raster 103 of impingement locations 5 which are formed in the plane 101. In FIG. 1, the number J of primary beamlets and of impingement locations is 25, which are arranged as a 5×5 raster pattern 103. The number J=25 of impingement locations is a small number chosen for reasons of simplified illustration. In practice, the number J of beamlets 3 or impingement locations 5 can be chosen to be significantly greater, such as, for example, 20×30, 100×100 and the like.

#In the embodiment illustrated, the raster 103 of impingement locations 5 is a substantially regular rectangular raster with a constant distance or pitch P1 between adjacent impingement locations. Exemplary values of the pitch P1 are 1 μm, 10 μm or 40 μm. However, it is also possible for the raster 103 to have other symmetries, such as, for example, a hexagonal symmetry.