Modern semiconductor technology has created a high demand for structuring and probing specimens in the nanometer or even in the sub-nanometer scale. Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams, e.g. electron beams, which are generated, shaped, deflected and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. For inspection purposes, charged particle beams offer superior spatial resolution compared to, e.g., photon beams because their wavelengths are shorter than the wavelengths of light beams.
Inspection devices using charged particle beams such as scanning electron microscopes (SEM) have many functions in a plurality of industrial fields, including, but not limited to, inspection of electronic circuits during manufacturing, exposure systems for lithography, detecting devices, defect inspection tools, and testing systems for integrated circuits. In such particle beam systems, fine probes with high current density can be used. For instance, in the case of an SEM, the primary electron (PE) beam generates particles like secondary electrons (SE) and/or backscattered electrons (BSE) that can be used to image and analyze a specimen.
Charged particle beams are typically directed, deflected, shaped, corrected, focused, and steered by electric and/or magnetic fields. For this purpose, electrostatic, magnetic and combined electrostatic-magnetic deflectors, lenses and stigmators, e.g. octupole devices, for providing magnetic and electric fields are typically arranged along the propagation path of the charged particle beam from the beam source to a beam target. In order to provide for a small focused spot on the beam target which allows for an increased spatial resolution, beam aberrations are compensated by applying exactly defined electric and magnetic correction fields to the charged particle beam. On the other hand, charged particle beams should be shielded from external electric and magnetic fields and environmental electromagnetic interferences, because low-mass charged particle beams such as electron beams are particularly sensitive to such electromagnetic interferences (EMI).
External magnetic fields in the typical laboratory environment can achieve a magnetic field strength of several mGauss. In order to guarantee a proper functioning of charged particle beam columns, these magnetic fields should be shielded by several orders of magnitude, leaving the residual fields inside the charged particle beam device in the range of sub μGauss. In order to obtain such a shielding within charged particle beam devices, the charged particle beam propagation path can be surrounded by housing devices configured for providing a magnetic shielding, for example, housing devices made of a high permeability material.
However, such shielding systems may not be sufficient. In particular, residual magnetic fields penetrating through the housing device into the inner volume of the charged particle beam device may negatively affect the beam shape quality or the beam direction and may superpose the electric and magnetic fields of beam deflector devices. Focal spot size and spatial resolution may be impaired.
Accordingly, there is a need for housing devices providing excellent magnetic shielding of charged particle beams, e.g. electron beams, along the propagation path from the beam source to the beam target, e.g. a specimen to be examined. In particular, a housing arrangement is needed which provides excellent shielding against EMI and can at the same time be provided as an enclosure of the charged particle beam in a quick and easy manner.