A modern semiconductor device is composed of approximately 20-30 pattern layers that collectively implement the intended functionality of the designer. In general, the designer describes the chip functionality with high level, behavior design languages like VHDL, and then a series of EDA tools translate the high-level description into a GDSII file. The GDSII file contains a geometrical description of polygons and other shapes that describe the patterns of the different layers. The GDSII file accompanied with process design rules for the fabrication process to be used to make the device describes the intended geometry on the layout with the relevant tolerances.
Modern photolithography presents several challenges, including those associated with moving from 90 nm to 45 nm and 32 nm while keeping the stepper wavelengths at e.g. 193 nm. This requires further transformation of the intended layout geometry to a post resolution enhancement technique (RET) version of the GDSII file. The new GDSII file includes pattern modifications for optical proximity corrections (OPC) and mask technology. The complex set of OPC corrections, mask-making and stepper conditions is required to print the intended geometry on the wafer.
In light of the above, semiconductor technologies have created a high demand for structuring and probing specimens within the nanometer scale. Micrometer and nanometer scale process control, inspection or structuring, is often done with charged particle beams. Probing or structuring is often performed with charged particle beams which are generated and focused in charged particle beam devices. Examples of charged particle beam devices are electron microscopes, electron beam pattern generators, ion microscopes as well as ion beam pattern generators. Charged particle beams, in particular electron beams, offer superior spatial resolution compared to photon beams, due to their short wavelengths at comparable particle energy.
Particle optics apparatuses like, e.g. Scanning Electron Microscopes (SEM), generate a primary beam illuminating or scanning a specimen. For instance in 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 the specimen. Many instruments use either electrostatic or compound electric-magnetic lenses to focus the primary beam onto the specimen. In some cases, the electrostatic field simultaneously collects the generated particles (SE and BSE) which are entering into the lens and must be guided onto a detector. This detector may be concentric to the PE axis, but this concept may result in signal loss due to the detector hole. If uniform high efficiency electron collection and detection is required, the secondary and/or backscattered particles must be separated from the primary beam, e.g. by a beam separator including magnetic deflection fields or a Wien filter element.
Both types of beam separator introduce dispersion of the primary beam and finally limit the attainable resolution. One type of Wien filter, an unbalanced type known as “achromatic Wien filter” can be used to avoid PE beam dispersion. However, these devices typically result in aberrations which can impair spot size and the spot resolution in e.g. high speed Electron Beam Inspection applications using large beam currents and beam diameters.