Particle Separation
Mass spectrometers utilize crossed electric and magnetic fields to select charged particles of a specific mass-to-charge ratio while allowing others to deflect out of the beamline. Implementing a wien mass filter allows process engineers to purify the ion beam used in implantation or sputtering systems by removing unwanted isotopes and contaminant ions. This filter operates on the principle that only ions of a specific velocity will experience equal and opposite forces from the orthogonal fields, allowing them to pass through straight.
Ions with other velocities are deflected and blocked by an exit aperture.
Field Configuration
Resolution is determined by the strength of the crossed fields and the width of the exit slit. By adjusting the electric field strength, the wien mass filter can be tuned to select different ion species without changing the physical geometry of the system. This electronic tuning provides a highly flexible method for beam purification.
Selectivity Limit
Beam divergence and energy spread can limit the resolution of the filter. If the incoming ions have a wide range of initial kinetic energies, the wien mass filter becomes less effective at resolving closely spaced masses. This limitation requires pre-focusing and energy-filtering steps upstream of the analyzer.
