The manufacturer of an electron beam lithography machine pushes a better understanding and higher performance of the optical column to provide a better product with each iteration. At the heart of the column is the source of electrons: the gun lens. It holds the field emitter from which the electrons originate and accelerates the beam to a first crossover. The main work in this thesis was concerned with development of a new and better gun lens design. Consideration of several physical phenomena is required in order for the gun lens to be more robust and with a more stable beam. It was found that the heating transient plays a large role in the operation of the gun lens. By defining the requirements clearly including by ray-tracing the optical geometry to find optical sensitivities, the main challenges of the project became evident. A new concept design is presented where the heat transport inside the gun lens is improved and thermal drift is greatly diminished. By using the ceramic insulators as flexures the short- and long-term stability of the lenses are improved and the thermal transient settling time is reduced from 26 hours to below 6 hours. By opening up the geometry inside the gun lens the local vacuum at the emitter is much better, which increases its lifetime. The electrostatic fields are made much more robust by burying the triple junction, which required using a new insulator shape. The final result is a gun lens concept design which improves in all aspects while remaining simple in construction.

The Wien filter is an important part in the multi-beam inspection microscope that is being developed at the Imaging Physics research group at the TU Delft. The multi-beam inspection microscope uses an array of 20x20 parallel beams with a pitch of 1mmthat scan the sample simultaneously. This way the low throughput of current scanning electron microscopes can be increased proportional to the number of parallel beams. The Wien filter uses a magnetic field to separate the array of primary beams from the secondary beams. A design for the Wien filter is described in [6] consisting of electric and magnetic deflection arrays. In this report a first model of the magnetic deflection array is presented and tested to investigate the uniformity of the magnetic field. The magnetic field strength was computed by measuring the deflection distance caused by the field. As predicted by theory, the field has been found to scale linearly with the applied current. Current optimization was done in simulations to find the most uniform distribution of the magnetic field. Experiments showed against expectation that the uniformity of themagnetic field between slits does not increase with increasing current on the auxiliary coil while current on the main coil is kept constant. An possible explanation is provided in this report. For the model presented in this report the current in the auxiliary coil should be
set to zero in order to obtain the most uniform magnetic field. It is proposed to provide every single winding
with its own power supply so that a better uniformity might be achieved by the individual optimization of the
currents applied.

In this paper two ways of modeling the secondary electron yields of an insula-
tor under electron irradiation, are discussed and coupled. The drift-diusion-
reaction model is used to investigate the secondary yields and charging eects.