Initial results with a point projection microscope

摘要

Conventional scanning electron microscopes are now close to the limit of their performance for task such as the metrology of sub-micron design rule devices. In order to overcome these limits we are investigating the use of in- line electron holography for device metrology. The in-line holograms are formed in a point projection microscope using ultra-low energy electrons (50-250eV) emitted from a nano- tip electron source. Holograms in the transmission mode and in the reelection mode of the microscope as well are possible. Sine these in-line holograms are equivalent to out of focus micro-graphs acquired in a transmission electron microscope with a field emission gun we can reconstruct the original wave front by means of Fourier optics. The resolution of the point projection microscope is given by the sharpness of the emitter. We investigate the electric potential of the emitter using off-axis electron holography in a transmission electron microscope and compare the results to simulations obtained by solving the appropriate Laplace equation.