Variable probe current using a condenser lens in a miniature electron beam column

Abstract

Miniature electron beam columns have the advantage of high resolution (<10 nm) at low beam energies (0.5 - 2 kV), making them well-suited for probing the surface structure of a wide variety of nano-scale materials. Because miniature columns have the further benefits of small form factor and low cost of manufacturing, they are uniquely suited for high resolution tabletop Scanning Electron Microscopy (SEM). Miniature columns are also good candidates for use in multiple beam lithography and high throughput mask writing systems. A miniature electrostatic column has been developed for the Novelx mySEM tabletop SEM using monolithically processed bonded stacks of silicon and glass, mounted to a ceramic substrate. It has been shown previously that this type of design can be used to produce a highly manufacturable and reliable column. This column design has demonstrated high resolution imaging and lithography capabilities. The column includes a condenser lens integrated into the source silicon stack, which provides variable beam current density at the limiting aperture in order to vary the probe current. This paper presents results from the condenser lens in the mySEM column, demonstrating continuously variable beam current over a wide range. Simulations presented in this paper show that this column is capable of >2 nA beam current using the condenser lens, with only a slight increase in beam size at high beam current. Measurements are in good agreement with the simulations, demonstrating > 7 nA beam current with the condenser turned on.