A very high spatial resolution all electrostatic, ultra high vacuum, electron optical column has been developed for fast Nano analysis of specimen surfaces. The electron optical column does not project any electric or magnetic fields to the analysis region or beyond.

The electrostatic column operates with a beam energy range of 1-10keV, at a specified working distance of 10mm, for all survey and analytical modes of operation. Spatial resolutions of 4-7nm for Auger Nano analysis and 3nm for a SEM mode correspond to probe currents that range from 1nA to 0.25nA. Other modes of operation are available and these include operation at intermediate spatial resolutions <100nm with high probe currents of 100’s nA and a very useful wide survey mode of ~5mm field of view at lower spatial resolutions <1µm. The electron optical column, having no magnetic lens components and therefore no hysteresis effects, is able to switch fast between these different modes.

Key to the electron optical column specification is the design of the probe forming electrostatic objective lens which operates in an accelerating mode. This lens design is a compact truncated cone with 80º apex angle at the analysis position (10mm WD) which enables a wide angular access (50º) to the specimen surface. Its electron optical design is an Einzel lens of asymmetrical electrode structure and operates with a positive potential of up to 50kV applied to its central electrode. The lens operation is extremely stable with no detectable electrical instabilities.

To aid the development of the electrostatic lens we use simulation software to calculate the lens parameters. At the objective lens WD of 10mm and object at infinity, low values of spherical aberration (75mm) and chromatic aberration (19mm) were computed. These values are comparable to the best magnetic lenses of similar external dimensions and working distance.

The column is mounted on a small analytical chamber for test purposes. We have demonstrated a 3nm SEM spatial resolution at beam energies of 10keV with 250pA of current. At a beam energy of 3keV with 150pA of current, we achieved and 7nm SEM spatial resolution.

An Auger signal was detected using a new form of hyperbolic field parallel energy analyser. A Gold Au (64eV) line scan demonstrated an edge resolution of 4.1nm using a primary probe of 10keV energy and 400pA of current.

For conventional energy analyzers, a probe current of 1nA is more appropriate and the spatial resolutions have been measured as 5nm and 7nm for respective beam energies of 10keV and 7keV.