Design and fabrication of a miniaturized gas ionization chamber for production of high quality ion beams

A high performance electron impact gas ion source for use in high resolution focused ion beam (HR FIB) applications is currently being developed. For high source brightness and low ion energy distribution operations this ion source requires a gas ionization chamber with small dimensions. We have designed and fabricated prototype gas chambers using MEMS fabrication techniques. The gas chamber is a sandwich structure of two silicon substrate pieces, each holding a 100 nm thick metal membrane, with a thin silicon nitride spacer in-between. Our first prototypes resulted in a gas chamber spacing of 1–2.5 μm caused by glue seepage and particle contaminations although our fabrication method is designed for 200 nm. A further increase in the gas chamber spacing has been observed under a high gas load. However, our analysis suggests that the load deflection can be sufficiently minimized by reducing the metal membrane size to <10 × 10 μm.

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► We detail a fabrication method of a miniaturized gas ionization chamber.
► The gas chamber consists of two 100 nm thick metal membranes and a Si3N4 spacer in-between.
► The prototypes resulted in a gas chamber spacing of 1–2.5 μm.
► Membrane deflection under a gas load additionally increases the spacing.
► Reduction of the membrane size can sufficiently minimize the spacing increase.