Low energy micron size beam from inductively coupled plasma ion source

Abstract

A high brightness inductively coupled plasma ion source based focused ion beam system is being developed. This system is intended to produce a low energy high current micron size beam of the heavier gaseous elements for high speed, micro milling applications. The basic aim of this development is to cater the needs of those applications which cannot be addressed by the conventional liquid metal ion source based FIB. A novel idea has been implemented in the design of the ion source where, a double plasma chamber is designed to initiate the plasma at low RF power. The plasma is first initiated by the capacitive coupling at low RF power in one chamber. This in turn triggers a strong, high density inductive discharge in another chamber, which is Faraday shielded by a thin slotted copper foil. The ion beam is extracted through 1 mm diameter aperture in the plasma electrode using a simple two electrode extraction system. The ion source has produced argon ion beam of 57 mA/cm2 with an angular current density of ∼10 mA/Sr at 160 W of RF power and 7kV of extraction voltage. In addition, the measurements show that the ion source has brightness of >8000 A/m2 Sr−1 V−1. The ion source is integrated with a two lens focusing column and beam currents from 2 nA to 2.5 μA were focused at a working distance of 5 mm. Measurements show that the currents in the range of 500 nA to 1 μA can be focused to spots having diameters in the range of 8–10 μm resulting in a current density of 450 mA/cm2 at the focused spot. In order to evaluate the milling rate of steel, experiments were carried out using 7 keV, 800 nA of argon ion beam. Preliminary results indicate that the milling rate of steel is >100 μm3/s.