Improvements in the angular current density of inductively coupled plasma ion source for focused heavy ion beams

• JΩ of ion beam from ICP ion source for high current FIB system is investigated.
• Achieved high JΩ at low RF powers.
• JΩ of this source is three orders higher than that of liquid metal ion source.
• Significant enhancement in JΩ achieved by modifying the plasma chamber.
• Heavier ions show better performance in terms of JΩ at lower RF power.

A compact inductively coupled plasma ion source (ICPIS) is developed for producing high current micron size beams for high speed micromachining applications. Angular current density (JΩ) of the beam extracted from ICPIS is measured and found to be three orders higher than that of the conventional liquid metal ion sources. An improvement in JΩ by >30% is achieved through the increase of RF power density in the plasma by reducing the plasma volume instead of operating ion source at high RF power. Studies on JΩ show that heavier ions have maximum JΩ at lower power and vice versa for the lighter ions. Ion beams of Neon, Argon, Krypton and Xenon extracted at 5 kV, have JΩ of 57, 51, 37 and 30 mA/Sr respectively at RF power in the range of 75 W–200 W. Measurements on proton beam which is very important for imaging applications show JΩ of 45 mA/Sr at 200 W.