Development of focused ion beam system attached to floating type low energy ion gun for surface finishing

Ion beams of several tens of keV are widely used for the analysis and materials processing, but the occurrence of damage to the surface is of concern. For surface treatment of the ion beam processed sample to remove the damaged layer, a floating-type low-energy ion gun (FLIG) producing 100-500 eV ions at a high current intensity has been developed. This ion gun consists of a permanent magnet-aided electron impact-type ionization cell, an extractor, and a cylindrical retarding immersion lens. The gun produced current intensities of order 1.81 μA (current density of 7.9 μA/cm2) for 100 eV ions. The entire system has been compactly constructed with an ionization cell that has an outer diameter of less than 3.3 cm and a lens system that has a length of 24 cm. In addition, a focused ion beam (FIB) system attached to the FLIG has been developed to remove damaged layers formed by previous high energy etching. The thickness of the damaged layer induced on a GaAs (111) surface by 25 kV Ga+ ions was of order 24 nm, assessed using a transmission electron microscope (TEM). This damaged layer was reduced to ∼2.6 nm by subsequent bombardment by low energy 200 eV Ar+ ions.