Development of large RF bucket ion sources for large area ion beam milling processes to fabricate micro-structures

Abstract

A novel RF ion source equipped with multi-cusp magnets was developed for higher availability of ion beam milling systems without filaments and for active ion species like oxygen. We call it RF bucket ion source. The multi cusp magnets are set inside the RF coil between slits on the Faraday shield around the discharge chamber to confine plasma. This configuration reduced plasma loss and sputtering of the side wall. It enabled high throughput process with long available operation time between maintenances and caused no disturbance in inductively coupling of RF power to plasma. The RF bucket sources produced large area ion beams with beam extraction area of 300mm diameter. Ar ion beam current density is more than 1mA/cm2 with beam current of 0.9A. The RF bucket ion sorces have been installed in the Ar+ ion beam milling systems, which are continuously operating for 24 hours per a day without stop in commercial industrial factories for fabrication processes of micro-structures. The SiO2 milling uniformity of ±0.47 % at the average milling rate of 48.8 nm/minutes was obtained with optimized conditions and grid structures. The ion source could also produce active ion species such as O, F and others, which are expected to contribute to other novel application processes.