Development of compact microwave ion source for low-energy application

A compact microwave ion source for the research of low-energy ion beam application such as ion beam assisted deposition or ion beam sputtering has been developed. The developed ion source is based on the previously reported compact microwave ion source, which was developed for higher-energy extraction. In order to extract the ions with a lower energy, it is necessary to lower the plasma density. The present ion source possesses a plasma expansion cup in order to make the plasma thinner. As a consequence of the thinner plasma, the extractable current becomes lower than that of the thicker plasma, thus the source has multiple extraction apertures. Current–voltage characteristics of the ion source were measured with an extraction system with 37 apertures and the extraction gap of 1.5 mm. At the voltage of 500 V, the current of the extraction electrode decreased rapidly and it was shown that at this voltage, an optimum ion optics was achieved. The argon ion current of 0.4 mA with the energy of 500 eV was extracted. The gas pressure in the processing chamber could be reduced to 5×10−4 Pa.