Magnetic-field configuration fitted to the microwave ion-source plasma

Abstract

Microwave ion sources for implantation have many advantages, such as the long life of source operation and the cleanliness of extracted beam, over the traditional dc-arc-discharge-type ion sources. We reported that optimizing the plasma-chamber structure made the microwave source exceed most of traditional dc-arc-discharge sources in extracted-ion currents of most species that are used for fabricating modern ultralarge scale integrations. After studying the source magnetic field in detail by computer simulation, the relationship between the magnetic-field profile and the plasma-chamber structure is found to be essential. Two-dimensional analysis is carried out since the plasma is generated between parallel plate electrodes. The optimum chamber structure with which the maximum current was obtained in the last beam-extraction experiments is shown to contain the major magnetic field that is focused by the iron pole pieces. Most of the magnetic-field lines that are crossing the region where ions are first generated do not disappear into the sidewalls of the chamber. Since the lifetimes of ions become longer, the plasma density increases.