Microwave ion sources for industrial applications (invited)

Microwave ion sources for industrial use are usually driven by 2.45 GHz microwaves and operated in a very wide range of magnetic field from zero to over the electron cyclotron resonance magnetic field. They are used mostly under off-resonant conditions. For ion implantation into usual semiconductor devices, the weak points of the microwave ion source against the conventional implanter sources, the Freeman and the Bernas, had been the lower ${\mathrm{B}}^{\mathrm{+}}\mathrm{ ion}$ current and the slightly narrower dynamic range of the current. However, the optimization of the discharge-chamber shape and volume resolved the problems. Consequently, the microwave sources exceed the conventional sources in most principal performances for implantation into semiconductor devices. For the sophisticated separation by implanted oxygen devices, the microwave ion source is very suitable for stable production of high-current ${\mathrm{O}}^{\mathrm{+}}\mathrm{ ion}$ beams. 100 mA class ${\mathrm{O}}^{\mathrm{+}}\mathrm{ ion}$ implanters dedicated to silicon on insulator technology were developed. On the other hand, for application to surface modification of materials, mass separation is completely eliminated in some cases. Recently, a new ion source for the purpose was developed, in which 2.45 GHz microwaves are absorbed by 13.56 MHz inductively coupled plasma without static magnetic field. The alternate magnetic field induced by 13.56 MHz rf power is considered to help microwaves penetrate into the plasma. Since the volume of the source is not restricted by solenoids as a usual microwave source, it can be applied to three dimensional implantation or plasma source ion implantation.