INITIAL OPERATION OF A LARGE-SCALE PLASMA SOURCE ION-IMPLANTATION EXPERIMENT

In plasma source ion implantation (PSII), a workpiece to be implanted is immersed in a weakly ionized plasma and pulsed to a high negative voltage. Plasma ions are accelerated toward the workpiece and implanted in its surface. A large-scale PSII experiment has recently been assembled at Los Alamos, in which stainless steel and aluminum workpieces with surface areas over 4 m2 have been implanted in a 1.5 m diam, 4.6 m length cylindrical vacuum chamber. Initial implants have been performed at 50 kV with 20 mus pulses of 53 A peak current, repeated at 500 Hz, although the pulse modulator will eventually supply 120 kV pulses of 60 A peak current at 2 kHz. A 1000 W, 13.56 MHz capacitively coupled source produces nitrogen plasma densities in the 10(15) M-3 range at neutral pressures as low as 0.02 mTorr. A variety of antenna configurations have been tried, with and without axial magnetic fields of up to 60 G. Measurements of sheath expansion, modulator voltage and current, and plasma density fill-in following a pulse are presented. We consider secondary electron emission, x-ray production, workpiece arcing, implant conformality, and workpiece and chamber heating.