Metallic contamination in hydrogen plasma immersion ion implantation of silicon

In plasma immersion ion implantation (PIII), ions bombard all surfaces insi de the PIII vacuum chamber, especially the negatively pulsed biased sample stage and to a lesser extent the interior of the vacuum chamber. As a resul t, contaminants sputtered from these exposed surfaces can be reimplanted in to or adsorb on the silicon wafer. Using particle-in-cell theoretical simul ation, we determine the relative ion doses incident on the top, side, and b ottom surfaces of three typical sample chuck configurations: (i) a bare con ducting stage with the entire sample platen and high-voltage feedthrough/su pporting rod exposed and under a high voltage, (ii) a stage with only the s ample platen exposed to the plasma but the high-voltage feedthrough protect ed by an insulating quartz shroud, and (iii) a bare stage with a silicon ex tension or guard ring to reduce the number of ions bombarding the side and bottom of the sample platen. Our simulation results reveal that the ratio o f the incident dose impacting the top of the sample platen to that impactin g the side and bottom of the sample stage can be improved to 49% using a gu ard ring. To corroborate our theoretical results, we experimentally determi ne the amounts of metallic contaminants on 100 mm silicon wafers implanted using a bare chuck and with a 150 mm silicon wafer inserted between the 100 mm wafer and sample stage to imitate the guard ring. We also discuss the e ffectiveness of a replaceable all-silicon liner inside the vacuum chamber t o address the second source of contamination, that from the interior wall o f the vacuum chamber. Our results indicate a significant improvement when a n all-silicon liner and silicon guard ring are used simultaneously. (C) 200 1 American Institute of Physics.