Charge exchange in Eaton´s NV-8250 medium current ion implanter

Charge exchange occurring as a result of interaction between incident ions and residual gases can cause electron capture and lose processes that can lead to partial neutralization or stripping of ions into higher charge state. Failure to account for these exchange phenomena can lead to dosing errors during implant. This can be particularly important for medium current implanters where most of the Vt-adjust implants are usually carried out. In this work are have studied the aforementioned effects by systematically introducing nitrogen gas into the process chamber of an Eaton´s 8250 implanter, resulting in pressure that ranges from 5E-7 to 7E-5 Torr. Sheet resistance measurements for high dose implants (B++, B+ E14/cm² ) and ThermaWave and Capacitance-Voltage measurements for low dose (BF2+ E12/cm²) have been performed on the implanted wafers. Results obtained from the present work clearly indicates a negligible effect on Vt due to any dose change that can be attributed to charge changing events for pressures up to 1E-5 Torr. However, for higher dose B+ implants charge exchange already occurs at pressure of 5E-6 Torr. Finally, investigation on possible implications of ion species on neutralization behavior has also been carried out by using B+ and BF2+ beams capable of producing equivalent implanted depth profiles