Method for implementing low dose implant in a plasma system

Abstract

Methods of decreasing the dose per pulse implanted into a workpiece disposed in a process chamber are disclosed. According to one embodiment, the plasma is generated by a RF power supply. This RF power supply may have two different modes, a first, referred to as continuous wave mode, where the RF power supply is continuously outputting a voltage. This mode allows creation of the plasma within the process chamber. During the second mode, referred to as pulsed plasma mode, the RF power supply outputs two different power levels. The platen bias voltage may be a more negative value when the lower RF power level is being applied. This pulsed (or multi-setpoint) plasma also assists in reducing dopant deposition on the wafer during the time when CW plasma is on but the bias voltage pulse is in the off-state. In a further embodiment, a delay is introduced between the transition to the pulsed plasma mode and the initiation of the implanting process. In yet another embodiment the plasma is generated at a location in the chamber more judicious to reducing the dose impinging on the wafer, thereby increasing the process time to allow adequate control of the process.