Operating characteristics of a 100 kV, 100 kW plasma ion implantation facility

Abstract

Plasma ion implantation of gaseous ion species is conducted in two different operating modes corresponding to two different gas pressure regimes, a low-pressure mode (1.33 × 10-3 -1.33 × 10-2Pa (10-5 -10-4Torr)) and a high-pressure mode (1.33 × 10-2 -0.133 Pa (10-4 -10-3Torr)). In the low-pressure operating mode, the plasma production and ion implantation processes are decoupled, i.e. a part to be implanted is immersed in a separately generated nitrogen plasma and then independently pulse biased to -100 kV to implant ions. The current-pulse waveform continuously decays from an initial high-current-spike value (300 A) to a low relatively steady-state value (30 A). A wide dynamic range of operation is possible in this mode. Pulse durations can extend from 10 to 50 us and frequencies can range from 100 to 1000 Hz. Total power levels of 100 kW have been demonstrated. In the high-pressure operating mode, the plasma production and ion implantation processes are coupled, i.e. the part is immersed in a gas, and the voltage used to pulse bias the part both initiates and sustains the plasma production process, as well as implanting ions. The current-pulse waveform increases during the initial part of the pulse duration and can attain a near-steady value of 150 A at 100 kV. The higher near-steady-state pulsed current of the high-pressure mode potentially allows faster implantation of parts as well as a smaller more conformal plasma sheath compared with the low-pressure mode. However, the dynamic range in this mode differs from the low-pressure mode. At 100 kV, pulse durations are limited to less than 5 μs at a frequency of less than 100 Hz. In this paper, we present the operating characteristics for both operating modes, as well as their implications for faster treatment and more conformal implants of complex-shaped parts.