Fluid simulation of the pulsed bias effect on inductively coupled nitrogen discharges for low-voltage plasma immersion ion implantation**Project supported by the National Natural Science Foundation of China (Grant Nos. 11175034, 11335004, and 11405019) and the Important National Science and Technology Specific Project of China (Grant No. 2011 ZX 02403-001.

Abstract

Planar radio frequency inductively coupled plasmas (ICP) are employed for low-voltage ion implantation processes, with capacitive pulse biasing of the substrate for modulation of the ion energy. In this work, a two-dimensional (2D) self-consistent fluid model has been employed to investigate the influence of the pulsed bias power on the nitrogen plasmas for various bias voltages and pulse frequencies. The results indicate that the plasma density as well as the inductive power density increase significantly when the bias voltage varies from 0 V to 4000 V, due to the heating of the capacitive field caused by the bias power. The fraction increases rapidly to a maximum at the beginning of the power-on time, and then it decreases and reaches the steady state at the end of the glow period. Moreover, it increases with the bias voltage during the power-on time, whereas the fraction exhibits a reverse behavior. When the pulse frequency increases to 25 kHz and 40 kHz, the plasma steady state cannot be obtained, and a rapid decrease of the ion density at the substrate surface at the beginning of the glow period is observed.