Role of high-frequency power in C_4F_8 dual-frequency capacitively coupled plasmas treating high-k HfO_2 films

摘要

Plasma treatment of HfO_2 films by octafluorocyclobutane (C _4F_8) 60 MHz(HF)/2 MHz(LF) dual-frequency capacitively coupled plasmas (DF-CCPs) was investigated. It is found that the fluorine atoms were incorporated into the HfO_2 films by C_4F_8 DF-CCP treatment, but the C: F films were formed on the surface of the HfO 2/Si gate stacks. The results also show that both the plasma treatment and the process of post-deposition annealing play major roles in stabilizing the tetragonal structure, leading to a large band gap and good electrical properties. The formation of t-HfO_2 is related to oxygen vacancy generation and Si diffusion into the HfO_2 films. The capacitance-voltage measurement showed that the smallest ΔV_(fb) and the lowest interface trap density were obtained at the HF power of 120 W and the LF power of 30 W. Therefore, the C_4F_8 DF-CCP is a suitable method to improve the electrical characteristics of HfO_2/Si gate stacks.