Improvement of the plasma uniformity via current amplitudes and phase shifts in dual-coil antenna driven inductively coupled electronegative chlorine discharges

Abstract

Inductively coupled plasmas (ICPs) are commonly utilized for etching processes in the microelectronic industry. Of which, dual-coil antenna is introduced as a potential technique to improve the plasma uniformity of ICPs in the literature. In this work, we investigate electronegative chlorine (Cl2) ICPs used in realistic processing and their improvement of radial uniformity via adjusting the current amplitudes and phase shift between the inner and outer coils of the dual-coil antenna. It is found that as the inner-to-outer coil current amplitude ratio decreases, the peak of electron and ion density gradually moves away from the radial center. When the wall recombination coefficient of Cl is 0.007, optimized uniformity for electrons and Cl+ is achieved at an inner-to-outer current ratio of 1:2, whereas Cl2+ attains best uniformity at a ratio of 1:1. Furthermore, the lower inner-to-outer coil current ratio is found to result in the better uniformity for the neutral Cl atom and excited state chlorine molecule species. In addition, adjusting the phase shift also significantly changes the plasma density profile. Simulation results show that the phase shift of π yields the highest uniformity for plasma neutrals, while charged particles show a species-dependent behavior. Furthermore, a comparison of different wall recombination coefficients of the Cl atom reveals its significant impact on species uniformity. Validations of the simulations are done against experiments through confirming the increasing trend of electron density vs coil power. This work demonstrates that the inner-to-outer current amplitude ratio and phase shift of the dual-coil antenna in electronegative Cl2 ICPs offers an effective control of the plasma uniformity for different plasma species, providing valuable insights into plasma processing applications that requires high uniformity.