Enhancement of etch rate and selectivity for tungsten carbide hardmask

As three-dimensional semiconductor device architectures with high-k materials are introduced in next-generation semiconductor processes, the etch resistance limit of the conventional amorphous carbon layer hard mask has become apparent. Tungsten carbide (WC), one of the metal-based hard mask materials, has attracted attention as a new hard mask material; however, removing the WC hard mask layer after high-aspect-ratio contact processing without damaging the underlying layers is required. In this study, a method to simultaneously improve the WC hard mask etch rate and etch selectivity toward SiO2 was proposed by tuning the antenna impedance of a conventional inductively coupled plasma (ICP) etching system operating in a Cl2/O2 plasma environment. The antenna impedance was adjusted by connecting series capacitors at the ground path of the antenna, which is referred to as capacitance termination, and changes in plasma characteristics were analyzed using a floating harmonic probe and optical emission spectroscopy (OES). The experimental results show that when a low capacitance of 80 pF was applied, both the antenna current and plasma density decreased; however, the plasma potential increased while the self-bias decreased, leading to higher ion energy and enhanced physical sputtering. Consequently, we achieved a significant increase in the WC etch rate, reaching a maximum of 881 Å/min. OES analysis confirmed that under the 80 pF condition, a plasma environment was formed that not only promoted sputtering but also suppressed WC oxidation. The results demonstrate that antenna-impedance tuning provides an effective control parameter for optimizing both throughput and selectivity of next-generation hard mask processes using existing ICP etching equipment.