Etching characteristics and modeling for oval-shaped contact

In this study, etching characteristics of oval-shaped contact were investigated. The oval-shaped contact showed different etching characteristics compared to the circular contact. The long axis cross-section of oval-shaped contact showed a more vertical profile and a less bowing compared to the short axis. To explain these phenomena, we simulated ion reflection from sloped oval-shaped hard-mask. From the simulation, we found that the ions reflected from hard-mask accumulated more toward short axis sidewall first. This ion accumulation and asymmetric charging explained the reason behind larger bowing and slopped profile phenomena of short axis.