Realizing Vertical Etch Profiles in Fluorine-Rich Ar/CF4 Plasma

Abstract

The fabrication of next-generation semiconductor and quantum devices with complex 3D architectures requires etching processes that enable highly anisotropic profiles while minimizing plasma-induced damage. However, conventional plasma processes face fundamental limitations, including plasma-induced damage and limited control over etch anisotropy. In particular, fluorine-rich plasmas such as CF4 inherently struggle to achieve vertical profiles due to insufficient sidewall passivation. This study demonstrates that vertical etch profiles can be achieved under ultra-low electron temperature (ULET) conditions in fluorine-rich Ar/CF4 plasma. Under conventional high electron temperature (T-e) conditions without radio-frequency (rf) bias power, Ar/CF4 plasma produces isotropic profiles characterized by undercut and a rounded trench bottom. When T-e is reduced to approximate to 0.5 eV, the profile transitions from isotropic to anisotropic, resulting in suppressed undercut and a flattened trench bottom. This transition is attributed to enhanced sidewall passivation, driven by an increased CFx/F ratio at low-T-e conditions. Moreover, applying moderate rf bias (7 W) to the ULET plasma improves the vertical etch rate and anisotropy without distortion. However, excessive bias power (>18 W) leads to electron heating, which reintroduces distortion. These findings establish T-e as a decisive parameter and demonstrate that ULET plasma enables highly anisotropic etching with minimized distortion in fluorine-rich chemistries.