Realizing Vertical Etch Profiles in Fluorine‐Rich Ar/CF ₄ 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 CF ₄ 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/CF ₄ plasma. Under conventional high electron temperature ( T _e ) conditions without radio‐frequency (rf) bias power, Ar/CF ₄ plasma produces isotropic profiles characterized by undercut and a rounded trench bottom. When T _e is reduced 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 CF _x /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.