The impact of electron temperature on etch profiles in Ar/CF4 plasmas

As high aspect ratio etching becomes increasingly essential in semiconductor manufacturing, vertical etching has gained significant importance. This study investigates the reduction of undercut in silicon (Si) patterned with a high aspect ratio SiO₂ mask, utilizing Ultra-Low Electron Temperature (ULET) plasma. A vertical etch profile devoid of undercut is achieved in the ULET plasma (T_e = 0.3 eV). This ULET plasma is generated through an inductively coupled plasma with a DC-biased grid. As the electron temperature decreases with increasing grid voltage, the lateral etch rate diminishes, resulting in a more vertical profile. Conversely, an increase in RF bias power leads to the observation of undercut and bowing in the etch profile due to a rise in electron temperature associated with the RF bias power. These findings demonstrate that the electron temperature, which influences the etch species, is a critical factor governing the etch profile. Consequently, this ULET plasma presents a viable approach for etching silicon at the atomic scale.