Highly Selective Isotropic Etching of Si to SiGe Using CF4/O2/N2 Plasma for Advanced GAA Nanosheet Transistor

The paradigm shift from FinFET to gate-all-around nanosheet (GAA-NS) transistor architectures necessitates fundamental innovations in channel material engineering. This work addresses the critical challenge of pFET performance degradation in GAA-NS technologies through the development of an advanced selective etching process for strain-engineered SiGe channel formation. We present a systematic investigation of Si selective etching using CF₄/O₂/N₂ gas mixture in a remote plasma source reactor. It is demonstrated that the addition of N₂ to CF₄/O₂ plasmas significantly improves the selectivity of Si to SiGe (up to 58), by promoting NO* radical-induced passivation layer disruption on Si surfaces. Furthermore, an increase in the F:O ratio has been shown to mitigate stress-induced lateral micro-trenching ("Si-tip"), achieving near-zero tip length at high CF₄ flow (500 sccm) while retaining selectivity (>40). Transmission electron microscopy and energy-dispersive X-ray spectroscopy confirm the complete removal of the Si sacrificial layer with minimal SiGe channel loss, validating the process for high-performance SiGe GAA-NS FET integration. These findings provide critical insights into strain-engineered SiGe channel fabrication, enabling balanced NFET/PFET performance in next-generation semiconductor technologies.