Electron-temperature control for selective etching of carbon-based masks over high-k/metal-gate and dielectric films

As semiconductor device architectures become increasingly complex and heterogeneous, repeated masking steps are required for processes such as threshold-voltage tuning, with carbon-based masks commonly used for this purpose. Consequently, high etch selectivity between these masks and functional thin films is essential to minimize unintended material loss. In this study, electron-temperature control in Ar/NF 3 plasma is investigated as a strategy for tuning thin-film etch selectivity through changes in ion-energy characteristics and plasma-surface reactions. The plasma is generated in an inductively coupled plasma system with a DC-biased grid, using a carbon-based bottom antireflective coating (BARC) as a reference mask layer and TiN, HfO 2 , SiO 2 , and SiN as representative high-k/metal-gate and dielectric films. As the grid voltage decreases from 0 to −50 V, the electron temperature decreases from 3.0 to 0.5 eV. Under these conditions, Ar-plasma measurements indicate decreases in mean ion energy and integrated ion current. Optical emission analysis shows a relatively stable F-to-Ar emission ratio but a decreased N-to-Ar ratio. Despite the reduced mean ion energy and integrated ion current, the BARC etch rate increases, and its etch selectivity over the functional films improves by approximately 3.0–3.4-fold. AFM and XPS analyses suggest that negative grid bias suppresses ion-induced surface roughening and carbon-network modification while increasing the relative fluorine content at the BARC surface, consistent with enhanced BARC etching. These results demonstrate electron-temperature control as an effective approach for selective BARC etching with reduced loss of functional films.