Selective atomic layer etching of HfO₂ over silicon by precursor and substrate-dependent selective deposition

The early work of John Coburn and Harold Winters revealed a synergistic effect in ion-enhanced Si etching by the concurrent irradiation of Ar⁺ and XeF₂. This finding provided an important foundation for the development of plasma dry etching processes. The experimental results of Coburn and Winters also found effects that are useful for the development of atomic layer etching (ALE) processes characterized by a self-limited etch rate. ALE approaches are widely established and can be utilized in either directional or isotropic etching by employing proper surface modification and product removal steps. Nevertheless, the development of material selective ALE processes is still limited. An approach that combines substrate-selective deposition with etching opens a new processing window for selective ALE. The authors studied the deposition behavior of mixtures of methane (CH₄) with trifluoromethane (CHF₃) and mixtures of methane with octafluorocyclobutane (C₄F₈) on HfO₂ and Si surfaces. The experimental results show that a CH₄/C₄F₈ mixture produces a comparable fluorocarbon (FC) deposition thickness on both HfO₂ and Si during the deposition step. In contrast, a CH₄/CHF₃ mixture deposits an FC film on Si, whereas it fluorinates the HfO₂ surface with negligible FC deposition. Utilizing these behaviors allows for an ALE process based on CH₄/CHF₃ for selective removal of HfO₂ over Si. Surface characterization data that provide mechanistic insights into these processes are also provided and discussed.