Strategies to Enhance Etch Selectivity During Fluorocarbon Plasma-Assisted Atomic Layer Etching of Silicon-Based Dielectrics*

Stringent processing windows are required for the fabrication of sub-7-nm semiconductor devices, which in turn place severe constraints on conventional plasma-assisted etching. Atomic layer etching (ALE) is a promising etching technique that can provide high etch fidelity, directionality, atomic-scale control, and selectivity to meet and even exceed the process constraints. In this presentation, I will primarily focus on two points: identification of the underlying surface phenomena during ALE of both SiO₂ and SiN_x with fluorocarbon gas (C₄F₈, C₄F₆) plasmas using in situ attenuated total reflection Fourier transform infrared spectroscopy combined with in situ four wavelength ellipsometry; and using selective gas-phase surface functionalization to enhance the overall etch selectivity of SiO₂ to SiN_x and vice versa. This approach of selective functionalization of surfaces is derived from area-selective atomic layer deposition and can be extended to other materials.