Surface evolution mechanism for atomic-scale smoothing of Si via atmospheric pressure plasma etching

Atmospheric plasma etching-based machining methods generally suffer from surface roughness deterioration. To achieve an atomic-scale smooth surface of Si via purely plasma etching, clarifying the etching evolution and mechanism is essential. In this study, we study surface evolution and smoothening mechanisms from the perspective of plasma etching modes comprehensively. The morphology and roughness evolutions of isotropic, orientation-selective, and atom-selective etching are investigated, respectively. The semi-finishing effect is realized through the growing and merging of hemispherical pits during isotropic etching, with the surface roughness being reduced from 103 nm to 0.79 nm. Orientation-selective etching is a roughening process, transforming square-opening pits into pyramid structures. Under the atom-selective mode, an atomically smooth surface with Sa 0.17 nm can be obtained. The top-down smoothing process of atom-selective is much more efficient than isotropic etching. Atom-selective etching with a maximum removal rate of 22 μm/min enables the rapid thinning of Si substrate thickness from 715 μm to 90.4 μm within 45 min. Additionally, atom-selective etching is a universal polishing approach regardless of pre-processed methods and is a damage-less process. This paper provides a promising strategy for atomic and close-to-atomic scale manufacturing.