Plasma-Assisted Atomic Layer Etching of Si in Cl and Br-Containing Plasma

Abstract

Atomic-scale precision in silicon plasma etching is indispensable for the fabrication of next-generation three-dimensional (3D) semiconductor devices. Yet plasma-assisted atomic layer etching (PA-ALE) continues to be limited by low throughput, poor self-limiting behavior, and an incomplete understanding of surface kinetics. My research tries to address these challenges through a systematic study performed in a modified continuous-wave (CW) inductively coupled plasma (ICP) reactor. Time-resolved, in-situ optical emission spectroscopy (OES) is established as a quantitative tool of surface reactions during ALE cycles employing Cl₂, HBr, and Br₂ chemistries. The measurements show that SiCl₂ and SiCl constitute the primary products in Cl₂-based ALE. Two process sequences—gas dosing and plasma gas dosing—are explored and compared: pseudo-self-limiting behavior emerges in HBr plasma gas dosing cycles, whereas Br₂ have greater Br surface coverage and higher etch rates under gas-dosing conditions compared to HBr. Because both Br₂ and HBr have high sticking coefficients, gas residence time experiments reveal a two-stage purge consisting of a volume-limited decay followed by wall retention limited desorption; wall passivation via temperature control, Ar/SF₆/O₂ conditioning, and increased total flow substantially shortens the wall retention time. Moreover, fast-pulsed substrate bias with continuous gas flow effectively decouples the dose and etch steps, eliminating mechanical gas-pulsing hardware and markedly increasing throughput. Simultaneously tracking the ALE percentage and the bias-on integrated intensity of dominant OES lines enables evaluation of both self-limiting fidelity and etch rate. Collectively, this work (i) elucidates the primary reaction products and pathways in Si ALE for multiple halogen chemistries, (ii) delivers robust, high-throughput recipes that achieve sub-nm precision with cycle times below 2 s, and (iii) provides diagnostic and hardware guidelines transferable to other ICP tools. These advances expedite the transition of PA-ALE from lab to high-volume manufacturing, making a further step to achieve damage-free patterning of sub-10 nm features for future logic and memory devices