Paper PS-TuP8
Atomic Layer Etching of Silicon Dioxide Using Alternating C₄F₈ and Energetic Ar⁺ Plasma Beams

Tuesday, October 31, 2017, 6:30 pm, Room Central Hall

Atomic layer etching (ALE) of SiO₂ was studied by alternating exposure of a 5 nm-thick SiO₂ film on Si substrate to (1) a plasma beam emanating from a c-C₄F₈ inductively coupled plasma (ICP), to grow a fluorocarbon (FC) film composed mainly of CF₂, and (2) an energetic (130 eV) Ar⁺ ion beam extracted from a separate Ar ICP. In-situ X-ray photoelectron spectroscopy was used to analyze the chemical composition of the near-surface region, and to quantify the thickness of the FC and SiO₂ films. A very thin (3-6 Å), near self-limiting thickness CF₂-rich FC film was found to deposit on the SiO₂ surface with exposure to continuous or pulsed power C₄F₈ plasma beams, under conditions that generated a large relative flux of CF₂. Following this, a FC film of similar composition grew at ~10 times slower rate. Exposure of the thin film to the Ar⁺ beam led to removal of 1.9 Å SiO₂. An estimated yield of 1.3 SiO₂ molecules-per-Ar⁺ was found for a single ALE step. The rate of 1.9 Å/cycle persisted over multiple ALE cycles, but a carbon-rich residual film did build up. This film can be removed by a brief exposure to an O₂-containing plasma beam. Support from Lam Research and NSF is gratefully acknowledged.