Atomic layer etching of silicon dioxide using alternating C₄F₈and energetic Ar⁺plasma beams

Abstract

Atomic layer etching (ALE) of SiO 2 was studied by alternating exposure of a 5 nm-thick SiO 2 film on Si substrate to (1) a plasma beam emanating from a c-C 4 F 8 inductively coupled plasma (ICP), to grow a fluorocarbon (FC) film composed mainly of CF 2 , 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 SiO 2 films. A very thin (3–6 Å), near self-limiting thickness CF 2 -rich FC film was found to deposit on the SiO 2 surface with exposure to continuous or pulsed power C 4 F 8 plasma beams, under conditions that generated a large relative flux of CF 2 . 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 SiO 2 . An estimated yield of 1.3 SiO 2 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 O 2 -containing plasma beam.