First Plasma Atomic Layer Etching of Diamond via O$_2$/Kr Chemistry

Abstract

We report the first plasma atomic layer etching (ALE) process for diamond using a cyclic plasma sequence composed of two separated steps: oxygen surface modification and krypton ion removal. The process is implemented in an inductively coupled plasma reactor using alternating O$_2$ plasma exposure and low-energy Kr ion bombardment. This cyclic process exhibits the characteristic self-limiting behavior of ALE and enables controlled material removal with atomic-scale precision. An etch depth per cycle of \SI{6.85}{\angstrom} was achieved. Surface analysis reveals that the etched diamond surfaces exhibit lower roughness than the pristine material, while XPS confirms the preservation of the diamond bonding structure and indicates essentially damage-free etching. These results demonstrate that plasma ALE based on O$_2$/Kr chemistry provides a viable route toward damage-controlled nanoscale processing of diamond, opening new opportunities for advanced device fabrication in power electronics, photonics, quantum sensing and quantum computing technologies.

Figures (9)

• Figure 1: Schematic illustration of the plasma atomic layer etching cycle used in this work, consisting of surface modification by reactive species followed by ion removal, with purge steps inserted between the two half-cycles.
• Figure 2: One ALE cycle consists of four sequential steps. Krypton is present throughout the cycle, whereas oxygen is introduced only during the surface-modification step. The source power is kept constant, and RF bias is applied only during the removal step.
• Figure 3: ALE experiment flow. After cleaning, lithography, and aluminum mask patterning, the diamond sample is etched inside an ICP reactor. After etching, the aluminum mask is removed using an aluminum etching solution. The etched diamond surface is then characterized by SEM, optical profilometry, AFM, and XPS.
• Figure 4: Etch per cycle (EPC) as a function of removal-step DC bias for the O$_2$/Kr ALE process. The trend identifies the ion-energy regime where the surface-modified diamond is preferentially removed, defining the practical ALE operating window. The red dot corresponds to etching without the removal step.
• Figure 5: Quantitative process-synergy analysis of the O$_2$/Kr diamond ALE cycle. Bar (i) shows the etch per cycle (EPC) for the full ALE sequence, while bars (ii) and (iii) show the EPC from modification-only and removal-only control cycles, respectively. The ALE EPC (6.85) exceeds the sum of the two individual contributions (0.87 + 2.35), yielding a synergy of approximately 53%.