Advanced Fabrication of Ultrathin Ruthenium Films Using Synergistic Atomic Layer Deposition and Etching.

Atomic-level surface preparation, using additive and subtractive atomic layer processes, has gradually become crucial for the more active process variations and highly selective process requirements. Precise control of surface roughness and coverage is a critical consideration in the fabrication of metal thin films. Herein, the fabrication of ultrathin, smooth Ru films with a thickness reduced to below 3 nm is reported. This process involves etching back after depositing a thick Ru film using a synergistic combination of atomic layer deposition (ALD) and atomic layer etching (ALE) techniques. The surface smoothing effect, while preserving surface coverage, is validated by initially performing the ALD process for Ru with (ethylbenzyl)(1-ethyl-1,4-cyclohexadienyl)Ru(0) precursor and O gas, followed by the ALE process with 2,4-pentanedione and O radicals. Under optimized conditions for atomically flat Ru surfaces, the surface quality of Ru films processed by ALD, and the combined ALD/ALE methods are compared. Consequently, it is demonstrated for the first time that the combined ALD/ALE process effectively reduces both thickness and asperities while smoothing the surface and maintaining nearly complete surface coverage down to the ≈1 nm scale. This approach enables the production of advanced electronic devices with precise control over surface properties at the Ångström level.