Electrochemical Atomic Layer Deposition of Copper: A Lead-Free Process Mediated by Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

A novel process for electrochemical atomic layer deposition (e-ALD) of copper is presented. In this process, a sacrificial monolayer of zinc (Zn) is formed via underpotential deposition (UPD) on a copper (Cu) or ruthenium (Ru) substrate. The sacrificial Zn monolayer then undergoes surface-limited redox replacement (SLRR) by nobler Cu. This provides a monolayer of Cu on the substrate surface. UPD-SLRR cycles are repeated to build multi-layers of Cu with controlled thickness while minimizing surface roughness. The proposed Cu e-ALD process is attractive from the point of view of scalability and commercial viability for the following reasons: (i) it eliminates the use of lead-containing chemistries used in previous formulations of Cu e-ALD; (ii) it utilizes a single alkaline (pH = 11.2) electrolyte, which minimizes parasitic reactions such as hydrogen co-evolution and eliminates the need for frequent electrolyte switching as needed in previous e-ALD processes. In this publication, we report cyclic voltammetry, electrochemical quartz crystal microgravimetry, and anodic stripping coulometry studies to gain insights into the process efficiency and deposit morphology characteristics of the Cu e-ALD process.