Local etching of copper films by the Scanning Electrochemical Microscope in the feedback mode: A theoretical and experimental investigation

A model of the Scanning Electrochemical Microscope (SECM) as a lithographic tool is presented and used to get quantitative kinetic information from lithographic experiments. It is illustrated in the specific case of the local etching by anodic dissolution of a copper substrate by the SECM in the feedback mode. A theoretical model presents the expected profile of the etched hole in the simple case of the positive feedback behaviour. A steady-state behaviour is expected for the dimensionless shape of the hole, which depends only on the tip-substrate separation distance. The hole depth is then expected to linearly depend on the etching time. The model is then confronted to different experimental conditions where a Cu substrate is locally oxidized by a tip-electrogenerated Fe(bpy)₃³⁺ oxidant. The experiments agree with the theoretical predictions (steady-state dimensionless profile and linear evolution of the depth with time). Even though the system behaves under positive feedback, the kinetics of the etching process can readily be extracted from the hole characterization and its conversion into Faradaic yield.