A photoinduced confined etching system was used for the unstressed chemical planarization of Cu. Cu deposits were found on the surface of TiO2 nanotubes of the tool during the photoinduced confined etching of the Cu workpiece. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy were used to analyze the morphology and composition of the Cu deposits, and the mechanism of the photodeposition of Cu in the micro/nanoscale liquid layer between the tool and the workpiece was investigated. Moreover, a simulated cupric solution was used to study the effect of the Cu deposits during the photoinduced confined etching. Several routes including stirring and complexing agent were used to investigate the inhibition of Cu deposition on the surface of TiO2 nanotubes and the simultaneous effect on the etching of Cu workpiece. The results showed that the Cu deposits enhanced the photocatalytic performance of TiO2 nanotubes, but the mechanism of enhancement changed with the increase in Cu deposits. Inhibition of Cu deposition by improving mass transfer can lead to the increase in the etching of Cu; addition of complexing agent combined with enhanced mass-transfer can inhibit Cu deposition, while improving the planing effect. Thus, the choice of inhibition methods and conditions should balance the effect of the micro/nano liquid layer between the tool and workpiece on multiple chemical reactions and mass transfer processes. The results provide an important guiding significance for further regulation and optimization of the photoinduced confined etching system.