Electroplating Cu on ALD TiN for high aspect ratio TSV

Abstract

TSV technology is one of the important methods to realize interconnection for 3D Integration and 3D-IC. Via filling will become more challenging for TSV with high aspect ratio. Atomic Layer Deposition (ALD) is a deposition method with great potentials to form high quality diffusion barrier layer for via filling as thin film made by ALD has excellent ability of step coverage, continuity, conformity, and lower deposition temperature. In this study, TiN thin film was prepared by ALD method for a TSV structure with aspect ratio of 10∶1. Due to the good electrical conductivity, TiN could also serve as seed layer for electroplating Cu. Pulse plating was applied for Cu filling. Different current density and electroplating time were examined to obtain the optimal parameters for Cu electroplating. The result showed that current density forward 0.8ASD and reverse 0.2ASD is the optimal plating parameters. Barrier effect of the ALD TiN was analyzed by Augur Electron Spectroscopy after annealing at different temperatures. Traditional sputtering TiW/Cu barrier/seed layer was also evaluated as reference. Results showed that electroplated Cu on the ALD TiN layer would reach higher filling ratio than TiW/Cu layer. The diffusion depth of Cu in TiN is similar to that in TiW/Cu. It can be concluded that ALD TiN is a good candidates in TSV for its excellent properties to work as seed layer and barrier layer.