Effect of W addition for Cu diffusion barrier property of electroless CoB films formed on SiO2

Abstract

Electroless plated film has an excellent property of conformal deposition on dielectric under layers. For this reason, electloless plated (ELP) barrier metals such as and CoB and CoWB alloys are promising to use as a barrier layer which prohibit Cu atom diffusion into SiU2 and Si in Through-Silicon Via (TSV) of 3-D integration. in this study, we evaluated Cu inter-diffusion properties after annealing at 400 °C against electroless plated CoB, and CoWB barrier layers with different W content formed on thin-SiU2/Si substrate. We changed W-content of CoWB film by controlling plating bath composition. The CoB plated film on SiU2 had almost amorphous structure even after 400 °C annealing, while CoWB films showed very weak Co (002) diffraction peak which suggested Co nano-crystals existed in amorphous matrix, and this peak grew slightly after 400 °C annealing. SIMS depth profile and cross-sectional TEM analysis of the stacked films of TiN/Cu/ELP Co-alloy/thin SiU2 (5nm)/Si suggest that CoWB film with larger W content has better suppression effect of Cu inter-diffusion irrespective of nano-crystalline structure. It is demonstrated that ELP-CoWB having large amount of W is promising technology as a barrier layer of high aspect TSVs for 3-dimensional integration.