Suppression of Stress-Induced Voiding by Controlling Microstructure of Cu Electroplated Films

Abstract

In advanced LSI devices, the filling capability for the electroplating (ECP) process, impurities in Cu film, and grain growth after ECP are important properties of Cu interconnect reliability. It has been reported that the Cu grain growth depends on the ECP-Cu film characteristics and the annealing conditions. In this study, we focus on the deposition thickness of ECP-Cu films to control their microstructure. It is revealed that a thicker ECP-Cu film enlarges the Cu grain size and reduces the number of small grains. It is also revealed that Cu grains in a wide line with a thicker ECP-Cu film are larger, leading to reliability improvement. A film with larger grains has fewer grain boundaries and fewer diffusion paths of vacancies, and a film with fewer small grains has a decreased number of vacancies. As a result, stress-induced voiding phenomena are apparently suppressed by increasing the thickness of deposited ECP-Cu film.