Reducing the electrodeposition time for filling microvias with copper for 3D technology

Abstract

We present two approaches to reduce the process time needed for filling vias of 5 mum diameter and 25 mum depth with copper by electrodeposition. In the first approach, the effect of model additives on the filling of vias with electroplated copper was investigated as well as the influence of the applied current density on the filling process. The variation of the concentration of leveler and accelerator additives was investigated. Their influence on the void-free filling of such vias was determined. A high leveler concentration allowed to achieve a void-free fill. The copper deposited on the top surface was in the range of 2.5 mum. The filling was completed within 45 minutes. The filling time could even be further reduced to 25 minutes by introducing a waveform with two galvanostatic steps. The second approach demonstrates void-free via filling with copper electrodeposition at the top of the wafer surface blocked with self-assembled monolayers of octadecanethiol. With thin Ta-films deposited at the top surface before electrodeposition is started, almost no copper was deposited at the top surface as well. The vias were filled within 30 minutes when the top surface was completely blocked.