Influence of current density on the adhesion of seedless electrodeposited copper layers on silicon

Abstract

Electrodeposition of metals directly on non-metal substrates without any seed layer reduces process steps; however, adhesion of the electrodeposited layer is a challenge. In this work, the influence of current density during seedless electroplating on the adhesion of Cu layers on Si substrates was investigated. Cu was electrodeposited on phosphorus-doped Si samples having different orientations in two stages. During the first stage, higher current densities were used for a few minutes to reach instantaneous nucleation and maximize the number of Cu islands on the substrate. The second stage had the goal of growing the nuclei previously formed. Therefore, lower current densities were used to create progressive nucleation. Adhesion values of Cu layers on Si were derived from scratch tests and tensile measurements. Higher adhesion was obtained either at higher current densities or at lower cathodic potentials at the beginning of potentiostatic or galvanostatic processes. To study the influence of hydrogen evolution on the adhesion of seedless electrodeposited Cu on Si, the transition time which indicates the moment when transferred charges are used to create hydrogen at the cathode, was determined experimentally. The transition time shows a strong dependence on current density. Therefore, control and optimization of adhesion by an appropriate choice of current densities within the two-stage process is possible.