Passivation Materials for a Reliable Fine Pitch RDL

Even if polymers are used for decades in electronics and microelectronics, one of the primary drawbacks is their susceptibility to moisture uptake. Moisture penetrating into polymers reduces their mechanical and electrical performances and consequently, moisture becomes a reliability issue for the RDL level. This paper presents results which highlight the need of choosing the right integration scheme in addition to the right polymer to ensure steady electrical performances of the Cu RDL level. The reliability studies using high temperature storages demonstrate that the main moisture diffusion path is through the polymer itself and the use of a bilayer (inorganic/organic) as passivation layer seems to be the best choice to minimize the moisture permeation. In addition, we have identify the failure modes, due to the electromigration phenomenon in the Cu RDL level, as being the grain boundaries and the Cu/SiN interface.