Using Azo As a Conductive and Adhesive Liner for through Glass Vias Filling By Cu Electroplating

Abstract

This study introduces a method using aluminum-doped zinc oxide (AZO) as a conductive and adhesive liner for through glass vias (TGVs) filling by Cu electroplating. AZO liner is formed on a glass surface by three steps: AZO sol-gel coating, sol-gel evaporation and annealing. AZO sol-gel evaporation was observed by thermogravimetry-differential thermal analysis (TG-DTA). Surface morphology was observed by OM and SEM, and crystallinity and grain size were measured by XRD. AZO sol-gel evaporation rate is key for forming a conformal AZO liner in TGVs. When AZO sol-gel coating was operated under the condition at lower evaporation rate, it would form thick and non-uniform liner and there was a risk of void formation after copper electrodeposition. On the contrary, when the AZO sol-gel coating was operated under the condition of ultrahigh evaporation rate, a thin and uniform AZO liner was formed on the sidewall of the TGVs. This phenomenon refers to the fast coffee ring effect in TGVs. Cu Electroplating was used after AZO liner was formed in the TGVs. This study combined an alkaline conformal copper plating bath with an acid button-up copper plating bath to fill the TGVs. AZO liner cannot only enhance the adhesive force between the deposited copper and the glass, but also play an important role for direct copper plating in TGVs.