Properties of copper layers deposited by electroplating on an agglomerated copper seed layer

Abstract

This paper describes the properties and adhesion strength of electroplated copper layers deposited onto two different seed layers. In a thin (10 nm) seed layer, which we term seed layer A, agglomeration occurs across the full thickness of the layer and a stress free of lower stress seed layer is formed with an annealing at 400°C. A highly (111)-oriented copper conductive layer is the result of this electroplating strategy. The adhesion strength is so high (40 gf) that no peeling occurs during chemical mechanical planarization (CMP) in this layer. When the layer is electroplated onto a thick (100 nm) seed layer, which we term seed layer B, agglomeration only occurs at the interface with Ta barrier layer with this annealing. Although a smooth copper layer still remains at the surface, a weakly (111)-oriented copper layer is electroplated. The adhesion strength of this type of copper layer is as low as 10 gf so that peeling can easily occur both during annealing and CMP. Correlation is found between the critical pressure defined by the pressure occurring of the peeling in the copper layers during the CMP with adhesion strength.