A quantitative adhesion study between contacting materials in Cu damascene structures

A quantitative determination of the adhesion strength between contacting materials, relevant for Cu/low-k damascene technology, is presented. Shear testing is combined with finite element modelling (FEM) to determine the critical shear stress at an interface. The critical shear stress is the maximum allowable stress at that interface to avoid adhesive failure. The presence of a metallic barrier between Cu and a low-k dielectric, also required to avoid possible Cu diffusion, increases the adhesion strength. The adhesion strength between contacting materials, including a low-k, depends strongly on the chemical composition of the low-k and degrades when creating porosity in or fluorinating the low-k. A weak interface is found between an oxide and a low-k.