Adhesion improvement for polymer dielectric to electrolytic-plated copper

Copper is one of the common metals used in the semiconductor backend process and wafer level packaging. A photo definable polymer layer is usually used to passivate the Cu metal. Acceptable adhesion between the polymer layer and Cu is a very important factor to achieve high reliability for the IC component. The purpose of this paper is to investigate how to improve the adhesion strength between spin-on polymer dielectric material and electrolytic-plated Cu. Because adhesion strength is affected by the type of metal surface treatment prior to polymer coating, it is important to find a practical method for Cu surface treatment wafer process. Three types of treatment methods, including plasma, thermal, and wet process, were tried on the plated Cu surface. X-ray photoelectron spectroscopy (XPS) results are reported for the surface properties after treatment. Adhesion strength between the polymer layer and the Cu surface is reported as measured by manual tape, nano-indentation scratch, and four-point bending methods. Our results show that cleaning the Cu surface with dilute acetic acid significantly increases the adhesion between Cu and the polymer layer. We also report results for the change in Cu surface properties as a function of time after clean.