Compressive stress relaxation through buckling of a low- k polymer-thin cap layer system

The thermomechanical stability of a system composed of a metallic cap layer on top of a low-k thermosetting polymer film is investigated. It is observed that, when metal layers with high compressive stresses are used, a stress relaxation takes place during thermal anneal at temperatures above 300 °C through buckling of the two-layer system (wrinkling on rigid base). When designing low-k films for interconnects, this should be considered through a careful analysis of structural stability. The onset of this instability is allowed by the high compliance of the polymeric film, due to its transition from elastic to viscoelastic behavior through creep phenomena. This mechanism is more pronounced when a polymer film with 20% subtractive porosity is used.