Oxygen Reactive Ion Beam Etching on Polyimide to Enhance Copper Film Adhesion

Polyimide(PI) films were modified by O2 reactive ion beam etching(RIBE) to make special surface features which enhance the adhesion of copper films. The top plane and the cross-sectional plane of PI films were changed to a grass-like structure and a plate-like structure, respectively. The reason for these surface morphological changes is presumably due to the structural inhomogeniety of PI. XPS studies show that the O2 RIBE oxygenates the PI, resulting in an increase in oxygen and a decrease in carbon and nitrogen. The adhesion of evaporated copper on the O2 RIBE modified PI was substantially increased. In this study, the maximum peel strength of modified PI, 70 grams/mm, is more than 25 times larger than that of the unmodified PI, 2.5 grams/mm. Two types of failure mechanisms were observed with various ion doses:adhesive failure at the Cu/PI interface and at very large doses cohesive failure at the roots of the thin and long grass blades of PI.