Evidence of roughness distributions and interface smoothing in Co/Cu multilayers deposited under energetic particle bombardment

The interfacial structure of Co/Cu multilayers deposited under energetic particle bombardment is investigated using x-ray reflectivity. The energetic bombardment is varied by controlling the ion bombardment of the growing film. Specially modified unbalanced magnetron sources are used in collaboration with bias sputtering techniques in order to independently vary both the ion flux and average ion energy of the bombardment. Quantitative analysis of the specular reflected intensity reveals the existence of variations of the interface roughness in multilayers deposited with high applied negative biases of 200 V, such that the interfaces become smoother towards the free surface. A maximum smoothing effect is observed for films deposited with the highest available levels of ion flux. A static interface roughness is observed when applied biases of < =50 V are applied.