Effects of polymer/metal interaction in thin-film multichip module applications

An investigation was conducted to examine the effects of different polyimide/metal combinations on structures similar to those used in thin-film multichip module applications. Three different metal structures and three commercially available spin-on polyimide materials which possess different molecular structures were examined. Transmission electron microscopy was used to study the polyimide/metal interfaces. Measurements of the transmission characteristics of line structures fabricated using the different metal/polyimide combinations were compared. It was found that the extent of interaction of polyimide with copper is dependent upon the type of polyimide used. Dupont 2611D polyimide showed the least amount of interaction with only a small band of precipitates present ~5 kÅ from the copper/polyimide interface, which do not affect the electrical transmission characteristics of lines spaced 22 μm a part. The use of an electrodes nickel layer on copper to retard copper/polyimide interaction from occurring during the curing cycle of the polyimide was found to be effective. However, increased loss of transmission at high frequencies and narrow spacing was seen for nickel-clad lines embedded in Dupont 2611D polyimide. Since nickel is a magnetic material, this increase in loss may be due to natural inductance from the nickel present in neighboring lines