Electrical Resistivity and Adhesion of Dilute Cu-Zn Alloy Films

Dilute Cu-TM alloy films (TM = Ni, Ti, Mn, Zn, Mg) were investigated in order to develop interconnect lines with low resistivity, high thermal stability and high adhesion to a glass substrate for the installation of an advanced thin film transistor (TFT)-liquid crystal display (LCD). We found that among these added impurities, Zn showed the lowest resistivity 2.8 mu Omega cm by adding less than 1 at% on annealing above 350 degrees C. Most of these dilute Cu alloy films except for Cu-Zn and Cu-Mn alloys show the formation of thermally grown hillocks on annealing above 300 degrees C. It was also found that the dilute Cu-Zn alloy films showed the highest adhesion to a glass substrate among present alloy systems. The high resolution EDS analysis of the cross section of the films after the 400 degrees C anneal shows not only a large segregation of Zn atoms at the interface between film and glass substrate, but also a relatively high concentration of Zn atoms at both free surface and grain boundaries. However, any precipitation of oxides, such as ZnO was not observed at the interface between film and glass substrate by using a high resolution cross-section TEM analysis. We conclude from these results that the segregation of Zn atoms in Cu alloy systems plays a large role not only to increase an adhesion to a glass substrate, but also suppress the formation of hillocks at elevated temperatures.