A study of hillock suppression in Al alloy interconnections for liquid crystal displays

Hillock formation mechanism and hillock suppression by alloying Al films is summarized. The hillock growth occurs at elevated temperature and under compressive film stress by migration of Al atoms along grain boundaries to film surface. Microstructure and its change upon heating of Al films directly affect stress relaxation behavior, and strongly affect hillock formation behavior. Therefore, microstructural altering and stress relaxation controlling of Al films by alloying are effective in suppressing hillocks. It is confirmed that Al-Ta, Al-Ta-Si and Al-Nd alloy films have strong effect in suppressing hillocks, and are most appropriate materials for interconnections of liquid crystal displays.