Isothermal stress relaxation in Al, AlCu and AlVPd films

Mechanical stress and its relaxation in aluminum metallization in integrated circuits (IC) are a major concern for the reliability of the material. It is known that adding Cu improves the reliability but complicates plasma etching and increases corrosion sensitivity. The mechanical behavior of AlVPd, AlCu and Al blanket films is investigated by wafer curvature measurements. During thermal cycling between 50 degrees C and 400 degrees C the highest tensile stress is found in AlVPd. In a subsequent experiment, the cooling was interrupted at several temperatures to investigate the stress behavior during an eight hour isothermal treatment. Isothermal stress relaxation has been observed in the three types of films and is discussed.