Post-deposition thermal treatments for improving the interconnection strength of a Ti-W/Au/Cu bonding system

The bonding combination of Ti-W/Au/Cu laminate strips deposited on an SiO₂/Si passivated substrate is strengthened through post-deposition age-hardening thermal treatment of the deposited metals in the amorphous state. For creating a copper layer of 10 m thickness at the top, both electrodeposition and physical vapour deposition (evaporation) methods are applied to obtain different strip properties. Peel tests, which can simulate the strip delamination process, are conducted to evaluate the strip-substrate bonding strength. A micro-mechanics analysis indicates that weak strip stiffness is a key cause for the frequent strip-substrate separations. Consequently, the laminate composite system is heated and cooled after deposition under different treatment conditions to strengthen the strip. The specimens are heated to a temperature of 220 to 400C, held there for a time and cooled quickly in air or water. The strengthening effect of the amorphous metals is obvious but complicated. The improved bonding strength will decrease again if the heating temperature is lower than 200C or the heating time is shorter than 50 min. At room temperature, indices of performance for strip-substrate bonding strength such as average peel force, peel energy and peak peel load continuously vary within approximately 100 h, depending upon the heating treatment history. Significant improvements of up to approximately 300% have been achieved according to peel strength tests. The sticking strength becomes so high after the thermal treatment that no part of a strip can initially leave its substrate during the tests.