POSTDEPOSITION 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 a ge-hardening thermal treatment of the deposited metals in the amorphou s state. For creating a copper layer of 10 mu m thickness at the top, both electrodeposition and physical vapour deposition (evaporation) me thods are applied to obtain different strip properties. Peel tests, wh ich can simulate the strip delamination process, are conducted to eval uate the strip-substrate bonding strength. A micro-mechanics analysis indicates that weak strip stiffness is a key cause for the frequent st rip-substrate separations. Consequently, the laminate composite system is heated and cooled after deposition under different treatment condi tions to strengthen the strip. The specimens are heated to a temperatu re of 220 to 400 degrees C, held there for a time and cooled quickly i n air or water. The strengthening effect of the amorphous metals is ob vious but complicated. The improved bonding strength will decrease aga in if the heating temperature is lower than 200 degrees C or the heati ng time is shorter than 50 min. At room temperature, indices of perfor mance 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 impr ovements of up to approximately 300% have been achieved according to p eel strength tests. The sticking strength becomes so high after the th ermal treatment that no part of a strip can initially leave its substr ate during the tests.