PREFERENTIAL REACTION AND STABILITY OF THE AU-SN/PT SYSTEM - METALLIZATION STRUCTURE FOR FLIP-CHIP INTEGRATION

Thermal reaction of a metallization system consisting of Au-Sn solder, Pt/Ti barrier, and Au/Zn/Au contact layers formed on an InP substrate has been studied using Auger electron spectroscopy, scanning electron microscopy, and x-ray diffractometry. Upon heating to 400-degrees-C, no degradation of the Au/Zn/Au contact was noticed and moderate reaction was observed between Au-Sn and Pt. The reaction shows a characteristic feature of preferential Pt-Sn interdiffusion to produce an intermediate layer involving the PtSn phase. The effective diffusion coefficient exhibits an activation energy of 1.35 eV. The lifetime of this Pt barrier has been determined to be in excess of 10(8) h for 50-degrees-C, being sufficient for the application of this metallization structure in practical device and flip-chip integrated circuit fabrication.