Investigation of the Ti‐Pt Diffusion Barrier for Gold Beam Leads on Aluminum

Abstract

In order to avoid Al‐Au interactions and to ensure the electrical and mechanical stability of the Au beam leaded structures using Al metallization, a Ti‐Pt diffusion barrier between Al and Au has been investigated. Ti and Pt films of different thicknesses were employed as diffusion barriers. The resulting Al‐Ti‐Pt‐Au thin film sandwich structures were aged at temperatures in the range of 300°–500°C to evaluate the effectiveness of the barrier in preventing Al‐Au interaction. The interaction was followed by use of optical and electron microscopy, x‐ray diffraction, and sheet resistance measurements. It was found that metallurgical interactions in these structures occurred at preferential sites which were shown to be hillocks in Al. On continued aging, reaction spread around these sites and finally covered the entire surface. The number of such reaction sites increased with decreasing barrier metal thickness and with increasing time and temperature of anneal. The reaction was considerably inhibited (i) by annealing Al at 450°C for hr prior to barrier metallization and (ii) by using at least 2000Å each of Ti and Pt in the barrier. An understanding of the effectiveness and need of a 2000Å Ti‐2000Å Pt diffusion barrier between Al and Au was obtained by additional studies of the metallurgical interactions induced in Al‐Pt, Al‐Ti, and Al‐Ti‐Au thin film sandwich structures by aging at temperatures in the range of 200°–500°C. Ti is required to cover Al well so as to prevent Al‐Pt interactions and Pt is required to prevent Ti‐Au interactions caused by diffusion of Au through Pt to Ti.