Titanium layers on aluminum bond pads: Characterisation of thin layers on rough substrates

A big challenge in the semiconductor industry is to control surface contamination, especially on bond pads, since they might take influence on bond wire adhesion and reliability behavior. The impact of fluorine and organic contamination on wire bonding is already well documented.1 Nevertheless, the influence of metal contamination has not yet been investigated in detail. As titanium contamination has been found on bond pad surfaces, owing to some manufacturing process steps, this presentation concerns preliminary investigations on titanium-contaminated aluminum structures. Titanium layers of different thicknesses in the nanometer range have been deposited by means of physical vapor deposition, either directly after aluminum deposition, or after an air break, in order to study their influence on wire bond quality in a systematic manner. Depth profile measurements have been carried out by means of TOF-SIMS. In order to study the oxide and the titanium distribution, those measurements have been performed in positive and negative modes. To overcome the big challenge to distinguish between the thicknesses of thin layers in the nanometer scale, depth profiling parameters were optimized regarding signal intensities. This work deals with our analytical results and shows the possibility to clearly identify nanoscale layers and interdiffusion areas between different materials by enhanced depth resolution. In the near future, we will quantitatively investigate the impact of different titanium contaminations on bond pads on the adherence of Al-wedge bonds. Copyright © 2010 John Wiley & Sons, Ltd.