Metal bonding strength in low-temperature processed titanium using atomic force microscopy with single-wall carbon nanotube tip

Abstract

We report the development of a Ti-Ti bonding process at a low bonding temperature below 200 degrees C using chemically surface-activated Ti thin films and a reliable evaluation method for measuring the Ti-Ti bond strength by means of atomic force microscopy (AFM). Using Ti as an interlayer enables void-free bonding because Ti exhibits fast diffusion and oxide solubility. On the other hand, wafer bonding is an important processing step for 3D circuit integration that requires a high reliability of the process. However, the reliability of bonding-strength values obtained by employing conventional measurement devices is limited by comparably large measurement errors and restricted the availability of suitable sample material. In this study, the use of AFM to measure the bonding strength is proposed. The interfacial bonding properties depend on the Ti deposition parameters. A bonding temperature of 200 degrees C was found to be appropriate for the development of a low bonding temperature wafer-bonding process. The pretreatment methods like plasma activation and chemical activation at 200 degrees C result in a Ti bonding strength of approximately 8.22 J/m(2), sufficient for applications in 3D circuit integration. ((c) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)