In nano-technology, new reliability issues and failure mechanisms are anticipated due to the small dimensions approaching the molecular or atomic scale. As an example, the Empa reliability centre started a project investigating the dependability of thin dielectric layers (SiO2) as used in CMOS technology between the poly-silicon (gate) and the active channel of the device. Reduced dielectric thickness improves device performance as speed, however increases the electric field reducing the useful product operating lifetime. Technology will reach a layer thickness 1 or 2 nm (nano meters) within the next few years, where a further thickness scaling will not be possible due to leakage current and reliability limitations. Alternative, high-k dielectric materials are currently under investigation internationally.

The infrastructure available for this project at the Empa reliability centre comprises shielded 8" wafer prober together with high resolution leakage current measurement equipment (as the well-known HP4140B pA-Meter) allowing a measurement resolution of 0.1 pA (pico-Ampère). Constant voltage and constant current stress testing is implemented, allowing TDDB (time dependent dielectric breakdown) experiments. Data analysis based on the Weibull distribution ("statistical modelling") allow lifetime prediction. New failure modes and failure physics are investigated in this project, using the vast knowledge and experience available in the literature as starting point. First results have been published on the Integrated Reliability Workshop 2002 [1].

Physical modelling of failure mechanisms will be based on both electrical testing and physical failure analysis. EMPA reliability centre’s FIB (focussed ion beam) based sample preparation techniques allow the analysis of failures in the TEM (transmission electron microscope). A new TEM-lamella preparation technique has been developed [2]. As an example, a TEM bright field image of a cross section of an MOS transistor is given in Fig. 1. In addition, the EMPA reliability centre has advanced defect localisation techniques available like emission microscopy, OBIRCH (optical beam induced resistance change detection), and others used for failure analysis of microelectronic circuits and devices, offered as service by the EMPA reliability centre.

Contact: Dr. Urs Sennhauser

[1] J.C. Reiner: "A systematic leakage current analysis of gate oxide soft breakdown", 2002 IEEE International Integrated Reliability Workshop - Final Report.
[2] J.C. Reiner, P. Gasser, U. Sennhauser: "Novel FIB-based sample preparation technique for TEM analysis of ultra-thin gate oxide breakdown", Microelectronics Reliability. vol.42, no. 9-10; Sept.-Oct. 2002