The semiconductor industry is continuously shrinking device dimensions to optimize costs and product performances. As a consequence of this, the products become highly sensitive to minor process variations and to the presence of small defects. To come to a stable and yielding process a full comprehension of the root cause of electrical device failures is essential. Failing and defective devices -as revealed by electrical tests- need, therefore, to be subjected to a detailed physical characterization. This is why TEM (Transmission Electron Microscopy) is becoming widely used for process and localised defect characterisation. It is the only method that allows to obtain images with resolution at the atomic scale and to determine chemical composition by means of EDX (Energy Dispersive X-ray) or EELS (Electron Energy Loss Spectroscopy). Nevertheless, this technique is hampered by one important drawback: the sample preparation is delicate and time consuming because TEM observations require electron transparency and, therefore, very thin samples (about one hundred nanometers). This sample thinning can be achieved by e.g. polishing plus final Ion-milling or by FIB (Focussed Ion Beam) milling. The major benefit of using the FIB based technique is that it permits to localize precisely the area of interest. Today, three FIB-based methods are available: the 'conventional' technique, the ex-situ and the in-situ lift-out techniques. In this paper we present the lift-out techniques, their respective advantages and disadvantages and, through real case studies, how TEM and combined chemical analysis techniques can be used effectively to determine root causes of failures. (C) 2002 Elsevier Science Ltd. All rights reserved.
