Use of electron beam position modulation in Auger depth profile analysis

Abstract

Auger analysis combined with ion etching in the scanning Auger microprobe (SAM) provides ‘‘three-dimensional’’ composition information not readily obtainable from other analytical methods. As this technique is being applied to the analysis of microelectronic devices with increasingly smaller dimensions, two major limitations became evident: (1) features of interest in microelectronic circuits are often comparable in size to the beam diameter of commercial Auger microprobes and (2) the electron beam tends to drift about on the specimen surface because of mechanical instability and differential thermal expansion. We describe a technique that will reduce the error and uncertainty caused by beam instability. In our technique, the analyzing beam is scanned repetitively across the feature to be profiled and the Auger signal is synchronously detected at the scan frequency. This position modulation technique allows a tradeoff between depth resolution and sensitivity on the one hand and drift in spatial position of the analyzing electron beam. Position modulation is particularly suited to the analysis of microelectronic devices (e.g., microwave field effect transistors), where the dimensions of features of interest are comparable to the electron beam diameter.