Lifetime and resistivity modifications induced by helium implantation in silicon: Experimental analysis with an ac profiling technique

The effect of He ion bombardment on silicon based devices can be seen observing a change of their electric properties, that are relevant for their application, as well as through the modification of some local properties, in particular, resistivity and recombination lifetime, that in turn reflect the microscopic modification of their structure. The knowledge of the relation between these two aspects of the modifications induced by ion implantation would represent a powerful tool to design new devices and processes. This paper presents the results of an experimental analysis, where the modifications of the electrical properties of power devices, induced by helium implantation, were correlated to both the local recombination lifetime and the resistivity depth profile measured using a differential ac technique. Various measurements were performed for a wide range of temperatures to obtain information on the energy levels of the recombination centers which are responsible for the observed variations of the local properties of the device. The investigation was performed varying both the beam energy (from 3.5 to 5.8 MeV) and dose (1x108-5x1011 ions/cm2), providing a complete picture of the implantation effects. Finally, an application to the switching behavior of a fast recovery power diode is presented