Charge collection with a Microbeam : Prospect for determination of ion track profile

Introduction Single event effects (SEE’s) induced by heavy-ions from cosmic-rays are a major problem for the reliability of microelectronic devices in space environment. The energy deposited by a heavy-ion through the sensitive structure of a device produces, in a very short time, a dense concentration of electron-hole pairs along the ion trajectory. Generated carriers are collected by drift (if there is a local electric field) or by diffusion over hundreds of picoseconds. Previous works showed that differences in charge collection depend on the initial ion track structure [1][2]. Codes proposed by atomic physicists for ion tracks as TRKRAD [3] or TRIPOS [4] calculate a track profile which does not take into account the carrier thermalization and the recombination in the core of the track. For actual and future device generations, the knowledge of the ion track structure becomes necessary to correctly simulate the interaction within a device which has dimensions smaller than the ion track radius. Test structures were fabricated in order to determine experimentally the effective size of an ion track and the carrier density profile [5][6]. They consist either of Schottky-barrier junctions or PN junctions on a silicon line.