Localized monitoring of electromigration with early resistance change measurements

A new approach is presented in order to study the local effects of electromigration in metallisations. So-called localized electrical resistance measurements allow us to detect and localize the formation of individual voids and hillocks in metallisation lines submitted to current and temperature stress. Localized electrical resistance measurements are performed by adding a number of voltage terminals at equal distances on the test structure and by measuring the resistance drift of each line segment. Through the use of such a multi-voltage probe (MVP) test structure, the sensitivity of the electrical resistance to the presence of defects is strongly increased. By comparing the observed electrical resistance drift results with the corresponding SEM micrographs? important conclusions can be drawn concerning the nature of the resistance changes. With finite element calculations a quantitative interpretation is obtained of the observed local resistance changes. An additional feature of localized electrical resistance measurements is the possibility to determine the actual temperature profile present in a test strip at the beginning of a current stress experiment, i.e., prior to failure formation. (C) 1998 Elsevier Science Ltd. All rights reserved.