LOCALIZED MONITORING OF ELECTROMIGRATION WITH EARLY RESISTANCE CHANGEMEASUREMENTS

A new approach is presented in order to study the local effects of ele ctromigration in metallisations. So-called localized electrical resist ance measurements allow us to detect and localize the formation of ind ividual 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 distanc es on the test structure and by measuring the resistance drift of each line segment. Through the use of such a multi-voltage probe (MVP) tes t structure, the sensitivity of the electrical resistance to the prese nce of defects is strongly increased. By comparing the observed electr ical resistance drift results with the corresponding SEM micrographs? important conclusions can be drawn concerning the nature of the resist ance changes. With finite element calculations a quantitative interpre tation is obtained of the observed local resistance changes. An additi onal feature of localized electrical resistance measurements is the po ssibility to determine the actual temperature profile present in a tes t strip at the beginning of a current stress experiment, i.e., prior t o failure formation. (C) 1998 Elsevier Science Ltd. All rights reserve d.