Abstract
With the development of intelligent electronic products, usage of fine-pitch interconnects became mainstream in high performance electronic devices. Electrochemical migration (ECM) of interconnects would be a serious reliability problem under temperature, humidity and biased voltage environments. In this study, ECM behavior of nanopaste Ag interconnects with pitch size from 20 um to 50 um was evaluated by thermal humidity bias (THB) and water drop (WD) tests through in-situ leakage current versus time (CVT) curve. The results indicate that the failure time of ECM in fine-pitch samples occurs within few seconds under WD test and it increases with increasing pitch size. The microstructure examination indicates that intensive dendrite formation of Ag through the whole interface was found to bridge the two electrodes. When samples tested in the THB test, the CVT curve exhibits two stages, incubation and ramp-up stages. Intensive dendrite formation was only observed at the protrusion of Ag interconnects due to the concentration of electric field at the protrusion of Ag interconnects. To understand the effect of chloride pollution in ECM behavior, solutions of 10 mS/cm NaCl、10 mS/cm HCl、1000 μS/cm NaCl and 1000 μS/cm HCl was used to conduct the water drop test. No dendrite was observed, however another failure mechanism caused by silver chloride may lead to open circuit. Also, this study proposed one of the approaches to prevent ECM failure by surface treatment after sample preparation. 10 mM ethanolic solutions of 1-Dodecanethiol was used to treat the samples after preparation to form Self-Assembled Monolayers(SAMs), which would act as the protective thin film for ECM failure. In WD test, the time to failure was increased to about 3~5 times longer while in THB test, it was about two times longer.