Time-dependent series resistance and implications for voltage acceleration models in BEOL TDDB

Abstract

A continuous down-scaling of BEOL pitch for advanced process technologies has drastically increased the resistance of Cu interconnects, which brings up a concern of a series resistance effect or IR drop within metal electrode during high voltage TDDB stresses. For accurate TDDB lifetime projections at operating voltages, it is of a critical importance to understand the iR drop in BEoL devices under typically applied high voltage stresses to accurately estimate effective stress voltages and the voltage acceleration parameter of a chosen TDDB model. In this work, we present transient behavior of IV characteristics of BEoL dielectric material (k=2.55, SiCOH), a method of accurately calculating effective stress voltages resulting from time-dependent IR drop, successive breakdown characteristics of comb-serp device to explain the IR drop effect and comparison of breakdown characteristics of various devices possibly with and without IR drop to show that the impact of the IR drop on voltage acceleration parameter is negligible. Finally, our long-term TDDB results (> 2 years) of 64-pitch interconnect made of Cu/ULK (k=2.55, SiCOH) with IR drop corrections on high stress voltages show that the power law model best describes the voltage acceleration behavior of the ULK dielectric material used for our studies.