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0914-F06-07

Effect of Cu Migration in a Field Induced Dielectric Failure Sang-Soo Hwang, Sung-Yup Jung, and Young-Chang Joo School of Material Sci. & Eng., Seoul National University, San 56-1 Sillim-dong Gwanak-gu, Seoul, 151-742, Korea, Republic of

ABSTRACT Cu-migration-induced failure of inter-layer dielectric (ILD) was studied using timedependent dielectric breakdown (TDDB) test and 1-D FDM simulation. A metal-insulatorsemiconductor (MIS) structure with Cu electrode was used for the TDDB tests. 1-D FDM simulation was performed with consideration on the space-charge effect due to Cu ions that migrated into the dielectric. Our results suggest that, while the TTF’s obey the E model in the accelerating conditions, the deviation from the E model in the TTF’s may occur in the service conditions. Such dependence of TTF characteristics on E field range can be explained by the fact that migration of Cu is enhanced by an applied E field. INTRODUCTION Cu interconnects with low-k dielectrics are widely used to reduce R-C delay. However, migration of Cu into inter-layer dielectrics (ILD) has been known as a significant failure mechanism under bias-temperature-stress (BTS) conditions; the formation of conductive paths between anode and cathode leads to dielectric failure [1]. There have been a lot of researches on the failures due to intrinsic defects. Most failure mechanisms can be classified into either of the E-model or the 1/E-model according to the E dependence characteristics of times-to–failure (TTF’s). The E model presumes that the broken bonds, by dipole-dipole interaction, form the conductive paths [2]. On the other hand, the 1/E model explains dielectric failure using the anode hole injection model [3]. There are a few studies on the failures induced by extrinsic defects, e.g. Cu ions in the dielectric. McBrayer studied the kinetics of Cu ion migration in the dielectric under BTS conditions [4]. Wu [5] suggested an extrinsic E-model based on McBrayer’s theory [4], which concludes that dielectric failure is caused by field-induced Cu migration. The dielectric failure due to Cu migration in the dielectric can be explained using the E-model as well. In the high field range, the effect of electric field dominates over that of thermal diffusion. Thus the TTF’s of which dielectric failure is caused by Cu migration can be described using an extrinsic E model [5]. However, in the actual service conditions, the electric filed is low and it is expected that contribution of the electric field effect is reduced. Recently, the experimental results of TDDB test for very long test time under the low field range were reported that there was deviation in TTF’s from what the E model predicted in the low field range: the TTF’s in such a low field were fitted well using the √E model rather than using the E model [6]. This observation has critical importance, since the TTF’s in the service conditions that are extrapolated from the results in the accelerating condition based on the E model may severely underestimate the electrical reli