Showing papers by "Jay Im published in 2006"

Electromigration enhanced intermetallic growth and void formation in Pb-free solder joints

Abstract: A kinetic analysis was formulated for electromigration enhanced intermetallic evolution of a Cu–Sn diffusion couple in the Sn-based Pb-free solder joints with Cu under bump metallurgy. The simulated diffusion couple comprised the two terminal phases, Cu and Sn, as well as the two intermetallic phases, Cu3Sn and Cu6Sn5, formed between them. The diffusion and electromigration parameters were obtained by solving the inverse problem of the electromigration enhanced intermetallic growth, and they were compatible with the literature values. Finite difference method was applied to the whole simulated domain to solve for the mass transport kinetics within the intermetallic phases and across each interface of interest. Simulation showed that, when electromigration effect was absent (zero current), intermetallic growth followed a parabolic law, suggesting a diffusion controlled mechanism for thermal aging. However, under significant current stressing (4×104A∕cm2), the growth of the dominant intermetallic Cu6Sn5 cle...

Effect of barrier process on electromigration reliability of Cu/porous low-k interconnects

Abstract: Electromigration (EM) reliability of Cu/low-k interconnects with a conventional preclean-first process, and an advanced barrier-first process has been investigated. Compared with the preclean-first process, extrinsic early failures were not observed for the barrier-first process. This suggests that process-induced defects, which are the most probable cause for early failures, are significantly reduced for the barrier-first process. Transmission electron microscopy observation demonstrated a more uniform and thicker Ta barrier for the barrier-first process than the preclean-first process. This led to a higher (jL)c product, and prolonged the EM lifetime accordingly. In addition, a predeposited Ta barrier during the barrier-first process protected the mechanically weak low-k dielectrics from plasma etch damage, and a uniform via profile resulted. In contrast, the via opening at the top was found to be larger than that of at the via bottom for the preclean process. The uniform via profile is another advantag...

Oxidation of the TA Diffusion Barrier and Its Effect on the Reliability of CU Interconnects

Abstract: The oxidation of the Ta diffusion barrier and its effect on the reliability of Cu interconnects were investigated by high temperature storage (HTS) and via-to-line biased temperature stressing (BTS) tests. Cu/FSG, Cu/OSG, and Cu/porous low-k interconnects were investigated in vacuum (~ 1 torr), 0.1 atm air, and air. The exponential increase of resistance over the entire temperature range of the test was commonly found during HTS in via-chain test structures of all interconnects. It was different from typical stress migration behavior as the failure rate did not exhibit a peak at an intermediate temperature but increased exponentially with temperature. No voids were found in the failed samples that had resistance increases up to infinity. Instead, the Ta diffusion barrier was oxidized partially according to transmission electron microscopy/electron energy-loss spectroscopy (TEM/EELS) analysis. The oxidation of the Ta barrier at the via bottom was determined to be the cause of the electrical failure during HTS, which agreed with experimental results. During HTS tests, the Ta diffusion barrier was found to be more oxidized at the via sidewalls than at the M1 or M2 trench sidewalls. This oxidized Ta barrier at the via sidewalls was less protective. In the case of Cu/porous low k interconnects, Cu was found to diffuse out through the oxidized barrier at the via sidewalls, whereas Cu out-diffusion through the M1 or M2 trench sidewall was not noticeable. In via-to-line BTS tests, failure was also found to be caused by Cu out-diffusion/drift through the oxidized Ta diffusion barrier at the via sidewalls. The preferential oxidation of the Ta barrier at the via sidewalls and Cu out-diffusion through it suggests that the Ta barrier was more oxidizable and more permeable at the via sidewalls than at the M1 or M2 trench sidewall. Among the three kinds of interconnects used in this study, Cu/porous low-k was the most susceptible to the Ta diffusion barrier oxidation