Reliability study on the via of dual damascene copper interconnects.

摘要

In this dissertation, reliability of the via of dual damascene Cu interconnects was investigated using electromigration (EM) early failure, high temperature storage (HTS), and via-to-line biased temperature stressing (BTS).; The major causes of EM early failures were observed to be reduced thickness and rough surface of the Ta diffusion barrier at via sidewalls. EM voids were observed at the interface of Cu/Ta barrier at the via sidewall where Ta was very thin while no voids were found at the interface in trench lines where Ta was thicker. The preferential void formation suggests that the very thin Ta diffusion barrier was defective. It seems that defects of the interface of Cu/thin Ta diffusion barrier accelerated diffusion of Cu at the via sidewall, leading to EM via voiding. In addition, rough surfaces of Ta diffusion barriers at the via sidewall induced EM early failures by fast void movement from the cathode end down to the via bottom. It was postulated that process-induced defects related with rough surfaces of non-intact Ta which was deposited on plasma-damaged low k were the main cause of the strong mode-induced early failure.; Both intrinsic and extrinsic SM behaviors were investigated. The intrinsic SM was the typical stressmigration behavior governed by two opposing factors: diffusivity of Cu and tensile stress of interconnects. The extrinsic SM mode was different from the intrinsic SM in that the failure rate was exponential with temperature without exhibiting a peak rate at a certain temperature. According to atomic number contrast of TEM micrographs and core loss and low loss nano-beam EELS analyses, the extrinsic SM was the result of oxidation of the Ta diffusion barrier.; Via failures caused by Cu out-diffusion through the Ta diffusion barrier at the via sidewall were studied in terms of via-to-line BTS and Cu oxidation. Unlike normal BTS failures due to Cu diffusion along the dielectric/capping layer interface, the weak Ta diffusion barrier at the via sidewall incurred fast Cu out-diffusion through it, reducing the BTS lifetime. Among the structures studied, Cu/porous low k was the weakest against the via-to-line BTS and oxidation of Cu.