Takashi Kawanoue

Electromigration‐induced void growth in bamboo structures

A novel resistometric technique enables the investigation of single void nucleation and growth induced by electromigration (EM) for aluminum (Al) lines having a perfect bamboo structure in comparison with single‐crystal Al lines. Fine tungsten (W) voltage probes were fabricated at every 4 μm along the Al line with grain sizes of 10 μm or more. Local electrical resistance changes have confirmed that a void nucleated only at the grain boundary and no damage appeared within the grains. The measured values of the local electrical resistance changes were converted to EM‐induced void growth rates. The vacancy flux was deduced from the void growth rate under the assumption that a vacancy volume is equal to the atomic volume. It has been clarified that the vacancy fluxes for a bamboo‐structured Al line were about one order magnitude smaller than the ideal vacancy fluxes in the Al lattice derived from the Nernst–Einstein relation. The vacancy fluxes for single‐crystal Al lines were also quantified under an acceler...

Single crystal aluminum lines with excellent endurance against stress induced failure

An excellent ability to withstand stress-induced failure and electromigration failure is demonstrated for single-crystal Al lines. In both single-crystal and polycrystalline Al lines, voids were surrounded by low surface energy planes, so that the shape of the voids would be affected by crystal orientation. The results suggest that single-crystal Al is a potential candidate for submicron lines in ULSIs.<<ETX>>

Improvement in the electromigration lifetime using hyper-textured aluminum formed on amorphous tantalum-aluminum underlayer

A new fabrication technique for hyper-textured aluminum (Al) films has been developed by using an amorphous tantalum-aluminum (Ta-Al) underlayer. The full width at half maximum (FWHM) value of the (111) rocking curve for Al film has been attained to be less than 1 degree. It has been clarified that the empirical relation between the electromigration (EM) lifetime of an Al interconnection /spl tau/ and the FWHM value /spl omega/ is described as /spl tausup /spl prop/spl omegasup -2/. This result has confirmed that a hyper-texture is a promising approach to withstand higher current densities required in future ULSIs.<<ETX>>

A newly developed model for stress induced slit-like voiding

Thermodynamic analysis of stress-induced voiding has indicated that a slit-like void is the origin of metal line open failures. Wedge-shaped voids nucleate initially at specific grain boundaries where

Double-Level Cu Inlaid Interconnects with Simultaneously Filled Via Plugs

A double-level Cu interconnection process for lower submicron generation ULSIs was developed. Cu interconnects were successfully formed by Cu/WSiN sputtering, XeCl excimer laser annealing and Cu/WSiN chemical mechanical polishing. The composition of the WSiN barrier metal was optimized to WSi0.6N and the diffusion barrier capability was confirmed by physical analyses and electrical measurements. The electrical resistivity of the inlaid Cu was 1.9±0.1 µ Ωcm and contact resistivity between the first-level Cu and the second-level Cu was (1.54–5.78)×10-9 Ωcm2. The electromigration lifetime of laser-annealed Cu/WSiN wiring was found to be one order of magnitude longer than that of previously reported Cu interconnects. The activation energy for electromigration was determined to be 1.1 eV.

Effects of aluminum texture on electromigration lifetime

A hyper-textured aluminum (Al) film has been fabricated by using a newly developed amorphous tantalum-aluminum (Ta-Al) underlayer. The full width at half maximum (FWHM) value of the (111) rocking curve of the Al film has been attained to be 0.5 degrees. It has been shown that the electromigration (EM) lifetime of Al interconnections increased inversely proportional to the square of the FWHM value. This lifetime improvement has been attributed to the reduction of the vacancy flux along the grain boundaries. The analysis of the grain boundary structure in the hyper-textured Al film with the transmission electron microscope (TEM) has revealed that the texture improvement not only eliminates the twist component of the boundary mismatch, but also controls the tilt one. It has been also clarified that the compressive stress relaxation and the hillock formation of Al film during the thermal cycling were restrained by the hyper-texture. This phenomenon has been well explained by the grain boundary diffusion suppr...

Reliability of single‐crystal aluminum lines and its limitation

The quantitative electromigration (EM) lifetime estimation for single‐crystal aluminum (Al) lines has been carried out for the first time. The lifetime limiting factor that degrades the excellent endurance against EM for single‐crystal Al lines has turned out to be the temperature difference between the line and the pad due to Joule heating by high current density. No voids were observed in the middle part of the line in accelerated test patterns for 15 hours at 283 °C even at a current density of 3.5×107 A/cm2. On the other hand, hillocks and/or extrusions were always observed in the line near the positive pad and voids in the negative pad. The voids, initially grown in the line near the negative pad, migrated and accumulated in the negative pad. Al atom flux divergence due to a large temperature difference near the line‐pad junction by Joule heating as large as 100 °C was the origin of the void and hillock formation. The Al atom flux in the line was calculated from the accumulated void volume with the t...

Investigation of Cu ion drift through CVD TiSiN into SiO2 under bias temperature stress conditions

Cu gate metal oxide semiconductor (MOS) capacitors with and without thin chemical vapor deposition (CVD) TiSiN diffusion barrier were subjected to bias temperature stress (BTS) conditions. Cu drift flux for the MOS capacitor with CVD TiSiN diffusion barrier was about one order of magnitude smaller than that without the diffusion barrier. The activation energy of the drift flux was larger by a factor of 1.5 than that without the diffusion barrier. Cu thermal diffusion in the CVD TiSiN is dominant for Cu ion drift into the plasma enhanced (PE)-CVD SiO2. The Cu concentration depth profile in SiO2 showed that the Cu dose in PECVD SiO2 under thermal stress is significantly smaller than that under BTS conditions.