Hisashi Kaneko

Electromigration in a single crystalline submicron width aluminum interconnection

Electromigration properties in a single crystalline submicron width aluminum interconnection formed on Si(111) have been examined by resistance change measurements and in situ observations using scanning electron microscopy. It was observed that single crystalline aluminum has an extremely high resistance to electromigration‐induced open circuit failures, when compared to polycrystalline copper and aluminum. The mechanism for the high resistance is considered to be a large activation energy, resulting from lattice diffusion. A tendency for void formation to become parallel to the longitudinal direction of the interconnection assisted the life time prolongation.

Electromigration‐induced abrupt changes in electrical resistance associated with void dynamics in aluminum interconnections

Electromigration‐induced failure mechanisms were investigated by means of extremely sensitive resistance change measurements and simultaneous observations using scanning electron microscopy. Abrupt changes in resistance (ACRs), classified into three types: downward steps, upward steps, and oscillations, were found to occur frequently during the dc current stressing test. It was conspicuously observed that there was a rapid void annihilation associated with an abrupt increase in resistance, and a rapid void formation with a decrease in resistance. ACRs are considered to be caused by a rapid change in the number of excess vacancies concomitant with void annihilations or formations. The thermodynamical analysis on the stability of a void strongly suggests that the change of a local stress from tensile to compressive causes a rapid annihilation of voids, and the opposite one causes a rapid formation. Temperature dependence of the intensity of ACRs exhibited an activation energy of 0.43 eV, which implied that ...

Stress-induced voiding phenomena for an actual CMOS LSI interconnects

Stress induced voiding (SIV) phenomena in Cu damascene interconnect has been studied in detail considering the actual CMOS LSI design for the first time. In order to understand the SIV mechanisms, the test structures were designed to monitor the interconnect pattern dependency, the additional via effectiveness. The SIV in wide metal can be explained by considering effective diffusion area. Also, the SIV occurred in narrow metal line if it has wide metal reservoir, and this is explained. It has been also found that the SIV failure has been drastically reduced by lowering the via anneal temperature.

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

Influence of substrate- and atmospheric-temperatures on diamond deposition

Abstract Diamond thin films have been formed on molybdenum substrates with a mixture of methane and hydrogen gas using the electron-assisted chemical vapor deposition (EACVD) method. The surface morphology, crystal structure and composition of the films obtained were characterized by scanning electron microscopy, reflection high energy electron diffraction and secondary ion mass spectrometry. The experimental results revealed that substrate heating is necessary to eliminate the hydrogen atoms occluded into the film during the course of diamond deposition. The hydrogen is frozen in the film without the substrate heating. This may prohibit the rearrangement of the carbon atoms in the film and will produce an amorphous film.

Impact of Residual Impurities on Annealing Properties of Vacancies in Electroplated Cu Studied Using Monoenergetic Positron Beams

Positron annihilation was used to probe vacancies in Cu films deposited by Ta/SiO2/Si using electroplating and sputtering techniques. During room temperature grain growth (i.e., self-annealing) of the Cu films, two different types of vacancies (small vacancy clusters such as divacancies and large vacancy agglomerates) were introduced into grains; the formation of such defects was enhanced by residual impurities. For electroplated Cu, isochronal annealing experiments revealed further agglomeration of vacancies when annealing was done below 300 °C, and these agglomerates started to dissociate above 350 °C. The effect of impurities on the vacancy agglomerates disappeared in the defect recovery stage (≥350 °C).

Electromigration induced aluminum atom migration retarding by grain boundary structure stabilization and copper doping

Abstract In order to clarify the relationship between Al line reliability and film microstructure, most notably grain boundary structure, we have tested three kinds of highly textured Al lines, namely a single-crystal Al line, a quasi single-crystal Al line and a hyper-textured Al line. Consequently, it has been shown that these kinds of lines have excellent endurance against electromigration (EM), compared with conventional Al lines deposited on TiN/Ti and SiO2. The improvement of Al line reliability is attributable to the following factors; firstly, homogeneous microstructure and high activation energy, 1.28 eV, of the single-crystal Al line (ω=0.18°); secondly, subgrain boundaries, consisting of dislocation arrays found in the quasi single-crystal Al line (ω=0.26°), have turned out to be no more effective mass transport paths because dislocation lines are perpendicular to the direction of electron wind; finally, the decrease of the (1 1 1) full width at half maximum (FWHM) value promotes the formation of subgrain boundaries and low-angle boundaries, which have small grain boundary diffusivity, as revealed by the detailed orientation analysis of individual grains in the hyper-textured line (FWHM=0.5°) formed by using an amorphous Ta–Al underlayer (Toyoda H, Kawanoue T, Hasunuma M, Kaneko H, Miyauchi M. Proc. 32nd Ann. Int. Reliab. Phys. Symp., IEEE, 1994;178). Moreover, the diffusivity reduction and the uniformity of atomic flux result in the suppression of void/hillock pair in the Al lines. It has been clarified that a FWHM value is a useful criterion of reliability for an interconnection. Also, the Cu doping effect against EM endurance by using Cu implantation of the single-crystal Al lines has been examined. It has been clarified that EM lifetime is lengthened by about one order of magnitude for the Cu concentration of 0.1 at% in spite of almost the same diffusion coefficients. Moreover, the incubation time for a void nucleation has been observed even in the case of a pure-Al line. Thus, in accordance with the stress evolution model, it is concluded that the mechanism of lifetime improvement by Cu doping is such that critical stress for EM void nucleation is increased by the Cu doping. These results have confirmed that control of texture and/or grain boundary structure so as to suppress EM induced metal atom migration is a promising approach for the development of Al lines and Cu lines capable of withstanding the higher current densities required in future ULSIs.