Masataka Hasegawa

Prediction of electromigration failure in passivated polycrystalline line

Mechanical stress or atomic density distribution in passivated metal lines is induced by electromigration, and plays an important role in the mechanism of electromigration damage. Recently, a governing parameter for electromigration damage in passivated polycrystalline lines, atomic flux divergence (AFDgen*), was formulated by adding the effect of the atomic density gradient to the governing parameter for electromigration damage in unpassivated polycrystalline lines, AFDgen. The latter has already been utilized to construct a prediction method for electromigration failure in unpassivated lines, as the first step toward the development of a practical method. In this article, a prediction method for electromigration failure in a passivated polycrystalline line is proposed using AFDgen*. It is shown that the proposed method is able to predict the failure location as well as the lifetime of the passivated polycrystalline lines. Both the lifetime and the failure location in a passivated polycrystalline line ar...

Silicon nanocrystals with high boron and phosphorus concentration hydrophilic shell—Raman scattering and X-ray photoelectron spectroscopic studies

Boron (B) and phosphorus (P) codoped silicon (Si) nanocrystals, which exhibit very wide range tunable luminescence due to the donor to acceptor transitions and can be dispersed in polar liquids without organic ligands, are studied by Raman scattering and X-ray photoelectron spectroscopies. Codoped Si nanocrystals exhibit a Raman spectrum significantly different from those of intrinsic ones. First, the Raman peak energy is almost insensitive to the size and is very close to that of bulk Si crystal in the diameter range of 2.7 to 14 nm. Second, the peak is much broader than that of intrinsic ones. Furthermore, an additional broad peak, the intensity of which is about 20% of the main peak, appears around 650 cm−1. The peak can be assigned to local vibrational modes of substitutional B and B-P pairs, B clusters, B-interstitial clusters, etc. in Si crystal. The Raman and X-ray photoelectron spectroscopic studies suggest that a crystalline shell heavily doped with these species is formed at the surface of a cod...

Governing parameter for electromigration damage in the polycrystalline line covered with a passivation layer

A governing parameter, called AFDgen*, which reflects electromigration damage in a polycrystalline line covered with a passivation layer is proposed. The formulation is based on the parameter AFDgen previously introduced in our studies. With the help of AFDgen we can calculate the atomic flux divergence due to electromigration by considering two-dimensional distributions of current density and temperature and also by simply considering the microstructure of polycrystalline lines and bamboo lines. AFDgen has been identified as a governing parameter for electromigration damage in unpassivated polycrystalline lines and bamboo lines through experimental verification. As the first step in the development of a practical and universal prediction method for electromigration damage, we treated metal lines not covered with a passivation layer. On the other hand, metal lines used in packaged silicon integrated circuits are covered with passivation. Electromigration induces a mechanical stress (atomic density) gradient in such lines. This gradient plays an important role in the mechanism of electromigration damage. The new parameter proposed here, AFDgen*, includes the effect of the atomic density gradient. We develop also an AFDgen*-based method for determination of film characteristics. This method is applied to both covered and uncovered metal lines made of the same Al film. The film characteristics of both line types are obtained experimentally. Based on a discussion about the validity of the obtained characteristic constants, we were finally able to conclude that the AFDgen* parameter and the proposed method for deriving film characteristics are useful.A governing parameter, called AFDgen*, which reflects electromigration damage in a polycrystalline line covered with a passivation layer is proposed. The formulation is based on the parameter AFDgen previously introduced in our studies. With the help of AFDgen we can calculate the atomic flux divergence due to electromigration by considering two-dimensional distributions of current density and temperature and also by simply considering the microstructure of polycrystalline lines and bamboo lines. AFDgen has been identified as a governing parameter for electromigration damage in unpassivated polycrystalline lines and bamboo lines through experimental verification. As the first step in the development of a practical and universal prediction method for electromigration damage, we treated metal lines not covered with a passivation layer. On the other hand, metal lines used in packaged silicon integrated circuits are covered with passivation. Electromigration induces a mechanical stress (atomic density) gradie...

Prediction of Electromigration Failure in Passivated Polycrystalline Line Considering Passivation Thickness

It is known that the lifetime of the passivated metal line varies depending on kind and thickness of the passivation layer. The appropriate consideration of the effect of passivation on electromigration damage makes it possible to evaluate the reliability of the metal line with choosing kind or thickness of the passivation. This paper is focused on the effect of passivation thickness on the failure prediction. The failure prediction considering the passivation thickness is shown. First, the film characteristic constants depending on the passivation thickness are experimentally determined in the lines with three kinds of passivation thickness. Next, by extrapolating the obtained dependencies, the characteristic constants are determined to predict the lifetime of the line covered with the thicker passivation than that employed in the experiment, and the lifetime is predicted by the reliability evaluation method based on the numerical simulation.Copyright

Expression of a Governing Parameter for Electromigration Damage on Metal Line Ends

Recently, a governing parameter for electromigration damage, AFD* gen , was identified and, utilizing the parameter, a prediction method of electromigration failure was developed for the passivated polycrystalline line. The parameter AFD* gen was formulated considering the divergence of atomic flux due to electromigration in grain boundary network, and the boundary condition of metal line ends was not taken into account. So far, therefore, failure prediction was exclusively done for the metal line connected by electric-current input/output pads at both ends, not for the line connected by vias at both ends. It is known that there is threshold current density, jth , below which no electromigration damage appears, in the line connected by vias. In this study, first, a governing parameter for electromigration damage on the ends of passivated polycrystalline line is expressed considering the boundary condition of line ends concerning the atomic diffusion. Next, the way to estimate the threshold current density of the metal line with vias is shown based on the numerical simulation using the governing parameter.Copyright

A governing parameter for electromigration damage in passivated polycrystalline line and its verification

The atomic flux divergence due to electromigration in unpassivated metal line, AFDgen, has been formulated considering two-dimensional distributions of current density and temperature and also, simply considering structures of polycrystalline and bamboo lines. The divergence AFDgen has been identified as a governing parameter for electromigration damage in unpassivated polycrystalline and bamboo lines thorough experimental verification. In those studies, we have employed the uncovered metal liens as the first step in the development of a practical and universal prediction method for electromigration damage. On the other hand, it is known that in passivated lines, a mechanical stress (atomic density) gradient is induced by electromigration, and plays an important role in electromigration mechanism. In this study, a governing parameter, AFDgen*, is formulated for electromigration damage in passivated polycrystalline lines. The formulation is carried out by adding the effect of the atomic density gradient to...

Failure Simulation of Angled Polycrystalline Lines Covered With Passivation Layer

The atomic flux divergence due to electromigration in a passivated polycrystalline line, AFD* gen , has been formulated adding the effect of a passivation on electromigration damage to the governing parameter for electromigration damage in an unpassivated polycrystalline line, AFDgen . The parameter, AFD* gen , has been identified as a governing parameter for electromigration damage in the passivated polycrystalline line by experimental verification process. Recently, a prediction method for electromigration failure in the passivated polycrystalline line was proposed using AFD* gen , and the usefulness of the method was verified through experiment. Both the lifetime and the failure location in the passivated polycrystalline line can be predicted by means of numerical simulation of the failure process covering the building up of atomic density distribution, void initiation, void growth and ultimately—line failure. In this study, AFD* gen -based method for predicting electromigration failure is applied angled polycrystalline lines covered with passivation. There are few works on prediction of failure in the angled lines, though such lines are widely used in IC (integrated circuit) products. The failures are simulated when the corner position and its angle are changed. The dependency of lifetime and failure location on line shape is investigated.Copyright