Reliability of Multi-Terminal Copper Dual-Damascene Interconnect Trees

Electromigration tests on different Cu dual-damascene interconnect tree structures consisting of various numbers of straight via-to-via lines connected at the common middle terminal have been carried out. Like Al-based interconnects, the reliability of a segment in a Cu-based interconnect tree strongly depends on the stress conditions of connected segments. The analytic model based on a nodal analysis developed for Al trees gives a conservative estimate of the lifetime of Cu-based interconnect trees. However, there are important differences in the results obtained under similar test conditions for Al-based and Cu-based interconnect trees. These differences are attributed to the variations in the architectural schemes of the two metallization systems. The absence of a conducting electromigration-resistant overlayer in Cu technology and the low critical stress for void nucleation at the Cu/inter-level diffusion barrier (i.e. Si₃N₄) interface leads to different failure modes between Cu and Al interconnects. As a result, the most highly stressed segment in a Cu-based interconnect tree is not always the least reliable. Moreover, the possibility of liner rupture at stressed dual-damascene vias leads to significant differences in tree reliabilities in Cu compared to Al. While an interconnect tree can be treated as a fundamental unit whose reliability is independent of that of other units in Al-based interconnect architectures, interconnect trees can not be treated as fundamental units for circuit-level reliability analyses for Cu-based interconnects.Singapore-MIT Alliance (SMA

Silicon spin diffusion transistor: materials, physics and device characteristics

The realisation that eaveryday electronics has ignored the spin of the carrier in favour of its charge is the foundation of the field of spintronics. Starting with simple two-terminal devices based on GMR and tunnel magnetoresistance, the technology has advanced to consider three-terminal devices that aim to combine spin sensitivity with a high current gain and a large current output. These devices require both efficient spin injection and semiconductor fabrication. In this paper, a discussion is presented of the design, operation and characteristics of the only spin transistor that has yielded a current gain greater than one in combination with reasonable output current

Electron correlation energy in confined two-electron systems

Radial, angular and total correlation energies are calculated for four two-electron systems with atomic numbers Z=0-3 confined within an impenetrable sphere of radius R. We report accurate results for the non-relativistic, restricted Hartree-Fock and radial limit energies over a range of confinement radii from 0.05 - 10 a0. At small R, the correlation energies approach limiting values that are independent of Z while at intermediate R, systems with Z > 1 exhibit a characteristic maximum in the correlation energy resulting from an increase in the angular correlation energy which is offset by a decrease in the radial correlation energy

Effects of Applied Loads, Effective Contact Area and Surface Roughness on the Dicing Yield of 3D Cu Bonded Interconnects

Bonded copper interconnects were created using thermo-compression bonding and the dicing yield was used as an indication of the bond quality. SEM images indicated that the Cu was plastically deformed. Our experimental and modeling results indicate that the effective contact area is directly proportional to the applied load. Furthermore, for first time, results have been obtained that indicate that the dicing yield is proportional to the measured bond strength, and the bond strength is proportional to the effective contact area. It is also shown that films with rougher surfaces (and corresponding lower effective bonding areas) have lower bond strengths and dicing yields. A quantitative model for the relationship between measured surface roughness and the corresponding dicing yield has been developed. An appropriate surface-roughness data acquisition methodology has also been developed. The maximum possible applied load and the minimum possible surface roughness are required to obtain the maximum effective contact area, and hence to achieve optimum yields (both mechanically and electrically).Singapore-MIT Alliance (SMA

Mortality Dependence of Cu Dual Damascene Interconnects on Adjacent Segments

Electromigration experiments have been carried out on straight interconnects that have single vias at each end, and are divided into two segments by a via in the center ("dotted-I" structures). For dotted-i structures in the second metal layer (M2) and with 25µm-long segments length, failures occurred even when the product of the current density and segment length (jL) was as low as 1250A/cm, even though via terminated 25µm-long lines are "immortal" when (jL)cr < 1500 A/cm. Moreover, we found the mortalities of the dotted-I segments to be dependent on the current density and current direction in the adjacent segment. These result suggest that there is not a definite value of jL product that defines true immortality in individual segments that are part of an interconnect tree, and that the critical value of jL for Cu dual damascene segments is dependent on the magnitude and direction of current flow in adjacent segments. Therefore, (jL)cr values determined in two-terminal via-terminated lines cannot be directly applied to interconnects with branched segments, but rather the magnitude as well as the direction of the current flow in the adjoining segments must be taken into consideration in determining the immortality of interconnect segments.Singapore-MIT Alliance (SMA

A fly in the buttermilk: Descriptions of university life by successful Black undergraduate students at a predominately white southeastern university

Although many predominantly white universities exert great effort to recruit minority students, statistics regarding retention and graduation for these students are disturbing. Previous research indicates that academic concerns are not paramount in the attrition of minority students, suggesting that greater attention must be given educational experiences of black students over and above academic matters. Using in-depth phenomenological interviewing, 11 graduating seniors from diverse majors were asked to describe salient incidents of their university experience. These interviews were transcribed verbatim and subjected to hermeneutic interpretation by an interdisciplinary research group. Dominant in student descriptions of their experiences were five themes: (1) It happens every day : Unfairness/Sabotage/Condescension; (2) You have to initiate the conversation ; (3) They seem the same; I\u27m the one who\u27s different ; (4) I have to prove I\u27m worthy to be here ; and (5) Sometimes I\u27m not even here/Sometimes I have to represent every black student : Invisibility and Supervisibility

Urbanization alters coastal plain stream carbon export and dissolved oxygen dynamics

Coastal plain streams in the southeastern United States supply carbon that supports important coastal ecosystems, but the effects of urbanization on carbon export from these streams have not been extensively studied. This study aimed to determine how urbanization changes coastal plain stream organic matter quality, rates of carbon export, and dissolved oxygen dynamics that have implications for stream ecosystem function. Organic matter quality, organic carbon export, and dissolved oxygen concentrations were measured for multiple years (2009 & 2013–2015) in North Carolina coastal plain streams that spanned a gradient of urbanization. Based on spectral characteristics, dissolved organic matter (DOM) quality appeared to shift from characteristic blackwater in minimally impacted streams to clear streamwater in urban streams due to large reductions in chromophoric DOM concentrations, aromaticity, and molecular weight. Differences in spectral indices and characteristics of dissolved organic carbon export suggest that urbanization reduced natural sources of DOM and provided various urban sources of DOM that were likely more bioavailable. Particulate organic matter in the urban streams was indicative of more labile autochthonous sources than that of the less impacted streams, and rates of particulate carbon export increased and shifted to higher flows with watershed impervious surface cover. Diel variation of dissolved oxygen increased with watershed impervious surface cover, indicating that urbanization and associated changes in carbon and nutrient cycling altered stream function. While the effects of urbanization on carbon export were similar to previous studies in other regions, the unique blackwater state of natural streams and receiving waters in the study area make them especially susceptible to negative ecological impacts from altered carbon and nutrient export. Management actions that conserve or restore natural carbon sources to the stream may help mitigate multiple negative effects of urbanization in southeastern US coastal plain streams

Luminosity distance and redshift in the Szekeres inhomogeneous cosmological models

The Szekeres inhomogeneous models can be used to model the true lumpy universe that we observe. This family of exact solutions to Einstein's equations was originally derived with a general metric that has no symmetries. In this work, we develop and use a framework to integrate the angular diameter and luminosity distances in the general Szekeres models. We use the affine null geodesic equations in order to derive a set of first-order ordinary differential equations that can be integrated numerically to calculate the partial derivatives of the null vector components. These equations allow the integration in all generality of the distances in the Szekeres models and some examples are given. The redshift is determined from simultaneous integration of the null geodesic equations. This work does not assume spherical or axial symmetry, and the results will be useful for comparisons of the general Szekeres inhomogeneous models to current and future cosmological data.Comment: 14 pages, 1 figure, matches JCAP accepted versio