摘要:

There has been considerable progress in the past decade in understanding electromigration failure. Some of this understanding has come from a belated appreciation of concepts introduced years earlier, but not fully incorporated into the “world picture” of electromigration until just recently. This paper will outline the progress made in the past 10 years from a personal viewpoint. Hopefully, it will reflect the opinions of the general worker in the field, but it must be viewed with that fact that there is inevitable personal bias in mind. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469887

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

We report the electromigration (EM) response of single-domain epitaxial Cu(001) lines on layers of Ta, TaN, and TiN. Epitaxial Cu(001) lines on nitride layers exhibit nearly two orders of magnitude higher mean-time-to-failure (MTTF) values than those on Ta, indicating the strong influence of the underlayer. The activation energy of EM for Cu on the nitrides is ∼0.8–1.2 eV, and that of Cu on Ta is ∼0.2 eV, for 200–300&hthinsp;°C. Our results also indicate that the MTTF values correlate inversely to the crystal quality of the Cu layers measured by X-ray diffraction. The EM resistance of epitaxial Cu lines with different crystal quality on TaN were measured to separate the effects of interface chemistry and crystal quality. While higher quality epitaxial films reveal a higher EM resistance, the magnitude of the change is smaller than that obtained by changing the interface chemistry. Epitaxial lines exhibit more than 3–4 orders of magnitude higher MTTF than polycrystalline lines on the same underlayer. Based upon our results, we propose that the Cu/underlayer interface chemistry and presence of grain boundary diffusion play important roles in unpassivated Cu films. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469888

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

We have studied short-line effects in fully-integrated Cu damascene interconnects through electromigration experiments on lines of various lengths and embedded in different dielectric materials. We compare these results with results from analogous experiments on subtractively-etched Al-based interconnects. It is known that Al-based interconnects exhibit three different behaviors, depending on the magnitude of the product of current density, j, and line length, L: For small values of (jL), no void nucleation occurs, and the line is immortal. For intermediate values, voids nucleate, but the line does not fail because the current can flow through the higher-resistivity refractory-metal-based shunt layers. Here, the resistance of the line increases but eventually saturates, and the relative resistance increase is proportional to (jL/B), where B is the effective elastic modulus of the metallization system. For large values of (jL/B), voiding leads to an unacceptably high resistance increase, and the line is considered failed. By contrast, we observed only two regimes for Cu-based interconnects: Either the resistance of the line stays constant during the duration of the experiment, and the line is considered immortal, or the line fails due to an abrupt open-circuit failure. The absence of an intermediate regime in which the resistance saturates is due to the absence of a shunt layer that is able to support a large amount of current once voiding occurs. Since voids nucleate much more easily in Cu- than in Al-based interconnects, a small fraction of short Cu lines fails even at low current densities. It is therefore more appropriate to consider the probability of immortality in the case of Cu rather than assuming a sharp boundary between mortality and immortality. The probability of immortality decreases with increasing amount of material depleted from the cathode, which is proportional to (jL2/B) at steady state. By contrast, the immortality of Al-based interconnects is described by (jL) if no voids nucleate, and (jL/B) if voids nucleate. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469889

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The electromigration short-length effect is investigated for AlCu and Cu interconnects inSiO2dielectrics. Simple models based on first principles are shown to accurately describe the length-dependent electromigration behavior of both metallization systems. The model for AlCu describes resistance saturation while the model for Cu describes the incubation time. Experimental results for different combinations of current density and stripe length are in good agreement with the predictions of both models. The effect of line width and temperature on the electromigration threshold are also investigated. In addition, an electromigration resistant power grid is proposed as a practical application of the short-length effect. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469890

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

A new via technology for improving electromigration (EM) reliability of copper (Cu) dual-damascene (DD) interconnection has been developed. Early failure mode of a conventional Cu DD structure is found as void formation at the via-bottom interface, where flux divergence of Cu ions is large due to diffusion barrier-layer. In order to avoid the early failures, direct-contact via (DCV) technology whose concept is “barrier-free” at the via-bottom has been developed. The early failure mode is eliminated by the DCV technology and lower via resistance is obtained. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469891

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

Electromigration (EM) tests have been performed to determine early failure statistics in submicron dual-damascene Cu/oxide interconnects. Monte Carlo simulation, based on the “weakest-link” model, was developed to characterize and determine the failure modes from the cumulative distribution function (CDF) of multi-link test structures. The existence of two district failure modes (weak and strong) in our test structures was identified, where the weak mode is responsible for early failures. The weak mode is found to be void formation within the dual-damascene via, while the strong mode is associated with voiding that occurs in the dual-damascene trench. The weak mode (early failure) activation energy is found to be1.0±0.05 eVand seems consistent with void formation that is controlled by interface diffusion between the Cu metal and its Ta diffusion barrier. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469892

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

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 divergenceAFDgenhas 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,AFD*gen,is formulated for electromigration damage in passivated polycrystalline lines. The formulation is carried out by adding the effect of the atomic density gradient toAFDgen.In addition, anAFD*gen-based method for determination of film characteristics is developed. Using this method, the characteristics included in theAFD*genare derived based on experimental data of void formation. The method was applied to both covered line and uncovered one, which were made of the same Al film. It was found that the obtained characteristic constants functioned well as the constants dependent of existence of the passivation layer or as the constants independent of passivation existence. Through the showing the validity of the obtained characteristic constants, the usefulness of theAFD*genand theAFD*gen-based method for determination of film characteristics was verified. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469893

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

The preceding trend of miniaturization in microelectronics industry leads to drastic increase of current density in the interconnect lines. Additionally, copper as new material and the double damascene technology poses new questions concerning the interconnect damage by electromigration (EM). In the work presented here, the influence of the grain boundary network on the formation of voids and hillocks in Cu interconnects is investigated. For this purpose, electromigration tests of unpassivated Cu lines (width 1 to 4 &mgr;m) were carried out in situ in a SEM, coupled with acquisition of their complete microstructural and orientation state by means of Electron Backscatter Diffraction (EBSD). After EM testing the line damages were investigated using a Focused Ion Beam device for studying the microstructural details in normal direction and around the defects. It was found that the strings of large angle grain boundaries in the electron flow direction are decisive for the formation of voids and hillocks. This was found for Cu lines produced by PVD as well as for electroplated lines, though they had rather different microstructure and texture. FIB cuts through hillocks showed that they have grown sometimes epitaxially, sometimes non-epitaxially, and they often consisted of more than one grain. The effect of misorientation state of a grain boundary on its transport properties is discussed and compared with former results on Al interconnects. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469894

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

A demand to increase current density of ULSI interconnections with shrinkage of feature sizes inevitably brings about temperature rise due to Joule heating. We studied how temperature distribution changes with an increase in the current density and further investigated its effect on electromigration-induced failures. We evaluated a temperature rise in a single level Al-alloy interconnection by the use of IR-CCD camera and 3-D fluid dynamical finite element analysis. A build-up of a significant temperature gradient was observed with an increase in the current density. Failure analysis of electromigration accelerating tests revealed that the degradation of MTF at high current density conditions was due to occurrence of a new failure mode of “evaporation mode.” The evaporation mode is most likely caused by an annihilation of a void. Further discussions concerning the relationship between the evaporation mode and the Joule heating effect are given. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469895

出版商:AIP    

年代:1902

数据来源: AIP

摘要:

New formula for the driving force of electromigration have been found using new concepts of (1) kinetic energy density, (2) tension density, and (3) effective charge tensor density. The new “dynamic” wind charge tensor densityZ⇊a dynamic wind(r&vec;)is revealed over and above the conventional “static” wind charge tensor densityZ⇊a static wind(r&vec;).Some numerical analysis will be demonstrated for possible application to electromigration reliability problems of ULSI devices where extremely high current densities should be maintained through ultra thin film interconnects. Key issues in this study are the comparative study of the dynamical electronic characteristics for the electromigrating regions in the bulk, surface, and grain boundary. ©2002 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1469896

出版商:AIP    

年代:1902

数据来源: AIP