摘要:

The early failure issue in electromigration has been an unresolved subject of study over the last several decades. A satisfying experimental approach for the detection and analysis of early fails has not been established yet. In this study, a new technique utilizing large interconnect arrays in conjunction with the well known Wheatstone Bridge is presented. Three types of structures with varying number of interconnects were used, starting from a small unit of five lines in parallel. A serial arrangement of this unit enabled testing of interconnect arrays encompassing 480 possible failure links. In addition, a Wheatstone Bridge-type wiring using four large arrays in each device enabled simultaneous testing of 1,920 interconnects. In conjunction with a statistical deconvolution to the single interconnect level, the results indicate that the electromigration failure mechanism studied here follows perfect lognormal behavior down to the four sigma level. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59923

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Electromigration failure is a complex process of void nucleation, growth, motion and shape evolution. A technique has been developed that allows the measurement of these individual stages of electromigration failure in a statistically meaningful way. Void nucleation times, growth rates and velocities have been measured in ten or more lines at each of 4 different accelerated test conditions. These stages scale as expected with temperature, however, the current scaling was more complex. Many models predict lifetimes to scale with the inverse square of the current density. In such models, the nucleation stage is often assumed to be dominant and to scale asj−2.In this work, lifetimes were found to scale with the inverse square of the current density, but the nucleation times of the voids that cause failure scaled with the inverse of the current. At the lowest current density, instead of increasing linearly with time to failure, void growth often saturated and led to an extension of the lifetime. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59903

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Four different metallization processes for AlCu dual damascene are investigated with respect to their electromigration lifetime and compared to a metallization using subtractive metal etching. It is shown that the electromigration reliability lifetime depends strongly on the metal stack and the metallization process used. Three fill processes that employ PVD Ti and PVD Ti/TiN liners result in poor electromigration, while a process using CVD TiN leads to superior electromigration performance. In this particular case the current density had to be increased to values as high as 2.5 MA/cm2in order to induce a statistically relevant number of fails in certain structures. Two of the most important parameters that determine the electromigration lifetime in damascene lines are (1) the quality of the Al sidewalls as determined for instance by the presence of aTiAl3reaction layer and (2) the amount ofTiAl3formation that reduces the bulk AlCu thickness. The texture of the AlCu matrix is of less importance. In fact, the damascene lines with the longest lifetime have no significantTiAl3formation and almost random texture. This is in contrast to electromigration of metal RIE structures where randomly textured lines generally have short electromigration lifetime. The excellent electromigration performance of the optimum damascene samples is attributed to the absence of an etchedAl-SiO2interface and the suppression of Ti-Al reactions. This results in reduced number of defects and void nucleation sites, and a low material diffusivity. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59917

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The drive toward smaller, faster microelectronics chips is requiring use of Cu and low-K dielectrics in place of presentAl/SiO2wiring systems in order to reduce RC signal delay. Cu addresses the resistive component of this delay. Besides having 30&percent; lower resistivity and a higher elastic modulus compared to Al, Cu is a relatively low-cost replacement. But Cu behaves differently from Al in several ways. Cu is not self-passivating like Al, and has been found to diffuse through oxide. Diffusion barriers must therefore be used around Cu lines to protect active devices from Cu poisoning. Because Cu oxidizes easily, wiring and bond pads must be protected from air during high-temperature testing. Cu adhesion toSiO2appears to be poorer and Cu interfacial diffusion higher, allowing for significant electrochemical migration. For electromigration and stress voiding, Cu is generally more robust than Al. However, the properties above combined with rapid grain growth rates can produce unexpected deleterious results. Introduction of low-K dielectrics, anticipated to address the capacitive component of signal delay, will present additional challenges, because most low-K materials have lower mechanical strength, lower thermal conductivity, and are more permeable thanSiO2.©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59922

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The use of a physically-based electromigration model as a means of validating design rules in aluminum-based microelectronic interconnects is presented. This model consider the migration of atoms through the line when driven by an applied current and mechanical stress gradients. The model is then applied to a specific interconnect geometry common to CMOS logic circuits. Here the saturation resistance in the interconnect is shown to agree well with experimental observations. The value of the effective charge(Z*)in this material is found to be −8.8. These results demonstrate the usefulness of electromigration modeling as a means of developing interconnect design rules. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59925

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

Most modeling and experimental characterization of interconnect reliability is focussed on simple straight lines terminating at pads or vias. However, laid-out integrated circuits often have interconnects with junctions and wide-to-narrow transitions. In carrying out circuit-level reliability assessments it is important to be able to assess the reliability of these more complex shapes, generally referred to as ‘trees.’ An interconnect tree consists of continuously connected high-conductivity metal within one layer of metallization. Trees terminate at diffusion barriers at vias and contacts, and, in the general case, can have more than one terminating branch when they include junctions. We have extended the understanding of ‘immortality’ demonstrated and analyzed for straight stud-to-stud lines, to trees of arbitrary complexity. This leads to a hierarchical approach for identifying immortal trees for specific circuit layouts and models for operation. To complete a circuit-level-reliability analysis, it is also necessary to estimate the lifetimes of the mortal trees. We have developed simulation tools that allow modeling of stress evolution and failure in arbitrarily complex trees. We are testing our models and simulations through comparisons with experiments on simple trees, such as lines broken into two segments with different currents in each segment. Models, simulations and early experimental results on the reliability of interconnect trees are shown to be consistent. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59926

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

During interdiffusion usually a net volume flow arises, which leads to a stress-free deformation. This is equivalent to an elastic stress field, which—due to its long range character—depends on the boundary conditions (e.g. on the shape of the sample) as well. The effect of these diffusion-induced stresses strongly depends on the possible relaxation’s (e.g. by creep or elastic bending) and their time scale as compared to the diffusion annealing time. The lecture will treat the possible origins of stress-free strains, and the possible effects of the stress field on the diffusion intermixing (across the driving force related to this field). Experimental examples when stresses of diffusional origin can lead to macroscopic failure of composite or layered materials (e.g. wires with coatings, contact points of microelectronics devices) as well as examples of stress stabilization of the structure (e.g. in multilayers) will be also presented. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59927

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

The influence of microstructure on electromigration damage of Al and Cu interconnects with different width and morphology was studied. At first, grain boundaries and local grain orientations before electromigration were registered and correlated with defect places. The investigations focussed onin-situelectromigration tests inside a SEM under accelerated loading conditions, on thein-situobservation of defect formation, and on orientation measurements at the interconnect grains. The position of individual grain boundaries and the misorientation of their neighbored grains seem to be decisive factors for the interconnect failure because of different diffusivities. Whereas the failure behavior of polycrystalline interconnects is sufficiently understood, bamboo structures require further investigations. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59924

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

A model system for investigating the formation of electromigration damage and the electromigration lifetime of thin film metallizations has been developed. This system contains fast diffusing segments consisting of plastically deformed regions created by nanoindentation in single-crystal pure Al conductor lines. These segments mimic the behavior of polygranular segments in lines having “near-bamboo” grain structure. We have used these model systems to investigate critical length effects and segment interaction effects, as well as the nucleation and evolution of electromigration voids as a function of orientation. Void nucleation is shown to depend on segment length and current density and segments are shown to interact to nucleate electromigration damage. Electromigration void evolution and electromigration lifetimes are shown to depend strongly on the crystallographic orientation of the conductor lines. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59899

出版商:AIP    

年代:1999

数据来源: AIP

摘要:

This paper reviews the measurements of local strain distribution in individual 10 &mgr;m-wide 200 &mgr;m-long passivated Al conductor lines using white-beam x-ray microdiffraction. Local strain changes were examined in real-time when the Al lines were subjected to temperature changes as well as to electrical current stressing. Results of thermal strain measurements show that the stress in the Al lines can be treated as equibiaxial, and that the passivation does not hinder the overall expansion of the conductor line along the film normal. Results of electromigration strain measurements show relief of the initial biaxial compressive stress near the cathode end of the conductor line, and increase of compressive stress near the anode end. A linear stress gradient was observed when steady-state electromigration was reached. Steady-state measurements at various current densities below the threshold value,jth=1.6×105&hthinsp;A/cm2,yield an effective valenceZ*=1.6for Al electromigration, and transient-state measurements as a function of time allow us to estimate the effective grain boundary diffusivityDeff≅8×10−11&hthinsp;cm2/secfor Al self-diffusion at 260&hthinsp;°C. Results of measurements withj=6×105&hthinsp;A/cm2,which is much higher than the threshold value, show fast stress relaxation near the anode end after about 15 hours of stressing, most likely due to fracture of delamination of passivation by the electromigration-induced compressive stress there. ©1999 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.59928

出版商:AIP    

年代:1999

数据来源: AIP