Electromigration Kinetics Research Articles

Synchrotron X-ray study of electromigration, whisker growth, and residual strain evolution in a Sn Blech structure

Synchrotron X-ray analysis of the Sn electromigration behavior and Sn whisker growth in a Blech structure using nano-X-ray fluorescence microscopy and white beam Laue nanodiffraction was conducted. Sn depletion at the cathode and whisker/extrusion formation at the anode were characterized in-situ, and the results obeyed the electromigration kinetics. This electromigration scenario gradually decayed because of the counterbalance between electron wind force and back stress. White beam Laue nanodiffraction analysis showed that a noticeable compressive deviatoric stress in the direction of electron flow built up at the anode of Sn strips, particularly in the roots of Sn whiskers, confirming that electromigration-induced atomic accumulation occurred downstream in a strip and that Sn whiskering was closely related to internal stress resulting from atomic accumulation in confined segments. Finally, a theoretical model based on fundamental electromigration theory revealed that Sn diffused predominately through lattice and grain boundary paths at Sn homologous temperature of 0.6.

Electromigration kinetics and critical current of Pb-free interconnects

Electromigration kinetics of Pb-free solder bump interconnects have been studied using a single bump parameter sweep technique. By removing bump to bump variations in structure, texture, and composition, the single bump sweep technique has provided both activation energy and power exponents that reflect atomic migration and interface reactions with fewer samples, shorter stress time, and better statistics than standard failure testing procedures. Contact metallurgies based on Cu and Ni have been studied. Critical current, which corresponds to the Blech limit, was found to exist in the Ni metallurgy, but not in the Cu metallurgy. A temperature dependence of critical current was also observed.

Effect of solution flow velocity and electric field strength on chitosan oligomer electromigration kinetics and their separation in an electrodialysis with ultrafiltration membrane (EDUF) system

The aim of the present work was to study the effect of solution flow velocity and electric field strength applied to an electrodialysis with ultrafiltration membrane (EDUF) cell on chitosan oligomer electromigration kinetics and on chitosan oligomer mixture fractionation. It was shown that the effect of solution flow velocity was not significant, while the electric field strength showed a significant effect on each chitosan oligomer electromigration rate. The effect of the electric field strength was also significant on the separation possibility of the studied oligomers. It was shown that by using electric field strength of 2.5 V/cm, it was possible to obtain a solution composed only of the dimer and trimer until an operating time of 2 h. By increasing the electric field up to 5 and 10 V/cm, it was no more possible to separate the chitosan oligomers. Chitosan oligomer transport numbers were measured. It was found that they contribute to about 7% of total electric current carrying, while about 93% of the total electric current could be carried by the electrolytes. The system performance was also evaluated through electric field intensity measurement and membrane integrity evaluation. It was found that the membranes kept their integrity and no significant fouling was detected. EDUF appeared consequently as a very interesting and innovative technology for the separation at a large scale of oligosaccharide.

Effect of microstructure on electromigration kinetics in Cu lines

Strong correlation of the modes of electromigration damage and microstructure is reported for Cu films. It is found that changes in the microstructure lead to qualitative variation in electromigration damage kinetics - from the traditional open circuit due to void growth across the line, to damage growing along the line, and not leading to failure. Some of our findings are consistent with the theoretical model based on interplay between surface and grain boundary diffusion. The activation energy eV of electromigration mass transport was measured using a modified electrical resistance method.

Electromigration kinetics of gold on a carbon thin film surface studied by scanning tunneling microscopy and scanning tunneling potentiometry

The techniques of scanning tunneling microscopy (STM) and scanning tunneling potentiometry (STP) have been used simultaneously to study the electromigration behavior of a gold covering (1–2 nm) on a carbon thin film surface over 200 h. The applied lateral direct-current (dc) voltage gradient corresponded to a mean current density j=1×104 A/cm2. The topography of the surface was measured by alternating-current (ac) tunneling. The spatial variation of the electric potential was determined from the dc component of the tunneling current. The surface was studied continuously without any interruptions of the tunneling contact on an area of about (2.3 μm)2. The topography and the potential distribution are drastically changed during this long-range experiment. In considerations of the local potential drop we were able to characterize the thickness of the Au covering. In the first stage of the experiment (t<60 h) the STM/STP results indicate a flux of Au atoms from the anode to the cathode. After that coalescence and faceting of the Au covering were observed. We assume that the surface is adjusted to a minimum surface energy configuration, involving in most cases (111) facets.

Stress Relaxation and Electromigration Kinetics in Short Metal Lines: Transition to Creep Controlled Regime

ABSTRACTAn analysis of transition from the electrotransport controlled to the creep controlled electromigration (EM) is made for the Blech test geometry. The analysis rests on the approach developed by the authors with relaxation of electromigration induced stress by diffusional creep and non-linear stress distribution along the line. The derived solution confirms the idea of Glickman and Vilenkin that for high current density as the length of the line decreases the transition from the electrotransport controlled to the creep controlled electromigration kinetics must occur. The value of introduced parameter r that relates electromigration behavior to the creep viscosity is estimated by the comparison with experimental observations for aluminum stripes and discussed in terms of the Coble creep mechanisms.

Electromigration at gold–aluminium interfaces and in thin aluminium tracks

The in situ method to study accelerated ageing of electronic interconnections under current stress has been applied to (a) Au ball bonds on A11% Si metallization, and (b) thin aluminium tracks. For the Au ball bonds, it has been shown that direct current stresses above 108 Am−2 cause electromigration effects at the Au-Al interface, and that the ageing behaviour depends on the direction of the applied direct current stress. It was also shown that the addition of 1 per cent Cu to the metallization strongly retards void formation, and hence open contact failure. For the thin aluminium tracks, it has been shown that the early stage of electromigration, which can be studied accurately with the in situ technique, is closely related to the stress relaxation within the track. It is therefore concluded that the kinetics of electromigration can only be described if the kinetics of stress relaxation are well understood.

The kinetics of electromigration

A well-known model for the rate of heterogeneous nucleation and growth of a second-phase precipitate in a solid matrix has successfully been applied to electromigration rate studies in metallic thin-film interconnects. The application of these rate equations is based on the analogy between the nucleation and growth of a second-phase precipitate in a solid solution matrix and the nucleation and growth of a void in a thin-film conductor. In the first case, the driving force, at constant composition, is temperature, whereas the driving force for electromigration is both temperature and the applied electric field. Once developed, the model is applied to the resistance versus time data of a variety of thin-film systems, i.e., Al, Al-0.3% Cu, Ti, Ag, Ti/Au, and Au. The results show that this model can accurately be used to describe the failure mechanism in electromigration. Furthermore, if the growth rate of voids is known for a particular thin film, then it is possible to predict failure times.

The effect of hydrogen ambients on electromigration kinetics in A1–2% Cu thin film conductors: R. W. Pasco, L. E. Felton and J. A. Schwarz Solid St. Electron. 26 (11), 1053 (1983)

The effect of hydrogen ambients on electromigration kinetics in A1–2% Cu thin film conductors: R. W. Pasco, L. E. Felton and J. A. Schwarz Solid St. Electron. 26 (11), 1053 (1983)

Determining electromigration kinetics of thin film interconnects : J. A. Schwarz. Semiconductor Int. 96 (March 1985)

Determining electromigration kinetics of thin film interconnects : J. A. Schwarz. Semiconductor Int. 96 (March 1985)

Effects of composition and structure on electromigration kinetics in aluminum-alloy thin films

Variations in time to failure data for electromigration processes have shown the importance to conductor design of factors that include composition, grain size, and passivation thickness. Traditionally, these variables have been studied separately. An understanding of the combined effects of these variables is necessary to design reliable conductors. Temperature-ramp resistance analysis to characterize electromigration (TRACE) has been applied to sample groups in which composition, passivation thickness, and grain size were varied. The results of these experiments provide the kinetic parameters for electromigration, and from these values, a calculation is proposed that allows an estimate of the conductors’ resistance to electromigration. The results suggest that the predominant factor controlling electromigration rates is the passivation thickness.

Compensating effects in electromigration kinetics

A diversity of physico-chemical, thermally activated phenomena, whose rates are described in the general form A exp (− Q kT ) , are found to exhibit a compensation effect. For a series of similar processes, when compensation exists, A and Q vary sympathetically; i.e. increases in Q are accompanied by increases in A. Temperature-ramp Resistance Analysis to Characterize Electromigration (TRACE) was applied to a series of aluminum and aluminum-alloy thin film conductors, providing the kinetic parameters for each conductor in one experiment. These data were tested for the possibility of a compensation effect, and a correlation was found between in A and Q. The existence of a compensation effect implies that there is a single temperature (isokinetic temperature) at which the electromigration rate is nearly the same for all the conductors tested. To utilize kinetic parameters determined by TRACE experiments in the comparison of electromigration lifetimes, a “time to failure” for each stripe is calculated at several temperatures spanning the isokinetic temperature. At each temperature, the generated distribution of “times to failure” is log-normal. The standard deviation of the distribution is a function of temperature with a minimum at the isokinetic temperature. The implication of these results with respect to extrapolation of mean time to failure data is discussed.

The effects of hydrogen ambients on electromigration kinetics in Al-2% Cu thin film conductors : R. W. Pasco, L. E. Felton and J. A. Schwarz. Solid-St. Electron.26 (11), 1053 (1983)

The effects of hydrogen ambients on electromigration kinetics in Al-2% Cu thin film conductors : R. W. Pasco, L. E. Felton and J. A. Schwarz. Solid-St. Electron.26 (11), 1053 (1983)

The effects of hydrogen ambients on electromigration kinetics in A1–2% Cu thin film conductors

Surface chemical phenomena are likely to dominate the overall behavior of a system when the majority of the mass in the system is present as surface mass. Thin film interconnections of small dimensions [Large Scale and Very Large Scale Integration (LSI and VLSI)]fall into this class due to the presence of external and internal (including grain and inter-phase boundaries) surfaces. Previous investigations have strongly suggested that the presence of H 2, presumably through surface interactions, can greatly reduce electromigration damage (EMD) leading to higher reliability for device operation. Yet, no systematic studies have been reported. We have applied the Temperature-ramp Resistance Analysis to Characterize Electromigration (TRACE) technique to examine the effect of hydrogen ambients on EMD kinetics and its effect on solid-state transport and on the void morphology of A1–2% Cu thin film conductors. Systematic variation of H 2 ambients of varying composition and variation of the heating rate during the TRACE experiment show that the apparent activation energy for EMD remains constant while the pre-exponent changes. The results confirm a substantial improvement in EMD resistance in H 2 containing ambients. The variation in the pre-exponential is consistent with a transport process controlled by the nucleation of voids and their subsequent growth.