Electromigration Activation Energy Research Articles

The effect of microstructure on the resistance to electromigration of AlCu thin film conductors

Aluminum-copper alloy films were prepared by vacuum evaporation under varying conditions of deposition rate and substrate temperature. They were subsequently subjected to electromigration testing using the median time to failure (MTF) and temperature-ramp resistance analysis to characterize electromigration (TRACE) methods and the resulting activation energies for electromigration were extracted. It was found that certain microstructural configurations affected the beneficial effects of copper on the resistance of thin films to electromigration. The magnitude of the activation energies ranged from 0.25 eV up to 0.95 eV. The differences in the activation energies Q were related to the deposition conditions, the films' grain size distributions, the copper content of the films, the Al 2Cu precipitate distributions in the films, and the possible presence of Guinier-Preston zones. The Avrami analysis of the resistometric data for the lifetime experiments was also employed. It was found that a single failure mechanism dominated over the temperature range of the MTF experiments, but this mechanism was dependent on the deposition conditions.

1/f2 Noise and Electromigration in Al-Cu Interconnects

ABSTRACTElectromigration in Al-1.5%Cu interconnects was studied using a direct current (d.c.) induced 1/f2 noise spectrum. The interconnects were fabricated with a multi-step sputter deposition process, with deposition temperatures of 25°C, 300° C, and 475°C. The resulting microstructures were analyzed using SEM and TEM, and grain size distribution parameters were measured. The minimum temperature at which 1/f2 noise could be detected was found to depend on the deposition temperature; for the 25°C, 300°C, and 475°C depositions the lowest temperature at which 1/f2 noise could be measured was 190°C, 220°C, and 265°C, respectively. The activation energy of 1/f2 noise was measured and compared with the electromigration activation energy. The noise activation energy was found to depend on deposition temperature; 0.56 eV, 0.64 eV, and 0.96 eV for the 25°C, 300°C, and 475° C depositions, respectively. SEM analysis of the samples after measurement show initial stages of void and hillock formation. Corresponding electromigration activation energies, 0.56 eV, 0.69 eV, and 1.04 eV were also dependent on deposition temperature. Noise measurements of interconnects made prior to electromigration testing were highly correlated with the electromigration failure times.

Electromigration behavior of ionized cluster beam deposited aluminum films on SiO2

Unpassivated, pure aluminum films on 7000-Å-thick SiO2 were prepared by ionized cluster beam deposition in a vacuum of 2×10−6 Torr from a carbon crucible which had a nozzle of 2 mm diameter. The resulting particle beam was ionized by impact of electrons and accelerated by an electrical potential towards the substrate. The activation energy for electromigration for these films at temperatures between 125 and 200 °C was found to be 1.1 eV. The initial resistivity of the films was about 12 μΩ cm which decreased to 8 μΩ cm due to annealing at temperatures between 400 and 450 °C.

Activation energy of electromigration in thin metal films

A new method for measuring the activation energy of electromigration in thin metal films has been established.

CHARGE TRANSFER AT In-Si (111) INTERFACE AND SURFACE ELECTROMIGRATION OF INDIUM ADATOMS

For the first time, we found by EHEED that a part of indium adatoms on the Si(lll) surface transports easily under the influence of an applied dc electric field. According to the observation of the surface electromigration process, it is shown that the states of adsorption of indium atoms on a clean Si (111) surface can be characterized as two phases - the first interface layer bound to silicon surface tightly is hardly affected by a electric field, it is called the tightly bound layer; overlayers on the first layer bound to the first interface layer loosely, can transport along the direction of an applied electric field, they are called transport layers. From the temperature dependence of the transport mobility, we find that the activation energy of surface electromigration is △H = 0.43 eV.The charge transfer in the process of In-Si(111) interface formation has been investigated by measurements of the surface conductance. The results show that indium atom is adsorbed as surface deep donor. Surface electromigration is attributed to Coulomb force applied on the ionized indium atom.

Electromigration mechanism in aluminium conductors

The mechanism of electromigration in the aluminium conductors of Integrated Circuits has been studied with radioactive tracers (Al 26 and Ni 63) employing high resolution autoradiographic techniques. It has been proved that the mass transport from the negative to the positive pole takes place predominantly by migration through the aluminium film grain boundaries. The surface diffusion mechanism was discarded as an important contribution to the process. Measurements of MTF (mean time to failure) in pure aluminium and in nickel-doped aluminium (200–700 ppm of nickel) showed a ten-fold advantage for the doped conductor. The electromigration activation energy of doped specimens was determined from the MTF variation with temperature. This result, 23.9 kcal mol −1, is in agreement with the activation energy for grain boundary diffusion of nickel in aluminium taken from the literature [1].

The threshold current density and incubation time to electromigration in gold films

The electromigration in thin gold films was studied by means of direct drift velocity measurements. A threshold in the electromigration drift velocity was found, and its value is inversely proportional to the gold stripe length. Electron-beam-deposited films, in contrast to sputtered ones, also demonstrated the presence of an incubation time for the cathode displacement. The electromigration activation energy was found to be 0.67–0.72 eV and the effective charge -0.3 to -186. In addition, alloyed Au-10 vol.% Mo specimens were examined. These films showed a much slower mass transport from the anode to the cathode—the opposite direction to that of non-alloyed gold films.

The activation energy for electromigration and grain-boundary self-diffusion in gold

The activation energy for electromigration and grain-boundary self-diffusion in gold

Activation Energy for Electromigration in Aluminum Films Alloyed with Copper

The rate of electromigration in thin films of aluminum and aluminum alloyed with copper has been determined by measuring the changes in resistance of stripes subjected to a current density of 4 × 106 A/cm2. At temperatures in the range from 100 to 200°C the activation energy for electromigration has been found to have the same value for both the pure and the copper-alloyed samples, namely, 0.6 eV. However, the rate of migration is much smaller, by a factor as large as 100, in the copper-bearing samples. These results are discussed in terms of grain boundary diffusion and the effect of alloying additions on diffusion mechanisms.