Paolo Emilio Bagnoli

Electromigration and low-frequency resistance fluctuations in aluminum thin-film interconnections

Low-frequency noise spectra originating from resistance fluctuations in Al films during electromigration were measured in the absolute temperature and current density intervals<tex>327 \leq T \leq 396</tex>K and<tex>1.34 \times 10^{6} \leq j \leq 2.22 \times 10^{6}</tex>A/cm². The values of S<inf>R</inf>, the resistance power spectral density, at 20 × 10^-3Hz allowed the construction of an Arrhenius plot from which a grain-boundary activation energy value of about 0.6 eV was deduced. This value lies in the range of values found by other authors using different techniques. A first attempt to model the observed dependence of S<inf>R</inf>on<tex>j</tex>and<tex>T</tex>is also described.

Electromigration detection by means of low-frequency noise measurements in thin-film interconnections

Low-frequency noise power spectral densities associated with displacements of atoms caused by electromigration were measured on Al-Si (1 percent) resistors at various current densities in the frequency range 5 × 10-2 ÷ 2Hz. The temperature of the resistors was the one set by the current density itself, all the samples having been tested at room temperature. After noise measurement, each resistor was subjected to the current density at which the measurement was performed up to failure. The total electromigration power, measured in the frequency interval 0.1 ÷ 1 Hz was plotted as a function of the failure time for three different series of resistors obtained by means of an RF sputtering process. The measurement system and the characteristic features of the electromigration spectra are described.

Analysis of laser diode thermal properties with spatial resolution by means of the TRAIT method

Abstract The thermal resistance analysis by induced transient (TRAIT) method is a characterization technique which allows experimental evaluation of the total thermal resistance Rth of a semiconductor device and its assembling structure with a spatial resolution. This means that Rth can be known as a sum of several contributions due to various parts of the system. This technique is mainly based on the analysis of the system thermal dynamic behaviour. The capabilities of the method were demonstrated by applying the analysis to semiconductor laser devices in order to investigate the thermal properties and reliability of their packages.

A study of electromigration in aluminum and aluminum-silicon thin film resistors using noise technique

Abstract Aluminum and aluminum-silicon (1%) thin film resistors, with and without an Si 3 N 4 passivating layer, were characterized by means of noise measurements in a low-frequency range (10 mHz-1 Hz), during electromigration. Activation energies for Al test patterns were found to be E a =0.64 eV and E ap =0.88 eV for non-passivated and passivated samples respectively, whereas for AlSi (1%) test patterns, E a =0.94 eV and E ap =1.07 eV. After noise measurements the samples were subjected, to the same stress conditions, current density and temperature, as during the noise measurements for a period of 165 h. Then both percentage resistance variation and damage in the stripes were evaluated and correlated with the power spectral density of resistance fluctuations. As a result, by means of noise technique one is able to obtain activation energy values that are consistent with the subsequent modification undergone by the resistors, so that activation energies determined in this way can be used as “true” reliability parameters. The time interval necessary to obtain such parameters (about 10 h for each series) is much shorter than those required by traditional techniques.

Noise measurements in thin‐film interconnections: A nondestructive technique to characterize electromigration

Electromigration in aluminum and aluminum‐silicon (1%) resistors was detected by means of a new technique based on the particular features of an ultralow‐noise amplifier, which made it possible to evaluate the stochastic resistance fluctuations associated with vacancy generation‐recombination processes. The power spectra of these fluctuations display a 1/f γ behavior with 2≤γ≤2.6, in the frequency range 10 mHz–1 Hz, and the analysis of these spectra, recorded at various current densities and temperatures, led to an evaluation of the activation energies characteristic of the process. Scanning electron microscope observation of the damage induced by stressing the resistors at the same current density and temperature as the spectra measurement but for a longer time, showed that what was being observed was the electromigration phenomenon in its early stages.

DJOSER: Analytical Thermal Simulator for Multilayer Electronic Structures. Theory and Numerical Implementation

This paper presents a steady-state thermal simulation strategy called DJOSER, which is dedicated primarily but not exclusively to packaging structures for electronic devices. It is applicable to structures that can be likened to a set of homogeneous layers stacked one on top of the other and possibly separated by thermal contact resistances, where the dissipated powers are due to two-dimensional heat sources distributed on the interfaces between the layers. A broad range of contour conditions and types of dissipated powers is included to make the models as close as possible to the typical structures of modern assembly technologies. Flow and temperature distributions are obtained via a system of integral equations that can be translated directly, with the usual squaring techniques, into a linear algebraic system

Validation of the DJOSER analytical thermal simulator for electronic power devices and assembling structures

The present communication deals with the tests for the validation of the DJOSER steady-state thermal simulation program, purposely designed for power electronic assembling structures and which is based on the resolution of analytical relationships. The validation experiments were carried out theoretically by comparing the thermal maps with those obtained using standard finite-elements programs and yielding temperature accuracy below 1%. Experimental tests were also performed on purposely built multi-layer structures and industrial circuits with power diodes mounted in naked-chip configuration. The simulated maps were compared with accurate thermo-graphic recordings and showed a good agreement, testifying the validity of the mathematical model.

Electrical characteristics of silicon nitride on silicon and InGaAs as a function of the insulator stoichiometry

Abstract The interface state density along the semiconductor energy gap and the fixed charge were evaluated in SiN x /InGaAs and SiN x /Si interfaces. The insulator layer was deposited by plasma-enhanced chemical vapour deposition (PECVD) using several ammonia / silane gas ratios. In both the samples the measurements revealed two main peaks of interface states whose height is a function of the insulator layer stoichiometry. Further analysis by infrared and Auger electron spectroscopy and electron spin resonance measurements enabled the peaks to be identified as the two silicon-related defects in silicon nitride cited in the literature. The nitrogen dangling bonds were found to affect the fixed charge of the structure. The role of hydrogen in passivating silicon and nitrogen dangling bonds will also be discussed.

Conductivity variations induced by water vapor adsorption in granular metal films

The resistance variations induced by relative humidity (RH) changes were measured on Pd/Al2O3 and Au/(C2F4)n granular films in the RH range 0%–97% at room temperature. It was verified that the contact‐film interface has no influence on the observed phenomena. A maximum ΔR/R0=26% was detected for the Au/(C2F4)n system.

Electromigration in Al based stripes: Low frequency noise measurements and MTF tests

Traditional [Median time to Failure (MTF)] and non traditional (Noise measurements) techniques have been used to characterize four types of Al based samples. Relatively weak stress conditions, which cause negligible modifications to the sample structure, have been used for noise measurements, whereas more accelerated stress conditions have been used for lifetime tests. Quite different results have been obtained by the two types of characterization. In fact, the experimental data showed that the noise measurements are useful to evaluate the activation energy at relatively weak stress conditions, but cannot be used to foresee the behavior of the samples at strongly accelerated stress conditions. This is particularly true in the case of samples containing copper which probably undergo significant microstructural modifications as the temperature goes up. Moreover, the results of a simple computer simulation which show the dramatic effect on the Time to Failure of the spreading of the values of the thermal resistance of the samples are reported.