Low frequency electromigration noise and film microstructure in Al/Si stripes: Electrical measurements and TEM analysis

Low frequency (l/f^γ) noise, generated by current densities at which electromigration occurs, and the temperature coefficient of resistance between 40 and 100°C were measured on Al/Si (1%) test patterns. The samples had different microstructures, obtained by sputtering the films onto substrates held at five different temperatures. The microscopic features of the samples (average grain dimension) were analyzed by means of transmission electron microscopy. It was found that, at a given frequency, the noise power spectral density of the voltage fluctuations is a decreasing function of the average grain dimension. This fact agrees with the hypothesis that low frequency electromigration noise is not a bulk effect, but originates mainly at grain boundaries.     

Ultra low-noise current sources

The solid state DC current sources available on the market are not suitable for applications in low noise measurement systems because of the high level of low-frequency noise introduced in the measurement chain. The most important cause of low-frequency noise in such instruments is the solid state device used as a voltage reference (usually a Zener diode). This problem has been solved, in the instrument described in this paper, by using a new circuit topology in which the solid-state voltage reference has been substituted by a low-noise battery. The instrument, capable of supplying a current as high as 100 mA, is characterized by a low-frequency noise level some orders of magnitude lower than that of similar commercial instrumentation     

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.     

Copper metallizations for integrated circuits: tem analysis and electrical characterization

Copper thin films have been deposited by means of three different techniques. Transmission electron microscopy analysis and electrical characterization revealed that the three types of film had different average grain size and resistivity. The two different contributions to the total resistivity, due to the scattering at the grain boundaries and at the intragranular defects, have been separated by using the Mayadas-Shatzkes theory. Microstructural analysis, electrical characterization, noise measurements, and lifetime tests have been performed in order to identify the deposition technique which leads to the most reliable interconnection lines.     

Influence of varying porogen loads and different UV cures on low-kappa film characteristics

Nanoporous low-kappa films were manufactured by using a 3-step process: co-deposition of a skeleton and porogens by PECVD, porogen removal by remote plasma and UV cure. In this study, the influence of both the variation of the porogen load and the different types of UV-cures on several film characteristics were investigated. Improved kappa-values were observed for increased porogen to skeleton ratios and a broad band cure, where the wavelength of the photons is always higher than 200 nm. However the Young's modulus and hardness decreased correspondingly. These variations can be attributed to the changing density and chemical composition of the different films. A wide range of low-kappa films was obtained by tuning the porogen load and applying different types of UV cures.