Michael L. Dreyer

The Effects of Test Condition, Microstructure and Linewidth on Electromigration Void Morphology

In this paper, experimental results for electromigration void morphology and failure time distribution are presented as a function of test condition, grain size distribution and conductor linewidth. Unpassivated Al-Cu(1.5%)-Si(1.5%) conductors with linewidths in the range lum ≤W ≤l0μm were subjected to accelerated temperature stresses of T=150° C and 250°C and current stresses in the range j= 0.5-4X10 6 A-cm -2 , for each temperature stress. Unlike previous reports, erosion-like voids dominated at all current densities and temperatures for both W/D 50 ≤1 and W/D 50 > 1. The void distribution within a line was strongly dependent on test conditions and linewidth. The critical current density was extracted from electromigration lifetimes measured as a function of current density. The results show that the linewidth dependence of electromigration lifetimes depend strongly on the Blech relation.

The effects of temperature and microstructure on the components of electromigration mass transport

Experimental data that support a recently proposed model for electromigration in the metal film interconnects are presented. The results indicate that the grain structure of the film coupled with the temperature dependence of the lattice and grain boundary diffusivities plays an important role in determining the relative contributions of these diffusion components to mass transport. For line widths in the range of the median grain size the line width dependence of median fail time, t/sub 50/, results from a change in the relative contribution of these components to the diffusional flux. The model correctly describes the experimental dependence of t/sub 50/ and activation energy on line width.<<ETX>>

Low frequency 1/f noise and current gain degradation in BiCMOS n-p-n transistors

The authors report experimental results on the effect of forward current gain (h/sub fe/ degradation on the low-frequency 1/f noise characteristics of polysilicon emitter n-p-n transistors. A direct relationship between progressively increasing levels of h/sub fe/ degradation and changes in the 1/f noise spectra has been observed. Measurement of the base Gummel characteristic and base current dependence of the noise suggests that surface recombination resulting from hot carrier stress degrades h/sub fe/ and is the dominant 1/f noise source.<<ETX>>

Effect of Annealing and Passivation on the Electromigration and Linewidth Dependence

Continued miniaturization of conductor geometry below 0.5μm has by a concomitant decrease in Al deposition temperature, typically below 300°C. The degree of reliability exhibited by these films is strongly dependent on the grain size distribution and metallurgical configuration. This investigation focuses on the impact of post-deposition processing on changes in conductor microstructure and electromigration for films deposited at low temperature. AlCu(l%)Si(l%) was deposited at 300°C on PECVD phosphosilicate glass. The impact of post-deposition thermal budget on the as deposited grain size and distribution, preferred orientation and stress/strain states were analyzed using scanning electron microscopy, X-Ray diffraction and bending beam technique, respectively. These characteristics were also measured on unpassivated films subjected to the same thermal budget as SiO 2 passivated films so that the geometric confinement and Al-SiO 2 surface interaction could be quantified. Electromigration characteristics were measured for linewidths in the range W=1.0μm to W=10μm, for passivated and unpassivated films. A direct correlation between passivation and grain size was observed for both failure modes. This paper will also discuss the relationship between film stress and preferred orientation, the observed failure modes and their linewidth dependence.

1/f 2 Noise and Electromigration in Al-Cu Interconnects

Electromigration in Al-1.5%Cu interconnects was studied using a direct current (d.c.) induced 1/f 2 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/f 2 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/f 2 noise could be measured was 190°C, 220°C, and 265°C, respectively. The activation energy of 1/f 2 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.