Stress Migration Failure Research Articles

A New Stress Migration Failure Mode in Highly Scaled Cu/Low-$k$ Interconnects

We identify a new stress migration (SM) failure mode in Cu/low-k interconnects whereby voids are formed in very narrow trenches close to large Cu plates. Finite-element analysis shows that the new failure mode is generated by large stress gradients associated with geometry changes in highly scaled Cu interconnects. This work indicates that management of mechanical stresses will be an important issue for future development of reliable Cu/low- k interconnects.

Effect of Layout Variation on Stress Migration in Dual Damascene Copper Interconnects

The effect of layout variation on stress migration (SM) in Cu damascene interconnects was investigated in detail. In an extrusion pattern in which narrow lines are connected to a wide line, the failure rate decreases as the narrow line becomes longer and wider. It was found that there is a maximum failure rate between 150 and 200 °C for all test patterns. The results for the SM failure rate showed that the initial rate of increase of SM failure for the extrusion pattern is much larger than that for the conventional wide pattern. The effect of the narrow linewidth on the SM failure rate cannot be understood by considering the previous diffusion mechanism. Based on these results, the dependence of vacancy diffusion path and SM failure mechanism on the layout variation is discussed.

Copper stress migration at narrow metal finger with wide lead

Copper stress migration (SM) at narrow metal finger connected with wide lead is investigated in this work. Voiding phenomenon is explored with respect to specific failure site. Metal geometric factors including lead width, lead length and finger length are also discussed in terms of SM failure rates. Meanwhile, in order to study the failure mechanism, a finite element analysis (FEA) is conducted to evaluate the influences from vacancy migration path, hydrostatic stress gradient and different metal geometries. As a result, a characterization regarding SM at narrow metal finger with wide lead is obtained for the reference of reliability assessment and process improvement.

Stress migration phenomenon in narrow copper interconnects

Stress migration (SM) behavior in Cu damascene interconnects was investigated in detail using different kinds of test patterns. SM failure was found in narrow lines that are very long, or connecting to a wide line. In the pattern in which narrow lines are connected to wide metal, the failure rate decreased as the narrow metal becomes longer. It was found that the failure rate in minimum 0.14μm wide lines is more than that in 0.2–0.42μm wide lines. The result of the test patterns with different via arrangements clarified that the placing of the vias at the edge of the M1 line plays an important role in the SM phenomenon in narrow copper lines. Failure analysis using scanning transmission electron microscopy revealed voiding beneath the via at the failure points for all test patterns. It is shown that the enhanced failure rate in the minimum wide lines and the via arrangement effect cannot be understood by the previous diffusion mechanism. Based on these results, the effect of the via arrangement close to the edge of the lower lines on SM failure in narrow lines is discussed.

Modelling Electromigration and Stress Migration Damage in Advanced Interconnect Structures

AbstractPhysical and statistical models have been used extensively to understand and improve electromigration and stress migration induced damage in narrow metal interconnects. As devices continue to shrink, and the interconnect delay becomes a more important fraction of overall circuit delay, the semiconductor industry has begun to make several important changes to the ‘standard’ Al-based interconnect technologies, including (i) a move from metal deposition and metal etch to metal deposition into damascene and dual-damascene structures, (ii) a move from Al-based to Cu-based metallizations, and (iii) a move from oxide to low-k dielectrics between the metal interconnects. The dominant electromigration and stress migration failure mechanisms associated with these advanced interconnect structures are typically different from the failure mechanisms associated with standard Al-based interconnects. In this work, physical and statistical models are used in conjunction with reliability data to compare the failure mechanisms in standard, Al-based interconnects with Cu-based, damascene interconnects. Methods are discussed for determining the dominant failure mechanisms and improving reliability in both types of interconnect.