Stress migration

Conventional CMP typically requires an overburden of copper of at least 4000 A due to low planarization efficiency. An overburden of 1000 A is sufficient for ECMP to achieve planarization without compromising performance in terms of dishing, erosion, and defectivity. A stress migration test was carried out at 250 °C for 333 h on a structure with metal level 1 and level 2 lines with thickness in the range of 0.14-0.16 pm. An increase in resistance by more than 10% is considered a fail. The reduction in electroplated copper thickness can reduce the number of fails in stress migration test as shown in Table 11.1. 

TABLE 11.1 Stress Migration Fails as a Function of Electroplated Copper Thickness. 

Nikolaevskiy, V.N. 1998. Tectonic stress migration as nonlinear wave process along earth crust faults. In Adachi, T. Oka, F. (eds.). Localization and Bifurcation for Solis and Rocks. Rotterdam Balkema. 

To evaluate the effect of temperature gradients on the failure of solder joints, one must keep in mind that the governing physics is described by Eq. (5). All driving forces are always acting. Therefore, the Soret effect is difiicult to separate from other effects such as electromigration and/ or stress migration. In addition, the presence of the other driving forces can produce various effects, such as the appearance of threshold effects. For instance, in one experiment, when the temperature difference across Pb-In solder balls was varied, failure did not occur unless the temperature difference exceeded 8.5°C. If the temperature difference was less than this, the joint essentially remained unaffected. 

Defect shape also plays an important role in the stress migration. The nature of stresses locked in the vicinity of defect depends on shape of the particle impinging the hot sheet. Two shapes have been numerically investigated in Ms analysis -... 

These shapes are modeled as rigid bodies, and pushed against the molten polymer, resulting in a stress field around the defect as shown in Figures 5a 5b. With this state of stress as initial conditions, the sheet is taken to thermoforming temperatures. The locked-in stress migrates to the top resulting in a bump in one case (Fig. 6a) and crater in the other case (Fig. 6b)... 

A series of events can take place in response to the thermal stresses (/) plastic deformation of the ductile metal matrix (sHp, twinning, cavitation, grain boundary sliding, and/or migration) (2) cracking and failure of the brittle fiber (5) an adverse reaction at the interface and (4) failure of the fiber—matrix interface (17—20). 

All three softeners migrate from one compound to another and this must be considered when compounding for a set range of stiffness (modulus) gradiations in the tire components designed to alleviate stress. 

It was shown earlier that the NabaiTO-Hemirg model of creep in solids involved the migration of vacancies out of the stressed solid accompanied by counter-migration of atoms to reduce dre length of the solid in the direction of the applied stress. This property could clearly contribute to densification under an external pressure, given sufficient time of application of the stress... 

Cathodoluminescence microscopy and spectroscopy techniques are powerful tools for analyzing the spatial uniformity of stresses in mismatched heterostructures, such as GaAs/Si and GaAs/InP. The stresses in such systems are due to the difference in thermal expansion coefficients between the epitaxial layer and the substrate. The presence of stress in the epitaxial layer leads to the modification of the band structure, and thus affects its electronic properties it also can cause the migration of dislocations, which may lead to the degradation of optoelectronic devices based on such mismatched heterostructures. This application employs low-temperature (preferably liquid-helium) CL microscopy and spectroscopy in conjunction with the known behavior of the optical transitions in the presence of stress to analyze the spatial uniformity of stress in GaAs epitaxial layers. This analysis can reveal,... 

It is shown that solute atoms differing in size from those of the solvent (carbon, in fact) can relieve hydrostatic stresses in a crystal and will thus migrate to the regions where they can relieve the most stress. As a result they will cluster round dislocations forming atmospheres similar to the ionic atmospheres of the Debye- Huckel theory ofeleeti oly tes. The conditions of formation and properties of these atmospheres are examined and the theory is applied to problems of precipitation, creep and the yield point."... 

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