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Thermal stress and stress relaxation in copper metallization for ULSI interconnects
textThermal stress and mass transport are key issues for Cu metallization yield and
reliability. In this study, thermal stresses in Cu films, and line structures with three types
of inter-level dielectric (ILD), SiOF, CDO (carbon doped oxide) and SiLK, and the
linewidths of 0.2µm and 0.4µm, were investigated using a bending beam technique, Xray
diffraction (XRD) and finite element analysis (FEA). During thermal cycling, plastic
yield was found to play an important role for the plastic deformation of Cu films. The
deformation was strongly affected by the presence of impurities in the films. The stress
in Cu lines was found dependent on annealing and the properties of the ILD, but not
sensitive to the change of linewidth in submicron range. FEA results indicated that the
stresses in the ILD’s as a function of Cu linewidth were quite different in the
interconnects.
Stress-induced void formation was studied in passivated Cu films during thermal
cycling and isothermal annealing. The void density was strongly affected by the ramp
rate, film stress and thermal history during thermal cycling. A kinetic model was
developed for the void growth, and an activation energy of 0.75eV was deduced. The
local stress gradients due to the mechanical anisotropy, and in the void vicinity were
evaluated by FEA models.
In order to characterize the Cu/passivation interface diffusivity, isothermal stress
relaxations of Cu films and line structures were studied. The isothermal stress relaxation
behaviors were shown significantly different for the films with different passivation
layers, SiNx, SiC, modified SiC and a metal cap layer. Diffusional kinetic models were
developed for the stress relaxation in thin films and then combined with experimental
results to deduce the interfacial diffusivities, which were found to be much smaller than
the grain boundary diffusivity. In the line structures with different ILD’s, the effects of
the passivation layers were found to be consistent with the results of the Cu films. The
mechanical confinement of the passivation layers on the stress in the Cu lines was
evaluated using FEA models. Results from this study demonstrate that stress relaxation
measurement is an effective method to evaluate electromigration (EM) performance in
Cu metallization.Materials Science and Engineerin
Application of fluorescence in situ hybridization in the detection of bladder transitional-cell carcinoma: A multi-center clinical study based on Chinese population
Objective: To evaluate the diagnostic value of fluorescence in situ hybridization (FISH) in bladder cancer. Methods: We enrolled healthy volunteers and patients who were clinically suspected to have bladder cancer and conducted FISH tests and cytology examinations from August 2007 to December 2008. Receiver operating characteristic (ROC) curve analysis was performed and the area under curve (AUC) values were calculated for both the FISH and urine cytology tests. Results: A cohort of 988 healthy volunteers was enrolled to establish a reference range for the normal population. A total of 4807 patients with hematuria were prospectively, randomly enrolled for the simultaneous analysis of urine cytology, FISH testing, and a final diagnosis as determined by the pathologic findings of a biopsy or a surgically-excised specimen. Overall, the sensitivity of FISH in detecting transitional-cell carcinoma was 82.7%, while that of cytology was 33.4% (p < 0.001). The sensitivity values of FISH for non-muscle invasive and muscle invasive bladder transitional-cell carcinoma were 81.7% and 89.6%, respectively (p = 0.004). The sensitivity values of FISH for low and high grade bladder cancer were 82.6% and 90.1%, respectively (p = 0.002). Conclusion: FISH is significantly more sensitive than voided urine cytology for detecting bladder cancer in patients evaluated for gross hematuria at all cancer grades and stages. Higher sensitivity using FISH was obtained in high grade and muscle invasive tumors. Keywords: Bladder transitional-cell carcinoma, Fluorescence in situ hybridization, Detection, Grade, Stag