No abstract

Therapeutic study, level IV.

The purpose of this study was to compare the fixation stability of proximal fragments and the mechanical characteristics in proximal femur models of basicervical femoral neck fracture fixed by the femoral neck system (FNS) versus the dynamic hip screw. The mean axial stiffness was 234 ± 35 N/mm in the FNS group and 253 ± 42 N/mm in the DHS group, showing no significant difference (p = 0.654). Mean values for x-axis rotation, y-axis rotation, and z-axis rotation after cycle load were 2.2 ± 0.5°, 6.5 ± 1.5°, and 2.5 ± 0.6°, respectively, in the FNS group and 2.5 ± 0.7°, 5.8 ± 2.1°, and 2.2 ± 0.9°, respectively, in the DHS group, showing no significant differences (p = 0.324, p = 0.245, and p = 0.312, respectively). The mean values of cranial and axial migration of screws within the femoral head were 1.5 ± 0.3 and 2.1 ± 0.2 mm, respectively, in the FNS group and 1.2 ± 0.3 and 2.4 ± 0.3 mm, respectively, in the DHS group, showing no significant differences (p = 0.425 and p = 0.625, respectively). The average failure load at vertical load was 1342 ± 201 N in the FNS group and 1450 ± 196 N in the DHS group, showing no significant difference (p = 0.452). FNS fixation might provide biomechanical stability comparable to that of DHS for treating displaced basicervical femoral neck fractures in young adults.

The stress of damascene Cu integrated with silicon dioxide (SiO2) and a low-k material was analyzed by x-ray diffraction, and that of the via-line structure was evaluated using finite element analysis. In both cases, the hydrostatic stress of the Cu line embedded in SiO2 was greater than that of the Cu line with low-k dielectric, whereas the opposite was true for the von Mises stress. In particular, the von Mises stress in the via embedded in the low-k dielectric was large. It was also shown that the yield strength of the via embedded in the low-k material is severely reduced compared with that of the via embedded in SiO2. Therefore, the deformation of the via, due to high von Mises stress and low yield strength, is expected to be the important failure mode in the interconnects made with low-k dielectrics which have higher coefficient of thermal expansion and lower elastic modulus.

Damascene Cu interconnects show significant differences in both their microstructural and stress behavior as compared to those of Al interconnects patterned using the etching process. Thermal stresses build up during the successive thermal cycles due to the differences in the coefficients of thermal expansion of the component materials. Other than these thermal stresses, growth stresses originating from grain growth develop in damascene Cu interconnects as well. In this study, the linewidth dependence of the stress in damascene Cu was examined experimentally, as well as by numerical simulation. The stresses of damascene Cu with widths ranging from 0.13to2μm were measured using x-ray diffraction, and the measured hydrostatic stress was found to increase with increasing linewidth, in contrast to the typical behavior of Al interconnects. Microstructure analysis using transmission electron microscopy revealed that the grain sizes increased with increasing line dimensions. The increase in stress in the interconnect with increasing dimensions is attributed to the larger grain size, which induces higher growth stress in addition to the thermal stress. The contribution of the growth and thermal stresses of the damascene lines were quantified based on the grain size data utilizing finite element analysis. In this way, the linewidth dependence of the hydrostatic stress of damascene Cu was clearly explained. Finally, the effect of growth stress on the stress-related reliability is discussed.