The continuous process of miniaturization in the microelectronics industry requires the introduction of new, thinner interlayer dielectric (ILD) materials with poorer mechanical properties. As a ...consequence, new mechanical characterization techniques are needed in the industry to evaluate very thin films. This work presents a new fracture characterization technique for thin films, called “dual tip indentation” (DTI). The technique takes advantage of a particular geometry of the indentation tip to provoke shallow and controlled cracking on the targeted brittle thin film. The technique is applied to the fracture characterization of two different ILD with four thicknesses, ranging from 100nm to 500nm. Further fractographic analysis, along with finite element modeling, shows that it is possible to extract intrinsic fracture properties from the fracture load. The technique allows one to discriminate between the ILD and, for both materials, 100nm films show lower strength. No effect of film thickness on strength is observed in the range between 200 and 500nm. The results from DTI compare well with those previously obtained for the same materials from membrane testing, taking into account the differences in volume tested.
Microelectronic industry is driven by the continuous miniaturization process conducing to the introduction of materials with better performance. These materials are subjected to stresses mainly due ...to thermal mismatch, microstructural changes or process integration which can be in the origin of mechanical reliability issues. To study these phenomena and even electromigration a good mechanical characterization of the materials is needed. This work aims at developing tests to assess fracture and elastoplastic behavior of thin Cu films. The tests developed are based on the deflection of microbeams (micromachined using a focused ion beam) using a nanoindenter. Different test geometries for microbeams have been evaluated and quantitative data have been obtained combining experimental results with analytical or numerical models, depending on the property under study. Microbeam response shows a strong dependence on the orientation of the grains close to the fixed end. Grain orientation has been measured by electron backscatter diffraction and the plastic behavior has been modeled by the finite element method using an in-house crystal plasticity subroutine. The effect of film thickness on fracture energy has been determined from tests of notched beams.
•Cu microbeams have been machined with a focused ion beam and tested at a TriboIndenter.•Crystal plasticity has been accounted for when modeling constitutive behavior of Cu.•Fracture energy has been calculated using notched microcantilever beams.•Fracture energy decreases with film thickness.
The continuous miniaturization process in the microelectronic industry, along with the introduction of Interlayer Dielectrics (ILDs) with poorer mechanical properties, makes necessary the development ...of characterization techniques to evaluate the mechanical performance of very thin films. This work presents a mechanical characterization technique for thin films based on membrane testing. Membranes, micromachined with anisotropic wet etching of Si, are tested to fracture using a nanoindenter to apply the load and register the provoked deflection. The technique is applied to the fracture characterization of two different ILDs with four thicknesses ranging from 100nm to 500nm. Combination of experiments and finite element simulations allows for the calculation of the strength of the materials from the fracture load. The technique permits to discriminate both ILDs and to establish clear thickness dependence: for both materials, 100nm films show a significant lower strength while no effect of film thickness on strength is observed in the range between 200 and 500nm. A sensitivity analysis of the outcome of the technique, the fracture stress, to the variability of the input parameters is presented, showing the robustness of the proposed approach: the experimental error in the fracture stress is smaller than the variation in the input parameters.
•Ceramic dielectric membranes have been micromachined and tested using a nanoindenter.•Constitutive behavior and residual stresses of the films are obtained through modeling.•Fracture loads and stresses allow classifying thin films.•Films 100nm thick show a weaker behavior than the thicker ones.
Comparative studies of the tetrapod raldh2 ( aldh1a2 ) gene, which encodes a retinoic acid (RA) synthesis enzyme, have led to the identification of a dorsal spinal cord enhancer. Enhancer activity is ...directed dorsally to the roof plate and dorsal-most (dI1) interneurons through predicted Tcf- and Cdx-homeodomain binding sites and is repressed ventrally via predicted Tgif homeobox and ventral Lim-homeodomain binding sites. Raldh2 and Math1/Cath1 expression in mouse and chicken highlights a novel, transient, endogenous Raldh2 expression domain in dI1 interneurons, which give rise to ascending circuits and intraspinal commissural interneurons, suggesting roles for RA in the ontogeny of spinocerebellar and intraspinal proprioceptive circuits. Consistent with expression of raldh2 in the dorsal interneurons of tetrapods, we also found that raldh2 is expressed in dorsal interneurons throughout the agnathan spinal cord, suggesting ancestral roles for RA signaling in the ontogenesis of intraspinal proprioception.
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