Browsing by Subject "Grain boundaries"
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Item Effect of downscaling copper interconnects on the microstructure revealed by high resolution tem orientation mapping(2011-12) Kameswaran, Jai Ganesh, 1983-; Ferreira, Paulo J. S. G.; Ho, Paul S.; Rabenberg, Llewellyn K.; Krishnan, Srikanth; Rhee, Seung-Hyun; Gall, MartinThe scaling required to accommodate faster chip performance in microelectronic devices has necessitated a reduction in the dimensions of copper interconnects at the back end of the line. The constant downscaling of copper interconnects has resulted in changes to the microstructure, and these variations are known to impact electrical resistivity and reliability issues in interconnects. In this work, a novel electron diffraction technique called Diffraction Scanning Transmission Electron Microscopy (D-STEM) has been developed and coupled with precession electron microscopy to obtain quantitative local texture information in damascene copper lines (1.8 \mu m to 70 nm in width) with a spatial resolution of less than 5 nm. Misorientation and trace analysis has been performed to investigate the the grain boundary distribution in these lines. The results reveal strong variations in texture and grain boundary distribution of the copper lines upon downscaling. 1.8 \mu m wide lines exhibit strong <111> normal texture and comprise large bamboo-type grains. Upon downscaling to 180 nm, a {111} <110> biaxial texture has been observed. In contrast, narrower lines of widths 120 nm and 70 nm reveal sidewall growth of {111} grains and a dominant <110> normal texture. The fraction of coherent twin boundaries also reduces with decreasing line width. The microstructure changes from bamboo-type in wider lines to one comprising clusters of small grains separated by high angle boundaries in the vicinity of large grains. The evolution of such a microstructure has been discussed in terms of overall energy minimization and dimensional constraints. Finite element analysis has been performed to correlate misorientations between grains and local thermal stresses associated with stress migration. Effect of variations in the copper interconnect microstructure on electromigration flux divergence has also been discussed.Item Study of shear localization using a novel test specimen loaded an a split-Hopkinson compression bar(Texas Tech University, 2003-12) Souther, Tappan GLarge plastic shearing of materials at various loading rates has been known to affect the material microstructure and behavior in a significant manner. These effects include: (1) localization of shear strain into bands of several microns to several tens of microns thick called shear bands, (2) strain and temperature induced phase transformations, (3) grain refinement, and (4) profuse twinning. In this research, a split-Hopkinson compression bar was used to study the effects of high strain rate loading and large plastic in three novel "shear" specimens. Each specimen had a unique geometry producing various degrees of shear deformation when dynamically loaded. The region of large shear deformation was known prior to testing, allowing research to be focused on that specific region of the test specimen. The specimens were tested using projectile velocities ranging from 11 m/s to 22 m/s. The objectives of this research were to investigate the effects of large shear deformation at high loading rates on various metals and furthermore to modal some of the experimentally observed phenomena using finite element analysis. The amount and nature of shear deformation varied depending on the specimen geometry, materials, and metallurgical condition. Adiabatic shear bands were generated within AISI Ti-6A1-4V titanium and AISI 4142 steel. AISI 4142 steel also underwent a significant refinement in grain structure. Profuse twinning and strain induced phase transformations were observed within AISI 304 stainless steel. The microstructure of AISI D-2 tool steel displayed rotation and fracture of carbide particles. Microstructural changes were analyzed by means of optical and scanning electron microscopy without having to cut, section or destroy the test specimens. The geometry of the test specimens allowed the microstructure to be analyzed before and after loading. Loading of the three specimen geometries were simulated for the titanium and steel alloys using the finite element analysis (FEA) software ABAQUS version 6.3. Simulations consisted of a 2-dimensional, plane strain full-scale model that included the effects of adiabatic heating and employed the Johnson-Cook equation in modeling plastic behavior. The FEA predicted adiabatic shear band formation to occur where shear banding was observed experimentally.