Crystallography and Microstructure of Manganese-Sulfide Inclusions in Steel.

Development of preferred orientation in manganese sulfide inclusions in hot-rolled steel was studied by electron diffraction. Specimens of resulfurized steel were examined as-cast, and at plane strains of 0.5, 1.0, and 1.5 using selected-area electron diffraction in a transmission electron microscope. Specimens were made electron transparent by a combination of mechanical grinding and ion-beam milling. Diffraction patterns and specimen tilts were measured and a microcomputer was used to plot inverse pole figures, and quantitatively evaluate the degree of crystallographic texture. It was found that the inclusions in the as-cast specimen had an essentially r and om orientation but plane strain brought about a texture that was most intense at a strain of 1.0. Clustering of the rolling direction, rolling plane normal, and transverse direction about the indicates a {100} ideal orientation. The behavior of the texture intensity as a function of strain is attributed to strain hardening of the primary {110}(' ) slip systems. Final shape of the inclusions was also studied as a function of inclusion orientation. It was found that there is only a moderate correlation between shape and orientation. This result is attributed, first to the fact that many as-cast inclusions are not round but are created elongated by being forced between dendrite arms. Also, the resolved shear stresses on the preferred slip planes cannot drop to zero under the normal stresses that lead to plane strain, as they can under uniaxial compression. Microstructures of as-cast and hot-rolled inclusions were studied by electron and light microscopy. As-cast inclusions frequently contained iron-rich, possibly iron-oxide, cores with a very fine grain size. Deformed inclusions showed a cold-worked and recovered structure consisting of dislocations, subgrains, low-angle boundaries, and precipitate particles in many places. Twins were observed occasionally, but not frequently enough to be considered an important deformation mechanism.Ph.D.Engineering, Materials scienceUniversity of Michiganhttp://deepblue.lib.umich.edu/bitstream/2027.42/158873/1/8215042.pd

HRTEM image simulations for the study of ultra-thin gate oxides

We have performed high resolution transmission electron microscope (HRTEM) image simulations to qualitatively assess the visibility of various structural defects in ultra-thin gate oxides of MOSFET devices, and to quantitatively examine the accuracy of HRTEM in performing gate oxide metrology. Structural models contained crystalline defects embedded in an amorphous 16 {angstrom}-thick gate oxide. Simulated images were calculated for structures viewed in cross-section. Defect visibility was assessed as a function of specimen thickness and defect morphology, composition, size and orientation. Defect morphologies included asperities lying on the substrate surface, as well as ''bridging'' defects connecting the substrate to the gate electrode. Measurements of gate oxide thickness extracted from simulated images were compared to actual dimensions in the model structure to assess TEM accuracy for metrology. The effects of specimen tilt, specimen thickness, objective lens defocus and coefficient of spherical aberration (C{sub s}) on measurement accuracy were explored for nominal 10{angstrom} gate oxide thickness. Results from this work suggest that accurate metrology of ultra-thin gate oxides (i.e. limited to several per cent error) is feasible on a consistent basis only by using a C{sub s}-corrected microscope. However, fundamental limitations remain for characterizing defects in gate oxides using HRTEM, even with the new generation of C{sub s}-corrected microscopes

HRTEM image simulations for gate oxide metrology

High resolution transmission electron microscopy (HRTEM) has found extensive use in the semiconductor industry for performing device metrology and characterization. However, shrinking device dimensions (gate oxides are rapidly approaching 10{angstrom}) present challenges to the use of HRTEM for many applications, including gate oxide metrology. In this study, we performed HRTEM image simulations of a MOSFET device to examine the accuracy of HRTEM in measuring gate oxide thickness. Length measurements extracted from simulated images were compared to actual dimensions in the model structure to assess TEM accuracy. The effects of specimen tilt, specimen thickness, objective lens defocus and coefficient of spherical aberration (C{sub s}) on measurement accuracy were explored for nominal 10{angstrom} and 16{angstrom} gate oxide thicknesses. The gate oxide was modeled as an amorphous silicon oxide situated between a gate electrode and substrate, both modeled as single crystal Si(100). Image simulations of the sandwich structure were performed in cross-section (with Si[110] parallel to beam direction) using the multislice approximation for a 200 kV microscope with C{sub s}=0.5mm. Amorphous slices were added to the top and bottom of the specimen to simulate the amorphization that occurs during typical specimen preparation. The actual gate oxide thickness, T, is defined as the distance between the bounding Si atoms in the model structure. The gate oxide thickness was also measured directly in pixels from the simulated image. We use a statistical routine to calculate the standard deviation in pixel intensity for each horizontal row (or y-coordinate) in the simulated image. Local minima in the standard deviation, which correspond to low-intensity regions between Si[110] dumbbells, were used to calibrate the image length scale. The measured gate oxide thickness was then compared to the actual (model) thickness to assess accuracy for a variety of microscope and specimen conditions. Results reveal no consistent trends in measurement accuracy as a function of specimen thickness, specimen tilt, or objective lens defocus

HRTEM image simulations of structural defects in gate oxides

We have performed high-resolution transmission electron microscope image simulations to assess the visibility of various structural defects in gate oxides at electron microscope resolutions

HRTEM image simulations for gate oxide metrology

High resolution transmission electron microscopy (HRTEM) has found extensive use in the semiconductor industry for performing device metrology and characterization. However, shrinking device dimensions (gate oxides are rapidly approaching 10{angstrom}) present challenges to the use of HRTEM for many applications, including gate oxide metrology. In this study, we performed HRTEM image simulations of a MOSFET device to examine the accuracy of HRTEM in measuring gate oxide thickness. Length measurements extracted from simulated images were compared to actual dimensions in the model structure to assess TEM accuracy. The effects of specimen tilt, specimen thickness, objective lens defocus and coefficient of spherical aberration (C{sub s}) on measurement accuracy were explored for nominal 10{angstrom} and 16{angstrom} gate oxide thicknesses. The gate oxide was modeled as an amorphous silicon oxide situated between a gate electrode and substrate, both modeled as single crystal Si(100). Image simulations of the sandwich structure were performed in cross-section (with Si[110] parallel to beam direction) using the multislice approximation for a 200 kV microscope with C{sub s}=0.5mm. Amorphous slices were added to the top and bottom of the specimen to simulate the amorphization that occurs during typical specimen preparation. The actual gate oxide thickness, T, is defined as the distance between the bounding Si atoms in the model structure. The gate oxide thickness was also measured directly in pixels from the simulated image. We use a statistical routine to calculate the standard deviation in pixel intensity for each horizontal row (or y-coordinate) in the simulated image. Local minima in the standard deviation, which correspond to low-intensity regions between Si[110] dumbbells, were used to calibrate the image length scale. The measured gate oxide thickness was then compared to the actual (model) thickness to assess accuracy for a variety of microscope and specimen conditions. Results reveal no consistent trends in measurement accuracy as a function of specimen thickness, specimen tilt, or objective lens defocus

Thermodynamic Strengthening of Heterointerfaces in Nanoceramics

Thermodynamic Strengthening of Heterointerfaces in Nanoceramic