Showing papers by "Samuel Graham published in 2003"

Void growth in 6061-aluminum alloy under triaxial stress state

Abstract: In numerous metals and alloys, ductile fracture involves void nucleation, growth, and coalescence. In this contribution, void growth has been quantitatively characterized in an extruded 6061-wrought Al-alloy as a function of stress state in notch tensile test specimens. Digital image analysis and Stereology have been used to estimate the volume fraction and three-dimensional number density of voids in a series of interrupted notch tensile test specimens where the local stress state is predominantly triaxial. Finite elements (FE) simulations have been used to compute the stress states at different locations in the specimens. The computed stress states and experimentally estimated average void volume are utilized to verify analytical void growth models. Lack of agreement between the predictions of the models and the experimental data is due to interactions between neighboring voids, which are ignored in the theoretical models, and continuous void nucleation. The following empirical damage evolution equation is obtained from the experimental data on void volume fraction expressed as % ( f ), and the corresponding local equivalent plastic strain ( e p ) and stress triaxiality ( I ) computed from FE simulations: f = a + b ln[ e p ]+ cI . In this equation, a , b and c are empirical constants whose values depend on the alloy chemistry, heat treatment, and microstructure. The equation is useful only for 6061(T6) Al-alloy.

Numerical analysis of the transverse thermal conductivity of composites with imperfect interfaces

Abstract: Estimation of the transverse thermal conductivity of continuous fiber reinforced composites containing a random fiber distribution with imperfect interfaces was performed using finite element analysis. FEA results were compared with the classical solution of Hasselman and Johnson to determine limits of applicability. The Hasselman and Johnson model predicts the effective thermal conductivity within 3 percent of the numerical estimates for interfacial conductance values of 1 × 10 -2 - 1 × 10 3 W/m 2 K, fiber-matrix conductivity ratios between 1 and 100, and fiber volume fractions up to 50 percent which are properties typical of ceramic composites

Three-dimensional particle cracking damage development in an Al–Mg-base wrought alloy

Abstract: Experiments have been performed to quantitatively characterize the three-dimensional (3-D) microstructural damage due to cracking of Fe-rich intermetallic particles in an Al/Mg-base extruded 5086(O) alloy as a function of strain under uniaxial compression and tension. The 3-D number density and average volume of the cracked particles are estimated using the unbiased and efficient large area disector (LAD) stereological technique. In each specimen, the two-dimensional (2-D) number fraction of cracked particles is significantly lower than the corresponding 3-D number fraction. Therefore, the conventional 2-D damage measurements considerably underestimate the true 3-D damage due to particle cracking in this alloy. Comparison of the 3-D damage data on the 5086(O) alloy and earlier data on 6061(T6) alloy reveals that at all tensile/compressive stress levels higher than the yield stress of both alloys, the 3-D number fraction of cracked Fe-rich intermetallic particles in the 5086(O) alloy is significantly lower than its corresponding value in the 6061(T6) alloy. Therefore, the 5086(O) alloy is less prone to damage progression due to particle cracking compared to the 6061(T6) alloy. In both the alloys, significant rotations of the Fe-rich intermetallic particles occur during deformation under uniaxial compression. These rotations tend to align the particles along the direction of induced tensile stretch. The particle rotations in turn affect the progression of damage due to particle cracking. For deformation under uniaxial compression, the average volume of cracked Fe-rich particles increases with the increase in the strain. These observations are explained on the basis of the particle rotations. # 2003 Elsevier Science B.V. All rights reserved.

Atomic hydrogen cleaning of EUV multilayer optics

Abstract: Recent studies have been conducted to investigate the use of atomic hydrogen as an in-situ contamination removal method for EUV optics. In these experiments, a commercial source was used to produce atomic hydrogen by thermal dissociation of molecular hydrogen using a hot filament. Samples for these experiments consisted of silicon wafers coated with sputtered carbon, Mo/Si optics with EUV-induced carbon, and bare Si-capped and Ru-B4C-capped Mo/Si optics. Samples were exposed to an atomic hydrogen source at a distance of 200 - 500 mm downstream and angles between 0-90° with respect to the source. Carbon removal rates and optic oxidation rates were measured using Auger electron spectroscopy depth profiling. In addition, at-wavelength peak reflectance (13.4 nm) was measured using the EUV reflectometer at the Advanced Light Source. Data from these experiments show carbon removal rates up to 20 A/hr for sputtered carbon and 40 A/hr for EUV deposited carbon at a distance of 200 mm downstream. The cleaning rate was also observed to be a strong function of distance and angular position. Experiments have also shown that the carbon etch rate can be increased by a factor of 4 by channeling atomic hydrogen through quartz tubes in order to direct the atomic hydrogen to the optic surface. Atomic hydrogen exposures of bare optic samples show a small risk in reflectivity degradation after extended periods. Extended exposures (up to 20 hours) of bare Si-capped Mo/Si optics show a 1.2% loss (absolute) in reflectivity while the Ru-B4C-capped Mo/Si optics show a loss on the order of 0.5%. In order to investigate the source of this reflectivity degradation, optic samples were exposed to atomic deuterium and analyzed using low energy ion scattering direct recoil spectroscopy to determine any reactions of the hydrogen with the multilayer stack. Overall, the results show that the risk of over-etching with atomic hydrogen is much less than previous studies using RF discharge cleaning while providing cleaning rates suitable for EUV lithography operations.

Rates and mechanisms of optic contamination in the EUV engineering test stand

Abstract: The EUV Engineering Test Stand (ETS) is a full field, alpha class Extreme Ultraviolet Lithography (EUVL) tool that has demonstrated the printing of 70 nm resolution scanned images. The tool employs Mo/Si multilayer optics that reflect EUV radiation (13.4nm / 92.5eV) with ~67% peak reflectance per optic. For good reflectivity, many (greater than or equal to 40)Mo/Si layers must be present. Consequently, processes such as plasma induced multilayer erosion, which reduces the number of bilayer pairs on plasma facing optics, need to be understood. Since most materials readily absorb EUV photons, it is important to prevent contamination of mirror surfaces with EUV absorbing material. Contamination can occur by EUV photons “cracking” hydrocarbons or other species absorbed on the optical surfaces. The first ETS condenser component, referred to as C1, is coated with Mo/Si multilayers. Data collected from Mo/Si witness plates placed at the C1 position indicate erosion, using the Xe Laser Produced Plasma (LPP) spray jet, of 1 bilayer per ~15 million shots. Preliminary experiments with a filament jet yielded a significantly higher erosion rate. In the spray jet studies, erosion was found to depend sensitively on the composition of the residual background environment. Addition of low levels, ~7x10 -7 Torr, of H 2 O to the vacuum background produced oxidation of the Si cap, and significantly slowed spray jet induced erosion. Operation of the plasma changed the environment in the Illuminator Chamber from oxidizing to carbonizing, thereby changing the nature of the contamination found environment at the C3 optic which does not view the plasma directly (and therefore does not erode). The change in environment is attributed to plasma induced outgassing of fluorocarbons in the Illuminator. Due to the non zero conductance between the Illuminator and Main Chambers, fluorocarbons were also found in the Main Chamber during Xe LPP operation. RGA data are presented that document the effect. In the presence of such outgassing, Carbon deposition rates were measured for the C3, and P.O. Box optics. For C3, a C deposition rate of 3 angstrom / 10 million shots was found, while for the PO Box, a C deposition rate of 0.02 angstrom / 10 million shots was found from the data. All data was acquired with no attempt to mitigate C deposition with gas phase additives such as O 2 .

Investigating the thermal response of a micro-optical shutter

Abstract: The thermal analysis of a fully integrated micro-switch for surety applications will be presented. Specifically, this study focuses on the temperature increase of a micromachined optical shutter with spot heating from a solid-state laser. To analyze the shutter response, a "design-to-analysis" interface has been developed that generates an accurate three-dimensional (3-D) solid geometry from the two-dimensional (2-D) mask layout. By building the "design-to-analysis" interface, engineers can use this solid modeler to virtually prototype and verify a design, and to simulate the performance of micro-devices before fabrication. To determine the effects of thermal conductivity and contact resistance on the thermal response of this passively cooled device, a sensitivity study is also performed.

System and process learning in a full-field, high-power EUVL alpha tool

Abstract: Full-field imaging with a developmental projection optic box (POB 1) was successfully demonstrated in the alpha tool Engineering Test Stand (ETS) last year. Since then, numerous improvements, including laser power for the laser-produced plasma (LPP) source, stages, sensors, and control system have been made. The LPP has been upgraded from the 40 W LPP cluster jet source used for initial demonstration of full-field imaging to a high-power (1500 W) LPP source with a liquid Xe spray jet. Scanned lithography at various laser drive powers of >500 W has been demonstrated with virtually identical lithographic performance.

The Effects of Processing Conditions on the Thermal Conductivity of Polycrystalline Silicon Films

Abstract: Polycrystalline silicon has been a primary material used in development of mocroelectrical mechanical systems due to its attractive structural properties and compatibility with CMOS processing. Among its many applications, polysilicon is currently being employed in MEMS devices that require thermal dissipation or thermal management to ensure functionality (thermal actuators, microengines, etc.). In these applications, heat conduction in polycrystalline silicon becomes a primary factor in the design, performance, and reliability of thermal MEMS.© 2003 ASME

Nondestructive Characterization of Thermal Shock and Oxidation-Induced Damage by Flash Diffusivity

Abstract: The effect of thermal shock and oxidation-induced damage on the thermal diffusivity of unidirectional Nicalon-LAS glass–ceramic composites is presented in this study. The data presented show that thermal diffusivity measurements provide a sensitive nondestructive method whereby damage progression may be assessed. Samples were exposed to isothermal oxidation and thermal shock environments. In addition, combined cycles of oxidation and thermal shock were also evaluated. The thermal diffusivity transverse to the fibers was measured to detect changes in material integrity. Significant decreases up to 23% were observed in the thermal diffusivity of the material.

Thermophysical Properties of Ni Films for LIGA Microsystems

Abstract: This work reports temperature dependent thermophysical properties characterization of electrodeposited Ni and NiMn alloys intended for LIGA Microsystems applications. A steady-state method is used to determine the in-plane thermal conductivity. Anisotropic thermal diffusivity characterization is performed using a photothermoelectric technique. The measured thermal properties are dependent on the deposition method and also on subsequent temperature annealing steps. The thermal transport measurement results are correlated with scanning electron microscopy studies of the grain structure and measurements of the electrical transport properties.