Showing papers by "Samuel Graham published in 2002"

Radio-frequency discharge cleaning of silicon-capped Mo/Si multilayer extreme ultraviolet optics

Abstract: Remote oxygen and hydrogen radio-frequency (rf) discharge cleaning experiments have been performed to explore their potential for cleaning carbon-contaminated extreme ultraviolet optics. The samples consisted of silicon wafers coated with 100 A sputtered carbon, as well as bare Mo/Si multilayer mirrors (Si terminated). The samples were exposed for 3 h to rf plasma discharges at 100, 200, and 300 W. The carbon removal and surface oxidation rates were evaluated using sputter through depth profiling Auger spectroscopy. Reflectivity changes and surface roughness measurements were performed using at-wavelength reflectometry (13.4 nm) and atomic force microscopy, respectively. Data show that excited rf O2 consistently removes carbon at a rate approximately six times faster than excited rf H2 for a given discharge power and pressure. rf O2 also induces loss of reflectivity that is related to the growth of SiO2 on the optic surface. rf H2 shows a much lower oxidation rate of the optic surface. In spite of the low...

Anisotropy of intermetallic particle cracking damage evolution in an Al-Mg-Si base wrought aluminum alloy under uniaxial compression

Abstract: Particle cracking is an important damage mode in numerous engineering alloys having anisotropic microstructures. In this contribution, cracking of anisotropic Fe-rich intermetallic particles in an extruded 6061 (T651) Al-alloy is quantitatively characterized as a function of compressive strain for two loading directions. The Fe-rich intermetallic particles rotate when a compressive load is applied parallel to the extrusion direction, which in turn affects the particle cracking process. At low compressive strains, the number fraction of cracked Fe-rich particles is higher in specimens loaded perpendicular to the extrusion axis as compared to that in specimens loaded parallel to the extrusion axis. However, the reverse is true at the high strain levels. These differences in damage evolution are explained on the basis of particle rotations and microstructural anisotropy.

Method for removing carbon contamination from optic surfaces

Abstract: A method using atomic hydrogen for removing carbon contamination from optical surfaces. The method is particularly useful for removing carbon and hydrocarbon contamination in-situ from the surface of the multilayer optics used for extreme ultraviolet lithography (EUVL) without degrading the quality of the optical surface. Atomic hydrogen at pressures in the range of about 10−3 and 10−4 Torr without the potentially detrimental heating of the optic is used to provide cleaning rates of about 6-60 Å/hr.

Quantitative characterization of three-dimensional damage evolution in a wrought Al-alloy under tension and compression

Abstract: Three-dimensional (3-D) microstructural damage due to cracking of Fe-rich intermetallic particles is quantitatively characterized as a function of strain under compression and tension in an Al-Mg-Si base wrought alloy. The 3-D number fraction of damaged (cracked) particles, their average volume, average surface area, and shape factor are estimated at different strain levels for deformation under uniaxial tension and compression. It is shown that, depending on the type of loading, loading direction, particle shape, and microstructural anisotropy, the two-dimensional (2-D) number fraction of the damaged particles can be smaller or larger than the corresponding true 3-D number fraction. Under uniaxial tension, the average volume and surface area of cracked particles decrease with the strain. However, the average volume and surface area of the cracked particles increase with the increase in the compressive strain, implying that more and more larger elongated particles crack at higher and higher stress levels, which is contrary to the predictions of the existing particle cracking theories. In this alloy, the damage development due to particle cracking is intimately coupled with the particle rotations. The differences in the damage evolution under tension and compression are explained on the basis of the differences in the particle rotation tendencies under these two loading conditions.

Rotations of brittle particles during plastic deformation of ductile alloys

Abstract: Experimental evidence is presented to show that significant rotations of brittle phase inclusions of a Fe-rich intermetallic phase occur during plastic deformation on an AlMgSi base wrought aluminum alloy. The particle rotations are quantitatively characterized, for uniaxial tension, compression, torsion, and notch-tension test specimens strained to different strain levels. The particle rotations are monitored by measuring the morphological orientation distribution function of the particles. Significant particle rotations occur under all loading conditions. The morphological orientation distribution function evolves with plastic strain under uniaxial tension, compression, and torsion. The particles tend to align themselves in the direction parallel to applied (or induced) tensile stress for deformation under tension and compression. In the case, of torsion test specimens, at least up to 98% torsion strain, the particles tend to align along the direction at an angle of 45° to torsion axis.

Distributions of Stretch and Rotation in Polycrystalline OFHC Cu

Abstract: High resolution experimental characterization of material stretch and rotation fields in relatively fine-grained polycrystals has been limited, inhibiting direct comparison with predictions of crystal plasticity theory. In this study, micron scale grids used more commonly in etching of substrates for microelectronic circuits were deposited on specimens of Oxygen Free High Conductivity Copper (OFHC Cu) subsequently subjected to uniaxial compressive deformations to effective strain levels up to unity. Material stretch and rotation fields were assessed for fields of view encompassing on the order of 20 grains. Some rather striking features emerge, including the apparent relative lack of deformation in regions sized on the order of large grains, and the apparent concentration of stretch and rotation in bands surrounding these relatively undeformed areas. Comparisons are drawn with results of 3D crystal plasticity calculations performed on digitized grain structures that conform to representative microstructures in terms of initial grain size and shape distributions. The crystal plasticity simulations predict regions of relatively large rotation and relatively localized stretch traversing multiple grains. The numerical solutions also exhibit slightly higher local stresses in the vicinity of grain boundaries and triple points than in grain interiors, a phenomenon attributed to local lattice misorientation among neighboring grains. However, the crystal plasticity calculations do not, in an average sense, predict larger-than-average maximum stretch or rotation in the grain boundary regions. The numerical solutions are also quite sensitive to initial lattice orientations assigned to the grains. Comments are made regarding the segmentation of slip within the grains and its implications for modeling, based upon direct comparison of results from experiments and simulations.

Investigating the thermal response of a micro-optical shutter

Abstract: This paper discusses the thermal analysis of a fully integrated micro-switch for surety applications. Specifically, this study focuses on the temperature increase of a micromachined optical shutter with spot heating from a micro-laser. To analyze the shutter response, a 'Design-to-Analysis' interface has been built that generates an accurate 3-D solid geometry from the 2-D mask layout. Besides performing analysis, engineers can also use this solid modeler to virtually prototype and verify a design before fabrication. A parametric study is performed to determine the effects of thermal conductivity and contact resistance on the thermal response of this passively cooled device.