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The bulk minority-carrier lifetime in p- and n-type kerfless epitaxial (epi) crystalline silicon wafers is shown to increase >500x during phosphorus gettering. We employ kinetic defect simulations and microstructural characterization techniques to elucidate the root cause of this exceptional gettering response. Simulations and deep-level transient spectroscopy (DLTS) indicate that a high concentration of point defects (likely Pt) is "locked in" during fast (60 °C/min) cooling during epi wafer growth. The fine dispersion of moderately fast-diffusing recombination-active point defects limits as-grown lifetime but can also be removed during gettering, confirmed by DLTS measurements. Synchrotron-based X-ray fluorescence microscopy indicates metal agglomerates at structural defects, yet the structural defect density is sufficiently low to enable high lifetimes. Consequently, after phosphorus diffusion gettering, epi silicon exhibits a higher lifetime than materials with similar bulk impurity contents but higher densities of structural defects, including multicrystalline ingot and ribbon silicon materials. Device simulations suggest a solar-cell efficiency potential of this material >23%. [ABSTRACT FROM AUTHOR]

Dislocation clusters in multicrystalline silicon limit solar cell performance by decreasing minority carrier diffusion length. Studies have shown that the recombination strength of dislocation clusters can vary by up to two orders of magnitude, even within the same wafer. In this contribution, we combine a surface-analysis approach with bulk characterization techniques to explore the underlying root cause of variations in recombination strength among different clusters. We observe that dislocation clusters with higher recombination strength consist of dislocations with a larger variation of line vector, correlated with a higher degree of variation in dislocation etch-pit shapes (ellipticities). Conversely, dislocation clusters exhibiting the lowest recombination strength contain mostly dislocations with identical line vectors, resulting in very similar etch-pit shapes. The disorder of dislocation line vector in high-recombination clusters appears to be correlated with impurity decoration, possibly the cause of the enhanced recombination activity. Based on our observations, we conclude that the relative recombination activity of different dislocation clusters in the device may be predicted via an optical inspection of the distribution and shape variation of dislocation etch pits in the as-grown wafer. [ABSTRACT FROM AUTHOR]

The efficacy of higher-temperature gettering processes in reducing precipitated iron concentrations is assessed by synchrotron-based micro-X-ray fluorescence. By measuring the same grain boundary before and after phosphorus diffusion in a set of wafers from adjacent ingot heights, the reduction in size of individual precipitates is measured as a function of gettering temperature in samples from the top of an ingot intentionally contaminated with iron in the melt. Compared to a baseline 820 °C phosphorus diffusion, 870 °C and 920 °C diffusions result in a larger reduction in iron-silicide precipitate size. Minority carrier lifetimes measured on wafers from the same ingot heights processed with the same treatments show that the greater reduction in precipitated metals is associated with a strong increase in lifetime. In a sample contaminated with both copper and iron in the melt, significant iron gettering and complete dissolution of detectable copper precipitates is observed despite the higher total metal concentration. Finally, a homogenization pre-anneal in N2 at 920 °C followed by an 820 °C phosphorus diffusion produces precipitate size reductions and lifetimes similar to an 870 °C phosphorus diffusion without lowering the emitter sheet resistance. [ABSTRACT FROM AUTHOR]

Strain distributions within a silicon-on-insulator (SOI) layer induced by overlying compressively stressed Si3N4 features were measured using x-ray microbeam diffraction. A comparison of analytical and numerical mechanical models of the depth-averaged strain distributions to the measured strain profiles in the SOI layer indicated a blanket film stress of -2.5 GPa in the Si3N4 features. A two-dimensional boundary element model, implemented to analyze thin film/substrate systems, reproduced the observed strain distributions better than an edge-force formulation due to the incorporation of loading along the Si3N4/Si interface. [ABSTRACT FROM AUTHOR]

Heteroepitaxial thin-film features that are lattice matched to the underlying substrate undergo elastic relaxation at the free edges of the feature. To characterize the degree of elastic relaxation, we employed synchrotron-based x-ray diffraction techniques to map the change in lattice spacing in the thin film at a submicron resolution. Measurements were conducted on 0.24-μm thick, heteroepitaxially grown SiGe strips of various widths on Si (001). A comparison of the SiGe diffraction peak positions across the features provides a real-space mapping of the extent of elastic relaxation as a function of linewidth. The resultant in-plane normal film stress measurements were compared to calculated values from several elastic mechanical models to assess their validity in predicting stress distributions within the features. [ABSTRACT FROM AUTHOR]

The manipulation of strain in micromachined silicon structures presents an opportunity in the control of surface processes in epitaxial growth. With appropriate fabrication techniques, the magnitude, crystallographic direction, and symmetry of the strain at a Si surface can be precisely controlled with this strategy. Synchrotron x-ray microdiffraction techniques allow simultaneous independent measurements of the strain and bending in these structures and serve to calibrate the fabrication process. Bending is the dominant source of strain in a microfabricated Si bridge loaded at its ends by silicon nitride thin films that we have used as a strained substrate in studies of Ge epitaxial growth. The total strain difference between the top and bottom of the bent bridge exceeds 10-3 in present structures and can potentially be increased in optimized devices. These micromachined substrates complement other methods for producing strained silicon and silicon- germanium structures for improved electrical device performance and for fundamental studies of epitaxial growth. [ABSTRACT FROM AUTHOR]

We used hard x-ray fluorescence and soft x-ray transmission microscopy to quantitatively measure “in situ” Cu/SiO[sub 2] interconnect dimensions down to 0.3 μm dimensions. We describe methods and analysis techniques for measuring submicron linewidths, lengths, and thicknesses with accuracies of 30–60 nm precision. The dimensions and shape of submicron Cu vias, W lines, and a 20 nm Ta liner and an electromigration defect (void) were determined by these methods. These nondestructive techniques promise to be useful for nanometer precision metrology studies of a variety of materials systems. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The precipitation and dissolution of copper impurities at oxygen precipitates and stacking faults in silicon were studied using thermal budgets commensurate with standard integrated circuit processing. Additionally, in order to develop a better understanding of the dissolution process, we have obtained results on the chemical state of the copper precipitates. The goal of this work was to determine the feasibility of removing and maintaining copper impurities away from the active device region of an integrated circuit device by use of oxygen precipitates and stacking faults in the bulk of the material. Based on our results, we provide a basis for a predictive understanding of copper precipitation and dissolution in silicon and we discuss the feasibility of copper impurity control in silicon integrated circuit devices. [ABSTRACT FROM AUTHOR]

Examines the electron transport characteristics of ZnS. Application of the Boltzmann transport equation in determining the transport characteristics of the zinc compound; Information on the treatment of electron scattering in ZnS; Evaluation of the transport measurement results on ZnS.

Radially oriented Nd-Fe-B ring magnets have been prepared by backward extrusion of melt-spun powder. The position dependent of the microstructure, the magnetic properties, and the crystal alignment of the extruded rings have been investigated. The magnetic properties in radial direction increase slightly along the axis from the bottom to the middle then steeply decrease at the upper end of the ring. The magnetic properties and x-ray diffraction patterns of the upper end are very close to that of the isotropic pressed precursor. It suggests that the extruded ring approximately retains the initial structure at its upper end which is because the formation of texture is difficult at the initial stage of hot extrusion. Characteristic microstructure morphologies were found at different spatial positions: flake-shaped grains for the inner, elongated grains for the middle, and particle-shaped grains for the outer region in the cross section. Only particle-shaped grains were observed at the upper end of the ring. But the circumferential homogeneity of the surface magnetic flux densities is better in an extruded ring magnet than in a radially oriented ring prepared by sintering method. The deformation and texture formation processes were discussed. The deformation and texture formation in backward extruded magnets from melt-spun Nd-Fe-B precursors may possibly involve grain boundary sliding and grain rotation, solution-precipitation process, and preferred growth of Nd2Fe14B nanograins along the easy growth a-axis. [ABSTRACT FROM AUTHOR]

Using x-ray submicrobeam, we spatially mapped the strain in epitaxial La[sub l-χ]Sr[sub χ]MnO[sub 3] films grown on SrTiO[sub 3](001) bicrystal substrates. Our results show that there is an elastic strain gradient at the artificial grain boundary, which decays over a length scale of ∼1 µm. The tensile strain at the interior of the grain—due to the lattice mismatch between La[sub l-χ]Sr[sub χ]MnO[sub 3] and SrTiO[sub 3]—relaxes as the film nears the grain boundary, yielding a grain boundary lattice constant which approaches the value of that in bulk La[sub l-χ]Sr[sub χ]MnO[sub 3]. [ABSTRACT FROM AUTHOR]

In situ characterization of micro- and nanoscale defects in polycrystalline thin-film materials is required to elucidate the physics governing defect formation and evolution during photovoltaic device fabrication and operation. X-ray fluorescence spectromicroscopy is particularly well-suited to study defects in compound semiconductors, as it has a large information depth appropriate to study thick and complex materials, is sensitive to trace amounts of atomic species, and provides quantitative elemental information, non-destructively. Current in situ methods using this technique typically require extensive sample preparation. In this work, we design and build an in situ temperature stage to study defect kinetics in thin-film solar cells under actual processing conditions, requiring minimal sample preparation. Careful selection of construction materials also enables controlled non-oxidizing atmospheres inside the sample chamber such as H2Se and H2S. Temperature ramp rates of up to 300°C/min are achieved, with a maximum sample temperature of 600 °C. As a case study, we use the stage for synchrotron X-ray fluorescence spectromicroscopy of CuInxGa1-xSe2 (CIGS) thin-films and demonstrate predictable sample thermal drift for temperatures 25-400°C, allowing features on the order of the resolution of the measurement technique (125 nm) to be tracked while heating. The stage enables previously unattainable in situ studies of nanoscale defect kinetics under industrially relevant processing conditions, allowing a deeper understanding of the relationship between material processing parameters, materials properties, and device performance. [ABSTRACT FROM AUTHOR]

Fabricates and characterizes a linear and circular zone plate with a blazed zone profile using synchrotron x rays. Improved performance in compared with a zone plate with a square profile; Experimental characterization; Special applications.

Examines nanometer focusing of hard x-rays by phase zone plates (PZP). Numerical aperture of the PZP; Flux density gain at first-order focus; Fabrication of the PZP; Experimental characterization.

A tapered undulator, in which the entrance and exit magnetic gaps are different, will show an increase in the energy width of the harmonics compared to the nontapered case. This increase can occur without substantial broadening in the collimation of the undulator radiation. We present the spectral properties measured for a tapered 3.3-cm period prototype undulator of the Advanced Photon Source at the Cornell High Energy Synchrotron Source. The width of the on-axis first harmonic at 6.9 keV increased from 0.32 to 0.66 keV for a gap tapering of 12%. Minimal angular broadening in the first harmonic x rays was detected and measurements of off-axis radiation were also performed. The results are found to be in good agreement with model calculations. [ABSTRACT FROM AUTHOR]

Coherent hard x-ray beams with a flux exceeding 10[sup 9] photons/sec with a bandwidth of 0.1% will be provided by undulators at the third-generation synchrotron radiation sources such as APS, ESRF, and Spring-8. The availability of such high flux coherent x-ray beams offers excellent opportunities for extending the coherence-based techniques developed in the visible and soft x-ray part of the electromagnetic spectrum to the hard x-ray region. These x-ray techniques (e.g., diffraction-limited microfocusing, holography, interferometry, phase contrast imaging, and signal enhancement) may offer substantial advantages over noncoherence-based x-ray techniques currently used. For example, the signalenhancement technique may be used to enhance an anomalous x-ray or magnetic x-ray scattering signal by several orders of magnitude. Coherent x rays can be focused to a very small (diffraction-limited) spot size, thus allowing construction of high spatial resolution microprobes. This paper will discuss the feasibility of extending some coherence-based techniques to the hard x-ray range and the significant progress that has been made in the development of diffraction-limited focusing optics. Specific experimental results for a transmission Fresnel phase zone plate that can focus 8.2 keV x rays to a spot size of about 2 microns will be briefly discussed. The comparison of measured focusing efficiency of the zone plate with that calculated will be made. Some specific applications of zone plates as coherent x-ray optics will be discussed. [ABSTRACT FROM AUTHOR]

A phosphorus diffusion gettering model is used to examine the efficacy of a standard gettering process on interstitial and precipitated iron in multicrystalline silicon. The model predicts a large concentration of precipitated iron remaining after standard gettering for most as-grown iron distributions. Although changes in the precipitated iron distribution are predicted to be small, the simulated post-processing interstitial iron concentration is predicted to depend strongly on the as-grown distribution of precipitates, indicating that precipitates must be considered as internal sources of contamination during processing. To inform and validate the model, the iron distributions before and after a standard phosphorus diffusion step are studied in samples from the bottom, middle, and top of an intentionally Fe-contaminated laboratory ingot. A census of iron-silicide precipitates taken by synchrotron-based X-ray fluorescence microscopy confirms the presence of a high density of iron-silicide precipitates both before and after phosphorus diffusion. A comparable precipitated iron distribution was measured in a sister wafer after hydrogenation during a firing step. The similar distributions of precipitated iron seen after each step in the solar cell process confirm that the effect of standard gettering on precipitated iron is strongly limited as predicted by simulation. Good agreement between the experimental and simulated data supports the hypothesis that gettering kinetics is governed by not only the total iron concentration but also by the distribution of precipitated iron. Finally, future directions based on the modeling are suggested for the improvement of effective minority carrier lifetime in multicrystalline silicon solar cells. [ABSTRACT FROM AUTHOR]

The evolution during silicon solar cell processing of performance-limiting iron impurities is investigated with synchrotron-based x-ray fluorescence microscopy. We find that during industrial phosphorus diffusion, bulk precipitate dissolution is incomplete in wafers with high metal content, specifically ingot border material. Postdiffusion low-temperature annealing is not found to alter appreciably the size or spatial distribution of FeSi2 precipitates, although cell efficiency improves due to a decrease in iron interstitial concentration. Gettering simulations successfully model experiment results and suggest the efficacy of high- and low-temperature processing to reduce both precipitated and interstitial iron concentrations, respectively. [ABSTRACT FROM AUTHOR]

Real-space maps of strain within silicon-on-insulator (SOI) features induced by adjacent, embedded shallow-trench-isolation (STI) SiO2 regions were obtained using x-ray microbeam diffraction. The quantitative strain mapping indicated that the SOI strain was largest at the SOI/STI interface and decreased as a function of distance from this interface. An out-of-plane residual strain of approximately -31μ[variant_greek_epsilon] was observed in the blanket regions of the SOI. A comparison of the depth-averaged strain distributions to the strain profiles calculated from an Eshelby inclusion model indicated an equivalent eigenstrain of -0.55% in the STI regions acting on the SOI features. [ABSTRACT FROM AUTHOR]

Surface migration of the group-III precursors and strain relaxation at the ridge sidewalls are compared for 2.5 μm wide waveguides based on InGaAsP and InGaAlAs multiple-quantum-well (MQW) structures. The cross-sectional thickness and strain variations have been measured using synchrotron radiation-based x-ray diffraction with an angular resolution of 2 arc s and a beam size of (0.24×0.35) μm2. Indium-rich overgrowth has been observed for the InGaAsP-based waveguides, while InGaAlAs-based waveguides demonstrate thickness uniformity of the MQW active region with a strain relief of 0.4%/μm at the sidewalls. [ABSTRACT FROM AUTHOR]

Synchrotron-based analytical x-ray microprobe techniques were employed to study the dissolution of iron, copper, and nickel silicide precipitates at structural defects in cast multicrystalline silicon in response to rapid thermal processing (RTP). A direct correlation was observed between iron silicide precipitate dissolution, increased minority carrier recombination, and decreased device performance after high-temperature (1000 °C) RTP. In contrast, iron precipitates comparable in size to as-grown material remained after lower-temperature RTP (860 °C); in this case the material exhibited higher minority carrier diffusion length and better solar cell performance. RTP at both temperatures effectively dissolved nickel and copper silicide precipitates. It is concluded that iron dissolved from structural defect reservoirs detrimentally affects the cell performance, likely by forming distributed point defects and smaller precipitates. For cast multicrystalline silicon, higher performance can be expected by inhibiting the dissolution of these precipitates, i.e., by reducing the time and/or temperature of processing steps. [ABSTRACT FROM AUTHOR]

The heteroepitaxial growth of Ge on thin Si membranes can lead to significant bending under self-assembled Ge hut nanostructures. Undercut silicon-on-insulator mesas approximate a Si freestanding membrane and serve as a crystalline substrate for the growth of Ge huts. Synchrotron x-ray microdiffraction shows a local curvature on the lateral scale of the size of the hut and an overall bending of the freestanding region. In comparison with conventional mechanically rigid substrates, the freestanding film can bend significantly. We have found a local radius of curvature of 6 μm beneath huts on 30-nm-thick Si membranes. [ABSTRACT FROM AUTHOR]

Substrate distortions were mapped near pseudomorphically grown SiGe thin film etched lines of various widths from 1.5 to 20 μm on Si(001) and 190 μm diameter Ni dots on Si(111) using reflection x-ray microdiffraction topography. The strain field extended 30–120 times the thickness of the film away from the feature edge. The profile of the enhanced diffracted intensity was found to follow a characteristic curve when the distance from the feature edge is normalized by a mean interaction distance that depends on the feature size. This normalization and the observed strain decay profiles cannot be predicted or modeled using existing micromechanical models. © 2003 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Can the photon energy dependence of coherence-enhanced radiographs lead to elemental identification? Our tests pave the way to a positive response by showing that image details do change as the photon energy crosses an absorption threshold. The observed changes are explained by a simple model of the interplay between the real and imaginary parts of the refractive index. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We describe the performance of the double-multilayer monochromator that is installed at bending magnet beamline 2-BM at the Advanced Photon Source. In order to achieve continuous operation over energies from 3.2 to 10.9 keV, four different multilayer stripes were deposited onto Si substrates using the in-house sputtering deposition facility at the APS. The optical performance of the four stripes depends on their operating energy ranges, and produces 45%–75% peak reflectivity at first-order reflection with a 1%–6% bandwidth and a total flux increase of 20–40 compared to the Si(111) double-crystal monochromator. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A hard x-ray Fresnel zone-plate-based microprobe has been designed and integrated into a Newport kappa diffractometer for microdiffraction studies at the 2ID-D beamline at the Advance Photon Source. The microprobe employs 10 and 40 cm (focal length at 8 keV) zone plates to provide high and moderate focusing power, respectively. Each zone-plate assembly has two identical zone plates stacked together to provide higher focusing efficiency for higher energy (30 keV) applications. The mounting base of the microprobe is supported by the side of the base of the diffractometer at one end and the central table of the diffractometer at the other end, thus minimizing the instability of relative positions between the focal spot and the specimen. A x-ray focal spot size smaller than 360 nm and angular repeatability of the sample circles smaller than 0.001° have been demonstrated with this setup. © 2002 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We demonstrate the capability of fluorescence x-ray microscopy with a 0.25 μm beam for in situ measurements of Cu-wiring interconnects of submicron dimensions. We are able to measure submicron line widths, lengths, and thicknesses of both Cu and W structures, and a Ta liner in the test vehicle, to the absolute accuracy of 0.03 μm, and a relative accuracy of ∼4% in lateral dimensions, and ∼10% in heights. The shape of a buried electromigration void was also determined. This nanoscale nondestructive characterization technique promises to be powerful for a variety of materials systems. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]