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Work is underway to develop composition standards and standardized assessment procedures for compound semiconductors. An AlGaAs composition standard with less than 2% uncertainty is being developed. The improved accuracy of this standard is being achieved by combining an array of analysis techniques, including reflection high energy electron diffraction, photoluminescence (PL), electron microprobe analysis and inductively coupled plasma–optical emission spectroscopy. A major part of the work has been quantification of the accuracy limits of each technique. The influence of peak fitting method, measurement temperature, and doping concentration on PL measurements of AlGaAs layers has been measured. Similar work is underway for PL analysis of InGaAsP and for X-ray diffraction (XRD) analysis of a wide variety of materials in order to develop standardized assessment procedures. An inter-laboratory comparison was made of XRD and PL measurements of InGaAsP layers. The study demonstrated that material nonuniformity dominated the variation in the XRD measurements; but the uniformity was sufficient to allow PL measurement variations to be assessed.

A method for analyzing x-ray reflectivity curves from multilayered structures with interfacial roughness using a wavelet transform approach has been developed. By using this approach, we have been able (1) to extract the contribution of a particular rough interface to a specular reflectivity curve, and (2) to determine the root-mean-square amplitude of the roughness of a particular interface independently of the other interfaces in the multilayered structure from the specular reflectivity data. Analytical procedures that allow the interpretation of the wavelet coefficients obtained from specular reflectivity curves have been developed. This approach has been successfully applied to experimental reflectivity curves obtained from Cu/Ta, Ta2O5/Ta, and Ta2O5/Ta2N bilayer structures.

We have used high-resolution triple-axis x-ray diffraction analyses to monitor the defect structure in tetragonal crystals of hen egg-white lysozyme as a function of x-ray irradiation time. At long irradiation times we observed the expected decrease in peak intensity and increase in the angular extent of the peak breadth. In contrast, the initial stages of irradiation showed relatively complex changes in both the peak breadth and the intensity; in fact, during the period from 25 to 45 h of irradiation the angular breadth of the intensity (both the full-width at half-maximum and the full-width at 1% of the maximum intensity) decreased to a minimum value. We have found that the unambiguous analysis of defects at high angular resolution is complicated by the fact that the diffraction characteristics of protein crystals apparently lie at the confluence of the kinematic (ideally imperfect) and dynamic (ideally perfect) treatments of diffraction.

We describe the implementation of a crossed graded parabolic x-ray mirror system that is suitable for incorporation into both conventional and high resolution x-ray diffraction systems. A novel optical alignment system has been devised that permits independent adjustment of the positions and the angular settings of the mirrors. This alignment system is simple and inexpensive to construct, yet is mechanically stable and easy to use. The crossed mirror system has been successfully introduced into both protein crystallography and high resolution x-ray diffraction systems.

High–resolution triple–axis X–ray diffraction analyses have been performed on tetragonal crystals of hen egg–white lysozyme (HEWL). In order to perform these analyses in a laboratory setting, an X–ray optical system consisting of a pair of parabolic graded X–ray mirrors and an asymmetric channel–cut crystal was employed. Analyses of thin silicon crystals confirmed the differences between the transmission geometry used for the HEWL crystals and the more common reflection geometry typically used for the characterization of inorganic crystals. Significant differences in the intensity distribution in the vicinity of the HEWL reciprocal lattice points between different reflections of the same crystal and between different crystals have been observed.

Lithium gallate (LiGaO2) is gaining increasing attention as a potential substrate for the growth of the important semiconductor GaN. In order to better understand this material we have performed high-resolution double- and triple-axis x-ray diffraction analyses of both the starting LiGaO2 and GaN/LiGaO2 following epitaxial growth. A high-resolution triple-axis reciprocal space map of the substrate showed a sharp, well-defined crystal truncation rod and a symmetric streak of intensity perpendicular to q002, suggesting high structural quality with mosaic spread. Triple-axis scans following GaN growth showed (1) the development of isotropic diffuse scatter around the LiGaO2 (002) reflection, (2) the presence of a semi-continuous intensity streak between the LiGaO2 (002) and GaN (0002) reflections, and (3) a compact pattern of diffuse scatter around the GaN (0002) reflection that becomes increasingly anisotropic as the growth temperature is increased. These results suggest that LiGaO2 permits the epitaxial growth of GaN with structural quality that may be superior to that observed when growth is performed on SiC or Al2O3.

A statistical method has been developed for the simulation, optimization and analysis of double-crystal X-ray rocking curves for epitaxial thin films in the Bragg case. This method is based on the approach of Bartels, Hornstra & Lobeek [Acta Cryst. (1986), A42, 539–545], where the diffracting medium is modeled as a set of lamellae on a semi-infinite substrate. The expressions of Bartels et al. have been recast in terms of a Mobius transform of the type G[X] − (aX + b)/(cX + d), where the constants a, b, c and d are equivalent to the complex quantities used by Bartels et al. and X is the amplitude ratio. The use of these parameters leads to a set of constraints on the fitting process, thus permitting the procedure to be automated. Convergence to a solution is determined by examination of a statistical criterion for goodness of fit; factors that contribute to the net error between the calculated and experimental rocking curves have been identified and have been incorporated into the method. The noise associated with an experimental rocking curve has been found to be very important to the fitting process, and a method is described for explicitly including noise in the procedure presented here. Statistically significant fits to a variety of experimental rocking curves (obtained by fully automated fitting with minimal user interventions) have demonstrated good agreement with experimental data.

High-resolution X-ray diffraction methods have been used to characterize the structural characteristics of GaAs grown by molecular beam epitaxy at low substrate temperatures. Triple-crystal X-ray diffraction scans demonstrate that, as the As4/Ga incorporation ratio was increased, there occurred increases in the magnitude of diffuse scattering as well as an anisotropy in the scattering. A degradation of the crystal truncation rod is also observed. Differences have also been observed in the diffuse scattering from n- and p-doped GaAs samples grown in this way; we attribute this to changes in the kinetics of arsenic incorporation due to the electrical characteristics of the material. Analysis of the annealed GaAs layers has shown the development of long-range strain fields from distortions generated by the growth of the arsenic precipitates. The diffuse scattering has been used to develop estimates of the average size of the arsenic precipitates.

In order to continue scaling metal oxide semiconductor field effect transistors (MOSFETs) with HfO2 gate oxides, efforts are being made to further improve the deposited high‐k film properties. Recently, a process whereby an HfO2 film is deposited through a series of depositions and anneals (so‐called DADA process) has been shown to result in films that give rise to MOS capacitors (MOSCAPs) which are electrically scaled compared to MOSCAPs with HfO2 films that only received post deposition anneals (PDA) or no anneals. We have measured as‐deposited, DADA and PDA HfO2 films using four measurement techniques, all of which are non‐destructive and capable of being used for in‐line processing, to evaluate their crystallinity and crystalline phases. Grazing incidence in‐plane X‐ray diffraction was used to determine the crystalline phases of the HfO2 films. We observed the crystalline phases of these films to be process dependent. Additionally, X‐ray and UV photoelectron spectroscopy were used to show the presence...

A simple relationship is reported defining the ratio of dynamical and kinematic values of the integrated reflectivity in absorbing single crystals in terms of the product μnξ, where μn is the linear absorption coefficient for depth measured along the normal to the diffracting crystal's surface and ξ is the extinction distance in a nonabsorbing crystal. This relationship is interpreted through comparison with existing (albeit mathematically complicated) expressions for the dynamical reflectivity in the two limits of negligible absorption and very strong absorption. It is shown to be valid for intermediate values of μnξ by comparison with calculated values of the integrated reflection from single-crystal CdTe using various wavelengths and 〈111〉-type reflections. This relationship's usefulness is discussed in the analysis of dynamical diffraction experiments commonly employed in semiconductor materials characterization.

The conversion of a commercial double crystal x‐ray diffractometer to a flexible, high‐resolution triple crystal diffractometer is described. This conversion, which has been accomplished at low cost, greatly enhances the flexibility of a double crystal diffractometer for the characterization of both highly perfect and relatively imperfect bulk single crystals and epitaxial layers. The conversion is easily reversible, thus allowing a single double crystal diffractometer to operate in either a double crystal or triple crystal mode. Specific examples of the capabilities of this instrument are presented.

High‐resolution triple crystal x‐ray diffraction has been used to monitor the magnitude of diffuse scattering from chemical‐mechanical (CM) polished GaAs. The diffuse scattering, which is attributed to kinematic scattering arising from polish‐induced crystallographic defects, was found to be only slightly affected when each of four CM polish parameters (bromine concentration in Br2/methanol, total polish time, polish pad rotation speed, and force on sample) was varied individually. The combined effect of increases in both the pad rotation speed and the force on the sample increased the magnitude of the diffuse scattering, suggesting the generation of mechanical damage. When all four variables were increased to their maximum values, the diffuse scattering increased dramatically and became anisotropic. We have expressed the magnitude of the diffuse scattering in terms of an ‘‘excess intensity’’ in reciprocal space to provide a semi‐quantitative relation between CM polish parameters and the generation of polish‐induced damage.

An empirical relationship has been developed that relates the product of the X-ray mass absorption coefficient μ and the extinction distance ξ from dynamical diffraction theory to the ratio of the integrated reflectivities that are predicted from both the kinematic and the dynamical theories of X-ray diffraction. The 111, 222 and 333 integrated reflectivities from samples of CdTe with significantly different etch-pit densities were then measured and analyzed in light of this relationship. The integrated reflectivity measurements suggest that the crystals are of similar crystalline perfection, while the etch-pit densities imply that one crystal is much more perfect than the other. The apparent similarity of the two samples in the diffraction experiments is interpreted with respect to a linear dependence of the ratio Rdyn/Rkin on the parameter In μξ. This result is consistent with the defect structures of the crystals observed using X-ray topography.

Two novel x-ray diffraction techniques with enhanced surface sensitivity, grazing incidence x-ray diffraction (GIXD) and inclined Bragg plane x-ray diffraction (IBXD), have been used to study surface damage in gallium arsenide (GaAs) due to bromine/methanol (Br2/MeOH) chemical mechanical (CM) polishing. A factorial design was implemented to determine the effects of four polishing variables on the surface structure of GaAs. Precise lattice parameter measurements were made in both the surface regions using GIXD and deeper into subsurface regions using IBXD after the various CM polishing treatments. Bromine concentration was found to primarily affect the surface lattice parameter, while the total polish time influenced both the surface and subsurface lattice parameters in GaAs samples that were heavily damaged prior to CM polishing. The combined effect of polishing pad rotation speed and the force exerted on the sample was found to have a much greater effect on the surface lattice parameter than either variable had alone.

X‐ray scattering is a non‐destructive analytical technique capable of detecting electron density fluctuations in mesoporous and nanoporous structures. X‐ray methods have the potential to provide fully quantitative porosity analyses of open and closed pore structures. Specular x‐ray reflectivity (XRR) offers accurate measurement of thickness, density, and roughness of uniformly deposited thin films. Diffuse scattering techniques are also studied by manipulation of the scattering geometry and approximation of the average pore size and pore size distribution. Effects of refraction and reflection from the surface and buried interface are corrected via the Distorted Wave Born Approximation (DWBA). Distortion of the scattering profile due to slit smearing is also taken into account to obtain an accurate interpretation of diffuse scattering phenomena. Preliminary results for average pore size and pore size distribution of PECVD‐prepared SiCOH thin films with both open and closed pore structures are reported, and show good agreement with positron annihilation lifetime spectroscopy (PALS) data.

Dynamical X‐ray diffraction theory is extensively used to evaluate the structure of single crystal materials, where information on composition and strain can be extracted from high resolution rocking curves. Many critical materials and structures (lattice‐mismatched semiconductor heterostructures, or materials modified by ion implantation processing) may contain process‐induced structural defects and cannot be modeled by conventional perfect crystal dynamical theory approaches. Statistical dynamical diffraction theory (SDDT) incorporates both incoherent (kinematical and diffuse) and coherent (dynamical) scattering. Treatments of the SDDT theory are typically mathematically intensive while lacking instructions on how to actually implement the theory in practice. This paper discusses the implementation of the SDDT and modifications that allow for successful SDDT analyses of fully relaxed SiGe on Si.

Variable angle spectroscopic ellipsometry (VASE) measurements from 30 μm (infrared) to 150 nm (vacuum ultraviolet) were used to measure the thickness, pore volume fraction, gradation in the refractive index and chemical bonding of porous low‐κ films. The VUV spectroscopic ellipsometry measurements were used to determine the pore volume fraction and gradation in the refractive index of the porous low‐κ films. Bruggeman’s effective medium approximation was used to calculate the total pore volume fraction. The IR spectroscopic ellipsometry measurements were used to characterize the chemical bonding of the porous low‐κ samples. Absorption coefficients in the IR wavelength were used to characterize the chemical bonding in the porous low‐κ films.

A novel pre-resonant conductance structure is observed in single and double well GaAs/Ga/sub x/Al/sub 1-x/As resonant tunneling heterostructures. This structure is attributed to single electron tunneling through donor bound states in the quantum well as they cross the Fermi level. Peaks in conductance are observed in devices as large as (64/spl mu/)/sup 2/. We observe for the first time donor binding energies in quantum wells as large as 35 meV, which is probably due to the formation of a donor complex. An impressive impurity tunneling conductance structure is observed in double quantum well structures with conductance peak heights varying over 3 orders of magnitude. Conductance peaks are observed before and after the main resonant current peak which are attributed to tunneling of electrons through impurities in one quantum well and the quantum state in the other well. >

An investigation of high dose rate effects in silicon subsurface morphology has been performed. The unique capability of plasma source ion implantation to operate in the high current/low energy regime, where the near-surface structure can be effectively controlled, has been studied. At an ion energy of ∼40 keV and an estimated dose of 1×1015 cm−2 Ar ions were implanted at various instantaneous dose rates (0.75–8.3 mA/cm2) and two different pulse widths (25–50 μs) into 2 in. diam silicon wafers at a constant repetition rate of 10 Hz. The irradiation damage to the wafers’ structures was characterized by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). A visual observation indicated amorphization of the silicon at 0.75 mA/cm2, but not at 8.3 mA/cm2. The transition from the crystalline-to-amorphous phase was confirmed by TEM electron diffraction studies. RBS data, however, indicated there was a large discrepancy in the total dose retained between the high dose rate (8.3...

An X-ray powder diffraction analysis has been performed on several samples from the naturally occuring patina of the Statue of Liberty. This work, which was conducted as a service to the National Park Service as part of the restoration activities for the Statue, was performed to assess the impact of acid deposition on the phase composition of the patina. Samples of the patina that were obtained from various locations on the copper skin of the Statue were found to consist primarily of the basic copper sulfate known as brochantite or CuSO4·3Cu(OH)2. Another less stable form of basic copper sulfate CuSO4·2Cu(OH)2 known as antlerite was also observed in samples taken from areas that are more exposed to the incoming weather in New York harbor. The presence of antlerite supports the contention that acid deposition is promoting undesirable changes in the phase composition of the patina. Analyses were also performed on patina samples that were taken from pieces of the Statue's copper skin that had been removed in the years 1905 and 1980. X-ray powder diffraction of the corrosion product on the 1905 sample showed that it consisted primarily of the stable brochantite phase, while the 1980 sample displayed both copper chlorides as well as the less stable antlerite. Both samples also contained cuprite (Cu2O) which appears to have formed prior to either of the sulfates.

The continuing drive in the semiconductor industry towards smaller and more complex electronic devices has placed increasing severe demands on the materials systems that are used in semiconductor circuits. The refractory metal silicides that are commonly used for electrodes and interconnects are particularly susceptible to the sometimes conflicting requirements of good electrical properties, ease of processing, and long term reliability. We have found that the characterization of metal silicides with a fully automated diffractometer based on the Seemann- Bohlin (S∼B) focusing geometry has proved to be an important aid in the development of several semiconductor metallization systems.Although a conventional Bragg-Brentano (B-B) diffractometer can provide adequate information for some thin film systems, the use of an S-B diffractometer in which the incident x-ray beam makes a very small angle of incidence with the sample surface results in a substantial improvement in the usable signal from very thin samples.

The small-angle x-ray scattering (SAXS) from an Epon 812 and two Epon 828 (one amine-cured and one anhydride-cured) epoxy resins has been measured using a Bonse-Hart system. The data cover the angular range (2θ) between 20 sec and 60 min. After correction for absorption, background and vertical beam divergence, they have been placed on an absolute basis by comparison with the scattering from a previously studied polycarbonate sample. The corrected absolute intensity decreases strongly with increasing angle between 20 sec and 2 min, decreases more gradually between 2 and 20–30 min, and reaches a nearly constant asymptotic value at larger angles. The magnitude of the intensity in the constant-intensity region is close to the value predicted by thermodynamic fluctuation theory for fluids applied at the glass transition temperature. The increase in intensity at angles smaller than 20–30 min is associated with heterogeneities in the cured resins. These heterogeneities cover a range of sizes in all samples, from less than 100 A to more than 1000 A, with the most frequently occurring size in the range 100–200 A.

The angular misorientation of GaAs epitaxial layers grown on silicon substrates by molecular beam epitaxy has been measured using x-ray diffraction. A significant misorientation, or tilt, between the epitaxial layer and the substrate has been observed. The magnitude of the tilt depends on the initial substrate orientation, the silicon substrate type (float zone or Czochralski), postgrowth annealing, and epitaxial layer thickness. In almost all cases, the sense of the tilt is such that the GaAs 〈001〉 lies between the surface normal and the silicon 〈001〉. While the presence of interfacial dislocations with Burgers vectors that are approximately parallel to the heterointerface does predict a tilt between the substrate and the epitaxial layer, the sense of the tilt that arises from these dislocations is opposite to that observed experimentally. A model, based on the relief of misfit by dislocations inclined approximately 45 degrees to the interface, is proposed that correctly describes the observed tilt.

Fibers of PET were drawn at 80°C and investigated by small-angle x-ray scattering (SAXS) after annealing with free ends at temperatures up to 240°C. While the as-drawn fiber had no identifiable discrete SAXS pattern, evidence for an alternating two-phase microstructure was seen after annealing at 100°C. Annealing at temperatures up to 200°C resulted in well oriented SAXS patterns which doubled in integrated intensity. During this stage of (low-temperature) annealing, it is envisioned that oriented amorphous regions partially crystallize, leading to transverse growth of oriented microfibrils. Annealing at or above 225°C causes the SAXS pattern to become arced, implying disorientation of the fiber via the presence of a largely molten structure. Quenching from these highest annealing temperatures results in a slight decrease in the SAXS intensity which is attributed to the formation of thicker transition zones at the crystal-amorphous interface during rapid crystallization. By comparison to previous...

Diffusion barrier properties of selective chemical vapor deposited (CVD) tungsten to silicon and aluminum interdiffusion have been investigated using secondary ion mass spectroscopy, x‐ray diffraction analysis, and scanning electron microscopy. Samples of titanium layered pure aluminum on selective CVD tungsten on cleaned silicon wafers were prepared and sintered between 450 and 520 °C. The Ti layered aluminum was used to increase the capacity for silicon to facilitate the outdiffusion from the substrate. Magnetron sputter deposited Ti:W samples were also included in the analysis for comparison purposes. The experimental results indicated that 73 nm of selective tungsten with sheet resistance of 1.5 Ω/⧠ was sufficient as a diffusion barrier for both aluminum and silicon at 450 °C for 30 min, but failed at 520 °C for 30 min. 33 nm thick selective tungsten with 7 Ω/⧠ sheet resistance failed to prevent interdiffusion of aluminum and silicon even at 450 °C for 30 min. 100 nm of Ti:W remained an excellent diff...

Thermal characteristics of p-n Al/sub x/Ga/sub 1-x/As-GaAs quantum-well heterostructure (QWH) diode lasers grown on Si substrates have been investigated. Continuous operation at 300 K for over 10 h has been demonstrated for lasers mounted with the junction side away from the heat sink (junction-up) and the heat dissipated through the Si substrate. Junction-up diodes grown on Si substrates had measured thermal impedances 38% lower than those grown on GaAs substrates, with further reductions possible. Measured values were consistent with calculated values for these structures. Low sensitivity of the lasing current to temperature has also been observed, with T/sub 0/ values as high 338 degrees C. >