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Thermal stress induced by rapid thermal oxidation (RTO) and rapid thermal doping (RTD) of 001 silicon wafers was analysed using micro-Raman spectroscopy and synchrotron x-ray topography. The RTO wafers exhibited elevated stress levels as the process time was increased. The maximum magnitude and topographical distribution of the strain was found to agree with theoretical predictions. A maximum compressive strain of 320 MPa was observed after 166 s of RTO. The introduction of boron into the silicon lattice via the RTD process enhanced the rate at which the stress in the wafer exceeded the yield stress. Stress relief was subsequently accomplished through the formation of slip and misfit dislocations. The thermally induced stress and dislocation density increased with the time spent at the process peak temperature.

Epitaxial lateral overgrowth of GaN on Al2O3 using a SiO2 mask with different fill factors (ratio of stripe opening width to stripe period) is examined with synchrotron X-ray topography (SXRT) and X-ray diffraction (XRD) techniques. The crystal misorientation in the lateral overgrown region (wing) and the normal region (window region and beneath the seed layer) is determined with SXRT. The wings tilt asymmetrically around the window and the tilts increase as the fill factor increases. XRD measurements confirm the same wing tilt tendency as the fill factor changes. The average wing tilt reaches approximately 1600 arcsec measured using the X-ray rocking curve method at a fill factor of 0.625, but the maximum wing tilts can reach values as large as 2400 arcsec measured by SXRT when the fill factor is only 0.571. The significance of this is explained. The crystal misorientation in the normal region is approximately an order of magnitude less than the wing tilt. r 2002 Elsevier Science B.V. All rights reserved.

The crystal quality of bulk GaN crystals is continuously improving due to advances in GaN growth techniques. Defect characterization of the GaN substrates by conventional methods is impeded by the very low dislocation density and a large scale defect analysis method is needed. White beam synchrotron radiation x-ray topography (SR-XRT) is a rapid and non-destructive technique for dislocation analysis on a large scale. In this study, the defect structure of an ammonothermal c-plane GaN substrate was recorded using SR-XRT and the image contrast caused by the dislocation induced microstrain was simulated. The simulations and experimental observations agree excellently and the SR-XRT image contrasts of mixed and screw dislocations were determined. Apart from a few exceptions, defect selective etching measurements were shown to correspond one to one with the SR-XRT results.

A detailed study of twin-, large-angle and small-angle grain boundaries over a small volume of multi-crystalline silicon is presented on the basis of electron backscatter diffraction and synchrotron X-ray topography (SXRT) measurements. Identical areas (ca6 mm2) of two nearest neighbour wafers from a directional solidified Si column were analysed in order to gain information about the evolution of grain boundaries during the crystal growth process. Therefore, the emphasis was placed on the evolution of one particular grain and its neighbouring grains. In the case of `straight line' Σ3 grain boundaries, no change is observed if the twin plane corresponds to a {211} plane. Significant changes are found for non-straight line boundaries: while curved Σ3 grain boundaries are formed and eliminated very frequently, the Σ9 and Σ27agrain boundaries undergo only minor changes. By means of SXRT imaging, it is shown that the microstructure of the analysed grain exhibits numerous small-angle grain boundaries with angles in the range between 0.003 and 0.02°, corresponding to a theoretical dislocation density of the order of 107–108 cm−2. The experiments give evidence that the small-angle grain boundaries with the larger angles extend, while those with smaller angles vanish during growth.

The white beam Synchrotron X-Ray Topography (SXRT) technique was used to assess the quality of sapphire wafers grown by the Heat-Exchanger Method (HEM) and the Modified Czochralski Method (MCM). Sapphire is a potential new material for X-ray crystal optics, especially for use as Bragg backscattering mirrors for X-rays and Mossbauer radiation. The dislocation distribution, dislocation density and Burgers vector of selected dislocations and stacking faults in the sapphire wafers were studied. A correlation between the sapphire quality and its performance as an X-ray backscattering mirror was established in this paper. The results reveal the high quality of the inspected HEM sapphire wafers and their subsequently improved performance as Bragg backscattering mirrors.

Section transmission white beam X-ray topography was applied to the evaluation of the growth of GaN on sapphire using the epitaxial lateral overgrowth (ELO) technique. Using openings in 100 nm thick SiO 2 windows, a new GaN growth took place, which resulted in nominal overgrowth thicknesses of 6.8 μm. Measurements of the recorded Laue section topographs revealed misorientation between the epilayer and the substrate. Neglecting the misorientation contribution due to the 30° rotation of the epilayer with respect to the substrate, the misorientation mechanism was found to be a consequence of lattice rotation and dilatation. In the case of the ELO sample, these parameters varied with the stripe/window dimensions. The quality of the ELO epilayer is improved when compared to the non-ELO sample, though some local deviations from lattice coherence were observed. These results were complemented by observations made using X-ray diffraction and transmission electron microscopy.

Thermal processing steps used during the production of packaged integrated circuits can lead to severe thermomechanical stresses. In addition, the process of bonding wires to contact pads can also lead to strain field generation. A feasibility study using the application of white beam synchrotron x-ray topography to packaged erasable programmable read-only memory (EPROM) Si integrated circuits (ICs) has been undertaken in order to produce maps of the strain fields induced by such processing steps. This technique provides depth-resolved mapping with spatial resolutions currently in the region of 5-10 /spl mu/m throughout the entire mapping volume. Furthermore, the use of different experimental geometries allows the user to nondestructively probe the strain fields present at the wafer surface right through to the back side.

Traveling heater method (THM) experiments on InP crystal growth from indium solution (SKAT-FD) were performed during the Russian FOTON-11 mission in October 1997. The aim of these experiments was to ascertain the effectiveness of controlling heat and mass transfer in the liquid phase by applying a rotating magnetic field (RMF). As an effort to understand the parameters influencing the crystal growth a mathematical model was developed for numerical simulation of these experiments. The SKAT-FD crystals were grown with RMF at an induction of 1 and 2 mT. As the calculations show, such magnetic fields influence remarkably the hydrodynamics of the melt, and consequently, the growth process. The change of the magnetic induction value (or switching off the RMF) led to an abrupt change of the growth rate, measured from artificial dopant striations produced in the growing crystals by the heat-pulse technique.

Failure analysis of ultra-bright LED arrays under varying degrees of electrical stress was performed. Green (565 nm), red (660 nm) and infrared (890 nm) LEDs were subjected to currents between 0 and 1 A and voltages between 0 and 7 V. Using white beam synchrotron X-ray topography (SXRT) in back reflection large-area and section modes, the failure modes of the devices were observed. As the power to each device was increased, a reduction in the definition of device lattice structure due to increased thermal stressing was observed. An increase in strain is witnessed in the devices as they are stressed to the point of near failure. It was noted that at or near failure, the strain fields in the ball-bonded regions of the device become anomalously large (0.08% for the red LED, 0.19% for the green LED and 0.27% for the infrared LED), as observed via orientational contrast on the topographs. This is most likely due to thermally induced damage. The onset of failure took place when the power supplied to each individual LED exceeded 600 mW in the case of the green LEDs, 500 mW for the red LEDs and 745 mW for the infrared LEDs. Surprisingly, this is approximately 25 times greater than the nominal recommended supply for each LED array. This was confirmed by studying the I –V characteristics of the devices in conjunction with their emission spectra. As the power supplied to the devices was increased a narrowing of the radiative bandgap was witnessed in the red and green LEDs; whereas a broadening occurred in the infrared LED. When complete failure occurred in the samples, it was observed that large lattice deformations of the original device structure took place. Optical micrographs indicated that the structure of the devices remains spatially unaltered although the gold bond wire became detached. This confirmed that the distortion observed in the X-ray topographs is mainly due to severe thermally induced lattice distortion. The induced lattice distortion is greatest for the red LEDs; the sample appears to possess distinct and completely misorientated sub-grains.

Crystal quality of radiation detector-grade TlBr material was analyzed by X-ray diffraction and synchrotron X-ray topography methods. The analyzed TlBr crystals were further processed for electrical characterization and current–voltage characteristics were measured at a temperature range of 210–320 K. The crystals studied in this work were grown by the Bridgman–Stockbarger process. X-ray diffraction measurements show the presence of small-angle grain boundaries in the crystals. The crystal with the most pronounced small-angle boundaries showed the lowest resistivity and the poorest spectroscopic characteristics.

S-doped InP crystals were grown from an In-solution in a THM arrangement during the EURECA-1 mission using the automatic mirror furnace (AMF) under microgravity conditions. The InP-crystals showed growth rate oscillations in the range of 0.8–2.0 μm/min with a period of 45 min, which is half the time of an orbit of the EURECA-1 satellite. The fluid dynamic conditions during this experiment are modelled using a 3D model with the commercial software FIDAP. The time-dependent simulation, considering thermal as well as solutal buoyancy effects, indicates a weak laminar flow in this material system. Due to the fixed attitude of the satellite with respect to the sun the residual gravity vector rotates relative to the sample axis. This rotation results in a significant change of the residual convection level. Its maximum is obtained, when the gravity is parallel to the growth interface (two times during each orbit). Due to a high Schmidt number Sc≈25 a time-dependent influence of the convection on the concentration field can also be observed.

The control and characterisation of wafer defect and strain distributions is of crucial importance for the development of advanced Ultra Large Scale Integration (ULSI) circuits. Within the IC manufacturing sector 0.35 μm linewidth-based advanced Complementary Metal Oxide Semiconductor (CMOS) logic has recently emerged at a high level of maturity, to be closely followed by an even more demanding 0.25 μm process. One very important issue is the need to ensure a uniform, high quality Si substrate, i.e. minimise defect densities and eliminate strain distributions in the starting wafer material. Synchrotron section and back-reflection topographic techniques were applied to 200 mm diameter p-Si wafers, upon which, boron and arsenic doped epitaxial silicon layers had been deposited. These wafers were supplied from manufacturers around the globe and revealed substantial differences in the overall quality of the epilayers and substrates. In all wafers the substrate quality varied significantly with position across the wafer, as measured by the presence of oxygen-related defects and dopant strain homogeneity. The strain field uniformity, induced by the growth of lightly doped Si epilayers, was also observed to vary qualitatively with location on a wafer. Back-reflection topographs verify that the quality of the epilayer-substrate interface improved as the thickness of the epilayer, or the gradient of dopant density across the interface, is reduced. Cellular strain-related structures, of the order of a few hundred μm in circumference, have been observed in the more stressed p on p + samples. Topographic results are in agreement with those obtained from X-ray diffraction measurements. Finally, an examination was carried out into the quality of commercially supplied 200 mm diameter Si wafers, revealing differences in the overall quality of the wafers.

Local oxidation of silicon (LOCOS) isolation technology is becoming increasingly unusable for critical dimensions of 0.25 μm and below, due to the intolerably large dimension of the oxide “bird'sbeak”. Therefore, this technique has been replaced by a process called shallow trench isolation (STI) which uses deposited dielectrics to fill trenches etched in the silicon between the active areas. One of the chief drawbacks to STI is the tendency of such structures to be highly stressed, especially after the oxide/dielectric backfill, which can have a deleterious impact on the electrical performance of fabricated devices. It is essential to monitor the stress/strain fields generated by shallow trench isolation structures. Synchrotron X-ray topography (SXRT), a genuinely non-destructive technique, has been employed to provide in situ stress evaluation during the development of an STI-based complimentary metal oxide semiconductor (CMOS) integrated circuit process. Various process options were evaluated and the data was compared with electrical n+/p diode leakage and micro-Raman spectroscopy data.

Synchrotron x-ray topography was used to evaluate dislocation generation for liquid phase heteroepitaxy of strained layer on n-type InAs substrates. Severe misfit dislocation generation is observed for epilayer thicknesses of 4 and many of these form threading dislocations which are observed at the surface. However, for thicker epilayer growth (up to 70 in this study), this misfit dislocation generation appears to be confined to a region close to the heterointerface, with few threading dislocations approaching the surface. These data correlates well with photoluminescence and optical microscopy measurements.

3d-transition metals are known to produce deep levels in III-V semiconductors like gallium arsenide or indium phosphide. In this work, gallium antimonide was doped with the most promising candidates vanadium, titanium and iron according to the predictions of the energetic positions of the 3+/2+-charge transfer levels in the bandgap. For optimum incorporation of dopants several growth methods (travelling heater method THM, Czochralski CZ and liquid phase electroepitaxy LPEE) were used. The grown crystals were characterized by photoluminescence and electrical measurements. No deep levels in the forbidden band were found in the case of vanadium and titanium. Vanadium shows a scavenging effect on unintentional impurities. Titanium tends to form inclusions. In gallium antimonide doped with iron an acceptor was found with an activation energy of 26 meV. The findings support the predictions of Tersoff concerning charge transfer levels.

4H-SiC homoepitaxial layers free of basal plane dislocations (BPDs) are urgently needed to overcome the so-called bipolar degradation of high-voltage devices. BPDs being present in substrates are able to either propagate to the epilayer or convert to harmless threading edge dislocations (TEDs) in the epilayer. The model by Klapper predicts the conversion of BPDs to TEDs to be more efficient for growth on vicinal substrates with low off-cut angle. This paper aims to verify the model by Klapper by an extensive variation of epitaxial growth parameters and the substrates' off-cut. It is shown that the off-cut angle is the key parameter for growth of BPD-free epilayers. Furthermore, it is shown that the model also describes adequately the behavior of different types of TEDs, i.e., TED II and TED III dislocations, during epitaxial growth. Therefore, the model by Klapper is verified successfully for 4H-SiC homoepitaxial growth on vicinal substrates.

GaSb bulk single crystals with low acceptor concentration were grown from a bismuth solution by the traveling heater method. The result is isoelectronic doping by Bi which gives a variation of the opto-electronic properties as a function of grown length as well as a pronounced microscopic segregation. Photoluminescence spectra at 4K show a decrease of the natural acceptor during growth, which is confirmed by Hall measurements. The electrical properties of this isoelectronic doped GaSb are hole concentrations and mobilities of NA − ND = 1.7 × 1016 cm−3 and μ = 870 cm2Vs at room temperature and NA­ND = 1 × 1016 cm−3 and μ = 4900 cm2/Vs at 77K, respectively. The lowest p-type carrier concentration measured at 300K is NA − ND = 3.3 × 1015 cm−3

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned EURECA-1 mission in the automatic mirror furnace (AMF). Two crystals of sulphur-doped InP with [001] and [111] orientation respectively were grown from indium solution by the travelling heater method (THM). The absence of time dependent buoyancy-driven convection is documented by the lack of type I striations in the space-grown crystals. The sulphur concentration is measured by spatially resolved photoluminescence. As expected, the macrosegregation can be described by a pure diffusion-controlled model which is in good agreement with the findings from the first German spacelab mission D1. Compared to the earth-grown reference samples, both of the space-grown InP crystals show strong disturbances such as inclusions and type II striations. The morphological instabilities are similar to growth disturbances already known from the space-grown MD-ELI-01 from the D1 mission.

Long-term crystal growth experiments were successfully performed under microgravity conditions during the first flight of the unmanned mission EURECA-1 in the automatic mirror furnace (AMF). Two crystals of Al x Ga 1-x Sb with [001] and [111] orientation respectively were grown from gallium solution by the travelling heater method. The grown length of the single crystals is 4.0 mm and 4.2 mm respectively. The space-grown samples show a high microscopic homogeneity which indicates the absence of time dependent convection. From pulse markers a constant growth rate of 0.6 ± 0.1 μm/min is measured which is lower than 0.8 ± 0.1 μm/min obtained in earth grown reference samples. Details about the experiment performance and the growth results are given.

The stability of an isolated macrostep under a temperature gradient is discussed theoretically for the growth of III–V-semiconductors from a metallic solution, such as liquid phase epitaxy (LPE) and the travelling heater method (THM). To find the distribution of solute at the surface of one macrostep, the two-dimensional diffusion equation is solved, taking into account anisotropic interface kinetics as an important boundary condition. By analyzing the influence of growth rates and additional temperature gradients at the growth face it is found for the behavior of a macrostep, that for decreasing growth rates and for increasing temperature gradients the macrostep gets unstable and disappears. Details about the calculation and a comparison with experimental results from space grown crystals are presented.

Manufacturing-induced thermal stress created during the fabrication of packaged integrated circuits can potentially lead to device failure. Therefore, the need to develop metrologies that can be used to effectively measure stress/strain in systems-on-chip or systems-in-package is identified by the International Technology Roadmap for Semiconductors (ITRS). In this study, a novel technique for non-destructive analysis of strain/warpage inside completely encapsulated packaged chips, at room temperature and processed at elevated temperatures up to 115°C, is developed using a laboratory-based X-ray diffraction tool. Maps are produced of the entire silicon die, which reveal warpage via mapping of rocking curve full-widths-at-half-maximum (FWHM) as a function of position across encapsulated packages, using a technique known as 3-dimensional surface modelling. We develop complete Si die maps of the large thermal stresses that are developed during the die attach process due to the coefficient of thermal expansion mismatch between different materials. These are confirmed by in situ X-ray diffraction annealing experiments, as well as finite element analysis (FEA).

Synchrotron X-Ray Topography has been used in Total Reflection Topography (TRT) mode to observe strain induced surface bumps due to the presence of underlying misfit dislocations in strained layer SiGe on Si epitaxial heterostructures. In these experiments the x-rays approached the sample surfaces at grazing incident angles below the total external reflection critical angles for a number of reflections and hence surface strain features nominally less than a few tens of Ångstroms from the sample surface have been observed. These are similar to the surface bumpiness observed by Atomic Force Microscopy, albeit on a much larger lateral length scale. The fact that TRT mode images were taken was confirmed by the observation of clear and conventional back reflection topographic images of misfit dislocations in all samples when the grazing incidence angle became greater than the critical angle.

Synchrotron radiation laminography with X-ray diffraction contrast enables three-dimensional imaging of dislocations in monocrystalline wafers. We outline the principle of the technique, the required experimental conditions, and the reconstruction procedure. The feasibility and the potential of the method are demonstrated by three-dimensional imaging of dislocation loops in an indent-damaged and annealed silicon wafer.

To examine the impact of mechanical defects on the crystal lattice of silicon, controlled damage was applied to silicon wafers by a nanoindendation method. With increasing loads of 1, 5 and 50 N, the area with micro-cracks and strain around the indents increases. The damage is characterised by high resolution diffractometry using a conventional X-ray tube. Spatially resolved rocking curves were recorded across the indents and analysed with respect to full width at half maximum. From reciprocal space maps the amount of strain and tilt around the indents is separated. (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Tellurium-doped GaAs was grown under reduced gravity during the Second German Spacelab-Mission D2. The growth experiment MD-ELI-TRABE is described and first results are presented.

In the semiconductor industry, wafer handling introduces micro-cracks at the wafer edge and the causal relationship of these cracks to wafer breakage is a difficult task. By way of understanding the wafer breakage process, a series of nano-indents were introduced both into 20 × 20 mm (100) wafer pieces and into whole wafers as a means of introducing controlled strain. Visualization of the three-dimensional structure of crystal defects has been demonstrated. The silicon samples were then treated by various thermal anneal processes to initiate the formation of dislocation loops around the indents. This article reports the three-dimensional X-ray diffraction imaging and visualization of the structure of these dislocations. A series of X-ray section topographs of both the indents and the dislocation loops were taken at the ANKA Synchrotron, Karlsruhe, Germany. The topographs were recorded on a CCD system combined with a high-resolution scintillator crystal and were measured by repeated cycles of exposure and sample translation along a direction perpendicular to the beam. The resulting images were then rendered into three dimensions utilizing open-source three-dimensional medical tomography algorithms that show the dislocation loops formed. Furthermore this technique allows for the production of a video (avi) file showing the rotation of the rendered topographs around any defined axis. The software also has the capability of splitting the image along a segmentation line and viewing the internal structure of the strain fields.

The practicality of plasma etching, combined with low temperature and directional process capabilities make it an integral part of the IC manufacturing process. A significant cause of damage to wafers during plasma processing is arcing damage. Plasma arcing damage results in large pits and non-uniformities on the wafer surface which can lead to wafer breakage and high yield losses. Thus a non-destructive wafer damage metrology is crucial to the understanding of wafer failure mechanisms. We report on the successful use of a combined suite of non-destructive metrology techniques to locate the arc damage sites and examine the physical processes which have occurred as a result of the damage. These consist of 3D X-ray diffraction imaging (3D-XRDI), micro-Raman spectroscopy (@mRS), and scanning electron microscopy (SEM). In the case of the two examples examined in this study the plasma induced damage on the wafer surface appears as regions of damage ranging from 100@mm to 1000@mm in diameter. 3D-XRDI shows that the strain fields propagate out from the damage site in all directions, with the damage penetrating up to @? of the way through the substrate. K-means clustering and false colouring algorithms are used to highlight the regions of interest in 3D-XRDI, and to enhance the analysis process. Sectioning of the 3D images has enabled non-destructive imaging of the internal damage in the samples at any location. Micro-Raman spectroscopy results indicate the presence of both crystalline and amorphous silicon. Strain measurements at the damage site show tensile strains as high as 500MPa in certain situations, with strain levels increasing from the surface towards the bottom of the dislocation cell structures, which can be distinguished in the synchrotron X-ray topographs. 3D-XRDI and @mRS results are in close correlation, proving the potential for 3D-XRDI as non-contact, non-destructive metrology particularly suited to these problems.

X-ray diffraction topographs of extremely pure and perfect silicon single crystals are made using low-energy undulator radiation from a positron storage ring. Typical defect images observed are rather large round images having a black-white contrast and a diameter of about 40 µm. Applying the dynamical theory of x-ray diffraction, the defect contrast is explained by tensile strain in the lattice around voids close to the exit surface. This discovery of void-like microdefects explains, at least in part, the reduced density of the crystal intended to be used for a redefinition of the unit of mass, the kilogram.

In the semiconductor manufacturing industry, wafer handling introduces micro-cracks at the wafer edge. During heat treatment these can produce larger, long range cracks in the wafer which can cause wafer breakage during manufacture. Two complimentary techniques, micro-Raman spectroscopy (μRS) and White Beam Synchrotron X-ray Topography (WBSXRT) were employed to study both the micro-cracks and the associated strain fields produced by nano-indentations in Si wafers, which were used as a means of introducing controlled strain in the wafers. It is shown that both the spatial lateral and depth distribution of these long range strain fields are relatively isotropic in nature. The Raman spectra suggest the presence of a region under tensile strain beneath the indents, which can indicate a crack beneath the indent and the data strongly suggests that there exists a minimum critical applied load below which cracking will not initiate.

The generation and propagation of dislocations in Si at high temperature is observed in situ with white beam X-ray topography. For the heating experiments a double ellipsoidal mirror furnace was installed at the Topo–Tomo beamline of the ANKA synchrotron light source, Research Centre Karlsruhe, Germany. Details of the experimental set-up and the first results on the occurrence of dislocations are presented. Artificial damage was generated in commercial (1 0 0) Si wafers using a nanoindenter with various loads. The applied forces for each set of indents were varied from 100 to 500 mN, respectively. After heating to approx. 790 °C large area transmission topographs were taken every 30 min which were then compared to room temperature topographs before and after heating. At the outset straight 60°-dislocations with b = a /2〈1 1 0〉 originate from the 500 mN indents into the direction of the strongest temperature gradient. After 60 min at constant temperature an increase in the length and number of the dislocations in other directions is also observed. As a result of the continual thermal stressing dislocations develop from the 100 mN indents too.

The nucleation of dislocations at controlled indents in silicon during rapid thermal annealing has been studied byin situX-ray diffraction imaging (topography). Concentric loops extending over pairs of inclined {111} planes were formed, the velocities of the inclined and parallel segments being almost equal. Following loss of the screw segment from the wafer, the velocity of the inclined segments almost doubled, owing to removal of the line tension of the screw segments. The loops acted as obstacles to slip band propagation.

The nucleation of dislocations at indents in silicon following rapid thermal annealing (RTA) has been examined by X-ray diffraction imaging (topography). For indentation loads below 200 mN, no slip bands were generated from the indent sites following RTA at 1000 °C under spike conditions. Upon plateau annealing at 1000 °C, slip dislocations were propagated from some indents but not all. Slip was also observed from edge defects not associated with indentation. For 500-mN indentation load, large scale dislocation sources were generated from the indent sites propagating on two of the four {111} slip planes. These dislocations multiplied into macroscopic-scale slip bands. A significant change in morphology was observed in the 60° dislocation segments after the screw segment reached the rear surface of the wafer. Dislocations changed line direction and in some cases appeared to leave the Peierls trough during glide.

III–V semiconductor crystals are grown by the travelling heater method in a homogeneous axial magnetic field. First results demonstrate an influence not only on transport phenomena but also on growth kinetics and morphological stability. An interpretation of the growth results is given by an order of magnitude analysis using the dimensionless Rayleigh and Hartmann numbers.

Considerable research is being carried out in the area of wide band gap semiconductor materials for light emission in the 300―400 nm spectral range. Current materials being used for such devices are typically based on II―VI and III-nitride compounds and variants thereof. However, one of the major obstacles to the successful fabrication of III-N devices is lattice mismatch-induced high dislocation densities for epitaxially grown layers on non-native substrates. γ-CuCl is a direct bandgap material and an ionic wide bandgap I―VII semiconductor with a room temperature free exciton binding energy of ∼ 190 meV (compared to ∼25 meV and ∼60 meV for GaN and ZnO, respectively) and has a band gap of 3.4 eV (λ ∼ 366 nm). The lattice constant of γ-CuCl (0.541 nm) is closely matched to that of Si (0.543 nm). This could, in principle, lead to the development of optoelectronic systems based on CuCl grown on Si. Research towards this end has successfully yielded polycrystalline γ-CuCl on Si(100) and Si(111) using vacuum-based deposition techniques [1]. We report on developments towards achieving single crystal growth of CuCl from solution via Liquid Phase Epitaxy (LPE) based techniques. Work is being carried out using alkali halide flux compounds to depress the liquidus temperature of the CuCl below its solid phase wurtzite-zincblende transition temperature (407 °C [2]) for solution based epitaxy on Si substrates. Initial results show that the resulting KCl flux-driven deposition of CuCl onto the Si substrate has yielded superior photoluminescence (PL) and X-ray excited optical luminescence (XEOL) behavior relative to comparitively observed spectra for GaN or polycrystalline CuCl. This enhancement is believed to be caused by an interaction between the KCl and CuCl material subsequent to the deposition process, perhaps involving a reduction in Cl vacancy distributions in CuCl. This paper presents a detailed discussion of a CuCl LPE growth system as well as the characterization of deposited materials using X-ray diffraction (XRD), room temperature and low temperature PL, and XEOL.

Diffraction and transmission synchrotron imaging methods have proven to be highly suitable for investigations in materials research and non‐destructive evaluation. The high flux and spatial coherence of X‐rays from modern synchrotron light sources allows one to work using high resolution and different contrast modalities. This article gives a short overview of different transmission and diffraction imaging methods with high potential for industrial applications, now available for commercial access via the German light source ANKA (Forschungszentrum Karlsruhe) and its new department ANKA Commercial Service (ANKA COS, http://www.anka‐cos.de).

Three dimensional (3D) chip or wafer stacking and through silicon via (TSV) technologies are regarded as key technologies for next generation high-speed memories and microprocessors. In comparison to conventional chip technologies, three dimensional electrical networks allow much shorter wire lengths. This allows higher frequencies, less power consumption and smaller devices. A main technology to realise through silicon vias is laser drilling. Using laser drilling instead of deep reactive ion etching or the Bosch process makes masks unnecessary and thus allows great flexibility and lower costs. Today, vias with diameters of 10-80 mum are possible and can be laser drilled at speeds of about 2000 vias/s. However, laser drilling technology causes damages to the surrounding single-crystalline silicon. The paper surveys existing methods for defect structure analysis and evaluates them concerning their suitability for analysis of silicon TSV wafers. White beam X-ray topography at the synchrotron radiation source ANKA, Research Centre Karlsruhe, was selected as the best non-destructive method. For this paper three different laser types with normal (ns), short (ps) and ultra-short (fs) pulse width with varying parameter sets were used to drill TSVs into silicon wafers. For the first time, large area and section transmission topography were used to measure the strain affected zone around the TSVs. On the basis of these measurements femtosecond lasers were identified as superior to laser with longer pulse widths. The methodology presented in this paper is well suited for continuing studies with UV lasers and miniaturised vias, while at the same time electrical measurements become essential to finally answer how this affects the circuit performance of transistors, capacitors etc. adjacent to the through silicon vias.

The BAMline at the BESSY light source in Berlin and the TopoTomo beamline at the ANKA synchrotron facility in Karlsruhe (both Germany) operate in the hard X-ray regime (above 6 keV) with similiar photon flux density. For typical imaging applications, a double multilayer monochromator or a filtered white beam is used. In order to optimise the field of view and the resolution of the available indirect pixel detectors, different optical systems have been installed, adapted, respectively, to a large field of view (macroscope) and to high spatial resolution (microscope). They can be combined with different camera systems, ranging from 16-bit dynamic range slow-scan CCDs to fast CMOS cameras. The spatial resolution can be brought substantially beyond the micrometer limit by using a Bragg magnifier. The moderate flux of both beamlines compared to other 3rd generation light sources is compensated by a dedicated scintillator concept. For selected applications, X-ray beam collimation has proven to be a reliable approach to increase the available photon flux density. Absorption contrast, phase contrast, holotomography and refraction-enhanced imaging are used depending on the application. Additionally, at the TopoTomo beamline digital white beam synchrotron topography is performed, using the digital X-ray pixel detectors installed.

Synchrotron X-ray topography is well suited for a detailed characterisation of the real structure of single crystals and devices based on single crystalline materials. The nature and distribution of dislocations, stacking faults, inclusions etc. as well as long range strain from processing are of high interest especially in semiconductor wafers and electronic devices. To overcome the limitations of the classical photographic film method, we use a high resolution digital imaging detector. The digital scan of selected reflections allows the fast mapping of large sample areas with high resolution in combination with the high dynamic range of the CCD-camera. We report our first applications to the metrology of 300 mm Si wafers.

GaN layers grown by metal organic vapour phase epitaxy on sapphire were imaged by synchrotron radiation X-ray topography. The threading dislocations could not be resolved in the topographs due to t ...

Hydride vapour phase epitaxy grown all-epitaxial p-i-n structures were studied by synchrotron X-ray topography. Three types of process induced dislocations were found: short threading dislocations, long straight interfacial dislocations and circular arc dislocations. The majority of the dislocations observed are short straight threading dislocations, the density of which is typically about 5000 cm−2. The dislocations at the p-i interface are long straight lines parallel to [110]. They are screw dislocations having their Burgers vector parallel to [110], calculated from the contrast analysis of the well resolved dislocation images. One sample also showed a dense misfit dislocation network at the n-side. However, no misfit dislocations were seen in the back-reflection topographs of the n-side of the other samples, which shows that it is possible to grow a misfit-dislocation free n-type GaAs layer onto the substrate side of a hydride vapour phase epitaxy grown GaAs surface after proper substrate removal.

For demanding GaN-based applications like laser diodes or high mobility transistors there is a need for substrate material with low defect densities, since threading dislocations act as centers of non-radiative recombination, increasing the leakage current, reducing the room temperature mobility and thereby limiting the efficiency, performance and lifetime of devices. Hydride vapor-phase epitaxy (HVPE) is the most common technique for the growth of large area freestanding GaN wafers with diameters up to 50 mm and a threading dislocation density below 107 cm−2. An alternative technique with great potential for the growth of GaN bulk crystals is the ammonothermal growth method. For this method GaN threading dislocation densities as low as 5 × 103 cm−2were reported [1]. We are interested examining significant differences in the defect structure of the GaN substrates which can be observed in samples obtained from different manufacturers or as a function of the growth technique. In this work we present a detailed analysis of defect structures of freestanding GaN (0001) crystals grown by HVPE and the ammonothermal method from different vendors. Synchrotron white-beam X-ray topography (SWXRT), high resolution X-ray diffraction (HRXRD) and microphotoluminescence (µPL) were used for this combined study. SWXRT in two principal X-ray topography geometries was used in the course of this analysis, namely the large-area back-reflection mode and section transmission mode. HRXRD reciprocal space mappings and in-plane measurements were used for mosaicity analyses. The combination of these methods allows a detailed statement of the nature, density and distribution of typical defects in GaN bulk crystals with a large field of view. As an example, Fig. 1 shows a large-area back-reflection topograph (0006 reflection) of a HVPE GaN substrate. The topograph shows dislocation free areas, surrounded by rather sharp lines, indicating good material quality with low defect density. These features are interpreted as dislocation cell walls, suggesting the formation of a cellular defect network within this GaN sample, analogous to what was commonly observed in LEC GaAs [2]. With the combination of the results from SWXRT, HRXRD and µPL a consistent model for different defect structures of the freestanding GaN samples grown by HVPE and the ammonothermal method is discussed. References P.J. R. Doradzinski, R. Dwilinski, J. Garczynski, L.P. Sierzputowski, Y. Kanbara, in Technology of Gallium Nitride Crystal Growth, edited by D.Ehrentraut, E. Meissner, and M. Bockowski, (Springer-Verlag, Heidelberg, ISBN 978-3-642-04828-9), 137-158, (2010). P.J. McNally, P.A.F. Herbert, T. Tuomi, M. Karilahti, and J.A. Higgins, J. Appl. Phys. (1996) 79, 8294. Figure 1

We present herein a first comparative analysis of the quality of 50 mm and 75 mm diameter SiC wafers, purchased directly from vendors across the world, types including the most widely available configurations. Large Area White Beam Synchrotron Back Reflection X-Ray Topography was used to analyse selected ~1cm2 regions at various locations on up to 10 different bulk SiC wafers. The study concentrated particularly on the density and distribution of threading screw dislocations (TSDs). We also examined all wafers for basal plane dislocation (BPDs) densities and distributions. Alarmingly large variation in wafer quality was observed. TSD densities vary from a minimum of 0 cm-2 (in a-plane material) to values as large as over 2,000 cm-2 on some n-type 4H-SiC wafers. TSD densities on individual wafers can also vary by similar magnitudes, e.g. 500cm-2 to 2,500 cm-2 on two regions only 2 cm apart on a 50 mm diameter wafer. Computer-based image process analysis was used to present a statistical analysis of the distributions of defects. For example algorithms created in MATLAB®, Image Processing Toolbox, isolated possible TSD locations allowing rapid counting to be performed. These counts were confirmed by manual counting of selected unmodified images.

Mechanical strains and stresses are a major concern in the development of copper-based on-chip metallization. Synchrotron x-ray topography (SXRT), micro-Raman spectroscopy, finite element modeling (FEM), and atomic force microscopy (AFM) have been used to examine the strain fields imposed by electroless Cu metallization on the underlying Si. As expected, we have observed enhanced strain regions close to the metal line edges. These strain fields tend to zero at annealing temperatures approaching 200 ° C, and thereafter the magnitudes of the strain fields at 300 ° C and 400 ° C are much higher, implying a return to a higher strain regime. Although the strain transition point is slightly different from the SXRT result, the FEM results confirm the existence of a zero-strain transition point as a function of thermal anneal. We have also examined the generated stress in Si as a function of Cu linewidth L. We have found that the stress sXX due to the electroless copper metallization is empirically related to the Cu linewidth in terms of an exponential distribution. For Cu linewidths less than 20 mm, the stress magnitudes increased with decreasing Cu linewidth due to the thermal stress in the absence of self-annealing, whereas the stress decreased with increasing linewidths in the range of 60‐ 100 mm due to a relief of the thermal stress possibly via the self-annealing effect. This self-annealing phenomenon was observed using AFM. It is observed that the stresses in the Si shifted to a compressive state after annealing at 400 ° C. © 2004 American Institute of Physics. [DOI: 10.1063/1.1811780]

The large-area defect structure of high-quality ammonothermal GaN was studied by synchrotron radiation X-ray topography (SR-XRT) and high-resolution X-ray diffraction (XRD). The threading dislocation densities of mixed and screw dislocations were determined separately by SR-XRT and were 3.2 × 104 and 3.1 × 103 cm−2, respectively. Threading edge dislocations were not observed. SR-XRT images show that TMDs are clustered on a large scale and form short dislocation arrays with an average spacing between dislocations of 12 µm. XRD rocking curves were used to measure an average lattice tilt of 10 arcsec caused by the dislocation arrays.

Synchrotron white beam x-ray topography techniques, in section and large-area transmission modes, have been applied to the evaluation of ELOG GaN on A12O3. Using the openings in 100 nm thick SiO2 windows, a new GaN growth took place, which resulted in typical overgrowth thicknesses of 6.8 μm. Measurements on the recorded Laue patterns indicate that the misorientation of GaN with respect to the sapphire substrate (excluding a 30° rotation between them) varies considerably along various crystalline directions, reaching a maximum of a ∼0.66° rotation of the (0001) plane about the [01•1] axis. This is ∼3% smaller than the misorientation measured in the non-ELOG reference, which reached a maximum of 0.68°. This misorientation varies measurably as the stripe or window dimensions are changed. The quality of the ELOG epilayers is improved when compared to the non- ELOG samples, though some local deviations from lattice coherence were observed. Long range and large-scale (order of 100 μm long) strain structures were observed in all multi quantum well epilayers.

Using a CdZnTe sample detector, a variety of diagnostic tools are applied, so as to assess the crystal characteristics and to compare these to the x-ray response measured with synchrotron radiation. Correlations are found, such that x-ray response degrading processes can be identified. In this respect the performance of the detector is found to be limited by both large scale defects such as some grain boundaries and also pipes and by crystal imperfections, together with impurities and other crystal defects, both at the surface and in the bulk crystal. The relatively soft CdZnTe crystals are very sensitive to improper handling, producing particularly surface damage, which in turn deteriorates the detector performance, as is rather clearly established by photoluminescence measurements.