Papers by Keyword: Dislocations

Abstract: It has been shown that account of elastic nonlinearity during the propagation of an acoustic wave in a solid lead to the appearance of a quadratic nonlinearity, which in its turn leads to the possibility of generating a wave of double frequency, the interaction of harmonics is asymmetric. The conditions under which nonlinear stationary waves are formed are considered. A phase portrait is constructed, and the dependence of the wavenumber of a nonlinear wave on its amplitude is estimated.

Abstract: Characterization of advanced materials by neutron powder diffraction provides information not accessible by other techniques. Thanks to the low absorption of neutrons, the bulk of the material and large-grain samples can be investigated, moreover in situ at elevated temperatures. The neutron diffraction use is demonstrated on two types of technologically important materials: Ti-Zr alloy and Co-Re high temperature alloy. In Ti-Zr alloy, the residual stress relief and microstrain evolution after ECAP was established. Boron influence on TaC strengthening precipitates in Co-Re high temperature alloys was shown not to be significant at the foreseen alloy operation temperatures, although boron content has a strong influence on the matrix phase.

Abstract: In this study, the correlation between the Emission Microscopy (Em.Mi.) related to the failure site of the 4H-SiC 650V MOSFET devices after reliability test and epitaxial dislocation defects is presented. Devices failed at the High-Temperature Reverse Bias (HTRB) test were considered. Device layers have been stripped out by chemical wet etching and etched in a high temperature KOH solution to characterize defects emerging at the SiC surface. This approach was used to correlate failure emission spots with underlying structure of the material. KOH etching process on delayered devices was performed at 500°C for 10 minutes and then analysis by optical microscopy and SEM was carried out for defect classification and correlation with failure location.

Abstract: X-ray topography is an effective tool to investigate dislocations in semiconductor crystals. Due to low X-ray absorption coefficients of diamond, X-rays can penetrate deep into the crystal. Thus, deep three-dimensional (3D) dislocations are projected on two-dimension (2D) film, which makes dislocation analysis particularly challenging. Dislocation vectors from the films obtained using a set of the same diffraction vectors were identified using topographical and geometrical analyses. The depth and position of the dislocations in a crystal that was projected on a film were determined using geometrical relationship. The proposed analysis method was verified by analyzing several dislocations using four <404> diffraction films. The types of dislocation were identified through Burgers vector analysis.

Abstract: In this work the effect of the ion implantation on the dislocations structure of the 4H-SiC epilayer after the KOH etching has been investigated. The study was conducted using both Aluminum (Al) and Phosphorous (P) species for p-type and n-type, respectively. The ion implantations of Al and P were carried out at different energies (30–200 keV) to achieve 300 nm thick acceptor box profiles with a concentration of about 10²⁰ at/cm3. The implanted samples were annealed at high temperatures. With sequential sacrificial and stopping layer both species has been implanted on the same sample. Morphological charaterization of the samples (optical microscope and SEM) shown different structural modification of the dislocations (experically TED) after the KOH etching of the samples.

Abstract: Dislocation behavior during the early stages of physical vapor transport (PVT) growth of 6-inch diameter 4H-SiC crystals has been investigated by synchrotron monochromatic beam X-ray topography (SMBXT) in conjunction with ray tracing simulations of dislocation images. Our studies reveal that most of the TSDs/TMDs are replicated into the newly grown layer while most TEDs are generated by either nucleation in pairs at the growth interface or by redirection of BPDs in the seed crystal. Most BPDs in the newly grown layer are of screw type with and this has been verified by comparison with ray tracing simulated images. TEDs with same and opposite sign of Burgers vector are found to be deflected on to the same basal plane by the overgrowth of macro-steps and they glide in the same and opposite directions respectively. TMDs deflected on to the basal plane by macro-steps get dissociated into c and a components, with the a segment undergoing glide to form V-shaped configurations.

Abstract: It is commonly thought that, in the development of SiC power devices with low on-state resistance (R_on), several critical processes in the device fabrication line can strongly impact the final warpage of wafers. High warpage would lead to bad definition of masks, preventing uniform deposition of resist materials and disturbing the normal handling procedures. All these factors would then result in a potential decrease of the electrical yield of the devices, especially for MOSFETs. This study reveals the lack of correlation between critical line processes such as epitaxial growth, oxidations, ion implantations, annealing processes with the final bending of wafers. Conversely, a strong dependence with the resistivity of the substrates is observed. A new parameter defined as RMR (Resistivity Modulation Rate) is taken proposed and, together with the starting value of ingot resistivity, this parameter shows a strong relationship with the final warpage after wafer thinning. A safe region having warpage low enough to allow the workability of the wafers is found.

Abstract: A non-destructive, fast and accurate extended defect counting method on large diameter SiC wafers is presented. Photoluminescence (PL) signals from extended defects on 4H-SiC substrates were correlated to the specific etch features of Basal Plane Dislocations (BPDs), Threading Screw Dislocations (TSDs), and Threading Edge Dislocations (TED). For our non-destructive technique (NDT), automated defect detection was developed using modern deep convolutional neural networks (DCNN). To train a robust network, we used our large volume data set from our selective etch method of 4H-SiC substrates, already established based on definitive correlations to Synchrotron X-Ray Topography (SXRT) [1]. The defect locations, classifications and counts determined by our DCNN correlate with the subsequently etch-delineated features and counts. Once our network is sufficiently trained we will no longer need destructive methods to characterize extended defects in 4H-SiC substrates.

Abstract: Large diameter aluminum nitride (AlN) substrates, up to 50 mm, were manufactured from single crystal boules grown by physical vapor transport (PVT). Synchrotron-based x-ray topography (XRT) was used to characterize the density, distribution, and type of dislocations. White beam topography images acquired in transmission geometry were used to analyze basal plane dislocations (BPDs) and low angle grain boundaries (LAGBs), while monochromatic beam, grazing incidence images were used to analyze threading dislocations. Boule diameter expansion, without the introduction of LAGBs around the periphery, was shown. A 48 mm substrate with a uniform threading dislocation density below 7.0 x 10² cm^-2 and a BPD of 0 cm^-2, the lowest dislocation densities reported to date for an AlN single crystal this size, was demonstrated.

Abstract: In the territory of the Russian Federation within a year, in connection with change of atmospheric conditions, the soil moisture content, saturation of its different layers, temperature and a physical status of soil changes. Depth of freezing of soil is much lower than the bottom level of the pipeline. Freezing, defrosting and uneven rainfall of soil are adverse factors in these conditions. Apparently from the above, there are conditions of forming of corrosion cracking energized (CCE) connected with seasonal and long-term variability of water content of soil. At the same time manifestation of specific features of CCE, characteristic of the specific region, is possible. For studying the reasons and the nature of destruction of the main gas pipeline, in this work a studying of a focal zone is carried out. When determining stress corrosion cracking, first of all, the attention to existence of a fragile component in a break, arrangement of fragile cracks in the lower half-perimeter of a pipe and orientation of the fragile cracks along the forming pipe, which are the main signs of manifestation of corrosion cracking, was paid. On the basis of the received results it is proved that the studied cracks have the corrosion and mechanical origin, characteristic of corrosion cracking energized. Actions for prevention of destruction of gas pipelines are offered further.