Papers by Keyword: KOH Etching

Abstract: The growing demand for wide-bandgap (WBG) materials in the microelectronics industry has led to increased investment in medium- and high-voltage power products based on SiC technology. SiC offers an excellent balance between high voltage blocking capability, high temperature operation and high switching frequencies [1]. One key step in preparing high-performance devices is improving the growth process of SiC ingot material by Physical Vapor Transport (PVT). Epitaxial growth occurs through the chemical vapor deposition (CVD) method [2]. However, this method is reported to generate extended defects such as Complex Stacking Faults (formerly referred to as carrots) and Polytype Inclusions (formerly referred to as triangles or comets) and propagate defects pre-existing in the bulk material, such as micropipes (MPs) and threading screw dislocations (TSDs), which have a very high killer ratio in SiC devices [3, 4]. In this work, the KOH molten etching method was used to investigate the nature of the defects that caused device failures; Raman spectroscopy was also employed to identify the spectroscopic correspondence of the peaks of interest.

Abstract: Accurate characterization of dislocations is crucial for optimizing the performance of SiC-based power devices. The traditional way to measure dislocation density in SiC industry is KOH etching, a destructive approach that makes the wafer no longer available for epitaxial growth. Another major limitation of this technique is the accuracy of the data since some dislocations can be hardly recognized. For example, the etch pit of threading screw dislocation is similar to that of threading edge dislocation, both of which are usually in hexagonal shape while the primary difference is the size. However, those challenges and limitations in KOH etching do not exist in X-ray topography. In this paper, the non-destructive approach, X-ray topography, is introduced to characterize dislocations in 4H-SiC industry. Threading screw dislocations were measured by both KOH etching and X-ray topography, the result of which indicates that some threading screw dislocations clearly visible in X-ray topograph are not recognizable in KOH etching image. In addition, some 60° prismatic dislocations not recognized in KOH etching image can be observed in X-ray topographs. Moreover, unlike destructive KOH etching, wafers measured by X-ray topography can be further used for annealing, epitaxial growth, ion implantation and etc., which is beneficial to SiC fundamental research.

Abstract: A whole wafer method for industrial high volume, non-destructive characterizing of extended defects is demonstrated for 150 mm and 200 mm 4H-SiC wafers. Deep learning (DL) coupled with non-destructive techniques (NDT, DL-NDT) involving high volume, fast optical microscopy methods correlates industry accepted chemistry and physics-based etch and diffraction techniques for defect characterization. The application of the DL-NDT method is shown to reproduce defect distributions achieved by accepted etch techniques for extended defects of threading dislocations (TD), basal plane dislocations (BPD), and threading screw dislocations (TSD). An example of algorithm development is described to show progress toward implementing the method, as well as DL-NDT defect density compared to etch density for multiple wafers. The development status for implementing this technique for large-scale industrial wafer production includes etch validation of the results to ensure the technique is consistent and reliable. The ability to use this non-destructive technique ultimately will result in better correlation with device behavior and provide feedback to crystal growth processes to improve substrate wafers, while reducing the need for etch methods.

Abstract: Screw-type dislocations like micropipes (MP) and threading screw dislocations (TSD) are prohibiting the function or at least diminishing the efficiency of electronic devices based on silicon carbide (SiC). Therefore, it is essential to characterize wafers in an efficient and fast manner. Molten potassium hydroxide (KOH) etching or white-beam X-ray topography (SWXRT) are either destructive or not economically viable for an in-depth characterization of every wafer of one SiC crystal. Birefringence microscopy is being utilized as a fast and non-destructive characterization method. Instead of microscopic setups, commercially available flat-bed scanners equipped with crossed polarizer foils can be used for fast large-area scans. This work investigates the feasibility of such a setup regarding the detection rate of MPs and TSDs. The results of a full-wafer mapping are compared with birefringence microscopy and KOH etching. In the investigated sample clusters of MPs caused by a polytype switch in the beginning of the growth could be identified by both birefringence microscopy and the flat-bed scanner setup, as well as small angle grain boundaries and TED arrays. However, the resolution of the scanner was not sufficient to identify TSDs. Nevertheless the setup proves to be an easy-to-setup and cheap characterization method, able to quickly identify defect clusters in 4H-SiC wafers.

Abstract: This study offers a comprehensive examination of the behavior of 3C-SiC crystals grown on 4° off-axis (100) Si substrates with different off-axis angles along <110> and <100> for N and Al doping, respectively. The investigation takes advantage of molten KOH etching to conduct an in-depth investigation of the average density and size of the SFs inside the crystal for both n- and p-type doped 3C-SiC epitaxial layers. Moreover, 3C-SiC grown on a <100> off-cut substrate was revealed to have a greater concentration of SFs due to the absence of self-annihilation along the plane (-1-10). Considering two different doping ranges suitable for IGBTs and MOSFETs development, the impact of doping and off-angle on the crystal quality, concentration, and length distribution of SFs was then investigated in order to quantify the influence of N and Al incorporation on the structural and optical characteristics of the semiconductor. It turned out that under heavy nitrogen doping (~10¹⁹ cm^-3), when the dopant concentration grew, the average length of the stacking faults (SFs) expanded while their density dropped.

Abstract: In this work, the effect of high temperature molten KOH wet etching on GaN/AlGaN epilayer has been investigated for different family of dislocations. The high etching temperature (up to 510°C) allows a good definition of the pits, making easy the observation and the counts. Such high temperature will allow a detailed study on the statistical distribution of the dislocations on whole wafer by optical microscope for screw/mixed dislocation. A comparison on dislocation density between AlGaN/GaN structure grown on Si (111) substrate and 4H-SiC substrate has been performed.

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: We propose the Si-Vapor Etching (Si-VE), which is thermal chemical etching process, as epi-ready treatment for Silicon Carbide (SiC). In this work, we report the evaluation results of BPD-TED conversion by Si-VE treatment using repeated KOH etching process. This method makes it possible to observe BPD-TED conversion in a very shallow surface region of the SiC substrate. 80% of BPDs is converted to TEDs with a depth of more than 80nm under optimized Si-VE 2000°C conditions. Furthermore, 53% of BPDs were converted to TEDs with 140nm or more depth, which has been confirmed under optimized 1800°C Si-VE conditions.

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: The thermoelastic stress, mechanical properties and defect content of bulk 4H n-type SiC crystals were investigated following adjustments to the PVT growth cell configuration that led to a 40% increase in growth rate. The resulting 150 mm wafers were compared with wafers produced from a control process in terms of wafer bow and warp, and dislocation density. Wafer shape was found to be comparable among the processes, indicating minimal impact on internal stress. Threading edge and threading screw dislocation densities increased and decreased, respectively, while basal plane dislocation densities were unaffected by the increase in growth rate. Loss of wafer planar stability was observed in certain cases. The elastic modulus was measured to be in the range of approximately 420-450 GPa for selected stable and unstable wafers, and was found to correspond to resistivity.