Advances in defect characterization techniques using polarized light observation in SiC wafers for power devices

Silicon carbide (SiC) is the leading wide bandgap semiconductor for high-power and high-temperature electronics, but the high defect density still limits device performance. This study investigates how inclusions, Basal Plane Dislocations (BPDs), and Threading Screw Dislocations (TSDs) in 4H-SiC substrates affect epitaxial defect formation. Twenty 200 mm SiC wafers were analyzed after epitaxial growth in two industrial Chemical Vapor Deposition (CVD) reactors, one using Trichlorosilane/Ethylene (Reactor A) and the other Silane/Propane (Reactor B). Defects were characterized using Candela (KLA), Altair (KLA), XRTmicron LAB (Rigaku), SICA (Lasertec), and Crossbeam (ZEISS) dual-beam SEM system. Statistical correlation showed that the conversion rate of embedded particles decreases with particle depth and increases with particle size. Reactor A exhibited lower propagation rates, indicating better suppression of substrate-related defects. SEM/FIB-EDX analyses suggested that carbon inclusions generate pits while metallic inclusions induce triangular defects. Dislocation analysis confirmed a strong correlation between TSDs and BPDs with carrots and triangular defects. BPD conversion rates were estimated at about 98.3% (Reactor A) and 99.8% (Reactor B). These results emphasize the importance of substrate quality and buffer layer optimization to minimize defect propagation.

Understanding the electronic properties of dislocations is key to tailoring their properties in silicon carbide (SiC)-based electronic devices. By combining the Kelvin probe force microscopy analysis and first-principles calculations, we investigate the effect of aluminum (Al) dopants and surface oxides on the electronic properties of dislocations in p-type SiC. It is found that dislocations, including threading screw dislocations (TSDs), threading edge dislocations (TEDs), and basal plane dislocations (BPDs) create deep acceptor-like states in p-type SiC. The defect levels move upwards in the order of BPD, TED and TSD, which closely relates with the lattice distortion of dislocations. Interestingly, we find that the defect levels of dislocations are higher than that of Al dopants in p-type SiC. First-principles calculations indicate that the defect formation energies of Al dopants at the cores of dislocations are higher than those in the perfect region of p-type SiC, as a result of the steric effect. This indicates that the concentration of Al acceptors at the dislocation cores is lower than that in the perfect region, resulting in the higher defect level positions of dislocations in p-type SiC. Additionally, we find that surface oxidation reduces the difference of defect-level positions between dislocations and the perfect region of p-type SiC, which paves the way for tailoring the electronic properties of dislocations in p-type SiC.

This paper demonstrates the X-ray three-dimensional topography of basal-plane dislocations (BPDs) and threading edge dislocations (TEDs) in 4H-SiC. Cross-sectional imaging shows the propagation of BPDs from a substrate to an epilayer and the conversion of BPDs into TEDs near the epilayer/substrate interface. The strain analysis of TEDs exhibits the image of strains in the order of ±10-5. The observed strain images correlate well to simulation results.

Silicon carbide (SiC) is a wide bandgap semiconductor with physical and electrical properties that provide superior performance in high-voltage or high-power applications. Compared to silicon used in many power devices, SiC provides better thermal conductivity, ~10x higher breakdown voltage, faster switching speeds and lower forward resistance (Rdson). However, even with many substantial performance advantages, the potential adoption rate of SiC is slowed by high cost and the inherent difficulty of growing and processing this material.Developing the knowledge, techniques, and methods to efficiently process this incredibly hard and inert material is essential for continued technological progress and commercial success. As a starting point, most engineers turn to experience with silicon which is by far the most established semiconductor wafer material. This can be useful, but it has limitations. If those limitations are not understood, this strategy can easily become frustrating and counterproductive. This presentation will compare and contrast some of the wafering processes for producing SiC and silicon wafers to give a better foundation for understanding how to implement a higher yielding and more cost-effective manufacturing strategy for SiC. One of the key learnings is to view the SiC wafer fabrication sequence in its entirety rather than as a series of discrete steps. This more holistic approach enables a better understanding of the relationships between process costs, throughput, and overall wafer yield.

Silicon carbide is an attractive material for next-generation power devices, it has wide band gap and high thermal conductivity. SiC power devices can operate at higher temperatures and voltages compared to silicon devices. But, electrical characteristics of the SiC power devices can be deteriorated by SiC defects. The killer defects such as micropipes and stacking faults have been reduced through the development of SiC growth technique. But still the threading dislocations (TDs) and basal plane dislocations (BPDs) lowered the breakdown voltage and increased the leakage current during device operation [1]. In this study, we fabricated the 5 kV 4H-SiC Schottky barrier diode (SBD) to study the effect of SiC defect on electrical properties of SiC SBDs. The thickness of epitaxial layer was 50 um and the doping concentration is 1E15 cm-3. The device was fabricated with various length of junction termination extension (JTE). Ion implantation was performed to form p surge (Al, 500 °C, 5E19 cm-3) and JTE (B, 500 °C, 2E18 cm-3) regions. Activation annealing was performed at 1700 °C for 60 m. 100 and 30-nm-thick Ni were deposited as the cathode and front-side ohmic metal respectively, and then annealed at 950 °C for 90 s in RTA system. Finally, 100-nm-thick Ni was sputtered on front-side as a Schottky contact metal. We investigated the forward, reverse characteristics, and reverse breakdown voltage of the fabricated 4H-SiC SBDs. The diode characteristics, ideality factor (IF) and Schottky barrier height (SBH) were obtained from the forward electrical characteristics, about the 1.23 and 1.3 eV, respectively. The relative highly ideality factor may be due to rough surface of thick epitaxial layer. The breakdown voltage was obtained above 5 kV with JTE length longer than 60 um. During reverse characteristics the electrically weak points were observed using electroluminescence (EL). The EL spot was mainly aroused from electrically leaky points, it mostly observed at the edge of JTE. Some EL spots were observed inside the JTE or active region. The defects of the fabricated 4H-SiC 5 kV SBDs were analyzed using non-destructive analysis method, X-ray topography (XRT) and electron beam induced current (EBIC). We tried to determine the correlation between the electrical characteristics of the device and the crystal defects in the device. [1] H. Fujiwara, H. Naruoka, M. Konishi, K. Hamada, T. Katsuno, T. Ishikawa, Y. Watanabe, and T. Endo, Appl. Phys. Lett. 100, 242102 (2012). Figure 1

Wide bandgap semiconductor, 6H-SiC, is being applied in photoconductive semiconductor switches (PCSS) due to its semi-insulating properties. This material is normally insulating but when illuminated, charge carriers are pumped to the conduction band and the material becomes conductive in proportion to the light intensity. Under the application of voltage and laser, the density as well as the movement of the defects will have an impact on the performance of the device. Characterization and understanding the mechanism of this potentially destructive defect process is of great scientific interest as well to the development of the device. X-ray topography is a powerful, non-destructive technique for the characterization of extended defects in large, single crystals. In this study, threading edge dislocations (TED), threading screw dislocations (TSD) as well as basal plane dislocations (BPD) in 6H-SiC axial samples are revealed using synchrotron rocking curve topography, where the atomic structure information (Burgers vector) of these dislocations are investigated using ray tracing simulation. The understanding of the nature of these dislocations is of great importance as to predict their propagation and movement under the application of voltage and laser, and eventually helps to improve the performance of the device. Figure 1

Fluorescent paramagnetic defects in solids have become attractive systems for quantum information processing in the recent years. One of the leading contenders is the negatively charged nitrogen-vacancy defect in diamond with visible emission but alternative solution in technologically mature host is an immediate quest for many applications in this field. It has been recently found that various polytypes of silicon carbide (SiC), that are standard semiconductors with wafer scale technology, can host nitrogen-vacancy defect (NV) that could be an alternative qubit candidate with emission in the near infrared region. However, it is much less known about this defect than its counterpart in diamond. The inequivalent sites within a polytype and the polytype variations offer a family of NV defects. However, there is an insufficient knowledge on the magneto-optical properties of these configurations. Here we carry out density functional theory calculations, in order to characterize the numerous forms of NV defects in the most common polytypes of SiC including 3C, 4H and 6H, and we also provide new experimental data in 4H SiC. Our calculations mediate the identification of individual NV qubits in SiC polytypes. In addition, we discuss the formation of NV defects in SiC with providing detailed ionization energies of NV defect in SiC which reveals the critical optical excitation energies for ionizing this qubits in SiC. Our calculations unravel the challenges to produce NV defects in SiC with a desirable spin bath.

Raman spectroscopy has been increasingly used, in recent years, to characterize irradiated materials, in particular silicon carbide. The interpretation of the spectra is nevertheless problematic. In this paper, we provide a first step toward a more quantitative interpretation, by providing first‐principles calculations of Raman intensities for various polytypes of silicon carbide (SiC) and for point defects in cubic SiC. We consider here, as benchmarks, the carbon antisite, CSi, and the doubly charged carbon vacancy/carbon antisite complex, VC. We show that some care is necessary to understand the contribution of point defects on the Raman spectrum of the material, due to supercell size effects.Calculated Raman spectra of cubic SiC with and without point defect, here a carbon antisite, CSi, in a 216‐atom supercell.

Defects in silicon carbide are of intense and increasing interest for quantum-based applications due to this material's properties and technological maturity. We calculate the multi-particle symmetry adapted wave functions of the negatively charged silicon vacancy defect in hexagonal silicon carbide via use of group theory and density functional theory and find the effects of spin-orbit and spin-spin interactions on these states. Although we focused on $\textrm{V}_{\textrm{Si}}^-$ in 4H-SiC, because of its unique fine structure due to odd number of active electrons, our methods can be easily applied to other defect centers of different polytpes, especially to the 6H-SiC. Based on these results we identify the mechanism that polarizes the spin under optical drive, obtain the ordering of its dark doublet states, point out a path for electric field or strain sensing, and find the theoretical value of its ground-state zero field splitting to be 68 MHz, in good agreement with experiment. Moreover, we present two distinct protocols of a spin-photon interface based on this defect. Our results pave the way toward novel quantum information and quantum metrology applications with silicon carbide.

An electrochemical method for making pores in a silicon carbide (SiC) wafer, in which a glassy-carbon (GC) needle electrode was used for processing, is described. By bringing the GC electrode into contact with SiC at its tip end in 20 mol dm(-3) HF solution and applying an anodic potential of or higher than 4 V vs Ag/AgCl to it, SiC was etched at the SiC/GC contact area, leading to pore formation in SiC. The diameter of the pore was almost the same as the diameter of the tip of the GC electrode (about 130 μm). By addition of sulfuric acid to the HF solution, the rate of pore formation was increased. As a result, the depth of pores formed after processing for 5 h at 10 V vs Ag/AgCl was increased from 15.3 μm to about 33 μm by addition of sulfuric acid at a concentration of 3.0 mol dm(-3).

A quantitative study was performed to investigate the impact of crystallographic dislocation defects, including screw dislocation, basal plane dislocation, and threading edge dislocation, and their locations in the active and JTE region, on the reverse performance of 4H-SiC p–n diodes. It was found that higher leakage current in diodes is associated with basal plane dislocations, while lower breakdown voltage is attributed to screw dislocations. The above influence increases in severity when the dislocation is in the active region than in the JTE region. Furthermore, due to the closed-core nature, the impact of threading edge dislocation on the reverse performance of the p–n diodes is less severe than that of other dislocations although its density is much higher.

Slurryless electrochemical mechanical polishing (ECMP) is very effective in the polishing of silicon carbide (SiC) wafers. To achieve a high material removal rate (MRR) of SiC wafer using ECMP with low electrical energy loss, charge utilization efficiency in the anodic oxidation of the SiC surface was investigated and the underlying mechanism was clarified by modeling the anodic oxidation system of SiC in 1 wt% NaCl aqueous solution. The charge utilization efficiency in the anodic oxidation of SiC was found to be constant when the current density was less than 20 mA cm−2 and significantly decreased when the current density was greater than 30 mA cm−2, resulting in a significant reduction in the MRR. Modeling of the anodic oxidation system indicates that the charge utilization efficiency depended on the potential applied on the SiC surface: the oxidation of SiC occupied the dominant position in the anodizing system when the potential is lower than 25 V vs Ag∣AgCl, charge utilization efficiency greatly decreased when the applied potential was greater than 25 V owing to the occurrence of oxidations of the H2O and Cl−. This research provides both a theoretical and practical foundation for using ECMP to polish SiC wafers.

Silicon carbide (SiC) substrates with chemical vapor deposition (CVD) grown epilayers have been characterized by synchrotron white beam X-ray topography (SWBXT). Large numbers of circular basal plane dislocation loops (BPDs) were observed in the substrate which were anchored by threading screw dislocations (SDs). Threading edge dislocations (TEDs) are not observed to play an important role in the multiplication of BPDs. A SD-assisted “conservative climb” model is proposed to explain the multiplication of BPDs during growth and/or post-growth processes. BPDs are shown to multiply on adjacent parallel basal planes via single SD-assisted as well as opposite sign SD-pair-assisted “conservative climb”.

In this paper, epitaxial growth on 4H-SiC (0001) substrates with 4° and 8° off-cut angles is investigated. Both growth rate and nitrogen doping show a dependence on the C∕Si ratio and off-cut angle. Good surface morphologies are obtained on the 8° off-angle substrates over a wide range of C∕Si ratios, while macrostep bunching is observed on the 4° off-angle substrates depending on C∕Si ratios. Step bunching behaviors on both substrate orientations are investigated by Nomarski microscopy and atomic force microscopy, and possible step bunching mechanisms are proposed to explain the results. Basal plane dislocation (BPD) densities are examined by means of molten KOH etching. Low off-cut angle is found to enhance the conversion of BPDs into threading edge dislocations. A BPD density of 2.6cm−2 is achieved on the 4° off-angle substrate under optimized growth conditions. The effects of changing the C∕Si ratio on BPD densities are also investigated.

Synchrotron X-ray topography was carried out for 4H-SiC crystals grown by high-temperature gas source method, and transmission topography analysis with g= or 0004 was carried out for the cross-sectional samples. Dislocation contrasts extended in the growth direction were observed and the propagation behavior of threading screw dislocations (TSDs), threading edge dislocations (TEDs), basal plane dislocations (BPDs) and stacking faults (SFs) in the facet and step-flow regions were discussed. The propagation of dislocations in the fast grown crystal with a growth rate of 3.1mm/h was also evaluated by cross-sectional topography.