Solid State Phenomena Vol. 375

Abstract: Power devices electronics based on silicon carbide (SiC) are emerging as a breakthrough technology for a wide range of applications [1]. SiC engineered substrates provide a solution that fulfills power devices requirements, namely supplying high quality, ultra low resistivity materials. SmartSiC^TM substrates, based on Smart Cut^TM technology, combine the advantages of high quality single-crystal SiC and innovative pSiC handle material [2]. To achieve high volume manufacturing (HVM) of prime grade SiC engineered substrates, defects monitoring is crucial. This paper explains how a commercially available Deep-Ultraviolet (DUV) laser-based inspection system (KLA Surfscan® SC1) was successfully used for the quality control of SmartSiC^TM and single-crystal 4H-SiC in a production environment. Detection of both surface and grown-in defects was investigated, on 150 mm and 200 mm substrates. Statistical data were collected and utilized for driving quality and yield continuous improvement.

Abstract: This paper details the defect inspection and characterization of the 200 mm 4H-SiC (0001) n-type substrate pre-and post-epitaxy. The findings in this paper focus on the characterization of the micropipes (MPs) present in the 200 mm SiC substrate. Following epitaxy, the observations include how the micropipes were propagated from the substrate to the epilayer. This study explores the closing of micropipes during epitaxial growth. As a part of our efforts to better understand the crystal structure and elemental composition of the micropipes in the epilayer, we have conducted SAED and EDX experiments. To the best of our knowledge, it is the first report to demonstrate the region near the micropipe sidewall surface, is remarkably Si-rich (~ 9:1) than in the region towards the bulk (~1:1) after SiC epitaxial growth.

Abstract: Bipolar degradation poses a significant concern for the reliability of SiC bipolar power devices. The basic cause for bipolar degradation is expansion of Shockley Stacking Faults SSFs. These glide planes can be pinned and prevented from expansion. This study involves 19 MeV Energy Filtered Ion Implantation of Nitrogen (i.e. resulting in an energy spectrum ranging from 0 MeV to nearly 19 MeV in one shot) to explore the pinning effect of Nitrogen ions that suppresses recombination glide, which minimizes SSF growth, while providing precise doping of the entire drift region by the same Nitrogen implantation. All is performed in one single step. This procedure paves the path to immobilize any nucleation sites in the entire drift layer, this way enhancing the reliability and facilitating mass production of SiC power devices. This study employs UV illumination as an optical stressing method to create e-/h+ pair, which subsequently induce 1SSF expansion. Both, UV induced 1SSF expansion and pining were observed by photoluminescence. Carrier lifetime measurements were employed for understanding the mechanism of pinning defects.

Abstract: In this study, we investigated the generation of trap centers through hydrogen implantation to understand its role in the suppression of forward bias degradation in 4H-silicon carbide (4H-SiC) bonded substrates. During the production of bonded substrates, hydrogen implantation is used for layer splitting. Transmission electron microscopy (TEM) observations revealed that the basal plane dislocation (BPD) in the bonded substrate did not extend into the Shockley-type stacking fault (SSF) and remained stable in the transferred layer below the epitaxial interface even under high forward current stress. Additionally, carrier lifetime, measured using microwave photoconductivity decay (μ-PCD), was considerably reduced by hydrogen implantation. Annealing at 1700°C reduced the implanted hydrogen to levels below the detection limit of secondary ion mass spectrometry (SIMS), yet the carrier lifetime remained short. Deep level transient spectroscopy (DLTS) revealed that, after annealing at 1700°C following hydrogen implantation, the concentration of the Z_1/2 center increased by more than two orders of magnitude compared to pre-implantation levels. Trap centers, including the Z_1/2 center, are believed to help prevent forward bias degradation in the bonded substrates by inhibiting the expansion of SSFs in the transferred layer.

Abstract: Multi-step high energy ion implantation enables uniform doping to depths up to 12 µm in 4H-SiC epiwafers for superjunction devices but extent of lattice damage is of significant concern for device fabrication. 4H-SiC wafers with 12 µm thick epilayers implanted with Al ions at a concentration of 5 x 10¹⁶ cm^-3 using the Tandem Van de Graaff accelerator at Brookhaven National Laboratory across an energy range of 13.8 to 65.7 MeV and at different temperatures: room temperature, 300 °C, and 600 °C were analyzed by reciprocal space mapping measurements. Implanted layers exhibited tensile strains that decreased with increasing implantation temperature indicating dynamic annealing effect reduces lattice damage. On annealing at 1700 °C, for recovery of the lattice strain, RSM measurements show that the highest implantation temperatures have the lowest residual strains. In addition, the use of a Silicon Energy-Filter for Ion Implantation (EFII) for Al implantation in a single stage to the depth of 15µm is found to further reduce lattice strain compared to wafers implanted without EFII to the same doping concentration. This preliminary study will assist in optimizing the implantation and annealing conditions for the development of superjunction devices.

Abstract: 4H-SiC with 180 μm epilayer was subjected to UV exposure. Stacking fault expanded from basal plane dislocation (BPD) loop generated during growth in the epilayer was observed by UV Photoluminescence Imaging (UVPL) and X-ray Topograph (XRT) techniques. Interactions between partial dislocation, emanating from the BPD loop and gliding via recombination-enhanced dislocation glide mechanism, and threading screw/mix dislocations are detected and analyzed, where stacking faults migrate to different basal plane after the interactions. Such migration increases the faulted volume that can severely degrade reliability and performance of high power SiC devices by increasing reverse leakage current and on-state resistance and could eventually lead to device failure.

Abstract: The increasing demand for WBG materials like SiC has led STMicroelectronics to expand wafer diameter from 150 mm to 200 mm, enhancing production yield and reducing costs. However, this expansion poses challenges in preserving crystalline quality. This investigation examines the impact of defects on 200 mm wafers, focusing on Total Usable Area (TUA) and electrical performance, particularly in wafers with polytype inclusions and high basal plane dislocation (BPD) density. Although the results for non-standard wafers show a significant reduction in TUA and an increase in electrical failures, the overall distribution of functional and non-functional devices remains stable, indicating process consistency.

Abstract: Gated Hall measurements are conducted to calculate interface trap density of a nitric oxide (NO) annealed 4H silicon carbide (4H-SiC) MOSFET. The free carriers are measured using split CV method. Application of body bias confirms that the total trap quantity does not change at the interface when changing the electric field through body bias for a given device. The effect of positive gate stress on Hall mobility is also studied. A stress voltage of +36 V is applied for different stress times (0, 10, 30, 100, and 300 sec). With the increased stress time, the Hall mobility value drops at low gate voltages, while at higher gate voltages they merge. Higher stress creates more interface traps that in turn increase Coulomb scattering which lowers mobility at low gate voltages. The effect of gate stress on Hall mobility provides accurate insight of the channel behavior due to interface traps at 4H-SiC / SiO₂ interface.

Abstract: We have proposed an E-V-C (Expansion-Visualization-Contraction) method by using UV irradiation, for screening potential defects which causes reliability issue called bipolar degradation in 4H-SiC devices. This method is based on the property that the REDG (recombination-enhanced dislocation glide) mechanism causing the bipolar degradation can be reproduced by UV irradiation. However, in order to apply this method as a screening, accurate quantification of the correlation between current density in forward bias and UV irradiance is required. This article describes how to set UV irradiation conditions (irradiance and irradiation time) to simulate forward biased current conditions.