Investigation of Inclusions and Associated Dislocation Configurations in 4H-SiC Wafers through Synchrotron X-Ray Topography and Ray-Tracing Simulation
Authors: Cheng Qianyu , Chen Zeyu , Hu Shanshan , Raghothamachar Balaji , Dudley Michael 
Published: December 2024

Silicon carbide (SiC) is a wide bandgap semiconductor that steadily replacing the application of conventional semiconducting materials such as silicon-based devices. Its superior properties such as larger bandgap, higher electron saturation velocity and thermal conductivity [1, 2] enables devices to be more effective and efficient with smaller volume, higher dielectric strength, and lower energy loss [3-5]. The prerequisite of expanding SiC devices industry is to achieve steady manufacture of large-scale, high-quality, polytypic stable SiC substrate wafers. Therefore, understanding the nature and origins of crystallographic defects within SiC is a major research pursuit since those can induce degradation that challenges device reliability while achieving high performance [6]. Synchrotron X-ray topography (XRT) [7, 8] is a powerful non-destructive characterization technique that generate high-resolution X-ray images of the internal structure of a crystal. Crystallographic defects and structural features are then revealed as topographic contrast features that can be identified applying contrast formation mechanisms. Extensive studies have been conducted to observe various dislocation configurations, stacking faults, and low-angle grain boundaries using this approach. In this study, optically observable hexagonal features on a 6-inch 4° off-axis 4H-SiC substrate wafer are investigated through synchrotron XRT in both transmission and grazing-incidence geometries. These hexagonal features are identified as inclusions as correlated topographic contrasts reveal the generation of large strain fields associated with them. Indentation behavior is found to be induced by the presence of inclusions as both regular (9keV) and high energy (18keV) grazing-incidence topographs show arrays of opposite-signed threading edge dislocation (TED) pairs expand from inclusions along <11-20> directions, which is the evidence of the generation of prismatic loop. Basal plane dislocation (BPD) half loops are also observed associated with inclusions. Using ray-tracing simulation technique based on orientation contrast mechanism [9, 10], contrasts of inclusion at different depth and associated dislocations can be simulated and compared to X-ray topographic images. This will provide insights on the behavior of inclusions embedded in SiC as well as the activation of associated dislocations.

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Figure 1: (a) Optical image showing hexagonal features on the upper region of a 4° off-axis 4H-SiC substrate wafer; (b) synchrotron white beam X-ray topograph recorded in 11-20 transmission geometry for the same region, showing the strain contrast induced by those hexagonal features; (c) synchrotron monochromatic beam X-ray topograph recorded in 11-28 grazing-incidence geometry for the same region, showing contrast of some hexagonal features (marked with blue arrows); (d) enlarged optical image of the hexagonal feature; (e) enlarged 11-28 grazing-incidence synchrotron X-ray topograph showing TED slip bands induced by a hexagonal feature; (f) enlarged 22-4,16 grazing-incidence synchrotron X-ray topograph showing TED slip bands induced by a hexagonal feature.

Figure 1