SiC Substrate and its Epitaxial Layers' Analysis by Spectroscopic Ellipsometry

Silicon carbide (SiC) is considered as one of the most promising third-generation semiconductor materials with many applications in the cutting-edge fields. For SiC-based device application, the quality of substrate and its epitaxial layer is of importance. Their optical and geometric characteristics are great indexes for quality assessment, which can be used to optimize the device structure, substrate machining process, and epitaxial growth process. Spectroscopic ellipsometry (SE) is an optical experimental technique that measures the change of polarized light by reflection upon or transmission through a sample to obtain the ellipsometric parameters (amplitude change-Psi/phase shift-Delta or Mueller matrix). As a highly sensitive and nondestructive method for the intrinsic (optical constants or dielectric function) and structural (thickness, roughness, uniformity, etc.) properties' determination of bulk materials and thin films, it is helpful to understand more about the properties of materials from an optical perspective. This chapter presents a fundamental understanding of SE first. Its measurement techniques and data analysis procedures are overviewed. Then, the methods of measuring and analyzing bulk silicon carbide materials based on SE transmission and reflection modes are discussed. Next, since 4H- and 6H-SiC are optically anisotropic uniaxial crystals, the partial and full Mueller matrix are specially introduced. Finally, the ellipsometric analysis of epitaxial layers, including SiC homoepitaxy layer and its heteroepitaxy layers (such as GaN, AlN, and graphene epitaxial layers, etc.) is also discussed together with temperature-dependent optical properties of GaN epitaxial layers on SiC substrate. A picture for the SE analysis of optical constants or dielectric function of SiC and SiC-related epilayers is drawn in this chapter.