Precise optical characterization of SiGe thin films for next generation transistor metrology

Abstract

Silicon germanium (SiGe), a well-established material in transistor technology, continues to play a crucial role in next-generation architectures, including complementary FETs (CFETs), gate-all-around FETs (GAAFETs), and FinFETs. Precise thickness control and material characterization at sub-nanometer precision are essential for optimizing device performance. Accurate determination of SiGe’s optical constants is fundamental for metrology, process modeling, and semiconductor fabrication. This work presents a detailed optical characterization of 45 nm and 50 nm SiGe thin films with 21% and 38% Ge content, respectively, focusing on the determination of optical constants (ñ = n + ik = (1 - δ) + iβ) in the extreme ultraviolet (EUV) range (5-20 nm). By analyzing the dispersive component (δ) and extinction coefficient (β), we provide essential data for modeling layer thickness, interface sharpness, and variations in Ge content. Our results enhance metrology techniques such as reflectometry, ellipsometry, and scatterometry, facilitating better control of SiGe-based device fabrication.