Mid-infrared ellipsometry for optical critical dimension metrology

Mid-infrared ellipsometry offers a powerful approach for non-destructive optical critical dimension (OCD) metrology in advanced semiconductor manufacturing. This technique supports in-line measurements of high aspect ratio structures, such as those found in 3D NAND memory devices. The incorporation of quantum cascade lasers and fast phase modulation allows rapid acquisition of Mueller matrix elements with high spatial resolution and sub-Å precision. Material-specific absorption in the mid-infrared range allows depth-resolved profiling of device structures, overcoming the limitations of conventional OCD. Rigorous coupled wave analysis is used to extract structural parameters from the measured spectra. Agreement with destructive reference metrology has been demonstrated on a variety of structures. The ability to measure multiple Mueller elements further enhances characterization of complex geometries, making mid-infrared ellipsometry a valuable tool for process control in semiconductor fabrication.