785-nm Frequency Comb-Based Time-of-Flight Detection for 3D Surface Profilometry of Silicon Devices

Abstract

Three-dimensional integrated circuits (3D-ICs) are becoming more significant in portable devices, autonomous vehicles, and data centers. As the demand for highly integrated and high-performance semiconductor devices grows, recent 3D integration technologies focus on lowering the size of the microstructures on such devices for high density. In order to inspect the 3D semiconductor devices, it is critical to measure the heights, depths, and overall surface profiles of the micro-structures made with silicon materials. Here, we demonstrate precise surface imaging for silicon devices by using a femtosecond mode-locked laser centered at 785 nm wavelength and an electro-optic sampling-based time-of-flight detection method with sub-10nanometer axial precision. We could successfully measure the surface profiles as well as the step heights of silicon wafer stacks and micro-scale structures on silicon substrates.