Ultra-thin-film characterization with vacuum ultraviolet spectroscopic reflectometry (VUV-SR)

Abstract

Vacuum ultraviolet spectroscopic reflectometry (VUV SR) is a non-destructive, thin film measurement technique extending traditional reflectance spectroscopy to complex, multi band-gap, films stacks. The VUV SR system is a high throughput, production worthy metrology tool, able to resolve ultra-thin, multi-layer films in a single, broad band (800nm down to 120nm) spectral measurement. The dispersion in the films at the smaller VUV wavelengths allows high resolution of disparate thickness, optical properties and composition within thin film systems, not possible with existing UV optical methods. Optical systems such as spectroscopic ellipsometers (SE) are unable to resolve wide band gap films such as the SiO2-like interface layer between a Hf-based high-k layer and a Si substrate due to intrinsic hardware limitations of the low wavelength range (typically below 150nm). Absorption in the films begins to dominate at incident wavelengths below 190nm, resulting in enhanced reflectance resolution. The resolution of multiple band-gap films being used in sub-45nm semiconductor device manufacturing technology, includes individual films with absorption peaks in the broadband, and less than 190nm (190-150nm, 150-130nm and 130-120nm) wavelength ranges. Applying fitting models and optical properties to the reflectance data, the thicknesses of individual films and their composition can be determined.