Specular spectroscopic scatterometry

TLDR

Scatterometry offers in‑situ metrology for deep sub‑micrometer critical dimensions, but most devices measure multiple incident angles at a single wavelength on periodic gratings. The study introduces specular spectroscopic scatterometry to address this limitation. Specular spectroscopic scatterometry records the zeroth‑order diffraction at a fixed incidence angle across multiple wavelengths, leveraging standard spectroscopic ellipsometers and a grating toolkit that implements rigorous coupled‑wave analysis to simulate 1‑D grating diffraction and enable library‑based profile extraction for resist and poly exposure matrices. Simulations confirm the method’s applicability to current semiconductor processes and its scalability to 0.07 µm nodes, and experimental application to 0.25 µm and 0.18 µm lithography demonstrates accurate cross‑sectional profiling with discrepancies between CD‑SEM, CD‑AFM, and SSS explained.

Abstract

Scatterometry is one of the few metrology candidates that has true in situ/in-line potential for deep submicrometer critical dimension (CD) and profile analysis. Most existing scatterometers are designed to measure multiple incident angles at a single wavelength on periodic gratings. We extend this idea by deploying specular spectroscopic scatterometry. Specular spectroscopic scatterometry (SS) is designed to measure the zeroth-order diffraction response at a fixed angle of incidence and multiple wavelengths. This mechanism allows the use of existing thin-film metrology equipment, such as spectroscopic ellipsometers, to accurately extract topographic profile information from one-dimensional (1-D) periodic structures. In this work, we developed the grating tool-kit (gtk), which implements several variants of rigorous coupled-wave analysis (RCWA) to accurately and efficiently simulate diffraction behavior of 1-D gratings. Theoretical simulations using this package show that specular spectroscopic scatterometry can be applied in the current semiconductor manufacturing technology, and can be easily extended to the 0.07-/spl mu/m generation. We have also applied a library-based profile extraction methodology to resist and poly focus-exposure matrices patterned using 0.25and 0.18-/spl mu/m lithography and etch technology, respectively, to extract their cross-sectional profiles. Discrepancies between CD-SEM, CD-AFM, and SSS measurements are discussed and explained.