3D-FEATURES ANALYSIS USING SPECTROSCOPIC SCATTEROMETRY

摘要

Spectroscopic scatterometry is an optical metrology technique based on light scattering aiming at measuring geometrical dimensions, such Critical Dimension (CD) but also height or depth, side-wall angle and even more tiny details in a line profile. Scatterometry tool measures and analyzes the spectrum scattered or diffracted from a periodic target patterned on a wafer. Scatterometry is strongly considered as an alternative or as a complementary technique to CDSEM for 90nm and below technology nodes. Like other optical metrology techniques, scatterometry measurements are rapid, non-destructive and highly repeatable. Actual tools have been assessed for dense to semi-isolated lines CD metrology and profiling. Developments are now targeting hole measurement. 2D-scatterometry (scatterometry on 3D patterns) becomes mature and begins to be used in advanced fab for CD control after lithography. This paper focuses on the capability of the spectroscopic scatterometry method to determine holes features and to try to give theoretical limits of method. Scatterometry uses an optical tool for spectra recording and a software tool including an advanced electromagnetic simulator and an optimization loop for data extraction. The first part of this study reports on the influence of bi-periodic structures in the experimental analysis of holes measurements. Then a limitation in holes density is defined. The second part of this study is a theoretical analysis based on simulation of the sensitivity of scatterometry with respect to various holes parameters. Following parameters are generally taken into account: holes diameter, holes ellipticity (elliptical ratio), holes roundness, holes depth and tilt angle for non-circular holes. We determine the respective influence of these parameters on ellipsometric spectra.