Model‐based CD–SEM metrology at low and ultralow landing energies: implementation and results for advanced IC manufacturing

Abstract

Critical Shape Metrology (CSM), a Critical Dimension Scanning Electron Microscope (CD-SEM)-basedtechnique that extracts accurate feature shape information from images obtained during routine in-line wafer inspection as a means of minimizing measurement bias, is described and explored experimentally. CSM uses intensity profiles from CD-SEM images of known materials that are compared in real time to profiles contained in an off-line generated Monte Carlo SEM simulation library. The library of intensity waveforms spans the range of expected geometric feature shapes and material compositions. Extensive comparison of CSM results to accepted reference measurement system measurements using Critical Dimension Atomic Force Microscopes, cross-sectional SEMs and Focused Ion Beams are made. Agreement of the CSM method to each of these is shown to be better than 1% or within experimental uncertainty and significantly better agreement than traditional CD metrology algorithms.

Modeling for accurate dimensional scanning electron microscope metrology: then and now

“…This concept has been demonstrated in many instances and several various software solutions were developed over time. The so‐called inverse scattering method that used commercially available MC software to generate a library of linescans and a fast algorithm to find the best match to the measured linescan was published by Davidson and Vladár ('99) and Gorelikov et al (2005). Villarrubia et al (2001, 2005) demonstrated that by using such an approach the precision of CD measurements could be improved by a factor of 3x, and information beyond just the width of the line, such as side wall angles, corner rounding, and feature height could be calculated with good certainty.…”

Monte Carlo Simulation of SEM and SAM Images

“…When the line/feature size is decreased to several tens nanometers, the bias due to the edge effect would become more obvious. A lot of works including both experimental study (Bunday et al, 2007;Choi et al, 2006;Jones et al, 2003;Kawada et al, 2003;Maeda et al, 2008;Matsumoto et al, 2006;Morokuma et al, 2004;Novikov et al, 2007;Rice et al, 2006;Shishido et al, 2002;Tanaka et al, 2003;Tanaka et al, 2004;Tanaka et al, 2005;Tanaka et al, 2007;Tanaka et al, 2008a;Tanaka et al, 2008b;Wang et al, 2007;Yamane & Hirano, 2005) and theoretical investigation (Abe et al, 2007;Babin et al, 2008a;Babin et al, 2008b;Bunday & Allgair, 2006;Dersch et al, 2005;Frase et al, 2007a;Frase et al, 2007b;Gorelikov et al, 2005;Villarrubia et al, 2004;Villarrubia et al, 2005a;Villarrubia et al, 2005b) with MC simulation methods have been done, aiming at accurate estimation of the CD values with CD-SEM. However, when the dimension decreases to tens nanometers most of the experiential methods, such as, the maximum derivative method, the regression to baseline method and the sigmoidal fit method, face different difficulties (ITRS, 2007;Villarrubia et al, 2005a).…”

“…Villarrubia et al have introduced a model-based library (MBL) method Villarrubia et al, 2005a;Villarrubia et al, 2005b) by which a library of the MC simulation results for various parameters spanning the process space of interest is constructed. Dmitry et al have also used an off-line generated MC simulation library and fitted the measured intensity profiles of the critical shape metrology (Gorelikov et al, 2005).…”

Sensitivity of SEM width measurements to model assumptions

“…3,4 Validation of such measurements can be difficult because of the very low desired uncertainties (which in a validation must be met by two independent techniques), but studies have shown good success. [5][6][7][8] The paper will address the components of uncertainty in linewidth determination in CD-SEM measurements that arise due to uncertainty about the physics model that ought to be used. There are standard statistical procedures (see, e.g., reference 9) for estimating the uncertainties in parameters from fits like the ones described in the preceding paragraph.…”