We present results using simulations and experiments to demonstrate metrological applications of the through-focus scanning optical microscopy (TSOM) down to features at and well below the International Technology Roadmap for Semiconductors' 22 nm node. The TSOM method shows the ability to detect sub-nanometer, three-dimensional shape variations such as line height, sidewall angle, width, and pitch in fins of fin-shaped field effect transistor structures using conventional optical microscopes. In addition, the method requires targets substantially smaller than the conventional target size. These results provide insight into the applicability of TSOM for economical critical dimension and yield enhancement metrology.

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We have developed a set of techniques, referred to as scatterfield microscopy, in which the illumination is engineered in combination with appropriately designed metrology targets to extend the limits of image-based optical metrology. Previously we reported results from samples with sub-50-nm-sized features having pitches larger than the conventional Rayleigh resolution criterion, which resulted in images having edge contrast and elements of conventional imaging. In this paper we extend these methods to targets composed of features much denser than the conventional Rayleigh resolution criterion. For these applications, a new approach is presented that uses a combination of zero-order optical response and edge-based imaging. The approach is, however, more general and a more comprehensive set of analyses using theoretical methods is presented. This analysis gives a direct measure of the ultimate size and density of features that can be measured with these optical techniques. We present both experimental results and optical simulations using different electromagnetic scattering packages to evaluate the ultimate sensitivity and extensibility of these techniques.

We experimentally demonstrate that the three-dimensional (3-D) shape variations of nanometer-scale objects can be resolved and measured with sub-nanometer scale sensitivity using conventional optical microscopes by analyzing 4-D optical data using the through-focus scanning optical microscopy (TSOM) method. These initial results show that TSOM-determined cross-sectional (3-D) shape differences of 30 nm–40 nm wide lines agree well with critical-dimension atomic force microscope measurements. The TSOM method showed a linewidth uncertainty of 1.22 nm (k = 2). Complex optical simulations are not needed for analysis using the TSOM method, making the process simple, economical, fast, and ideally suited for high volume nanomanufacturing process monitoring.

We present a novel optical technique that produces nanometer dimensional measurement sensitivity using a conventional bright-field optical microscope, by analyzing through-focus scanning-optical-microscope images obtained at different focus positions. In principle, this technique can be used to identify which dimension is changing between two nanosized targets and to determine the dimension using a library-matching method. This methodology has potential utility for a wide range of target geometries and application areas, including nanometrology, nanomanufacturing, semiconductor process control, and biotechnology.

Through-focus scanning optical microscopy (TSOM) is a new metrology method that achieves 3D nanoscale measurement sensitivity using conventional optical microscopes; measurement sensitivities are comparable to what is typical when using scatterometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). TSOM can be used in both reflection and transmission modes and is applicable to a variety of target materials and shapes. Nanometrology applications that have been demonstrated by experiments or simulations include defect analysis, inspection and process control; critical dimension, photomask, overlay, nanoparticle, thin film, and 3D interconnect metrologies; line-edge roughness measurements; and nanoscale movements of parts in MEMS/NEMS. Industries that could benefit include semiconductor, data storage, photonics, biotechnology, and nanomanufacturing. TSOM is relatively simple and inexpensive, has a high throughput, and provides nanoscale sensitivity for 3D measurements with potentially significant savings and yield improvements in manufacturing.

We present an initial review of a novel through-focus scanning optical microscopy (TSOM pronounced as 'tee-som') imaging method that produces nanometer-dimensional measurement sensitivity using a conventional bright-field optical microscope. In the TSOM method a target is scanned through the focus of an optical microscope, acquiring conventional optical images at different focal positions. The TSOM images are constructed using the through-focus optical images. A TSOM image is unique under given experimental conditions and is sensitive to changes in the dimensions of a target in a distinct way. We use this characteristic for nanoscale-dimensional metrology. This technique can be used to identify the dimension which is changing between two nanosized targets and to determine the dimensions using a library-matching method. This methodology has potential utility for a wide range of target geometries and application areas, including nanometrology, nanomanufacturing, defect analysis, inspection, process control and biotechnology.

We present a simple method for size determination of nanoparticles using conventional optical microscopes. The method, called through-focus scanning optical microscopy, makes use of the four-dimensional optical information collected at different focus positions. Low partial coherence illumination combined with analysis of through-focus optical content enables nanoparticle size determination with nanometer scale sensitivity. We experimentally demonstrate this using fabricated Si nanodots and spherical gold nanoparticles. The method is economical, as no hardware modifications to conventional optical microscopes are needed. In addition, the method also has high throughput and potential for soft nanoparticle size determination without distortion.