Three-Dimensional Nanometer Metrology

Three-dimensional measurements of nanometer-scale structures are of increasing importance for nanoscience and nanomanufacturing, including the present and future generations of semiconductor and photonic devices. Our main goals are to advance measurement science for 3D nanostructures, to develop the necessary SI-traceable reference artifacts, measurement methods and dimensionally accurate modeling of the imaging and measurement processes for scanned electron, ion and optical microscopy.

Our world is three-dimensional, so are the smallest, even nanometer-size structures ranging from integrated circuits (ICs) to tiny particles comprised only of a few (dozen) atoms and to the minuscule building elements created by the emerging nanotechnology. Methods that directly image and measure these structures are as important as others that acquire and interpret some kind of characteristic information associated to their three-dimensional properties. The research and development of imaging and non-imaging dimensional metrology methods of our project makes high-resolution and traceable measurements for scientific, technology and standards uses possible.

The scanning electron microscope (SEM) is one of the workhorse techniques for imaging and characterization for nanotechnology. Significant performance improvements are still possible, and especially for nano-scale imaging and dimensional metrology. The work in the Project deals with all significant error sources and is aimed at finding the best performing solutions. Sophisticated measurement methods and advanced algorithms are under development; some of them have already proved to be superior to current commercially available solutions. State-of-the-art instruments, superb laboratory, many years of expertise and excellent international cooperation are key to the success of the Project.

Beyond the state-of-the-art instrumentation and measurement methods it is indispensable to use accurate, physics-based modeling in the interpretation of the results. Therefore, the SEM-based dimensional measurements are supported by accurate Monte Carlo simulation modeling (JMONSEL) of the incident measurement beam-specimen interactions to determine the instrument response profile from various nanometers-scale shapes. JMONSEL supports secondary electron generation modeling for samples in high- vacuum or a gaseous environment SEM (ESEM) mode and utilizes a "model-based library (MBL)" method pioneered by this project to provide accurate edge detection by comparing the measured image intensity distributions to a library of pre-computed images that can be quickly scanned and interpolated to determine the best match. The use 3D version of MBL to quickly determine the shapes of various nanometer-scale objects is under development.

3D modeling of IC defect structure. The measurement (left) and the JMONSEL simulation (right).

Through-focus scanning optical microscopy (TSOM) transforms a conventional optical microscope into non-imaging, three-dimensional shape metrology tool. It makes use of the effects of intensity and phase variations as a function of focus position and demonstrated sub-nanometer 3D shape measurement sensitivity. The TSOM method was found to be applicable for target sizes ranging from sub-10 nm to over 50 μm, both in transmission and reflection modes. It can be used with wide variety of target sizes, shapes and materials with potentially numerous applications. This measurement method is economical, robust, non-contaminating and has high throughput. It has been demonstrated to be an effective method for nanotechnology in general and especially for IC process control and inspection.

TSOM measurement method (left and center) and TSOM image (right).

• SEMATECH recognizes and recommends TSOM method for the future 3D metrology of FinFET and HAR structures
• SEMI included TSOM as potential tool for "Metrology techniques to be used in measurement of geometrical parameters of through-silicon vias (TSVs) in 3DS-IC structures"
• Obtained a funded project from Intel for defect analysis using TSOM and established collaborations in area of TSOM with several major semiconductor industries and institutes, including Intel, IBM, Nova, ASML and SEMATECH
• A paper published on TSOM method was recognized as one of the Top Ten Best Papers in Measurement Science and Technology Journal
• TSOM received an R&D 100 award in 2010
• Completed a contract with Intel to include the ability to simulate Voltage Contrast Imaging (VCI) of floating regions with device-like connections between them. VCI is how contact defects are often detected