High-Throughput Nanometrology with Scatterfield Microscopy

Develop optical methods with extremely high throughput rates to accurately measure nanoscale features and objects. High-throughput is a requirement for effective control of manufacturing processes that incorporate billions of nanoscale objects and features. Optical microscopy (OM) is a high-throughput metrology methodology that provides a unique advantage since it is a high-bandwidth measurement method that is inherently parallel. However, OM techniques have not traditionally been considered useful for nanometrology applications because their resolution is conventionally thought to be limited by the Rayleigh limit to one half the illumination wavelength, or at best roughly 200 nm for visible or near ultra-violet illumination. This project is a leader in the research and development of new optical nanometrology technologies such as Scatterfield microscopy, designed to push well past traditional optical resolution barriers. These techniques are based complex control of the angle, polarization, and focus-height dependent optical interaction signals, and the subsequent extraction of quantitative information on features as small as one-twentieth the wavelength of light. This project is currently developing an advanced 193 nm illumination metrology microscope to further extend the resolution limits and enabling accurate metrology of next generation lithography processes. With significant accomplishments already achieved, the nascent technique of Scatterfield microscopy is already being transferred to industry. Scatterfield microscopy will have a major impact to help enable the cost-effective mass-production of nanotechnology products.

This new microscopy technique, Scatterfield microscopy (SM), combines the best attributes of optical microscopy (OM) and scatterometry. Significant dimensional information with sensitivity to features one-twentieth the measurement wavelength can be extracted from the analysis of scattered light profiles through the use of structured illumination, specifically engineered targets, and physics-based image process modeling. These concepts will be applied to making measurements of linewidth, line spacing, line height, super-resolution overlay metrology, and defect metrology. Application of Scatterfield Microscopy will extend the resolution limits of current technology by at least a factor of ten.

193 nm Scatterfield microscope.

Key project deliverables include completion of the 193 nm Scatterfield optical tool platform and demonstration of full instrument operation in a cleanroom environment with controlled temperature. This includes the extensive application of illumination engineering and optical field control at 193 nm wavelengths.

A critical part of this project is the development and transfer to industry of new optical characterization methods for optical aberration and illumination control using structured illumination. This also includes the advanced optical train characterization and normalization methods now recognized as essential for accurate optical microscopy. An important element of this is the test and implementation of a new class of structured illumination using active back focal plane engineered illumination.

As a part of the research NIST will develop appropriate Scatterfield test patterns such as those based on optical superstructures applicable to nanotechnology process control to enable high throughput measurements with nanometer resolution. Demonstration of the highest resolution optical measurements possible using the Scatterfield concept for dimensional metrology of sub-15 nm sized features with measurement sensitivity significantly better than 1 nm is a main long term goal.

Challenge/Problem Addressed: Nanomanufacturing requires innovative high-throughput, non-contact metrology methods to minimize defects, quantify critical dimensions, and sample large areas effectively for maximum yield. This presents a tremendous challenge, to quantify features and identify defects at the nanometer scale over areas ranging from 1000 µm² to 1 m² in dimension.

• Constructed a dedicated platform for scatterfield microscopy (λ = 450 nm).
• Quantitative agreement achieved between rigorous modeling and experimental data. Published results demonstrate quantitative agreement for scatterfield measurements of densely arrayed 100 nm sized lines which vary in 1 nm increments, validating the utility of optical metrology methods for far sub-wavelength features.