Through-focus scanning optical microscopy applications

Abstract

We present a partial application space of the metrology method referred to as through-focus scanning optical microscopy (TSOM), with most number of favorable attributes as a metrology and process control tool. TSOM is a NIST-developed, high-throughput and low-cost optical metrology tool for dimensional characterization with sub-nanometer measurement resolution of nano-scale to microscale targets using conventional optical microscopes, with many unique benefits and advantages. In TSOM the complete set of out-of-focus images are acquired using a conventional optical microscope and used for dimensional analysis. One of the unique characteristics of the TSOM method is its ability to reduce or eliminate optical cross correlations, often challenging for optical based metrology tools. TSOM usually has the ability to separate different dimensional differences (i.e., the ability to distinguish, for example, linewidth difference from line height difference) and hence it is expected to reduce measurement uncertainty. TSOM is applicable to a wide variety of target materials ranging from transparent to opaque, and shapes ranging from simple nanoparticles to complex semiconductor memory structures, including buried structures under transparent films. TSOM has been successfully applied to targets ranging from one nm to over 100 μm (over five orders or magnitude size range). Demonstrated applications of TSOM include critical dimension (linewidth), overlay, patterned defect detection and analysis, FinFETs, nanoparticles, photo-mask linewidth, thin-film (less than 0.5 nm to 10 nm) thickness, throughsilicon vias (TSVs), high-aspect-ratio (HAR) targets and others with several potential three-dimensional shape process monitoring applications such as MEMS/NEMS devices, micro/nanofluidic channels, flexible electronics, self-assembled nanostructures, and waveguides. Numerous industries could benefit from the TSOM method —such as the semiconductor industry, MEMS, NEMS, biotechnology, nanomanufacturing, nanometrology, data storage, and photonics.