Abstract
Low-cost, high-throughput and nondestructive metrology of truly three-dimensional (3D) targets for process control/monitoring is a critically needed enabling technology for high-volume manufacturing (HVM) of nano/micro technologies in multi-disciplinary areas. In particular, a survey of the typically used metrology tools indicates the lack of a tool that truly satisfies the HVM metrology needs of 3D targets, such as high-aspect-ratio (HAR) targets. Using HAR targets here we demonstrate that through-focus scanning optical microscopy (TSOM) is a strong contender to fill the gap for 3D shape metrology. Differential TSOM (D-TSOM) images are extremely sensitive to small and/or dissimilar types of 3D shape variations. Based on this, we here propose a TSOM method that involves creating a database of cross-sectional profiles of the HAR targets along with their respective D-TSOM signals. Using the database, we present a simple-to-use, low-cost, high-throughput and nondestructive process-monitoring method suitable for HVM of truly 3D targets, which also does not require optical simulations, making its use straightforward and automatable. Even though HAR targets are used for this demonstration, the similar process can be applied to any truly 3D targets with dimensions ranging from micro-scale to nano-scale. The TSOM method couples the advantage of analyzing truly isolated targets with the ability to simultaneously analyze many targets present in the large field-of-view of a conventional optical microscope.
Highlights
With the increase in the use of three-dimensional (3-D) structures in nano/micro technologies, high-throughput and economical 3-D shape metrology and process monitoring of nanoscale to microscale objects is critically necessary [1,2,3,4,5,6,7,8,9,10]
Using high aspect ratio (HAR) targets here we demonstrate that through-focus scanning optical microscopy (TSOM) is a strong contender to fill the gap for 3-D shape metrology
Differential TSOM (D-TSOM) images are extremely sensitive to small and/or dissimilar types of 3-D shape variations. Based on this here we propose a TSOM method that involves creating a database of cross-sectional profiles of the HAR targets along with their respective D-TSOM signals
Summary
With the increase in the use of three-dimensional (3-D) structures in nano/micro technologies, high-throughput and economical 3-D shape metrology and process monitoring of nanoscale to microscale objects is critically necessary [1,2,3,4,5,6,7,8,9,10] This is technically challenging [4, 5, 7, 11,12,13,14], especially for high aspect ratio (HAR) targets, including through-silicon vias (TSVs) [13,14,15,16,17,18]. Combination of the results of more than one measurement technique, referred to as either hybrid or holistic metrology, initially pioneered at NIST further improved nanometer-scale dimensional measurements [36, 43]
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