Low-cost, high-throughput and nondestructive metrology of truly three-dimensional (3-D) targets for process control/monitoring is a critically needed enabling technology for high-volume manufacturing (HVM) of nano/micro technologies in multi-disciplinary areas. A survey of the typically used metrology tools indicates the lack of a tool that truly satisfies the HVM metrology needs of 3-D targets, such as high aspect ratio (HAR) targets and through- silicon vias (TSVs). TSVs are a key component to enable 3-D stacked integrated circuits (3DS-IC), which themselves are key to extended scaling of integrated circuits and enabling heterogeneous integration. Hence, it is crucial to find suitable metrology solutions for truly 3-D targets such as HAR targets.
To be used in high-volume manufacturing, a metrology tool must – in addition to providing statistically significant results – be fast (high-throughput), low-cost, inline capable, automated, robust, easy to use, non-contact and non-destructive. The requirements for satisfactory measurement sensitivity and resolution have been identified in the International Technology Roadmap for Semiconductors (ITRS) and International Roadmap for Devices and Systems (IRDS) 2017 Edition: Metrology. All currently available tools have certain advantages and disadvantages. It is difficult to find a metrology tool that satisfies all the above-mentioned requirements, especially for metrology of 3-D/HAR targets. Here we present that through-focus scanning optical microscopy (TSOM) could supplement currently available metrology tools in filling this gap for 3-D shape metrology. However, there is still room to improve optical tools.
Here we have briefly presented potential applications of TSOM for dimensional metrology of deep structures such as HAR targets and TSVs using a reference library. It is also a nondestructive, low-cost, and high-throughput 3-D shape process monitoring method using conventional optical microscopes. TSOM could fill the gap by satisfying the HVM metrology needs of not only HAR targets and TSVs but also other types of truly 3-D targets for which 3-D shape process control/monitoring is needed, and complements other widely used metrology tools.