Pre-Development Positional Metrology for Exposed Photoresist Patterns Using a High-Sensitivity Focus Sensor Integrated with a Nanopositioning System

This study investigates a positional metrology technique for detecting exposed photoresist patterns using a focus sensor. General applications of latent metrology include process optimization, defect detection, and pattern alignment in micro- and nanofabrication. This work could be used in the alignment to previously exposed resist pattern written on different machines/technologies in Mix-and-Match lithography applications. The core of the technique is based on the differential Foucault knife-edge principle. Here it is shown that the differential focus sensor signal exhibits an enhanced sensitivity compa- red to the sum signal, which is considered to be comparable to a regular confocal sensor. To showcase its sensitivity, the measurements are also compared to offline latent methods such as Differential Interference Contrast (DIC) microscopy and Scanning Electron Microscopy (SEM). The system demonstrates robust performance across various resist types, thicknesses, and scanning parameters. This work highlights the synergy between the focus sensor and the nanopositioning machine, showing a practical route to real-time in-situ pattern registration in pre-developed resist metrology. 112 technik