Constant period line gratings as a metric for patterning fidelity in electron beam lithography

Abstract

As smaller critical dimensions of devices fabricated via electron-beam lithography (EBL) are achieved over large areas, the need for new metrology techniques follows. Large (cm × cm) substrates have traditionally been both time and labor intensive to measure using traditional techniques such as scanning electron microscopy (SEM) or atomic force microscopy. When optimizing an EBL process over large areas, stitch error must be eliminated to maximize feature placement fidelity. Simultaneously, traditional EBL requirements, such as low line-edge roughness, proximity effect correction, and appropriate write times, must be maintained. With this plethora of requirements, we propose a technique to characterize placement errors over large areas using interferometric measurements. This method, when combined with traditional techniques like SEM and optical microscopy, assesses the full domain of potential errors over large areas in a time- and cost-efficient manner. As a proof of concept, a set of five small format (5 × 10 mm2) gratings with an 855 nm period were written twice, each set produced under two different tool error conditions. We report on the efficacy of interferometric metrology to accurately assess feature placement errors and report measured groove displacement across all ten gratings.