E-beam metrology for high-NA: revisiting the imec protocol

Recently, High Numerical Aperture Extreme Ultraviolet Lithography (High NA EUVL) started delivering its first wafers, showing its potential by printing 18 and 16nm pitch line/space. However, as features size is dropping below 10nm, questions are raised on the ability of the current metrology procedures and tools to properly characterize such small targets. In particular, it is critical to assess the impact of limited spatial resolution and identify possible ways forward. A high-resolution, low damage strategy based on high Landing Energy (LE) is proposed. High LE setting (15keV) and standard low LE (500eV) best-known methods are compared using both rigorous simulation and experiments. The comparison is performed for Metal Oxide Resist as well as for Chemical Amplified Resist, After Development Inspection (ADI) and After Etch Inspection (AEI). Our results indicated that the 15keV setting provides 3x better resolution and less ADI damages as compared to the 500eV setting. AEI damages, throughput and precision are comparable. Using high LE provides the needed resolution for High NA EUVL, with similar or better impact in terms of damages compared to low LE.