E-beam metrology-based EUVL aberration monitoring

Abstract

Aberration is one of the contributors to edge placement error (EPE) variation and overlay error in the scanner system. In the EUV system, aberration-induced wavefront errors can have a much bigger impact than the in a DUV system due to significantly reduced wavelength and heating effect from illumination energy loss through reflective optics. Although in-situ metrology of the scanner system can extract wavefront information accurately and it can be feedbacked for aberration control, dynamic heating effects during long-time full-field exposures and tool-to-tool performance gap by aberration variation in high volume manufacturing (HVM) should be directly monitored on the wafer patterning result for reliable process control.

This study aims to identify the feasibility of aberration monitoring on the wafer by using an e-beam metrology tool. Simulation work is performed first for source adjustment and the selection of generic designs of aberration-sensitive patterns of dark field Ta-based EUV masks. For quantitative analysis, the wavefront phase error is directly modulated (dialed-in) in the EUV system, and a wafer is exposed for each modulation condition. The wavefront error induced by the modulated aberration is extracted from measured CD data, using an optical simulation model. We finally discuss the correlation between the extracted aberration and the modulated wavefront error. Based on the result in this work, we investigate the feasibility of the potential application of e-beam metrology on dynamic aberration variation in HVM.