Holographic method for detecting amplitude and phase-shift errors and features in EUV ML reticle blanks

Abstract

A method for actinic inspection of EUV mask blanks is described, in which EUV photoresist is applied to the blank, flood exposed with EUV, and developed. The effect of both phase and reflectivity defects on the reticle is described in terms of a variation in intensity and phase of the standing wave in the resist. Thin film simulations are performed to evaluate the contrast generating mechanism for various blank defects. The method was introduced earlier by others 3 and was shown in experiments to transfer reflectivity defects on the reticle to the developed resist. We propose to reevaluate the technique with current state-of-the-industry capabilities of resist processing, contamination control and inspection. Various possible development directions are described.