High-Resolution Photomask Phase Measurement Tool

摘要

We describe the application of a novel imaging technique to ultra-high spatial resolution measurements of photomask phase shift. An Actinix TMT-193 photomask transmission tool has been retrofitted with a breadboard Mach-Zehnder interferometer and ancillary signal detection electronics and software to demonstrate actinic phase shift measurement capability for ArF-generation photomasks. Using a simple proof-of-principle layout, we have successfully acquired high-contrast interference fringe data on ultra-high resolution (250 nm) photomask geometries. Minimum detectable feature sizes are limited only by the resolution of the imaging system. The measurement techniques are suited to both embedded-attenuator and alternating-aperture phase-shift masks, and may be directly applied to F2-generation mask tools. Engineering advances in the laser source will increase measurement precisions to the 0.4° level as called for in the 2001 ITRS. We discuss the tool architecture and measurement method, and present recent results of phase scans performed on a customer-supplied MoSi EAPSM.