fotomaski

Fotomaski, or photomasks, are precision-patterned substrates used to transfer circuit layouts and other microstructures onto photosensitive materials during photolithography and related processes in microfabrication. A typical mask is a flat plate, usually quartz or glass, coated with a thin opaque layer such as chromium. The patterned areas allow or block ultraviolet light or other wavelengths, forming the inverse of the desired pattern onto a photoresist-coated substrate.

Various mask types exist: binary masks, where regions are fully opaque or transparent; attenuated or grey-scale masks, with partial transmission; and phase-shift masks, which alter the phase of transmitted light to enhance resolution and image contrast. In the most advanced UV and DUV exposures, masks are produced with high-precision features containing alignment marks and defect-free patterns. In extreme ultraviolet (EUV) lithography, masks use reflective multilayer mirrors and a patterned absorber, since transmissive materials are not suitable at EUV wavelengths.

Mask production involves writing the desired pattern on a blank mask (often via electron-beam or laser writing), followed by material deposition, etching, and polishing. Masks undergo inspection for defects, and the final mask set is aligned and tested in mask aligners, steppers, or scanners. Applications include semiconductor device fabrication, MEMS, microfluidics, and nanoimprint-related processes. The term reticle is often used synonymously in industry for a single mask used in a lithography step.