Imaging Characteristics of Multi-Phase-Shifting and Halftone Phase-Shifting Masks

Phase-shifting masks and imaging characteristics are discussed and compared with those of conventional transmission masks. Then, new phase-shifting masks with intermediate values of phase shifting or transmittance are proposed, and their imaging characteristics are investigated. A phase-shifting mask with a 90° phase difference can ease the restrictions on pattern geometries used in phase-shifting technology but does not increase the focus latitude. It is also suggested that a halftone phase-shifting mask is suitable for printing isolated patterns and it gives wider focus latitude than conventional mask technology.