Use of attenuating phase-shifting mask for improved printability of clear-field patterns

摘要

An improved photolithographic method employs a pattern of subresolution openings to enhance the printability of clear-field patterns. Incorporating a subresolution opening along the edges of the transmission areas prevents the printing of side lobe light and enables incorporation of a positive bias in the clear-field pattern. This is turn increases the lithographic process latitudes. The photomask must be significantly overexposed as a result of using a positive bias. To compensate for the impact of increased exposure on large transmission areas and avoid degradation of the corresponding resist, a pattern of subresolution openings is incorporated in the large transmission areas. The size and orientation of the subresolution areas creates a diffraction grating effect, reducing the exposure of the area under each transmission area.