Projection lithography

Imaging a patterned mask onto a resist-coated substrate using projection optics.

Splitting a final pattern between separate lithographic steps to reduce the feature density that each exposure must resolve. The steps need a suitable intervening fixation, transfer or spacer process. Minimum single-feature width, pattern decomposition and overlay remain limitations.

A sequence that exposes and transfers one sparse pattern, then applies fresh resist and transfers a second aligned pattern. Their union defines a denser final mask or etched layer. Pattern transfer between exposures prevents simple addition of optical dose from replacing two independently resolved exposures.

Pattern-dependent modification of mask edges or assist features to compensate the finite imaging and pattern-transfer process. It is assessed by the resulting printed dimensions, not by similarity of the mask to the desired layout.

Illumination using noncentral pupil directions to place useful mask diffraction orders inside a projection lens. Grating orientation, coherence and process window affect the benefit.

A lithographic mask that controls optical phase as well as transmission to improve useful interference contrast. Benefits and phase conflicts depend on the pattern.