Microlithography projection-exposure masks, and methods and apparatus employing same

A method of microlithographically projecting a pattern onto a photosensitive substrate comprising single- and multiple-exposure areas, the method comprising the steps of:

• (a) exposing the single-exposure areas of the photosensitive substrate with an illumination-light flux transmitted through a first mask pattern;
• (b) exposing the multiple-exposure areas of the photosensitive substrate a first time with an illumination-light flux transmitted through a second mask pattern;
• and
• (c) exposing the multiple-exposure areas of the photosensitive substrate a second time with an illumination-light flux transmitted through a third mask pattern, wherein an average intensity of the illumination-light flux distributed to the single-exposure areas using the first mask pattern is substantially equal to an average intensity of the illumination-light flux distributed to the multiple-exposure areas using at least the second and third mask patterns.

A microlithographic projection-exposure apparatus, comprising:

• (a) an illumination-optical system for producing an illumination-light flux;
• (b) a first mask comprising a first mask pattern for projection, by one exposure, onto single-exposure areas of a photosensitive substrate and a second mask pattern for projection, by a predetermined number of multiple exposures, onto multiple-exposure areas of the substrate, the first mask being positionable downstream of the illumination-optical system for illumination by the illumination-light flux;
• (c) a second mask comprising a third mask pattern for projection, by a predetermined number of multiple exposures, onto the multiple-exposure areas of the substrate, the second mask being positionable downstream of the illumination-optical system for illumination by the illumination-light flux when the first mask is not being illuminated with the illumination-light flux;
• (d) a projection-optical system for receiving illumination light transmitted through the first or second mask from the illumination-optical system and projection-distributing the illumination light to the substrate, the second and third mask patterns being configured relative to the first mask pattern so as to produce, after a total predetermined number of multiple exposures of the multiple-exposure areas of the substrate, a total average intensity of illumination light on the multiple-exposure areas that is substantially equal to a total average intensity of illumination light produced by the one exposure of the first mask pattern on the single-exposure areas of the substrate.