Patent ID: 7046340

Claim:
An apparatus for irradiating a microlithographic substrate, comprising: a substrate support having a support surface positioned to carry a microlithographic substrate; a radiation source positioned to direct a radiation beam along a radiation path toward the substrate support; a selectively transmissive medium positioned in the radiation path, the selectively transmissive medium having a first portion aligned with a first portion of the radiation beam when the radiation beam is emitted from the radiation source, the selectively transmissive medium having a second portion aligned with a second portion of the radiation beam when the radiation beam is emitted by the radiation source, each of the first and second portions of the selectively transmissive medium having a transmissivity that is changeable from a first transmissivity to a second transmissivity different than the first transmissivity, wherein at least one of the first and second portions is configured to change to the second transmissivity without becoming opaque; a reticle positioned between the selectively transmissive medium and the substrate support, the reticle having at least one reticle aperture positioned to pass radiation toward the substrate support; and a controller operatively coupled to the selectively transmissive medium to direct at least one of the first and second portions to change from the first transmissivity to the second transmissivity.