1. Field of the Invention
The present invention is related to a lithography system.
2. Background Art
In lithography systems, pattern generators are used to pattern substrates during an exposure process. Example lithography systems include, but are not limited to, reflective or transmissive maskless, immersion, and mask-based system. Example substrates include, but are not limited to, semiconductor wafers, flat panel display substrates, flexible substrates, and the like. Light interacting with an illumination spot on the pattern generator becomes patterned. The patterned light is projected using a projection optical system onto one or more target areas of the substrate during the exposure process to form features on a photosensitive material (e.g., a photoresist) on the substrate.
In some applications of the lithography system, it is desired to have double telecentric illumination, which means that a chief ray of an illumination beam is telecentric in both object space and image space. Object space is proximate an object plane, typically defined by the pattern generator. Image space is proximate an image plane, typically defined by the substrate. Conventional systems having double telecentric illumination generally use a transmissive optic to direct the illumination from an illuminator towards the pattern generator and from the pattern generator towards a projection optical system. However, transmissive optics tend to absorb illumination, and thus can have low efficiency. For example, a typical transmissive optic can sometimes transmit as little as about 20–25% of the light between the illuminator and the projection system. Also, transmissive optics can cause polarization, aberration, distortion, birefringence, and other errors in the illumination, which sometimes requires complex optics to correct.
Therefore, what is needed is a system and method that can be used to provide a double telecentric system, which eliminates or substantially reduces absorption of illumination and/or that eliminates or substantially reduces polarization change, birefringence, aberration, distortion, and/or other errors being introduced in the illumination beam.