ABSTRACT
Optical lithography involves the creation of relief image patterns through the projection of radiation within or near the ultraviolet (UV) visible portion of the electromagnetic spectrum. Techniques of optical lithography, or photolithography, have been used to create patterns for engravings, photographs, and printing plates. The optical configuration for projection microlithography tools most closely resembles a microscope system. The diffraction of light is responsible for image creation in all optical situations. Several properties of optical materials must be considered in order to effectively design, optimize, and fabricate optical components. Optical lithography below 300 nm is made difficult because of the increase in absorption in optical materials. Few transparent materials exist below 200 nm, limiting design and fabrication flexibility in optical systems. The optical characteristics of glasses in the UV are important when considering photolithographic systems containing refractive elements. Optical absorption and luminescence can be caused by a lack of stoichiometry in the fused silica molecular matrix.
