| 7973 is a titania-silicate low expansion glass that has been tailored to meet the needs for mask and optical substrates for EUVL applications. 7973 has a similar composition to ULE® 7972 glass and is made using the same flame deposition process. The lithography transition from 193nm to 13.4nm required a major design shift in stepper optics from refractive to reflective. In reflective optics, substrate materials should be purely passive. The incident light should reflect off of the multilayer coatings of the optics and the photomask without the introduction of any mechanical or optical distortion caused by the underlying substrate. To minimize distortion from the minute temperature changes and meet the stringent EUVL specifications, the substrates must have a near-zero coefficient of thermal expansion (CTE) and tightly controlled zero cross over range. Excellent resistance to weathering. Exhibits virtually no surface clouding or electrical surface leakage when subjected to attack by water, sulfur dioxide, and other atmospheric gases. High resistance to attack by nearly all chemical agents. ULE® 7973 comes in several grades with varying size/levels of inclusions and striae; CTE control, and birefringence. The distinguishing attributes of the Premium Grade are low birefringence and low axial and radial CTE range. Information provided by Corning Incorporated. |
