| Pulsed lasers are investigated as possible radiation sources for deep-UV lithography. A KrF excimer laser (248.4nm) is used to test long term transmission stability of deep-UV optical materials. A quintupled Nd-YAG laser (212.8nm) is used to investigate problems associated with using a highly coherent pulsed laser as a lithographic radiation source.; Pellicles and fluids are two important classes of materials used in lithography systems. The large photon energy and high peak power of the KrF excimer laser degrades most pellicle materials and optical fluids. An exposure system with in situ transmission and optical thickness monitoring is used to test candidate materials. A flouropolymer pellicle material is shown to have a stable transmission lifetime up to exposures of 10,000J/cm{dollar}sp2.{dollar} Several candidate optical fluids are described with long transmission lifetimes and suitable refractive index values; including Dupont Krytox (n = 1.319), deionized water (n = 1.374), Dow 200 (n = 1.467), and ethylene glycol (n = 1.484).; The relevant characteristics of an 0.25W, 10Hz quintupled Nd-YAG laser, such as energy stability, spectral linewidth, and coherence length, are described. This laser exhibits a spectral linewidth of 0.035pm, well within the requirements of the all-fused silica deep-UV lenses. The narrow linewidth, combined with single transverse mode operation, causes high-contrast speckle intensity variations, severely degrading illumination uniformity.; Two novel speckle reduction schemes are employed. One scheme uses two closely spaced counter-rotating diffusers. A diffuser-speckle model is developed to determine the speckle reduction capabilities of a given diffuser. Significant speckle reduction is produced during a single 4.2ns laser pulse with rotation speeds less than 30,000RPM. A second speckle reduction scheme that uses no moving parts nor employs any special optics is demonstrated. This scheme produces several sub-pulses from a single incident pulse, each delayed by an amount greater than the coherence length. The delayed sub-pulses do not interfere, thus reducing speckle contrast by {dollar}1/sqrt{lcub}rm (N){rcub},{dollar} where N is the number of sub-pulses.; An all-refractive 20:1 reduction lens, designed for use at 212.8nm, is used in combination with the speckle reduction schemes to print speckle-free 0.2{dollar}mu{dollar}m line/space patterns in PMMA. These line/space patterns represent {dollar}0.56{lcub}lambdaoverrm NA{rcub}{dollar} features for this 0.6NA objective. |
