Experimental performance of several different unstable resonators with annual cylindrical mode volumes is reported. Laser output beam quality and its sensitivity to resonator component misalignments and figure errors are described. Near diffraction-limited beam quality was obtained from an annular cylindrical He-Xe laser employing a half-symmetric unstable resonator with an intracavity axicon.

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Catadioptric step-and-scan lithography offers specific advantages over step-and-repeat all-refractive (dioptric) systems as resolution requirements drive to 0.25pm in volume production. For the Micrascan family ofstep-and-scan tools this step in the evolutionary path from 0.35.tm to 0.25.tm has involved changes to both the projection optics and illumination system.

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A bilevel system, consisting of PMMA and RD2000N (Hitachi) is described which has no discernable interaction between the resists and no processing interaction. The thin RD2000N resolution layer has very high absorption below 2900 Å and forms a high contrast mask for optical pattern transfer to the thick base PMMA layer. High fidelity step coverage of wet and dry etched oxides 7200 Å high is demonstrated with good linewidth control. The bilevel is capable of resolving 0.75 μm features over steps with good acuity. Preliminary results indicate that linewidth control with the bilevel process is comparable to a single level RD2000N process and has a lσ value of ∼.09 μm nearly independent of linewidth. The RD2000N layer shows a greater sensitivity to process variation than the PMMA. A parametric evaluation shows a dependence of linewidth on development time of 0.02 μm/s and a dependence of 0.11 μm/s for a 17 s exposure time. The resist system has enough dry etch resistance to use plasma etch pattern transfer as a complement to optical pattern transfer.