Patent Number: 054882290
Section: description

DESCRIPTION OF PARTICULAR EMBODIMENT With reference to FIG. 1, the system includes twenty watt argon fluoride excimer laser source 12 that generates deep UV (193 nanometer) radiation in a beam 14 along axis 16 for passage through illumination optics 18 for impingement on beam splitter mirror 20. Disposed along axis 22, that is orthogonal to axis 16, is a viewing port diagrammatically indicated at 29 illuminated by tungsten lamp 26. The radiation on axis 16 is reflected by beam splitter mirror 20 for passage along beam axis 22 and through reticle or mask 28 with a pattern of lines of about one micron width is disposed. The deep UV radiation emerging from mask 28 passes through beam splitter 27 and through compensated 10X reduction optical system 30 that has a numerical aperture of 0.6 for imaging a 10:1 or other optical reduction ratio such as 5:1 or 20:1 image of mask 28 on UV sensitive wafer target structure 36 that is supported on adjustable stage 38. Video camera 29 monitors the photo lithography process, and optical correction lens 31 compensates for the focus shift change between the exposing radiation wavelength from laser source 12 and the viewing radiation from tungsten lamp 26. That is, because the UV energy is in focus at the target structure 36 and the viewing energy is out of focus at the target structure 36, lens 31 is provided to, in effect, focus the camera 29 at the target structure 36. Optical system 30 includes refractive lenses 42, 44, 46, 48, 50; optical component 52 that includes aperture 53, lens component 54 and a spherical reflective surface 56 and optical component 58 that includes lens component 60 and mirror 62 with a central clear area (non-reflective) portion 64 through which radiation passes for impingement on wafer target structure 36. Each lens has leading surface A and trailing surface B (see the following table). Specific values of optical components 42-62 are set out in the following table: ______________________________________ Radius Spacing Surface (millimeter) (millimeter) Material ______________________________________ Mask 28 -- 267.2 Air 42A 33.95 7.00 Fused Silica 42B 37.68 5.00 Air 44A 87.99 5.00 Fused Silica 44B 33.36 12.17 Air 46A 82.07 7.00 Fused Silica 46B -251.23 71.35 Air 48A 47.92 9.00 Fused Silica 48B -- 68.02 Air 50A 23.61 3.00 Fused Silica 50B 190.05 87.26 Air 60A -- 8.00 Fused Silica 60R 1180.56 -8.00 Reflector -- -70.98 Air 54A 82.97 -11.00 Fused Silica 56R 105.25 11.00 Reflector 54A 82.97 70.98 Air 60A -- 8.00 Fused Silica 60B 1180.56 2.75 Air Wafer 36 -- -- ______________________________________ In the optical system shown in FIG. 2, lenses 42, 44 and 46 provide compensation for aberrations such as coma, astigmatism and chromatic variations, lens 48 provides focusing, lens 50 is a field lens, and lenses 54 and 60 provides field flattening. Lens-mirror combinations 52 and 58 provide compensation for primary and secondary and tertiary color, respectively. An aperture stop or iris is at 64. While a particular embodiment of the invention has been shown and described, various modifications will be apparent to those skilled in the art, and therefore, it is not intended that the invention be limited to the disclosed embodiment, or to details thereof, and departures may be made therefrom within the spirit and scope of the invention.