MARKLE-DYSON OPTICS FOR 0.25-MU-M LITHOGRAPHY AND BEYOND

Using a modified Dyson design working at 0.7 NA with 248 nm illumination, reflective 1X masks, and conventional single-layer resists, 0.25-mu-m lithographic resolution has been obtained over a semicircular field 4 mm in diameter. 0.19-mu-m lines and spaces have been printed using an experimental bilayer resist. To offset the small depth of focus, two precision autofocus schemes have been demonstrated and FLEX has been shown by computer simulation to triple the depth of focus for isolated features. A full size system has been designed with a 20 x 40 mm2 field sufficiently large for patterning 256 Mbit DRAM chips. This concept can be extended to shorter wavelengths limited only by availability of one refractive material and a suitable light source. Thus optical projection lithography appears feasible for features at least as small as 0.15-mu-m.