0.5-μm photolithography using high-numerical-aperture I-line wafer steppers

Results are presented from a new high numerical aperture (NA 0. 48) iline 5X reduction lens which resolves 0. 5 micron lines and spaces over greater than 1 micron depth of focus in several commercially available i-line resists. The performance of this lens is contrasted with that of a NA 0. 40 i-line lens. The NA 0. 40 lens has better depth of focus for 0. 7 microns lines and spaces (L/S) and larger while the NA 0. 48 lens has better depth of focus for L/S smaller than 0. 7 microns down to a resolution cutoff near 0. 35 micron L/S. Other characteristics of the lens such as its relative insensitivity to absorption heating effects and its behavior as a function of the overpressure of He gas within the lens are explored. Simulation work suggests that a NA of between 0. 5 and 0. 55 is optimum for printing 0. 5 micron L/S. Further it suggests that there may be sufficient depth of focus at 0. 4 micron L/S to make i-line a competitor to DUV lithography for the 64 Mbit DRAM generation. 1.