Preliminary evaluation of a laser-based proximity x-ray stepper

This paper reports on the initial lithographic evaluation of a commercial 1:1 proximity stepper that uses a laser-based plasma x-ray source. Our preliminary tests have shown that 0.4- and 0.5-μm lines and spaces can be printed consistently on Si wafers using a positive resist, which has a sensitivity of 6–10 mJ/cm2. Features smaller than 0.4 μm can be obtained, but the overlay accuracy of this system is targeted at 0.5-μm design rules. The 3σ spread in linewidth is greater than 0.05 μm, however, the stepper contribution must be separated from the resist processing issues, reticle critical dimension variations, and scanning electron micrograph measurement precision.