Resolution and overlay precision of a 10 to 1 step-and-repeat projection printer for VLSI circuit fabrication

A step-and-repeat projection printer called NSR-2 has been developed for VLSI circuit fabrication. The NSR-2 exhibits high resolution due to projection optics with high numerical aperture (NA = 0.35), and high overlay precision resulting from both an off-axis alignment scheme and a supplementary through-the-lens (TTL) alignment scheme. The total overlay precision, using the off-axis alignment scheme, was found to be less than ±0.34 µm(2σ). Using the TTL alignment scheme, the value was improved to be less than ±0.26 µm(2σ). 1-µm resolution was obtained all over the 10-mm²image field. Practical resolution, which can be assured in a production line, was estimated, by SEM observation and MTF measurement, to be 1.2 to 1.4 µm.