Ultrafast High-Resolution Contact Lithography with Excimer Lasers

A new technique for speckle-free, fine-line high-speed lithography using high-power pulsed excimer lasers is described and demonstrated. Use of stimulated Raman shifting is proposed for obtaining the most desirable set of spectral lines for any resist. This permits, for the first time, the optimization of the exposure wavelengths for a given resist, rather than the reverse situation. Excellent-quality images are obtained in 1-µm-thick diazo-type photoresists such as ®AZ-2400 and a diazonaphthoquinone-®Novolak resist system by means of contact printing with a XeCl laser at 308 nm and a KrF laser at 248 nm. Resolution down to 1000 line pairs per millimeter is experimentally demonstrated. These images are comparable to state-of-the-art contact lithography obtained with conventional lamps. The major difference is that the excimer laser technique is approximately two orders of magnitude faster. Tests on reciprocity failure in several resists indicate a decrease in sensitivity by only a factor of three, despite the ≈10
⁸
times larger power density used in the laser exposures. The possibility of photochemical reactions being different from those taking place in the case of lamp exposures is discussed in view of these results.