Since the initial demonstration of X-ray lithography (D. L. Spears and H. I. Smith Electronics Lett. 8 102-104 (1972)) there has been considerable development in masks, sources, and resists. The need for close matching of all elements of the system has been recognized and several alternatives are being pursued including electron beam impact anode sources, pulsed plasma sources, and electron storage ring sources. An advantage of the storage ring source is a combination of highly collimated and intense radiation: this combination relaxes some of the constraints on a resist and process which are inherent in the anode or plasma source systems. For example, the past emphasis for X-ray resists has been on increasing sensitivity with requirements of 1-10mJ/cm2 doses to provide sufficient wafer writing throughput. Sensitivity is no longer an overriding concern if storage ring and to some extent plasma sources are developed: storage ring sources for step and repeat are feasible with 100-300mJ/cm2 resist sensitivities. A survey of resists which have been used for X-ray exposure is made with the advantages of the storage ring source in mind: materials are evaluated primarily on the basis of sensitivity and RIE resistance. Results are shown from the IBM lithography beam line at the National Synchrotron Light Source at Brookhaven National Laboratory which demonstrate some of the capabilities for single layer resists. Finally, some future directions are suggested for resist development to improve storage ring resists.
J G. Lane, J G. Lane,
"Resists For Storage Ring X-Ray Lithography", Proc. SPIE 0448, X-Ray Lithography and Applications of Soft X-Rays to Technology, (19 March 1984); doi: 10.1117/12.939215; https://doi.org/10.1117/12.939215