Proximity projection lithography

For the next generation of submicrometer ground rules, a fourfold reduction in alignment and other errors will be necessary. Almost every type of mask aligner—contact/proximity, projection scanner, and step and repeat—is used for some of the lithography steps in the fabrication of state of the art integrated circuitry today. For a detailed description of mask alignment equipment we refer to the literature [2, 3]. 

Figure 15.8 Schematicof three ways of employing ion beams in lithography (a) focused ion beam lithography, (b) proximity ion-beam lithography, (c) ion projection lithography.

Moreau and Schmidt (7) demonstrated the sensitivity of poly(methyl methacrylate) (PMMA) to DUV radiation in 1970 and described most of the features of DUV lithography. The main objective of their work was to employ DUV radiation to allow larger mask-to-wafer separation at constant resolution in proximity printing. Their work demonstrated the utility of PMMA as a DUV resist, and they predicted that DUV radiation would be employed with an acrylate polymer of some type in future projection printing systems that should allow reliable printing of submicrometer features. 

---