Optical lithography at 193nm with resolution enhancements and immersion is widely expected to meet the needs of the 45nm node. Beyond this, at 32nm and below, the solution is not as clear. In this article we present simulation results and experimental demonstrations of an all-optical approach capable of high-throughput 32nm lithography (hybrid optical maskless lithography). In this method high-resolution dense gratings are defined in a first exposure using maskless interference lithography. A second “trim” exposure, using conventional projection lithography, customizes these gratings into useful patterns. Our simulations indicate that 32nm node patterning can be achieved using trim tools and masks of significantly lower resolution. We also present experimental feasibility results using 157nm “dry” interference in combination with projection 248nm or e-beam trim exposures. The technological requirements and extendibility of such a method beyond the 32nm node are also examined.

Development of manufacturing infrastructure is required to ensure a commercial source of mask substrates for the timely introduction of EUVL. Improvements to the low thermal expansion materials that compose the substrate have been made, but need to be scaled to production quantities. We have been evaluating three challenging substrate characteristics to determine the state of the infrastructure for the finishing of substrates. First, surface roughness is on track and little risk is associated with achieving the roughness requirement as an independent specification. Second, with new flatnessmeasuring equipment just coming on line, the vendors are poised for improvement toward the SEMI P37 flatness specification. Third, significant acceleration is needed in the reduction of defect levels on substrates. The lack of highsensitivity defect metrology at the vendors' sites is limiting progress in developing substrates for EUVL.

We analyze the performance and process latitudes of a high-throughput, all-optical lithography method that addresses the requirements of the 32-nm node. This hybrid scheme involves a double exposure and only a single photomask. The first exposure forms dense gratings using maskless immersion interference lithography. These regular grating patterns are then trimmed in a second exposure with conventional projection lithography. While the highest resolution features are formed with interference imaging, the trimming operation requires significantly lower resolution. We have performed lithography simulations examining a number of representative 32-nm node patterns; both one-dimensional and two-dimensional. The results indicate that 32-nm node lithography requirements can be met using a hybrid optical maskless (HOMA) approach. Trim photomasks can be two to three generations behind the fine features, while the trim projection tools can be one to two generations behind the fine features. This hybrid optical maskless method has many of the benefits of maskless lithography without the severe throughput challenge of currently proposed maskless technologies.

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