Dense plasma focus for production-level EUV lithography

摘要

Optical lithography will be replaced by a nonoptical technique at some point for device shrinks to 35nm. Extreme ultraviolet lithography is currently showing the most promise. However, issues such as power scaling and cost of consumables, necessary for a production-level source, are still works in progress. Cymer is proposing a concept for a 13.5nm source based on dense plasma focus to meet these challenges. Performance increases and productivity gains through device shrinks have been the main drivers in IC manufacturing for the last 30 years. This trend is unlikely to change until the functional limits of conventional logic devices are reached at ～35nm. This is expected by the end of the decade. When analyzing imaging requirements of future lithographic tools, the equations for critical dimension (CD) and depth of focus (DOF) shown in Fig. 1 provide a guide to some design requirements. For example, CDs can be reduced by decreasing the illumination wavelength or increasing the numerical aperture (NA) of the imaging lens. Increasing NA, however, reduces DOF and with it, process control.