C over S tory
Immersion Lithography Process and Control Challenges Irfan Malik, Viral Hazari, Kevin Monahan, Matt Hankinson, Mike Adel, Marcus Liesching, Edward Charrier – KLA-Tencor Corporation
Immersion lithography enables higher resolution, but also introduces new defect mechanisms. Process development, characterization, and ongoing cell qualification and monitoring must be adjusted to represent the new interactions and dynamics of immersion technology. It is critical for fabs to implement new defect management strategies that can handle immersion-specific defects, immersion-related overlay errors, and new sources of CD variations. Hyper-NA immersion 193nm (ArF) lithography provides the technological advances required to obtain production yields in 65nm (half-pitch) patterning and to progress towards 45nm. With added technology, such as double patterning and fluids with indices of refraction greater than that of water, immersion lithography (ilitho) is likely to extend to 32nm and beyond. Immersion optics enable the printing of smaller design rules by increasing the effective numerical aperture (NA) of the imaging lens.1 In the case of water immersion, NAs up to 1.35 have been achieved.2 While this allows printing of smaller features at higher yields with a better process window than equivalent dry systems,3, 4 immersion imaging is a more complex process that presents numerous challenges. Process integration for ilitho is more challenging as it involves a tighter coupling of illumination, mask, imaging optics, optomechanics, wafer, materials, dynamics, and process control. Immersion lithography also introduces several new problems in the areas of image modeling and creation, defectivity, systematic errors, and materials. While some of these problems are understood and contained, solutions are still needed for others in order to reach competitive manufacturing yields.