From hyper NA to low NA

As we move forward into the hyper NA regime (NA>1.0) for the first time through Immersion lithography, polarization control will be a pre-requisite. At such high NA's, the approach angle of the rays that form the images becomes very high, due to the orthogonal nature of the electric and magnetic components of a light wave the interference is not good for both components, it then becomes necessary to eliminate one in order to maintain the overall contrast of the image produced. The effect upon imaging is very stark and makes the difference between producing an image and producing a manufacturing process. As well as being a pre-requisite for immersion, this also has the potential to extend dry lithography well below 65nm. Beyond Immersion at 193nm we are expecting the introduction of EUV. This works in the soft X-ray regime with a wavelength of 13.5nm to suit the Mo/Si multi-layer stack chosen for the mirror optics. There are many areas where EUV departs from conventional photolithography evolution, one of the most interesting of these is that we will greatly reduce the NA of the initial tools. We will go from a dry NA of >0.9 with 193nm down to 0.25 to 0.30 with EUV. There are many reasons for this related to the unique aspects of EUV including all reflective optics and the order of magnitude change in illumination wavelength. This has necessitated a different approach to EUV technology development where, instead of simply building upon what we already had, we have had to develop from first principles the building blocks of an exposure tool. Much progress has been made here and is leading to beta tools in the near future.