Dry Resist Metrology Readiness for High-NA EUVL

As High Numerical Aperture Extreme Ultraviolet Lithography (High NA EUVL) gets ready to step in the integrated circuit manufacturing ( ICM) world, more and more work is being devoted to ensuring that all the elements involved in the process, from materials to equipment, will be ready to meet the required specifications when the time comes. One of the most critical pieces in such an ecosystem is the photoresist (PR), the material used to accurately transfer the design to the wafer. In the last years we have observed the introduction of various effective alternative approaches, such as dry metal oxide photoresist. PR always had to meet daunting specifications in terms of resolution, roughness, and sensitivity. However, in the brave new world of High NA EUVL, this is not enough. In fact, as the size of the printed features shrink, it is essential to limit the aspect ratio to avoid pattern collapse. Furthermore, the larger NA will reduce the Depth of Focus (DOF), thus requiring the use of ultra-thin resist films. The direct consequence of that is that the resist thicknesses used nowadays will not be suitable for High NA EUVL, where target thickness is expected to drop down to 20nm or less. Such a dramatic reduction in thickness has the potential to negatively impact, beside printing performances, the quality of the metrology and inspection as well, as discussed in our previous work. In the present work, we study the effects of reducing thickness in the case dry resist using various metrology and inspection techniques, such as Critical Dimension Scanning Electron Microscope ( CDSEM), Atomic Force Microscopy (AFM), and e-beam defect inspection. As resist thickness decreases, noise level and image contrast are expected to be reduced, with a potential negative impact on the quality of the CD measurements both in terms of accuracy and precision.