Printability of contact-hole patterns in EUVL using 0.3-NA HiNA optics

Although 50-56-nm contact-hole (C/H) patterns will be required in 2010, it is very difficult to fabricate such small C/H pattern by optical lithography. Since extreme-ultraviolet lithography (EUVL) uses a much shorter wavelength than optical lithography, it should provide better image contrast. We have installed a high-numerical-aperture (NA = 0.3) small-field EUV exposure tool (HiNA) and are now evaluating the printability of various kinds of patterns. In this study, C/H patterns with sizes of 50-150 nm were printed using the HiNA optics under the annular illumination (σ=0.5-0.8), and the printability was assessed. Fine C/H patterns, such as dense 55-nm C/H and isolated 50-nm C/H, were successfully fabricated using a binary mask without optical proximity correction. The slope of the mask linearity was about 1.0-3.0 for dense C/H (mask CD: 80-150 nm) and about 1.0-4.0 for isolated C/H (mask CD: 90-150 nm). Simulation results indicate that the aberration, the flare and the central obscuration of the HiNA optics considerably degraded the aerial images of fine C/H patterns. They also indicate that annular illumination (σ=0.5-0.8) is not suitable for obtaining good mask linearity in C/H patterns. A smaller central obscuration, less aberration, less flare and the optimization of σ should improve the resolution limit and mask linearity for C/H patterns.