Challenges in 1 Teradot/in.2 dot patterning using electron beam lithography for bit-patterned media

Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots/in.(2)) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist ZEP520 and 12 nm for a negative-tone resist silsesquioxane, corresponding to the areal density of similar to 2.0 and similar to 4.5 Tdots/in.(2), respectively. Using the ZEP520 resist process, a Cr dot array with a pitch of 21 nm (similar to 1.5 Tdots/in.(2)) for template fabrication is demonstrated. High-quality scanning electron microscopy and atomic force microscopy images were used as primary metrology for both the dot size uniformity and the placement accuracy analysis. (c) 2007 American Vacuum Society.