| In order to achieve the best results possible by electron beam lithography (EBL), many aspects of the different stages of EBL have to be carefully optimized. In the exposure stage, dose, energy, aperture size, step size and working distance have to be carefully set. In the development stage, an appropriate developer formula corresponding to the resist has to be chosen, as well as development temperature, duration, rinsing and drying method. There are many challenges present in the co-optimization of the conditions mentioned above. Particularly in the development stage, resist swelling, line edge roughness (LER) and pattern collapse are the major obstacles to achieving the ultimate in resolution. What is noteworthy is that all three of these development problems are related to the liquid environment. Therefore, if there is a way to avoid liquid developers, all problems associated with the liquid behaviour will be eliminated. This thesis presents an approach that has the potential to fabricate dense structures without using liquid developers. The work was mainly conducted in the low exposure energy regimes from 1 keV to 5 keV. Two kinds of electron beam resist, 950k PMMA and ZEP 520A, were studied for their properties and behaviours throughout various processes such as optimized exposure, thermal development and reactive ion etching (RIE). So far, 70 nm half-pitch gratings have been successfully patterned on both 950k PMMA and ZEP 520A without liquid development. This validates a concept that may ultimately lead to widespread use of dry processing of EBL structures. |
