Evaporated electron beam sensitive organic resist for the back-patterning of X-ray lithography masks

One of the most important issue in the choice of a next generation lithography technology is the availability of adequate mask fabrication technology to demonstrate the extendibility of the technology to future technology nodes. In the case of X-ray lithography, it has been demonstrated that it is necessary to reduce the mask-to-wafer gap in order to achieve very high resolution. In order to do that, one solution is to pattern the absorber on the back of the membrane. This allows a reduction of the risks of accidental contact between the absorber patterns and the wafer during exposure and reduces turbulence in the gas flow in the mask-to-wafer gap. This paper presents characteristics of QSR-5, a negative organic sterol-based resist that is used to perform such patterning on the back of membrane. As it is impossible to spin-coat a resist on the back of a membrane substrate, one interesting characteristic of QSR-5 is that it is deposited by evaporation. This evaporation is performed using a joule-effect evaporator with an initial pressure of 3x10/sup -7/ torr. The temperature of the evaporation boat is kept below 200°C to maintain the integrity of the evaporated organic molecules. A LEO 1530 FEG-SEM with external control of the beam position is then used to pattern QSR-5, forming polymerized structures in the exposed regions. The resist is developed by immersion in a solvent solution.