Patterning 220nm pitch DRAM patterns by using double mask exposure

The acceleration of the design rule shrinkage and delayed ArF technology currently put pressure upon KrF technology for device development despite the increase of technology difficulties, so that the extension of KrF lithography to 220nm pitch patterning is under test carefully without using ArF technology. In this context, double mask exposure (DOME;) technology with two different sets of off-axis illumination (OAI) for 220nm pitch DRAM patterns is investigated as an option of the KrF lithography. A first mask of periodic cell patterns with a fixed pitch is exposed using the dipole illumination. Then after switching the previous illumination set to the annular illumination, a second mask is used to expose the peripheral patterns of DRAM. The obtained patterns have the reasonable process latitude because different optimum illumination set is utilized for different pitch patterning. The simulation results show that the image contrast of 220nm pitch patterns with dipole illumination has a higher value than that of 300nm pitch patterns, which are currently being printed for DRAM device development. And the result of the mask error factor and the required overlay specification for the exposure tool are also presented.