Improved uniformity of nanoscale phase change material pitch line for high-density data storage

The optical proximity effect (OPE) in the lithography process always causes variation in the critical dimension of the array patterns as the geometrical dimension is reduced. To achieve a high uniform phase change material pitch line array on a 300 mm wafer with a linewidth down to sub-100 nm, the sub-resolution assist feature (SRAF) is employed to mitigate the OPE in the immersion lithography process in this work. The correction effect of the width of SRAF is simulated and verified by experimental results. The focus-energy matrix is designed, which demonstrates that the incorporation of 30 nm-wide SRAF yields a favorable correction to the main feature without printing the assist feature in the final pattern. With 30 nm-wide SRAF and elevated exposure energy, the phase change material pitch line array is scaled down to around 60 nm-wide while maintaining structural integrity. This work suggests a promising pathway to optimize the uniformity of nanoscale phase change material arrays by the implementation of SRAF, which is beneficial to achieve high-density phase change material structures. It maintains the consistency in geometrical dimension of the phase change material array and thus in the switching performance.