Towards 280 nm i-line random logic lithography with off-axis illumination and optical proximity correction

Abstract

The feasibility of imaging 280 nm features for random logic using i-line technology is examined. Theoretical and experimental studies are carried out to evaluate the effects of subresolution assist lines on the printing of an isolated 280 nm line. Optical proximity effect bias corrections for the 280 nm gaps were investigated as well. Simulations and experiments are conducted to study the exposure field nonuniformity and to evaluate the capability of modern i-line high numerical aperture (NA) exposure tools for 280 nm patterning. It is found that for NA=0.63, independent of illumination conditions, the optimum position and width of assist lines are in the range of 260–320 and 140–160 nm, respectively. The 2/3 annular off-axis illumination shows good performance and provides a greater than 1.6 μm depth of focus (DOF) for the assisted 280 nm isolated line. For the 280 nm gap, with the appropriate mask correction features (“hammerheads”), the 2/3 annular illumination also offers more than 1 μm DOF. The image uniformity studies show that the level of variations of the spatial partial coherence factor σ and the coma aberration in modern tools have practically no effect on the across field linewidth variation (AFLV) under the 2/3 annular condition. For the isolated 280 nm assisted line, an AFLV as small as 10 nm was observed over a 17×17 mm2 exposure field.