A study of photomask defects on nanometer feature photolithography

Abstract

As scaling down of transistor gate length progresses to sub-wavelength region, Mask Error Enhancement Factor (MEEF), which is a measure of non-linear relation between mask Critical Dimension (CD) and printed CD on a wafer plays an important role in Optical Proximity Correction (OPC). MEEF is mainly attributed to the degradation of aerial image integrity at low k1 values photolithography. A general equation is derived to compare the MEEF values between two conditions using aerial images and it shows that the change in intensity with respect to the displacement is inversely proportional to the MEEF. Studies are performed for the effect of 6% attenuated PSM on MEEF, effect of off axis illumination on MEEF and effect of assist feature on MEEF. Experimental work is performed to verify the simulated results. A new parameter, kt is also introduced in studying the effect of transmission error of attenuated PSM on the printed CD.