LER Transfer from a Mask to Wafers

摘要

Contribution of mask line edge roughness (LER) to resist LER on wafers was studied both by simulations and experiments. LER transfer function (LTF) introduced by Naulleau and Gallatin was generalized to include the effect of mask error enhancement factor (MEEF). Low spatial frequency part of LTF was enhanced by MEEF while high spatial frequency part was suppressed due to the numerical aperture limit of a stepper. Our model was experimentally verified as follows. First LER of a mask was measured by a scanning electron microscope. Then the mask LER was multiplied by LTF to simulate the aerial image LER on wafers. It was confirmed that the simulated LER agreed well with the LER measured by AIMS~TM. Based on our model the contribution of the mask LER to the resist LER on wafers was estimated. According to our estimation the requirement of the mask LER should be as tight as that of the resist LER on wafers.