Improvement of local CDU by using low speckle imaging

Local CD uniformity (LCDU) is being considered as one of key parameter indicators of patterning quality control due to continuous pattern shrinkage and maintaining wafer quality in lithography process. In optical DUV lithography, LCDU has various contributors and they are systematic mask/OPC items, SEM metrology reproducibility, and stochastic effects. In stochastic term, it includes photoresist and speckle contrast. In general, photoresist is considered as the dominant factor in LCDU control, but speckle contrast is drawing attention due to importance of controlling LCDU in new device. Speckle is a light interference effect which causes the non-uniform dose delivery to mask and wafer, and we experimentally confirmed the effect of speckle contrast in several layers. In this paper, we will propose estimated the speckle budget of total LCDU in the target layers through the experiment.