About the influence of Line Edge Roughness on measured effective-CD

Various reports state that Line Edge/Width Roughness (LER/LWR) has a significant impact on the integrated circuits fabricated by means of lithography, hence there is a need to determine the LER in-line so that it never exceeds certain specified limits. In our work we deal with the challenge of measuring LER on 50 nm resist gratings using scatterometry. We show by simulation that there is a difference between LER and no-LER scatter signatures which first: depends on the polarization and second: is proportional to the amount of LER. Moreover, we show that the mentioned difference is very specific, that is - a grating with LER acts like a grating without LER but showing another width (CD, Critical Dimension), which we refer-to as effective-CD.