Impact of long-period line-edge roughness (LER) on accuracy in critical dimension (CD) measurement and new guideline for CD metrology

The influence of long-period line-edge roughness (LER) on measured critical dimension (CD) is identified, and a guideline is proposed for CD measurement which is free from LER impact. The width of a line pattern measured by critical dimension scanning electron microscope (CD-SEM) is a local CD, which deviates from the averaged CD due to long-period LER. This LER impact on the CD measurement is investigated in two typical measurements of CD-SEM, namely, the evaluation of across-wafer CD variation and the dynamic repeatability of the equipment. It is shown that both results strongly depend upon the height of the inspection area along the pattern edge (L) due to long-period LER. To obtain an accurate CD, this LER impact on variation in measured CD should be reduced sufficiently. It is found that a large L can reduce LER impact, and a 2-mu m-high inspection area is recommended for CD-measurement. Furthermore, the validity and limitation of the "patchwork method", in which plural inspection areas are connected to obtain one large area, are examined.