In this work, the measurement of local variables such as Line Edge Roughness (LER) and Line Width Roughness (LWR) in large field of view (FoV) Scanning Electron Microscopic (SEM) images is demonstrated. We show that larger FoV images include more of the lower frequency components in the roughness profile and hence these variables are measured more accurately. We also show that larger FoV images provide a better statistics which improves the precision of the measurement significantly. We also address the impact of image distortion on LER as the main challenge of large FoVs. The study is performed on large FoV 8µm×8µm images with line/space features, acquired by massive metrology capability of a high throughput eP5 SEM. We crop the images to smaller ones and compare the results measured for different FoVs, with and without distortion correction. We see that by the distortion correction, especially in low frequency, we can calculate the local variables accurately.
We demonstrate the use of EPE (Edge Placement Error) as an early defect detection metric in an EUV self-aligned lithoetch-litho-etch (eSALELE) patterning process. Pitch 21nm test structures were investigated on an eSALELE flow consisting of 4 EUV exposures, 2 of which are lines-spaces while the other 2 exposures are for block patterns that defines the tip-to-tip. An HMI eP5 SEM with large field-of-view (8x8µm FOV) was used to measure critical dimension (CD) on wafer at each critical processing step while the overlay between multiple exposures were measured optically on uDBO marks using a YieldStar (YS). On top of CD metrology, patterning defects were measured at the final patterning transfer into dielectric material using an eP5 SEM and built-in defect inspection capability. Line-break defects are reported. Although each metric like CD, LWR or OVL is expected to contribute to the defect performance of the final pattern transfer, using only one information or another is not fully descriptive. Combining these information into an EPE metric on this complicated patterning process showed better correlation to the defect rates at dielectric transfer.
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