Absolute coordinate system adjustment and calibration by using standalone alignment metrology system

Absolute alignment measurement of underlayer and overlayer of diffraction-based overlay mark by image-based alignment metrology system

“…Even if the underlayer mainly caused the overlay error, usually the error is fed back to overlayer because we cannot distinguish whether it was the underlayer or overlayer that caused the error from the overlay error. In contrast, we have developed a method that would separate the overlay error into the grid errors of underlayer and overlayer and directly correct each of them by absolute alignment measurement against overlay marks using a standalone, image-based alignment metrology system named Litho Booster as shown in figure1 (b) [1,2,3]. The key to this direct grid control depends on how one measures overlay marks to obtain underlayer's and overlayer's grid despite there are 2 types of overlay marks that are Image-Based Overlay (IBO) and Diffraction-Based Overlay (DBO) marks, which are assumed to be measured by different systems respectively.…”