Optimization of sampling method for overlay and alignment accuracy improvement

The authors have investigated the sample plan dependency of global alignment repeatability and overlay measurement accuracy. To achieve better alignment repeatability is critical for improving not only in-wafer overlay but also wafer-to-wafer overlay control. Global alignment repeatability and its results are significantly affected by which chips in a wafer map are selected as global alignment use. Several sampling methods which are limited to symmetric group (translation, inversion, rotation symmetric) are tested.