Iterative algorithm for automatic alignment by object transformation

Mathematical model for automatic alignment of wafers was derived under the assumption of the ideal condition of alignment marks. Because wafers were fabricated under nonideal conditions at the factory level, the wafers were difficult to handle during the manufacturing process. The difficulty arose from distortion due to dust, water and contaminant. The errors from the distortion could be reduced when an ideal algorithm was applied to the alignment sequence repeatedly. The alignment algorithm, which was modified to be iterative, is based on the object transformation and composed of matrix operations like a linear model. The accuracy of the algorithm was demonstrated with a dicing machine in our experiment. The result showed that this iterative algorithm was simple but accurate enough to be applied at the manufacturing level.