A Precise Inspection Technique for Wafer Pre-sawing Lines using Affine Transformation

This study proposes a simple and fast technique for detecting wafer cutting lines using the Affine transformation before sawing. This technique was developed for the purpose of wafer alignment when alignment marks are unavailable. The edges of the pre-sawing lines are complex and there are bright shapes in the sawing lines, so it is difficult to apply the conventional edge finding method. The sawing lines are represented by rectangular windows which are deformed by an Affine transformation. The amount of deformation is determined when the grey level in the window is a global minimum in the image. The global minimum is found by the golden section search. The algorithm was tested using 13 sample images and repeated 10 times for each image. The results showed that the processing time was below 1200 m sec and the deviation was in the sub-pixel level. We found that the proposed method can be applied to align wafers in the dicing process.