An Automatic Calibration Method for Kerf Angle in Wafer Automated Optical Inspection

To improve the accuracy of kerf angle, an automatic calibration method for kerf angle in wafer automated optical inspection is presented. First, the error model of inspection system is established and system angle deviations are calibrated. Next, normalized positioning-based the kerf edges of interest in multiple images are extracted. Then, the coordinate transformation considering the system angle deviation compensation is performed. Finally, the kerf edge line is fitted based on the least squares method to obtain the kerf angle and the kerf angle can be automatically calibrated by rotating the stage. The experimental results show that the kerf angle obtained is relatively stable by coordinate transformation of multiple images to enhance the information of kerf edge and the accuracy of kerf angle can reach within 0.02 degree. Besides, the kerf angle is more sensitive to the system angle deviation and the result is basically a linear increase.