Auto-alignment for incident angle of ellipsometer

In this paper, we present a 3-step auto-alignment algorithm for the incident angle of an ellipsometer without auxiliary equipment. The 3-step algorithm uses only a 3-axis precision stage (two rotation and one translation) for ellipsometric incident angle alignment, and consists of two incident angles and its following corrective process. The corrective process is to position the spot on the center of the detector's aperture plane, and consists of accessing and centering on the detector's aperture. In the first step, the polarizer and analyzer arm are set at a proper incident angle and the spot is centered on the detector's aperture by the corrective process. In the second step, the polarizer and analyzer arm are set at a measured incident angle and the spot is centered on the detector's aperture by the corrective process. In the third step, height error and angle errors of the specimen are calculated with the stage's angle from the first and second steps. Finally, locating the specimen stage at an errorless position completes incident angle alignment. We modeled 3-D optical paths using a homogeneous transformation matrix (HTM), and simulated the developed alignment algorithm. The results showed that the developed alignment algorithm works well. Experiment results also revealed good agreement on the simulation. The developed alignment algorithm may be applied to other alignment problems, such as tilt alignment of lithography.