The demand for high precision stage is increasing in the fields of nanotechnology. This paper handles a novel design of 3-axis (z-axis, pitch, roll) motion stage and an application to incident angle alignment of ellipsometer. Ellipsometer is known as the best inspection instrument for measuring optical indices and thickness of thin films. It is notable that the ellipsometry parameters psi and delta, not the physical quantity of interest, are measured by an ellipsometer. Ellipsometery parameters are functions of the incidence angle and depend strongly on the incidence angle factor. So it is clear that the accuracy of the incident angle is important in ellipsometer.
To develop several properties of stage for ellipsometer, the kinematic coupling is used in this paper. Generally the kinematic coupling has many advantages, such as closed form motion solution, high repeatability on the sub-micron level, low construction cost, and no play between mating parts. The forward and inverse kinematic equations of the stage are derived in this paper. The kinematic equations represent the relation between the positions of actuators and tilting angles. And the kinematic error analysis is performed in order to minimize angle errors of the stage. As a result of that, the alignment error of actuator is a dominant error source. Also this result is used in the design and manufacturing process of the stage.
The incident angle auto-alignment algorithm of ellipsometer consists of two steps, searching the spot and alignment to the center of detector. The first step, searching the spot, makes that the spot is in the detectable area of detector. The second step, alignment to the center of detector, is aligning the spot to the center of detector. It is possible the incident angle auto-alignment without additional alignment sensor by this algorithm. The experimental result shows that it takes about 30 seconds to align incident angle automatically.
