Grating Encoder for Measurement of In-plane and Out-of-plane Motion

Abstract

In nanomanufacturing, it is necessary to generate not only XY in-plane motions but also Z-directional out-of-plane motions [1]. A lot of stages employed for generation of both in-plane and out-of-plane motions require large strokes in the XY-axes and a relatively small stroke in the Z-axis. Displacement measurement along the three-axes with nanometric resolution is essential for precision positioning of such a stage. Three-axis displacement measurement can be realized by combining a surface encoder described in Chapter 3 for measurement of the translational motion in the XY-plane and a short-range displacement sensor for measurement in the Z-axis. Compared with laser interferometers, the combination of the surface encoder and the displacement sensor are more thermally stable and less expensive, which are important for practical use. However, it is difficult for the two sensors to measure the same point, resulting in large Abbe errors. The difference in the sensor type also causes difficulties in the stage controlling system. It is thus desired to improve the surface encoder from XY in-plane measurement to three-axis in-plane (XY) and out-of-plane (Z) measurement.