Development of a three-dimensional encoder for highly accurate positioning

To satisfy the miniaturization requirements of semiconductor manufacturing and metrology, orthogonal Z-axis stage controllability of equipment using highly accurate position detectors are necessary in addition to fundamental XY-axes stage movement control. The Z-axis position detector must have high accuracy, high resolution, and high stability against environmental changes in temperature, humidity, and air pressure. In this paper, a two-dimensional encoder based on a grating interferometer detection method is presented, A prototype XZ-axes encoder was built and evaluated for long-term stability against variations in environmental conditions as well as short-range linear accuracy. The evaluation results show that it is feasible to integrate the encoder with a highly accurate two-dimensional (XZ or YZ) stage control with sub-nanometer resolution. The performance of the encoder as a Z-axis position detector satisfies the demands of industry. By applying the methods developed to the third axis, it can be possible to upgrade the position detection system to three dimensions.