A method for optical CMM calibration using a grid plate

摘要

The reduction in feature size on microchips has generated an urgent need to improve the accuracy of lithography machines and optical CMMs. Error calibration and compensation of these machines can meet this need. The geometry of an optical CMM or a lithography machine can be calibrated in two dimensions by measuring an uncalibrated reversible grid plate in three different positions. In the initial position the plate is aligned with the machine coordinate system. Next it is reversed about the Y axis of the machine. In the third position the grid plate is rotated 90 degrees about the Z axis of the machine. In order to determine the scale error (establish the metric) one of the machine axes should be calibrated using a stabilized laser interferometer. This paper presents a new and simple algorithm for obtaining the compensation data from grid plate measurements assuming that one axis has been calibrated with a laser. Both computer simulation and experiments have been performed to access the effectiveness of the proposed method.