A NOVEL METHOD FOR MEASURING THE NON-ORTHOGONALITY AND SCALING OF THE COORDINATES OF THE WAFER STAGE USING OPTICAL ALIGNMENT TECHNIQUE

摘要

During the lithographic process, the deviation between the real and ideal exposure positions due to the existing non-orthogonality and scaling of the wafer stage coordinate system will result in the aberration of the mask image on the wafer and degradation of the overlay of the lithographic tool. In this paper, a novel method for measuring the non-orthogonality and scaling of the wafer stage coordinates using optical alignment technique is presented. Firstly, the relationship between ideal positions and measurement positions of alignment marks is found by theoretical deduction. Secondly, the alignment marks are transferred to the wafer by real lithographic process and the real positions of marks are read out by the optical alignment system in the same lithographic tool. Finally, the non-orthogonality and scaling of the wafer-stage coordinate axes are calculated with the deduced formula from the measured real position values. The upload position error, rotation error and expanding of the wafer can be calculated as well by this method. Experiment results show that the measurement repeatability of the non-orthogonal factor is better than O.Olurad, and measurement repeatability of the y to x scaling factor is better than 0.7ppm with the same wafer in different rotations. The measurement reproducibility of the non-orthogonal factor is better than 0.012urad, and the measurement reproducibility of the y to x scaling factor is better than 0.6ppm with different wafers in the same condition.