Silicon wafer alignment system focal plane calibration method

Abstract

The invention relates to a silicon wafer alignment system focal plane calibration method comprises the steps that: 1, a workpiece stage is maintained non-inclined; a height stepping method is adopted, and a focal plane position of an alignment optical system is roughly detected according to reflected light intensity of an alignment mark; 2, the workpiece stage is maintained at the focal plane position of the alignment optical system; under a plurality of different inclinations, the alignment mark is aligned by the alignment optical system, such that a relationship curve between the alignment position and the inclinations is obtained; and an interferometer Abbe error is further obtained; 3, the inclination is maintained, the height of the workpiece stage is continuously changed, and a straight line representing the relationship between the alignment position and the heights under the corresponding inclination is obtained; the inclination is changed, and the above step is repeated, such that the focal plane height and the focal plane inclination angle of the alignment optical system are obtained; and 4, the focal plane height and the focal plane inclination angle obtained in the step 3 are adopted; the step 2 is repeated with an iterative approach, such that a precise calibration interferometer Abbe error is obtained; and the step 3 is repeated, such that the focal plane of the alignment optical system is precisely calibrated.

Description

technical field [0001] The invention relates to the field of photolithography, in particular to a method for calibrating a focal plane of a silicon wafer alignment system. Background technique [0002] In the optical alignment system (hereinafter referred to as WA) that uses reflective gratings for silicon wafer alignment, it is necessary to ensure that the alignment measurement process is performed on the focal plane of the optical system (hereinafter referred to as WA focal plane), so as to ensure the alignment results accuracy. When the marker is not aligned on the focal plane, the following phenomena will occur: [0003] When the mark is on the focal plane, but there is an inclination to the focal plane, it will not affect the alignment position, but only affect the contrast; [0004] The markers are not on the focal plane, but the markers are parallel to the focal plane, with no inclination, which does not affect the alignment position, only the contrast. [0005] Wh...

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