Heterodyne interferometer measuring system for measuring displacement and its measurement method

Abstract

The invention relates to a heterodyne interferometer measurement system for measuring displacement and a measuring method thereof. The measurement system comprises a workbench reflector set and a laser heterodyne interferometer; the workbench reflector set comprises a first plant reflector disposed on the lateral side of the workbench and parallel with an optical axis, and a second plant reflector having certain angle with the optical axis; and the laser heterodyne interferometer comprises a polarization slitting prism, a cube corner prism, a reference plane reflector having certain angle with the optical axis, and two quarter-wave plates. The measuring method comprises the following steps of: allowing a reference beam and a measuring beam generated by a laser passing through the polarization slitting prism to respectively enter a photoelectric conversion element after multiple reflections and transmissions, processing to obtain an optical path difference (OPD), and then obtaining Z-axis displacement Z of the workbench. The invention needs not to use the plane reflectors disposed at two sides of a projection objective lens, resulting in simple structure; and needs not to increase extra size of the projection objective lens at X-axis direction. The cost of the measurement system is reduced due to less number of the used plane reflectors.

Description

technical field [0001] The invention relates to a heterodyne interferometric measurement system for measuring displacement and a measurement method thereof. Background technique [0002] As the size of lithographic features decreases, the depth of focus becomes smaller and smaller. In order to enable silicon wafers to be exposed within the focal depth range, the Z-direction (along the optical axis) position measurement of the workpiece table is indispensable to ensure the excellent lithography performance of the lithography machine. [0003] The Z-direction position of the workpiece table can be accurately measured by using a laser heterodyne interferometry system (see prior art 1, Erik R. Loopstra, "Method and apparatus for repeatedly projecting mask pattern on a substrate, using a time-saving height measurement”, US Patent Application No.: 6208407). FIG. 1 shows the measurement system proposed in the prior art 1. As shown in FIG. The silicon wafer 3 is placed on the wor...

AI Technical Summary

Problems solved by technology

[0004] The interferometric measurement system proposed in the prior art 1 can accurately measure the displacement of the workpiece table 4 in the z direction, but since the reflector 2 needs to have the same size as the travel of the workpiece table 4 in the x direction, the projection objective lens system needs to be in the x direction. The size in the direction becomes larger, which is not conducive to installation

In addition, in order to achieve a smaller feature size, the size of the projection objective lens is constantly increasing. If there are larger flat mirrors installed on both sides, this will increase the difficulty in achieving smaller feature size exposure.

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