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...

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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.

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