Fig. 1. Schematic diagrams of wafer stage and six-degree-of-freedom positioning in lithography machine. (a) Schematic diagram of lithography system; (b) photo of worktable of lithography machine; (c) error sources of precision displacement parts of worktable; (d) schematic diagram of six-degree-of-freedom motion error

Fig. 2. Comparison of laser interferometer and grating interferometer measurement system used by ASML lithography machine in the Netherlands. (a) Laser interferometer measurement system; (b) grating interferometer measurement system

Fig. 3. Basic principle of high precision grating interferometer and sub-nano measurement scheme. (a) Principle of one dimensional diffraction grating displacement measurement; (b) Magnescale grating interferometer; (c) self-collimating grating interferometer

Fig. 4. Two-degree-of-freedom grating interferometer

Fig. 5. KGM 282 two-degree-of-freedom grating interferometer developed by Heidenhain company^[37]

Fig. 6. Schematic of absolute displacement measurement

Fig. 7. XY two-degree-of-freedom grating interferometer based on two-dimensional grating

Fig. 8. XYZ three-degree-of-freedom grating interferometer with out of plane measurement capability based on two-dimensional grating. (a) Three-DOF grating interferometer; (b) three-DOF grating interferometer with self-collimating structure

Fig. 9. Heterodyne three-degree-of-freedom grating interferometer based on two gratings

Fig. 10. Heterodyne three-degree-of-freedom grating interferometer with single grating and common optical path

Fig. 11. Single-measuring-point six-degree-of-freedom measuring system

Fig. 12. Multi-measuring-point six-degree-of-freedom measuring system. (a) Three-beam six-DOF measurement system based on two-dimensional grating; (b) six-DOF measurement system based on two measuring points and three measuring units

Fig. 13. Heterodyne three measuring points and six-degree-of-freedom measuring system

Fig. 14. Illustration of large-area, high-resolution projection lithography technology

Fig. 15. Interference exposure system based on the orthogonal two-axis Lloyd’s mirror interference unit

Fig. 16. Technical route of “four gratings-four reading heads” adopted by ASML company

Fig. 17. Geometric relation calculation of multi grating multi reading head coordinate system and test of two-degree-of-freedom grating interferometer

Fig. 18. Grating profile error and periodic deviation obtained based on large-area wavefront interference and their comparison results

Fig. 19. Virtual reflection phenomenon of different Doppler shift orders

Table 1. Performance requirements for advanced node 14 nm lithography machine workpiece stage

Table 2. Performance comparison of grating interferometer