Fig. 1. Principle of surface shape measurement of wafer polishing pad utilizing beam expanding dynamic interferometer

Fig. 2. Schematic of sub-aperture planning. (a) Full-aperture planning result; (b) sub-aperture planning result

Fig. 3. Schematic of mapping relationship between coordinate system of measured surface and CCD target surface under grazing incidence measurement

Fig. 4. Schematic of uniform coordinate system principle

Fig. 5. Influence of systematic error on grazing incidence measurement. (a) Compressed phase data; (b) decompressed data

Fig. 6. Schematic of overlapping area of sub-apertures

Fig. 7. Flow chart of measurement

Fig. 8. Wavefront simulation results. (a) Wavefront results; (b) sub-aperture planning results

Fig. 9. System defocus error simulation results. (a) Output wavefront of interferometer; (b) sub-aperture data including system defocus error

Fig. 10. Comparison of simulation results of stitching algorithms. (a) Full aperture surface restored by common sub-aperture stitching algorithm; (b) full aperture surface restored by self-calibration astigmatism aperture stitching algorithm

Fig. 11. Comparison of residual values of stitching algorithms. (a) Residual diagram of normal stitching algorithm; (b) residual diagram of self-calibration astigmatism aperture stitching algorithm

Fig. 12. Photograph of experimental setup for calibration of output wavefront from beam expanding dynamic interferometer

Fig. 13. Result of each stage of calibration of output wavefront from beam expanding dynamic interferometer. (a) Astigmatic wavefront; (b) coma wavefront; (c) defocused wavefront; (d) calibrated wavefront

Fig. 14. Test results of stability of output wavefronts of beam expanding dynamic interferometer under clamping schemes of PTFE gasket and distributed fastening screws

Fig. 15. Experimental setup for wafer polishing pad surface measurement based on grazing-incidence beam expanding dynamic interferometer

Fig. 16. Surface shape result at 0° sub-aperture

Fig. 17. Surface test results of Φ576 mm wafer polishing pad sample. (a) General algorithm; (b) self-calibration astigmatic aperture algorithm