The wafer polishing pad is a critical component in achieving global planarization of the wafer surface during the integrated circuit manufacturing process. Its surface shape has a significant effect on wafer yield. To optimize the shape of the wafer polishing pad, strict quality control measures are necessary. Precision measurement technology plays a vital role in ensuring quality. Currently, the integrated circuit industry is moving towards larger wafer sizes and smaller feature dimensions, presenting new challenges for measuring the shape of wafer polishing pads. Interferometry is one of the most effective and intuitive methods for surface measurement due to its non-contact nature, high accuracy, and rapid operation. However, traditional large-aperture Fizeau interferometers face significant manufacturing difficulties and high costs. Moreover, they often struggle to accurately measure the surface shapes of large-diameter wafer polishing pads due to limitations such as restricted dynamic range, light scattering, and diminished stripe contrast. Grazing-incidence interferometry provides an effective solution to these limitations, addressing issues related to aperture size, dynamic range, and contrast. Nevertheless, when measuring large-diameter wafer polishing pads with long interferometric cavity lengths, new challenges such as airflow disturbances and vibrations emerge. To address these issues, we propose to measure the surface shape of large-aperture wafer polishing pads using a grazing incidence splicing technique within a beam-expanding dynamic interferometer.

The challenges related to aperture size, dynamic range, and contrast in the interferometric measurement of large-aperture wafer polishing pad surfaces are effectively addressed through grazing incidence interferometry and sub-aperture stitching techniques. A high-precision and high-stability beam expansion system effectively compensates for the limitations of the dynamic interferometer regarding measurement aperture. At the same time, the inherent anti-interference capabilities of the dynamic interferometer can address the issue of environmental disturbances affecting the grazing incidence light path of large-aperture optical components. Based on a self-calibrating sub-aperture stitching algorithm, the influence of system defocus on grazing incidence measurements is decomposed into unequal astigmatic circles in the x and y directions, which are then deducted. This approach enables the measurement of the surface shape of large-diameter rough optical elements by correcting the defocus-induced errors of the beam-expanding dynamic interferometer.

We develop a 150 mm beam-expanding dynamic interferometer to conduct wavefront calibration experiments. We perform outgoing wavefront stability monitoring experiments with different clamping configurations for the beam expansion collimators. The results indicate that the distributed fastening screw clamping scheme has better stability than the hard-contact clamping scheme using polytetrafluoroethylene (PTFE) pads. It maintains a wavefront peak valley (PV) value stable at approximately 0.1λ over a period of 9 h, with a maximum deviation not exceeding 0.108λ. Using the 150 mm beam-expanding dynamic interferometer, we collect sub-aperture data from a Ф576 mm polishing pad sample produced by KYOCERA Corporation in Japan. The data are stitched together using both a standard stitching algorithm and a self-calibrating astigmatic circle algorithm. The results reveal that the standard stitching algorithm is significantly affected by defocus-induced system errors, resulting in jump errors at the sub-aperture junctions. In contrast, the self-calibrating sub-aperture stitching algorithm effectively mitigates the influence of system errors, yielding a smooth transition. Ultimately, the stitched wavefront yields a PV value of 4.784λ and a root-mean-square value of 1.151λ. A comparison is made between the central cross-sections of the composite surface shape at angles of 0°, 45°, 90°, and 135° and the measurements from a coordinate measuring machine provided in the sample’s factory report. The average measurement error for the cross-section heights is 0.1375 μm, while the flatness error is 0.17 μm, both within acceptable limits.

We develop a grazing incidence splicing surface error measurement method based on beam expanding dynamic interferometer, which can solve the problem of surface error detection of large diameter wafer polishing pad in workshop environment. We investigate the issue of defocus variation in the system’s outgoing wavefront and employ a self-calibrating astigmatic circle sub-aperture stitching algorithm to decompose the influence of system defocus on grazing incidence measurements into unequal astigmatic circles in the x and y directions, which are then corrected. Simulation results demonstrate that this algorithm can effectively eliminate the interference caused by system defocus during sub-aperture stitching, providing a robust algorithmic foundation for high-precision sub-aperture measurements. Experimental comparisons are conducted to assess the degradation of the system’s outgoing wavefront under different clamping configurations over the same period. The results indicate that the distributed fastening screw clamping scheme significantly enhances system stability. A sub-aperture stitching detection device based on a grazing incidence beam-expanding dynamic interferometer is established to measure a Ф576 mm wafer polishing pad sample. Comparing the measurement results with those from the factory’s coordinate measuring machine reveals that the average measurement error for cross-section heights is 0.1375 μm, while the flatness error is 0.17 μm. Experimental results demonstrate that this method can inspect the surface error of wafer polishing pads, thereby expanding the application scope of dynamic interferometers.