Abstract: [Background] Silicon crystal is one of the key optical materials in synchrotron radiation beam line. It is mainly used in double-crystal monochromator. Its main function is to separate the single-wavelength beam for the specific analytical experiments. Therefore, the processing quality of the crystal has an important impact on the synchrotron radiation quality, and the quality inspection on the beam-receiving surface of the crystal is also particularly important. The current conventional method is mainly to use optical microscopy and scanning electron microscopy (SEM) to detect the surface quality of the crystal, then discover the invisible micro-cracks, protrusions, scratches, grooves or other type of damage. [Purpose] The aim is to introduce and propose a simple and feasible detection & characterization approach based on optical interference method. [Methods] With the experimental methods, to detect and characterize the above-mentioned damage on the silicon crystal surface by using Fizeau laser interferometer and atomic force microscopy (AFM). By determining the specific location of the micro-damage and quantitatively characterizing its size (length, width, height/depth, etc.), the possible impacts of the micro-damage on the optical performance of the crystal is evaluated. [Results] The surface morphology of the tested crystal has been detected using Fizeau laser interferometer, and the interference pattern has been obtained. For the surface with micro-damage, an obvious abnormal structure is found to distinguish the location of the micro-damage. It is found as a slight bulge-type injury. The size parameters (width, height) are measured by AFM and compared with the lattice constant respectively. It is found that the former is much larger than the latter, therefore, the re-polishing process is necessary for the crystal. [Conclusion] An effective and feasible method for quality detection and characterization of silicon crystal surface has been proposed.

Key words: Synchrotron radiation, Silicon crystal, Micro-damage, Optical interference method