研究目的
To present a fast imaging method based on sub-dark-field illumination in white-light interferometry for resolving the surface profile of test structures, including smooth surfaces with roughness on the order of a few angstroms.
研究成果
A fast imaging method with SDFI was presented, capable of obtaining the FDI and superficial 3D profile for a test surface with roughness on the order of a nanometre or even an angstrom. The method is a static-state technique, providing true-colour images without scanning.
研究不足
The tested surface should not be excessively rough; the OPD should be less than 3/4λ. The precision is limited when the surface roughness is too high.
1：Experimental Design and Method Selection:
A WLI with a 10× Mirau interference objective was used. The interference mechanism was constructed by combining the non-luminous tested surface and the reflected image of a reference mirror circle in the Mirau objective.
2：Sample Selection and Data Sources:
Tested samples included GaN-on sapphire, HVPE GaN, GaN-on Si, and a CdZnO/ZnO MQW LED, among others.
3：List of Experimental Equipment and Materials:
A WLI of type MM200 provided by The Nanjing BMODPEC Photo-Electronic Company in China, a halogen lamp (6 V, 20 W).
4：Experimental Procedures and Operational Workflow:
The horizontal level of the object plane was carefully regulated to ensure the tested surface entered the PIF and was evenly illuminated by the PIF. The OPD was regulated to shift the PIF.
5：Data Analysis Methods:
The surface roughness RMS was calculated using the formula provided, and the interference intensity in the image plane was analyzed.
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