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Metrology tool for fast measurement of patterned sapphire substrate used in LED manufacturing

Increasing demand for high-brightness (HB) LEDs is prompting manufacturers to refine production methods and improve performance of LED light sources. Achieving either of these requires high precision metrology tools that are also fast and non-destructive. In particular, there is a need for the metrology for patterned sapphire substrates (PSS) used in LED manufacturing to enhance light-extraction efficiency. This article describes a gauge-capable metrology tool that is currently used for these purposes: the 3D optical microscope based on white-light interferometer (WLI) which with special algorithms for fringe analysis can specifically quantify the height, width and pitch for each individual PSS structure. We have measured a variety of structures and their dimensions and compared them to SEM or AFM results. The white-light interferometer (WLI) is a tool that better meets the needs of these applications because of the ease of its full field measurement and for faster defects detection. 3D optical microscopes also provide excellent repeatability, especially when employing the automated position calibration of the reference mirror position in the interferometric objective.