Semiconductor inspection includes many different techniques, some of which use lasers, for the metrology and inspection of semiconductor wafers during the manufacturing process.
A few of the inspection techniques used during this inspection process include interferometry, ellipsometry, particle analysis, photoluminescence, fluorescence and Raman spectroscopy.
Interferometry is commonly used to measure the flatness of substrates. A coherent laser beam shines on a wafer surface and reflected light forms interference pattern that is analyzed. The interferograms require a good beam quality, long coherence length, and outstanding wavelength and pointing stability.
Ellipsometry is a flexible technique which can be used to analyze a variety of material properties, for example, composition, roughness, crystalline nature, doping concentration, electrical conductivity, refractive index measurements. It is based on analysing the polarization change of incident light during interaction with the material being investigated. Although optical techniques are inherently diffraction-limited, ellipsometry exploits phase information (polarization state) and can achieve sub-nanometer resolution by providing information about the layers thinner than the wavelength of light used for the investigation.
Lasers from HÜBNER Photonics which are used for interferometric measurements as well as ellipsometry during semiconductor inspection are Cobolt diode pumped lasers (DPL). They are inherently single frequency with excellent power stability, beam profile and low noise.