Optical technique for material characterization
A technology of polycrystalline materials and Raman spectroscopy, applied in the field of parameter systems, can solve problems such as inaccuracy and difficulty in interpretation
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[0083] According to some embodiments of the invention, the following are several specific system aspects necessary for the method:
[0084] - Numerical aperture (NA):
[0085] (a) A high numerical aperture is necessary to allow efficient collection of Raman signals with short acquisition times. In the current context, a high NA also results in a small spot size, as shown by the diffraction:
[0086]
[0087] where λ is the wavelength. Therefore, high NA can characterize small grain sizes.
[0088] It should be noted that Equation 4 is simplified for clarity - for Raman metrology, the illumination, and collection wavelengths are slightly different, and the illumination and collection NAs may be different.
[0089] (b) Controlling the illumination NA and / or collection NA affects the measured spot size, ie the number of grains within the spot can be changed, and thus affect the grain statistics. Specifically, measurements can be made at a set of different NA values (illu...
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