- The SMFL has two Nanometrics Spectrophotometers
- Nanometrics Model 210 is in Wet Etch 1.
- Nanometrics Model 200 is in Wet Etch 2
- The basic operating principle of a spectrophotometer is that the intensity of monochromatic reflected light depends strongly on film thickness because of interference.
- The film thicknesses are comparable to the wavelength of the incident light.
- The machine uses a computer-controlled grating monochromator and a photomultiplier tube detector to measure the reflected optical spectrum over the 350 to 800 nm wavelength band) from a bare silicon reference wafer and from the wafer under test.
- Given an index of refraction for a thin film and the two measured spectrums, the computer will analyze the interference pattern to determine film thickness.
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