REAL-TIME ADSORPTION-DESORPTION THIN-FILM OPTICAL MONITOR USING A WINDOWLESS REFLECTIVE SILICON PHOTODETECTOR

A thin-film deposition monitor is described that employs a windowless reflective Si photodetector as the sensing element. When the detector is illuminated by a monochromatic light beam at oblique incidence, the generated photoelectric signal becomes a sensitive function of the th ickness and refractive index of the deposited film. For high sensitivi ty, the incident light is linearly polarized perpendicular to the plan e of incidence, and an angle of incidence >60 degrees is used. Further , the passivation SiO2 layer thickness is also judiciously selected fo r this application. A sensor of this kind is employed to follow the ad sorption/desorption kinetics of an H2O film at the detector surface (a t 633 nm wavelength) and the results are interpreted with the help of Bruggeman's effective medium theory. (C) 1995 American Institute of Ph ysics.