Combined beam profile reflectometry, beam profile ellipsometry and ultraviolet-visible spectrophotometry for the characterization of ultrathin oxide-nitride-oxide films on silicon

We show that a combination of beam profile reflectometry, beam profile elli psometry, and deep ultraviolet-visible spectroreflectometry can accurately characterize ultrathin oxide on nitride on oxide films with total thickness es of less than 200 Angstrom. Beam profile ellipsometry establishes the tot al thickness, while beam profile reflectometry provides the key data to det ect the multilayer structure. Optical absorption of the nitride layer at wa velengths shorter than 270 nm as measured by spectroreflectometry provides additional accuracy in determining the thicknesses of the individual layers . The fit to the data is improved by including a '12 Angstrom, interlayer b etween the Si substrate and the bottom oxide. Determined thicknesses are in excellent agreement with these deduced by cross-sectional transmission ele ctron microscopy. (C) 1999 American Vacuum Society. [S0734-2101(99)05702-4] .