Multichannel ellipsometer for real time spectroscopy of thin film deposition from 1.5 to 6.5 eV

Abstract

A rotating polarizer multichannel ellipsometer has been optimized for operation well into the ultraviolet (UV) spectral range. With this instrument, 132 spectral points in the ellipsometric parameters (ψ, Δ) over the photon energy range from 1.5 eV (827 nm) to 6.5 eV (191 nm) can be collected in a minimum acquisition time of 24.5 ms, corresponding to one optical cycle of the rotating polarizer. Averages over two and 80 optical cycles (obtained in 49 ms and 1.96 s, respectively) give standard deviations in (ψ, Δ) of less than (0.04°, 0.08°) and (0.007°, 0.015°), respectively, for the energy range from 3.5 to 6.0 eV, as determined from successive measurements of a stable thermally oxidized silicon wafer. Key modifications to previous instrument designs include: (i) a tandem in-line Xe/D2 source configuration for usable spectral output from 1.5 to 6.5 eV; (ii) MgF2 Rochon polarizers for high transmission in the UV without the need for optical activity corrections; (iii) a spectrograph with a grating blazed at 250 nm and two stages of internally mounted order-sorting filters; and (iv) nonuniform grouping of the pixels of the photodiode array detector for a more uniform spectral resolution versus photon energy, with energy spreads per pixel group ranging from 0.02 eV at 1.6 eV to 0.05 eV at 5.1 eV. As an example of the application of this instrument, results of real time spectroscopic ellipsometry studies are reported for the deposition of an amorphous silicon nitride thin film by radio-frequency magnetron sputtering onto a silicon wafer substrate.