The ultimate in real-time ellipsometry: Multichannel Mueller matrix spectroscopy

A review of the techniques and applications of multichannel ellipsometry in the dual-rotating-compensator configuration is given. This ellipsometric approach has been established as the ultimate in real-time, single-spot optical measurement, as it determines the entire 16-element Mueller matrix of a sample over a wide spectral range (up to 1.7-5.3 eV) from raw data collected over a single optical period of 0.25 s. The sequence of optical elements for this ellipsometer is denoted PC_1rSC_2rA, where P, S, and A represent the polarizer, sample, and analyzer. C_1r and C_2r represent two MgF₂ rotating compensators, either biplates or monoplates that rotate synchronously at frequencies of ω₁ = 5ω and ω₂ = 3ω, where π/ω is the fundamental optical period. Previous high-speed Mueller matrix measurements with this instrument have been performed on uniform, weakly anisotropic samples such as (110) Si, in which case one can extract the bulk isotropic and near-surface anisotropic optical responses simultaneously. In such an application, the instrument is operated at its precision/accuracy limits. Here, ex situ results on a strongly anisotropic, locally biaxial film are presented that demonstrate instrument capabilities for real-time analysis of such films during fabrication or modification. In addition, the use of the instrument as a real-time probe to extract surface roughness evolution on three different in-plane scales for an isotropic film surface is demonstrated for the first time.