Advances in multichannel ellipsometric techniques for in-situ and real-time characterization of thin films

Recent advances in the design of multichannel ellipsometers based on rotating-element principles have significantly increased their power for applications involving in-situ, real-time analysis of thin films and surfaces. These advances include: (i) extensions in the upper spectral limit beyond the typical value of 4.5 eV, and (ii) increases in the number of extracted parameters beyond the usual two, namely the ellipsometric angles (ψ, Δ). An extended spectral range is enabled, for example, by use of a tandem light source configuration and a grating spectrograph having two stages of order-sorting filters mounted over the window of the linear array detector. With an upper spectral limit of 6.5 eV, such ellipsometers are particularly useful in growth analysis for wide band gap thin films. The larger parameter set is enabled by use of dual or single rotating compensators for polarization state modulation and/or analysis, replacing the traditional rotating polarizer. For the single rotating-compensator instrument in the PSCrA configuration, one can extract the Stokes vector of the reflected beam, and thus its degree of polarization. This in turn can provide information on sample thickness variations over the beam cross-section and can suppress the effects of multiply-scattered light so that non-uniform and macroscopically rough surfaces can be analyzed. For the dual rotating compensator in the PCr1SCr2A configuration, one can extract the entire Mueller matrix of the sample and thus the characteristics of anisotropic surfaces and thin films. Applications of these advances include studies of thickness evolution of the phase for boron nitride and silicon film growth, and the nature and origin of surface-induced optical anisotropy of (110) silicon.