Recent progress in thin film growth analysis by multichannel spectroscopic ellipsometry

In this article we review recent advances in instrumentation for multichannel spectroscopic ellipsometry (SE) and its applications in real time analysis of thin film growth. An established approach for multichannel SE utilizes the rotating polarizer configuration to provide 50- to 100-point spectra in the ellipsometric angles and the polarized reflectance for photon energies ranging from 1.5 to 4.5 eV, with a minimum acquisition time of 15 ms. In a recent advance, the upper photon energy limit in rotating-polarizer multichannel SE has been extended to 6.5 eV for the study of wide bandgap thin films. In addition, multichannel SE in the rotating-compensator configuration has also been developed recently. This new instrument configuration provides spectra in the four parameters that define the Stokes vector of the light beam reflected from the film surface, with a minimum acquisition time of 25 ms. The additional information in the Stokes vector allows one to assess sample non-idealities that lead to depolarization of the incident beam upon reflection. Real time SE data analysis procedures have been developed to handle a variety of problems in thin film deposition including (i) nucleation and bulk layer growth on smooth and rough substrates, (ii) nucleation and bulk layer growth on rough substrates accompanied by modification of the substrates, and (iii) graded layer growth with rough surfaces. Illustrative examples from our studies of amorphous semiconductor materials and devices demonstrate these capabilities.