Optical diagnostics currently provide the only means of assessing deposition and growth of materials in the relatively high pressure environments characteristic of OMCVD and plasma deposition. Capabilities in this area have been significantly enhanced by three recent developments: first, replacement of the rotating-analyzer and -polarizer SE configurations that have dominated optical characterization for the last 30 years with more powerful rotating-compensator (RCE) designs; second, taking advantage of the polarimetric capabilities of these configurations; and third, use of array detectors that now allow complete polarimetric spectra to be obtained at rates as high as 5 Hz. These advances are being driven in part by the need of the semiconductor industry to replace the scanning electron microscope with optical techniques for the determination of critical dimensions, an application that requires spectral data to be obtained rapidly at accuracies approaching the 0.1-0.2% range.
Here, I discuss these advances and provide relevant examples illustrating their impact on real-time studies of surface and interfaces under dynamic (growth) conditions. These include measuring thickness of SiO2 on Si to precisions of 0.1 pm (about 100 times a typical nuclear diameter) and the determination of growth-surface properties resulting from precursor exposures during OMCVD. As general examples I discuss the use of polarimetry and light scattering in an integrated OMCVD reactor for heteroepitaxy of GaSb on GaAs, and GaP on Si. In the former case real-time characterization allowed growth conditions to be optimized such that interface defects were limited to those needed to accommodate the 7.8% lattice mismatch between the materials. Assessment at 1 s (0.2 nm) increments of the critical initial stages of heteroepitaxy showed that in this case growth initiated as GaSb islands in GaAs. In the latter case we find nanoroughening of the Si substrate is necessary to produce continuous films, but that the nanoroughened substrates are more reactive than III-V growth surfaces to trimethylgallium, leading to the presence of metallic Ga at the heteroepitaxial interface unless reduced initial concentrations of TMG are used.