The use of in situ laser interferometry for MOCVD process control

Abstract

This paper reports on the technique of single-wavelength laser interferometry for remote monitoring of the thin-film growth of semiconductors by metal-organic chemical vapour deposition (MOCVD). By on-line fitting of factors governing the complex refractive index of a growing layer, the quality of epitaxial growth can be monitored and early identification of a degradation in film growth identified. For example, sub-bandgap 633 nm (HeNe) radiation was used to monitor the pyrolytic and photo-assisted growth of several films of ZnTe on GaAs. Fitting of the effective extinction coefficient, , at each turning point (peaks and troughs) in the interferogram revealed that different growth mechanisms are dominant under photo-assisted conditions compared to strictly pyrolytic conditions. We propose a variation on the virtual-interface approach for the mathematical treatment of a dielectric stack for the real-time fitting of complex reflectance interferograms from multilayers. Using this model, interferograms for vertical cavity surface emitting laser structures have been theoretically generated and are in excellent agreement with the experimental interferograms recorded by Killeen and coworkers. Finally data are presented which demonstrate the use of laser interferometry for process control on an industrial reactor.