REAL-TIME MONITORING OF SURFACE PROCESSES BY P-POLARIZED REFLECTANCE

Understanding surface chemistry under steady-state epitaxial growth in volving organo-metallic chemical precursor molecules is essential for optimizing growth processes. Surface-sensitive optical real-time senso r techniques are very well suited for this task as their applications are not limited to a high vacuum environment. In this article we repor t the combined application of the optical sensor techniques p-polarize d reflectance (PR) and laser light scattering for the real-time monito ring of low temperature growth of epitaxial GaP/GaxIn1-xP heterostruct ures on Si(001) and GaAs(001) substrates by pulsed chemical beam epita xy. The high surface sensitivity of PR allows to follow growth process es with submonolayer resolution during the sequential precursor exposu re of the surface that causes periodic alterations in composition and thickness of a surface reaction layer (SRL), the effect of which is mo nitored by PR as a periodic fine structure. This fine structure is sup erimposed on interference oscillations, resulting from back reflection at the substrate-layer interface with increasing layer thickness. In a linear approximation of the complex four-layer stack reflectance amp litude RR4 in the phase factor Phi(1), the optical response to the SRL is formulated as an additive term in the three-layer model that descr ibes the underlying film growth process. Analytical expressions for th e first derivative of the PR signal are presented and discussed with r espect to the time scale of observation that allows the separation of film growth induced changes from SRL effects. The amplitude modulation and the turning points in the fine structure are assessed and compare d to experimental results, showing that an average complex dielectric function of an ultrathin SRL can be quantified, independent of surface coverage. (C) 1997 American Vacuum Society.