In situ real time ellipsometry for GaN remote plasma MOCVD technology

Abstract
The potentiality of non-intrusive, non-destructive and non-perturbing ellipsometry in the remote plasma metalorganic chemical vapor (RP-MOCVD) technology of GaN is briefly reviewed. It is shown that in situ spectroscopic ellipsometry (SE) is a powerful technique to provide (i) accurate thickness measurements, (ii) depth-profiles of interfaces and thin films structure, (iii) the composition of layers and (iv) the microroughness of the surface layer. With respect to this, the processes of GaAs substrates cleaning and of GaAs and GaP substrates nitridation by in situ remote plasmas of, respectively, H₂ and N₂ are investigated. These processes are extremely important in the growth of GaN epitaxial layer, since they prepare the substrate to be a good template for the heteroepitaxial growth. Furthermore, it will be shown that the results obtained by SE are reliable and corroborated by the results of XPS and AFM. Single wavelength ellipsometry (SWE) is used for the real time monitoring of the kinetics of the GaAs and GaP substrate cleaning and nitridation and of GaN epigrowth by trimethylgallium and plasma pre-activated nitrogen. Thus, the chemical and kinetic model of the above processes is presented. Also, the capability of the real time ellipsometry in monitoring adsorption equilibrium is discussed through the process of sapphire plasma nitridation.