Spectroellipsometric method for process monitoring semiconductor thin films and interfaces

Real-time monitoring by multiwavelength phase-modulated ellipsometry of the growth of plasma-deposited microcrystalline silicon (muc-Si) is presented. We discuss the construction of a growth model for process monitoring, and, in particular, we treat the inhomogeneity in the muc-Si layer by using an approximation of the reflection coefficient known as the WKBJ method. By also using the Bruggeman effective medium theory to describe the optical properties of muc-Si, we demonstrate monitoring the crystallinity in the upper and the lower part of the layer together with the thickness. The inversion algorithms thus remain very fast, with calculation times within 5 s on a standard Pentium computer. This makes possible precise control of the thickness and the crystallization of both the top and the bottom interface of the layer during the elaboration of devices such as solar cells and thin-film transistors.