Ellipsometric characterization of multilayer transistor structures

Variable angle spectroscopic ellipsometry has been used to determine layer thicknesses, alloy compositions and lateral homogeneity in the relatively complex semiconductor multilayer structures used for modulation-doped field effect transistors. Specifically, we have simultaneously determined five GaAs/Al_xGa₁As layer thicknesses and the alloy compositions x in two of these layers. Good fits between experimental data, and predicted data based on parameter-dependent models were found. In a system with seven unknown ellipsometric parameters to be solved there is potential for the correlation of variables. Thus, we have made a careful study of correlation and the dependence of solved parameter values on the mean-square error value determined in the regression analysis. Lateral homogeneity of molecular beam epitaxial-grown layer thicknesses in similar structures has also been investigated.