Variable angle spectroscopic ellipsometry: Application to GaAs-AlGaAs multilayer homogeneity characterization

Variable angle spectroscopic ellipsometry has been applied to a GaAs-AlGaAs multilayer structure to obtain a three-dimensional characterization using repetitive measurements at several spots on the same sample. The reproducibility of the layer thickness measurements is of order 10 Å, while the lateral dimension is limited by beam diameter, presently of order 1 mm. Thus, the three-dimensional result mainly gives the sample homogeneity. In the present case we used three spots to scan the homogeneity over 1 in. of a wafer, which had molecular-beam epitaxially grown layers. The thickness of the AlGaAs, GaAs, and oxide layers and the Al concentration x varied by 1% or less from edge to edge. This result was confirmed by two methods of data analysis. No evidence of an interfacial layer was observed on top of the AlGaAs.