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 A˚, 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 concentrationxvaried 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.
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