Spectroscopic ellipsometry characterization of high-k gate stacks with Vt shift layers

We have used spectroscopic ellipsometry (SE) to measure layer thicknesses of HfO2/La2O3 and La2O3/HfO2 stacks on SiO2/p-Si. Two approaches to extract layer thicknesses from a single SE measurement were shown to be inaccurate, possibly due to similarities in the optical dispersions of HfO2 and La2O3. The approach where SE data was collected after deposition of each layer and only the thickness of the top layer was determined by modeling was found to be capable of accurately measuring the thickness of each layer. These conclusions are supported by angle resolved X-ray photoelectron spectroscopy (ARXPS), X-ray reflectivity (XRR) and Rutherford backscattering spectroscopy (RBS) measurements.