Subnanoscale Lanthanum Distribution in Lanthanum-Incorporated Hafnium Oxide Thin Films Grown Using Atomic Layer Deposition

Abstract

The subnanoscale spatial distribution of La in La-incorporated HfO2 thin films grown by atomic layer deposition (ALD) is characterized using angle resolved X-ray photoelectron spectroscopy (AR-XPS) and ellipsometry. The (La 3d)/(O 1s) photoelectron intensity ratios and film void fractions are acquired by conducting AR-XPS at small take off angles and processing the ellipsometry data through the effective medium approximation model. The existence of a HfLaxOy−HfO2−HfLaxOy structure is confirmed by AR-XPS. The ellipsometry data reveal an abrupt decrease of film void fraction after two HfO2 growth cycles. More than two and less than three ALD HfO2 layers interact with one ALD layer of La2O3 in such a way that the first two ALD HfO2 layers mismatch with La2O3 and form a HfO2−La2O3 mixture with a different structure compared to films with a third ALD HfO2 layer that completes the formation of a continuous HfO2 surface. At least four ALD HfO2 layers are required for La free HfO2 interval layers to exist in the film. This AR-XPS-ellipsometry method is potentially applicable to characterizing other amorphous ALD grown systems containing incorporated elements with subnanoscale variations.