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

The subnanoscale spatial distribution of La in La-incorporated HfO 2 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 HfLa x O y −HfO 2 −HfLa x O y structure is confirmed by AR-XPS. The ellipsometry data reveal an abrupt decrease of film void fraction after two HfO 2 growth cycles. More than two and less than three ALD HfO 2 layers interact with one ALD layer of La 2 O 3 in such a way that the first two ALD HfO 2 layers mismatch with La 2 O 3 and form a HfO 2 −La 2 O 3 mixture with a different structure compared to films with a third ALD HfO 2 layer that completes the formation of a continuous HfO 2 surface. At least four ALD HfO 2 layers are required for La free HfO 2 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.