Two-step interfacial reaction of HfO2 high-k gate dielectric thin films on Si

HfO2thin films have been deposited on p-type (100) Si substrates by pulsed laser deposition. Transmission electron microscopy observation illustrated that the HfO2films are in polycrystalline structure and the interface with Si substrate is free from amorphous layer. The rough feature of the film/Si interface suggested interfacial reaction and diffusion. Depth profile X-ray photoelectron spectroscopy (XPS) analysis results revealed the formation of Hf silicate and Hf silicide at the interface. A two-step reaction model was proposed to interpret the interfacial reaction. At initial stage of film growth, insufficient oxidation of Hf atoms on bare Si surface resulted in reaction of Hf with Si leading to silicidation of Hf, at least Hf-Si bonds formation. During the following film growth, the preformed Hf silicide was further oxidized leading to Hf silicate formation. This two-step reaction model suggests a gradient distribution of the film stack, that is, HfO2/Hf silicate/Hf silicide/Si. It was found that with sufficient oxygen during film growth, the Hf silicide formation was suppressed.