Formation of interfacial layer during reactive sputtering of hafnium oxide

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Abstract
Hafnium oxide is one of the most promising high dielectric constantmaterials to replace silicon dioxide as the gate dielectric. To take the advantages of high dielectric constant of HfO 2 thoroughly, the relatively low dielectric constant interfacial layer must be controlled carefully. In this work, the formation of an interfacial SiO 2 layer at the HfO 2 / Si interface was studied comprehensively. It is observed that during reactive sputteringdeposition of the HfO 2 layer, a very thick interfacial SiO 2 layer, thicker than 3 nm, would be grown. O-radical signals, instead of O 2 -radicl signals, are detected in the sputtering chamber. An O-radical enhanced oxidation model is proposed to explain such an unusual thick SiO 2 layer. The adoption of a two-step deposition method, the thickness of interfacial SiO 2 layer can be reduced only if the bottom Hf layer is thicker than 5 nm. However, the reduction of effective oxide thickness would be limited. Reoxidation of Hf film sounds a better choice. A 1.0–1.5-nm-thick interfacial SiO 2 layer is still observed. This implies that the traced oxygen in the sputtering chamber plays a critical role on the formation of the interfacial layer. It is thus concluded that reactive sputtering is not a suitable method to prepare a HfO 2 layer with a negligible interfacial SiO 2 layer. Reoxidation of Hf film is a better choice, but the oxygen content in the sputtering chamber must be well controlled.

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