Interface reactions in ZrO2 based gate dielectric stacks

Abstract

Interface reactions in Si/SiOx(Ny)/ZrO2 and Si/SiOx(Ny)/ZrO2/poly-Si gate stacks have been studied by high-resolution transmission electron microscopy. In the case of an uncapped stack ZrSi and ZrSi2 phases form during an ultrahigh vacuum anneal at temperatures above 900 °C. Both phases show an island-type growth with an epitaxial relationship with Si (100). Gate dielectric stacks with a poly-Si cap are found to be thermally unstable at T=1000 °C, so that the reaction is initiated at the ZrO2/poly-Si interface. Here a different reaction mechanism is identified, which involves the reduction of ZrO2 and the growth of a bottom interfacial layer between ZrOx and Si. Replacement of the bottom SiO2 layer by an ultrathin Si oxinitride does not completely suppress these interfacial reactions at T⩾1000 °C. We suggest that control of the poly-Si/ZrO2 interfacial reactions may be an important factor in modifying the thermal stability of a stack. These results shed a new light on understanding the material challenges involved in the integration of ZrO2 for the next generation of complementary metal–oxide–semiconductor technologies.