Interface reactions in ZrO ₂ based gate dielectric stacks

Abstract

Interface reactions in Si/SiO x(N y)/ZrO 2 and Si/SiO x(N y)/ZrO 2/poly-Si gate stacks have been studied by high-resolution transmission electron microscopy. In the case of an uncapped stack ZrSi and ZrSi 2 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 ZrO 2/poly-Si interface. Here a different reaction mechanism is identified, which involves the reduction of ZrO 2 and the growth of a bottom interfacial layer between ZrO x and Si. Replacement of the bottom SiO 2 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/ZrO 2 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 ZrO 2 for the next generation of complementary metal-oxide-semiconductor technologies. © 2002 American Institute of Physics.