We perform ab initio calculations, based on density functional theory, of substitutional and vacancy defects in the monoclinic hafnium oxide (m-HfO2) and α-quartz (SiO2). The neutral oxygen vacancies and substitutional Si and Hf defects in HfO2 and SiO2, respectively, are investigated. Our calculations show that, for a large range of Hf chemical potential, Si substitutional defects are most likely to form in HfO2, leading to the formation of a silicate layer at the HfO2/Si interface. We also find that it is energetically more favorable to form oxygen vacancies in SiO2 than in HfO2, which implies that oxygen deficient HfO2 grown on top of SiO2 will consume oxygen from the SiO2.
PACS numbers:The continuous device miniaturization in the microelectronic industry will eventually lead, within the present technology, to the end of the use of amorphous SiO 2 (a-SiO 2 ) as gate dielectric in metal-oxidesemiconductor field-effect transistors (MOSFETs). The existence of a thickness limit for the a-SiO 2 around 10-12 A, has clearly been established experimentally [1]. One way to circumvent this problem, still keeping Si as the basic device material, is to employ high-permitivity materials as alternative gate dielectrics in place of the conventional a-SiO 2 . Among them, hafnium oxide is emerging as the material with greatest potential to substitute SiO 2 , mainly due to its high dieletric constant and thermodynamic stability, when it forms interface with Si.Even though hafnium oxide is thermodynamically stable against an overall decomposition as Hf and SiO 2 when grown on Si, interfacial reactions can occur. Thereby the formation of a thin interfacial layer (oxides, silicates and silicides) between the HfO 2 and the Si surface, has been recently observed [2,3]. This interfacial layer occurs during almost any film growth processes or post-annealing, which is an intrinsic part of any growth cycle. Therefore, the thermodynamic stability of the hafnium oxide in contact with silicon is identified as a critical issue for the application of alternative gate dielectric in silicon-based devices [4,5]. Moreover, the study of possible defects related to the migration of atoms across the interface is of fundamental importance. In particular, a significant source of defects in this system is the interface itself, which has been shown [6] to consist of Hf silicates with dielectric constant lower than that of HfO 2 [7,8].In the present work we address the formation of neutral defects through first-principles calculations, based on the density functional theory (DFT). We analyze the formation of Si substitutional defects in HfO 2 , as well as Hf substitutional defects in SiO 2 , for different growth conditions. Finally, the energetics of an oxygen vacancy in SiO 2 is compared to a similar vacancy in HfO 2 , in order to understand the growth of hafnium oxide under oxygen-poor conditions. * Electronic address: fazzio@if.usp.br Many experimental works [9,10,11,12] have addressed the chemical reactions that could occur in the HfO 2 /Si interfa...
