Research on c-HfO2 (0 0 1)/α-Al2O3 (1 -1 0 2) interface in CTM devices based on first principle theory

Wenjuan Lu,Xu Zhang,Yuehua Dai,Chengzhi Ma,Feifei Wang,Fei Yang,Xianwei Jiang

doi:10.1063/1.5001904

Abstract

With the growing application of high-k dielectrics, the interface between HfO2 and Al2O3 play a crucial role in CTM devices. To clearly understand the interaction of the HfO-AlO interface at the atomic and electronic scale, the bonding feature, electronic properties and charge localized character of c- HfO2 (0 0 1)/α-Al2O3 (1 -1 0 2) interface has been investigated by first principle calculations. The c- HfO2 (0 0 1)/α-Al2O3 (1 -1 0 2) interface has adhesive energy about -1.754 J/m2, suggesting that this interface can exist stably. Through analysis of Bader charge and charge density difference, the intrinsic interfacial gap states are mainly originated from the OII and OIII types oxygen atoms at the interface, and only OIII type oxygen atoms can localized electrons effectively and are provided with good reliability during P/E cycles, which theoretically validate the experimental results that HfO2/Al2O3 multi-layered charge trapping layer can generate more effective traps in memory device. Furthermore, the influence of interfacial gap states during P/E cycles in the defective interface system have also been studied, and the results imply that defective system displays the degradation on the reliability during P/E cycles, while, the charge localized ability of interfacial states is stronger than intrinsic oxygen vacancy in the trapping layer. Besides, these charge localized characters are further explained by the analysis of the density of states correspondingly. In sum, our results compare well with similar experimental observations in other literatures, and the study of the interfacial gap states in this work would facilitate further development of interface passivation.

Highlights

Due to the high compatible with the complementary metal-oxide semiconductor (CMOS) fabrication process, the charge trapping memory (CTM) as one promising candidate of the generation nonvolatile semiconductor memories has been studied experimentally or theoretically for many years
Comparing to the ideal interface system, the total density of states (DOS) of defective system move to the lower energy direction, and it should be noted that the energy level originated from the OIII type oxygen atoms in the defective system have been split to three peaks, which implies the enhanced charge localized ability of these atoms
It can be figure out that the charge localized ability of interfacial states is stronger than intrinsic oxygen vacancy in the trapping layer, which signifies that interfacial states in the HfO-AlO interface may be an adverse factor to the performance of the traditional metal/Al2O3/HfO2/Al2O3/Si (MAHAS) or MAHOS memory devices

Summary

INTRODUCTION

Reference 20 investigated the effects of interfacial fluorination on performance of metal/Al2O3/HfO2/SiO2/Si (MAHOS) memory structure. First-principles calculations, which are capable of revealing the atomic and electronic structures of interfaces as well as the interfacial stability and adhesion strength, are used extensively to study solid-solid interfaces.[23] A variety of atomic simulations has been made to HfO224–29 and Al2O330–34 materials or their surfaces separately, and yet very few researches have examined the atomic mechanism of the HfO2/Al2O3 interface. A first principle study on the HfO2/Al2O3 interface is carried out which aims to investigate its atomic structure and electronic properties, including the bonding at the interface, the origin of the intrinsic gap states, trapping characteristics of gap states and its effect on the performance of CTM devices

Methodology

Bulk properties

Stability of interface

Interfacial gap states

CONCLUSION