First-principles dopant screening to suppress shallow traps in HfO2 charge-trap layers for 3D nand flash memory

초록

As three-dimensional (3D) nand flash memory continues to scale toward higher integration, lateral and vertical thinning of the Si3N4 charge-trap layer (CTL) leads to memory window narrowing and accelerates lateral charge loss. Hafnium oxide (HfO2) has emerged as a promising alternative CTL material due to its high-dielectric-constant (high-k) permittivity, which enables effective-oxide-thickness scaling without excessive physical thinning. However, shallow traps caused by oxygen vacancies (VO) still induce critical lateral charge loss in HfO2-based CTLs. In this work, density functional theory calculations are employed to identify suitable dopants capable of mitigating these shallow traps in HfO2. Various dopant species are systematically evaluated at hafnium and oxygen substitutional sites as well as interstitial sites to assess how possible dopant site occupations influence trap level formation. Furthermore, the local coordination environments are analyzed to obtain structural insight into the observed trends in trap levels. In addition, VO-induced defect structures are characterized to establish correlations between vacancy configurations and trap state characteristics. The results indicate that, among the dopants considered, Al and Bi show robust trap level characteristics for suppressing VO-related shallow traps in HfO2, suggesting a route to mitigate lateral charge loss. Technology computer-aided design simulations further support the resulting reduction in lateral charge loss at the device level. These findings demonstrate dopant-based trap engineering as a viable strategy for mitigating lateral charge loss in HfO2, enabling scalable CTLs for next-generation 3D nand flash memory.

키워드