Al₂O₃/HfO₂ Multilayer High‐k Dielectric Stacks for Charge Trapping Flash Memories

Abstract

Dielectric and electrical properties of Al2O3/HfO2 multilayer stacks deposited by atomic layer deposition (ALD) in dependence on the thickness of Al2О3 and HfO2 layers and the post‐deposition annealing (PDA) in different ambient (O2, N2, air) are investigated in terms of their application as trapping layers in emerging charge‐trapping non‐volatile flash memories. Differentiation is made between different processes giving rise to hysteresis effects: trapping of electrons and holes under positive and negative gate bias, respectively (as useful processes which define the memory window), and the generation of positive charge under high electric field stress (which degrades the stacks and results in permanent damage and ultimately in breakdown). Dependence of these processes on HfO2 and Al2O3 thickness as well as annealing ambient is analyzed. It is established that electrically active defects and trapping phenomena are most strongly affected by the annealing ambient. Oxygen annealing is favorable in terms of charge storage ability as it increases electron trapping and improves the electric field stress stability of Al2О3/HfO2 multilayer stacks.

Electrical characterization of memory capacitors for nonvolatile memory applications based on nanolaminated HfO2/Al2O3 and Al-doped HfO2 stacks

“…Both HfO2 and Al2O3 ALD films have been reported to show negative oxide charges [10,12], although for HfO2 a more frequently positive Qox has been found [10]. Previously [6], positive Qox was observed for HfO2/Al2O3 nanolaminated layers in test capacitor structures without BO and TO. A dipole formation between the first Al2O3 sublayer and the SiO2 TO could partially explain the Vfb values leading to a negative Qox (a Vfb shift due to an Al2O3-SiO2 dipole ~ 0.55 eV was found in [13]).…”

“…Since the modern MOSFET technology for ultra-high-density circuits requires the employment of high-k dielectrics in the gate stacks, it is quite tempting to use these materials as charge storage media; moreover, the high-k insulators turned out to be trap-rich materials. Among the various high-k dielectrics, HfO2-based dielectric stacks have been recently pointed out as very promising candidates for replacing Si3N4 in the future CTM generations [1,[3][4][5][6]. The attractiveness of employing HfO2 as a charge-trapping material is additionally reinforced by the fact that the HfO2 MOSFET technology has already reached a state of maturity.…”

Nanosystems, Edge Computing, and the Next Generation Computing Systems

“…For example, a semiconductor material engineered by spatial confinement, creating subbands and thus intersubband transitions, can lead to the generation of radiation (e.g., quantum cascade lasers). In all-dielectric stacks [134,135], similar to semiconductor heterostructures [136], the alternating layers of specific dielectric functions (e.g., small imaginary part, high and low real part dielectrics) create useful photonic band structures [137] or giant (~10 4 ) surface [137] or bulk field enhancement [135].…”

Depth profiling of very thin HfO2/Al2O3 stacks by ellipsometry

“…As HfO2 is already being employed in the production of highperformance logical integrated circuits such as microprocessors, the opportunity of using the HfO2 technology in non-volatile memory applications is quite attractive. It has also been shown recently that the charge-trapping efficiency and retention characteristics of HfO2 can be substantially enhanced by incorporation of Al in its matrix, either by creating bi-layered stacks or by Al-doping [1,2]. Thus, (HfO2):(Al2O3) stacks have been considered as a promising candidate for the next generation of nonvolatile flash memories.…”