Remote Oxygen Scavenging of the Interfacial Oxide Layer in Ferroelectric Hafnium–Zirconium Oxide-Based Metal–Oxide–Semiconductor Structures

Abstract

Discovery of ferroelectricity in HfO2 has sparked a lot of interest in its use in memory and logic due to its CMOS compatibility and scalability. Devices that use ferroelectric HfO2 are being investigated; for example, the ferroelectric field-effect transistor (FEFET) is one of the leading candidates for next generation memory technology, due to its area, energy efficiency and fast operation. In an FEFET, a ferroelectric layer is deposited on Si, with an SiO2 layer of ∼1 nm thickness inevitably forming at the interface. This interfacial layer (IL) increases the gate voltage required to switch the polarization and write into the memory device, thereby increasing the energy required to operate FEFETs, and makes the technology incompatible with logic circuits. In this work, it is shown that a Pt/Ti/thin TiN gate electrode in a ferroelectric Hf0.5Zr0.5O2 based metal-oxide-semiconductor (MOS) structure can remotely scavenge oxygen from the IL, thinning it down to ∼0.5 nm. This IL reduction significantly reduces the ferroelectric polarization switching voltage with a ∼2× concomitant increase in the remnant polarization and a ∼3× increase in the abruptness of polarization switching consistent with density functional theory (DFT) calculations modeling the role of the IL layer in the gate stack electrostatics. The large increase in remnant polarization and abruptness of polarization switching are consistent with the oxygen diffusion in the scavenging process reducing oxygen vacancies in the HZO layer, thereby depinning the polarization of some of the HZO grains.

Hafnia-Based High-Disturbance-Immune and Selector-Free Cross-Point FeRAM

“…In this work, Ti/Pt as a top contact layer is applied for IL optimization. Due to the high binding energy of Ti-O [26], oxygen in the bottom and top TiON IL will be removed, illustrated in Fig.…”

“…. This process is called remote oxygen scavenge (ROS) and can decrease the IL thickness, which will increase the voltage drop on FE layer [26]. Fig.…”

Perspective on Ferroelectric Devices: Lessons from Interfacial Chemistry

“…These techniques can be categorized as direct or remote scavenging if the scavenging elements are incorporated in or isolated from the high- k layer, respectively. Many studies have attempted to remove the low- k IL in HfO 2 -based FeFETs using scavenging techniques. ,, Lee et al reduced the thickness of the low- k ILs in Al:HfO 2 -based MFIS capacitors using a remote scavenging technique with TiN/Ti/TiN top electrodes. As is evident from the HRTEM image in Figure (a), the top TiN/Ti/TiN electrode decomposes SiO 2 during annealing at 800 °C.…”

“…Many studies have attempted to remove the low-k IL in HfO 2 -based FeFETs using scavenging techniques. 97,102,103 Lee et al 97 Oxygen vacancies, which tend to migrate to the interface between the Al:HfO 2 and SiO 2 layers, play a role in decomposing the SiO 2 layer, simultaneously serving as mediators for transporting scavenged oxygen to the upper TiN layer. The capacitor, including the TiN/Ti/TiN top electrode, shows a lower 2V c value and a higher 2P r value compared to the case without the Ti capacitor and also maintains stable endurance characteristics up to 10 9 cycles.…”

Tunable defect engineering of Mo/TiON electrode in angstrom-laminated HfO2/ZrO2 ferroelectric capacitors towards long endurance and high temperature retention

“…Kashir et al proposed W/Pt that accounts for the advantages of both a low TEC and high work function (WF) to extend FE endurance [11]. Tasneem et al [18] proposed using Ti as an oxygen scavenging layer (OSL) (Pt/Ti/TiN/HZO/Si) to capture the native oxide (SiO 2 ) on the silicon substrate. The reduction of this interfacial layer can improve remnant polarization.…”