Low-Damage Processed and High-Pressure Annealed High-k Hafnium Zirconium Oxide Capacitors near Morphotropic Phase Boundary with Record-Low EOT of 2.4Å & high-k of 70 for DRAM Technology

We present record-low equivalent oxide thickness (EOT) of 2.4 Å with a remarkable dielectric constant (K) of 64 at 4.1nm-thick hafnium-based films with no wake-up characteristics. In comparison to conventional HZO films, our remarkable achievement stems from the high-quality crystalline structure with less oxygen vacancies formed by a low-damage process, as evidenced by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) images and electron energy-loss spectroscopy (EELS) analysis. In addition, with high-pressure annealing (HP A), we were able to reduce the annealing temperature to 450°C leading to a decrease in leakage current (1. 5 order). Further, increasing the measurement temperature from 298K to 389K results in the high-K from 66 to 70, which is the theoretical limit of the K value of t-phase.

Introduction

Current DRAM technology demands a low equivalent oxide thickness (EOT) of < 5 Å at a physical thickness of≤ 5 nm and a lower leakage current density (J ~ 1 0⁻⁷A/cm² at 0.8 V) [1–3]. Reducing the physical thickness decreases the EOT but it also leads to increased leakage [4–5]. Recently, HZO films near the morphotropic phase boundary (MPB) offer high- and low EOT with acceptable leakage current density [6–9]. The ferroelectric o/t-phase of HZO exhibits high K values with applied voltage exceeding its coercive voltage . For DRAM cell applications, the of HZO should be < 0.6 V (DDR5 operational voltage), requiring the film thickness to less than 5 nm [10]. Scaling conventional hafnia films to 4 nm results in improper crystallinity with defects or amorphous nature due to difficulties in crystallizing thinner films [11]. Hence, we propose a low-damage process [12] for crystallizing ultra-thin hafnia films to achieve low EOT and high near MPB. The low-damage process reduces the defect concentration, mainly oxygen vacancies, thereby suppressing the formation of a dead layer and promoting the effective formation of the MPB layer. Crucially, HPA is the key process in enhancing ferroelectric properties in hafnia at lower annealing temperatures (≤450 °C).