Defect-Induced Phase Transition in Hafnium Oxide Thin Films: Comparing Heavy Ion Irradiation and Oxygen-Engineering Effects

Tobias Vogel,Christina Trautmann,Christophe Vallee,Nico Kaiser,Eszter Piros,Etienne Nowak,Sylvain David,Lambert Alff,Nicolas Guillaume,Gauthier Lefevre,Christelle Charpin-Nicolle,Stefan Petzold

doi:10.1109/tns.2021.3085962

Abstract

Hafnium oxide acts as a functional dielectric in a variety of traditional and emerging nonvolatile memory technologies. To investigate the effect of heavy ion irradiation on its crystalline structure, highly textured hafnium oxide films were irradiated with 1.635 GeV Au ions of fluences ranging from 1×10 9 to 7×10 12 ions/cm 2 . For monoclinic hafnium oxide films, a fluence-dependent defect-induced phase transition to a defect-stabilized tetragonal phase is identified. In low-temperature tetragonal hafnium oxide films, the X-ray diffraction (XRD) patterns show an out-of-plane lattice constant decrease with increasing irradiation fluence. Observed crystalline changes are strikingly similar to trends found for oxygen-engineered hafnium oxide films, directly grown at varying oxidation conditions. The correlation of structural changes with in vacuo electron spectroscopy data of oxygen-engineered films suggests that the irradiation of hafnium oxide leads to an oxygen loss that increases with fluence. Therefore, the underlying mechanism of the monoclinic to tetragonal phase transition is obviously directly related to oxygen defects. This new information allows predictions of device stability under swift heavy ion irradiation of hafnium oxide-based devices.

Highlights

A S THE memory state of common complementary metal– oxide–semiconductor (CMOS) technology memories, such as DRAM, SRAM, and Flash, is charge-based, they are proved to be sensitive to ionizing radiation [1], including single-event upsets (SEU), single-event latch-up (SEL), and single-event functional interruptions (SEFI) [2]
A combination with X-ray photoelectron spectroscopy (XPS) investigations in the discussion regarding oxygen deficiency can hereby enhance the understanding of the defect-induced phase transition in hafnium oxide films and further improve the understanding of the role of oxygen in this process
In series (A), textured, stoichiometric m-HfO2 films were irradiated to investigate the effect of heavy ion irradiation on the crystalline structure by using X-ray diffraction (XRD)

Summary

INTRODUCTION

A S THE memory state of common complementary metal– oxide–semiconductor (CMOS) technology memories, such as DRAM, SRAM, and Flash, is charge-based, they are proved to be sensitive to ionizing radiation [1], including single-event upsets (SEU), single-event latch-up (SEL), and single-event functional interruptions (SEFI) [2]. For RRAM devices based on hafnium oxide, polycrystalline monoclinic films are achieved at CMOS-compatible growth temperatures (down to 200 ◦C [4]). VOGEL et al.: DEFECT-INDUCED PHASE TRANSITION IN HAFNIUM OXIDE THIN FILMS of oxygen vacancies. For powder samples of stoichiometric hafnium oxide (HfO2), the ions induce a monoclinic to tetragonal phase transition [25]–[28]. The objective of our study is to better understand the mechanism of this ion-beam-induced phase transition and to investigate whether the existing knowledge of irradiated powder hafnium oxide applies to thin films. We performed irradiations under similar swift heavy ion conditions as applied in [27] and exposed stoichiometric textured monoclinic (m-HfO2) films as well as intentionally grown oxygen-deficient, textured tetragonal (t-HfOx) hafnium oxide films. A combination with X-ray photoelectron spectroscopy (XPS) investigations in the discussion regarding oxygen deficiency can hereby enhance the understanding of the defect-induced phase transition in hafnium oxide films and further improve the understanding of the role of oxygen in this process

EXPERIMENT

RESULTS AND DISCUSSION

Irradiated Textured m-HfO2 Films

Comparison With Oxygen-Engineered HfOx Films

Irradiation of Textured Defect-Stabilized t-HfOx Films

CONCLUSION