In-Situ Reflectance Absorption Infra-Red Spectroscopy (RAIRS) Study on ALD of HfO2 on TiN and Pt Electrodes

Abstract

Ferroelectricity in hafnia fluoride analogues has been widely investigated for nonvolatile memory applications. Although ALD of HfO2 technology is enough mature for CMOS technology, hafnia-based ferroelectrics still suffer from major reliability issues such as relaxation, imprint, fatigue, and breakdown.1 These reliability characteristics are thought to be related to the interface conditions between the ferroelectric film and the electrode. Thus, many reports suggested routes to enhance reliability and ferroelectric characteristics by modifying the interface states of the metal-ferroelectric-metal (MFM) capacitors. Unfortunately, only few reports disclose direct observation on evolution of interface formation and its mechanism. Recently, it is reported that scaling down the ferroelectric hafnia-based films to a few nm range dramatically improves the MFM capacitors’ reliability where the series capacitance and surface effect dominate, making it crucial to understand the interface properties carefully.2 In this presentation, we perform In-situ characterization using reflectance absorption infrared spectroscopy (RAIRS) to monitor the surface reaction and interface formation while HfOx ALD using TDMA-Hf with various oxidation reactants, such as H2O, O3, and anhydrous H2O2. TiN and Pt bottom electrodes are investigated at 250 °C. The RAIRS results show that the initial exposure of the oxidant generates the most amount of oxidation on the TiN surface by showing Ti-O and TiN-O peaks which were not observed for the Pt substrate. Moreover, the Ti-O and TiN-O peak area increase versus the dosing time of oxidant was minimum for H2O, and O3 showed continuous peak increase even after 12 s exposure. Interestingly, for the H2O2 case, there was almost no peak increase in the Ti-O bond region like H2O, but the TiN-O and TiO-O peaks appeared after the first 3 s and saturated after 6 s exposure. Also, not only on the TiN substrate, the peak for O-O stretching was observed for the Pt substrate as well, indicating that the H2O2 generates self-limiting peroxide bonds on the surface with a minimum interface formation. This suppressed interface formation with superior film properties using H2O2 might be the reason behind the robust reliability of the H2O2-based HZO capacitor. We are going to report reliability characteristics in conjunction with interface evolution.Acknowledements: We thank to YEST and KEIT for supporting the project through ISTD Program (No.20010806). This work is also supported by GRC-LMD program (task#3001.001) through SRC. The BRUTE hydrogen peroxide was provided by RASIRC. Ozone generator for TMEICReferences 1 J. Mohan et al., ACS AELM, 4, 4 (2022). 2 K. Toprasertpong et al., ACS AMI, 14 (2022).